Medical treatment of horses with deep digital flexor tendon injuries diagnosed with high-field-strength magnetic resonance imaging: 118 cases (2000–2010)

John D. Lutter Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman WA 99164.

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Robert K. Schneider Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman WA 99164.

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Sarah N. Sampson Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman WA 99164.

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Julie A. Cary Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman WA 99164.

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Greg D. Roberts Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman WA 99164.

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Christopher I. Vahl Department of Statistics, College of Arts and Sciences, Kansas State University, Manhattan, KS 66506.

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Abstract

Objective—To describe the location and severity of deep digital flexor tendon (DDFT) lesions diagnosed by means of high-field-strength MRI in horses and to identify variables associated with return to activity following medical treatment.

Design—Retrospective case series.

Animals—118 horses.

Procedures—Medical records of horses with DDFT injury diagnosed with MRI over a 10-year period (2000–2010) and treated medically (intrasynovial administration of corticosteroids and sodium hyaluronan, rest and rehabilitation, or both) were reviewed. History, signalment, use, results of lameness examination and diagnostic local anesthesia, MRI findings, and treatment details were recorded. Outcome was obtained by telephone interview or follow-up examination. Horses were grouped by predictor variables and analyzed with logistic regression to identify significant effects.

Results—Overall, of 97 horses available for follow-up (median time to follow-up, 5 years; range, 1 to 12 years), 59 (61%) returned to activity for a mean duration of 22.6 months (median, 18 months; range, 3 to 72 months), with 25 (26%) still sound at follow-up. Of horses with mild, moderate, and severe injury, 21 of 29 (72%), 20 of 36 (56%), and 18 of 32 (56%), respectively, returned to use. Horses treated with intrasynovial corticosteroid injection and 6 months of rest and rehabilitation returned to use for a significantly longer duration than did horses treated without rest. Western performance horses returned to use for a significantly longer duration than did English performance horses.

Conclusions and Clinical Relevance—Results of the present study suggested that outcome for horses with DDFT injuries treated medically depended on injury severity, presence of concurrent injury to other structures in the foot, type of activity, and owner compliance with specific treatment recommendations. Although some horses successfully returned to prior activity, additional treatment options are needed to improve outcome in horses with severe injuries and to improve long-term prognosis.

Abstract

Objective—To describe the location and severity of deep digital flexor tendon (DDFT) lesions diagnosed by means of high-field-strength MRI in horses and to identify variables associated with return to activity following medical treatment.

Design—Retrospective case series.

Animals—118 horses.

Procedures—Medical records of horses with DDFT injury diagnosed with MRI over a 10-year period (2000–2010) and treated medically (intrasynovial administration of corticosteroids and sodium hyaluronan, rest and rehabilitation, or both) were reviewed. History, signalment, use, results of lameness examination and diagnostic local anesthesia, MRI findings, and treatment details were recorded. Outcome was obtained by telephone interview or follow-up examination. Horses were grouped by predictor variables and analyzed with logistic regression to identify significant effects.

Results—Overall, of 97 horses available for follow-up (median time to follow-up, 5 years; range, 1 to 12 years), 59 (61%) returned to activity for a mean duration of 22.6 months (median, 18 months; range, 3 to 72 months), with 25 (26%) still sound at follow-up. Of horses with mild, moderate, and severe injury, 21 of 29 (72%), 20 of 36 (56%), and 18 of 32 (56%), respectively, returned to use. Horses treated with intrasynovial corticosteroid injection and 6 months of rest and rehabilitation returned to use for a significantly longer duration than did horses treated without rest. Western performance horses returned to use for a significantly longer duration than did English performance horses.

Conclusions and Clinical Relevance—Results of the present study suggested that outcome for horses with DDFT injuries treated medically depended on injury severity, presence of concurrent injury to other structures in the foot, type of activity, and owner compliance with specific treatment recommendations. Although some horses successfully returned to prior activity, additional treatment options are needed to improve outcome in horses with severe injuries and to improve long-term prognosis.

Deep digital flexor tendon injury in horses is a complex lameness problem because lesions can occur at 4 anatomic locations—distal to the distal sesamoid bone (navicular bone), at the level of the navicular bone, proximal to the navicular bone, and at the level of the pastern—as single lesions or in multiple combinations.1–3 Deep digital flexor tendon lesions have been described as dorsal border fibrillation, core lesions, or sagittal splits.1–6 These different lesion types can also occur alone or in combination at any level within the digit.1–6 However, certain lesion types have shown a predisposition for specific areas of the digit: for example, lesions within the pastern region are most commonly core lesions, whereas injuries proximal to the navicular bone more frequently include dorsal border lesions. Injuries in the region of the navicular bone tend to be sagittal splits, whereas lesions distal to the navicular bone are more frequently core lesions.1,2

The most commonly reported treatment for this injury is 4 to 6 months of rest and rehabilitation, although ≥ 12 months of rest and rehabilitation before return to full activity has also been reported.7–12 Medical management with a variety of treatments, most commonly corticosteroid injection, has also been recommended.8,9,12–15 Prognosis for horses with DDFT injury to successfully return to their previous level of activity is generally considered guarded to poor, but conflicting evidence exists in the literature.7,9–12 In retrospective studies7,8,11,13 of horses with an MRI diagnosis of DDFT injury, 25% to 94% of horses treated medically returned to their previous use. The prognosis decreases if other abnormalities are present within the digit.8,9 These reports of DDFT injury describe various prognoses, but none have attempted to correlate the specific DDFT lesions with the ability to return to activity for an extended period of time.

As such, detailed information regarding prognosis for horses with DDFT injury is lacking. Therefore, the objectives of the study reported here were to determine the location and severity of DDFT injury in horses on the basis of results of high-field-strength MRI and to evaluate the relationship between these findings and the ability of affected horses to return to prior activity following medical treatment. Treatment consisted of injection of the navicular bursa, digital flexor tendon sheath, or both with corticosteroid and sodium hyaluronan and completion of a 6-month rest and rehabilitation period. We hypothesized that the prognosis for affected horses returning to their intended activity would decrease as severity of DDFT injury and duration of associated lameness increased.

Materials and Methods

Case selection criteria—Medical records of all horses with DDFT injury diagnosed on the basis of results of high-field-strength MRI at the Washington State University Veterinary Teaching Hospital between March 2000 and October 2010 were retrospectively reviewed. Inclusion criteria for the study were as follows: high-field-strength MRI diagnosis of DDFT injury within the digit determined to be the most clinically important or severe abnormality, lameness improved by at least 50% (as assessed subjectively by the treating clinician) after a palmar or plantar digital nerve block (with or without local anesthesia of the dorsal branches), and treatment with medical management. Medical management was defined as any nonsurgical treatment involving either a rest and rehabilitation program, intrasynovial administration of corticosteroids and sodium hyaluronan, or concurrent use of both.

Medical records review—Signalment, history, use of the horse (ie, activity), lameness severity, limb location, response to diagnostic local anesthesia, and treatment were obtained from the medical records.

Horses were evaluated on a paved surface at a trot on a straight line and in a circle. The severity of the lameness was described as either mild and inconsistent, mild and consistent, mild to moderate and consistent, or moderate to severe while trotting in a straight line and visible at a walk. Lameness grades were not routinely assigned in the medical record.

Diagnostic local anesthesia—Palmar or plantar digital nerve blocks were completed by means of injection of 1.5 to 2 mL of 2% mepivacaine hydrochloridea SC over the palmar or plantar digital nerves proximal to the ungular cartilages. Medial and lateral dorsal branch blocks were performed by full insertion of a 22-gauge, 1-inch needle perpendicular to the axis of the limb, at the level of the ungular cartilages, and depositing 1.5 to 2 mL of 2% mepivacaine SC on the abaxial aspect of the pastern 1 to 2 cm proximal to the coronary band. If lameness switched to the contralateral limb following local anesthesia of the lame limb, local anesthesia was then performed in the contralateral limb until lameness was eliminated.

Radiography—Horses were evaluated radiographically with 4 views of the affected digit: a lateromedial view, a dorsal 60° proximal-palmarodistal oblique view of the navicular bone, a dorsal 45° proximal-palmarodistal oblique view of the distal phalanx, and a palmaroproximal-palmarodistal view of the navicular bone.

MRI—Horses were anesthetized and placed in right lateral recumbency with the affected forelimbs or hind limbs placed in a 1.0-T high-field-strength magnet.b A human knee quadrature receiver coilb was placed on the digit being imaged, and the digit was positioned in the isocenter of the magnet. Proton density, T2-weighted, and STIR fast spin-echo sequences as well as 3-D gradient echo sequences were used for image acquisition. Transverse, sagittal, and dorsal plane images were obtained in accordance with standard imaging protocols.8,14 All images were interpreted at the time of diagnosis and treatment by a board-certified radiologist in addition to a board-certified equine surgeon (RKS or SNS) as well as retrospectively by a veterinarian experienced in equine MRI (JDL).

Injuries within the DDFT were categorized as core, sagittal splits, or dorsal border lesions as previously described4 (Figures 1–3). Anatomic lesion location was recorded as distal to the navicular bone, at the navicular bone, proximal to the navicular bone, or within the pastern region1–3 (Figure 4). Lesion severity at each level was subjectively graded by one of the authors (JDL) during retrospective MRI evaluation on a scale that was modified from a published scale15 with increasing severity from 1 to 3. Areas of increased signal intensity on proton density sequences within the DDFT that covered < 2 mm2, had mild irregularity of the dorsal tendon border, or both were graded as 1. Areas of increased signal intensity on proton density sequences covering < 30% of tendon lobe area, had moderate irregularity of the dorsal tendon border, or both were graded as 2. Areas of increased signal intensity on proton density sequences that covered > 30% of tendon lobe area, had severe irregularity of the dorsal tendon border, or both were graded as 3. Suspected adhesions between the navicular bone or collateral sesamoidean ligament and the DDFT were diagnosed on the basis of the presence of hypointense tissue spanning the space between the structures that was clearly identifiable on proton density, STIR, and 3-D gradient echo images.8 The severity of the DDFT injury was categorized as mild, moderate, or severe on the basis of the tendon injury grades. Horses were classified with a mild injury if the DDFT injury was no worse than grade 2 at only 1 level and was grade 1 or less at any other level. Horses were classified with a moderate injury if the DDFT injury was grade 2 at more than 1 level or grade 3 at 1 level with any remaining injury being grade 1. Horses were classified with a severe injury if the DDFT injury was grade 3 at 1 or more levels and any remaining injury was grade 2. These criteria were developed to maintain consistency with clinical impressions of mild, moderate, and severe injury on MRI evaluation. Horses were then divided into 5 groups at the time of retrospective MRI evaluation on the basis of the identified abnormalities and number of structures affected (Table 1).

Figure 1—
Figure 1—

Transverse proton density magnetic resonance images of the foot and pastern region from horses demonstrating representative examples of DDFT core lesions. The dorsal aspect is at the top of the image. Tendon lesions are indicated by the open arrowheads. Lesion severity at each anatomic level was subjectively graded during retrospective evaluation of MRI images on a scale from 1 to 3 (least to most severe) as modified from a published scale.15 A—Core lesion at the level of the pastern joint covering < 2 mm2 (grade 1). B—Core lesion in the region proximal to the navicular bone covering > 2 mm2 but < 30% of the injured lobe (grade 2). C—Core lesion in the region distal to the navicular bone just proximal to the DDFT insertion on the distal phalanx covering > 30% of the injured lobe (grade 3).

Citation: Journal of the American Veterinary Medical Association 247, 11; 10.2460/javma.247.11.1309

Figure 2—
Figure 2—

Transverse proton density magnetic resonance images of the foot and pastern region demonstrating representative examples of DDFT sagittal split lesions. The dorsal aspect is at the top of the image. Tendon lesions are indicated by the open arrowheads. Notice the distention of the navicular bursa (borders indicated by the white arrows) as well as the intermediate signal intensity strands of tissue connecting the borders of the navicular bursa with the DDFT. This was interpreted as navicular bursitis with suspected adhesion formation. A—Sagittal split lesion at the level of the navicular bone covering < 2 mm2 (grade 1). B—Sagittal split lesion at the level of the navicular bone covering > 2 mm2 but < 30% of the injured lobe (grade 2). C—Sagittal split lesion in the region proximal to the navicular bone covering > 30% of the injured lobe (grade 3). See Figure 1 for remainder of key.

Citation: Journal of the American Veterinary Medical Association 247, 11; 10.2460/javma.247.11.1309

Figure 3—
Figure 3—

Transverse proton density magnetic resonance images of the foot and pastern region demonstrating representative examples of DDFT dorsal border lesions. The dorsal aspect is at the top of the image. Tendon lesions are indicated by open arrowheads. Notice the thickening and increase in signal intensity of the collateral sesamoidean ligament (white arrows). Notice the intermediate signal intensity strands of tissue occupying the space between the DDFT and collateral sesamoidean ligament. A—Dorsal border lesion exhibiting mild undulation of the dorsal border of the DDFT (grade 1). B—Dorsal border lesion exhibiting moderate irregularity of the dorsal border of the DDFT (grade 2). C—Dorsal border lesion exhibiting severe irregularity of the dorsal border of the DDFT (grade 3). All images were obtained in the region proximal to the navicular bone. See Figure 1 for remainder of key.

Citation: Journal of the American Veterinary Medical Association 247, 11; 10.2460/javma.247.11.1309

Table 1—

Criteria for injury severity for 118 horses with DDFT injury diagnosed by means of high-field-strength MRI examination of the digit at Washington State University from 2000 to 2010.

GroupMRI characteristics
Group 1Horses with DDFT injury without injury to additional structures
Group 2Horses with DDFT injury in addition to moderate to severe distal sesamoid bone (navicular bone) degeneration, navicular bone STIR hyperintensity, or defect in the facies flexoria of the navicular bone
Group 3Horses with DDFT injury in addition to injury to 1 or more other soft tissue structures within the digit (including distal sesamoidean impar ligament, distal digital annular ligament, distal interphalangeal joint collateral ligaments, and collateral sesamoidean ligament)
Group 4Horses with DDFT injury in addition to a cartilage or bone abnormality seen on MRI of the digit
Group 5Horses with lameness in a different leg or different part of the same limb as the deep digital flexor injury

Horses were divided into 5 groups on the basis of the identified abnormalities and number of structures affected at the time of retrospective evaluation of the MRI examination.

Treatment—Treatment involved injection of the navicular bursa, the digital flexor tendon sheath, or both followed by a 6-month rest and rehabilitation program.8 The decision of which synovial structures to inject was based on the presence of DDFT injury within the respective structures. The navicular bursa was injected with 40 mg of methylprednisolone acetatec and 10 mg of sodium hyaluronan,d and the digital flexor tendon sheath was injected with 80 mg of methylprednisolone acetatec and 20 mg of sodium hyaluronan.d The doses were chosen empirically on the basis of the relative volume of each synovial structure. Navicular bursa injections were performed with horses under general anesthesia and positioned in lateral recumbency as previously described.8 Correct placement of the needle was confirmed fluoroscopically. Following navicular bursa injection, horses received phenylbutazone (2.2 mg/kg [1.0 mg/lb], PO, q 12 h) for 2 days. Digital flexor tendon sheath injections were performed with horses under general anesthesia, concurrently with a navicular bursa injection, or standing if only a digital flexor tendon sheath injection was being performed via the basilar sesamoidean approach as previously described.16 When multiple structures were injected, the dose of corticosteroid and hyaluronic acid for each structure remained unchanged.

Figure 4—
Figure 4—

Sagittal proton density image of the foot and pastern region demonstrating the levels of the DDFT within the digit where injury commonly occurs. a = Pastern region. b = Region proximal to the navicular bone. c = Region at the navicular bone. d = Region distal to the navicular bone.

Citation: Journal of the American Veterinary Medical Association 247, 11; 10.2460/javma.247.11.1309

Rest and rehabilitation—Horses treated with rest and rehabilitation were placed in a 6-month program. Although the preferred recommendation was to place horses into the rehabilitation program, some horses either were not placed in the program or did not complete the program because the owners desired to keep the horse in competition or because of unknown reasons. Horses were confined to a stall for the initial 60 days of the rest and rehabilitation period with increasing amounts of hand-walking up to 45 min/d. They were then turned out into a small paddock (approx 30 × 30 feet) while continuing daily hand-walking. Horses that were not lame at a trot after 4 months of rehabilitation were allowed to begin a walk and trot exercise regimen under saddle for the remainder of the rehabilitation period. Horses were not allowed free exercise in a large area and did not resume regular training until the 6 months of rest and rehabilitation was completed. Specific trimming and shoeing recommendations were made for each horse to correct any conformational imbalances, primarily by keeping the toe short and balancing the foot. The specific techniques used to achieve this were left to the discretion of each horse's farrier.

Follow-up—Follow-up information was obtained via telephone interview or by follow-up examination of the horse. The following information was obtained: duration of ownership, prior and current use, ability to return to previous level of activity, time to return to previous activity, duration of activity after return to activity, and time to recurrence of lameness. Outcome was considered successful if horses returned to activity, regardless of the level of performance attained. Return to activity was defined as returning to the same activity the horse had been involved in prior to diagnosis of DDFT injury. Outcomes were categorized as excellent, good, and poor to facilitate comparison with previous studies. Outcome was considered excellent for horses that returned to previous activity and level of performance. Horses that returned to previous activity but at a lower level of performance or that returned to a lower level of activity were considered to have a good outcome. Horses that were retired from activity regardless of soundness or were unable to return to activity were considered to have a poor outcome. If horses were placed in a rest and rehabilitation program, the time horses were able to continue performing was measured beginning after completion of the rest and rehabilitation program. Duration of return was defined as the time following completion of the prescribed treatment until recurrence of lameness or the administration of additional medication or treatment. Horses were considered sound at follow-up if the horse was able to return to its intended use and the owner reported no recurrence of lameness at the time of follow-up.

Statistical analysis—Summary statistics for outcome including return to activity and duration of return to activity were calculated. Statistical analyses were performed on 2 outcome variables: return to activity (yes or no) and duration of return to activity. Predictors included lesion location, group, severity, treatment, and discipline. Values of P < 0.05 were considered significant for all comparisons. For the binary outcome return to activity, the predictors were evaluated in a logistic regression model.e For analysis of duration of return to activity, horses reported as sound at follow-up were right censored; horses for which lameness recurrence was reported but the exact duration of return to activity was unknown were left censored. The presence of these 2 types of censoring was accounted for in a parametric model for survival analysis.f Several candidate distributions were evaluated, and the model with the best fit was further confirmed by a cumulative hazard plot as well as a plot of deviance residuals.17 The Bonferroni method was used to adjust P values to account for multiplicity during the pairwise comparisons of the levels within the significant predictors.

Results

Signalment and history—One hundred eighteen horses with a diagnosis of primary DDFT injury were identified that met the study criteria. Mean duration of lameness was 15 months (SD, 18.5 months; median, 8 months; range, 1 to 96 months). There were 84 geldings, 31 mares, and 3 stallions with a mean age of 10.2 years (SD, 3.3 years; median, 10 years; range, 3 to 20 years). There were 85 Quarter Horses, 15 warmblood or warmblood crosses, 8 American Paint Horses, 4 Thoroughbreds, 2 Tennessee Walking Horses, 2 mules, 1 Appaloosa, and 1 Arabian.

Follow-up information was available for 97 horses. Of these, 66 were used for Western performance (barrel racing, cutting, reining, reined cow horse, roping, working ranch horse, Western pleasure, mounted shooting, and team penning), 11 were used for pleasure riding, 12 were used for 3-day eventing or as hunter-jumpers, and 6 were used as dressage horses. Use was not recorded during the interview for 2 horses for which the owners were able to provide follow-up information. Use was not recorded in the medical record, and follow-up was not obtained for the remaining 21 horses.

Clinical findings—One hundred ten horses had forelimb lameness (67 bilateral and 43 unilateral), 5 horses had hind limb lameness (3 bilateral and 2 unilateral), and 3 horses had forelimb and hind limb lameness (DDFT injury was diagnosed in the right forelimb of all 3 horses). Mild to moderate consistent lameness (n = 97) was most frequently observed, with lameness ranging from mild and consistent (9) to moderate to severe with lameness visible at a walk (12). Signs of pain causing lameness were localized to the digit in 93 of 118 horses following a palmar or plantar digital nerve block. Eight horses required a dorsal branch block to eliminate the lameness. Three horses remained lame following the dorsal branch block, having only improved 50% in response to a palmar or plantar digital nerve block. The remaining lameness in these 3 horses was abolished in 2 by a low 4-point nerve block and in 1 by a high palmar nerve block.18 In addition to the DDFT injury, all 3 of these horses had soft tissue injuries that were not within the foot and pastern region. In the remaining 17 horses, lameness was localized to the foot, with no further details recorded.

Radiography—Nine of 118 horses in the study had abnormalities diagnosed on the basis of radiographic findings, including distal phalanx subchondral cyst-like lesions (2), bilateral erosions of the facies flexoria of the navicular bone (2), unilateral dorsal remodeling of the distal phalanx (1), unilateral distal phalanx extensor process fragment (1), bilateral distal interphalangeal joint osteoarthritis (1), keratoma (1), proximal phalanx palmar eminence fragments (1), and third tarsal bone slab fracture (chronic; 1). These findings were used to categorize the affected horses into either group 4 or group 5. The radiographic findings for the remaining horses were recorded as either no clinically important findings or within expected limits (104) or mild to moderate remodeling of the navicular bone (5).

MRI—Sixty-nine horses had bilateral (67 forelimb and 2 hind limb) and 49 had unilateral (46 forelimb and 3 hind limb) DDFT injury. The type of lesion present within the DDFT frequently transitioned between types as the injury crossed different levels of the digit. Of 188 limbs with DDFT injury, 84 had injuries distal to the navicular bone, 73 had injuries at the level of the navicular bone, 170 had injuries in the region proximal to the navicular bone, and 93 had injuries within the pastern region. Multiple types of lesions (core, sagittal splits, or dorsal border lesions) occasionally occurred at the same anatomic level either within the same lobe or within both lobes of the tendon, especially as the severity of injury increased. Of the 85 lesions distal to the navicular bone, 53 (63%) were core lesions, 30 (35%) were sagittal splits, and 2 (2%) were dorsal border lesions. Of the 74 lesions at the navicular bone, 54 (73%) were sagittal splits, 17 (23%) were core lesions, and 3 (4%) were dorsal border lesions. Of 172 lesions proximal to the navicular bone, 105 (54%) were dorsal border lesions, 63 (33%) were core lesions, and 25 (13%) were sagittal splits. Of 94 lesions in the pastern region, 90 (96%) were core lesions, 3 (3%) were dorsal border lesions, and 1 (1%) was a sagittal split. Ten of 118 (8.5%) horses had injury at 1 level of the digit, 43 (36%) at 2 levels, 37 (31%) at 3 levels, and 28 (24%) at all 4 levels evaluated.

The most severe DDFT injury was found in the limb in which the horse was most lame in 106 of 118 (90%) horses. Subjectively, there was no obvious difference in lesion type, distribution, or severity for hind limb DDFT injury (n = 5), compared with forelimb DDFT injuries (113). Suspected adhesion formation between the DDFT and collateral sesamoidean ligament was diagnosed in 70 of 118 horses. In 7 horses without radiographic evidence of a defect in the facies flexoria of the navicular bone, the diagnosis of a partial thickness defect was made on the basis of MRI findings alone. Three of these horses had bilateral navicular bone defects. The mean medial to lateral length of the defect was 6 mm (SD, 2.9 mm; median, 5.5 mm; range, 3 to 8 mm) in the horses for which diagnosis was made from MRI alone (10 erosions) and 13 mm (SD, 6.8 mm; median, 13.5 mm; range, 5 to 20 mm) in the horses for which diagnosis was made from radiographs and MRI (4 erosions), as measured on the 3-D gradient echo axial sequence. Suspected adhesion formation was seen between the DDFT and navicular bone in 5 horses and between the DDFT and distal digital annular ligament in 2 horses.

For the 12 horses in group 4, 8 had abnormalities of the foot and pastern region diagnosed on the basis of results of MRI, in addition to the DDFT injury, including type II distal phalanx fracture19 (chronic; 1), middle and distal phalanx intraosseous STIR hyperintensity (1), distal phalanx cartilage defect (2), distal phalanx subchondral bone cyst (1), distal phalanx bone cyst at the distal sesamoidean impar ligament insertion (2), and cartilage defect with subchondral bone damage at the distal aspect of the proximal phalanx (1).

For 12 horses in group 5, 10 had abnormalities of the foot and pastern diagnosed on separate sequences obtained during the single MRI examination: oblique sesamoidean desmopathy (3 hind limbs), straight sesamoidean desmopathy (1 hind limb and 1 forelimb), desmopathy of the accessory ligament of the DDFT (1 forelimb), suspensory branch desmopathy (1 forelimb), proximal suspensory desmopathy (1 forelimb and 1 hind limb), and intraosseous STIR hyperintensity of the distal aspect of the third metacarpal bone (1 forelimb).

Outcome—Follow-up information was obtained for 97 of the 118 horses included in the study. Of the 21 horses lost to follow-up, 17 were lost because their owner did not answer or the telephone number was not in service, with the final 4 owners requesting not to participate. Median time to follow-up was 5 years (range, 1 to 12 years). For 73 of 97 horses, median time to return to previous use following completion of the prescribed treatment with follow-up was 6 months (range, 0 to 24 months). Overall, 59 of 97 horses (61%) were able to return to previous use. In 43 of those 59 horses for which data were available, the median duration of return to activity was 18 months (range, 3 to > 72 months; Table 2), with 25 of 97 (26%) sound at follow-up. Outcomes based on factors that may have affected prognosis were summarized (Tables 2 and 3).

Table 2—

Clinical outcome of 97 horses with DDFT injury diagnosed by means of high-field-strength MRI, grouped by lesion severity or injury group.

 Return to activityDuration of return (mo)Sound at follow-up
VariableYesNo%TotalMedianRangeNo. of horsesYes%
Overall59386197183 to > 72432526
Lesion severity
 Mild2187229184 to > 7214828
 Moderate20165636183 to > 4815925
 Severe18145632185 to > 4814825
Injury group
 124107134244 to > 72211132
 29104719123 to 42515
 316106226154 to > 4812831
 47464111512 to > 182327
 534437364 to > 483229

Injury groups are defined in Table 1. Follow-up was obtained for 97 of the 118 horses initially included in the study. The lesion was considered mild if the affected region was < 30% of the affected tendon lobe area at any 1 location and otherwise < 2 mm2, moderate if the affected region was > 2 mm2 but < 30% of the affected tendon lobe area at multiple locations or if the affected region was > 30% of the tendon lobe area at 1 location with the remaining locations < 2 mm2, and severe if the affected region was > 30% of the affected tendon lobe area at more than 1 location and affecting > 2 mm2 at the remaining locations.

Table 3—

Clinical outcome for horses (n = 97) with DDFT injury diagnosed by means of high-field-strength MRI.

 Return to previous activityDuration of return (mo)Sound at follow-up
VariableYesNo%TotalMedianRangeNo. of horsesYes%
Lameness duration
 < 3 mo1567121245 to > 7211838
 > 3 mo28205848183 to > 48181021
Lesion location
 At and below navicular bone1128513184 to > 729538
 Above navicular bone19135932124 to > 4811619
 Above and below navicular bone29235652183 to > 48231427
Treatment
 Medical2497333123 to > 4817515
 Rest7113918424 to > 724528
 Both28186146215 to > 48221533
Discipline
 Western40266166184 to > 72281421
 English1276319123 to > 4810842
 Pleasure737010185 to > 485330

Medical treatment consisted of corticosteroid and sodium hyaluronate injection into the navicular bursa, the digital flexor tendon sheath, or both and was determined by the presence of tendon injury in those structures. Treatment with rest consisted of completion of a structured 6-month rest and rehabilitation program.

Of 97 horses, 50 (52%) had an excellent outcome. For 38 of these horses for which data were available, median duration of return to activity was 18 months (range, 4 to > 72 months), and 24 of 50 (48%) were sound at follow-up. Outcome was considered good in 15 of 97 (15%) horses that returned to use. For the 5 horses for which data were available, median duration of return to activity was 24 months (range, 3 to 36 months), with 1 horse sound at follow-up. Outcome was considered poor in 32 of 97 (33%) horses.

When considering the 79 horses with only soft tissue injuries within the digit or digits with DDFT injury (ie, removing groups 4 and 5), the outcome was successful in 49 (62%). Seventeen of 24 (71%) horses in this group with mild DDFT injury returned to use. Eighteen of 28 (64%) and 14 of 27 (52%) horses with moderate or severe DDFT injury, respectively, returned to use.

Statistical analysis—Ninety-five of the 97 horses with follow-up were included in the analysis for return to activity. Two horses that had returned to use could not be included because type of use was not reported. Fitness of the logistic regression model for analyzing return to activity was considered acceptable because the deviance-to-df ratio was 1.41. No significant effect was seen on return to activity for treatment (P = 0.136), group (P = 0.707), use (P = 0.857), lesion severity (P = 0.371), or lesion location (P = 0.266). The percentage of horses to return to activity in each predictor category was estimated (Table 4).

Table 4—

Percentage of horses predicted to return to activity, as estimated by means of logistic regression analysis of 95 horses with DDFT injury diagnosed by high-field-strength MRI at Washington State University.

PredictorReturn to activity (%)SE (%)
Injury group
 17310
 25515
 36612
 47813
 56421
Lesion location
 Above navicular bone5312
 Below navicular bone8312
 Both639
Lesion severity
 Mild7710
 Moderate5812
 Severe6814
Treatment
 Medical819
 Rest4816
 Both7110
Discipline
 English6813
 Pleasure7216
 Western649

Horses were categorized according to injury group as shown in Table 1, and lesion severity as shown in Table 2. On the basis of the logistic regression model, the expected return to activity for horses that fit the criteria of each predictor grouping was estimated (ie, return to activity expected in 73 ± 10% of horses that fit the defined criteria for group 1). See Table 3 for remainder of key.

Fifty-nine of 97 horses were included in the analysis for duration of return to activity. The 38 horses that did not return to activity could not be included in the analysis. The exact duration of return was known for 44 horses. Five horses were right censored, and 10 horses were left censored. Model selection indicated a log-normal model had the best fit. This model showed a significant effect on duration of return for treatment (P = 0.003) and use (P = 0.023). No significant effect was found for group (P = 0.523), lesion severity (P = 0.811), or lesion location (P = 0.355). Western performance horses returned to use for a significantly (adjusted P = 0.019) longer duration (Table 3; median, 18 months; 40 of 66 horses) than English performance horses (median, 12 months; 12 of 19 horses). Duration of return for pleasure horses was not significantly different from that for horses used for Western (adjusted P = 1.000) or English performance (adjusted P = 0.329). Horses treated with both rest and corticosteroid injection returned to use for significantly (adjusted P = 0.007) longer than horses that were treated with only corticosteroid injection. The duration of return for horses treated with only rest was not significantly different from that for horses treated by injection alone (adjusted P = 0.098) or those treated with both rest and injection (adjusted P = 1.000). Median duration of return for each predictor was estimated (Table 5). The duration of return was estimated by the model containing the effect of treatment and use (significant predictor variables) as 25th, 50th, and 75th percentiles (Table 6).

Table 5—

Predicted median duration of return for horses able to return to prior activity, as estimated by log-normal regression analysis for horses (n = 59) with DDFT injury.

PredictorMedian duration of return (mo)SE (mo)
Injury group
 120.84.5
 212.34.5
 315.73.8
 422.88.0
 519.19.3
Lesion location
 Above navicular bone14.03.7
 Below navicular bone21.36.3
 Both18.63.5
Lesion severity
 Mild17.63.7
 Moderate19.54.3
 Severe16.24.9
Treatment
 Medical*10.52.4
 Rest24.78.4
 Both*21.45.4
Discipline
 English11.22.7
 Pleasure21.17.7
 Western23.63.9

Horses are categorized according to injury group as shown in Table 1 and lesion severity as shown in Table 2.

Treatment with both rest and injection was significantly different from medical treatment alone.

Duration of return for English performance horses was significantly different from that of Western performance horses.

See Table 3 for remainder of key.

Table 6—

Duration of return to activity as estimated by log-normal regression analysis of horses (n = 59) with DDFT injury.

TreatmentUsePercentileDuration of return to activity (mo)95% confidence interval
MedicalEnglish25th4.22.4–7.5
  50th7.04.0–12.2
  75th11.56.5–20.4
 Pleasure25th7.43.8–14.3
  50th12.26.4–23.3
  75th20.210.6–38.7
 Western25th8.25.7–11.9
  50th13.69.6–19.3
  75th22.515.6–32.3
RestEnglish25th11.65.5–24.2
  50th19.19.2–39.9
  75th31.615.0–66.7
 Pleasure25th20.38.3–49.6
  50th33.613.8–81.5
  75th55.522.7–135.5
 Western25th22.612.3–41.4
  50th37.320.5–68.0
  75th61.733.5–113.7
BothEnglish25th8.85.6–13.8
  50th14.59.4–22.6
  75th24.015.3–37.8
 Pleasure25th15.47.8–30.3
  50th25.513.1–49.5
  75th42.121.6–82.2
 Western25th17.211.8–24.9
  50th28.319.9–40.4
  75th46.932.5–67.6

On the basis of logistic regression modeling, the expected duration of return for horses that fit the criteria of each predictor grouping was estimated. The 50th percentile can also be interpreted as the median expected duration of return (ie, median expected duration of return was 14.5 months [95% confidence interval, 9.4 to 22.6 months] for horses used for English performance and treated by both injection and rest).

Discussion

Results of the present 10-year retrospective study of horses with DDFT injury diagnosed by means of high-field-strength MRI and treated medically suggested that although some horses with DDFT injury can return to their prior activity for a substantial period of time, specific outcome depends on severity of injury, use, presence of concurrent lesions, and specific treatment recommendations. In this study of 118 horses, 59 of 97 (61%) horses available at follow-up returned to their prior activity. For 43 horses for which data were available, median duration of activity after return to activity was 18 months (range, 3 to > 72 months), with 50 of 97 (52%) having an excellent outcome (ie, returned to previous activity and level of performance). Of the 34 horses in group 1 (ie, with DDFT injury without injury to additional structures on the basis of MRI findings), 22 (65%) had an excellent outcome. With the logistic regression model, treatment and use predictors were found to have a significant effect on duration of return to activity. Horses used for Western performance returned to use for a significantly longer duration than those used for English performance. Horses treated with injection and the rehabilitation program returned to use for a significantly longer duration than horses treated by injection alone. Our hypotheses that outcome would be related to lesion severity and lameness duration were not supported. Statistical analysis of a larger, more homogenous population of horses (eg, only Western performance horses treated with rest or rest and corticosteroid injection) would allow a more specific determination of the effects of lesion severity and lameness duration on outcomes.

Rest and rehabilitation appears to be an important part of treatment. In the present study, horses (n = 22) that were injected with corticosteroids and sodium hyaluronan with a subsequent 6-month rehabilitation program returned to use for a significantly (P = 0.007) longer duration (median, 21 months; range, 5 to > 48 months) than horses (n = 17) treated with corticosteroid and sodium hyaluronan injection only (median, 12 months; range, 3 to > 48 months). For horses treated with either rest or both rest and injection, a significant (adjusted P = 0.098) effect of the injection was not seen. However, we suggest that this treatment may be clinically important as evidenced by the high rate of return to activity in horses treated with rest and injection (28/46 [69%]), compared with that in horses treated with rest alone (7/18). A larger study with greater statistical power would be needed to determine whether treatment with corticosteroids and sodium hyaluronan in addition to rest is truly beneficial. An even higher proportion (24/33 [73%]) of horses treated with only injection returned to activity in this study. This may be due to the short-term effect of the medication relieving the pain and inflammation in the area, an unknown effect of the drugs on tendon healing, or the desire of the owners to return their horses to activity. Other studies8,20,21 have reported a high percentage of horses returning to prior activity without a rehabilitation period following injection of the navicular bursa with corticosteroids and sodium hyaluronan. However, the effects of treatment on the outcomes reported must also be considered with the concurrent effects of activity.

Previous studies have reported neither the effect of the type of performance on outcome nor the outcome of a large number of Western performance horses with DDFT injury as the most clinically important abnormality. In the present study, Western performance horses (n = 40/66) returned to use for a significantly (P = 0.019) longer duration (median, 18 months; range, 4 to > 72 months) than horses used for English performance (n = 12/19; median, 12 month; range, 3 to > 48 months). The reasons for this difference are likely multifactorial and may be affected by factors outside of those directly related to the patient such as owner perceptions and expectations. It is also possible that horses competing in different types of events could be affected differently by mild levels of lameness. Thus, some horses performing in a certain discipline might remain in use while others competing in a different discipline are unable to perform. The potential for horses to perform at the intended level with mild lameness could affect examination findings at initial examination such as lameness duration and grade, lesion location and severity, and the number of additional structures that are injured. This could ultimately affect overall outcome.

We are aware of only 1 prior study9 evaluating outcome for horses with primary DDFT injury diagnosed with high-field-strength MRI. Comparison of our results with that study9 is difficult because of differences in the definition of treatment success and reporting of outcomes. In the previous study,9 13 of 47 (28%) horses with a primary DDFT injury were reported to have returned to previous level of use without recurrence of lameness at the time of follow-up, whereas in the present study, 22 of 34 (65%) horses returned to previous level of use. Navicular bone injury diagnosed on the basis of MRI resulted in a poorer prognosis, with 5 of 19 horses in the present study having an excellent outcome, compared with 1 of 18 horses in the previous report.9 Although the previous study reported a number of horses with abnormalities in addition to the DDFT injury, further comparison is difficult because outcome for those horses was not reported. Furthermore, though a high proportion (25/47 [53%]) of horses in that study were reported to have persistent or recurrent lameness, duration of soundness prior to recurrence of lameness was also not reported.9

In 2 previous studies10,11 of horses with DDFT injury diagnosed with low-field-strength MRI, the authors reported significant associations between either injury severity or injury type and outcome on the basis of regression analysis. Vanel et al10 found that DDFT injury with lesions > 30 mm in length or > 10% of total tendon cross-sectional area on initial MRI was associated with a poor outcome following medical management. Multivariate regression analysis by Cillán-García et al11 revealed that horses with less severe lameness and with dorsal border lesions were significantly more likely to return to any level of activity than horses with core or parasagittal split lesions. Although the primary diagnosis from both studies was DDFT injury, 22 of 34 (63%)10 and 108 of 168 (67%)11 included horses had concurrent injury to other structures in the foot. The effect of additional injuries on outcomes in these 2 previous studies10,11 is unknown but likely contributed to the reported low percentage of horses returning to the previous level of activity. Although a significant effect of lesion severity (P = 0.811) or lesion location (P = 0.355) was not detected in the present study, a higher percentage of horses with mild injury returned to use than horses with moderate or severe injury. Additionally, successful outcomes decreased as the number of injured locations within the foot increased. Determination of the primary DDFT lesion type was not possible in most horses in the present study because of the large number of horses with biaxial and bilateral injuries with different lesion types.

Of 97 horses in the present study, 25 (26%) were sound at the time of follow-up. This is similar to previous reports that reported excellent outcomes of 28%,9 26%,10 and 25%11 of horses as sound, with soundness at the time of follow up part of the criteria for an excellent outcome. Considering that previous reports do not account for the possibility that affected horses could have become sound, successfully returned to use for a period of time, and then developed recurrent lameness prior to follow-up, we suggest it is likely that the outcomes in those 3 previous reports9–11 may more accurately reflect the prognosis for long-term soundness for horses with soft tissue injuries in the digit rather than reflecting the prognosis for these horses to successfully return to the previous level of performance.

Horses in groups 4 and 5 in this study had abnormalities on MRI that did not allow them to be grouped with the remaining horses (Table 1). However, they were not excluded because of the presence of clinically relevant DDFT injury. Our intent in reporting information on horses in both groups was to document possible injuries that can occur concurrently with deep digital flexor tendinopathy and to document successful outcomes.

Despite the overall sample size (n = 118) for this study, it was limited by the number of horses in each group, missing information in the medical records, and patients lost to follow-up. As with many retrospective studies, a major limitation was that many of the outcomes were determined from a telephone interview with the owner. Owner assessment of soundness may not be as accurate as that of a veterinarian and recollection of specific events or durations may be incomplete. Additionally, it is possible that owners did not recall or report the use of other treatments by their veterinarians that could affect the reported outcomes. Furthermore, repeatability of the cross-sectional lesion grading was not assessed. The subjective nature by which the DDFT injuries were assessed and subsequently used to group the horses could be interpreted differently at later time points or by different veterinarians. This could then potentially change the categorization of some horses and affect the reported outcomes. The methods used in the assessment of the DDFT injury were developed to have some clinical utility and to be easily implemented in the assessment of clinical cases.

The information gained from this study suggested that some horses with DDFT injury were able to return to activity for a substantial period of time and that many had a good to excellent short-term outcome. Although many horses successfully returned to activity, additional treatment options are needed to improve outcome in horses with severe DDFT injuries as well as to improve the long-term prognosis for all affected horses. Further research is needed to enhance our ability to predict which horses have the best chance of successfully returning to performance.

ABBREVIATIONS

DDFT

Deep digital flexor tendon

STIR

Short tau inversion recovery

a.

Carbocaine, Pfizer Inc, New York, NY.

b.

Philips Gyroscan, Medical Systems, Best, The Netherlands.

c.

DepoMedrol, Pfizer Inc, New York, NY.

d.

Hylartin V, Pfizer Inc, New York, NY.

e.

Proc LOGISTIC, SAS/STAT, version 9.3, SAS Institute Inc, Cary, NC.

f.

Proc LIFEREG, SAS/STAT, version 9.3, SAS Institute Inc, Cary, NC.

References

  • 1. Sampson SN, Schneider RK, Gavin PR, et al. Magnetic resonance imaging findings in horses with recent onset navicular syndrome but without radiographic abnormalities. Vet Radiol Ultrasound 2009; 50: 339346.

    • Search Google Scholar
    • Export Citation
  • 2. Dyson S, Murray R. Magnetic resonance imaging evaluation of 264 horses with foot pain: the podotrochlear apparatus, deep digital flexor tendon and collateral ligaments of the distal interphalangeal joint. Equine Vet J 2007; 39: 340343.

    • Search Google Scholar
    • Export Citation
  • 3. Busoni V, Heimann M, Trenteseaux J, et al. Magnetic resonance imaging findings in the equine deep digital flexor tendon and distal sesamoid bone in advanced navicular disease—an ex vivo study. Vet Radiol Ultrasound 2005; 46: 279286.

    • Search Google Scholar
    • Export Citation
  • 4. Dyson S, Murray R, Schramme M, et al. Lameness in 46 horses associated with deep digital flexor tendonitis in the digit: diagnosis confirmed with magnetic resonance imaging. Equine Vet J 2003; 35: 681690.

    • Search Google Scholar
    • Export Citation
  • 5. Mair TS, Kinns J. Deep digital flexor tendonitis in the equine foot diagnosed by low-field magnetic resonance imaging in the standing patient: 18 cases. Vet Radiol Ultrasound 2005; 46: 458466.

    • Search Google Scholar
    • Export Citation
  • 6. Schramme MC, Murray RC, Blunden AS, et al. A comparison between magnetic resonance imaging, pathology, and radiology in 34 limbs with navicular syndrome and 25 control limbs, in Proceedings. 51st Annu Conv Am Assoc Equine Pract 2005;348358.

    • Search Google Scholar
    • Export Citation
  • 7. Gutierrez-Nibeyro SD, White NA, Werpy NM. Outcome of medical treatment for horses with foot pain: 56 cases. Equine Vet J 2010; 42: 680685.

    • Search Google Scholar
    • Export Citation
  • 8. Marsh CA, Schneider RK, Sampson SN, et al. Response to injection of the navicular bursa with corticosteroid and hyaluronan following high-field magnetic resonance imaging in horses with signs of navicular syndrome: 101 cases (2000–2008). J Am Vet Med Assoc 2012; 241: 13531364.

    • Search Google Scholar
    • Export Citation
  • 9. Dyson SJ, Murray R, Schramme MC. Lameness associated with foot pain: results of magnetic resonance imaging in 199 horses (January 2001–December 2003) and response to treatment. Equine Vet J 2005; 37: 113121.

    • Search Google Scholar
    • Export Citation
  • 10. Vanel M, Olive J, Gold S, et al. Clinical significance and prognosis of deep digital flexor tendinopathy assessed over time using MRI. Vet Radiol Ultrasound 2012; 53: 621627.

    • Search Google Scholar
    • Export Citation
  • 11. Cillán-García E, Milner PI, Talbot A, et al. Deep digital flexor tendon injury within the hoof capsule; does lesion type or location predict prognosis? Vet Rec 2013; 173: 70.

    • Search Google Scholar
    • Export Citation
  • 12. Sherlock CE, Kinns J, Mair TS. Evaluation of foot pain in the standing horse by magnetic resonance imaging. Vet Rec 2007; 161: 739744.

    • Search Google Scholar
    • Export Citation
  • 13. Dyson S, Murray R, Schramme M, et al. Magnetic resonance imaging of the equine foot: 15 horses. Equine Vet J 2003; 35: 1826.

  • 14. Tucker RL, Sampson SN. Magnetic resonance imaging protocols for the horse. Clin Tech Equine Pract 2007; 6: 215.

  • 15. Murray RC, Schramme MC, Dyson SJ, et al. Magnetic resonance imaging characteristics of the foot in horses with palmar foot pain and control horses. Vet Radiol Ultrasound 2006; 47: 116.

    • Search Google Scholar
    • Export Citation
  • 16. Rocconi RA, Sampson SN. Comparison of basilar and axial sesamoidean approaches for digital flexor tendon sheath synoviocentesis and injection in horses. J Am Vet Med Assoc 2013; 243: 869873.

    • Search Google Scholar
    • Export Citation
  • 17. Klein JP, Moeschberger ML. Survival analysis: techniques for censored and truncated data. 2nd ed. New York: Springer Science & Business Media Inc, 2003.

    • Search Google Scholar
    • Export Citation
  • 18. Bassage LH II, Ross MW. Diagnostic analgesia. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. 2nd ed. St Louis: Elsevier Saunders, 2011; 113114.

    • Search Google Scholar
    • Export Citation
  • 19. Scott EA. McDole M, Shires MH. A review of third phalanx fractures in the horse: sixty-five cases. J Am Vet Med Assoc 1979; 174: 13371343.

    • Search Google Scholar
    • Export Citation
  • 20. Dabareiner RM, Carter GK, Honnas CM. Injection of corticosteroids, hyaluronate, and amikacin into the navicular bursa in horses with signs of navicular area pain unresponsive to other treatments: 25 cases (1999–2002). J Am Vet Med Assoc 2003; 223: 14691474.

    • Search Google Scholar
    • Export Citation
  • 21. Bell CD, Howard RD, Taylor DS, et al. Outcomes of podotrochlear (navicular) bursa injections for signs of foot pain in horses evaluated via magnetic resonance imaging: 23 cases (2005–2007). J Am Vet Med Assoc 2009; 234: 920925.

    • Search Google Scholar
    • Export Citation
  • Figure 1—

    Transverse proton density magnetic resonance images of the foot and pastern region from horses demonstrating representative examples of DDFT core lesions. The dorsal aspect is at the top of the image. Tendon lesions are indicated by the open arrowheads. Lesion severity at each anatomic level was subjectively graded during retrospective evaluation of MRI images on a scale from 1 to 3 (least to most severe) as modified from a published scale.15 A—Core lesion at the level of the pastern joint covering < 2 mm2 (grade 1). B—Core lesion in the region proximal to the navicular bone covering > 2 mm2 but < 30% of the injured lobe (grade 2). C—Core lesion in the region distal to the navicular bone just proximal to the DDFT insertion on the distal phalanx covering > 30% of the injured lobe (grade 3).

  • Figure 2—

    Transverse proton density magnetic resonance images of the foot and pastern region demonstrating representative examples of DDFT sagittal split lesions. The dorsal aspect is at the top of the image. Tendon lesions are indicated by the open arrowheads. Notice the distention of the navicular bursa (borders indicated by the white arrows) as well as the intermediate signal intensity strands of tissue connecting the borders of the navicular bursa with the DDFT. This was interpreted as navicular bursitis with suspected adhesion formation. A—Sagittal split lesion at the level of the navicular bone covering < 2 mm2 (grade 1). B—Sagittal split lesion at the level of the navicular bone covering > 2 mm2 but < 30% of the injured lobe (grade 2). C—Sagittal split lesion in the region proximal to the navicular bone covering > 30% of the injured lobe (grade 3). See Figure 1 for remainder of key.

  • Figure 3—

    Transverse proton density magnetic resonance images of the foot and pastern region demonstrating representative examples of DDFT dorsal border lesions. The dorsal aspect is at the top of the image. Tendon lesions are indicated by open arrowheads. Notice the thickening and increase in signal intensity of the collateral sesamoidean ligament (white arrows). Notice the intermediate signal intensity strands of tissue occupying the space between the DDFT and collateral sesamoidean ligament. A—Dorsal border lesion exhibiting mild undulation of the dorsal border of the DDFT (grade 1). B—Dorsal border lesion exhibiting moderate irregularity of the dorsal border of the DDFT (grade 2). C—Dorsal border lesion exhibiting severe irregularity of the dorsal border of the DDFT (grade 3). All images were obtained in the region proximal to the navicular bone. See Figure 1 for remainder of key.

  • Figure 4—

    Sagittal proton density image of the foot and pastern region demonstrating the levels of the DDFT within the digit where injury commonly occurs. a = Pastern region. b = Region proximal to the navicular bone. c = Region at the navicular bone. d = Region distal to the navicular bone.

  • 1. Sampson SN, Schneider RK, Gavin PR, et al. Magnetic resonance imaging findings in horses with recent onset navicular syndrome but without radiographic abnormalities. Vet Radiol Ultrasound 2009; 50: 339346.

    • Search Google Scholar
    • Export Citation
  • 2. Dyson S, Murray R. Magnetic resonance imaging evaluation of 264 horses with foot pain: the podotrochlear apparatus, deep digital flexor tendon and collateral ligaments of the distal interphalangeal joint. Equine Vet J 2007; 39: 340343.

    • Search Google Scholar
    • Export Citation
  • 3. Busoni V, Heimann M, Trenteseaux J, et al. Magnetic resonance imaging findings in the equine deep digital flexor tendon and distal sesamoid bone in advanced navicular disease—an ex vivo study. Vet Radiol Ultrasound 2005; 46: 279286.

    • Search Google Scholar
    • Export Citation
  • 4. Dyson S, Murray R, Schramme M, et al. Lameness in 46 horses associated with deep digital flexor tendonitis in the digit: diagnosis confirmed with magnetic resonance imaging. Equine Vet J 2003; 35: 681690.

    • Search Google Scholar
    • Export Citation
  • 5. Mair TS, Kinns J. Deep digital flexor tendonitis in the equine foot diagnosed by low-field magnetic resonance imaging in the standing patient: 18 cases. Vet Radiol Ultrasound 2005; 46: 458466.

    • Search Google Scholar
    • Export Citation
  • 6. Schramme MC, Murray RC, Blunden AS, et al. A comparison between magnetic resonance imaging, pathology, and radiology in 34 limbs with navicular syndrome and 25 control limbs, in Proceedings. 51st Annu Conv Am Assoc Equine Pract 2005;348358.

    • Search Google Scholar
    • Export Citation
  • 7. Gutierrez-Nibeyro SD, White NA, Werpy NM. Outcome of medical treatment for horses with foot pain: 56 cases. Equine Vet J 2010; 42: 680685.

    • Search Google Scholar
    • Export Citation
  • 8. Marsh CA, Schneider RK, Sampson SN, et al. Response to injection of the navicular bursa with corticosteroid and hyaluronan following high-field magnetic resonance imaging in horses with signs of navicular syndrome: 101 cases (2000–2008). J Am Vet Med Assoc 2012; 241: 13531364.

    • Search Google Scholar
    • Export Citation
  • 9. Dyson SJ, Murray R, Schramme MC. Lameness associated with foot pain: results of magnetic resonance imaging in 199 horses (January 2001–December 2003) and response to treatment. Equine Vet J 2005; 37: 113121.

    • Search Google Scholar
    • Export Citation
  • 10. Vanel M, Olive J, Gold S, et al. Clinical significance and prognosis of deep digital flexor tendinopathy assessed over time using MRI. Vet Radiol Ultrasound 2012; 53: 621627.

    • Search Google Scholar
    • Export Citation
  • 11. Cillán-García E, Milner PI, Talbot A, et al. Deep digital flexor tendon injury within the hoof capsule; does lesion type or location predict prognosis? Vet Rec 2013; 173: 70.

    • Search Google Scholar
    • Export Citation
  • 12. Sherlock CE, Kinns J, Mair TS. Evaluation of foot pain in the standing horse by magnetic resonance imaging. Vet Rec 2007; 161: 739744.

    • Search Google Scholar
    • Export Citation
  • 13. Dyson S, Murray R, Schramme M, et al. Magnetic resonance imaging of the equine foot: 15 horses. Equine Vet J 2003; 35: 1826.

  • 14. Tucker RL, Sampson SN. Magnetic resonance imaging protocols for the horse. Clin Tech Equine Pract 2007; 6: 215.

  • 15. Murray RC, Schramme MC, Dyson SJ, et al. Magnetic resonance imaging characteristics of the foot in horses with palmar foot pain and control horses. Vet Radiol Ultrasound 2006; 47: 116.

    • Search Google Scholar
    • Export Citation
  • 16. Rocconi RA, Sampson SN. Comparison of basilar and axial sesamoidean approaches for digital flexor tendon sheath synoviocentesis and injection in horses. J Am Vet Med Assoc 2013; 243: 869873.

    • Search Google Scholar
    • Export Citation
  • 17. Klein JP, Moeschberger ML. Survival analysis: techniques for censored and truncated data. 2nd ed. New York: Springer Science & Business Media Inc, 2003.

    • Search Google Scholar
    • Export Citation
  • 18. Bassage LH II, Ross MW. Diagnostic analgesia. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. 2nd ed. St Louis: Elsevier Saunders, 2011; 113114.

    • Search Google Scholar
    • Export Citation
  • 19. Scott EA. McDole M, Shires MH. A review of third phalanx fractures in the horse: sixty-five cases. J Am Vet Med Assoc 1979; 174: 13371343.

    • Search Google Scholar
    • Export Citation
  • 20. Dabareiner RM, Carter GK, Honnas CM. Injection of corticosteroids, hyaluronate, and amikacin into the navicular bursa in horses with signs of navicular area pain unresponsive to other treatments: 25 cases (1999–2002). J Am Vet Med Assoc 2003; 223: 14691474.

    • Search Google Scholar
    • Export Citation
  • 21. Bell CD, Howard RD, Taylor DS, et al. Outcomes of podotrochlear (navicular) bursa injections for signs of foot pain in horses evaluated via magnetic resonance imaging: 23 cases (2005–2007). J Am Vet Med Assoc 2009; 234: 920925.

    • Search Google Scholar
    • Export Citation

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