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)

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

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Abstract

Objective—To determine treatment outcome on the basis of pathological changes identified on MRI and lameness duration in horses with navicular syndrome that underwent injection of corticosteroid and hyaluronan into the navicular bursa.

Design—Retrospective case series.

Animals—101 horses with navicular syndrome.

Procedures—Medical records of horses with signs of navicular syndrome evaluated between January 2000 and December 2008 were reviewed. Data on signalment, use of the horse, history, affected limbs, duration of lameness, findings on lameness examination, radiographic findings, MRI findings, treatment, and outcome were collected from the medical records. Follow-up information was obtained a minimum of 10 months after navicular bursa injection.

Results—Following navicular bursa injection, 76 of 101 (75%) horses returned to their intended use for a mean of 9.66 months, and 35 (35%) were sound at follow-up. Horses that had been lame for < 6 months before treatment were significantly more likely to return to their intended use, have a longer positive response to treatment, and be sound at follow-up, compared with horses that had a longer lameness history. Horses with primary deep digital flexor (DDF) tendonitis responded best to navicular bursa injection with rest and rehabilitation, followed by horses with navicular bursitis and horses with DDF tendonitis and adhesions to the collateral sesamoidean ligament of the distal sesamoid (navicular) bone. Horses with scar tissue in the proximal portion of the navicular bursa, adhesions from the navicular bone to the DDF tendon, or multiple abnormalities did not respond as well to treatment.

Conclusions and Clinical Relevance—Response to navicular bursa injection with corticosteroid and hyaluronan in horses with navicular syndrome was dependent on the disease process detected on MRI and duration of lameness.

Abstract

Objective—To determine treatment outcome on the basis of pathological changes identified on MRI and lameness duration in horses with navicular syndrome that underwent injection of corticosteroid and hyaluronan into the navicular bursa.

Design—Retrospective case series.

Animals—101 horses with navicular syndrome.

Procedures—Medical records of horses with signs of navicular syndrome evaluated between January 2000 and December 2008 were reviewed. Data on signalment, use of the horse, history, affected limbs, duration of lameness, findings on lameness examination, radiographic findings, MRI findings, treatment, and outcome were collected from the medical records. Follow-up information was obtained a minimum of 10 months after navicular bursa injection.

Results—Following navicular bursa injection, 76 of 101 (75%) horses returned to their intended use for a mean of 9.66 months, and 35 (35%) were sound at follow-up. Horses that had been lame for < 6 months before treatment were significantly more likely to return to their intended use, have a longer positive response to treatment, and be sound at follow-up, compared with horses that had a longer lameness history. Horses with primary deep digital flexor (DDF) tendonitis responded best to navicular bursa injection with rest and rehabilitation, followed by horses with navicular bursitis and horses with DDF tendonitis and adhesions to the collateral sesamoidean ligament of the distal sesamoid (navicular) bone. Horses with scar tissue in the proximal portion of the navicular bursa, adhesions from the navicular bone to the DDF tendon, or multiple abnormalities did not respond as well to treatment.

Conclusions and Clinical Relevance—Response to navicular bursa injection with corticosteroid and hyaluronan in horses with navicular syndrome was dependent on the disease process detected on MRI and duration of lameness.

Navicular syndrome continues to be one of the most common causes of forelimb lameness in many types of athletic horses.1 Diagnosis of navicular syndrome in the past has been made on the basis of clinical signs, response to diagnostic local anesthesia, radiographic findings, nuclear scintigraphy, and in some horses, ultrasonography and response to treatment.2–8 Experience with MRI over the past 12 years has improved the detection of bone and soft tissue injuries within the feet of horses with navicular syndrome.9,10 Magnetic resonance imaging has become a valuable diagnostic tool that allows recognition of many abnormalities within horses with navicular syndrome. As a result, treatment can now be based on the localization of the pathological abnormalities within the foot. Pathological changes in numerous structures within the foot, including the distal sesamoid (navicular) bone, distal sesamoidean impar ligament, CSL, navicular bursa, DDF tendon, collateral ligaments of the distal or proximal interphalangeal joint, distal digital annular ligament, distal phalanx, middle phalanx, or laminae, can cause clinical signs of navicular syndrome.9–19 Abnormalities in any of these structures have the potential to cause signs of pain, which is alleviated by injection of local anesthetic around the palmar digital nerves.9–19 Treatment depends on the duration of the problem and the location of the pathological change.15,20

Prior to MRI, case selection for injection of the navicular bursa was performed on the basis of clinical signs and failure to respond to treatment.21 Magnetic resonance imaging has allowed more specific identification of causes of lameness localized to the foot in horses. Horses with pathological changes in and adjacent to the navicular bursa can be identified on MRI images from a high-field (≥ 1.0-T) magnet.9–17,22,23 Outcome in a group of 23 horses treated by injection of the navicular bursa has been reported.20 Improved case selection on the basis of high-field MRI findings may improve the success of this treatment.

A frequent abnormality observed in horses with chronic navicular syndrome is fibrous tissue in the proximal aspect of the navicular bursa creating adhesions between the DDF tendon and the CSL.9 In an attempt to break down some of the scar tissue and adhesions, the navicular bursa may be injected with 4 to 5 mL (40 to 50 mg) of hyaluronan to create volume distention and high pressure within the bursa. Creating fluid pressure in the bursa may break down some of the restrictive scar tissue and increase relative movement of the DDF tendon through the proximal aspect of the navicular bursa.

The purpose of the study reported here was to determine the outcome in a large group of horses treated with injections of corticosteroids and hyaluronan into the navicular bursa on the basis of pathological changes identified on MRI. In addition, a new technique for pressurizing the navicular bursa is described and the outcome in treated horses is reported. We hypothesized that abnormalities detected on MRI would affect outcome in horses treated with injection of corticosteroids and hyaluronan into the navicular bursa.

Materials and Methods

Case selection—Medical records of all horses with signs of navicular syndrome examined at Washington State University between January 2000 and December 2008 were evaluated retrospectively. All horses had lameness localized to the heel region of the foot by injection of local anesthetic around the palmar or plantar digital nerves. Horses were selected for inclusion in the study if their lameness was improved by blocking the palmar or plantar digital nerves, they had undergone MRI of both front or hind feet, they were treated by injection of the navicular bursa with corticosteroids and hyaluronan, and if follow-up information from owners was available. Horses were excluded from the study if injection of the distal interphalangeal joint was performed in addition to injection of the navicular bursa.

Medical records review—Information obtained from the medical record included signalment, use of the horse, history, affected limbs, duration of lameness, radiographic findings, MRI findings, and treatment. Lameness was assessed by having horses move in straight lines and in circles in both clockwise and counterclockwise directions on a smooth hard surface. Lameness was scored by means of a modification of the American Association of Equine Practitioners grading system.24 Lameness grades were assigned as follows: 0 = no lameness observed, 1 = mild lameness without an observed head nod, 2 = mild head nod observed, 3 = obvious head nod observed, 4 = severe head nod and lameness noted at the walk, and 5 = non–weight bearing on the limb.

Horses were assigned to 2 groups on the basis of the duration of their lameness: < 6 months (short term) and ≥ 6 months (long term). In all horses, lameness was localized to the foot by means of injection of local anesthetic around the palmar or plantar digital nerves; 1.5 to 2 mL of 2% mepivacaine solution was injected over the medial and lateral palmar or plantar digital nerve of the lame limb, proximal to the collateral cartilages of the foot. Following local anesthesia in the affected limb, if the horse was then lame in the opposite limb, local anesthesia was performed in the contralateral limb. In some horses, analgesia of the DFTS was also performed on a separate day. Intrathecal anesthesia of the DFTS was performed with an 18 × 1.5-inch needle placed through the skin just distal and abaxial to the base of the lateral aspect of the proximal sesamoid bone and palmar or plantar to the digital neurovascular bundle.22 The needle was inserted at a 45° angle to the sagittal plane and directed proximal under the palmar or plantar annular ligament. This procedure was performed to determine the relative contribution to the horse's lameness as a result of DDF tendonitis that extended proximal to the navicular bursa.

Radiography—Horses were evaluated radiographically with 4 standard views of the front foot as follows: 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 palmar 45° proximal-palmarodistal oblique view of the navicular bone. Equivalent radiographic views of the hind foot were obtained as needed.

MRI—Magnetic resonance imaging evaluation was performed in all horses following induction of general anesthesia. Horses were anesthetized and placed in right lateral recumbency. The foot and pastern region of the forelimb or hind limb was evaluated by MRI with a high-field (1.0-T) magnet.a A human quadrate receiver coil was placed on the foot, and the foot was positioned in the isocenter of the magnet. Proton-density, T2-weighted, STIR, and 3-D gradient echo images were acquired. Sagittal, axial, and coronal MRI images were obtained via a standardized imaging protocol designed for evaluation of the front feet of horses (Appendix). All images were interpreted by a veterinarian experienced in MRI of horses' feet. Magnetic resonance images of lame horses were compared with images obtained from clinically normal horses.

Horses in the study were assigned to groups on the basis of the pathological abnormalities observed on MRI and the rationale for injecting the navicular bursa. Groups included horses that had increased fluid observed in the navicular bursa, horses that had fibrous scar tissue in the proximal aspect of the navicular bursa (with or without fluid), horses with DDF tendonitis in the area of the tendon that is covered by the bursa, horses with DDF tendonitis and adhesions to the CSL in the proximal portion of the navicular bursa, horses with cortical defects in the flexor surface of the navicular bone only, horses with adhesions between the navicular bone and the DDF tendon, and horses with multiple abnormalities, including DDF tendonitis, bursitis, and cortical defects in the flexor surface of the navicular bone. Adhesions from the navicular bone to the DDF tendon were diagnosed by the presence of hypointense tissue spanning the space between the DDF tendon and the navicular bone. Scar tissue in the bursa was diagnosed by the presence of hypointense tissue in the proximal aspect of the bursa. For the purpose of classification, adhesions had to be clearly identifiable on proton-density and STIR sequences and confirmed on the 3-D gradient echo.

Determination of treatment protocol was multifactorial and was made on the basis of pathological changes observed on MRI, history of lameness, and the desire to continue to have horses ridden. Horses with fluid or fibrous scar tissue within the navicular bursa underwent navicular bursa injection to decrease inflammation in the bursa. Horses with injury to the DDF tendon in the area of the tendon within the navicular bursa underwent navicular bursa injection to decrease inflammation in the DDF tendon. Horses with cortical defects in the flexor surface of the navicular bone underwent navicular bursa injection to decrease inflammation in the bursa and overlying DDF tendon. Some horses with adhesions between the navicular bone and DDF tendon or in the proximal aspect of the navicular bursa between the DDF tendon and CSL underwent navicular bursa injection with the application of injection pressure in an effort to break down the adhesions as well as decrease inflammation. Some horses underwent navicular bursa injection to decrease signs of pain and inflammation to allow them to continue in exercise, and others underwent navicular bursa injection and were placed in a 6-month rest and rehabilitation program. These decisions were made on the basis of duration of lameness, abnormalities observed on MRI, and the horse's intended use and performance schedule.

Navicular bursa injection and pressurization—All horses were treated with corticosteroids (40 mg of methylprednisolone acetate) and hyaluronan (10 mg of sodium hyaluronate) by injection into the navicular bursa.b,c Horses were premedicated with phenylbutazone (2.2 mg/kg [1.0 mg/lb], PO, q 12 h), and anesthesia was routinely induced with xylazine (1.1 mg/kg [0.5 mg/lb], IV), diazepam (0.5 mg/kg [0.23 mg/lb], IV), and ketamine (2.2 mg/kg, IV) and maintained with inhalation of isoflurane in oxygen or IV administration of a mixture of 10% guaifenesin solution, 1 g of ketamine, and 500 mg of xylazine. Horses were placed in lateral recumbency, and hair was shaved on the palmar or plantar aspect of the limb proximal to the heel bulbs and the skin aseptically prepped. A sterile 18-gauge, 3.5-inch-long spinal needle with stylet was used for the injections. The needle was inserted on midline in the depression between the junction of the collateral cartilages and the DDF tendon, proximal to the digital cushion. Correct placement of the needle was confirmed with fluoroscopy.d Following the navicular bursa injection, horses received phenylbutazone (2.2 mg/kg, PO, q 12 h) for 2 days.

While under anesthesia, horses with adhesions in the navicular bursa underwent navicular bursa injection with 3 to 5 mL (30 to 50 mg) of hyaluronan to create high pressure within the bursa in an attempt to break down some of the adhesions. The volume required to create distention and pressure varied with the size of the horse and the amount of fibrous tissue in the bursa. Sufficient pressure was determined by subjective assessment of pressure in the syringe. Under back pressure, the hyaluronan would return to the syringe; the navicular bursa was distended multiple times in this manner. Thereafter the hyaluronan was allowed to drain from the bursa into a syringe, leaving a volume of 1 to 2 mL (10 to 20 mg) within the bursa. The bursa was then injected with 1 mL of corticosteroid (40 mg of methylprednisolone acetate).b All horses were placed in padded compression bandages following injection of the navicular bursa.

Rest and rehabilitation—Horses treated with rest were placed in a 6-month rehabilitation program. Horses were confined to a stall with hand walking for the first 60 days. They were then turned out into a small paddock (approx 30 × 30 ft). Horses were not turned out in a large area for free exercise and were not returned to a regular riding program until 6 months after the start of rehabilitation. Some horses that were not lame at a trot at 4 months after injection were returned to a walk and trot exercise program with a rider in the fifth and sixth months of the program. Horses that continued in exercise after injection of the navicular bursa were given 2 days of stall rest and then returned to being ridden. All horses were correctively shod for navicular syndrome following treatment. Hoof imbalance was corrected, and the toe was shortened to aid in break over. Some horses were shod with pads over the frog and sole, and some horses were shod to provide elevation of their heels.

Follow-up—Follow-up information was obtained at a minimum of 10 months after injection of the navicular bursa by phone conversations with the owners. Follow-up information obtained included the ability of the horse to return to its intended use, length of time until back in performance, length of time that the horse was able to continue performing, whether the horse was still sound, whether injection of the navicular bursa had been repeated, other treatments, and whether corrective shoeing had been implemented. Outcome was considered successful if the horse was able to successfully return to its previous and intended use. If horses were placed in a rest and rehabilitation program, the length of time that the horse was able to continue performing was considered to begin following completion of the rest program. Horses were considered sound at follow-up if no reoccurrence of lameness was noted at the time of follow-up.

Statistical analysis—Overall outcome and outcome of treatment within groups was summarized. Outcome of treatment for horses that underwent pressurization of the navicular bursa by injection was also summarized. For purposes of analysis, horses were grouped according to lesion type, duration of lameness (< 6 months or ≥ 6 months), whether they were rested, and whether they were still sound at the time of follow-up. Data analysis was performed with a computer-based statistical program.e Continuous data were analyzed by use of the Kruskal-Wallis test and unpaired t test with Welch correction. Categorical data were compared via a Fisher exact test followed by a Bonferroni adjustment after finding significant differences among groups as a whole. A Fisher exact test was also used to test for associations between variables. Correlation of outcome with multiple variables was determined by logistic regression analysis. Values of P < 0.05 were considered significant.

Results

Signalment and history—One hundred one horses met the inclusion criteria; 70 were geldings, 29 mares, and 2 stallions. Mean age was 9.5 years (median, 9 years; range, 3 to 19 years). There were 66 Quarter Horses, 18 warm-bloods, 8 American Paint Horses, 5 Thoroughbreds, 2 Arabians, 1 Andalusian, and 1 Saddlebred. Total mean duration of lameness for all horses (prior to MRI) was 12 months (median, 6.5 months; range, 0.5 to 72 months). Mean duration of lameness in 40 horses that had been lame for ≤ 6 months was 3 months (median, 3 months; range, 0.5 to 5 months); mean duration of lameness in 61 horses that had been lame for ≥ 6 months was 17.6 months (median, 12 months; range, 6 to 72 months). Fifty-five horses were used for western performance (including roping, barrel racing, cutting, and reigning), 12 were used for dressage, 13 were used as hunters or jumpers, 12 were used for pleasure or trail riding, 4 were used as western pleasure show horses, and 5 were used as 3-day eventing horses.

Clinical findings—The mean lameness grade for all groups was similar. Mean ± SD lameness grades were 1.8 ± 0.034 for horses with increased fluid observed in the navicular bursa, 2.0 ± 0.014 for horses with fibrous scar tissue in the proximal aspect of the navicular bursa (with or without fluid), 2.0 ± 0.016 for horses with primary DDF tendonitis in the area of the tendon covered by the bursa, 2.14 ± 0.025 for horses with DDF tendonitis and adhesions to the CSL in the proximal portion of the navicular bursa, 2.66 ± 0.23 for horses with cortical defects in the flexor surface of the navicular bone only, 2.73 ± 0.256 for horses with adhesions between the navicular bone and the DDF tendon, and 2.8 ± 0.356 for horses with multiple abnormalities including DDF tendonitis, bursitis, and cortical defects in the flexor surface of the navicular bone. There was no significant difference in lameness grades among groups. Seventy of 101 (69%) horses had bilateral forelimb lameness, and 31 (31%) had unilateral lameness. Two horses had unilateral hind limb lameness. Mean lameness grades were 2.2 for unilateral and bilateral lameness. Seventy-eight of 101 (77%) horses had sensitivity to hoof testers over the middle third of the frog on at least 1 foot.

Radiography—All horses underwent radiography of the affected feet. Radiography was performed at Washington State University, or radiographs were sent for evaluation from the referring veterinarian. A specific cause of lameness could not be determined from radiographs in 93 of 101 (92%) horses. Four horses had radiographic defects in the flexor cortex of the navicular bone that were evident on palmar 45° proximal-palmarodistal oblique images of the navicular bone. One horse had a navicular bone cyst observed on a dorsal 60° proximal-palmarodistal oblique view of the navicular bone. Two horses had sclerosis of the navicular bone defined by loss of the corticomedullary junction on a palmar 45° proximal-palmarodistal oblique view of the navicular bone and lateromedial view of the foot. One horse had small periarticular bone proliferation observed on the middle phalanx and the extensor process of the distal phalanx on a lateromedial view of the foot.

MRI—All horses were placed into groups on the basis of pathological changes identified on MRI as follows: increased fluid observed in the navicular bursa (15 horses), fibrous scar tissue in the proximal aspect of the navicular bursa with or without increased fluid in the bursa (4 horses), primary DDF tendonitis (17 horses), DDF tendonitis with adhesions to the CSL in the proximal portion of the navicular bursa (41 horses), cortical defects in the flexor surface of the navicular bone only (6 horses), adhesions from the navicular bone to the DDF tendon (10 horses), and multiple abnormalities (8 horses; Table 1). Sixty-six of 101 (65%) of horses had injury to the DDF tendon in the portion of the tendon covered by the navicular bursa; in 47 (71%) of these horses, the tendonitis also extended proximally from the navicular bursa.

Table 1—

Summary of outcome by group and duration of lameness prior to treatment in 101 horses grouped by MRI findings.

MRI findingsDuration of lameness before injectionNo. of horsesNo. of horses that returned to intended useMean (range) months of soundness following injectionNo. of horses sound at follow-up
Navicular bursitis with increased fluid onlyAny15147 (1–24)3
< 6 mo7710 (2–24)3
≥ 6 mo874.5 (1–10)0
Navicular bursitis with scar tissue with or without fluidAny411.5 (0–5)0
< 6 mo0NANANA
≥ 6 mo411.5 (0–5)0
Primary DDF tendonitisAny171617 (0–48)11
< 6 mo121119.4 (0–48)8
≥ 6 mo5510 (3–12)3
DDF tendonitis with adhesions to the CSLAny413011 (0–36)15
< 6 mo171418 (0–48)9
≥ 6 mo24166.4 (0–30)6
Cortical defects in the flexor surface of the navicular bone onlyAny669.6 (2–30)2
< 6 mo2221 (12–30)2
≥ 6 mo444 (3–6)0
Adhesions from navicular bone to the DDF tendonAny1054 (0–24)1
< 6 mo1140
≥ 6 mo943.6 (0–24)1
Multiple abnormalitiesAny843.5 (0–18)1
< 6 mo11181
≥ 6 mo731.5 (0–6)0

NA = Not applicable.

Treatment—In addition to injection of the navicular bursa, 47 horses were also injected in the DFTS because the injured portion of the DDF tendon extended proximally from the navicular bursa. The 47 horses with additional injections of the DFTS included 9 horses with DDF tendonitis in the area of the tendon that is covered by the bursa, 33 horses with DDF tendonitis and adhesions to the CSL in the proximal portion of the navicular bursa, and 5 horses with multiple abnormalities. The DFTS was injected with corticosteroids (100 mg of methylprednisolone acetate) and hyaluronan (20 mg of sodium hyaluronate).c,d Logistic regression analysis revealed that DFTS injection, navicular bursa injection, and lameness < 6 months in duration were significantly (P < 0.001) correlated with a horse's ability to return to intended use for a longer time and remain sound.

Pressurization of the navicular bursa by injection was performed in 26 of 101 (26%) horses. All horses treated in this manner had scar tissue in the proximal portion of the navicular bursa (n = 1), adhesions present from the CSL to the DDF tendon (13), or adhesions from the navicular bone to the DDF tendon (10). Two other horses with scar tissue in the navicular bursa underwent pressurization of the navicular bursa by injection; 1 horse had cortical defects in the flexor surface of the navicular bone, and another horse had multiple abnormalities.

Thirty-one of 101 (31%) horses were placed in a 6-month rest and rehabilitation program, and 70 of 101 (69%) horses were returned to intended use 2 to 3 days following injections. Rested horses that were still working at the time of follow-up had been back in work a mean of 19 months (range, 4 months to 4 years). Recommendations for corrective shoeing were made following injections on the basis of foot conformation and hoof-pastern axis at the time of treatment.

Outcome—Seventy-six of 101 (75%) horses returned to their intended use for a mean of 9.62 months (median, 5 months; range, 0 to 48 months), and 35 of 101 (35%) horses were still sound at the time of follow-up. Outcome within groups was summarized (Table 1).

All horses with navicular bursitis as identified by excessive fluid in the bursa (n = 15) on MRI were returned to work 2 days following injections (Figure 1). Horses that had been lame for < 6 months and had navicular bursitis characterized by excessive fluid had an improved outcome over horses in the same group that had been lame > 6 months. Horses with a navicular bursitis consisting of scar tissue in the proximal portion of the navicular bursa (n = 4) had a poor outcome (Figure 2).

Figure 1—
Figure 1—

Representative sagittal (A) and transverse (B) proton-density MRI images of a foot of a horse in a group of horses characterized by detection of increased fluid in the navicular bursa (n = 15). Notice the severe navicular bursitis (arrow). Dashed line indicates plane (slice) of transverse image (B).

Citation: Journal of the American Veterinary Medical Association 241, 10; 10.2460/javma.241.10.1353

Figure 2—
Figure 2—

Representative sagittal (A) and transverse (B) proton-density MRI images of the foot of a horse in a group of horses characterized by detection of scar tissue in the proximal aspect of the navicular bursa (with or without fluid; n = 4). Notice the large amount of scar tissue (arrow). Dashed line indicates plane (slice) of transverse image (B).

Citation: Journal of the American Veterinary Medical Association 241, 10; 10.2460/javma.241.10.1353

The 17 horses with primary DDF tendonitis had the best outcome of any group (Figure 3; Table 1). All but 1 of 12 horses with primary DDF tendonitis that had been lame for < 6 months were rested after treatment; 10 of the 11 rested horses were able to return to their intended use for a mean of 21 months (range, 0 to 48 months), with 8 still sound at follow-up. The 1 horse with primary DDF tendonitis that had been lame for < 6 months that was not rested was able to return to its intended use for 7 months but did not remain sound. Two of 5 horses with primary DDF tendonitis that had been lame for > 6 months were rested, and both were sound at follow-up 15 months after treatment. Three of 5 horses that had been lame for > 6 months were not rested, and all returned to their intended use (mean, 7 months), with 1 sound at follow-up. Rested horses with primary DDF tendonitis that were still working at the time of follow-up had been back in work a mean of 25 months (range, 12 to 48 months).

Figure 3—
Figure 3—

Representative transverse proton-density MRI images of the foot of a horse in a group of horses characterized by detection of DDF tendonitis in the area of the tendon that is covered by the navicular bursa (n = 17). The DDF tendon is imaged distal to the distal sesamoid (navicular) bone (A), at the level of the navicular bone (B), and just proximal to the navicular bone (C). Notice the DDF tendon lesion (arrow).

Citation: Journal of the American Veterinary Medical Association 241, 10; 10.2460/javma.241.10.1353

There were more horses with DDF tendonitis and adhesions from the CSL to the DDF tendon (n = 41) than in any other group (Figure 4; Table 1). Twelve of 17 horses with DDF tendonitis with adhesions from the CSL to the DDF tendon that had been lame for < 6 months were rested after treatment; 10 of the 12 rested horses were able to return to their intended use for a mean of 22 months (range, 0 to 48 months), with 8 sound at follow-up. Five horses in this group with lameness < 6 months in duration were not rested after treatment, and 4 of these horses returned to their intended use for a mean of 7 months, but only 1 horse was still sound at follow-up. Four of the 24 horses with DDF tendonitis with adhesions from the CSL to the DDF tendon that had been lame for > 6 months were rested after treatment, and 3 were able to return to their intended use for a mean of 12 months (range, 0 to 18 months), with 3 horses sound at follow-up. The majority (20/24 [83%]) of horses with DDF tendonitis and adhesions to the CSL in the proximal portion of the navicular bursa that had been lame for > 6 months were not rested; 13 of 20 (65%) horses were able to return to their intended use for a mean of 5.25 months (range, 0 to 30 months), with 3 sound at follow-up. Within this group, horses that were rested were significantly (P < 0.001) more likely to be sound. Logistic regression analysis revealed that for horses with DDT tendonitis and adhesions to the CSL, lameness for < 6 months before treatment and rest after treatment was significantly (P < 0.001) correlated with a horse's ability to return to intended use for a longer time and remain sound.

Figure 4—
Figure 4—

Representative sagittal (A) and transverse (B) proton-density MRI images of the foot of a horse in a group of horses characterized by detection of DDF tendonitis and adhesions to the CSL in the proximal portion of the navicular bursa (n = 41). Notice the DDF tendon lesion (arrow) just proximal to the navicular bone with adhesions (arrowhead) to the CSL of the navicular bone. Dashed line indicates plane (slice) of transverse image (B).

Citation: Journal of the American Veterinary Medical Association 241, 10; 10.2460/javma.241.10.1353

All 6 horses with cortical defects in the flexor surface of the navicular bone returned to their intended use (Figure 5; Table 1). No horses with cortical defects in the flexor surface of the navicular bone were rested after treatment. None of the horses had radiographic evidence of cortical defects in the flexor surface of the navicular bone, and all 6 horses also had navicular bone edema evident on MRI.

Figure 5—
Figure 5—

Representative sagittal (A) and transverse (B) STIR MRI images of the foot of a horse in a group of horses characterized by detection of cortical defects in the flexor surface of the navicular bone only (n = 6). Notice the cortical defect (arrows) on the palmar surface of the navicular bone. Dashed line indicates plane (slice) of transverse image (B).

Citation: Journal of the American Veterinary Medical Association 241, 10; 10.2460/javma.241.10.1353

Horses with adhesions from the navicular bone to the DDF tendon (n = 10) had a poor outcome (Figure 6). All horses with this lesion were immediately returned to their intended use 2 days following injection. Horses with multiple abnormalities (n = 8) detected on MRI also had a poor outcome (Figure 7); abnormalities included defects in the flexor cortex of the navicular bone, navicular bone edema, CSL desmitis, DDF tendonitis, adhesions between the CSL and DDF tendon, or increased fluid in the navicular bursa.

Figure 6—
Figure 6—

Representative transverse proton-density (A) and axial 3-D gradient echo (B) MRI images of the foot of a horse in a group of horses characterized by detection of adhesions between the navicular bone and the DDF tendon (n = 10). Notice the area of abnormal hypointense tissue, relative to bursal fluid, within the navicular bursa at the palmar aspect of the navicular bone (arrow) representing an adhesion from the navicular bone to the DDF tendon. Cortical erosion on the flexor surface of the navicular bone is evident.

Citation: Journal of the American Veterinary Medical Association 241, 10; 10.2460/javma.241.10.1353

Figure 7—
Figure 7—

Representative sagittal (A) and transverse (B) proton-density MRI images of the foot of a horse in a group of horses characterized by detection of multiple abnormalities including DDF tendonitis, bursitis, and cortical defects in the flexor surface of the navicular bone (n = 8). A—Notice the enlarged collateral suspensory ligament of the navicular bone (star), a cortical defect in the flexor surface of the navicular bone (arrowhead), and an enlarged distal sesamoidean impar ligament (arrow). B—The DDF tendon lesion (arrowhead) and adhesions from the collateral suspensory ligament of the navicular bone to the DDF tendon (arrow) are evident.

Citation: Journal of the American Veterinary Medical Association 241, 10; 10.2460/javma.241.10.1353

Duration of lameness affected outcome. Thirty-six of 40 (90%) horses with lameness < 6 months in duration were able to return to their intended use after treatment for a mean of 16 months (range, 0 to 48 months), with 22 of 40 (55%) horses still sound at follow-up. In comparison, 40 of 61 (66%) horses with lameness ≥ 6 months in duration were able to return to their intended use after treatment for a mean of 5.4 months (range, 0 to 30 months), with 12 of 61 (20%) horses still sound at follow-up. Horses with lameness < 6 months in duration were significantly more likely to return to their previous use (P = 0.009) for a longer time (P < 0.001) and be sound at follow-up (P = 0.002) than were horses with lameness > 6 months in duration. Early detection of DDF tendonitis also affected outcome. Horses with primary DDF tendonitis (n = 17) that had been lame for < 6 months were more likely to be sound after treatment and the positive effects of injection of the navicular bursa lasted longer in these horses, compared with horses with primary DDF tendonitis that had been lame for > 6 months before treatment. In horses with DDF tendonitis and adhesions from the CSL to the DDF tendon (n = 41), positive effects of injection of the navicular bursa were significantly (P = 0.023) longer lasting in horses with lameness < 6 months in duration, compared with horses in the same group with lameness > 6 months in duration. Positive effects of injection of the navicular bursa also were significantly (P = 0.045) longer lasting in horses with navicular bursitis < 6 months in duration, compared with horses in the same group with lameness > 6 months in duration. Logistic regression analysis revealed that lameness < 6 months in duration before treatment was significantly (P < 0.001) correlated with a horse's ability to return to intended use for a longer time and remain sound.

Rest also affected outcome. Fifty of the 70 (71%) horses that were immediately returned to work after treatment were able to return to their intended use for a mean of 5.5 months (range, 0 to 30 months), with 12 of 70 (17%) still sound at follow-up; 26 of 31 (84%) horses placed into a rest and rehabilitation program after treatment returned to their intended use for a mean of 19 months (range, 0 to 48 months), and 22 of 31 (71%) were still sound at follow-up. Horses that were rested were significantly more likely to be sound (P < 0.001) and for a longer time (P < 0.001), compared with horses that were not rested. When comparing horses with lameness < 6 months in duration (n = 40) that were rested (24) after treatment versus those that were not rested (16), significantly (P = 0.025) more rested horses were sound (17) than were nonrested horses (5) and for a significantly (P < 0.001) longer mean time (21 vs 8.3 months, respectively). Logistic regression analysis revealed that for horses that have been lame for < 6 months before treatment, rest after treatment was significantly (P < 0.001) correlated with a horse's ability to return to intended use for a longer time and remain sound.

Fifty-one of 70 (73%) horses with bilateral lameness were able to return to their intended use for a mean of 7.5 months (range, 0 to 36 months), and 18 of 70 (26%) were still sound at follow-up. In comparison, 24 of 31 (77%) horses with unilateral lameness were able to return to their intended use for a mean of 15 months (range 0 to 48 months), and 16 of 31 (52%) were sound at follow-up. Positive effects of injection of the navicular bursa were significantly (P = 0.023) longer lasting in horses with unilateral lameness. Logistic regression analysis revealed that unilateral lameness < 6 months in duration in horses was significantly (P < 0.001) correlated with primary DDF tendonitis or DDF tendonitis with adhesions from the CSL to the DDF tendon.

Twenty-six of 101 (26%) horses underwent pressurization of the navicular bursa by injection; all horses that underwent this procedure had scar tissue or adhesions detected on MRI in the navicular bursa. Sixteen of 26 (62%) horses that underwent pressurization of the navicular bursa returned to their intended use for a mean of 6.7 months (range, 0 to 36 months), and 6 of 26 (23%) horses were still sound at follow-up. Eleven of 13 horses with DDF tendonitis and adhesions to the CSL underwent pressurization of the navicular bursa and returned to their intended use for a mean of 10 months; 5 were still sound at follow-up. All horses with adhesions between the navicular bone and the DDF tendon underwent pressurization of the navicular bursa.

Most horses that underwent pressurization of the navicular bursa by injection had been lame for > 6 months (n = 20). Six horses that had been lame for < 6 months (mean, 3 months) returned to their intended use for a mean of 16 months (range, 4 to 36 months), and 3 were still sound at follow-up. All 3 horses that were still sound at follow-up had been rested after treatment. Of the 20 horses that were lame for > 6 months, 11 (55%) were able to return to their intended use for a mean of 4.6 months. Only 3 of 20 the horses that had been lame for > 6 months were sound at follow-up; 2 of these horses had been rested after treatment. In horses that underwent pressurization of the navicular bursa by injection, rest after treatment significantly (P < 0.001) improved long-term soundness.

The entire study population was evaluated to determine whether there was a significant difference in outcome on the basis of pathological abnormalities detected on MRI. There was a significant difference among all groups in the ability of horses to return to their previous use (P = 0.003), longevity of the positive effects from injection of the navicular bursa (P < 0.001), and percentage of horses sound at follow-up (P = 0.012), so a pairwise comparison via Bonferroni adjustment was used to determine difference in outcome among groups on the basis of disease detected on MRI. Horses with DDF tendonitis were more likely to return to their intended use and positive effects of injection of the navicular bursa lasted longer in these horses, compared with horses with scar tissue in the proximal portion of the navicular bursa, adhesions from the navicular bone to the DDF tendon, and multiple abnormalities. Additionally, the number of horses still sound at follow-up was significantly greater if primary DDF tendonitis was diagnosed, compared with all other groups. Rested horses with primary DDF tendonitis were more likely to be sound, compared with nonrested horses in the same group. Horses with adhesions from the CSL to the DDF tendon were compared with horses with primary DDF tendonitis to determine the effect of adhesions to the CSL on outcome. Additionally, horses with DDF tendonitis and adhesions present from the DDF tendon to the CSL were less likely to be sound at follow-up than were horses with primary tendonitis alone.

Horses with navicular bursitis were more likely to return to their intended use than were horses with scar tissue present in the proximal portion of the navicular bursa (P = 0.016), adhesions from the navicular bone to the DDF tendon (P = 0.022), and multiple abnormalities (P = 0.033). Horses with cortical defects in the flexor surface of the navicular bone with adhesions from the navicular bone to the DDF tendon were significantly less likely to return to their intended use than were horses with navicular bursitis, primary DDF tendonitis, DDF tendonitis with adhesions from the CSL to the DDF tendon, and cortical defects in the flexor surface of the navicular bone only. Horses with multiple abnormalities detected on MRI were significantly less likely to return to their intended use than were horses with navicular bursitis, primary DDF tendonitis, or DDF tendonitis and adhesions from the CSL to the DDF tendon.

Discussion

The marked differences in outcome between groups of horses in this study indicate that identification of specific abnormalities via MRI does affect prognosis and supports our hypothesis. Previously, injection of the navicular bursa with corticosteroids and hyaluronan had been reserved for cases of lameness that did not respond to corrective shoeing, administration of NSAIDs, or injections of corticosteroids in the distal interphalangeal joint.2,3,21 The horses in this study were injected in the navicular bursa or the navicular bursa and DFTS after MRI revealed pathological changes in the bursa or within the portion of the DDF tendon covered by the navicular bursa. The fact that > 70% of horses with DDF tendonitis were able to return to their intended use for a mean of 14 months and that > 50% were still sound at follow-up demonstrates the importance of having an accurate detection of abnormalities from MRI. It also suggests that horses with injuries in the portion of the DDF tendon covered by the bursa that also extend proximally in the tendon to the area covered by the sheath may benefit from additional injection of the DFTS. The poor outcome in horses with multiple abnormalities observed on MRI also supports the importance of MRI findings when making treatment decisions and giving owners a prognosis for a horse to return to its intended use.

The efficacy of injection of the navicular bursa was highly dependent on the disease process detected by MRI. When pathological changes were evaluated among groups, there were some abnormalities that were associated with a poor outcome. Horses that had a severe amount of scar tissue in the proximal aspect of the bursa (return intended use rate, 25%) responded poorly to injection of the navicular bursa; however, there were only 4 horses in this group. Horses with multiple abnormalities (return intended use rate, 50%) and adhesions from the navicular bone to the DDF tendon (return intended use rate, 50%) also had poor results. Only 4 horses had radiographically detectable cortical defects in the flexor surface of the navicular bone, and all of these horses had multiple abnormalities detected on MRI. Many horses in these groups were able to return to their intended use; however, the mean time that a positive injection effect lasted in these horses was < 4 months. Repeat injections may be necessary for horses to continue to be ridden for longer periods. Corticosteroids decrease inflammation, but their inability to eliminate the restrictive scar tissue adhesions is a possible reason for the poor response to injections. Horses with cortical defects in the flexor surface of the navicular bone alone responded well to injection of the navicular bursa (return to intended use rate, 100%). This is in contrast to other reports20,21 that horses with cortical defects in the flexor surface of the navicular bone respond poorly to injection of the navicular bursa. However, in the present study, horses with cortical defects in the flexor surface of the navicular bone only did not have radiographic evidence of lucency in the flexor cortex of the navicular bone. Magnetic resonance imaging of the foot can recognize small cortical defects in the flexor surface of the navicular bone that are not visible on radiographs.

Horses with DDF tendonitis responded significantly better to injection of the navicular bursa, compared with horses with other MRI findings. Injection of the navicular bursa in many horses was only part of the treatment; horses were also injected in the DFTS. Magnetic resonance imaging findings allow us to treat all of the horse's problems, and injection of the sheath was important in these horses. It is not possible to determine which of these treatments was more important to a successful outcome. Deep digital flexor tendonitis was the most common injury (58%), with primary injury to the DDF tendon in 17 of 101 (17%) horses and DDF tendonitis with adhesions to the CSL in 41 of 101 (41%) horses. The incidence of DDF tendonitis in the present study is similar to reports9,10,13 of an incidence of 59% as detected by MRI. In 1 study,10 following MRI detection of DDF tendonitis, 28% of affected horses were sound at follow-up. In contrast, results in the present study were better; horses with primary DDF tendonitis had better rates of return to intended use (94%) and long-term soundness (65%). When DDF tendonitis is present in close proximity to the navicular bone, the addition of injection of the navicular bursa may be beneficial to long-term soundness, compared with rest and rehabilitation alone. Two horses with primary DDF tendonitis > 6 months in duration were placed into a rest and rehabilitation program following navicular bursa and DFTS injections. Both horses were still sound at the time of follow-up. This suggests that some horses with DDF tendonitis > 6 months in duration may be able to return to their intended use and be sound long term following injections and rehabilitation.

The most common injury detected by MRI in the present study was DDF tendonitis with concurrent adhesions from the CSL to the DDF tendon. Recent reports9 suggest that a high proportion (64%) of horses with DDF tendonitis at the level of the navicular bone or just proximal to the navicular bone also have adhesions from the DDF tendon to the CSL of the navicular bone. The incidence was similar in the present study in that 70% of horses with a DDF tendon also had adhesion from the CSL of the navicular bone to the DDF tendon. Deep digital flexor tendonitis was present in all horses in this group, and all horses also had mild to moderate desmitis of the CSL of the navicular bone. The response to injections (return to intended use and duration of the positive response) in horses with concurrent adhesions from the CSL to the DDF tendon was low; fewer of those horses were sound at follow-up, compared with horses with primary DDF tendonitis alone. However, outcome following injections when adhesions were present from the CSL to the DDF tendon was significantly better, compared with groups with adhesions from the navicular bone to the DDF tendon, scar tissue in the proximal portion of the navicular bursa, and multiple abnormalities. The presence of adhesions between the DDF tendon and the CSL appears to worsen the prognosis for horses to respond to injection of the navicular bursa.

Horses in the present study with primary bursitis had a good response to injection of the navicular bursa. Studies20 suggest that horses with bursitis respond better to injection of the navicular bursa than do horses with other MRI findings, which was not the case in the present study when other outcome variables were evaluated. Return to intended use of horses with bursitis was similar to that of horses with DDF tendonitis; however, duration of positive response to injection (P = 0.009) and number of horses sound at follow-up (P = 0.032) were significantly decreased. Injections of the bursa with corticosteroid decrease inflammation of the navicular bursa and surrounding structures, which could explain the excellent short-term response. However, a decreased long-term response may occur because the source of inflammation is not eliminated. Despite reoccurrence of lameness, injections of the navicular bursa did allow most horses to return to their intended use for a reasonable amount of time.

Rest has not been a routinely recommended treatment for horses with navicular syndrome or signs of palmar heel pain.2,3,20,21 In the present study, rested horses were able to return to their intended use for a mean of 19 months, and 71% were still sound at follow-up, which contrasts with nonrested horses being only able to return to their intended use for a mean of 5.5 months, with only 17% still sound at follow-up. This supports the value of resting some of these horses. The successful outcome cannot be solely attributed to injection of the navicular bursa; rest alone may result in improvement in these horses. Rest and rehabilitation were used most frequently in horses with DDF tendonitis. The favorable response to rest was related to specific MRI findings as well as the treatment.

Pressurization of the navicular bursa by injection was performed in an attempt to break down restrictive scar tissue adhesions. It appears that restrictive scar tissue adhesions considerably worsen the prognosis for return to intended use and long-term soundness. Creating fluid pressure within the confines of the bursa may disrupt some of the restrictive scar tissue. Twenty-six horses in this study had this treatment. Most horses that underwent pressurization of the navicular bursa had more severe adhesion and severe abnormalities than horses that did not receive this treatment. With no control horses, it is difficult to predict the outcome response in creating fluid pressure within the bursa.

In this study, horses with unilateral lameness that received injections of the navicular bursa responded better than horses with bilateral lameness. Injections in horses with unilateral lameness lasted for a longer period, and more horses were sound at follow-up. Most horses that were lame in only 1 limb had DDF tendonitis that had caused lameness for < 6 months, which explains the improved outcome. Horses with injuries to the DDF tendon that had caused lameness for < 6 months had a better chance of being sound long term.

More than three-fourths of the horses in the present study had sensitivity to hoof testers over the middle of the frog on at least 1 limb, which correlates with the location of the pathological changes in all of the horses. However, not all horses were sensitive to hoof testers, despite pathological changes observed on MRI of the navicular area. This indicates that sensitivity to hoof testers is an inconsistent clinical sign. Degree of lameness was uniform among groups, indicating that the severity of lameness cannot always be used to determine degree of disease present.

Horses with lameness < 6 months in duration, independent of pathological changes within the foot, responded significantly better to injection of the navicular bursa than horses with lameness > 6 months in duration. This stresses the importance of early MRI evaluation and treatment when dealing with problems in the foot.

Success (75% return to intended use) following injection of the navicular bursa was similar to that in other studies, which found 80%21 and 74%20 of horses were able to return to their intended use for a duration of 4.621 and 7.320 months. In contrast to previous studies, duration of the positive effects of navicular bursa injection in the present study was substantially longer (ie, 9.66 months). This difference is likely the result of treatment of horses with DDF tendonitis in the region of the navicular bursa.

ABBREVIATIONS

CSL

Collateral sesamoidean ligament

DDF

Deep digital flexor

DFTS

Digital flexor tendon sheath

STIR

Short tau inversion recovery

a.

Gyroscan, Philips Medical Systems, Best, The Netherlands.

b.

Depomedrol, Pfizer Inc, New York, NY.

c.

Hylartin V, Pfizer Inc, New York, NY.

d.

BV-29, Phillips Medical Systems, Best, The Netherlands.

e.

Statistical Analysis System (SAS), version 9.2, SAS Institute Inc, Cary, NC.

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Appendix

Parameters of high-field (≥ 1.0-T magnet) MRI used for the evaluation of the equine forelimb foot and pastern region.

Image planeSequenceRT (ms)ET (ms)FA (°)FOV (cm)RFOV (cm)MatrixNo. of slicesThickness (mm)Gap (mm)Time (min)
TransTSE T2W2,116100901510.5256 × 5123040.55:08*
TransTSE PD2,11611901510.5256 × 5123040.55:08*
TransTSE PD2,00030901515512 × 5122020.22:54
TransSTIR1,72535901510.5192 × 256303.51.04:42
Trans3-D GE479251010192 × 256301.5−1.53:13
SagTSE T2W3,395110901410256 × 5122240.52:21
SagTSE PD3,39514901410256 × 5122240.52:21
SagSTIR1,50035901410256 × 256223.50.55:48
Dorsal3-D GE479251010192 × 256301.5−1.53:13

T2-weighted and proton-density sequences are collected together during the turbo spin echo scan.

Inversion time for STIR sequences is 140 milliseconds.

ET = Echo time. FA = Flip angle. FOV = Field of view. GE = Gradient echo. PD = Proton density. RFOV = Related field of view. RT = Repetition time. Sag = Sagittal. Trans = Transverse. TSE = Turbo spin echo. T2W = T2-weighted.

Contributor Notes

Dr. Marsh's present address is Department of Large Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843.

Address correspondence to Dr. Marsh (cmarsh@cvm.tamu.edu).
  • Figure 1—

    Representative sagittal (A) and transverse (B) proton-density MRI images of a foot of a horse in a group of horses characterized by detection of increased fluid in the navicular bursa (n = 15). Notice the severe navicular bursitis (arrow). Dashed line indicates plane (slice) of transverse image (B).

  • Figure 2—

    Representative sagittal (A) and transverse (B) proton-density MRI images of the foot of a horse in a group of horses characterized by detection of scar tissue in the proximal aspect of the navicular bursa (with or without fluid; n = 4). Notice the large amount of scar tissue (arrow). Dashed line indicates plane (slice) of transverse image (B).

  • Figure 3—

    Representative transverse proton-density MRI images of the foot of a horse in a group of horses characterized by detection of DDF tendonitis in the area of the tendon that is covered by the navicular bursa (n = 17). The DDF tendon is imaged distal to the distal sesamoid (navicular) bone (A), at the level of the navicular bone (B), and just proximal to the navicular bone (C). Notice the DDF tendon lesion (arrow).

  • Figure 4—

    Representative sagittal (A) and transverse (B) proton-density MRI images of the foot of a horse in a group of horses characterized by detection of DDF tendonitis and adhesions to the CSL in the proximal portion of the navicular bursa (n = 41). Notice the DDF tendon lesion (arrow) just proximal to the navicular bone with adhesions (arrowhead) to the CSL of the navicular bone. Dashed line indicates plane (slice) of transverse image (B).

  • Figure 5—

    Representative sagittal (A) and transverse (B) STIR MRI images of the foot of a horse in a group of horses characterized by detection of cortical defects in the flexor surface of the navicular bone only (n = 6). Notice the cortical defect (arrows) on the palmar surface of the navicular bone. Dashed line indicates plane (slice) of transverse image (B).

  • Figure 6—

    Representative transverse proton-density (A) and axial 3-D gradient echo (B) MRI images of the foot of a horse in a group of horses characterized by detection of adhesions between the navicular bone and the DDF tendon (n = 10). Notice the area of abnormal hypointense tissue, relative to bursal fluid, within the navicular bursa at the palmar aspect of the navicular bone (arrow) representing an adhesion from the navicular bone to the DDF tendon. Cortical erosion on the flexor surface of the navicular bone is evident.

  • Figure 7—

    Representative sagittal (A) and transverse (B) proton-density MRI images of the foot of a horse in a group of horses characterized by detection of multiple abnormalities including DDF tendonitis, bursitis, and cortical defects in the flexor surface of the navicular bone (n = 8). A—Notice the enlarged collateral suspensory ligament of the navicular bone (star), a cortical defect in the flexor surface of the navicular bone (arrowhead), and an enlarged distal sesamoidean impar ligament (arrow). B—The DDF tendon lesion (arrowhead) and adhesions from the collateral suspensory ligament of the navicular bone to the DDF tendon (arrow) are evident.

  • 1.

    Ackerman N, Johnson JH, Dorn CR. Navicular disease in the horse: risk factors, radiographic changes, and response to therapy. J Am Vet Med Assoc 1977; 170: 183187.

    • Search Google Scholar
    • Export Citation
  • 2.

    Dabareiner RM, Carter GK. Diagnosis, treatment, and farriery for horses with chronic heel pain. Vet Clin North Am Equine Pract 2003; 19: 417441.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3.

    Turner TA. Diagnosis and treatment of the navicular syndrome in horses. Vet Clin North Am Equine Pract 1989; 5: 131144.

  • 4.

    Wright IM. A study of 118 cases of navicular disease: radiological features. Equine Vet J 1993; 25: 493500.

  • 5.

    Wright IM. A study of 118 cases of navicular disease: clinical features. Equine Vet J 1993; 25: 488492.

  • 6.

    Widmer WR, Buckwalter KA, Fessler JF, et al. Use of radiography, computed tomography and magnetic resonance imaging for evaluation of navicular syndrome in the horse. Vet Radiol Ultrasound 2000; 41: 108116.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7.

    Busoni V, Denoix JM. Ultrasonography of the podotrochlear apparatus in the horse using a transcuneal approach: technique and reference images. Vet Radiol Ultrasound 2000; 42: 534540.

    • Search Google Scholar
    • Export Citation
  • 8.

    Bolen G, Busoni V, Jacqmot O, et al. Sonographic anatomy of the palmarodistal aspect of the equine digit. Vet Radiol Ultrasound 2007; 48: 270275.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9.

    Sampson SN. Magnetic resonance evaluation of the foot in lame horses, in Proceedings. Am Coll Vet Surg Vet Symp 2010; 127129.

  • 10.

    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
  • 11.

    Dyson SJ, Murray RC, Schramme MC, et al. Magnetic resonance imaging of the equine foot: 15 horses. Equine Vet J 2003; 35: 1826.

  • 12.

    Dyson SJ, Murray RC, Schramme MC, et al. Magnetic resonance imaging in 18 horses with palmar foot pain, in Proceedings. 48th Annu Meet Am Assoc Equine Pract 2002; 145154.

    • Search Google Scholar
    • Export Citation
  • 13.

    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.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14.

    Zubrod CJ, Barrett MF. Magnetic resonance imaging of tendon and ligament injuries. Clin Tech Equine Pract 2007; 6: 217229.

  • 15.

    Kofler J, Kneissl S, Malleczek D. MRI and CT diagnosis of acute desmopathy of the lateral collateral semoidean (navicular) ligament and long-term outcome in a horse. Vet J 2007; 174: 410413.

    • Crossref
    • Search Google Scholar
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  • 16.

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