Conservative management of equine tarsal collateral ligament injuries may allow return to normal performance

Claudia Fraschetto Center of Imaging and Research on the Equine Locomotor Injuries, Normandie Equine Vallée, Goustranville, France

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 DVM
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Michaël Dancot Diagnostic Imaging Unit, Faculty of Veterinary Medicine, University of Liège, Liège, Belgium

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 DVM, ISELP-Certified
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Maxime Vandersmissen Diagnostic Imaging Unit, Faculty of Veterinary Medicine, University of Liège, Liège, Belgium

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Jean-Marie Denoix Center of Imaging and Research on the Equine Locomotor Injuries, Normandie Equine Vallée, Goustranville, France

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 DVM, PhD, DECVSMR, DACVSMR
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Virginie Coudry Center of Imaging and Research on the Equine Locomotor Injuries, Normandie Equine Vallée, Goustranville, France

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Abstract

OBJECTIVE

To describe type and distribution of tarsal collateral ligament (CL) injuries and to assess the long-term outcome in horses treated conservatively.

ANIMALS

78 horses (median age, 7 years [IQR, 4 to 9.75 years]) of different breeds and disciplines.

PROCEDURES

Retrospective analysis (2000 through 2020) of horses with tarsal CL lesions diagnosed on ultrasound. The resting time, ability to return to work, and performance level after the injury were compared between horses having a single ligament (group S) or multiple ligaments (group M) affected and according to the case severity.

RESULTS

Most of the horses (57/78) presented a single CL injury, while 21 had multiple CLs affected simultaneously, for a total of 108 CLs injured and 111 lesions. In both groups, the short lateral CL (SLCL) was the most commonly affected (44/108), followed by the long medial CL (LMCL; 27/108). Enthesopathies (72.1%) were more frequent than desmopathies alone (27.9%) and involved mostly the proximal insertion of the SLCL and the distal attachment of the LMCL. Conservative treatment (n = 62) consisted mainly of stall rest. The median resting time (120 days [IQR, 60 to 180 days]) did not significantly differ between the 2 groups (group S vs M) or according to the severity. Most horses (50/62) were able to return to work within 6 months. Horses that did not return (12/62) were more likely to have severe lesions (P = .01). Thirty-eight horses were able to perform at a level equal to or higher than before the injury.

CLINICAL RELEVANCE

This study highlights the importance of thorough ultrasound assessment of tarsal CL injuries and demonstrates that conservative management is a viable option to allow these horses to return to previous performance level.

Abstract

OBJECTIVE

To describe type and distribution of tarsal collateral ligament (CL) injuries and to assess the long-term outcome in horses treated conservatively.

ANIMALS

78 horses (median age, 7 years [IQR, 4 to 9.75 years]) of different breeds and disciplines.

PROCEDURES

Retrospective analysis (2000 through 2020) of horses with tarsal CL lesions diagnosed on ultrasound. The resting time, ability to return to work, and performance level after the injury were compared between horses having a single ligament (group S) or multiple ligaments (group M) affected and according to the case severity.

RESULTS

Most of the horses (57/78) presented a single CL injury, while 21 had multiple CLs affected simultaneously, for a total of 108 CLs injured and 111 lesions. In both groups, the short lateral CL (SLCL) was the most commonly affected (44/108), followed by the long medial CL (LMCL; 27/108). Enthesopathies (72.1%) were more frequent than desmopathies alone (27.9%) and involved mostly the proximal insertion of the SLCL and the distal attachment of the LMCL. Conservative treatment (n = 62) consisted mainly of stall rest. The median resting time (120 days [IQR, 60 to 180 days]) did not significantly differ between the 2 groups (group S vs M) or according to the severity. Most horses (50/62) were able to return to work within 6 months. Horses that did not return (12/62) were more likely to have severe lesions (P = .01). Thirty-eight horses were able to perform at a level equal to or higher than before the injury.

CLINICAL RELEVANCE

This study highlights the importance of thorough ultrasound assessment of tarsal CL injuries and demonstrates that conservative management is a viable option to allow these horses to return to previous performance level.

Introduction

Injuries of the tarsal collateral ligaments (CLs) have been recognized as a sporadic cause of hind limb lameness in the horse.1,2 These lesions are often associated with marked lameness of sudden onset following trauma,38 but they have also been reported in cases of chronic lameness and poor performance.2,9

Both medial and lateral CLs of the tarsus consist of 1 long (superficial) and 1 short (deep) component.1013 Tension of the long CLs occurs when the hock is extended and the limb is weight bearing, while short CLs are tensed during hock flexion, contributing to hock stability during both stance and swing phase.12,14

Diagnosis of tarsal CL injuries is challenging because they are associated with nonspecific physical signs, including joint effusion, periarticular swelling, and local pain with subtle early radiological findings.3,68 In addition, investigation of tarsal soft tissue lesions requires deep knowledge of the complex anatomy of this region.15,16

Ultrasonography is a noninvasive and inexpensive technique to assess soft tissue lesions.15,1720 This modality has been reported to detect CL injuries as the most common soft tissue pathology in horses with suspected tarsal pain.10,21 Long and short CLs can be affected alone or simultaneously21; however, there are relatively few published reports describing the ultrasonographic appearance of CL injuries of the equine tarsus with attention to their 4 components.15,16,21

Successful outcome has been reported for surgical treatment of avulsion fractures of the lateral malleolus involving the origin of the lateral CLs,2226 while outcome with conservative management has been described in only a limited number of cases5 or for a single lesion type.8 Prognosis in horses with single or concurrent lesions of several CLs in the same tarsus has not been previously assessed.

This retrospective study aimed (1) to describe type and distribution of tarsal CL injuries in a large population of horses presented to 2 referral centers and (2) to assess the long-term outcome following conservative management of these injuries. Based on the authors’ clinical experience, it was hypothesized that conservative management would allow a return to previous activity and performance level, but that the number of CLs affected in the same tarsus and the severity of the case at the time of diagnosis could worsen the prognosis.

Materials and methods

Population and inclusion criteria

Medical records of horses examined over a period of twenty years (2000 to 2020) at the Center of Imaging and Research on the Equine Locomotor Injuries (France) and at the Diagnostic Imaging Unit of the University of Liège (Belgium) were reviewed. Horses were included in the study if they had a lesion of at least 1 tarsal CL with definitive diagnosis made by ultrasound. Data obtained from the medical records included signalment (age, breed, sex, use of the horse), history prior to referral (known trauma or not), and owner’s complaint (hock examination or general locomotor exam). Time between occurrence of the injury and presentation to the referral center was also calculated. Clinical information about the affected limb, physical and lameness examinations, diagnostic imaging modalities, and findings were documented. The severity of lameness and response to flexion tests were graded on a scale from 0 to 5 points (American Association of Equine Practitioners grading scale).27

Diagnostic imaging

Ultrasonographic examination of the tarsal CLs was performed in transverse and longitudinal scans using a 7.5- to 13-MHz linear transducer and a stand-off pad as well established.14,1820 Images were obtained on the weight-bearing limb, and in some cases additional scans were performed with the limb in flexed position for the evaluation of the short CLs.14

Diagnosis of CL injury was made based on changes in size, echogenicity, fibers pattern of the ligament, and bone abnormalities at the enthesis, in comparison with the contralateral limb.

CL lesions were categorized into 2 main types: desmopathy, which is characterized by alterations in size, echogenicity and/or the fiber pattern of the ligament only, including complete rupture of the fibers; and enthesopathy, which is characterized by alterations in the bone insertional surface, including fragmentations or avulsed fragments, always accompanied by a lesion of the ligament itself.

Grade of lesion severity was assigned at the time of diagnosis based on ultrasonographic abnormalities of the ligament and/or its bone enthesis. Lesion severity was graded (Supplementary Table S1) as mild (less than one-third increase of the cross-sectional area [CSA] of the ligament, mild and/or focal alterations in echogenicity, mild irregularity/bony production [enthesophyte] of the insertional surface), moderate (between one-third and two-thirds increase of the ligament CSA, extensive regions of alterations in echogenicity and/or focal disruptions of the fibrillar pattern, moderate bony production [enthesophyte] at the insertional surface), or severe (more than two-thirds increase of the ligament CSA, marked and diffuse alterations in echogenicity and/or complete loss of the fibrillar pattern, severe bony production [enthesophyte], and/or fragmentation of the insertional surface and/or avulsed fragments).

The highest ultrasonographic grade observed for bone and ligament changes was used to assess the severity of each individual case.

Presence of synovial effusion, periarticular osteophytes, or periligamentous soft tissue abnormalities was also recorded independently of the severity grading.

The population was divided into 2 groups: horses with a single CL ligament affected (group S) and horses having multiple ligamentous injuries (group M) if lesions of at least 2 CLs were present at the same time in the same tarsus. The frequency and distribution of the affected CL were described in each group based on the anatomical location for the long lateral CL (LLCL), the short lateral CL (SLCL), the long medial CL (LMCL) and the short medial CL (SMCL).

In addition to the ultrasonographic examination, a complete radiological evaluation of the affected hock was performed at the time of diagnosis and included at least the dorsoplantar, lateromedial, dorsal 10° latero-plantaromedial and 45° latero-plantaromedial obliques and dorsal 45° medial-plantarolateral oblique views.

Management and follow-up

For each horse, information about the treatment and management (stall rest, paddock, field, or continuous work) was collected from the medical records when available. Duration of the rest period and the ability to return to work 6 months after the diagnosis were calculated. A further telephone survey was conducted with owners to obtain details on the clinical condition of patients after the injury.

Performance analysis

When available, performance data were obtained from different online sources depending on the athletic discipline: Fédération Française d’Equitation (www.ffe.com) and Fédération Equestre Internationale (www.fei.org) for sport horses, Le Trot (www.letrot.com) and France Galop (www.france-galop.com) for racing horses. The performance of each horse was compared with 1 year before the injury and classified as high for a higher or equal level or as low for a lower level of performance. Sport horses were evaluated according to the competition category; for racing horses, the total race earnings per year and the number of races before and after the injury were recorded.

Statistical analysis

Data were collected in a spreadsheet for statistical analysis (XLSTAT Biomed; Addinsoft).

Descriptive statistics—Qualitative variables were described as percentages (%) and included the breed (Warmbloods, Standardbreds, Thoroughbreds, other), sex (gelding, male, female), discipline (sport horse [show jumping, dressage, eventing], racehorse, pleasure horse, other), history (trauma or not), complaint (hock examination/general exam), nature of clinical signs (hock swelling, synovial effusion, reduced range of motion), number of affected ligaments (≥ 1), lesions distribution (limb, type of CL, type of lesion), ultrasonography grade (mild, moderate, severe), treatment (medication or other modalities), and performance level (high or low). Quantitative variables, including age (years), lameness grade, time between the injury occurrence and referral (days), and duration of the resting period after diagnosis (days), were described as median followed by their interquartile range in square brackets (median [IQR]).

Inferential statistics—Horses with incomplete follow-up information or bilateral lesions or that were not treated conservatively were excluded from this analysis. Horses that were not rested after diagnosis were excluded from the calculation of the resting period duration.

The severity of each individual case was assessed using the highest ultrasonographic grade observed for bone and ligament changes. Horses were dichotomized into 2 severity groups (moderate and severe) to analyze the outcome. A χ2 test or a Fisher exact test was used when appropriate to determine the differences between groups for number of affected ligaments (group S or group M) and for case severity (moderate or severe) for the ability to return to work at 6 months (yes or no) and the performance level at 1 year (high or low). The Mann-Whitney U test was used to compare the durations of the resting period between the 2 groups (group S/group M) and between moderate and severe cases. The statistical significance was defined as P < .05 for all the tests.

Results

Population

Seventy-eight cases of tarsal CLs injury were recorded (57 cases at the Center of Imaging and Research on the Equine Locomotor Injuries and 21 at the Diagnostic Imaging Unit of the University of Liège). The affected population consisted of 36 geldings, 27 females, and 15 males and included a majority of Warmbloods (45/78 [57.7%]) with 15 Selle-Français and 30 non-French Warmbloods, French Standardbreds (22/78 [28.2%]), Arabians (6/78 [7.7%]), Ponies (3/78 [3.8%]), and Thoroughbreds (2/78 [2.6%]). The median age at the time of presentation was 7 years old (IQR, 4 to 9.75). Horses were used for a variety of disciplines. Most of them were sport horses (38/78 [48.7%]) used for show jumping (n = 32), eventing (4), or dressage (2); racing horses (20/78 [25.7%]) that were mainly used for harness trot (18); and pleasure horses (16/78 [20.6%]). Other less represented disciplines were endurance, polo, carriage, and reining (4/78 [5.1%]).

History—The main cause of tarsal CL injury was a traumatic event (48/78 [61.5%]) that occurred in the field (n = 28), in the stall (6), during transport (3) or following a car accident (2); other horses fell or were reported as slipping during competition (3) or training (6). Four of these horses presented concomitant wound at the lateral aspect of the hock. The exact etiology of the injury was unknown in 30 cases.

The reason for referral was a detailed examination of the hock in most cases (44/78 [56.4%]). The most common owner concern was the sudden onset of a local deformity or synovial distension of the hock, with acute moderate to severe hind limb lameness reported in 36 of these cases. The remaining (34/78 [43.6%]) were presented for a locomotor exam to explore an acute lameness (n = 11), or a chronic (10) and intermittent (3) lameness and gait irregularity (10). A wide proportion of the Standardbred population (10/18 [55.5%]) was presented for chronic lameness.

The time at which the injury occurred and the duration of lameness prior to referral were unknown in 20 cases. In the remaining, 26 of 58 (44.8%) were presented in the acute phase (within 30 days after injury), while the other horses were presented between 30 and 90 days (10/58 [17.2%]) and more than 90 days (22/58 [38%]) after the reported event.

Clinical presentation—Physical examination revealed localized or diffuse swelling of the hock in almost all horses (74/78 [94.9%]) and moderate to marked tibiotarsal joint (TTj) effusion (40/78 [51.2%]). Some horses had concomitant conformational limb deformity of the affected hind limb: varus (n = 4) or valgus (3) of the hock. Reduced range of motion of the hock was noted in 14 horses.

Lameness grade varied from absence to grade 4/5 hind limb lameness (median, 1 [IQR, 0.5 to 3]) at the time of presentation. Absence of lameness was reported in 12 horses; most of them (n = 10) were presented more than 90 days after the injury occurrence. Lameness equal or above 3/5 was observed mostly in horses presented with acute onset (18/26 [69.2%]). When performed (47/78 [60.2%]), a global flexion test of the affected limb resulted in mild to moderate exacerbation of the lameness, except for 5 horses.

Diagnostic imaging findings

Distribution of CL injuries—The frequency and distribution of the affected CLs were reported in each group (Table 1). Most horses (57/78 [73.1%]) had injury of a single CL (group S), while approximately one-third of horses (21/78 [26.9%]) had multiple CLs affected simultaneously (group M). A total of 108 CLs were injured in 78 cases (group S, 58 CLs; group M, 50 CLs). Lesions were unilateral in all but 2 horses. One of those horses developed bilateral LLCL desmopathy subsequently to severe varus deformity of the hocks, while the other sustained severe trauma of the hocks and injury of multiple CLs.

Table 1

Distribution and frequency of collateral ligament (CL) injuries diagnosed in 78 horses (108 CLs).

Horses Group S (n = 57) n (%) Group M (n = 21) n (%) Total (n = 78) n (%)
Side Ligament
Lateral LLCL 11 (19) 11 (22) 22 (20.4)
SLCL 28 (48.3) 16 (32) 44 (40.7)
Medial LMCL 12 (20.7) 15 (27) 27 (25)
SMCL 7 (12.1) 8 (16) 15 (13.9)
Total 58 (100) 50 (100) 108 (100)

Data are reported as number of affected CLs. Group S comprised horses that had a single ligament affected in the same tarsus. Group M comprised horses that had multiple ligaments affected in the same tarsus.

LLCL = Long lateral CL. LMCL = Long medial CL. SLCL = Short lateral CL. SMCL = Short medial CL.

The SLCL was the most affected CL of the tarsus (group S, 48.3%; group M, 32%), followed by the long components of the medial (group S, 20.7%; group M, 30%) and lateral (group S, 19%; group M, 22%) CLs. Lesions of the SMCL were less commonly observed in both groups (group S, 12%; group M, 15%).

Ultrasonographic findings—Ultrasonographic examination provided definitive diagnosis of CLs injury in all cases. A total of 111 lesions were detected in the 108 CLs affected and reported for descriptive purpose (Table 2).

Table 2

Details of the ultrasonographic lesions detected alone or in combination in 78 horses with tarsal CL injuries (n = 111).

Side Ligament Type of CLs lesions (No. [%] of injuries)
Enthesopathy (80 [72.1%]) Proximal enthesis Distal enthesis Total number Desmopathy (31 [27.9%]) Total number
Lateral LLCL 14 (17.5) 7 (22.6)
Without fragmentation 1 9 10 Without rupture 6
Avulsion fracture 3 1 4 Rupture 1
SLCL 37 (46.3) 11 (35.5)
Without fragmentation 15 8 23 Without rupture 8
Avulsion fracture 9 5 14 Rupture 3
Medial LMCL 20 (25) 7 (22.6)
Without fragmentation 1 10 11 Without rupture 11
Avulsion fracture 1 8 9 Rupture 2
SMCL 9 (11.2) 6 (19.4)
Without fragmentation 3 5 8 Without rupture 5
Avulsion fracture 1 1 Rupture 1

See Table 1 for key.

CL enthesopathy was the most frequent lesion type (80/111 [72.1%]) and most affected the SLCL (46.25%) followed by the LMCL (25%). Enthesopathies were mainly characterized by irregularities of the insertional bone surface with abnormal echogenicity of the adjacent ligament. In only 3 horses (2 cases of SLCL injury and 1 case of LLCL injury), the proximal and distal enthesis of the ligament were simultaneously involved and lesions were counted separately. The proximal insertion of the SLCL at the lateral tibial malleolus (n = 23) and the distal attachment of the LMCL at the distal tuberculum of the talus (18) were the most commonly affected sites (Figures 1 and 2). Enthesopathies of the distolateral aspect of the talus and calcaneus involved mainly the talean fasciculus of the SLCL (n = 9), with occasional fragmentation of the insertional surface (5). Avulsion fractures were imaged as osseous fragments attached to the disrupted ligament and appearing as hyperechogenic materials creating an acoustic shadow. Fracture of the lateral malleolus involved its cranial part and fibers of the SLCL in all cases (n = 9), but large fragments also involved the LLCL (3).

Figure 1
Figure 1
Figure 1

Radiographic and corresponding ultrasonographic findings in a horse with severe enthesopathy of the short lateral collateral ligament (SLCL). A—Dorsoplantar radiographic view of the left tarsus demonstrating a diffuse soft tissue swelling (arrows) at the lateral and medial sides and mild bone irregularities at the lateral aspect of the talus (arrowhead). B—Longitudinal ultrasonographic scan of the SLCL obtained with the probe oriented obliquely in a craniodistal direction (proximal is to the left). There is a marked increase in size, a diffuse hypoechogenic appearance with loss of the fibrillar pattern of the ligament, new bone formations (arrowheads) at the proximal enthesis, and mild bone irregularities of the lateral aspect of the talus. 1 = SLCL; 2 = lateral tibial malleolus; 3 = talus.

Citation: Journal of the American Veterinary Medical Association 261, 7; 10.2460/javma.22.12.0597

Figure 2
Figure 2
Figure 2

Radiographic and corresponding ultrasonographic findings in a horse with moderate distal enthesopathy of the long medial collateral ligament (LMCL). A—Dorsal 45° latero-plantaromedial radiographic view of the left tarsus showing marked soft tissue thickening (arrows) at the medial aspect and new bone formations at the distal tuberculum of the talus (arrowhead). B—Longitudinal ultrasonographic scan of the medial aspect of the hock showing the insertion of the LMCL at the distal tuberculum of the talus (proximal is to the left). There is an increase in size and small areas of decreased echogenicity in the ligament, new bone formations at the enthesis (arrowheads), and associated synovial effusion of the tibiotarsal joint. 1 = LMCL; 2 = dorsomedial recess of the tibiotarsal joint; 3 = distal tuberculum of the talus.

Citation: Journal of the American Veterinary Medical Association 261, 7; 10.2460/javma.22.12.0597

For the SMCL the most common lesion involved the calcaneal fasciculus and its distal attachment at the sustantaculum tali (n = 5).

Desmopathies without associated osseous abnormalities were less frequently identified (31/111 [27.9%]). CL desmopathies were characterized by a diffuse enlargement in the size of the ligament and changes in the echogenicity seen on transverse scans or by alterations of the fibrillar pattern on longitudinal sections. Acute injuries appeared mostly as hypoechoic lesions with loss of architecture within the fibers, while chronic lesions appeared mainly with heterogeneous fibers coarsely organized; in the shorts components of the CLs, this resulted in a loss of normal relaxation artifacts typically observed on the weight-bearing limb.14 Complete or partial rupture of the CLs was rarely seen and involved mainly the SLCL (n = 3). Infiltration of the synovial fluid between the disrupted ligament fibers was typically observed in these cases (Figure 3).

Figure 3
Figure 3

Oblique ultrasonographic scan of the lateral aspect of the tarsus in a horse with rupture of the SLCL (proximal is to the left). There is a complete loss of architecture and heterogeneous echogenicity of the ligament with retraction of the fibers and infiltration of synovial fluid (asterisk) within the disrupted ligament. 1 = SLCL; 2 = lateral tibial malleolus; 3 = talus.

Citation: Journal of the American Veterinary Medical Association 261, 7; 10.2460/javma.22.12.0597

Synovial effusion (60/78 [77%]) with proliferations and/or thickening of the synovial membrane (41/60 [68.3%]) was another common ultrasound finding. Hyperechoic swirling synovial fluid within the TTj suggestive of hemarthrosis was also observed in 3 acute cases. Moderate to marked periligamentous soft tissue thickening was reported (31/78 [39.7%]) in addition to the synovial distension.

Based on the highest ultrasonographic grade observed, 35 of 78 (44.9%) horses were categorized as moderate cases and 43 of 78 (55.1%) as severe cases. The relative percentage of severe cases was higher in group M (14/21 [66.7%]) than in group S (29/57 [50.9%]); however, no significant statistical difference was found between the 2 groups (P = .21).

Only 29 horses underwent an ultrasonographic follow-up during the rehabilitation period between 1 and 10 months after the diagnosis (median, 4 months [IQR, 4 to 6 months]). Complete ultrasonographic healing of the affected ligament was observed within 6 months in all but 2 horses. Both cases had severe lesions of the SLCL with infiltration of synovial fluid within the fibers and incomplete healing still observed at 9 months after diagnosis.

Radiographic findings—Radiographic examination was performed in all horses, and lesions distribution on radiographs was reported for descriptive purposes (Supplementary Table S2). In 18 of 78 (23%) cases, there was no osteoarticular or soft tissue radiographic abnormality noted at the time of presentation. However, in 14 cases, bone lesions (enthesophytes or small fragments) were detected on ultrasound examination.

Radiographic abnormalities suggestive of CL injuries were found in 60 of 78 horses; moderate to marked soft tissue thickening, either diffuse or concentrated around the injured ligament, was a common finding (54/60 [90%]), and this was the only detected abnormality in 17 of 54 (31%) of these cases. New bone formation (enthesophytes) or bone irregularities at the insertion surface of the CLs were identified radiographically in 43 of 60 horses (71.6%), with the distal insertion of the SLCL at the lateral aspect of the talus being the most detected site (10/43 [23.2%]; Figure 1). Avulsed fragments were seen in 24 of 60 cases (40%), most often affecting the lateral malleolus of the tibia and the distal tuberculum of the talus with involvement of the SLCL and the LMCL respectively. In 24 of 60 cases (40%), concomitant degenerative joint disease (DJD) was present at the time of diagnosis. In all these cases, radiographs were obtained more than 60 days after initial injury. Degenerative joint disease involved ≥ 1 joint at the same time, for a total of 38 tarsal joints affected. The distal intertarsal joint was the most commonly affected (15/38 [39.5%]); however, lesions were more severe when the tibiotarsal (7/38) and the talocalcaneal (3/38) joints were affected. In 3 cases, suspected instability of the TTj observed as abnormal opening of the joint space was present on the dorsoplantar view.

Treatment and management

For 7 of 78 horses, there was no information available about the treatment and management, while 1 horse having bilateral lesions of the LLCL was excluded for the outcome analysis. Eight horses underwent surgical treatment; 1 of those 8 had bilateral lesions and avulsion fracture of the lateral malleolus on the left hock. Arthroscopic removal of fragments was performed in 4 cases (3 cases of avulsion fracture of the lateral malleolus involving the SLCL only [n = 2] or both lateral CLs [1], and 1 case of fracture of the distolateral aspect of the talus, affecting the SLCL). Arthroscopic lavage of the TTj because of synovial distension was performed in 4 horses prior to referral. In these cases, CL injury was misdiagnosed.

Conservative treatment was adopted in 62 cases of CL injury (group S, 47/62; group M, 15/62). Management consisted of complete stall rest for most cases (41/62 [66.2%]), with additional access to a small paddock (n = 11) or daily hand walking (7). In some horses having a single CL injured, the recovery period was conducted in a small paddock (4/62 [6.4%]) or in the field (3/62 [4.8%]). Fourteen horses (22.6%) that were allowed to continue light work were not lame or were mildly lame at the time of diagnosis. In the remaining horses (n = 48), the median rest period was 120 days (IQR, 60 to 180 days), and this did not significantly differ between the 2 groups of affected CLs (P = .66), nor did it differ according to severity (P = .06; Table 3).

Table 3

Summary of the outcome following conservative management in horses diagnosed with tarsal CL injuries according to the number of the affected ligament and lesion severity.

Follow-up criteria Horses No. of affected CLs Case severity Total
Group S Group M Moderate Severe
Resting period (d)a n = 48 120 [30–180] 120 [60–150] 110 [30–165] 120 [60–195]
Return at 6 mo (n [%]) n = 62
Yes 39 (83) 11 (73.3) 29 (93.5) 21 (67.7) 50 (80.6)
No 8 (17) 4 (26.7) 2* (6.5) 10* (32.3) 12 (19.4)
Total 47 (100) 15 (100) 31(100) 31 (100) 62 (100)
Performance level n (%) n = 44
High 29 (87.9) 9 (81.8) 21 (87.5) 17 (85) 38 (86.4)
Low 4 (12.1) 2 (18.2) 3 (12.5) 3 (15) 6 (13.6)
Total 33 (100) 11(100) 24 (100) 20 (100) 44 (100)

Data are reported as number (%) of horses unless otherwise indicated.

aData are reported as median and interquartile range. *Values of P were < .05.

High = Higher or equal level of performance than 1 year before injury. Low = Lower level of performance than 1 year before injury.

See Table 1 for remainder of key.

Fourteen out of 62 horses (22.6%) did not receive any additional treatment during the convalescence. Of the remaining, 43 of 48 (89.6%) horses received medication (systemic only, n = 17; intra-articular only, 14; combination of both, 12). The drugs employed systemically were nonsteroidal anti-inflammatory drugs (n = 16), combined with hyaluronic acid (2) or antibiotics (4) in presence of a local wound. Intravenous injection of bisphosphonates was used in some cases (n = 13) of CL enthesopathy and concomitant arthropathy (6). For local injection, corticosteroids (n = 25) alone or combined with hyaluronic acid (7) were employed, as was platelet-rich plasma (1). The TTj was the most injected site (n = 20), followed by the tarsometatarsal (6) joint.

Other modalities were used as the only treatment in 5 of 48 (10.4%) horses and consisted of topical application of blisters (n = 2) or ice therapy (1), physiotherapy (extracorporeal shock waves; 1), and shoeing adaptation (1). In 27 of 48 horses, these modalities were combined with medication (blisters, n = 6; ice therapy, 5; extracorporeal shock waves and laser, 5; shoeing adaptation, 11). Corrective shoeing was used in cases of a single medial or lateral CL lesion and consisted of an asymmetrical shoe with a wide branch on the side of the affected ligament.

Outcome

Long-term follow-up—Most (50/62 [80.6%]) of the horses treated conservatively were able to return to work 6 months after diagnosis, while 12 horses did not resume their activity within this time because of persistent lameness (n = 9) or had a prolonged period of rest (3). There was a significant higher number of severe cases (10/31 [32.3%]) that did not return to work compared with those considered moderate (2/31 [6.5%]; P = .01; Table 3). Secondary DJD of the proximal tarsus or joint instability was observed in most cases (9/12) that did not have a successful outcome. These horses experienced rupture of 1 (n = 1) CL or multiple (1) CLs or severe desmopathy and distal enthesopathy of 1 (3) short CL or both (1) short CLs or 1 (1) CL or both (2) long CLs. One of the horses that developed severe TTj disease secondary to SLCL rupture was euthanized 15 months later for ethical reasons due to marked discomfort.

Performances analysis—Performance data were available for 44 of 62 cases. Most of them (38/44 [86.4%]) returned to competition at a similar or better level than 1 year before the injury, whereas 6 of them (13.6%) performed at a lower level (Table 3). Performance data of horses in group S did not significantly differ from those of horses of group M (P = .63) or according to the case severity at the time of diagnosis (P = .81).

Discussion

This descriptive study provides a comprehensive assessment of CL injuries of the equine hock and outcome following conservative treatment. In contrast to previous reports,5,8 about half of the horses were able to successfully return to work and to compete at a level equal to or higher than before the injury.

In this study, 78 horses with tarsal CL lesions were identified in a period of 20 years, suggesting that this condition is not common in the selected population, as previously observed.1,2,5 In the past, CL lesions have been most described as secondary to traumatic fractures of the tarsus at their insertion sites,23,28,29 while primary CL desmopathies or enthesopathies have been recognized as an infrequent cause of tarsal pain and lameness in the horse.5,8,15,16,21,30

In the current population, the SLCL was the most commonly affected CL of the tarsus, which is in contrast with previous studies.5,15,21 Medial lesions have been described as the most prevalent ones,15,21 with predominant implication of the long component. A single study5 observed lateral lesions more frequently than medial; however, the short component was not affected in any case. Concurrent lesions of multiple CLs have been encountered occasionally.15,21

Knowledge of the functional anatomy of the tarsal CLs in the horse allows the understanding of the etiopathogenesis of these injuries.12,14 As the long CLs are under tension during extension of the hock and the short CLs are stretched during flexion, injuries occurring with the hock in a flexed position involve mainly the short CLs, whereas lesions occurring with an extended hock angle cause damage to their long parts.12,14 Rotational forces beyond the normal range of motion of a joint occur especially during tight turns or forced and asymmetrical movements, increasing the strain on the CLs.31,32 This probably explains why CL injuries are in general traumatically induced and often seen in horses from slipping or when turning out in the pasture.5,8,24 Moreover, during a fall and while the limb is flexed, the horse tries to control the sliding with a simultaneous abduction of the limb, resulting in concentration of stresses on the SLCL, while the long CLs are relaxed.11,14 This can explain the prevalence of SLCL observed in this study. Thus, these injuries can affect every type of breed and discipline.2,15 On the other hand, chronic lameness without history of trauma has been described in Standardbred horses with lateral CL enthesopathy.9 Similarly, in the present study, a high proportion of the examined trotters were presented for lameness that was chronic and progressive in onset. The repetitive cyclic stress on the CLs at racing speed may be the cause of injury in these cases.3,9

More commonly, CL injuries present as acute lameness with TTj effusion and should therefore be included in the differential diagnosis of the swollen hock.33 This physical presentation may lead to misdiagnosis, as 4 horses in this study underwent exploratory arthroscopy because of synovial distension and lameness without evident radiographic signs.

Radiography should be advised as an initial diagnostic procedure, especially in case of reported trauma. It is useful in the diagnosis of avulsion fractures and their configuration24,29; however, in acute cases of CL desmopathy or enthesopathy without fragmentation of the insertional surface, it may reveal only soft tissue swelling.3

Ultrasonographic examination of the tarsus is readily available and allows definitive diagnosis of tarsal CL injuries in either acute or chronic cases. Although technically demanding, this modality is essential to identify the involved structures, to accurately evaluate the soft tissues and joints abnormalities, and to assess the severity of lesions.1720 In this study, ultrasonography was also more sensitive than radiography in detecting osseous abnormalities, as previously reported.15,16 Desmopathies appeared mainly as an enlargement of the ligament and diffuse alterations in echogenicity, in agreement with previous reports.15,16,1921

In this study, the number of affected ligaments in the same tarsus did not negatively impact the outcome, and some horses with severe lesions at the time of diagnosis were able to return to full athletic function, as previously observed in clinical settings.1 However, among the horses who did not resume the work, there was a higher proportion of severe lesions concomitant to DJD or instability of the proximal tarsus. Although osteoarthritic changes were not included in the severity criteria at the time of diagnosis and a causal effect was not assessed, it can be assumed that the risk of developing secondary DJD of the tarsus is higher in horses with severe CL lesions, which has the potential to drastically impact the outcome.

Because of their intimate relation with the joint capsule, CL lesions are often observed as primary injuries of the joint.1820,34 Thus, it is not surprising that TTj effusion was a common physical and ultrasonographic finding in the current population. In some cases, hemarthrosis secondary to bleeding from the synovial membrane can also result from acute and traumatic damage of the CLs.4,5 Instability and inflammation of the synovial structures can progressively lead to joint disease.19 In previous studies,5,8 deterioration of the clinical signs and poor response to conservative treatment of CL injuries were observed in horses with persistent synovitis that developed DJD. In both reports, only a few numbers of them returned to their previous level of activity, and a guarded prognosis following conservative management of these injuries was given.5,8

Horses with persistent synovitis may undergo arthroscopic surgery with lavage and partial synoviectomy.5,8 The short CLs are subsynovial within the TTj22,24,35; therefore, arthroscopy may be also used for assessment and treatment of intra-articular tear of the CLs associated with either extra- or intra-articular avulsion fractures of their insertion sites’ CLs.2226,35 Surgical removal of avulsion fractures of the lateral or medial tibial malleolus has been described as the treatment of choice for return to normal athletic function.2326 In the present study, only few cases were treated surgically; therefore, no conclusion can be drawn regarding the superior benefit of arthroscopy in these horses.

Systemic or intra-articular medication has been also frequently used to contain the synovial inflammation and pain.1,3,30 However, adequate management with a period of rest and restricted exercise is essential to prevent the risk of joint instability in case of CL damage.7

In the studied population, the median resting period for tarsal CL injuries was 4 months, which is in agreement with the current literature.1,9,30 However, the appropriate period of rest should be established by the clinician according to the lesions’ severity and the individual horse condition. Immobilization with bandages has been recommended in case of prolonged tarsal swelling,3 but it was not used in any of the horses of this study.

A rehabilitation program for CL injuries should limit tight turns that increase movements in the frontal plane and strain on these ligaments.36 If short CLs are involved, situations that require a significant increase in tarsal flexion should be also avoided (eg, water treadmill exercise).37 Corrective asymmetrical shoeing with more support (wider branch) on the side of the injured CL is recommended based on the identification of lesions whether on the medial or lateral side of the hock.36,38

The main limitations of this study are its retrospective nature, the lack of a control group, and reliance on owner-reported information for outcome assessment. The diagnosis and recognition of the exact localization and severity of lesions based on recorded patient data might have introduced some bias. The large variation in the lesion types and combinations limited the analysis to description only and precluded more formal assessment. In addition, some of the horses included in the study were used for general-purpose riding, and long-term follow-up was obtained via conversations with the owners, so the level of athletic activity before and after injury was not objectively assessed.

In conclusion, this retrospective study provides evidence that outcome following CL injuries of the equine tarsus is favorable after conservative treatment. The prognosis may potentially be affected by the development of concomitant joint disease. Although uncommon, these lesions should be considered in the differential diagnosis of a swollen hock with associated lameness, emphasizing the importance of a careful clinical and ultrasonographic examination for a correct diagnosis and appropriate management.

Supplementary Materials

Supplementary materials are posted online at the journal website: avmajournals.avma.org

Acknowledgments

No external funding was used in this study. The authors have nothing to declare.

This study was not submitted to an ethics committee as it is a retrospective study on clinical cases. Explicit owner consent for inclusion of the horses was not obtained, but all owners consented to the use of all case information and images for scientific publication.

The authors thank their referring vets for providing the cases.

References

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    Bramlage L. Traumatic and developmental lesions of the tarsus. In: Proceedings of the 52nd Annual Meeting of the American Association of Equine Practitioners. American Association of Equine Practitioners; 2006:1-4.

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    Byron CR. Collateral ligament injuries in horses. Equine Vet Educ. 2016;30(7):367-369. doi:10.1111/eve.12694

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    Sherlock CE, Eggleston RB, Peroni JF, Parks AH. Desmitis of the medial tarsal collateral ligament in 7 horses. Equine Vet Educ. 2013;24(2):72-80. doi:10.1111/j.2042-3292.2011.00272.x

    • Search Google Scholar
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    Boero MJ, Kneller SK, Baker GJ, Metcalf MR, Twardock AR. Clinical, radiographic, and scintigraphic findings associated with enthesitis of the lateral collateral ligaments of the tarsocrural joint in Standardbred racehorses. Equine Vet J Suppl. 1988;6:53-59. doi:10.1111/j.2042-3306.1988.tb04648.x

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    Denoix J-M. Hock and crus. International Society of Equine Locomotor Pathology workshop presentation at: Kleider Veterinary Services; September 29 to October 1, 2016; Langley, BC, Canada.

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    Raes EV, Vanderperren K, Pille F, Saunders JH. Ultrasonographic findings in 100 horses with tarsal region disorders. Vet J. 2010;186(2):201-209. doi:10.1016/j.tvjl.2009.07.026

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    Vanderperren K, Raes E, Hoegaerts M, Saunders JH. Diagnostic imaging of the equine tarsal region using radiography and ultrasonography. Part 1: the soft tissues. Vet J. 2009;179(2):179-187. doi:10.1016/j.tvjl.2007.08.030

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    Denoix J-M. Diagnostic techniques for identification and documentation of tendon and ligament injuries. Vet Clin North Am Equine Pract. 1994;10(2):365-407. doi:10.1016/s0749-0739(17)30361-9

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    • Export Citation
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    Denoix JM. Ultrasonographic examination in diagnosis of joint disease. In: McIlwraith C, Trotter GW, Saunders WB, eds. Joint Disease in the Horse. Saunders; 1996:165-202.

    • Search Google Scholar
    • Export Citation
  • 19.

    Denoix JM. Ultrasound examination of joints and miscellaneous tendons. In: Rantanen N, McKinnon A, eds. Equine Diagnostic Ultrasound. Saunders; 1998:475-514.

    • Search Google Scholar
    • Export Citation
  • 20.

    Denoix JM, Busoni V. Ultrasonography of joints and synovia. In: White NA, Moore JN. Current Techniques in Equine Surgery and Lameness. 2nd ed. Saunders; 1998;643-654.

    • Search Google Scholar
    • Export Citation
  • 21.

    Whitcomb MB. Ultrasonography of the tarsus. In: Proceedings of the 52nd Annual Meeting of the American Association of Equine Practitioners. American Association of Equine Practitioners; 2006:13-30.

    • Search Google Scholar
    • Export Citation
  • 22.

    McIlwraith CW, Nixon AJ, Wright IM, Boening KJ. Diagnostic and surgical arthroscopy of the tarsocrural (tibiotarsal) joint. In: Diagnostic and Surgical Arthroscopy in the Horse. 3rd ed. Mosby Elsevier; 2005:269-306. doi:10.1016/B978-0-7234-3281-4.50011-7

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    Wright IM. Fractures of the lateral malleolus of the tibia in 16 horses. Equine Vet J. 1992;24(6):424-429. doi:10.1111/j.2042-3306.1992.tb02871.x

    • Search Google Scholar
    • Export Citation
  • 24.

    Smith MR, Wright IM. Arthroscopic treatment of fractures of the lateral malleolus of the tibia: 26 cases. Equine Vet J. 2011;43(3):280-287. doi:10.1111/j.2042-3306.2010.00183.x

    • Search Google Scholar
    • Export Citation
  • 25.

    O’Neill HD, Bladon BM. Arthroscopic removal of fractures of the lateral malleolus of the tibia in the tarsocrural joint: a retrospective study of 13 cases. Equine Vet J. 2010;42(6):558-562. doi:10.1111/j.2042-3306.2010.00103.x

    • Search Google Scholar
    • Export Citation
  • 26.

    Gentman LM, Ross MW, Smith AS. Surgical repair of fractures of the lateral and medial tibial malleoli in a yearling Arabian filly. Equine Vet Educ. 2012;24(10):496-502. doi:10.1111/j.2042-3292.2011.00328.x

    • Search Google Scholar
    • Export Citation
  • 27.

    American Association of Equine Practitioners. American Association of Equine Practitioners definition and classification of lameness. In: Veterinarian’s Guide to Equestrian Competition Official Duties. American Association of Equine Practitioners; 2020.

    • Search Google Scholar
    • Export Citation
  • 28.

    Jakovljevic S, Gibbs C, Yeats JJ. Traumatic fractures of the equine hock: a report of 13 cases. Equine Vet J. 1982;14(1):62-68. doi:10.1111/j.2042-3306.1982.tb02338.x

    • Search Google Scholar
    • Export Citation
  • 29.

    Rose PL, Moore I. Imaging diagnosis—avulsion of the medial collateral ligament of the tarsus in a horse. Vet Radiol Ultrasound. 2003;44(6):657-659. doi:10.1111/j.1740-8261.2003.tb00528.x

    • Search Google Scholar
    • Export Citation
  • 30.

    Elliott CRB, Lumsden JM. Desmitis of the short lateral collateral ligament of the tarsus in a Thoroughbred racehorse. Aust Equine Vet. 2016;35(2):63-67.

    • Search Google Scholar
    • Export Citation
  • 31.

    Lanovaz JL, Khumsap S, Clayton HM, Stick JA, Brown J. Three-dimensional kinematics of the tarsal joint at the trot. Equine Vet J Suppl. 2002;34:308-313. doi:10.1111/j.2042-3306.2002.tb05438.x

    • Search Google Scholar
    • Export Citation
  • 32.

    Denoix J-M. Functional anatomy of tendons and ligaments in the distal limbs (manus and pes). Vet Clin North Am Equine Pract. 1994;10(2):273-322. doi:10.1016/s0749-0739(17)30358-9

    • Search Google Scholar
    • Export Citation
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    Clegg P. Differential diagnosis of a swollen hock in the horse. In Pract. 2003;6:328-341. doi:10.1136/inpract.25.6.328

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    Wright IM. Ligaments associated with joints. In: Dyson S, ed. Tendon and Ligament Injuries II. Saunders; 1995:283-286.

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    Barker WH, Smith MRW, Minshall GJ, Wright IM. Soft tissue injuries of the tarsocrural joint: a retrospective analysis of 30 cases evaluated arthroscopically. Equine Vet J. 2013;45(4):435-441. doi:10.1111/j.2042-3306.2012.00685.x

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  • Figure 1

    Radiographic and corresponding ultrasonographic findings in a horse with severe enthesopathy of the short lateral collateral ligament (SLCL). A—Dorsoplantar radiographic view of the left tarsus demonstrating a diffuse soft tissue swelling (arrows) at the lateral and medial sides and mild bone irregularities at the lateral aspect of the talus (arrowhead). B—Longitudinal ultrasonographic scan of the SLCL obtained with the probe oriented obliquely in a craniodistal direction (proximal is to the left). There is a marked increase in size, a diffuse hypoechogenic appearance with loss of the fibrillar pattern of the ligament, new bone formations (arrowheads) at the proximal enthesis, and mild bone irregularities of the lateral aspect of the talus. 1 = SLCL; 2 = lateral tibial malleolus; 3 = talus.

  • Figure 2

    Radiographic and corresponding ultrasonographic findings in a horse with moderate distal enthesopathy of the long medial collateral ligament (LMCL). A—Dorsal 45° latero-plantaromedial radiographic view of the left tarsus showing marked soft tissue thickening (arrows) at the medial aspect and new bone formations at the distal tuberculum of the talus (arrowhead). B—Longitudinal ultrasonographic scan of the medial aspect of the hock showing the insertion of the LMCL at the distal tuberculum of the talus (proximal is to the left). There is an increase in size and small areas of decreased echogenicity in the ligament, new bone formations at the enthesis (arrowheads), and associated synovial effusion of the tibiotarsal joint. 1 = LMCL; 2 = dorsomedial recess of the tibiotarsal joint; 3 = distal tuberculum of the talus.

  • Figure 3

    Oblique ultrasonographic scan of the lateral aspect of the tarsus in a horse with rupture of the SLCL (proximal is to the left). There is a complete loss of architecture and heterogeneous echogenicity of the ligament with retraction of the fibers and infiltration of synovial fluid (asterisk) within the disrupted ligament. 1 = SLCL; 2 = lateral tibial malleolus; 3 = talus.

  • 1.

    Dyson SJ, Ross MW. The tarsus. In: Dyson SJ, Ross MW, eds. Diagnosis and management of lameness in the horse. 2nd ed. Elsevier Saunders; 2011:508-526. doi:10.1016/B978-1-4160-6069-7.00044-4

    • Search Google Scholar
    • Export Citation
  • 2.

    Whitton C. Tarsus and stifle. In: Equine Sport Medicine and Surgery. 2nd ed. Elsevier Saunders Ltd; 2014:367-398. doi:10.1016/B978-0-7020-4771-8.00019-3

    • Search Google Scholar
    • Export Citation
  • 3.

    Sullins KE. The tarsus. In: Stashak TS, ed. Adams’ Lameness in Horses. 5th ed. Lippincott Williams and Wilkins; 2002:930-987.

  • 4.

    Tokateloff N, Carmalt J, Manning S. Trauma resulting in hemarthrosis and long medial collateral ligament desmitis of the tarsocrural joint in a horse. Can Vet J. 2011;52(5):519-523.

    • Search Google Scholar
    • Export Citation
  • 5.

    Lamb L, Zubrod C, Hague B, Brakenhoff J, Major M. Clinical outcome of collateral ligament injuries of the tarsus. Can Vet J. 2012;53(5):518-524.

    • Search Google Scholar
    • Export Citation
  • 6.

    Bramlage L. Traumatic and developmental lesions of the tarsus. In: Proceedings of the 52nd Annual Meeting of the American Association of Equine Practitioners. American Association of Equine Practitioners; 2006:1-4.

    • Search Google Scholar
    • Export Citation
  • 7.

    Byron CR. Collateral ligament injuries in horses. Equine Vet Educ. 2016;30(7):367-369. doi:10.1111/eve.12694

  • 8.

    Sherlock CE, Eggleston RB, Peroni JF, Parks AH. Desmitis of the medial tarsal collateral ligament in 7 horses. Equine Vet Educ. 2013;24(2):72-80. doi:10.1111/j.2042-3292.2011.00272.x

    • Search Google Scholar
    • Export Citation
  • 9.

    Boero MJ, Kneller SK, Baker GJ, Metcalf MR, Twardock AR. Clinical, radiographic, and scintigraphic findings associated with enthesitis of the lateral collateral ligaments of the tarsocrural joint in Standardbred racehorses. Equine Vet J Suppl. 1988;6:53-59. doi:10.1111/j.2042-3306.1988.tb04648.x

    • Search Google Scholar
    • Export Citation
  • 10.

    Barone R. Anatomie Comparée des Mammifères Domestiques. Tome 2: Arthrologie et Myologie. Barrone; 1969:307-309.

  • 11.

    Denoix J-M. The tarsus. In: Essential of Clinical Anatomy of the Equine Locomotor System. Taylor & Francis; 2018:229-255.

  • 12.

    Updike SJ. Functional anatomy of the equine tarsocrural collateral ligaments. Am J Vet Res. 1984;45(5):867-874.

  • 13.

    Kümmerle JM, Kummer MR. Arthroscopically accessible anatomy of the tarsal collateral ligaments in the horse. Vet Surg. 2013;42(3):267-274. doi:10.1111/j.1532-950X.2013.01100.x

    • Search Google Scholar
    • Export Citation
  • 14.

    Denoix J-M. Hock and crus. International Society of Equine Locomotor Pathology workshop presentation at: Kleider Veterinary Services; September 29 to October 1, 2016; Langley, BC, Canada.

    • Search Google Scholar
    • Export Citation
  • 15.

    Raes EV, Vanderperren K, Pille F, Saunders JH. Ultrasonographic findings in 100 horses with tarsal region disorders. Vet J. 2010;186(2):201-209. doi:10.1016/j.tvjl.2009.07.026

    • Search Google Scholar
    • Export Citation
  • 16.

    Vanderperren K, Raes E, Hoegaerts M, Saunders JH. Diagnostic imaging of the equine tarsal region using radiography and ultrasonography. Part 1: the soft tissues. Vet J. 2009;179(2):179-187. doi:10.1016/j.tvjl.2007.08.030

    • Search Google Scholar
    • Export Citation
  • 17.

    Denoix J-M. Diagnostic techniques for identification and documentation of tendon and ligament injuries. Vet Clin North Am Equine Pract. 1994;10(2):365-407. doi:10.1016/s0749-0739(17)30361-9

    • Search Google Scholar
    • Export Citation
  • 18.

    Denoix JM. Ultrasonographic examination in diagnosis of joint disease. In: McIlwraith C, Trotter GW, Saunders WB, eds. Joint Disease in the Horse. Saunders; 1996:165-202.

    • Search Google Scholar
    • Export Citation
  • 19.

    Denoix JM. Ultrasound examination of joints and miscellaneous tendons. In: Rantanen N, McKinnon A, eds. Equine Diagnostic Ultrasound. Saunders; 1998:475-514.

    • Search Google Scholar
    • Export Citation
  • 20.

    Denoix JM, Busoni V. Ultrasonography of joints and synovia. In: White NA, Moore JN. Current Techniques in Equine Surgery and Lameness. 2nd ed. Saunders; 1998;643-654.

    • Search Google Scholar
    • Export Citation
  • 21.

    Whitcomb MB. Ultrasonography of the tarsus. In: Proceedings of the 52nd Annual Meeting of the American Association of Equine Practitioners. American Association of Equine Practitioners; 2006:13-30.

    • Search Google Scholar
    • Export Citation
  • 22.

    McIlwraith CW, Nixon AJ, Wright IM, Boening KJ. Diagnostic and surgical arthroscopy of the tarsocrural (tibiotarsal) joint. In: Diagnostic and Surgical Arthroscopy in the Horse. 3rd ed. Mosby Elsevier; 2005:269-306. doi:10.1016/B978-0-7234-3281-4.50011-7

    • Search Google Scholar
    • Export Citation
  • 23.

    Wright IM. Fractures of the lateral malleolus of the tibia in 16 horses. Equine Vet J. 1992;24(6):424-429. doi:10.1111/j.2042-3306.1992.tb02871.x

    • Search Google Scholar
    • Export Citation
  • 24.

    Smith MR, Wright IM. Arthroscopic treatment of fractures of the lateral malleolus of the tibia: 26 cases. Equine Vet J. 2011;43(3):280-287. doi:10.1111/j.2042-3306.2010.00183.x

    • Search Google Scholar
    • Export Citation
  • 25.

    O’Neill HD, Bladon BM. Arthroscopic removal of fractures of the lateral malleolus of the tibia in the tarsocrural joint: a retrospective study of 13 cases. Equine Vet J. 2010;42(6):558-562. doi:10.1111/j.2042-3306.2010.00103.x

    • Search Google Scholar
    • Export Citation
  • 26.

    Gentman LM, Ross MW, Smith AS. Surgical repair of fractures of the lateral and medial tibial malleoli in a yearling Arabian filly. Equine Vet Educ. 2012;24(10):496-502. doi:10.1111/j.2042-3292.2011.00328.x

    • Search Google Scholar
    • Export Citation
  • 27.

    American Association of Equine Practitioners. American Association of Equine Practitioners definition and classification of lameness. In: Veterinarian’s Guide to Equestrian Competition Official Duties. American Association of Equine Practitioners; 2020.

    • Search Google Scholar
    • Export Citation
  • 28.

    Jakovljevic S, Gibbs C, Yeats JJ. Traumatic fractures of the equine hock: a report of 13 cases. Equine Vet J. 1982;14(1):62-68. doi:10.1111/j.2042-3306.1982.tb02338.x

    • Search Google Scholar
    • Export Citation
  • 29.

    Rose PL, Moore I. Imaging diagnosis—avulsion of the medial collateral ligament of the tarsus in a horse. Vet Radiol Ultrasound. 2003;44(6):657-659. doi:10.1111/j.1740-8261.2003.tb00528.x

    • Search Google Scholar
    • Export Citation
  • 30.

    Elliott CRB, Lumsden JM. Desmitis of the short lateral collateral ligament of the tarsus in a Thoroughbred racehorse. Aust Equine Vet. 2016;35(2):63-67.

    • Search Google Scholar
    • Export Citation
  • 31.

    Lanovaz JL, Khumsap S, Clayton HM, Stick JA, Brown J. Three-dimensional kinematics of the tarsal joint at the trot. Equine Vet J Suppl. 2002;34:308-313. doi:10.1111/j.2042-3306.2002.tb05438.x

    • Search Google Scholar
    • Export Citation
  • 32.

    Denoix J-M. Functional anatomy of tendons and ligaments in the distal limbs (manus and pes). Vet Clin North Am Equine Pract. 1994;10(2):273-322. doi:10.1016/s0749-0739(17)30358-9

    • Search Google Scholar
    • Export Citation
  • 33.

    Clegg P. Differential diagnosis of a swollen hock in the horse. In Pract. 2003;6:328-341. doi:10.1136/inpract.25.6.328

  • 34.

    Wright IM. Ligaments associated with joints. In: Dyson S, ed. Tendon and Ligament Injuries II. Saunders; 1995:283-286.

  • 35.

    Barker WH, Smith MRW, Minshall GJ, Wright IM. Soft tissue injuries of the tarsocrural joint: a retrospective analysis of 30 cases evaluated arthroscopically. Equine Vet J. 2013;45(4):435-441. doi:10.1111/j.2042-3306.2012.00685.x

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