Surgical arthrodesis of distal tarsal joints in 17 horses clinically affected with osteoarthritis

Objective To evaluate the outcome of 17 horses that underwent surgical arthrodesis of the tarsometatarsal and distal intertarsal joints for treatment of lameness due to osteoarthritis.
Design Retrospective clinical study using client-owned animals.
Procedure Horses with hindlimb lameness were diagnosed with osteoarthritis of the distal tarsal joints following relief of lameness after intra-articular anaesthesia or intra-articular corticosteroid injection. Surgery to stimulate ankylosis was performed on 27 hocks by placing 3 diverging 3.2 mm drill holes approximately 3 cm through the tarsometatarsal and distal intertarsal joints from the medial aspect of the limb. The results of surgery were assessed by postoperative examinations, telephone communication with clients and analysis of race results.
Results In 71% of horses, surgery was considered to be successful as determined by clinical examination or telephone communication with clients: six of these horses had unilateral surgery and six had bilateral surgery. This represented 85% (6/7) of horses undergoing unilateral surgery and 60% (6/10) of horses having bilateral surgery. All (8/8) racing Standardbreds and 67% (4/6) of racing Thoroughbreds were considered a success. The average time between surgery and a return to racing was 9.5 months.
Conclusions The surgical technique used here can provide resolution of lameness from osteoarthritis of distal tarsal joints with a success rate similar to other reported surgical arthrodesis techniques that are more invasive and have a greater morbidity.     

Chemical arthrodesis of the distal tarsal joints using sodium monoiodoacetate in 104 horses

OBJECTIVE: To evaluate chemical arthrodesis using sodium monoiodoacetate for treatment of degenerative joint disease of the tarsometatarsal and distal intertarsal joints. DESIGN: Retrospective clinical study. METHOD: Horses were diagnosed with degenerative joint disease of one or more of the tarsometatarsal or distal intertarsal joints based on history, lameness examination, radiographic findings and, in some cases, response to intra-articular anaesthesia or medication. Intra-articular injections of sodium monoiodoacetate were performed using 23 gauge needles in the sedated, standing horse. Positive contrast arthrography of the distal intertarsal joint was performed in all horses to evaluate needle placement and the presence or absence of communication with other synovial structures. The mean intra-articular dose of sodium monoiodoacetate was 192 mg. Horses were subject to a graded exercise program commencing 7 to 10 days after treatment. Where possible, follow up lameness examination and radiography was performed at 3, 6, 12 and 24 months after treatment. RESULTS: At 3, 6, 12 and 24 months after treatment, respectively, 0/57, 14/55, 41/50, and 29/34 of horses were sound. At 3, 6, 12 and 24 months after treatment, respectively, 5/55, 24/38, 26/30 and 18/18 of horses had radiographic evidence of ankylosis of treated joints. Post injection pain was marked in 6.7% of horses and significant complications requiring further treatment occurred in 3.8% of horses. CONCLUSIONS: Chemical arthrodesis using sodium monoiodoacetate was an effective treatment method for degenerative joint disease of the distal tarsal joints. The technique was performed in the sedated standing horse and required minimal equipment. Results were comparable to those achieved following surgical arthrodesis. The risk of significant complications was minimised through good technique using an appropriate injection volume and concentration.     

Laser-Facilitated arthrodesis of the distal tarsal joints

Arthritis of the distal tarsal joints is a common cause of lameness in performance horses. Clinical signs of distal tarsal arthritis are variable and may include gait abnormalities typical for tarsal lameness, including accentuated elevation of the affected limb, shortened cranial phase of the stride, and decreased arc of the foot. Affected horses frequently resent palpation of the lumbar and gluteal musculature. The lameness is usually increased after a hind limb flexion test. This condition is most commonly treated with intra-articular injections of sodium hyaluronate and corticosteroids in conjunction with controlled exercise and systemic nonsteroidal anti-inflammatory medication. Horses that are refractory to this form of treatment have traditionally been treated by cunean tenectomy with inconsistent results. Various surgical techniques have been used to achieve arthrodesis of these joints in an effort to eliminate the lameness associated with arthritic changes in these joints. Laser-assisted arthrodesis offers a minimally invasive surgical procedure with a relatively short convalescent period that eliminates the clinical signs of lameness in a high number of cases.     

Comparison of intra-articular drilling and diode laser treatment for arthrodesis of the distal tarsal joints in normal horses

REASONS FOR PERFORMING STUDY: Anecdotal reports suggest that laser-facilitated arthrodesis of the distal tarsal joints improves the prognosis compared with intra-articular drilling but no objective comparisons have been performed. OBJECTIVES: To evaluate intra-articular drilling and laser-facilitated arthrodesis using in situ and in vivo techniques. METHODS: Fourteen cadaver limbs were evaluated in situ for chondrocyte viability after both surgical techniques. In vivo, one randomly selected limb was subjected to laser-facilitated arthrodesis and the other underwent intra-articular drilling in 6 normal horses. Clinical examinations were performed at 1, 3 and 5 months. Two horses were subjected to euthanasia at 1, 3 and 5 months. RESULTS: Significantly more chondrocyte death was observed with laser-facilitated arthrodesis compared to drilling, but the overall degree suggested only a focal effect. In vivo, both groups demonstrated minimal post operative morbidity. There was more evidence of arthrodesis seen at all time points with intra-articular drilling. CONCLUSIONS: This study demonstrated that changes associated with ultimate arthrodesis occur earlier after intra-articular drilling of the distal tarsal joints than laser-facilitated arthrodesis, although clinically affected horses may respond differently. POTENTIAL RELEVANCE: Intra-articular drilling may provide earlier arthrodesis of the distal tarsal joints, but not necessarily a better long-term result.     

Use of ethanol in the treatment of distal tarsal joint osteoarthritis: 24 cases

Reasons for performing this study: Intra‐articular ethanol has been described to promote distal tarsal joint ankylosis. Its use and results in clinical cases affected by osteoarthritis (OA) have not been reported. Objectives: To describe and evaluate the results of treatment of distal tarsal joint OA by facilitated ankylosis stimulated by intra‐articular ethanol injection. Methods: Twenty‐four horses met the inclusion criteria of tarsometatarsal and centrodistal joint OA diagnosed by a positive response to intra‐articular analgesia, radiographic evaluation and recurrence of lameness ≤4 months after intra‐articular medication with a corticosteroid. Horses were sedated and, following a radiographic contrast study of the tarsometatarsal joint, medication with 2–4 ml of either 100% pure ethanol (G100) or a 70% ethanol (G70) solution was applied. Horses were classified as improved based on a 50% reduction from initial lameness grade combined with an increase in exercise level. Results: Of the 24 horses included in this study, 20 had the treatment performed bilaterally and 4 unilaterally. All horses were available for initial follow‐up examination and 21 for a second one 6–9 months after treatment. This represented a total of 44 treated limbs and 35 available for long‐term follow‐up. Of these, 21/35 (60%) were considered improved, which corresponds to 11/21 horses (52%). Of 21 horses, 4 (19%) deteriorated and 2 of these developed significant complications related to treatment. Conclusions: Distal tarsal joint ankylosis with ethanol should be considered a safe and economic treatment in cases of distal tarsal joint OA that fail to show long‐term improvement with intra‐articular corticosteroid treatment. Potential relevance: Ethanol should be considered in the treatment of certain cases of distal tarsal joint OA. The importance of performing an adequate radiographic contrast study of the tarsometatarsal joint prior to treatment is highlighted.     

Retrospective study of the effect of intra-articular treatment of osteoarthritis of the distal tarsal joints in 51 horses

Osteoarthritis of the distal tarsal joints, affecting the centrodistal and tarsometatarsal joints, is a common cause of hindlimb lameness in horses. This paper describes the outcome of the intra-articular treatment of 51 horses with the condition with either methylprednisolone acetate (mpa) or triamcinolone acetonide (tr), either with or without hyaluronic acid (ha). The outcome was assessed in terms of the changes in the horses' grade of lameness. Follow-up information was obtained from the owners by means of a telephone questionnaire. Horses treated once with mpa or tr, either with or without ha, improved after a median of 56 days (P<0.0001), and there was no significant difference between mpa and tr. There was no significant further improvement in the horses treated twice. In the horses in which there was a diffuse increase in the uptake of a radiopharmaceutical by the distal tarsal joints, identified by scintigraphy, the lameness tended to improve (P=0.032), whereas in the horses in which the uptake was focal, it did not. At telephone follow-up 13 of 34 horses were reported to have had a positive outcome, but the outcome in the other 21 was reported to have been negative.     

Analysis of risk factors for recurrent airway obstruction in North American horses: 1,444 cases (1990-1999)

OBJECTIVE: To identify risk factors for recurrent airway obstruction (RAO) among horses examined at veterinary teaching hospitals in North America. DESIGN: Retrospective case-control study. ANIMALS: 1,444 horses with RAO and 1,444 control horses examined for other reasons. PROCEDURE: The Veterinary Medical Database was searched for records of horses in which RAO was diagnosed. A control group was identified by randomly selecting a horse with a diagnosis other than RAO that matched the institution and year of admission for each of the horses with RAO. Information obtained included hospital, admission year and month, age, sex, breed, and discharge status. The association between risk factors and diagnosis of RAO was estimated with logistic regression models. RESULTS: The risk of RAO increased significantly with age, with horses > or = 7 years old being 6 to 7 times as likely to have RAO as were horses < or = 4 years old. Thoroughbreds were 3 times as likely to have RAO as were ponies. Horses were 1.6 and 1.5 times as likely to be examined because of RAO during winter and spring, respectively, than they were during summer. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that RAO was more likely to be diagnosed in females, horses > or = 4 years old, and Thoroughbreds and that RAO has a seasonal distribution.     

Comparison of three methods for arthrodesis of the distal intertarsal and tarsometatarsal joints in horses

OBJECTIVE: To evaluate the effects of diode laser surgery (LS), surgical drilling (SD), and intraarticular sodium monoiodoacetate (MIA) as methods for fusing the distal intertarsal (DIT) and tarsometatarsal (TMT) joints in horses. STUDY DESIGN: Experimental study. ANIMALS: Adult horses (15) without radiographic signs of osteoarthritis (OA) of the DIT and TMT joints. METHODS: Group 1 (n=3) had LS performed bilaterally on DIT and TMT joints; 1 horse was evaluated for 1 week and 2 horses were evaluated for 2 weeks. Group 2 (n=6) had LS on DIT and TMT joints of 1 tarsus and MIA administration into the contralateral DIT and TMT joints and were evaluated for 6 months. Group 3 (n=6) had LS performed on DIT and TMT joints of 1 tarsus and SD of the contralateral DIT and TMT joints and were evaluated for 12 months. Postoperative comfort, lameness, radiography, microradiography, and histology scores were compared using repeated measures ANOVA, and paired or 2 sample t-tests; significance was set at P<.05. RESULTS: LS caused the least postoperative morbidity. In group 2, horses were less lame in 4 LS-treated limbs and 2 MIA-treated limbs at 6 months when compared with the contralateral limb. In group 3, horses were less lame in 5 LS-treated limbs and 1 SD-treated limb at 6 and 12 months compared with the contralateral limb. On microradiography, 11 MIA joints and 2 LS joints had bone bridging the joint at 6 months whereas 8 SD joints and 5 LS joints had bone bridging at 12 months. Significantly more joint space was bridged by bone in MIA- (51.4%) and SD (46.2%)-treated joints compared with LS joints at 6 (30.6%) and 12 (28.5%) months, respectively (P<.05). CLINICAL RELEVANCE: SD and MIA resulted in more bone bridging of the distal 2 tarsal joints, than LS. However, LS seemingly caused less pain and discomfort to horses in the immediate postoperative period; horses were generally less lame in the LS limb. More laser energy may need to be applied to these joints to promote fusion; however, it may also have beneficial effects beyond fusion. Further research on horses with OA of the distal 2 tarsal joints is needed to determine whether LS can cause soundness without facilitating bony fusion.     

Laryngeal paralysis in cats: 16 cases (1990-1999)

OBJECTIVE: To determine clinical signs, physical examination findings, radiographic features, and concurrent diseases in cats with laryngeal paralysis, as well as evaluate the outcome of medical or surgical management. DESIGN: Retrospective study. ANIMALS: 16 cats. PROCEDURE: Medical records from January 1990 to April 1999 were examined for cats with laryngeal paralysis. Signalment, clinical signs, physical examination findings, cervical and thoracic radiographic findings, laryngeal examination results, and clinical outcome were reviewed. RESULTS: No breed or sex predilection was identified in 16 cats with laryngeal paralysis. The most common clinical signs included tachypnea or dyspnea, dysphagia, weight loss, change in vocalization, coughing, and lethargy. Clinical signs were evident for a median of 245 days. Airway obstruction was apparent on cervical and thoracic radiographic views in 9 cats. Examination of the larynx revealed bilateral laryngeal paralysis in 12 cats and unilateral laryngeal paralysis in 4 cats. The 4 cats with unilateral disease were managed with medical treatment, and 3 of these had acceptable long-term outcomes. Seven of 12 cats with bilateral paralysis underwent surgery; procedures performed included left arytenoid tie back, bilateral arytenoid tie back and ventriculo-cordectomy, and partial left arytenoidectomy. One cat was euthanatized as a result of complications from surgery. CONCLUSIONS AND CLINICAL RELEVANCE: Laryngeal paralysis is an uncommon cause of airway obstruction in cats. Cats with less severe clinical signs (often with unilateral paralysis) may be successfully managed with medical treatment, whereas cats with severe airway obstruction (often with bilateral paralysis) may benefit from surgical intervention.     

Use of magnetic resonance imaging for identifying subchondral bone damage in horses: 11 cases (1999-2003)

OBJECTIVE: To assess the use of magnetic resonance (MR) imaging for identifying subchondral bone damage in the distal limbs of horses. DESIGN: Retrospective study. ANIMALS: 11 horses. PROCEDURE: Medical records of horses with lameness and subsequent evidence of subchondral bone damage as determined by MR imaging were reviewed. Severity and duration of lameness, results of diagnostic local anesthesia and diagnostic testing, surgical and necropsy findings, and treatment were recorded. Outcome was determined by follow-up information obtained from the owner or referring veterinarian. RESULTS: Lameness was localized by physical examination and diagnostic local anesthesia. Lameness was localized to the metacarpophalangeal or metatarsophalangeal joint in 4 horses, distal interphalangeal joint in 5 horses, and tarsocrural joint in 2 horses. The duration of lameness ranged from 2 weeks to 20 months. Magnetic resonance imaging of the affected joints revealed abnormal fluid accumulation within the subchondral bone. None of the abnormalities observed by MR imaging were detected by radiography. Subchondral bone damage was diagnosed in all horses. Arthroscopy of the affected joint was performed in 4 horses. Communication with the articular surface of the affected bone was suspected on the basis of results of MR imaging in 4 horses and was confirmed by arthroscopy in 1 horse and by necropsy in 1 horse. CONCLUSIONS AND CLINICAL RELEVANCE: Magnetic resonance imaging was useful for providing a diagnosis when other imaging techniques did not definitively identify the cause of lameness. Subchondral bone damage was clearly identified by MR imaging and should be considered as a cause of lameness in horses in which radiographic findings are unremarkable.     

Alteration of distal tarsal subchondral bone thickness pattern in horses with tarsal pain

REASONS FOR PERFORMING STUDY: Understanding of the development of pathology and source of pain in distal tarsal osteoarthritis is poorly understood. Magnetic resonance imaging is often used in the analysis of human osteoarthritis (OA) because it is sensitive to early changes. HYPOTHESIS: In association with distal tarsal joint (DTJ) pain, there will be an alteration in the characteristic subchondral bone (SCB) thickness pattern of horses with no history of pain when subjected to low-level exercise. METHODS: Sixteen cadaver tarsal joints were collected from 9 mature horses with a history of tarsal pain and radiographic evidence of OA; 3 cadaver tarsi were collected from 2 mature horses with a history of tarsal pain and no radiographic abnormality. Magnetic resonance images were acquired using high-resolution sagittal 3D T1 weighted spoiled gradient echo sequence. Subchondral bone thickness was measured on sagittal images at dorsal and plantar locations on the proximal and distal aspects of the central (CT) and third (T3) tarsal bones and proximal aspect of the third metatarsal bone (MT3). RESULTS: In tarsi with radiographic evidence of OA medial and lateral SCB thicknesses were greater than midline on the proximal and distal aspects of CT and T3. Lateral SCB thickness was greater than medial on the proximal aspect of MT3. There was an increase in SCB thickness at the majority of sites compared with normal horses. There were too few joints in the group without radiographic changes to analyse statistically. In painful tarsi SCB thickness was greater medially than laterally at all sites. In horses without tarsal pain all lateral sites had greater SCB thickness, except the proximal aspect of CT. CONCLUSIONS: There is alteration of normal SCB thickness patterns in painful tarsi. Different thickness patterns could represent different types of pathological processes. Potential clinical relevance: Further work is required to elucidate the pathological processes leading to OA of the DTJs.     

Radiographic and clinical survey of degenerative joint disease in the distal tarsal joints in Icelandic horses

The prevalence of degenerative joint disease (DJD) in the distal tarsal joints and the relation between radiographic and clinical signs compatible with the disease were estimated in a population of Icelandic horses used for riding. The material consisted of 614 horses age 6-12 years (mean age = 7.9 years). Radiographs with 3 projections of each tarsus were made and a clinical examination, including palpation of the medial aspect of the distal tarsus and motion evaluation of the hindlimbs before and after a flexion test of the tarsus, was performed. Radiographic signs of DJD in the distal tarsal joints were found in 30.3% of the horses and the prevalence was strongly correlated with age. Hindlimb lameness before and after flexion test and palpation abnormalities were significantly associated with the radiographic findings. The lameness was usually mild and, in most cases, detectable only after the flexion test. The prevalence of lameness was not significantly correlated with age. Lameness could not be predicted by details of the radiographic findings.     

Bacterial meningoencephalomyelitis in dogs: a retrospective study of 23 cases (1990-1999)

The clinical records of 23 dogs (1990-1999) with histopathologically confirmed bacterial meningoencephalomyelitis were evaluated retrospectively. No breed, age, sex, or weight predisposition was found. All the dogs presented with clinical signs of a brain lesion, whereas 5 of 23 had neck pain. Pyrexia was detected in 11 of 23 dogs on admission. CBCs revealed neutrophilic leucocytosis in 7 of 21 dogs and thrombocytopenia in 3 of 21 dogs. The serum chemistry profiles were abnormal in 15 of 21 dogs. The results of cerebrospinal fluid (CSF) analysis were abnormal in 13 of 14 dogs and aerobic CSF culture was positive for bacteria in 1of 8 samples. At postmortem examination, the lesions were localized to the central nervous system. Escherichia coli, Streptococcus, and Klebsiella spp were the most frequently isolated bacteria from cultures collected at postmortem examination. Twelve papers reporting 51 total clinical cases of canine bacterial meningoencephalomyelitis were reviewed. The clinical signs and results of the CBC, serum chemistry, blood culture, and CSF analysis were collated and compared with those of this study. The results of the CSF analysis in this study were similar to those in the literature. CSF cultures documented in the literature were positive for Staphylococcus, Pasteurella. Actinomyces, Nocardia spp, and various anaerobic species including Peptostreptococcus, Eubacterium, and Bacteroides spp.     

Rabies in horses: 21 cases (1970-1990).

The records of 21 horses with rabies were reviewed. Results of fluorescent antibody testing for rabies antigen in brain tissue were positive in each case. According to the histories, 5 of the horses had been vaccinated for rabies between 4 to 24 months prior to the onset of the clinical signs. Bite wounds were not observed on any of the horses, and exposure to a suspected rabid animal was witnessed in only 5 cases. Clinical signs of disease at the time of initial examination included ataxia and paresis of the hindquarters (9/21, 43%), lameness (5/21, 24%), recumbency (3/21, 14%), pharyngeal paralysis (2/21, 10%), and colic (2/21, 10%). The major clinical signs observed over the course of hospitalization included recumbency (21/21; 100%), hyperesthesia (17/21; 81%), loss of tail and anal sphincter tone (12/21; 57%), fever (11/21; 52%), and ataxia and paresis of the hindquarters (11/21; 52%). Mean survival time after the onset of clinical signs was 4.47 days (range, 1 to 7 days). Supportive treatment, given to 9 horses, had no effect on survival time and did not correlate with the detection of negri bodies at necropsy. Cerebrospinal fluid (CSF) was obtained from 6 horses and was determined to be abnormal in 5. The most common abnormality was a slightly high total cell count (5/6), with a predominance of lymphocytes (4/6). The CSF total protein concentration was high in only 2 horses. At necropsy, there was gross evidence of diffuse brain edema, meningeal congestion, and focal areas of hemorrhage in 5 horses (24%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Musculoskeletal Corynebacterium pseudotuberculosis infection in horses: 35 cases (1999-2009)

Objective-To describe the clinical course and outcome in horses in which Corynebacterium pseudotuberculosis infections were associated with musculoskeletal disease and lameness. Design-Retrospective case series. Animals-35 horses. Procedures-Clinical and clinicopathologic data were collected from horses diagnosed with lameness associated with C pseudotuberculosis infection between 1999 and 2009. Results-32 (91.4%) horses had grade 4/5 lameness. Three (8.6%) horses had grade 5/5 lameness. Abscesses were diagnosed by clinical or ultrasonographic examination. Abscesses were located in the axillary or triceps region in 25 (71.4%) horses, the stifle region in 2 (5.7%), and the popliteal lymph node in 1 (2.9%). Diffuse lymphangitis was seen in 4 (11.4%) horses, osteomyelitis in 2 (5.7%) horses, and septic arthritis in 2 (5.7%) horses. Horses commonly had clinicopathologic abnormalities characterized by neutrophilia (96.4%), anemia (67.8%), hypoalbuminemia (66.6%), or hyperfibrinogenemia (42.8%). Treatment included surgical drainage of the abscess in 21 (60%) horses, performed under ultrasonography in 20 horses; anti-inflammatory medications in 34 (97.1 %) horses; and antimicrobials in 30 (85.7%) horses. Conclusions and Clinical Relevance-C pseudotuberculosis infection of the limbs in horses typically results in severe lameness but may have a favorable prognosis. The diagnosis may be challenging, and results of blood work consistent with inflammation are nonspecific, but anemia, hyperglobulinemia, and increased synergistic hemolysis inhibition titers are common. Ultrasonography may localize the lesions and facilitate surgical drainage to alleviate lameness. When C pseudotuberculosis musculoskeletal infection results in osteomyelitis or septic arthritis, the prognosis for survival is poor.     

Proximal interphalangeal joint arthrodesis using a combination plate-screw technique in 53 horses (1994-2003)

REASONS FOR PERFORMING STUDY: A method for proximal interphalangeal joint (PIP joint) arthrodesis that provides a stable fixation and minimal duration of cast support is evaluated retrospectively. OBJECTIVES: Evaluate the clinical use of a combined plate-screw method for PIP joint arthrodesis in a large number of horses. METHODS: The records of 53 horses undergoing PIP joint arthrodesis were reviewed. Arthrodesis was performed with a dorsally placed 3-, 4- or 5-hole narrow dynamic compression plate (DCP) with 2 transarticular cortex screws placed in lag fashion either side of the plate. Subject details, clinical presentation, radiographic findings, surgical technique, post operative treatment and complications were recorded. Long-term follow up (mean 3 years) was obtained for 46 horses. RESULTS: Arthrodesis procedures (n = 58) were performed on 53 horses with a DCP in combination with transarticular cortex screws placed in lag fashion. Conditions treated were osteoarthritis (OA) of the PIP joint, fracture of middle phalanx, PIP joint subluxation, subchondral cystic lesions and degenerative joint disease secondary to sepsis. Time of post operative cast application was 14 days. Overall 40/46 (87%) horses could be used as intended including 20/25 (81%) forelimb and 20/21 (95%) hindlimb arthrodeses. Twenty-three of 27 (85%) horses used for performance had successful outcomes. Complications included implant infection, cast sores and partial implant failure. CONCLUSIONS: PIP joint arthrodesis using a DCP and transarticular cortex screws placed in lag fashion provides a stable construct and short casting period with minimal complications. The prognosis for return to performance was excellent for horses treated with hindlimb PIP joint arthrodesis and good for forelimb arthrodesis. POTENTIAL RELEVANCE: Use of a combination technique for PIP joint arthrodesis allows a high proportion of horses with pastern joint disease to be returned to their athletic potential.     

Rupture of collateral ligaments in metacarpophalangeal and metatarsophalangeal joints in horses: 17 cases (1999--2005)

OBJECTIVE: To characterize ruptures of collateral ligaments (CLs) in metacarpophalangeal and metatarsophalangeal joints in horses. DESIGN: Retrospective case series. ANIMALS: 17 horses with ruptured CLs. PROCEDURES: Data were obtained from medical records, including signalment, history, clinical signs, ultrasonographic and radiographic findings, treatment, and outcome. Additional follow-up information was obtained from owners or referring veterinarians. RESULTS: The lateral CL was ruptured in 11 horses; the medial CL was ruptured in 6 horses. Ultrasonography revealed ipsilateral rupture of the short and long components of the CL in 11 horses and rupture of only 1 component in 6 horses. No biaxial ruptures were detected, but 9 horses had desmitis of the CL on the nonruptured side of the affected joint. All horses were lame (lameness score range, 2/5 to 4/5). Joint instability was palpable in 9 horses; only 4 horses had episodes of joint luxation. Avulsion fractures were identified radiographically in 6 horses and ultrasonographically in another 2 horses. Stress radiography revealed joint instability in 10 horses. Horses were managed by stall confinement, limb immobilization, and gradual return to exercise. Eight horses returned to riding, 2 resumed breeding, 2 were retired, 2 were euthanized, and 3 were doing well 86 to 139 days after injury. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasonographic examination is indicated in horses with acute lameness and swelling at the metacarpophalangeal or metatarsophalangeal joint, particularly when stress radiography cannot be performed or findings are equivocal. Affected horses can be conservatively managed. Prognosis for athletic use may be better than originally believed.