Osseous Cyst-like Lesions Research Articles

Osseous pathologic changes in the thoracic region of the equine vertebral column: A descriptive post-mortem study in three breeds.

Data on equine thoracic pathology hardly exist in breeds other than Thoroughbreds. To describe pathological changes of the osseous thoracic vertebral column in Warmblood horses, Shetland ponies and Konik horses, and to compare prevalence and severity. Descriptive post-mortem study. Computed tomography was used to examine the thoracic vertebral column of 34 Warmblood horses, 28 Shetland ponies, and 18 Konik horses. Osteoarthritis (OA), periarticular osteolysis, osseous cyst-like lesions and fragments of articular processes (APJs), costovertebral and costotransverse joints, soft tissue mineralisation surrounding these joints, intervertebral disc (IVD) mineralisation, impingement of spinous processes (SPs) and spondylosis were scored. APJ aplasia (98%; 58/59) occurred in 14 Shetland ponies. OA predominated in Warmblood horses across all joints (45% vs. 29 and 32%, p < 0.001). OA and periarticular osteolysis were found in particular in the costotransverse joints (p < 0.001) across all breeds. Warmblood and Konik horses had more and severe soft tissue mineralisation than Shetland ponies (2.3%, score 1.5 and 3.2%, score 1.3, respectively, vs. 0.3%, score 0.9, p < 0.01). Mid location was most often affected with highest severity score (4.2%, 1.5, p < 0.001). Konik horses displayed the highest IVD mineralisation (20%, p < 0.001), which notably increased with age (p < 0.001) compared with Warmblood horses (4.5%) and Shetland ponies (1.1%). SPs impingement was absent in Shetland ponies, and most prevalent in Warmblood horses (11.2%, p < 0.001) compared with Konik horses (2.2%). Osseous cyst-like lesions, fragments and spondylosis were minimal in all breeds and nearly absent in Shetland ponies. Clinical histories and macroscopic and histologic examinations were unavailable. Distinct breed differences exist in prevalence and severity of thoracic vertebral column osseous pathologies. Costotransverse joint pathology is more common than APJ pathology in all breeds. Warmblood horses are prone to OA, spondylosis and SPs impingement; Konik horses exhibit significant IVD mineralisation, and Shetland ponies demonstrate a high prevalence of APJ aplasia. Periarticular osteolysis, osseous cyst-like lesions, fragments and soft tissue mineralisation are notably low in Shetland ponies.

A Randomized, Self-Controlled Case Series Evaluating Core Osteostixis of Osseous Cyst-Like Lesions of the Navicular Bone to Improve Lameness in Horses with Podotrochlear Syndrome.

Podotrochlear syndrome is a common cause of lameness in Quarter Horses involving both soft tissue and bony structures within the heel region. Current surgical treatment of podotrochlear syndrome addresses pathological changes affecting the soft tissue structures of the navicular region but does not address either edema or cyst-like lesions of the navicular bone. The objective of this randomized, self-controlled case series was to determine whether core osteostixis improved lameness in Quarter Horses with podotrochlear syndrome characterized by bilateral magnetic resonance imaging (MRI) findings of osseous cyst-like lesions of the navicular bone. Seven Quarter Horses that had not responded to standard medical management were included. Each horse had an affected forefoot randomly assigned to surgical treatment with navicular bursoscopy and core osteostixis; the contralateral limb was assigned to navicular bursoscopy only. Video recordings were used to assign lameness scores and make comparisons of each limb at baseline and 24 weeks post-operatively by an observer blinded to the surgical treatment. A second MRI was performed 24 weeks after surgery to reevaluate navicular bone edema, osseous cyst-like lesions of the navicular bone, and tears of the deep digital flexor tendon (DDFT). Reduction of lameness score from baseline was significantly (P = 0.0254) greater for the limbs treated with core osteostixis than limbs treated with bursoscopy. New DDFT tears were noted in 3 of 7 limbs treated with core osteostixis and in 1 of 7 bursoscopy limbs. Results of this study suggest that core osteostixis of the navicular bone combined with navicular bursoscopy can improve lameness in horses with osseous cyst-like lesions. Further evaluation of this technique is warranted.

Radiographic and magnetic resonance imaging evaluation and characteristics of osseous cyst-like lesions in the equine hoof

Radiographic and magnetic resonance imaging evaluation and characteristics of osseous cyst-like lesions in the equine hoof

A detailed radiographic description and correlated magnetic resonance imaging findings of an infrequently identified articular indentation of the articular margin of the distal phalanx

SummaryBackgroundEquine veterinarians frequently obtain lateromedial radiographs of the feet. During assessment, one infrequently encounters a triangular‐shaped articular indentation of the articular surface of the distal phalanx (P3). To the authors’ knowledge, there are no detailed radiographic or MRI descriptions of this specific articular indentation in the literature so far.ObjectivesThe main purpose of this study was to give a detailed morphological description of this radiographical identified articular indentation.Study designDescriptive study.MethodsAll LM and DP radiographs of the feet of horses presented at our hospital between August 2016 and August 2019 were retrospectively reviewed for presence of an articular indentation. Following selection, patient information, patient history, clinical findings, MRI‐finding and surgical details were retrieved. In total, 30 horses were included of which 12 underwent magnetic resonance imaging. Radiographs and MRI results were evaluated for the precise location, shape and extent of the articular indentation and for signs of degenerative joint disease of the DIPJ.ResultsFour different indentation types were identified radiographically. Concomitant low field MRI proved to be a useful and excellent imaging modality for evaluation of this rare articular indentation and its surrounding subchondral bone. MRI findings were various and ranged from slight subchondral contour deviations to obvious OCLL (Osseous Cyst Like Lesions). Furthermore, MRI identified some additional indentation related OCLLs that were not noted on plain radiographs.Main limitationsThe limited number of horses that were included and the absence of complementary histopathology.ConclusionsArticular indentations are typically identified in the third quarter of the articular margin of P3 and may have underlying OCLLs. Since OCLLs are known to be a potential cause of future unsoundness, careful radiographic assessment is advised if an indentation is encountered. If needed, Standing Low‐Field MRI can give additional and detailed information.

Inter- and intra-observer agreement for grading radiographs of thoracolumbar spinous processes in healthy horses during a pre-purchase examination.

There is wide variability in radiographic grading systems in thoracolumbar spinous processes in horses. The aim of this study was to determine the agreement of grading different parameters, and combinations of those, in radiographs of the spinous processes of the equine thoracolumbar spine in the scope of a pre-purchase examination. We hypothesized that agreement is variable and interpretation of these radiographs is difficult. Radiographs of the thoracolumbar spine of healthy horses (N=100) were assessed by three observers. Spinous processes were separately graded for interspinous space width, modelling, radiopacities, radiolucencies and isolated opacities dorsally. Inter- and intra-observer agreement was assessed for individual and combinations of parameters. Agreement (inter- and intra-observer) was good for the following parameters: interspinous space width, isolated opacities dorsally, beak-shaped formations craniodorsally and modelling cranioventrally. The agreement increased slightly for a sum of specific parameters such as radiopacities, modelling, dorsal abnormalities and related abnormalities involving increased opacity, modelling and osseous cyst-like lesions. Agreement for the total radiographic abnormalities per back was moderate. Grading of thoracolumbar radiographs in horses without back pain showed good inter- and intra-observer agreement for specific parameters and these should be used in future grading of spinous processes. Limitations should be considered in pre-purchase examinations.

A case‐control study of the morphological measurements of equine distal interphalangeal joints affected by osseous cyst‐like lesions

SummaryBackgroundThe aetiology and effects of osseous cyst‐like lesions (OCLLs) affecting the distal interphalangeal (DIP) joint are poorly understood.ObjectivesTo describe the magnetic resonance (MR) imaging appearance of OCLLs of the DIP joint and morphological measurements of affected joints.Study designRetrospective case–control study.MethodsThe low‐field MR imaging appearance of OCLLs affecting the DIP joint diagnosed over a 5‐year period was reviewed. Each case was matched to two horses with foot lameness not affected by OCLLs. Morphological measurements of the articular surfaces were recorded.ResultsThere were 23 horses with OCLLs of the DIP joint (Group 1) and 45 controls (Group 2). The Group 1 horses had a total of 30 OCLLs. Twenty‐one OCLLs were present in the distal phalanx and 9 were present in the middle phalanx. Eight lesions were indentations of the articular surface and 22 had subchondral and trabecular bone involvement. OCLLs were commonly located in the centre of the articular surface of the distal phalanx. The dorsal‐palmar/plantar length of the articular surface of the distal and middle phalanges was greater in Group 1. The depth of the articular surface of the distal phalanx and the height of the articular surface of the middle phalanx were greater in the Group 1. 22/23 horses in Group 1 had evidence of osteoarthritis of the DIP joint compared to 22/45 in Group 2.Main limitationsSmall number of cases and small values of measurements.ConclusionsOCLLs of the DIP joint occur at consistent sites, most commonly the central third of the articular surface of the distal phalanx. Measurements of the joint surfaces suggest that DIP joints affected by OCLLs have different morphology than joints without OCLLs. These findings are consistent with the theory that OCLLs of the DIP joint could be associated with dysplasia of the joint.

Radiographic Identification of Osseous Cyst- Like Lesions in the Distal Phalanx in 22 Lame Thoroughbred Horses Managed Conservatively and Their Racing Performance.

Reasons for performing study: To investigate the racing performance of Thoroughbred horses with osseous cyst-like lesions (OCLLs) in the distal phalanx causing lameness and treated conservatively.Objectives: To assess horses' ability to race and perform after radiographic identification of OCLL in the distal phalanx of Thoroughbred horses with lameness at the time of detection and undergoing conservative treatment.Study Design: Retrospective case control study.Methods: The clinical database of one equine clinic was reviewed in a 10-year period for Thoroughbreds showing lameness localized to the foot and a radiographic diagnosis of OCLL in the distal phalanx. Sex, age at time of detection of the OCLL, degree of lameness, affected limb, and treatment were recorded. Successful performance of horses was assessed by racing at least once after detection of the OCLL and maximum racing performance rating (RPR). Radiographic features such as size, location, sclerotic rim of the OCLL and irregularity of the articular surface of the distal phalanx were compared to successful performance using univariable statistical analysis. Successful performance of horses with OCLL was compared to a control group of maternal siblings by parametric testing.Results: Twenty-two horses met the inclusion criteria. Thirteen horses raced after the detection of OCLLs. Eight did not race, one case had not yet reached racing age, resulting in 62% (13/21) of racing age racing at least once. The number of successfully performing horses with an OCCL was significantly lower compared to their maternal siblings [p = 0.03, Odds ratio (OR) = 0.30]. If horses with OCLL in the distal phalanx raced, their RPR was similar to their maternal siblings. No significant association was found between radiographic features of OCLLs and successful performance, but OCLLs in the left forelimb carried a more favorable outcome for racing (p = 0.02, OR = 2.33 95%CI 1.27, 4.27) compared to OCLLs in any other limb.Conclusions: Horses with lameness and an OCLL in the distal phalanx managed conservatively are less likely to race when compared to their maternal siblings. If horses with OCLLs in the distal phalanx are able to race, their performance, measured as RPR, was comparable to their maternal siblings. Due to the small numbers in this study the results should be interpreted carefully.

Nonarticular osseous cyst-like lesions of the intermedioradial carpal bone may be incidental magnetic resonance imaging findings in dogs.

As magnetic resonance imaging (MRI) becomes more readily available and more frequently utilized in the assessment of canine carpal lameness, both normal variations and early pathologic conditions must be recognized to optimize patient care and provide accurate diagnosis. On cross sectional studies of the canine carpus, cyst-like lesions have been detected at the dorsolateral aspect of the intermedioradial carpal bone. The cross-sectional imaging and histologic properties of these lesions have not been described. The purpose of this observational study is to evaluate the MRI and histologic features of these cyst-like lesions in a cohort of clinically sound dogs. It was hypothesized that the lesions would show features similar to intraosseous ganglion cysts of the human wrist. Twenty-five cadaveric canine carpi were obtained and a total of 13 lesions were detected on MRI. Based on MRI, six carpi with lesions of varying size and one normal carpus were submitted for histological evaluation. Five of the abnormal carpi had nonarticular cyst-like lesions; one specimen with a positive magnetic resonance image for a cyst-like lesion had no cyst-like lesion on histology. Conspicuity of a medium-size lesion as evaluated on radiographs was poor. Given the presence of these nonarticular cyst-like lesions in a population of clinically sound patients, their clinical importance is uncertain. The development of these lesions may relate to altered mechanics or genetic predispositions, requiring additional study.

Diagnostic investigation of an unusually large osseous cyst‐like lesion of the radial carpal bone

SummaryA 10‐year‐old Irish Sports Horse presented for intermittent, fluctuating lameness of the left forelimb. Nuclear scintigraphy, radiography and computed tomography identified a large osseous cyst‐like lesion (OCLL) occupying approximately 50% of the radial carpal bone with an articular communication to the antebrachiocarpal joint. A transcortical surgical approach was used to curette the lining of the lesion prior to injection with triamcinolone acetonide. This imaging report describes the detailed diagnostic findings of an unusually extensive OCLL in the radial carpal bone.

Skeletal pathology and variable anatomy in elephant feet assessed using computed tomography.

Foot problems are a major cause of morbidity and mortality in elephants, but are underreported due to difficulties in diagnosis, particularly of conditions affecting the bones and internal structures. Here we evaluate post-mortem computer tomographic (CT) scans of 52 feet from 21 elephants (seven African Loxodonta africana and 14 Asian Elephas maximus), describing both pathology and variant anatomy (including the appearance of phalangeal and sesamoid bones) that could be mistaken for disease. We found all the elephants in our study to have pathology of some type in at least one foot. The most common pathological changes observed were bone remodelling, enthesopathy, osseous cyst-like lesions, and osteoarthritis, with soft tissue mineralisation, osteitis, infectious osteoarthriti, subluxation, fracture and enostoses observed less frequently. Most feet had multiple categories of pathological change (81% with two or more diagnoses, versus 10% with a single diagnosis, and 9% without significant pathology). Much of the pathological change was focused over the middle/lateral digits, which bear most weight and experience high peak pressures during walking. We found remodelling and osteoarthritis to be correlated with increasing age, more enthesopathy in Asian elephants, and more cyst-like lesions in females. We also observed multipartite, missing and misshapen phalanges as common and apparently incidental findings. The proximal (paired) sesamoids can appear fused or absent, and the predigits (radial/tibial sesamoids) can be variably ossified, though are significantly more ossified in Asian elephants. Our study reinforces the need for regular examination and radiography of elephant feet to monitor for pathology and as a tool for improving welfare.

An assessment of intra‐ and interobserver agreement of reporting orthopaedic findings on presale radiographs of Thoroughbred yearlings

Radiography is commonly used in clinical practice but agreement of reporting of radiographically detected orthopaedic findings in horses has rarely been studied. To assess agreement within and between observers for reporting of orthopaedic findings on presale radiographs of Thoroughbred yearlings. Retrospective analysis of archived radiographs. Four veterinary radiology specialists each twice examined 167 sets of radiographs for orthopaedic findings in the fore feet, fore and hind fetlocks, carpi, tarsi and stifles. There were 27 findings analysed for agreement. Kappa statistic (κ), percentage of positive agreement (Ppos) and percentage of negative agreement are reported. An excellent percentage of negative agreement was observed for all findings, with the exception of regular vascular channels of the proximal sesamoid bones. Ppos and κ results were variable. The presence of extra carpal bones, osseous cyst-like lesions of the ulnar carpal bone, sagittal ridge defects of the third metacarpus, fracture of the fore and hind proximal sesamoid bones, regular vascular channels in the hind proximal sesamoids, osteochondrosis lesions of the distal intermediate ridge and/or medial malleoli of the tibia, and osseous cyst-like lesions in the medial femoral condyle was consistently observed with an intra- and interagreement κ≥0.5 and Ppos≥50%. Lucency within the proximal sesamoids consistently had an observed intra- and interagreement κ<0.4 and Ppos<40%. Observation of orthopaedic findings on yearling repository radiographs showed generally excellent agreement on the absence of findings, but variable agreement on the presence of findings. Agreement was good for larger and easy to categorise radiographic findings. More accurate definitions and training need to be developed to improve agreement within and between observers for orthopaedic findings with poor or fair to good agreement.

PREVALENCE OF COMPUTED TOMOGRAPHIC SUBCHONDRAL BONE LESIONS IN THE SCAPULOHUMERAL JOINT OF 32 IMMATURE DOGS WITH THORACIC LIMB LAMENESS

Osteochondrosis is a common developmental abnormality affecting the subchondral bone of immature, large breed dogs. The purpose of this retrospective study was to describe CT lesions detected in scapulohumeral joints of 32 immature dogs undergoing CT for thoracic limb lameness. Eight dogs (14 scapulohumeral joints) had arthroscopy following imaging. Thirteen dogs (19 scapulohumeral joints) were found to have CT lesions, including 10 dogs (16 scapulohumeral joints) with subchondral bone lesions and 3 dogs with enthesopathy of the supraspinatus tendon. In one dog, subchondral bone lesions appeared as large oval defects within the mid-aspect of the glenoid cavities, bilaterally. These lesions resembled osseous cyst-like lesions commonly identified in the horse. This is the first report of such a presentation of a subchondral bone lesion in the glenoid cavity of a dog. In all dogs, small, focal, round or linear lucent defects were visible within the cortical bone at the junction of the greater tubercle and intertubercular groove. These structures were thought to represent vascular channels. Findings from this study support the use of CT as an adjunct modality for the identification and characterization of scapulohumeral subchondral bone lesions in immature dogs with thoracic limb lameness.

Development of an Increased Signal Intensity in Fat-Suppressed Images into a Navicular Cyst of an 11-Year-Old Warmblood Horse Evidenced by Six Follow-Up Standing Low-Field Magnetic Resonance Imaging Examinations Over 2 Years

This case report demonstrates the development and management of an osseous cyst-like lesion in the spongiosa of the navicular bone in a high-level show jumper with chronic intermittent forelimb lameness. The first evidence of navicular bone pathology was increased signal intensity on fat-suppressed images in the medulla of the right navicular bone, which progressed to a cystic lucency identified on radiographs at 24 months. The horse's progress was documented over a period of 2 years and 2 months, including lameness investigation, treatment, radiographs, and six follow-up standing low-field magnetic resonance imagings. At the last clinical recheck, the horse showed no signs of lameness and continued to compete in show jumping at an international level event.

Lameness Associated with Mineralization of the Central Tarsal Bone and a Small Osseous Cyst-Like Lesion in Two Sport Horses

The clinical features, response to local analgesia, and imaging findings of two mature sport horses with lameness associated with abnormal mineralization of the dorsal aspect of the central tarsal bone and a small osseous cyst-like lesion are described. Although the radiological findings and the lesions identified using magnetic resonance imaging were similar, the lameness characteristics and responses to perineural analgesia differed. One horse failed to respond to treatment and was retired. The second horse was humanely destroyed. Postmortem examination confirmed the presence of an osseous cyst-like lesion distal to the subchondral bone plate of the central tarsal bone and extensive dense cancellous bone extending one-half the dorsoplantar depth of the bone.

Can distal border fragments of the navicular bone be a primary cause of lameness?

SummaryA horse with unilateral forelimb lameness and pain localised to the palmar aspect of the foot was evaluated using radiography and low field magnetic resonance (MR) imaging. A distal border fragment of the navicular bone, an osseous cyst‐like lesion (OCLL) in the distal third of the navicular bone and focal distal sesamoidean impar desmitis were identified as the most likely causes of pain and lameness. No other lesions likely to contribute to pain and lameness were identified on MR images or gross post mortem examination. The OCLL was characterised histologically by enlarged bone lacunae containing proliferative fibrovascular tissue. Focal lesions of the distal aspect of the navicular bone are rarely found in isolation but can be causes of pain and lameness in horses.

Osseous cyst-like lesions/subchondral bone cysts of the phalanges

Summary In the horse, the phalanges are the second most common location for the occurrence of osseous cyst-like lesions (OCLLs) after the medial femoral condyle of the stifle. Phalangeal OCLLs occur in a variety of locations, most of which are adjacent to, if not communicating with, a joint. The aetiology of these lesions is considered to be multifactorial by most authors. Horses with OCLLs demonstrate lameness of varying severity. Diagnostic analgesia should be used to localise the lameness. After localisation of the lameness, standard radiographic views of the isolated area should be performed. The radiographic characteristics of OCLLs are dependent on the stage of development of the OCLL; OCLLs may first be identified as a small lucent flattening or depression in the articular surface; however, they may progress to a circular, oval or conical single or multi chambered radiolucency within the bone. There may be a rim of radiodense sclerosis around the lucency. Diagnosis of some OCLLs may only be achieved using nonstandard radiographic views or may require advanced diagnostic imaging modalities such as computed tomography or magnetic resonance imaging. Treatment of phalangeal cysts may be conservative or surgical. Surgical treatment options generally aim to prevent cyst enlargement and promote filling of the lesion with osseous material. Depending on the cyst, this can be performed arthroscopically or via an extra-articular approach. Occasionally, the severity of proximal interphalangeal joint OCLLs warrants surgical arthrodesis. Overall the prognosis for return to performance for horses with OCLLs ranges from 30–90% but is dependent on the breed, age and intended use of the horse, surface area of weightbearing cartilage affected, concurrent osteoarthritis within the joint and treatment administered.

High-field magnetic resonance imaging investigation of distal border fragments of the navicular bone in horses with foot pain

Distal border fragments of the navicular bone can be seen in lame and nonlame horses and their clinical significance remains open to debate. To describe the magnetic resonance imaging (MRI) appearance of distal border fragments and the adjacent navicular bone. To investigate the relationship between fragments and other abnormalities of the navicular bone and the distal sesamoidean impar ligament (DSIL). Horses were included if pain causing forelimb lameness was localised to the foot and high-field MR images were acquired. The size and location of distal border fragments were recorded. Abnormalities in the adjacent navicular bone were graded to obtain a fragment grade. A total navicular bone grade was assigned. The DSIL was also graded. A Chi-squared test was used to test for associations between the presence of a fragment and specific lesions involving the distal border of the navicular bone, the total grade of the navicular bone, and the grade of the DSIL. 427 horses were included and 111 fragments observed. There was a significant association between the presence of a fragment and the total navicular bone grade, osseous cyst-like lesions, increased number and size of the synovial invaginations of the distal border, increased signal intensity on fat suppressed images and size of distal border entheseophytes. There is an association between distal border fragments and other pathological MRI abnormalities of the navicular bone. Distal border fragments are part of navicular disease, but their contribution to pain and lameness remains to be clarified.

Comparison between radiological and magnetic resonance imaging lesions in the distal border of the navicular bone with particular reference to distal border fragments and osseous cyst-like lesions

There are no data concerning the accuracy of conventional and computed or digital radiography for evaluation of the equine foot. To compare conventional film-screen and computed radiography with magnetic resonance imaging (MRI) for detection of distal border fragments of the navicular bone; and to establish which type of fragment was more likely to be detected radiologically. Horses were included if forelimb lameness was localised to the foot and both radiography and high-field MR images had been acquired. Horses were divided into 2 groups based on acquisition of conventional (Group A) or computed (Group B) radiographs. The presence of distal border fragments was recorded. From MR images, distal border fragments were graded based on their size and changes in signal intensity in the adjacent navicular bone. Sensitivity and specificity of conventional and computed radiography for detection of fragments were calculated using MRI as the gold standard. A Chi-squared test was used to test for associations between specific radiological and MRI findings in the distal border of the navicular bone. In Group A 46 and 18 fragments were identified on MR and radiographic images, respectively; in Group B 45 and 17 fragments were seen. There was no significant difference between computed and conventional radiography. Grades 4 and 5 fragments or large-sized fragments were identified most frequently; low-grade fragments were unlikely to be observed. There was a significant correlation between radiological and MRI abnormalities of the distal border of the navicular bone. Conventional and computed radiography had similar, rather low sensitivity for identification of distal border fragments of the navicular bone, but specificity was high. Large-sized and high-grade fragments were most likely to be identified radiologically. Fragments observed radiologically are likely to be associated with other pathological abnormalities of the distal border of the navicular bone.

Surgical treatment of osseous cyst-like lesions in the distal phalanx arising from collateral ligament insertional injury

Surgical treatment of osseous cyst-like lesions in the distal phalanx arising from collateral ligament insertional injury

Long‐Term Outcome in 44 Horses with Stifle Lameness After Arthroscopic Exploration and Debridement

To (1) examine the outcome in horses with osteoarthritis or intra-articular soft tissue injuries of the stifle after arthroscopic exploration and debridement and (2) to determine any imaging or surgical findings that may influence prognosis. Case series. Horses (n=44) with lameness referable to the stifle, diagnosed with osteoarthritis, meniscal tears, or other intra-articular soft tissue injuries based on arthroscopic examination. Medical records of horses with stifle lameness that had arthroscopic exploration were reviewed. Horses with osteochondrosis lesions, intra-articular fractures, or osseous cyst-like lesions were excluded. Pertinent case information was analyzed and short- and long-term outcome was assessed. There was no association between radiographic score and surgery score. Diagnostic ultrasound had a sensitivity of 79% and a specificity of 56% for identifying meniscal injuries. Follow-up information was available for 35 horses; 23 horses (60%) improved after surgery, 16 (46%) became sound, and 13 (37%) returned to their previous level of function. A negative association was observed between age and degree of preoperative lameness and outcome. More severe changes observed on preoperative radiographs were also negatively associated with prognosis. No horses with grade 3 meniscal tears improved postoperatively and increasing meniscal pathology was negatively associated with return to previous function. A weak association between surgery grade and outcome was also observed. Degree of chondral damage, location of primary pathology, and microfracture techniques had no effect on outcome. Advanced horse age, severe lameness and preoperative radiographic changes, and presence of large meniscal tears are associated with a negative postoperative outcome for horses with stifle lameness. Appearance of the articular surface at surgery appears to be an inconsistent prognostic indicator. Some horses with extensive cartilage damage may return to athletic function after arthroscopic debridement and lavage. A more pessimistic prognosis may be given to older horses, those with more severe preoperative lameness, and those with severe radiographic changes or large meniscal tears.