A novel transcoronal surgical technique for the treatment of cystic lesions of the distal phalanx: A cadaveric study.

OBJECTIVE: To assess the feasibility of a novel transcoronal approach for the treatment of axial type 3 cysts of the palmar/plantar aspect of the distal phalanx (P3). STUDY DESIGN: Ex vivo, experimental study. SAMPLE POPULATION: Ten cadaveric specimens, four forelimbs and six hindlimbs. METHODS: All cadaveric specimens underwent radiographically guided drilling, followed by cortical screw placement. The cartilage was macroscopically assessed after disarticulation of the distal interphalangeal joint. The entry point and trajectory were evaluated with computed tomography. Results were categorized as: axial, near-axial and abaxial. The minimal distance from the outer margin of the drill hole and the proximal border of the subchondral bone plate was measured using frontal computed tomographic slices. RESULTS: Eight of the 10 screws were in an axial to near-axial position and nine followed the desired axial to near-axial trajectory. One screw was inserted axially but continued in an abaxial trajectory. Iatrogenic damage to the joint cartilage, flexor cortex and solar canal of P3 was not observed. All cortical screws were placed close to the proximal subchondral bone-plate of P3. CONCLUSION: The desired axial/near-axial drilling and screw placement, under radiographic guidance, was achieved in nine out of 10 specimens. CLINICAL SIGNIFICANCE: This novel technique seems promising for the treatment of inaccessible P3 cysts. Additional studies are required to investigate its feasibility in clinical cases, and the long-term outcome following transcystic screw placement of type 3 P3 cysts.

Equine subchondral lucencies: Knowledge from the medial femoral condyle.

Equine subchondral lucencies (SCL) have been described since the first availability of suitable radiographic equipment. The initial clinical sign can be lameness, but SCLs are often first found on surveys of juvenile horses and are primarily a radiographic concern for public auctions. When lameness is present, it varies from subtle to obvious and can be intermittent. Some SCLs heal spontaneously, and some remain blemishes, but when the SCL and lameness are persistent, further damage to the joint and limitations to an athletic career are likely. SCLs were initially described in the distal limb followed by the stifle, and the medial femoral condyle (MFC) is now considered the most common location. The aim of this review is to highlight the initial pathology and discuss the clinical and experimental information available on equine SCLs. SCL treatment has evolved from rest alone and has progressed to debridement, grafting, intralesional injection, and most recently, transcondylar screw and absorbable implant placement. Comparison of success rates between techniques is difficult due to variations in follow-up and outcome measures, and no single technique is best for all SCLs. Treatment appears to increase success by 15%-20% over rest alone, but the method chosen depends on many factors. This review emphasizes the need for further work to fully understand SCL formation and all aspects of trabecular bone healing to optimize surgical therapy and improve treatment success.

Maxillary Aneurysmal Bone Cyst in a Young Dog-A Case Report.

This case report describes an aneurysmal bone cyst in the maxilla of a young dog. It describes the clinical presentation, diagnostics, management, and successful outcome of this highly unusual case. Bone cysts are described as benign, cavitated lesions within bone that are lined by reactive tissues. There is no epithelial lining in the lesions. Bone cysts usually contain hemorrhage or serosanguinous fluid. They usually appear in the long bones, and present as a swelling with or without pain.

Evaluation of subchondral bone cysts in canine elbows with radiographic osteoarthritis secondary to elbow dysplasia.

OBJECTIVE: To investigate whether subchondral bone cysts (SBCs) were present in dogs with radiographic elbow osteoarthritis (OA) and to investigate their relationship with radiographic OA severity. STUDY DESIGN: Retrospective cross-sectional study. SAMPLE POPULATION: Thirty-eight Labrador retrievers (total of 76 elbows). METHODS: Elbow computed tomography (CT) images of 18 young (≤2 years old) and 20 old (>2 years old) Labrador retrievers, which presented for elbow-associated lameness, were reviewed. Radiographic elbow OA was graded into four groups based on the largest osteophyte size on CT. The presence, number, and maximum diameter of SBCs were determined. RESULTS: Subchondral bone cysts were only identified in elbows with osteophytic new bone formation. The number and size of SBCs were associated with radiographic OA severity (p < .001 and p = .041 respectively). Specifically, the rate at which SBCs were present increased for both moderate and severe OA in comparison with the mild OA (moderate OA RR = 2.46, 95% CI 2.08-2.92, p < .001; severe OA RR = 5.60, 95% CI 4.79-6.55, p < .001). For dogs with severe OA, there was an increased likelihood that their SBCs were larger than SBCs from dogs with mild OA (OR = 1.056, 95% CI 1.012-1.101, p = .012). No SBCs were observed in elbows without radiographic evidence of OA. CONCLUSION: Subchondral bone cysts were identified as a feature of radiographic elbow osteoarthritis in Labrador retrievers, and their number and size were indicative of the presence and severity of radiographic elbow OA. CLINICAL SIGNIFICANCE: Subchondral bone cysts are a potential imaging biomarker for quantitative assessment for canine OA.

Arthroscopically guided lag screw fixation of subchondral bone cysts in the medial femoral condyle in Thoroughbred racehorses: description of technique and comparative results.

OBJECTIVE: To describe an arthroscopically guided technique for lag screw placement across subchondral bone cyst (SBC) in the medial femoral condyle (MFC) and to compare postoperative racing performance with corticosteroid injection and cyst debridement. STUDY DESIGN: Retrospective cohort study. ANIMALS: One hundred twenty-three horses with 134 MFC SBCs undergoing treatment at a single referral hospital in the UK between January, 2009, and December, 2020. METHODS: Sex, age, limb affected, radiographic cyst dimensions, preoperative and postoperative lameness, surgical technique (lag screw placement, cyst debridement, intralesional corticosteroid injection), and, where applicable, screw positioning were recorded retrospectively. A ratio was calculated using measurements from preoperative and postoperative radiographs. Outcome was assessed by resolution or improvement in lameness, reduction in cyst size, and starting one race after treatment. Outcome data was compared between treatment groups. RESULTS: Twenty-six of 45 (57.8%) horses that underwent transcondylar screw placement raced postoperatively, at a median of 403 days between surgery and first postoperative race. There was no difference between treatment groups with regard to racing or preoperative and postoperative lameness. Cysts treated with transcondylar screw placement had a greater reduction in cyst size and a reduced period of convalescence in comparison with those that underwent debridement; the results were similar to those treated by intralesional corticosteroid injection. CONCLUSION: Postoperative racing rates were similar for all techniques. Convalescence was reduced for lag screw placement and corticosteroid injection compared to debridement. CLINICAL SIGNIFICANCE: The arthroscopically guided technique results in radiographically consistent screw placement and cyst engagement and offers a viable alternative to other treatments.

Osteochondral allograft transplantation for treating medial femoral condyle subchondral bone cyst in a 14-year-old standardbred horse: a case report.

Allograft arthroplasty is a promising cartilage-resurfacing technique. A 14-year-old horse was diagnosed with a medial femoral condyle subchondral bone cyst. Allografts were harvested from a young donor animal and implanted to fill the cyst cavity. A visual assessment of the surgical site was possible during follow-up arthroscopy. In addition to a desirable gliding surface and a good adaptation of the grafts, fibrillation of the cranial ligament of the medial meniscus was noted and debrided. The recipient horse became sound four months after follow-up surgery with a high level of owner satisfaction. In conclusion allograft transplantation is a promising technique for treating subchondral bone cysts.

Differences of morphological attributes between 62 proximal and distal subchondral cystic lesions of the proximal phalanx as determined by radiography and computed tomography.

OBJECTIVE: To determine morphological characteristics of subchondral cystic lesions (SCLs) in the proximal phalanx (PP) of adult horses. SAMPLE: Radiographs and/or CT scans of PP from 46 horses. PROCEDURES: There were horses with a SCL in PP, which was diagnosed by radiography and/or computed tomography, included. Additional data (signalment, history, orthopedic examination) were collected retrospectively for each case. RESULTS: Forty-six horses met the required inclusion criteria, with a total of 62 SCLs. Forty-three SCLs (70.5%) were located in the proximal PP (group A). Forty-four percent of these were associated with short, incomplete fractures, while 30 of the proximal PP SCLs (69.7%) were found mid sagittal. Proximal SCLs mostly showed a blurred, irregular shape (62.8%) and long, as well as wide, but shallow shapes in CT. Eighteen SCLs (29.5%) were found in the distal PP, near the proximal interphalangeal joint (group B). In contrast to the described proximal SCLs, the distal SCLs were of circular or oval shape, well delineated (77.8%), and distinctly larger. Horses of group A were significantly older (mean age, 11.47 years) than horses of group B (mean age, 6.72 years). CLINICAL RELEVANCE: The distribution and morphological attributes of proximal PP SCLs as well as their association to subchondral bone lesions and short, incomplete proximal fractures indicate more recently developed lesions due to chronic stress factors, such as repetitive trauma to the cartilage and subchondral bone. In contrast, morphology and distribution of distal SCLs showed high accordance with developmental bone cysts originating from a failure of endochondral ossification.

An Extra-Articular Surgical Approach to Subchondral Bone Cysts in the Humeral Head and Talus in Two Horses.

To date, only a few reports describe the treatment. The present report describes an extraarticular surgical approach, with the insertion of an absorbable implant, to treat a Subchondral cystic lesion (SCL) in the humeral head 3year old racing Thoroughbred & in the talus of a 11year old Arabian horse. SCLs were radiographically visible and associated with severe lameness. Scintigraphy showed focal intense radiopharmaceutical uptake in both cases, and CT scan revealed signs of osteoarthrosis associated with SCL in the talus. The use of a biocompatible, osteoinductive and osteoconductive implant allowed a reduction of the SCL radiographic appearance of at least 70% in both cases and horses returned to their previous athletic activity. The results of the present study might provide substantial information about a new surgical option to treat SCLs in the scapulohumeral and tarsocrural joints and may broaden prognosis and prolong future athletic ability of affected horses.

Comparative results of 3 treatments for medial femoral condyle subchondral cystic lesions in Thoroughbred racehorses.

OBJECTIVES: To compare 3 different methods for treatment of medial femoral condyle (MFC) subchondral cystic lesions in Thoroughbred horses <24 months old based on the criterion of ability to race post-treatment. STUDY DESIGN: Retrospective cohort study. ANIMALS: Thoroughbreds (n = 107, age < 24 months) diagnosed with MFC subchondral cystic lesions. METHODS: Medical records between January 2004 and December 2017 were reviewed. Three treatment methods were used in these horses during that time frame: arthroscopic debridement, intralesional autologous mesenchymal stem cell (MSC) injection, and intralesional corticosteroid injection. The outcome evaluated was the ability to compete in a pari-mutuel race. RESULTS: Seventy-eight of 107 Thoroughbreds (73%) raced post-treatment; 41/57 (72%) of horses treated by arthroscopic debridement raced; 16/19 (84%) of horses treated with intralesional MSCs raced; 21/31 (68%) of horses treated with intralesional corticosteroids raced. There was no difference between groups in the ability to start a race. Sex, limb affected, and lesion size also had no effect on the ability to start a race. There was a trend for increasing lesion size reducing the probability of racing. CONCLUSIONS: Seventy-three percent of the horses raced, but there was no difference in the ability of unraced Thoroughbreds to race after treatment of MFC subchondral cystic lesions with arthroscopic debridement, intralesional mesenchymal stem cells, or intralesional corticosteroids. CLINICAL SIGNIFICANCE: The 3 reported treatment options may be considered for treatment of MFC subchondral cystic lesions with a good prognosis for racing post-treatment. Owners should be advised that increasing lesion size decreases the probability of racing.

Effects of Internal Fluid Pressure on Stresses in Subchondral Bone Cysts of the Medial Femoral Condyle.

The etiology of subchondral bone cysts (SBCs) is not fully understood. Mechanical trauma and fluid pressure are two mechanisms believed to cause their formation and growth. The equine stifle joint provides a natural animal model for studying SBCs. Computed tomography images of an extended yearling cadaveric stifle joint were segmented using ScanIP to isolate bones and relevant soft tissues. Three model geometries were created to simulate cyst sizes of approximately 0.03 cm3 (C1), 0.5 cm3 (C2), and 1 cm3 (C3). A uniform pressure resulting in 3000 N force was applied at the proximal end of the femur. Two types of simulations, filled-cyst and empty-cysts with uniform pressure loads, were used to simulate fluid pressurization. Our models suggest that shear stresses are likely the cause of failure for the subchondral bone and not pressurized fluid from the joint. Bone stresses did not begin to increase until cyst pressures were greater than 3 MPa. For all cyst sizes, fluid pressure must rise above what is likely to occur in vivo in order to increase bone shear stress, shown to be most critical. Synovial fluid pressure acts upon a porous trabecular bone network, soft tissue, and marrow, so the continuum nature of our model likely overestimates the predicted effects of fluid pressures.

Osteochondral regeneration of the femoral medial condyle by using a scaffold-free 3D construct of synovial membrane-derived mesenchymal stem cells in horses.

BACKGROUND: Medical interventions for subchondral bone cysts in horses have been extensively studied. This study investigated the regeneration of articular cartilage and subchondral bone with scaffold-free three-dimensional (3D) constructs of equine synovial membrane-derived mesenchymal stem cells (SM-MSCs) isolated from three ponies and expanded until over 1.0 × 107 cells at passage 2 (P2). RESULTS: SM-MSCs were strongly positive for CD11a/CD18, CD44, and major histocompatibility complex (MHC) class I; moderately positive for CD90, CD105, and MHC class II; and negative for CD34 and CD45 on flow cytometry and differentiated into osteogenic, chondrogenic, and adipogenic lineages in the tri-lineage differentiation assay. After culturing SM-MSCs until P3, we prepared a construct (diameter, 6.3 mm; height, 5.0 mm) comprising approximately 1920 spheroids containing 3.0 × 104 cells each. This construct was confirmed to be positive for type I collagen and negative for type II collagen, Alcian blue, and Safranin-O upon histological analysis and was subsequently implanted into an osteochondral defect (diameter, 6.8 mm; depth, 5.0 mm) at the right femoral medial condyle. The contralateral (left femoral) defect served as the control. At 3 and 6 months after surgery, the radiolucent volume (RV, mm3) of the defects was calculated based on multiplanar reconstruction of computed tomography (CT) images. Magnetic resonance (MR) images were evaluated using a modified two-dimensional MR observation of cartilage repair tissue (MOCART) grading system, while macroscopic (gross) and microscopic histological characteristics were scored according to the International Cartilage Repair Society (ICRS) scale. Compared to the control sites, the implanted defects showed lower RV percentages, better total MOCART scores, higher average gross scores, and higher average histological scores. CONCLUSIONS: Implantation of a scaffold-free 3D-construct of SM-MSCs into an osteochondral defect could regenerate the original structure of the cartilage and subchondral bone over 6 months post-surgery in horses, indicating the potential of this technique in treating equine subchondral bone cysts.

A composite absorbable implant used to treat subchondral bone cysts in 38 horses.

BACKGROUND: In the last 30 years, several treatments have been proposed to treat subchondral cystic lesions (SCLs) but there have been no randomised studies to compare different methods and there is no consensus as to the optimal treatment. OBJECTIVES: To evaluate a biocompatible absorbable implant for the treatment of SCLs in young horses in different anatomical locations. STUDY DESIGN: Retrospective case series. METHODS: Horses with SCLs were treated with debridement through a trans-cortical extra-articular approach and an absorbable implant was inserted in the cavity. Clinical and radiographic follow-up was recorded and follow up ranged from 28 to 46 months (mean 37 months). Racing records were reviewed. RESULTS: Thirty-eight horses between 10 and 24 months of age were included in the study. In 36 of 38 horses treated, lameness resolved, and 77% average filling of the cyst was measured 120 days after surgery on radiographs. In two cases, surgical complications were recorded. MAIN LIMITATIONS: Information about the resorption of the implant is not available. Radiographs were performed in various hospitals or at farms or training stables, therefore, possible minor variations in technique and positioning occurred. CONCLUSIONS: The extra-articular approach to the SCLs followed by the insertion of the absorbable implant led to clinical and radiographic improvement of the SCLs at 120 days after surgery. This technique, feasible in different anatomical locations, may offer an alternative to treat SCLs in young horses.

SIRT1+ Adipose Derived Mesenchymal Stromal Stem Cells (ASCs) Suspended in Alginate Hydrogel for the Treatment of Subchondral Bone Cyst in Medial Femoral Condyle in the Horse. Clinical Report.

Stem cell based therapy are now commonly applied in human and veterinary medical practice especially in orthopaedics. Mesenchymal stromal stem cells isolated from adipose tissue (ASC) are first choice option due to relatively non-invasive and safe procedure of tissue harvesting. However, ASC therapeutic potential strongly rely on patients general health condition, age and life-style. For that reason, to enhance therapeutic potential of cells, they are modified in vitro using different approaches. Previous studies have shown, that ASC treated with resveratrol, herein called SIRT+, are characterised by decreased senescence, increased proliferation rate and improved clinical outcome in autologous therapies. Herein, SIRT + cells in alginate hydrogel were applied to 5 years old warm breed mare was clinically evaluated due to the left hind lameness due to subchondral bone cyst. The therapeutic effect was assessed by the analysis of lameness score and radiological evaluation. This case report demonstrates the therapeutic potential of SIRT + cells in the treatment of orthopaedics disorders in horses as complete bone remodelling occurred after therapy and horse came back to training.

Case Report of a Complex Lateral Femorotibial Joint Injury With Popliteal Tendonitis in a Foal.

A two-month-old, Spanish breed, foal was referred with right hind limb lameness of two weeks duration. Clinical examinations confirmed a complex combination of lesions within the lateral femorotibial joint, including a subchondral bone cyst in the lateral femoral condyle, a severe popliteal tendonitis, and a delayed cartilage detachment of the lateral femoral condyle. Because of the complex association of these lesions, poor prognosis for an athletic career was given to the owner. Four years later, the filly is pasture sound. Lesions of the popliteal tendon in the horse are uncommon. The popliteal tendon should also be investigated in cases of trauma to the lateral femorotibial joint, as it could be associated with other affected structures.

Surgical Treatment of an Osseous Cyst-Like Lesion in the Middle Phalanx Communicating With the Distal Interphalangeal Joint of a Horse.

Subchondral or osseous cyst-like lesions within the distal aspect of the middle phalanx are not commonly reported in equids. These osseous lesions, which can communicate with the distal interphalangeal joint, can result in significant lameness and may not respond well to medical management. This report describes the clinical, diagnostic imaging, and surgical management of a 4-year-old mixed breed gelding where medical management of a chronic subchondral osseous cyst-like lesion of the middle phalanx, which communicated with the distal interphalangeal joint, was unsuccessful. A successful outcome was accomplished after surgical cyst debridement and packing with tricalcium phosphate, a bone marrow aspirate, and platelet-rich plasma.

Stimulation of subchondral bone cyst healing by placement of a transcondylar screw in the equine medial femoral condyle.

OBJECTIVE: To predict the bone formation stimulus of a transcondylar screw across an equine subchondral bone cyst (SBC) in an equine medial femoral condyle (MFC). STUDY DESIGN: Finite element modeling (FEM) of an equine MFC with a 2 cm3 SBC under several transcondylar screw conditions. SAMPLE POPULATION: The right stifle of a yearling thoroughbred without stifle disease that had been euthanized for reasons unrelated to this study and donated to the University. METHODS: The FEM was derived from computed tomography of a yearling thoroughbred and analyzed in ABAQUS v6.14. The transcondylar screw was modeled as a 4.5-mm stainless steel cylinder. The region of interest was the centrodistal MFC, and bone stimulus was calculated. The stimulus threshold for bone formation (BFT) was >60 MPa and is presented as the percentage of total bone surface area (BFA) and frontal plane maps. Principal compressive stress vectors were also determined. Tested variables were daily cycles, load, and screw compression and position. RESULTS: At 750 cycles and 900-N load, <3% of the BFA exceeded the BFT. Increases in BFA > BFT occurred proportionally with load, screw compression, and daily cycles (steps). Compressive stress was oriented vertically on the SBC surface without a screw but aligned with the long axis of well-placed lag screws. Screw placement through the void also increased the number and magnitude of compressive vectors. CONCLUSION: This model predicted that a transcondylar lag screw across an MFC SBC increased surface BFA stimulation and reoriented the compression vector. Increasing screw compression, load, and steps per day increased the bone formation stimulus. CLINICAL SIGNIFICANCE: This study provides evidence that supports the use of a lag screw thorough an MFC SBC to promote bone formation.

Use of an aiming device and computed tomography for assisted debridement of subchondral cystic lesions in the limbs of horses.

OBJECTIVE: To describe the use of an aiming device (AD) and computed tomography (CT) for preoperative planning and intraoperative guided debridement of subchondral cystic lesions (SCL) in the limbs of horses and to determine the outcome 12 months after surgery. STUDY DESIGN: Prospective case series. ANIMALS: Twelve horses referred because of lameness caused by 1 or 2 SCL (total of 14 SCL). METHODS: All horses underwent CT-guided debridement of the SCL. The entry point of the drill bit and direction of drilling were planned and controlled by using a series of CT images and the AD. The SCL were curetted and filled with recombinant human bone morphogenetic protein-2. Surgical times were calculated, and the outcome was determined 12 months after surgery. RESULTS: The use of an AD and CT allowed precise and straightforward drilling of the SCL. The entry point of the drill bit into the SCL was considered optimal in 11 SCL and satisfactory in 3 SCL, and the lesions could be precisely debrided with preservation of the adjacent subchondral bone in all cases. There were no complications. Mean (range) surgery time was 75 (45-115) minutes. The outcome 12 months postoperatively was favorable in 10 of 11 horses. One horse died due to unrelated reasons. CONCLUSION: The use of CT and an AD allowed precise debridement of all SCL in the limbs of 12 horses. CLINICAL SIGNIFICANCE: CT-guided surgical debridement of SCL of the equine digit appears to result in a favorable outcome.

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.

Multiloculated solitary (unicameral) bone cyst in a young dog.

A 20-month-old female spayed Staffordshire Terrier (22.3 kg) presented to the Orthopedic Surgery Service at North Carolina State University Veterinary Teaching Hospital for evaluation of a 6-week history of toe-touching to nonweight-bearing lameness in the right hind limb. Radiographs of the right stifle revealed a multiloculated lytic lesion of the distal femur, with a large open lytic zone centrally, numerous osseous septations peripherally, and focal areas of cortical thinning and loss. An aspirate of the right distal femoral lesion yielded mildly cloudy serosanguineous fluid. Cytologic examination of the fluid revealed a pleomorphic population of discrete cells that exhibited marked anisocytosis and anisokaryosis and a variable nuclear-to-cytoplasmic (N:C) ratio, which were interpreted as probable neoplastic cells, with few macrophages, and evidence of hemorrhage. Given the clinical signs of pain, lesion size, and concern for malignant neoplasia, amputation of the right hind limb was performed. Histologically, the lesion had undulating walls 1-3 mm thick with a continuous outer layer of dense fibrous tissue and an inner layer composed of reactive cancellous bone with no cortical compacta remaining. Remnants of thin fibrous or fibro-osseous septa projected from the bony wall into the cyst lumen. The final histologic diagnosis was a benign multiloculated solitary (unicameral) bone cyst of the distal right femur. Based on the histopathologic findings, it was speculated that the cells identified on cytology were a mixture of developing osteoclasts, osteoblasts, endothelial, and stromal cells. This is the first report describing the cytologic examination of a solitary bone cyst in veterinary medicine.

Concurrent or sequential tibial subchondral cystic lesions in 4 horses with medial femoral condyle subchondral cystic lesions.

CASE DESCRIPTION 4 horses were examined because of signs of chronic hind limb lameness. CLINICAL FINDINGS 3 horses had a history of lameness for > 6 months; specific duration was unknown for 1 horse. On initial evaluation, grade 3 to 4 (on a scale from 1 to 5) hind limb lameness was present in all 4 horses. Radiography of the stifle joint of the affected limb revealed medial femoral condyle subchondral lucencies or subchondral cystic lesions (SCLs) in all 4 horses, medial femorotibial osteoarthritis in 3 horses, and medial tibial condyle SCLs in 3 horses. TREATMENT AND OUTCOME 2 horses were treated medically (stall rest and oral NSAID administration), and 2 horses were treated surgically by means of medial femoral transcondylar lag screw placement through the medial femoral condyle SCLs. The 2 horses treated medically did not improve and were euthanized. Necropsy confirmed the presence of medial femoral condyle and medial tibial condyle SCLs. Surgical treatment did not resolve the lameness in 1 horse with SCLs in the medial tibial condyle and medial femoral condyle, and euthanasia was performed 150 days after surgery. In the second horse, a medial tibial condyle SCL was evident on radiographs obtained 3 months after surgery; however, this was not addressed surgically, and signs of lameness resolved 11 months after surgery. CLINICAL RELEVANCE Results of this small case series suggested that SCLs in the medial tibial condyle can occur in association with SCLs of the medial femoral condyle, with a poor prognosis for return to athletic function in affected horses. Further investigation is indicated.