There are few published reports of CT findings for the diagnosis of stifle osteochondritis dissecans (OCD) in the dog. This report describes the radiographic and multidetector CT (MDCT) findings of two cases with bilateral stifle osteochondrosis and OCD lesions. In both cases, radiographs did not provide a complete picture of the pathology and CT was needed for a definitive diagnosis. In case 1, CT showed bilateral defects on the caudomedial part of the lateral femoral condyles with joint mice within the cranial right stifle joint. In case 2, CT showed large bilateral joint mice within the intercondylar fossa originating from the medial aspect of the lateral femoral condyles as well as a defect on the right medial femoral condyle. MDCT provided an accurate diagnosis in both these cases and facilitated surgical planning.
- computed tomography (ct)
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Osteochondrosis (OC) is a disruption of endochondral ossification that involves the articular cartilage and underlying bone.1 In osteochondritis dissecans (OCD), cracks and fissures are formed in areas of necrotic cartilage, which can extend towards the articular cartilage creating a cartilage flap or loose body (joint mouse).1 The stifle can be a diagnostic challenge because of its complex anatomy.2 Where radiographs fail to identify an OC or OCD lesion in the stifle, multidetector CT (MDCT) is a useful imaging modality to evaluate for occult intra-articular or subchondral bone changes.3
The aim of this manuscript was to describe the radiographic and CT findings of two cases with bilateral OC and OCD lesions in an unusual location of the distal femur, with emphasis on the use of MDCT to produce an accurate diagnosis and to facilitate surgical planning in cases where radiographs do not provide a complete picture of the problem.
Signalment, history and clinical findings
An eight-month-old female entire labrador retriever dog was referred for evaluation of bilateral hindlimb lameness of six weeks duration. Conservative treatment with rest and non-steroidal anti-inflammatories (0.2 mg/kg meloxicam once daily, Boehringer Ingelheim, UK) had improved the lameness initially, however, when exercise was reintroduced, the lameness reappeared. Although the problem was bilateral, the owner had noticed that it was more evident in the left hindlimb. Orthopaedic examination revealed bilateral stifle effusion and very mild bilateral joint instability. Both hindlimbs showed a hyperextended posture. The rest of the clinical and orthopaedic examination was unremarkable.
Radiographs of the stifles and hips taken by the referring veterinarian revealed bilateral changes of the stifles. There was evidence of moderate to severe bilateral joint effusion, mild bilateral osteoarthrosis and presence of bilateral calcified intra-articular bodies located cranially to the femoral condyles. No obvious evidence of flattening or subchondral bone sclerosis of the femoral condyles was noted at this stage (Fig 1). At this point the main differentials included bilateral partial cranial cruciate rupture with bony avulsion or bilateral stifle OCD, given the age and clinical presentation of the dog.
To further characterise the initial findings, and given that radiography and the orthopaedic examination were not sufficiently comprehensive for reaching a definitive diagnosis, a CT examination of both stifles was performed. The patient was anaesthetised and placed in sternal recumbency with the hindlimbs in a semiextended position and the long axis parallel to the scanning table. Images were acquired as a helical run with a 16-slice system (Aquilion 16, Toshiba America Medical Systems, Tustin, California, USA). Slice thickness was 0.5 mm. Bone (window level (WL) 1000, window width (WW) 3500) and soft tissue (WL 35, WW 350) algorithms were acquired and reviewed by a certifying radiologist using a dedicated three-dimensional workstation (Osirix, Pixmeo, Geneva, Switzerland).
The CT revealed marked bilateral hypoattenuating joint effusion (20–30 HU) and mild periarticular osteophytosis. There was a bilaterally irregular surface of the medial aspect of the very caudal part of the lateral femoral condyles outlining a circular hypoattenuating defect within the subchondral bone. The surfaces of both femoral intercondylar fossae were also irregular. At least two, 1-mm, bone-density fragments (joint mice) were visible within the cranial aspect of the right stifle joint, cranially to the lateral femoral condyle (Fig 2). There were also several small (at least 3×1 mm) fragments cranial to the medial femoral condyle and in the caudal aspect of the joint, caudal to the lateral femoral condyle (at least 3×1 mm). In the left stifle there were fewer joint mice, with one large fragment (3.2×3.6 mm) located cranial to the lateral femoral condyle and a further fragment (2.2×2.3 mm) within the caudal aspect of the joint, caudal to the lateral femoral condyle.
Following the CT scan a diagnosis of bilateral OCD of the medial aspect of the most caudal part of the lateral femoral condyle was made. The intra-articular bodies were thought to represent subchondral bone fragments originating from the lesion itself. This was unusual as the fragments migrated a long distance from the site of origin through the intercondylar fossa and were lodged in the area where the cranial cruciate ligaments originate, becoming a potential source of damage to the ligaments themselves.
Surgical treatment was advised for this patient. An arthroscopically assisted abrasion arthroplasty, bilaterally staged, was performed with the aim to aid resurfacing of the defects with fibrous cartilage. The left stifle was operated on first. A large lesion of approximately 3×3×2 mm, which appeared biparted in a vertical direction, was visualised in a location consistent with what was seen on the CT images. The lesion was debrided down to viable subchondral bone and the bony fragments flushed out of the joint. A similar procedure was repeated for the right stifle three weeks later.
The patient recovered well and was discharged 48 hours later with analgesia (0.2 mg/kg meloxicam once daily, Boehringer Ingelheim, UK) and joint supplements (glucosamine and chondroitin, VetPlus, UK). Exercise restriction was recommended with cage rest and short toilet lead walks only for the following six weeks. Afterwards, a progressive programme of controlled lead exercise with hydrotherapy was encouraged.
The dog recovered well from both procedures, with occasional lameness and some fibrous reaction around the surgical sites detected at the three-week postoperative check. Follow-up radiographs seven months after the surgery showed moderate bilateral effusion and mild bilateral osteophytosis. The patient was re-evaluated by the referring veterinarian nine months postoperatively, where no clinical evidence of stifle effusion or lameness was detected. The owner reported that the patient occasionally would become stiff and very slightly lame after long exercise, but that the dog was otherwise well.
Signalment, history and clinical findings
A five-month-old female entire labrador was referred for evaluation of left hindlimb lameness of approximately three weeks duration. The dog had initially presented to the referring veterinarian with an acute non-weightbearing lameness on the left hindlimb three weeks previously. Conservative treatment with rest and non-steroidal anti-inflammatories (2 mg/kg carprofen twice daily for five days, Zoetis, UK) had markedly improved the lameness but the dog remained stiff on rising and the lameness worsened after exercise. On orthopaedic examination at the referral hospital the dog was moderately lame on the left hindlimb, stifle palpation elicited a pain response and revealed marked bilateral joint effusion. Crepitus was also palpated in the left stifle.
Radiographs of the stifles, taken by the referring veterinarian were reviewed at the time of examination at the referral hospital. They showed moderate bilateral stifle effusion and mild flattening of the right medial femoral condyle (Fig 3). No radiographic changes suggestive of intra-articular bodies were noted on the radiographs.
As for case 1, to further describe the radiographic findings, a CT scan of both stifles was performed using the same protocol as previously described.
Changes were almost bilaterally symmetrical revealing a moderate amount of hypoattenuating joint effusion (average 25 HU) and several joint mice at the level of the intercondylar fossae (3×1.5 mm on the right, and slightly larger ones on the left (4×2 mm)) originating from the medial aspect of the lateral femoral condyles. Two of the mentioned bodies on each stifle were still attached to the underlying bone. The surface of the medial aspect of both lateral femoral condyles was irregular with the presence of moderate subchondral sclerosis of the underlying bone (Figs 4,5). There was a small defect (3 mm length) on the articular surface of the right medial femoral condyle with regional subchondral sclerosis (Fig 5).
A diagnosis of bilateral stifle OCD involving the medial aspect of the lateral femoral condyles, and OC of the articular surface of right medial femoral condyle was made.
The patient was anaesthetised and a left stifle arthrotomy was performed to remove the bone fragments, carry out abrasion arthroplasty and osteostixis to encourage fibrocartilage repair. The dog recovered well from surgery and was discharged the following day with analgesia (2 mg/kg tramadol twice daily, Bristol Laboratories, UK and 2 mg/kg carprofen twice daily, Zoetis, UK) and antibiotics (15 mg/kg cephalexin twice daily, Virbac, UK). The dog received four weeks of cage rest followed by a further four weeks of gradually increasing exercise. Long-term, it was advised that the dog was subjected to steady, moderate exercise as well as maintain a lean body weight and receive joint supplements (glucosamine and chondroitin, VetPlus, UK).
Recheck six months after presentation at the referral hospital, revealed no lameness with improved muscle mass in both hindlimbs and minimal stifle effusion but pain persisted at full extension of the right stifle. At this point an arthrotomy on the right stifle was performed, which revealed a partial cranial cruciate ligament tear and healing of the medial condylar lesion with fibrocartilage. A small fragment was removed from the lateral femoral condyle as well. The dog recovered well after this procedure.
At clinical examination for routine vaccination three years postsurgery it was noted that the dog had some hindlimb muscle atrophy and it was referred for physiotherapy.
OCD of the stifle joint is an infrequently reported cause of lameness in young, large breed dogs.4–8
The most common localisation of OCD in the stifle is the articular surface (medial aspect) of the lateral femoral condyle.6–10 There are two previous reports of stifle OCD presenting CT features.10 11 One describes a unilateral OCD-like lesion located on the medial aspect of the medial femoral condyle in a crossbreed dog with a large osseous fragment within the intercondylar fossa.11 The second publication reports a boxer with a unilateral OCD lesion on the medial aspect of the lateral femoral condyle at the level of the intercondylar fossa.10 In both cases, the lesion was unilateral. Moreover, the radiographs were highly suggestive of an OCD lesion and the CT appearance was not described in detail.
In the present cases, only CT imaging enabled us to diagnose with certainty OCD lesions in an uncommon location, and to plan and tailor adequate surgical treatment for them. The radiographic findings were compatible, but not definitive for the presence of an OCD lesion, and further imaging studies were needed in order to reach the diagnosis. It is possible that taking oblique views might have helped in depicting the actual defect at the level of the femoral condyle. CT to evaluate the intercondylar fossa of canine stifles can be easily obtained and is more reliable when compared with conventional radiographs, which is what the authors found in the present two cases.12 13 This may be because it avoids osseous and/or soft tissue superimposition.12 The use of multiplanar reconstructions (MPR) and volume rendered (VR) images in these cases was very helpful both for diagnostic purposes and to show the precise location of the lesions to help with the surgical approach. In addition to plain CT scans, CT-arthrography could have been used to look for evidence of intra-articular ligamentous abnormalities; however, arthroscopic evaluation and direct inspection were selected for this purpose in these cases.
The prognosis in OCD cases is variable and depends on several factors, such as the chronicity of the lesion and the degree of degenerative joint disease present at the time of the treatment.14 Surgical treatment involves removal of the cartilage flap via arthroscopy or arthrotomy and, traditionally, debridement with the aim to stimulate the development of fibrous cartilage.14 15 More recently, the application of an osteochondral autograft as a potential superior method of resurfacing has been introduced to veterinary surgery.16 17
In summary, these two cases show unusual localisations of bilateral stifle OCD. They support the importance of cross-sectional imaging techniques like MDCT for determining the exact location and appearance of an OCD lesion in order to optimise planning for surgery. With modern MDCT scanners, anatomical volumes can be acquired with isotropic resolution along any plane, making the interpretation of normal anatomy and pathology much easier with the use of MPRs and VR reconstructed images.18 In these cases CT was superior to radiography, which underestimated the extent of the stifle OCD lesions.
Contributors NFE drafted and revised the paper as primary author. VP was the radiologist who reported case 1 and provided the images for this case. VP also edited the drafted paper. HR was the surgeon involved and primary clinician in both cases. HR also edited the drafted paper. RS was the radiologist who reported case 2 and provided the images for this case. RS provided feedback throughout the drafting of the manuscript and was the supervisor for the manuscript.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement There are no additional data available for this paper.
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