Lateral patellar luxation associated with severe osteochondritis dissecans (OCD) of the lateral trochlear ridge

Abstract

This case report draws attention to an unusual clinical manifestation of OCD in the lateral trochlear ridge of the femur leading to lateral patellar luxation and the poor outcome associated with such a case. CASE HISTORY A four-month-old Hanoverian colt foal presented for evaluation of left stifle swelling and gait abnormality. The owner had noticed that the foal had been intermittently lame for approximately four weeks previously and one week prior to referral a swelling around the stifle had developed. The owner reported that the foal had slipped in the field when about one month old, but had not shown clinical signs at the time. The foal was bright and alert but noted to be large for its age (212 kg). A marked femoropatellar effusion was evident on the left hind limb and lateral displacement of the patella was palpable (Fig. 1). On manipulation, this could be reduced by hand (Grade III/IV). Mild muscle wastage was noted over the left gluteal region when the foal was able to bear weight on the leg once the patella was reduced. A mild femoropatellar effusion was detected in the right hind limb, but no other effusions were evident in the rest of the limbs. At walk, the foal displayed discomfort, being worse at the end of the cranial swing phase and initial weightbearing phase. An audible clicking noise was present on full extension at the end of the cranial phase. At trot, a 3/10 lameness was present in the left hind limb. Flexion tests were not performed. INVESTIGATION Radiography Radiographic examination of the left stifle revealed abnormal location of the patella, lateral to the lateral trochlear ridge of the femur (Figs. 2a and 2b). The lateral trochlear ridge itself had irregular subchondral bone with areas of reduced radiopacity deeper in the trabecular bone. No abnormalities were detected in the right stifle.