The mechanism and diagnosis of a sleeve fracture of the upper pole of the patella in children

Sleeve fracture is one of the commoner types of patellar fracture in children. It is an avulsion of an osteochondral fragment at the periphery of the immature patella due to trauma associated with rapid quadriceps muscle contraction. It occurs usually at the inferior pole of the patella, but rarely the superior pole of the patella is affected. The sleeve fracture may be occult on plain X-ray, especially if the ossification centre is small and only a cartilaginous avulsion occurred, yet if not diagnosed and treated at the time of the injury it may cause permanent disability.A case of superior pole sleeve fracture is presented with a review of the previously reported cases in the literature. Our objective was to look for a pattern (in terms of mechanism of injury and clinical features), which may predispose to superior pole sleeve fracture and to provide insight in the radiological signs, which may be helpful to diagnose a sleeve fracture soon after injury.We found that the sleeve fracture of the superior pole of the patella occurs in the under 16's. The mechanism of injury is a rapid quadriceps contraction with the knee in a certain degree of flexion, for example forced flexion due to a fall.In all cases the plain X-ray showed abnormalities, although these were initially missed in half of the cases. The key radiological features are a joint effusion; anterior tilt of the patella and a shell of bone lying proximally to the patella. Ultrasound is very helpful in diagnosing a sleeve fracture of the patella, differentiating it from a quadriceps rupture and in the follow-up of a sleeve fracture.