Patellar sleeve fracture

Avulsionsfraktur

unterer Patellapol bei einem 12-Jährigen. Links Röntgenbild, Mitte CT sagittal und axial, rechts Volumen Rendering.

Patellar sleeve fractures (also commonly, patellar sleeve avulsion fracture) represent chondral or osteochondral avulsion injury commonly at the inferior pole of the patella (including cartilage from the articular surface, as well as periosteum and cartilage over the dorsal surface).

Very rarely it can involve the upper pole .

This is an important diagnosis as the displaced bone-forming tissue will continue to grow and ossify, enlarging, and possibly duplicating the patella.

Epidemiology

Patellar sleeve fractures occur in the pediatric population between 8 and 16 years of age, with a peak incidence at 12.7 years, predominantly boys (3:1). Adolescents are more susceptible due to rapid growth, increased sports activity, and relative patella instability.

Clinical presentation

Unlike Sinding-Larsen-Johansson disease, these injuries are acute and result from sudden and forceful contraction of quadriceps muscle (indirect mechanism). Acute focal pain and tenderness occur at the time of the injury, and a palpable gap may be present.

Radiographic features

Plain radiograph

Lateral knee x-rays demonstrate swelling at the lower pole of the patella and some degree of patella alta. If a small bony fragment has been avulsed with the cartilage, then this too may be seen. A joint effusion may not be present.

Ultrasound

Ultrasound may be helpful in the absence of a radiographically visible fracture fragment. A disruption of the cartilage may be seen, and the degree of separation estimated. Ancillary findings of soft-tissue edema, fluid, and hyperemia may be helpful.

MRI

MRI is critical if the diagnosis is suspected as the degree of chondral injury cannot be assessed on plain radiography, and coexistent extensor mechanism injury may be present.