Teaching Case

A previously fit 24-year-old gentleman presented to the Emergency Department following a valgus injury to his left knee. He fell through a table whilst standing on it and his foot became stuck. On examination he was unable to weight bear with gross swelling to the medial aspect of his knee.

Anteroposterior radiographs demonstrated a fracture to the medial aspect of the medial femoral condyle (Fig. 1) with associated lipohaemarthrosis seen on the lateral images (Fig. 2). There was no proximal tibial or fibular fracture seen.
A subsequent MRI was performed for further evaluation of the extent of the injury. MRI demonstrated the presence of an acute displaced bony avulsion of the femoral attachment of the medial collateral ligament with an avulsed medial femoral condyle fragment measuring 19mm across craniocaudal extent (Fig. 3). Evidence of a near full-thickness anterior cruciate ligament tear was present, with only a few intact posterolateral bundle fibres (Grade II). The surrounding supporting structures were intact. Periarticular subcutaneous oedema was most marked medially.

A Stieda fracture is defined as an avulsion injury from the medial femoral condyle at the origin of the tibial collateral ligament (also known as the superficial medial collateral ligament) [1]. The medial collateral ligament is a membranous band that acts to restrain valgus forces on the knee. It originates superiorly from the medial femoral condyle and has superficial and deep fibres. The deeper fibres attach to the medial meniscus and fuse with the capsule. The superficial portion attaches to the upper third of the tibia as far as down to the tibial tuberosity level [2].

This presentation is frequently seen in sports that involve valgus knee loading and forceful shifts of direction, such as skiing, ice hockey and football [3]. These injuries result in pain, instability and loss of function. Without acute intervention the avulsion fracture can lead to Pellegrini-Stieda syndrome, which refers to the development of ossification in or near the tibial collateral ligament near the margin of the medial femoral condyle [1]. Although it is usually asymptomatic, in rare cases the gradual ossification can lead to increased pain and limitations in movement of the knee joint [4].

The diagnosis of a Stieda fracture is made on imaging. Knee radiographs are the first imaging used in acute knee trauma. Plain radiographs of the knee demonstrate a linear opacity near the medial femoral condyle, however, these may be difficult to spot. Lipohaemarthrosis on lateral radiographs of the knee is indicative of an intra-articular fracture, even when the fracture may be radiographically occult [5]. MRI is an invaluable diagnostic procedure to demonstrate the site of the fracture and other possible injuries to the knee. This helps to guide further management.

Initial treatment should involve non-surgical techniques. Regular analgesia and immobilisation will encourage bony union. Serial radiographs after 4-6 weeks can help demonstrate bony union [6]. If this is unsuccessful then surgery is required with an aim to improve pain and movement in the joint.