Teaching Case

A twelve-year-old male football player with an intensive practice of five times a week, presented with a one-year history of activity-related pain on the right (dominant) knee. He had no history of previous trauma. The physical exam demonstrated a full painless passive and active range of motion, without any deformity.

The radiograph of the right knee (Figure 1) was almost unremarkable, only demonstrating a subtle physeal irregularity of the lateral proximal tibia and distal femoral physis.

On the MRI of the knee, a widening of the lateral physis on the proximal tibia and distal femoral physis was noted. The physis widening was dominant on the metaphyseal side, and it demonstrated a similar appearance to the adjacent cartilage, both on the T1-weighted (Figure 2) and on the proton-density fat-saturation sequences (Figure 3).

Background

Repetitive microtrauma and stress can lead to a disruption of the metaphyseal vasculature that supplies the physis with calcium, vitamin D and phosphates needed to promote normal endochondral ossification [1]. In the absence of normal blood flow, ossification is halted, causing chondrocytes to accumulate in the proliferative zone and form long columns of hypertrophic cartilage cells [1]. This aberrancy can be temporary; however, if a significant insult persists, a permanent growth disturbance may occur [2,3].

Clinical Perspective

This condition is typical of skeletally immature children who participate in high-level sports and sustain repetitive microtrauma [3]. The affected knee is frequently described as the dominant leg, the “kicking leg”, and the pain is activity-related [4].

Imaging Perspective

Radiographs may show widening/irregularity of the physis, but the knee MRI is the cornerstone for the final diagnosis.

The accumulation of chondrocytes in the proliferative zone is responsible for the cartilage signal intensity and the apparent physeal widening seen on MRI [3]. The widening of the physis is isointense to the adjacent cartilage on the T1-weighted sequence and hyperintense to the physeal cartilage signal on the proton-density fat-suppression sequence or T2-weighted sequence. These findings can be present not only on the lateral hemiphysis of the distal femur and/or proximal tibia but also on the proximal peroneus [3]. These anatomical regions are prone to repetitive valgus stress due to kicking a football ball, causing repetitive compression, and damaging the lateral physis.

This condition should be differentiated from Salter–Harris type I injuries. No discrete fracture is identified through the cartilage, the widening can be quite focal, and neither epiphyseal nor apophyseal displacement is seen. Salter–Harris fractures are also often the result of an acute insult [3].

Outcome

Overuse injuries in the growing child can cause significant long-term problems such as growing arrest and, consequently, significant limb deformity requiring surgical intervention [4]. In the presented case, limb deformity was not noted, and strict rest for two months was enough for the clinical resolution of the symptoms [3]. With strict rest, healing occurs, and normal osteogenesis resumes [5].

Take Home Message

Hemiphyseal arrest secondary to chronic repetitive microtrauma of the knee (youth kicker’s knee) is a rare condition but should be recognised from its differentials. Typically, lateral physis is affected. If unrecognised, it may lead to permanent disability and growth arrest.

Written informed patient consent for publication has been obtained.