DISCUSSION
Strain injuries of the rectus femoris muscle are common. These injuries can occur during both eccentric and explosive forceful contractions of the muscle.1–3 Gait analysis has shown that the primary function of the quadriceps during running is deceleration of knee flexion at heel strike, which is accompanied by simultaneous contraction with the hamstrings during the support phase.4 The rectus femoris muscle is therefore most often injured while regulating hip and knee motion. During soccer, the rectus femoris can be injured as the quadriceps contracts forcefully to extend the knee and flex the hip to strike the ball. The muscle has a high percentage of type II muscle fibres which enable it to produce rapid forceful activity.5 As the rectus femoris is the only biarticular muscle of the quadriceps, it is not surprising that it is the one most commonly injured.6
Avulsion type ruptures of the direct head of the rectus femoris muscle from its origin, the anterior inferior iliac spine, are well documented, as are ruptures occurring at the distal tendon junction where the rectus inserts into the quadriceps tendon.7 Less common are injuries at the musculotendinous junction. Injuries at this level have been identified by Temple et al,8 who described tears appearing as pseudotumours in seven cases. However, we have found no reports of complete ruptures at this level. In addition, we have found no reports describing the operative repair of a chronic rupture.
Clinical examination showed a unique feature in that the muscle belly retracted distally (towards the knee) during quadriceps contraction.
Ehman and Berquist9 have shown that contrast enhanced magnetic resonance imaging should be the investigation of choice.
Concentric and eccentric strength testing was performed before and after surgery using the KIN-COM III isokinetic dynamometer. Before the operation, the quadriceps showed considerable reduction in concentric power compared with the normal side with no peak of power (fig 2). Interestingly, the hamstrings also showed reduced power. This was despite intensive physiotherapy, and we speculate that this was due to the lack of a normally functioning quadriceps mechanism resulting in wasting of its antagonists. Concentric power was restored to both the quadriceps and hamstrings after surgery, with peak power similar to the normal side.
Because of the paucity of literature on this injury, there was no definitive treatment protocol. However, Cross et al10 report satisfactory results after surgical reattachment of chronic complete proximal hamstring tendon avulsions. We felt that this article was a reasonable guide for setting up our own treatment protocol for this case, as both injuries deal with proximal injuries rather than the more common distal tendon avulsions. Cross et al also immobilised the knee after surgical reattachment of thigh muscles (albeit posteriorly compared with our anterior injury) rather than immobilising the hip, and we felt that immobilising the hip would have been more impractical. Non-operative treatment can be considered in inactive people, but in this patient we believe that surgical repair was indicated. We felt that immobilisation of the hip after surgery would have been both impractical and perhaps detrimental to the eventual outcome. Immobilisation of the hip alone would have been insufficient to protect the repair and would therefore still have necessitated immobilisation of the knee where the arc of movement and hence excursion of the hamstrings is greater than in the hip. We felt that immobilisation of the knee alone would provide satisfactory protection of the repair.