We describe a symptomatic, progressive restriction
of knee flexion due to an accessory quadriceps femoris in a nine-year-old
girl. There was no history or findings of post-injection fibrosis,
nor any obvious swelling of the affected quadriceps. At arthroscopy
no intra-articular pathology was found. An accessory ‘quinticeps
femoris’ was diagnosed by ultrasonography and MRI. Following excision
of the muscle and tendon full flexion of the knee was regained and
there was no recurrence of the contracture.