Quads or quins? Atraumatic restricted knee flexion due to accessory quadriceps bands in children

Recent anatomical investigations have emphasized the variability in the knee extensor apparatus, with particular attention to a fifth component of the quadriceps femoris termed the tensor vastus intermedius or accessory "quinticeps femoris." Disorders of this structure have not been described in the pediatric imaging literature.

To review the clinical features, pathoanatomy and imaging findings of children presenting with derangement of the accessory quadriceps femoris, with a particular emphasis on the utility of early magnetic resonance imaging (MRI) of the thigh.

This is a retrospective analysis of 3 children, ages 3-10 years at presentation, who underwent imaging evaluation with subsequent surgically proven accessory quadriceps femoris muscles. Their clinical histories, including duration of symptoms, MRI findings, intervention and surgical outcomes, are reported.

All patients presented with progressive unilateral restricted knee flexion and had multiple imaging studies targeting the knee before diagnosis. Diagnosis in all patients was made on MRI of the thighs, which demonstrated a fusiform low signal intensity structure with muscle-like architecture arising from the anterior or anterolateral proximal femur and blending with the common quadriceps tendon distally. All patients underwent surgical release of the anomalous band with significant functional improvement.

In cases of progressive limited knee flexion without intrinsic pathology, an accessory quadriceps muscle should be considered as an extrinsic cause. Our experience demonstrated this to be readily identifiable on MRI, with symptomatic improvement following surgical release. Early recognition of this condition should prevent unnecessary intervention such as knee arthroscopy and the debilitating loss of flexion due to delayed diagnosis.