Patellofemoral pain during step descents with and without fatigue-induced hip internal rotation

Weakness of hip external rotator muscles may cause excessive hip internal rotation during functional activity and it is associated with the development of patellofemoral pain (PFP). The aetiology of PFP is multifactorial in nature. Therefore, routine enrolment of patients into a hip-strengthening programme may not be effective and cost-effective. The present study examined the effect of fatigue-induced hip internal rotation during functional activity. Twenty subjects with PFP were asked to descend a step in barefoot before and after an isokinetic exercise protocol to induce muscle fatigue of hip external rotators. The hip motion was captured by eight high-speed cameras and analysed by a three-dimensional motion analysis system. The level of PFP during step descent and their usual PFP level were measured by validated instruments. Patients with PFP presented with more pronounced hip pathomechanics (p<0.001) and greater level of PFP (p=0.001) after muscle fatigue. The pain score after muscle fatigue during step descent better reflects the usual functional disturbance associated with PFP (rs=-0.655, p=0.002). Physical examination with induced muscle fatigue may be helpful in clinical decisions on the management programme for patients with PFP, which are related to altered hip mechanics.