Local neuromuscular characteristics associated with patellofemoral pain: A systematic review and meta-analysis

Background: Local neuromuscular deficits have been reported in people with patellofemoral pain. We synthesised the neuromuscular characteristics associated with patellofemoral pain to help identify interventional targets and potential mechanisms. Methods: Five databases were searched for local neuromuscular characteristics in case-control studies. Electromyography, flexibility, muscle performance and cross-sectional area data were derived from functional or isolated task investigations and synthesised accordingly. An evidence gap map was constructed. Findings: Sixty-seven studies were included. In functional tasks, electromyographic investigations showed moderate evidence of small effect for vastus medialis onset-delays relative to vastus lateralis (0.44 [0.03, 0.85]) during stepping/stair negotiation tasks, and higher biceps femoris mean excitation amplitudes (0.55 [0.06, 1.04]) in single-leg triple-hop test. In isolated tasks, we found moderate evidence of medium effect for lower Hoffman-reflex amplitude of vastus medialis (-1.12 [-1.56,-0.67]). Muscle performance investigations showed; strong evidence with medium and small effects for lower extensors concentric (-0.61 [-0.81, -0.40]) and eccentric (-0.56 [-0.79,-0.33]) strength, and moderate evidence of medium effect of lower isometric (-0.64 [-0.87,-0.41]) strength, moderate evidence with small effect for rate of force development to 30% (-0.55[-0.89,-0.21]), 60% (-0.57[-0.90,-0.25]) and medium effect to 90% (-0.76[-1.43,-0.10]) of maximum voluntary contraction, and small effect for lower flexors concentric strength (-0.46 [-0.74,-0.19]) and extensors total work (-0.48 [-0.90,-0.07]). Flexibility investigations showed tighter hamstrings (-0.57 [-0.99,-0.14]). Interpretation: Differences within quadriceps and hamstrings motor-control, hamstrings tightness, and quadriceps and hamstrings weakness are associated with patellofemoral pain, and can be used to guide investigations of treatment effects.