Patients with chronic unilateral anterior knee pain experience bilateral deficits in quadriceps function and lower quarter flexibility: a cross-sectional study.

Little is known about how chronic unilateral anterior knee pain (AKP) affects bilateral quadriceps function and lower quarter flexibility. To determine if patients with chronic unilateral AKP present bilateral deficits in quadriceps function and lower quarter flexibility. Twenty-two patients with chronic unilateral AKP (pain duration: 48.6 months) and 22 matched healthy controls were evaluated. Pain perception and functional outcomes were obtained. Knee joint and thigh circumferences, quadriceps subcutaneous tissue thickness and function (i.e. maximal and explosive strength, activation, and endurance), and lower quarter flexibility (i.e. hamstrings and iliopsoas/rectus femoris muscle) in both legs were compared across conditions. Knee joint and thigh circumferences, and quadriceps subcutaneous tissue thickness were not different between conditions (P ≥.39). Compared with matched healthy controls, patients with chronic unilateral AKP showed: 1) greater pain perception (0.0 versus 4.4 cm, P <.0001); 2) a lower score for functional outcomes (79.6 versus 53.9, P <.0001); 3) less bilateral quadriceps maximal (3.5 versus 2.8 Nm/kg, P <.0001) and explosive (10.8 versus 8.7 Nm/kg/s, P =.01) strength, activation (0.95 versus 0.83, P <.0001), and endurance (1.66 versus 1.52 Nm/kg, P =.02); and 4) less bilateral hamstrings (86.8 versus 72.6°, P =.002) and iliopsoas/rectus femoris (11.6 versus 7.8°, P <.05) flexibility. Patients with chronic unilateral AKP (without knee joint effusion or quadriceps muscle atrophy) appear to have bilateral deficits in quadriceps function and lower quarter flexibility, which should be addressed with pain reduction. [ABSTRACT FROM AUTHOR]