Lower Extremity Biomechanics During a Drop-Vertical Jump and Muscle Strength in Women With Patellofemoral Pain

Context: Patellofemoral pain (PFP) is one of the most prevalent knee conditions observed in women. Current research suggests that individuals with PFP have altered muscle activity, kinematics, and kinetics during functional tasks. However, few authors have examined differences in lower extremity biomechanics in this population during the drop-vertical jump (DVJ). Objective: To determine how lower extremity electromyography, kinematics, and kinetics during a DVJ and lower extremity isometric strength differed between women with and those without PFP. Design: Cross-sectional study. Setting: Laboratory. Patients or Other Participants: Fifteen healthy women (age = 20.23 +/- 1.39 years, height = 169.32 +/- 5.38 cm, mass = 67.73 +/- 9.57 kg) and 15 women with PFP (age = 22.33 +/- 3.49 years, height = 166.42 +/- 6.01 cm, mass = 65.67 +/- 13.75 kg). Intervention(s): Three trials of a DVJ. Main Outcome Measure(s): Surface electromyography, kinematics, and kinetics were collected simultaneously during a DVJ. Lower extremity strength was measured isometrically. Independent-samples t tests were performed to assess group differences. Results: Normalized muscle activity in the vastus medialis (healthy group = 120.84 +/- 80.73, PFP group = 235.84 +/- 152.29), gluteus maximus (healthy group = 43.81 +/- 65.63, PFP group = 13.37 +/- 13.55), and biceps femoris (healthy group = 36.68 +/- 62.71, PFP group = 11.04 +/- 8.9) during the landing phase of the DVJ differed between groups. Compared with healthy women, those with PFP completed the DVJ with greater hip internal-rotation moment (0.04 +/- 0.28 N/kg versus 0.06 +/- 0.14 N/kg, respectively) and had decreased knee-flexion excursion (76.76 degrees +/- 7.50 degrees versus PFP = 74.14 degrees +/- 19.85 degrees, respectively); they took less time to reach peak trunk flexion (0.19 +/- 0.01 seconds versus 0.19 +/- 0.02 seconds, respectively) and lateral trunk flexion (0.12 +/- 0.07 seconds versus 0.11 +/- 0.04 seconds, respectively). Conclusions: During the DVJ, women with PFP had increased hip internal-rotation moment and decreased knee-flexion excursion with less time to peak trunk flexion and lateral flexion. Muscle activation was increased in the vastus medialis but decreased in the gluteus maximus and biceps femoris. This suggests that altered motor-unit recruitment in the hip and thigh may result in changes in biomechanics during a DVJ that are often associated with an increased risk of injury.