The neuromechanics of patellofemoral pain syndrome

Patellofemoral pain (PFP) syndrome is one of the most common complaints involving the knee. My purpose was to determine whether imbalances in the soft tissue structures surrounding the knee contribute to abnormal patellar tracking associated with PFP and to investigate the effects of bracing on the pressure in the patellofemoral joint.;Three-dimensional patellar kinematics were recorded in vivo during squatting using a custom-molded patellar clamp and a motion capture system in ten healthy and nine PFP subjects. For PFP subjects, the patella rotated laterally (-9.89° +/-3.06° at 90° knee flexion) and translated laterally (5.05 +/-3.73 mm at 90° knee flexion) significantly more than healthy subjects (medial rotation: 3.03° +/-0.62°, p<0.001; medial translation: -4.93 +/-3.93mm, p<0.001). Increased lateral translation and rotation in PFP subjects suggests the patella is not adequately stabilized during functional activities.;Seven healthy and seven PFP subjects performed voluntary isometric contractions to seven torque levels (1, 3, 5, 7, 9, 15, 20 Nm). The elongation of the VMO and VL tendons was directly measured by ultrasonography. VMO tendon stiffness (p=0.013) and Young's modulus (p=0.029) was significantly greater in PFP (551.59 +/-270.07 N/mm and 172.32 +/-70.84 MPa at 20 Nm) than in control subjects (316.52 +/-213.06 N/mm and 103.20 +/-53.57 MPa); however, there was no difference in VL tendon stiffness (P=0.881) or Young's modulus (p=0.887). Healthy subjects may possess a physiological control mechanism to ensure that the stiffness of the quadriceps tendons is consistent medial-laterally. Increases in the Young's modulus in the medial tendon in PFP may be related to healing from a previous sub-clinical injury.;Nine cadaveric knees were tested with: no brace, knee sleeve, dynamic stabilization sleeve, wrap-style dynamic stabilization brace. Contact area and pressure were measured using a dynamic pressure sensor in the patellofemoral joint. All braces increased contact area while only the wrap-style brace decreased peak pressure. Effects of bracing were limited to <40° knee flexion. Sleeve-type braces may cause the patella to engage the trochlear groove earlier during knee flexion. The wrap-style brace reduced peak pressure by shifting the peak pressure location to a region of the patella with increased cartilage thickness.