Role of peripatellar retinaculum in transmission of forces within the extensor mechanism

Background: The role of the peripatellar retinaculum as a frontal plane stabilizer of the patellofemoral joint has been well established. However, as a result of its unique orientation, the retinaculum also may influence the distribution of forces within the extensor mechanism. The objective of this study was to determine the extent to which the peripatellar retinaculum affects the magnitude of forces experienced by the patellar tendon. Methods: Ten cadaver knees were used in this investigation. Each was mounted on a custom test apparatus that was fixed to an Instron frame. The extensor mechanism was loaded by applying forces through the individual heads of the quadriceps femoris. Patellar tendon tension was measured at 0°, 20°, 40°, and 60° of knee flexion with use of a buckle transducer under two conditions: (1) with the peripatellar retinaculum intact, and (2) with the peripatellar retinaculum removed. Patellar tendon tension was compared between the two conditions across the knee flexion angles. Results: At each knee flexion angle, the patellar tendon tension was greater with the retinaculum removed than it was with the retinaculum intact. However, the difference was significant only at 0° and 60°, at which positions the force transmitted to the patellar tendon was increased by 16.6% and 9.6%, respectively. Conclusions: The observed increases in patellar tendon tension after removal of the peripatellar retinaculum is an indication of the load-sharing function of that structure as a part of the extensor mechanism. Clinical Relevance: Our results suggest that compromise of the peripatellar retinaculum may alter patellar tendon and/or patellofemoral joint forces.