Tensile properties of the medial patellofemoral ligament: The effect of specimen orientation

Abstract

For recurrent patellar dislocation, reconstruction of the medial patellofemoral ligament (MPFL) with replacement autografts has often been performed but with only little data on the tensile properties of the MPFL to guide graft selection. With its complex anatomy and geometry, these properties are difficult to obtain. In this study, we showed how the orientation of the femur-MPFL-patella complex (FMPC) during uniaxial tensile testing can have a significant effect on its structural properties. Twenty two FMPCs were isolated from porcine stifle joints and randomly assigned to two groups of 11 each. For the first group, the specimens were loaded to failure with the patella oriented 30 degrees away from the direction of the applied load to mimic its orientation in situ, called natural orientation. In the second group, the patella was aligned in the direction of the tensile load, called non-natural orientation. The stiffness for the natural orientation group was 65 ± 13 N/mm, 32% higher than that for the non-natural orientation group (50 ± 17 N/mm; p < 0.05). The ultimate loads were 438 ± 128 N and 386 ± 136 N, respectively (p > 0.05). Ten out of 11 specimens in the natural orientation group failed at the femoral attachment (the narrowest portion of the MPFL) compared to 6 out of 11 in the non-natural orientation group. Our findings suggest that the specimen orientation that mimics the in-situ loading conditions of the MPFL should be used to obtain more representative data for the structural properties of the FMPC.

Biomechanical evaluation of medial patello-femoral ligament reconstruction: comparison between a double-bundle converging tunnels technique versus a single-bundle technique

“…As found by Kim et al in a porcine study [16], the natural orientation mimics the in situ loading condition of the MPFL and should be used to obtain representative data.…”

“…Kim et al [16] demonstrated that 90 % of failures at the femoral attachment of the native MPFL, where there is the narrowest portion of the ligament. In our study, we found 89 % of failure at the graft midsubstance.…”

“…Then, the femur and the tibia were completely dissected from the soft tissue except the MPFL reconstructed and potted in cylinders using cement and fixed to the tensile machine (Instron Inc., Norwood, MA, USA) by custom-made clamps. The tensile testing was performed in anatomical orientation with the femur 37°± 2°internally rotated to the coronal plane [16,19] and the patella placed with an angle of 90°to the MPFL (Fig. 3a, b).…”

“…However, the orientation of the specimen can have significant influence on the final results [16,17].…”

Beneficial and limiting factors for return to work following anterior cruciate ligament reconstruction: a retrospective cohort study

“…Young adults (17–45 years) are at higher risk for ACL injury, especially those who are active in pivoting sports, such as soccer and skiing [4–6]. In most cases, the ACL injury occurs during sports participation and usually follows an abrupt deceleration, i.e., jumping or sideways cutting [7, 8].…”