Biomechanics of the Pediatric MPFL and MQTFL: Native Tissue Strength and Implications for Graft Choice
Luis Fernando Viegas de Moraes Leme, Bryan W. Khoo, Alan D. Anaya Gallegos, Katelin J. Isakoff, Amin Alayleh, Hubert Tuyishime, Paul J. Bergeron, Iris Cong, Calvin Chan, Amishi Jobanputra, Akbar Syed, Brendon Mitchell, Marc Tompkins, Yi-Meng Yen, Molly Meadows, Charles M. Chan, Matthew R. Schmitz, Philip L. Wilson, Henry B. Ellis, Theodore J. Ganley, Kevin SheaBackground:
The medial patellofemoral ligament (MPFL) and medial quadriceps tendon–femoral ligament (MQTFL) are considered the primary restraints against lateral patellar translation and studies suggest that combined reconstruction of the MPFL and MQTFL may yield improved clinical outcomes compared with MPFL reconstruction alone. Although failure loads of the isolated MPFL have been quantified in adult specimens, the biomechanical properties of the native MPFL/MQTFL complex have not previously been described. This study aims to characterize the biomechanical role and native strength of the pediatric MPFL/MQTFL complex.
Hypothesis:
It was hypothesized that biomechanical testing of MPFL/MQTFL will demonstrate consistent mechanical properties across pediatric specimens and will be similar to isolated adult MPFL/MQTFL values.
Study Design:
Descriptive laboratory study.
Methods:
Seven fresh-frozen pediatric cadaveric knees (aged 8-16 years old) underwent stepwise dissection. The MPFL/MQTFL complex was isolated and clamped on a servomechanical tensile loading apparatus. Specimens were then tested through preconditioning (20 cycles; 1-10 N), cyclic loading (500 cycles; 10-30 N), and load to failure (all at 100 mm/min). Displacement, stiffness, and maximal load were recorded. Data were summarized using descriptive statistics. Adult values for MPFL strength were obtained from the literature for comparison.
Results:
The MPFL/MQTFL complex had a mean failure load of 166.9 ± 52.9 N. Cyclic elongation at 30 N was 0.9 ± 0.6 mm, and stiffness was 30.9 ± 10.1 N/mm. In all cases failure occurred intrasubstance closer to the femoral attachment. The failure load of the MPFL/MQTFL complex in pediatric specimens fell within the range of values reported for the isolated MPFL in adult literature (158.3 ± 76.3 N).
Conclusion:
The MPFL/MQTFL complex in pediatric knees demonstrated similar failure loads to the isolated adult MPFL benchmarks, suggesting substantial native strength in skeletally immature tissue.
Clinical Relevance:
These data provide an important biomechanical context that may inform future investigations of reconstruction techniques, graft selection, and surgical planning in MPFL/MQTFL reconstruction in skeletally immature patients.