Biomechanics

Background/Objectives: Quadriceps tendon (QT) rupture in non-native knees (such as post-total knee arthroplasty) is catastrophic. Primary repair of the poor-quality tendon with significant gapping has led to a high failure rate and poor functional outcomes. Synthetic polypropylene mesh graft (PMG) reconstruction of QT tears has been introduced to address this issue. This cadaveric study compared the biomechanical performance of a novel synthetic mesh reconstruction technique for QT rupture with the commonly used patellar transosseous tunnel fixation (TTF) technique. Methods: Cadaveric patellar bone-quadriceps tendons were harvested with the QT cut at the superior pole of the patella to simulate tendon rupture. The tears were repaired using either patellar TTF or PMG reconstruction. After repair, each specimen was subjected to 250 cycles of biomechanical cyclic loading. Early and late local displacement (gap between the PMG and superior pole of the patella), overall construct elongation, ultimate tensile load, and failure mode were recorded. Results: Displacements measured at the 20th and 250th cycles demonstrated significantly smaller displacement at the patellar bone–mesh fixation site for the PMG reconstruction group (though it should be noted that this measurement did not account for movement at the tendon–mesh interface). Overall construct elongation was significantly lower in the new technique compared to TTF. The new technique also demonstrated a significantly higher ultimate tensile load. Conclusions: The novel technique of the composite PMG construct—utilising synthetic mesh, bone cement, and K-wire augmentation to reconstruct the QT—has demonstrated enhanced biomechanical performance. The construct shows biomechanical potential and warrants further evaluation in non-native knees and clinical settings.

Background/Objectives: Shaft stiffness (“flex”) is the only routinely individualised ice hockey stick specification, yet evidence on its effect on shooting is inconsistent; this is because previous studies have used fixed stiffness levels for players of different sizes and strengths. We determined the effect of deviating, in either direction, from the player’s habitual flex, congruent with the body mass reference flex, on on-ice shooting velocity and snap-shot accuracy in junior players. Methods: Thirty male junior players (18–19 years) whose habitual effective flex was within ±10 units of the body mass reference flex completed a complete counterbalanced (Williams-type) crossover with three sticks differing only in nominal shaft flex—the habitual flex (FLEX₀), a shaft 15 units more compliant (FLEX₋₁₅), and one 15 units stiffer (FLEX₊₁₅)—each preceded by three familiarisation sessions. Wrist- and snap-shot velocity (radar) and snap-shot accuracy in an externally paced target task were analysed with linear mixed models. Results: Flex affected wrist-shot velocity (ηp² = 0.35), snap-shot velocity (ηp² = 0.68) and snap-shot accuracy (ηp² = 0.34), with all three outcomes highest at FLEX₀. The wrist shot lost 2.9% with both deviations, whereas the snap shot lost 5.6% with the compliant shaft, but only 1.6% with the stiff shaft (Flex × Technique ηp² = 0.29). Snap-shot accuracy fell by 9.1 and 14.4 percentage points. Conclusions: In players fitted within ±10 units of the body mass reference flex, deviations of ±15 flex units from the habitual flex were associated with lower shooting velocity and snap-shot accuracy; for the snap shot, an over-compliant shaft was the costlier deviation.

Background: There is still a controversial debate regarding the pressure in the patellofemoral joint (PFJ) following deepening trochleoplasty (DTP). Objective: The purpose of this pilot study was to compare the PFJ contact area before and after DTP in patients treated for trochlear dysplasia and to discuss the biomechanical aspects regarding patellofemoral pressure. Methods: DTP was performed on four female patients to treat lateral patellar instability due to trochlear dysplasia. The preoperative and postoperative articular patellofemoral contact area was evaluated using three-dimensional (3D) MRI. Bone and cartilage were traced slice by slice in the acquired dimension, while the AMIRA segmentation software reconstructed the 3D model. This model was then transferred to the Rhinoceros software for measurement. Contour lines along the 3D model containing trochlear and patellar cartilage were placed, and the boundary and the curvature of the contact area were defined. The contact surfaces before and after DTP were compared. Results: The size of the articular contact area of the PFJ increased after DTP in three out of four cases compared to the preoperative condition. The preoperative average size of the contact area was 153 mm² (range, 68–185); postoperatively, it was 289 mm² (range, 200–370). The increase in contact area was, on average, 53% (−6% to 444%). Conclusions: The size of the articular contact area of the PFJ increased after DTP compared to the preoperative condition. The results provide biomechanical evidence that pressure in the PFJ decreases following DTP. The use of 3D MRI scans has demonstrated several advantages.