Posterior Tibial Slope Characteristics and Their Relationships With Thigh Muscle Morphology, Activation Patterns, and Dynamic Knee Valgus in Male and Female Soccer Players Before and After Fatigue: A Descriptive Laboratory Study.

Background: Soccer players are at high risk of anterior cruciate ligament injury as well as reinjury, with higher rates in women and in the supporting leg, and fatigue impairs the neuromuscular control of the knee joint. However, little is known about the bony anatomy of the knee joint and its relationship with neuromuscular measures related to knee stabilization, and studies investigating anatomic and biomechanical measures simultaneously are widely lacking.

Purpose: To investigate (1) whether posterior tibial slope (PTS) characteristics and thigh muscle morphology differ between sexes; (2) whether thigh muscle activation patterns and dynamic knee valgus differ between sexes and fatiguing states during a drop jump (DJ); and (3) whether certain relationships among PTS characteristics, thigh muscle morphology, thigh muscle activation patterns, and dynamic knee valgus exist.

Study design: Descriptive laboratory study.

Methods: Magnetic resonance images of 32 healthy national-level soccer players (15 female, 17 male) were acquired, and their PTS characteristics and thigh muscle anatomic cross-sectional areas (CSAs) were determined. Muscle activation patterns, as well as dynamic knee valgus (quantified as medial displacement of the knee joint center [medial knee displacement, or MKD] in the anatomic frontal plane), were assessed via surface electromyography and 3-dimensional motion capture while participants performed DJs before and after a fatigue protocol.

Results: Female players had smaller hamstring and quadriceps CSAs (P < .001). During DJ landing, female players demonstrated significantly greater hamstring activity (P = .04). There were significant sex differences in the lateromedial hamstring activation ratio (P = .03), with female players exhibiting greater medial than lateral hamstring activation (ratio <1.0), whereas male players presented opposite activation patterns (ratio >1.0). MKD was greater in female players than in male players (P = .02). Moreover, in female players, the steeper their lateral PTS was, (1) the greater their quadriceps-to-hamstring activation ratio and the lower their hamstring activity, (2) the smaller their lateromedial hamstring activation ratio, and (3) the lower their MKD. In male players, a steeper lateral PTS was associated with greater quadriceps activity only. No fatigue-induced differences were observed.

Conclusion: Among soccer players, thigh muscle morphology, muscle activation patterns, and dynamic knee valgus during DJ landing are sex dependent. Moreover, there are distinct sex-specific associations between PTS characteristics, thigh muscle morphology, and measures related to neuromuscular control of the knee joint.

Clinical relevance: These study results may further highlight the importance of also considering sex and the bony anatomy of the knee joint in the design of neuromuscular prevention and rehabilitation, or the choice of graft type. However, future studies are needed to assess the effects of sex- and/or knee anatomy-dependent prevention efforts or graft choice on clinical outcomes.