AJSM - 2026-09-22 - Journal Article
Lateral Tibial Posterior Slope Induces Anterior Tibial Translation While Lateral-Medial Slope Difference Induces Internal Rotation: A Cadaveric Biomechanical Study.
Nejima S, Holt J, van Arkel R, Metcalfe A, Smith N, Amis A
Topics
Key Takeaway
In a cadaveric model, a +10° increase in lateral PTS significantly increased anterior tibial translation (P=.012), while a +10° delta PTS (lateral minus medial) produced 7.6° more internal rotation (P=.015), demonstrating that lateral and medial slopes have mechanistically distinct kinematic effects.
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Summary
This study investigated whether medial and lateral PTS independently drive anterior tibial translation (ATT) and internal rotation (IR) under 500-N axial compression at 0° and 20° flexion using unicondylar osteotomies with 3D-printed wedges adjusted from -5° to +10°. Lateral PTS increase drove ATT (P=.012) while medial PTS change had no effect on ATT (P>.99); delta PTS was the primary driver of IR, with a +10° delta producing 7.6° additional rotation at 0° flexion and a near-perfect correlation between opposing delta PTS values and rotational difference (r=0.960, P=.0006). These findings mechanistically separate the roles of medial and lateral slope in ACL-relevant kinematics.
Key Limitation
All specimens had intact ACLs, so the kinematic effects of PTS manipulation in the ACL-deficient or post-reconstruction state—the clinical scenario where slope correction is actually performed—remain untested.
Original Abstract
BACKGROUND
Posterior tibial slope (PTS) influences tibiofemoral kinematics and anterior cruciate ligament (ACL) function. While previous studies have evaluated symmetrical slope modifications, the isolated influences of the medial or lateral PTS remain unclear. This study investigated the influence of medial and lateral PTS changes on anterior tibial translation (ATT) and internal rotation (IR) under axial loading, using unicondylar slope-changing osteotomies.
HYPOTHESIS
Increased lateral PTS increases ATT, while a greater delta PTS (lateral minus medial PTS) increases IR.
STUDY DESIGN
Controlled laboratory study.
METHODS
Eight fresh-frozen knee specimens were mounted in a custom-built fixture in a compression/torsion loading machine. Tibiofemoral translation/rotation kinematics were measured under a 500-N axial compression load at 0° and 20° of knee flexion using optical motion tracking. Unicondylar tibial slope-changing osteotomies were performed on the medial and lateral tibial plateaus with a custom cutting guide, preserving key ligament and meniscus root attachments. Medial and lateral PTS were independently adjusted to -5°, 0°, +5°, and +10°, resulting in medial and lateral PTS ranging from -5° to +10°, using 3-dimensionally printed wedges. Repeated-measures analyses of variance, post hoc t tests, and Pearson correlations were used for analysis.
RESULTS
An increase of +10° in lateral PTS significantly increased ATT ( P = .012), while increasing medial PTS did not ( P > .99). IR was most influenced by delta PTS. At 0° of flexion, altering lateral or medial PTS alone was insufficient to significantly change rotation, but changing delta PTS +10° produced 7.6° more rotation ( P = .015). At 20° of flexion, changing individual slopes ±10° significantly increased/decreased rotation ( P < .036). The largest rotational differences correlated with opposing delta PTS values ( r = 0.960; P = .0006).
CONCLUSION
Lateral PTS was the principal determinant of ATT, whereas delta PTS was the principal determinant of IR under axial loading.
CLINICAL RELEVANCE
Understanding the independent biomechanical roles of the medial and lateral PTS provides insight into mechanisms of anterior and rotational instability in ACL injury and reconstruction. These findings suggest the potential utility of differential correction of PTS as a novel surgical approach for optimizing tibiofemoral rotational kinematics.