Varus alignment increases medial meniscus extrusion and peak contact pressure: a biomechanical study
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Assessment of medial meniscus extrusion (MME) has become increasingly popular in clinical practice to evaluate the dynamic meniscus function and diagnose meniscus pathologies. The purpose of this biomechanical study was to investigate the correlation between MME and the changes in joint contact pressure in varus and valgus alignment. It was hypothesized that varus alignment would result in significantly higher MME along with a higher joint contact pressure in the medial compartment.
Eight fresh-frozen human cadaveric knees were axially loaded, with a 750 N compressive load, in full extension with the mechanical axis shifted to intersect the tibial plateau at 30% and 40% (varus), 50% (neutral), 60% and 70% (valgus) of its width (TPW). Tibiofemoral peak contact pressure (PCP), mean contact pressure (MCP) and contact area (CA) were determined using pressure-sensitive films. MME was obtained via ultrasound at maximum load.
MME was significantly increased from valgus (1.32 ± 0.22 mm) to varus alignment (3.16 ± 0.24 mm; p < 0.001). Peak contact pressure at 30% TPW varus alignment was significantly higher compared to 60% TPW valgus (p = 0.018) and 70% TPW valgus (p < 0.01). MME significantly correlated with PCP (r = 0.56; p < 0.001) and MCP (r = 0.47, p < 0.01) but not with CA (r = 0.23; n.s.).
MME was significantly increased in varus alignment, compared to neutral or valgus alignment, with an intact medial meniscus. It was also significantly correlated with PCP and MCP within the medial compartment. However, valgus malalignment and neutral axis resulted in reduced MME and contact pressure. Lower limb alignment must be taken into account while assessing MME in clinical practice.
Level of evidence
Controlled laboratory study.
KeywordsMedial meniscus extrusion Varus Valgus Lower limb alignment Ultrasound Contact pressure
LW, JL, AA and CvD designed the study, collected data, performed the statistical analysis and wrote the manuscript. LW drafted the manuscript. TD, WP and RB helped to design the study, assisted with data collection, statistical analysis and data interpretation, and critically reviewed the manuscript. ABI conceived the study, helped with data interpretation and critically reviewed the manuscript. All authors read and approved the final manuscript.
Compliance with ethical standards
Conflict of interest
A.B.I. is a consultant of Arthrosurface and medi GmbH, and receives royalties from Arthrex Inc. and Arthrosurface. W.P. is a consultant of and receives royalties from Karl Storz Endoscopy and Otto Bock Health Care and Össur. All other authors declare no conflict of interest. The authors did not receive financial support or other benefits from commercial sources for the work reported in this manuscript or any other financial support that could create a potential or the appearance of a conflict of interest regarding to the work.
The Technical University of Munich did not receive funding for this study.
Ethics approval and consent to participate
All procedures performed in this study involving human participants were in accordance with the 1964 Helsinki declaration and its later amendments or comparable ethical standard. An approval of the institutional ethic committee (Ethic committee, Faculty of Medicine, Technical University of Munich, Munich, Germany) was not applicable for this study.
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