Varus alignment of 4 degrees leads to significant increase of medial meniscus extrusion and is positively correlated to mean and peak contact pressure
Medial meniscus extrusion (MME) has been considered as an indirect sign of meniscus pathology and is associated with a loss of function of the affected meniscus. However, adaption of meniscus extrusion has also been found in healthy population and has recently been described as a dynamic phenomenon that adapt to age and activity.
The purpose of this biomechanical study was to biomechanically investigate the effect of lower limb alignment on medial meniscus extrusion. It was hypothesized that varus alignment leads to higher MME compared to neutral or valgus alignment.
Material And Methods
Ten fresh-frozen human cadaveric knees were axially loaded with a 750N compressive load in full extension and in 0°, 2° and 4° varus and valgus alignment, respectively. To confirm meniscus and cartilage integrity, MRI was performed of each subject prior to testing. Tibiofemoral peak contact pressure and contact area of the medial compartment were determined using pressure sensitive foils (Tekscan, K-Scan 4000) in each alignment. MME was obtained via ultrasound (MSK Ultrasound, Arthrex Inc.) at maximal load. Data were analyzed using SPSS statistics software version 23 (IBM, New York, USA). ANOVA and Bonferroni-adjusted t tests were used for statistical analysis. Statistical significance was set at a p value of < 0.05.
MME significantly increased from valgus to varus alignment: 1.29 ± 0.21mm (unloaded), 1.54 ± 0.16mm (4° valgus), 1.99 ± 0.18mm (2° valgus), 2.01 ± 0.17mm (neutral), 2.35 ± 0.13mm (2° varus), 3.10 ± 0.26mm (4° varus). 4° of valgus and varus alignment were significantly different to all other tested conditions (p<0.01). MME was positively correlated to joint peak pressure (PCC=0.29, p<0.01) and mean pressure (PCC=0.28, p<0.05). Peak pressure increased during varus shift without reaching statistical significance (n.s.).
MME was significantly increased in varus alignment compared to neutral or valgus alignment in intact meniscus state. It was also positively correlated to peak and mean pressure within the medial compartment. However, valgus malalignment and neutral axis does not affect MME and contact pressure. Our findings suggest that varus alignment of 4° leads to significant increase of MME and contact pressure. The contribution to medial compartment overload might be relevant in case of treatment of meniscus pathologies or meniscus allograft.