3D geometry analysis of the medial meniscus – a statistical shape modeling approach

Abstract

The geometry-dependent functioning of the meniscus indicates that detailed knowledge on 3D meniscus geometry and its inter-subject variation is essential to design well functioning anatomically shaped meniscus replacements. Therefore, the aim of this study was to quantify 3D meniscus geometry and to determine whether variation in medial meniscus geometry is size-or shape-driven. Also we performed a cluster analysis to identify distinct morphological groups of medial menisci and assessed whether meniscal geometry is genderdependent. A statistical shape model was created, containing the meniscus geometries of 35 subjects (20 females, 15 males) that were obtained from MR images. A principal component analysis was performed to determine the most important modes of geometry variation and the characteristic changes per principal component were evaluated. Each meniscus from the original dataset was then reconstructed as a linear combination of principal components. This allowed the comparison of male and female menisci, and a cluster analysis to determine distinct morphological meniscus groups. Of the variation in medial meniscus geometry, 53.8% was found to be due to primarily size-related differences and 29.6% due to shape differences. Shape changes were most prominent in the cross-sectional plane, rather than in the transverse plane. Significant differences between male and female menisci were only found for principal component 1, which predominantly reflected size differences. The cluster analysis resulted in four clusters, yet these clusters represented two statistically different meniscal shapes, as differences between cluster 1, 2 and 4 were only present for principal component 1. This study illustrates that differences in meniscal geometry cannot be explained by scaling only, but that different meniscal shapes can be distinguished. Functional analysis, e.g. through finite element modeling, is required to assess whether these distinct shapes actually influence the biomechanical performance of the meniscus.

The sensitivity of cartilage contact pressures in the knee joint to the size and shape of an anatomically shaped meniscal implant

“…The mesh geometry of the medial meniscal allograft and all implant variations was derived from a SSM of the medial meniscus, which was based on 35 healthy medial menisci (15 males and 20 females, 21 left and 14 right knees, mean age7 SD:33712 years) (Vrancken et al, 2014). The average meniscal geometry of this SSM was adopted as the geometry for the medial allograft and the average implant (Fig.…”

“…Second, the simulations were repeated for a medial meniscal allograft. Last, the allograft was replaced by the implant and the simulations were repeated for 16 meniscal size and shape variations that were derived from a SSM of the medial meniscus (Vrancken et al, 2014). For each meniscal condition studied, the articular cartilage contact pressures and principal compressive strains were monitored.…”

“…Given the importance of the geometry for native meniscus biomechanical functioning, careful consideration of the implant geometry is necessary to obtain optimal implant functioning. To address this problem, we have developed a statistical shape model (SSM) that describes the variations in 3D meniscal geometry (Vrancken et al, 2014). In this study, six independent modes were identified that together determine the variations in meniscal geometry; one size configuration (predominantly representing linear scaling) and five shape configurations.…”

“…Superior view of the studied implant geometries, which were defined based on the outcomes of a statistical shape model of the medial meniscus(Vrancken et al, 2014) (a) The size-related variations (mode 1), with 7 1 standard deviation (SD) increments compared to the average implant geometry. (b) The shape-related variations (modes 2 À 6), with 7 3 SD increments compared to the average implant geometry.…”

The implications of non-anatomical positioning of a meniscus prosthesis on predicted human knee joint biomechanics

“…In our lab, a novel anatomically shaped, polycarbonate urethane total meniscus prosthesis was recently developed. The prosthesis geometry was extracted using statistical shape modeling based on 35 subjects [17], and optimized implementing computational modeling [18]. The meniscus prosthesis consists of a stiff core embedded in a soft flexible (polymer) body.…”