Summary

This newly established classification system for biconcave medial tibial plateaus (BMTP) will help surgeons identify and understand the Type II BMTP and provide the basis on which further research will determine the impact of tibial morphology on medial meniscal pathology and a treatment algorithm as type II BMTPs are at an increased risk of complex medial meniscus tears.

Abstract

Introduction

There has been limited investigation regarding the consequence of tibial plateau morphology on the meniscus. A biconcave medial tibial plateau (BMTP) has been previously described as a coronal plane ridge of the medial tibial plateau, typically aligned near the inner margin of the posterior body of the medial meniscus. Further investigation of the designated BMTP morphology demonstrated specific patterns in the topographical anatomy and shape compared to the normal, flat medial tibial plateau. However, it remains unknown whether patients with BMTP morphology are more prone to complex medial meniscus tears which could have implications on treatment. As such, the purpose of this study was to: 1) present a classification system for BMTP morphology, and 2) determine whether patients with a certain type of BMTP and more susceptible to complex medial meniscus tears.

Methods

Evaluated a 6-month consecutive series of all knee arthroscopies for BMTP morphology and meniscal tears using intraoperative video at time of surgery. Three distinct morphologies were identified. Those with a “flat” medial tibial plateau were classified as normal and served as the control group. Type I BMTP consisted of an oblique, narrow ridge of the medial tibial plateau. Type II BMTP of a transverse, wide, coronal plane ridge, separating the front two-thirds from the back of the medial tibial plateau. Demographic data, and arthroscopic knee pathology characteristics were also recorded. Intraclass correlation coefficient (ICC) was used to determine the interobserver reliability of the classification system. A Fisher’s exact test was used to determine differences in categorical data (i.e., complex medial meniscus tear) between groups while a single factor ANOVA was used to determine differences in continuous variables (i.e. age) between groups.

Results

147 consecutive knee arthroscopies were evaluated - 55 (37.4%) had a normal plateau, 43 (29.3%) had a Type I BMTP, and 49 (33.3%) had a Type II BMTP. There was excellent inter-observer reliability (kappa statistic=0.842). Those patients with Type II BMTP were three times more likely to have a complex medial meniscus tear than those with a Type I BMTP (odds ratio 3.2 [1.4, 7.6])(p=0.01) and two times more likely to have a complex medial meniscus tear compared to those with a flat plateau morphology or Type I BMTP (odds ratio 2.2 [1.1, .5])(p=0.04). There was no increased risk of a complex medial meniscus tear with a Type I BMTP compared to a flat plateau morphology (odds ratio 0.5 [0.3, 1.2])(p=0.15).

Conclusion

Biconcave medial tibial plateau is best diagnosed at the time of arthroscopy and can be reliably classified into two distinct types. Type II BMTP occur in approximately 1/3rd of patients and are at an increased risk for complex medial meniscus tear when compared to patients with Type I BMTP or flat plateau. This newly established classification system will help surgeons identify and understand the Type II BMTP and provide the basis on which further research will determine the impact of tibial morphology on medial meniscal pathology and a treatment algorithm.