POSTERIOR LATERAL MENISCAL ROOT AND OBLIQUE RADIAL TEARS: THE BIOMECHANICAL EVIDENCE SUPPORTS REPAIR OF THESE TEARS, ALTHOUGH LONG-TERM CLINICAL STUDIES ARE NECESSARY
Figure 1 - An arthroscopic view of a lateral meniscus posterior root tear elevated with a probe is shown. Reprinted from Shumborski et al.
To provide a framework for discussion of our concerns, the posterior lateral meniscal anatomy and tear classification systems are reviewed. We then discuss the biomechanical influence of these tears in the context of knee laxity and contact mechanics. Next, the epidemiology of this tear type and the clinical importance of meniscal preservation in the setting of concomitant ACL reconstruction is discussed.
Posterior Lateral Meniscal Anatomy and Tear Classification
The lateral meniscus is stabilized by multiple structures in the posterolateral knee. The root attachment is of primary importance for discussion of the articles by Shumborski et al. and Shelbourne, and it is located posteromedial to the lateral tibial eminence apex and anterolateral to the medial meniscus posterior root attachment. The adjacent anatomy is complex and has been described in detail recently by Aman et al and Masferrer-Pino et al. Several posterior lateral meniscus tear classification systems have been described. In 2004, West et al. categorized posterior lateral meniscal tears based on the location in relation to the root attachment as well as tear complexity. LaPrade et al. provided an expanded classification of meniscal root tears based on tear completeness, proximity to the root attachment, tear obliquity, and adjacent meniscal integrity. Forkel et al. described tears with regard to their involvement of the root and meniscofemoral ligaments. Krych et al. classified the posterior lateral meniscus oblique radial tear that occurs between the root attachment and the meniscofemoral ligaments.
The classification systems by West, LaPrade, Forkel, and Krych categorize tears anatomically, which is necessary for the discussion of tear subtypes, biomechanical consequences, clinical importance, and surgical repair techniques. Shumborski et al.grouped “root avulsion[s] within 9 mm of [the bony] insertion and parrot beak tears with the integrity of the root attachment maintained” and referred to them collectively as “lateral meniscal posterior root (LMPR)” tears, although we would argue that they are anatomically distinct. This grouping may be convenient due to the anatomic proximity, although it oversimplifies the injury pattern and applicable repair techniques. Therefore, for the purposes of this letter to the editor and to avoid confusion regarding nomenclature, we will refer to specific posterior lateral meniscal tear subtypes and will not use the “LMPR” abbreviation.
Influence of Posterior Lateral Meniscus Tears on Knee Biomechanics
Several studies have evaluated the influence of lateral meniscus sectioning, often in the setting of ACL deficiency, leading to increased knee laxity and deleterious changes in lateral compartment contact mechanics. An early study by Musahl et al. reported increased anterior tibial translation with lateral meniscal deficiency during a simulated pivot shift test, although this study was not solely focused on the root attachment. More recently, studies have evaluated the influence of sectioning directly at the root attachment, at a measured distance away from the root attachment, root and meniscofemoral ligaments, and oblique radial tears between the root and meniscofemoral ligaments.
The importance of the lateral meniscus for knee stability has been widely studied in the context of tibial translation and rotation. Although the study designs and individual results varied, multiple biomechanical studies in the last decade have reported increased knee laxity after lateral meniscal root sectioning,Smith et al, studied the lateral meniscus oblique radial tear in a biomechanical model and reported increased anterior laxity and meniscal extrusion compared to the intact state. Several studies have evaluated the influence of the lateral meniscal posterior root attachment on contact mechanics in response to a compressive load. Loss of the meniscal root attachment reduced contact area due to displacement of the meniscus resulting in increased peak contact pressure, which is known to have deleterious long-term effects on articular cartilage. Anatomic root repair was found to restore contact mechanics to the near normal state which may reduce the risk of developing post-traumatic osteoarthritis (PTOA).
Figure 2 - An arthroscopic view of a lateral meniscus posterior root tear elevated with a probe is shown. Reprinted from Shumborski et al.
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Published December 2022 in Arthroscopy: The Journal of Arthroscopic and Related Surgery (Volume 38 - Issue 12).