Summary

This is an observational study analyzing the posteromedial capsuloligamentous anatomy of the knee and its correlation with the presence of popliteal cysts.

Abstract

Introduction

The posteromedial compartment of the knee houses several important anatomical structures, including the oblique popliteal ligament (OPL), the accessory insertion tendon of the semimembranosus muscle. Popliteal cysts develop at the expense of the bursa located between the medial gastrocnemius and the semimembranosus following intra-articular pathologies generating effusion. In this work, we aimed to describe the normal anatomy of the posteromedial knee capsule and its anatomical variations, particularly in the presence of popliteal cysts.

Material And Methods

We conducted a prospective descriptive study over 4 consecutive months, including 96 knees from 96 patients, operated on arthroscopically for various intra-articular pathologies. Oblique popliteal ligament anatomy was divided into four groups: Integrated LPO (Type 1), cord-like protruding LPO (Type 2A), normal protruding LPO (Type 2B), bulging LPO (Type 3). The presence of a popliteal cyst at the back of the knee was assessed on preoperative MRI.

Results

Type 1 was observed in 13 knees (13.5%), type 2A in 22 (22.9%), type 2B in 40 (41.7%) and type 3 in 21 (21.9%). A popliteal cyst was found in 20 knees (20.8%) by MRI. Of these, 8 were symptomatic (8.3%). Of 13 type 1 knees, none showed a popliteal cyst on MRI, 2 knees (9.1%) in 22 type 2A knees, 6 knees (15%) in 40 type 2B knees, and 12 knees (57.1%) in 21 type 3 knees. There was a statistically significant relationship between the anatomical type of the posteromedial capsule and the presence of a popliteal cyst (p < 0.001).

Conclusion

The arthroscopic anatomy of the posteromedial capsule appears to be modified when a popliteal cyst is present. This change is reflected in a bulging of the LPO within the joint, revealing a communication port to the cyst at its superior border. Posteromedial synovectomies to treat the unidirectional flow mechanism to the cyst should be located in a triangle between the medial gastrocnemius, the semimembranosus and the oblique popliteal ligament.