Cam Impingement of the Knee: Arthroscopic Correction of Posteromedial Tibiofemoral Incongruence

Abstract

One of the anatomic variations observable within the knee joint is a reduction in the posterior curvature of the femoral metaphysis proximal to the medial femoral condyle. This curvature is usually concave enough to fit the posterior horn of the medial meniscus (PHMM) during full knee flexion. A reduction in curvature may result in posteromedial tibiofemoral incongruence, a condition characterized by compression of the PHMM in full knee flexion, similar to cam incongruence in the hip joint. Clinical symptoms may occur in deep knee flexion, and progressive degeneration of the PHMM can be observed if this position is not prohibited. For patients in whom activity modification and conservative treatment have failed, surgery may be indicated. We describe arthroscopic treatment allowing for final intraoperative confirmation of the clinical indication for posteromedial tibiofemoral incongruence correction, as well as allowing for the least possible, yet sufficient, amount of correction.

© 2022 The Authors.

Figures

Fig 1

Magnetic resonance imaging of right, extended knee joint (sagittal view of medial side of knee). (A) The physiological, concave shape of the metaphysis proximal to the posteromedial part of the medial femoral condyle (proper congruence) is marked (red line). (B) An anatomic variant with insufficient concavity (incongruence) is marked (red line). Signal alterations and deformation of the medial meniscus can be seen, suggesting degenerative structural abnormalities.

Fig 2

Magnetic resonance imaging of right knee joint in maximal knee flexion (sagittal view of medial side of knee in “sitting MRI” position). The incongruence between the metaphysis proximal to the medial femoral condyle (MFC) and medial tibial condyle (MTC) is marked (black circle). Because of the lack of space, the medial meniscus is compressed. Signal alterations, deformation, and posterior extrusion of the posterior horn of the medial meniscus can be seen, suggesting degenerative structural abnormalities.

Fig 3

Arthroscopic view of posteromedial recess of right knee via trans-notch maneuver. The surgical knife is used to make the posteromedial portal. The visible structures are the posterior part of the medial femoral condyle (MFC) and the posterior part of the medial meniscus (MM).

Fig 4

Arthroscopic view of right knee from posteromedial portal. The shaver is inserted through the medial parapatellar portal to remove the medial part of the septum. The visible structures are the posterior part of the medial femoral condyle (MFC) and the knee septum.

Fig 5

Arthroscopic view of posterolateral recess of right knee from medial parapatellar portal. The surgical knife is used to make the posterolateral portal. The visible structures are the posterior part of the lateral femoral condyle (LFC), the posterolateral capsule of the knee, and the posterior part of the lateral meniscus (LM).

Fig 6

Arthroscopic view of right knee from posterolateral portal. The ablation probe is inserted through the medial parapatellar portal and is used to remove the lateral part of the septum. The visible structures are the posterior part of the lateral femoral condyle (LFC), the lateral part of the septum, and the posterior part of the lateral meniscus (LM).

Fig 7

Arthroscopic view of right knee from posterolateral and trans-septal portals. The maximally flexed, right knee joint is visible. In the case of proper congruence, the space for the posterior part of the medial meniscus (MM) is seen as a triangle behind the posterior part of the medial femoral condyle (MFC)

Fig 8

Arthroscopic view of right knee from posterolateral portal. The maximally flexed, right knee joint is visible. In the case of incongruence, the space for the posterior part of the medial meniscus (MM) in full flexion closes completely. (MFC, medial femoral condyle.)

Fig 9

Arthroscopic view of right knee from posterolateral portal. The ablation probe is used to detach capsular fibers that are attached directly proximal to the cartilage on the posterior part of the medial femoral condyle (MFC). (MM, medial meniscus.)

Fig 10

Arthroscopic view of right knee from posterolateral portal. The arthroscopic burr is used to deepen the area proximal to the cartilage margin of the posterior part of the medial femoral condyle (MFC). (MM, medial meniscus.)

Fig 11

Arthroscopic view of right knee from posterolateral portal. The switching stick is inserted through the posteromedial portal, which is visible above the posterior part of the medial femoral condyle (MFC). (MM, medial meniscus.)

Fig 12

Arthroscopic view of the right knee after changing the view from the posterolateral portal to the posteromedial portal using the switching stick, encompassing better visualization of all parts of the posteromedial tibiofemoral incongruence. With the use of an arthroscopic burr inserted through the posterolateral portal, the most laterally extended part of the metaphysis proximal to the posterior part of the medial femoral condyle (MFC) impingement (near the posterior part of the intercondylar notch) is corrected.

Fig 13

Arthroscopic view of right knee in full flexion from posterolateral portal, confirming successful correction of posteromedial tibiofemoral incongruence. The surgeon verifies whether the proper amount of bone was removed from the metaphysis proximal to the cartilage on the posterior part of the medial femoral condyle (MFC). Proper congruence, represented by a sufficient space for the medial meniscus (MM), is visible.