Structure and Function
Tibiofemoral and Patellofemoral Joints
The knee is composed of two distinct articulations enclosed within a single joint capsule: the tibiofemoral joint and the patellofemoral joint. At the tibiofemoral joint, the proximal joint surfaces are the convex medial and the lateral condyles of the distal femur (Fig. 9.1). Posteriorly and inferiorly, the longer medial condyle is separated from the lateral condyle by a deep groove called the intercondylar notch. Anteriorly, the condyles are separated by a shallow area of bone called the femoral patellar surface. The distal articulating surfaces are the two shallow concave medial and lateral condyles on the proximal end of the tibia. Two bony spines called the intercondylar tubercles separate the medial condyle from the lateral condyle. Two joint discs called menisci are attached to the articulating surfaces on the tibial condyles (Fig. 9.2). At the patellofemoral joint, the articulating surfaces are the posterior surface of the patella and the femoral patellar surface (Fig. 9.3).
An anterior view of a right knee showing the tibiofemoral joint.
An anterior view of a right knee in the flexed position showing femoral and tibial condyles, medial and lateral menisci, and cruciate and collateral ligaments.
A view of a right knee showing the medial aspect, where the cut tendons of the three muscles that insert into the anteromedial aspect of the tibia make up the pes anserinus. Also included are the patellofemoral joint, the patellar ligament, and the patellar tendon.
The joint capsule that encloses both joints is large, loose, and reinforced by tendons and expansions from the surrounding muscles and ligaments. The quadriceps tendon, patellar ligament, and expansions from the extensor muscles provide anterior stability (see Fig. 9.3). The lateral and medial collateral ligaments, iliotibial band, and pes anserinus help to provide medial–lateral stability, and the knee flexors help to provide posterior stability. In addition, the tibiofemoral joint is reinforced by the anterior and posterior cruciate ligaments, which are located within the joint (see Fig. 9.2).
The tibiofemoral joint is a double condyloid joint with 2 degrees of freedom. Flexion–extension occurs in the sagittal plane around a medial–lateral axis and rotation occurs in the transverse plane around a vertical (longitudinal) axis.1 The incongruence and asymmetry of the tibiofemoral joint surfaces combined with muscle activity and ligamentous restraints produce an automatic rotation. This automatic rotation is involuntary and occurs primarily toward the end of extension when motion stops on the shorter lateral femoral condyle but continues on the longer medial condylar surface. During the last portion of the active extension range of motion ...