The knee is a complex joint that is commonly injured. The accurate diagnosis of knee injuries requires a rather detailed knowledge of anatomy.
The knee is composed of three articulations: the medial and lateral condylar joints and the patellofemoral joint. The knee is capable of a wide range of motion, including flexion, extension, internal and external rotation, abduction, and adduction. In full extension, no rotary motion is permitted as the ligamentous structures are taut. This tightening with extension is referred to as "the screwing home mechanism." Beyond 20-degree flexion, the supporting ligaments are relaxed and axial rotation is permitted.1 At 90-degree flexion, there is a maximum of laxity allowing up to 40 degrees of rotation.
The surface anatomy, including the major muscles surrounding the knee, can be easily visualized and palpated. With the knee extended, the large, dominant vastus medialis and the smaller vastus lateralis can be visualized and palpated (Fig. 20–1A). The larger medialis pulls the patella medially during extension, thus preventing lateral subluxation or dislocation. The sartorius, gracilis, and semitendinosus muscles are palpable medially along their common insertion on the tibia, referred to as the pes anserinus (Fig. 20–1B). Laterally, the iliotibial tract and the tendon of the biceps femoris can be palpated.
Anatomy of the knee. A. Anterior view. B. Medial view. C. Posterior view. The semimembranosus tendon sends extensions to the medial meniscus and to the posterior aspect of the capsule. D. Lateral view.
The bony anatomy of the knee can also be palpated. The patella and patellar tendon are palpated along the anterior surface of the knee. Medially, the medial tibial plateau and medial femoral condyle are noted. The adductor tubercle extends posteriorly from the medial femoral condyle and can be palpated. The joint line can be readily located by noting the natural depression just medial and lateral to the patellar tendon with the knee in flexion. These indentations overlie the articular surfaces.
The patellar tendon inserts on the anterior tibial tubercle, which is easily palpable. The lateral tibial plateau is located just lateral to the tubercle. Posterior and lateral to the plateau is the fibular head, palpable just inferior to the lateral femoral condyle.
The medial meniscus is palpable along the medial joint line as the knee is internally rotated and gently extended. The lateral meniscus is not palpable, although injury to this structure reliably produces joint line tenderness. The menisci of the knee migrate anteriorly with extension. The medial meniscus is less mobile because of its attachment to the medial collateral ligament (MCL). With flexion, there is ...