258


PART IV THE LOWER EXTREMITY


TABLE 12.2 Knee Bursae Bursa


Suprapatellar bursa Deep infrapatellar bursa Subcutaneous prepatellar bursa Infrapatellar bursa Gastrocnemius bursa Biceps femoris bursa Semitendinosus bursa Gracilis bursa


Location Posterior to the quadriceps tendon Between the patellar ligament and tibial tuberosity Between the skin and patella Between the skin and patellar ligament Between the medial head of the gastrocnemius tendon and medial femoral condyle Between the LCL and biceps femoris tendon Between the medial tibial condyle and semitendinosus tendon Between the MCL and gracilis muscle tendon LCL, lateral collateral ligament; MCL, medial collateral ligament.


The medial capsule is reinforced by retinacular fi bers and by the tendons of the sartorius, gracilis, and semiten- dinosus that collectively are referred to as the pes anse- rinus tendons. The medial collateral ligament (MCL) fortifi es the medial aspect of the joint. The MCL is a fl at, broad ligament that arises from the medial femoral epi- condyle and attaches to the medial proximal tibia. Fibers of the ligament also blend with the retinacular fi bers, the medial meniscus, and the tendon of the semimembrano- sus muscle (Fig. 12.13C).


The primary function of the MCL and LCL is to provide medial and lateral joint stability by resisting forces applied to the knee joint in the frontal plane. The MCL resists valgus forces, and the LCL resists varus forces. The collateral ligaments also stabilize the knee during joint motion in the sagittal plane. Some of the ligament fi bers are taut throughout the full range of knee fl exion and extension. Most of the fi bers are pulled taut at the end range of extension. The ligaments also resist the extremes of medial and lateral rotation at the knee. The ligaments are often injured when the foot is planted on the ground and the femur, along with the pelvis and body, rotates on the stabilized lower leg.


Anterior and Posterior Cruciate Ligaments


In contrast to the collateral ligaments, which are extra- capsular, the cruciate ligaments are intracapsular, located within the joint capsule. A vascular synovial lining that provides blood supply to the ligaments covers them. The thick and strong cruciate ligaments restrict excessive motion between the femur and tibia in several planes. The ligaments also play a role in indirect control of the knee because they contain mechanoreceptors that


provide proprioceptive feedback to the nervous system related to the position and movement of the joint. The location and function of these ligaments are evident from their names: The anterior cruciate liga- ment (ACL) attaches on the anterior intercondylar area of the tibial plateau. From this anterior attachment, it runs obliquely in a superior, lateral, and posterior direc- tion to attach to the lateral femoral condyle (Fig. 12.14). Although some of the ligament fi bers are taut during the full range of sagittal motion, most of the ACL fi bers become taut as the knee approaches full extension. As the knee approaches the last 50° to 60° of active knee exten- sion, the quadriceps mechanism pulls the tibia anteriorly as the muscle slides it across the femoral condyles. As the ACL fi bers become more taut, they help limit this anterior slide of the tibia so that it remains in contact with the femur (Fig. 12.15). As the quadriceps works to extend the knee, the ACL works as an antagonist to oppose excessive anterior tibial translation. The ACL is the ligament in the knee that is most fre- quently completely ruptured (torn). The tear is often due to a noncontact injury, resulting when the foot is planted and there is excessive genu valgus and lateral rotation of the knee. The excessive genu valgus is often combined with hip adduction and medial rotation. This injury often results in secondary involvement of the menisci, MCL, or articular cartilage and bone (Fig. 12.16). The posterior cruciate ligament (PCL), as the name implies, attaches from the posterior intercondylar area of the tibia to the medial femoral condyle. It runs in a supe- rior, oblique, and medial direction (Fig. 12.17). Similar to the ACL, some fi bers are taut through full fl exion and extension. However, most PCL fi bers become taut with


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