Applied Surgical Anatomy of the Medial Side of the Knee

Applied Surgical Anatomy of the Medial Side of the Knee‌

 

 

Overview

As Warren and Marshall pointed out, the ligaments on the medial side of the knee are merely “condensations within tissue planes.”17 They blend with each other at various points, making definition of each layer difficult, especially in cases of trauma, when bleeding and edema can complicate the problem further. For this reason, it is important to have an understanding of the normal anatomy and supporting structures on the medial side of the knee.

The anatomy of the medial side is understood readily when it is described in three separate layers.17 Approaches to the knee enter the joint by incising these layers sequentially, from outside to inside.

Outer Layer

The outer layer consists of the proximal continuation of the deep fascia of the thigh. It encloses the sartorius muscle, whose fibers blend with the fascial layer before they insert into the tibia.

Anteriorly, the outer layer blends with fibrous tissue derived from the vastus medialis muscle to form the medial patellar retinaculum. Posteriorly, the layer is continuous with the deep fascia, which covers the gastrocnemius muscle and the roof of the popliteal fossa (Fig. 10-35; see Fig. 10-32).

Middle Layer

The middle layer consists of the superficial medial ligament (the tibial or medial collateral ligament), which is attached superiorly just below the adductor tubercle of the femur. The ligament, which is quadrangular, fans out as it travels down to insert into the subcutaneous border of the tibia some 6 to 7 cm below the knee joint. It lies behind the axis of rotation of the knee (Figs. 10-33 and 10-34).

Above the superficial medial ligament, fibrous tissue from the middle layer passes to the medial side of the patella, forming the medial patellofemoral ligament (see Fig. 10-34).

Posterior to the superficial medial ligament, the fibrous tissue of the middle layer merges with that of the true joint capsule (deep layer) and the tendon of the semimembranosus muscle (Fig. 10-36).

The semimembranosus muscle runs down across the popliteal fossa before it inserts into the back of the medial condyle of the tibia. Three expansions of fibrous tissue come from the muscle’s tendon to reinforce the supporting structures of the knee. The tough oblique popliteal ligament, one of the expansions, crosses the popliteal fossa, extending upward and laterally before attaching to the lateral femoral condyle (Fig.

10-38). Another expansion of the tendon of the semimembranosus muscle passes forward along the medial surface of the tibial plateau and under the superficial medial ligament before attaching to bone (Fig. 10-39). The expansion lies below the inferior attachment of the joint capsule (in the deep layer). A third, thin expansion passes over the popliteus muscle (see Fig. 10-38). These muscular insertions are thought to be very important for the dynamic stabilization of the knee. In cases of damage to the posteromedial corner of the knee, they should be reattached in their anatomic position, if possible.

The semitendinosus and gracilis muscles run between the superficial and middle layers of the supporting structures of the knee. They insert into the tibia under the tendon of the sartorius muscle (in the outer layer), where they become part of the outer layer (see Figs. 10-34 and 10-36).

Deep Layer

The deep layer consists of the joint capsule itself as it attaches just above and below the margins of the articular surfaces of the tibia and femur. Anteriorly, the true capsule lies over the fat pad; it is not part of the medial retinaculum that covers it.

The deep layer is thickened in only one place on the medial side of the knee: By the deep medial ligament, which extends from the medial epicondyle of the femur to the medial meniscus. The deep medial ligament is deep to and separate from the superficial medial ligament. In addition, the deep layer anchors the meniscus to the tibia (the coronary ligament). This results in the limitation of meniscal motion, which may be a factor in the genesis of meniscal tears (see Figs. 10-34 and 10-39).

 

Incision

 

The relaxed skin tension lines run roughly transversely across the knee joint. Therefore, the more transverse the incision, the more cosmetic the resulting scar. Longitudinal incisions, such as those that are used for the medial parapatellar approaches, often leave broad, obvious scars, which are distressing, especially in young women.

 

Superficial and Deep Surgical Dissections

 

The three-layer pattern offers a step-by-step approach to the medial exposure of the knee that is consistent with the anatomy.

1. Medial exposure of the knee and its supporting structures

   1. With anterior arthrotomy

      1. The outer layer is incised in front of the sartorius muscle for exposure of the middle and deep layers (see Fig. 10-35).

      2. Retraction of the sartorius muscle posteriorly uncovers the two structures lying between the superficial and middle layers: The semitendinosus and gracilis muscles (see Fig. 10-36).

      3. Retraction of all three muscles of the pes anserinus reveals the

         middle layer, the superficial medial ligament (see Fig. 10-36).

      4. Vertical incision through the medial patellar retinaculum exposes the thin underlying capsule, the deep layer (see Fig. 10-36).

      5. Incision of this capsule makes accessible the intra-articular structures of the anterior half of the joint (see Fig. 10-34).

   2. With posterior arthrotomy

      1. Incision of the outer layer anterior to the sartorius muscle (and posterior retraction of this muscle, the semitendinosus muscle, and the gracilis muscle) reveals the superficial medial ligament (see Fig. 10-37).

          

          

         Figure 10-33 The sartorius and the medial patellar retinaculum (outer layer) have been resected to reveal the superficial medial ligament of the middle layer. The true joint capsule (deep layer) also is exposed.

          

          

         Figure 10-34 The joint cavity of the knee, with all the more superficial structures removed.

          

          

         Figure 10-35 The outer layer of the medial aspect of the knee joint consists of the sartorius, the fascia of the thigh, and the medial patellar retinaculum.

          

          

         Figure 10-36 The outer layer has been resected to reveal the intermediate layer, consisting of the superficial medial ligament. Between the superficial and middle layers run the semitendinosus and gracilis muscles. The deep medial ligament (meniscofemoral ligament) of the deep layer is visible. The true joint capsule anterior to the superficial medial ligament also is visible.

          

          

         Figure 10-37 A more posteromedial view of the knee joint. The sartorius, the deep fascia of the outer layer, the gracilis, the semitendinosus, and the semimembranosus have been resected to reveal the superficial medial ligament (middle layer), the posteromedial joint capsule (deep layer), and the medial head of the gastrocnemius.

          

          

         Figure 10-38 The medial head of the gastrocnemius has been resected to reveal the three expansions of the semimembranosus.

          

          

         Figure 10-39 The posterior aspect of the superficial medial ligament (middle layer) has been excised to reveal the true joint capsule and its thickening, the deep medial ligament (the meniscofemoral ligament and the coronary ligaments). The posteromedial joint capsule has been excised to reveal the corner of the joint. The insertion of the semimembranosus and a portion of its expansion are visible.

          

      2. Further posterior retraction brings the posteromedial corner of the joint into view. The cover consists of fibrous tissue derived from the semimembranosus muscle (the middle layer), which has fused with the true joint capsule (the deep layer; see Fig. 10-38).

      3. Covering the medial side of the posterior joint capsule is the

         medial head of the gastrocnemius muscle. This head can be reflected backward off the capsule to extend the exposure posteriorly (see Figs. 10-37 and 10-39).

      4. Arthrotomy posterior to the superficial medial ligament consists of incising the deep and middle layers together, exposing the intra-articular structures in the posterior half of the joint (Fig. 10-40; see Fig. 10-39).

2. Approach for medial meniscectomy

   1. Incising the medial patellar retinaculum exposes the true capsule of the joint, which is very thin at this point.

   2. The true capsule of the joint, incised with the synovium, allows access to the anteromedial portion of the joint (see Figs. 10-33 and 10-34).

3. Medial parapatellar approach to the knee

   1. The joint is dissected through the same fascial layers as in the approach for the medial meniscus.

 

Special Anatomic Points

 

Three muscles, the sartorius, semitendinosus, and gracilis, insert into the upper part of the subcutaneous surface of the tibia. Each muscle has a different nerve supply: The sartorius is innervated by the femoral nerve, the semitendinosus by the sciatic nerve, and the gracilis by the obturator nerve. In addition, each muscle crosses both the hip and the knee.

The actions of the three muscles are duplicated by other, more powerful, muscles. At their pelvic origins, the three attach to three points on the bony pelvis that are separated as widely as the pelvis allows: The anterior-superior iliac spine (sartorius), the ischial tuberosity (semitendinosus), and the inferior pubic ramus (gracilis). With these origins and insertions, the muscles are arranged ideally to stabilize the pelvis on the leg.

The sartorius, semitendinosus, and gracilis insert into the subcutaneous surface of the tibia at a point called the pes anserinus (goose foot). Acting together, they not only flex the knee, but also internally rotate the tibia.

 

 

Figure 10-40 Osteology of the posteromedial aspect of the knee joint.