Posterior Approach to the Knee

Posterior Approach to the Knee ‌

The posterior approach3,22 is primarily a neurovascular approach. Orthopedically, it rarely is needed because the medial and lateral approaches each provide good access to half the posterior capsule. Reconstruction of fractures of the posterior column of the tibial plateau is best carried out through the posterior approach to the tibial plateau (see Chapter 11). Its uses include the following:

1. Repair of the neurovascular structures that run behind the knee in cases of trauma

2. Repair of avulsion fractures of the site of attachment of the posterior cruciate ligament to the tibia

3. Recession of gastrocnemius muscle heads in cases of contracture

4. Lengthening of hamstring tendons

5. Excision of Baker cyst and other popliteal cysts

6. Access to the posterior capsule of the knee

 

Position of the Patient

 

Place the patient prone on the operating table. Use a tourniquet for all procedures except vascular repairs (Fig. 10-52).

 

Landmarks and Incision

Landmarks

Palpate the two heads of the gastrocnemius muscle at their origin on the posterior femoral surface just above the medial and lateral condyles. They are not as easy to feel as the hamstring tendons just above them.

Palpate the semimembranosus and semitendinosus muscles on the medial border of the popliteal fossa. The semitendinosus feels round; the semimembranosus is deeper and remains muscular to its insertion.

Because this approach is rarely performed by orthopedic surgeons and is carried out in the prone position palpate the head of the fibula and draw the letter L (lateral) over it using a skin marker. This will aid many surgeons with orientation during the surgical dissection.

Incision

Use a gently curved incision. Start laterally over the biceps femoris muscle, and bring the incision obliquely across the popliteal fossa. Turn downward over the medial head of the gastrocnemius muscle, and run the incision inferiorly into the calf (Fig. 10-53).

 

 

 

Figure 10-52 Position of the patient on the operating table for the posterior approach to the knee.

 

 

Figure 10-53 Make a curved incision over the popliteal fossa. Start laterally over the biceps femoris, and bring the incision obliquely across the popliteal fossa. Turn the incision downward over the medial head of the gastrocnemius.

 

Internervous Plane

There is no true internervous plane in this dissection, which exposes the contents of the popliteal fossa by incising the deep fascia over it and pulling apart the three muscles that form its boundaries.

 

Superficial Surgical Dissection

 

Reflect the skin flaps with the underlying subcutaneous fat. The vein is easier to identify if the leg is not exsanguinated fully before the tourniquet is inflated. Running on the lateral side of the vein is the medial sural cutaneous nerve. The small saphenous vein can be used as a guide to the nerve, and the nerve can be used as a guide to dissecting the popliteal fossa. The nerve, which continues beneath the deep fascia of the calf, is a branch of the tibial nerve (Fig. 10-54; see Fig. 10-57).

Incise the fascia of the popliteal fossa just medial to the small saphenous vein. Trace the medial sural cutaneous nerve proximally back to its source, the tibial nerve. Dissect up to the apex of the popliteal fossa, following the tibial nerve (Fig. 10-55).

 

 

Figure 10-54 Reflect the skin flaps. Identify the small saphenous vein as it passes upward in the midline of the calf. On the lateral side of the vein is the medial sural cutaneous nerve. Incise the fascia of the fossa just lateral to the small saphenous vein.

 

The apex of the popliteal fossa is formed by the semimembranosus

muscle on the medial side and the biceps femoris muscle on the lateral side. Roughly at the apex, the common peroneal nerve separates from the tibial nerve. Dissect out the common peroneal nerve in a proximal to distal direction as it runs along the posterior border of the biceps femoris muscle (Fig. 10-56; see Fig. 10-59).

Now, turn to the popliteal artery and vein, which lie deep and medial to the tibial nerve (Fig. 10-57). The artery has five branches around the knee: Two superior, two inferior, and one middle genicular artery. One or more of these branches may have to be ligated if the artery needs to be mobilized (see Fig. 10-60).

The popliteal vein lies medial to the artery as it enters the popliteal fossa from below. Then it curves, lying directly posterior to the artery while in the fossa. Above the knee joint, it moves to the posterolateral side of the artery. Be very careful in mobilizing this structure. Intimal damage may cause thrombosis.

 

 

Figure 10-55 Incise the fascia of the popliteal fossa. Trace the medial sural cutaneous nerve proximally, back to its source, the tibial nerve.

 

Deep Surgical Dissection

 

Retracting the muscles that form the boundaries of the popliteal fossa exposes various parts of the posterior joint capsule. There are two ways to gain greater access to the joint if this is necessary:

1. Posteromedial joint capsule. Detach the tendinous origin of the medial head of the gastrocnemius muscle from the back of the femur. Retract

   the head laterally and inferiorly, retracting the nerves and vessels out of the way to reach the posteromedial corner of the joint. The exposure now is the same as that achieved by posterior extension of the medial approach to the knee (Fig. 10-58; see Fig. 10-57).

2. Posterolateral corner of the joint. Detach the origin of the lateral head of the gastrocnemius muscle from the lateral femoral condyle. Develop the interval between it and the biceps femoris muscle, creating the same exposure as in the lateral approach to the knee (see Figs. 10-57 and 10-58).

 

 

 

Figure 10-56 Dissect out the common peroneal nerve in a proximal to distal

direction as it runs along the posterior border of the biceps femoris muscle.

 

Note that the posterior approach is no better than the lateral and medial approaches in dealing with pathology of the posteromedial and posterolateral corners of the knee joint. It should be used mainly for exploring structures within the popliteal fossa and for reattaching the avulsed tibial insertion of the posterior cruciate ligament.

 

 

Dang

 

 

Nerves

The medial sural cutaneous nerve, which lies lateral to the small saphenous vein, may be damaged as it travels beneath the deep fascia of the calf. Incising the deep fascia of the calf medial to the vein, therefore, will preserve the nerve. Cutting the medial sural cutaneous nerve may produce a painful neuroma, but the resulting anesthesia usually is not significant (Fig. 10-59; see Fig. 10-54).

The tibial nerve may be damaged in the popliteal fossa. Damage to the nerve at this level produces paralysis of all the flexors of the toes and feet (Fig. 10-60; see Fig. 10-58).

The common peroneal nerve also is susceptible to damage in the popliteal fossa. Damage to the nerve at this level produces paralysis of the extensors and the evertors of the foot (see Figs. 10-58 and 10-59).

 

 

Figure 10-57 The popliteal vein lies lateral to the artery as it enters the popliteal fossa from below. Then it curves, lying directly posterior to the artery while in the fossa.

 

Vessels

The small saphenous vein may need to be ligated; this is an uncomplicated procedure.

The popliteal vessels can be damaged during deep dissection, producing ischemia of the calf and foot (see Fig. 10-58).

How to Enlarge the Approach

Local Measures

The exposure described gives an adequate view of the contents of the popliteal fossa. Retracting the muscles of the fossa improves the view. To expose the knee capsule itself, detach one or both of the heads of the gastrocnemius muscle.

Extend the approach inferiorly to expose the trifurcation of the popliteal artery. At that point, the anterior tibial artery passes forward above the upper border of the interosseous membrane into the extensor compartment of the leg tethering the artery. It is a common site for arterial pathology in association with fractures in this area. This pattern makes it difficult to mobilize the artery; anastomoses in these areas are quite challenging.

 

 

Figure 10-58 Retract the muscles that form the boundaries of the popliteal fossa, exposing the various parts of the posterior joint capsule. Detach the tendinous origin of the medial head of the gastrocnemius in the back of the femur to expose the posteromedial portion of the joint capsule. Detach the origin of the lateral head of the gastrocnemius from the lateral femoral condyle to expose the posterolateral corner of the joint capsule.