Posterior Approach

POSTERIOR APPROACH

USES

This approach is used to access any of the posterior structures of the knee, for neurolysis, neurectomies, phenol injections into the motor branches in spastic patients, capsulodesis for recurvatum deformities, Baker’s cyst excisions, and open posterior cruciate ligament reconstructions.

ADVANTAGES

This approach exposes all of the structures in the posterior aspect of the knee, including the neurovascular structures.

DISADVANTAGES

This large approach passes directly past the neurovascular structures. The most difficult to work around are the geniculate arteries.

STRUCTURES AT RISK

Because this approach comes directly onto the neurovascular structures, the whole point of the approach is to identify them. They need to be clearly identified and protected.

TECHNIQUE

A curved incision crosses the joint parallel to the flexor crease. Whether the proximal arm is medial or lateral depends on what the goal of surgery is. The incision is carried through the subcutaneous tissue, exposing the superficial fascia. The sural nerve is identified just below this fascia. It can then be retracted out of the way and the fascia can be spread. In the fat that is deep to the fascia is the posterior tibial nerve, in between the two heads of the gastrocnemius. The only branch of the posterior tibial nerve coming off and going laterally is the branch to the lateral head of the gastrocnemius. Typically, the nerve is retracted medially to protect all of the other branches, and care must be taken not to put too much tension on the branch to the lateral head of the gastrocnemius. Deep to those branches you will find the vein and artery, which are also midline structures at this level. As they are retracted, care must be taken not to damage the geniculate branches. Commonly one of the geniculates has to be clamped and sacrificed to retract the artery far enough away to access the posterior capsule of the knee.

TRICKS

The horizontal component of the incision is placed into the knee flexor crease, which is slightly proximal to the knee joint. Typically, the proximal portion is medial and the distal portion is lateral. The sciatic nerve splits into its posterior tibia and peroneal nerve branches at the proximal end of this incision. Finding the larger nerve proximally and dissecting its branches facilitate identifying the branches. It is important also to realize that the nerve is superficial to the vascular structures. The vein is the structure closest to the femur. The artery and vein are tethered to the posterior tibia just distal to the posterior cruciate ligament insertion.

HOW TO TELL IF YOU ARE LOST

It is relatively easy to get lost medially or laterally in this approach, but as long as you are careful with your dissection, it is easy to recover. The main way to tell that you are lost proximally or distally is if you do not feel the posterior aspect of the joint. Once you are deep to the subcutaneous tissue, that is usually palpable. It is not a big deal if you are lost proximally or distally; you must simply adjust yourself as needed.

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