Posterior Approach To Knee Joint

The posterior approach to knee joint is neurovascular approach primarily, it’s rarely is needed by orthopedic surgeon because the medial and lateral approaches each provide good access to half the posterior capsule.

The posterior approach to knee joint uses include:

1. Repair of the neurovascular structures in the popliteal fossa.
2. Repair of avulsion fractures of the posterior cruciate ligament (it’s insertion to the tibia).
3. Recession of gastrocnemius muscle heads in cases of contracture.
4. Lengthening of hamstring tendons.
5. Excision of Baker’s 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.

Landmarks and Incision

• Landmarks:
  1. Gastrocnemius muscle.
  2. Semimembranosus and semitendinosus muscles.
• 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.

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 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 applied. 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.
• 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.
• 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.
• Now, turn to the popliteal artery and vein, which lie deep and medial to the tibial nerve.
• 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.
• 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.

Deep 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, pulling 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.
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.

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.

Approach Extension

• If additional medial access is necessary, the medial head of the gastrocnemius can be released.
• Posterolateral extension of the posterior approach to knee joint should be limited due to risk of common peroneal nerve injury.

Dangers

The structures at risk during  the posterior approach to knee joint includes:

1. Popliteal artery:
   • Risk to popliteal artery is minimized with maintenance of access under the gastrocnemius muscle.
2. Tibial nerve:
   • Tibial nerve injury is minimized with maintenance of access under the gastrocnemius muscle.
3. Sural nerve and short saphenous vein.

References

• Surgical Exposures in Orthopaedics book – 4th Edition
• Campbel’s Operative Orthopaedics book 12th