The posterolateral corner is the region on the outer side of the knee towards the back. It is very complex anatomically, and damage one or more of the structures here can lead to instability of the knee.
The authors of this paper start by pointing out that injuries to the posterolateral corner of the knee were first described only in 1976 - that is not a very long time ago. Early attempts to repair injuries of this complex region of the knee led to increased understanding of the anatomy - and with improved imaging techniques, diagnostic skills and arthroscopic assessment it is now clear to most knee surgeons that in the past these injuries have been missed or poorly appreciated.
Anatomy of the injuries
Less commonly injured posterolateral structures [not in the image] include -
- fabellofibular ligament
- mid third of lateral capsular ligament
- insertion of short head of biceps femoris
- the deep layer of the iliotibial band (ITB)
Other posterolateral structures that can be damaged and usually confirmed at arthroscopy include -
- coronary ligament
- popliteomeniscal fascicle
- posterior capsule
- ligament of Wrisberg
Associated injuries often include -
- anterior cruciate ligament
- posterior cruciate ligament
- medial collateral ligament
- joint cartilage
History of surgical procedures
The first surgical operations to this region were reported in 1983. They were simple repairs - suturing (sewing) or anchoring down of the torn structures. This is called a 'primary repair'.
Primary Repair with Augmentation
Primary repair, however, proved in most cases insufficient to contain the forces in this region and further techniques were developed to augment the repair. An early (1985) augmentation procedure was known as arcuate complex advancement where the insertion sites of existing anatomical structures in the postero-lateral corner were advanced to a new position to tighten the structures - but new mechanical problems arose because some of these tendons were shifted to the front of the rotational axis of the knee and they became repetitively stretched and ultimately many of these procedures failed. [Arcuate complex advancement moved the insertion of the fibular collateral ligament, the popliteus tendon, the posterolateral capsule and the popliteofibular (arcuate) ligament.] A variant of this procedure - popliteal tendon recession - met also with poor success in terms of fully stabilising the knee.
Both of those procedures tightened up the weakened structures at the posterolateral corner. Surgeons also tried an opposite approach - biceps tendodesis - where instead of tightening the weakened structures at the back of the knee the surgeon simply moved the biceps tendon to a position where its contraction would not compromise the weakness of the other structures but would instead act as a stabiliser. But this needed precision in order to be effective, and even then was only really applicable when the posterolateral corner damage was relatively minor. For cases where the damage was extensive, the procedure of popliteal bypass was developed. In this procedure the popliteus tendon and the fibular collateral ligament were separately repaired, and the former was then augmented by a static restraint across the area where the popliteus tendon would normally offer support.
Other augmentation procedures have been developed.
As more understanding has developed about the contribution of each element of the complex anatomy of this region the procedures have become more sophisticated. It has become appreciated that stability in the postero-lateral corner is normally achieved by -
- two dynamic stabilisers - the popliteus muscle and its tendon, and the popliteofibular ligament
- three static stabilisers - the fibular collateral ligament complex, the posterolateral capsule and the posterior cruciate ligament
Reconstruction techniques use autograft, allograft or synthetic material to provide static restraints from either the top of the fibular bone or the lateral upper tibia to the lateral femur in the region known as the epicondyle. The most successful of these techniques are those that most accurately mimic the normal anatomy.
Surgery to the Posterolateral Corner
Indications for surgery
Disability because of pain and instability is the main problem taking people to surgery. In acute (ie recent) injury the pain is usually on the lateral (outer) side while in more chronic (older) injury the pain tends to be medial (on the inner side). The instability tends to be with any form of activity.
When the injury is still new examination can be difficult. In older cases it is easier to examine the knee and pick up the signs of posterolateral corner dificiency. The two most sensitive examination tests are -
[Editorial note: The relevant tests can be seen on this site.] but even these tests can miss about 30% of cases. The authors point out that different examination tests are more specific than others for certain anatomical structures damaged -
- a positive reverse pivot shift test suggests a tear of the fibular collateral ligament, the popliteus and/or the mid third of the lateral capsular ligament
- a positive posterolateral external rotation (dial) test in 30 degrees of flexion suggests damage to the fibular collateral and/or lateral gastrocnemius tendon
- varus instability at 30 degrees of flexion suggests a problem in the posterior capsular complex, the fibular collateral ligament and/or the posterior capsule
You will need to look these tests up if you are very interested to know more. The basic message is that it is a skilled matter to diagnosis what exactly is wrong. The surgeon is likely to use special investigations to help with the diagnosis.
An MRI is advised to evaluate all the structures of the posterolateral corner, especially the popliteus tendon and to identify any associated damage such as -
- nerve damage, especially to the peroneal nerve, which classically shows up as a numb spot in the webspace by the big toe, weakness of the ankle movements and drop foot (foot drag)
- blood vessel damage
- bone fracture (especially a Segond fracture and an arcuate fracture [you will need to look these up if you are interested]
- associated meniscus, cruciate and joint surface damage
Grade III injury -
- more than 1 cm varus opening at 30 degrees flexion
- more than 10 degrees external rotation at 30 degrees flexion
- an increase in the drawer test of 1-2 grades at 90 degrees flexion compared to the good side.
Proceeding to surgery
The surgeon can proceed to a reconstruction in acute cases with Grade III injury or in chronic cases where there is a reduced activity level secondary to feelings of disability and instability as long as there is no varus deformity. Varus is when the leg has a tendency to bow outwards at the side and it is demonstrated by 'long leg' X-rays (so the patient is standing up at the time and putting their body weight on the leg).
The issue is that if varus deformity is present this could cause increased forces on the repaired structures and they could stretch and weaken. The varus can be corrected mechanically with an 'unloader brace' or surgically with a procedure that breaks and realigns the tibia bone ('proximal tibial opening wedge osteotomy'). This surgical procedure will tighten some of the structures at the back of the knee, after which the patient needs six months of rehab focusing on quads strengthening before deciding on the necessity of a second-stage posterolateral corner reconstruction.
Contraindications to surgery
Surgery is not advised when there is -
- severe soft tissue injury of the posterolateral corner (eg car accident)
- multi-trauma (like other broken bones)
- marked obesity
- diabetes (or similar conditions where the blood vessels may not be so great)
- varus (as mentioned above)
- severe osteoarthritis of the knee
The surgery itself
The authors give full details and illustrations of their recommended standard procedure, where they use achilles tendon allograft for the reconstruction. If you feel you could follow the details then it is best to get the original article from the library, but basically they advocate opening the posterolateral corner to do the reconstruction, threading the graft material through drill holes in the bones and anchoring it with screws. Then they proceed to an arthroscopy to examine all the internal structures as well. At arthroscopy they particularly examine -
- the popliteus tendon insertion
- the popliteomeniscal fascicles
- the coronary ligaments
- the lateral capsule
- the ligament of Wrisberg
- the posterior capsule
Even if you do not understand the anatomy fully, you get the idea that this procedure is for the true expert surgeon and not to be undertaken by anyone else.
Post operative management
Possible complications after surgery
These might include -
- recurrent instability - this could happen from failure of the graft itself or failure of the graft fixation (eg screw). Also the structures can fail from infection or from rehabbing too fast. The authors stress that patients must strictly adhere to the rehab protocol ordered by the surgeon.
- deep vein thrombosis (DVT) - ie leg clots. They give their patients aspirin for six weeks to prevent this complication
- infection and skin breakdown - these are commonly secondary to soft tissue damage at the time of injury when there has been a high velocity impact. The authors advocate waiting until things have settled in such cases before doing surgery.
- peroneal nerve injury - this can occur with the original injury but can also be a consequence of the surgery. The surgeon is advised to carefully identify the nerve during surgery to avoid any damage.
- arthrofibrosis - they consider this to be one of the most difficult complications to treat, and the first priority of rehabilitation is to restore range of movement to prevent the formation of adhesions and scarring within the knee.
The early post operative period focuses on adequate pain relief. The patient should be non weight bearing for six weeks with the knee immobilised in extension for the first week. Physiotherapy should begin on the first post op day with instructions on the use of crutches, and exercises include quads sets and straight-leg-raises four times a day.
After the first week range-of-motion (ROM) exercises begin with the objective of achieving full ROM before commencing strengthening exercises. Hamstrings exercises are avoided for four months. Closed chain quads exercises begin at 6-8 weeks (eg cycling). Three months after surgery the patient progresses leg presses and squats. Jogging and progressive strengthening may begin at 4-6 months after surgery.
The authors expect that at six months the patient should have achieved at least 0 degrees of extension and more than 90 degrees of flexion, with return to full activities at 6-9 months.