INJURY TREATMENT

Graft choice Synthetic grafts were a popular choice until the mid-eighties. They involve no trauma to the patient in harvesting the graft and can be fixed firmly. Unfortunately, they have a tendency to stretch and fragment. Some unfortunately generate marked biological reactions causing synovitis and bony cavitation which can present a major challenge to revision surgery. Although they have been abandoned as a sensible option, if better versions can be developed they could represent a good future option and replace the need to harvest autografts such as patellar tendon or hamstrings.

Worldwide most ACL grafts are from the central one third of the patellar tendon (Figure 1). This was the first reliable graft employed and the results of ACL reconstruction using this graft have been excellent. The graft is strong and the bone blocks at each end allow excellent fixation. Its harvest however is with significant morbidity to the patient. A significant number of patients develop extensor mechanism pain and problems with kneeling. Good technique how- ever does minimise these problems but they remain more of a prob- lem than with other grafts such as hamstrings.

Hamstring tendon was initially thought to be too weak and felt not to be able to be fixed firmly enough. However, with the use of gra- cilis and semitendinosus tendons (Figure 2) folded double to make a four-strand graft the overall strength of the graft is stronger than the one third patellar tendon, and modern fixation devices allow confidence of solid fixation. The main muscle group controlling anterior tibial translation is of course the hamstrings, and one crit- icism of the hamstring graft is that this dynamic control might be affected. The majority of control needs to be on the lateral side of the joint and the biceps tendon is left alone with this operation. A possibly more important issue regarding harvest of medial hamstrings, is the dynamic control of valgus stress. If a patient has significant medial collateral ligament injury I will often take the hamstring tendons from the opposite limb to prevent loss of dynamic control where most needed.

Extensor mechanism pain can still occur with the use of hamstring grafts but rather than direct trauma to the extensor mechanism, these cases are more often related to fat pad scarring secondary to surgical trauma (not always avoidable) and substandard rehabilita- tion regimes. The incidence is however less than with patellar tendon grafts. The early recovery is somewhat quicker than using patellar tendon as well. The graft can be harvested through a small hole and the area of numbness resulting is usually much less than with patellar tendon harvest.

Great debate has raged regarding the pros and cons of hamstring versus patellar tendon graft. In reality, both provide an excellent source of tissue and should, if implanted properly, give excellent results. I have noticed when I use patellar tendon grafts nowadays my incidence of problems is much less than previously. This is due to improved surgical technique but most importantly appreciation of better rehabilitation regimes - especially the stressing of achievement of hyperextension as soon after surgery as possible.

Donated tendon from cadavers is also employed. This is particular- ly popular in the USA. In my practice I tend to reserve their use for cases where I need a lot of tendon such as in multi-ligament recon- structions where several knee ligaments require reconstruction at

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one time, or in revision cases. In the USA they are popular even as a primary ACL reconstruction graft. The results are comparable to those of autograft but probably slightly inferior. There is, of course, no deficit related to graft harvest and the scars required for implan- tation are very small. My view is that for the primary ACL recon- struction there is only one real indication for use of allograft apart from, of course, patient preference, and that is in the elite track athlete. These patients can't afford any interference with their lower limb muscle function.

When to operate Part of the folklore regarding ACL reconstruction was that surgery should not be undertaken for at least three weeks after injury. This was because it was thought that earlier surgery had an unaccept- ably high incidence of joint stiffness (due to scarring in the joint- 'arthrofibrosis'). There is some truth in this but rather than specify exact timeframes it is sensible to delay surgery until the knee is 'quiet'. In reality this means that the knee has full extension, bends freely but not necessarily fully, and has little swelling within it. For some knees this is any time from injury. Particularly when using hamstring tendons with the low morbidity to their harvest, the risk of stiffness is extremely low if the surgery is undertaken properly. For professional athletes, there is a good reason for early surgery and that is to minimise the period of 'downtime' when muscle wastes and neuromuscular co-ordination diminishes. With this special group I offer surgery as soon as practical.

The most important issue to make clear is that if ACL reconstruc- tion is undertaken in a knee that has not achieved full extension, problems will result and often permanent deficit of extension occurs. Regardless of how well the ACL reconstruction is undertak- en and how stable the knee is, the patient will be always unhappy with the result.

Graft fixation techniques A significant breakthrough in ACL surgery was the development of fixation techniques which were strong enough to allow early physiotherapy to commence post operatively. This came in the form of

interference fit screws (figures 3 and 4).

The graft is pulled into tunnels drilled in the tibia and femur which are of the same diameter as the graft itself. Screws are then introduced in the tight gap between the graft and the wall of the bone tunnel thus squeezing the graft up against the remain- der of the tunnel. This method of fixation allows the graft to be fixed at the aperture of the bone tunnel into the joint. This effec- tively shortens the amount of the graft and therefore provides a stiffer construct. Particularly for hamstring tendons, the grafts can be also fixed by devices that hold into the bone away from the joint

Figure 3: Interference screw being introduced alongside hamstring graft

Figure 4: A lateral radiograph showing ACL graft fixation with an interference screw in the tibia and a suspensory device providing fixation in the femur.

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