ACL RECONSTRUCTION

Figure 5a: The normal ACL on MRI

Figure 5b: MRI of a well placed ACL graft

surface (Figure 4). These so called suspensory fixation methods pro- vide great strength, but at the expense of less stiffness. The reality is that employing modern fixation techniques should allow rapid rehabilitation from the outset.

Where to place the graft Rather surprisingly debate still rages about the optimal graft posi- tioning. Whilst it is agreed that the graft should be positioned as close to the natural ACL position as possible, there is still confusion as to where the ACL actually attaches, and there is the difficulty of the fact that the graft diameters are less than the cross-sectional areas of the bony attachments of the native ACL. Part of this uncertainty is understandable due to the shape of the ligament which 'fans-out' somewhat and so cannot be replicated by a graft which is 'straight-line' in nature (Figure 5).

One of the early technical problems was impingement of the graft on the intercondylar notch due to excessive anterior placement in the tibia. This was overcome by placing the graft more posteriorly in the tibia and results improved. Excessive anterior placement of the graft in the femur causes a restriction in flexion, if the graft is taut. Alternatively whilst a slack graft in this position allows flexion it is ineffective functionally. For the graft to be effective, it should be positioned very posterior in the femur.

Although debate remains in reality it is an argument regarding refinement. Therefore surgeons undertaking this surgery should have a technique that should allow reproducible, good functional outcomes. Hence revision ACL surgery should, in the ideal world, be in cases where there is failure of healing, or a new injury has ruptured the graft. Sadly the vast majority of revision ACL reconstructions undertaken in the UK are secondary to surgeons' mal-positioning of tunnels.

Due to the debate on positioning, and the understanding that individual fibres within the ACL seem to form two functional rather than actual units, there has been development of so called 'double bundle' ACL reconstruction using a doubled loop of gracilis and a double loop of semitendinosus placed separately via two tunnels in the femur and two tunnels in the tibia to replicate the two functional bands of ACL. This may be of theoretical advantage but clinical advantage has not yet been proven. The technique is certainly more demanding and the risk of compromising overall graft quality is present. Furthermore, since more bony damage is created by the surgery, one must consider that failure of this operation and the need for revision reconstruction may provide a much greater challenge than revision of a single bundle technique. Nevertheless, this represents an interesting development and the

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Figure 5c: X-ray of well placed ACL graft/screws

Figure 5d: X-ray showing sub-opti- mal placement of ACL screws/graft

situation will become clear over time.

The biology of ACL reconstruction In reality although a lot is talked about how the graft integrates and heals, very little is actually understood about it. Another part of ACL folklore is that when a graft is placed it is strong and under- goes a process whereby dead material is removed by macrophages in an inflammatory phase followed by laying down of new tissue which in time leads to strengthening of the graft. After a period of initial weakening, strength is restored. It is thought that the weak- ness of the graft is maximal around six to eight weeks from implan- tation but that most of the graft strength that will be achieved is present by twelve weeks.

The reality is that this supposition is based on one or two case reports and animal studies. The relevance of these reports has to be questioned. The notion of graft weakness around six to eight weeks is an understandable one but there is no proof of it. In truth, I am very happy for my patients to have a 'holiday' from rehabilitation during this period, but I doubt it is necessary. During daily activity there is probably very little stress on the ACL. Its function for these activities is as a proprioceptive organ detecting changes in tension across it. It is only in sport and in accidents that the ACL is stressed and its integrity tested. If our ligaments were always close to break- ing, then they would fail more readily. Given that in the first few months the patient is not exposed to sporting activity, it is unlike- ly that the graft however weak, will be excessively tested. I am certainly comfortable with the notion that by twelve weeks graft healing is sufficiently strong to allow increased activity.

OPEN OR ARTHROSCOPIC SURGERY? The simple truth is that good results can be obtained with both methods of surgery. It is best for a surgeon to undertake surgery as they feel most comfortable. There are advantages to arthroscopic surgery because the early recovery is much quicker and the poten- tial for scar production (particularly in the fat pad) is reduced.

ALTERNATIVES TO RECONSTRUCTION - REPAIR AND ‘THE HEALING RESPONSE’ Although historically attempts to suture the torn ends of the ACL were thought doomed to failure, there has recently been some renewed interest in this area. It has been recognised that there is some potential in repair. New techniques may develop but it remains to be seen how effective they will be. Perhaps a role for using engineered growth factors will be useful.

The 'healing response' technique involves perforating the bone adjacent to the femoral attachment of the ACL to produce bleeding

sportex medicine 2007:33(Jul):10-15