The anterior cruciate ligament (ACL) is perhaps the most valuable piece of collagen in the human body. The recent, and well publicised, case of a striker about to sign for Manchester United for £20,000,000, reduced to being worth nothing overnight following his ACL injury, shows the devastating effect that rupture of this 35mm length of connective tissue can have.
The last 10 years has seen an explosion in the published literature concerning all aspects of management of this very common injury. We know from previous studies (1) that there is an incidence of approximately 30/100,000 population/year and so a medium sized hospital in the UK should see about two fresh injuries a week.
Despite the wealth of publications there are very few randomised, controlled trials and as Mark Twain said, " the great advantage of medicine is the large amount of conjecture so get for such a small investment in fact"! Whilst this makes evidence based practice difficult, there have been some reasonable studies on assessment, surgical techniques and rehabilitation.
In 1983 Frank Noyes published a seminal paper (2) in which one of the observations was that the diagnosis of ACL rupture was made by the original treating physician in only 6.8% of cases. This aspect of care was studied in the UK some 12 years later and the results published in 1996 (3). Surprisingly, despite the explosion of literature and the increasingly high profile of this injury, the diagnosis of ACL rupture was made by the original treating physician in only 9.8% of cases, a hardly significant improvement.
Perhaps even more worryingly 30% of cases had been seen by an orthopaedic consultant and not had the diagnosis made and 28% of the patients had had an arthroscopy or arthrotomy and still not had their injury correctly identified.
It may be argued that the increasing use of MRI may reduce the incidence of missed injuries but MRI has been shown to be less sensitive and specific than an experienced clinical examiner (4) and rarely if ever alters clinical decision making (5). As a classical history can be obtained in approximately 90% of cases (3) the routine use of MRI to establish the diagnosis in suspected cases of ACL cannot be supported.
It was appreciated in the early 90's that the symptom questionnaires that existed were not directly comparable (6) and assessment of symptoms and function in an objective fashion, so that results from different series can be compared, has undergone a steady evolution. The IKDC (International Knee Documentation Committee) is now the gold standard for recording data with respect to ACL injury and surgery. The latest and thoroughly validated version, is available for downloading through the AAOSM website.
Part of the IKDC assessment relies on arthrometric measurements of knee laxity, despite the fact that this has never been shown to correlate with a patient's symptoms and function. Indeed a study published in 1997 (7) showed there was no correlation between measured anterior laxity measured by both KT1000 and on stress radiography and patient symptoms and function, a conclusion reinforced by subsequent similar studies (8,9,10), and it is perhaps curious as to why such emphasis is placed on this measurement by some surgeons. This emphasis has, especially in the USA, led to the terms instability and laxity becoming almost synonymous whereas they have, of course, very different implications for the patient.
There have been no radical changes in the surgery for ACL injuries but more of a steady consolidation of existing techniques. The use of synthetic ligaments has all but faded from the scene, although they may still have a place in the older patient or for salvage procedures.
The main thrust of clinical research has been to compare results between different autograft reconstructions and various methods of graft fixation. The particular debate that has been to the fore over the last five years has been the various advantages and disadvantages of hamstring versus patella tendon reconstructions.
There is however no one graft that is suitable for all patients. Patients with kneeling occupations or involved in sports with a lot of eccentric loading such as netball may not be suitable for a middle third patella tendon graft. Patella tendon grafts have stood the test of time as far as professional sportsmen go and offer more dependable and quicker biological fixation. Studies have shown however that there is little to choose between the two types of graft in the long term (11), and so the graft should be selected to suit the patient and not the patient to fit the graft.
If a surgeon is performing large numbers of ACL reconstructions he or she will undoubtedly start facing the situation of graft failure and the requirement for revision when a variety of the less common reconstruction techniques such as utilising quadriceps tendon grafts (12) or allografts (13), may be called upon. A useful adage for the prospective ligament surgeon is "you don't play a game of golf with only one club in your bag"!
The search still continues for the ideal form of graft fixation. Interference screws for the fixation of patella tendon graft are the most commonly used technique and initial fixation strengths are able to cope with the loads placed on the graft by activities of daily living. Recent years have seen the introduction of "bioscrews" which offer the theoretical advantage of slow absorption over a period of 2-5 years. Certainly laboratory and clinical data shows they do not differ significantly in their properties from traditional titanium screws (14,15)
The ideal fixation for hamstring reconstructions is much less clear-cut. There have been concerns about the effect of cyclical loading on hamstring reconstructions producing graft loosening. A good deal of laboratory work has been done comparing one method of fixation with another. Certainly suspensory fixations such as the endo-button marketed by Smith and Nephew, the transfix system marketed by Arthrex or the Rigidfix marketed by Mitek offer theoretical advantages in terms the load to failure of their femoral fixation, and the weakest fixation is with soft tissue interference screws.
The laboratory data is not supported in clinical practice however. Some of the best series of results that have been published are by surgeons using sutures tied over a button for patella tendon grafts and interference screw fixation for hamstring grafts (11,16)!. These conundrums remain to be answered but at least part of the answer may be that in the laboratory a biological healing response does not occur, and certainly there are anecdotal reports that in bone-patella-bone grafts some bony union has been demonstrated on CT scanning by two weeks post surgery.
In terms of timing of surgical intervention there a general concensus that it is sensible to wait until the initial inflammatory response has subsided and a full range of motion has been regained (17,18,19). There appears to be no long term deficit with this approach and the problematic complication of arthrofibrosis is much reduced.
There is still debate about whether early ACL reconstruction is justified. Certainly there is some evidence that early ACL reconstruction when the rest of the knee is "normal", can diminish the likelihood of meniscal damage and slow down the progression of radiographic osteoarthritis (20,21) and the functional results of early reconstruction are better (22).
It must be remembered that the patient populations from series in different countries of the world are very different. In the USA the definition of a chronic ACL injury is often anything over six weeks post injury! In the UK the mean delay to diagnosis is in the region of 2 years (3) and then there is often a waiting time of at least a further 12 months before surgery can be carried out.
By this time many patients will have suffered further injury to articular surfaces and menisci, but even in this situation ACL reconstruction has been shown to reduce symptoms and improve function (23,24). Similarly, age is not a preclusion to ACL reconstruction if symptomatic instability is a major problem. In my own practice my oldest patient undergoing ACL reconstruction with a successful result was 72!
It is perhaps in the rehabilitation following ACL injuries and surgery that we have moved furthest forward in the last 10 years. Ten years ago it was common practice to brace or even plaster patients post-operatively, often restricting the range of movement and making the patient partial or non-weight bear for prolonged periods.
It is to Don Shelbourne that we owe the greatest debt for moving things forward. It was when he critically reviewed his post operative patients and discovered that the patients who ignored the standard post operative advice, did just as well or better, than the patients who were carefully nurtured after their surgery, that he began to question whether overprotecting patients was actually doing any good or whether in fact, it was causing problems in terms of range of movement and return to functional activities.
He started to publish data at the beginning of the 1990's (25) and has continued to do so since. Certainly his approach of an immediate return to full hyperextension and early functional activity has not been shown to be deleterious to long term knee joint stability, a finding that has been duplicated in other centres (26,27). This also avoids troublesome joint motion complications and returns patients to activities of daily living by a few weeks, and sporting activity by six months, post surgery.
In addition to overprotection, other commonly used and popular post-operative tools such as continuous passive motion, cryotherapy and bracing have also been shown not to produce any significant benefit to patient recovery. (28,29,30,31).
"Accelerated" rehabilitation must not be confused with "aggressive" rehabilitation. Exercises utilised are those that are known to produce least strain in the graft and most post-operative protocols consist of a graduated functional programme that only needs to be supervised by a physiotherapist on an intermittent basis. Perhaps one of the most important aspects of rehabilitation is patient education so they can contribute to looking after their reconstructed knee.
Whatever the graft choice, surgical technique and rehabilitation protocol the reconstructed ACL is no stronger then the one that God put in originally and patients must understand that if the same set of circumstances arise as at the first injury the same thing will happen!
These choices are also less important than that the operation is performed correctly, with accurate graft placement. It is sobering to note that in a 4 centre survey on the causes of ACL failure in patients referred as tertiary referrals for revision ACL reconstruction, the most common reason for failure, in nearly 75% of cases, was technical error on the part of the operating surgeon (34).
As to the future, there are a number of promising developments on the horizon. The prospect of biological grafts of synthetic collagen, implanted with the patients' own fibroblasts and fixed with biological fixation that will turn to bone, is reasonably close. Whether society will be able to afford these developments is another matter. In any aspect of orthopaedics, when the potential morbidity of a procedure decreases the indications for performing it increase. The potential numbers of people who would benefit is enormous.
Whatever the outcome, we will still require surgeons who can place the grafts in the right place, time after time, and then this injury will no longer hold the fearsome reputation it currently has in active sportsmen and women of all abilities and disciplines.
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