Winter 2001 Newsletter

Diagnosis
Unfortunately, the ability to recognize the anterior cruciate ligament (ACL) deficient knee is lacking, even among orthopaedic surgeons. The history of an acute ACL tear is remarkably constant, as the injury is often non-contact and patients usually report a twist on the flexed knee, turning to the same side as the injured knee. Hyperextension is the next most common mechanism of injury. Although direct trauma is common in some sports, the precise mechanism is difficult to elicit. Often patients remember a pop ­ as there are no nociceptors in the ACL, pain is not an immediate feature in the isolated lesion. Athletes may attempt to continue to play their sport but usually stop because the knee feels insecure. Pain ensues when haemarthrosis develops; 70 percent of acute haemarthroses of the knee are associated with a tear of the ACL.

The suspicion of a haemarthrosis can be confirmed by arthrocentesis. It is mandatory to confirm the diagnosis before treatment is offered. Depending on resources, examination under anesthesia and arthroscopy can be necessary, unless MRI is readily available. This may show a peripheral tear of the meniscus or an osteochondral lesion. These constitute 30 percent of the causes of a haemarthrosis that are not a torn ACL, and can then be treated. The peripheral tear of the meniscus must be sutured, as having bled, by definition it has a blood supply and thus can heal. Osteochondral fragments from weight-bearing areas must be replaced and fixed, if this is technically possible.

In the symptomatic ACL-deficient knee, the disability is specific. Patients can run in a straight line, but when turning to the side of the lesion, the knee gives way. The giving-way can be unpleasant but is not inevitably painful. When painful, it is often associated with swelling representing damage to the articular surface or meniscus. Locking is a symptom of an associated meniscal tear either caused by the original injury or by attrition from the shearing force associated with recurrent giving-way.

The physical signs seem to give rise to the most difficulty despite the description by Hey Groves of the sudden relocation (from the anterior subluxation position) of the lateral part of the tibia, redescribed by Galway et al. Batchelor described the test that Torg et al ascribed to Lachman.

The experienced surgeon encounters many knees in which clinical examination reveals a complete lesion of the ACL unknown to the athlete or the coach. Only with knowledge and understanding of the natural history can rational treatment decisions be made. Despite what is claimed in the literature, there is no well-conducted prospective unbiased long-term study reporting the natural history of the totally asymptomatic ACL-deficient knee.

The Dispute
In discussions with North American, Australian and Continental European colleagues, we have noted that many firmly believe the indication for ACL reconstruction is a complete tear of the ACL. I teach and practice that the main indication for surgery in skeletally mature patients is the functional instability (not the laxity) a torn ACL may cause. Unfortunately, the recent literature has developed the frightening and incorrect habit of using the terms "laxity" and "instability" as synonyms. Laxity is an objective finding (i.e., a sign), while instability is what patients may complain of following an ACL tear (i.e., a symptom).

In these countries, the indication for ACL surgery seems to be more and more just laxity, i.e., a (complete) lesion of the ACL. Laxity in the antero-posterior plane is not correlated with instability, and paradoxically, a reconstruction may totally annihilate antero-posterior laxity but still allow rotatory instability. Although there is a correlation with instrumentally or manually measured antero-posterior laxity, not all patients with antero-posterior laxity develop instability (the authors is one such patient, who despite a very marked antero-posterior laxity due to an arthroscopically proven ACL tear, never experienced instability).

In clinical practice, one encounters high-performance athletes who have suffered from a complete ACL tear and have not undergone a reconstruction. This has been reported anecdotally and quantified recently. In soccer, for example, there is a significant percentage of asymptomatic players who exhibit antero-posterior and rotatory laxity but do not develop instability. They do not need a reconstruction. Most of the patients we see in our National Health Service practice are the symptomatic ones; therefore, the picture is biased, and it is wrong to think that all patients with a lesion of the ACL end up with destroyed knees.

There are inevitable differences between countries, and where sport is very important, more patients will apparently require an ACL reconstruction. However, the fact that a patient wants to continue to take part in high-level sport is not in itself an indication for surgery.

Patients with an ACL tear follow the "rule of thirds" (one-third does badly, one-third does well and one-third does well if they modify their activities, or badly if they continue with their potentially injurious activities). At present, with the lack of scientifically reliable predictors of instability, we offer surgery to our patients with an ACL tear only after failure of a period of six to 12 weeks of intensive rehabilitation with hamstring strengthening and proprioception training.

There is no doubt that the objective results of conservative management of ACL tears deteriorate with time. The argument advanced by some that ACL reconstruction results in a lesser degree or in a slower development of degenerative joint disease is far from being proven. Even a prompt reconstruction and excellent rehabilitation do not alter the natural history of a major intra-articular derangement of the knee. A recent well-controlled prospective study from Sweden has shown that, seven years after an ACL tear, there is no significant difference in the number of professional soccer players who had retired from the sport and no difference in the degree of degenerative joint disease between the reconstructed or conservatively managed players. Unfortunately, after the major initial trauma, the reconstruction produces even greater injury to the intra-articular structures, with a possible additive effect.

The recent studies that seem to suggest early reconstruction prevents osteoarthritis are biased, as the entry criteria were just a complete tear of the ACL, not necessarily giving symptomatic instability. If this were the case, following the rule of thirds would mean up to a staggering two-thirds of these patients would not have needed a reconstruction!

We are fully aware of the dangers of recurrent episodes of instability on the articular cartilage and the menisci, but we stress that the patients that come to our observations are the ones who do develop instability, i.e., probably only one-third of the total, if that. More efforts should be put into identifying patients who will develop instability after an ACL tear, as they are at risk of developing secondary meniscal tears and articular cartilage lesions. Such patients should be offered early reconstruction, but the answer does not lie in reconstructing everybody with a torn ACL.

References available upon request from the author.