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REHABILITATION FOCUS REHABILITATION OF ACL INJURY By Lee Herrington, MCSP

Injury to the anterior cruciate ligament (ACL) was once regarded as career end- ing for the professional sportsperson and the end of active sports participa- tion for the keen amateur, because of the functional instability this injury caused. Now, because of the advances in surgery and rehabilitation tech- niques, the sportsperson is able to return to their chosen sport often with- in six months of surgery without com- plications. This article will outline the principles behind and the significant features of, the rehabilitation pro- grammes following ACL injury and specifically reconstruction.

Anatomy and function The ACL is located in the intercondylar notch of the femur anterior to the poste- rior cruciate ligament. It originates from the postero-medial aspect of the lateral femoral condyle, inserting into the anteri- or part of the tibial plateau between the anterior horns of the menisci.

The ACL is comprised of two main bun- dles: the antero-medial and postero-later- al bundles. It is the different rotary orien- tation of each of these bundles, which allows some fibres to be taught in flexion (antero-medial) and the other to become taught as the knee moves towards exten- sion. The arrangement of the bundles in this manner allows the ACL to maintain a constant length (therefore tension) throughout the entire range of knee movement.

The primary role of the ACL is to act as a restraint to anterior translation of the tibia, which occurs as a result of the pull of the quadriceps as they contract and slide the tibia forwards. It also acts to restrain knee extension, abduction and internal rotation. The twisted configuration of the ACL in combination with the posterior cru- ciate ligament form a system known as the ‘four bar linkage system’. This configuration of ligaments along with the shape of the femoral condyles, allow the ‘screw home mechanism’ of the knee to occur during the final 20º of knee extension, thus the lock- ing of the knee is controlled.

Figure 1: Position of the knee during a non- contact ACL rupture

The mechanism most commonly reported as leading to an ACL rupture, is one of the patients body moving forward, with the hip flexed and adducted, the femur inter- nally rotated, the knee is in 20-30º flex- ion, with the tibia internally rotated and the foot pronated. The patient then attempts a sudden acceleration or decel- eration, usually whilst changing direction, in a pattern of movement similar to a side step in rugby or a turn skiing (Fig.1).

The ACL is richly innervated with 2.5% of its total volume comprising of nociceptors and mechanoreceptors. Without input from these receptors the proprioceptive ability of the knee is severely limited. These receptors also mediate a protective reflex arc to the hamstring muscles. Reflex contraction of the hamstring muscles when the ligament is stressed reduces some of the anterior translation of the tibia.

ACL injury Ligament injuries of the knee are far more common than those of the menisci (meniscus injury is often a secondary result of the primary ligament damage), with the ACL being the most frequently injured ligament of the knee. Injuries to the ACL account for about 30 injuries per 100,000 of the population. The classic mechanism for rupturing the ACL does not normally involve a direct extrinsic trauma such as being tackled in soccer or rugby. In 62-78% of occasions of ACL rupture it occurs by non-contact trauma that is due to intrinsically developed forces.

At the time of injury the patient usually reports hearing a pop or snap and a sen- sation of the knee separating. They then normally experience a sharp intense pain for a short period, on occasion often feel- ing able to return to play within a few minutes. The next thing to occur is a haemarthrosis of the knee, a gross swelling of the knee, with the aspirate containing blood. This swelling develops within 72 hours. The development of a joint haemarthrosis correlates significant- ly with the presence of an ACL rupture, 72% of patients presenting with joint haemarthrosis had ACL rupture.

In the presence of a joint haemarthrosis, ACL rupture should always be suspected as a cause, 72% of patients presenting with joint haemarthrosis had a rupture of the ACL.

When a patient presents with the above history there is a 72% chance that they will have sustained an ACL injury. If this classical history is combined with a cor- rectly carried out clinical examination, 90% of all ACL injuries can be diagnosed without further confirmatory investiga- tions being required. MRI scans of the knee are far less reliable in diagnosing an ACL rupture than an experienced clinician with a good examination technique.

FACT: Only 9.8% of ACL ruptures are correctly diagnosed by the original treating doctor, despite a classical history of ACL rup- ture (1).

The three most commonly used and reli- able tests for ACL deficiency are the Lachman’s, anterior draw and pivot shift tests. When using these laxity tests, it is the range of movement and quality of end feel available that is important, not the presence of pain.

ACL tests LACHMAN’S TEST This is a highly reliable uniplanar test for detecting the degree of anterior tibial translation. The knee is held in slight flex- ion, with the femur being held firm whilst the tibia is translated anteriorly (Fig.2). Excessive translation (greater than a 3mm

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