Anatomy

Injury

The ACL is the most frequently injured ligament of the knee [73, 87]. In the United States it is estimated that one in every 3000 individuals sustains an ACL injury every year, corresponding to approximately 100 000 injuries per year, with a rate 2 to 8 times higher in women than in men participating in the same sports [35]. Injury most often occurs as a result of a sudden pivoting or cutting movement, causing excessive forces on the ligament however injury may also occur due to hyperextension, hyperflexion or trauma to the knee, particularly in weightbearing [13, 44].

Diagnosis

Further evidence may be gained from radiographic tests such as X-rays or magnetic resonance imaging (MRI).

Any disruption of the ligament may lead to an unstable joint and functional impairment. In the great majority of cases, a ruptured ACL will not heal due to a combination of relatively poor blood supply to the ligament and the presence of joint fluid washing over the torn ligament [46]. Without treatment, the ACL-deficient knee is at a high risk of developing substantial degenerative changes [89, 90].

Conservative Management

There are few treatment options for the management of ACL ruptures. Non-surgical (conservative) programs are based on the enhancement of muscle function and strength around the injured knee to help control stability. Specific functional exercises are prescribed and progressed according to the demands expected to be placed on the knee. This improved muscle function may also be supplemented by the use of bracing or taping as a further attempt to improve stability. Activity modification is usually necessary. Sedentary individuals and recreational athletes may choose a conservative rehabilitation program and some may lead normal lives without reconstruction however full recovery and return to pre-injury levels of performance is questionable [17, 18].

Surgical Management

For those athletes who need to regain their pre-injury level of performance, surgical intervention is generally considered to provide the only viable alternative [77]. The first cruciate repair was reported in 1845, with the first documented reconstruction performed by Groves in 1917 [15, 67, 77]. More recently, the most common forms of surgery involve the use of arthroscopically assisted techniques to remove and replace (reconstruct) the torn ACL with another structure in its anatomical orientation to replicate the function of the ACL. These are usually in the form of a graft from other tendons around the injured patient's knee (autograft), either from the central third of the patella tendon or from the hamstring tendons, or occasionally from the iliotibial band [23, 25, 30, 32, 41, 62]. Historically, synthetic grafts made from such materials as Goretex, polypropylene, carbon fibre, dacron and polyester have been used with limited success [25]. In some cases, allografts (tissue obtained from another donor harvested at the time of their death and sent to a tissue bank) may also be used [61, 67, 73]. The type of surgery undertaken depends on a number of factors including the presence of injuries to other structures in the knee, history of previous surgery on the knee, occupational demands and the surgeon's preference. Other factors that need to be taken into consideration when deciding on a course of management include the age of the patient and the ability to commit to a post-operative rehabilitation program [14].

The specifics of any surgical intervention will depend on the individual surgeon. Surgery is usually performed under a general anaesthetic with duration depending on the type of surgery being performed, any additional surgery to be carried out on other structures and the type of graft being used. There is also a degree of variability in the duration of the hospital stay, depending on similar factors however discharge usually occurs 1 or 2 days after surgery. A brace may be used for a short period, along with crutches for progress from partial to full weightbearing to facilitate isometric muscle activity around the joint [88]. In some cases a continuous passive movement machine (CPM) may be used to help regain range of movement quickly and to help decrease swelling. A home exercise program is usually begun immediately, followed up with a course of guided therapeutic exercises under the supervision of a physiotherapist. Time off work will vary according to occupational requirements but in general, office workers may return to work within 2 weeks while workers needing to perform heavy lifting, climbing, kneeling or pivoting may require 3 to 4 months before returning to work [13, 14, 47, 55].

Rehabilitation

Physiotherapy rehabilitation is often underestimated and the commitment of the patient to their rehabilitation program and the quality of work done throughout the program will contribute significantly in determining the success or failure of the reconstruction. Progress is closely monitored by the physiotherapist and the surgeon. In the early stages of rehabilitation the main aims are early restoration of range of movement, early return of muscle strength, reduction of pain and swelling and normalisation of gait. Muscle function is regained by progressing through activities emphasising control, endurance and strength/power. Progress is determined by the achievement of specific functional goals rather than by simple time frames. Therapeutic modalities may be used to help reduce pain and swelling. Muscle stimulation may be necessary to re-educate some muscle function. Early exercise may begin in the pool as well as on the stationary cycle. Exercises become more functional and dynamic as the program progresses.

Around 6 to 8 weeks post-operatively, the vascularisation of the grafted tissue is at its poorest, the original vessels having died and the new vascularisation is immature and incomplete. While these factors are taken into account by the rehabilitation protocols, it is important to use caution with any new activities which may stress the immature graft. Revascularisation is usually complete after approximately 6 months but may go on for up to 2 years. In general, straight line jogging may begin around the 8 to 12th post-operative week with cutting/pivoting drills beginning once strength and fitness have further improved. Sports specific skills are introduced around the 3 to 4 month period and return to normal activities occurs at around the 6 to 9 month period [4, 13, 14, 16, 47, 55, 61, 78].

Outcomes

Most patients experience no complications following surgery and are able to return to their normal function, however common complications include anterior knee pain, loss of knee range of movement, swelling and hypermobility of the knee. Anterior knee pain is usually a result of abnormal muscle function related to the inhibitory effects of surgery, pain and swelling and is usually resolved by specific treatment by the physiotherapist and focusing exercises on the resumption of normal muscle firing patterns and resolution of any strength/length imbalances around the knee musculature. Loss of range of movement, particularly extension, is usually avoided by careful attention in the early stages of rehabilitation and when identified, more aggressive therapy is instituted. In a small proportion of cases where excessive fibrous scarring in the intercondylar notch or new bone formation around the graft has occurred, further surgery may be necessary. Occasionally, failure of revascularisation and subsequent weakening of the graft may lead to some persistent laxity [4, 13, 14, 16, 47, 55, 61, 78].

Research

Progress in surgical techniques, rehabilitation protocols and evaluative procedures has been made due to ongoing research into all areas of ACL injury management. Accelerated rehabilitation programs aim to adequately identify milestones in strength and function to allow the optimal timeframe in which return to activity can safely take place [76]. In this regard, numerous studies have been undertaken aiming to measure the return of strength of the injured knee as well as attempts to correlate and quantify return of function in the limb. The School of Physiotherapy at Curtin University of Technology has been investigating ACL reconstruction for a number of years and is committed to ongoing research in this area [1]. It is hoped that research programs such as these will enable both clinicians and patients to safely evaluate progress during recovery and achieve an optimal return to full function following ACL injury.