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Mervyn J. Cross
North Sydney Orthopaedic and Sports Medicine Centre
Sydney, NSW 2065

Cross, M.J. (1998). Anterior cruciate ligament injuries: treatment and rehabilitation. In: Encyclopedia of Sports Medicine and Science, T.D.Fahey (Editor). Internet Society for Sport Science: http://sportsci.org. 26 Feb 1998.

Functional Anatomy
Rationale for Treatment
Causes of ACL Rupture
Management of the Ruptured ACL
Surgical Techniques

Over the past decade, there has been an increase in interest and participation in sports. Concomitant with this, there has been an increase in sports related injuries, particularly to the lower limbs. Of specifically ligamentous injuries to the knee, rupture of the Anterior Cruciate Ligament (ACL) has been the commonest, and has the greatest potential to cause both short term and long term disability.

Functional Anatomy

The ACL is a broad ligament joining the anterior tibial plateau to the posterior femoral intercondylar notch. The tibial attachment is to a facet, in front of, and lateral to the anterior tibial spine. The femoral attachment is high on the posterior aspect of the lateral wall of the intercondylar notch.

It is composed of multiple non-parallel fibers, which, though not anatomically separate, act as three functionally distinct bundles i.e. anteromedial, posterolateral and intermediate. Owing to their wide attachments, variable fiber lengths and the rotation of the ACL that accompanies flexion, the tension in each bundle varies throughout the range of motion.

The biomechanical function of the ACL is complex for it provides both mechanical stability and proprioceptive feedback to the knee. In its stabilizing role it has four (main) functions:

  • Restrains anterior translation of the tibia;
  • Prevents hyperextension of the knee;
  • Acts as a secondary stabilizer to valgus stress, reinforcing the medial collateral ligament; and
  • Controls rotation of the tibia on the femur in femoral extensions of 0-30°.

This final role is the main clinical function of the ACL. ACL deficiency causes failure of this screw-home mechanism, resulting in subluxation of the tibia on the femur. This critical function in the range of 0 - 30° is important for movements such a side-stepping and pivoting.

Rationale for Treatment

Rupture of the ACL causes significant short term and long term disability. With each episode of ACL instability there is subluxation of the tibia on the femur, causing stretching of the enveloping capsular ligaments and abnormal shear forces on the menisci and on the articular cartilage. Delay in diagnosis and treatment gives rise to increased intra-articular damage as well as stretching of the secondary stabilizing capsular structures.

Evidence to support this has been documented by research undertaken in my practice over the past 15 years. In 1976 I studied the relationship of anterior cruciate ligament rupture to meniscal pathology in three groups of patients. The first group comprised 100 consecutive patients who had a primary diagnosis of medial meniscal tear. At surgery 40% of these patients had a ruptured ACL. The next group comprised 100 patients who were operated on primarily for a diagnosis of a lateral meniscal tear. At surgery 60% had a ruptured ACL. The final groups comprised 100 consecutive patients who had tears in both menisci at arthroscopy. It was fascinating that 95% of these patients had a ruptured ACL.

Since that time, a number of authors have supported this view that a significant function of the ACL is to protect the menisci and if the ACL is ruptured then meniscal damage will occur.

The long-term outlook for an ACL deficient knee is for the development of significant osteoarthrosis. Evidence to support this view has also been documented in my practice. A series of 100 consecutive total knee replacements demonstrated a 15% incidence of previous ACL rupture. This incidence of ACL rupture is five times higher than that in the general population. Thus it is important to make an early diagnosis of ACL rupture Meniscal injury and long term degenerative damage is to be minimized.

Causes of ACL Rupture

The most common cause of ACL rupture is a traumatic force being applied to the knee in a twisting moment. This can occur with either a direct or an indirect force. In my practice, about half of the cases of ACL rupture occur without contact, i.e., while side-stepping, pivoting or landing from a jump. The other half are associated with some type of contact, whether it be on the football field, on the snow fields or in a motor vehicle accident. Skiing injuries usually occur during a fall in the inexperienced skier, on hired skis when the bindings do not release.

The question arises as to whether there is a predisposition in some people to ACL rupture. I have a significant number of patients who have sustained bilateral ACL tears. These patients comprise approximately 15% of the total number of patients sustaining rupture of their ACL. I also have a series of patients in my practice where ACL rupture appears to be familial. I have a number of families where up to four members have ruptured their ACL's. Furthermore, I have recorded two cases of ACL rupture in twins.

Another group of patients, I believe, have agenesis of the ACL. In some cases, when I have explored the knee within 3 to 4 days of their injury, there is minimal ACL tissue present in the notch. It has been well documented that patients with narrow intercondylar notches are more prone to rupture their ACL's. I believe that their notch is narrow because they have a hypoplastic ACL and hence are more prone to rupture.

Another interesting factor is that patients with recurvatum tend to be more likely to rupture their ACL and are more difficult to treat. I have also noticed a significant number of patients having ruptured their ACL who also have instability of the shoulder. I believe both these groups have a generalized ligamentous disorder.


The classic story of a patient cutting, side-stepping or landing from a jump, and the knee giving way, followed by immediate pain and swelling should alert the diagnostician to the most likely diagnosis of ACL rupture. In my practice a "snap" or "pop" was noted by 60% of the patients. Rapid intra-articular swelling following injury is nearly always due to hemarthrosis. An ACL rupture is present in 75% of patients presenting with an acute hemarthrosis and is due to bleeding from vessels within the torn ligament. Differential diagnoses include osteochondral fracture, peripheral meniscal tear, retinacular tear associated with patella dislocation or subluxation, PCL tear or bleeding disorders.


The diagnosis of ACL tear can be confirmed by three tests: the Lachman test, the dynamic extension test, and the Pivot Jerk test. While the Lachman test and dynamic extension test are helpful in making a diagnosis, particularly in the acute injury, the lateral-pivot jerk test is the most important

The lateral pivot jerk test reproduces the rotatory subluxation that occurs in ACL deficiency. The test is difficult to perform and takes residents and fellows in my practice approximately three months of intensive training to be able to adequately perform the jerk test in the unanaesthetised patient. The test is important because the demonstration of the lateral pivot jerk is the replication of the instability that the patient has.

Some authors consider the Lachman test to be the chief confirmation of rupture of the ACL. I do not agree, as a negative Lachman test may be misleading. The ACL commonly heals onto the posterior cruciate ligament producing a falsely negative Lachman test with a fairly firm end point. These patients, however, may still have a positive lateral pivot jerk and clinical instability.

Management of the Ruptured ACL

Once the diagnosis of ruptured ACL is made, management can be divided into conservative and surgical. Correct choice of treatment depends on assessment of three patient factors:

  • Age
  • Functional disability
  • Functional requirements.

A small percentage of the population, perhaps 15%, can survive happily with a ruptured ACL, so a patient profile is important in assessing the indications for surgery. The child, the adolescent, the young adult, the middle aged, and the elderly, represent different surgical problems. Functional disability may vary from an undiagnosed asymptomatic rupture, to the patient whose knee gives way on a daily basis. I believe these differences are due to variations in proprioception muscle control about the knee. Functional requirements vary from sedentary patients with low activity requirements, through those patients with an active social sporting life or physically demanding work, to the elite athlete whose fame and fortune depends upon a highly functional knee.

Rupture of the ACL in the child or the elderly is rare and comprises of less than 5% of all ruptured ACLs I see and are usually treated conservatively.

Rupture in the adolescent is not uncommon and presents its own problems because of skeletal immaturity. Most isometric reconstructions place the growth plate at risk so I attempt to treat most of these patients with a conservative program, with proprioceptive rehabilitation and the avoidance of side stepping sports. Reconstruction is delayed to skeletal maturity. However, in elite adolescent athletes with an acute rupture, I believe it is possible to repair their ligament early and to supplement this with a semitendonosis and gracilis reconstruction. It is possible to achieve this acute repair and augmentation while avoiding the growth late by performing the surgery within the epiphyses.

The vast majority of patients, however, fall into the young adult and middle aged groups. Males are more frequently seen than females, though this pattern is reversed in skiers where a disproportionate number of female skiers are injured.

The overall type of patient that one sees can be divided into those who definitely need or demand surgery, those who do not want nor warrant surgery, and those patients who require counseling about life style, functional requirements and the expectations of surgery. On one hand there are patients who are not very active, who are not sports minded and who, perhaps, ruptured their ACL on their first skiing holiday. These patients can be recommended a conservative approach.

At the other end of the scale is the athlete at the height of their career who depends on side-stepping activities for their continued economic well-being. The diagnosis having been made, there is little doubt that they should be recommended for early surgery and will be fit to resume full activities within six months. Not everyone is in agreement with this approach, as some athletes feel they would like to try conservative therapy first followed by reconstruction later if necessary. In many sports this may mean that a patient may miss two seasons of professional sport and they may only have 6 or 7 years at the top of their sport. This could therefore account for something like 30% of their playing life whereas if they are operated on urgently they can be back, after rehabilitation, in six months, and therefore only miss one season.

Between these two groups are those people who are keen to participate in community sports such as football, tennis and skiing. With these patients one needs to sit down and discuss the techniques and complications of the procedure, including the costs of the procedure and rehabilitation, the complications and morbidity of the technique, the time and commitment required in the rehabilitation phase and the expected results.

A further group requiring special consideration are those patients who present with a chronic ACL rupture with significant osteoarthrosis. They usually present with medial compartment osteoarthrosis following medial meniscectomy and an untreated ACL tear. It is important in these patients to determine and treat their chief complaint. An ACL reconstruction will stabilize the knee but will not result in significant improvement in the arthritic ache. Moreover, as the arthrosis progresses, capsular inflammation will result in significant stiffening of the knee, reducing the clinical instability.

Those patients who present with a chief complaint of arthritic medial compartment ache are best treated by a high tibial osteotomy. Those patients who present with instability as their primary problem will benefit from an ACL reconstruction accompanied with advice that the reconstruction will not significantly improve the medial compartment pain. Those patients who present with both significant instability and pain will benefit from a combined ACL reconstruction followed by high tibial osteotomy.

Surgical Techniques

The development of surgery for ACL instability has been proceeding over the last century. Techniques at the turn of the 20th Century used autograft semitendinosus and gracilis with variable results. Xenografts were employed in Germany in 1912, using Kangaroo tail tendon for ACL substitution. However, results were poor due to problems with infection and graft rejection.

It was not until the 1950's when Don O'Donoghue began to aggressively treat knee ligament injuries in American footballers, that a renewed interest in ACL surgery began. Don Slocum from Eugene, Oregon invented the pes plasty in association Bob Larson. This operation was a dynamic tendon transfer attempting to prevent the anterior draw by dynamic muscle contraction. This operation enabled many athletes to return to the sporting arena and I believe that its main function was that it enhanced the proprioceptive control of the knee joint.

With the advent of arthroscopy came renewed research into the anatomy and biomechanics of the normal and injured knee joint. Early anatomical studies finding damage to the lateral capsular ligaments at the time of ACL rupture, caused many of the operative procedures to be aimed at repairing the capsule. Dr. Jack Hughston from Columbus, Georgia, drew the world's attention to the significant of capsular lesions causing knee joint instability.

Following the failure of repair techniques to ensure stability, focus became centered on substitution-type intra-articular reconstructions. Various graft materials have been tried including autograft, allograft, xenograft and artificial ligaments.

Many centers in the world are using allograft patella or Achilles tendon, or allograft anterior cruciate transfers. I have been unhappy to use these techniques, as a rule, because of concerns about sterility and the possible transmission of viruses. In the past, xenografts have been tried and have failed due to infection and failure to be incorporated.

Artificial ligaments made of fibres such as Dacron or Gortex have also been tried with mixed success. There is an unacceptable failure rate within two years due to either mechanical failure or inflammatory synovitis secondary to breakdown products shed for the graft.

A ligament augmentation device (LAD, invented by Kennedy in London) has also been widely used. Most studies, however, have not demonstrated that the use of the LAD has any significant advantage over the patella tendon transfer alone.

The use of autograft reconstructions have so far shown the best long term results. The two most common techniques use either the semitendonosis and gracilis, or the middle third of the patella tendon.

Currently, my preferred surgical technique for the routine case, is one using an isolated mid-third patella tendon graft placed, and secured arthroscopically. This technique has many advantages over the previous types of surgery. The procedure is relatively non-invasive requiring only small incisions. The graft can be placed accurately at the isometric points and the fixation of the bone blocks within the femur and tibia with the interference fit screw technique is very secure. This allows early motion and rehabilitation. There is a low perioperative morbidity and a rapid return to the activities of daily living and employment.

I personally believe that the operation should be performed in the first week following injury when advantage can be taken of the second phase healing factors. Many authors disagree with this approach, stating that there is an increased rate of arthrofibrosis. It is this second phase healing that causes arthrofibrosis, and I feel that with excellent fixation of the graft and accelerated rehabilitation, this arthrofibrosis factor can be utilized to an advantageous effect towards the graft revascularization and regeneration. It is my practice therefore, to recommend operation within the first week to ten days following injury.


Anterior cruciate ligament rehabilitation has undergone considerable changes over the past decade. Intensive research into the biomechanics of the injured and the operated knee have led to a movement away from the techniques of the early 1980's characterized by post operative casting and delayed rehabilitation, to the current early rehabilitation program.

The major goals of rehabilitation following ACL surgery are:

  • restoration of joint anatomy;
  • provision of static and dynamic stability;
  • maintenance of the aerobic conditioning and psychological well being; and
  • early return to work and sport.

These have required the development of an intensive rehabilitation program in which the patient has to take an active involvement.

The graft undergoes physiological changes during its incorporation, as fibroblastic activity changes the biology of the graft to become more ligamentous. The graft is weakest between six and twelve weeks post operatively so programs must be designed to protect the graft during this period. On the other hand investigations into ligamentous healing have shown that progressive controlled loading provides a stimulus for healing which improves the quality of graft incorporation. More over, early immobilization has advantages such as maintenance of articular cartilage nutrition and retention of bone mineralization.

Kinematic research has shown quadriceps contraction causes greatest strain on the anterior cruciate ligament graft between 10° and 45° of flexion. The anterior cruciate ligament graft lacks the normal mechanoreceptors that provide biofeedback in the uninjured knee. All these factors must be taken into account when designing rehabilitation programs.

Our current accelerated rehabilitation program is divided into four phases. In the first one to two weeks the aims of therapy are to decrease pain and swelling, and increase the range of motion of the knee. A post-operative brace is ranged from 30 to 90° and is used until there is adequate quadriceps control. Physiotherapy including CPM is used immediately post operatively. In this early phase there is an emphasis on static contraction of the hamstrings and co-contractions of the hamstrings and the quadriceps. Crutch -walking with partial weight bearing is allowed and the usual modalities are used to reduce pain and swelling.

During the second phase, from two to six weeks, the emphasis is on increasing the range of motion, increasing weight bearing and gaining hamstring and quadriceps control. The patient is usually out of the brace by the third to fourth week. During this phase gait re-education and static proprioception exercises commence. This may include balancing on the affected leg, biofeedback techniques and pool work to maintain conditioning and range of motion.

During the third stage, from six to twelve weeks, emphasis is placed on improved muscular control, proprioception and general muscular strengthening. Proprioceptive work progresses from static to dynamic techniques including balance exercises on the wobble board and eventually jogging on a mini-tramp. The patient should have a full range of motion during this stage and gentle resistance work should be added. By the end of this period the patient should be able to cycle normally, swim with a straight leg kick and be able to jog freely on the mini-tramp.

The fourth phase of rehabilitation from twelve weeks to six months involves the gradual re-introduction of sports specific exercises aimed at improving agility and reaction times and increasing total leg strength.

An elite athlete who has had a technically well performed early reconstruction of the anterior cruciate ligament followed by an adequate and successful rehabilitation program, should be able to return to the field of his chosen sport between six and nine months. This has been achieved in many Australian, Olympic and professional athletes.


I would like to thank Dr. Bruce Caldwell for his support with the editing and reading of this text.

References (incomplete)

Hughston, J.C. Knee Ligaments - Injury and Repair, 1993.

O'Donohue, D.H. Treatment of Injuries to Athletes (4th Edition), 1984.

Cross, M.J. & Crichton, K.J. Clinical Examination of the Injured Knee, 1987.

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