What is the ACL?

exercise - phyiscal therapy

Ligaments are living ‘ropes’ which join one bone to another helping to form a joint. They guide, control and limit the motion of the bones.

The Anterior Cruciate Ligament (ACL) is one of the four distinct ligaments at the knee which connect the tibia to the femur (shin bone to thigh bone). It is commonly injured and does not commonly heal (even with immediate surgical repair). The result is a loss of stability and the development of abnormal motion causing excessive stress which may lead to damage of the knee joint.

How is the ACL Injured?

The ACL can be injured by contact or trauma, but it can also be injured in other ways such as landing from a jump with a twisting motion, or from a sudden change in direction. A severe direct force to the knee from the front or side may also tear the ACL, along with causing injury to bone and other ligaments.


Rehabilitation following anterior cruciate ligament (ACL) reconstruction has changed dramatically over the past few decades. The staff of Rehab Experts has several years of experience with patients sustaining injury to the anterior cruciate ligament. Over this time we have developed a progressive philosophical approach to rehabilitation following ACL reconstruction.

Our present philosophy on rehabilitation following ACL reconstruction has evolved through observation of our patients and documented clinical results. We have continually attempted to modify and update our protocol as a means of improving patients’ final outcome following surgical reconstruction. The ideal situation is one in which the patient with ACL deficiency undergoing surgical reconstruction will ultimately have a result of excellent stability, full range of motion and strength, and normal function.


Rehabilitation should commence prior to surgery. After an ACL injury, deficits occur in strength, proprioception, muscle timing and gait patterns. In fact, strength and proprioceptive alterations occur in both the injured and uninjured limb. The primary impairment with an ACL deficient knee is instability. This is manifested by episodes of ‘giving way’, which can lead to further joint damage and ultimately, long term degenerative changes. Research has demonstrated that physical therapy provided pre-operatively is effective in increasing strength and balance which may limit the number the episodes of ‘giving way’ and decrease the incidence of re-injury in the ACL deficient knee. The main goals of a ‘pre-rehabilitative’ program prior to surgery include: full range of motion equal to the opposite knee, minimal joint swelling, adequate strength and neuromuscular control, and a positive state of mind. All of these factors facilitate optimal post-operative recovery. It is important to maintain the highest level of strength and function possible in the unaffected leg as it will be used for comparison to assess the progress of the reconstructed knee, in the later stages of rehabilitation.


After ACLR it is important to restore and maintain full range of motion (ROM) in the knee. Quadriceps re-training has been found to improve ROM in the early stages. Attaining full knee extension as early as possible is not deleterious to the graft or to joint stability and may prevent patellofemoral pain and compensatory gait pathologies. A stretching program is incorporated to maintain lower extremity flexibility. Research recommends that a 30 second stretch is sufficient to increase ROM in most healthy people. It is likely that longer periods of time, or more repetitions, are required for those individuals with injuries or with larger muscles. Body mass has been shown to be positively correlated with muscle stiffness (i.e., the bigger the muscle, the more stiffness/tension there exists). Therefore, for larger muscle groups in the lower extremity, it is suggested to increase in the number of repetitions (ie. 3-5 times) for optimal flexibility.



Altered gait kinematics from quadriceps dysfunction is typical during the first stages post ACL reconstruction. Typical adaptations include reduced cadence, stride length, altered swing and stance phase knee ROM, and decreased knee extensor torque with hip and/or ankle extensor adaptations. Early weight bearing is advocated post ACLR in an attempt to restore gait kinematics in a timely fashion, facilitate vastus medialis function and decrease the incidence of anterior knee pain.

Treadmill training in the middle stages of rehabilitation can further assist in normalizing lowerextremity ROM across all joints, especially with incline or backwards walking. Backwards treadmill walking has been shown in the literature to increase ROM and increase functional quadriceps strength, while minimizing patellofemoral stress. It is also beneficial for specific return-to-sport preparation requiring a re-training of backwards locomotion.


Muscle analyses of the quadriceps post ACL injury have shown: i) similar degrees of atrophy in both type I (oxidative/endurance) and II (glycolytic/fast-twitch) muscle fibres, and ii) physiological metabolic shifts in muscle fibres from gylcolytic into oxidative compositions. This means that ACL rehabilitation must include variable training parameters, which range from an endurance program of low load/ high repetitions to a strength oriented phase of high load/low repetitions to focus on these deficits.

Depending on the graft type used for ACLR (patellar tendon vs. semitendonosis/gracilis),specific strength deficits have been found. With the patellar tendon graft, there are low velocity concentric extensor deficits specific to 60-95°; with the hamstring graft, there are high velocity, eccentric flexor deficits specific to 60-95°. Strengthening exercises need to be velocity, ROM and contraction specific to address these deficits.

  • Open (OKC) and Closed (CKC) Kinetic Chain Exercises

OKC exercises have previously been contraindicated in ACLR patients for 6 months up to a year post-operatively, although the concern about the safety of OKC training in the early period after ACLR may not be well founded. It was originally thought that OKC exercises increased anterior tibial translation, with the possibility of increasing strain on the new graft. However, research has demonstrated that there are minimal strain differences between OKC leg extension and CKC activities such as squatting. With the addition of OKC training, subjects have shown increased quadriceps torque increases without significant increases in laxity. Researchers are now advocating the addition OKC exercises, at the appropriate time and within a restricted range, to complement the classic CKC rehabilitative program.

  • Quality vs. Compensation

Physical therapist often feel compelled to progress patients by giving them new exercises each time they are in for therapy. It cannot be stressed enough that it is not beneficial to give patients exercises they are not neuromuscularly ready for. It is very important to observe the quality of the exercises that are being performed, specifically with CKC exercises. Weaknesses in specific muscle groups lead to compensations, which produce faulty movement patterns. These faulty patterns are then integrated into unconscious motor programs, which perpetuate the original weakness. Specifically, the research has indicated that knee extensor moment deficits are compensated for by hip and/or ankle extensor moments. If these are allowed to occur and are not corrected, any joint or structure along the kinetic chain may be exposed to injury.

For example: A squat or lunge must be performed with the trunk perpendicular to the ground (to avoid excessive hip flexion), the iliac crests must be level (to avoid Trendelenburg/hip hiking), and the knee must be over the foot with the tibia perpendicular to the floor (to avoid excessive dorsiflexion). It is better to decrease the range of movement (half squat vs. full squat) than to do the exercise at a level that is too difficult to perform correctly without compensation.

  • Precautions with Hamstring Grafts

The typical donor graft for ACLR at this facility is the hamstring (semitendinosis / gracilis). Careful measures must be taken to avoid overstressing the donor area while it heals. Although, isolated hamstring strengthening is initiated around the six-week mark in this group, it is important for the therapist to be aware of the natural stages of healing. There may be too much stress too early if the patient reports pain at the donor site during or after specific exercises.


Ideally proprioception should be initiated immediately after injury (prior to surgery), as it is known that proprioceptive input and neuromuscular control are altered after ACL injury. By challenging the proprioceptive system though specific exercises, other knee joint mechanoreceptors are activated that produce compensatory muscle activation patterns in the neuromuscular system that may assist with joint stability. Post-operatively, proprioceptive training should commence early in the rehabilitation process in order to begin neuromuscular integration and should continue as proprioceptive deficits have been found beyond 1 year post ACLR.

Proprioceptive exercises have been shown to enhance strength gains in the quadriceps and hamstring muscles post ACLR. In the later stages of rehabilitation, anticipated and unanticipated perturbation training is effective in improving dynamic stability of the knee. A dynamically stable joint is the result of an optimally functioning proprioceptive and neuromuscular system and functional outcome has been proven to be highly correlated with balance in the reconstructed ACL.


Gradual return to sport is initiated at the 6-9 month mark only if the individual’s knee does not present with pain or effusion, during or after functional sport specific training drills. The individual must also be able to demonstrate the appropriate strength and endurance needed for their specific sport. This recommendation is based on the evidence that knee cartilage and subchondral bone are damaged during the initial ACL trauma and may need additional time to recover in order to minimize the predisposition for future joint arthrosis.

A further consideration when returning the patient to sport is that a cautionary approach should be taken with the use of the uninjured limb as a comparison for a rehabilitation endpoint. It has been demonstrated in the literature that a significant detraining effect occurs in the quadriceps and hamstring muscles in both injured and uninjured extremities.


Bracing should be discussed with the physical therapist and surgeon prior to return to sport or strenuous activities post ACLR. The decision will be dependent on a number of factors including: type of sport, position, activity level and complexity of the initial injury. Some surgeons may recommend a rigid, functional knee brace or a neoprene sleeve. Research has demonstrated that a rigid knee brace does not provide superior outcomes when compared with a neoprene sleeve after ACLR. Bracing has not been proven to prevent re-injury or improve clinical outcomes after ACLR. However, there is evidence that any type of knee bracing (rigid /soft) improves proprioception measures.

Who can guide me for these protocols?

Our group handles such cases. We can guide the patient in following his or her assigned program from pre-operative to his or her resumption of sports or other activities. We provide physical therapy home program in Metro Manila.

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University of Calgary faculty of kinesiology http://www.sportmed.ucalgary.ca/node/100
Chester Knee Clinic and Cartilage Repaie Center http://www.kneeclinic.info/rehab_markdecarlo.php
Fowler Kenedy Sports Clinic

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