ACL Injury Rehabilitation: What to Expect from Physio

What Is the ACL?

The anterior cruciate ligament (ACL) is one of four major ligaments in the knee joint. It runs diagonally through the centre of the knee, connecting the femur (thighbone) to the tibia (shinbone). The ACL's primary function is to prevent excessive forward translation of the tibia relative to the femur and to provide rotational stability to the knee.

The ACL works in concert with the posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL) to maintain knee joint stability during weight-bearing activities. It is particularly important during cutting, pivoting, and deceleration movements — which is why ACL injuries are so common in sports such as football, netball, basketball, and skiing.

How ACL Injuries Occur

Approximately 70% of ACL injuries occur through non-contact mechanisms. The most common scenario involves a sudden deceleration, change of direction, or landing from a jump with the knee in a vulnerable position — typically near full extension with the knee collapsing inward (valgus). Contact injuries, such as a direct blow to the outer knee, account for the remaining 30%.

In Australia, ACL injuries are a significant public health concern. Research published in the Medical Journal of Australia found that Australia has one of the highest rates of ACL reconstruction surgery in the world, with approximately 200,000 reconstructions performed over a 15-year period.

Diagnosis

ACL injuries are typically diagnosed through a combination of clinical assessment and imaging. Common signs include an audible "pop" at the time of injury, rapid knee swelling (within hours), knee instability (the knee giving way), and difficulty bearing weight. Physiotherapists and sports doctors use specific clinical tests — including the Lachman test, anterior drawer test, and pivot shift test — to assess ACL integrity.

MRI is the gold standard imaging modality for confirming ACL tears and identifying associated injuries to the menisci, cartilage, or other ligaments. These associated injuries occur in approximately 50–70% of ACL ruptures and can influence management decisions.

Surgical vs Conservative Management

ACL Reconstruction Surgery

ACL reconstruction involves replacing the torn ligament with a graft, most commonly harvested from the patient's own hamstring tendons or patellar tendon (autograft). The procedure is performed arthroscopically and typically takes one to two hours.

Surgical reconstruction is generally recommended for:

• Active individuals who wish to return to pivoting or cutting sports
• Patients with recurrent episodes of knee instability
• Combined ligament injuries or significant associated meniscal tears
• Young, active patients with high functional demands

Conservative (Non-Surgical) Management

Conservative management involves structured physiotherapy rehabilitation without surgical reconstruction. The landmark KANON trial (Frobell et al., 2013) demonstrated that early reconstruction was not superior to initial rehabilitation plus optional delayed reconstruction for young, active adults. This finding established that conservative management with physiotherapy is a viable option for many patients.

Conservative management may be appropriate for:

• Older or less active individuals
• Patients without functional instability during daily activities
• Partial ACL tears with preserved stability
• Patients who do not intend to return to high-level pivoting sports

Rehabilitation Phases

ACL rehabilitation follows a criterion-based progression, meaning advancement to the next phase depends on achieving specific milestones rather than fixed timelines. The timeframes below are approximate guides for post-surgical rehabilitation.

Phase 1: Protection and Early Recovery (Weeks 0–2)

The primary goals in this phase are to manage pain and swelling, protect the healing graft (if surgical), and restore basic knee range of motion.

• RICE protocol: Rest, ice, compression, and elevation to manage acute inflammation
• Range of motion: Gentle passive and active-assisted knee flexion and extension; achieving full extension (0°) is a priority
• Quadriceps activation: Isometric quadriceps contractions, straight leg raises, and electrical muscle stimulation if needed
• Weight bearing: Typically weight-bearing as tolerated with crutches; gait training to normalise walking pattern
• Bracing: A hinged knee brace may be prescribed, depending on surgeon preference

Phase 2: Early Strengthening (Weeks 2–6)

This phase focuses on progressively restoring range of motion, improving quadriceps and hamstring strength, and normalising gait without crutches.

• Range of motion target: Full extension; flexion progressing towards 120°
• Exercises: Seated knee extensions (limited range), leg press, calf raises, stationary cycling, pool-based exercises
• Gait training: Progressing from crutches to unaided walking with a normal gait pattern
• Proprioception: Basic balance exercises on stable surfaces progressing to unstable surfaces
• Milestone: Full knee extension, ability to perform a straight leg raise without quadriceps lag

Phase 3: Progressive Strengthening (Weeks 6–12)

Strengthening intensifies with the goal of restoring muscle bulk and endurance, particularly in the quadriceps and hamstrings.

• Exercises: Squats, lunges, step-ups, Romanian deadlifts, hamstring curls, leg press with increasing load
• Balance and proprioception: Single-leg balance, perturbation training, wobble board exercises
• Cardiovascular fitness: Cycling, swimming, aqua jogging, elliptical trainer
• Milestones: Full pain-free range of motion, limb symmetry in basic strength tests approaching 60–70%

Phase 4: Running and Agility (Months 3–6)

Return to running is a significant milestone in ACL rehabilitation. It is typically permitted around three to four months post-surgery, provided specific criteria are met.

• Running criteria: Full pain-free range of motion, quadriceps strength at least 70% of the uninjured limb, ability to hop on the affected leg without pain or apprehension
• Running progression: Walk/jog programme progressing to continuous jogging, then interval running
• Agility drills: Lateral shuffles, carioca, figure-of-eight running, progressive cutting drills
• Strengthening: Continued heavy resistance training, plyometric introductions (box jumps, drop landings)
• Milestones: Limb symmetry index above 80% for quadriceps and hamstrings, symmetrical running mechanics

Phase 5: Return to Sport (Months 6–12)

The final phase focuses on sport-specific training, psychological readiness, and meeting objective return-to-sport criteria.

• Sport-specific drills: Position-specific skills, reactive agility, contact preparation (if applicable)
• Plyometrics: Advanced jumping, bounding, and landing exercises
• Graduated return to training: Modified training → full team training → match play
• Psychological readiness: Confidence in the knee, reduced fear of re-injury, assessed using validated questionnaires (e.g., ACL-RSI)

Return-to-Sport Criteria

Returning to sport too early is the single greatest risk factor for ACL re-injury. Research shows that for every month return to sport is delayed (up to nine months post-surgery), the re-injury rate decreases by 51%. Current best-practice guidelines recommend meeting all of the following criteria before returning to pivoting sports:

• At least nine months post-surgery (some surgeons recommend 12 months)
• Quadriceps strength limb symmetry index (LSI) ≥ 90%
• Hamstring strength LSI ≥ 90%
• Hop test battery LSI ≥ 90% (single hop, triple hop, crossover hop, timed hop)
• Successful completion of on-field sport-specific training without symptoms
• Psychological readiness (ACL-RSI score ≥ 56)

The Role of Physiotherapy

A physiotherapist is your primary guide throughout ACL rehabilitation. Their role includes:

• Pre-operative rehabilitation (prehab): Optimising knee range of motion and quadriceps strength before surgery has been shown to improve post-operative outcomes
• Post-operative management: Guiding safe progression through each rehabilitation phase
• Exercise prescription: Designing and progressing your individualised exercise programme
• Manual therapy: Mobilisation techniques to restore range of motion and manage scar tissue
• Objective testing: Performing strength and hop tests to guide progression and return-to-sport decisions
• Education and support: Addressing concerns, managing expectations, and supporting psychological recovery

Preventing ACL Injuries

Neuromuscular training programmes have been shown to reduce ACL injury rates by 50–70% in at-risk populations. The FIFA 11+ warm-up programme, the Netball KNEE programme, and similar protocols focus on:

• Landing and cutting technique (avoiding knee valgus collapse)
• Hamstring and gluteal strengthening
• Proprioception and balance training
• Plyometric control drills
• Core stability exercises

These programmes are most effective when performed at least two to three times per week as part of a regular warm-up routine.

For related reading, see our guides on knee pain physiotherapy, sports physiotherapy in Australia, and lower back pain.