Not Just Rest and Ice: The Science of ACL Rehabilitation

Written By VENUS CHENG

Anterior Cruciate Ligament (ACL) injuries are among the most common knee injuries faced by athletes and active individuals. Whether you're recovering from surgical reconstruction or managing a partial tear conservatively, a structured and evidence-based rehabilitation program is essential for restoring knee function and preventing re-injury.

Understanding the ACL – Anatomy & Function

The Anterior Cruciate Ligament (ACL) is one of the four key ligaments in the knee joint connecting the femur (thigh bone) to the tibia (shin bone). It originates from the anterior intercondylar area of the tibia and inserts into the posteromedial side of the lateral femoral condyle. The orientation enables three critical biomechanical functions:

  • Prevents Anterior Tibial Translation

  • Stabilizes rotational forces

  • Restricts Knee Hyperextension

ACL injuries most commonly occur during sports that involve sudden deceleration, pivoting, or awkward landings - such as football, basketball and skiing. The ligament is particularly vulnerable when an athlete plants their foot and rapidly changes direction, creating excessive rotational forces on the knee joint. When the ACL tears, people often describe a “popping” sound or sensation, followed by swelling, pain and a sense of instability.

ACL Rehabilitation Protocol

The ACL rehabilitation protocol progresses through five phases, each with specific objectives, exercises and criteria for advancement.

Phase 1: Recovery from Surgery

  • Reduce swelling and pain

  • Restore full passive knee extension

  • Reactivate quadriceps muscles

Immediate intervention following ACL injury or reconstruction is critical for optimal recovery. The initial rehabilitation phase focuses on restoration of full passive knee extension and quadriceps muscle function through range of motion exercises (e.g., quadriceps sets, active straight leg raise, prone hang, and heel slides), as well as effusion management.

Phase 2: Strength & Neuromuscular Control

  • Regain single leg balance

  • Regain muscle strength

  • Perform single leg squat with good technique and alignment

This phase integrates strength and neuromuscular training to restore dynamic stability and functional capacity. Neuromuscular exercises—including perturbation training and balance drills—progress from internal focus on proper movement patterns to external challenges like unstable surfaces. Concurrent strength training evolves from high-repetition, low-load exercises to heavy resistance training with lower repetitions, systematically incorporating both bilateral and unilateral movements to rebuild power and endurance.

Phase 3: Running, Agility and Landings

  • Regain full strength and balance

  • Attain excellent hopping performance

  • Progress through an agility program

This phase builds dynamic function through progressive running, jumping, and agility drills. Athletes start with straight-line running, advance to cutting maneuvers, and master proper landing mechanics. Plyometrics progress from double-leg to single-leg jumps while monitoring knee alignment.

Phase 4: Return to Sport

This phase adopts a patient-centered approach, meticulously tailored to the specific biomechanical demands and psychological readiness of each individual.

Phase 5: Prevention of Re-injury

To sustain recovery and prevent re-injury, athletes should continue structured prevention programs at least twice per week. Careful load management remains critical to avoid sudden spikes in training intensity that could compromise knee stability.

ACL recovery isn’t just about healing—it’s about rebuilding smarter. A structured, evidence-based rehabilitation program restores strength, stability, and confidence while reducing re-injury risks. The key? Progress through phases, meet objective milestones, and commit to long-term injury prevention. Your strongest comeback starts with patience and follows the evidence.

Reference

[1] Cooper, Randall, et al. ACL Melbourne ACL Rehabilitation Guide 2.0 a Criteria Driven ACL Rehabilitation Protocol and Guide for Both Clinicians and People Who Have Undergone a Surgical Reconstruction of the Anterior Cruciate Ligament (ACL). Melbourne ACL Rehabilitation Guide ACL Rehab. 2018.

[2] Filbay, Stephanie R, and Hege Grindem. “Evidence-based recommendations for the management of anterior cruciate ligament (ACL) rupture.” Best practice & research. Clinical rheumatology vol. 33,1 (2019): 33-47. doi:10.1016/j.berh.2019.01.018

[3] Ocran, Edwin. “Anterior Cruciate Ligament.” Kenhub, 30 Oct. 2023, www.kenhub.com/en/library/anatomy/anterior-cruciate-ligament.

[4] Physiopedia. “Anterior Cruciate Ligament (ACL) Rehabilitation.” Physiopedia, 2010, www.physio-pedia.com/Anterior_Cruciate_Ligament_(ACL)_Rehabilitation.

VENUS CHENG