Anterior Cruciate Ligament (ACL) Injuries
What is an ACL Injury or Rupture?
An ACL rupture is a tear of the anterior cruciate ligament (ACL), one of the main ligaments that helps keep your knee stable. The ACL runs inside the knee and connects your thigh bone (femur) to your shin bone (tibia). Its job is to control twisting and forward movement of the shin bone, especially during cutting, pivoting, or sudden stops.
When the ACL ruptures, the knee can feel unstable, weak, or like it might “give way.” This often happens during sport or activity that involves rapid direction changes, landing awkwardly, or sudden deceleration. Many people feel or hear a “pop” at the time of injury, followed by swelling and difficulty continuing activity.
Impact of ACL Injuries
Anterior cruciate ligament (ACL) injuries are common, particularly among young, physically active individuals, with an estimated 200,000 cases annually in the US.[1-2] These injuries disproportionately affect females participating in similar sports, with a two- to eightfold higher rate compared to males.[2] Functional consequences include recurrent instability, reduced activity, and increased risk of secondary osteoarthritis.[1-2] Key risk factors for both initial injury and re-injury include younger age, higher pre-injury activity level, and participation in pivoting/cutting sports.[2]
The consequences of a knee with an untreated or continuously unstable anterior cruciate ligament (ACL) injury that does not undergo surgery or rehabilitation are significant for both healthcare costs and patient quality of life.
For patient quality of life, persistent knee instability leads to recurrent episodes of “giving way,” decreased activity levels, and poor knee-related quality of life. There is a substantially increased risk of secondary meniscal injury and accelerated development of knee osteoarthritis, which further impairs function and quality of life over time.[1-2] Long-term studies show that knee-related quality of life remains impaired for decades after ACL injury, regardless of initial treatment, but untreated instability is associated with greater symptomatic osteoarthritis and functional limitations.[3-4] Patients often experience chronic pain, reduced ability to participate in sports or physically demanding work, and psychological distress due to ongoing disability.[1-2][5]
For healthcare costs, untreated or unstable ACL injuries result in higher long-term costs due to increased rates of secondary injuries (meniscal injuries, and osteoarthritis), subsequent surgeries (including meniscectomy, late ACL reconstruction, and even total knee replacement), and management of osteoarthritis.[4][6] Economic analyses demonstrate that unstable knees without appropriate intervention incur greater indirect costs from lost productivity, work disability, and increased healthcare utilisation over a patient’s lifetime.[6] The societal cost of non-reconstructed, unstable ACL injuries is substantially higher than that of early surgical reconstruction or structured rehabilitation, primarily due to the downstream effects of chronic instability and joint degeneration
Overview of Treatment
Management options include conservative rehabilitation, surgical reconstruction, and, more recently, the cross-bracing protocol. [1][3]
- Conservative management involves structured physiotherapy focused on strength, proprioception, and gradual return to activity.
- Surgical reconstruction typically uses autografts (patellar tendon, hamstring, or quadriceps) to restore stability, especially in patients with high functional demands or persistent instability. [2]
- Cross-bracing protocol immobilizes the knee at 90° flexion for 4 weeks, followed by progressive range-of-motion and supervised rehabilitation. [3]
Indications for surgery include persistent instability, and failed conservative management. Contraindications for surgery include advanced age, and comorbidities – however the most important factor is to ensure you have engaged in shared decision making with your physiotehrapist and specialist.[2]
Randomized Controlled Trials: Key Results and Takeaways
Major RCTs (KANON, COMPARE, ACL SNNAP) confirm that structured rehabilitation is a reasonable first-line approach for many patients, with up to 40–50% of those initially managed nonoperatively eventually opting for delayed reconstruction due to instability or functional limitations. [1][7]
- The COMPARE trial found that younger, more active patients were more likely to fail nonoperative management and require delayed surgery, typically within 3–6 months. [7]
- The ACL SNNAP trial showed no significant difference in quality-of-life or functional outcomes between rehabilitation and reconstruction at 1 year, but a substantial proportion of conservatively managed patients ultimately required surgery. [1]
- The cross-bracing protocol demonstrated MRI evidence of ACL healing in 90% of patients at 3 months, with better functional outcomes and return-to-sport rates in those with more complete healing. [3]
Guideline Recommendations and Decision-Making
The American Academy of Orthopaedic Surgeons (AAOS) recommends a patient-centered, risk-stratified approach, emphasizing shared decision-making. [2]
- Initial management should be individualized based on instability, age, and patient preferences. [2][7]
- Criteria for surgery include persistent instability, and failure of rehabilitation. [2]
- Rehabilitation protocols are be criterion-based, with return-to-sport only after achieving ≥90% limb symmetry in strength and hop tests, and psychological readiness.[2]
Special Scenarios: First-Time Ruptures, Graft Failures, and High-Risk Groups
For first-time ACL ruptures, initial rehabilitation is appropriate for most, with better outcomes for surgery for those with high recurrent instability.
- Graft failures are typically managed with revision reconstruction, especially in younger, active patients. [2]
- High-risk groups (skeletally immature, elite athletes, or those with concomitant meniscal injuries) may benefit from early surgical intervention. [2]
- Skeletally immature patients require careful consideration of growth plate status and may need specialized surgical techniques.[2]
In summary, both structured rehabilitation and surgical reconstruction are valid options for ACL injury, with management tailored to patient-specific risk factors, activity demands, and preferences.
How Physiotherapy Helps
Physiotherapy is central to anterior cruciate ligament (ACL) rupture rehabilitation, whether managed conservatively (including cross bracing) or surgically. For conservative management, physiotherapy focuses on restoring range of motion, progressive strengthening of the quadriceps, hamstrings, hip abductors, and core, and neuromuscular training to optimize knee stability and function. Supervised rehabilitation is recommended for at least 3 months, with regular reevaluation to assess progress and determine if delayed surgery is needed. Functional bracing is not shown to restore stability, but protocols such as cross bracing (immobilization at 90° flexion, gradual ROM increase, and goal-oriented physiotherapy) have demonstrated MRI evidence of ACL healing and improved patient-reported outcomes, especially when healing is robust.[1-3]
For surgical management, physiotherapy begins within the first week postoperatively and continues for 6–9 months. The goals are to restore full range of motion, prevent muscle hypotrophy, reduce pain and swelling, and protect the reconstructed ligament and any meniscal repairs. Rehabilitation includes cryotherapy, immediate weight bearing as tolerated, eccentric quadriceps and hamstring strengthening, closed and open kinetic-chain exercises, and neuromuscular/agility training. Progression is criterion-based, with objective milestones guiding return to sport, typically at 9–12 months post-op. Psychological readiness and functional performance are also assessed before clearance for sport.[1][4-5]
The value physiotherapy adds includes improved functional outcomes, reduced risk of reinjury, and optimised return to activity. The American Academy of Orthopaedic Surgeons emphasises individualised management based on patient goals and activity demands, with physiotherapy as a cornerstone in both nonoperative and operative pathways.[6] Supervised rehabilitation is consistently more effective than unsupervised programs.[5]
References
1.
Beard DJ, Davies L, Cook JA, et al.
Lancet (London, England). 2022;400(10352):605-615. doi:10.1016/S0140-6736(22)01424-6.
2.
Brophy RH, Lowry KJ.
The Journal of the American Academy of Orthopaedic Surgeons. 2023;31(11):531-537. doi:10.5435/JAAOS-D-22-01020.
3.
Filbay SR, Dowsett M, Chaker Jomaa M, et al.
British Journal of Sports Medicine. 2023;57(23):1490-1497. doi:10.1136/bjsports-2023-106931.
Leading Journal
4.
Saueressig T, Braun T, Steglich N, et al.
British Journal of Sports Medicine. 2022;56(21):1241-1251. doi:10.1136/bjsports-2021-105359.
5.
Surgical Versus Conservative Interventions for Treating Anterior Cruciate Ligament Injuries.
Monk AP, Davies LJ, Hopewell S, et al.
The Cochrane Database of Systematic Reviews. 2016;4:CD011166. doi:10.1002/14651858.CD011166.pub2.
6.
Filbay SR, Bullock G, Russell S, et al.
Sports Medicine (Auckland, N.Z.). 2025;:10.1007/s40279-025-02268-5. doi:10.1007/s40279-025-02268-5.
7.
van der Graaff SJA, Meuffels DE, Bierma-Zeinstra SMA, et al.
The American Journal of Sports Medicine. 2022;50(3):645-651. doi:10.1177/03635465211068532.
Beyond Rehab Physiotherapy 