What is an ACL Injury?
Anterior Cruciate Ligament (ACL) injuries are common among athletes, typically occurring during pivoting, planting, or cutting movements. Patients often report hearing a “pop” at the time of injury, followed by immediate swelling, pain, and knee instability, which often halts athletic activity. Swelling generally peaks within 72 hours due to the ligament’s high vascularity, and knee effusion may persist for 2-3 months.
Effects on Mobility and Function
ACL injuries can cause stiffness and difficulty extending the knee, impacting both walking and functional movements. Surrounding structures, such as the meniscus, ligaments (LCL, MCL), cartilage, and muscles, may also be affected, leading to deficits in dynamic knee stability. These deficits arise from structural, muscular, and neural factors, and while some individuals compensate through neuromuscular adaptations, others may require surgery.
The Sensory Role of the ACL
The ACL functions as a sensory organ, and its injury disrupts proprioception, making movement planning more challenging. Arthrogenic inhibition from swelling can hinder quadriceps activation, contributing to muscle atrophy and rapid strength decline. This not only affects short-term sports performance but also increases the risk of long-term issues, like knee osteoarthritis (OA).
Expectations vs. Reality Post-Injury
Research highlights a gap between athletes’ expectations and reality post-ACL injury. Feucht et al. (2016) found most individuals expect to return to normal function after surgery, but Grindem et al. (2015) reported only 57% achieve this outcome. Among those undergoing ACL reconstruction (ACLR), only 42% return to sport within a year, despite 91% expecting to do so (Ardern et al., 2014). Long-term, 58% of individuals develop mild osteoarthritis 20 years after an ACL injury (Risberg et al., 2016).
Rehabilitation Strategies
There are three primary rehabilitation pathways following an ACL injury:
- Rehabilitation Alone
- ACL Reconstruction (ACLR) and Rehabilitation
- Rehabilitation-ACLR-Rehabilitation
Prehabilitation and early rehabilitation enhance outcomes post-ACLR. Some patients manage knee instability with rehabilitation alone, while others may opt for surgery if symptoms persist.
The Role of Prehabilitation
The KANON Trial (Frobell, 2010), one of the largest and longest ACL studies, showed that prehabilitation can be as effective as immediate surgery, with both surgical and non-surgical groups achieving similar functional outcomes (KOOS 75-80/100). The Compare Trial revealed comparable results between ACLR and conservative management in less active individuals, with 50% of the non-surgical group avoiding surgery (Reijman, 2021). Filbay (2023) found spontaneous ACL healing in 30% of non-surgical participants after 2 years, suggesting that a patient-centered approach, rather than an automatic return to pivoting sports, may be more appropriate.
Types of Grafts and Recovery
For patients who experience instability post-rehabilitation, surgery may be recommended. Graft options include patellar, hamstring, quadriceps, or allograft, each with its own pros and cons. Recovery has shifted from time-based to criteria-based, focusing on functional milestones rather than a strict timeline. Despite the importance of rehabilitation, only 5% of patients complete the recommended rehab, with 95% receiving sub-optimal care. Most ACLR patients complete less than 6 months of rehab, falling short of the 9-month minimum required for safe return to sport.
Key Factors Influencing Recovery
Key predictors of successful ACLR recovery include the absence of meniscus injury, better function post-injury, lower BMI, and non-smoking status. Young male athletes and those with a positive psychological response to injury also tend to have better outcomes. The most important factor for recovery is quadriceps strength. In high-quality rehab programs, 80% of patients achieve >90% quad symmetry within a year, compared to only 30% in undertreated patients (Eber et al., 2017; Logerstedt et al., 2012).
A clinical trial (Hazzard, 2023) showed that females typically achieve 90% quad symmetry between 8.4-10.2 months, while males reach this milestone between 7-8.7 months, depending on graft type.
Recovery Phases and Goals
ACL recovery is divided into several phases:
- Pre-Op
- No knee effusion
- Full range of motion (ROM)
- 90% quadriceps strength symmetry
- Early Stage
- No effusion
- Full ROM
- Strength without quad lag
- Mid-Stage
- Control of terminal knee extension in weight-bearing
- 80% strength and hop test symmetry
- Late Stage
- 90% quadriceps strength symmetry
- Progression of functional skills and confidence
- Return to Sport
- Maintain muscle strength and dynamic knee stability
- Manage activity load
Conclusion
ACL injuries can significantly impact both lifestyle and athletic participation. Growing evidence suggests conservative management can be just as effective as surgery. It’s important to focus on criteria-based rehabilitation instead of rushing into surgery. The traditional idea of returning to pivoting sports as a benchmark for ACLR may no longer be valid, especially with evidence of spontaneous healing and comparable outcomes in conservative management.
If you or someone you know is navigating an ACL injury or considering surgery, reach out to us for an appointment or a free discovery visit to explore your options.
References:
- Feucht, M. J., et al. (2016). Patient expectations of primary and revision anterior cruciate ligament reconstruction. Knee Surgery, Sports Traumatology, Arthroscopy, 24, 201-207.
- Grindem, H., et al. (2015). How does a combined preoperative and postoperative rehabilitation programme influence ACL reconstruction outcomes? British Journal of Sports Medicine, 49(6), 385-389.
- Ardern, C. L., et al. (2014). Fifty-five per cent return to competitive sport after ACL reconstruction: a systematic review and meta-analysis. British Journal of Sports Medicine, 48(21), 1543-1552.
- Filbay, S. R., et al. (2023). Evidence of ACL healing on MRI following ACL rupture treated with rehabilitation alone. British Journal of Sports Medicine, 57(2), 91-99.
- Frobell, R. B., et al. (2010). A randomized trial of treatment for acute anterior cruciate ligament tears. New England Journal of Medicine, 363(4), 331-342.
- Reijman, M., et al. (2021). Early surgical reconstruction versus rehabilitation for ACL rupture: COMPARE trial. BMJ, 372.
- Hazzard, S., et al. (2024). Establishing quadriceps symmetry expectations based on time from surgery after ACL reconstruction. International Journal of Sports Physical Therapy, 19(4), 410.