Anterior Cruciate Ligament (ACL) Injury.
What is the ACL?
The ACL is a ligament that connects the femur (thigh bone) to the tibia (shinbone) and is responsible for stabilising the knee joint. More specifically, it runs diagonally inside the knee from the posterior lateral femoral condyle to the anterior medial tibial plateau, and its primary roles are preventing anterior translation of the tibia on the femur and resisting rotational forces — the combined loading that makes pivoting sports so demanding on this structure.
The ACL has poor intrinsic healing capacity compared to the MCL — it lies within the joint capsule in a relatively avascular environment, meaning it does not spontaneously repair after complete rupture the way extra-articular ligaments do. This biological reality is central to the surgery versus conservative management decision.
How do ACL injuries occur?
ACL injuries occur when the ligament is stretched or torn, often as a result of a sudden twisting motion or direct impact to the knee. The most common mechanism is a non-contact pivoting or cutting action — landing from a jump with the knee in valgus, decelerating suddenly and changing direction, or rotating on a planted foot. Contact injuries — typically a direct blow to the lateral knee producing valgus collapse — are less common but well recognised.
ACL injuries are disproportionately common in female athletes — the incidence in sports like netball, football and basketball is two to eight times higher in women than men, attributable to a combination of anatomical, hormonal and neuromuscular factors. Understanding this disparity has driven significant research into ACL injury prevention programs — of which the FIFA 11+ and equivalent neuromuscular training protocols have strong evidence for reducing ACL injury rates in at-risk populations.
Surgery or conservative management — what does the evidence say?
This is the most important and most debated question in ACL management, and the answer has shifted considerably in recent years.
Traditionally, ACL reconstruction was considered the default for active patients, particularly those returning to pivoting sport. The evidence base for this position has been substantially revised. Several high-quality randomised controlled trials — including the landmark KANON trial and the more recent COMPARE trial — have shown that a significant proportion of patients with complete ACL tears can achieve excellent long-term outcomes with structured rehabilitation alone, without surgery. The five-year outcomes for physical activity level, knee function and osteoarthritis rates between surgical and non-surgical groups are more similar than previously appreciated.
The current evidence supports an individualised approach: younger patients returning to high-level pivoting sport, those with associated injuries (meniscal tears, multi-ligament injuries), and those with significant persistent instability after rehabilitation are more likely to benefit from surgery. Older patients, those in lower-demand activities, and those who achieve good stability with rehabilitation are increasingly managed conservatively with comparable outcomes.
The concept of "ACL rehabilitation and return-to-sport first" — also called the MOON and KANON protocol approach — involves completing a structured rehabilitation program and then making the surgery decision based on whether instability persists, rather than defaulting to surgery immediately. This approach is gaining traction in evidence-based practice
.
What are the symptoms?
Symptoms of an ACL injury include sudden pain, swelling, a popping sound or sensation in the knee, and difficulty moving the joint. The acute haemarthrosis — rapid swelling from blood filling the joint — typically develops within two to four hours of the injury and is one of the most consistent features of a significant intra-articular knee injury. After the acute swelling settles, the primary symptom of ACL deficiency is instability — a giving way or unreliable feeling in the knee with pivoting, cutting and rotational movements.
How is it diagnosed?
A healthcare provider will typically perform a physical examination to assess the knee's stability and range of motion. They may also order imaging tests, such as an MRI, to confirm the diagnosis and evaluate the extent of the injury. The Lachman test — assessing anterior tibial translation with the knee at 30 degrees of flexion — is the most sensitive clinical test for ACL rupture. The pivot shift test, which reproduces the rotational instability, is the most specific. MRI confirms the diagnosis, assesses associated injuries (meniscal tears are present in 50 to 70% of acute ACL ruptures), and guides the surgical decision.
What does rehabilitation involve?
Whether surgical or conservative management is chosen, physiotherapy is central to outcomes in both pathways.
For conservative management, the goal is restoring dynamic knee stability through progressive quadriceps, hamstring, hip and calf strengthening combined with progressive neuromuscular and proprioceptive training. The rehabilitation progresses through criteria-based stages — each stage is entered when objective strength and functional benchmarks are met rather than on a fixed calendar. Return to pivoting sport is cleared when single-leg strength testing shows adequate symmetry, hop testing meets established thresholds, and sport-specific movement quality is assessed as adequate.
For ACL reconstruction, the rehabilitation follows a similar framework but with surgical precautions in the early phase protecting graft healing and integration. Graft selection — hamstring autograft, bone-patellar tendon-bone autograft, or quadriceps tendon graft — influences the early rehabilitation approach, particularly regarding the speed of open-chain quadriceps loading.
The most critical and most frequently rushed phase of ACL rehabilitation is return to sport. Research consistently shows that return to pivoting sport before nine months from surgery carries significantly higher re-rupture risk — and re-rupture of a reconstructed ACL carries substantially worse prognosis than the first injury. Objective criteria including limb symmetry index on strength testing above 90%, hop test symmetry, and psychological readiness should all be met before return to competitive sport is cleared.
Real time ultrasound guides VMO and deep hip stabiliser retraining where arthrogenic inhibition is limiting quadriceps recruitment. Clinical Pilates provides controlled closed-chain knee loading through precisely managed ranges during rehabilitation. For athletes combining ACL rehabilitation with broader performance goals, our Exercise Physiologist Ash O'Regan contributes to the conditioning component of the return-to-sport program.
For patients whose ACL injury occurred in a workplace or motor vehicle context, WorkCover and CTP funded rehabilitation is available.
Our physiotherapists Eliane Machado, Bethany Kippen and Emma Cameron all have experience in ACL rehabilitation and are members of the Australian Physiotherapy Association. Eliane's doctoral research in knee biomechanics is directly relevant to the movement analysis and return-to-sport testing that governs safe ACL rehabilitation.
To book or find out more, call us on 07 3706 3407 or book online below. We see patients from across Brisbane's southside including Tarragindi, Coorparoo, Holland Park, Greenslopes and Mt Gravatt.
The ACL is a ligament that connects the femur (thigh bone) to the tibia (shinbone) and is responsible for stabilising the knee joint. More specifically, it runs diagonally inside the knee from the posterior lateral femoral condyle to the anterior medial tibial plateau, and its primary roles are preventing anterior translation of the tibia on the femur and resisting rotational forces — the combined loading that makes pivoting sports so demanding on this structure.
The ACL has poor intrinsic healing capacity compared to the MCL — it lies within the joint capsule in a relatively avascular environment, meaning it does not spontaneously repair after complete rupture the way extra-articular ligaments do. This biological reality is central to the surgery versus conservative management decision.
How do ACL injuries occur?
ACL injuries occur when the ligament is stretched or torn, often as a result of a sudden twisting motion or direct impact to the knee. The most common mechanism is a non-contact pivoting or cutting action — landing from a jump with the knee in valgus, decelerating suddenly and changing direction, or rotating on a planted foot. Contact injuries — typically a direct blow to the lateral knee producing valgus collapse — are less common but well recognised.
ACL injuries are disproportionately common in female athletes — the incidence in sports like netball, football and basketball is two to eight times higher in women than men, attributable to a combination of anatomical, hormonal and neuromuscular factors. Understanding this disparity has driven significant research into ACL injury prevention programs — of which the FIFA 11+ and equivalent neuromuscular training protocols have strong evidence for reducing ACL injury rates in at-risk populations.
Surgery or conservative management — what does the evidence say?
This is the most important and most debated question in ACL management, and the answer has shifted considerably in recent years.
Traditionally, ACL reconstruction was considered the default for active patients, particularly those returning to pivoting sport. The evidence base for this position has been substantially revised. Several high-quality randomised controlled trials — including the landmark KANON trial and the more recent COMPARE trial — have shown that a significant proportion of patients with complete ACL tears can achieve excellent long-term outcomes with structured rehabilitation alone, without surgery. The five-year outcomes for physical activity level, knee function and osteoarthritis rates between surgical and non-surgical groups are more similar than previously appreciated.
The current evidence supports an individualised approach: younger patients returning to high-level pivoting sport, those with associated injuries (meniscal tears, multi-ligament injuries), and those with significant persistent instability after rehabilitation are more likely to benefit from surgery. Older patients, those in lower-demand activities, and those who achieve good stability with rehabilitation are increasingly managed conservatively with comparable outcomes.
The concept of "ACL rehabilitation and return-to-sport first" — also called the MOON and KANON protocol approach — involves completing a structured rehabilitation program and then making the surgery decision based on whether instability persists, rather than defaulting to surgery immediately. This approach is gaining traction in evidence-based practice
.
What are the symptoms?
Symptoms of an ACL injury include sudden pain, swelling, a popping sound or sensation in the knee, and difficulty moving the joint. The acute haemarthrosis — rapid swelling from blood filling the joint — typically develops within two to four hours of the injury and is one of the most consistent features of a significant intra-articular knee injury. After the acute swelling settles, the primary symptom of ACL deficiency is instability — a giving way or unreliable feeling in the knee with pivoting, cutting and rotational movements.
How is it diagnosed?
A healthcare provider will typically perform a physical examination to assess the knee's stability and range of motion. They may also order imaging tests, such as an MRI, to confirm the diagnosis and evaluate the extent of the injury. The Lachman test — assessing anterior tibial translation with the knee at 30 degrees of flexion — is the most sensitive clinical test for ACL rupture. The pivot shift test, which reproduces the rotational instability, is the most specific. MRI confirms the diagnosis, assesses associated injuries (meniscal tears are present in 50 to 70% of acute ACL ruptures), and guides the surgical decision.
What does rehabilitation involve?
Whether surgical or conservative management is chosen, physiotherapy is central to outcomes in both pathways.
For conservative management, the goal is restoring dynamic knee stability through progressive quadriceps, hamstring, hip and calf strengthening combined with progressive neuromuscular and proprioceptive training. The rehabilitation progresses through criteria-based stages — each stage is entered when objective strength and functional benchmarks are met rather than on a fixed calendar. Return to pivoting sport is cleared when single-leg strength testing shows adequate symmetry, hop testing meets established thresholds, and sport-specific movement quality is assessed as adequate.
For ACL reconstruction, the rehabilitation follows a similar framework but with surgical precautions in the early phase protecting graft healing and integration. Graft selection — hamstring autograft, bone-patellar tendon-bone autograft, or quadriceps tendon graft — influences the early rehabilitation approach, particularly regarding the speed of open-chain quadriceps loading.
The most critical and most frequently rushed phase of ACL rehabilitation is return to sport. Research consistently shows that return to pivoting sport before nine months from surgery carries significantly higher re-rupture risk — and re-rupture of a reconstructed ACL carries substantially worse prognosis than the first injury. Objective criteria including limb symmetry index on strength testing above 90%, hop test symmetry, and psychological readiness should all be met before return to competitive sport is cleared.
Real time ultrasound guides VMO and deep hip stabiliser retraining where arthrogenic inhibition is limiting quadriceps recruitment. Clinical Pilates provides controlled closed-chain knee loading through precisely managed ranges during rehabilitation. For athletes combining ACL rehabilitation with broader performance goals, our Exercise Physiologist Ash O'Regan contributes to the conditioning component of the return-to-sport program.
For patients whose ACL injury occurred in a workplace or motor vehicle context, WorkCover and CTP funded rehabilitation is available.
Our physiotherapists Eliane Machado, Bethany Kippen and Emma Cameron all have experience in ACL rehabilitation and are members of the Australian Physiotherapy Association. Eliane's doctoral research in knee biomechanics is directly relevant to the movement analysis and return-to-sport testing that governs safe ACL rehabilitation.
To book or find out more, call us on 07 3706 3407 or book online below. We see patients from across Brisbane's southside including Tarragindi, Coorparoo, Holland Park, Greenslopes and Mt Gravatt.
