Anterior Cruciate Ligament (ACL) Injury
What is the Anatomy and Function of the ACL?
The anterior cruciate ligament (ACL) is one of the four major ligaments that stabilize the knee.
It connects the femur (thigh bone) to the tibia (shin bone) and runs diagonally through the center of the knee joint.
The ACL’s main functions are to:
Prevent the tibia from moving forward relative to the femur
Control rotational stability during twisting, pivoting, and cutting movements
A healthy ACL is essential for sports that involve sudden changes in direction, such as Australian rules football, soccer, basketball, and netball.
How Does the ACL Tear?
An ACL tear most commonly occurs through a non-contact mechanism, often during:
Sudden stopping or pivoting while the foot is planted
Landing awkwardly from a jump
Hyperextension of the knee
Direct collision or impact to the knee less commonly causes ACL injuries.
Patients often report:
A “popping” sound or sensation at the time of injury
Immediate pain and swelling
A feeling of the knee “giving way” or instability
How Do you Diagnose an ACL Tear?
Diagnosis is based on a combination of history, physical examination, and imaging. MRIs are the gold standard for diagnosing ACL tears and associated injuries. X-rays are also obtained to assess the knee joint for arthritis and to evaluate the anatomical morphology and alignment of the knee.
What Other Concomitant Injuries Occur with an ACL Tear?
ACL tears often occur with other knee injuries. Common associated injuries include:
Meniscal tears (especially the lateral meniscus)
MCL (medial collateral ligament) sprains/tears
Lateral collateral ligament or posterior cruciate ligament injuries (less common)
Bone bruises or articular cartilage injuries
These combined injuries can influence treatment decisions and long-term outcomes.
What are the Long-Term Consequences of Having an ACL Injury?
An ACL injury can have significant long-term effects on knee function and joint health, including:
Chronic instability: Ongoing “giving way” episodes that impair confidence and activity level. This can occur even after reconstructive surgery or non-operative management.
Recurrent meniscal tears: Due to repeated instability and abnormal joint motion.
Reduced athletic performance: Difficulty returning to pre-injury sport level, especially in pivoting sports.
Post-traumatic osteoarthritis: Even with successful reconstruction, studies show a higher risk of degenerative changes compared to uninjured knees, particularly if associated meniscal or chondral damage is present.
What are the Indications for Conservative Management of ACL Tears?
Conservative treatment is appropriate for certain patients, especially when the knee is stable and symptoms are mild.
It may be considered if:
The patient is older or has low physical activity demands
There is no significant instability or recurrent giving-way episodes
The patient is willing to modify activities (avoid pivoting or cutting sports)
There are partial ACL tears
Associated injuries (meniscus, cartilage) do not require surgical repair
Conservative treatment typically includes:
Structured physiotherapy focusing on strength, balance, and neuromuscular control
Ongoing activity modification and conditioning to prevent further injury
There is a risk of further injuring the native meniscus when treating ACL tears conservatively in the setting of knee instability.
What are the Indications for Surgical Management of ACL Tears?
ACL reconstruction is recommended when instability is significant or when the patient wishes to return to pivoting or high-demand sports. Surgical management is indicated if:
The patient experiences recurrent giving-way episodes or instability during daily or athletic activities
There is a complete ACL rupture with associated repairable meniscal injury
The patient is young and active and wishes to resume cutting, pivoting, or contact sports
There is a combined ligament injury requiring knee stabilization
Surgical treatment involves reconstructing the ACL using the patient’s own tendon graft (hamstring, quadriceps, or patellar tendon) or a cadaver graft. This reconstructed graft will restore knee stability and help protect any other injury in the knee which is being repaired.
MELBOURNE ORTHOPAEDIC SURGERY