The ACL & How It Is Injured
The anterior cruciate ligament (ACL) is one of the two cruciate ligaments within the knee, running diagonally from the femur to the tibia. It is the primary restraint against anterior translation of the tibia relative to the femur and plays a critical role in rotational stability — the foundation of cutting, pivoting, and direction-change movements.
ACL injuries most commonly occur via a non-contact mechanism — a sudden deceleration, change of direction, or landing from a jump — with the knee in slight flexion and valgus. Contact injuries account for a minority. The characteristic findings are immediate pain, a sense of giving way, rapid joint effusion (haemarthrosis), and an inability to continue activity. MRI is the definitive imaging investigation and also assesses for associated meniscal and cartilage injuries, which are common.
The ACL has a very limited capacity for spontaneous healing. The intra-articular environment of the knee, combined with the mechanical demands placed on the ligament, prevents satisfactory scar tissue formation. Reconstruction using a tendon graft is required to restore stability in patients who wish to remain active.
Graft Options
ACL reconstruction involves replacing the torn ligament with a tendon graft that becomes incorporated into the bone tunnels and remodels over time to function as a ligament (a process called ligamentisation). Graft selection is guided by patient age, activity level, anatomy, and surgeon preference.
- Hamstring autograft (gracilis and semitendinosus) — the most commonly used graft in Australia; taken from the patient’s own hamstring tendons through a small incision, offering good strength and a reliable donor site
- Patellar tendon autograft (bone-patella-bone) — the “gold standard” in many centres, with bone plugs facilitating strong early fixation; associated with a higher rate of anterior knee pain
- Quadriceps tendon autograft — an increasingly used option, offering a large graft with minimal donor site morbidity
- Allograft (donor tendon) — used in revision ACL surgery or in older, less active patients; avoids donor site morbidity but carries a small risk of biological transmission and slower incorporation
Surgery & Rehabilitation
ACL reconstruction is performed arthroscopically under general anaesthesia as a day procedure. Bone tunnels are drilled in the femur and tibia at the anatomical footprints of the native ACL, the graft is passed through and fixed under appropriate tension, and any associated meniscal or cartilage pathology is addressed simultaneously.
The surgery itself takes one to one and a half hours. Recovery and rehabilitation are the most critical elements of a successful outcome.
Weeks 0–6
Swelling and pain management, early range of motion exercises, quadriceps activation, and progressive weight-bearing. Crutches weaned as comfort and strength allow.
Months 2–4
Progressive strength and neuromuscular training. Return to jogging when quadriceps strength reaches 70–80% of the uninjured side.
Months 4–9
Sport-specific training, agility drills, and graduated return to training. Psychological readiness is assessed alongside physical criteria.
9–12 Months
Return to full competition when objective strength and movement criteria are met. Returning before 9 months significantly increases re-rupture risk.
Discuss ACL Reconstruction
For a personalised assessment and treatment plan, contact Dr. Pirpiris’s rooms at Cabrini Medical Centre, Malvern.
📞 Call 03 9508 9600