Anterior Cruciate Ligament Reconstruction
Anterior cruciate ligament injury
The anterior cruciate ligament is an important ligament inside the knee. It is one of four main ligaments that connects the tibia to the femur. Its main functions are to provide rotational stability to the knee and resist the tibia sliding forward on the femur (anterior translation of the tibia). Knee rotational stability is particularly important for sports that involve rapid changes of direction (pivoting).
The ACL can be injured due to a variety of mechanism. The most common mechanism of injury is in a ‘non-contact’, twisting movement involving rapid deceleration on the leg, or a sudden change of direction, such as during side stepping, pivoting or landing from a jump. This frequently occurs during contact ball sports such as football, rugby, netball and skiing. The ACL can also be injured as a result of direct contact to the injured leg.
Injuries associated with ACL injury
Other structures in the knee can also be injured at the time of an ACL tear. The most common associated injury is a tear of one of the menisci. Sprains or partial tears of the medial collateral ligament (MCL) are also commonly seen, particularly in non-contact ACL injuries caused by twisting or pivoting movements. More severe injuries involving the MCL, the posterior cruciate ligament (PCL), and the posterolateral corner can occur following direct contact or higher-energy trauma
Diagnosis
A history of injury as described above should raise a strong suspicion of an ACL injury. Examination of the knee is helpful in assessing instability associated with anterior cruciate ligament injury, as well as identifying other significant ligament injuries. Clinical examination can be more difficult to interpret in the acute phase due to pain and restricted knee movement. MRI is usually required to confirm the diagnosis of ACL injury and to assess for associated injuries.
Treatment of ACL injury
Early treatment should focus on pain relief, reducing swelling (ice, elevation and compression), regaining control of the muscles around the knee, and restoring knee range of motion.
ACL rupture can be treated with either:
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ACL reconstruction
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Rehabilitation
The main aim of surgery is to treat symptomatic knee instability.
The decision to undergo ACL reconstruction can be made either early after injury or following a period of rehabilitation. This decision is individualised for each patient to determine whether they are likely to benefit from reconstruction or whether surgery may be avoided.
The ACL has limited healing potential. Although the ligament can heal, it often heals in a non-anatomical position, meaning the knee may remain slightly looser than before the injury. Muscles around the knee can compensate for this residual instability to a certain extent.
Once recovered from the initial injury, most people will have a knee that is stable for day-to-day activities and for some sports or activities that do not involve sudden twisting or pivoting movements. A small proportion of patients (approximately 15%) may be able to return to all activities, including pivoting sports, without ACL reconstruction. However, most patients with an ACL-deficient knee are unable to return reliably to pivoting sports without reconstruction. ACL reconstruction provides the best chance of returning to pivoting sports, with return-to-sport rates typically reported between 60–80%.
Some patients experience significant instability, with the knee giving way even during day-to-day activities despite rehabilitation. In these situations, ACL reconstruction is often recommended.
Another important consideration is that recurrent episodes of instability may lead to further injury to the menisci or articular cartilage.
Factors to consider when deciding between rehabilitation and ACL reconstruction
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Future functional demands
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Symptoms of instability
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Associated injuries
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Ability to comply with rehabilitation
What does ACL reconstruction surgery involve?
Steps of ACL reconstruction:
1. Anaesthetic
The surgery is usually performed under a general anaesthetic.
2. Graft harvest
Bone-patella tendon bone (BTB) graft
In the case of a patellar tendon graft, a vertical incision is made over the front of the knee. The central third of the patellar tendon (approximately 10 mm wide) is harvested together with a small block of bone from the patella at one end and a block of bone from the tibia at the other end.
Neufeld EV, Sgaglione J, Sgaglione NA. Anterior Cruciate Ligament Reconstruction Graft Options. Arthroscopy. 2025 Jan;41(1):16-18. doi: 10.1016/j.arthro.2024.10.004. PMID: 39674612.
Hamstrings tendon graft
In the case of a hamstring tendon graft, a vertical incision is made over the upper inner part of the tibia. The semitendinosus tendon, with or without the gracilis tendon, is harvested. The tendons are folded in different configurations to create a graft of adequate size and strength to reconstruct the ACL.
Neufeld EV, Sgaglione J, Sgaglione NA. Anterior Cruciate Ligament Reconstruction Graft Options. Arthroscopy. 2025 Jan;41(1):16-18. doi: 10.1016/j.arthro.2024.10.004. PMID: 39674612.
3. Diagnostic arthroscopy
An arthroscopic inspection of the knee is performed to assess the menisci and articular cartilage for associated injuries. If an unstable meniscal tear is identified, it may either be trimmed or repaired.
4. Femoral tunnel preparation
A tunnel is drilled in the femur at the insertion site of the ACL on the lateral wall of the intercondylar notch. This tunnel will receive the graft.
5. Tibial tunnel preparation
A tunnel is drilled in the tibia at the anatomical attachment site of the ACL.
6. Graft insertion and fixation
The graft is passed into the knee through the prepared tunnels, secured within the femur, tensioned appropriately, and then fixed securely within the tibia.
7. Wound closure
The wounds are closed using buried dissolvable sutures and covered with waterproof dressings. A supportive wool and crepe bandage is then applied.
Lateral extra-articular tenodesis (LET)
This is an additional procedure that can be performed alongside ACL reconstruction to improve rotational stability of the knee. It works by tightening structures on the outer (lateral) side of the knee, most commonly using part of the iliotibial band.
LET may be recommended in patients considered to be at higher risk of recurrent instability or ACL graft failure, such as those returning to high-demand pivoting sports, patients with marked rotational laxity, or revision ACL surgery.
Figure: Ellison lateral extra-articular tenodesis.
Post operative care
Most patients are able to go home on the same day as surgery.
Following the operation, patients are monitored in the recovery area before returning to the ward. Pain relief medication is provided regularly. Patients are encouraged to begin moving the knee and walking with crutches shortly after surgery under the guidance of the physiotherapy team. Most patients are allowed to fully weight bear unless additional procedures, such as meniscal repair, have been performed.
Before discharge, patients should be:
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Comfortable on oral pain medication
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Safe mobilising with crutches
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Able to manage stairs if required
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Provided with physiotherapy exercises and rehabilitation advice
Recovery and rehabilitation
Rehabilitation following ACL injury or reconstruction is essential in order to restore knee function, optimise performance and reduce the risk of re-injury. If ACL reconstruction is undertaken, rehabilitation is just as important as the surgery itself and should not be neglected.
Recovery following ACL injury and reconstruction takes time. Graft healing, biological recovery and restoration of muscle strength occur gradually, and returning to sport too early may increase the risk of further injury.
Rehabilitation should consist of a structured programme. Progression is goal directed rather than purely time based. After successful surgery and rehabilitation, the earliest one should consider returning to match play is 9-12 months. Returning to sport earlier than this may increase the risk of re-injury.
Rehabilitation is usually divided into phases:
Prehabilitation / Acute Recovery Phase
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Reduce swelling and pain
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Restore full extension
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Regain quadriceps activation
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Normalise gait
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Prepare for surgery (if planned)
Phase 1 — Early Recovery
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Reduce pain and swelling
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Restore full knee extension
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Regain quadriceps control
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Normalise walking (wean from crutches)
Phase 2 — Strength and Neuromuscular Control
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Progressive strengthening
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Balance and proprioception
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Single-leg control
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Core and hip stability
Phase 3 — Running, Agility and Plyometrics
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Return to running
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Landing mechanics
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Plyometrics
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Change of direction
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Agility work
Phase 4 — Return to Sport
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Sport-specific rehabilitation
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Functional testing
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Return to training and competition
Phase 5 — Prevention of Re-Injury
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Full return to sport
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Ongoing strength maintenance
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Fatigue management
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Injury prevention strategies
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Optimising performance
Following ACL reconstruction, the graft undergoes a gradual healing and remodelling process known as ‘ligamentisation’. Over time the graft incorporates into the bone tunnels, develops a new blood supply and gradually becomes more ligament-like in structure and function. During the early stages of healing the graft actually becomes temporarily weaker as it remodels and revascularises before gradually strengthening over time. This process takes many months, which is one reason rehabilitation and delayed return to sport are so important.
