What is the Anterior Cruciate Ligament (ACL)?

The anterior cruciate ligament, commonly known as the ACL, is one of the four main ligaments within the knee. It connects the thigh bone (femur) to the shin bone (tibia). This ligament plays a crucial role in stabilising the knee, particularly during physical movements such as walking, running, or jumping. A tear or rupture of this ligament is often associated with abrupt stops and changes in direction – movements common in sports like football, basketball, or skiing.

What Is An ACL Tear?

An ACL tear is a common knee injury, especially among athletes. Tears can range from mild (a small number of fibres are torn) to severe (the ligament is completely ruptured). Partial tears involve the ligament becoming loose, while a complete tear occurs when the ligament is divided into two pieces. The injury can sometimes include damage to other parts of the knee, such as the cartilage or other ligaments.

Causes and Risk Factors for ACL Injuries

ACL injuries can be the result of abrupt, jerky movements, especially those involving stopping suddenly and changing direction rapidly while running, pivoting, or landing from a jump — often seen in sports such as basketball, football, tennis, and skiing. Other scenarios for injury may include direct collision or contact, such as a football tackle.

Certain factors can increase the likelihood of an ACL injury, which include:

  • Participating in certain sports: Athletes who participate in sports like football, basketball, soccer, and skiing are more likely to suffer from ACL injuries due to the high-intensity athletic demand.
  • Gender: Research has shown that female athletes have a higher incidence of ACL injury when compared with their male counterparts participating in the same sports.
  • Weak Muscles: If the surrounding muscles, particularly the hamstrings, are weak, it can increase the risk of ACL injury.

Symptoms of ACL tears

When an ACL tear occurs, individuals may experience one or more of the following symptoms:

  • Sudden and severe pain: Often, there will be intense pain at the knee joint at the moment of injury.
  • Audible “pop” sound: Some people may hear a loud “pop” or sense a “popping” feeling at the time of injury.
  • Swelling: Swelling typically occurs within a few hours of the injury due to bleeding within the knee joint.
  • Restricted mobility: Difficulty in moving the knee, bending it or straightening it fully can be a symptom of an ACL tear.
  • Unstable knee: If the knee feels unstable or like it’s giving away during weight-bearing activities, it could indicate an ACL injury.

Diagnosis of an ACL Tear

If an ACL injury is suspected, consult a healthcare provider for a thorough evaluation. The diagnosis typically involves the following steps:

  • Medical history: The practitioner will ask about the circumstances of the injury, the nature of the pain, and any previous knee problems.
  • Physical examination: The doctor will assess the knee for swelling and evaluate its range of motion. The doctor may also perform specific tests to see if the knee is stable or if there’s apparent laxity.
  • Imaging tests: These may include X-rays to rule out any bone fractures, and an MRI to have a detailed view of the ligaments and tissues in the knee.

How do you know if you need ACL surgery?

Not all ACL tears require surgical intervention. The decision to opt for surgery depends on various factors, including:

  • Severity of the Injury: Complete tears of the ACL or injuries involving other knee structures often require surgical repair.
  • Lifestyle: Active individuals or those who participate in sports involving pivoting or jumping may opt for surgery to safely return to their activities.
  • Age and Overall Health: Younger, active individuals often opt for surgery, while older individuals or those with health conditions that could complicate surgery might choose non-surgical treatments.
  • Stability Of The Knee: If the knee frequently gives way during daily activities, surgery may be recommended to restore stability.

How soon should you get ACL surgery?

The timeline for undergoing ACL surgery can vary greatly, being influenced by several individual and clinical factors. The decision of when to have surgery primarily depends on the patient’s specific circumstances and the professional advice from their orthopaedic surgeon, depending on several factors:

  • Initial Injury Management: Following an ACL tear, immediate care often involves the RICE method — rest, ice, compression, and elevation. This is critical to manage initial swelling and protect the knee from further injury.
  • Reducing Swelling and Restoring Mobility: Typically, it is recommended to wait until the joint swelling decreases and a good range of motion returns before surgery is performed. After an ACL injury, the knee often swells significantly and can become stiff. This can range from 2 weeks to 2 months, depending on the severity of the injury and the individual’s response to initial management strategies.
  • Pre-Surgery Rehabilitation: Before surgery, some physicians recommend prehabilitation – exercise regimens meant to increase the strength and flexibility of the knee, which can help in a smoother post-operative recovery. This can extend the time before surgery.
  • Personal and Lifestyle Factors: Consideration is given to the individual’s lifestyle, professional obligations, and personal circumstances. If the patient has a physically demanding job or is an athlete hoping to return to their sport, they might decide to go for surgery sooner. However, the decision must align with the readiness of the knee for surgery.
  • Associated Injuries: Comorbid health conditions may delay surgery as the overall health of the patient must be able to endure the surgical procedure and subsequent recovery. Co-existing injuries to the knee, such as damage to the meniscus or other ligaments, may also impact the timing of ACL surgery.

These are general guidelines, and all decisions about surgery should be made in consultation with a knee surgeon to ensure optimal outcomes.

Understanding ACL Reconstruction Surgery

This procedure aims to restore the stability and function of the knee after an ACL tear. Before surgery, patients are typically put under general anaesthesia.

The Procedure

ACL reconstruction is an arthroscopic procedure, meaning it’s minimally invasive. The surgeon will make small incisions around the knee and insert a small camera, known as an arthroscope, to view the knee joint. This approach allows the surgeon to accurately evaluate the ACL and other structures of the knee.

Removing the Damaged Ligament

The ACL is situated deep within the knee. Therefore, the surgeon will remove the damaged ACL during the procedure to make room for the graft.

Graft Selection

The surgeon uses a graft to replace the torn ACL. This graft can come from the patient’s own body (autograft) or a donor (allograft). There are pros and cons for each graft type, and the selection typically depends on the patient’s needs and the surgeon’s discretion. Common autograft sources include the patellar tendon, hamstring tendons, or quadriceps tendon.

Placing the Graft

The surgeon affixes the graft where the original ACL was located. Special surgical tools and hardware such as screws or other fixation devices are used to anchor the graft in place. The graft acts as a scaffold for a new ligament to grow on.

Types of ACL Surgery

There are different surgical options available for treating ACL tears. These include:

  • Anatomic ACL Reconstruction: This is the most common form of ACL surgery. This technique aims to replicate the original ACL’s size, position, and inclination, thereby restoring the knee’s normal anatomy. This procedure utilises a graft, either autograft or allograft, as mentioned in previous sections.
  • Non-Anatomic ACL Reconstruction: Here, the graft is not placed in the exact position of the original ACL. It is used less often as it doesn’t restore the knee’s anatomy to as close to normal as anatomic reconstruction does.
  • ACL Repair: In some cases, particularly when the tear occurs very close to where the ligament attaches to the bone, the surgeon may choose to repair the existing ligament rather than replace it. This is less common and is only suitable for certain types of ACL tears.
  • Revision ACL Reconstruction: This procedure is needed when a previous ACL reconstruction fails, and a second surgery is required. The surgeon will remove the old graft, clean the area and then implant the new graft.

Each surgical approach comes with its potential benefits and risks, and the selection depends on patient-specific factors such as the type of tear, the patient’s age, activity level, and expectations from the surgery.

Alternatives to ACL Reconstruction

ACL reconstruction surgery might not be the best solution for everyone. Non-surgical management, or conservative treatment, could be a viable alternative for some individuals.

Conservative Management

This typically includes a combination of rest, physical therapy, and using a knee brace. Physical therapy can help regain muscle strength around the knee joint and restore a good range of motion. Some people, particularly those who live a less active lifestyle, may find that their knee joint is stable and functional enough for daily activities with conservative treatment.

Rehabilitation and Lifestyle Modification

For some individuals, especially those who are not involved in sports requiring a high level of agility or pivoting, a regimented physiotherapy program and lifestyle modifications may allow them to return to normal activities without the need for surgery.

Injection Therapies

In some circumstances, therapies involving injections, such as platelet-rich plasma (PRP) or stem cell therapy may be explored. However, these treatments are typically used in conjunction with other treatments and the evidence for their effectiveness in treating ACL tears is still being explored.

Steps in ACL Reconstruction Surgery

The surgical procedure of ACL reconstruction usually follows the following steps:

  1. Administration of Anaesthesia: Firstly, the patient is given either general anaesthesia, spinal block, or a combination of both depending on individual circumstances and surgeon’s preference.
  2. Knee Examination: The surgeon will then utilise an arthroscope to inspect the interior of the knee joint for any additional injuries that might not have been apparent in previous imaging tests.
  3. Graft Preparation: While inspecting the knee, the surgical team prepares the graft tissue. If an autograft is being used, the tissue is harvested from the patient.
  4. Removing the Damaged ACL: The surgeon will then remove the torn ACL, making space for the graft.
  5. Constructing the Tunnel: To anchor the new graft in place, the surgeon drills a tunnel in the thigh and shin bones at the specific points where the ACL attaches.
  6. Graft Placement: The prepared graft is then fed through these tunnels and secured with specially designed screws or other fixation devices.
  7. Final Inspection and Closure: Once the graft is secure, the surgeon will check the graft and overall knee function, making any necessary adjustments. The knee incisions are then closed, marking the end of the surgical procedure.

ACL reconstruction generally takes approximately 1 to 1.5 hours to complete, provided no additional procedures are being done simultaneously. The basic flow of the procedure involves putting the patient under anaesthesia, removing the damaged ACL, preparing and placing the graft, and then finally closing up the incisions. You’ll be required to be warded for a very short period for post-surgical care within the hospital setting before getting discharged home.

Post-operative care and Rehabilitation

Post-operative care and rehabilitation play a vital role in helping individuals regain normal knee function and return to their usual activities. It generally involves:

  • Initial Care: Post-operative care starts immediately after the surgery, involving wound care, pain management, and managing initial stiffness and swelling. Orthopaedic surgeons usually prescribe medicines for pain relief.
  • Physiotherapy Program: Patients are usually guided by a physiotherapist to perform a series of exercises to restore strength and mobility. The program usually begins with simple range-of-motion exercises and gradually moves to more strengthening workouts.
  • Use of Assistive Devices: A knee brace might be used to protect the knee, and crutches might be required initially to avoid bearing weight on the operated knee.
  • Regular Follow-ups: Follow-up appointments allow the surgeon to monitor healing and address any issues promptly.

Recovery time for ACL Surgery

The recovery process and time from ACL surgery can be quite variable, depending largely on individual factors such as the specific surgical procedure performed, the patient’s overall health, and the aggressiveness of the rehabilitation program.

  • Short-Term Recovery: During this initial phase, which usually lasts 4 to 6 weeks post-surgery, the focus is on reducing swelling, controlling pain, and gradually improving knee mobility. The patient often starts to weight-bear with the aid of crutches and progresses to fully weight-bearing as tolerated.
  • Mid-Term Recovery: This phase can last from 3 months to 6 months post-surgery. Rehabilitation shifts towards strengthening exercises aiming to regain muscle strength and knee function. Most individuals can gradually return to daily activities and light physical activities.
  • Long-Term Recovery: This final phase extends from 6 months up to a year, with a focus on slowly returning to high-demand sports and other strenuous activities. The ultimate objective is to regain knee stability and function comparable to the pre-injury state.

Every individual has a unique recovery timeline, which should be guided by your surgeon and physiotherapy team to ensure safety and effectiveness.

Implications of delaying ACL reconstruction

Delaying an ACL reconstruction has specific implications and can potentially contribute to further degradation of knee health.

Potential For Further Knee Damage

An unstable knee due to a torn ACL might lead to other injuries. For instance, abnormal movement and increased laxity in the knee joint can induce strains on the menisci, the shock-absorbing structures in the knee. This can lead to tears in the meniscus, which can exacerbate knee instability and cause persistent pain. Additionally, the altered biomechanics of the knee joint may lead to degeneration of the articular cartilage, the smooth surface covering the ends of bones within the knee joint. This cartilage damage can accelerate the onset of knee osteoarthritis, a degenerative joint disease causing pain and stiffness.

Compromised Activity Level

Individuals could experience limitations in physical activities. High-demand sports, which involve sudden stops and changes in direction, could be especially hard to perform with an unstable knee.

Quality of Life

Prolonging ACL reconstruction might impact an individual’s overall quality of life. Symptoms like joint instability, pain, and activity limitations could persist and may affect daily living activities.

Increased Risk of Chronic Instability

Chronic instability is a long-term complication in untreated ACL injuries. The knee may ‘give way’ during certain movements, making it unpredictable and unreliable.

These implications underscore the importance of a timely decision regarding ACL reconstruction, aiming for the restoration of normal knee anatomy, function, and long-term well-being.

Can a teenager have ACL surgery?

Yes, teenagers can have ACL surgery. In fact, due to the active nature of teenagers and their involvement in sports, they represent a significant portion of individuals undergoing ACL reconstruction procedures. The decision to perform ACL surgery on a teenager takes into consideration the nature of the tear, the level of activity, and the potential risk for further knee damage.

In children and adolescents whose bones are still growing, the surgical approach may be adjusted as some techniques risk damaging the growth plates, potentially leading to uneven bone growth. In such cases, modified surgical techniques or specific graft choices may be opted for.

The long-term prognosis for ACL surgery in teenagers is generally good, with many returning to pre-injury levels of sport and physical activity following comprehensive rehab.

Risks and Complications

While ACL reconstruction is generally a safe procedure, it’s not free of risks. Potential complications, though rare, could include:

  • Infection: As with any surgical procedure, there’s a risk of infection. Surgeons minimise this risk by ensuring a sterile operating environment and may administer antibiotics.
  • Blood Clots: Immobility following surgery may lead to the formation of blood clots, known as deep vein thrombosis (DVT). It’s important to follow the surgeon’s instructions to minimise this risk, which can include mobility exercises and occasionally medications.
  • Poor Graft Healing: In some rare instances, the graft may not heal effectively, or may stretch over time, leading to recurrent knee instability.
  • Stiffness or Loss of Range of Motion: Some patients might struggle with stiffness or a limited range of motion in the knee following surgery, often overcome with a targeted physiotherapy program.
  • Nerve and Vessel damage: Although extremely rare, there can be accidental damage to blood vessels or nerves surrounding the knee during the surgical procedure.

While it’s important to keep potential risks in mind, ACL reconstruction surgery boasts a high success rate, particularly when patients adhere to extensive rehabilitation and follow-up care. According to various scientific studies, more than 90% of patients return to their previous levels of activity after ACL reconstruction.

The rate of severe complications remains relatively low. A comprehensive review published in The Journal of Bone & Joint Surgery reported that major complications occurred in less than 0.6% of patients who underwent ACL reconstruction surgery.


ACL injuries are common, especially among athletes and active individuals. If they cause considerable instability in the knee and affect the quality of life, ACL reconstruction surgery can be a reliable solution to regain function and stability. Early consultation with an orthopaedic surgeon who specialises in ACL reconstruction will pave the way for the best possible outcomes.