[Dr Yau’s Health Insights] Does an anterior cruciate ligament (ACL) tear always require surgery? How long does recovery take? A complete guide to rehabilitation and prevention
Health2026-11-02
8 Mins Read
A sudden change of direction or an awkward landing after a jump, followed by a distinct "pop" in the knee. At first, it may seem like nothing more than a simple sprain. However, within a few hours, the knee may become increasingly swollen, and walking may start to feel unstable. These could all be warning signs of an anterior cruciate ligament (ACL) tear.
An ACL tear is one of the most common sports-related knee injuries. Whether in football, basketball, skiing or volleyball, any activity that involves sudden stopping, pivoting or landing from a jump carries a risk of ACL injury. After an injury, most people tend to have two questions: Do I need surgery? And how long will it take to recover? In this article, we will look at the causes and symptoms of ACL tears, as well as treatment options and recovery timelines, helping sports enthusiasts understand how best to manage this injury.
Quick answers about ACL tear
Q1: Does an ACL tear always require surgery?
Answer: Not necessarily. Some patients can manage their symptoms through physiotherapy and muscle strengthening exercises. However, ACL reconstruction surgery is often considered for younger individuals, those with a high level of physical activity, or those with significant knee instability.
Q2: How soon can I walk after ACL reconstruction?
Answer: Most patients can gradually resume walking within a few days to several weeks after surgery, although the actual timeline depends on the surgical procedure performed and individual rehabilitation progress.
Q3: When can I start running after ACL reconstruction?
Answer: Straight-line jogging can generally begin around 3 to 4 months after surgery, subject to assessment by a doctor or physiotherapist.
Q4: When can I return to sport after ACL reconstruction?
Answer: In most cases, returning to sport takes around 9 to 12 months. Recent studies have suggested waiting at least 12 months before returning to unrestricted high-intensity sports to help reduce the risk of re-injury.
Q5: If I can still walk after an ACL tear, does that mean the injury is not serious?
Answer: Not necessarily. Some patients with an ACL tear can still walk and may even be able to carry out their daily activities. However, the stability of the knee joint may already be compromised. If an ACL injury is suspected, it is important to seek prompt assessment by an orthopaedic specialist and undergo an MRI scan if required.
What is the anterior cruciate ligament (ACL), and why is it so important?
The anterior cruciate ligament (ACL) is located deep within the centre of the knee joint, connecting the femur (thigh bone) to the tibia (shin bone).
Its primary function is to maintain the stability of the knee joint in the forward and backward directions, preventing the tibia from sliding excessively forwards relative to the femur. In addition, the ACL plays an important role in proprioception - the body's ability to sense the position and movement of its joints. This directly affects balance and coordination during physical activity. When the ACL is torn, the stability of the knee joint is compromised. This can affect not only sporting performance, but also everyday activities such as walking and climbing stairs, which may become more difficult and less stable.
What causes an ACL tear?
Most ACL tears occur as a non-contact injury, meaning the injury happens without any direct collision with another person. Instead, it is usually caused by the body's own movement mechanics or an awkward change in direction. Common causes of ACL tears include:
- Sudden pivoting or stopping (for example, changing direction while playing basketball or turning sharply while dribbling in football)
- Incorrect landing technique after a jump (such as landing after a volleyball block or after jumping for a rebound in basketball)
- Hyperextension or excessive twisting of the knee
- Direct impact (such as a rugby tackle or a collision during a football slide tackle)
High-risk sports
Sports that involve frequent pivoting, jumping and sudden changes of direction, such as football, basketball, rugby, skiing, volleyball and tennis, carry a particularly high risk of ACL injury.
High-risk groups
Certain groups are more likely to sustain an ACL injury:
- Female athletes, whose risk is generally higher than that of males due to a combination of anatomical, hormonal and neuromuscular factors
- Individuals with insufficient lower-limb strength, particularly when there is an imbalance between the muscles at the front and back of the thigh
- People with a history of knee injuries, as previous injuries may affect joint stability and proprioception
Symptoms and diagnosis of an ACL tear
The symptoms of an ACL tear are often quite characteristic, and many patients can clearly recall the moment the injury occurred.
Common symptoms
- Hearing a loud "pop" or "snap" at the time of injury
- Severe knee pain, making it difficult to continue exercising or even remain standing
- Rapid swelling of the knee (caused by bleeding within the joint, known as haemarthrosis)
- A feeling that the knee is weak or unstable, as though it is "giving way"
- A noticeable reduction in the range of motion of the knee joint
Diagnosis
Clinical examination: Your doctor may perform a Lachman test, which involves gently pulling the tibia (shin bone) forwards to assess whether there is excessive forward movement. This test is considered most accurate when performed soon after the injury.
Imaging tests:
- X-ray: Used to rule out fractures.
- Magnetic resonance imaging (MRI): Used to assess damage to the ligaments and other soft tissues, and to check for associated injuries such as meniscal tears or damage to the medial collateral ligament (MCL).
Your Health Tomorrow. Mastered Today.
AXA's comprehensive healthcare protection spans from prevention and diagnosis to treatment and recovery, with our extensive medical network providing complete coverage across all locations. Whether protecting yourself or safeguarding your loved ones, AXA has prepared the answers for every step of your life journey.
Does an ACL tear always require surgery?
Not every ACL tear requires surgery. The decision between conservative treatment and ACL reconstruction surgery depends on factors such as the patient's age, activity level, knee stability and the severity of the injury.
When is conservative (non-surgical) treatment appropriate?
- Older individuals with lower physical activity demands
- Patients with minimal symptoms of knee instability
- Individuals whose daily activities place relatively low demands on the knee joint
- Partial ACL tears rather than complete ruptures
Conservative treatment may include physiotherapy, knee bracing and muscle-strengthening exercises. Approximately half of patients may be able to avoid surgery through conservative management.
When is surgery (ACL reconstruction) recommended?
- Young individuals, those with high activity levels or competitive athletes
- Patients with significant knee instability
- Cases where conservative treatment has been unsuccessful
- Complete ligament tears
- ACL injuries accompanied by a meniscus tear or other knee injuries
Overview of ACL reconstruction surgery
ACL reconstruction is typically performed using a minimally invasive arthroscopic technique. During the procedure, the surgeon harvests a portion of tendon tissue, usually from the patient's hamstring tendon or patellar tendon, to reconstruct a new anterior cruciate ligament. At the same time, any associated injuries, such as a torn meniscus or other soft tissue damage, can also be repaired. Compared with direct ligament repair, ACL reconstruction generally produces more favourable outcomes and is currently considered the standard surgical approach.
The decision of whether to undergo surgery should consider factors such as age, activity level, lifestyle needs and the stability of the knee joint. A thorough assessment by an orthopaedic specialist is therefore essential before deciding on the most appropriate treatment option.
How long does recovery take after ACL reconstruction?
Recovery after ACL reconstruction is a gradual process, and the overall rehabilitation period typically ranges from 9 to 12 months.
Overview of the recovery timeline
Phase | Timeline | Main goals |
Acute phase | ||
Acute phase | 0-2 weeks after surgery | Control pain and swelling, gentle range-of-motion exercises, and isometric muscle contractions |
Early rehabilitation | ||
Early rehabilitation | 2-6 weeks after surgery | Restore 0°-90° knee flexion and extension, and begin progressive weight-bearing |
Functional recovery phase | ||
Functional recovery phase | 6-12 weeks after surgery | Advanced strengthening exercises and straight-line jogging |
Strengthening phase | ||
Strengthening phase | 3-6 months after surgery | Dynamic training, single-leg exercises and the introduction of change-of-direction movements |
Return-to | ||
Return-to | 6-12 months after surgery | Sport-specific training and gradual return to competitive play |
The ability to resume normal daily activities is usually regained around 3 to 6 months after surgery. However, returning to high-intensity sports such as basketball and football generally takes around 9 to 12 months. In recent years, studies have suggested extending the timeframe for a full return to unrestricted activity from nine months to at least 12 months in order to reduce the risk of re-injury.
Factors that affect recovery progress
Several factors can influence how quickly and successfully a patient recovers after ACL reconstruction:
- Age: Younger patients generally recover more quickly.
- Severity of the injury: Recovery may take longer if the injury is accompanied by a meniscus tear or damage to other ligaments.
- Surgical technique and graft choice
- Commitment to rehabilitation
- Psychological factors: Confidence and readiness to return to sport can also affect rehabilitation outcomes.
What is the "golden period" for rehabilitation?
Defining the golden period
The rehabilitation "golden period" generally refers to the first 3 to 6 months after surgery. This is a critical stage for restoring joint mobility, rebuilding muscle strength and regaining neuromuscular control.
Specifically:
- Early post-operative phase (0-2 weeks): The main goals are to achieve full knee extension and control swelling.
- 2-6 weeks after surgery: This is an important period for restoring basic range of motion and rebuilding muscle strength.
Why is this period so important?
After ACL reconstruction, joint fibrosis is one of the main reasons for reduced knee mobility. This is why early rehabilitation is so important. Timely intervention can help prevent muscle wasting, joint stiffness and abnormal walking patterns.
Studies have shown that joint effusion and soft tissue swelling are significantly reduced by around four months after surgery, while knee stability at 12 months is markedly better than at one month and four months after surgery.
What if you miss the "golden period" for rehabilitation?
The good news is that it is never too late to start rehabilitation. However, recovery may take longer and require greater effort. Patients who have missed the early rehabilitation phase should seek assessment from a qualified physiotherapist and follow an individualised rehabilitation programme. Progress should be gradual and carefully monitored, as pushing too hard too soon may increase the risk of a second injury.
Your Health Tomorrow. Mastered Today.
AXA's comprehensive healthcare protection spans from prevention and diagnosis to treatment and recovery, with our extensive medical network providing complete coverage across all locations. Whether protecting yourself or safeguarding your loved ones, AXA has prepared the answers for every step of your life journey.
Five key principles of ACL rehabilitation
1. Control swelling and pain early
Follow the RICE principle: Rest, Ice, Compression and Elevation. During the early post-operative period, apply ice regularly for 15 to 20 minutes at a time to help reduce pain and swelling.
2. Restore range of motion gradually
During the first two to three weeks after surgery, the priority is to regain full knee extension, while knee flexion should be increased progressively. Pushing too hard too soon may increase the risk of joint fibrosis and restrict long-term mobility.
3. Strengthen key muscle groups
Rehabilitation should focus on strengthening the quadriceps, hamstrings, gluteal muscles and core muscles. Training typically begins with isometric exercises before progressing gradually to dynamic strengthening exercises.
- Anti-gravity treadmill
For many patients recovering from surgery, one of the biggest rehabilitation challenges is how to resume walking and running without placing excessive stress on the healing joint. The anti-gravity treadmill was developed to help address this challenge.
The technology was originally developed to help NASA astronauts maintain their health during prolonged space missions. It works by using a sealed chamber to generate positive air pressure, lifting the lower body and reducing weight-bearing forces to between 20% and 80% of normal body weight. In other words, users can choose to train while bearing as little as 20% of their body weight, or progress to light weight-bearing exercise at around 80% of their normal weight. In recent years, anti-gravity treadmills have become available at selected healthcare institutions in Hong Kong and Chinese mainland, providing an additional rehabilitation option for suitable patients. Patients may explore the rehabilitation programmes available in either location based on their condition, their doctor's advice and their individual needs.
- Key benefits
Precise control with measurable progress: Body-weight support can be adjusted precisely between 20% and 80% in 1% increments, allowing rehabilitation progress to be tracked and measured at every stage.
Low-impact training with reduced discomfort: Patients can train throughout different phases of the gait cycle while placing less stress on the joints, helping to improve muscle strength, cardiovascular fitness and walking mechanics.
Real-time biomechanical feedback: High-precision sensors built into the treadmill can capture data such as cadence, stride length, ground contact time and left-right balance in real time. This enables rehabilitation specialists to correct abnormal movement patterns promptly and help reduce the risk of re-injury.
- Who may benefit from an anti-gravity treadmill?
Patients recovering from joint surgery: Including ACL reconstruction, meniscus repair and total knee replacement. Following total knee replacement, for example, rehabilitation training with an anti-gravity treadmill may begin as early as the first postoperative day.
Individuals who are overweight or obese: Greater body weight places increased stress on the joints and may increase the risk of injury during exercise.
Professional athletes: Used for post-injury conditioning, performance enhancement and low-impact training.
4. Proprioception and balance training
Restoring neuromuscular control is essential for a successful return to sport. Exercises such as single-leg standing and balance board training help the knee relearn how to sense body movement.
5. Returning to sport gradually
Avoid rushing the process. Returning to sport too early is one of the leading causes of a second ACL injury. Recent studies suggest that extending the rehabilitation period may support graft remodelling, giving the reconstructed ligament sufficient time to adapt to the demands of high-intensity sporting activities.
Your Health Tomorrow. Mastered Today.
AXA's comprehensive healthcare protection spans from prevention and diagnosis to treatment and recovery, with our extensive medical network providing complete coverage across all locations. Whether protecting yourself or safeguarding your loved ones, AXA has prepared the answers for every step of your life journey.
How can ACL tears be prevented, both for first-time injuries and re-injuries?
Prevention training programme
An effective ACL injury prevention programme should include strength training, proprioception training, agility training and proper landing techniques. Particular emphasis should be placed on maintaining a balance in strength between the hamstrings (the muscles at the back of the thigh) and the quadriceps (the muscles at the front of the thigh), as muscle imbalance is a recognised risk factor for ACL injury.
Tips for exercising safely
- Warm up adequately before exercise and avoid high-intensity activity when fatigued.
- Learn proper jumping and landing techniques by keeping the knees aligned with the toes and slightly bent on landing, avoiding excessive knee extension.
- Wear appropriate sports protective equipment. While it cannot completely prevent injury, it may provide additional support and protection.
For patients who have undergone ACL reconstruction
- A full rehabilitation programme (at least 9 to 12 months) should be completed before returning to high-intensity sports.
- Even after returning to sport, ongoing maintenance training is recommended. Strength and balance exercises should remain part of a long-term training routine.
Seek early treatment and follow medical advice
Although an ACL tear is a serious sports injury, the vast majority of patients are able to return to sporting activities with appropriate treatment and a structured rehabilitation programme.
Surgery is only one part of the treatment journey; rehabilitation is the key to recovery. Completing the critical rehabilitation period patiently is far more important than rushing back into sport. Returning too soon is one of the biggest risk factors for a repeat ACL injury. If you suspect that you have injured your ACL, seek medical attention as soon as possible. Early assessment and treatment may help prevent secondary injuries, such as a meniscal tear, that can occur if diagnosis and management are delayed.
The above content is reviewed by Dr Yau - Chief Medical Officer of AXA Hong Kong and Macau.
Information and materials provided is general in nature and does not constitute medical or health advice from AXA Hong Kong and is on an “as is” and “as-available” basis without representation and/or warranty of any kind, either express or implied. While AXA Hong Kong has taken reasonable care in providing such information and materials, they are not specific to your investment objective, financial situation, health or medical conditions or particular needs. No warranty or responsibility is assumed by AXA Hong Kong and our related or holding companies regarding non-infringement, security, accuracy, completeness, adequacy, reasonableness, fitness for a purpose or free from computer viruses in connection with the information and materials provided. AXA Hong Kong and our related companies and holding companies do not accept any liability for any loss, damage, cost or other expense, whether wholly or partially, directly or indirectly, arising from any error, inaccuracy or omission of the information and materials to the extent that such liability is not excluded by law.
Reference:
- Urreiztieta, Hayley C et al. “Treatment strategies for concomitant ligament injury in anterior cruciate ligament-injured athletes, a narrative review.” Annals of joint vol. 10 41. 27 Oct. 2025, doi:10.21037/aoj-25-28
- Castellanos Dolk, D., Sarakatsianos, V., Wörner, T. et al. Semitendinosus vs quadriceps tendon autograft in anterior cruciate ligament reconstruction (SEQUAR): protocol for a prospective randomized controlled trial. BMC Musculoskelet Disord 26, 951 (2025). https://doi.org/10.1186/s12891-025-09183-w
- Jonathon Lewis, Essa H Gul, Stephanie Boden & John Nyland (2025) Deciding Between ACL Reconstruction, Repair, and Conservative Treatment in Young Athletes: A Systematic Narrative Review, Open Access Journal of Sports Medicine, 16:, 255-278, DOI: 10.2147/OAJSM.S534937
- 郭春花,徐曉燕,何劼,等. 反重力跑台系統在前交叉韌帶重建術後步行訓練的應用[J/OL]中華關節外科雜誌（電子版）,2023,17(04)：485-491. DOI:10.3877/cma.j.issn.1674-134X.2023.04.005
You may also be interested in
Your Health Tomorrow. Mastered Today.
AXA's comprehensive healthcare protection spans from prevention and diagnosis to treatment and recovery, with our extensive medical network providing complete coverage across all locations. Whether protecting yourself or safeguarding your loved ones, AXA has prepared the answers for every step of your life journey.
Follow AXA
