Can an ACL tear heal on its own or need surgery?

A torn ACL can be a life-altering injury, and the question of whether it can heal on its own has been a topic of debate. Recent studies have suggested that a torn ACL may have the potential to heal without surgery. This finding challenges the traditional belief that surgical intervention is necessary for ACL injuries. Some experts have observed spontaneous healing in a significant percentage of ACL tears, indicating that the ACL may have self-healing potential. While this concept is still a subject of debate among medical professionals, the possibility of an ACL injury healing on its own has sparked interest in alternative treatment approaches, such as stem cell therapy and non-operative management. This article explores the emerging evidence regarding the self-healing potential of a torn ACL and its implications for treatment options and patient outcomes.


What is the ACL and what happens when it tears?

The anterior cruciate ligament (ACL) is a crucial structure in the knee joint, responsible for stabilising the joint by preventing excessive forward movements of the tibia and limiting rotational knee movements. It is one of the two cruciate ligaments in the knee and is essential for maintaining the stability of the joint during various activities such as walking, running, and jumping by connecting the thigh bone (femur) to the shin bone (tibia). The ACL is a band of dense connective tissue that runs from the femur to the tibia, providing approximately 85% of the total restraining force of anterior translation and preventing excessive tibial medial and lateral rotation. In addition, it plays a small role in resisting internal rotation and excessive movements. The ACL is commonly injured during sports activities that involve sudden stops, changes in direction, or direct blows to the knee, such as basketball, football, and skiing. When injured, the ACL can cause significant instability and functional impairment of the knee joint, often requiring medical attention and, in some cases, surgical intervention for optimal recovery.

ACL injuries are a fairly common injury in sports that involve sudden stops, changes in direction, jumping, and landing, such as soccer, basketball, football, and downhill skiing. When the ACL is damaged, there is usually a partial or complete tear of the tissue, leading to symptoms such as a popping sensation in the knee, swelling, instability, and pain that makes weight-bearing difficult. Treatment for ACL injuries varies depending on the severity of the injury. For less severe cases, medical treatment may involve several weeks of rehabilitative therapy, including exercises to reduce pain and swelling, restore the knee's full range of motion, and strengthen muscles. In some cases, a brace may be used to stabilise the injured knee, and crutches may be recommended to avoid putting weight on the knee. For more severe injuries, surgery may be recommended to reconstruct the torn ligament, followed by a rigorous rehabilitation program to restore stability and function to the knee. However, recent studies have suggested that up to 30% of ACLs in people who did not undergo surgery showed signs of healing on MRI scans two years after the injury, challenging the traditional belief that surgical intervention is always necessary.


Partial ACL Tears

Partial ACL tears are estimated to account for 10% to 27% of isolated ACL injuries and can be challenging to diagnose clinically. The decision to proceed with surgery for a partial tear is based on careful history and physical exam findings that suggest either a "functional" or "nonfunctional" ACL. Some studies have shown that younger, active patients with partial tears have the risk of progressing to a complete ACL rupture with conservative treatment. However, conservative treatments such as physical therapy have also been associated with good results when correctly indicated via a science-backed treatment plan, with minimal reduction of activity level and without impairing stability. An orthopedic surgeon may advise surgical ACL treatment for partial tears, which involves augmenting the intact bundle with a selective bundle reconstruction or a traditional ACL reconstruction, with the best evidence supporting traditional ACL surgery for the surgical management of patients with documented nonfunctional partial tears of the ACL. The prognosis for a partially torn ACL is generally good, with the recovery and rehabilitation period typically lasting at least three months. Nonsurgical treatment may be recommended for patients with partial tears and no instability symptoms, as well as for those with complete tears who don't experience symptoms of knee pain or instability during low-demand sports and are willing to give up high-demand sports.


Complete ACL Tears

The protocols for complete ACL ruptures can vary depending on whether the injury is managed non-operatively or requires surgical reconstruction. For non-operative management, a time-based and criterion-based rehabilitation protocol is often followed to guide clinicians through the course of treatment. This may involve a combination of exercises to reduce pain and swelling, restore the knee's range of motion, and strengthen the surrounding muscles. Additionally, the use of a knee brace and crutches may be recommended to provide stability and support to the knee during the healing process. On the other hand, for post-operative management after ACL reconstruction, a specific rehabilitation protocol is followed to restore and maximise the stability of the knee and prevent recurrent injuries or degenerative changes. This protocol is also time-based and criterion-based, with specific interventions tailored to the individual's needs and clinical findings. The rehabilitation process typically involves progressive exercises, range of motion activities, and functional training to facilitate the recovery of knee function and strength. Whether managed with non-surgical treatment or through surgical reconstruction, rehabilitation plays a crucial role in optimising outcomes and restoring the function of the knee joint after a complete ACL tear.


Recovery time of ACL injuries

The recovery time for a torn ACL varies depending on the severity of the injury and the chosen treatment approach. In general, the recovery time for a complete ACL tear is usually six to nine months, with competitive athletes potentially needing a little longer to heal fully before returning to their sport. However, research has suggested that over 50% of ACL tears can heal by themselves with no focused treatment, with 56% of tears spontaneously healing at two years. On the other hand, the recovery time for a partial ACL tear without surgery is generally around three months after the initial injury, although some knee joint instability may persist indefinitely. Surgical treatment for partial ACL tears may involve selective bundle reconstructive surgery or traditional ACL reconstruction surgery, with a recovery period lasting at least three months. It's important to note that the recovery time can vary among individuals, and rehabilitation plays a crucial role in optimizing outcomes and restoring the function of the knee joint after both partial and complete ACL tears. Professional athletes typically have more available access to medical teams and healthcare professionals which naturally means they generally have a more efficient rehabilitation, however with carefully management, it is not impossible for the average personal to return to pre-injury physical activity within the same timeframes.


Returning to sport after an ACL injury

Returning to sport after an injury is a critical decision that involves various factors and considerations. Athletes must undergo a comprehensive assessment to ensure that physiological healing has occurred, and parameters such as pain, swelling, range of motion, and strength have been evaluated to minimize deficits. The decision to return to play is not made in isolation but involves input from the medical team, physical therapists, coaches, and family members. The return to play process is a continuum, involving a progression from participation in rehabilitation or sport at a lower level to full return to sport. It is essential to ensure that athletes are mentally prepared to return to play, as some may be ready physically but not prepared mentally, which could lead to decreased confidence, re-injury, stress, and anxiety. The return-to-play process should complement the rehabilitation process and match the re-entry point, with conditioning and endurance training infused throughout all phases to reduce the risk of re-injury and optimise performance.


In conclusion, the impact of an ACL tear on an athlete's career is significant, given the frequency of the injury in sports, the heightened risk of re-injury, and the potential complications following surgery. Returning to sports after an ACL injury is a complex process that involves careful consideration of the physical and mental readiness of the athlete. The fear of re-injury and the challenge of regaining stability often affect an athlete's confidence and performance. While some athletes may successfully return to their sport, the risk of re-injury remains a concern. The decision to return to play should be guided by a comprehensive assessment and a well-structured rehabilitation program to minimise the risk of re-injury and optimize performance. Ultimately, the management of ACL injuries, whether partial or complete, requires a holistic approach that considers the individual's physical and psychological well-being, as well as the long-term implications for their athletic career and overall health.

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Arun Gray sports therapist strength and conditioning coach skegness

The author

Arun Gray is a sports therapist and strength & conditioning coach with over 15 years experience in the industry. He also has a personal history with chronic shoulder and back pain along with a range of other sporting injuries.

Arun writes about common injuries and aims to help people understand and manage their pain to prevent having to rely on national healthcare.

Read more about Arun