When Does A Partial ACL Tear Require Surgery?

Male athlete injured his knee on a sports training.
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The anterior cruciate ligament (or ACL) is one of the primary ligaments in the knee joint. The ACL is important to allow for normal movement and mechanics of the knee joint. When the ACL is torn, people may notice problems in the way their knee functions. Common symptoms of an injured anterior cruciate ligament include:

  • Knee swelling
  • Pain around the knee joint
  • Sensations of buckling or giving out of the knee
  • Knee instability
  • Difficulty with sports activities

ACL injuries can either be complete or partial. When there is a partial ACL tear, a difficult decision about surgery needs to be made. An ACL reconstruction involves significant rehabilitation and other operative risks. Deciding when ACL reconstruction is necessary can be a difficult problem, especially when the ACL is only partially torn. So how do we decide when to reconstruct a partially torn ACL?

Partial ACL Tears

The anterior cruciate ligament is one of the four major ligaments of the knee, and it attaches the thigh bone to the shin bone, the femur to the tibia. It keeps the tibia from sliding too far forward and performs other functions to maintain the stability of the knee during rotation. When a ligament is injured, it is called a sprain. It is most commonly sprained or torn during landing a jump or making a sudden change in running direction, or having a fall.

ACL sprains are graded based on how much the ligament is damaged. A Grade 1 sprain in only minor stretching to the ligament and your knee is still fairly stable. A Grade 2 is a partial ACL tear, with the ligament stretched so much that it is loose and damaged. These are relatively rare. Meanwhile, in the more common Grade 3 sprain, there is a complete tear of the ACL, with the knee joint becoming unstable and surgery almost inevitable if it is to be corrected.

Surgery for Partial ACL Tears

Treatment of an ACL tear is most dependent on how much knee instability is caused by the injury. Therefore, there is no critical cutoff in terms of how much of the ACL is torn. I have heard some people say they were told if more than 50% of the ligament is torn, then surgery would be necessary. This might be a reasonable way to think about things, but there is no cutoff that has every been shown to be important in the decision process. Rather, most surgeons base a decision on how much instability the injury has caused. If the knee is unstable, then surgery is recommended. If the knee is stable, then non surgical treatments may be considered.

The decision is usually based on a combination of symptoms and physical examination findings. If you feel knee instability and have episodes of feeling the knee giving way, that can be a determining factor. The doctor will also consider the tests done in the physical exam, which often include the Lachman test and pivot-shift test. If these are consistent with laxity of the ACL, then reconstruction is a reasonable option.

Unfortunately, incomplete tears of the ACL are difficult to assess. When looking at an injured ACL during an arthroscopy, your surgeon can assess the look and feel of the ligament to make a judgment on the extent of the injury.

However, this look and feel method of assessing an ACL is very subjective. Not everyone will agree on what looks good and what looks bad. The better method of assessing a partial ACL injury is based on the aforementioned symptoms and examination findings.

If non-surgical treatment is preferred, you will likely be given a brace and crutches to protect your knee. Physical therapy for rehabilitation will be started once the swelling improves. The goal of nonsurgical treatment will be to maintain strength of the muscles surrounding the joint, and to try to optimize stability of the joint with muscle balancing and neuromuscular training.

A custom sports brace may be fitted for patients who want to return to athletic activity.

When surgical treatment is selected, usually the ACL will be reconstructed using tissue obtained either from somewhere else in the body or from a donor. The new ligament will be created to replace the damaged ligament. Efforts to repair a damaged ligament have yet to show as good results, although there are some new, experimental procedures, that are focused on healing of ACL injuries.

A Word From Verywell

The most common treatment for an injured anterior cruciate ligament in a young, athletic person is with surgical reconstruction of the ligament. The decision to proceed with surgery is best made by determining the amount of knee instability. Trying to determine how many of the ACL fibers are intact is difficult, whereas individuals with significant instability are unlikely to be able to return to sports activities. If a partial ACL tear is suspected, an orthopedic surgeon can help assess the degree of instability and whether or not ACL reconstruction might be a reasonable treatment.

Source:

Anterior Cruciate Ligament (ACL) Injuries, American Orthopaedic Society for Sports Medicine, March, 2014.

Carey JL, Shea KG. "AAOS Clinical Practice Guideline: Management of Anterior Cruciate Ligament Injuries: Evidence-Based Guideline" J Am Acad Orthop Surg. 2015 May;23(5):e6-8.

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