Five Facts to Understanding ACL Injury

1) Natural History: ACL injuries are among the most common sports-related knee injuries resulting in significant disability among athletes. Injury to the ACL can occur either due to a trauma or, more commonly, secondary to a ‘non-contact’ twisting injury. The latter is often experienced by athletes who plant and rapidly twist their knee prior to the onset of symptoms. In the majority of cases, injury to the ACL is accompanied by rapid swelling and difficulty with walking that occurs within minutes to hours.

2) ACL Structure and Function: The ACL or ‘Anterior Cruciate Ligament’ is x-shaped (‘cruciate’) in nature and is localized to the front (‘anterior’) aspect of the knee. The ACL’s primary function is to prevent excessive anterior or frontward motion of the shin-bone (tibia). The ACL’s secondary function is to provide stability with rotation or side-to-side type movements. Failure to properly address this second function is among the most common reasons for patient dissatisfaction following ACL reconstruction.

3) Treatment: The current standard of care for an injured ACL is reconstruction, with attempts to repair the torn tissue demonstrating poor results in terms of restoring knee stability. Reconstruction requires a ‘graft’ or replacement tissue, which is used to fashion a new ligament. While allografts (donor tissue from a cadaver) are a possible source of new tissue, it is generally not recommended for more active or younger patients due to an exponentially higher failure rate. When compared to a patient’s own ‘autograft’ tissue,  the use of an allograft can result in signficantly higher rates of reinjury. 

4) Surgical Considerations: Emerging data has greatly advanced understanding of ACL surgical techniques. The main rule for successful ACL reconstruction is to ensure that the graft is positioned in the knee in an ‘anatomic’ position, recreating the configuration of the natural ligament prior to injury. A second key factor to successful reconstruction is proper graft choice. While a hamstring based graft has been widely used, newer data suggests that hamstring-based ACL reconstruction may lead to sub-optimal results in certain populations, especially younger females and higher level athletes of young age. Currently, ‘BTB’ or patella-tendon reconstruction remains the gold standard, though recent trends suggest that a quadriceps based ACL reconstruction may soon become the method of choice for ACL injury.

5) ACL Rehabilitation: A multi-modal approach of physical therapy is mandatory following ACL surgery, beginning with ensuring full range of motion and progressing to strengthen the knee and especially quadriceps musculature. An improved understanding of return to sport has also effected timing of return to sport following ACL reconstruction. One study in particular, known as the ‘Delware-Oslo’ criteria, has demonstrated an exponential reduction in the risk of re-tear by allowing sufficient time for healing and muscular rehabilitation. Newer evidence has also shown that long-term bracing is not needed in a well-done, ‘anatomic’ reconstruction. Interestingly, returning too early can actually increase the risk of injury to the opposite knee.

Elan Golan, MD

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