Anterior cruciate ligament (ACL) reconstruction is one of the most commonly performed procedures in sports medicine. Young athletes—male and female—sustain ACL injury at alarming rates, but females seem to be at increased risk for injury, especially when they engage in activities that involve pivoting, cutting, and landing from a jump.

Because surgical treatment of ACL injury costs close to $1 billion a year, the orthopaedic community has understandably focused its efforts on the identification and reduction of ACL risk factors and on injury prevention, particularly in females. Yet despite the abundant research on ACL injury, little emphasis has been placed on gender differences in ACL reconstruction, including graft choice, graft position, fixation types, rehabilitation, outcome, and long-term results.

ACL risk and the impact of gender
Risk factors for ACL injury are typically categorized in the following ways: intrinsic versus extrinsic and environmental, anatomic, hormonal, and neuromuscular. Extrinsic factors include weather conditions, shoe and equipment type, the shoe-surface interface, playing surface, and bracing. Intrinsic factors include Q angle, static and dynamic alignment issues, notch width, ACL size, hormones, balance, and muscle control.

Although some reports of gender differences in extrinsic factors exist, most of the literature has focused on gender differences in intrinsic factors. No single anatomic reason has been identified as a specific cause of ACL injury, but recently, a specific gene has been associated with the risk of ACL tear in females.

Hormones may be an obvious reason for differences in gender and ACL injury. Sex hormones, such as estrogen, influence collagen synthesis and degradation and are suspected to play a role in ACL injury. Sex hormone receptors have been identified in the ACL and may have some influence on ACL integrity, although no specific mechanism has yet been identified.

In addition, ACL tears in females demonstrate a pattern of occurrence and are associated with the pre-ovulatory and perimenstrual stages. Despite this research, no one is suggesting that female athletes limit their playing at any time during the menstrual cycle.

Recently, neuromuscular risk factors and their impact on ACL tears have become the focus of investigation. ACL tears, particularly noncontact tears, occur in activities that involve pivoting, cutting, and/or landing from a jump. If clear differences could be identified between males and females during these activities, then perhaps these injuries could be prevented.

Although males can have similar injury patterns, females tend to land with a straight, internally rotated hip, a straight valgus knee with the tibia in external rotation, and foot pronation. Differences in muscle-firing patterns and muscle stiffness between males and females may also contribute to the increased risk of ACL tears in females. As we begin to better understand these injury patterns, we can create more effective prevention programs.

Preventing ACL injury
Anatomic and hormonal issues are difficult to modify and do not seem plausible mechanisms to prevent ACL injury in males or females. Neuromuscular training appears to be the easiest means of preventing ACL injuries and may have the greatest potential for reducing the risk of injury. Most ACL prevention studies have been done in females, and the conclusions may not apply to the prevention of ACL tears in males.

A recent meta-analysis of the effect of neuromuscular training on ACL prevention found only seven studies that were randomized and controlled or that had prospective cohorts. The analysis concluded that pre- and in-season neuromuscular training, with an emphasis on plyometrics (rapid sequence loading and contracting) and strengthening exercises, was effective in preventing ACL injury in female athletes. Many prevention programs exist, and further randomized controlled studies are needed to determine their effectiveness for both males and females.

Who fares better after ACL reconstruction?
Very few studies have looked specifically at the role of gender in ACL reconstruction surgery outcomes. The studies that do exist show very little difference in outcome based on gender. This is not to say, however, that there are no differences. Strength recovery has been reported to be different in males and females, at least in the first 4 months following surgery. If differences in postoperative recovery exist between males and females, we may need to develop gender-specific protocols.

In addition, little is known about gender differences in graft choice, graft fixation type, or rehabilitation protocols. The rate of development of arthritis as a long-term complication of ACL injury as it relates to gender is another area that remains to be explored. Recent multicenter studies on long-term outcomes and causes of ACL reconstruction failure may be helpful.

Recommendations on whether or not to reconstruct the ACL should not be based solely on the patient’s gender. Further research in all areas of ACL injury—including prevention, graft choice, fixation choice, and rehabilitation protocols—should involve gender-specific components so that we can answer these questions for both our male and female patients.

Sharon L. Hame, MD, is associate clinical professor, University of California, Los Angeles, Department of Orthopaedic Surgery. She can be reached at shame@mednet.ucla.edu

Putting sex in your orthopaedic practice
This quarterly column from the AAOS Women’s Health Issues Advisory Board and the Ruth Jackson Orthopaedic Society provides important information for your practice about issues related to sex (determined by our chromosomes) and gender (how we present ourselves as male or female, which can be influenced by environment, families and peers, and social institutions). It is our mission to promote the philosophy that male and female patients experience and react to musculoskeletal conditions differently; when it comes to patient care, surgeons should not have a one-size-fits-all mentality.