Page 29 - ISAKOS 2019 Newsletter Volume 1
P. 29

Intrinsic Risk Factors
Anatomical factors:
Several anatomical factors unique to females have been implicated in the disparity between the sexes in terms of ACL injuries, including increased quadriceps angle (Q angle), smaller femoral notch width, smaller ACL size, increased tibial slope, increased ligamentous laxity, and increased body mass index (BMI)1. With regard to knee geometry, Sturnick et al. found that a 1-mm decrease in notch width and a 1° increase in posteroinferiorly-directed lateral tibial slope in females were associated with 50% and 32% increases in the risk of ACL injury, respectively. While many of these anatomical features are more common in females, they are not necessarily specific to the female sex and are independent risk factors associated with ACL injury.
Hormonal factors:
Hormonal factors also have been associated with an increased risk of ACL injury. Estradiol, progesterone, and relaxin are the main hormones that have been noted to be related to ACL laxity and phases of the menstrual cycle2. Testosterone also has been suggested to be protective against ACL injury, with animal studies having shown a higher ACL load to failure and ultimate stress in rats with comparatively higher circulating levels of testosterone3. Studies have shown that estradiol exposure can lead to a dose-dependent decrease in fibroblast and collagen synthesis in the ACL and that this effect can be lessened by the presence of progestins2. These cyclical hormonal levels have been correlated with a higher risk of ACL injury in the follicular and pre-ovulatory phases of the menstrual cycle. A number of studies have shown that oral contraceptive use may be associated with a reduced risk of ACL injury, with Gray et al. finding that females 15 to 19 years of age who underwent ACL reconstruction were 18% less likely to use oral contraceptives than matched controls. Similarly, a Danish registry study by Rahr-Wagner et al. showed that the relative risk of ACL injury was 0.82 (95% CI, 0.75-0.90) when “ever users” (defined as those who had used oral contraceptives in the previous 5 years) were compared with “never users.”
Biomechanical and neuromuscular factors:
Biomechanical and neuromuscular factors also may predispose female athletes to ACL injuries by contributing to risky landing mechanics1. Much research has focused in these areas as they encompass potential dynamically modifiable factors. Females tend to specifically recruit the quadriceps muscles at a greater rate than the hamstrings, resulting in a relative weakness of the hamstrings and a possible decrease in their knee-stabilizing properties. Additionally, research has suggested that preferential firing of the lateral hamstrings and lateral quadriceps in females increases the valgus stress on the knee. Decreased core and pelvic stability in females as compared with males also has been linked to inefficient lower-extremity landing mechanics.
All of these factors have been implicated as causing increased knee abduction angles and an increased risk of ACL injury.
Management and Outcomes
The treatment options for ACL injuries include both nonoperative measures (e.g., rehabilitation and bracing) and surgical reconstruction. The Delaware-Oslo ACL Cohort study showed that 53.6% of patients with ACL tears that were treated with rehabilitation alone had successful outcomes and that female patients and older patients were more likely to have a good outcome in association with nonoperative treatment. Females have also been found to be less likely to undergo ACL reconstruction than males3. Numerous studies evaluating sex-related disparities in terms of treatment outcomes following ACL reconstruction have revealed that subjective and functional outcomes and the ability to return to sports were inferior in females (Table II). Although some studies have suggested that females may be at greater risk for graft failure or contralateral ACL injury1, others have shown no significant differences in terms of the risk of graft failure, the risk of contralateral ACL rupture, or postoperative knee laxity on physical examination3.
Table II Treatment Considerations and Outcomes Related to ACL Injury in Females
Treatment Considerations
• Improved outcomes for females vs. males with nonoperative treatment
• Possible increased risk of graft failure in association with use of hamstring autograft vs. bone-patellar tendon-bone autograft
in females
• Possible increased
risk of postoperative arthrofibrosis in females
• Studies have shown inferior results in females concerning:
- Functional outcome scores
- Ability to return to sports
- Postoperative knee laxity
- Postoperative limb symmetry
- Graft failure
- Contralateral ACL injury
     With regard to surgical factors, graft choice and sizing are important considerations for the female patient. Several studies have shown that females who undergo ACL reconstruction with hamstring autograft are at a higher risk for failure postoperatively than those managed with bone- patellar tendon-bone autograft4,5. Nwachukwu et al. reported that female sex was a specific risk factor for postoperative arthrofibrosis after ACL reconstruction in patients 7 to 18 years old. Su et al., in a retrospective study, found that 65% of arthrofibrosis cases after ACL reconstruction occurred in females even though fewer than half the patients in the study were female and that a 1-mm increase in graft size was associated with a 3.2-times increased odds of arthrofibrosis.

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