Commentary & Perspective

Commentary & Perspective on
"Gender Differences in Muscular Protection of the Knee in Torsion in Size-Matched Athletes"
by Edward M. Wojtys, MD, et al.

Commentary & Perspective by
Frank R. Noyes, MD*,
Cincinnati Sports Medicine, Cincinnati, OH

As the epidemic of anterior cruciate ligament injuries in female athletes continues¹, the need for scientific investigation of the factors related to this problem has become paramount. This article documents gender-related differences in response time, recruitment order, strength, and endurance of the lower-extremity muscles²; sagittal-plane shear stiffness³; and knee flexion angles on landing from a drop-jump⁴. The authors are to be commended for their efforts and their contributions to the current knowledge of these factors.

The authors hypothesized that collegiate female athletes would have less torsional stiffness of the knee following muscle activation than would size and sport-matched male athletes. This reduction in stiffness, which results in loss of the intrinsic protection that the knee muscles provide to the ligaments, is postulated to be a factor in the relative increase in the prevalence of serious knee-ligament injuries in female athletes when compared to that in male athletes. Twelve male and twelve female collegiate athletes competing in sports that involved pivoting and cutting (associated with high rates of anterior cruciate ligament injuries) were compared with fourteen male and fourteen female collegiate athletes participating in non-pivoting and endurance sports (bicycling, crew, and running), which are associated with a low risk of these injuries. An apparatus was designed that applied an 80-N medially-directed impulse force to the lateral aspect of the forefoot at the fifth metatarsophalangeal joint to simulate the ground reaction force under the landing foot of an athlete attempting a cutting or pivoting maneuver. Then the resulting internal rotation of the leg was optically measured. All subjects were tested in both active and passive conditions (with and without muscle activation). The results indicated that under both conditions, female athletes had greater amounts of internal tibial rotation than did male athletes. Female athletes who participated in pivoting sports had significantly smaller increases in apparent torsional stiffness across the knee under loading conditions than did size and sport-matched male athletes participating in similar sports (p = 0.014). Wojtys et al. concluded that the female athletes exhibited less muscular protection for their knee ligaments under external rotation forces than did the male athletes and suggested that improving active muscle protection of the knee through training programs might help decrease rates of knee injury in female athletes.

We agree with the authors' general conclusions regarding the importance of training female athletes involved in jumping and cutting sports to develop activation of the hamstring muscles on landing. Our neuromuscular training⁵ program stresses pre-positioning of the lower extremity and knee joint, to avoid landing positions associated with a high risk of injury, as well as increasing hamstring strength and endurance. However, further studies are warranted to determine the clinical significance of the reported difference of only 3° (7.4° versus 4.4°, respectively, at 30° of knee flexion) in active internal tibial rotation between the female and the male athletes who were involved in pivoting sports. Additionally, the testing apparatus, which required that the subjects be in a seated position, did not truly replicate actual pivoting conditions that occur during sports activities. If the hamstring muscles are activated prior to ground contact, the intrinsic increase in knee-joint stiffness is postulated to aid in protecting the ligaments of the knee⁶. It has been well established by these authors and others that men and woman activate lower-extremity muscles differently in response to anterior tibial forces generated during athletic maneuvers^1,2.

There are many gender-related differences in neuromuscular function and anatomy, all of which probably contribute to the higher prevalence of serious knee-ligament injuries in female athletes. We previously reported⁵ that female athletes, in comparison with male athletes, have substantially lower hamstring-to-quadriceps muscle peak torque ratios; higher knee adduction and abduction moments on landing from a jump; lower external knee extension moments on landing; and a marked imbalance between the quadriceps and hamstring musculature. We found that a neuromuscular training program effectively increased the peak torque and the power of the hamstrings, thereby reducing the quadriceps-hamstrings imbalance, decreased knee adduction and abduction moments (medially and laterally directed torques) by 50%, lowered peak landing forces (103 pounds [46.7 kg] or 80% of mean body weight), and improved vertical jump height by an average of 3.5 cm. Our six-week program consists of a dynamic warm-up, plyometric training, muscle-strength training, and flexibility exercises. We also found that this training program⁷ substantially reduced the prevalence of serious knee-ligament injuries in high-school female athletes (aged 14 to 18) to rates comparable to those found in male athletes.

Further research is required not only to deepen our understanding of gender-related neuromuscular differences in young athletes but also to determine the effectiveness of specific training programs in reducing the incidence of serious knee-ligament injuries in female athletes. We agree with Wojtys et al. that improving the strength of the hamstrings and training female athletes to volitionally activate these muscles prior to ground contact may help to decrease their rates of knee injury. Additionally, female athletes need to be taught to instinctively avoid positions that place the knee joint at increased risk of injury by improving total body awareness and proprioception, upper body and trunk control, hip and ankle-joint control, and lower-extremity muscular strength.

*The author did not receive grants or outside funding in support of the research or preparation of this manuscript. He did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.

References

1. Huston LJ, Wojtys EM. Neuromuscular performance characteristics in elite female athletes. Am J Sports Med. 1996;24:427-36.
2. Wojtys EM, Ashton-Miller JA, Huston LJ. A gender-related difference in the contribution of the knee musculature to sagittal-plane shear stiffness in subjects with similar knee laxity. J Bone Joint Surg Am. 2002;84:10-6.
3. Huston LJ, Vibert B, Ashton-Miller JA, Wojtys EM. Gender differences in knee angle when landing from a drop-jump. Am J Knee Surg. 2001;14:215-9; discussion 219-20.
4. Griffin LY, Agel J, Albohm MJ, Arendt EA, Dick RW, Garrett WE, Garrick JG, Hewett TE, Huston L, Ireland ML, Johnson RJ, Kibler WB, Lephart S, Lewis JL, Lindenfeld TN, Mandelbaum BR, Marchak P, Teitz CC, Wojtys EM. Noncontact anterior cruciate ligament injuries: risk factors and prevention strategies. J Am Acad Orthop Surg. 2000;8:141-50.
5. Hewett TE, Stroupe AL, Nance TA, Noyes FR. Plyometric training in female athletes. Decreased impact forces and increased hamstring torques. Am J Sports Med. 1996;24:765-73.
6. Markolf KL, Graff-Radford A, Amstutz HC. In vivo knee stability. A quantitative assessment using an instrumented clinical testing apparatus. J Bone Joint Surg Am. 1978;60:664-74.
7. Hewett TE, Lindenfeld TN, Riccobene JV, Noyes FR. The effect of neuromuscular training on the incidence of knee injury in female athletes. A prospective study. Am J Sports Med. 1999;27:699-706.