Cruciate knee injuries in female atheletes (neuromuscular control strategies)
Neuromuscular control strategies and anterior cruciate ligament injury in female athletes. Motor Control, sports injuries and neuromuscular performance - Iain Mactier
Anterior cruciate ligament (ACL) injury remains a significant, yet largely unsolved clinical issue (McLean et al. 2008). The increased incidence of ACL injuries in females is well recognised with females experiencing ACL injuries at a 2-10 fold greater rate than male athletes (Hewett et al. 2009). Many factors to explain this difference have been suggested, including anatomic variables and hormonal differences but there is lack of consensus on the roles of these factors. (Griffin et al. 2000). Insufficient neuromuscular (NM) control whilst performing high risk manoeuvres has also been suggested to increase the risk of non-contact ACL injury (Myer et al. 2005,Mclean et al. 2008). This abstract aims to explore if differences in neuromuscular (NM) control strategies can account for some of the difference in non-contact ACL injury rates between female and male athletes.
The basic mechanism for ACL injury is not fully understood, but it is recognised to occur whilst landing with external rotation of the tibia, the knee close to full extension, and the foot planted (Myer et al. 2005). This positioning, in combination with rapid deceleration (experienced during high risk manoeuvres such as pivoting or sidestepping), can result in valgus collapse and ACL injury (Griffin et al. 2000). A recent study by Hewitt et al. (2009) sought to understand the effect of trunk, and subsequent knee position in the ACL injury mechanism. 23 video tapes of athletes were analysed (10 female and 7 male athletes sustaining an ACL injury that required reconstruction, and 6 female controls). Females were shown to land with higher lateral trunk and knee abduction angles than male athletes during ACL injury (p<0.05) suggesting these motions may also be important components of the ACL injury mechanism. The authors hypothesised that deficits in NM control of the trunk may contribute to the knee instability. The stability of the knee is recognised to rely on both static (ligament) and dynamic (fine NM control of skeletal muscles crossing the joint) stabilisers (Griffin et al. 2000). Perturbations in NM control strategies, resulting from a sudden change in planned activity can give the central nervous system insufficient time to recover, leading to loss of balance and potentially contributing to non-contact ACL injury (Griffin et al. 2000). McLean et al. (2008) recently investigated the effects of such perturbations in a computer controlled simulation. 20 subjects, 10 male and 10 female had individual musculoskeletal computer models generated following the performance of sidestep manoeuvres. This was achieved through the recording of 3D kinematic data captured by skin markers attached to various anatomical points. NM control perturbations were applied initially to baseline models, and then to models with modifications in limb positions applied. ACL injury was deemed to occur if peak anterior force exceeded 2000N or peak valgus loads exceeded 125N. No perturbed model sustained injury due to peak anterior force exceeding threshold value, but 19.7% of male and 27.5% of female baseline simulations demonstrated ACL injury as a result of excessive valgus loading. Certain modification in limb positions, including increased hip and knee flexion were shown to significantly reduce the incidence of injury (p<0.05). Females have previously shown to utilise less knee flexion when performing high risk sports manoeuvres (Myer et al. 2005).
Wojtys et al. (1999) postulated that fatigue, and its effect on NM activation, is another factor that may contribute to ACL injury. 10 subjects, 6 males and 4 females, were evaluated. Anterior tibial translation was measured through use of 2 linear potentiometers, and levels of NM function established from electromyographic (EMG) recordings from five muscle locations in the dominant leg. Average anterior tibial translation before exercise was 4.25 (range, 1.77-8.93) mm with the knee relaxed and 2.08 (0.6-4.66) mm whilst resisting the displacing force. The exercise test involved the subject’s dominant leg being fatigued on an isokinetic dynamometer until a 50% decrease in work output was demonstrated. An average increase in anterior tibial translation of 32.5 (11.4-85.2) % was observed, suggesting knee laxity can increase as a result of muscle fatigue. The recruitment order of the lower extremity muscles to anterior muscles did not change in response to fatigue although significant delays (p<0.05) in lateral (LQ) and medial (MQ) quadriceps muscle reactions, both voluntary and those originating at the spinal cord and cortical level, were observed. Myer et al. (2005) sought to understand if differences exist between male and female quadriceps NM activation strategies. 20 physically active subjects were evaluated, 10 male and 10 female. EMG recordings were taken whilst subjects performed a manoeuvre mimicking an ACL injury position to measure the ratio of activation between LQ and MQ. Females on average, demonstrated a decreased RMS MQ to LQ ratio compared to males (0.783 vs. 1.249, p=0.026) suggesting they utilise NM activation strategies that may contribute to a dynamic knee valgus, which in combination with rapid deceleration could result in ACL injury.
It seems likely that the increased incidence of ACL injuries in females may be, at least partially, due to a lack of NM control of the trunk and a lower MQ to LQ activation ratio, both of which contribute to knee instability. Fatigue and NM perturbations, both of which are likely to occur during intensive exercise, are likely contribute to this predisposition and increase the risk of injury further. Dynamic NM training may help female athletes adopt NM control strategies to minimise the risk of ACL injury although further research is needed to optimise the benefit of this training (Myer et al. 2005).
- Griffin, L.Y. et al. (2000) Noncontact anterior cruciate ligament injuries: risk factors and prevention strategies. J Am Acad Orthop Surg. 8(3), 141-150.
- Hewett, T.E., Torg, J.S., Boden, B.P. (2009) Video analysis of trunk and knee motion during non-contact anterior cruciate ligament injury in female athletes: lateral trunk and knee abduction motion are combined components of the injury mechanism. Br J Sports Med. 43(6), 417-422
- McLean, S.G., Huang, X., Bogert, A.J. van den. (2008) Investigating isolated neuromuscular control contributions to non-contact anterior cruciate ligament injury risk via computer simulation methods. J Clin Biomech. 23(7), 926-936
- Myer, G.D., Ford, K.R., Hewett, T.E. (2005) The effects of gender on quadriceps muscle activation strategies during a maneuver that mimics a high ACL injury risk position. J Electromyog Kinesiol. 15(2), 181-189
- Wojtys, E.M., Wylie, B.B., Huston, L.J. (1996) The effects of muscle fatigue on neuromuscular function and anterior tibial translation in healthy knees. Am J Sports Med. 24(5), 615-621