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Anterior Cruciate Ligament Injury in Female Athletes: Why are women so vulnerable?
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Anterior Cruciate Ligament Injury in Female Athletes: Why are women so vulnerable?
Key Words ACL, female, injury, athlete. by Trevor Lewis
Literature review
Summary Female athletes are more likely to suffer certain sportsrelated injuries than their male counterparts. The knee joint in particular is a troublesome site and the anterior cruciate ligament is a structure especially susceptible to injury. Many explanations regarding possible contributing factors to this increased prevalence have been put forward, including sex-related skeletal variation such as pelvic width, femoral anteversion, femoral intercondylar notch dimensions, and increased Q-angle. Some of these explanations appear to be dubious. However, recent research into pronation control, ligament laxity, neuromuscular characteristics and the effect of menstrual hormones on the ACL has produced some enlightening data. Awareness of the possible causes of increased ACL injury rates in women and girls provides a basis for strategies to help to prevent this potentially devastating injury. It seems that co-ordination and agility work combined with proprioceptive exercises could play a large part in reducing injury rates.
Introduction ‘The paramount destiny and mission of woman is to fulfil the noble and benign offices of wife and mother. This is the law of the Creator and the roles of society must be adapted to the constitution of things’ (Bradley, 1872).
Lewis, T (2000). ‘Anterior cruciate ligament injury in female athletes: Why are women so vulnerable? Literature review’, Physiotherapy, 86, 9, 464-472.
Fortunately the above statement is not representative of the current climate of opinion, but it serves to illustrate that with such ideas recommending subjugation of women in 19th century society, it is not surprising that female participation in sport was quite limited until recent times. A defining moment in the involvement of females in sport in the US was Title IX of the Education Amendment Act of 1972 (Bradley, 1872), the final regulations of which required equal opportunities in athletics; the US Congress implemented Title IX in 1974. Since this statute there has
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been a quantum leap in the number of females participating in sport at all levels. Before Title IX fewer than 10,000 females competed in collegiate sport (Ireland et al, 1997). Recent figures published by the National Collegiate Athletic Association Surveillance System reported that there were 107,605 female participants in 16 sports (NCAA, 1994-95). Both participation and disciplines have changed; women have ventured from traditional, non-contact sports such as swimming and track and field to physical games like basketball, hockey and soccer. Women’s sports, once dominated by a slow, defensive style are now played with speed, precision and power (Moeller and Lamb, 1997). Increased injury rates have accompanied the rise in participation and while foot, shoulder and patellofemoral problems are common, so too is disruption of the anterior cruciate ligament (ACL) (Arendt, 1996). Such injuries are particularly catastrophic due to the length of time lost from sport and the financial implications of care (Freeman et al, 1995). Sports in the US associated with female ACL injury are quoted as soccer, basketball, skiing, volleyball and gymnastics (Huston and Wojtys, 1996). In Europe soccer is again implicated, along with handball and skiing (Bjordal et al, 1997). Injuries occur more often in competitive games than in practice matches (Anderson et al, 1991). This has been stated as up to three times the likelihood and appears to be due to the increased intensity of the competitive match atmosphere (Garrick and Requa, 1978). ACL injury rates of both sexes have been compared at all levels from junior to élite professional. Bjordal et al (1997) compared ACL injury rates in 15- to 18-year-old footballers, and found that females were 5.4 times more likely to sustain injury than males.
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The NCAA Injury Surveillance System in the 1989/90 season reported that female athletes injured their ACL at a rate of 7.8 times more than male athletes (Pearl, 1993). Malone et al (1993) compared injury rates by sex in college basketball players and reported females as eight times more likely to sustain ACL injury. In the US in 1988 participants in the Olympic basketball trials completed an injury questionnaire. The population sample consisted of 64 women and 80 men adjudged to be the country’s élite athletes. Thirteen of the women had sustained an ACL injury compared to only three of the 80 men. Eight women had undergone ACL reconstruction compared with three of the men (Ireland and Wall, 1990). The higher ratio of female injury was said to be understandable due to the steep rise in their participation levels (Protzman, 1980). A high incidence of stress fractures was observed in women when they first entered military service (Cox and Lenz, 1984). With time the injury rates of these fractures eventually equalised with those of men; however, this has not been the case with female ACL injury rates. Sports involving physical contact, ballistic movement and weight-bearing rotation such as basketball, soccer and volleyball are noted for producing ACL injuries (Moeller and Lamb, 1997). In potentially less injurious, non-contact track events, however, Jackson et al (1980) observed double the injury rate among female athletes. Five non-contact mechanisms of ACL injury have been recognised: planting and cutting (a sudden change in body direction following foot-toground contact), straight-knee landing, sudden deceleration, pivoting, and one-step stop landing with knee hyperextension (Moeller and Lamb, 1997). Given these findings, a review of some of the most commonly cited factors which are said to contribute to female ACL injury is needed to clarify which of them are significant in the aetiology of such injuries. Anatomy and Biomechanics The ACL helps to limit anterior translation of the tibia on the femur. It works with the posterior cruciate ligament to control gliding and rolling of the tibia on the femur during normal flexion and extension. It provides secondary restraint limiting internal rotation of the tibia and also seems to make at least a minor contribution to restraining both varus and valgus stresses
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across the knee joint (Norkin and Levange, 1992). The ligament is made up of two bands: the anteromedial and posterolateral (and occasionally there is also an intermediate band). The ACL runs from the posteromedial portion of the lateral femoral condyle through the femoral intercondylar notch in an inferior, anterior and medial direction to an area lateral to the medial tibial eminence. The posterolateral band is tightest during knee extension, and the anteromedial band is tightest in knee flexion (Moeller and Lamb, 1997). The twisted configuration of the ACL fibres and the shape of the femoral condyles allow for the screw-home mechanism of the knee during the final 20° of extension when the tibia externally rotates on the femur. The ligament is under varying degrees of tension in all positions of motion, but maximal tibial anterior translation is observed at 30° flexion when both the ACL bands display their minimum tension (Torzilli et al, 1981). Schultz et al (1984) identified mechanoreceptors in the ligament, and Yahia and Newman (1991) and Zimny and Wink (1991) have both reported that mechanoreceptor density is highest at the proximal and distal bony attachments. The proprioceptive function of the ACL has been intensively studied. Schutte et al (1987) stated that 1% of the ligament’s dry weight was neural tissue and Barrack et al (1989) observed significant proprioceptive deficit in knees with ACL disruption. A neurological link between the ACL and the cerebral cortex has been established from cortical EEG signals produced by ACL stimulation during arthroscopy (Pitman et al, 1992).
Author and Address for Correspondence Mr Trevor Lewis GradDipPhys MCSP is a clinical physiotherapy specialist (musculoskeletal service) in the physiotherapy department at The Royal Liverpool University Hospitals, Prescot Street, Liverpool L7 8XP. e-mail: [email protected] This essay was submitted this year as coursework towards a master’s degree in sports science at John Moores’ University, Liverpool. It was received by Physiotherapy on June 28, 1999, and accepted on March 1, 2000.
Funding This research was funded by the Hospital Savings Association.
Structural Factors The ‘miserable malalignment syndrome’ of high Q-angle, increased pelvic width, anter verted femur, valgus knee, and pronated foot (James, 1976) is often quoted as an explanation for increased knee injury rates in females (see figure overleaf). The different components of this syndrome will now be discussed separately along with a review of more recent work concerning joint laxity, sex-related neuromuscular characteristics, and menstrual hormones. Q-angle The Q-angle is described as being formed between the vectors for the combined pull of the quadriceps femoris muscle and the Physiotherapy September 2000/vol 86/no 9
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Wider pelvis
Less muscular thigh development
Femoral anteversion
Less developed VMO Increased flexibility/hyperextension
Narrow notch
Genu valgum
External tibial torsion
Narrower pelvis
More developed thigh musculature VMO hypertrophy Wider notch Less flexibility Internal or neutral tibial torsion
Genu varum
A
B
Lower extremity alignments that may predispose athletes to over-use problems of hips and knees, especially ACL and patellofemoral injuries: A females, B males. Reproduced with permission from Fu, F H and Stone, D A (1984). Sports Injuries: Mechanisms, prevention, treatment, Williams and Wilkins, Philadelphia
patellar tendon (Hungerford and Barry, 1979). Hahn and Foldspang (1997) investigated 339 athletes and observed Q-angle asymmetry within subjects, and their experiment also found that the Q-angle was greater in females. There is no strict agreement regarding standardised reference values, but Q-angles exceeding 15° in males and 20° in females are considered abnormal (Horton and Hall, 1989). Anecdotally, increased female Qangle is often explained by females possessing a wider pelvis than males, thus increasing the obliquity of the femora and consequently the valgus orientation of the knee (Moeller and Lamb, 1997; Ireland et al, 1997; Caylor et al, 1993). There is a recognised relationship between high Q-angle, patellar maltracking and anterior knee pain, and several authors have speculated that this sex-related anatomical difference may also lead to increased risk of ACL injury (Hutchinson and Ireland, 1995; Moeller and Lamb, 1997). However, several studies have found no relationship between Q-angle and predisposition to ACL injury (Gray et al, 1985; Loudon et al, 1996). Not only is there no clear link between ACL injury and Q-angle but there is no consensus in the literature as regards Q-angle measurement. In a review of literature regarding the Q-angle, Livingston (1998) states that it is question-able whether Physiotherapy September 2000/vol 86/no 9
a static Q-angle measurement has any bearing on dynamic activities. The current literature suggests that the Q-angle is an unreliable measurement and even if it were reliable its role in female ACL injury is uncertain. Pelvic Width Females are said to have a wider pelvis than males and this is quoted regularly in the literature (Hutchinson and Ireland, 1995; Ireland et al, 1997; Moeller and Lamb, 1997). Ireland et al (1997) state that a wider female pelvis increases ACL injury risk by creating a greater coxa vara/genu valgum alignment with a concurrent increase in tibio-femoral rotational force, thus imposing greater stress on the ACL. Unfortunately no research was presented by these authors to substantiate this comment. Even though soft tissue outlines may suggest otherwise, there is a significant amount of evidence to refute the idea that the female pelvis is wider than that of males. The absolute width using anterior superior iliac spine measurements (Guerra et al, 1994) biiliocristal (Atwater, 1990), and bitrochanteric measurements (Horton and Hall, 1989) was found to be virtually the same in both sexes. Despite the frequent assumption of increased pelvic width in females, this notion is not well founded. Studies that have been conducted in this
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area strongly refute anatomical sex differences and thus any possible contribution to female ACL injury. Femoral Intercondylar Notch An association has been suggested between a small intercondylar notch and sustaining an ACL tear (Laprade and Burnett, 1994). Notch dimensions have been widely reported as a causative factor in higher female ACL injury rates due to women possessing a smaller ‘notch width index’ (NWI) than men (Souryal and Freeman, 1993). Souryal et al (1988) defined the NWI as ‘the ratio of notch width to that of the distal femur at the level of the popliteal groove’. This is measured using a ‘tunnel view’ radiograph, and a ‘normal’ ratio was quoted as 0.2. Souryal et al (1988) proposed prophylactic bracing and notchplasty in the unaffected knee of patients who had torn the contralateral ACL and whose NWI was below normal. These recommendations assume that notch anatomy is the most decisive component in ACL injury. Muneta et al (1997) investigated whether ACL dimensions could be predicted by notch width and found that both narrow and wide notches house the same size ACL. They hypothesised that injury is due to normal-sized ligaments being ‘frayed’ in stenotic notches. However, this was a cadaveric study of only 16 elderly knees (average age 74.8 years) and using ACL moulds cast from dental silicone to arrive at their results. Possible age-related changes in either bone or ligament were not mentioned. Additionally, the accuracy of their ligament moulds to the biological ACL proportions was not evaluated. Teitz et al (1997) compared bilateral NWI in 40 male and 40 female patients using radiographs. They found that NWI were symmetrical within subjects and there was considerable overlap in dimensions between sexes. Females displayed a smaller NWI than males but this was not statistically significant, There was also no difference in NWI between patients with and without ACL tears. Disagreement between studies may be a product of different imaging techniques used to map the dimensions of the notch. Magnetic resonance imaging (MRI) has displayed no difference in NWI between normal and ACL deficient knees (Herzog et al, 1994). MRI was also used by Staeubli et al (1999) on 51 knees (25 females, 26 males)
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to assess any sex-related differences. They found that the absolute widths of the ACL with respect to intercondylar notch widths were not significantly different between sexes. It seems that more contemporary research using the anatomical precision of MR images is gradually rejecting femoral notch dimensions as a predictive factor in ACL injury. Subtalar Pronation Pronation is defined as a combined motion involving subtalar eversion, foot abduction and ankle dorsiflexion (Norkin and Levange, 1992). Subtalar pronation and internal rotation of the tibia occur concurrently in the contact phase of the gait cycle and the ACL becomes taut with tibial rotation (Woodford-Rogers et al, 1994). Coplan (1989) reported that abnormal pronators were found to have increased passive knee rotation at 5° of knee flexion and that there is a very important relationship between pronation and rotational knee joint laxity. It has been concluded that prolonged pronation of the subtalar joint produces increased internal tibial rotation which in turn stresses the medial structures of the knee (Vogelbach and Combs, 1987). The navicular drop test involves measuring navicular height in sitting in sub-talar neutral, then in full weight bearing, and is described as a measure of pronation in an experiment by Woodford-Rogers et al (1994). Drop height was recorded in 22 ACL-injured athletes (14 male and 8 female) and compared with 22 age- and sport-matched controls. A statistically significant difference was noted where non-injured subjects dropped 5.9 mm while ACL-injured athletes dropped 8.4 mm. Loudon et al (1996) observed similar results and found that excessive navicular drop and excessive subtalar joint pronation were statistically significant discriminators between ACL-injured and non-injured groups. It seems that a consensus is developing regarding a relationship between excessive pronation and ACL injury, but experiments to establish any significant differences between males and females have not been carried out. Femoral Anteversion Feagin et al (1982) discussed the importance of femoral rotation in the transverse plane as a mechanism of injury to the ACL. Tiberio (1987) has stated that internal rotation of the femur predisposes an individual to Physiotherapy September 2000/vol 86/no 9
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excessive pronation of the subtalar joint and thus concomitant ACL injury. The angle of anteversion is said to be measurable using the clinical method described by Ruwe et al (1992). The patient is placed prone with the knee flexed to 90°. The greater trochanter is palpated while passive medial and lateral hip rotation are conducted. The trochanter should be most prominent in neutral rotation; anteversion is present if there is medial hip rotation greater than 15°. Loudon et al (1996) used the above test to assess whether there was a relationship between femoral anteversion and the prevalence of non-contact ACL injury. Their study found no difference in anteversion between ACL-injured and non-injured knees. However they conceded that a weightbearing measurement might have yielded different results. No other work has been undertaken to investigate the role of femoral anteversion concerning either any possible sex-related differences or the role of anteversion in ACL injury per se. Further work needs to be undertaken in this area. Joint Laxity It has long been suggested that there is a relationship between joint laxity and joint injury including ACL injuries in females (Nicholas, 1970). Huston and Wojtys (1996), using arthrometric measurements, found that both female athletic and non-athletic controls exhibited more anterior tibial laxity than their male counterparts. Beck and Wildermuth (1985) stated that ligamentous laxity can be related to conditioning as much as to hereditary factors. This statement appears to be supported by the work of Huston and Wojtys (1996) who found that female athletes tended to have less ligamentous laxity than sedentary females. Woodford-Rogers et al (1994), also using a KT-1000 arthrometer, found that anterior knee joint laxity was significantly greater in ACL-injured subjects than in non-injured subjects. Knapik et al (1991) found that knee joint laxity has no direct relationship with ACL injury in female athletes. However, their study assessed joint flexibility using goniometry against active range of motion rather than with arthrometry. Loudon et al (1996) investigated the discriminatory value of knee recurvatum in female athletes and the prevalence of non-contact ACL injury. They found that subjects with knee hyperextension had a statistically greater predisposition to ACL injury. The contemporary trend of measuring joint Physiotherapy September 2000/vol 86/no 9
laxity using arthrometers appears to be producing a consensus regarding the role of joint laxity in female ACL injury. It has been stated that individuals with hypermobile joints often have concomitant motor delay with proprioceptive deficits (Russeck, 1999). This means that female ACL injury in joint laxity states could be attributed to motor deficit as much as hypermobility. Neuromuscular Performance Anecdotally, Beck and Wildermuth (1985) suggested that the main reason behind the higher incidence of non-contact ACL injury in females was a result of inadequate motor skills. Studies have shown that the ACL operating in isolation is not capable of withstanding the forces produced across the knee during sporting activity (Woo et al, 1991). A reflex arc between the ACL and the hamstrings mediates protective reflex contraction of these muscles when the ligament is stressed which limits anterior tibial translation (Skoglund, 1973; Hagood et al, 1990). Huston and Wojtys (1996) investigated EMG neuromuscular patterns along with lower extremity muscle strength, endurance, and muscle reaction times and recruitment order in response to anterior tibial translation by arthrometer. Sixty male athletes, 40 female athletes, and 40 healthy non-athletic controls from both sexes were investigated. Significantly less muscle strength and endurance was demonstrated in female athletes and the muscle recruitment order in some female athletes was noticeably different. They relied on the quadriceps muscles in response to anterior tibial translation; this muscle group being an ACL antagonist. The other three groups relied more on their hamstring muscle group. Female athletes were also weaker in the hamstrings and quadriceps and also took significantly longer to generate maximal hamstring torque. Huston and Wojtys’ careful study investigated female athletes from basketball, field hockey, gymnastics and volleyball. Larger numbers of males and females should be tested across a wider range of sports in order to confirm these results. Hormonal/Menstrual Factors Throughout their sporting lives, female athletes are subject to cyclical variation in endogenous hormones and possibly exogenous hormones via oral contra-
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ceptives. Recent research has investigated the influence of hormones on ligaments, and oestrogen and progesterone receptors have been isolated in the ACL (Liu et al, 1997). Their research found that collagen synthesis was significantly reduced with increasing estradiol concentrations. The subsequent structural changes were said to result in reduced strength of the ACL, rendering the ligament more susceptible to injury. Slauterbeck et al (1999) investigated the effect of experimentally increased serum oestrogen levels on failure load of the ACL, and found that load-at-failure was significantly reduced in the experimental group (446 ± 54 N) compared to that of a control group (503 ± 48 N). The experimenters report that elevated oestrogen levels produce a reduction in the tensile strength of the ACL. The work of Liu et al (1997) and Slauterbeck (1999) was conducted using animal models. Liu et al (1996) observed similar results in an experiment using human tissue. Wojtys et al (1998) collected data from 40 female athletes with ACL injury regarding mechanism of injury, menstrual cycle, contraceptive use and previous injury. A statistically significant association was found with injury during the ovulatory phase of the cycle when oestrogen levels are high (days 10-14) and with reduced injury likelihood in the follicular phase (days 1-9) when oestrogen levels are lower. Thus sex hormones may be a factor in the knee ligament problems in women. However, oestrogen is said to affect the central ner vous system and motor function (Wojtys et al, 1998). This means that impaired muscle recruitment or compromised co-ordination could be just as significant as diminished ACL tensile strength in ovulatory phase injury. Discussion Traditional explanations for female ACL injury implicating alignment (Q-angle, pelvic width, femoral anteversion and configuration of the femoral intercondylar notch) appear spurious and without scientific basis in the current literature. The literature reviewed in this article indicates a consensus of opinion recognising the effect of subtalar pronation control, ligamentous laxity, neuromuscular performance and menstrual hormones in increased female ACL injury rates. This goes some way to negate the ‘isolated component’ mode of thought and suggests a multifactorial basis to the problem.
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The work of Huston and Wojtys (1996) has provided data regarding a delay in the protective hamstring reflex in females. Tibone et al (1986) found that simple hamstring strengthening alone was not enough to improve voluntary or reflex level hamstring control. Lutz et al (1993) showed that closed kinetic chain exercises were effective in increasing the level of hamstring co-contraction in ACL patients. Ihara and Nakayama (1996) found that the reflex arc between the ACL and hamstrings can be shortened with training using wobble boards. These researchers also found that simple hamstring strengthening had no effect on the reflex arc. Wojtys et al (1996) investigated the neuromuscular effects of training and conditioning at the knee joint. Four groups of subjects were assessed: an isokineticallytrained group; an isotonically-trained group; a third group trained with agility exercises; and a control group. The agility exercises consisted of figure-of-eight, backwards and sideways running, sliding board work and one-legged hops. It was found that the muscle response time to anterior tibial translation was significantly reduced in gastrocnemius and the medial hamstrings in the agility group. No such improvement was noted in the other three groups. Caraffa et al (1996) conducted a prospective, controlled study of 600 soccer players on 40 teams during three full seasons. The prevalence of injury of the ACL in 300 soccer players who participated in proprioceptive training was significantly lower (a mean 0.15 injury per team) than that in a group of 300 players who did not participate in proprioceptive training (a mean 1.15 injuries per team). Griffis et al (1989) investigated the effect of modifying female athletes’ technique on ACL injury, plant-and-cut, straight-leg-landing, and onestep stop were replaced with rounding off turns, knee flexion on landing and threestep stop. A significant decrease in noncontact ACL injury occurred when these techniques were taught prospectively. It seems fair to conclude that if protective muscle reaction times can be reduced with proprioceptive, co-ordination and agility regimes then this could come some way to reducing female ACL injury rates. Whether such training regimes would be effective in reducing particularly high injury rates during the ovulatory phase of the menstrual cycle (Wojtys et al, 1998) has not yet been investigated. Physiotherapy September 2000/vol 86/no 9
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Excessive subtalar pronation has been found to be a predictive factor in noncontact ACL injury and it seems reasonable to suggest that proprioceptive and coordination work may also improve dynamic control of pronation. This would then reduce the concomitant stress on the ACL. This is only an hypothesis but could be proved experimentally using pre- and postregime navicular drop measurements. No work has been conducted to investigate the effect of orthotics on pronation control in relation to ACL injury rates but this is said to be popular in the treatment of patellofemoral pain (Tria et al, 1992). Pre-season screening is becoming increasingly popular (Knapik et al, 1991) and the predictive factors in female ACL injury could be identified at this stage. Obviously resource issues come into play as not all clubs have access to EMG and arthrometry equipment. However, the work of Carrafa et al (1996) and Griffis et al (1989) appears convincing with respect to the effect of proprioceptive and co-ordination work on reducing ACL injury rates. Prophylactic implementation of such regimes seems worth while and would be simple and inexpensive. References Anderson, C, Odensten, M and Gillquist, J (1991). ‘Knee function after surgical or non-surgical treatment of acute rupture of the anterior cruciate ligament: A randomised study with long-term follow-up period’, Clinical Orthopaedics, 264, March, 255-263. Arendt, E A (1996). ‘Common musculoskeletal injuries in women’, Physician and Sportsmedicine, 24, 7, 39-48. Atwater, A E (1990). ‘Gender differences in distance running’ in: Cavanagh, P R (ed) Biomechanics of Distance Running, Human Kinetics, Champaign, IL, pages 321-362. Barrack, R L, Skinner, H B and Buckley, S L (1989). ‘Proprioception in the anterior cruciate deficient knee’, American Journal of Sports Medicine, 17, 1-6. Beard, D J and Dodd, C A F (1998). ‘Home or supervised rehabilitation following anterior cruciate ligament reconstruction: A randomised controlled trial’, Journal of Orthopaedic and Sports Physical Therapy, 2, 134-143. Beck, J L and Wildermuth, B P (1985). ‘The female athlete's knee’, Clinics in Sports Medicine, 4, 2, 345-366. Bjordal, J M, Arnoy, F, Hannestad, B and Strand, T (1997). ‘Epidemiology of anterior cruciate Physiotherapy September 2000/vol 86/no 9
Physiotherapists and coaches working with both male and female athletes could benefit the players by making such exercises a component of rehabilitation and training, and there is a significant amount of literature to act as guidance in compiling such regimes (Griffis et al, 1989; Ihara and Nakayama, 1986; Lutz et al, 1993; Wojtys et al, 1996). Conclusion If ACL injury rates are to be optimally minimised we must be able to identify those athletes at greatest risk. Pre-season screening of athletes is a useful tool and could prove invaluable in identifying athletes with predisposing factors to anterior cruciate ligament injury. Physiotherapists, doctors and coaches involved in screening, training and treating female athletes should be aware of the warning signs and consider implementing basic and then sport-specific regimes to improve proprioception, agility and neuromuscular co-ordination as a prophylactic measure. While the aetiology of female ACL injury is becoming clearer, this remains an area for future research.
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Livingston, L (1998). ‘The quadriceps angle: A review of the literature’, Journal of Orthopaedic and Sports Physical Therapy, 28, 2, 105-109. Loudon, J K, Jenkins, W and Loudon, K L (1996). ‘The relationship between static posture and ACL injury in female athletes’, Journal of Sports Physical Therapy, 24, 2, 91-97. Lutz, G E, Palmitier, K A, An, K A and Chao, E Y S (1993). ‘Comparison of tibiofemoral joint forces during open kinetic chain and closed kinetic chain exercises’, Journal of Bone and Joint Surgery, 75A, 732-739. Malone, T R, Hardaker, W T, Garret, W E et al (1993). ‘Relationship of gender to anterior cruciate ligament injuries in intercollegiate basketball players’, Journal of the Southern Orthopaedic Association, 2, 36-39. Moeller, J L and Lamb, M M (1997). ‘Anterior cruciate ligament injuries in female athletes: Why are women more susceptible?’ Physician and Sportsmedicine, 25, 4, 31-54. Muneta, T, Takakuda, K and Yamamoto, H (1997). ‘Intercondylar notch width and its relationship to the configuration and crosssectional area of the anterior cruciate ligament. A cadaveric knee study’, American Journal of Sports Medicine, 25, 1, 69-72.
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Key Messages ■ In certain sports female athletes are said to be up to eight times more likely to suffer anterior cruciate ligament disruption than their male counterparts. ■ These injuries are largely non-contact and are dependent upon certain intrinsic factors. ■ There is evidence that sub-talar pronation control, ligamentous laxity and neuromuscular performance characteristics play significant roles in female ACL injury. ■ Recent research also implicates menstrual hormones in female ACL injury. ■ Pre-season screening is a useful tool in determining those at risk of anterior cruciate ligament disruption. ■ Proprioceptive, co-ordination and agility exercises have been found to improve ‘ACL-protective’ EMG characteristics at the knee.
National Collegiate Athletic Association (1994-95). NCAA Injury Surveillance System, NCAA, Overland Park, KS.
Teitz, C C, Lind, B K and Sacks, B M (1997). ‘Symmetry of the femoral notch width index’, American Journal of Sports Medicine, 25, 5, 687-690.
Nicholas, J A (1970). ‘Injuries to knee ligaments’, Journal of the American Medical Association, 212, 13, 2236-39.
Tiberio, D (1987). ‘The effect of excessive subtalar joint pronation on patellofemoral mechanics: A theoretical model’, Journal of Orthopaedic and Sports Physical Therapy, 9, 160-165.
Norkin, C and Levange, P (1992). Joint Structure and Function: A Comprehensive Analysis, F A Davis, Pennsylvania, 2nd edn. Pearl, A J (1993). The Athletic Female, Human Kinetics, Champaign, IL, pages 302-303. Pitman, M I, Nainzadeh, N, Menche, D, Galsaberti, R and Song, E K (1992). ‘The intraoperative evaluation of the neurosensory function of the anterior cruciate in humans using somatosensory evoked potentials’, Arthroscopy, 8, 4, 442-447. Protzman, R R (1980). ‘Women in sports: Women athletes. II. Legal aspects’, American Journal of Sports Medicine, 8, 4, 290. Russeck, L (1999). ‘Hypermobility syndrome’, Physical Therapy, 79, 6, 591-599. Ruwe, P A, Gage, J R, Oyonoff, M B and DeLuca, P A (1992). ‘Clinical determination of femoral anterversion’, Journal of Bone and Joint Surgery, 74A, 820-830. Schultz, R A, Miller, D C, Kerr, C S et al (1984). ‘Mechanoreceptors in human cruciate ligaments: A histological study’, Journal of Bone and Joint Surgery, 66A, 1072-76. Schutte, M J, Dabezies, E J, Zimny, M L et al (1987). ‘Neural anatomy of the human anterior cruciate ligament’, Journal of Bone and Joint Surgery, 69A, 243-247. Skoglund, S T (1973). ‘Joint receptors and kinesthesis’ in: Iggo, A (ed) Handbook of Sensory Physiology, Springer-Verlag, Berlin/New York, pages 111-136. Slauterbeck, J, Clevenger, C, Lundberg, W and Burchfield, D M (1999). ‘Estrogen levels alter the failure load of the rabbit anterior cruciate ligament’, Journal of Orthopaedic Research, 17, 3, 405-408. Souryal, T O and Freeman, T R (1993). ‘Intercondylar notch size and anterior cruciate ligament injuries in athletes: A prospective study’, American Journal of Sports Medicine, 21, 4, 535-539. Souryal, T O, Moore, H A and Evans, J P (1988). ‘Bilaterality in anterior cruciate ligament injuries: Associated intercondylar notch stenosis’, American Journal of Sports Medicine, 16, 5, 449-454. Staeubli, H U, Adam, O, Becker, W and Burgkart, R (1999). ‘Anterior cruciate ligament and intercondylar notch in the coronal oblique plane: Anatomy complemented by magnetic resonance imaging in cruciate ligament-intact knees’, Arthroscopy, 15, 4, 349-359.
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Tibone, J E, Antich, T J, Funton, G S, Moynes, D R and Perry, J (1986). ‘Functional analysis of anterior cruciate instability’, American Journal of Sports Medicine, 14, 40, 276-284. Torzilli, P A, Greenberg, R L and Insall, J (1981). ‘An in vivo biomechanical evaluation of anteriorposterior motion of the knee’, Journal of Bone and Joint Surgery, 63A, 960-968. Tria, A J, Palumbo, R C and Alicea, J A (1992). ‘Conservative care for patellofemoral pain’, Orthopaedic Clinics of North America, 23, 4, 545-554. Vogelbach, W D and Combs, L C (1987). ‘A biomechanical approach to the management of chronic lower extremity pathologies as they relate to ecessive pronation’, Journal of Athletic Training, 22, 6-16. Wojtys, E M, Huston, L J, Taylor, P D and Bastian, S D (1996). ‘Neuromuscular adaptations in isokinetic, isotonic and agility training programmes’, American Journal of Sports Medicine, 24, 187-192. Wojtys, E M, Huston, L J, Lindenfeld, T N, Hewett, T E and Greenfield, M L (1998). ’Association between the menstrual cycle and anterior cruciate ligament injuries in female athletes’, American Journal of Sports Medicine, 26, 5, 614-619. Woo, S L Y, Hollis, J M, Adams, D J, Lyon, R M and Takai, S (1991). ‘Tensile properties of the human femur-anterior cruciate ligament-tibia complex: The effect of specimen age and orientation’, American Journal of Sports Medicine, 192, 217-225. Woodford-Rogers, B, Cyphert, L and Denegar, C R (1994). ‘Risk factors for anterior cruciate ligament injury for high school and college athletes’, Journal of Athletic Training, 29, 4, 343-346. Yahia, L H and Newman, N (1991). ‘Mechanoreceptors in the canine anterior cruciate ligament’, Anatomische Anzeiger, 173, 4, 233-238. Zimny, M L and Wink, C S (1991). ‘Neuroreceptors in the tissues of the knee joint’, Journal of Electromyography and Kinesiology, 1, 3, 148-157.
Anterior Cruciate Ligament Injury in Female Athletes: Why are women so vulnerable?
Key Words ACL, female, injury, athlete. by Trevor Lewis
Literature review
Summary Female athletes are more likely to suffer certain sportsrelated injuries than their male counterparts. The knee joint in particular is a troublesome site and the anterior cruciate ligament is a structure especially susceptible to injury. Many explanations regarding possible contributing factors to this increased prevalence have been put forward, including sex-related skeletal variation such as pelvic width, femoral anteversion, femoral intercondylar notch dimensions, and increased Q-angle. Some of these explanations appear to be dubious. However, recent research into pronation control, ligament laxity, neuromuscular characteristics and the effect of menstrual hormones on the ACL has produced some enlightening data. Awareness of the possible causes of increased ACL injury rates in women and girls provides a basis for strategies to help to prevent this potentially devastating injury. It seems that co-ordination and agility work combined with proprioceptive exercises could play a large part in reducing injury rates.
Introduction ‘The paramount destiny and mission of woman is to fulfil the noble and benign offices of wife and mother. This is the law of the Creator and the roles of society must be adapted to the constitution of things’ (Bradley, 1872).
Lewis, T (2000). ‘Anterior cruciate ligament injury in female athletes: Why are women so vulnerable? Literature review’, Physiotherapy, 86, 9, 464-472.
Fortunately the above statement is not representative of the current climate of opinion, but it serves to illustrate that with such ideas recommending subjugation of women in 19th century society, it is not surprising that female participation in sport was quite limited until recent times. A defining moment in the involvement of females in sport in the US was Title IX of the Education Amendment Act of 1972 (Bradley, 1872), the final regulations of which required equal opportunities in athletics; the US Congress implemented Title IX in 1974. Since this statute there has
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been a quantum leap in the number of females participating in sport at all levels. Before Title IX fewer than 10,000 females competed in collegiate sport (Ireland et al, 1997). Recent figures published by the National Collegiate Athletic Association Surveillance System reported that there were 107,605 female participants in 16 sports (NCAA, 1994-95). Both participation and disciplines have changed; women have ventured from traditional, non-contact sports such as swimming and track and field to physical games like basketball, hockey and soccer. Women’s sports, once dominated by a slow, defensive style are now played with speed, precision and power (Moeller and Lamb, 1997). Increased injury rates have accompanied the rise in participation and while foot, shoulder and patellofemoral problems are common, so too is disruption of the anterior cruciate ligament (ACL) (Arendt, 1996). Such injuries are particularly catastrophic due to the length of time lost from sport and the financial implications of care (Freeman et al, 1995). Sports in the US associated with female ACL injury are quoted as soccer, basketball, skiing, volleyball and gymnastics (Huston and Wojtys, 1996). In Europe soccer is again implicated, along with handball and skiing (Bjordal et al, 1997). Injuries occur more often in competitive games than in practice matches (Anderson et al, 1991). This has been stated as up to three times the likelihood and appears to be due to the increased intensity of the competitive match atmosphere (Garrick and Requa, 1978). ACL injury rates of both sexes have been compared at all levels from junior to élite professional. Bjordal et al (1997) compared ACL injury rates in 15- to 18-year-old footballers, and found that females were 5.4 times more likely to sustain injury than males.
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The NCAA Injury Surveillance System in the 1989/90 season reported that female athletes injured their ACL at a rate of 7.8 times more than male athletes (Pearl, 1993). Malone et al (1993) compared injury rates by sex in college basketball players and reported females as eight times more likely to sustain ACL injury. In the US in 1988 participants in the Olympic basketball trials completed an injury questionnaire. The population sample consisted of 64 women and 80 men adjudged to be the country’s élite athletes. Thirteen of the women had sustained an ACL injury compared to only three of the 80 men. Eight women had undergone ACL reconstruction compared with three of the men (Ireland and Wall, 1990). The higher ratio of female injury was said to be understandable due to the steep rise in their participation levels (Protzman, 1980). A high incidence of stress fractures was observed in women when they first entered military service (Cox and Lenz, 1984). With time the injury rates of these fractures eventually equalised with those of men; however, this has not been the case with female ACL injury rates. Sports involving physical contact, ballistic movement and weight-bearing rotation such as basketball, soccer and volleyball are noted for producing ACL injuries (Moeller and Lamb, 1997). In potentially less injurious, non-contact track events, however, Jackson et al (1980) observed double the injury rate among female athletes. Five non-contact mechanisms of ACL injury have been recognised: planting and cutting (a sudden change in body direction following foot-toground contact), straight-knee landing, sudden deceleration, pivoting, and one-step stop landing with knee hyperextension (Moeller and Lamb, 1997). Given these findings, a review of some of the most commonly cited factors which are said to contribute to female ACL injury is needed to clarify which of them are significant in the aetiology of such injuries. Anatomy and Biomechanics The ACL helps to limit anterior translation of the tibia on the femur. It works with the posterior cruciate ligament to control gliding and rolling of the tibia on the femur during normal flexion and extension. It provides secondary restraint limiting internal rotation of the tibia and also seems to make at least a minor contribution to restraining both varus and valgus stresses
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across the knee joint (Norkin and Levange, 1992). The ligament is made up of two bands: the anteromedial and posterolateral (and occasionally there is also an intermediate band). The ACL runs from the posteromedial portion of the lateral femoral condyle through the femoral intercondylar notch in an inferior, anterior and medial direction to an area lateral to the medial tibial eminence. The posterolateral band is tightest during knee extension, and the anteromedial band is tightest in knee flexion (Moeller and Lamb, 1997). The twisted configuration of the ACL fibres and the shape of the femoral condyles allow for the screw-home mechanism of the knee during the final 20° of extension when the tibia externally rotates on the femur. The ligament is under varying degrees of tension in all positions of motion, but maximal tibial anterior translation is observed at 30° flexion when both the ACL bands display their minimum tension (Torzilli et al, 1981). Schultz et al (1984) identified mechanoreceptors in the ligament, and Yahia and Newman (1991) and Zimny and Wink (1991) have both reported that mechanoreceptor density is highest at the proximal and distal bony attachments. The proprioceptive function of the ACL has been intensively studied. Schutte et al (1987) stated that 1% of the ligament’s dry weight was neural tissue and Barrack et al (1989) observed significant proprioceptive deficit in knees with ACL disruption. A neurological link between the ACL and the cerebral cortex has been established from cortical EEG signals produced by ACL stimulation during arthroscopy (Pitman et al, 1992).
Author and Address for Correspondence Mr Trevor Lewis GradDipPhys MCSP is a clinical physiotherapy specialist (musculoskeletal service) in the physiotherapy department at The Royal Liverpool University Hospitals, Prescot Street, Liverpool L7 8XP. e-mail: [email protected] This essay was submitted this year as coursework towards a master’s degree in sports science at John Moores’ University, Liverpool. It was received by Physiotherapy on June 28, 1999, and accepted on March 1, 2000.
Funding This research was funded by the Hospital Savings Association.
Structural Factors The ‘miserable malalignment syndrome’ of high Q-angle, increased pelvic width, anter verted femur, valgus knee, and pronated foot (James, 1976) is often quoted as an explanation for increased knee injury rates in females (see figure overleaf). The different components of this syndrome will now be discussed separately along with a review of more recent work concerning joint laxity, sex-related neuromuscular characteristics, and menstrual hormones. Q-angle The Q-angle is described as being formed between the vectors for the combined pull of the quadriceps femoris muscle and the Physiotherapy September 2000/vol 86/no 9
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Wider pelvis
Less muscular thigh development
Femoral anteversion
Less developed VMO Increased flexibility/hyperextension
Narrow notch
Genu valgum
External tibial torsion
Narrower pelvis
More developed thigh musculature VMO hypertrophy Wider notch Less flexibility Internal or neutral tibial torsion
Genu varum
A
B
Lower extremity alignments that may predispose athletes to over-use problems of hips and knees, especially ACL and patellofemoral injuries: A females, B males. Reproduced with permission from Fu, F H and Stone, D A (1984). Sports Injuries: Mechanisms, prevention, treatment, Williams and Wilkins, Philadelphia
patellar tendon (Hungerford and Barry, 1979). Hahn and Foldspang (1997) investigated 339 athletes and observed Q-angle asymmetry within subjects, and their experiment also found that the Q-angle was greater in females. There is no strict agreement regarding standardised reference values, but Q-angles exceeding 15° in males and 20° in females are considered abnormal (Horton and Hall, 1989). Anecdotally, increased female Qangle is often explained by females possessing a wider pelvis than males, thus increasing the obliquity of the femora and consequently the valgus orientation of the knee (Moeller and Lamb, 1997; Ireland et al, 1997; Caylor et al, 1993). There is a recognised relationship between high Q-angle, patellar maltracking and anterior knee pain, and several authors have speculated that this sex-related anatomical difference may also lead to increased risk of ACL injury (Hutchinson and Ireland, 1995; Moeller and Lamb, 1997). However, several studies have found no relationship between Q-angle and predisposition to ACL injury (Gray et al, 1985; Loudon et al, 1996). Not only is there no clear link between ACL injury and Q-angle but there is no consensus in the literature as regards Q-angle measurement. In a review of literature regarding the Q-angle, Livingston (1998) states that it is question-able whether Physiotherapy September 2000/vol 86/no 9
a static Q-angle measurement has any bearing on dynamic activities. The current literature suggests that the Q-angle is an unreliable measurement and even if it were reliable its role in female ACL injury is uncertain. Pelvic Width Females are said to have a wider pelvis than males and this is quoted regularly in the literature (Hutchinson and Ireland, 1995; Ireland et al, 1997; Moeller and Lamb, 1997). Ireland et al (1997) state that a wider female pelvis increases ACL injury risk by creating a greater coxa vara/genu valgum alignment with a concurrent increase in tibio-femoral rotational force, thus imposing greater stress on the ACL. Unfortunately no research was presented by these authors to substantiate this comment. Even though soft tissue outlines may suggest otherwise, there is a significant amount of evidence to refute the idea that the female pelvis is wider than that of males. The absolute width using anterior superior iliac spine measurements (Guerra et al, 1994) biiliocristal (Atwater, 1990), and bitrochanteric measurements (Horton and Hall, 1989) was found to be virtually the same in both sexes. Despite the frequent assumption of increased pelvic width in females, this notion is not well founded. Studies that have been conducted in this
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area strongly refute anatomical sex differences and thus any possible contribution to female ACL injury. Femoral Intercondylar Notch An association has been suggested between a small intercondylar notch and sustaining an ACL tear (Laprade and Burnett, 1994). Notch dimensions have been widely reported as a causative factor in higher female ACL injury rates due to women possessing a smaller ‘notch width index’ (NWI) than men (Souryal and Freeman, 1993). Souryal et al (1988) defined the NWI as ‘the ratio of notch width to that of the distal femur at the level of the popliteal groove’. This is measured using a ‘tunnel view’ radiograph, and a ‘normal’ ratio was quoted as 0.2. Souryal et al (1988) proposed prophylactic bracing and notchplasty in the unaffected knee of patients who had torn the contralateral ACL and whose NWI was below normal. These recommendations assume that notch anatomy is the most decisive component in ACL injury. Muneta et al (1997) investigated whether ACL dimensions could be predicted by notch width and found that both narrow and wide notches house the same size ACL. They hypothesised that injury is due to normal-sized ligaments being ‘frayed’ in stenotic notches. However, this was a cadaveric study of only 16 elderly knees (average age 74.8 years) and using ACL moulds cast from dental silicone to arrive at their results. Possible age-related changes in either bone or ligament were not mentioned. Additionally, the accuracy of their ligament moulds to the biological ACL proportions was not evaluated. Teitz et al (1997) compared bilateral NWI in 40 male and 40 female patients using radiographs. They found that NWI were symmetrical within subjects and there was considerable overlap in dimensions between sexes. Females displayed a smaller NWI than males but this was not statistically significant, There was also no difference in NWI between patients with and without ACL tears. Disagreement between studies may be a product of different imaging techniques used to map the dimensions of the notch. Magnetic resonance imaging (MRI) has displayed no difference in NWI between normal and ACL deficient knees (Herzog et al, 1994). MRI was also used by Staeubli et al (1999) on 51 knees (25 females, 26 males)
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to assess any sex-related differences. They found that the absolute widths of the ACL with respect to intercondylar notch widths were not significantly different between sexes. It seems that more contemporary research using the anatomical precision of MR images is gradually rejecting femoral notch dimensions as a predictive factor in ACL injury. Subtalar Pronation Pronation is defined as a combined motion involving subtalar eversion, foot abduction and ankle dorsiflexion (Norkin and Levange, 1992). Subtalar pronation and internal rotation of the tibia occur concurrently in the contact phase of the gait cycle and the ACL becomes taut with tibial rotation (Woodford-Rogers et al, 1994). Coplan (1989) reported that abnormal pronators were found to have increased passive knee rotation at 5° of knee flexion and that there is a very important relationship between pronation and rotational knee joint laxity. It has been concluded that prolonged pronation of the subtalar joint produces increased internal tibial rotation which in turn stresses the medial structures of the knee (Vogelbach and Combs, 1987). The navicular drop test involves measuring navicular height in sitting in sub-talar neutral, then in full weight bearing, and is described as a measure of pronation in an experiment by Woodford-Rogers et al (1994). Drop height was recorded in 22 ACL-injured athletes (14 male and 8 female) and compared with 22 age- and sport-matched controls. A statistically significant difference was noted where non-injured subjects dropped 5.9 mm while ACL-injured athletes dropped 8.4 mm. Loudon et al (1996) observed similar results and found that excessive navicular drop and excessive subtalar joint pronation were statistically significant discriminators between ACL-injured and non-injured groups. It seems that a consensus is developing regarding a relationship between excessive pronation and ACL injury, but experiments to establish any significant differences between males and females have not been carried out. Femoral Anteversion Feagin et al (1982) discussed the importance of femoral rotation in the transverse plane as a mechanism of injury to the ACL. Tiberio (1987) has stated that internal rotation of the femur predisposes an individual to Physiotherapy September 2000/vol 86/no 9
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excessive pronation of the subtalar joint and thus concomitant ACL injury. The angle of anteversion is said to be measurable using the clinical method described by Ruwe et al (1992). The patient is placed prone with the knee flexed to 90°. The greater trochanter is palpated while passive medial and lateral hip rotation are conducted. The trochanter should be most prominent in neutral rotation; anteversion is present if there is medial hip rotation greater than 15°. Loudon et al (1996) used the above test to assess whether there was a relationship between femoral anteversion and the prevalence of non-contact ACL injury. Their study found no difference in anteversion between ACL-injured and non-injured knees. However they conceded that a weightbearing measurement might have yielded different results. No other work has been undertaken to investigate the role of femoral anteversion concerning either any possible sex-related differences or the role of anteversion in ACL injury per se. Further work needs to be undertaken in this area. Joint Laxity It has long been suggested that there is a relationship between joint laxity and joint injury including ACL injuries in females (Nicholas, 1970). Huston and Wojtys (1996), using arthrometric measurements, found that both female athletic and non-athletic controls exhibited more anterior tibial laxity than their male counterparts. Beck and Wildermuth (1985) stated that ligamentous laxity can be related to conditioning as much as to hereditary factors. This statement appears to be supported by the work of Huston and Wojtys (1996) who found that female athletes tended to have less ligamentous laxity than sedentary females. Woodford-Rogers et al (1994), also using a KT-1000 arthrometer, found that anterior knee joint laxity was significantly greater in ACL-injured subjects than in non-injured subjects. Knapik et al (1991) found that knee joint laxity has no direct relationship with ACL injury in female athletes. However, their study assessed joint flexibility using goniometry against active range of motion rather than with arthrometry. Loudon et al (1996) investigated the discriminatory value of knee recurvatum in female athletes and the prevalence of non-contact ACL injury. They found that subjects with knee hyperextension had a statistically greater predisposition to ACL injury. The contemporary trend of measuring joint Physiotherapy September 2000/vol 86/no 9
laxity using arthrometers appears to be producing a consensus regarding the role of joint laxity in female ACL injury. It has been stated that individuals with hypermobile joints often have concomitant motor delay with proprioceptive deficits (Russeck, 1999). This means that female ACL injury in joint laxity states could be attributed to motor deficit as much as hypermobility. Neuromuscular Performance Anecdotally, Beck and Wildermuth (1985) suggested that the main reason behind the higher incidence of non-contact ACL injury in females was a result of inadequate motor skills. Studies have shown that the ACL operating in isolation is not capable of withstanding the forces produced across the knee during sporting activity (Woo et al, 1991). A reflex arc between the ACL and the hamstrings mediates protective reflex contraction of these muscles when the ligament is stressed which limits anterior tibial translation (Skoglund, 1973; Hagood et al, 1990). Huston and Wojtys (1996) investigated EMG neuromuscular patterns along with lower extremity muscle strength, endurance, and muscle reaction times and recruitment order in response to anterior tibial translation by arthrometer. Sixty male athletes, 40 female athletes, and 40 healthy non-athletic controls from both sexes were investigated. Significantly less muscle strength and endurance was demonstrated in female athletes and the muscle recruitment order in some female athletes was noticeably different. They relied on the quadriceps muscles in response to anterior tibial translation; this muscle group being an ACL antagonist. The other three groups relied more on their hamstring muscle group. Female athletes were also weaker in the hamstrings and quadriceps and also took significantly longer to generate maximal hamstring torque. Huston and Wojtys’ careful study investigated female athletes from basketball, field hockey, gymnastics and volleyball. Larger numbers of males and females should be tested across a wider range of sports in order to confirm these results. Hormonal/Menstrual Factors Throughout their sporting lives, female athletes are subject to cyclical variation in endogenous hormones and possibly exogenous hormones via oral contra-
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ceptives. Recent research has investigated the influence of hormones on ligaments, and oestrogen and progesterone receptors have been isolated in the ACL (Liu et al, 1997). Their research found that collagen synthesis was significantly reduced with increasing estradiol concentrations. The subsequent structural changes were said to result in reduced strength of the ACL, rendering the ligament more susceptible to injury. Slauterbeck et al (1999) investigated the effect of experimentally increased serum oestrogen levels on failure load of the ACL, and found that load-at-failure was significantly reduced in the experimental group (446 ± 54 N) compared to that of a control group (503 ± 48 N). The experimenters report that elevated oestrogen levels produce a reduction in the tensile strength of the ACL. The work of Liu et al (1997) and Slauterbeck (1999) was conducted using animal models. Liu et al (1996) observed similar results in an experiment using human tissue. Wojtys et al (1998) collected data from 40 female athletes with ACL injury regarding mechanism of injury, menstrual cycle, contraceptive use and previous injury. A statistically significant association was found with injury during the ovulatory phase of the cycle when oestrogen levels are high (days 10-14) and with reduced injury likelihood in the follicular phase (days 1-9) when oestrogen levels are lower. Thus sex hormones may be a factor in the knee ligament problems in women. However, oestrogen is said to affect the central ner vous system and motor function (Wojtys et al, 1998). This means that impaired muscle recruitment or compromised co-ordination could be just as significant as diminished ACL tensile strength in ovulatory phase injury. Discussion Traditional explanations for female ACL injury implicating alignment (Q-angle, pelvic width, femoral anteversion and configuration of the femoral intercondylar notch) appear spurious and without scientific basis in the current literature. The literature reviewed in this article indicates a consensus of opinion recognising the effect of subtalar pronation control, ligamentous laxity, neuromuscular performance and menstrual hormones in increased female ACL injury rates. This goes some way to negate the ‘isolated component’ mode of thought and suggests a multifactorial basis to the problem.
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The work of Huston and Wojtys (1996) has provided data regarding a delay in the protective hamstring reflex in females. Tibone et al (1986) found that simple hamstring strengthening alone was not enough to improve voluntary or reflex level hamstring control. Lutz et al (1993) showed that closed kinetic chain exercises were effective in increasing the level of hamstring co-contraction in ACL patients. Ihara and Nakayama (1996) found that the reflex arc between the ACL and hamstrings can be shortened with training using wobble boards. These researchers also found that simple hamstring strengthening had no effect on the reflex arc. Wojtys et al (1996) investigated the neuromuscular effects of training and conditioning at the knee joint. Four groups of subjects were assessed: an isokineticallytrained group; an isotonically-trained group; a third group trained with agility exercises; and a control group. The agility exercises consisted of figure-of-eight, backwards and sideways running, sliding board work and one-legged hops. It was found that the muscle response time to anterior tibial translation was significantly reduced in gastrocnemius and the medial hamstrings in the agility group. No such improvement was noted in the other three groups. Caraffa et al (1996) conducted a prospective, controlled study of 600 soccer players on 40 teams during three full seasons. The prevalence of injury of the ACL in 300 soccer players who participated in proprioceptive training was significantly lower (a mean 0.15 injury per team) than that in a group of 300 players who did not participate in proprioceptive training (a mean 1.15 injuries per team). Griffis et al (1989) investigated the effect of modifying female athletes’ technique on ACL injury, plant-and-cut, straight-leg-landing, and onestep stop were replaced with rounding off turns, knee flexion on landing and threestep stop. A significant decrease in noncontact ACL injury occurred when these techniques were taught prospectively. It seems fair to conclude that if protective muscle reaction times can be reduced with proprioceptive, co-ordination and agility regimes then this could come some way to reducing female ACL injury rates. Whether such training regimes would be effective in reducing particularly high injury rates during the ovulatory phase of the menstrual cycle (Wojtys et al, 1998) has not yet been investigated. Physiotherapy September 2000/vol 86/no 9
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Excessive subtalar pronation has been found to be a predictive factor in noncontact ACL injury and it seems reasonable to suggest that proprioceptive and coordination work may also improve dynamic control of pronation. This would then reduce the concomitant stress on the ACL. This is only an hypothesis but could be proved experimentally using pre- and postregime navicular drop measurements. No work has been conducted to investigate the effect of orthotics on pronation control in relation to ACL injury rates but this is said to be popular in the treatment of patellofemoral pain (Tria et al, 1992). Pre-season screening is becoming increasingly popular (Knapik et al, 1991) and the predictive factors in female ACL injury could be identified at this stage. Obviously resource issues come into play as not all clubs have access to EMG and arthrometry equipment. However, the work of Carrafa et al (1996) and Griffis et al (1989) appears convincing with respect to the effect of proprioceptive and co-ordination work on reducing ACL injury rates. Prophylactic implementation of such regimes seems worth while and would be simple and inexpensive. References Anderson, C, Odensten, M and Gillquist, J (1991). ‘Knee function after surgical or non-surgical treatment of acute rupture of the anterior cruciate ligament: A randomised study with long-term follow-up period’, Clinical Orthopaedics, 264, March, 255-263. Arendt, E A (1996). ‘Common musculoskeletal injuries in women’, Physician and Sportsmedicine, 24, 7, 39-48. Atwater, A E (1990). ‘Gender differences in distance running’ in: Cavanagh, P R (ed) Biomechanics of Distance Running, Human Kinetics, Champaign, IL, pages 321-362. Barrack, R L, Skinner, H B and Buckley, S L (1989). ‘Proprioception in the anterior cruciate deficient knee’, American Journal of Sports Medicine, 17, 1-6. Beard, D J and Dodd, C A F (1998). ‘Home or supervised rehabilitation following anterior cruciate ligament reconstruction: A randomised controlled trial’, Journal of Orthopaedic and Sports Physical Therapy, 2, 134-143. Beck, J L and Wildermuth, B P (1985). ‘The female athlete's knee’, Clinics in Sports Medicine, 4, 2, 345-366. Bjordal, J M, Arnoy, F, Hannestad, B and Strand, T (1997). ‘Epidemiology of anterior cruciate Physiotherapy September 2000/vol 86/no 9
Physiotherapists and coaches working with both male and female athletes could benefit the players by making such exercises a component of rehabilitation and training, and there is a significant amount of literature to act as guidance in compiling such regimes (Griffis et al, 1989; Ihara and Nakayama, 1986; Lutz et al, 1993; Wojtys et al, 1996). Conclusion If ACL injury rates are to be optimally minimised we must be able to identify those athletes at greatest risk. Pre-season screening of athletes is a useful tool and could prove invaluable in identifying athletes with predisposing factors to anterior cruciate ligament injury. Physiotherapists, doctors and coaches involved in screening, training and treating female athletes should be aware of the warning signs and consider implementing basic and then sport-specific regimes to improve proprioception, agility and neuromuscular co-ordination as a prophylactic measure. While the aetiology of female ACL injury is becoming clearer, this remains an area for future research.
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Professional articles
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Key Messages ■ In certain sports female athletes are said to be up to eight times more likely to suffer anterior cruciate ligament disruption than their male counterparts. ■ These injuries are largely non-contact and are dependent upon certain intrinsic factors. ■ There is evidence that sub-talar pronation control, ligamentous laxity and neuromuscular performance characteristics play significant roles in female ACL injury. ■ Recent research also implicates menstrual hormones in female ACL injury. ■ Pre-season screening is a useful tool in determining those at risk of anterior cruciate ligament disruption. ■ Proprioceptive, co-ordination and agility exercises have been found to improve ‘ACL-protective’ EMG characteristics at the knee.
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