Sports injuries science development - Anterior cruciate ligament knee injuries

These are some of the current challenges in the scientific support of the injured high-performance athlete

Acute and chronic exposure to episodes of stress associated with high-performance sporting performance may elicit strain responses from the athlete that are capable of exceeding the biological tolerance of synovial joint systems and may be the cause of musculoskeletal injury. In many respects, the surgical interventions associated with the treatment of muscular, ligamentous and chondral injuries have reached prodigious levels of sophistication. In conjunction with appropriate exercise stresses associated with physical conditioning, surgical interventions can reassure the athlete of a successful outcome and eventual return to full participation in the highest levels of sports.

However, some injuries such as disruption of knee ligaments and injury to the chondral surfaces remain as threats to both professional and recreational sporting careers. Successful and rapid outcomes may depend critically on evidence-based treatment in which there is an optimised interaction of biological responses to surgical interventions, dose-response relationships associated with psychobiological rehabilitative conditioning and the idiosyncratic responses of the injured athlete. Such issues relating to the optimised rehabilitation from injury sustained during high-performance sporting endeavours and importantly, strategies for their prevention wherever feasible, remain as supreme challenges for the exercise scientist.

Theoretical and applied research in this area may offer insights associated with the minimisation of long-term risks to musculoskeletal health and facilitate the maintenance of competitive advantage within the realm of professional sport where the potential cost of injuries to high-performance athletes throughout the competitive season is dramatic. For example, evidence from professional soccer in the UK and abroad suggests that the total time-cost of injury is likely to be more than 15% of total player-time availability (Hawkins and Fuller, 1999; Rees, 1994). Furthermore, over 30% of such injuries will involve individual players being away from normal training practice for between one and four weeks. This makes severe disruption to team performance extremely likely at crucial times of the season.

Injuries to the knee
The knee is one of the most frequently injured joints in sportspeople (Bollen, 1998) and injury to the anterior cruciate ligament (anterior cruciate ligament) is an important example of a mechanism that may lead to functional debilitation. The anterior cruciate ligament (see also issues 9 and 13 of SIB) is considered to be the principal ligamentous restraint to anterior tibio-femoral displacement and is the most commonly injured of the major knee joint ligaments. There is accumulating evidence of increased risk and an anterior cruciate ligament injury epidemic via non-contact aetiologies in team sport athletes (Hutchinson and Ireland, 1998). Non-contact mechanisms have consistently accounted for more than 80% of anterior cruciate ligament injuries with the majority occurring near end range extension (Rees and Gleeson, 1999).

Injuries to the anterior cruciate ligament range from partial to complete rupture and result in varying degrees of knee joint instability and loss of function. A conceptual model that defines the limits of normal knee movement comprises primary ligamentous restraints interacting with the other static stabilisers (osseous geometry, capsular structures, and menisci) and with the dynamic muscle stabilisers. An unfavourable interaction of the dynamic and static stabilising factors may predispose team-game players to increased threat of anterior cruciate ligament disruption. In particular, optimal functioning of the dynamic muscle stabilisers of the knee joint may be fundamental to the prevention of or limit the severity of ligamentous injury. This may be important also in preventing re-injury since, if not treated by means of surgery or aggressive compensatory muscle rehabilitation towards optimal function, the extent of the original tear is highly related to the extent of subsequent further injury to the anterior cruciate ligament. The knee joint instability associated with the anterior cruciate ligament-deficient knee is thought to be related to significant and progressive damage to articular components, which may ultimately lead to early onset osteoarthritis.

'Contemporary surgical interventions demand typically a six-month rehabilitation programme'
The implications of complete anterior cruciate ligament rupture to the professional team-games player and other high-performance athletes are substantial. This injury has progressed from representing a career-threatening event to that of an extended absence from the game for most players. Contemporary surgical interventions demand typically a subsequent six-month rehabilitation programme prior to the player recommencing competitive match-play. Thus this injury still presents extensive physiological and psychological challenges to the player and often a logistical threat to the employer. Despite the advances in contemporary treatment, the latter potential costs suggest that wherever possible, factors that may contribute to the prevention of this injury or a reduction of its severity should be explored fully. However, in the absence of appropriate compensatory rehabilitation, even relatively minor anterior cruciate ligament trauma (which may remain undiagnosed) may act as a precursor for more severe subsequent ligamentous injury and other co-morbidity factors such as meniscal injury.

The neuromuscular performance of the dynamic muscle stabilisers of the knee joint system may be particularly implicated in the non-contact aetiology of anterior cruciate ligament injury in female athletes (Hewett et al., 1999). Optimal functioning of the knee flexors has achieved prominence as a factor in the prevention of injury and in successful outcomes following injury and surgical interventions (Gleeson et al., 1998: Mercer et al., 1998). The latter may be especially important in female athletes who have demonstrated a six-fold greater relative risk of anterior cruciate ligament injury compared to male counterparts, when normalised per player hour (Hewett, 2000; Hutchinson and Ireland, 1995).

What the research teams are doing
Strong collaboration has been established over several years between research teams led by the present writer (Dr. Nigel Gleeson, School of Sport, Health and Exercise, University of Wales, Bangor) and the sports medical team at the The National Centre for Sports Injury Surgery, Robert Jones and Agnes Hunt NHS Trust, Oswestry under the Clinical Directorship of Mr. Dai Rees. The National Centre for Sports Injury Surgery provides a rapid and comprehensive service of assessment together with non-invasive or surgical treatment and full rehabilitation for the injured sports person of any sport or ability. The clinical team provides equally high standards of research-based care to both professional and recreational sports persons by means of the NHS. Examples of injuries treated from a wide range of sporting activities include meniscal and ligament problems of the knee and ankle, stress fractures of the lumbar spine and groin dysfunction, in addition to the treatment of patients with upper limb injuries.

The collaborative research efforts have attempted to address issues associated with sports-related injury systematically and to enhance the clinical service by evidence-based outcome. As was intimated earlier, damage to the anterior cruciate ligament is one of the injuries occurring most frequently during sporting competition. One strand of the research programme led jointly by Dr. Nigel Gleeson and Mr. Dai Rees has evaluated neuromuscular, biomechanical and musculoskletal models associated with the aetiology of anterior cruciate ligament injury. The research has led to the development of innovative techniques for the evaluation of ligament dysfunction including specialised arthrometry instrumentation and the ability to assess anterior cruciate ligament strain during dynamic physical activity. The latter has been developed as a non-invasive technique using 3-D motion analysis.

Further aspects of the research have evaluated the effects of acute endurance exercise and fatigue on the musculoskeletal performance of the knee joint and joint injury including the ability of the athlete to control joint stability. This research has helped the sports medicine team in the identification of prophylactic physical intervention strategies to decrease the likelihood of anterior cruciate ligament injury and specific markers for recovery during the rehabilitation process following surgery.
Current research includes a major prospective and random-allocation controlled study investigating the effects of reconstruction surgery and physical rehabilitation on musculoskeletal performance, function and psychobiology in the anterior cruciate ligament-deficient knee. Data from this study will facilitate both the understanding of mechanisms underpinning pathophysiological, functional and psychobiological responses associated with the anterior cruciate ligament-deficient and surgically reconstructed knee joint and the optimisation of injury treatment for the individual athlete.

The effects of a resistance-conditioning programme
Recent contributions of the research literature have included papers presented to the British Association of Sport and Exercise Sciences Annual Conference, Newport, September, 2001. Since women appear to be at greater relative risk of injury to the anterior cruciate ligament, one paper sought to investigate the effects of a three-week prophylactic resistance-conditioning programme on indices of neuromuscular and musculoskeletal performance of the knee joint in women (Gleeson et al., 2001a). Such an intervention was designed to be representative of the type of conditioning that might be possible within the framework of pre-season training for team-game sports.

Eight physically active females were assessed at base-line and 48 hours after the completion of a standardised three-week conditioning programme of the dynamic muscle stabilisers of knee joint in the non-preferred limb. The preferred limb was not trained and acted as a control. Outcome measures included peak force and electromechanical delay (EMD) associated with maximal voluntary muscle actions of the knee flexors and an indirect measure of anterior cruciate ligament robustness (anterior tibio-femoral displacement). The results indicated that while the control limb's performance remained constant over the period of training, the trained leg showed a 20-38% improvement in volitional peak force and EMD performance. By contrast, the duration and intensity of the conditioning appeared to be insufficient to promote improved ligamentous performance. Importantly however, the magnitude of enhancements to group mean EMD performance and capability for generating force rapidly of the knee flexor musculature conferred by the acute conditioning programme (38% approx.) may be sufficient to contribute to protective 'strain-shielding' of the anterior cruciate ligament in female athletes.

Thus the use of specific conditioning of this type over and above the normal training routines practised by female athletes might ultimately afford a reduction in the risk of injury to the anterior cruciate ligament. As would be the case with all exploratory studies of this type, care must be taken in the extrapolation of such findings to wider populations of female athletes due to the limited experimental design sensitivity. Nevertheless, such findings offer further insights into how the 'female' knee might be protected from the risk of ligamentous injury optimally.

Other research findings presented to the BASES conference focused attention on the nature of potential for sex differences in EMD performance and capability for generating force rapidly of the knee flexor musculature (Gleeson et al., 2001b). This study looked at the latter performance characteristics under conditions in which the knee joint system has been challenged by an acute 'all-out' fatiguing exercise task of the type that might be experienced in a 'worst-case' scenario within a game situation. Fatigue has been associated with an increased risk of injury (Gleeson et al, 1998). Results suggested that while both sexes demonstrated a significant impairment of performance associated with the 30 s fatigue task, females showed greater decrement in volitional EMD performance compared to male counterparts (22.1% vs. 11.8 % compared to pre-fatigue scores, respectively).
This potentially may result in a lengthening of the time period over which unrestrained forces/moments accumulate on the knee joint and may highlight one potential mechanism for the six-fold increased incidence of serious knee injury in female athletes.

Both sexes demonstrated a small enhancement of evoked EMD performance associated with the fatigue task and consistent with physiological potentiation (<6%, measured by means of trans-spinal supra-maximal magnetic stimulation of the sciatic nerve). These observations suggest that while volitional neuromuscular performance was impaired at joint positions in which the knee has been shown to be vulnerable to injury, ultimate physiological capability for rapid muscle activation was preserved during acute fatiguing exercise in the knee flexors of both men and women. The differential between 'volitional' and 'evoked' capability for generating force rapidly in the knee flexor musculature under conditions of 'fatigue' suggests it may be possible to marshal even greater protective responses with specific conditioning or under conditions in which the true nature of the 'emergency' threat to the joint has been 'consciously'or 'sub-consciously' recognised by the athlete. The latter may offer innovative insights into the mechanisms by which optimised prophylactic and rehabilitative evidence-based conditioning interventions may be achieved.

Nigel Gleeson

Bollen, S. (2000). Epidemiology of knee injuries: diagnosis and triage. British Journal of Sports Medicine, 4: 153.

Doyle. J., Gleeson, N.P., Hale, B., Rees, D. and Parfitt, G. (1998). The validity of the performance profile technique associated with anterior cruciate ligament-reconstructive surgery and subsequent rehabilitation. British Association of Sports and Exercise Sciences Annual Conference, Worcester College, November.

Doyle, J. and Gleeson, N.P. and Rees, D. (1999). Psychobiology and the anterior cruciate ligament (anterior cruciate ligament) injured athlete. Sports Medicine, 26: 379-393.

Doyle, J., Gleeson, N.P., Rees, D, Hollows, M., Walters, M. and Minshull, C. (2001). Performance profiling and self-perceived performance associated with the knee joint during acute fatiguing exercise. Paper presented to the British Association of Sport and Exercise Sciences Annual Conference, Newport, September.

Gleeson, N.P., Rees, D., Doyle, J. et al. (1998). The effects of anterior cruciate
ligament-reconstructive surgery and acute physical rehabilitation on neuromuscular modelling associated with the knee joint. British Association of Sports and Exercise Sciences Annual Conference, Worcester College, November.

Gleeson, N.P., Mercer, T.H., Reilly, T., Rakowski, S. and Rees, D. (1998). The influence of acute endurance activity on leg neuromuscular and musculoskeletal performance. Medicine and Science in Sports and Exercise, 30: 596-608.

Gleeson, N.P., Rees, D., Walters, M., Minshull, C., Kyffin, I. and Mercer, T.H. (2001a). The effects of a three-week resistance conditioning programme on indices of neuromuscular and musculoskeletal performance of the knee joint in women. Paper presented to the British Association of Sport and Exercise Sciences Annual Conference, Newport, September.

Gleeson, N.P., Rees, D., Walters, M., Minshull, C., Harvey, J. and Mercer, T.H. (2001b). Effects of a fatigue task on indices of electromechanical delay of knee flexors in men and women. Paper presented to the British Association of Sport and Exercise Sciences Annual Conference, Newport, September.
Gleeson, N.P., Naish, P.F., Mercer, T.H. Wilcock, J.E. and Hine, J. (under review). Reliability of indices of neuromuscular leg performance in end-stage renal failure. Scandinavian Journal of Rehabilitation Medicine.

Hawkins, R.D. and Fuller, C. (1999). A prospective epidemiological study of injuries in four English professional football clubs. British Journal of Sports Medicine, 33: 196 - 203.

Hewett, T.E., Lindenfield, T.N., Riccobebe, J.V. et al. (1999). The effects of neuromuscular training on the incidence of knee injury in female athletes: A prospective study. American Journal of Sports Medicine 27: 699-705, 1999.

Hewett, T.E. (2000). Neuromuscular and hormonal factors associated with knee injuries in female athletes. Sports Medicine, 29: 313-327.

Hutchinson, M.R. and Ireland, M.L. (1995). Knee injuries in female athletes. Sports Medicine, 19: 288-302.

Mercer, T.H., Naish, P., Gleeson, N.P., Wilcock, J. and Hine, J. (1998). Development of a walking test to predict