The Anterior Cruciate Ligament (ACL) is one of the major stabilising ligaments of the knee.  The ligament spans between the inner surfaces of the femur (thigh bone) and the tibia (shin bone), limiting the forward motion of the tibia in relation to the femur.

The ACL is most commonly injured in ball sports and skiing (up to 70-80% of all injuries), where rapid changes of direction, pivoting on a static foot and side stepping during weight-bearing are involved.

The remaining 20-30% of injuries are seen in contact scenarios e.g. forced knee hyper-extension (>15º) during a leg tackle in rugby union. http://www.youtube.com/watch?v=sV-gjm-ZVys 

How to tell if you have an ACL injury

The mechanism of an ACL injury can be quite defined, usually presenting with a “pop or crack” at the time of injury, followed by a large joint swelling within 2-3 hours. Often feeling quite unstable on weight-bearing, players often report a deep joint pain which can be poorly localised.

There are certain specialised tests which can be performed by a physio or an orthopaedic surgeon to assess for ACL rupture in combination with an MRI scan for complete diagnosis. Due to the initial high forces involved in the ACL injury, an ACL rupture can be compounded by the meniscus (cartilage) and/or medial collateral ligament being affected (O'Donoghue's Triad).

The majority of individuals returning to sport following an ACL rupture will require essential reconstructive surgery. There will be an extensive post-operative (up to 1 year) period before returning to sport. http://www.youtube.com/watch?v=LoFimQmMrbM 

ACL injury risk factors

Physios, strength & conditioners and sports trainers spend a considerable amount of time collating and analysing injury stats to determine preventative practices which positively impact on the number of ACL injuries sustained. In essence, an ACL injury will side-line a player for a whole season more informed preventative practice will extend playing careers!

Contact-related ACL injuries in sports such as rugby union, will always happen, having no control over the collision factors involved. Pre-identified risk factors for ACL injury such as; genetic make-up, male/female gender and individual bone geometry also cannot be controlled. Acknowledging that women have a higher incidence of ACL injury, mainly because of their body biomechanics thus creating a higher risk of injury.

The good news is that the other major pre-disposing factors to ACL injury can be addressed through improved biomechanical and neuromuscular control. In this is area of expertise knowledgeable physios, trainers, coaches and athletes can positively influence reducing the potential of ACL injury.

The study of biomechanics

The term 'biomechanics' is used to describe the study of human movement and how patterns of joint and muscle activity co-ordinate effective movements, essentially without injury. With regard to ACL prevention biomechanics we must consider lower limb muscle strength, joint flexibility, pelvic stability and control, movement patterning and control, joint position sense and control (proprioception) and landing control.

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Recent literature indicates a correlation between increased frictions created with shoes on playing surface, with increased incidence of ACL injury. Some studies have suggested that harder, drier surfaces are associated with a higher ACL injury rate (mainly related to the sports of soccer, rugby league and AFL). Australian researchers have begun to explore the potential of the warmer 'dry season' and how different grass types can impact on ACL injury rates. This is less applicable for the variable Scottish weather, where appropriate footwear selection for certain pitch types (both artificial and grass) and especially use of longer studs and blades are important.

How to reduce the likelihood of injury

Recent studies have shown that the incidence of ACL injury can be reduced by up to 70% with the implementation of a weekly preventative rehab programme (PEP). Introducing preventative exercises into an athlete’s weekly training schedule, can help reduce some of the biomechanical risk factors associated with ACL injury.

Top knee surgeons highly recommend the following programme, adapted from Gilchrist et. al AJSM (2008), for use both as a preventative strategy but also for those returning to sport post ACL injury to prevent re-rupture. Advising that this programme, or one similar, be performed 2-3 times per week throughout the season. Many of the drills can be integrated logically into part of a team warm up. It is important that this programme is not performed at the end of training sessions as fatigue will result in poor technique and potential injury.

The programme consists of warm up, stretching, strengthening, plyometrics and sport-specific drills. This can be adapted to suit individual sports, progression of reps and distances performed should be increased as the athlete's ability improves.

The WARM-UP component, as with all warm ups, is designed to slowly prepare the body for exercise, both mentally and physically. Blood flow increases to the working muscles and in turn can reduce the incidence of muscle injury.

The STRETCHING component of the PEP follows on from the warm up (although can be moved to the end of the session) allowing players to improve and maintain muscle range of motion, reduce joint stiffness and improve general mobility. Individuals should be encouraged to gently stretch to the point of muscle tension onset (never pain) and hold, concentrating on lengthening the muscles as the stretch progresses. Remember, the stretches outlined below are those felt beneficial in the prevention of ACL injury, and other sport-specific stretches and mobility drills will be required as part of a full warm up before and after a training session.

The STRENGTH component of the regime focuses on increasing leg strength, and subsequently leads towards a more stable knee joint. Special attention must be given to perfect technique outlined are some tips beside the individual exercises below. The walking lunges mainly address quadriceps and gluteal strength. Russian hamstrings obviously address the hamstring strength component, and calf raises strengthen the calf muscles and increase balance.

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The PLYOMETRICS component of the PEP is designed to help build power, strength and speed. The most important focus must be placed on performing the landing technique correctly- it must be soft and cushioned. Concentrate on gently landing on balls of the feet then rolling back onto the heel with a bent knee and hip. Begin these exercises either with a line on the pitch, broom stick or flat 2″ cone, and progress as ability and technique improves.

Finally the AGILITY component which is designed to work on dynamic control of the knee complex and 'tie-up' all the other components of the programme. Care should be taken to continue to promote good knee position i.e. not to allow the knee to cave inwards or let the bent knee drift forwards too far so that the player cannot see their toes.

Preventative Rehab Programme (PEP)

Further information on this programme can be found at www.aclprevent.com.

Variations on the above exercises can also be used, or integrated with ball passing and catching to create a more sport specific routine.

Adaptations to the PEP should be made to suit children under the age of 12 years:

• During the plyometric component of the PEP, children should be made to jump over a line on the ground or 2″ high cone only, with emphasis given to landing technique rather than the height being jumped.
• Children should perform all plyometrics with two-legged jumps rather on a single leg. Again, emphasis should be placed on the landing technique, ensuring that the knee does not cave inwards and that the landing force is absorbed by softly bent knees, and hips.
• Time spent on good technique is more important than repetitions in the young athlete. Fewer repetitions which take longer but are done with perfect technique are preferred to high repetition with poor form.

Written by Gemma Scott of The Sports Physio Clinic.

Gemma is a Sports Physiotherapist currently working at The Sports Physio Clinic based at the Academy of Sport in Sydney, Australia. She spent five years working at the Scottish Rugby Union, with the majority of her time in the post of Lead Physiotherapist for the Scotland 7s rugby squad. She has an extensive background of physiotherapy work in Rugby Union, as well as time spent working in netball, soccer, athletics and rowing. Gemma has an MSc in Sport and Exercise Medicine from Trinity College Dublin, as well as a BSc (Hons) in Physiotherapy from Glasgow Caledonian University.

To find out more about Gemma visit her website at http://www.nsmcp.com.au/