TABLE 2: HEALTH AND ECONOMIC BURDEN OF ACL INJURIES

Approximately 250,000 ACL injuries every year in the US, with over $2 billion/ year (34) spent on:

n MRI scans n Reconstructive surgery n Post-operative bracing n Rehabilitation.

Complete ACL injuries can lead to chronic knee pathology, including: n Instability n Secondary injury to the menisci n Damage to the articular cartilage of the femur, patella or tibia n Early-onset osteoarthritis.

Long-term consequences also impact negatively on: n Activities of daily living n Quality of life n Psychological well-being

a two-fold to a ten-fold higher incidence of ACL injuries than their male counterparts. Arendt and Dick (35) examined the increased incidence of ACL injury among NCAA Division 1 athletes participating in basketball and soccer over a 5-year period. The injury rate was recorded and analysed per athlete-exposure, where one practice session or game counted as one exposure. The average ACL injury rate for females was 0.31 per 1000 athlete-exposures (AE) for soccer and 0.29 per 1000 AE for basketball. This compares with males, where the rate was 0.13 for soccer and 0.07 for basketball per 1000 AE. This sex difference is statistically significant (35). Complete ACL injuries can lead to chronic knee

pathology, including instability, secondary injury to the menisci and articular cartilage, and early onset of osteoarthritis. Approximately 66% of all patients with a complete injury incur damage to the menisci and the articular cartilage of the femur, patella and/or tibia (36). This injury, coupled with the risk of secondary injury, can significantly decreases the ability of an athlete to carry out their activities of daily living and has a major impact on their quality of life. Surgical reconstruction of a ruptured ACL can greatly reduce the risk of secondary injury. Seitz et al. (37) noted that 65% of ACL-deficient patients sustained a secondary meniscal injury

within 2.5 years of the initial injury. The health and economic burden of ACL injuries is summarised in Table 2. Despite earnest efforts from orthopaedic surgeons

to preserve the integrity of the knee joint during ACL reconstructive surgery, ACL-reconstructed individuals continue to present with degenerative changes of the articular cartilage and, inevitably, early-onset osteoarthritis. Lohmander et al. (38) completed a 12-year longitudinal follow- up study on female athletes who previously underwent ACL reconstruction after sustaining an injury while playing soccer. They found that 55 women (82%) had radiographic changes in their injured knee and 34 (51%) fulfilled the criterion for radiographic knee osteoarthritis. Their mean age was 31. The implications of this research highlight the need for preventing these injuries from occurring in the first place (38).

Mechanism of injury There are two mechanisms of ACL injury – contact and non- contact (Table 3).

Around 70% of all reported ACL injuries are the non-

contact type, while the remaining 30% involve contact from an outside force such as another player, a goal-post, or an object on the field or court. A non-contact ACL injury in field and court sports commonly involves a manoeuvre like a one-step stop deceleration, a cutting task, a sudden change of direction, or landing from a jump with inadequate knee and hip flexion (at or near full extension). It can also result from a lapse of concentration, for instance, due to an unanticipated change in the direction of play. Non-contact ACL injuries typically occur during a deceleration manoeuvre combined with a change of direction while the foot is in a closed-chain position. While the foot is in a closed-chain position and pronated, the tibia is internally rotated, and the knee is near or at full extension (range of 0–20o

of flexion). If the athlete

attempts to change direction, the result is an excessive torsional force that can potentially strain or rupture the ACL (4,5,8–10) (Figure 2). A recent study by Brophy et al. (39) examined the role

of leg dominance in ACL injury risk in soccer athletes. They hypothesised that soccer players of both genders rupture the ACL in their preferred supporting leg more often than the ACL in their preferred kicking leg, particularly in non-contact

Figure 4: Partial

Figure 5: Complete

Figure 3: ACL injuries occur when bones of the leg twist in opposite directions under full body weight

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Figure 6: Avulsion sportEX medicine 2011;47(Jan):14-21