- Anterior cruciate ligament (ACL) injury affects as many as 250,000 individuals in the U.S. annually, resulting in an annual health care cost exceeding $2 billion.
- Women suffer ACL tears at 3x the rate of men.
- Multiple reviews have found minor differences between single-bundle versus double-bundle surgical reconstruction techniques.
- Analysis included 240 full-text articles.
Anterior cruciate ligament (ACL) injury (Figure 1) affects as many as 250,000 individuals in the U.S. per year, resulting in an annual healthcare expenditure of more than $2 billion, according to the Centers for Disease and Prevention. Women have been found to be at 3x the risk of ACL tear compared with men, according to results of a large meta-analysis published recently in the Orthopaedic Journal of Sports Medicine (OJSM).
The traditional view regarding the incidence of ACL injury in specific athletic populations was reevaluated in the OJSM review. The authors reported that an analysis of 25 epidemiologic studies and found a 5% rate of ACL tear in females who participated in year-round soccer and basketball. Females had 3x the risk of ACL tear versus males participating in the same sport.
Female-male ACL tear incidence ratios were as follows: basketball, 3.5; soccer, 2.67; lacrosse, 1.18; and Alpine skiing, 1.0. The collegiate soccer tear rate was 0.32 for females and 0.12 for males. For basketball, the rates were 0.29 and 0.08, respectively. The rate for recreational Alpine skiers was 0.63, and that for experts was 0.03, with no gender variance. The two volleyball studies had no ACL tears. Training reduced the ACL tear incidence in soccer by 0.24 but did not reduce it at all in basketball, according to a 2007 report in Arthroscopy. (Figure 2.)
There has been a substantial increase in the number of systematic reviews and meta-analyses published on ACL injury (Figure 3) in the past decade. The researchers performed a systematic review of all ACL-related systematic reviews and meta-analyses published between January 2004 and September 2014. Studies were retrieved from the PubMed, MEDLINE, and Cochrane databases. Narrative reviews and non-English articles were excluded.
In all, 240 studies met the inclusion criteria. The articles were subsequently summarized and divided into 17 topics: anatomy, epidemiology, prevention, associated injuries, diagnosis, operative versus nonoperative management, graft choice, surgical technique, fixation methods, computer-assisted surgery, platelet-rich plasma, rehabilitation, return to play, outcomes assessment, arthritis, complications, and miscellaneous.
The increased risk of ACL injury found in female athletes was conjectured to be. The OJSM reviewers noted there have been multiple studies indicating that hormonal factors are responsible. The risk of ACL injury (Figure 4) related to timing of the menstrual cycle was evaluated in 3 recent systematic reviews that focused on risk in female athletes and 2 general risk factor reviews. Each review arrived at a similar conclusion, demonstrating increased risk of ACL injury in female athletes due to changes in ligament tension in the first half of the menstrual cycle during the preovulatory phase. The biochemical explanation for these changes is most likely related to the increased levels of relaxin and the estrogen-mediated reduction in procollagen I resulting in altered ligamentous tensile properties. Oral contraceptive use, in addition to neuromuscular training, may increase dynamic knee stability and lessen the risk of ACL injury that can hormonal changes during the menstrual cycle.
Two systematic reviews examined extrinsic risk factors of ACL injury. Shoes with a more adhesive surface grip that increased ground friction as well as a position of play that predisposed the athlete to unanticipated sidestepping seemed to cause more ACL injury, according to Serpell et al. A study conducted by Balazs et al found an increased risk of ACL injury in football players (Figure 5) who performed on synthetic playing surfaces but, interestingly, no increased risk in soccer players on similar surfaces.
The OJSM reviewers found 3 systematic reviews that examined studies of prevention of ACL injury in males Alentorn-Geli et al performed a systematic review of 34 articles and found that dry weather conditions, artificial turf, and increased posterior tibial slope were associated with increased risk of ACL injury in males. Three of 7 studies included in another review by Alentorn-Geli et al found that prevention programs were successful in reducing ACL injuries or modifying risk factors for ACL injuries in males. In 2012, Sadoghi et al estimated an 85% reduction in ACL injuries in males after participation in an injury prevention program.
The majority of systematic reviews examining the effects of prevention programs on ACL injury have focused on female athletes. The most common areas of study in female athletes have been overall effectiveness, effectiveness of specific program components, effectiveness by age, and compliance on effectiveness,” according to the OJSM reviewers.
The OJSM reviewers found that autografts offered improved outcomes and greater patient satisfaction compared with allografts, and autografts were preferred in young, active populations. On the other hand, allograft sterilization method, specifically irradiation, was found to affect outcome measures and is a valid option in older, less active populations. Nonirradiated allografts were associated with lower failure rates compared with radiated allografts.
Numerous systematic reviews have focused on single-bundle (SB) versus double-bundle (DB) ACL repair. "In summary, there appears to be a small difference between DB and SB reconstruction in terms of rotational and AP [anteroposterior] stability in the hands of some surgeons. It is unclear whether these differences are clinically significant. Long-term follow-up appears to show comparable results between the techniques," the OJSM reviewers reported. (Figures 6 and 7.)
The OJSM review is intended to provide a comprehensive summary of published systematic reviews and meta-analyses on various topics pertaining to the ACL. “A large body of literature with substantial evidence has been established for several topics,” the reviewers reported. “The epidemiology of ACL injuries has been well researched, particularly intrinsic and extrinsic risk factors as well as the incidence of ACL injury by sport. There is also a plethora of studies on diagnostic criteria for ACL injuries as well as outcomes assessments. Many studies have compared single- and double-bundle ACL reconstructions and in general have found comparable outcomes. There is substantial evidence in the rehabilitation literature supporting the notions that (1) there is no added benefit from knee brace or CPM, (2) accelerated rehabilitation and open chain exercises may be beneficial, (3) cryotherapy is safe and effective, and (4) resistance and proprioceptive training can be beneficial after surgery. Several reviews have also shown that ACL injuries, treated operatively or nonoperatively, are associated with increased risk of knee arthritis,” they wrote.