Knee injuries are a common occurrence of sport participation and it has become increasing apparent that such injuries can have a lifelong consequence for the athlete. One of the most serious knee injuries is an anterior cruciate ligament (ACL) tear and this injury will be used throughout this talk to illustrate concepts pertaining to injury prevention or risk reduction.
There is evidence to show that degenerative changes in the knee can occur early, within one to two years, after an anterior cruciate ligament (ACL) injury and that on average 50% of patients are estimated to develop disabling osteoarthritis in the longer term. Although there is some evidence that ACL reconstruction reduces the risk of osteoarthritis there is stronger evidence that it does little to protect the knee from long term degeneration. Associated damage which may occur to the menisci or articular surfaces, has also been shown to increase the risk of developing osteoarthritis. Therefore, injury prevention is key. Unfortunately, the rates of ACL injury are steadily increasing, particularly at the younger end of the age spectrum. Concerning new data also shows that rates of concomitant meniscal injuries have also substantially increased, and again the younger aged athlete is more susceptible. This increasing prevalence of meniscal involvement is of concern for long term knee health.
Fortunately, injury prevention programs can reduce the risk of both knee injuries and ACL injuries. Most programs have targeted female athletes and incorporate neuromuscular training interventions to address modifiable risk factors. Most evidence is available for ACL injury risk reduction in female athletes although there is emerging evidence for male athletes. It has been recommended that such programs should include a combination of plyometric, strength and balance training for at least 6 weeks with a minimum of 1 session per week. For optimal results training should take place both pre and in-season. Critical components for the success of such training programs have been shown to be age (younger athletes gaining most benefit), dosage (superior results with longer and more frequent training), exercise variation and verbal feedback. Including any one of these four components has been shown to reduce injury risk by 18%. Injury prevention programs additionally have the potential to reduce further medical costs, with cost analysis showing that the optimum implementation strategy is to target high risk athletes aged 12-25 years. For this group US$17,000 can be spent per participant on the program. However, perhaps one of the biggest challenges with injury prevention training programs is in their implementation. Regular compliance is a critical factor for injury risk reduction and barriers to high compliance have been therefore been investigated. Program design has been shown to be a key influencing factor with programs that contain sport specific tasks and less than 15 minutes to complete positively associated with compliance.
Despite bests efforts to reduce ACL injury risk, ACL injuries still occur, and attention must also be directed to secondary prevention strategies. These include prevention of further ACL injury as well as prevention of post traumatic knee osteoarthritis. In terms of second ACL injury prevention, although numerous risk factors have been identified it is clear that younger athletes who return to pivot and contact sports have high rates of further injury and must therefore be a focus. Return to sport testing has become popular over recent years. It is unclear though whether such testing is designed to determine whether an athlete is capable of returning to sport or determine whether it is safe. Despite the current discussions around return to sport testing following ACL reconstruction, the evidence around it is relatively limited, and the available evidence is somewhat conflicting. A common theme however is that a surprisingly low number of athletes meet return to sport thresholds and criteria with a recent systematic review showing an overall rate of 23% of patients passing return to sport test batteries both prior to and after return to strenuous sports. Caution should therefore be used in applying information gained from current return to sport testing and advising athletes about the risk for further injury.
It has recently been argued that there is no clear evidence that current ACL rehabilitation programs include approaches to prevent future development of knee osteoarthritis and that such an approach should include aggressive knee extensor strengthening, as well as strategies for optimal loading of the vulnerable joint. Patient education should also be a key component to ensure realistic expectations for long term knee heath.
Whilst injury prevention and risk reduction strategies for primary and secondary ACL injury and osteoarthritis has been a focus of current research the challenge remains to extrapolate from this body of evidence to other lower limb musculoskeletal injuries for which data is scarce.
Marked quadriceps weakness has been demonstrated prior to undergoing cartilage restoration procedures, and these deficits often persist postoperatively. Blood flow restriction training (BFRT) continues to gain interest amongst rehabilitation specialists as a novel method to improve quadriceps strength. Blood flow restriction training (BFRT) involves the use of an inflatable cuff applied to the thigh to slow blood flow as subjects exercise with a light weight allowing them to receive the same training benefits as if they were training under high loads. The premise for using BFRT after cartilage procedures was initially based off successful use in healthy populations but more recently in patients knee disorders demonstrating greater strength gains than traditional forms of exercise. There is evidence supporting the premise that BFRT will result in both improved quadriceps and hip strength. This then holds promise as greater muscle strength in turn will result in improved lower extremity biomechanics, improved functional capacity, and an accelerated recovery.
In this presentation, we will discuss the physiologic mechanisms of BFRT. We and others have shown BFRT is able to preferentially improve muscle fiber cross-sectional area, increase satellite cell proliferation and may reduce the extracellular matrix in healthy subjects. We are further motivated by our recently published data in anterior cruciate ligament reconstructed subjects which show that these are the precise properties of muscle that are negatively impacted after the injury and rehabilitation so should be positively altered by BFRT.We have also seen that improved quadriceps strength is associated with reducedfear of re-injury and improved self-reported ability to perform quadriceps-dominant activities such as ascending stairs.
BFRT could potentially benefit those with patellofemoral lesions as well. Increased quadriceps strength has been shown to be protective against patellofemoral cartilage loss as well as less pain and improved function.BFRT may not only result in improved quadriceps strength but also proximal changes in hip strength and muscular characteristics. Hip weakness and increased knee adduction angles increase the forces born by the articular cartilage. Improving quadriceps and hip strength may also be chondroprotective by reducing femoral internal rotation thereby lessening compressive forces borne by the cartilage of the lateral patella and trochlea. BFRT with the cuff placed around the proximal thigh has been demonstrated to improve quadriceps strength but has also resulted in changes proximal to the cuff. In healthy volunteers, thigh girth and hip abduction and external rotation strength have both been shown to have significantly greater improvements following a BFRT program when compared to those that completed the same exercise program without BFRT. In older adults, BFRT has also been demonstrated to increase cross sectional area of the hip adductor and gluteus maximus muscle groups in addition to the quadriceps.
Despite rapid adoption in the clinical setting, there is a great deal of variability in BFRT treatment protocols being used. This variability then results in variable strength gains with BFRT. In a balanced presentation of the literature to date, we will also discuss the treatment protocols that have been the most effective as well as contraindications that must be considered prior to using BFRT.