There’s no question that exercise is good for kids. But the trauma associated with some youth sports can dramatically increase the risk that those kids will develop knee or ankle osteoarthritis by the time they reach adulthood. The key next step is to determine what can be done about it.
By Yvonne M. Golightly, PT, PhD, Stephen W. Marshall, PhD, and Dennis J. Caine, PhD
Participating in youth sports has many benefits, such as supporting good cardiovascular health and curbing youth obesity. However, there are important health risks that should be considered, particularly the risk of joint injury and subsequent development of osteoarthritis (OA).1,2
Epidemiology of osteoarthritis
OA is a leading cause of disability3 and the most common type of arthritis. Almost 59% (27 million) of the U.S population has arthritis or another rheumatic condition.4 Although OA generally affects older adults, injury-mediated OA (also known as post-traumatic OA) has been observed in former athletes who are only in their early 30s and can be traced back to youth sports.5,6
OA is characterized by breakdown of articular cartilage and the appearance of osteophytes. The course of OA development may include a deterioration of cartilage elasticity, increased bone growth in response to cartilage wear, the appearance of bone fragments in the joint space, and synovial membrane inflammation. This joint failure may contribute to pain, aching, tenderness, stiffness, and loss of range of motion with associated daily activity limitations and a consequent decline in patient-reported quality of life.7-9 Although evidence of cartilage and bone changes on radiographs or magnetic resonance imaging are needed for OA diagnosis, the presence of these features is not considered clinically relevant unless the patient is symptomatic.
Projections indicate that the incidence of OA in the U.S. will nearly double in the next few decades.10 This increase reflects the general aging of the population and the rise in obesity prevalence, and will place a considerable burden on the U.S. healthcare system.10 OA was the primary diagnosis for 25% of nontraumatic ambulatory care visits in the U.S. in 2004.11 In that year, general arthritis was the primary diagnosis for 3.1% of all nonfederal, short-stay hospitalizations.11 Joint replacement procedures to treat OA are increasingly common, with 418,000 knee replacements reported annually in the U.S. Sixty-six percent of cases with a primary diagnosis of arthritis involve joint replacement procedures.11 Outcomes after knee replacement are generally positive, but these procedures are expensive and require a hospital stay, extensive rehabilitation, and a long recovery time.
The most common joint site for OA is the knee. Factors that may increase the risk of developing knee OA or having a more progressive form of this disease include older age, female gender, African American race, and mechanical issues (e.g., history of lower extremity injuries, obesity, abnormal lower limb biomechanics, frontal plane malalignment of the knee, and lower extremity muscle weakness).12,13 In the U.S., 14% of adults aged 26 years and older14 and approximately 33% of persons older than 63 years have radiographic evidence of knee OA.12 By age 85 years, nearly half of all adults (46%) are expected to develop symptomatic knee OA.15
Reports indicate that ankle OA affects 1% to 4% of adults.16,17 Among 500 consecutive patients in the United Kingdom with OA, the ankle was the fourth most common site for OA after the knee, hand, and hip.17 Ankle OA has been reported to occur most often as a result of trauma18 and is associated with chronic ankle instability.19,20
In youth sports, knee and ankle injuries are common. These injuries occur frequently during football, wrestling, basketball, and soccer.21 In a sample of high school athletes from 2005 to 2007, the ankle was the most common injury location (20.9%), followed by the knee (15.2%).22 Severe injuries (more than 21 days of time lost from activity) occurred most frequently at the knee (29%), and 45% of these injuries involved ligament tears, 15% included contusions, and 8% involved torn cartilage.21 In a separate study of U.S. high school athletes between 2005 and 2008, ankle sprains accounted for the majority of all ankle injuries (83.4%), and fractures occurred in 5.2% of ankle injuries.23
Knee and ankle injuries during youth sport participation include not only first-time injuries, but also recurrent injuries, suggesting that young athletes are returning to sport prior to full recovery or without adequate rehabilitation to ensure good biomechanics. Youth athletes with a prior history of lower extremity injury have rates of incident lower extremity injury that are three to five times greater than those with no prior history.24,25 Among high school athletes between 2005 and 2008, recurrent injuries accounted for 10.5% of all injuries, which occurred primarily at the ankle (28.3%) and knee (16.8%).23
The current emphasis on high intensity physical activity during practice and games, increased sports participation at younger ages, and the increasing prevalence of obesity among children and adolescents may compound the risk for acute and overuse injuries among young athletes.22, 26-29 Rates of injuries sustained during youth sport competition and practice that require emergency department visits are relatively stable or declining in some sports, such as seen in studies of high school football from 1990 to 200730 and youth basketball from 1997 to 2007,31 possibly due to injury prevention efforts. However, the injury rates during high school sport competitions in the U.S. remain high (4.10 injuries per 1000 athlete exposures, with more than 700,000 cases during the 2010-2011 school year, as estimated by the High School Sports-Related Injury Surveillance Study). Among these injuries, the ankle and knee were the second and third most commonly injured body sites, respectively.32 These rates may be rising among girls and young women who are increasingly participating in sports, and with the epidemic of obesity among children and adolescents.28,33
Data from the U.S. Consumer Product Safety Commission’s National Electronic Injury Surveillance System (NEISS), a sample of approximately 100 U.S. emergency departments, support an increase from 1990 to 2003 in the rates of all injuries associated with girl’s high school soccer.33 Young athletes who are overweight or obese are more than twice as likely to sustain an injury during sport and recreational activities as their normal-weight peers.28 Ankle sprains are three times more likely to occur among obese versus normal-weight adolescent athletes. 28
Sports injury and lower extremity OA
Anterior cruciate ligament (ACL), meniscus, and articular cartilage injuries of the knee are closely linked to knee OA.13,34,35 In a prospective study of young adults (1321 students with a mean age of 22 years at baseline), the risk of self-reported knee OA later in life was five times higher among those with a history of knee injury compared with those without injury (relative risk = 5.17, 95% CI = 3.07-8.71, over a median follow up of 36 years).34 Forty-seven men reported knee injury during adolescence or young adulthood (mean age, 16 years) and, among those, nearly one-third (n=15) reported the injury was sports-related. By age 65 years, the cumulative incidence of knee OA was 13.9% in participants who had a knee injury during adolescence or young adulthood and 6% in those without injury during this stage of life.
Studies of meniscus and ACL injuries suggest an association between injury and OA development. In 67 Swedish female soccer players with a confirmed ACL injury sustained before age 20 years, radiographic evidence of OA was present in 51% of the injured knees after 12 years, compared with 8% of the uninjured knees.36 Similarly, in 219 Swedish male soccer players 14 years after ACL injury (age range at injury, 16-42 years), the incidence of radiographic knee OA was 41% in the injured knees versus 4% in the uninjured knees.6
Removal of part or all of the load-bearing meniscus is also associated with knee OA.37 In a review of 41 studies of surgically treated isolated meniscus tears (mean age 30 years, with adolescents included in some studies), radiographic knee OA was present in approximately 50% of those who had undergone meniscectomy 10 to 20 years earlier.5 In long-term follow up of young athletes undergoing meniscus surgery, more than 50% developed knee OA with accompanying pain and physical decline.38-42 These epidemiologic studies are supported by evidence from animal models of ACL/meniscus injury and OA development.43,44
Population-based prospective studies of ankle injury and OA are lacking, but clinical observations suggest that many cases of ankle OA are post-traumatic and sport-related. Medical chart data from 30 patients with ligamentous post-traumatic OA referred to an ankle arthritis center revealed that 55% of ankles with OA (18 of 33 ankles) were sprained during sport (mean age of athletes, 24 years, range 15-38 years), and 39% (7 of 18 ankles) of these injuries occurred between the ages of 15-19 years.45 Although not specific to youth sports, the prevalence of ankle OA in 2552 retired football players was 2.3 times greater in those who had experienced at least one ankle sprain during their professional careers compared with those who reported no history of ankle sprain.46
It is evident that injury contributes to OA development in some individuals, as supported by animal models and human studies.47,48 A number of biological mechanisms have been proposed. In a weight-bearing joint, the tissues may be weakened and less able to attenuate and moderate dynamic forces after injury, leading to altered loading of joint cartilage. Joint alignment and biomechanics may become altered, and forces across the joint that occur during walking or other physical activities may load cartilage and bone unevenly, contributing to cartilage degeneration and disruption of bone growth.
Surgical reconstruction, if required, means an additional set of insults to the joint. ACL reconstruction is intended to restore function at the knee, but biomechanical studies of reconstructed patients show that motion, particularly internal-external rotation during walking, of the reconstructed knee differs from that of the contralateral uninjured knee.49-53 Increased tibial internal rotation during the stance phase of gait may contribute to uneven loading of knee joint cartilage, increasing the risk of cartilage degeneration in regions subject to excessive loads.54
Alternatively, the injury itself may be the result of biomechanical characteristics present before injury, and some of those biomechanical factors may increase the risk for both ligament injury and OA. A range of pre-existing factors—including joint alignment, neuromuscular control of movement during activity (quality of movement biomechanics), hormonal variations by gender, and genetics—may render some individuals more prone to injury and OA than others.2,55,56 Of particular interest are variables that may increase the knee adduction moment during gait, which is hypothesized to alter loading and increase risk of medical compartment knee OA.54
Clinically, insufficient attention has been paid to correction of faulty movement biomechanics of the lower extremity prior to injury, during postinjury rehabilitation, and following onset of OA. Correction of poor biomechanics has potential to ameliorate the abnormal joint loading that can contribute to OA development and progression following injury; this type of biomechanical correction can also help decrease the risk of injury recurrence. Primary prevention of lower extremity injury through injury prevention programs in combination with sound postinjury rehabilitation strategies are critical for children and adolescents; abnormal joint stresses and loading at young ages can alter cartilage and bone development and, in turn, increase risk for earlier onset of OA.5 Finally, among those with OA, correction of biomechanics may improve physical function and slow disease progression.
Interventions for primary prevention
Neuromuscular training programs effectively reduce sport-related injuries in adolescents and young adults (12-24 years), as illustrated in a meta-analysis of seven high-quality randomized control trials (RCTs) of pivoting sports (i.e., basketball, volleyball, soccer, team handball, hockey, and floorball).57 A pooled analysis showed that multi-intervention training programs (i.e., balance activities, weight training, plyometric exercise, agility drills, and sport-specific exercises) reduced the risk of knee injuries by 54% and ankle sprains by 50%. Balance training alone reduced the risk of ankle sprain injuries by 36% and was particularly effective for those with prior ankle injury, but did not alter the risk of knee injuries.
Another systematic review confirmed the effectiveness of training programs plus shock-absorbing insoles in military recruits and of external joint supports among young athletes as valuable interventions for lower extremity injury prevention.58 Neuromuscular training programs that promote injury prevention among high school and college-aged athletes need to be adapted for use in younger children (10 to12 years) to be effective in this population.59-61
Whether or not neuromuscular training programs are effective in preventing or reducing progression of OA in athletes with injuries is not known; however, it is logical to assume that better-quality movement patterns and improved joint stability will preserve joint health. Additionally, obesity increases the risk of youth sport injury, and this risk factor can be modified through dietary and physical activity strategies for young athletes that promote a healthy weight, physical fitness, and good neuromuscular coordination.28 Research has found that bracing and taping are effective for prevention of ankle sprains among athletes.63
Treatment of knee and ankle injuries often consists of surgical intervention, especially to repair ligament ruptures or meniscus damage, and physical rehabilitation. Reconstruction of an ACL tear may not provide advantages beyond a good multidimensional rehabilitation program, however. A RCT of active adults aged 18 to 35 years with ACL tears (62 assigned to rehabilitation plus early ACL repair, 59 to rehabilitation plus optional delayed ACL repair) found no difference in symptoms, functional outcomes, and quality of life two years postintervention.62 Interestingly, by year two of the study, only 23 (37%) of patients in the rehabilitation plus optional delayed ACL repair group had opted for surgical repair.62
RCTs suggest that knee instability is observed less frequently in those who receive surgical ACL repair, but evidence is lacking to support surgical intervention over more conservative approaches for prevention of knee OA.63,64 A 10-year follow-up study of 50 high-level athletes with ACL tears (25 patients treated with surgical repair and 25 treated conservatively) found no statistically significant differences between groups with regard to knee OA, activity level, or functional level.63
Among those who have ACL reconstruction, rehabilitation to achieve normal range of motion may be important for both optimal physical function and reducing OA risk. A recent study of 780 patients ≥5 years postsurgery (mean time, 10.5 years) reported that loss of normal symmetric knee range of motion was associated with radiographic changes consistent with OA (joint space narrowing, sclerosis, or osteophytes).65
Taping and bracing are the most commonly used interventions for ankle instability and have been shown to help reduce ankle sprain recurrence.66,67 Neuromuscular training may be an important addition to a rehabilitation program after sport-related ankle injury to improve ankle stability and prevent recurrent ankle injury;67-69 strengthening programs alone do not appear to be as effective as strengthening with proprioceptive training.67,69,70
Two studies have examined whether neuromuscular training in patients with knee OA affects physical function outcomes, with differing results.71.72 In a study of 66 women aged 35 to 65 years with knee OA, those who performed kinesthetic, balance, and strengthening exercises showed greater improvement in self-reported and performance-based function measures compared with those who performed strengthening exercises alone.71 In a recent study of 183 people aged ≥50 years with knee OA, adding agility and perturbation training did not add benefit to an already advantageous standard exercise program.72
To date there have been no comparable studies in younger populations with injury-mediated OA. This is a promising area for further research, since it is plausible that former athletes would be more responsive to this intervention than adults older than 50 years. Cases of injury-mediated OA have been documented in individuals in their early 30s.6,36 Maintaining physical activity in these populations is critical to preserving a healthy weight, especially in sports that promote weight gain (such as football, which can also predispose athletes to obesity in later life).28
Athletic injuries to the knee and ankle clearly elevate the risk of OA. Further investigation is needed, however, to determine the nature and extent of this relationship and whether intense participation in high-stress elite sports at a young age accelerates OA development, leading to disease onset at an earlier age. Based on current knowledge, intervention on several fronts may be warranted.
Health professionals working with child and adolescent athletes should counsel the athletes and their families on the benefits and risks associated with athletic activity, including the possible long-term risk of OA. Physical activity should be vigorous (but not excessive in frequency, intensity, or duration) to promote healthy joint development and reduce the risk of obesity.73 Assessments (i.e., medical examination and screening) prior to sport participation should be performed to identify children and adolescents at high risk for injury or joint problems who may benefit from neuromuscular training programs, including those with prior injuries, abnormal biomechanics, joint malalignment, and lower extremity muscle weakness or imbalances.74
Programs that focus on neuromuscular training, including balance, proprioception, and agility, may be useful not only for primary prevention of injury and OA, but also for promoting optimal biomechanics, stability, and postinjury joint health. The goal should be to allow the child or adolescent to enjoy the benefits of sport participation while reducing the risk of OA.
Yvonne M. Golightly, PT, PhD, is a postdoctoral fellow in the Thurston Arthritis Research Center and Stephen W. Marshall, PhD, is associate professor of epidemiology and orthopedics and interim director of the UNC Injury Prevention Research Center at the University of North Carolina at Chapel Hill. Dennis J. Caine, PhD, is professor and chair of the Department of Physical Education, Exercise Science and Wellness at the University of North Dakota in Grand Forks, ND.
Disclosure: The authors report no conflicts of interest in relation to this work.
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