Although the traditional sports like basketball, football, golf, and baseball have been around for generally more than a century and receive the majority of the attention in the public media, in the United States participation in these sports have not necessarily seen any recent, dramatic increases.1 In contrast, sports like triathlon, road and off-road running events, obstacle or adventure races, open water swimming, etc are relatively new and receive on average little media attention. However, they continue to see increasing participation rates in terms of number of athletes with increasing number of events as well. One common feature of these sports is the emphasis on aerobic endurance and mental toughness rather than anaerobic strength or skill. Initially standard running races and triathlons were considered examples of endurance sports. But as their popularity increased, they lost their label of “extreme” sports. Looking for new ways to differentiate and challenge themselves in endurance sports participants have moved to a special subset of events that feature ultra-endurance distances. Ultra-endurance events include foot races, both on the road and off-road, beyond the marathon distance (26.2 miles), triathlons with Ironman distance (2.4 mile swim, 112 mile bike, and 26.2 mile run) and beyond, multileg and often multiday obstacle and adventure races as well as open water distance swims (6.2 miles and beyond). It should be no surprise that musculoskeletal injuries can be a common problem in these athletes. Both the extended time spent preparing and training for these events as well as the events themselves are obviously associated with dramatic and prolonged physical stresses on the musculoskeletal structures that can lead to breakdown and injury. Many of these injuries can be seen in other sports. However, the frequency of certain injuries as well the manner in which these athletes deal with them can be dramatically different. In addition, there are some unique injuries that are rarely seen in nonendurance sports. This review article will give an overview of the common and uncommon musculoskeletal injuries seen in these ultra-endurance athletes and review the guidelines in terms of treatment both during training as well as during competition.
Accurate injury data can be difficult to ascertain in certain sports. In order for injury data to be accurate and meaningful is has to be controlled for exposure. In addition, an “injury” needs to be carefully defined. In organized team sports, exposures are often defined as practice and game sessions. Ultra-endurance athletes are generally not part of an organized team and tend to train and prepare on their own. Training and race sessions can vary dramatically in terms of length, distance, and intensity. In organized team sports, an “injury” is often defined and one or more missed training or game session because of the problem. Some level of musculoskeletal pain in a training or race session is an accepted feature of the sport for the ultra-endurance athlete. It seems common to “train and race through” suspected injuries as many ultra-endurance athletes self-diagnose and self-treat their aches and pains. As a result both exposure as well as injury is more difficult to define in ultra-endurance sports.
Findings from the Ultrarunners Longitudinal Tracking (ULTRA) study indicate a high incidence of injuries.2 In this database of ultramarathon runners with self-reported injuries almost 65% reported an exercise-related injury that resulted in lost training days over the time span of 1 year. Injuries were associated with younger and less experienced runners. The knee was most commonly involved. There also was a 5.5% incidence of stress fractures, nearly half of them involving the foot, and they were more common in women than in men.
A similar high rate of injury has been reported in long-distance triathletes. O’Toole et al3 originally reported that 91% of the respondents of a survey of Hawaii Ironman competitors acknowledged a soft tissue overuse injury in the preceding year. Edgerman et al4 reported injuries in 74.8% of Ironman triathletes based on a written questionnaire. Most injuries in this study occurred from trauma during cycling training sessions. Injuries were also associated with older athletes, high performance athletes and large number of weekly training hours. In addition, injury rates in long-distance triathletes are correlated with the amount of intensive speed sessions done in the time leading up to the injury.5
Injury rates during ultra-endurance competition events also seem high. In multiday ultramarathon events injury rates ranging from 56% to 85% have been reported.6,7 It should be noted that a significant portion of these injuries includes skin-related disorders such as blisters and chafing. The skin problems themselves can seem minor but at the same time can lead to gait changes that can put other structures at risks. In addition, longer and multiday races may require the participants to carry their own nutrition and hydration. This adds significant weight and possibly increases injury risk. It is also worth mentioning that only a small portion of the reported injuries caused athletes to abandon the race confirming the “race through the injury” attitude of many of these athletes.
The exact contribution the various risk factors for musculoskeletal injuries in ultra-endurance athletes can not be determined from these few, mostly observational and epidemiological studies. Many factors such as morphologic characteristics, training regimens, running style, shoe wear, etc have not been carefully studied. It seems likely that there is a complex relationship between the various factors and injury occurrence as suggested by Kienstra et al.8 However, it seems also reasonable to assume that training volume and intensity is a key variable. Particularly in stress fractures, sex likely plays a role with women being at higher risk.
For many health care providers of ultra-endurance athletes a stress fracture represents the quintessential overuse injury. Repeated physical stress on solid structure is known to eventually cause mechanical failure of the structure with bone not being an exception. It is important to recognize however that the preinjury mechanical strength of the bone can be variable and is dependent on several factors. Recognition of these factors can be important in the prevention and treatment of stress fractures. Lack of weight-bearing exercise will lead to relatively decreased bone strength and possible predisposition to stress fracture. As such, novice ultra-endurance athletes with a rapidly increasing training volume are likely at increased risk for stress fractures as evidenced by the preliminary results of the ULTRA study. Nutritional status also has been associated with bone quality. It is not uncommon for ultra-endurance athletes to have fairly strict dietary rules for themselves. Some of this can be grounded in the fear of weight gain leading to decreased performance. Others have different health concerns causing them so avoid certain food items such as meats or other animal products. These dietary restrictions can potentially lead to suboptimal bone health. Finally hormonal factors especially in women can lead to poor bone strength. The association of running, amenorrhea and stress fractures has been well documented9 and should be considered in the treatment and prevention of stress fractures. It may be important to aggressively pursue the potential diagnosis of a stress fracture if suspected as an undiagnosed and untreated stress fracture can progress to a complete acute fracture potentially requiring emergency surgery.10 This may not necessarily be an uncommon scenario in ultra-endurance athletes who assume that a certain level of physical discomfort and pain is a routine part of their training and racing events (Fig. 1).
As previously mentioned the foot is reported to be the most common area affected by stress fractures. Although any bone can potentially sustain a stress fracture, the metatarsals are by far the most likely affected. The bending stresses of the running cycle seem to frequently exceed the strength of the metatarsal.11 In particular the second and third metatarsal bones are most commonly affected as opposed to the fifth metatarsal seen in sports that require sudden cutting and turning movements. Localized pain with running is generally the initial sign of this problem. As the problem progresses, localized swelling and even pain at rest can become evident. Physical examination generally reveals a localized, dorsal tenderness direct over the affected metatarsal. Radiographs initially may be negative. Occasionally, the first radiographic finding may be some callus forming as the actual fracture line may be difficult to visualize. If neither is present but a stress fracture is suspected, then MRI is generally used to confirm the diagnosis. Treatment may simply be the cessation of running for at least 3 to 4 weeks with gradually resumption after that if the pain and tenderness has resolved. If the fracture has progressed to a complete cortical break with pain even on regular weight bearing such as walking or standing, a walking boot or cast during the healing phase can be helpful to minimize any bending stresses on the bone.
Tibial stress fractures can occur in several locations. Common locations are the distal medial side, anterior mid-tibia and the proximal medial metaphysis. Similar to what was described under metatarsal stress fractures, the localized pain and tenderness that worsens with running are the typical symptoms and findings. The radiographic diagnosis can be challenging as the fracture line and any callus can be difficult to ascertain. The signs and symptoms of a tibial stress fracture can also be easily confused with other causes of shin pain such as medial tibial stress syndrome or even exercise-induced compartment syndrome. Again, MRI is generally used to determine the presence of a stress fracture if there is uncertainty. The more proximal and distal tibial stress fractures being in cancellous bone have good healing potential with cessation of running and jumping exercise. However, cessation of running for at least 6 to 8 weeks is frequently needed. A protective walking boot can be helpful initially. The mid-tibia cortical stress fractures, frequently called the dreaded black line because of their radiographic appearance, have a relatively poor prognosis with regards to spontaneous healing. Surgical treatment with internal fixation is frequently recommended.12
The cause of pain in the hip and low back area in athletes can pose significant diagnostic challenges. Although this can indicate a stress fracture in the hip, pelvis, or sacrum, other conditions such as femoro-acetabular impingement, adductor strains, osteitis pubis, and abdominal wall pathology should be considered. With regards to stress fractures, the majority of these affect the femur as pelvis and sacral fractures account for <3% of the stress fractures.2 Hip femoral neck stress fractures can have disastrous consequences if not recognized and treated appropriately. The main symptom is hip pain with weight-bearing exercise, generally in the groin area. Physical examination is often normal as the femoral neck can not be assessed for local tenderness because of its deep anatomic position. Radiographs may show a subtle fracture line but MRI is generally definitive. Inferior femoral neck fractures (the compression side) are generally treated with conservative care similar to other stress fractures. However, superior femoral neck fractures (the tension side) have more of a tendency to fracture through, displace and potentially injure the retinacular blood vessels causing avascular necrosis of the femoral head. Many authors advocate surgical fixation of this fracture type.13
Although knee injuries in epidemiological studies have been often the most common site of injury, the exact nature of the injury is often unclear. Several reports on injuries during multiday running races classify the majority of knee pain as patellofemoral or retropatellar pain.14,15 The patellofemoral compartment is highly stressed during the running motion cycle. At foot strike an eccentric contraction of the quadriceps is needed to dampen the impact on the knee and prevent the slightly bent knee from going into more flexion. Eccentric contractions are associated with higher forces than concentric contractions. This creates high tensile forces in the quadriceps and patellar tendons which can lead to injury. Failure or injury of the tendons tends to occurs at the bony insertion site or enthesis. The lesion that develops may fail to heal and can lead to a chronic tendon pain. As classic signs of inflammation are generally absent, this injury is generally not called tendinitis anymore. Most authors favor the term tendinopathy or tendinosis as the tendons more likely show signs of a failed healing response without inflammatory features. Both the patellar and quadriceps tendon can develop these lesions and consequently called patellar and quadriceps tendinopathy. They tend to occur preferentially at the patellar insertion sites. The athlete will have localized pain with high impact exercise and localized tenderness at those sites as the main findings. MRI can visualize these lesions but may not be needed as clinical examination can generally yield the diagnosis. Initial treatment is generally conservatively with relatively rest, physical therapy concentrating on eccentric strengthening, nonsteroidal anti-inflammatory medications (NSAID) and lately platelet-rich plasma injection (PRP). However, it should be recognized that the exact efficacy of some of these treatment modalities has not been fully determined in controlled studies. Corticosteroid injections in and around the tendons are not recommend because of the potential for tendon rupture. In chronic cases, surgical treatment with debridement of the tendon lesion and possibly drilling of curetting the bony insertion site has been advocated.16
The running motion and contraction of the quadriceps also creates high compressive forces on the patellofemoral chondral surfaces. Whether this can actually lead to chondral damage is unclear. However, it is common to find chondral damage in human knees either from a preexisting condition or possibly as part of the aging process. The repetitive compressive forces of the running motion can create pain in knees with compromised chondral surfaces. This can be complicated by preexisting malalignment of the patellofemoral joint. Lateral tracking or even lateral subluxation is not uncommon in human knees, especially in women. This will tend to concentrate the compressive forces on the lateral patellar facet and lateral trochlea resulting in pain and possible accelerated wear and tear. It is not always clear where the pain exactly originates in this condition. There are high performance athletes with patellofemoral chondral damage that seem to have little or no pain from this condition (Fig. 2). The chondral surface itself has no known sensory nerve ending and by itself does not seem to be a cause of pain. It seems likely that the subchondral bone can cause pain. This may be particularly the cause of pain in patients who have developed bone edema on their MRI in the area of their chondral loss. The surrounding synovium and infrapatellar fat pad can seemingly react to the chondral damage as well and has been implicated as a source of pain. Most patients complain of a diffuse anterior knee pain. Other than possibly an effusion, physical examination is generally unremarkable. Signs of malalignment may be important to note such as a high Q-angle or J-sign. Treatment is invariably conservative at the onset.17 Relative rest with avoidance of hill running, physical therapy, and possibly NSAIDs are frequently used. In resistant cases, injection can be considered. Corticosteroid injections may give some relief of the pain from the reactive synovitis in the surrounding synovium and fat pad. However, frequent repeated injections are generally not recommended. Hyaluronic acid injections may have a place in this condition as the chondral loss could be considered a localized form of osteoarthritis. However, the efficacy of this approach is controversial. Surgical treatment of this condition is challenging.18 Isolated arthroscopic chondroplasty tends to yield unpredictable outcomes. More formal grafting procedures for full thickness cartilage lesion such as osteochondral grafts or cell-based techniques like chondrocyte implantation can be considered. However, this requires a prolonged recovery and rehab while the return-to-sports rates to high intensity sports such as long distance running are unknown. Isolated lateral releases seem only indicated in rare cases where there is a tight lateral retinaculum both no gross malalignment. Malalignment with marked lateral tracking or even lateral subluxation may require a more formal realignment procedure. Again, this requires a prolonged recovery and rehab while the return-to-sports rates are largely unknown.
Finally, the incidence of lateral knee pain has been reported as high as 15% in in ultra-endurance athletes.2 The condition frequently is diagnosed as iliotibial band syndrome (ITBS) or iliotibial band friction syndrome. Relatively little is known about the exact cause of the pain in this condition, and the role of friction of the IT band over the lateral femoral epicondyle has been questioned.19 Treatment initially is through activity modification, IT band stretching and hip abductor strengthening. Resistant cases can require corticosteroid injection or even surgical release.
LOWER LEG, FOOT, AND ANKLE INJURIES
Following the knee, the foot, and ankle are the common source of injuries in ultra-endurance athletes. As discussed previously, a significant number of these will fall under the stress fracture category. This section will focus on soft tissue injuries. An ankle soft tissue injury that seems to be relatively unique to the ultra marathoner is a tendon injury to the foot and toe dorsiflexors at the level of the anterior ankle, sometimes termed the “ultramarathoner’s ankle.”20 It manifests itself by pain and possibly swelling most commonly at the inferior extent of the extensor retinaculum of the ankle. Runners tend to adapt with a shorter stride that is more of a shuffling gait in an attempt to minimize the stress and motion in the affected tendons. The injury is seemingly a peritendinitis likely associated with repetitive friction as the dorsiflexors pass underneath the anterior retinaculum. Tibialis anterior, extensor digitorum, and hallucis longus tendons can be involved. It has been postulated that excessive pressure from tightly laced running shoes exacerbated by diffuse foot swelling that can occur in ultra-endurance events are causative factors.14 Lately, it has become common for ultra-endurance runners to wear compressive calf sleeves as they are thought to promote circulation and enhance performance. Anecdotally, one of the authors (CE) has seen and experienced that the tightness of the material at the distal aspect of the sleeve can potentially create excessive pressure and friction problems as well. Excessive foot pronation, hard surface, overstriding, and the trauma from repetitive eccentric load in these tendons may also play a role in the etiology. This ankle problem frequently has been reported during competition. It is not uncommon for it to lead to a “DNF” (Did Not Finish) as there is no simple immediate treatment known to resolve this. Relative rest, icing, cross training, oral nonsteroidal anti-inflammatory medication generally lead to complete resolution of the problem. However, it can be several weeks before unlimited, pain free running can be resumed.
Similarly, on the posterior aspect of the ankle Achilles tendon injuries can create painful problems for ultra-endurance athletes. Achilles tendon problems can manifest themselves in different ways. There seem to be 3 distinct forms of overuse injuries in and around the Achilles tendon. The problem can occur in the sheath or peritendinous tissues, in the midsubstance of the tendon or at the insertion or enthesis. Peritendinous Achilles pain and swelling is somewhat similar to the anterior tendon problem, as it presents itself with diffuse pain and swelling sometimes caused by friction of the shoe. During the more acute phase swelling and crepitation can be noted as the fibrnous exudate fills the tendon sheath. The midsubstance problem tends to occur about once inch about the calcaneal insertion and typically create a local pain and thickening of the tendon (Fig. 3). This condition is often characterized by some degenerative tissue in the tendon, and therefore often termed tendinosis or tendinopathy. The examination reveal swelling without crepitation and the tendinopathic tissue can only be visualized by MRI or ultrasound imaging. Insertional tendon problems at the calcaneus often are associated with bony reaction created a hard, enlarged, and tendon bump on the posterior calcaneus. When recognized, all forms of Achilles tendinopathy are initially treated conservatively with relatively rest and activity modifications. It is unclear how effective NSAIDs are with regards to the final outcome but simply may provide some analgesia in the painful stages of this condition.21 Physical therapy is frequently used and should focus on tendon flexibility and eccentric strengthening. Many of these conditions resolve with conservative treatment but it should be recognized that this can take months in some athletes. Persistent cases can be treatment with surgery but, again, it should be recognized that postoperative recovery and rehabilitation generally takes many months even in successful surgery. Many different surgical approached have be proposed.22 For chronic and scarred peritendinous problems, a release or excision of the affected sheath can be sufficient although care should be taken not to damage the anterior blood supply to the tendon. The midsubstance tendinopathic tissue is generally treated with excision of the lesion although simple longitudinal tenotomies have also been described. Resistant insertional tendon problems often require both the excision of diseased tendon tissue and impinging bone or osteophytes. This may result in near-complete detachment the tendon and necessitate a tendon transfer to reinforce the affected area.
Lower leg pain is another relatively common complaint in ultra-endurance athletes. There are several main causes that will be briefly discussed here. Again, stress fractures especially of the tibia should be included in the differential diagnosis of this complaint, as discussed previously. Two other main causes of lower leg pain are chronic exercise-induced compartment syndrome (CECS) and medial tibial stress syndrome (MTSS).
CECS mostly commonly affects the anterior compartment but can also occur in the lateral and deep posterior compartments. It is still mostly considered to be a mismatch of the volume that the compartment can accommodate and the size of the muscle as they engorge and possibly swell during exercise. This mismatch during exercise creates increased tissue pressure that impedes muscle perfusion and leads to pain. The condition is considered reversible as the pressure subsides with rest. However is should be noted that some athletes may be able to push themselves to into an irreversible, acute stage as they are accustomed to a certain level of pain especially during ultra-endurance competition in remote areas under stressful conditions.23 Development of acute, irreversible compartment syndrome without direct muscle trauma is possible in this scenario and may also be precipitated by rhabdomyolysis that can develop with prolonged intense exercise.24 Hallmarks of CECS are a feeling of tightness and pain over the affected compartment that starts relatively predictably at a certain amount of running and subsides with rest. Other symptoms such as weakness and numbness, tingling in the foot can occur as the condition progresses. Physical examination at rest is generally entirely normal. The gold standard for diagnosing CECS remains invasive compartment pressure testing (Fig. 4). Once diagnosed, surgical fasciotomy of the affected compartment is generally done in an attempt to alleviate symptoms.25 It has been reported that running style modifications can alleviate symptoms in some runners.26
MTSS remains a poorly understood condition.27 It manifests itself with chronic, slightly distal, posteromedial tibial pain during and sometimes after running. Examination often reveals a diffuse tenderness of the affected area of the posteromedial tibia. It is generally considered a diffuse bone reaction possibly a local soft tissue problem as well. Advanced imaging such as an MRI can distinguish it from a stress fracture which is a more localized stress reaction. Treatment is conservative with activity and shoe modifications, cross-training until the pain and tenderness subside.
Ultra-endurance athletes can be affected by a wide variety of injuries. Many injuries can be managed with relatively simple, conservative means. However, careful attention and a relatively high index of suspicion are needed to recognize a few of the serious injuries that can have dramatic consequences if left untreated.
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