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Description
Stress fractures occur when a cycle of repetitive forces, none on their own sufficient to cause injury, is applied such that these forces can, cumulatively, damage the bone. In cases where the bone is entirely healthy and the cause is simply too many cycles of load, the injury is denoted as a fatigue fracture. Stress fractures can also occur in bone that is not healthy and does not stand up to even few cycles of repetitive forces: these are called insufficiency fractures. Activities such as walking, running, and repeated jumping can subject the bones of the foot to large forces that often lead to stress fractures. These injuries are commonly seen in the 2nd or 3rd metatarsal neck region, the base of 5th metatarsal (Jones Fracture), the sesamoid of the great toe, and the navicular bone.
Structure and function
Bone is built to withstand load. Of course, a sufficiently high load can be presented and the bone may break. That is the typical etiology of a fracture. Bones can also be broken by cyclical application of subcritical loads—loads which if applied only once will do no damage at all– provided too many cycles are applied.
Repetitive application of a subcritical force causes microscopic damage to the bone. This damage is not a problem, as long as the bone remodeling cycle (osteoclasts removing the damaged tissue and osteoblasts synthesizing a healthy replacement) can keep up. There are, however, two instances where cyclical loads do lead to clinical problems. The first is when the bone metabolism is normal, yet the number of cycles is just too high to manage. The failure normal bone remodeling to match the demands of high cycles of subcritical load is called a fatigue fracture. The second type of stress fracture is the so-called insufficiency fracture. This is found when the bone itself is abnormal, as in osteoporosis, for example, and the cycle of loading seems to be normal.
Note that in a stress fracture the gross contour of the bone is normal; the damage is internal. Nonetheless, when internal damage accumulates, the macroscopic architecture may fail, and the bone may overtly fracture into two or more pieces. (This is how paper clips are broken: repetitive small loads are applied by bending the clip back and forth, until enough damage accumulates and the clip is broken in two.)
Stress fractures of the feet occur in those bones, and in locations within those bones, that are absorb repetitive force. Although each person’s foot absorbs force in a slightly different manner that is dictated by that person’s foot shape, alignment, foot stiffness, and gait pattern, certain areas are characteristically the recipient of such load.
In the foot, the necks of the 2nd and 3rd metatarsals (and adjacents regions) are subject to bending forces with walking. Thus, too much walking, especially with too little rest to allow repair, can cause stress fractures in these regions. This has been seen commonly in military recruits, subject to long hikes with heavy backpacks, hence the name applied to this condition: “march fractures.”
Especially in patients with a high arched foot, running may subject the base of the 5th metatarsal to overload and stress fracture. These are called “Jones’ fractures”.
The navicular bone, too, is a site of stress fractures especially if the patient has a stiff, high arched foot, a relatively long second metatarsal, and participates in activities that involve repetitive loading through the forefoot such as sprinting. The mechanism of injury is felt to be repetitive loading through the second metatarsal and middle cuneiform into the navicular.
The sesamoid bones beneath the great toe can develop stress fractures, as found in patients who suddenly increase in running distance.
Patient presentation
Patients with stress fractures will usually report focal aching in the affected area. They will give a history of some increase in their normal activity level. This pain typically increases with activity and decreases with rest. They may have a history of a condition that predisposes them to weaker bones such as osteoporosis (weak thin bone), amenorrhea (loss of normal menstrual cycle), or a history of smoking.
Stress fractures involving the lesser metatarsal bones (typically 2nd or 3rd) will often present with pain and swelling near the metatarsal neck, distally. Occasionally, high-level ballet and modern dancers will generate stress fractures at the base of the metatarsal near the midfoot. The foot type, in general, may be flat, often with a long second and possibly third toe. Patients usually can walk without a limp.
Individuals who suffer a Jones’ fracture will report pain on the outside of the midfoot (Figure). They have difficulty bearing weight and may walk with a limp. That’s because patients with this stress fracture often persist in their activity until there is overt failure of the bone. (That is to say, the stress fracture is often the precursor of the presenting complaint, namely an overt fracture.)
Patients who develop navicular stress fractures will present with a chronic mid-foot ache. Although anyone can get a navicular stress fracture, the most common presentation is in the athlete. The symptoms of a navicular stress fracture are often generalized to the mid-foot. The relatively nonspecific location of the symptoms makes this condition difficult to diagnose.
Sesamoid stress fractures do occur, but in most instances “fracture” of the sesamoid is actually a bipartite sesamoid–a normal variant– with superimposed sesamoiditis. The pain is usually isolated to under the great toe region.
Objective Evidence
Stress fractures will not show up on x-rays unless there is marked damage or a healing response (fracture callus) is found. An MRI can demonstrate a stress fracture or a stress reaction (edema without a fracture line). Bone scans, too, will be positive in areas of bone turnover, though the distinction between a stress fracture and a stress reaction is lost: lines are never seen on bone scans.
The importance of MRI is that a normal result can effectively exclude the diagnosis of a stress fracture. This test, then, can help an athlete avoid unnecessary periods of enforced rest. Also, a positive test can provide strong, visual reinforcement for the prescription of unwanted periods of enforced rest. Last, the study can be used, if necessary, to monitor progress and allow timely return to sport (early, but not too early, that is). Navicular stress fracture almost always need an MRI for timely diagnosis.
Plain x-rays will identify a Jones’ fracture (Figure ). The fracture itself occurs at the metadiaphyseal area where the more flexible bone at the base of the 5th metatarsal meets the more rigid bone of the shaft of the metatarsal. The fracture is different from a Dancer’s fracture which occurs when one of the ligaments pulls off (avulses) the tip of the 5th metatarsal base.
Routine x-rays of the foot can be very helpful in distinguishing a stress fracture of the sesamoid from a bipartite sesamoid. The distinction is that the bone fragments of a bipartite sesamoid have a clearly identified smooth margin, whereas a traumatic fracture has ragged edges. Still, an MRI may be required to differentiate a bipartite sesamoid from a sesamoid stress fracture.
Epidemiology
Stress fractures are common and affect people of all ages. They are more likely to occur in females than in males, especially among females with the female athlete triad of amenorrhea, disordered eating, and osteoporosis. The estimated incidence in athletes and military recruits is 5-30%, depending on the sport and other risk factors. It is estimated that among people who run regularly for exercise, more than half will sustain an overuse injury that keeps them from running for 1 week (PMID:10496574); stress fractures are among the more common injuries in recreational athletes. Stress fractures do not occur as often in the non-active population unless there is an underlying pathology that causes bone weakness.
Differential diagnosis
The main alternative diagnosis for stress fractures of the foot are trauma (including bone contusions, which may be surprisingly painful) and tendinitis.
Red flags
Stress fracture in a female athlete might be part of the Female Athletic Triad: namely, disordered eating, amenorrhea, and osteoporosis. Disordered eating (which may be manifest as compulsive exercising, as an indirect means of purging) leads to decreased body fat. Because fat is precursor of estrogen, there are lower levels of this hormone in emaciated women. In turn, disordered eating leads to irregular menses and excessive bone resorption (as may be seen with osteoporosis). A poor diet also leads to inadequate bone maintenance owing to inadequate calcium and vitamin D intake as well.
Treatment options and Outcomes
Most stress fractures respond to rest. After all, stress fractures are overuse injuries, and rest (which may be thought of as “under-use”) removes the harmful cause. For a stress fracture of the foot, crutches and a CAM walker boot may be helpful. Once healing has occurred, a gradual return to activity in a stiff-soled shoe is advised.
Certain stress fractures may require surgery in order to aid in healing or prevent non-healing (i.e., non-union) or re-fracture. These “high risk” stress fractures include the Jones' fracture of the 5th metatarsal, navicular stress fractures, and those in other locations that have recurred despite adequate rest.
Surgery for a Jones’ fracture stabilizes the fracture site by placing a strong screw through the middle of the bone (Figure). The screw itself resists deforming forces and the drilling needed to place it stimulates blood flow to help healing. A patient that has a non-union of the Jones’ fracture or a recurrent fracture after it had appeared to have healed may need more involved reconstructive foot surgery. This would comprise not only repair the fracture (often with bone grafting) but an osteotomy of the calcaneus or other bones to reposition the areas subjected to greatest force.
Navicular stress fractures can also be difficult to treat due to the relative lack of blood supply to the navicular. Nonetheless, treating non-displaced navicular stress fractures with casting and a non-weight-bearing succeeds in 90% of cases if patients are compliant. Despite the lack of clear evidence of efficacy, many doctors will also recommend use of a bone stimulator (which employs electrical and electromagnetic stimulation, ultrasound, and extracorporeal shock waves to encourage bone formation and growth). Because the failure rate is even higher if patients are not compliant with non-weightbearing, because the period of immobilization may be unacceptably long, and because the consequences of displacement are so high (the bone may die and collapse), surgery may be recommended for some patients even without an initial period of non-operative treatment. Surgery may include drilling across the fracture, placement of one or more screws, and possibly the addition of bone graft to improve healing.
Sesamoid stress fractures are treated with an orthotic under the base of the first metatarsal head. This is combined with the cushioned insole and a very stiff sole of the shoe with a slight contour. A stiff sole with a rocker bottom contour will allow for a smoother dispersion of the force away from the base of the great toe. If this does not lead to symptom resolution, complete rest may be needed. The results of surgical treatment are unpredictable and thus surgery (in the form of repairing the fracture or removing part or all of the sesamoid bone) is chosen last.
Risk factors and prevention
Risk factors for stress fractures include intrinsic mechanical factors (e.g. decreased bone density, foot structure), nutritional factors, hormonal factors, physical training, and extrinsic mechanical factors (e.g. footwear, running surface) (PMID: 10492029). Patient's with metabolic bone diseases such as osteoporosis, osteomalacia, osteogenesis imperfecta, Paget's disease, and fibrous dysplasia are at a higher risk for stress fractures (insufficiency fractures).
Preventative measures to prevent stress fractures include avoiding increasing the intensity of training too quickly, eating a diet with adequate amounts of calcium and vitamin D, and getting new running shoes every 300 miles. A study by Lappe et al. showed that female military recruits given calcium and vitamin D supplements were significantly less likely to sustain a stress fracture than recruits that did not take supplements (PMID: 18433305).
Stress fractures may be prevented by a wise program of gradually increased intensity and good shoes. Running shoes may lose their resilience and fail to protect the feet from excessive load well before they look tattered and worn. Runners may be able to prolong the longevity of their running shoes by considering them to be sports equipment and don them specifically for running, and not use them for ordinary, day to day activities.
Miscellany
Running shoes may cushion for the feet, but may promote an unhealthy pattern of mechanical load and thus actually increase the risk of a stress fracture. The theory is that because humans evolved to run barefoot, a barefoot running style may be more natural and less likely to cause abnormal loading. This controversial conjecture is not proven, but it may stimulate important research on shoewear and injury prevention. Professor Daniel E. Lieberman, chair of the department of Human Evolutionary Biology at Harvard has put it this way: “how one runs probably is more important than what is on one’s feet, but what is on one’s feet may affect how one runs" (see https://www.ncbi.nlm.nih.gov/pubmed/22257937) Lieberman
2
also, emphasises that
“
how one runs
probably is more important than what is on one
’
s feet, but what
is on one
’
s feet may affect how one runs
Key terms
Bone remodeling; osteoporosis; female athlete triad; Jones’ fracture; calcium; vitamin D; amenorrhea; insufficiency vs fatuigue fractures
Skills
Bedside skills for the diagnosis stress fractures include the ability to take a detailed but focused history and perform a thorough musculoskeletal examination.
Figure Location of pain: Jones’ fracture
Figure , Footprint demonstrating a high-arched foot. This pattern in more common in patient with a Jones’ fracture (among others)
Figure Jones fracture denoted by red lines
Figure Screw fixation to treat a Jones fracture
Bone is built to withstand load. Of course, a sufficiently high load can presented and the bone may break. Bones can also be broken by cyclical application of subcritical loads—those which if applied only once will do no damage at all– provided too many cycles are applied.
Repetitive application of a subcritical force causes microscopic damage to the bone. This damage is not a problem, as long as the bone remodeling cycle (osteoclasts removing the damaged tissue and osteoblasts synthesizing a healthy replacement) can keep up. There are, however, two instances where cyclical loads do lead to clinical problems. The first is when the bone metabolism is normal yet the cycle of load is just too high to manage. The failure normal bone remodeling to match the demands of high cycles of subcritical load is called a fatigue fracture. The second type of stress fracture is the so-called insufficiency fracture. This is found when the bone itself is abnormal, as in osteoporosis, for example, and the cycle of loading seems to be normal.
Note that in a stress fracture the gross contour of the bone is normal; the damage is internal. Nonetheless, when internal damage accumulates, the macroscopic architecture may fail, and the bone may overtly fracture into two or more pieces. (This is how paper clips are broken: repetitive small loads are applied by bending the clip back and forth, until enough damage accumulates and the clip is broken in two.)
Stress fractures of the feet occur in those bones, and in locations within those bones, that are absorb repetitive force. Although each person’s foot absorbs force in a slightly different manner that is dictated by that person’s foot shape, alignment, foot stiffness, and gait pattern, certain areas are characteristically the recipient of such load.
In the foot, the necks of the 2nd and 3rd metatarsals region are subject to two bending forces with walking. Thus, too much walking, especially with too little rest to allow repair, can cause stress fractures in these regions. This has been seen commonly in military recruits, subject to long hikes with heavy backpacks, hence the name applied to this condition: “march fractures.”
Especially in patients with a high arched foot, running may subject the base of the 5th metatarsal to overload and stress fracture. These are called “Jones’ fractures”.
The navicular bone, too, is a site of stress fractures especially if the patient has a stiff, high arched foot, a relatively long second metatarsal, and participates in activities that involve repetitive loading through the forefoot such as sprinting. The mechanism of injury is felt to be repetitive loading through the second metatarsal and middle cuneiform into the navicular.
The sesamoid bones beneath the great toe can develop stress fractures, as found in patients who suddenly increase in running distance.
Patient presentation
Patients with stress fractures will usually report focal aching in the affected area. They will give a history of some increase in their normal activity level. This pain typically increases with activity and decreases with rest. They may have a history of a condition that predisposes them to weaker bones such as osteoporosis (weak thin bone), amenorrhea (loss of normal menstrual cycle), or a history of smoking.
Stress fractures involving the lesser metatarsal bones (typically 2nd or 3rd) will often present with pain and swelling near the metatarsal neck, distally. Occasionally, high-level ballet and modern dancers will generate stress fractures at the base of the metatarsal near the midfoot. The foot type in general may be flat, often with a long second and possibly third toe. Patients usually can walk without a limp.
Individuals who suffer a Jones’ fracture will report pain on the outside of the midfoot (Figure 2). They have difficulty bearing weight and may walk with a limp. That’s because in the case of fifth metatarsal, patients persist in their activity until there is overt failure of the bone, often after landing heavily.
Navicular Stress Fractures
Patients who develop navicular stress fractures will present with a chronic mid-foot ache. Although anyone can get a navicular stress fracture, the most common presentation is in the athlete. The symptoms of a navicular stress fracture are often generalized to the mid-foot. The relatively nonspecific location of the symptoms makes this condition difficult to diagnose.
Sesamoid stress fractures do occur, but in most instances “fracture” of the sesamoid is actually a bipartite sesamoid–a normal variant– with superimposed sesamoiditis. The pain is usually isolated to under the great toe region.
Objective Evidence
Stress fractures will not show up on x-rays unless there is marked damage or a healing response (fracture callus) is found. An MRI can demonstrate a stress fracture or a stress reaction (edema without a fracture line). Bone scans, too, will be positive in areas of bone turnover, though the distinction between a stress fracture and a stress reaction is lost: lines are never seen on bone scans.
The importance of MRI is that a normal result can effectively exclude the diagnosis of a stress fracture. This, then, can help an athlete avoid unnecessary periods of enforced rest. Also, a positive test can provide visual reinforcement for the prescription of unwanted period of enforced rest. Last, the study can be used, if necessary, to monitor progress and allow timely return to sport (early, but not too early, that is).
Navicular stress fracture almost always need and an MRI for timely diagnosis.
Plain x-rays will identify a Jones’ fracture (Figure 5). The fracture itself occurs at the metadiaphyseal area where the more flexible bone at the base of the 5th metatarsal meets the more rigid bone of the shaft of the metatarsal. The fracture is different from a Dancer’s fracture (Figure 6) which occurs when one of the ligaments pulls off (avulses) the tip of the 5th metatarsal base.
Routine x-rays of the foot can be very helpful in distinguishing a stress fracture of the sesamoid from a bipartite sesamoid. The distinction is that the bone fragments of a bipartite sesamoid have a clearly identified smooth margin, whereas a traumatic fracture has ragged edges. Still, an MRI may be required to differentiate a bipartite sesamoid from a sesamoid stress fracture.
Epidemiology
Stress fractures are common and affect people of all ages. They are more likely to occur in females than in males, especially among females with the female athlete triad of amenorrhea, disordered eating, and osteoporosis. The estimated incidence in athletes and military recruits is 5-30%, depending on the sport and other risk factors. It is estimated that among people who run regularly for exercise, more than half will sustain an overuse injury that keeps them from running for 1 week (PMID:10496574), with stress fracture among the more common. Stress fractures do not occur as often in the non-active population unless there is an underlying pathology that causes bone weakness.
Differential diagnosis
The main differential diagnoses for stress fractures of the foot include overt trauma, including (surprisingly painful) bone contusions.
Red flags
Stress fracture in a female athlete might be part of the Female Athletic Triad of amenorrhea, disordered eating, and osteoporosis. Disordered eating (which may include dieting, bulimia and compulsive exercising, as an indirect means of purging) leads to decreased body fat. Because fat is precursor of estrogen, there are lower levels of this hormone in emaciated women; in turn, they have irregular menses and excessive bone resorption (as may be seen with osteoporosis). A poor diet leads to inadequate bone maintenance owing to inadequate calcium and vitamin D intake as well.
Treatment options and Outcomes
Most stress fractures respond to rest. After all, stress fractures are overuse injuries, and rest (which may be thought of as “under-use”) removes the harmful cause. For a stress fracture of the foot, crutches and a CAM walker boot may be helpful. Once healing has occurred, a gradual return to activity in a stiff-soled shoe is advised.
Certain stress fractures may require surgery in order to aid in healing or prevent non-healing (i.e., non-union) or re-fracture. These “high risk” stress fractures include the Jones' fracture of the 5th metatarsal, navicular stress fractures, and those in other locations that have recurred despite adequate rest.
Surgery for a Jones’ fracture stabilizes the fracture site by placing a strong screw through the middle of the bone (Figure 7). The screw itself resists deforming forces and the drilling needed to place it stimulates blood flow to help healing. A patient that has a non-union of the Jones’ fracture or a recurrent fracture after it had appeared to have healed may need more involved reconstructive foot surgery. This would comprise not only repair the fracture (often with bone grafting) but an osteotomy of the calcaneus or other bones to reposition the areas subjected to greatest force.
Navicular stress fractures can also be difficult to treat due to the relative lack of blood supply to the navicular. Nonetheless, treating non-displaced navicular stress fractures with casting and a non-weight-bearing succeeds in 90% of cases if patients are compliant. Despite the lack of clear evidence of efficacy, many doctors will also recommend use of a bone stimulator (which employs electrical and electromagnetic stimulation, ultrasound, and extracorporeal shock waves to encourage bone formation and growth). Because the failure rate is even higher if patients are not compliant with non-weightbearing, because the period of immobilization may be unacceptably long, and because the consequences of displacement are so high (the bone may die and collapse), surgery may be recommended for some patients even without an initial period of non-operative treatment. Surgery may include drilling across the fracture, placement of one or more screws, and possibly the addition of bone graft to improve healing.
Sesamoid stress fractures are treated with an orthotic under the base of the first metatarsal head. This is combined with the cushioned insole and a very stiff sole of the shoe with a slight contour. A stiff sole with a rocker bottom contour will allow for a smoother dispersion of the force away from the base of the great toe. If this does not lead to symptom resolution, complete rest may be needed. The results of surgical treatment are unpredictable and thus surgery (in the form of repairing the fracture or removing part or all of the sesamoid bone) is chosen last.
Risk factors and prevention
Risk factors for stress fractures include intrinsic mechanical factors (e.g. decreased bone density, foot structure), nutritional factors, hormonal factors, physical training, and extrinsic mechanical factors (e.g. footwear, running surface) (PMID: 10492029). Patient's with metabolic bone diseases such as osteoporosis, osteomalacia, osteogenesis imperfecta, Paget's disease, and fibrous dysplasia are at a higher risk for stress fractures (insufficiency fractures).
Preventative measures to prevent stress fractures include avoiding increasing the intensity of training too quickly, eating a diet with adequate amounts of calcium and vitamin D, and changing out running shoes every 300-500 miles. A study by Lappe et al. showed that female military recruits given calcium and vitamin D supplements were significantly less likely to sustain a stress fracture than recruits that did not take supplements (PMID: 18433305).
Miscellany
Because women with amenorrhea have low estrogen levels and estrogen is important in bone health, one possible way to reduce the risk of stress fractures in these women may be to put them on oral contraceptive pills (OCPs). Theoretically, exogenous estrogen may help to decrease bone resorption and increase bone mineral density.
Key terms
Bone remodeling; csteoporosis; female athlete triad; Jones’ fracture; calcium; vitamin D; amenorrhea
Skills
Bedside skills for the diagnosis stress fractures include the ability to take a detailed but focused history and perform a thorough musculoskeletal examination.
Risk factors for development of a stress fractures include an increase in activity level, a foot shape that overloads those metatarsals, and/or relatively weak bones (as might be seen with osteoporosis). A foot with a relatively long second metatarsal will have an increased predisposition to develop a stress fracture in the second metatarsal shaft or neck region. This will be especially true if the first ray (great toe and first metatarsal) is hypermobile and does not take its share of force during walking or running.
