Stress Fractures and Stress Reactions of Bone: A Chronic Repetitive Stress Injury

by Stephen M. Pribut, DPM

Discussion and Definition:

The term "stress fracture", in many cases of overuse injury, is a misnomer. This term does not represent the nature and diversity of this frequently found injury. The term, “Chronic Repetitive Stress Injury of Bone”, better suits this injury in its myriad manifestations. Quite often, “stress reaction” of bone is used by sports medicine clinicians to encompass the diversity within this injury category. Unfortunately, this term, used in an office setting most often results in puzzled looks, which then lead to long explanations.  This may make the term “chronic repetitive stress injury of bone” more palatable, although it is more of a tongue twister. Most patients, however, while having heard of stress fratures wonder what is meant by a “stress fracture”. Is the bone broken? Is it split into two pieces? Will it heal? How did it happen? Normal bone is deemed to not fail under a single, but not, abnormal stress load. Cumulative loads, however, do take a toll.

Runners most often have stress fracture or stress reaction injuries to the tibia, metatarsals and calcaneus. But all lower extremity bones can be affected including the femur, navicular, fibular, cuboid, pelvis, and cuneiform bones. The majority of "stress fractures" diagnosed do not demonstrate a fracture line and technically are not well termed as a stress fracture. The more severe stress injuries of bone actually result in a true fracture line and are simlar to a fatigue fracture of other materials.

Stress fractures and stress reactions, both repetitive stress injuries of bone (RSI of Bone) is a reaction of bone to repetitive forces. These forces may be either compressive, tensile or complex in nature. The initial injury seems to be to the bone matrix itself and is hard to clinically measure or detect.This injury is caused by repetitive stress and overload to the bone. Bone resporption may be taking place without significant bone production. The forces contributing to the injury include both direct impact and also forces generated by the “pull” of ligaments and tendons on the bone.

Injury may first be seen on a bone scan (scintigraphy) which demonstrates metabolic activity of bone. Then on an MRI, and finally the injury may eventually be visible on an x-ray.

Background

Chronic repetitive stress injury of bone, most commonly called a "stress fracture" has been described in the literature for many years. Cases have appeared in the literature going back to the 1800's. Briethaupt (Briethaupt, 1855), a military physician, first reported this injury in 1855. He presented the first description of a metatarsal stress fracture when he noted swelling and pain in the feet of Prussian military recruits. In 1897 radiographic examination (x-ray) revealed the nature of these injuries. Injuries such as these were called "march fractures" because of their common occurence in military recruits who suddenly found themselves on long forced marches. (Stechow, 1897) Much of the literature on stress fractures is derived from experience within the mililtary.

Bone Scan Heel Stress Fracture

Bone Scan -
Calcaneus Stress Fracture

Bone is a dynamic structure. As a biological material, it is subject to change as a result of environmental stimuli and in response to genetic predilection. The initial injury might be a biological or biochemical abnormality or failure at the cellular or Bone Multicellular Unit (BMU) level. Bone adapts to many levels of intermittent, repetitive compressive and tension strains by an increase in density. However, in the presence of abnormally high and repetitive forces the ability to heal by microdamage repair is not adequate and damage than repair occurs. (Akkus and Rimnac 2001) In short an excessive amount of stress or repetitive stress is occurring without the bone having adequate rest to allow for adaptation to the stress. In essence, the stress that creates these injuries is too much, too soon for the bone.

Contributing Factors

Chronic Repetitive Stress Injuries to Bone (stress fractures and stress reactions) often result from dramatic changes in training. Training errors of a variety of types are a major contributing factor to this type of injury. The use of the word “fracture” in many cases is a misnomer. There is in most grades of this injury no actual fracture line, although in the most significant and severe cases a fracture line is visible and seen on X-ray or more readily on an MRI scan.

The higher grades of stress injury are similar to fatigue fractures of other materials. Bone is noted to fail more readily in tension than in compression. This means that the forces which  tend to “pull” are more dangerous to bone failure and injury than compressive forces. 

Bones Affected:

Virtually any of the bones of the lower extremity can suffer a stress reaction or stress fracture. Some of the most often injured bones include the tibia, metatarsal bones, navicular, femur, fibula, calcaneus, and cuboid. A few quick observations:

Metatarsals - most commonly affected foot bone for stress fractures. Injury most often occurs at the neck and shaft. If the injury has occurred at the base of the metatarsal, this may have been contributed to by vertical forces caused by too much speedwork, hill running (not as often as the speed work), or running on the ball of your foot.

Cuneiform stress fractures - These injuries seem to occur from a similar manner as do those at the base of the metatarsals. Vertical forces are a potential contributor to this injury and may be caused by too much speedwork, hill running (not as often as the speed work), or running on the ball of your foot. Several years ago I had a patient who was nationally competitive in his age group for the 400 meter run with multiple cuneiform stress fractures caused by over training. Luckily he recovered to compete and fair well in the national championship race. While the forces here could be demonstrated with a simple vector diagram, you may look at the hard science in the article on the angular relationship of forces to trabecular patterns by Shi et. al. (February 2009), cited below.

Calcaneus - Clinical diagnostic test: squeeze the body of the calcaneus to elicit tenderness. Trace out the probable fracture line. If this area is not tender, and only the medial calcaneal tuberosity is tender, you more likely are dealing with ann injury to the plantar fascia.

Tibia - Most frequently injured lower extremity bone.

Pelvic Stress fractures - May happen in running. Keep them in mind. Likewise the femur should be kept in mind as a potential site of stress reaction and stress fracture.

Etiology:

Training Errors:

Training errors may be one of the greatest contributors to this injury. A change in training such as increasing the frequency, intensity, or duration too quickly may contribute. What has been termed the “terrible too’s” of too much, too often, too soon, and too fast over stress the bone before it can appropriately react to the stress by reinforcing itself by new bone growth and increased density.

Increased forces into the bones of the foot and leg have been found to be generated in the presence of fatigue. In other words, you are likely to be at higher risk if you often run to the point of fatigue or exhaustion. The muscles are tired and can not properly position the bones, slow the forces, or attenuate the forces in any of several ways that normally functioning muscles may do.

...avoid doing too much too soon.

Equipment Errors:

An improper match of foot type and structure to shoe may contribute to a chronic repetitive stress injury to bone (stress fracture, stress reaction).

Old shoes, worn out shoes, shoes that look bad even to the person wearing them are obvious contributors to injuries of all sorts.

Running on a hard and unyielding surface may increase forces into the bones of the foot and leg. Those who have suffered this injury should obviously avoid running on concrete.

Other Factors:

It is important to keep in mind other contributing factors in the development of RSI of bone. In addition to the training errors and the biomechanical causes we often think of first, a variety of systemic conditions can contribute to this injury. These conditions include osteopenia, osteoporosis, other metabolic bone disorder, hormonal abnormalities, inadequate nutritional intake, and collagen disorders. In women amenorrhea or oligomenorrhea may lead to deficient estrogen and low bone mineral density. The female athlete triad includes low bone density by definition along with disordered eating and amenorrhea.(Lebrun 2007) Overtraining may lead to decreased testosterone levels in men resulting in osteopenia. Patients of either gender having multiple stress fractures should likely have a bone density (DEXA) scan performed.

Avoidance of Injury or Recurrence:

There is no better advice to be given on avoiding this injury or to prevent it from recurring than to gradually increase the time and distance run. After an adequate aerobic base has been achieved a slow and gradual increase in other stressors may be added such as hill work, fartlak, limited bursts of moderate speed into a run and then later more intense and structured speed work (which should often not  exceed 10% of the weekly mileage for a marathoner). A track athlete needs to follow a similar build up and to avoid running excessive mileage around the track. Spikes need to be worn only in a very limited manner and should not be used for most training.

The dynamic nature of bone structure by continuous active remodeling needs to be kept in mind as one tries to avoid this injury or to recover from it. There is a continuous process of bone absorption and bone growth. A slow and easy approach to increasing exercise is helpful. Dietary calcium should reach recommended levels. Supplements may assist in this. Make certain to also meet your daily requirements of Vitamin D which aids in both absorption of calcium and in the development of bone.

Diagnosis:

 

Bone Scan Heel Stress Fracture

Xray -
Suspected Calcaneus Stress Fracture
(confirmed on bone scan)

The patient’s history of relatively sudden or subactute onset of injury, a changing pattern of exercise, the physical examination, and imaging studies lead the practitioner to a high suspicion of a diagnosis of stress fracture, stress reaction or repetitive stress injury of bone. The classical presentation is in an athlete who reports the sudden onset of pain during or after a run. Usually there has been a substantial change in training habits. Mileage may have increased, twice a day runs begun, speed work initiated, a new pair of running shoes, or the aging of running shoes along with any other contributing factor. Physical examination will usually reveal a discrete area of tenderness. Certain bones are not as accessible to palpation as others are. The pelvic bones, femur, talus, and midtarsal bones are notoriously difficult to palpate (touch) and examine clinically. Likewise, in the rearfoot and midfoot a high level of suspicion must be present to reach the diagnosis and the use of imaging should be considered.

On the tibia, a horizontal line of tenderness is often the differentiating clinical sign from the vertical tenderness of medial tibial stress syndrome. Immobilization in a Pneumatic walker for 4 to 6 weeks or more is often helpful for tibial stress fractures, and a variety of other stress injuries of bone. Calcaneal stress fractures may be suspected when there is tenderness upon lateral compression of the body, rather than at the medial calcaneal tuberosity or tenderness that is only plantar to the calcaneus. In a group of military recruits the majority (56%) of calcaneal stress reactions occurred in the posterior third of the bone and 79% occur in the upper half of the calcaneus. (Sormaala, Niva et al. 2006) It should be noted that earlier reviews noted that the injury occurred primarily in the posterior aspect of the calcaneus, but Sormaala notes the importance of suspecting a stress reaction in the more anterior portion of the bone. Stress fractures of the tarsal navicular should be suspected when there is dorsal tenderness extending proximally to distally. In addition to tenderness, tenderness to percussion or to the vibrations of a tuning fork have been used as pathognomonic signs.

Diagnostic imaging includes radiographic evaluation, technetium-99 bone scan, and MRI. Often an injury is not visible on radiographic examination. Bone scintigraphy is considered sensitive, while MRI is considered to be both sensitive and specific. (Niva, Sormaala et al. 2007) At early stages the MRI shows marrow edema as an increased STIR signal and in fat-suppressed T2 images. On T1 sequences a decreased signal is noted. (Stafford, Rosenthal et al. 1986). As the injury progresses to a stage of increasing severity a low signal fracture line and bone callus may be visible.

A number of conditions may confound diagnosis and appear similar to stress fracture on certain imaging studies. In other cases asymptomatic bone marrow edema may be visible on MRI. (Niva, Sormaala et al. 2007)

Selected lower extremity conditions that may appear to be a stress fracture

Patellofemoral pain syndrome
Osteoid osteoma
Osteomyelitis
Osteosarcoma
Ewing Tumor
Bone metastases
Osteochondral fracture
Accessory Navicular (painful)
Inflammatory disorders
Medial Tibial Stress Syndrome

 

Treatment:

Conservative treatment works well for most stress fractures and stress reactions (RSI, repetitive stress injury) of bone. The key is finding the appropriate mechanical treatment to eliminate the pain of weight bearing. With the elimination of pain the forces should be sufficiently low for healing and remodeling to take place. Weight bearing exercise should be avoided. Multiple authors have recommended the use of a pneumatic walker for tibial stress fractures. (Fredericson, Bergman et al. 1995; Swenson, DeHaven et al. 1997) This may be used alone or with crutches as needed. A cam walker, pneumatic walker or low pneumatic walker may alleviate pain faster and be clinically superior to a post operative shoe for stress reactions of the metatarsal area and for other foot stress reactions. An added benefit of the pneumatic walker is that it can be removed for hygiene purposes and to allow for limited exercise of the limb. So that makes showers easier and will allow the patient to do range of motion exercises of the leg.

During recovery, one should guide the athlete to appropriate cross training activity. Swimming, bicycling, and maintenance of upper body strength should be implemented. Lower extremity exercises should be chosen as appropriate and if deemed to not risk delayed healing or further injury.

A phased return to activity following allowing sufficient time for healing is the key to a successful return to activity. In clinical practice, the author has found that weaning from the pneumatic walker seems to lessen the time to comfortable exit from the walker and prevent pain from returning and the necessity of returning to the use of the pneumatic walker. Most lower extremity stress reactions take between 8 and 17 weeks for recovery. (Matheson, Clement et al. 1987)

Significance To Military Training

Military research as described in published studies have included alterations in shoes, customized foot inserts and even has employed a one week rest period. A tiered approach to the basic military recruit should work best. The recruits should be sorted into 3 fitness groups: Good Aerobic Fitness, Average Aerobic Fitness and Poor Aerobic fitness. Positive intervention where needed should take place prior to arrival for basic training. These individuals should not be left on their own to train or to devise a training program before they arrive for basic training. Although there currently is a paucity of material available to guide military recruits on the best way to get in shape to avoid injury during the basic training regimen, a gradual and incremental training program should be laid out for the recruits. Perhaps a special web site might also be constructed where they could keep an online training log. These logs could be individual and private or they could link to an area for social interaction such as a blogging site. Web 2.0 is happenning and could be useful in this undertaking. It is important to encourage healthy running, and a gradual improvement in stamina, muscle strength and aerobic fitness.

Also see: Avoiding The Doctors's Office
Shin Splints, Medial Tibial Stress Syndrome


References

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Jansen M. March foot. J Bone Joint Surg 1926;8:262–72.
Jones B.H. et. al. Epidemiologic Reviews 24:228-247 (2002)
Lebrun, M. (2007). "The Female Athlete Triad: What's a Doctor to Do?" Current Sports Medicine Reports 6: 397–404.
Matheson, G. O., D. B. Clement, et al. (1987). "Stress fractures in athletes. A study of 320 cases." Am J Sports Med 15(1): 46-58.
Niva, M. H., M. J. Sormaala, et al. (2007). "Bone stress injuries of the ankle and foot: an 86-month magnetic resonance imaging-based study of physically active young adults." Am J Sports Med 35(4): 643-9.
Shi, X., Wang,X., Niebur, "Effects of Loading Orientation on the Morphology of the Predicted Yielded Regions in Trabecular Bone "G. Annals of Biomedical Engineering, Vol. 37, No. 2, February 2009 pp. 354–362 DOI: 10.1007/s10439-008-9619-4
Sormaala, M. J., M. H. Niva, et al. (2006). "Stress Injuries of the Calcaneus Detected with Magnetic Resonance Imaging in Military Recruits." J Bone Joint Surg Am 88: 2237-2242.
Stafford, S. A., D. I. Rosenthal, et al. (1986). "MRI in Stress Fracture." AJR Am J Roentgenol 147: 553-556.
Stechow (1897). "Fussödem und Röntgenstrahlen." Deutsche Militärärztliche Zeitschrift 26: 465.
Swenson, E. J., K. E. DeHaven, et al. (1997). "The Effect of a Pneumatic Leg Brace on Return to Play in Athletes with Tibial Stress Fractures." Am. J. Sports Med. 25(June): 322 - 328.

 

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Copyright 2006-2009 Stephen M. Pribut