Vol. 13 Issue 7
Stress Fractures Of the Pelvis and Lower Extremities
Diagnosis and Management
Musculoskeletal injuries are frequent presentations in primary care settings. Given the common nature of these injuries and the limited education about them in nurse practitioner programs, it is essential to build the skills and knowledge necessary to diagnose and treat them effectively. Musculoskeletal injuries typically have a vague presentation, and this contributes to misdiagnosis. To make matters worse, conventional radiologic tests often provide limited diagnostic information. The end result is that stress fractures are frequently misdiagnosed and progress to conventional fractures, often with catastrophic consequences for patients.
Stress fractures are often called insufficiency fractures due to their relationship with alterations in cortical bone. Although the involved bone is considered healthy, repetitive and prolonged use causes pathology due to an imbalance of the recuperative properties of the bone. These injuries present similarly to other common athletic injuries, complicating diagnosis.1 From a clinical perspective, it is reasonable to consider the most epidemiologically likely diagnosis.
Stress fractures are most common in bones that bear weight during physical activity.1 The first through third metatarsals, calcaneous, tibia, femurs and lower pelvic girdle are common sites of injury, with the specific site largely dependent on the particular activity.2 Stress fractures evolve insidiously. Overuse and repetitive movements are initial insults to the bone. The initial periosteal stress reaction occurs due to excessive muscle pull and fatigue loading.3,4 Patients develop pain as a result of the inflammatory and traumatic nature of this initial reaction. Shin splints, a common form of periosteal stress reaction, are a prime example of this form of injury. Given sufficiently stressful and repetitive trauma, shin splints will become stress fractures. The keys to this progression are the presence of biomechanically insufficient bone and high levels of stress exerted over a prolonged period.
Bone is composed of a collagen matrix that supports a bony cortex.5,6 The cortical structure of the bone forms the durable outer covering of the bone. The cortex contains the bulk of calcium in the bone, which is the element we associate with bone strength. When a bone is injured, an inflammatory response in effect begins to remodel the bone. Repeated stress results in very small amounts of non-viable bone.6 The osteoclasts respond by removing this non-viable tissue. Initially, a paradox occurs in which circumferential lamellar bone is lost.6 The body's intent is to replace lost bone with stronger osteonal bone.3
Given appropriate rest, osteoblastic activity will occur before the stress reaction progresses to stress fracture. In fact, there is a lag between osteoclastic activity and the replacement of lost bone by the osteoblasts. Studies have shown that rest periods as short as a week result in sufficient healing to avert stress fracture.7 Stress fractures result when traumatic stress occurs between initial osteoclastic action and callous formation by the osteoblasts. Repeated stress can result in progression from the characteristic stable stress fracture to a complete break in the cortex.
Stress fractures are relatively uncommon in the general population and tend to affect athletes most often. Statistics vary primarily based on setting, activity and the population being studied. For instance, a study of track-and-field competitors undergoing strenuous training showed an annual incidence of 20%.2 A similar study of a more diverse population of athletes showed rates of 1.9% in men and 1.8% in women.2 Variation in data is often attributed to differing diagnostic methods. Military personnel have been the subjects of significant research about stress fractures. A study of U.S. Marines undergoing training documented a rate of 11.8% in women and 7.5% in men.8 In Israel, a study of Army trainees documented a rate of 8.8% in men.9 Other studies have documented similar rates: 2% in men and 11.8% in women.10 A trend documented in multiple studies is a higher incidence of stress fracture in women, primarily due to biomechanical factors such as differences in bone geometry and physique.10-12
When seeing athletes with musculoskeletal complaints, the possibility of stress fracture should be at the forefront of the differential. Remember that women are at greater risk.13 Athletic competition by women is much more common today, and the risk of stress fracture injury is particularly magnified in high-impact and endurance events. When risk stratifying patients, couple the epidemiologic likelihood of stress fractures with the individual patient's presentation.
Clinical Presentation and Symptoms
Musculoskeletal injuries can be quite enigmatic given the similar symptom patterns associated with them. Patients with stress fractures present with one of several symptom patterns, all involving pain along a weight-bearing or long bone frequently isolated from a large muscle group.14 This is particularly true of metatarsal, tibial and distal femoral fractures. The pain can be quite ubiquitous, involving the lower pelvic girdle and proximal femur.
The history of a patient with a stress fracture involves some sort of athletic endeavor or vigorous exercise. Avoid making determinations based on the intensity of the exercise, because stress fractures can present atypically. It is true that the typical stress fracture occurs in substantial endurance-type activity with prolonged periods of weight-bearing exertion. Typical examples are marathon or distance running, training for triathlon or ultra-endurance sporting events, or strenuous military or police training.14 But athletic participation is not the only setting for stress fracture; biomechanical challenge can result in injuries as well. Some studies indicate that bone density abnormalities, poor conditioning and gender-related factors can set the stage for stress fracture.15,16 Suspect stress fractures in patients who may have these risk factors, even if their level of exertion seems insufficient to induce such catastrophic injuries. For instance, a formerly sedentary patient who begins what appears to be a conservative workout program may sustain a stress fracture since he was so poorly conditioned.
Patients with evolving overuse injuries of the mid-shaft to distal femur, tibia and metatarsals initially develop some level of pain. With continued training, this pain worsens and evolves to induce a limp.2 The limp is a telltale sign an ominous precursor to a stress fracture. Remember, biomechanical abnormalities predispose the bone to fracture. In essence, a limp induces an additional biomechanical challenge, altering the normal pattern of weight bearing. With continued training despite a limp, the patient is certain to develop a fracture. As a rule, all patients who limp and in whom you suspect stress fracture should limit their weight bearing. It is essential to consider the level of risk associated with a given fracture. For instance, a pelvic or femoral fracture represents a far higher risk than a tibial or metatarsal injury.1 Prescribe crutches that allow partial or no weight bearing.
Pathology of the pelvic girdle and proximal femur offers additional diagnostic challenges. The pelvic structures are quite extensive, with close proximity to one another. Aside from the obvious musculoskeletal structures, abdominal, rectal and genitourinary pathologies can mimic pathology of the bony structures.17 The history is key to appropriate diagnosis of these problems. As with lower extremities, pain may induce limitations on weight bearing. Patients with stress fractures of the pelvis or femur are more likely to develop abnormal or antalgic gait in response to these injuries.
Injuries to the lower extremities are more easily pinpointed. Involvement of the associated muscle groups tends to cause these injuries to mimic muscle strains and ligament sprains. The most common sites for these fractures are the inferior and superior pubic rami, the femoral neck, and areas around the greater trochanter or sacrum.12,18 In particular, the pubic rami are susceptible due to the pull of the hip flexor and adductor groups. Closely investigate any suspicion of pelvic or femoral stress fractures. Failure to diagnose these fractures leads to subsequent completion of the stress fracture and is likely to result in surgical treatment and long-term rehabilitation with some level of lasting disability.12
Examination of gait is essential to any orthopedic examination. Instruct the patient to walk with a natural gait and not to try masking any limp or difficulty. This is an especially important directive for elite athletes, who fear being sidelined from competition due to what they perceive to be a minor injury. Be clear in communicating the consequences of a completed stress fracture. Educate patients that although they may be out 6 weeks with an uncomplicated stress fracture, a complete fracture can be career ending. Even a slight limp or gait alteration can be significant. It may be necessary to observe the patient for more than a few steps, so consider using a long hallway or even going outdoors to observe gait.
The gait exam can be skewed by the patient's ability to maldistribute weight to diminish symptoms. The patient may do this purposefully, or it may be an unconscious form of adaptation to the injury. It is helpful at this point to establish whether the patient can bear weight. First, have the patient stand on one leg. If the patient can do this without pain, ask him or her to hop several times on a single leg. Document this as a single-leg stand and single-leg hop with or without pain. Do not ask the patient to hop if the single-leg stand is positive or painful. This test can be used diagnostically and to track progress during recovery.
Physical examination then proceeds to inspection of the affected extremity. In the case of nonpelvic injuries, it is not uncommon to see edema, which is often pitting in nature. As with conventional fractures, point tenderness is indicative of stress fractures. Conversely, diffuse swelling or edema is less indicative of fracture. Pitting edema is often present in varying degrees, particularly in injuries involving the metatarsals or tibia. It is important to document the location of the edema and to describe it on any radiology orders to assist you and the radiologist in identifying abnormalities.
Leverage is another diagnostic tool that can be used to identify the fracture site. Grasp an uninjured portion of the affected extremity and exert uniform gentle pressure (a bit like exerting varus or valgus stress during a knee exam). Pain is generally referred to the fracture site.
The pelvis offers obvious examination challenges. Palpation will help identify painful areas. The pubic rami can be directly palpated, as can the femoral structures. Evaluation of hip flexion and extension can provide additional diagnostic information about the pubic rami. Weakness and pain are common. When performed gently, internal and external rotation often reproduce pain in the femoral neck. The pelvic rock is best avoided due to likely pain and the possibility of displacement if a complete fracture is present. It is more expeditious and safe to apply bilateral medial pressure inferior to the iliac crests. Pain referred to the rami is indicative of fracture. These are dangerous fractures, so take great care in ruling them out.
Metatarsal fractures are characterized by dorsal swelling of the foot. Point tenderness is frequently present, although inflammation may result in diffuse swelling and pain. Often, these fractures are confused with tendonitis of the extensor tendons of the dorsum of the foot. Consider stress fracture in the differential of any patient who appears to have tendonitis of the foot and participates in characteristic physical exertion. Examination of the calcaneous differs as well. The presence of fat pad tenderness and pain with gentle heel pinch is indicative of stress fracture.
Despite limitations in diagnostic validity, the initial evaluation of a patient with possible stress fracture requires plain radiographs. Their usefulness is largely dependent on the stage of the injury, and should be considered in conjunction with your clinical impression. During the early stages of injury, plain radiographs can yield rates of fracture detection as low as 15%.3 This increases to 50% with subsequent films, a rate that is of obvious clinical utility.3 Positive plain films might negate the need for further studies that are far more costly. When advanced imaging is not obtained, order sequential radiographs during the course of follow up.
Several radiographic signs of stress fracture may be evident on plain films. The majority of films will be negative, and any visualized abnormality may be slight, requiring close examination. It is imperative that a radiologist read the films to corroborate your reading and to detect any unnoticed abnormalities. The radiologic signs of stress fracture include:5
• a periosteal reaction characterized by a sometimes slight "fluffing" of the periosteum (Figures 1, 2 and 3)
• a sub-periosteal reaction characterized by thickening of the periosteum
• presence of a sclerotic line (Figures 4 and 5)
• a cortical break, seen in stress fractures that are dangerously close to completing themselves (Figures 6 and 7).
If you strongly suspect stress fracture but x-rays provide no supportive evidence, advanced diagnostic studies may be warranted. Scintigraphy, a multiple-phase bone scan, can offer more in-depth information. This test can detect the increased blood flow and metabolic activity characteristic of early injury.4 Studies show that scintigraphy can be 100% sensitive as early as 2 days after injury.19 The technology has limitations, however, not the least of which is that it indicates the likely site of a stress fracture but does not quantify its magnitude. This information does come at a discount, costing approximately two-thirds less than an MRI.20
Recent studies show that MRI is more specific and equally sensitive to scintigraphy in the diagnosis of stress fracture.21 The primary advantage of MRI is that it yields added information about the extent and nature of the fracture. Research clearly supports bone scan as a diagnostic modality for stress fracture, but in cases of high-risk fractures or with atypical presentations, MRI may be more desirable.
The hallmark of treatment for stress fractures is cessation of the offending activity.1,6 Contrary to treatment for many musculoskeletal injuries, activity limitation is not an option. Avoidance of activity involving the affected area is particularly important in athletes, who frequently want to continue their training despite injury. Unlike common strains and sprains, stress fractures are not likely to improve without a period of strict activity limitation.1,22
Prescribe limitations on weight bearing and activity involving the affected extremity. The length of this cessation will vary considerably. Healing is measured clinically, with recovery indicated by sustained improvement in pain and the recovery of physical capacity.1,6,22 The patient should not bear weight on the affected extremity until he or she can do so without pain.23 Then prescribe partial weight bearing status, which continues until partial weight bearing can be accomplished without pain. Once released from crutch use, the patient should ambulate for a minimum of 1 week. If this does not cause pain, the patient can gradually resume activity. The recovery period for a noncomplicated, stable stress fracture is typically 6 to 8 weeks.
Casts and splints are seldom required for stress fractures. Studies have shown that splinting devices are sometimes detrimental to recovery because they slow rehabilitation, and casts are not required to support a stable stress fracture.24 These devices can, however, be useful in patients who are resistant to activity limitations. When this is a concern, casts or splints can facilitate safety while the bone heals. This is particularly useful in athletes who insist on continued training.
Diagnose Accurately and Early
Stress fractures are relatively uncommon in the general population but common in athletes, particularly elite competitors or people who participate in endurance events. It is essential to exercise diagnostic skill with these injuries, since failure to diagnose them can result in significant pain and disability. With proper management and patient education, recovery without any residual disability is the norm.
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17. Lacroix VJ. A complete approach to groin pain. The Physician and Sportsmedicine. 2000;28:1-17.
18. Pope RP. Prevention of pelvic stress fractures in female army recruits. Military Medicine. 1999;164:370-373.
19. Nielsen PT, Hedeboe J, Thommesen P. Bone scintigraphy in the evaluation of fracture of the carpal scaphoid bone. Acta Orthopedics Scandanavia. 1983;54:303-306.
20. Martire JR. Differentiating stress fracture from periostitis: the finer points of bone scans. The Physician and Sportsmedicine. 1994;22:71-81.
21. Kiuru MJ, Pihlajamaki HK, Hietanen HJ, Ahovuo JA. MR imaging, bone scintigraphy, and radiology in bone stress injuries of the pelvis and lower extremity. Acta Radiology. 2002;43:207-212.
22. Boden BP, Osbahr DC. High-risk stress fractures: evaluation and treatment. Journal of the American Academy of Orthopedic Surgeons. 2000;8:344-353.
23. Perron AD, Brady WJ, Keats TA. Management of common stress fractures. When to apply conservative therapy, when to take an aggressive approach. Postgraduate Medicine. 2002;111:99-106.
24. Swenson EJ, Dehaven KE, Sebstianelli WJ, et al. The effect of a pneumatic leg brace on return to play in patients with tibial stress fractures. American Journal of Sports Medicine. 1997;25:322-328.
James Whyte is a certified family, pediatric and acute care nurse practitioner with a doctorate in nursing. He is also a lieutenant in the U.S. Navy Reserves and an assistant professor at Florida State University in Tallahassee. He practices in a primary care clinic associated with Florida State University and at the Naval Hospital in Jacksonville, Fla.