Atypical Heel Pain CLINICALLY SPEAKING. Hyperparathyroidism-Induced Stress Fracture of the Calcaneus WILLIAM D. FISHCO, DPM, MS* RICHARD G.

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1 CLINICALLY SPEAKING Atypical Heel Pain Hyperparathyroidism-Induced Stress Fracture of the Calcaneus WILLIAM D. FISHCO, DPM, MS* RICHARD G. STILES, MD The authors present a case of atypical heel pain masquerading as plantar fasciitis. The patient was subsequently diagnosed with hyperparathyroidism-induced stress fracture of the calcaneus. The clinical entity of hyperparathyroidism and its manifestations in the skeletal system are presented, as well as a review of stress fractures and pertinent imaging studies. (J Am Podiatr Med Assoc 89(8): , 1999) Heel pain is one of the most common complaints encountered by foot and ankle specialists. In most cases, plantar heel pain is attributed to heel spur syndrome or plantar fasciitis. In the case of recalcitrant heel pain that does not respond to traditional therapy, one should suspect an atypical cause of heel pain. Examples of these atypical causes include infection, fracture, vascular disease, tumor, systemic arthropathy, crystalline arthropathy, metabolic bone disease, entrapment neuropathy (first branch of the lateral plantar nerve), and lumbar radiculopathy. 1 Metabolic bone disease is a general term used to describe metabolic disorders that result in pathology of the skeleton, regardless of the cause. Hyperparathyroidism is a common metabolic disorder. The parathyroid gland secretes parathyroid hormone, which regulates calcium, phosphate, and vitamin D homeostasis. Parathyroid hormone stimulates the kidney to excrete phosphate, retain calcium, and promote synthesis of 1,25-dihydroxyvitamin D from 25 (OH) vitamin D. The influence of parathyroid hormone causes resorption of calcium from its bone reservoir. When the parathyroid gland is functioning properly, elevated levels of calcium will result in a negative-feedback mechanism, which inhibits the release of parathyroid hormone. In pathologic states, *Associate, American College of Foot and Ankle Surgeons; private practice, 1515 E Cedar Ave, Ste A-2, Flagstaff, AZ Private practice, Atlanta, GA. parathyroid hormone can be secreted in either excessively low or high amounts. In hyperparathyroidism, excess production of parathyroid hormone causes calcium to be leached from its bone reservoir. The hypercalcemic state results in failure to inhibit parathyroid secretion, creating a vicious cycle. 2 Clinical features of hyperparathyroidism may include gastrointestinal distress, mental changes, recurrent nephrolithiasis, back pain, and nonspecific complaints of anorexia, malaise, fatigue, and depression. Hypercalcemia is often the first finding that raises suspicion of hyperparathyroidism. There are many causes of hypercalcemia, including hyperparathyroidism, malignancy, infection, vitamin A and D intoxication, immobilization, drug-related effects, and renal failure. The most common cause of hyperparathyroidism is a solitary, benign glandular adenoma. Less common causes include a group of metabolic disorders called multiple endocrine neoplasia syndromes. In cases of hyperparathyroidism, incidental radiographic findings of a washed-out appearance of bone may cause one to suspect osteoporosis. The terms osteoporosis, osteomalacia, and osteopenia are often confused. Osteoporosis describes diseases that cause a decrease in bone mass per unit volume. 3 Osteomalacia is a disorder of the osteoid matrix of bone and cartilage in which there is inadequate mineralization. Osteopenia describes reduced bone density or calcification due to inadequate osteoid synthesis. In the patient with hyper- Volume 89 Number 8 August

2 Table 1. Medical Conditions Associated with Insufficiency Stress Fractures Senile/postmenopausal osteoporosis Drug-induced osteoporosis (alcohol, steroids, heparin) Disuse/immobilization-induced osteoporosis Idiopathic juvenile osteoporosis Osteogenesis imperfecta Hyperparathyroidism Hypoparathyroidism Pseudohypoparathyroidism Pseudopseudohypoparathyroidism Paget s disease Rickets/osteomalacia Nutritional deficiencies Chronic liver disease Anemic states Neoplasms Glycogen storage diseases Diabetes mellitus parathyroidism, osteoporosis is a common finding because of the leaching of calcium from the skeleton. Lower-extremity stress fractures are well-documented entities. They are commonly associated with an abrupt increase in activity level and repetitive loading, particularly in new armed-services recruits and exercise enthusiasts. 4 Stress fractures, however, may also occur without changes in physical activity, and may be related to the bone quality of the patient. Stress fractures are classified as either fatigue or insufficiency fractures. Fatigue stress fractures involve abnormal or repetitive forces exerted on normal bone. Insufficiency stress fractures occur when normal forces are applied to abnormal bone, causing a cortical break. 5 In either case, the result is an incomplete fracture that can cause pain and disability. Several studies have documented the incidence, frequency, sex distribution, risk factors, and other parameters of fatigue fractures in large military recruit populations. 4, 6-8 While insufficiency stress fractures have not been studied as extensively in large populations, they have been associated with numerous medical conditions (Table 1). 9 Stress fractures have been reported to occur in several lower-extremity bones, including the metatarsals, midfoot bones, calcaneus, tibia, fibula, and femur. 10 Pedal stress fractures commonly involve the metatarsals and calcaneus; less commonly, they involve the navicular and other tarsal bones. 8 Tarsal stress fractures may present a diagnostic challenge; in particular, the calcaneal stress fracture may be difficult to diagnose because it may mimic several other conditions, including plantar fasciitis. Diagnosis of calcaneal stress fractures involves the correlation of clinical and imaging findings. Gradual onset and progressive and generalized heel pain with or without antecedent changes in activity are common findings. Historical and physical aspects of calcaneal stress fractures may be similar to those of plantar fasciitis, but the physical findings more often reveal the diagnosis. Physically, pericalcaneal edema is common and maximal pain is usually elicited with side-to-side compression of the calcaneal body. Other reported findings include heel pain when the patient is toe walking and with muscle testing of ankle plantar flexors. 11 Calcaneal stress fractures are believed to be initiated by the normal physiologic action of the Achilles tendon. Characteristically, the fracture pattern begins posterior to the subtalar joint at the superior aspect of the calcaneal body and extends inferiorly. Initial radiographs are commonly interpreted as negative because of the radiographic lag time for new bone formation. Serial radiographs for up to 4 to 6 weeks may be required to make the diagnosis, with positive radiographs revealing a sclerotic band at the stress fracture site. When initial radiographs are reevaluated, a small cortical break may be detectable at the superior aspect of the calcaneus. Imaging modalities for further evaluating stress fractures are bone scans, magnetic resonance imaging (MRI), and computed tomography. 12 Conservative treatment is effective in the management of stress fractures. This treatment involves antiinflammatory medications, protected weightbearing, radiographic monitoring of the stress fracture, and prevention of fracture progression. When metabolic bone disease is suspected, a referral to a specialist is warranted to identify the cause of the fracture. Case Report On July 7, 1994, a 56-year-old woman presented with a chief complaint of left heel pain. Her medical history was significant for dysphonia, recurrent nephrolithiasis, multiple spinal fractures, gastrointestinal disease (delayed gastric emptying, gastritis, and esophagitis), and asthma. Her surgical history included a splenectomy, an esophagogastroduodenoscopy, and multiple spinal fusions in 1983, 1986, and She had no known drug allergies. On her initial visit, she stated that she had pain located on the bottom of her left heel. She described symptoms typical of plantar fasciitis. Neurovascular and dermatologic findings were unremarkable. Palpation revealed pain 414 Journal of the American Podiatric Medical Association

3 Figure 1. Note the significant degree of edema of the left foot and ankle that was apparent upon admission to the hospital. located at the plantar medial tubercle of the calcaneus. Plain film radiographs of the foot were taken and were unremarkable. The diagnosis of plantar fasciitis was made and the patient was given a cortisone injection. The patient returned 5 months later. On her return visit, she complained of acute exacerbation of pain of the same heel and received another cortisone injection. The patient returned to the office 3 months later stating that her heel was doing substantially better; however, now the right heel was exquisitely tender. The diagnosis of plantar fasciitis was made and she was given a cortisone injection in her right heel. The patient presented again several times during the subsequent 18 months complaining of bilateral heel pain. Three days after receiving a cortisone injection in her left heel at the 18-month mark, the patient returned to the office concerned about increased pain, swelling, and redness. At this time, plain film radiographs were taken of the left foot and were read as normal. On clinical examination, there appeared to be slight edema over the medial aspect of the left foot and ankle. There was mild erythema and increased skin temperature. The diagnosis was a postinjection steroid flare. The patient was then started on dicloxacillin, 250 mg orally every 6 hours. She was instructed to return to the office in 1 week. Clinically, the patient was not improving and the edema and erythema were worsening. The patient was admitted to the hospital because of cellulitis of the left foot and leg (Fig. 1). Parenteral antibiotics were ordered. An MRI study was obtained that revealed bony destruction of the left calcaneus. The differential diagnosis was stress fracture or osteomyelitis. In light of the significant cellulitis, a bone biopsy was ordered; the results were consistent with healing fracture. No evidence of infection was seen. The patient was discharged from the hospital in a nonweightbearing below-the-knee cast. Approximately 2 months later, the patient was seen because of identical pain, swelling, and erythema of the right foot and leg. Radiographs were consistent with stress fracture of the calcaneus. For academic purposes, an MRI study was performed on the right foot; it yielded classic images of a calcaneal stress fracture. Because bilateral stress fractures of the calcaneus are uncommon, a referral to a metabolic bone disease specialist was made. Blood tests were performed and, in spite of a normal calcium level of 9.7 mg/dl (normal range, 8.5 to 10.3 mg/dl), parathyroid hormone was significantly elevated at 100 pg/ml (normal range, 10 to 65 pg/ml). 25-Hydroxyvitamin D was mildly decreased at 9 ng/ml (normal range, 10 to 55 ng/ml). The remaining elements of a blood chemistry profile, thyroid panel, and urine analysis were essentially unremarkable. Bone-densitometry studies were performed and revealed osteoporosis. In May 1997, the patient underwent a tetracycline-labeled bone biopsy of the iliac crest. Results of the biopsy revealed highturnover osteoporosis without osteomalacia, consistent with hyperparathyroid-induced lesions. Imaging The key to this diagnosis was a careful review of the chronology of imaging studies. The first study was from the initial presentation on July 7, 1994, and included lateral radiographic views; it was essentially normal (Fig. 2). Several studies were then performed of the left foot on October 24, The lateral plain film radiograph is underexposed, making it difficult to interpret. However, upon critical examination, the image shows a classic stress fracture of the calcaneal tuberosity (Fig. 3). An MRI study of the feet was performed on November 22, 1996, and showed the left calcaneus to be abnormal. The sagittal T1-weighted images show diffuse low-signal pattern in the calcaneal tuberosity, replacing the normal marrow fat. Also, a very important finding is a curvilinear low-signal line that can be differentiated from the surrounding low-signal edema in the marrow (Fig. 4). The T2-weighted images show a diffuse low signal in the left calcaneal tuberosity, which represents the actual fracture. The decreased signal intensity on the T1-weighted image is consistent with increased water content from the inflammatory reaction. There Volume 89 Number 8 August

4 Figure 2. The lateral radiograph of the left foot at initial presentation was read as essentially normal. Figure 3. Although the lateral radiograph is underexposed, a stress fracture is visible in the posterior calcaneus. is also surrounding soft-tissue swelling and edema. Again, a crucial observation is the presence of a curvilinear line in the posterior aspect of the calcaneal tuberosity, which is a low signal on the T2-weighted images and also a low signal on the T1-weighted images (Fig. 5). The magnetic resonance pattern described previously is classic for a calcaneal stress fracture; however, it does not permit differentiation between a fatigue and an insufficiency stress fracture. When the curvilinear line is present, it is important not to allow the degree of surrounding edema to dissuade one from making a definitive diagnosis of a stress fracture. The degree of edema present can cause one to think of infection or tumerous conditions. However, again, when the curvilinear line is present, and no marginated mass is seen, a stress fracture should be diagnosed. It is unusual for osteomyelitis to produce a curvilinear fracture line. The low-signal line about the stress fracture is thought to be related to the actual fracture line and the type of cells present. Of course, the edema is related to the inflammatory response or healing response to the fracture. Marrow edema by itself is generally nonspecific and can be seen in many different abnormalities in- Figure 4. The sagittal T1-weighted image shows the characteristic curvilinear low-signal line consistent with stress fracture. Also note the diffuse low-signal pattern in the calcaneus. Figure 5. The frontal T2-weighted image shows a high signal intensity consistent with edema and hemorrhage. This T2-weighted image also reveals a lowsignal-intensity curvilinear fracture line, similar to that in the T1-weighted image. 416 Journal of the American Podiatric Medical Association

5 cluding infection, infarction, injury (acute or chronic), and response to tumor. The challenge is to evaluate findings related to the edema to attempt to determine the cause. This is not always possible. However, when a curvilinear line is present in a site such as the calcaneus or other sites at risk for stress fractures, then this diagnosis can be made confidently. In the absence of this curvilinear line, other diagnoses should be entertained. Tumors will generally have a discretely marginated mass with or without associated cortical destruction. The pattern of marrow edema is usually surrounding the mass. In cases of infection, the curvilinear line is generally not present. It may be possible to have a pathologic fracture in an infected bone, although this is rare. In order for infection to cause such extensive destruction of bone, the infection would have to be severe and of several weeks duration. Infarctions may also demonstrate a type of curvilinear line, but the pattern is different from that seen in this case. Generally speaking, one can demonstrate the so-called double-line sign, which is characteristic of infarction. The patient had postoperative radiographs of the left foot on December 2, 1996, that showed the characteristic sclerotic curvilinear pattern in the tuberosity consistent with an insufficiency fracture, now with a core biopsy site at the site of the sclerosis (Fig. 6). Upright lateral views of both feet were obtained on January 20, 1997, again showing the stress fracture and biopsy pattern on the left side. No definite radiographic abnormality was seen on the right side. An MRI study of the right calcaneus on February 10, 1997, again shows characteristic findings of a stress fracture with a low-signal curvilinear line in the right calcaneal tuberosity just posterior to the posterior subtalar joint corresponding to the sclerotic line seen radiographically. The right calcaneal MRI scan shows the same pattern as previously seen on the left calcaneus, except in a slightly different location. These patterns include the low-signal fracture line on T1- and T2-weighted sequences with surrounding edema. The degree of edema about this stress fracture is slightly less than that seen on the other fracture on the left side (Fig. 7). Subsequent radiographs from September 9, 1997, continue to show the pattern of insufficiency fracture on the right side. However, they also show development of a second sclerotic band in the left calcaneal tuberosity, consistent with an additional stress fracture (Fig. 8). This demonstrates the healing of multiple, bilateral stress fractures. Discussion This case exemplifies how atypical heel pain can be misinterpreted as heel spur syndrome. Making an accurate diagnosis is difficult, especially when concomitant disease processes are present. The authors believe that in this case the original diagnosis of heel spur syndrome or plantar fasciitis was accurate, and the patient later developed an insufficiency stress fracture of the calcaneus that should have been diagnosed earlier. This case demonstrated classic findings of both hyperparathyroid disease and the evolution of stress fractures of the calcaneus. Stress fractures of the calcaneus are not uncommon among active people, such as athletes, sports enthusiasts, and military personnel. When insufficiency Figure 6. Note the trephine-core biopsy site through the sclerotic band in the posterior calcaneus that is clearly visible on the lateral radiograph of the left foot. Figure 7. The sagittal T1-weighted MR image of the right foot displays classic findings of stress fracture. Volume 89 Number 8 August

6 nosed frequently because of the MRI technology. Injuries that are frequently radiographically occult, especially in the early phases, can be glaringly obvious on MRI scans. Conclusion Figure 8. Note the two sclerotic bands in the lateral radiograph of the right foot consistent with two healing stress fracture sites. stress fractures are diagnosed, one should rule out an underlying metabolic bone disease. The overview of this patient s imaging studies demonstrates bilateral insufficiency fractures. The MRI and plain film radiographic findings are characteristic of this diagnosis; on the basis of these images alone, the diagnosis would be straightforward. From an imaging standpoint, one of the most important points is that the marrow edema seen on MRI scans surrounding a stress fracture can be quite prominent and somewhat disconcerting. As described here, one must look for the low-signal curvilinear band of fracture line that helps confirm that the edema is related to a fracture. The degree of edema should not dissuade one from making this diagnosis confidently if the other features are present. Finally, although MRI is more sensitive than plain film radiography, it is not superior to radiography or radionucleotide imaging for the diagnosis of this condition. Assuming that the patient does not have overt signs of infection, it is safe to treat the patient for a stress fracture in such cases, and obtain follow-up radiography in a few days. Typically, the follow-up radiographs show a classic pattern of stress fracture. If the characteristic curvilinear lines are not present, or if the characteristic sclerotic band is not formed on subsequent radiographs, then tissue diagnosis may be required. The authors categorize these types of abnormalities as occult injury. This pattern of abnormality is relatively new to imaging, but is now diag- Plantar heel pain is usually consistent with plantar fasciitis or heel spur syndrome. When historical or physical findings are unusual or routine treatment proves ineffective, one should suspect an atypical cause of the heel pain. The authors have presented a case of insufficiency stress fractures of both calcanei in a patient who was subsequently diagnosed with hyperparathyroidism. References 1. GROVES MJ: Atypical Heel Pain, in Reconstructive Surgery of the Foot and Leg: Update 97, ed by NS Vickers, SJ Miller, KT Mahan, et al, p 220, The Podiatry Institute, Tucker, GA, POTTS JT: Diseases of the Parathyroid Gland and Other Hyper- and Hypocalcemic Disorders, in Harrison s Principles of Internal Medicine, Vol 2, ed by AS Fauci, E Braunwald, KJ Isselbacher, et al, p 2227, McGraw- Hill, New York, KRANE SM, HOLICK MF: Metabolic Bone Disease, in Harrison s Principles of Internal Medicine, Vol 2, ed by AS Fauci, E Braunwald, KJ Isselbacher, et al, p 2247, McGraw-Hill, New York, ORAVA S, PURANEN J, ALA-KETOLA L: Stress fractures caused by physical exercise. Acta Orthop Scand 49: 19, MORRIS JM, BLICKENSTAFF LD: Fatigue Fractures: A Clinical Study, Charles C Thomas, Springfield, IL, DAFFNER RH: Stress fractures: current concepts. Skeletal Radiol 2: 221, GILBERT RS, JOHNSON HA: Stress fractures in military recruits: a review of twelve years experience. Mil Med 131: 716, HOPSON CN, PERRY DR: Stress fractures of the calcaneus in women marine recruits. Clin Orthop 128: 159, RESNICK D, NIWAYAMA G: Osteoporosis, in Diagnosis of Bone and Joint Disorders, Vol 2, ed by D Resnick, G Niwayama, p 1638, WB Saunders, Philadelphia, PENTECOST RL, MURRAY JM, BRINDLEY HH: Fatigue, insufficiency, and pathologic fractures. JAMA 187: 1001, DUDDY RK, DUGGAN RJ, VISSER HJ, ET AL: Diagnosis, treatment, and rehabilitation of injuries to the lower leg and foot. Clin Sports Med 8: 961, PRATHER JL, NUSYNOWITZ ML, SNOWDY HA, ET AL: Scintigraphic findings in stress fractures. J Bone Joint Surg Am 59: 869, Journal of the American Podiatric Medical Association