Sacral Insufficiency Fractures: A Report of Two Cases and a Review of the Literature

Transcription

1 JOURNAL OF WOMEN S HEALTH & GENDER-BASED MEDICINE Volume 10, Number 7, 2001 Mary Ann Liebert, Inc. Sacral Insufficiency Fractures: A Report of Two Cases and a Review of the Literature JULIE LIN, M.D., ELISABETH LACHMANN, M.D., and WILLIBALD NAGLER, M.D. ABSTRACT Sacral insufficiency fractures (SIF) are a type of stress fracture that occur primarily in postmenopausal women. They were first described in 1982 by Lourie and have since been frequently overlooked as a cause of low back, buttock, or groin pain. We present two cases of SIF to demonstrate the clinical presentation, diagnosis, and treatment of patients with SIF. Both patients were elderly women with complaints of pelvic and low back pain in the absence of significant trauma. Physical examination was significant for marked sacral tenderness. Diagnostic imaging supported the diagnosis of SIF. Both patients underwent early rehabilitation, including early ambulation, and had good functional outcomes. These patients serve to illustrate how conservative treatment yields excellent clinical results in the majority of patients, with most reporting improvement within 1 2 weeks after fracture and complete resolution of symptoms after 6 12 months of treatment. INTRODUCTION SACRAL INSUFFICIENCY FRACTURES (SIF) are a type of stress fracture that occur when normal stresses are placed on bone with decreased mineralization and elastic resistance. Fatigue fractures are another type of stress fracture, and they occur when abnormal forces are applied to normal bone, such as in tibial stress fractures in long distance runners. Stress fractures occur secondary to repeated cyclic loading that eventually exceeds its elastic resistance. SIF were first recognized by Lourie in 1982 as a distinct clinical entity of spontaneous osteoporotic fracture of the sacrum. 1 Since their initial description, they have remained a little known entity and are likely a frequently underdiagnosed cause of low back or pelvic pain. Clinicians may not diagnose SIF because of its nonspecific clinical picture and subtle radiographic findings. 2 We present two cases of SIF to illustrate the clinical presentation, management, and rehabilitation of these patients. Both patients complained of low back and pelvic pain with a minimal history of trauma. Physical examination demonstrated sacral tenderness to palpation. The clinical findings were corroborated by diagnostic imaging, which demonstrated SIF. Both patients underwent rehabilitation, including early mobilization, which resulted in good functional outcomes. Our two cases serve to illustrate that patients with SIF who receive appropriate pain management and early rehabilitation have good functional outcomes. Conservative treatment yields excellent clinical results in the majority of patients, with most reporting improvement within 1 2 weeks af- Department of Rehabilitation Medicine, The New York Presbyterian Hospital-Weill Medical College of Cornell University, New York, New York. 699

2 700 ter fracture and complete resolution of symptoms after 6 12 months of treatment. Case 1 CASE REPORTS An 81-year-old Caucasian woman with a long history of asthma treated with oral corticosteroids had a chief complaint of low back pain and difficulty with ambulation after slipping in the bathroom. Physical examination revealed an elderly kyphotic woman with cushingoid facial features. Heart, lung, and abdominal examination results were within normal limits. There was tenderness to light palpation in the sacral region. Neurological examination revealed normal manual muscle testing (MMT), sensation, proprioception, and deep tendon reflexes. Straight leg raise was negative bilaterally. Initial lumbosacral spine radiographs were negative for fracture and revealed osteopenia and degenerative joint disease. The patient was admitted to our inpatient rehabilitation unit for further management. The patient refused a bone scan, but computed tomography (CT) of the pelvis revealed a stable sacral fracture. The patient was placed on a cyclooxygenase-2 (COX-2) inhibitor, opioids as needed for breakthrough pain, and calcium supplementation. She began a rehabilitation program immediately, including ambulation with a standard walker, with significant improvement in pain and function after several weeks. The patient was discharged home on a COX-2 inhibitor and received home physical therapy. Case 2 A 68-year-old Caucasian woman with no significant past medical history had a chief complaint of right hip pain after a fall and was unable to weight bear. Physical examination revealed an elderly female in no acute distress. Abdominal examination results were within normal limits. There was tenderness to palpation in the right groin and over the right sacral region. Passive and active range of motion of bilateral hips was 90 degrees. Neurological examination was within normal limits, with negative straight leg raise bilaterally. Initial pelvic and femoral radiographs were negative except for diffuse osteopenia. The patient was admitted to the inpatient orthopedic unit, where magnetic resonance imaging (MRI) showed a right superior pubic ramus fracture and marrow edema consistent with sacral fracture in the right sacral ala extending to the right body of the sacrum. The patient was transferred to our inpatient rehabilitation unit, where she underwent immediate rehabilitation. The patient received pain medications and within 1 week was able to ambulate with the assistance of a rolling walker. The patient was discharged home at this time with pain medications and home physical therapy. DISCUSSION LIN ET AL. SIF occur almost exclusively in postmenopausal osteoporotic women with a history of no or minimal trauma. Incidence rates have ranged in the literature from 0.14% to 2.0%. 3 However, the true rate may be much higher, as many cases of SIF probably remain undiagnosed. Postmenopausal women comprised 93% of cases reported in the literature several years ago. 4 The mean age of patients with SIF has been estimated in various reports as 71.3 years 5 and 81 years. 6 Stress fractures typically occur in young athletes as a result of repeated trauma and typically involve the tibia, tarsals, metatarsals, femur, fibula, pelvis, sesamoids, and spine. 7 Sacral stress fractures are very uncommon. 8 Typically, sacral stress fractures occur in amenorrheic female athletes 9 11 and are differentiated from insufficiency fractures in that they are likely caused by a fatigue type of mechanism 12 secondary to repetitive cyclic loading. 13 There have been a few case reports in the literature describing sacral stress fractures in a younger population than in patients with SIF. These case reports have described long distance runners, 11,14,15 a college basketball player after the use of a jumping machine, 16 and a pregnant woman. 17 The average age of patients reported in one series of three cases was 27 years. 12 It is believed that stress fractures may be nutritionally based in the female athlete, 13 and the amenorrhea that causes osteopenia likely contributes to these fractures. 12,13 The location of sacral stress fracture is similar to that of SIF. 13 Symptoms of sacral stress fracture may be similar to those seen in SIF, including low back and sacral pain that may radiate into the buttocks or may be referred to the groin and into the leg. 15,18,19 In addition, similar diagnostic imaging studies may be used in confirming a sacral stress fracture. 7

3 SACRAL INSUFFICIENCY FRACTURES 701 Major risk factors for SIF include osteoporosis, osteopenia, rheumatoid arthritis, local pelvic irradiation, and corticosteroid use. Additional risk factors include Paget s disease, hyperparathyroidism, scurvy, osteomalacia, renal osteodystrophy, Tarlov cysts, joint arthroplasty, and lumbar sclerosis The National Osteoporosis Foundation 23 has categorized risk factors for osteoporosis into nonmodifiable and potentially modifiable risk factors. Nonmodifiable risk factors include personal history of fracture as an adult, history of fracture in a first-degree relative, Caucasian race, advanced age, female sex, dementia, and poor health/frailty. Potentially modifiable risk factors include current cigarette smoking, low body weight (,127 pounds), estrogen deficiency, early menopause or bilateral ovariectomy, prolonged premenopausal amenorrhea, impaired vision despite correction, alcoholism, recurrent falls, inadequate physical activity, low lifelong calcium intake, and poor health/frailty. Secondary causes of osteoporosis include hormonal imbalances, carcinoma, gastrointestinal disorders, medication use, chronic renal disease, inflammatory arthritis, inactivity, and poor nutrition. Clinical SIF occurs in patients with either documented osteoporosis demonstrated by bone mineral density (BMD) on dual energy x-ray absorptiometry (DEXA), osteoporosis manifested by prior insufficiency fractures, or osteopenia noted on plain radiographs. The World Health Organization (WHO) has defined osteoporosis as a BMD of.2.5 standard deviations (SD) below the mean for young normal people and osteopenia as a BMD between 1 and 2.5 SD below the mean for young normal people. Patients typically report a history of minimal trauma, such as a fall sustained from a sitting or standing position. Patients describe buttock, sacral, groin, or low back pain that is often severe and incapacitating, resulting in limited function or even bed rest. Symptoms are typically exacerbated by weight bearing and activity and relieved by rest. 24 Associated radicular pain may also be present. On physical examination, there may be marked sacral tenderness to palpation. Neurological examination, including straight leg raise, is typically normal. 24,25 Laboratory studies are usually within normal limits except for a mildly elevated alkaline phosphatase. 26 Differential diagnosis of SIF includes degenerative lumbar spine disease, vertebral body compression fractures, spinal stenosis, and neo- plasms. 6 Consideration of these more common diagnoses often results in delayed diagnosis, and delayed diagnosis and treatment of SIF may cause prolonged bed rest and immobility. This, in turn, can lead to excessive osteolysis and slow healing of insufficiency fractures secondary to lack of bone opposition and abnormal fragment mobility, autonomic nervous system dysfunction, and vascular insufficiency to bone In addition, there are multiple harmful effects of prolonged immobility discussed elsewhere in this paper. Diagnostic imaging can be valuable in the diagnosis of these fractures, including plain radiographs, technetium-99m ( 99m Tc) methylene disphosphonate bone scan, CT, and MRI. Plain pelvic anteroposterior (AP) and lateral radiographs may serve as an initial screening tool, although they are usually negative for fracture. This may be due in part to overlying bowel gas and stool, vascular calcification, or sacral curvature (Fig. 1). 22,30,31 In addition, radiographic abnormalities, such as areas of sclerosis or the fracture line, can be subtle and may be missed or misinterpreted, 31,32 even by experienced radiologists. The timing of plain radiographs should also be considered, as demineralization, subtle cortical interruption, or callus formation may not appear on radiographs until several weeks or months postfracture. 6,33 Standard lateral radiographs of the sacrum may aid in revealing anterior cortical fractures of the sacrum. 34 Vertebral and pelvic insufficiency fractures are often associated with SIF. It has been estimated that there is an almost 33% concomitant association of pelvic insufficiency fracture and SIF. 30 In addition, the triad of sacral, pubic, and supraacetabular lesions is common. 35 Therefore, the presence of any vertebral, pelvic, or hip fractures in patients with unexplained buttock, groin, or low back pain should heighten clinical suspicion for SIF. 99m Tc bone scans are the most sensitive imaging study to diagnose SIF and may detect fractures within hours of occurrence. 27,35 An acute fracture imaged before onset of healing and metabolic bone activity may result in a negative bone scan. Characteristically, bone scan demonstrates the H-shaped, butterfly-shaped, or bowtie-shaped Honda sign (Fig. 2), which represents the increased uptake pattern corresponding to bilateral vertical sacral fractures associated with a transverse fracture. 36 Less characteristic appearances include unilateral, linear, or focal sacral activity or partial H configuration, 20 and in

4 702 LIN ET AL. FIG. 1. Stool and bowel air obscure evaluation of the sacrum on this AP radiograph of the pelvis. There is no obvious sacral fracture. these nonspecific cases, CT may complement bone scan. 37 CT can illustrate fractures or sclerosis and can also help exclude pathological fractures (Fig. 3). MRI is highly sensitive but nonspecific to the marrow edema seen with SIF. There is typically low signal intensity on T1- weighted images, with a correspondingly high FIG. 2. Bone scan with 99m Tc reveals increased radiotracer uptake in both sacroiliac joint regions and linearly traversing the midsacrum, consistent with SIF, giving the classic Honda sign appearance (arrow). signal on T2-weighted images (Fig. 4), usually parallel to the sacroiliac joint. Occasionally, a discrete fracture line may also be visualized. MRI is often performed in patients with low back pain to rule out disc or spinal cord involvement, and it is important to be familiar with the appearance of SIF on these studies. Rarely, results may be falsely attributed to skeletal metastasis. Appropriate diagnosis of SIF can obviate the need for invasive procedures, such as sacral biopsy. 38 There have been several case reports in the literature of patients who underwent bone biopsy to rule out malignancy and were later diagnosed with SIF. 6,20 Rehabilitation of patients with SIF should be initiated as early as possible. Delayed diagnosis and treatment of SIF may cause multiple deleterious effects related to immobility and deconditioning. The costs of diagnostic imaging, including MRI, CT, and bone scan, certainly outweigh the risks of immobility when all the adverse effects are considered. Immobility may affect multiple organ systems, causing increased morbidity and mortality. Some of the harmful effects include formation of deep venous thrombosis (DVT) and pulmonary embolus, loss of muscle strength, postural hypotension, decreased stroke volume and cardiac output, urinary calculus formation, urinary retention, decreased appetite, constipation, pressure ulcer formation, anxiety,

5 SACRAL INSUFFICIENCY FRACTURES 703 FIG. 3. CT scan of the pelvis demonstrates cortical disruption of the right sacrum, indicating a minimally displaced fracture (arrow). depression, increased bone resorption and calcium excretion, and impaired ciliary clearance and coughing mechanisms that may result in atelectasis and pneumonia. 39 The positive stress of weight bearing outweighs the negative effects of bed rest and prolonged immobilization. Osteoblastic bone-forming activity is stimulated by weight bearing or muscle tension strength, whereas immobilization leads to unrestrained osteoclast-mediated bone resorption and decreased osteoblast-mediated bone formation. Analgesics should be used liberally for pain management, including nonsteroidal anti-inflammatory drugs (NSAIDs), COX-2 inhibitors, calcitonin, and bisphosphonates. The association between NSAID use and fracture healing has been somewhat controversial. Van Staa et al. 40 hypothesized that NSAIDs, secondary to their inhibitory effects on prostaglandin synthesis, may actually play a role in osteoporosis prevention. The authors study did not support clinically significant effects of NSAIDs on bone metabolism. Giannoudis et al. 41 demonstrated a marked association between nonunion and the use of NSAIDs after injury. They noted delayed healing in patients with fracture of the diaphysis of the femur who took NSAIDs compared with patients who did not take NSAIDs. Furthermore, Banovac et al. 42 showed that NSAID use in control rats and animals resulted in delayed fracture healing. There have been no studies in the literature, to our knowledge, investigating the role of NSAIDs and SIF healing. We have used NSAIDs in our patient population as an adjunct medication with other analgesics, with good results. Patients with SIF are typically elderly and cannot tolerate large doses of opioids. We, therefore, do not disagree with the use of NSAIDs in association with other analgesics to minimize pain and to maximize mobility and full participation in a rehabilitation program. Precautions to consider in SIF patients include DVT prophylaxis with intermittent pneumatic stockings or graded elastic stockings and anticoagulant therapy with injectable heparin or low molecular weight heparin in the absence of contraindications. Sacral decubiti may be prevented by turning and positioning the patient regularly and by using an air flow mattress. Early mobilization and rehabilitation will help to minimize these and additional adverse complications. Although some authors have predicted a poor long-term prognosis, 26 we have found that functional outcome is usually positive. Symptomatic improvement is typically seen after 1 2 weeks of treatment, with most patients becoming pain free 6 12 months after fracture. Our two case presentations illustrate the significant improvements in symptoms and function that take place early after pain management and rehabilitation are initiated. In conclusion, SIF should be suspected in patients, particularly those with SIF risk factors, with hip, groin, low back, or buttock pain who report a history of minimal or no trauma. Physicians should have a high index of suspicion for FIG. 4. Fat-suppressed T2-weighted MRI of the sacrum demonstrates SIF. There is high signal intensity throughout the entire sacrum (arrowheads), consistent with marrow edema and SIF, compared with the normal fat-suppressed low signal marrow of the adjacent iliac bone.

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