|Ahead of print publication
Sacral stress fractures in military recruits: A commonly missed uncommon entity
Mohammed Schezan Iqbal1, Debraj Sen2, Rajiv Kaul3, Shikha Awasthi4
1 Department of Orthopaedics, INHS Kalyani, Visakhapatnam, Andhra Pradesh, India
2 Department of Radiodiagnosis, AFMC, Pune, Maharashtra, India
3 Department of Orthopaedics, AFMC, Pune, Maharashtra, India
4 Department of Radiodiagnosis, INHS Kalyani, Visakhapatnam, Andhra Pradesh, India
|Date of Submission||05-Apr-2020|
|Date of Decision||06-Jul-2020|
|Date of Acceptance||04-Aug-2020|
|Date of Web Publication||09-Oct-2020|
Mohammed Schezan Iqbal,
Department of Orthopaedics, INHS Kalyani, Visakhapatnam - 530 005, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
Sacral stress fractures are a relatively rare entity which are particularly difficult to identify and diagnose. A high index of suspicion, especially in individuals at risk, like long-distance runners, female athletes, military recruits, and individuals who have recently started training for competitive sports and are hence unaccustomed to training, who complain of low backache with or without buttock or groin pain, will indeed help the physician in not missing out on this diagnosis. A thorough evaluation, including tests to rule out insufficiency fractures due to associated illnesses along with a magnetic resonance imaging of the sacroiliac joints, is mandatory to recognize this problem and institute early, appropriate treatment.
Keywords: Diagnosis, evaluation, sacrum, stress fracture
| Introduction|| |
Sacral stress fractures are an established yet unusual cause of lower back or buttock pain in the young individual. These fractures could be either fatigue type due to undue stress to a normal bone or insufficiency type due to normal stress on an underlying pathologic or weak bone. Fatigue fractures are known to happen in long-distance runners, especially military recruits and female athletes, and occur due to an increasing range, a variation of running surface, an alteration of shoes, or a previously unknown leg length discrepancy. Insufficiency fractures may be due to osteoporosis, Vitamin D deficiency, osteomalacia, hyperparathyroidism, or underlying bone tumors and prior radiation therapy. The purpose of this article was to describe a case of a sacral stress fracture in a military recruit.
| Case Report|| |
A 19-year-old military recruit with no past afflictions reported with a history of pain in his left buttock and groin a month's duration. The pain was insidious in onset and gradually progressive; he did not associate a definite event with the onset of pain. The pain was not associated with any radiation to the left lower limb or tingling sensation. The pain had been interrupting his exercise and military training for the past 1 month, for which he was being managed with intermittent rest and occasional analgesics. Clinical examination revealed no swelling or signs of local inflammation around the hip or lower back. Paraspinal muscle spasm and deep tenderness over the lower back on the left side were noted. Gaenslen's and flexion, abduction and external rotation (FABER) tests were positive on the left side. The neurological examination was normal. Radiographs of the pelvis, including both sacroiliac and hip joints were normal [Figure 1]. Subsequently, magnetic resonance imaging (MRI) was requisitioned. It revealed a vertically oriented fracture of the left sacral ala with surrounding marrow edema [Figure 2]. There was no associated fracture of the pubic ramus. The sacroiliac and hip joints were normal on both sides.
|Figure 1: Panel of radiographs of the sacroiliac joints (a) and the pelvis including both hip joints (b) do not reveal any abnormality|
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|Figure 2: Panel of magnetic resonance imaging images of the sacrum: Short-tau inversion recovery images (a) and T1-weighted images (b) showing a vertically oriented hypointense fracture line with surrounding bone marrow edema (thick white arrow)|
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To rule out bone insufficiency as the cause of stress fracture, the patient's serum alkaline phosphatase, thyroid-stimulating hormone, parathormone (PTH), calcium, phosphorus, and 25-hydroxy Vitamin D levels were evaluated. The results of these tests were within the normal range. His complete blood count, erythrocyte sedimentation rate, liver function tests, C-reactive protein, and renal function tests were also normal.
The patient was advised complete rest for 6 weeks post diagnosis of the fatigue stress fracture of the sacrum, with a subsequent gradual return to activities with strength conditioning and resumption to sporting activities and military training.
| Discussion|| |
It was Laurie who first described the entity of sacral stress fracture in 1982. Sacral insufficiency fractures have been reported sporadically in literature, mainly because they are presumed to be an unusual cause of low back pain. Nevertheless, their prevalence is probably underestimated due to the lack of specific symptoms.
In the general population, sacral stress fractures have an incidence of 1%. These are mainly of two types: insufficiency fractures and fatigue fractures. Insufficiency stress fractures are mostly seen in osteoporotic women and are frequently bilateral. The average age at presentation is 71 years. Fatigue fractures are mostly observed in female athletes, particularly long-distance runners and volleyball players. The incidence in this group of individuals may be as high as 20%.
The two theories that have been propounded to describe stress fractures are the overload theory and the muscle fatigue theory. In the former, excessive stress is produced at the osseous insertions of muscles due to repetitive contractile muscle activity. In the latter, the capacity of the muscles to work as shock absorbers is reduced due to repetitive muscle activity. It is likely that both play a role in causing stress fractures. An effort at bone remodeling is induced by recurring microtrauma; however, the recurrent cyclic stress precedes an enhanced rate of osteoclastic activity, in consonance with the raised osteoblastic activity of new bone. A weakening of the bone and consequent fracture results from insufficient rest which does not allow formation of new bone.
The sacrum can be likened to the keystone of an arch and large stresses pass down from the upper spine down through it into the lower limbs. Sacral stress fractures, therefore, are oriented vertically parallel to the sacroiliac joints. Increased stresses may lead to complete fractures of the lateral sacral alae, and the consequent loss of the lateral support and may lead to a transverse fracture through the central sacrum “the H-shaped fracture” morphology. Owing to the closed-ring structure of the pelvis, any disruption of this structure leads to undue and abnormal forces being transferred to different parts of the ring; sacral stress fractures thus often coexist with fractures of the pubic ramus.
These fatigue fractures are believed to result from faulty training, when an undue or rapid increase in the training regimen causes muscle fatigue, with subsequent stress on the bone that exceeds its capability to regenerate. Abnormal biomechanics due to leg length discrepancy leading to unequal stride length and corresponding asymmetrical movements of hips, sacroiliac structures, and the lower spine is also believed to play a role in the causation of these fractures.
Clinical features of sacral stress fractures are variable, ranging from low backache to buttock and groin pain, and even possible radiation down to the lower limbs. The differential diagnosis at the time of presentation includes musculotendinous strain, femoro-acetabular impingement, stress fracture of the neck of the femur, and perhaps lumbar disc disease. The clinical examination may not provide consistent signs initially, as many of these patients have diffuse low back, sacral, and buttock pain. Most patients have localized tenderness over the sacrum and sacroiliac joint and have a FABER test positive.
The diagnostic workup begins with plain radiography, which is good to exclude any obvious fracture or tumors in the pelvis. Stress fractures of the sacrum may not be readily obvious as they tend to not produce a callus and associated bowel gas may obscure them further. MRI is the best modality for the diagnosis of sacral stress fractures. Fat-suppressed T2-weighted images and short-tau inversion recovery images are sensitive sequences to detect bone marrow edema (suggestive of micro-fractures). At a later stage, when a fracture line develops, it will be seen as a linear low signal intensity area.
Recovery from a sacral stress fracture is generally the rule. Symptoms usually resolve with 4–6 weeks of rest from activities in cases of fatigue fractures. Treatment of the underlying pathology may require medications in the form of Vitamin D supplementation, bisphosphonate therapy, calcitonin, or recombinant PTH for the management of osteoporosis or osteomalacia. Pulsed electromagnetic fields, Low-intensity pulsed ultrasound and extracorporeal shock wave therapy are noninvasive modalities of treatment targeting fracture healing but have not yet been conclusively shown to be superior to conservative means by randomized controlled trials.
| Conclusion|| |
Stress fracture of the sacrum is an unusual and relatively rare occurrence which must be kept as a differential diagnosis in patients complaining of low back or buttock pain, to ensure timely imaging, prompt diagnosis, and appropriate treatment.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]