Stress fractures of the sacrum should be considered in individuals with insidious onset of asymmetric low back pain or buttock pain. Patients most commonly present with lumbar back or gluteal pain, although hip, groin, and radicular type pain have also been reported. Symptoms are usually worsened with weight-bearing activities and relieved with rest. Sacral stress fractures are often misdiagnosed as the history and physical exam can be suggestive of more common etiologies such as spondylolysis, spondylolisthesis, sacroiliac joint dysfunction, piriformis syndrome, lumbago, vertebral compression fractures, or spinal stenosis.

Denis et al. classified sacral fractures into three zones (Fig. 3) [43]. Zone 1 involves the sacral ala or wing and is the most common part of the sacrum to sustain a stress fracture. Zone 2 extends from the sacral foramina to the sacral body. Fractures in zone 2 can result in unilateral lumbosacral radiculopathies. Fractures in zone 3 involve the sacral body or canal of the sacrum. Fractures in zone 3 can cause bilateral neurological symptoms, saddle anesthesia, and sphincter tone dysfunction.

Physical exam may reveal sacral tenderness with palpation which is a nonspecific finding. The patient may have pain with the flexion-abduction-external rotation (FABER) test or Gaenslen’s test. The FABER test is performed by flexing the hip of the affected side to 90°. The examiner then places the hip in external rotation while pushing the knee on the affected side toward the exam table. The Gaenslen’s test is done with the patient lying supine with the knee on the affected side fully flexed with the contralateral leg dangling off the exam table. The examiner then simultaneously applies flexion to the affected hip while hyperextending the contralateral side. The test is positive if pain is elicited. Having the patient hop on the leg of the affected side might also elicit pain. About 70 % of patients may complain of neurologic symptoms that suggest a radiculopathy or myelopathy; objective neurological findings may only be found in 2–14 % of cases [42]. In the rare case where the fracture involves the sacral body, neurologic symptoms such as sphincter tone dysfunction or limb paresthesias can be found. Careful attention should also be put into examining the pubic rami. As discussed above, there is an association of concomitant pelvic stress fractures. One study found that 78 % of patients with a sacral stress fracture also had a coexisting pubic ramus fracture [44]. Disruption of the pelvic ring can cause increased stress in other areas and may be the reason why concomitant pelvic stress fractures occur.

Fractures are usually found in the sacral ala (Fig. 4) and run parallel to the sacroiliac joint [42]. Radiographs are of limited utility as stress fractures in this area may be obscured by the presence of stool, bowel gas pattern, and calcified vessels. Bilateral sacral fractures may be seen and in some cases can be connected by a horizontal fracture through the sacral body creating the so-called H sign which can be seen on bone scintigraphy. The presence of the “H sign” has been reported to be highly specific for an insufficiency fracture [45].

Pubic ramus fractures account for 1.25 % of all stress fractures [46]. Most pubic ramus stress fractures occur at the medial portion of the pubic ramus or at the junction between the inferior pubic ramus and the ischial ramus (Fig. 5) [47]. The adductor magnus muscle originates at this junction, and its repetitive contraction has been attributed to contribute to the development of a pubic ramus stress fracture [46]. Patients often complain of insidious onset of groin pain but can also present with perineal, anterior thigh, or buttock pain. On physical exam there may be direct tenderness to palpation over the pubic ramus. There may also be an antalgic gait, pain with abduction, or pain with resisted adduction and external rotation of the hip.