Is magnetic resonance imaging (MRI) necessary to exclude occult hip fracture?

The possibility of occult hip fracture in older patients after a fall is a common problem in emergency and orthopaedic departments. Magnetic resonance imaging (MRI) scanning is the best investigation, but is expensive and may be difficult to obtain. The value of various clinical signs to determine which patients are at risk of occult hip fracture has not been reported. We reviewed all patients who had MRI scan for suspected hip fractures but had normal initial X-rays over a 6-year period. We identified 76 patients. Twelve patients were excluded. Two patients had MRI scan for suspected stress fracture and two patients had metastatic fractures. Eight patients had inadequate or untraceable clinical notes. Each patient's personal details, mobility, independence and detail clinical details were recorded. Following case review of 64 patients we excluded 5 patients with associated osteoarthritis of the hip joint, 1 patient with fibromyalgia and 1 patient with pre-existing multiple myeloma. Thirty-five patients had occult proximal femoral fractures. Of them four patients had isolated pubic ramus fractures and five patients had isolated greater trochanter fractures. Twenty-two patients had no fracture. The value of the individual tests was evaluated using Fisher exact and chi square analysis; with Bonferroni correction for multiple comparisons (10 tests) p<0.005 was deemed significant. Pain on axial loading of the limb and pre-fracture restricted patient mobility were both associated with the presence of a fracture (p<0.005). Both factors had identical positive predictive value=0.76, a negative predictive value=0.69 and post-test probability of disease given a negative test=0.30. Predictive values remained the same when both factors were considered together. Patients who were independently mobile before the fall and who do not have pain on axial compression of the limb are less likely to have a fracture, but these signs alone or in combination do not exclude a fracture. The clinical signs investigated cannot distinguish between patients with and without a hip fracture, and MRI scanning is necessary to establish whether some patients have an occult fracture.