RecommendationOffer magnetic resonance imaging (MRI) if hip fracture is suspected despite negative anteroposterior pelvis and lateral hip X-rays. If MRI is not available within 24 hours or is contraindicated, consider computed tomography (CT).
Relative values of different outcomesReliability (in terms of diagnostic accuracy) was considered the primary outcome of interest. A false positive diagnosis carries the risks either of unnecessary surgery or of delay and increased cost caused by the need for additional radiographic investigation; a false negative result carries the risks associated with subsequent fracture displacement and its consequences as well as avoidable prolonged immobility and pain. It is therefore important for the selected method to minimise both false positives and false negatives.
Trade off between clinical benefits and harmsMRI cannot be used in patients with certain types of metallic implants but does not otherwise have known harmful effects other than the potential to cause claustrophobia due to the need for patients to remain in a confined space for a considerable length of time. MRI was considered to be the first choice option in view of its superior diagnostic accuracy (up to 100% specificity and sensitivity).

If limitations in the local availability of MRI lead to unacceptably prolonged delay to diagnosis offering an RNS or CT may have a net benefit to the patient even though both carry the risks of exposure to ionising radiation. A delay of several days may, however, be required for RNS to achieve the required sensitivity, it is also generally unavailable out-of-hours (a further cause of delay), and may provide less precise information for surgical planning.

Repeat radiographs after 48 hours have limited sensitivity and carry the risks of displacement during the intervening period, as well as those of delay to surgery.

Ultrasound (US) has no known harms but it's low specificity means that further imaging confirmation (with resulting delay) is required to determine whether a positive US represents a fracture, thus limiting its use. Conversely, a negative US reliably excludes fracture and could in theory enable immediate discharge of this small subset of patients from Emergency departments.

The advent of MRI has enabled the accurate early identification of occult hip fractures that would previously have been missed. The precise natural history of such occult fractures (and therefore the precise place of surgical intervention) has therefore only begun to be fully clarified. It is at least theoretically possible that a proportion of occult fractures might not require surgery. At the same time techniques of fracture fixation have also become less traumatic and invasive. Unless and until these issues of benefit/harm are fully resolved, precise and reliable early diagnosis as a basis for surgical decision making remains a clinical priority.

Economic considerationsIn England and Wales, the cost of a radionuclide scan (RNS) and of an MRI is very similar: a category 3 RNS costs £205, and an MRI (one area, no contrast) costs £206. However, an MRI is cost saving compared to an RNS, as the latter may result in a longer length of hospital stay (and the possible consequences of delay to surgery) before the fracture is diagnosed.

The GDG also considered MRI to be cost-effective compared to US, since in the case of a positive US, its low specificity would still necessitate additional imaging (notably MRI or CT) to confirm the diagnosis. The possible consequences of delay to surgery would need to be added to those of additional imaging.
Quality of evidenceTwo cross sectional studies comparing RNS to MRI were identified. These studies had serious methodological limitations due to the limited reporting of patient demographics and lack of clarity as to whether the assessors were blinded to the results of the index test when interpreting the results of the reference standard and vice versa.

One cross sectional study comparing ultrasound (US) to MRI was identified. This study was of moderate quality. The GDG considered that the reproducibility was a potential limitation as the sonographic readings were performed by highly experienced muskuloskeletal radiologists.There were no serious inconsistencies or indirectness in any of the identified studies.

The assumption that MRI is the gold standard for detecting occult hip fracture and the recommendation advising use of CT as an alternative to MRI were based on unanimous GDG consensus.
Other considerationsThe diagnosis and management of occult hip fracture is still very much an evolving area of practice. In the absence of an evidence-based clinical decision rule clinicians must exert clinical judgement to decide when suspicion of hip fracture after normal plain radiographs is great enough to warrant additional imaging.

Before radiographs are regarded as excluding a hip fracture one should ensure that radiographic quality is optimized. When AP pelvic or hip radiographs are performed the leg should be a little internally rotated with the great toes of the feet overlapping so as to bring the anteverted femoral neck parallel to the X-ray table. In this position little of the lesser trochanter should be visible medial to the femoral cortex (the more externally rotated is the leg the more obvious is the lesser trochanter). Optimising the positioning enables the greater trochanter to be better visualized and not obscured behind the femur. When a hip fracture is present it may prove impossible to position the leg in this optimum position because of pain, but this may be compensated for by appropriate X-ray tube angulation. It should also be ensured that the X-ray exposure factors are optimum to demonstrate both the entire pelvis, to check that fractures are not present in sites additional to the hip, and also for the hip suspected of fracture. To attain this separate exposures and radiographs may be required.

Whilst the GDG considered that MRI was the best test to use to detect occult hip fracture and that this should be the first choice, they noted that there may be occasions where MRI is not available and thought it was important to give guidance as to which test to use in these circumstances. The GDG's consensus decision to recommend CT over RNS is based on greater availability, especially outside the working week, and shorter delay to diagnosis. It also reflects current NHS practice.

In addition, the technical aspects of RNS of bone (a 3 hour delay after radionuclide is given until gamma emission can be recorded; also increased uptake of radionuclide depends on increased osteoblastic activity which may take several days to occur following fracture; lack of availability out of hours) makes this the least appropriate now for imaging occult hip fractures and is now not often used in this scenario, since the advent of CT and MRI.

The GDG were also aware that rapid advances in CT technology, such as 64-slice scanners and sophisticated 3 dimensional reconstruction algorithms, may well overcome the limitations of CT reported in the published literature about its value for detection of occult hip fractures.

From: 5, Imaging options in occult hip fracture

Cover of The Management of Hip Fracture in Adults
The Management of Hip Fracture in Adults [Internet].
NICE Clinical Guidelines, No. 124.
National Clinical Guideline Centre (UK).
Copyright © 2011, National Clinical Guideline Centre.

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