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CT vs. MRI in the occult hip fracture

Three Part Question

In [elderly patients who present to the ED with suspected hip fracture and inconclusive plain XR] is [CT or MRI] better at detecting [occult hip fracture/fractured neck of femur]?

Clinical Scenario

A 75 year old female patient presents by ambulance to the Emergency Department after a fall from standing on to her left hip. On clinical examination she is unable to straight leg raise and cannot weight bear. You suspect a fractured neck of femur. Plain radiographs of her pelvis and hip are inconclusive. You remain suspicious for a hip fracture. Is CT or MRI the next most appropriate imaging modality?

Search Strategy

Ovid MEDLINE(R) 1946 to January Week 1 2018
(exp Tomography, X-Ray Computed/ or CT.mp. AND exp Magnetic Resonance Imaging/ or MRI.mp.) AND (hip fracture.mp. or exp Hip Fractures/ OR exp Femoral Fractures/ or femur fracture.mp. OR exp Femoral Neck Fractures/ or neck of femur.mp.) AND (occult.mp. OR suspected.mp.)

Search Outcome

From this search strategy 38 papers were found of which six were relevant. One review article published in 2011 identified only one paper which compared MR and CT imaging. That study is included in the table below.

Relevant Paper(s)

Author, date and country Patient group Study type (level of evidence) Outcomes Key results Study Weaknesses
Collin et al.
2016
Sweden
Forty four consecutive patients with low energy trauma and clinical suspicion of hip fracture who had negative or inconclusive radiographs followed by an inconclusive CT scans and then had MRI scans. The primary reports were classified into negative, suspicious or definite fracture. All images were independently reviewed as part of this study by two different experienced radiologists and classified into negative, suspicious or definite fracture. Single centre retrospective study. CT compared with MRIMRI changed the primary CT diagnosis in 27 cases (61%). 20 fractures were identified and seven suspected fractures were found to be normal.Small single centre retrospective study. MR scanning may have been avoided if the initial CT scans had been reported or reviewed by the more experienced radiologists in the first place.
Radiologist variability in reporting the CT/MRI Senior reviewers of CT disagreed with primary CT report in 24/44 cases.
MRIInitial reports and reviews identified 20 fractures and 24 cases with no fracture. Observer agreement for MRI kappa=1.00
CT Twenty six CTs initially reported as no fracture - 20 remained so after review. Eighteen suspicious CTs - 10 and nine declared negative by each of the two reviewers. Seven and eight cervical fractures identified by the two reviewers and one trochanteric fracture identified by both reviewers. Observer agreement kappa=0.87 (95% CI 0.72-1.00).
Haubro et al.
2015
Denmark
Prospective recruitment of patients with hip pain after low energy fall with no fracture on plain XR between 2008-2012. A total of 1588 proximal hip fractures were identified. 67 patients underwent both CT and MRI as primary XR was inconclusive. The scans were then reported by junior and senior radiologists.Prospective cohort study.Occult fracturesFifteen occult fractures identified by MRI. In six cases there was a discrepancy between CT and MR findings. Three CT missed fractures needed surgery.Presumed gold standard of MRI.
Sensitivity of CT 0.87 95% CI [0.6; 0.98] vs 0.67 95% CI [0.38; 0.88] senior vs resident raadiologist
Rehman et al.
2016
Scotland
Single centre between 2008-2012. Patients included had post-traumatic hip pain with no fracture on XR. Patients had either CT or MRI depending on physician choice, patient compliance or availability. Retrospective review.Occult fracturesOccult fractures were suspected in 179 patients over a four year period, 71 (39.6%) of these had confirmed occult hip fracture. Thirty seven of these were detected using CT and 34 using MRI. Fifty-one of those had operative management. No readmissions to hospital with missed fractures in the following 12 months.Retrospective. Single centre. No direct comparison of images for each patient. Not known if any fractures were missed or presented to other Emergency Departments.
Time to further imagingTime to MRI scan was longer than CT (3.78 days +/-3.014 vs 1.78+/- 1.68, p<0.05)
Hakkarinen et al.
2012
United States
Patients over 60 years old who had a discharge diagnosis of hip fracture. Notes review over three years.Retrospective notes review, single centre. Occult fracturesOccult hip fracture rate about 1% (24 out of a total of 235 hip fractures). Single centre, retrospective. No direct comparison between CT and MR imaging. Potential to have missed patients with negative hip plain films that were sent home without further imaging.
Incidence of occult hip fractures missed by CTCT detected 18/24 occult fractures. Three patients had positive fracture on MRI which was missed on CT.
Gill et al.
2013
United Kingdom
Patients presenting with a clinical suspicion of hip fracture with inconclusive plain films. All patients were subsequently sent for either MRI or CT depending on availability and clinician choice. Retrospective notes review, single centre. Occult fracturesThirty four patients had a confirmed occult hip fracture out of the 1353 hip fractures identified. Single centre, retrospective. No direct comparison between imaging modalities as no patient had both CT and MRI.
CT detection vs MRI detection CT was performed in 61 cases 23 of whom had a fracture (38%). 31 patients received MRI 11 of whom had a fracture (36%). No patient had both imaging modalities.
Lubovsky et al.
2005
Israel
13 patients who fell and had no evidence of a fracture on plain XRs. Six patients had a CT scan and MRI, seven only had MRI.CohortCT vs MRI4 of the 6 CTs produced incorrect diagnoses based on MRI.Very small cohort study. MRI assumed as the Gold Standard. Single radiologist viewing all images, potential for bias.
MRIAll MR scans deemed accurate.

Comment(s)

A small but significant proportion of hip fractures are missed on plain XR. In the studies presented this is around 1%. Timely diagnosis of hip fracture is important to ensure early fixation and to improve outcome. This literature search showed six relevant papers. All were cohort studies and only one was prospective. Only three studies made direct comparisons of CT and MR scans. Both Collins et al. and Haubro et al. show variability in the interpretation of CT scans depending on the expertise of the radiologist. Rehman et al. showed a significantly longer time to perform MRI compared to CT scan. MRI scans did pick up a small number of missed fractures. In Haubro et al. less than 1% of hip fractures were missed on the initial XRs. Of the 67 patients who had both CT and MR scans only 6 showed a discrepancy between CT and MR diagnoses and in only three did the MR confirm a fracture which needed surgery. In the earlier study by Lubovsky the CT diagnosis was incorrect in 4 out of 6 cases after MRI. However, in this latter study CT slices werer much thicker than in Haubro et al (3.2mm vs <1mm). The NICE Hip Fracture Management Guideline (CG124, published in 2011) clearly states that MR imaging is the investigation choice for an occult hip fracture, with CT as second line if MRI is contraindicated or cannot be obtained within 24 hours. The evidence from this BET suggests a more pragmatic approach is valid with early/ out of hours CT if readily available, as in practice there will often be a 24 hour delay to MRI scan.

Clinical Bottom Line

CT is a valid first line imaging technique in suspected occult hip fracture and is easily accessible in most centres. Early diagnosis is important for patient outcomes. Reporting variability of CT scans means that a experienced musculoskeletal radiologist should review negative or inconclusive CT scans. However, when a clinical suspicion remains, despite a normal or inconclusive CT scan, an MR scan is warranted.

References

  1. David Collin, Mats Geijer, Jan H Gothlin Computed tomography compared to magnetic resonance imaging in occult or suspected hip fractures. A retrospective study of 44 patients. European Radiology 2016; 26: 3932-3938.
  2. M Haubro, C Stougaard, T Torfing, S Overgaard Sensitivity and specificity of CT- and MRI- scanning in evaluation of occult fracture of the proximal femur Injury 2015; 46:1557-1561.
  3. H Rehman, R Clement, F Perks, T O White. Imaging of occult hip fractures: CT or MRI? Injury 2016: 1297-1301.
  4. Hakkarinen DK, Banh KV, Hendey GW. Magnetic resonance imaging identifies occult hip fractures missed by 64- slice computed tomography The Journal of Emergency Medicine 2012; 43: 303-307.
  5. Gill SK, Smith J, Fox R, Chesser TJS Investigation of occult hip fractures: the use of CT and MRI The Scientific World Journal 2013; 4 pages.
  6. Lubovsky O, Liebergall M, Mattan Y et al. Early diagnosis of occult hip fractures. Injury 2005 : 788-792.