Presentation on theme: "Does early Computerised Tomography exclude fracture in ‘Clinical Scaphoid Fracture’? Dr. Mark Harris Dr Jaycen Cruickshank Department of Orthopaedics,"— Presentation transcript:
Does early Computerised Tomography exclude fracture in ‘Clinical Scaphoid Fracture’? Dr. Mark Harris Dr Jaycen Cruickshank Department of Orthopaedics, Emergency Medicine & Radiology Ballarat Health Services
Why this research question? Unique blood supply of scaphoid: vulnerable to non-union and AVN ? ^ by delayed diagnosis Do we over-treat people to avoid missing it – our fracture clinic felt “many unnecessary patients” On one occasion a difficult case solved with a CT, which prompted a literature review and research question. Insert trapezium fracture.
Scaphoid fracture Clinical examination –Anatomical snuff box –AP compression scaphoid –Axial compression thumb –All more sensitive than specific 10 to 25% not seen on initial radiographs Diagnostic uncertainty and fear of complications /litigation: days in plaster, with 10% of those patients subsequently having a scaphoid # MRI has increased yield to 33%, + other fractures
Investigations Scaphoid XR series 9Cheap 9Available 91st line screening –Low sensitivity on Day 1, and also at Day 10.
Investigations – Bone Scan Murphy et al Day 4 Scan n=100 9Sensitivity 100% 9 specificity 98%???? –NPV 100% (97-100) –PPV 66% –radiation –Variable availability –MBS $ –Earlier less reliable
Investigations - MRI Compared to Bone Scan Sensitivity 100% –N = 187, 37 scaphoid, 28 radius, 9 carpals 1 –Now gold standard More specific 2 MBS $475 Specialists only 1 Brydie & Raby 2 Fowler et al, and Gabler et al
CT Compared to bone scan N=29 1 –100% NPV & PPV –Also some small studies, early & late. MBS $190 Accessible to GP/ED Newer multi-slice CTs 1 Breederveld and Tuinebreijer
Study design A prospective observational study of Emergency Department [ED] patients with clinical scaphoid fracture. Hypothesis: Does early CT rule out fracture in “clinical scaphoid fracture”? –Does early CT confirm fracture scaphoid or alternative diagnosis? Aim to avoid unnecessary plaster immobilisation in up to 9/10 patients
Study population Inclusion criteria: –A clinical scaphoid fracture will be defined as the presence of “anatomical snuffbox tenderness” in a patient with a mechanism of injury consistent with scaphoid trauma but normal initial radiographs. Exclusion criteria –Patients under 18 years of age –Patients who are known to be pregnant –Patients who are unable to give informed consent
Study population (2) Ballarat Emergency Department –Regional trauma centre –36,000 patients/yr, 27% paeds Recruitment by ED staff of varying seniority and experience.
Sample size & Statistics. If the Ct is 90% sensitive and 95% specific, and the prevalence of scaphoid fracture is 10%, the negative predictive value will be 99% in this patient group. We used a formula that calculates the standard error of a %, relating it to the % figure and sample size.
Assessment. The diagnostic value of an early computerized tomography [CT] scan will be validated compared to the gold standard diagnostic clinical protocol. Diagnosis of true scaphoid fracture is confirmed radiographically at the time of reassessment or, in the case of persistent tenderness and negative repeat radiographs, by Magnetic Resonance Imaging. This gold standard is similar to that used in studies using bone scans (Murphy and Eisenhauer )
CT vs Gold Standard Diagnosis Gold Standard Diagnosis CT Fractured Scaphoid CT no Fractured Scaphoid Fractured Scaphoid71 No Fractured Scaphoid 027 NPV = 96.4% ( )Sensitivity = 87.5% PPV = 100%Specificity = 100 %
Discussion Prevalence of injuries(#) = 43% –7/35 occult scaphoid fractures (20%) –8/35 other injuries (sensitivity & specificity 100%) –PPV 100% for scaphoid fracture and other fractures. NPV 96.4% for scaphoid fracture –1 False negative – to discuss –1 patient had MRI reported NAD – when CT unblinded, triquetral fracture – review MRI then confirmed diagnosis.
Conclusion CT has a very high NPV for ruling out scaphoid fracture Continuing to a sample size of 100 will narrow the confidence interval CT good for excellent other injuries
External validity – can we extrapolate? Groups similar to study population –Similar patient groups and treating doctors are out there. In other populations –Similar CT –Prevalence 10%, NPV ^ to 98% –Larger sample may demostrate better sensitivity, and thus ^NPV also. In children?