SGEM#420: I get knocked down, but I get up again – do I have a scaphoid fracture?

Reference: Coventry et al. Which clinical features best predict occult scaphoid fractures? A systematic review of diagnostic test accuracy studies. Emerg Med J. Aug 2023

Guest Skeptic: Dr. Matt Schmitz is an Orthopaedic Surgeon who sub-specializes in adolescent sports and hip preservation. He will soon be transitioning out of the US military after a 20-year career in the Air Force and is soon to be Clinical Professor of Orthopaedics at UC San Diego.

DISCLAIMER: THE VIEWS AND OPINIONS OF THIS BLOG AND PODCAST DO NOT REPRESENT THE UNITED STATES GOVERNMENT OR THE US MILITARY.

Case: A 24-year-old manual labourer presents to the emergency department (ED) after drinking a few too many beers, having a disagreement with another beer drinker and gets knocked down. The mechanism was described as a classic FOOSH (fall on outstretched hand) injury. Examination reveals pain along the wrist and in his anatomical snuffbox. However, the x-rays read as “normal” by radiology.

Background: Fractures of the scaphoid are the most common carpal fractures presenting to the ED. One of the best systematic reviews and meta-analyses on the topic discussing the diagnostic accuracy of the history, physical examination and imaging is by Carpenter et al from AEM 2014 [1]. We went into some detail on SGEM#385.

Many potential scaphoid fractures are immobilized but this can be a detriment to job, school, and activities of daily living. Initial Xray’s pick up only about 17% of fractures [2]. Having patients follow-up in a couple of weeks for repeat x-rays can pick up about 7% more [3].

MRIs have greater diagnostic accuracy [1] but may not be available in some areas and can be expensive and not always readily available. A CT scan is not as accurate as an MRI but does come with a different type of cost, radiation exposure [1].

Clinical Question: What to do with a patient who presents with a FOOSH injury and has a normal x-ray; are there clinical exam findings that can help rule in/rule out a scaphoid fracture?

Reference: Coventry et al. Which clinical features best predict occult scaphoid fractures? A systematic review of diagnostic test accuracy studies. Emerg Med J. Aug 2023

• Population: Patients with a clinical suspicion of having a scaphoid fracture but a normal initial x-ray
  • Excluded: Studies that did not have enough information to create a 2×2 table even after contacting study authors.
• Intervention: Various physical examination maneuvers
• Comparison: N/A
• Outcome: Diagnostic accuracy expressed as sensitivities, specificity, and likelihood ratios

Authors’ Conclusions: “No single feature satisfactorily excludes an occult scaphoid fracture. Further work should explore whether a combination of clinical features, possibly in conjunction with injury characteristics (such as mechanism) and a normal initial radiograph might exclude fracture. Pain on supination against resistance would benefit from external validation.”

Quality Checklist for Systematic Review Diagnostic Studies:

1. The diagnostic question is clinically relevant with an established criterion standard. Yes
2. The search for studies was detailed and exhaustive. Yes
3. The methodological quality of primary studies were assessed for common forms of diagnostic research bias. No
4. The assessment of studies were reproducible. Yes
5. There was low heterogeneity for estimates of sensitivity or specificity. No 
   6. The summary diagnostic accuracy is sufficiently precise to improve upon existing clinical decision-making models. No

Results: They searched the worlds literature, followed the PRISMA guidelines and found eight studies of which four included a small number of children. There were 1,685 wrist injuries included in the SRMA of which there were 123 (9%) occult scaphoid fractures (normal initial x-rays). Most studies were reported as having an overall low risk of bias.

Key Results: There was no physical examination that could rule-out an occult scaphoid fracture with any confidence.

• Primary Outcome: Diagnostic accuracy
  • The best test for both positive and negative likelihood ratios as the pain on supination against resistance test based upon one small study of only 53 patients with 9 occult fractures (17%)
  • LR+ 45.0 (95% CI; 6.5 to 312.5)
  • LR- 0.1 (95% CI; 0.0 to 0.7)

1) Selection Bias: The authors mention that findings on physical examination contributed to the clinical suspicion of a fracture. This could be a source of selection bias. The definition according to the Centre for Evidence Based Medicine at Oxford University “occurs when individuals or groups in a study differ systematically from the population of interest leading to a systematic error in an association or outcome”.

2) Prevalence: Sensitivity depends on the spectrum of disease, while specificity depends on the spectrum of non-disease. So, you can falsely raise sensitivity if the clinical practice has lots of very sick people (sicker than who you see in the ED). Specificity can look great if you have no sick patients in the cohort (worried well) [4].

Prevalence of occult fractures in this study was 9%. It is unclear if this prevalence would have changed the diagnostic accuracy of the various tests to make a clinically important difference. For more information about prevalence and its impact on sensitivity and specificity there are a couple of articles in CMAJ [5,6].

3) Imperfect Gold Standard Bias (Copper standard bias): This is what can happen if the ‘gold’ standard is not that good of a test. The test that is used to determine a patient’s true disease status misclassifies some patients. A copper standard can result in more false positives and/or false negatives [4]. The others in this SRMA mention that MRIs could be false positives based upon bone bruising or non-specific signal changes. In addition, CT scans can show vascular channels which can be misinterpreted as a fracture (false positive).

4) Clinical Decision Tool: While each individual exam was not enough to rule out an occult fracture it is possible a combination of tests could work. This would be like the many clinical decision tools the smart people out of Ottawa have created over the years including the ankle, knee, head, c-spine, and subarachnoid hemorrhage We have covered these on the SGEM. I know Dr. Justin Morgenstern from First10EM has some strong thoughts on CDTs and how they are “ruining medicine”.

5) Chronological Bias: This is a form of bias that is not often mentioned. Chronological bias is when there are long gaps between when patients were recruited into a study or when studies were performed. In this case, technology has improved over the 34 years of research (1987-2021). Gone are the days of plain films with “wet reads”. Now we have digital radiology allowing us to change the grey scale, alter the contrast and zoom in on the image.

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We generally agree with the authors conclusions.

SGEM Bottom Line: There was no single physical examination maneuver that can reliably rule-out an occult scaphoid fracture.

Case Resolution: You immobilize the patient with a splint and arrange for him to have follow-up at the fracture clinic.

Dr. Matt Schmitz

Clinical Application: This study confirms that we still do not have a good method of ruling out an occult scaphoid fracture with physical examination alone. Each clinician will need to decide what is the best way forward in managing these patients in their own practice environment. Some places will get an MRI, others a CT, some a bone scan and others will have clinical follow-up in a couple of weeks. Each of these is a reasonable approach to this common injury. In our area it is clinical follow-up with repeat x-rays. This study will not change our local practice.

What Do I Tell the Patient? You have the classic injury called a FOOSH – fall on outstretched hand. This mechanism can break an important wrist bone. The scaphoid bone in the wrist is very important. Plain x-rays often can’t pick up this type of broken bone. The scaphoid bone might still be broken (fractured/cracked) and the x-ray doctor (radiologist) can’t even see the break. We will get you into a splint for pain control and in case it is broken. Acetaminophen and/or ibuprofen can be used for pain. The broken bone doctors’ (orthopedic surgeons) office will give you a call to arrange an appointment. They may get a different imaging test (CT scan, MRI or bone scan) to see if your wrist is broken or not.

Keener Kontest: There was no winner last episode. Vicodin is made of hydrocodone which is about six times as potent as codeine. Therefore, it is thought that the manufacturer named it VI (roman numerals for 6) times codin (Codeine). Alas, VIcodin.

Listen to this weeks’ show to hear the keener contest question. If you think you know the answer then send an email to TheSGEM@gmail.com with “keener” in the subject line. The first correct answer will receive a cool skeptical prize. 

Remember to be skeptical of anything you learn, even if you heard it on the Skeptics’ Guide to Emergency Medicine.

References:

1. Carpenter CR, Pines JM, Schuur JD, Muir M, Calfee RP, Raja AS. Adult scaphoid fracture. Acad Emerg Med. 2014 Feb;21(2):101-21. doi: 10.1111/acem.12317. PMID: 24673666.
2. Grover R. Clinical assessment of scaphoid injuries and the detection of fractures. J Hand Surg Br 1996;21:341–3.
3. Pillai A, Jain M. Management of clinical fractures of the scaphoid: results of an audit and literature review. Eur J Emerg Med 2005;12:47–51.
4. Kohn MA, Carpenter CR, Newman TB. Understanding the direction of bias in studies of diagnostic test accuracy. Acad Emerg Med. 2013 Nov;20(11):1194-206. doi: 10.1111/acem.12255. PMID: 24238322.
5. Leeflang MM, Rutjes AW, Reitsma JB, Hooft L, Bossuyt PM. Variation of a test’s sensitivity and specificity with disease prevalence. CMAJ. 2013 Aug 6;185(11):E537-44. doi: 10.1503/cmaj.121286. Epub 2013 Jun 24. PMID: 23798453; PMCID: PMC3735771.
6. Murad MH, Lin L, Chu H, Hasan B, Alsibai RA, Abbas AS, Mustafa RA, Wang Z. The association of sensitivity and specificity with disease prevalence: analysis of 6909 studies of diagnostic test accuracy. CMAJ. 2023 Jul 17;195(27):E925-E931. doi: 10.1503/cmaj.221802. PMID: 37460126; PMCID: PMC10356012.