Thursday, July 12, 2012

Snuffbox tenderness: The D-dimer of orthopedics.

The conventional wisdom goes something like this:
Scaphoid fractures are a huge pitfall in emergency medicine. They can be subtle, and easily missed on the x-ray. If you find any tenderness in the anatomic snuffbox, you need to place a thumb spica splint, and have the patient referred to get a repeat x-ray in 7-10 days.
Bollocks. Pure felgercarb.

In a way, the EM approach to the suspected scaphoid fracture is a lot like our approach to the suspected PE. Based on data from the 60s and before, clinicians believe that a disease is difficult to clinically diagnose, radiographically elusive, and requires maximal therapy to avoid devastating outcomes. Some believe that new technologies and tests will provide an solution.

Maybe. But before we try to spend and irradiate our way out of this, let's take a step back, and look at some clinical wisdom you may not have heard about. Research that questions the "conventional wisdom."

And what better fount of conventional wisdom is there, than UpToDate? Let us examine some of the standard clinical advice from the article "Scaphoid Fractures."

Myth 1. Snuffbox tenderness is the cornerstone of diagnosis.
At Yale, there is no shortage of tweed-wearing attendings who solemnly intone rubbish about the decline of the physical exam, about the master diagnosticians of yesteryear, blah, blah, blah...

Cute. Now let's actually look inside.

Hey, you know why we use the ultrasound? Because the physical exams for AAA, CHF, peritoneal blood and gallstones aren't so good, that's why.

Uh, better stop tapping.
Many clinicians cannot recall any other test for scaphoid injury aside from snuffbox tenderness, and this isn't good, because the physical exam is key in determining your clinical suspicion here. This is also a problem since snuffbox tenderness is a lousy test, by itself.

UpToDate, however, assigns it a central role, despite having mentioned other exam techniques (my emphasis):
"Scaphoid fractures are often occult and a high index of suspicion should be maintained for any patient with wrist pain following trauma. Any tenderness in the snuffbox should be treated as a scaphoid fracture until proven otherwise."  (UTD)
This is unfortunate advice, since snuffbox tenderness, while usually very sensitive, is utterly non-specific. Parvizi 1998 found it to be only 19% specific, while Pillai 2005 only found 7% specificity!  Grover 1996 found 29%, and Freeland 1989 must have had a very light touch, determining a specificity of 40%. This makes the d-dimer look good.

With these shortcomings in mind, there are two other important exam techniques you should know:
  • Axial compression/impaction - Pressure is exerted in-line with the extended thumb, towards the radius. 
  • Tubercle tenderness - Palpate the bony prominence found on the distal flexor crease of the wrist. It is especially pronounced when the wrist is radially deviated and extended.
These aren't just "nice to know," or for historical interest. They might keep you from needlessly working patients up for fractures they don't have.

For instance, tubercle tenderness can be much more specific for fracture, but just as sensitive, according to Freeland 1989 and Parvizi 1998. Along the same lines, Grover 1996 found that the axial compression test was 80% specific, and 100% sensitive.

Parvizi 1998 found, in fact, that requiring a patient to be positive for all 3 exams would still be perfectly sensitive, while boosting specificity to 74%.

Myth 2. Despite negative intial x-rays, 10-25% of patients will have occult scaphoid fractures.
This actually phrased as
"[Splinting] of symptomatic patients with negative x-rays ... may result in approximately 75 to 90 percent of patients being immobilized for a week or more, [needlessly]." (UTD)
 Twenty five percent is a high number, and certainly would justify wrist immobilization if there's any doubt about the diagnosis. It would suggest that radiography is practically useless to detect fractures.

Except that Grover 1996 found that, of the 29 patients who had a scaphoid fracture in their series, all but one was picked up on the initial set of x-rays. Pillai 2005 only had a 7% rate of "occult" scaphoid fracture, while Duncan 1985 saw that none of their 108 patients had an "occult" fracture on follow-up.

So, your mileage may vary, but if both you and the radiologist don't see a fracture, you can feel pretty good about that.

Myth 3. If you don't immobilize the scaphoid soon, there is a huge risk of devastating complications.
The problem with a missed fracture is that non- or mal-union may cause the scaphoid to necrose, which leads to terrible functional outcomes. This is not rare, and it has lead to the perception that immobilization of the wrist needs to take precedence over all other considerations, such as cost, time off from work, and discomfort.
"[N]onunion rates can reach 40 percent when diagnosis and treatment are delayed by four weeks."(UTD)
The reference for this statement, Langhoff 1988, looked at a series of 289 scaphoid fractures. While there was an overall rate of non-union of 3-9%, they found no increase in this rate if the wrist was immobilized up to 28 days following the injury. On the other hand, after 28 days the rate of complications went up. The authors went on to conclude (my emphasis):
"As fractures not visible at the primary X-ray examination were identical with the rest as regards localization and healing characteristics, we assume that these fractures will behave in the same way when subjected to a delay of immobilization of less than four weeks. We therefore consider it unnecessary to immobilize the wrist when there is clinical suspicion of a fracture, but it is not demonstrable at X-ray examination."
They do consider it appropriate to obtain repeat x-rays at 2 weeks if clinical suspicion exists, and forgo immobilization until then.

Myth 4. The presumed scaphoid fracture must be immobilized in a thumb-spica splint.
Well, if my first 2 points are true, this is redundant. But for the sake of argument...
"When a definitive diagnosis cannot be determined at presentation and a scaphoid fracture is suspected on clinical grounds, even if radiographs are negative, the patient should be placed in a thumb spica splint or preferably, a thumb spica cast until a definitive imaging study can be performed." (UTD)
This is a pain in the ass to apply, and probably even worse to wear for the next 10 days, while you try to get into ortho clinic. Good luck using your hand for anything beyond a regal wave.

Hello!

Clay 1991 looked at patients with radiographic fractures, and randomized them to either a "Colles" cast, with the thumb waggling free, or a standard thumb spica.



The nonunion rate was the same in both groups.

Okay, maybe we don't need to immobilize the thumb. But surely we need a hard splint of some sort!

Eh, maybe not. Sjolin 1988 randomized patients with a clinical suspicion for scaphoid fracture, but negative x-rays,, to receive either a dorsal splint (no thumb immobilization) or a "supportive bandage" that could be removed for ADLs.

Everyone got rechecked in 2 weeks, and while there was no difference in complications (all fractures were incomplete or small avulsions), the bandage people were able to go back to work a lot sooner.

And residents need to be able to use their fingers!

2 comments:

  1. Brooks..thanks for including links to the references... must be a PITA, but it's really helpful for making sure you're not *completely* FOS. Great post! --Brock

    ReplyDelete
    Replies
    1. It's what I aspire to - being incompletely FOS!

      Delete