The tangential treasure trove hidden in one peer-reviewed research article

I mentioned in my last post that I am only working 20 hours/week. So, what am I *doing* for those 20 fabulous hours? Reading research articles! PubMed, GoogleScholar, and ILL all day, accompanied by several cups of delicious (i.e. not from a crusty lab coffeepot) coffee.

A little background: This past Fall I was only TAing part-time (~13 hrs/week) and was in rather uncomfortable financial straits after missing my thesis deadline and unexpectedly needing to pay for an additional 3-credit semester. I was fortunate to get an internship with an amazing start-up company that is developing patient education/health communication apps for medical professionals. They are basically taking those standard health info pamphlets that doctor’s offices and student health centers hand out and turning them into interactive iPad apps full of really brilliant 3-D animations and other nifty tools to allow clinicians to more effectively communicate with patients. My role is to go through the medical research literature and pull out data on outcomes (success rates, side effects, etc) for different treatment routes for various medical conditions.

I have extensive experience with the diving-into-the-literature-and-pulling-out-important-bits part of the work, but hadn’t done much with clinical research literature. It’s been a great learning opportunity. Reading about such a broad range of conditions and treatments is giving me a great overview of what conditions and treatments are really lacking in research, as well as where the more challenging problems exist in various medical fields.

On occasion, the frustration of a sparsely researched condition combined with the slight tedium of searching through mounds of articles can be frustrating. I usually deal with this by going off-the-clock for a few minutes and allowing myself to do fun things, like browsing interesting surgical images, or wandering off down the literature trail of an interesting tidbit.

This second boredom-busting method led to the inspiration for this post. I started off in a typical article about the effectiveness of taping for flexor tendon pulley tears in rock climbers, and ended up learning fabulous facts and theories about bat (the flying mammal kind) toe flexor tendon adaptations!

This journey started as I was skimming through Impact of Taping After Finger Flexor Tendon Pulley Ruptures in Rock Climbers, by Isabelle Schoffl et al., in which the authors bravely discuss gruesome finger injuries without letting even a hit of discomfort or disgust creep into their writing. (In contrast, there’s this Reddit thread with a lovely video in which you can hear someone’s flexor tendon pulley tearing with an audible snap. Ugh…)

Here’s a nice illustration (from climbing blog Crux Crush) of what this ‘snap’ means anatomically and what Schoffl et al. were looking at preventing/correcting via athletic taping techniques:


The athletic tape typical wraps around the phalanxes (finger bones), applying pressure over the tendon and (hopefully) preventing bowstringing where the tendon moves away from the phalanx. Usually the flexor tendon sheaths (A1 – A5) do this job – here they are all torn up (A2, A3 in this figure).

Here’s a view of a proximal flexor tendon pulley injury (A2) as it would look for a person trying to flex their finger (from this article in the Indian Journal of Plastic Surgery):


Eeesh. I’m usually not too squeamish, but hand injuries make me a little squirmy.

Anyhow, the article by Schoffl et al. was focused on testing new and existing finger-taping techniques commonly used by climbers as both preventative measures and post-pulley-tear reinforcement. This part was actually really cool – force diagrams, finger-flexor resistance contraptions, and ultrasound-based tendon-to-bone distance measurement techniques galore! So nifty!

BUT…the really random, unexpected bit occurred in the 2nd of these two sentences:

“The friction between tendon and tendon sheath is maximal over the pulley and especially over the pulley edge (Zhao et al., 2000). This was first observed on chiropterans (Quinn & Baumel, 1993), which are able to use the friction between pulley and tendon in order to dangle without muscular activity.”

Wait, we just went from talking about ouch-painfully-rubbing-tendons to BAT FEET?!? Awesome! And totally unexpected. So, off I went into the Quinn & Baumel article in the Journal of Morphology** to learn more. It turns out that many bats have a cool ratchet system in place between their flexor tendons and the surrounding tendon sheath. The tendon has small bumps, or tubercles, on it right near the base of the digit on the sole/palm side. The corresponding tendon sheath has little ridges, which interact with the tubercles to allow the bat to lock its digits into a flexed position and then hang using its hook-like toes without having to maintain a strong isometric contraction in its flexor muscles. The bat’s body weight holds the ratchet mechanism in place, allowing the bat to eat, groom, and even sleep in the upside-down hanging position. There is a really cool detailed description with magnified images of the tubercles and corresponding ridges here (page 2).

It makes makes me extremely happy (and just a little amused) that the authors of the article on finger taping in human rock climbers decided to stick in a citation related to bat morphology. They could totally have skipped that second sentence, leaving us with the initial statement about high friction over the pulley edges, and left out the slightly tangential link to the bat tendon-locking mechanism paper. However, the little snippet and resulting swerve into the literature of bats and tendon locking mechanisms was perfectly delightful. Not only did the authors succeed in mentioning bats, which are just plain amazing and should be mentioned *whenever possible*, but they also provided the reader with a possible prompt to think about the idea of tendon-pulley friction in a wider context. Personally, this article totally made my day by sending me off into a lunch-hour literature search!

**For any climbers out there, the article by Quinn and Baumel has some fascinating ‘cited-by’ articles in Google Scholar. The citing articles talk about everything from finger taping techniques to estimations of the hanging force produced by tendon-pulley friction in humans. A heads up: there are also lots of slightly jarring cadaver-finger testing images.


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