Understanding Wrist Mechanics: A Long and Winding Road^[*]

The title of this Clinical Perspective has been borrowed from a song by Paul McCartney, a song that emphasizes the difficulties of reaching one's dreams. If I choose that title, it is because it describes quite well my own experience as wrist investigator. Truly, my struggling to understand carpal mechanics has been like a long and winding road; an exciting road, indeed, but one not devoid of unexpected curves and misleading signposts: an endless road for a hopeless wrist enthusiast ([Fig. 1]).

Fig. 1 Preparing a specimen to investigate the effects of partial carpal fusions in the kinematics of the wrist. Biomechanics Laboratory, Mayo Clinic, Rochester MN. October 1987.

I got “infected” by the carpal virus in the early 1980s, when I had the chance of attending a seminar organized by Carlos Irisarri in Madrid about wrist injuries. The program was unusual. I was expecting to learn some tips about the management of scaphoid fractures, but I found myself diving in a pool of unknown terminology: carpal misalignment, segmental instability, rotary subluxation. What a tsunami of thought-provoking concepts! What a challenge for a poorly trained orthopedic surgeon from the suburbs of Barcelona like me! I'll never forget the thrill of questioning Ron Linscheid and Julio Taleisnik that day, Of course, I hardly understood their kind answers: I was too inexperienced to comprehend that new world. Later that week I read the seminal papers of Drs. Linscheid, Dobyns, and Taleisnik about carpal instability,[1] [2] but I could not get the message. If I wanted to swim in that pool, I first needed to learn the basics of swimming. So I went back to the Anatomy department and started from scratch.

The history of how we all got to know the wrist is a long one. Vesalius, in the 16th century, had already made precise drawings of the carpal bones.[3] Their function, however, was pretty much ignored for centuries. See, for instance, the only two lines that Sir Charles Bell wrote in 1833 about the wrist in his classical Bridgewater treatise.[4] “The carpal bones,” he said, “are so closely connected that they form a sort of ball which moves on the end of the radius.” Surprisingly, only 8 years later, a 143-page book about the functional anatomy of the wrist was published by Gustav Günther from Hamburg in Germany.[5] Not only had he spent hours and hours in the laboratory dissecting and observing wrist specimens, but he had measured radii of curvatures at both radiocarpal and midcarpal levels at a time when X-rays were not available. As far as I know, this recently rediscovered book was the first ever published about the wrist.

After Günther's publication, the carpus became a hot issue to explore, and luminaries such as Wilhelm Henke[6] and Friedrich Henle[7] added new discoveries about intracarpal motion. Henke[6] was the first to suggest differential mobility between the proximal and distal rows, while Henle[7] came out with the first description of the two major axes of wrist motion. The discovery of X-rays triggered an explosion of new data in just few years. Bryce[8] was the first to recognize that there is also differential motion between scaphoid and lunate. Corson[9] noticed how important the so-called dart-throwing rotation is in most daily activities. Fick[10] realized that the two axes of wrist rotation were not orthogonal, intersecting on the same plane, but oblique and biplanar. Destot[11] was the first to describe scapholunate dissociation. Yes, those were the early golden years after which the wrist was no longer a block of fixed bones but a fascinating mechanism of small joints, each with its own motion. Unfortunately, the First World War put an end to all of that, and the carpus had to wait 50 more years until it again drew some attention … but this is not the story I wanted to write about. I am not a historian.

The story I promised to report on is my own experience: the story of my journey to understand carpal stability. I could as well have told you about my struggles to understand carpal motion, but the message would have been the same: Knowledge does not progress if one is not willing to reconsider one's viewpoints when new evidence suggests them to be untrue.

In the early 1980s, I read everything about the subject, but my level of dissatisfaction was still high. I wanted certainties, not speculations. Infected as I was by the carpal virus, I needed to see things for myself. Cooney and Chao[12] had, not long before, demonstrated that the amount of force transmitted across the carpus was much larger than previously thought. Indeed, the wrist resists substantial amounts of load, but how can this little joint resist that without yielding? That was one of the questions I was obsessed with. I spent 5 years in the anatomy laboratory of the Universitat Autònoma de Barcelona, and I earned my PhD studying ulnar-side carpal injuries. I struggled to find a mechanical model that could explain carpal stability, and I found it. The scaphoid had to be the key to unveil that riddle. Of course, as stated in Ecclesiastes, “there is nothing new under the sun”—most of my thoughts had been thought already. My long and winding journey had just started. My first stop would be the scaphoid.

Note

^* Adapted from the text of the International Guest Lecture delivered at the 63rd Meeting of the American Society for Surgery of the Hand, Chicago, Illinois, September 2008.

• References

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