Thumbs vs Shoulders

What a good boy!

Those therapists that have written pages of trivia about the instability of the shoulder joint need to take some time out, breathe a little less of their own self-importance, and have a look at the humble thumb. True thumb opposition is a movement unique to humans, and if that's not enough evidence as to why its' stability should rate more highly, it can also take credit for allowing Jack Horner to stuff his face with the best bit of his Christmas pie. Try doing that with your shoulder! 

The thumb carpometacarpal (CMC) joint is a saddle joint. It is capable of 360 degrees of circumduction, as well as abduction, adduction, extension and flexion. It is crucial to good grasp, and essential to pinch. Like the shoulder, it is not solely dependent upon bony congruity for stability, relying significantly upon a network of soft tissue structures. When these structures fail, the stability of the thumb's base is threatened and daily function, let alone sporting function, is significantly impacted.

Not Ivy, but can you see how the downward pressure
 of the bar could force the metacarpal anteriorly?

I see this most usually in older patients who have degenerative osteoarthritis of that CMC joint. Today I saw it in a young, female elite power lifter. At the top of the snatch move apparently, good form combined with normal shoulder bio-mechanics, dictates that the bar with all its weight, rest not in the palm transferring weight down through the arm, but across the first web space. 

For a woman with naturally hyper-mobile joints, this is not ideal. Ivy (not her real name) had developed a subtle palmar instability at the CMC joint in one hand. When under load at the top of the snatch, with the bar's pressure over the distal end of the metacarpal, the joint would feel as if it were about to dislocate anteriorly. It had become painful, and clicky with circumduction. It was perfectly stable with pinch and grip, and her global strength was unaffected, but crucially abductor pollicis longus (APL), extensor pollicis longus and brevis (EPL/B), and extensor carpi radialis brevis (ECRB) were all weak compared to the contra-lateral hand. And surprise, surprise, a national competition was two weeks away.

I did two things, well three really. The first was that I let Ivy educate me in the technique she uses to lift. We then broke down the mechanics of that, and I applied my understanding of anatomy. Based on that, I could explain to Ivy exactly what I felt was happening and why.

The second thing I did was to splint and tape the hand to provide the CMC with the support it was currently lacking. I didn't want a rigid material, so I used a flexible thermoplastic promoted with the potential to enhance joint proprioception. Whether it does or not, an impressive sentence like that is worthy of its' own blog! I then taped in such a way that the CMC had solid AP pressure. Immediately Ivy had relief.

Needs dynamic stability training ASAP.
Might need an opposable thumb first.

Finally, I set Ivy up with a strengthening program which concentrated on the thumb extensors in an attempt to rebuild some of the lost stability. I do think that a lot of why Ivy is having this difficulty is because she is a young woman whose joints are still immature and hypermobile. The problem is that the stresses of her sport have meant that abnormal stress has been placed across a joint that is no longer able to tolerate it. My theory is simple (FYI it's not really my theory. I've borrowed it from Virginia. See the reference below re dynamic stability training for thumbs). If Ivy can strengthen and tighten the muscles that provide her CMC joint with secondary stability, then she can regain control over that joint at the top of the snatch. Then she can take over the world, marry Jack Horner, and become a shoulder physio. 

Look after those fingers,

H

Ref
O'Brien, V., Giveans, M. Effects of a dynamic stability approach in conservative intervention
of the carpometacarpal joint of the thumb: A retrospective study. Journal of Hand therapy (26) 2013 44-52.