The biomechanics of the Radio ulnar Joint

By Brett Windsor, PT

 

I had the opportunity to discuss the superior radio-ulnar joint with a colleague yesterday in the context of NAIOMT’s written exams. It appears, at least anecdotally, that students are increasingly performing poorly in the area of detailed joint biomechanics. Are we not teaching it well? Are students not studying the detail enough? Somewhere in between? Perhaps detailed joint biomechanics just aren’t part of the in-crowd anymore. Maybe they’re irrelevant? I know when I went through our system, little was considered more important than detailed joint biomechanics. It was a way of understanding the world and it gave me a base to develop problem solving skills related to movement analysis. I’m glad I took the time. It has helped me tremendously.

Let’s look at the Radio-ulnar joint specifically. It’s a three degrees of freedom joint (take the ulna away). Osteokinematically, it can spin on its own axis. It can flex and extend, it can adduct and abduct (take the ulna away). Arthrokinematically, it seems logical that the joint does indeed glide superiorly on the capitulum with flexion, and it glides inferiorly on the capitulum with extension. But are there glides accessory to this? What about supination and pronation? I was always taught that there is a postero-lateral glide with pronation and an antero-medial glide with supination. Is this true? Clinically, it has always seemed as though these movements could be felt.

However, I was in the anatomy lab yesterday and got the opportunity to dissect a few elbows. Interestingly, 2 of them had severe arthritis in the elbow joint. One had a tumor in the lateral compartment. Most of the rest had fairly pristine looking joints. After removing the muscle tissue to isolate the joint, pronation and supination both appeared to produce only a spin on the axis of the radius. There were no adjunct or associated glides. None at all. It was only after the annular ligament was cut that the joint become somewhat more unstable and further glides were seen with movement of the joint. Also interesting was how little lateral gapping was available in the joint when the lateral collateral and annular ligaments were intact. None. Only flexion-extension and rotation. It’s a remarkably stable joint – most vulnerable of course to tractional forces along the long axis of the radius…nursemaids elbow.

This was far from a scientific study…and I’m no anatomical dissection expert for sure…but it was interesting how what I saw was consistently different than what I was taught.

So…how important are biomechanics in the education of manual therapists? What do they mean to you? Should we get ‘back to the detail? Or should we move on….

Best regards

Brett

2 thoughts on “The biomechanics of the Radio ulnar Joint

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  2. Do you think the inherent tissue quality (lack of tissue extensibility for example and lack of a coordinated nervous system) of cadavers could have impacted your inability to see that movement compared to what we see in a live model?

    Like

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