Except from NF260 Osteoarthritic joint pain, published by Wiley, Chichester in May 2004

(The following comments were made after Professor Kenneth Brandt's presentation on the Neuromuscular aspects of OA joint pain, during the meeting on Osteoarthritic joint pain, June 2003)

Herzog: I was interested in your two different categories of people according to how they walk: the diggers and gliders (This refers to work carried out by Dr Eric Radin from 
Tufts University School of Medicine, Tufts University, Marion, Massachusetts, USA). I noticed that even in the diggers where the impact occurred relatively fast, the total load was one times bodyweight. I know from people who run and contact the ground with their heel first that the initial impact is much higher. Would this suggest that if you are a runner who strikes the ground with your heel first, that you are more likely to develop osteoarthritis?

Brandt: The data would suggest that. It isn’t so much the magnitude of the load as the rate of loading. The rabbit experiments support this.

Herzog: We have just finished a small study looking at loading of joints by maximal muscular stimulation, and also by blunt impact. When you match the loading inside the joint to the pressure that goes across the joint, we find that the maximum muscular loading at the maximum rate will not produce cell death whatsoever. However, if you reach the same load in 3ms by impact loading, there is an enormous amount of cell death. These preliminary data would agree with your qualitative argument that the rate of joint loading has a greater influence on the adaptive/degenerative response of articular cartilage than the absolute load. However, we should keep in mind that studies in this area are still preliminary, and the precise link between in vivo joint loading, stress-strain fields inside the joint, and the corresponding biological response of joint structures (such as the articular cartilage) is not known at present.

Brandt: To come back to bone, rapid impulsive loading may also reactivate the secondary centre of ossification, and initiate changes at the tide mark. It affects more than only muscle and cartilage.

Hunter: The heel strike is very interesting. You made a comment that you could negate the effect of the heel strike by anaesthetizing a femoral nerve. Was that purely by way of inactivating a quadriceps muscle? The quadriceps muscle is presumably responsible for that heel strike impulse.

Brandt: Yes, and it attenuates it.

Hunter: Are there other ways that you think the heel strike could be attenuated? 

Brandt: Shoes may make a difference. Radin has designed a study using biofeedback to change diggers into gliders, by placing an accelerometer anchored around the knee that beeps if the knee is loaded too rapidly in gait.

Hunter: I understood that their load through mid-stance was greater, not just on the heel strike.

Brandt: Yes, but the most striking change is the heel strike transient. John O’Connor estimated this to be some 15 times greater in the knees of diggers than of gliders. This would fit the changes seen in the animal models.

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