Selective changes in size and distribution of fibre types in vastus muscle from cases of different knee joint affections.

Different knee joint affections are apt to initiate different specific atrophy forms in quadriceps muscle. By a biopsy-technique using the histochemical demonstration of ATPase and succinate dehydrogenase fast twitch fibre atrophy can be correlated with increasing age and a moderate impairment but still ambulatory condition. Fast twitch and slow twitch fibres together show atrophy in those cases which are severely impaired and nearly immobilized. An isolated atrophy of slow twitch fibres was found in three patients suffering from frequent sudden short-lasting pain in the knee joint, although this condition may not be alone the cause for slow twitch fibre atrophy. The mechanisms leading to a selective atrophy of muscle fibre types are not fully understood. Nevertheless, a more clear understanding of the nature of skeletal muscle atrophy brought about by joint affections should be of benefit for a better concept of physiotherapeutical approaches: In fast twitch fibre atrophy maximal short lasting contractions followed by rather long periods of recovery should be performed (30). Slow twitch fibre atrophy should be influenced beneficially by chronic submaximal activity (46), whereas both fibre type atrophy should be treated by a combination of isometric techniques and chronic submaximal activities.