Position sense in a damaged knee.

Hypothesis relevant to defective position sense in a damaged knee Sir: Detailed descriptions of personal clinical experience following a knee injury and subsequent surgical intervention' are of great interest in light of recent morphological findings related to the innervation of mammalian knee joints. The general controversy which has surrounded this subject for several decades can be attributed, in part at least, to the dearth of interdisciplinary studies. Morphologists have concentrated almost exclusively on the detailed structure of conventional receptors2 while phys-iologists have given increasing attention to "single unit recording".3 The likelihood that either of these research approaches will arrive at a satisfactory explanation of the problems' seems quite remote. Our current investigation has been based upon a comprehensive, holistic approach to periarticular structures and their neural components. Traditional methods, applied initially, became increasingly unacceptable and entrenched theories of distinguishing between "articular" and "muscular" afferent mechanisms were abandoned. Large specimens for histological study were preferred , comprising, for example, the entire anterior apparatus of mammalian knee joints. These portions of tissue, having the patella as the central feature, were serially sectioned at an optimum thickness of 150 microns for subsequent impregnation with either gold or silver salts using standard procedures for the demonstration of neural components. A conspicuous peripatellar plexus was present in every species examined including mice, rats, rabbits, guinea pigs, cats and man. This consistent finding led to quantitative studies in adult male rats which provided three-dimensional evidence that this network is composed of nerve fibres ranging in diameter from 2 to 8 pm which are arranged in a series of polygonal patterns and extend to a depth of 1-5 mm from the superficial fascia.4 In view of the similarities of arrangements in all the species examined a hypothesis was formulated that the nerve plexus may constitute an integral part of the hierarchy of afferent mechanisms. Its function may be to modulate afferent feedback by acting as a "transducer" in response to distortion during joint movement.5 Functional studies were postponed pending further quantitative analysis subsequent to selective partial denervation experiments. The most dramatic observation in these investigations was the widespread proximo-distal, Wallerian degeneration of fibres within the plexus following transection of the tibial division of the sciatic nerve. This was confirmed in a series of five animals establishing that a substantial majority of afferent fibres which constitute the peri-patellar plexus form accessions which join the posteriorly placed tibial division …