Abstract
To quantify the variation in strain between the deep and superficial layers of the supraspinatus tendon, ten cadaveric shoulders were tested on a purpose built rig. Differential Variable Reluctance Transducers (DVRTs) were inserted into the superficial and deep aspects of the tendon spanning the critical zone. DVRTs accurately measured linear displacement and from this strain was calculated.
The strain was measured for two aspects of supraspinatus action, abduction from 0 to 120 degrees with a tensile load (100 Newtons) and static load increases at zero abduction (20, 50, 100, 150 and 200 Newtons). After preconditioning, ten sets of results were recorded for each load/position.
The hypothesis, there is a statistically significant difference in strain between the superficial/deep supraspinatus tendon during abduction and with static loading, was tested using a one way ANOVA.
During abduction a statistically significant difference in strain was measured between the layers of the supraspinatus tendon at thirty degrees (p=0.000428) and this increased with further abduction.
Tensile loading increased tendon strain more in the deep layer of the tendon. This was statistically significant at loads greater than 150N (p= 0.007).
The variation in properties between the superficial and deep layers of the supraspinatus tendon has been proposed as a cause of differential strain (1). This study confirms statistically different strains between the superficial and deep tendon layers. It is proposed that the resulting shearing effect initiates intratendinous defects and ultimately tears.
The abstracts were prepared by Mr Simon Donell. Correspondence should be addressed to him at the Department of Orthopaedics, Norfolk & Norwich Hospital, Level 4, Centre Block, Colney Lane, Norwich NR4 7UY, United Kingdom.
