Strain effects of placing an arthroscopic portal through the subscapularis tendon

HypothesisThe biomechanical effects of placing a portal through the subscapularis tendon have not been studied. Our hypothesis is that placing a portal through the subscapularis tendon will affect the strain properties of the tendon.Materials and methodsEight shoulders from deceased donors were dissected to expose the subscapularis musculotendinous unit. The subscapularis muscle was isolated, the arm was locked at neutral (0° abduction, 0° flexion/extension, 0° external rotation/internal rotation), and 3 cables were sutured to the subscapularis musculotendinous junction. Each cable was connected to a static weight. Three differential variable reluctance transducers (DVRTs) from Microstrain were sutured into the subscapularis tendon—superior, inferior, and in line with the proposed 5 o’clock portal. The musculotendinous unit was loaded along its line of action with 3, 9, and then 15 kg. Strain at each DVRT was measured in the native subscapularis tendon at each load level. The same strain measurement was taken after placing and removing a 5-mm suture anchor through the 5 o’clock portal and in the tendon after placing and removing an 8-mm cannula.ResultsPenetrating the subscapularis tendon with either a 5-mm suture anchor or an 8-mm cannula does not produce any statistically significant change in strain compared with the native tendon.ConclusionPlacing an anchor, or even an 8-mm cannulated portal, does not significantly alter the strain properties of the subscapularis tendon. This lack of effect on the strain characteristics of the subscapularis does not preclude the possibility of clinical effects.