Interaction between the supraspinatus and infraspinatus tendons: effect of anterior supraspinatus tendon full-thickness tears on infraspinatus tendon strain.
BACKGROUND
Rotator cuff tears are common and not well-understood shoulder problems. Structural and mechanical inhomogeneity of the supraspinatus tendon complicates accurate prediction of risk of tear propagation and may affect appropriate clinical treatment.


OBJECTIVE
We propose that interactions between the supraspinatus and infraspinatus tendons are critical to load bearing at the glenohumeral joint and warrant investigation.


METHODS
Controlled laboratory study.


METHODS
Principal strains in the infraspinatus tendon of cadaveric human shoulders were evaluated with increasing anterior full-thickness supraspinatus tendon tear sizes and loading to evaluate whether a mechanical interaction between the supraspinatus and infraspinatus tendons exists. A constant nominal load was attached to the infraspinatus throughout all experimental conditions.


RESULTS
Increasing supraspinatus tendon tear width from intact and 33% to 66% and increasing supraspinatus tendon load caused an increase in maximum and a decrease in minimum principal strain in the infraspinatus tendon. Increasing the supraspinatus tendon tear size from intact to 33% of the width had no significant effect on infraspinatus tendon strain.


CONCLUSIONS
Supraspinatus and infraspinatus tendons mechanically interact. The observed significant increase in maximum and decrease in minimum principal strain was concurrent in both the infraspinatus and supraspinatus tendons.


CONCLUSIONS
Changes in infraspinatus tendon strain associated with increases in supraspinatus tendon tear size and loading may shield a torn supraspinatus tendon from further injury or may have an effect on the load-bearing capacity of the infraspinatus tendon. Results also imply that the effect of a small tear that does not compromise the confluent region between the supraspinatus and infraspinatus tendon may be localized, eliminating its effect on infraspinatus tendon strain.
Andarawis-Puri
Nelly
N
McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA 19104, USA.
Ricchetti
Eric T
ET
Soslowsky
Louis J
LJ
D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D008875:Middle Aged; D019637:Orthopedic Procedures; D000070636:Rotator Cuff Injuries; D012421:Rupture / Q000150:complications*; D012785:Shoulder Joint / Q000503:physiopathology; D013180:Sprains and Strains / Q000503:physiopathology; D013708:Tendon Injuries / Q000150:complications*; D016474:Weight-Bearing / Q000502:physiology*