Tensioning of anterior cruciate ligament hamstring grafts: comparing equal tension versus equal stress.
OBJECTIVE
A biomechanical study was undertaken to determine whether equal-stress or equal-tension tensioning of anterior cruciate ligament 4-stranded semitendinosus and gracilis grafts provides a stronger graft construct when testing to ultimate failure.


METHODS
Eighteen fresh-frozen cadaveric semitendinosus and gracilis tendons were each positioned over a cylinder rod/cryo-clamp connected to an MTS machine (MTS Systems, Eden Prairie, MN) by another cryo-clamp. In the equal-tension group the 4 strands were equally tensioned by weights. In the equal-stress group a tensioning device applied equal stress based on the cross-sectional areas of the tendons. The tendons were preconditioned with 10 cycles and then tested to failure. Graft creep during the preconditioning cycle was determined by MTS measurement of the change in clamp distance.


RESULTS
The maximum loads of 4-stranded semitendinosus and gracilis grafts tensioned by equal stress were found to be similar to those of the grafts tensioned by equal tension (2,803 +/- 431 N and 2,772 +/- 461 N, respectively). The loads at first failure were 2,640 +/- 468 N and 2,452 +/- 461 N, respectively (P = .17). The preconditioning cycles showed that the equal-stress group resisted graft creep significantly better (P = .0003).


CONCLUSIONS
The strength of the 4-stranded hamstring graft when equally tensioned or equally stressed was equivalent when tested to failure. After 10 preconditioning cycles, equal stress resisted graft creep significantly better. Equal-stress tensioning offers an alternative tensioning method for 4-stranded hamstring grafts.


CONCLUSIONS
Equal-stress tensioning offers an alternative tensioning method for 4-stranded hamstring grafts.
Conner
Chad S
CS
Department of Orthopaedic Surgery and Rehabilitation, The University of Texas Medical Branch, Galveston, TX 77555-0165, USA. csconner@utmb.edu
Morris
Randal P
RP
Vallurupalli
Santaram
S
Buford
William L
WL
Ivey
Frank M
FM
D000328:Adult; D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery* / Q000637:transplantation*; D050376:Bone-Patellar Tendon-Bone Grafting / Q000379:methods*; D002102:Cadaver; D006801:Humans; D008875:Middle Aged; D011093:Polyethylene Terephthalates; D019651:Plastic Surgery Procedures; D013314:Stress, Mechanical; D013537:Sutures; D013710:Tendons / Q000601:surgery / Q000637:transplantation*; D013718:Tensile Strength; D016474:Weight-Bearing
C014534:Ethibond; D011093:Polyethylene Terephthalates