Repair of lesser tuberosity osteotomy for shoulder arthroplasty: biomechanical evaluation of the Backpack and Dual Row techniques.
BACKGROUND
Subscapularis dysfunction following total shoulder arthroplasty can result in permanent loss of function. The lesser tuberosity osteotomy (LTO) has been proposed as a method which utilizes bone-to-bone healing to improve subscapularis function. This study evaluates the biomechanical properties of two described techniques for LTO repair. We hypothesized that a Dual Row repair would be stronger and demonstrate less cyclic displacement than a Backpack repair.


METHODS
Ten matched pairs of cadaveric humeri were dissected, leaving the subscapularis intact, and a lesser tuberosity osteotomy was performed. Matched shoulders were randomized to either a Backpack repair or a Dual Row repair. Repairs were subjected to cyclic loading to 180 N for 500 cycles, followed by ramp-up loading to ultimate failure. Clinical failure was defined as displacement >5 mm after 500 cycles.


RESULTS
Displacement after 500 cycles was significantly greater for the Backpack repair (6.9 mm) than for the Dual Row repair (4.6 mm) (P = .007). Most displacement occurred on the first cycle (Backpack, 4.6 mm; Dual Row, 2.1 mm) (P < .001). There was a trend toward a higher clinical failure rate for the Backpack repair (8/10) than the Dual Row repair (3/10). Ultimate tensile strength was significantly greater for the Dual Row repair (632.3 N) than for the Backpack repair (510.9 N) (P = .01).


CONCLUSIONS
The Dual Row technique is significantly stronger and demonstrates less cyclic displacement than the Backpack technique. Clinical studies are needed to determine the impact of LTO repair technique on subscapularis function following shoulder arthroplasty.
Heckman
Daniel S
DS
Department of Orthopaedics, University of North Carolina-Chapel Hill, Chapel Hill, NC, USA. dsheckman11@yahoo.com
Hoover
Stephen A
SA
Weinhold
Paul S
PS
Spang
Jeffrey T
JT
Creighton
R Alexander
RA
D019643:Arthroplasty, Replacement / Q000379:methods*; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D016555:Matched-Pair Analysis; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology / Q000601:surgery; D010027:Osteotomy / Q000379:methods*; D020127:Recovery of Function; D012785:Shoulder Joint / Q000601:surgery; D013536:Suture Techniques; D013718:Tensile Strength