title: Quadrupled Hamstring Graft Strength as a Function of Clinical Sizing.
abstract: OBJECTIVE
  This study sought to compare the strength of quadrupled hamstring tendon (QHT) grafts of 6 to 9.5 mm in clinical diameter with that of 10-mm bone-patellar tendon-bone (BPTB) grafts.
  
  
  METHODS
  Twenty cadaveric semitendinosus and gracilis tendons were combined into QHT grafts. These were sized using a standard graft-sizing device and an area micrometer, yielding grafts ranging from 6 to 9.5 mm in diameter. The grafts were tested to failure. Five 10-mm BPTB grafts were also sized and tested.
  
  
  RESULTS
  Clinical sizing did predict the strength of the graft but not profoundly. As a material alone, without consideration of fixation in bone tunnels, QHT grafts were stronger than BPTB grafts. Graft strength decreased with size, but a linear relation between strength and diameter (r(2) = 0.715, P < .001) was found to be as good as the expected quadratic fit (r(2) = 0.709). Compared with BPTB grafts, even the smallest QHT grafts (diameter <6.5 mm) were still significantly stronger than 10-mm BPTB grafts (P = .004). The elastic moduli of the QHT and BPTB grafts were 761 ± 187 MPa and 615 ± 403 MPa, respectively; elongations at failure were 12.0% ± 2.0% and 7.5% ± 1.6%, respectively; and failure stresses were 105 ± 18 MPa and 50 ± 14 MPa, respectively.
  
  
  CONCLUSIONS
  This work shows that a clinical size of QHT grafts of 6 mm in diameter is not a concern regarding the strength itself. For a possible lower-end prediction of acceptable size, assuming that a gracilis-semitendinosus graft would have only the stress of the weakest measured QHT graft of 88 MPa, a graft of 5.5 mm in diameter would suffice, having more strength in newtons than the average patellar tendon.
  
  
  CONCLUSIONS
  Clinically sized QHT grafts have a higher failure strength than 10-mm patellar tendon grafts. Therefore the strength of the graft cannot account for the higher clinical failure rates of smaller hamstring grafts in active patients in clinical studies.
authors: Department of Orthopaedic Surgery, Allegheny General Hospital, Pittsburgh, Pennsylvania, U.S.A.; Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, U.S.A.
authors: Patrick J
authors: PJ
authors: Schimoler
authors: Department of Orthopaedic Surgery, Allegheny General Hospital, Pittsburgh, Pennsylvania, U.S.A.
authors: David T
authors: DT
authors: Braun
authors: Department of Orthopaedic Surgery, Allegheny General Hospital, Pittsburgh, Pennsylvania, U.S.A.; Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, U.S.A.
authors: Mark Carl
authors: MC
authors: Miller
authors: Department of Orthopaedic Surgery, Allegheny General Hospital, Pittsburgh, Pennsylvania, U.S.A.. Electronic address: Sak475@yahoo.com.
authors: Sam
authors: S
authors: Akhavan
mesh_terms: D000328:Adult; D000368:Aged; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods*; D050376:Bone-Patellar Tendon-Bone Grafting / Q000379:methods; D002102:Cadaver; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017847:Patellar Ligament / Q000033:anatomy & histology / Q000502:physiology / Q000637:transplantation; D013710:Tendons / Q000033:anatomy & histology / Q000502:physiology / Q000637:transplantation*; D016474:Weight-Bearing