title: Biomechanical analysis of subpectoral biceps tenodesis: effect of screw malpositioning on proximal humeral strength.
abstract: BACKGROUND
  Humeral fracture after subpectoral tenodesis of the long head of biceps tendon (LHB) is a rare but devastating complication.
  
  
  OBJECTIVE
  To determine whether malpositioned (laterally eccentric) tenodesis screw placement has an influence on humerus strength reduction compared with central placement.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Two groups, each consisting of 10 matched pairs of human humeri, were used for this study. Biceps tendons were fixed subpectorally with 8-mm screws in unicortical 8-mm sockets. In the first group, the socket was placed concentrically in the bicipital groove and the tendon was fixed with an interference screw. In the second group, the socket was malpositioned 30% eccentrically to the lateral (tension) side of the humerus. Contralateral humeri remained intact as positive controls. Specimens were aligned in 40° of abduction, and a uniaxial compressive force was applied to the humeral head until failure. Strength reduction was reported as percentage reduction in ultimate failure load between paired humeri. Relative defect size was calculated as a percentage of the total humeral width at the height of the tenodesis.
  
  
  RESULTS
  Laterally eccentric malpositioned biceps tenodeses significantly decreased humeral strength compared with intact (mean change, -25%; SD, 23%; P=.017), while concentrically placed biceps tenodeses did not (mean change, -10%; SD, 15%; P=.059). A linear regression between relative defect size and strength reduction in the malpositioned group showed a significant negative linear correlation (beta=-2.577; R2=0.423; P=.042).
  
  
  CONCLUSIONS
  Humeral fracture after subpectoral tenodesis of the LHB is a complication that may be minimized with careful surgical technique. Laterally eccentric malpositioned biceps tenodesis caused significant reduction (25%) in humeral strength, which might be clinically relevant and contribute to postsurgical humeral shaft fracture. Strength reduction was also significantly correlated with relative defect size. Surgeons using this technique should ensure central and orthogonal placement of the socket, especially in smaller individuals. This study lends biomechanical evidence to support the clinical procedure of a correctly, concentrically placed tenodesis screw.
  
  
  CONCLUSIONS
  These biomechanical results indicate that in a clinical setting, special attention should be drawn to patient selection for LHB tenodesis. This study reveals that central screw positioning is critical, particularly in high-impact and overhead athletes, as well as for patients with small humeral widths or osteoporotic bone quality. Alternative surgical options such as smaller screws or other fixation methods might be considered to diminish the postoperative risk of humeral fracture.
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA Department of Trauma Surgery and Sports Traumatology, Medical University Innsbruck, Innsbruck, Austria.
authors.forename: Simon A
authors.initials: SA
authors.lastname: Euler
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Sean D
authors.initials: SD
authors.lastname: Smith
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Brady T
authors.initials: BT
authors.lastname: Williams
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Grant J
authors.initials: GJ
authors.lastname: Dornan
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA The Steadman Clinic, Vail, Colorado, USA drmillett@thesteadmanclinic.com.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Millett
authors.affiliation: Steadman Philippon Research Institute, Vail, Colorado, USA.
authors.forename: Coen A
authors.initials: CA
authors.lastname: Wijdicks
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000009:adverse effects*; D002102:Cadaver; D005260:Female; D006801:Humans; D006810:Humeral Fractures / Q000209:etiology*; D006811:Humerus / Q000033:anatomy & histology / Q000601:surgery; D008297:Male; D019300:Medical Errors / Q000009:adverse effects; D008875:Middle Aged; D013710:Tendons / Q000601:surgery; D053656:Tenodesis / Q000009:adverse effects* / Q000379:methods*
keywords: biceps tendon; humeral strength; interference screw; shoulder