title: Delayed administration of recombinant human parathyroid hormone improves early biomechanical strength in a rat rotator cuff repair model.
abstract: BACKGROUND
  Despite advances in intraoperative techniques, rotator cuff repairs frequently do not heal. Recombinant human parathyroid hormone (rhPTH) has been shown to improve healing at the tendon-to-bone interface in an established acute rat rotator cuff repair model. We hypothesized that administration of rhPTH beginning on postoperative day 7 would result in improved early load to failure after acute rotator cuff repair in an established rat model.
  
  
  METHODS
  Acute rotator cuff repairs were performed in 108 male Sprague-Dawley rats. Fifty-four rats received daily injections of rhPTH beginning on postoperative day 7 until euthanasia or a maximum of 12 weeks postoperatively. The remaining 54 rats received no injections and served as the control group. Animals were euthanized at 2 and 16 weeks postoperatively and evaluated by gross inspection, biomechanical testing, and histologic analysis.
  
  
  RESULTS
  At 2 weeks postoperatively, rats treated with rhPTH demonstrated significantly higher load to failure than controls (10.9 vs. 5.2 N; P = .003). No difference in load to failure was found between the 2 groups at 16 weeks postoperatively, although control repairs more frequently failed at the tendon-to-bone interface (45.5% vs. 22.7%; P = .111). Blood vessel density appeared equivalent between the 2 groups at both time points, but increased intracellular and extracellular vascular endothelial growth factor expression was noted in the rhPTH-treated group at 2 weeks.
  
  
  CONCLUSIONS
  Delayed daily administration of rhPTH resulted in increased early load to failure and equivalent blood vessel density in an acute rotator cuff repair model.
authors.affiliation: Department of Orthopaedics & Rehabilitation, University of Iowa Hospitals and Clinics, Iowa City, IA, USA. Electronic address: kyle-duchman@uiowa.edu.
authors.forename: Kyle R
authors.initials: KR
authors.lastname: Duchman
authors.affiliation: Department of Orthopaedics & Rehabilitation, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.
authors.forename: Jessica E
authors.initials: JE
authors.lastname: Goetz
authors.affiliation: Department of Orthopaedics & Rehabilitation, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.
authors.forename: Bastian U
authors.initials: BU
authors.lastname: Uribe
authors.affiliation: Department of Orthopaedics & Rehabilitation, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Amendola
authors.affiliation: Department of Orthopaedics & Rehabilitation, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Barber
authors.affiliation: Department of Orthopaedics & Rehabilitation, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.
authors.forename: Allison E
authors.initials: AE
authors.lastname: Malandra
authors.affiliation: Department of Orthopaedics & Rehabilitation, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Fredericks
authors.affiliation: Department of Orthopaedics & Rehabilitation, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.
authors.forename: Carolyn M
authors.initials: CM
authors.lastname: Hettrich
mesh_terms: D000818:Animals; D050071:Bone Density Conservation Agents / Q000008:administration & dosage*; D004195:Disease Models, Animal; D004334:Drug Administration Schedule; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D000070636:Rotator Cuff Injuries / Q000188:drug therapy* / Q000503:physiopathology / Q000601:surgery*; D013536:Suture Techniques; D013718:Tensile Strength; D019379:Teriparatide / Q000008:administration & dosage*; D042461:Vascular Endothelial Growth Factor A; D016474:Weight-Bearing; D014945:Wound Healing
chemical_list: D050071:Bone Density Conservation Agents; D042461:Vascular Endothelial Growth Factor A; D019379:Teriparatide
keywords: Rotator cuff repair; biomechanics; parathyroid hormone; rat; rhPTH; tendon healing