title: Advanced age diminishes tendon-to-bone healing in a rat model of rotator cuff repair.
abstract: BACKGROUND
  Advanced patient age is associated with recurrent tearing and failure of rotator cuff repairs clinically; however, basic science studies have not evaluated the influence of aging on tendon-to-bone healing after rotator cuff repair in an animal model. Hypothesis/
  
  
  OBJECTIVE
  This study examined the effect of aging on tendon-to-bone healing in an established rat model of rotator cuff repair using the aged animal colony from the National Institute on Aging of the National Institutes of Health. The authors hypothesized that normal aging decreases biomechanical strength and histologic organization at the tendon-to-bone junction after acute repair.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  In 56 F344xBN rats, 28 old and 28 young (24 and 8 months of age, respectively), the supraspinatus tendon was transected and repaired. At 2 or 8 weeks after surgery, shoulder specimens underwent biomechanical testing to compare load-to-failure and load-relaxation response between age groups. Histologic sections of the tendon-to-bone interface were assessed with hematoxylin and eosin staining, and collagen fiber organization was assessed by semiquantitative analysis of picrosirius red birefringence under polarized light.
  
  
  RESULTS
  Peak failure load was similar between young and old animals at 2 weeks after repair (31% vs 26% of age-matched uninjured controls, respectively; P > .05) but significantly higher in young animals compared with old animals 8 weeks after repair (86% vs 65% of age-matched uninjured controls, respectively; P < .01). Eight weeks after repair, fibroblasts appeared more organized and uniformly aligned in young animals on hematoxylin and eosin slides compared with old animals. Collagen birefringence analysis of the tendon-to-bone junction demonstrated that young animals had increased collagen fiber organization and similar histologic structure compared with age-matched controls (53.7 ± 2.4 gray scales; P > .05). In contrast, old animals had decreased collagen fiber organization and altered structure compared with age-matched controls (49.8 ± 3.1 gray scales; P < .01).
  
  
  CONCLUSIONS
  In a rat model of aging, old animals demonstrated diminished tendon-to-bone healing after rotator cuff injury and repair. Old animals had significantly decreased failure strength and collagen fiber organization at the tendon-to-bone junction compared with young animals. This study implies that animal age may need to be considered in future studies of rotator cuff repair in animal models.
  
  
  CONCLUSIONS
  With increasing age and activity level of the population, the incidence of rotator cuff tears is predicted to rise. Despite advances in rotator cuff repair technique, the retear rate remains specifically high in elderly patients. The findings of this research suggest that aging negatively influences tendon-to-bone healing after rotator cuff repair in a validated animal model.
authors: Johannes F. Plate, Department of Orthopaedic Surgery, Wake Forest School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA. jplate@wakehealth.edu).
authors: Johannes F
authors: JF
authors: Plate
authors: Philip J
authors: PJ
authors: Brown
authors: Jordan
authors: J
authors: Walters
authors: John A
authors: JA
authors: Clark
authors: Thomas L
authors: TL
authors: Smith
authors: Michael T
authors: MT
authors: Freehill
authors: Christopher J
authors: CJ
authors: Tuohy
authors: Joel D
authors: JD
authors: Stitzel
authors: Sandeep
authors: S
authors: Mannava
mesh_terms: D000367:Age Factors; D000818:Animals; D001178:Arthroplasty; D001696:Biomechanical Phenomena; D003094:Collagen / Q000502:physiology; D004195:Disease Models, Animal; D006811:Humerus / Q000503:physiopathology / Q000601:surgery*; D051381:Rats; D011916:Rats, Inbred F344; D017006:Rotator Cuff / Q000503:physiopathology / Q000601:surgery*; D013314:Stress, Mechanical; D014945:Wound Healing / Q000502:physiology*
chemical_list: D003094:Collagen
keywords: aging; biomechanics; elderly; quasi-linear viscoelastic; rehabilitation; rotator cuff tear; shoulder