title: Effect of Bone Mineral Density on Rotator Cuff Tear: An Osteoporotic Rabbit Model.
abstract: BACKGROUND
  An increased bone mineral density (BMD) in the proximity to tendon insertion can improve rotator cuff repair and healing. However, how a decrease of BMD in the humeral head affects the biomechanical properties of the rotator cuff tendon is still unclear. Previous studies have demonstrated ovariectomy in animals to lead to osteoporosis and decreased BMD, and Teriparatide (PTH) administration to improve BMD and strength of bone. This study aimed to explore the correlation between humeral head BMD and infraspinatus (ISP) tendon insertion strength, and if an increase in bone quantity of the humeral head can improve the strength of the rotator cuff.
  
  
  METHODS
  Eighteen New England white rabbits were divided into the 3 groups: Control, Ovariectomy-Saline (OVX-Saline), and Ovariectomy-PTH (OVX-PTH). The OVX-Saline group and the OVX-PTH were administered daily saline and Teriparatide injections for 8 weeks starting at 17 weeks of OVX. BMD of the humeral head was measured, the ISP tendon failure load was tested and the failure stress was calculated. One specimen from each group was used for histological analysis. Linear regression analysis was used to derive equations for the BMD and failure stress.
  
  
  RESULTS
  Significant differences were observed in the measured humeral head BMD of the Control and OVX-PTH groups compared to the OVX-Saline group (P = 0.0004 and P = 0.0024, respectively). No significant difference was found in failure stress among the three groups, but an expected trend with the control group and OVX-PTH group presenting higher failure strength compared to the OVX-Saline group. BMD at the humeral head showed a positive linear correlation with stress (r2 = 0.54). Histology results showed the superiority in OVX-PTH group ISP enthesis compared to the OVX-Saline group.
  
  
  CONCLUSIONS
  Bone loss of the humeral head leads to decreased tendon/bone insertion strength of the infraspinatus tendon enthesis. Teriparatide administration can increase bone density of the humeral head and may improve the mechanical properties of the infraspinatus tendon enthesis.
authors.affiliation: Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, Rochester, Minnesota, United States of America; Institute of Orthopaedics, Chinese PLA, Beijing Army General Hospital, Beijing, China.
authors.forename: Xiaobin
authors.initials: X
authors.lastname: Chen
authors.affiliation: Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, Rochester, Minnesota, United States of America; Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota, United States of America.
authors.forename: Hugo
authors.initials: H
authors.lastname: Giambini
authors.affiliation: Department of Radiology, Mayo Clinic, Rochester, Minnesota, United States of America.
authors.forename: Ephraim
authors.initials: E
authors.lastname: Ben-Abraham
authors.affiliation: Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, Rochester, Minnesota, United States of America.
authors.forename: Kai-Nan
authors.initials: KN
authors.lastname: An
authors.affiliation: Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota, United States of America.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Nassr
authors.affiliation: Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, Rochester, Minnesota, United States of America.
authors.forename: Chunfeng
authors.initials: C
authors.lastname: Zhao
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density; D004195:Disease Models, Animal; D005260:Female; D058430:Humeral Head / Q000473:pathology; D006811:Humerus / Q000473:pathology; D016014:Linear Models; D010024:Osteoporosis / Q000378:metabolism*; D010052:Ovariectomy; D011817:Rabbits; D012307:Risk Factors; D017006:Rotator Cuff / Q000503:physiopathology*; D000070636:Rotator Cuff Injuries; D013710:Tendons / Q000503:physiopathology; D019379:Teriparatide / Q000737:chemistry; D014945:Wound Healing
chemical_list: D019379:Teriparatide