title: An analysis of soft tissue allograft anterior cruciate ligament reconstruction in a rabbit model: a short-term study of the use of mesenchymal stem cells to enhance tendon osteointegration.
abstract: BACKGROUND
  Soft tissue allografts are essential for revision and multiple ligament surgeries in the knee, where donor-site morbidity is an issue. However, the use of allografts is associated with a higher failure rate of osteointegration. Mesenchymal stem cells (MSCs) are investigated as potential agents to enhance bone tunnel and tendon healing.
  
  
  OBJECTIVE
  This study was conducted to analyze the effect of coating allografts with MSCs on the quality and rate of osteointegration at the allograft tendon and bone interface, and the biomechanical properties of these enhanced anterior cruciate ligament (ACL) grafts compared with controls.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  Bilateral ACL reconstructions using Achilles tendon allografts were performed in 36 rabbits. On 1 limb, the graft was coated with autogenous MSCs in a fibrin glue carrier, while the contralateral limb served as a control with no MSCs. The reconstructions were assessed histologically and biomechanically at 2, 4, and 8 weeks.
  
  
  RESULTS
  At 8 weeks, histologic analysis of the controls revealed the development of mature scar tissue resembling Sharpey fibers spanning the tendon-bone interface. In contrast, the MSC-enhanced reconstructions showed a mature zone of fibrocartilage blending from bone to the allograft, strongly resembling a normal ACL insertion. On biomechanical testing, the MSC-enhanced grafts had significantly higher load-to-failure rates than controls. However, the stiffness and Young's modulus were lower in the treatment group.
  
  
  CONCLUSIONS
  The application of MSCs at the allograft tendon-bone interface during ACL reconstruction results in the development of an intervening zone of fibrocartilage. The use of MSCs to enhance allograft osteointegration is a novel method offering the potential of more physiologic and earlier healing, although further investigation must be conducted to improve the biomechanical strength.
  
  
  CONCLUSIONS
  Mesenchymal stem cells can improve the biologic properties of soft tissue allograft healing. Combined with the decrease in donor-site morbidity, allografts are a viable choice for the sports medicine surgeon.
authors.affiliation: Department of Orthopaedic Surgery, Alexandra Hospital, Singapore.
authors.forename: Michael Y H
authors.initials: MY
authors.lastname: Soon
authors.forename: Afizah
authors.initials: A
authors.lastname: Hassan
authors.forename: James H P
authors.initials: JH
authors.lastname: Hui
authors.forename: James C H
authors.initials: JC
authors.lastname: Goh
authors.forename: E H
authors.initials: EH
authors.lastname: Lee
mesh_terms: D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D003238:Connective Tissue / Q000601:surgery*; D045164:Mesenchymal Stem Cell Transplantation; D023421:Models, Animal; D017063:Outcome Assessment, Health Care; D011817:Rabbits; D019651:Plastic Surgery Procedures; D012846:Singapore; D014184:Transplantation, Homologous; D014945:Wound Healing / Q000502:physiology