title: Histological changes of semitendinosus autograft after anterior cruciate ligament reconstruction in an immature rabbit model.
abstract: BACKGROUND
  The anterior cruciate ligament (ACL) injury is one of the most common in the knee. Tendons can be used as alternative grafts for ACL repair, with tendon "ligamentization" often reported in literature. The purpose of this study was to evaluate the morphological and histological changes occurring in a semitendinosus tendon (ST) during ACL reconstruction in growing rabbits.
  
  
  METHODS
  Twenty-one 8-week-old New Zealand white rabbits, weighing about 1500 g underwent reconstructive surgery on the right knee. In two cases the left knee was used to verify the normal microstructure of the ACL and ST in rabbits. The rabbits were then randomly divided into seven groups and sacrificed at 1, 4, 6, 8, 12, 24 and 48 weeks after surgery. The specimens were evaluated under light microscopy to analyze the changes in the intra-articular tract of the graft. The evidence of necrosis, neovascularization and organization of the collagen fibers were investigated.
  
  
  RESULTS
  One month after surgery, numerous disorganized fibroblasts and collagenous fibers were identified. A marked reduction of cellular necrosis was observed in the early phase of the neo-ligament healing process. After 4 weeks, these fusiform-like cells became more rounded. By 8 weeks, the collagen fibers had become aligned in parallel with newly formed capillaries and highly differentiated fibroblasts. At 24 and 48 weeks the transplanted tendon differed histologically from both tendon and ligament.
  
  
  CONCLUSIONS
  The data of the present study showed that ligamentization did not occur until at least 24 months post-operatively and, during healing, the grafted tendon assumed a unique micro-architecture that was a middle between a tendon and a ligament. The ACL reconstruction in pediatric age has become more frequent in these past recent years. The use of semitendinosus graft with preservation of its distal attachment should be the gold standard in skeletally immature patients.
authors.affiliation: Orthopaedics and Traumatology Division, Bambino Gesù Children's Hospital, Institute of Scientific Research, Piazza San Onofrio 4, I-00165, Rome, Italy. marco.giordano@opbg.net.
authors.forename: Marco
authors.initials: M
authors.lastname: Giordano
authors.affiliation: Orthopaedics and Traumatology Division, Bambino Gesù Children's Hospital, Institute of Scientific Research, Piazza San Onofrio 4, I-00165, Rome, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Falciglia
authors.affiliation: Orthopaedics and Traumatology Division, Bambino Gesù Children's Hospital, Institute of Scientific Research, Piazza San Onofrio 4, I-00165, Rome, Italy.
authors.forename: Alessia
authors.initials: A
authors.lastname: Poggiaroni
authors.affiliation: Orthopaedics and Traumatology Division, Bambino Gesù Children's Hospital, Institute of Scientific Research, Piazza San Onofrio 4, I-00165, Rome, Italy.
authors.forename: Angelo Gabriele
authors.initials: AG
authors.lastname: Aulisa
authors.affiliation: Orthopaedics and Traumatology Division, Bambino Gesù Children's Hospital, Institute of Scientific Research, Piazza San Onofrio 4, I-00165, Rome, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Savignoni
authors.affiliation: Orthopaedics and Traumatology Division, Bambino Gesù Children's Hospital, Institute of Scientific Research, Piazza San Onofrio 4, I-00165, Rome, Italy.|University of Cassino (FR), Cassino, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Guzzanti
keywords: Anterior cruciate ligament; Immature animal models; Intra-articular tract; Ligamentization; Semitendinosus tendon