title: Arthroscopic fixation of matrix-associated autologous chondrocyte implantation: importance of fixation pin angle on joint compression forces.
abstract: OBJECTIVE
  The aim of the study was to investigate the effect of pin fixation perpendicular and 30° tilted to the matrix surface on the joint compression forces.
  
  
  METHODS
  In a porcine knee model, joint compression forces were recorded with a digital pressure sensor above the medial meniscus and with axial compression of 100 N by use of a material testing machine. The forces were recorded for an intact femoral condyle, as well as a standardized cartilage defect of 25 × 20 mm, after matrix-associated autologous chondrocyte implantation (m-ACI) (BioSeed C; Biotissue Technologies, Freiburg, Germany), fixed by use of a conventional suture technique and pin fixation with a biodegradable pin perpendicular and 30° tilted to the matrix surface.
  
  
  RESULTS
  In knees with cartilage defects, the peak compression forces (mean, 824 kPa) were significantly increased compared with the intact knee joint (564 kPa). After m-ACI implantation with a chondral suture (581.3 kPa) and perpendicular pin fixation, the joint compression forces of the cartilage defect were significantly decreased (630.7 kPa). There were no significant differences compared with the intact knee. After 30° tilted pin insertion, mean joint compression forces were significantly increased (1,740 kPa).
  
  
  CONCLUSIONS
  This study shows that after chondral suture and perpendicular pin fixation, there are no increased compression forces in the knee joint in comparison to an intact knee. Thirty degree tilted pin insertion contributes to increased joint compression forces.
  
  
  CONCLUSIONS
  A tilted insertion during pin fixation in m-ACI should be avoided because it may lead to increased joint compression forces, especially after cartilage defect lesions on the tibial side.
authors.affiliation: Department of Trauma-, Hand- and Reconstructive Surgery, Westfaelische Wilhelms-University Muenster, Muenster, Germany. Mirco.Herbort@ukmuenster.de
authors.forename: Mirco
authors.initials: M
authors.lastname: Herbort
authors.forename: Sandra
authors.initials: S
authors.lastname: Zelle
authors.forename: Dieter
authors.initials: D
authors.lastname: Rosenbaum
authors.forename: Nani
authors.initials: N
authors.lastname: Osada
authors.forename: Michael
authors.initials: M
authors.lastname: Raschke
authors.forename: Wolf
authors.initials: W
authors.lastname: Petersen
authors.forename: Thore
authors.initials: T
authors.lastname: Zantop
mesh_terms: D020341:Absorbable Implants; D000818:Animals; D001182:Arthroscopy / Q000379:methods*; D001696:Biomechanical Phenomena; D001857:Bone Matrix / Q000637:transplantation*; D001858:Bone Nails; D002358:Cartilage, Articular / Q000293:injuries / Q000503:physiopathology / Q000601:surgery*; D019902:Chondrocytes / Q000637:transplantation*; D004195:Disease Models, Animal; D007718:Knee Injuries / Q000503:physiopathology / Q000601:surgery*; D011474:Prosthesis Design; D013536:Suture Techniques / Q000295:instrumentation*; D013552:Swine; D013977:Tibia / Q000601:surgery; D014182:Transplantation, Autologous