title: Comparison of the efficiency of an extra-articular absorber system and high tibial osteotomy for unloading the medial knee compartment: an in vitro study.
abstract: OBJECTIVE
  The unloading effect of an extra-articular absorber system on the knee joint medial compartment was compared with high tibial osteotomy (HTO) under physiological conditions in vitro.
  
  
  METHODS
  Seven fresh-frozen cadaveric knees were used to test isokinetic flexion-extension motions under physiological loading using a biomechanical knee simulator. Tibiofemoral area contact and peak contact pressures were measured using pressure-sensitive film in the untreated medial compartment. Pressures were measured after KineSpring System implantation and HTO (5° and 10° correction angles) performed with an angular-stable internal fixator (Tomofix).
  
  
  RESULTS
  Implantation of the unloading device resulted in significantly decreased medial compartment area contact pressure (Δ0.02 ± 0.01 MPa, p = 0.001) and peak contact pressure (Δ0.3 ± 0.1 MPa, p = 0.001) compared with the first test cycle results in the untreated knee. HTO significantly decreased the pressure (p = 0.001). Compared with the first test cycle, HTO (5° correction angle) decreased the mean contact pressure by Δ0.03 ± 0.01 MPa and peak contact pressure by Δ0.3 ± 0.01 MPa. With a 10° correction angle, HTO decreased contact pressure by Δ0.04 ± 0.02 MPa and peak contact pressure by Δ0.4 ± 0.1 MPa compared with that at the 5° correction angle.
  
  
  CONCLUSIONS
  Implantation of an extra-capsular unloading device resulted in a significant unloading effect on the medial compartment comparable to that achieved with HTO at 5° and 10° correction angles. Thus, implantation of an extra-articular, extra-capsular absorber could become the method of choice when treating patients with unicompartmental osteoarthritis that cannot be adequately treated by HTO because of their straight-leg axis.
authors.affiliation: Department of Orthopedic Surgery and Traumatology, Clinic of Orthopedic Surgery and Traumatology, Freiburg University Hospital, Hugstetter Str. 55, 79098, Freiburg, Germany. gerrit.bode@uniklinik-freiburg.de.
authors.forename: Gerrit
authors.identifier: http://orcid.org/0000-0001-5788-6875
authors.initials: G
authors.lastname: Bode
authors.affiliation: Department of Orthopedic Surgery and Traumatology, Clinic of Orthopedic Surgery and Traumatology, Freiburg University Hospital, Hugstetter Str. 55, 79098, Freiburg, Germany.
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Kloos
authors.affiliation: Department of Orthopedic Surgery and Traumatology, Clinic of Orthopedic Surgery and Traumatology, Freiburg University Hospital, Hugstetter Str. 55, 79098, Freiburg, Germany.
authors.forename: Matthias J
authors.initials: MJ
authors.lastname: Feucht
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Hannover, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Fleischer
authors.affiliation: Department of Orthopedic Surgery and Traumatology, Clinic of Orthopedic Surgery and Traumatology, Freiburg University Hospital, Hugstetter Str. 55, 79098, Freiburg, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Südkamp
authors.affiliation: Department of Orthopedic Surgery and Traumatology, Clinic of Orthopedic Surgery and Traumatology, Freiburg University Hospital, Hugstetter Str. 55, 79098, Freiburg, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Niemeyer
authors.affiliation: Department of Orthopedic Surgery, Hannover Medical School, Hannover, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Becher
mesh_terms: D000368:Aged; D002102:Cadaver; D006801:Humans; D007719:Knee Joint / Q000601:surgery; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery*; D010027:Osteotomy / Q000379:methods*; D011312:Pressure; D012107:Research Design; D012399:Rotation; D013977:Tibia / Q000601:surgery*
keywords: Medial compartment; Osteotomy; Unicompartmental osteoarthritis; Unloading