title: Primary stability of unicompartmental knee arthroplasty under dynamic flexion movement in human femora.
abstract: BACKGROUND
  The objective of our study was to evaluate the impact of a trabecular stem fixation versus a cortical teeth fixation technique on the primary stability of cemented unicompartmental femoral components under dynamic flexion movement loading conditions in human femora.
  
  
  METHODS
  Ten fresh-frozen human knees of a mean donor age of 73.9years were used to perform medial unicompartmental knee arthroplasty under a less invasive parapatellar surgical approach. The femora were divided into two groups of matched pairs based on comparable trabecular bone mineral density. To assess the primary stability, a new method based on a combination of dynamic flexion movement, double-peak loading simulating stair climbing, kinematic analysis of the femoral component migration relative to the bone and an evaluation of the cement layer by fragments cut through the implant-cement-bone interface in the sagittal plane of the medial condyle was introduced.
  
  
  RESULTS
  For the "trabecular stem fixation" technique the mean load to failure was 2340 (SD 650) N and for "cortical teeth fixation" it was 1080 (SD 455) N, with a substantially enhanced dynamic fixation strength for the "trabecular stem fixation" (p=0.008). In the distal area the cement layer of the "trabecular stem fixation" showed a significant decreased thickness compared to the "cortical teeth fixation" (p=0.029), while a substantially deeper cement penetration (p=0.044) has been achieved for the "trabecular stem fixation".
  
  
  CONCLUSIONS
  From our observations, we conclude that there is a significantly enhanced primary stability with a "trabecular stem fixation" compared to a "cortical teeth fixation" technique of cemented unicompartmental femoral components, in terms of dynamic failure load and migration characteristics.
authors.affiliation: Aesculap AG Research & Development,Tuttlingen, Germany; Ludwig Maximilians University Munich, Department of Orthopaedic Surgery, Physical Medicine & Rehabilitation, Campus Grosshadern, Munich, Germany. Electronic address: thomas.grupp@aesculap.de.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Grupp
authors.affiliation: Aesculap AG Research & Development,Tuttlingen, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Holderied
authors.affiliation: Ludwig Maximilians University Munich, Department of Orthopaedic Surgery, Physical Medicine & Rehabilitation, Campus Grosshadern, Munich, Germany.
authors.forename: Matthias F
authors.initials: MF
authors.lastname: Pietschmann
authors.affiliation: Ludwig Maximilians University Munich, Department of Orthopaedic Surgery, Physical Medicine & Rehabilitation, Campus Grosshadern, Munich, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Schröder
authors.affiliation: Tecnológico de Monterrey, Ciudad de México, Mexico.
authors.forename: Angélica P
authors.initials: AP
authors.lastname: Islas Padilla
authors.affiliation: Aesculap AG Research & Development,Tuttlingen, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Schilling
authors.affiliation: Ludwig Maximilians University Munich, Department of Orthopaedic Surgery, Physical Medicine & Rehabilitation, Campus Grosshadern, Munich, Germany.
authors.forename: Volkmar
authors.initials: V
authors.lastname: Jansson
authors.affiliation: Ludwig Maximilians University Munich, Department of Orthopaedic Surgery, Physical Medicine & Rehabilitation, Campus Grosshadern, Munich, Germany.
authors.forename: Peter E
authors.initials: PE
authors.lastname: Müller
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena; D001843:Bone Cements; D015519:Bone Density; D005260:Female; D005269:Femur / Q000502:physiology*; D006801:Humans; D007717:Knee / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009068:Movement; D016059:Range of Motion, Articular; D013718:Tensile Strength
chemical_list: D001843:Bone Cements
keywords: Bone fixation area; Dynamic flexion movement loading conditions; Femoral component; Primary stability; Unicompartmental knee arthroplasty