title: Does core mobility of lumbar total disc arthroplasty influence sagittal and frontal intervertebral displacement? Radiologic comparison with fixed-core prosthesis.
abstract: BACKGROUND
  An artificial disc prosthesis is thought to restore segmental motion in the lumbar spine. However, it is reported that disc prosthesis can increase the intervertebral translation (VT). The concept of the mobile-core prosthesis is to mimic the kinematic effects of the migration of the natural nucleus and therefore core mobility should minimize the VT. This study explored the hypothesis that core translation should influence VT and that a mobile core prosthesis may facilitate physiological motion.
  
  
  METHODS
  Vertebral translation (measured with a new method presented here), core translation, range of motion (ROM), and distribution of flexion-extension were measured on flexion-extension, neutral standing, and lateral bending films in 89 patients (63 mobile-core [M]; 33 fixed-core [F]).
  
  
  RESULTS
  At L4-5 levels the VT with M was lower than with F and similar to the VT of untreated levels. At L5-S1 levels the VT with M was lower than with F but was significantly different compared to untreated levels. At M levels a strong correlation was found between VT and core translation; the VT decreases as the core translation increases. At F levels the VT increases as the ROM increases. No significant difference was found between the ROM of untreated levels and levels implanted with either M or F. Regarding the mobility distribution with M and F we observed a deficit in extension at L5-S1 levels and a similar distribution at L4-5 levels compared to untreated levels.
  
  
  CONCLUSIONS
  The intervertebral mobility was different between M and F. The M at L4-5 levels succeeded to replicate mobility similar to L4-5 untreated levels. The M at L5-S1 succeeded in ROM, but failed regarding VT and mobility distribution. Nevertheless M minimized VT at L5-S1 levels. The F increased VT at both L4-5 and L5-S1.
  
  
  CONCLUSIONS
  This study validates the concept that the core translation of an artificial lumbar disc prosthesis minimizes the VT.
authors: University Hospital - Orthopedic, CHU Hôtel Dieu, Nantes, France.
authors: Joël
authors: J
authors: Delécrin
authors: University Hospital - Orthopedic, Paris Creteil, France.
authors: Jérôme
authors: J
authors: Allain
authors: University Hospital - Neurosurgery, Dijon, France.
authors: Jacques
authors: J
authors: Beaurain
authors: University Hospital - Spine, Strasbourg, France.
authors: Jean-Paul
authors: JP
authors: Steib
authors: Private Hospital - Orthopaedic, Besancon, France.
authors: Hervé
authors: H
authors: Chataigner
authors: Employee, LDR Compagny, Troyes, France.
authors: Lucie
authors: L
authors: Aubourg
authors: Private Hospital - Neurosurgery, Saint Etienne, France.
authors: Jean
authors: J
authors: Huppert
authors: Private Hospital - Orthopaedic, Reims, France.
authors: Marc
authors: M
authors: Ameil
authors: University Hospital - Biostatistic, Nantes, France.
authors: Jean-Michel
authors: JM
authors: Nguyen
keywords: Fixed-core prosthesis; Lumbar segmental motion; Mobile-core prosthesis; Translation measurement method