title: Kinematics of a selectively constrained radiolucent anterior lumbar disc: comparisons to hybrid and circumferential fusion.
abstract: BACKGROUND
  Despite encouraging clinical outcomes of one-level total disc replacements reported in literature, there is no compelling evidence regarding the stability following two-level disc replacement and hybrid constructs. The current study is aimed at evaluating the multidirectional kinematics of a two-level disc arthroplasty and hybrid construct with disc replacement adjacent to rigid circumferential fusion, compared to two-level fusion using a novel selectively constrained radiolucent anterior lumbar disc.
  
  
  METHODS
  Nine osteoligamentous lumbosacral spines (L1-S1) were tested in the following sequence: 1) Intact; 2) One-level disc replacement; 3) Hybrid; 4) Two-level disc replacement; and 5) Two-level fusion. Range of motion (at both implanted and adjacent level), and center of rotation in sagittal plane were recorded and calculated.
  
  
  RESULTS
  At the level of implantation, motion was restored when one-level disc replacement was used but tended to decrease with two-level disc arthroplasty. The findings also revealed that both one-level and two-level disc replacement and hybrid constructs did not significantly change adjacent level kinematics compared to the intact condition, whereas the two-level fusion construct demonstrated a significant increase in flexibility at the adjacent level. The location of center of rotation in the sagittal plane at L4-L5 for the one-level disc replacement construct was similar to that of the intact condition.
  
  
  CONCLUSIONS
  The one-level disc arthroplasty tended to mimic a motion profile similar to the intact spine. However, the two-level disc replacement construct tended to reduce motion and clinical stability of a two-level disc arthroplasty requires additional investigation. Hybrid constructs may be used as a surgical alternative for treating two-level lumbar degenerative disc disease.
authors: Resurgens Orthopaedics Spine Center, 270 Chastain Rd, Kennesaw, GA 30067, USA. spinetkd@mindspring.com
authors: Tapan K
authors: TK
authors: Daftari
authors: Suresh R
authors: SR
authors: Chinthakunta
authors: Aditya
authors: A
authors: Ingalhalikar
authors: Manasa
authors: M
authors: Gudipally
authors: Mir
authors: M
authors: Hussain
authors: Saif
authors: S
authors: Khalil
mesh_terms: D000368:Aged; D001178:Arthroplasty / Q000379:methods*; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000473:pathology; D055959:Intervertebral Disc Degeneration / Q000601:surgery; D008022:Ligaments / Q000473:pathology; D008159:Lumbar Vertebrae / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D009038:Motion; D016059:Range of Motion, Articular; D012447:Sacrum / Q000473:pathology*; D013123:Spinal Fusion