title: Which radiographic parameters are linked to failure of a dynamic spinal implant?
abstract: BACKGROUND
  Knowledge about factors leading to failure of posterior dynamic stabilization implants is essential to design future implants and establish surgical indications. Therefore, we analyzed an implant for single-level or hybrid configuration (adjacent to spondylodesis), which was recalled due to high failure rates.
  
  
  OBJECTIVE
  We asked: (1) Were postoperative radiographic changes linked to implant failure? (2) Were radiographic parameters different between the two configurations? And (3) was implant failure related to inferior clinical scores?
  
  
  METHODS
  The implant was used in 18 patients with lumbar single-level spinal stenosis or with (recurrent) disc herniation and concurrent degenerative disc disease and in 22 patients with an initially degenerated segment adjacent and superior to a fusion site. We prospectively obtained preoperative and postoperative (immediate, 6-, 12- and 24-month) clinical and radiographic evaluations; 37 of the 40 patients completed the 24-month followup. Using plain and extension-flexion radiographs, we compared implant failure rates and their association with postoperative implant translation, anterior and posterior disc height, and ROM for each configuration and between configurations. We assessed associations between clinical scores (VAS pain scores for back and leg, Oswestry Disability Index) and implant failure.
  
  
  RESULTS
  Implant failure occurred in 10 of the 37 implants and corresponded to greater posterior disc height (single-level only) and implant translation. Adjacent-segment ROM increases and posterior disc height decreases over time were greater with the hybrid configuration. Implant failure rate related to higher Oswestry Disability Index (single-level only) and higher back pain scores.
  
  
  CONCLUSIONS
  Implant translation is associated with failure likely due to insufficient resistance to shear forces. Load transfer may cause progressive degeneration in the dynamic and adjacent segments, especially in the hybrid configuration.
authors: Center for Musculoskeletal Surgery and Julius Wolff Institute, Klinik für Orthopädie-Charité Campus Mitte, Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117, Berlin, Germany. eike.hoff@charite.de
authors: Eike
authors: E
authors: Hoff
authors: Patrick
authors: P
authors: Strube
authors: Antonius
authors: A
authors: Rohlmann
authors: Christian
authors: C
authors: Gross
authors: Michael
authors: M
authors: Putzier
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D020878:Device Removal; D004185:Disability Evaluation; D019544:Equipment Failure Analysis; D005260:Female; D005858:Germany; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D007405:Intervertebral Disc Displacement / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D057052:Medical Device Recalls; D008875:Middle Aged; D011446:Prospective Studies; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011859:Radiography; D016059:Range of Motion, Articular; D012086:Reoperation; D012720:Severity of Illness Index; D013123:Spinal Fusion / Q000009:adverse effects / Q000295:instrumentation*; D013130:Spinal Stenosis / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D013314:Stress, Mechanical; D013997:Time Factors; D017211:Treatment Failure