title: Comparison of Cobb technique, quantitative motion analysis, and radiostereometric analysis in measurement of segmental range of motions after lumbar total disc arthroplasty.
abstract: METHODS
  Prospective clinical study.
  
  
  OBJECTIVE
  To compare the amount of segmental motion in the sagittal plane after lumbar total disc arthroplasty (TDA) measured by using the Cobb technique, quantitative motion analysis (QMA), and radiostereometric analysis (RSA).
  
  
  BACKGROUND
  The aim of TDA is preservation of motion and therefore essential to properly quantify the motion. Clinically, segmental motion is measured by using the Cobb technique, which involves either the endplates or the implant as radiographic landmarks. This technique has been reported to have large intraobserver and interobserver variability. QMA and RSA are in vivo techniques that can measure the segmental motion with accuracy, but have not been compared with each other or compared with the Cobb technique in the literature.
  
  
  METHODS
  Ten patients (6 males and 4 females, 47 + or - 7 y) with lumbar disc degeneration were surgically treated with ProDisc-L (Synthes Inc). Intraoperatively, tantalum beads were inserted into each vertebra and patients were followed postoperatively at 1 month, 1 year, and 2 years. At each follow-up time-point, biplanar flexion/extension radiographs were obtained and sagittal range of motion (ROM) of the index level was calculated by using the RSA technique. Clinical flexion/extension radiographs were also obtained and the sagittal ROM at the same level was calculated by using a modified Cobb technique. The clinical films were additionally analyzed by Medical Metrics for sagittal ROM using QMA. The results of the 3 measurement techniques were statistically analyzed and compared in pairwise fashion.
  
  
  RESULTS
  A significant difference (P = 0.02) was observed between the Cobb technique (5.9 + or - 4.9) and RSA (3.5 + or - 2.4). A trend (P = 0.069) was also seen between QMA (5.7 + or - 4.7) and RSA. On paired-samples correlation, a significantly high correlation was seen between Cobb technique and QMA (r = 0.868, P < 0.001). A larger variability was seen when using the Cobb technique or QMA in comparison to the RSA.
  
  
  CONCLUSIONS
  Sagittal ROM after TDA was similar between QMA and digital Cobb technique. A larger variability was seen between these techniques and RSA.
authors: Department of Orthopedic Surgery, Asan Medical Center, University of Ulsan, Seoul, South Korea.
authors: Soo-An
authors: SA
authors: Park
authors: Nathaniel R
authors: NR
authors: Ordway
authors: Amir H
authors: AH
authors: Fayyazi
authors: Bruce E
authors: BE
authors: Fredrickson
authors: Hansen A
authors: HA
authors: Yuan
mesh_terms: D000368:Aged; D000886:Anthropometry; D001175:Arthrography / Q000379:methods*; D019643:Arthroplasty, Replacement / Q000379:methods; D001696:Biomechanical Phenomena; D004185:Disability Evaluation; D017586:Diskectomy / Q000295:instrumentation / Q000379:methods; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007403:Intervertebral Disc / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery; D055959:Intervertebral Disc Degeneration / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging* / Q000502:physiology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D018583:Pliability; D011237:Predictive Value of Tests; D011446:Prospective Studies; D019736:Prostheses and Implants / Q000592:standards; D019919:Prosthesis Implantation / Q000379:methods; D011871:Radiology / Q000379:methods; D016059:Range of Motion, Articular / Q000502:physiology*; D020127:Recovery of Function / Q000502:physiology; D016896:Treatment Outcome; D021801:Zygapophyseal Joint / Q000033:anatomy & histology / Q000502:physiology*