Anatomic midline marking during cervical arthroplasty with ProDisc-C: an alternative, simple, and reliable method: technical note.

ABSTRACT

STUDY DESIGN: Retrospective study. OBJECTIVE: To report the results of a different, and previously undescribed, technique to anatomically mark the midline during cervical arthroplasty. SUMMARY OF BACKGROUND DATA The ProDisc-C prosthesis should be implanted in the vertebral body midline. Current standard technique for midline marking usually relies on intraoperative fluoroscopy to locate on anteroposterior (AP) x-rays a midpoint between the uncinate processes and superimposed to the intervening spinous process. Nevertheless, uncinate process can be used as anatomic landmarks to size the proper width of the prosthesis and implant a suitable device well centered in the midline. METHODS: Two groups of ProDisc-C prostheses were analyzed and compared for midline alignment. Group 1 68 prostheses were implanted using a different technique to identify the anatomic midline. Soft disc hernia and/or spondylotic disease (whose degree was not a contraindication for arthroplasty), either at single or multiple levels, were the underlying diseases. Group 2 19 ProDisc-C implanted using the standard fluoroscopic technique to mark the midline. RESULTS: Postoperative analysis of AP digital x-rays revealed in group 1a mean difference of -0.35 mm between the 2 halves of the prosthesis' inferior plate in respect to the defined midline. Sixty prostheses (88.2%) had an eccentric position ranging between 0.1 and 2.2 mm. Five prostheses (7.3%) were in a more significantly eccentric position by 4 to 5.5 mm. In 3 cases (4.4%), the eccentric positioning was between 2.5 and 4 mm. SD was + or - 2.18. In group 2, the mean difference was -0.07 mm. Only 1 prosthesis (5.2%) was in eccentric position by 6.14 mm. Five devices (26.3%) were in eccentric position by > or = 2 mm. The remaining 13 prostheses (68.4%) showed an eccentric position ranging between 0.36 and 1.82 mm. SD was + or - 2.02. Statistical analysis was performed using the Student t test. CONCLUSIONS: This study confirms that in cases of soft disc hernia or moderate spondylosis, the anatomic midline marking technique is a safe, reliable, and effective option. It is as accurate as the current fluoroscopic-guided technique and gives the opportunity either to reduce patient's and surgeons' exposure to radiations or to shorten the operation time by reducing the overall fluoroscopy and avoiding performing AP x-rays.