Lightning Podiums: Spinal Gumbo - 803A

Presented by: S. Khayatzadeh

Author(s):

S. Khayatzadeh(1), R. Havey(1), L. Voronov(1), G. Carandang(1), F. Phillips(2), A. Patwardhan(1,3)

(1) Edward Hines Jr. VA Hospital, Musculoskeletal Biomechanics Laboratory, Hines, IL, United States
(2) Rush University Medical Center, Orthopaedic Surgery, Chicago, IL, United States
(3) Loyola University Medical Center, Orthopaedic Surgery & Rehabilitation, Maywood, IL, United States

Abstract

Introduction: Motion segment degeneration adjacent to previous arthrodesis is well documented in the literature. It is reported that up to 25% of patients that have cervical fusion will develop adjacent segment disease (ASD) within 10 years of surgery. Risk factors for ASD are increased stress adjacent to a previous fusion, existence of degenerative changes at an adjacent level prior to the original fusion, and sagittal misalignment of the original fusion. Cervical total disc arthroplasty (TDA) is intended to alleviate adjacent level stresses imposed by fusion. Previous studies have evaluated the kinematics of cervical TDA in the laboratory but do not provide an explanation of how spine kinematics are altered to prevent ASD. With the wide variety of TDA devices available, there is no objective data on how these devices function to alleviate adjacent level stresses. We investigated the sequence of motion segment recruitment in the cervical spine before and after implantation of a mobile-core cervical TDA in 1- and 2-level reconstructions.

Methods: Eight cadaveric specimens (C3-T1) (age:42±6) were tested in flexion-extension (FE) with 150N of follower preload. Specimens were tested intact, after implantation of disc prosthesis (Mobi-C, Zimmer Biomet) at C5-C6 (1-level), and then at C6-C7 (2-level). TDA implantation was performed by an experienced surgeon following the manufacturer's surgical technique. Motion data were analyzed to determine the sequence of segmental motion and percent contribution of the implanted levels for all test conditions.

Results: The FE range of motion (ROM) increased after TDA at C5C6 (13.8±4.2 to 16.8±3.7 degrees, P< 0.05) and at C6C7 (13.7±4.7 to 16.7±4.9 degrees, P< 0.05). While ROM increased after TDA, the percent contribution of segmental motion to total C3-T1 ROM remained constant (25%±3%, 28±5%).Ideally each motion segment makes a constant percent contribution to the total cervical motion as shown in Figure 1A by the intact response. Intact segments deviated from this ideal contribution by 3.9%±2.9% at C5C6 and 6.9%±5.7% at C6C7. After C5C6 TDA mean deviation from ideal motion was 17.3%±9.6% (P< 0.01), after C6C7 TDA deviation was 19.9%±8.3% (P< 0.01).Peak deviation is demonstrated in Figure 1B by a 64% contribution of the implanted segment during a portion of the flexion motion. Intact peak deviation at C5C6 changed from 11%±6% to 35%±20% (P< 0.01) after TDA, and at C6C7 from 20%±13% to 51%±24% (P< 0.01).

Conclusions: Figure1 shows motion contribution from extension to flexion of two C5C6 motion segments intact and after TDA. Both specimens show near constant contribution by intact motion segments suggesting normal healthy motion. Specimen#6 shows nearly constant contribution by the TDA, while Specimen#5 shows non-uniform contribution by the implanted motion segment. This non-uniform contribution suggests delayed motion followed by sudden large segmental motions. Quality of motion of segments implanted with the Mobi-C TDA was variable. Some levels closely mimicked the intact quality while others showed non-physiologic motion and poor quality.

Figure 1