671 - In vivo Study on the Effect of Cervical Arthroplasty on Cervical Spine...

General Session: Cervical Degenerative

Presented by: O.L. Alves - View Audio/Video Presentation (Members Only)


O.L. Alves(1), R. Reinas(1), D. Kitumba(1), F. Pagaimo(2)

(1) Centro Hospitalar de Gaia/ Espinho, Neurocirurgia, Gaia, Portugal
(2) Universidade de Lisboa, Lisboa, Portugal


Background: Despite being the gold standard treatment for cervical disc herniation, ACDF may be considered a non-physiological procedure as it results in loss of segmental motion and induces biomechanical changes at adjacent disc levels. The purpose of this study is to investigate the effect of cervical arthroplasty on cervical spine disc center of rotation and range of motion at instrumented and adjacent levels

Material and Methods: Thirty-one patients were submitted to one or more cervical arthroplasties with M6. Radiological parameters were measured preoperatively and postoperatively at 6 months, and 1-year FU. Ranges of motion (ROM), global and segmental, and center of rotations (CORs) at instrumented and adjacent levels were analyzed using specific validated motion analysis software (SpineView 2.4)

Results: Thirty-one patients with a mean age of 51.7 (range 35-69) were implanted with forty-six M6 cervical disc prosthesis. Mean FU is 12 months. Fourteen were pure M6 cases, whereas seventeen were hybrid constructs adding fusion to M6. In single level cervical disc prosthesis, CORs at index level tend to locate superior and posterior at 6-months post-operatively normalizing at 1-year. Measuring the distance to an elliptic distribution of normalized asymptomatic confirms the same tendency, from 7% to the ellipse pre-OP to 12% at 6-month (p< 0,05), and 6% at 12-year (p>0,05). Minimal changes at adjacent levels CORs were observed in different time-points. At instrumented level, the mean X-COR was pre- operatively calculated to 34.8 % versus 30.2 % at 6-months and 33.4% at 1-year (p>0,05); the mean Y-COR was preoperatively calculated to -23.5% versus -2 % at 6.months (p< 0,05), and -31.6 % at 1-year (p>0,05). At index level, an increase of ROM from a mean pre-OP of 6º (4-7º) to 11º (6-15º) at 6-months, and 14º (16-12º) at 1-year was observed (p< 0,05), with a non significant decrease at inferior adjacent level ROM from a mean of 7º to 5º and no change at superior adjacent level (mean 11 to 12º) (p>0,05). Implanting a single level cervical disc prosthesis did improve without statistical significance the global range of motion (C2-C7) from 40 to 45º, at pre-OP to 1-year post-OP, respectively (p>0,05). When inserted adjacent to a fusion, M6 arthroplasty tended to normalized the CORs of the index level at 6 months, without affecting the location of CORs of the superior natural level. The ROM remained unchanged both at index and superior adjacent level at 1-year. The decrease at 12months of global ROM (mean 46 to 47º) equals the decrease of ROM at the fusion level (p>0,05). These changes are observed whether M6 is implanted above or below a fusion. In multilevel M6, index levels ROM changes from a mean of 9º to 11º and from 11º to 9º with minimal decrease in ROM at natural superior level (12º to 11ª) (p>0,05).

Conclusions: M6 tends to considerably restore qualitative kinematics in the cervical spine at the index level at 1-year, with minimal changes at adjacent levels. Restoring mobility and CORs at index level and at adjacent levels may elude hypermobility and biomechanical stresses at adjacent levels. The extent of motion was preserved along with quality of motion.