Thursday, September 27, 2018 3:35 PM–5:05 PM Section on Motion Technology Abstract Presentations: 135. Influence of preoperative segmental range of motion on postoperative motion after cervical disc arthroplasty using fixed-core, mobile-core and restrained compressible-core prostheses

Abstract

BACKGROUND CONTEXT One of the primary functional goals of cervical total disc arthroplasty (TDA) is to restore pain free physiologic motion at the index level with the premise that it will reduce the incidence of adjacent segment disease. Yet, we do not have enough objective data to understand the influence of preoperative patient-specific parameters on postoperative flexion-extension range of motion (FE-ROM). Cervical disc prostheses have evolved, and prosthesis design is likely to influence postoperative motion. PURPOSE To investigate the influence of preoperative FE-ROM on cervical motion after TDA surgery using fixed-core, mobile-core and restrained compressible-core prostheses. STUDY DESIGN/SETTING Biomechanical investigation using cadaveric cervical spine specimens. PATIENT SAMPLE A total of 65 cervical motion segments from 44 male and female donors. OUTCOME MEASURES Flexion-extension ROM (degrees) before and after TDA. METHODS The motion response of cervical TDA on FE-ROM was investigated using five different cervical disc prostheses classified into three design groups: Fixed-Core (PRODISC C, DISCOVER and PCM): (Age: 56±10, 19M/9F, 28 C5-C6 and 5 C6-C7), Mobile-Core (Mobi-C): (Age: 42±6, 5M/3F, 8 C5-C6 and 8 C6-C7) and Restrained Compressible-Core(M6 C): (Age: 43±5, 5M/3F, 8 C5-C6 and 8 C6-C7). Each cervical spine specimen underwent kinematic testing (FE moment=±1.5 Nm, compressive follower preload=150 N) using the same testing apparatus and protocol. RESULTS Fixed-Core: FE-ROM after TDA was positively correlated with preoperative FE-ROM (R2 = 0.65, p<.0001). Preoperative FE-ROM ranged from 5° to 19°; whereas, motion after disc arthroplasty ranged 2°–23°. The mean increase in FE-ROM was 1.7±2.8° (p=.001). Mobile-Core: FE-ROM after TDA was positively correlated with preoperative FE-ROM (R2 = 0.36, p=.014). Preoperative FE-ROM ranged from 6° to 20°; whereas, motion after disc arthroplasty ranged 8°–24°. The mean increase in FE-ROM was 3.0±3.8° (p=.006). Restrained Compressible-Core:FE-ROM after TDA was not correlated with preoperative FE-ROM (R2 = 0.17, p=.12). Preoperative FE-ROM ranged from 5° to 21°; whereas, motion after disc arthroplasty ranged 8°–17°. The mean decrease in FE-ROM was −1.4±4.1° (p=.19). CONCLUSIONS The biomechanical goal of the TDA surgery is two-fold:1) restore physiologic motion, and 2) maintain stability at the index segment. In the case of a patient with limited mobility at the index segment the prosthesis should increase the segmental motion to within normal physiologic range. On the other hand, if a motion segment is unstable, the TDA should restore stability by eliminating hypermobility. We observed that TDA using either a fixed-core or moving-core design yielded postoperative FE-ROM that was positively and significantly correlated with preoperative FE-ROM (p<.05). That is, the post-TDA motion was not capped; if the preoperative motion was high, on average the post-TDA motion was even higher. Arthroplasty with the mobile-core prosthesis allowed segmental motions far exceeding the physiologic range; with 6/16 implanted segments yielding motions of 20° or greater. Motion after disc arthroplasty using a restrained compressible-core prosthesis was not influenced by preoperative ROM. Segments with limited mobility had increased ROM after TDA and unstable segments showed more controlled motion after TDA. These results suggest an artificial disc that can provide progressive resistance to angular motion like the natural anatomy, can better achieve both biomechanical goals of restoring physiologic motion without sacrificing stability. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs. One of the primary functional goals of cervical total disc arthroplasty (TDA) is to restore pain free physiologic motion at the index level with the premise that it will reduce the incidence of adjacent segment disease. Yet, we do not have enough objective data to understand the influence of preoperative patient-specific parameters on postoperative flexion-extension range of motion (FE-ROM). Cervical disc prostheses have evolved, and prosthesis design is likely to influence postoperative motion. To investigate the influence of preoperative FE-ROM on cervical motion after TDA surgery using fixed-core, mobile-core and restrained compressible-core prostheses. Biomechanical investigation using cadaveric cervical spine specimens. A total of 65 cervical motion segments from 44 male and female donors. Flexion-extension ROM (degrees) before and after TDA. The motion response of cervical TDA on FE-ROM was investigated using five different cervical disc prostheses classified into three design groups: Fixed-Core (PRODISC C, DISCOVER and PCM): (Age: 56±10, 19M/9F, 28 C5-C6 and 5 C6-C7), Mobile-Core (Mobi-C): (Age: 42±6, 5M/3F, 8 C5-C6 and 8 C6-C7) and Restrained Compressible-Core(M6 C): (Age: 43±5, 5M/3F, 8 C5-C6 and 8 C6-C7). Each cervical spine specimen underwent kinematic testing (FE moment=±1.5 Nm, compressive follower preload=150 N) using the same testing apparatus and protocol. Fixed-Core: FE-ROM after TDA was positively correlated with preoperative FE-ROM (R2 = 0.65, p<.0001). Preoperative FE-ROM ranged from 5° to 19°; whereas, motion after disc arthroplasty ranged 2°–23°. The mean increase in FE-ROM was 1.7±2.8° (p=.001). Mobile-Core: FE-ROM after TDA was positively correlated with preoperative FE-ROM (R2 = 0.36, p=.014). Preoperative FE-ROM ranged from 6° to 20°; whereas, motion after disc arthroplasty ranged 8°–24°. The mean increase in FE-ROM was 3.0±3.8° (p=.006). Restrained Compressible-Core:FE-ROM after TDA was not correlated with preoperative FE-ROM (R2 = 0.17, p=.12). Preoperative FE-ROM ranged from 5° to 21°; whereas, motion after disc arthroplasty ranged 8°–17°. The mean decrease in FE-ROM was −1.4±4.1° (p=.19). The biomechanical goal of the TDA surgery is two-fold:1) restore physiologic motion, and 2) maintain stability at the index segment. In the case of a patient with limited mobility at the index segment the prosthesis should increase the segmental motion to within normal physiologic range. On the other hand, if a motion segment is unstable, the TDA should restore stability by eliminating hypermobility. We observed that TDA using either a fixed-core or moving-core design yielded postoperative FE-ROM that was positively and significantly correlated with preoperative FE-ROM (p<.05). That is, the post-TDA motion was not capped; if the preoperative motion was high, on average the post-TDA motion was even higher. Arthroplasty with the mobile-core prosthesis allowed segmental motions far exceeding the physiologic range; with 6/16 implanted segments yielding motions of 20° or greater. Motion after disc arthroplasty using a restrained compressible-core prosthesis was not influenced by preoperative ROM. Segments with limited mobility had increased ROM after TDA and unstable segments showed more controlled motion after TDA. These results suggest an artificial disc that can provide progressive resistance to angular motion like the natural anatomy, can better achieve both biomechanical goals of restoring physiologic motion without sacrificing stability.