The Impact of Disc Height on Outcomes Following Cervical Disc Replacement: A Systematic Review.

Study design: Systematic review.

Objective: Describe the impact of disc height on outcomes following cervical disc replacement (CDR).

Summary of background data: Implant sizing and positioning may impact outcomes following CDR.

Methods: A systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using the EMBASE and PubMed databases. The goal of this review was to assess the impact of postoperative "disc height" on clinical and radiologic outcomes following CDR.

Results: A total of 12 studies were included in the systematic review. In the literature. "disc height" was assessed using multiple different measures: postoperative disc height (DH; n=4), disc height change (DHC; n=4), degree of disc distraction (DDD; n=2), prosthesis height (PH; n=2), functional spinal unit height (FSUH; n=2), and facet distraction (FD; n=1). DH and DHC were the most common measures studied. DHC was associated with statistically and clinically significant differences in several patient-reported outcomes measures (PROMs). However, DH was not associated with any statistically or clinically significant differences in PROMs. With respect to cervical range of motion (ROM), DHC appeared to demonstrate statistically and clinically relevant differences in some of the studies included in this review, while DH was associated with statistically, but not clinically, significant differences. The majority of studies identified DHC <2 mm as an important cutoff to optimize outcomes.

Conclusions: "Disc height," especially as measured by DHC, may be an important intraoperative consideration when selecting implant size during CDR. Maintaining DHC <2 mm may optimize PROMs and ROM. Improving technique and implant sizing may aid in translating ex vivo advantages in implant mobility to in vivo improvements in ROM and PROMs.