Impact of Heterotopic Ossification on Range of Motion Following Cervical Disc Replacement

Retrospective cohort study. To evaluate the impact of heterotopic ossification (HO) severity on segmental and global cervical range of motion (ROM) following cervical disc replacement (CDR). Heterotopic ossification is the most commonly reported complication following CDR, with rates ranging from 40% to over 70% at mid-term to long-term follow-up. While high-grade HO is known to restrict motion, the dose-response relationship between HO severity and ROM across multiple spinal levels remains incompletely characterized. Patients who underwent single-level CDR with a minimum one-year follow-up and flexion-extension radiographs were identified from a single-institution database. HO was graded per McAfee (Grade 0-4) and patients were stratified into Grade 0-2 (nonsevere HO), Grade 3 (severe HO), and Grade 4 (severe HO with bridging ankylosis). ROM was measured at the operative disc space and C2-7 levels at final follow-up. Pairwise Mann-Whitney comparisons were Bonferroni-corrected across six planned tests (three disc space, three C2-7). Reported pairwise P -values reflect adjustment. Kruskal-Wallis omnibus tests were not adjusted. A total of 146 patients met the inclusion criteria (mean age 45.6&#xb1;9.0&#xa0;yr, 63.7% male, mean follow-up 2.8&#xb1;1.9&#xa0;yr). Grade 0-2 HO was present in 88 (60.3%), Grade 3 in 47 (32.2%), and Grade 4 in 11 (7.5%). Disc space ROM differed significantly across groups (Kruskal-Wallis P <0.001): Grade 0-2 mean 9.1&#xb0;&#xb1;5.4&#xb0;, Grade 3 mean 6.2&#xb0;&#xb1;4.2&#xb0; ( P =0.009), Grade 4 mean 1.3&#xb0;&#xb1;2.0&#xb0; ( P <0.001). C2-7 ROM did not differ significantly across HO groups (Kruskal-Wallis P =0.090), with all pairwise comparisons nonsignificant. Higher-grade HO following CDR is associated with a stepwise reduction in disc space ROM. Grade 3 HO significantly reduces segmental motion compared with Grade 0-2, and Grade 4 HO leads to near-complete segmental motion loss. Regardless of HO severity, C2-7 ROM is preserved, potentially suggesting transfer of motion to adjacent segments. Level IV.