The value of the Pfirrmann grading standard for disc degeneration in the quantification of heterotopic ossification after artificial cervical disc replacement / 中华骨科杂志

ABSTRACT

Objective:To explore the value of the Pfirrmann grading standard for disc degeneration in the quantification of heterotopic ossification (HO) after artificial cervical disc replacement (ACDR).Methods:Data of 120 patients who underwent ACDR from January 2009 to December 2016 were retrospectively analyzed. There were 88 males and 32 females with an average age of 43.86±8.69 (range, 27-67) years old. There were 100 single-level replacements (9 Hybrid cases) and 20 double-level replacements (3 Hybrid cases). The occurrence of HO was observed by lateral radiographs of the cervical spine. The HO severity was assessed using the McAfee rating system. Degeneration degrees of cervical intervertebral discs were evaluated by the Pfirrmann grading standard based on the preoperative cervical MRI. The weighted Kappa test was used to analyze the consistency of evaluations between different observers of the Pfirrmann scoring system and the McAfee grading system. Pfirrmann scores for preoperative disc degeneration in the HO and non-HO groups were compared using the t-test. The chi-square test was used to analyze the effect of the Pfirrmann score on the incidence of postoperative segmental HO. The correlation between Pfirrmann score and McAfee grade, as well as postoperative ROM of HO group were analyzed by the Spearman rank-sum test. Quantitative indicators for risks of HO after ACDR surgery were proposed based on the incidence of segment HO in different Pfirrmann score groups. Results:One hundred and twenty patients were followed up for an average of 74.08±28.05 (range, 31-125) months. Based on statistics of cases 2 years after surgery, the overall HO incidence was 31.67% (38/120). The HO incidence was 27% (27/100) and 55% (11/20) for single-level and double-level replacements, respectively. There were 46 replacement segments in the HO group and 94 replacement segments in the non-HO group. The Pfirrmann score of HO group (3.17±1.08) was 25.80% significantly higher than that of the non-HO group (2.52±0.98) ( t=3.46, P=0.01). The incidence of HO in the replacement segment increased significantly with the preoperative Pfirrmann score ( χ2=12.44, P=0.01). The Pfirrmann score of the intervertebral disc in the HO group had a significant positive correlation with the McAfee grade ( R=0.54, P=0.01) and a significant negative correlation with the ROM ( R=-0.75, P=0.01). At 2 years after the operation, when the Pfirrmann score of the intervertebral disc was less than 3, the incidence of HO in the replacement segment was 20.55%(15/73); when the Pfirrmann score was equal to 3, the incidence of HO was 38.46% (10/26); when the Pfirrmann score was greater than 3, HO incidence was 51.22% (21/41). Conclusion:The Pfirrmann score of cervical disc degeneration was significantly related to the incidence of HO, McAfee grade, and ROM in the postoperative replacement segment. The Pfirrmann score of cervical disc degeneration can be used as a quantitativeindicator of HO risk in ACDR.