The Effect Of Heterotopic Ossification On The Mid-term Efficacy Of Prestige LP Cervical Disc Arthroplasty

Objective:To evaluate the incidence and feature of heterotopic ossification( HO) in single-level Prestige LP cervical disc arthroplasty(CDA).To identify the relationship between the occurrence and grading of HO and mid-term efficacy of CDA.Method:A retrospective study of 29 patients( 20 myelopathy and 9radiculopathy) undergoing single-level Prestige LP disc arthroplasty between June 2009 and December 2013. All the patients had been followed up for more than 2 years and less than 6 years. There were 19 males and 10 females with an average age of( 45.4±7.6) years old(range, 28-58years).Clinical symptoms were evaluated using neck and arm visual analog scale(VAS) scores and Japanese orthopaedic association scores(JOA).Functional outcomes were measured using Neck Disability Index(NDI) scores.Opreation segmental Range of motion(ROM) were evaluated with follow-up dynamic X-ray.Occurrence of HO was investigated with the McAfee classification on the follow-up cervical lateral X-ray. The VAS,NDI,JOA and ROM were evaluated in correlation with the occurrence andgrading of HO at mid-term follow-up.Results:Twenty-nine patients were followed up 24~62 months(mean,31.5±10.4 months). A total of 14 HOs were detectable in 29 treated patients(48.2%). Grade ⅠHO occurred in 4 patients(13.8%),gradeⅡHO occurred in 5 patients( 17.2%), gradeⅢ HO occurred in 4 patients(13.8%),gradeⅣ HO occurred in 1 patient(3.4%).The clinical outcomes and operation segmental ROM were not significantly correlated with the occurrence of HO at mid-term follow-up.But the patients with high grade HO(gradeⅢ and gradeⅣ)had a high scores of neck VAS and NDI than non-HO and low grade HO( gradeⅠ and gradeⅡ) patients at mid-term follow-up(P<0.05).The restriction of the operation segmental ROM only present in patients with high grade HO(P<0.05).Conclusion:The incidence of HO after single-level Prestige LP disc arthroplsty is relatively high.However,the occurrence of HO has no significantly effect on clinical outcomes and operation segmental ROM at mid-term follow-up. The reverse effect is more likely basis on the severity and the portion of high grade HO than the occurrence of HO.