Heterotopic Ossification in Vertebral Interlaminar/Interspinous Instrumentation: Report of a Case
BACKGROUND CONTEXT Heterotopic ossification (HO) is a well-known phenomenon occurring after joint arthroplasty. However, its incidence and clinical effects have not yet been clearly identified with cervical disc replacement. PURPOSE The first aim of this study was to evaluate the incidence of HO in single-level cervical disc replacement. The second aim was to identify the relationship of HO with clinical outcomes and radiological findings. STUDY DESIGN A retrospective study of 48 patients who underwent single-level artificial disc replacement in one of our clinics. PATIENT SAMPLE Between November 2004 and December 2008, 48 consecutive patients underwent single-level cervical artificial disc replacement in Seoul Wooridul Hospital, Seoul, Korea. OUTCOMES MEASURES Clinical outcomes were graded using visual analog scale (VAS) scores (score range, 0-10, with 0 reflecting no pain). Functional outcomes were measured using Oswestry Disability Index (ODI) scores. Radiological outcomes were evaluated with follow-up dynamic X-ray. METHODS Occurrence of HO was investigated with the McAfee classification on the follow-up cervical dynamic X-ray. We also measured cervical range of motion (ROM) to identify HO's biomechanical effects. For the clinical effects, the VAS and the ODI were evaluated in correlation with the occurrence of HO. RESULTS In 48 treated patients, a total of 13 HOs were detectable. Grade 1 and 2 HO occurred in 11 patients and Grade 3 HO in two patients. Mean occurrence of HO was observed on the 11th month after the surgery. HO that led to the restriction of the ROM was not present in any patients. The clinical outcome was not significantly correlated with the occurrence of HO. CONCLUSIONS The overall incidence of HO after cervical artificial disc replacement was relatively high. However, Grade 3 and 4 HO that limit the ROM rarely occurred. Moreover, the occurrence of HO did not affect the clinical symptoms and biomechanical dynamics. A longer follow-up with a larger group of patients should be undertaken, which may demonstrate a higher rate of HO and long-term effects on the ROM.