Introduction
Evidence & Methods
HO following cervical disc arthroplasty can potentially impact mobility and performance of the device. In this retrospective radiographic review, the authors characterize HO in their patients who underwent surgery using three different devices.
The authors found that HO was most common when the PCM implant was used (80%), followed by Prestige (60%), and Bryan (49%). They also characterize the type of ossification noted.
The design of the study is strictly observational. The study design does not allow conclusion that a particular device is responsible for more or less HO given that patient and surgeon-specific (technical) confounders may well be present. Nonetheless, the large differences in observed rates of HO suggest that high-quality, controlled, comparative trials are needed and would not require very large numbers of subjects to detect this magnitude of effect.
—The Editors
Cervical total disc replacement (TDR) is known to be a good surgical option for cervical disc disease and have satisfactory radiological and clinical outcomes compared with anterior cervical discectomy and fusion. However, heterotopic ossification (HO) after TDR, one of the midterm complications, is an embarrassing phenomenon. Many studies indicated that HO after TDR did not have negative influence on the clinical outcome, but it is important to note that HO impairs the range of motion in index segments [1], [2], [3], [4], [5], [6], [7], [8]. Several clinical studies have focused on the incidence and risk factors of HO. The occurrence rate of HO varied according to disc prostheses: 21% to 76% at 2 years for Bryan (Medtronic Sofamor Danek, Memphis, TN, USA) [1], [2], [3], [4], 71% to 79% at 2 years for Prodisc-C (Synthes Inc., Paoli, PA, USA) [2], [5], [6], 14% at 14 months for Prestige LP (Medtronic Sofamor Danek, Memphis, TN, USA) [7], and 0.4% at 1 year for PCM (Cervitech, Rockaway, NJ, USA) [8]. It has recently been reported that the incidence and grade of HO increased as time passed and spontaneous fusion must be anticipated during long-term follow-up [6]. Male sex, older age, and multisegmental operation were found to be the risk factors for the development of HO [1]. Factors suggested to contribute to the HO included bone dust, wear debris of the metal on the polyethylene component, the keeling procedure in the Prodisc-C prosthesis, and stress at the interface between the end plate and prosthesis [1], [2], [9].
Heterotopic ossifications in TDR are quite different from HOs in hip and knee joint surgery in terms of location, absence of preceding inflammatory symptoms or signs, and the temporal pattern of growth. Heterotopic ossification in TDR looks more likely to fusion mass after interbody fusion or osteophyte in the aging spine rather than usual heterotopic ossification. Therefore, the authors hypothesized that mechanical factors might play a key role in the development of HO in TDR and the configuration of HO would be different according to the mechanical environment. Recently, we developed a novel morphologic classification of HO in cervical TDR. The purpose of this study was to understand the pathogenetic mechanism and risk factors for HO in cervical TDR based on the morphologic subtype and location.