Heterotopic Ossification (AKA autofusion)

[Harrison]

Old news, but worth reposting for newbies. This is one of many abstracts from the SAS 2010 meeting in New Orleans. I've been squeaking about this problem for almost five years now; at least patients and docs are finally getting the message of NSAIDs after cervical ADR...but there are still NO standards!

Ironically, this post was called to my attention by a patient who had concerns about HO, borrowed $40,000 to have surgeries overseas, came home, then had complications. He needed a revision which he obtained from another surgeon.

(No, I can't provide more information than that.)
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A Comparison of Prodisc-C and Mobi-C Artificial Discs in Heterotopic Ossification after Cervical Arthroplasty The Leon Wiltse Memorial Hospital, Neurosurgery, Suwon, Korea, Republic of

Purpose: To compare the incidence of HO (heterotopic ossification), the preservation of segmental motion, and the relationship of HO with clinical outcomes of Prodisc-C and Mobi-C artificial discs after arthroplasty.

Materials and methods: This prospective study included 35 patients who had undergone implantation of the Prodisc-C and 31 patients who had undergone implantation of the Mobi-C. Radiologic (static and dynamic plain radiographs) and clinical (Neck Disability Index (NDI) and Short Form-36 (SF-36) questionnaire) assessments were made preoperatively and at 1.5, 3, 6, 12, and 24 months postoperatively. Occurrence of HO was defined by the McAfee classification on cervical lateral x-rays after surgery.

Results: A single-level procedure was performed in all patients. The mean follow-up duration was approximately 26.3 months. The incidences of HO in the Prodisc-C and the Mobi-C at one year after surgery were 2.7% (1/35) and 6.5% (2/31), respectively. However, upon a two-year postoperative assessment, the incidences of HO in the Prodisc-C and the Mobi-C were found to be 60.0% (21/35) and 80.6% (25/31), respectively. 5 (14.3%) of patients with Prodisc-C and 7 (22.6%) of patients with Mobi-C experienced Grade 3 and 4 HO. Seven patients‘ (20.0%) Prodisc-C and Eight patients‘ (25.8%) Mobi-C artificial discs were shown to have movement of less than 2 degrees according to flexion and extension cervical x-rays at 24 months, with 4 (Prodisc-C) and 6 (Mobi-C) of these patients having HO of Grade 3 or 4. No association was found between the presence of HO and all of the clinical outcomes for both artificial discs.

Conclusion: In contrast to expectations, the incidences of HO in both types of artificial disc showed a very rapid increase one year after surgery. The presence of HO was associated with a subsequent loss of movement of implanted Prodisc-C and Mobi-C artificial discs. Therefore, additional long-term follow-up studies concerning the spontaneous fusion related to HO and the preservation of segmental motion after cervical arthroplasty are necessary for outcome evaluations of these artificial discs.

Source to this and other abstracts:

ISASS.org - Conference Information - SAS10 New Orleans Scientific Program Abstracts

[Reddy2ride]

Here's another study from Sept. 2010 which correlates post-surgical HO with pre-surgical calcification of the Posterior longitudinal ligament. The HO stats really scare me. I'm don't recall seeing imaging reports identifying calcification of ligaments unless that's generally lumped into statements of hypertrophy? Anyone know?

On a more positive note I have had doctors respond to these concerns by saying that in many cases the results of HO around an ADR which has fixated in a state of good positioning (not defined) is often better than what would have occurred via congenital fusion due to the disc height preservation. However, I also agree that this somewhat defeats the purpose of a motion-based ADR. This really is a scary topic and probably dictates a lot of future radiation for frequent check-ups to keep one's sanity. Another doctor commented that HO and autofusion around an ADR are two different processes. I didn't ask to many follow-up questions but apparently HO is more associated with soft tissue calcification (ligaments, muscle, scar tissue) and autofusion is bone growth/osteophyte growth into/around the ADR. These two terms (HO and autofusion) may be used interchangeably in many of these studies and I guess the results are similar in loss of motion. Only time will tell how to minimize this likelihood. It will be interesting to see how non-metallic artificial discs such as Ranier's Cadisc will eventually perform.


Loving life with DDD! On a funny note I was watching the news last night with a segment on a guy who runs a $20M a year business selling medically-prescribed marijuana in California which is apparently legal. When asked if he was also a patient/user of his medicine he responded positively and said he had DDD and it helped his pain and allowed him to sleep better!

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Journal of Neurosurgery: Spine

Sep 2010 / Vol. 13 / No. 3 / Pages 299-307


Article Radiological changes of the operated and adjacent segments following cervical arthroplasty after a minimum 24-month follow-up: comparison between the Bryan and Prodisc-C devices
Clinical article

• Kyeong-Sik Ryu, M.D., Ph.D.,
• Chun-Kun Park, M.D., Ph.D.,
• Sung-Chul Jun, M.D., and
• Han-Yong Huh, M.D.

Department of Neurosurgery, Seoul St. Mary's Hospital, The Catholic University of Korea, Seoul, Korea
Abbreviations used in this paper: FSU = functional spinal unit; HO = heterotopic ossification; NDI = Neck Disability Index; PFA = progression of facet arthrosis; PLL = posterior longitudinal ligament; ROM = range of motion; VAS = visual analog scale.
Address correspondence to: Chun-Kun Park, M.D., Department of Neurosurgery, Seoul St. Mary's Hospital, 505 Banpo-Dong, Seocho-Ku, Seoul, Korea 137-701. email: ckpmd@catholic.ac.kr.

Related Articles

By Keywords:degenerative cervical spine disease, cervical arthroplasty, facet arthrosis, heterotopic ossification, Bryan disc, Prodisc-C


Abstract

Object

The purposes of this retrospective study were to determine the radiological changes at the index and adjacent levels after cervical arthroplasty using the Bryan disc and Prodisc-C disc after a minimum 24 months follow-up, and to demonstrate the possible clinical factors related to these changes.

Methods

Following single-level cervical arthroplasty using either the Bryan disc or Prodisc-C, the degree of facet degeneration and other radiological changes at the index and adjacent levels were assessed by observing radiographs and CT scans at a minimum 24 months after the operations. These findings were determined in relation to the clinical outcome, various perioperative factors, and prosthesis factors. Thirty-six patients were included in this investigation (19 in the Bryan disc group and 17 in the Prodisc-C group).

Results

At the index level, progression of facet arthrosis (PFA) was observed in 7 of 36 levels (1 level with the Bryan disc, 6 with the Prodisc-C). At adjacent levels, PFA was minimally observed. Heterotopic ossification (HO) was observed at 19 levels (11 with the Bryan disc, 8 with Prodisc-C). Progression of facet arthrosis at the index segments was positively related to malposition of the prosthesis on the frontal plane, and decreased postoperative functional spinal unit range of motion at the index level. Occurrence of HO was correlated with the preoperative calcification of the posterior longitudinal ligament at the operated level, regardless of prosthesis type. Clinical outcome and the occurrence of PFA or HO did not show any significant relationship.

Conclusions

This study demonstrates that the incidence of PFA at the index level is 19.4% after a minimum 24-month follow-up, and occurs more frequently in the Prodisc-C group. Progression of facet arthrosis is related to less functional spinal unit range of motion and anterior placement of the prosthesis. The occurrence rate of HO is high, regardless of the type of prosthesis, and it is significantly correlated with preoperative calcification of the posterior longitudinal ligament at the operated level.