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fortitudine 12-08-2006 01:54 PM

Heterotopic ossification in ProDisc-C????
Do we know any more about this issue? As I'm a potential ProDisc-C candidate, this worries me.

Posted December 03, 2006 10:56 AM December 03, 2006 10:56 AM

An informed member was kind enough to share some recent information on ProDisc cervical and heterotopic ossification (autofusion).

I am quite puzzled by this and would have liked to have had the “story behind the numbers” before posting. However, I urge you all to NOT jump to any conclusions about the efficacy of the ProDisc C (or any other cervical discs) until more contextual information can be found on this issue. As you seasoned folks know, ProDisc C patients on this forum have done quite well.

Related topics from this board on HO here.

Heterotopic Ossification in Total Cervical Artificial Disc Replacement.

Spine. 31(24):2802-2806, November 15, 2006.
Mehren, Christoph MD *; Suchomel, Petr MD, PhD +; Grochulla, Frank MD *; Barsa, Pavel MD +; Sourkova, Petra MD +; Hradil, Jan MD +; Korge, Andreas MD *; Mayer, H Michael MD, PhD *

Study Design. Prospective clinical study enrolled in 2 centers (Munich and Liberec) as part of a prospective European multicenter study with ProDisc C (Synthes Inc., Paoli, PA).
Objectives. The first goal of the study was to evaluate the rate of heterotopic ossifications identified with plain radiograph following total cervical disc replacement (TCDR). The second goal was to show whether segmental motion can be preserved, and whether TCDR can provide improvement of the patient's ability to perform activities of daily living as well as a decrease of pain.

Summary of Background Data. Only a few reports about the radiologic outcome after TCDR are published so far. Heterotopic ossification is a well-known phenomenon after total hip arthroplasty. The rate of heterotopic ossification following TCDR is unclear.

Methods. The radiographs of 54 patients (in total, 77 implanted prostheses) were analyzed 1 year after TCDR with a ProDisc C prosthesis. We classified the heterotopic ossification in 5 grades according to a recently published classification system for lumbar total disc replacement. For clinical parameters, the visual analog scale and the Neck Disability Index were evaluated preoperatively and 1 year postoperatively. The Student t test and Wilcoxon test were used for statistical analysis.

Results. In 26 treated segments (33.8%), no heterotopic ossification was detectable. Grade 1 ossifications were present in 6 levels (7.8%). A total of 30 segments (39.0%) showed grade 2 ossifications. Heterotopic ossifications that led to restrictions of the range of motion were present in 8 cases (10.4%). One year postoperatively, 7 cases (9.1%) had a spontaneous fusion of the treated segment. The clinical parameters improved significantly and were similar to previous reports about TCDR.

Conclusions. Only 33.8% of the patients did not show any signs of heterotopic ossification, and the rate of spontaneous fusion after TCDR 1 year after surgery was unexpectedly high. There were 49.4% of the patients with grade 2-3 ossification, which lets us suspect an even higher rate of spontaneous fusion after long-term follow-ups. Motion preservation after TCDR is only guaranteed if spontaneous fusion can be prevented. Thus, mobility of the implanted segments needs to be further studied.

Michelle 12-08-2006 11:57 PM

Consider me highly uninformed here, but are these painful or something? Granted, it wouldn't be good to fuse when you're looking for motion preservation with ADR, but how are you any worse off than going straight for fusion??? I'm asking, not being a smart-alek. Anybody?

KL Aguilar 12-09-2006 02:46 AM

I met Dr. Zeegers at a luncheon sponsored by Global Patients Network. Dr. Z talked about applying a type of wax that acted as a deterent to new bone spur growth. Perhaps someone like Mark will come along and answer this in more detail.

mmglobal 12-09-2006 08:24 AM

Greetings from Munich (AlphaKlinik room 905). I'm still in running the marathon that I do on these trips, but the last surgery was yesterday... hopefully I'll get more time to spend here soon. (It's Saturday morning and I've been here since before the surgeries started yesterday.)

This study is interesting. I've been seeing Bertagnoli do ProDisc-C procedures for more than 3 years. I've been seeing presentations about many different systems, now for the last 4 SAS and NASS meetings. I will see if I can get some perspective on this result.

I found the classification system that was referenced in the study. An article that references the system is posted here: Advances in Disc Technology.

Note that this article is from 2002, but I believe that the system they are talking about. Here is an overview of the grading system:
  • Class 0: no heterotopic ossification (HO)
  • Class I: islands of bone in soft tissue, bone not present between planes formed by the endplates
  • Class II: bone present between the planes of the endplates, but not blocking motion
  • Class III: motion blocked by HO and/or postoperative osteophytes
  • Class IV: inadvertent bony ankylosis

"A member of the audience raised the point that the presence of HO may not correlate with outcome."

I know dozens of patients with prodisc-C and know ZERO with HO problems. (I suppose it's possible that some have Class I or II HO but it's not been discussed as a relevant issue.) Also note that my experience is with patients who are all less than three years out.

Look here for much of the data that was presented regarding the Charite.

Search for heterotopic and you'll find charite studies with fairly large numbers and enormous percentages of HO... > 50%, as high as 80%. Horrible results! However, in the hundreds of charite patients I know, HO has only been an issue in extreme cases and for the most part, it's in people that should be fusing and autofusing represents a good result. (The HO patients that I know can be counted on one hand, without using 1/2 of your fingers.) IMHO, what we are seeing here is that early in the process with new devices, there will be a huge difference in outcomes depending on surgeon and technique. Early in the process, the appropriate techniques are not fully developed. I remember when there was a ProDisc surgeon in the Bay Area who was telling patients that his lumbar ProDisc experience was, "1/3 got better, 1/3 stayed the same, and 1/3 got worse!" Again... horrible results... but that is not the experience with the device across the board and there are surgeons who's outcomes far exceed the mean... just as there are surgeons who's results come no where near the mean.

I wish I had time to write more. This is an important discussion. It really shows why I'm always skeptical about data and studies. Many patients go through the process of searching for the Holy Grail of data and studies and evidence based medicine... only to be discouraged (and sometimes kept for seeking treatment) by finding things like this. I'm not suggesting that we should ignore data and studies... just don't panic... take your time and find out... dig deeper than what the paper says... dig deeper than what your doctor says.

All the best,


necknose 12-10-2006 02:54 AM

MM Global: Balance from a Spiney Maven!

Excellent, steady response as always. As one can glean from your signature: when the questions of efficacy and outcome are raised in relation to ADR you literally "walk the walk". You have more than a dilettante's interest in these questions and so far, in your experience, ADR has represented the salvation of a life: yours! You and the other successful ADR/spineys are to be congratulated. It's your Christmas present for this year and many more to come.

Glad the pressure of your escort duties is over, I assume till after Christmas 2006.

In your next post I hope you touch on some of the points mentioned below.

It should be pointed out that the study referred to is of Cervical not Lumbar ADR outcomes.

It seems that the essence of your post is that the surgeon is THE pivotal variable. You've pointed this out before.

What needs clarifying, besides the surgeon variable, across the Cervical (not Lumbar) ADR patient population is are these results: prosthesis specific, due to poor patient selection, a function of the degree of disease progression, patient age, other pathology related, etc..

Clarification Please:
"HO has only been an issue in extreme cases and for the most part, it's in people that [[[[should be fusing and autofusing represents a good result]]]]."

I'm acquainted with your oft cited observation that a single level cervical fusion is the "gold standard" of care in treating cervical DDD (DDD = all spine disease appropriately treated w/fusion), etc..

However I'm unclear about your statement: "should be fusing and autofusing". Is this observation based on the idea that: auto-fusing is a desirable outcome in DDD and further that if it's the end state of an ADR implantation it's desirable because auto-fusion in the presence of an ADR is preferable to auto-fusion as the result of "natural" end state HO, or some other explanation?

As other's have observed: auto-fusion as an outcome, is counterintuitive to the premise of ADR: motion preservation. This is esp. the case for multi-level cervical spine disease where 3+ levels of fusion leaves the patient w/greatly reduced ROM and in all probability significant chronic pain requiring constant medication for "life" is it possibility. Might it be posited that in cases where central spinal cord stenosis is the main concern, if auto-fusion is highly probable regardless of the surgical treatment applied, that low impact posterior approaches, e.g. split laminectomy, could ultimately be just as effective as ADR: esp. reduced the financial impact on the patient as well as elimination of the additional trauma, for some patients, of going to a foreign land for treatment, assuming split lami for example is in fact available in the US.

What, if you will, is the cost benefit equation in cases of probable HO of: ADR versus the best "traditional" treatments?

If you have the opportunity, enlargement on these aspects and others of auto-fusion would be appreciated.

************************************************** *******
Happy Holidays to you and all my fellow spineys. May we all have at least a brief respite from from the pains, fears, and the angst that all to often is the spiney's lot.

Good luck to us all!


mmglobal 12-17-2006 05:58 PM

I hope that someone can do the research to discover the background for this study. There are 8 authors listed. Are there 8 surgeons involved in this series of 54 patients. It is my understanding that while in, where studies are allowed to exclude 'training cases', they are not allowed to exclude these cases in Europe.

I do not know the details of this series, but are there 40 training cases out of 56 patients? Why should their experience be so much worse than other reported data?

Studies and data are useful, but must always be examined with a very critical eye. Now, for years to come, we'll be reading about literature reviews that will say something like, "Incidence of HO between 0% and 66%".


rob_zzz 03-05-2007 03:31 AM

reading through the pubmed abstracts and came across this article again (about heterotopic ossification with prodisc-C - see first post in this thread).

I'd definitely be interested to know if anyone has gotten any further information from surgeons that do these procedures on whether there are any measures to counter this problem. Also its fair to say that without knowing the background of the study its hard to know how useful the results are, however its also true that similar studies in relation to other cervical prosthesis (e.g. bryan) have also showed results of this nature, so it sounds like HO is real in that it is something that occurs - but what level of impact it has is another question.

One surgeon I spoke to said that they prescribe NSAIDS after the surgery to help reduce early bone growth. I'd be interested to know if there are chemicals (almost the 'opposite' of bmp I suppose) that could be used during surgery to prevent HO in certain areas.

Also for those that have had a cervical prodisc-C - have you had x-rays at 1 or 2 year followup and what did they show?

Finally - it seems that even if there is a high incidence of HO, the patients are still doing ok - i.e. there are other studies that show patient satisfaction scores etc. one or two years on that still show good results. So this possibly comes back to the most important thing about a surgery being succesful decompression of the nerves causing the problems (spinal cord or peripheral nerves) without damaging them during the surgical process. And if this is acheived then the likelihood of a good outcome is high regardless of the implant used. Similarly quality of placement of the implant by the surgeon etc. selection of appropriate heights etc. etc. would all be factors - possibly more so than the actual 'thing' put in place.

i.e. on that basis it might be that the surgeon rather than the implant is the key determiner of the result. If this were the case it would also arguably still be a reason for travelling/expense to visit a surgeon with consistently good results.

mmglobal 03-05-2007 03:05 PM

This study really shows the problem trying to mine the data. I have spoken to several of the most experienced cervical ADR surgeons in the world and int he US about the study. None of them are experiencing rampant HO numbers as this study would suggest. None of them is experiencing HO numbers at a level that would even give them pause.

HO with the Bryan disc is a completely different topic. The Bryan procedure involves milling a negative into the endplate to accomodate the implant. It's a difficult procedure that is error prone. Excessive milling of the bone and potential positioning issues greatly increases the risk of HO. I believe that is why we have not seen Bryan approval and I never hear any buzz about it. Medtronic believes so strongly in the Bryan that they purchased the Bristol disc (now the prestige). IMHO, they knew that the Bryan was a non-starter.

I believe that what we see in this study is a prime example of why we must do everything we can to make sure that we are dealing with surgeons that are highly experienced with the technology they are using. I don't care if I'm dealing with the most experienced ADR guy in the world... I don't want to be his first, fifth, or tenth procedure with new devices or new instrumentation. This study lists nine surgeons and 54 patients? What was their training like? What other cervical ADR experience do they have? Is there an axe to grind?

There is one tidbit of incredibly valuable information that I take from that study. If you need ProDisc-C, don't go to those guys!


rob_zzz 03-06-2007 02:47 AM


Thanks for the detailed reply and first hand feedback. I'd still be interested to know if there is anything in particular that these more experienced surgeons do that helps to prevent HO.

It must also have been/be a problem with other joint replacements (hips, knees) so you'd think there'd be already be a fair bit of information about the nature of the process that occurs, and the types of measures that can be done to prevent it.

I guess the more conservative fusion surgeons would be liking seeing this sort of research to justify holding off on ADR which is unfortunate. On the other hand I'm hoping the developers of the prosthetics will be open about the realities of these problems if they do in fact exist, and put active research into ways of preventing it.


sahuaro 03-06-2007 03:37 AM

Thank you, rob, for always asking important questions.;)
Mark: Since I am considering the Prestige LP cervica disk, I'd like to clarify your comments about the Bryan: is the increased risk of HO theoretical or have there been actual data reported? Since my understanding of the Prestige LP is that it also requires milling, then would the same concerns apply?

rob_zzz 03-06-2007 04:20 AM

thanks - I should probably add that I'm not trying to be deliberately difficult by raising the topic :o - I want this technology to work as much as anyone and think that we're all lucky to have the options available today that we do.
(and wish they were available a little closer to home from my own perspective but thats another story).

There are also known problems with fusion so even if there are some problems with ADR they still need to be compared contextually to the problems with fusion. (e.g. with fusions there are problems with the anterior plates that don't occur with ADR because there's no plating, problems with hip graft site for autograft fusions that don't occur with ADR etc.).

Sahuaro my laymans understanding is that the milling for the bryan is much more extensive than for the other discs (prestige and prodisc). As I understand it, with the other discs they use a tool to cut a relatively small slot(s) for the disc to lock into, while with the bryan they gouge/drill out a fairly large hollow that the ends of the disc fit into.


mmglobal 03-07-2007 06:25 PM

I don't think you are being difficult, Rob. These are tough questions and unfortunately, when you decide what to do, you still won't have all the answers as they don't exist yet.

Yes, with the Bryan disc, there is much more milling and the process is complicated and difficult. They must mill a negative in the bone that provides a 'cup' that the prosthesis fits into. Imagine the jig that is used to mill into both the superior and inferior endplates. Too many steps... to easy to get it wrong. I don't have the Bryan data at my fingertips and am relying on memory and impressions made when I attended the sessions where Bryan experience was presented.

For me, this really highlights the problem with the data and with this whole process. There is no question in my mind that there is a huge disconnect between the data and the experience. Especially with an extra-difficult surgery, there will be a greater disparity between the more skilled and experienced surgeons and the ones that are less so. I know several top surgeons that have done many Bryan procedures, but all of them stopped using Bryan when newer designs became available. They all talk about HO rates and the difficulty of the surgery. However, when I see Bryan data presented at the conferences, it looks much the same as for the other cervical discs. (And for the lumbar discs, and for fusion, and for.....) Maybe they all use the same computer program and it's stuck... only outputting 85% success rate, regardless of the input.

Regarding avoiding HO... I believe that it comes along with doing excellent carpentry. It comes with experience. There is a trade-off at many places in the surgery. Unless you have totally regular shaped end plates, some remodeling will be in order. How much? Too much or inappropriate remodeling and you increase the risk of HO, subsidence, migration. Too little remodeling and you don't have a good platform for the prosthesis, increasing the risk of migration, toggling (motion of the prosthesis), or ??? Use of bone wax may reduce the risk of HO, but inappropriate use of bone wax will come along with an entirely new set of risks. Again... experience, care, skilled surgeon are paramount.

Regarding Sahauro's question about theoretical vs. numbers... I don't know. My impression is that they abandoned Bryan because there was something that was much better... not because of HO rates. If there was only a choice between Bryan and fusion, I suspect that they would still be doing Bryan procedures where ADR is indicated and that, as with other surgeries, better surgeons will have better success.


rob_zzz 03-07-2007 10:16 PM

good comments - thanks again Mark.

sahuaro 03-08-2007 01:28 AM

Yes, thank you Rob and Mark. Mark, you must get tired of having to emphasize the importance of choice of surgeon, but please realize how important these exchanges are!:)

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