Dr. Gross Receives 2012 Hap Paul Award - Study Safe Zone Acetabular Placement

[Pat Walter]

Dr. Gross recently received the 2012 Hap Paul Award International Society for Technology in Arthroplasty.

He posted the study from that award  on his website and given me permission to post the information:

2012 HAP PAUL AWARD INTERNATIONAL SOCIETY FOR TECHNOLOGY IN ARTHROPLASTY:A SAFE ZONE FOR ACETABULAR COMPONENT POSITION IN METAL-ON-METAL HIP RESURFACING ARTHROPLASTY.

http://www.grossortho.com/Journals/Metal%20safe%20zone.pdf

THOMAS P. GROSS, MD
FEI LIU, PHD

Here is the Abstract:
ABSTRACT:

Background:
Adverse wear reaction after metal-on-metal hip resurfacing has been described as a new failure mechanism. Established causes include poor implant design, small implant size and acetabular malpositioning. The purpose of this study is to establish a safe zone of acetabular inclination angle (AIA) in order to reduce the high metal ion level rate after hip resurfacing.

Methods:
761 cases in 613 patients with minimal two years follow-up had both metal ion levels and quality pelvis X-ray available in our database and are included in this study. The UCLA activity score, femoral shaft angle, body mass index, weight, American Society of Anesthesiologists (ASA) score, combined range of motion (CROM), diagnosis, age, implant brand, gender, AIA, bearing size, and duration of implantation were analyzed to determine the potential risk factors for elevated metal ion levels with use of uni- and multi-variable logistic regression models. A safe zone for hip resurfacing (RAIL: Relative Acetabular Inclination Limit) was calculated based onimplant size and AIA on AP pelvis X-ray.

Results:
For AIA below the RAIL, there were no adverse wear failures or dislocations, and only 1% of cases with ion levels above 10ug/L. We have not found a lower limit of AIA where failures occurred. Other than high inclination angle and small bearing size, female gender was the only other factor that correlated with high ion levels in the multivariate analysis.

Conclusion:
We have described the robust "safe zone" for acetabular component position based on metal ion levels in a large patient cohort for metal-on-metal hip resurfacing arthroplasty. Our study suggests that adverse wear failures with hip resurfacing may be highly predictable and avoidable. If the AIA is below the RAIL, rare dislocations are also prevented.

The Full Study is very interesting and it can be viewed here:

http://www.grossortho.com/Journals/Metal%20safe%20zone.pdf

[Baby Barista]

It cannot be overstated how remarkable this is for the future of HSR surgery.

As I have said on this board before, there needed to be a peer reviewed study of cup angle, relative to bearing size, and it's affect on outcome. As Dr. Gross notes at the top of page 15 in the study, this is the first time anyone has actually studied this. Doctors have speculated... but this is an actual, tangible study, that will be peer reviewed.

Hats off to Dr. Gross for doing this. It will be a powerful piece of evidence in supporting the use of metal-on-metal arthroplasty in suitable patients.

[John C]

Exciting to note that activity level was not a risk factor for higher ion levels. Very good news for all athletes out there. :) :)
Kudos to Dr Gross for publishing such an in depth study on this subject that has gotten so much uninformed press. Worthy of note is that there was no outside funding; the cost of the study came out of his pocket.

[hernanu]

Great study, and like John says, very good to see that high activity is not related to failure.

[John C]

Hi Hernanu,
The way that I read it, the higher activity levels were shown not to be related to higher ion levels. It did not go on to discuss a correlation between activity levels and failures. Obviously high ion levels would be one possible cause of failures, so low numbers is good; but correlating activity levels to failure rates was outside the parameters of this study.
Still, it is good news.

[hernanu]

You're right John, I should have been a bit more careful with that. Ion levels. It is good news, but it's better to be more exact.

[Tin Soldier]

This is great.  I recall Pritchett saying, at least, anecdotally that he didn't think failures from metal's issues and wear were related to excess activity.  As far as placement, as BB points out, this is the first time we've seen a realy study on it.  Cool.

[Ross]

Dr Gross is always dedicating himself to research papers, better methods, etc.  I enjoyed his case study and thought that it was well written.  Guess we will probably see a lot more clinical studies like these from him.