3rd Annual Hip Resurfacing Course Overview September 2009

By Vicky Marlow

Another very exciting course with a lot of great quotes.  This year there were 200 attendees, 18 different companies supporting the course and over 40 Faculty members.  I want to first extend my gratitude and thanks to Dr. Michael Mont for allowing me to attend and Dr. Thomas Schmalzried who was incredible as a Moderator at this course.  They were the two surgeons that put on this incredible course.

Now in no way is this any scientific paper.  It is just an overview written by a patient, with parts taken from the syllabus that was provided to me on a CD for accuracy purpose, please remember, this is from a patent’s perspective. The course started off on Friday morning, September 4, 2009 with a Continental breakfast that started at 6:30 a.m. (3:30 a.m. my time) and right at 7:30 a.m. the conference began.  We only had one short 10 minute break and about 30 minutes for lunch then it lasted until 6:30pm.  Wow!  Long day, then dinner was at 7:30pm, stayed till around 10:30 – 11p.m. went back to my hotel and checked emails, got up the next day and it started all over again.  Went to Derek McMinn’s book signing and tried to head out to the cadaver lab, but I guess because I did not show up when it began at 2pm, I could not get in, that was a bummer.  I learned a ton and met some new docs and was able to fit in my video interview with Dr. Antoniou.  I even met two great patients that came out to see me and we had dinner and their infamous crab the last night there.  Dr. Mont was kind enough to invite Pat and I to the Faculty dinner on Friday night and that was a pleasure.  The following are notes that I took.

Thomas Schmalzried Course Objectives

Dr. Schmalzried mentioned that this is now an established technology in the right people and we just need to help spread the word on Hip Resurfacing Arthroplasty more. Although actual clinical options have not, market forces HAVE stopped the outcome of more resurfacings.

Metal on Metal (MoM) bearings needs to be separate from resurfacing.

The first quote came from Dr. Schmalzried, he said, folks we have found the enemy and he is us, the surgeon.  The biggest problem is with the surgeons and is in component positioning especially on the acetabular side.  So this reinforces my statement of the  importance of SKILL and experience.  Remember, from all that I have learned, numbers alone do NOT tell the whole story.  Look at failure rates, speak to other patients, call or email me any time.  There is so much that goes on offline the most just do not hear about.

32% of surgeons use MoM (Metal on Metal) devices

Men younger than 60 years are expected to have a 98% percent survival with resurfacing at 5 years.

Best results of resurfacing regarding the different approaches have been reported to show no difference in Ronan Treacy’s 8 year study.

Studies show higher activity levels with Hip resurfacings than with http://health.groups.yahoo.com/group/Hipresurfacingsite/

International Hip Resurfacing Society James Richardson from UK

Was formed in 2007, surgeons and engineers : a society for the advancement of hip resurfacing and other methods of bone conservation in hip replacement with the aim of improving patient care.

Before age 65 you should try to give a patient hip resurfacing to preserve the bone over their lifetime
1988 Derek came up with the idea of metal-metal hip resurfacing

Metallosis-related failure 1.9% at 3.5 years

Past Present & Future Moderator Thomas Schmalzried, MD

1^st Generation Hip Resurfacing with PE (Polyetheline) was all Cemented

1973 – 1983 there were 8 designs in 5 countries

Hip Resurfacing with PE – Lessons learned 1973 – 1983

Ø       Avasularity not a problem – Trans troch. Approach

 THARIES  

Ø      Most Failures due to PE wear osteolysis!

Ø      Fracture Incidence low

Ø      Acetabulum:  not conservative

From where have we come with resurfacing? Harlan Amstutz, MD

Double cup designs of hip resurfacing, the first design appeared in the early 1970’s, it followed the same component fixation techniques as THR, going from all cemented (THARIES) to cementless designs (PSR).  The majority of these showed poor long-term performance because of increased polyethylene wear debris generated by large femoral heads articulations with UHMWPE.  The resurfacing concept itself was abandoned until an alternative bearing material allowing to manufacture a thin one-piece acetabular component strong enough to accommodate large femoral heads was available.  Currently, only metallic devices combine a low wear bearing with a suitable coating for cementless fixation.  Wagner in Germany and McMinn in England were the first to introduce metal-on-metal (MoM) hip resurfacing prosthesis and long term results of these devices are now available. 

Conserve® Plus designed in 1992 with experience from 1996, it is the longest for currently available designs, and included all hips that could technically be resurfaced, irrespective of etiology, gender, or femoral defect size.

The first 100 C+ were implanted in 89 patients.  The mean age was 49.1 years and 66% were male.  Primary OA was the in 64%, ON (Osteonecrosis) was 20%, DDH ( Developmental Dysplasia of the Hip) was 7% and others were 9%.  12% of the hips had had a previous surgery.  Mean follow-up was 11.4 years (10.4 to 12.6).  UCLA activity score was 6.8 and 20 patients engaged in high impact sporting activities.  Post-operative Harris hip score was 90.0 (45 to 100).

 10 Year Minimum Follow-up MM Conserve Plus – Resurfacing

Ø      N = 100 of 1250 (89 patients)

Ø      Avg. age = 49 yrs., 68% Males

Ø      Mean F/U = 11.6 yrs (10.7 – 13)

Ø      5 Patients dies – 98% Follow-up

Ø      Etiology & diagnosis:

-63% OA, 19% ON, 8% DDH, 2% post trauma, 5% Inflammatory, 2% LCP + SCFE, 1% melorheostosis

There were 11 conversions to Total Hip Arhtroplasty.  8 loosening of the femoral component at an average of 62 months (23 to 103), one neck fracture, one recurrent subluxation, and one lat sepsis.  In light of 13 year experience and the lessons learned since 1996, while the ten year survival rate can seem disappointing, but most of the failures that happened in this series could have been prevented with improved technigues.  The Kaplan-Meier survivorship was 88.5% at 10 years.  Compared to 55.1% survival at 10 years with first generation M/PE SR  1975 – 1993
Results including all patients with risk factors using 2^nd generatiion techniques are

96.7% at 8 years

There has been 100% of patients with good bone qualityand component size >46mm

MM Resurfacing 1^st 100 CONSERVE PLUS

Clinical Results

N=100, F/U min. 10 years – 2 LFUP, 5 deaths

Ø      ROM normalizes

Ø      HHS mean score for Charnley class A: 91.0

Ø      UCLA scores are higher than in any THR series

Ø      Pain = 9.5

Ø      Walking = 9.3

Ø      Function = 8.9

Ø      Activity = 6.8

Conversion to THA

• 8 Femoral Component Loosening @ avg of 62 mos. (23 – 103 mos.)
• 1 Fracture of the femoral neck
• 1 Recurrent subluxations
• 1 Hematogenous Sepsis

Conclusion – Survivorship

*  Risk Factors for failure included hips with :

1. Small head size

2. Large Cystic Defects

Review of intra-op photo and correlation with retrieval analysis led to substantial improvement in femoral head preparation and durability 

• No socket lossening
• No Leg Length Issues
• No Dislocations
• No cases have failed due to wear!!
• No local adverse local tissue reactions or Allergy!

 MM Resurfacing 1^st 100 CONSERVE®  Plus 

          CONCLUSION

Ø      M/M Results much better than M/PE which had severe Osteolysis Consequences

Ø      Results compare favorably with THA from the Swedish Registry for similar:

§         Patient population

§         Date of implantation

§         Follow-up time

Ø      Before:

-          Use of alternative bearings in THA

-          Optimal resurfacing surgical technique

·        Drying

·        Cleaning

·        Instrumentation

Taken from syllabus:

The 10 years survivorship of Conserve^®Plus by far surpasses that of the THARIES (89.8% vs. 61.5%, p=0.0000) or the ten year 35% survival reported by other authors¹. The ten year survivorship of the present series is comparable or better than that of THA reported in the Swedish registry² in a similar patient population implanted during the same era, (before the introduction of cross-linked polyethylene, metal-on-metal and alumina-on-alumina bearings for Total Hip Arthroplasty) where the reported survivorship for hybrid and cementless Total Hip Replacement all ages combined was 90% and 85%, and for patients under 50 years of age 83% and 84%, respectively. Our multi-variate analysis showed that low BMI, small femoral component size, and the presence of large femoral defects in the femoral head were risk factors for the procedure. In hips with a femoral component >46mm and no defects >1cm (ideal cases, n=28), the survivorship was 100% . These results are remarkable in patients without risk factors because they performed during the early development period. Improved 10-year results are anticipated in patients with risk factors because of the substantial progress made in bone preparation and cementing technique

Today early failures are rare and most are preventable with appropriate surgical technique or patient selection for the inexperienced surgeon The main modes of failure associated with modern resurfacing designs are femoral neck fractures and component loosening due to lack of initial fixation. High wear has been associated with increased lateral socket opening especially with the BHR prosthesis where the coverage angle is less than the Conserve^®Plus. Optimal component orientation is essental to minimize wear and impingement. There is a rare incidence of adverse local tissue reaction (so-called “pseudotumors”) mostly associated with poor component orientation and high wear. There are rare hypersensitivity reports from Europe and Australia but none noted in our experience with >1500 MM Conserve^®Plus bearings.

References

Costi K, Howie D, Campbell D, McGee M, Cornish B. Long-Term Survival and Reason for Revision of Wagner Resurfacing Hip Arthroplasty. J Arthroplasty. 2009;E-Pub ahead of print -June 9.

Sahlgrenska University Hospital DoO. The Swedish national hip arthroplasty register - Annual report. www .jru. orthop.gu.se 2007:1-107.

Technique Trumps Risk Factors

Post-op Activity – Cautions

Ø      Optimize Bone Preparation

Ø      Maximize Surface Area including stem cementation for <48mm and cyst size .1cm

Ø      Provide uniform cement penetration- ~1mm mantle optimal

Ø      Restrict Impact Activities

Minimum 10 year follow-up of Hip Resurfacing Ronan Treacy

BHR minimum 10 year follow up started in July 1997

1992 – 1997 nothing available for younger patients

98% survivorship first 144 consecutive BHR’s by Treacy

144 BHRs in 130 patients mostly OA some AVN

August 1997 to May 1998

107 male and 37 female cases

Mean age 52 years (range 17 – 75)

No 2mm increments and no 38mm femoral component sizes at that time.

Changes in Technique

              Acetabulum

Ø      Under ream by 1mm in acetabulum

Ø      Emphasis on Cup closure

              Femur

Ø      Capsular preservation

Ø      Suction venting

Ø      Tapered expansion drill

Protocol and Follow-up

·        FWB from time of surgery – protected with x 2 sticks for 3 weeks

·        Review 6/52, yearly till 5 years and then 10 years or study follow up

·        AP and lateral radiographs, OHS, UCLA

·        Details of revisions and deaths during follow-up

Results

• Mean follow up 10.7 years (10.2 – 12.2)
• 4 hips in 4 patients lost to follow-up (one moved to Spain, one to Greece)
• 9 patients (10 hips) died (unrelated to surgery) during follow-up (2.8 – 10.7 yr)
• 121 hips, mean follow-up time 11.1 yr (min 10.1 – max 11.5)
• 9 revisions in 9 patients

94.7% survival 96% at 10 years male only 98% at 10 years

Femoral Head sizes less than 46 need to be cautious

Conclusion; Promising good results for The Birmingham Hip Resurfacing published at 5 years are now proving to be more durable in the longer term.

What is on the Technology Horizon for Resurfacing? Michael Manley

Unsolved technology issues in HSR 2008

Component placement bone remodeling and bearing couples first having impact on second two

Edge loading more at 50 degrees rather than 65 degrees

Edge loading due to joint laxity

Problems and Opportunities for Short Stems Derek McMinn

Aussie registry

National registers and the curse of being the first to market with learning curve

MMT

Most surgeons got their learning curve using the BHR then switched to other devices and yet

97% survivor at 10 years for McMinn

97.5 % survivorship overall

Worst is with AVN best OA

If you preserve the neck and still use a long stem the neck will disappear due to stress shielding of the neck

BMHR

Changed to straight stems, then shorter stem due to the longer stem causing neck stress shielding

Taken from syllabus:

By Derek McMinn

Methods: We present a 2 to 6-year survival and clinico-radiological study of 60 consecutive hips treated with this mid-head resection device. Mean age 58 years (30-73), mean BMI 24 (15-42). There was no loss to follow-up. Unrevised patients were assessed clinically and with Oxford hip scores and AP, lateral radiographs. RSA assessment was performed up to two years in the first 13 consecutive patients.

Results: The mean Oxford score at follow-up is 13. With revision of either component as the end­point there were no failures. One patient developed continuous lucent line around the stem and mild varus tilt. No other patient shows clinical or radiological adverse signs. Anteroposterior and lateral radiographs show good femoral neck density demonstrating that the problem of stress-shielding bone loss has been overcome. RSA assessment showed no significant migration at 2 years.

Conclusion: Poor quality femoral head bone in a youngster with hip arthritis is a therapeutic challenge. The Mid Head Resection device offers a good conservative arthroplasty option for arthritic hips with poor quality femoral head bone. However caution is needed until long-term results are available.

110k resurfacing done to date with good results.  BMHR not enough results yet at only 2 years

98% 5 – 20 years with AVN dropped down to 90% so for AVN BMHR is good

Now 10 year survivorship for HSR better than Total Hip Replacement’s in Australian Registry

General Overview of Bearing Surfaces Thomas Schmalzried

Recognize trade offs for bearing surfaces M-M issues should be considered different than resurfacing

There are theoretical concerns regarding long-term exposure to metal particles and ions. An increase in cancer risk has not been identified. Accumulating evidence

indicates that the risk of an adverse local tissue reaction (ALTR), ALVAL, pseudotumor, metallosis, etc., is related to component position. Lateral opening (abduction) angles >55 degrees and high combined anteversion (femoral plus acetabular) should be avoided.

The enemy is the surgeon

Trade offs and compromises, age is NOT the salient criteria for prosthesis selection, some older patients are very active, males have higher wear rate

If you do a good job biomechanically you get lower wear.

Bearings other than Metal – on– Metal for Resurfacing Derek McMinn

Coatings ceramic coated

At 6 months the ceramic came off

Modify the surface causes carbon to go into metal and it hardens the metal and

Compliant bearings

Tried a ceramic resurfacing, in the future but not for widespread use today.  Ceramic on metal in the future

Taken from syllabus:

The 1970s and 80s era of hip resurfacing where metal-on-conventional polyethylene articulations were used was a failure, mainly due to high volume polyethlene debris production. Metal-on-metal resurfacing introduced by the author in Feb 1991 has been a success but there are problems. When the metallurgy and manufacturing of the metal-on-metal implant are optimal then the problem relates to edge loading of the cup. This is mainly due to surgeon error in cup positioning, but also due to poor selection of patients, especially those with high combined anteversion angle of the femoral neck and acetabulum. The final common pathway of failure may well be due to excessive wear debris or development of a hypersensitivity response, resulting in pseudotumor production. The incidence of pseudotumors in any particular metal on metal series equals the incidence of surgeon error in that series leading to edge loading of the implant.

There are several possibilities for the future. The first is reduction of wear from metal-on-metal articulations by reduction of clearance. However this requires considerable care as intra-operative cup deformation can lead to clamping on the femoral head and high frictional torque. The next possibility is using hardened femoral heads against regular metal cups. The most extreme example of a hard femoral head is the use of ceramic-on-metal bearings. In the laboratory these have been associated with exceptionally low wear of the articulation. Our own clinical experience with this bearing has just begun.

Using soft materials for the articulations there are several possibilities. We have a small clinical series extending out to maximum follow-up of one year using a ceramic coated femoral component on a ceramic/polyurethane acetabular cup liner. Others have used ceramic heads against PEEK/carbon fibre acetabular components although currently the clinical trial on this device has been stopped because of bearing squeaking. The excellent low wear of cross-linked polyethylene is of interest in conservative hip arthroplasty but there remains the insurmountable challenge of mechanical weakening of polyethylene as a result of the cross-linking and re-melting process and the inevitable use of exceptionally thin polymer layers for conservative hip arthroplasty.

The Neck’s Best Thing – Steven Stuchin

Negative comments on the wide short stem devices

Stem sizes are getting smaller

Shorter stems preserve more bone stock

Metal on metal articulations maximize head neck ratios

Presumed benefits of resurfacing include the promise of Unrestricted impact activities.  At this point, no hip replacement can make the same offer.

Survivorship of resurfacing in patients younger than 50: we do not need a different bearing Ronan Treacy

Total Hip Replacement for patients under age 50 not good. 

In Treacy’s own series of 448 BHR’s he had 10 revisions or a 98.8% survivorship at 10 years

No aseptic failure in male with OA higher failure rate in females but still acceptable.

Oxford studies showed a 95% survival at 5 years even though they complained about pseudotumors, etc.

In more detail

Ronan Treacy was said that in his OWN series of

Ø      448 BHR's in 394 patients

Ø       August 1997 to April 2006

Ø       267 (60%) male and 181 (40%) female

Ø       Mean age 41.1 years (range 17 - 49)

Ø       Mean follow up 6.6 years (range 2 - 11.9)

Ø      OA (64%), AVN (9%), Dysplasia (8%)

Ø      6 patients (7 hips) were lost to follow up

Ø      10 patients required revision, 4 for infection, 4 for AVN, one socket lossening and one neck fracture

He had a 98.8% Success rate at 11 years, very promising..

Then he said so what have Oxford brought to the Resurfacing party?

Ø      Cement Thermal Necrosis

Ø      Bilateral simultaneous surgery is fracture risk

Ø      Osteonecrosis as cause of femoral neck fractures

Ø      Posterior approach cause of devascularization

Ø      “Pseudotumors" reserved exclusively for MoM

BUT DESPITE ALL, JBJS 90B 2008 Steffen et al.  The five years results of Birmingham Hip Arthroplasty in Oxford still showed a 95% survival rate at minimum 5 years. Treacy's own results at 10 years with 448 patients is a 98.8% success rate, so he concluded,

I will quote Treacy here: "BHR is good for resurfacing and Oxford is good for site seeing"

Large vs. Small Heads in Standard Metal-on-Metal Hip Arthroscopy  Adolph Lombardi Jr.

Large increase jump distance to dislocation 

Optimized ROM Data for standardized tapered design

Large Head ROM increases 45 degree abduction don’t get the cups vertical

38mm heads considered larger heads in THR’s

Larger the head size reduces dislocation stability

95.8% survival at 50 months for all designs

Indications based on follow-up of 3,000 resurfacing  Ronan Treacy

Aim of study was to identify risk factors in hip resurfacing

From database at The Royal Orthopaedic Hospital in Birmingham, UK

Between August 1997 and July 2006

45 degree is ideal for cup placement

95 – 100% at 10 years 

OA or Osteoarthritis was ideal for resurfacing, more failures found in other  diagnosis

Not good for Developmental Dysplasia, AVN or smaller femoral heads

Success in Challenging Cases:  Do not try this at Home  Harlan Amstutz

Large cysts small component size, abonromal anatomies

14 year old post traumatic right hip

Amstutz has done some extremely difficult cases that have lasted, he cements the stem and limits their activities but normally they would otherwise not be resurfacable, good long term results.

Taken from Syllubus:

  Success in Challenging Cases: Do Not Try This at Home
Harlan C. Amstutz, MD

There is a general agreement among surgeons who perform hip resurfacing about the characteristics of the ideal candidate. However every surgeon has a different set of inclusion criteria and patients who would not be suitable candidates in one center can be viewed as challenging cases in another. The purpose of this presentation is to:

a)         Identify which cases are particularly challenging.

b)        Propose surgical solutions to overcome the specific challenges.

Several factors can increase the difficulty of performing a successful hip resurfacing: the geometry of the proximal femur and of the acetabulum, the extent of the defects present in the femoral head or the acetabulum or the presence of hardware from previous bone­preserving procedures

Patients with childhood disorders can present with shallow acetabular cavities (DDH), or flattened and retroverted femoral heads with a reduced head-neck ratio (LCP and SCFE). In patients with DDH, a deeper reaming of the acetabular cavity helps medialize the hip center of rotation and restore normal biomechanics. However it is also possible to leave the Conserve Plus acetabular cup uncovered 5 to 10mm to preserve acetabular bone. In patients with LCP or SCFE, the margin before notching the neck with the cylindrical reamer is small because of reduced head-neck ratio and every effort should be made to preserve the superolateral cortex. If notching is necessary, the medial part of the neck seems appropriate because the cortex is generally thicker. In our recent LCP and SCFE patients notching has been avoided with the use of a thin (3.5mm) socket.

Large defects (>1cm) are usually present in patients with ON and patients with longstanding OA or other secondary OA. The altered area for fixation benefits from thoroughly cleaning all the cystic or necrotic material, increasing the fixation area with multiple drill holes in both the dome and the chamfered areas, and cementing the metaphyseal stem.

In our series of 1000 hips, 441 were identified as presenting at least one of these challenges. The survivorship of this series of patients was 94.8 at 5 years and 91.1 at 8 years with nearly all of the failures occurring in the hips resurfaced with the 1 st generation of femoral fixation technique (p=0.0396). (The first 300)

Challenging cases can successfully be treated with resurfacing, provided that extra care in the preparation of the femoral head and surgical techniques specific to each etiology are employed.

Conserve Plus Study

Effects of Changing Indications and Techniques on Hip Resurfacing – Michael Mont

Started in 2000 10 centers 5 years 1892 patients

2000 -  2002 Indications and contraindication similar to THR few exclusions

Higher risk patients Cysts >1 cm, Osteopenica

Higher early failure rate in first 292 patients, after cgabges were nade in the indications and technique, the overall complications rate decreased from 13.4% to 2.1% with the femoral neck facture rate reduced from 7.2% to 0.8

5after 2002 new exclusion criteria

Cysts > 1 cm

Multiple cysts

Severe ssteopenia

Insufficient femoral head remaining

Notching of neck

Avoid extreme cup angle should be 40 -50 degrees

Poor seating

724 patients

Overall complications rate 2.1%

Femoral neck fracture 0.8%

93% of patients had good to excellent results

First 69 patients 12 fractures 17.4%

Last 1000 2 fractures

Expanded Indications Osteonecrosis, perthes disease hp dysplasia older patients > 55 extra-articular deformities, implanted hardware

95% 5 year survival rate

FDA approval should be emphasis on surgeon training

2-3% overall revision rates

FDA Indications and the U.S. Learning Curve  Robert Barrack.

Acceptable complication rate

lower complication rate among experienced hip surgeons’

Taken from Syllabus:

  FDA Indications and the United States Learning Curve
Robert L. Barrack, MD

In May of 2006, the FDA approved the first metal-on-metal resurfacing device for use in the United States.(1) Soon thereafter, widespread use began largely by surgeons inexperienced in the more demanding technique of hip resurfacing. There was widespread concern for the potential for high complication rate. A safety survey was completed to ensure that this new procedure did not constitute public health risk. The total number of major adverse events was 32 of 449 (7.1% of cases with 1 year follow-up), which included 12 fractures, 8 dislocations, 9 nerve injuries, 2 aseptic acetabular loosening, and 1 deep infection.(2) These cases were performed by 89 surgeons with a mean of only 6 cases per surgeon and a variable (unknown) level of experience and expertise. A similar complication rate may occur from this group of surgeons in primary total hip replacement.

A follow-up study was undertaken to determine the results of hip resurfacing among hip specialists compared to the initial national experience. Complete clinical and radiographic follow-up was obtained to assess the clinical and radiographic learning curve. The first five of the surgeons to complete more than 100 procedures in the first 15 months following FDA approval contributed all of their cases to this series.(3) None of these surgeons had prior experience with modern hip resurfacing. The incidence of every major complication was substantially lower including fracture (0.5% vs. 2.2%, p<.01), nerve injury (.5% vs. 2%, p<.01), reoperation rate (.9% vs. 3.1%, p<.05), dislocation (.8% vs. 1.8%, p = .11), an occurrence of any major complication (2% vs. 7.1 %, p<.001). Objective radiographic measurements indicated that the radiographic learning curve for major goals of surgery is between 50 and 100 cases.

When the FDA approved BHR, contraindications were listed on the federal website (www.fda.gov)(1) including osteoporosis, cysts >1cm, AVN >50%, females of child-bearing age, moderate renal disease, severe obesity, metal sensitivity, infection, skeletal immaturity, HIV/steroid use, neuromuscular disease, and vascular insufficiency. Surgeons performing this procedure should be aware of the stated contraindications. Performing the procedure in a patient with a contraindication is tandem out to off­label use. If the surgeon does elect to perform the procedure in a patient with a contraindication, it would probably be advisable to include this in the informed consent discussion and document this in the patient’s record.

References:

1.                         Medical Devices: Birmingham Hip Resurfacing (BHR) System - P040033. U.S. Department of Health and Human Services, Food and Drug Administration; 2006 [cited 2009 August 6]; Available from:

http://www.fda. gov/MedicalDevices/ProductsandMedicalProcedures/DeviceApprovalsandClea rances/Recently-ApprovedDevices/ucm078189.htm.

2.                       Della Valle CJ, Nunley RM, Raterman SJ, Barrack RL. Initial American experience with hip

resurfacing following FDA approval. Clin Orthop Relat Res. 2009 Jan;467(1):72-8.

3.                       Nunley R, Zhu, J, Brooks, PJ, Engh, CA, Raterman, SJ, Rogerson, JS, Barrack, RL. The

Learning Curve for Adopting Hip Resurfacing Among Hip Specialists. Clin Orthop Relat Res.

In press.

Volume Effect (Experience) on Outcomes in Australia  Tom Schmalzried

Surgical technique extremely important and surgeon experience

9/1999and dec 2006

8945

Taken from Syllabus:

  The Effect of Volume (Experience) on Outcomes of Hip Resurfacing

Thomas P. Schmalzried, M.D.
(Thanks to Andrew Shimmin, M.D.)

  The Australian Joint Registry indicates that between September 1999 and December 2006 there were 8,945 total hip resurfacings performed in 196 hospitals (avg. 46 per hospital). 74% of hospitals performed less than 30 resurfacing procedures over the 7 year study period. 64% of the procedures were performed at 16 "high volume" hospitals (>100 cases). At 4 years, the cumulative revision rate was 5.8% for hospitals performing <50 cases , 4.7% for between 50-99 cases and 2.7% for >100 cases. The risk of revision was 66% higher in hospitals performing <25 cases over the 7 year study period (Shimmin et al 2009 AAOS). A similar experience-effect was also reported from Oswestry (Aulakh et al. 2009 AAOS)

The initial American experience with the Birmingham Hip Resurfacing (BHR) further demonstrates the importance of surgeon experience. Safety surveys were completed on the first 537 cases performed. Adverse events occurred in 40 (32 major, 8 minor) of the 537 cases including nine nerve injuries and eight dislocations. There were 14 component revisions (3.1 %) within the first year, including 10 for femoral neck fracture, two for dislocations, and two for acetabular component loosening. Complications were frequently seen among patients older than 55 years of age and in women, emphasizing the importance of appropriate patient selection for the procedure.

In a subsequent study of the first 650 hip resurfacings performed by 5 experienced hip surgeons there were 13 major complications (2.0 %), which was 3.7 times lower than the national safety survey rate of 7.4% (p<0.001). All neck fractures occurred in the first 25 cases and the complication rate was significantly higher for the first 25 procedures (5.6%) compared to the second 25 procedures (1.6%) (p<0.003). On this basis, the learning curve for avoiding early complications was 25 cases or less. Based on a concurrent radiographic analysis, the learning curve for achieving optimal component positioning is much longer, 75-100 cases or more – with persistent inconsistency (Nunley et al. AAOS 2009).

Della Valle CJ, Nunley RM, Raterman SJ, Barrack RL. Initial American experience with hip resurfacing following FDA approval. Clin Orthop Relat Res. 2009 Jan;467(1):72-8.

Canadian Learning Experience with Resurfacing  Paul Kim

Canadians, too busy to learn new technique

One center stopped doing resurfacing

Mont: A surgeon should do at least 50 resurfacings a year to stay good at it.

Treacy answered that not all surgeons can do resurfacings, only respected surgeons should be doing them.  Expertise of the surgeon.

Schmalzried not that many centers that support resurfacing, it has to get into the training programs

McMinn says that the whole US system is a mess as far as surgeons have a real hard time to get started   Experienced scrub nurses, can’t scrub in

Schmalzried thinks that our system is badly broken and the US is going to continue to fall behind.

Resurfacing versus Conventional THR Review of Comparitive Clinial and Basic Science Studies   Michael Zywiel

Of the studies done, two found that Total Hip ReplacementsS were favored over Resurfacing,.  Three favored Resurfacing

The gait studies suggested that resurfacing  provides a more natural gait than conventional Total Hip Replacement.

Still a lot of debate on the subject and room for more research, but all midterm clinical  results suggested that resurfacing represents a safe, effective althernative to Total Hip Replacement, especially for younger, active patients.

Are there Gender Differences  Peter Brooks

Resurfacing is discouraged for women of child bearing age and older women.  The 2008 Australian Registry found a 2 ½ times higher revision rate for females than males, yet there was no difference when adjusted for component size.

BHR performed on 121 women between September 2006 and July 2009. 

Average age 52.8 range (33-68).

Follow up was 2 years for 22, and 1 year for 69, 56 patients currently are less than 1 year post op.

OA in 94 (77%). Dysplasia in 22 (18%). AVM om 4 (3%). One JRA and one lupus.

Those judged to be at risk for osteoporosis were given bone density tests.

Results – NO failures in these 121 women, no femoral neck fractures, reoperations, or revisions for any reason.

Conclusion: Hip resurfacing in women can be associated with a very high success rate.

Evaluations of Painful Hip Resurfacing

Taken from Syllabus:

  Evaluation of Painful Hip Resurfacing

John Antoniou

Background: Despite improved technology and understanding, hip resurfacing remains a technically difficult procedure requiring appropriate clinical indications, and good surgical technique to avoid complications and early failure. Patients occasionally complain of post-operative hip pain. Determining the cause(s) of this pain is sometimes clinically challenging. This presentation will focus on the differential diagnosis and the diagnostic modalities used to evaluate early and late post-operative hip pain.

Evaluation of Painful Hip: As in any total hip replacement, there are several investigative tools to elicit the underlying causes of pain for diagnosis and treatment. A detailed history, with specific questions on the onset and timing of the pain as well as the pain-free interval after the surgery, and a thorough physical examination to identify causes such as hernia and bursitis, are the most important first step in the diagnosis of the intrinsic and extrinsic etiologies of the pain. Serial radiographs should also be reviewed and compared for changes indicative of loosening, migration, and osteolysis. Diagnostic injections with local anesthetics can additionally be performed to localize the origin of pain. Bone scintigraphy, hip joint aspiration, and laboratory tests, including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), should be requested routinely to exclude an occult infection. The use of ultrasound, magnetic resonance imaging, and hip arthroscopy have been also suggested as potential diagnostic tools. These may be particularly valuable when metal sensitivity is suspected. Iliopsoas tendinopathy and anterior impingement of the femoral neck are other well recognized causes of pain and should be included in the differential diagnosis.

Conclusion: Determining the source of hip pain following hip resurfacing is challenging and it is essential to recognize the different causes of pain following surgery in order to make an accurate diagnosis and initiate the appropriate treatment.

Fractures Following Resurfacing  Michael Jacobs

Risk factors Controversial

Surgeon Experience

• Some papers said yes ( ¾ Mont had 12 fractures in first 69 cases, and only 2 in next 48)   J Arthro 2007     Amastutz JBJD Am 2004

• Some said no. ( ¾ Shimmin did not find a correlation with surgeon experience based upon Australian experience of 3500 cases    JBJS Br2005

Risk factors Not Controversial

• Osteoporosis or cystic changes of femoral head
• Women three time more likely than men - ?(osteoporosis, bone size)
• Obesity (may be increased with obesity directly or by difficult exposure and poor component positioning)
• Femoral neck notching
• Poor femoral component positioning
• Interruption of blood supply
• Failure to seat femoral component

How to Avoid Fracture

• Full seat femoral component
• Femoral component position is a key to prevent fracture or failure

How to Treat Neck Fractures

Non Operative and revision to a THR

There were some cases that were treatable non operatively those were non displaced fractures or  minimally displaced.

For non-operative treatment of Non Displaced fracture, conservative management with a period of 4-8 weeks non weight bearing followed by WBAT  (Cossey reported on 7 of 7 non displaced fractures that all healed by 16 weeks with excellent function – J Arto 2005

Non operative treatment of displaced femoral neck fracture with component shift

§         Modest varus shift of femoral neck AND component can be treated non operatively – D. Cumning, M.J.F, Fordyce reported on case treated non operatively that healed in varus with excellent clinical results at 15 month f/u ¾ JBJS Br 2003

§         Jacobs presented one case treated non operatively that helaed in varus with excellent clinical result at 48 months

§         Patients must be aware of the risks choosing the non operative route, potential for early or late failure.

Operative - Revision to a Total Hip Replacement, depending on if the components are available, the patients should have a straight forward revision to a Total Hip Replacement and most can keep the cup.

Conversion of Resurfacing  Harlan Amstutz

Taken from Syllabus:

  Conversiion of Resurfaciing

  Harrlan C.. Amstutz,, MD

Introduction: One of the proposed advantages of modern generation metal-on-metal hip resurfacing is easy conversion to total hip arthroplasty (THA).should it become necessary. We will review our experience updating our published article in JBJSA 2007. .

Methods: From our series of the first 1000 hip resurfacing procedures who have a minimum 3 year follow up (max 12.9yrs), 42 were converted to a Total Hip Replacement including 25 (in 24 patients) performed by the senior author. The average age of the patients at the time of conversion to Total Hip Replacement was 50.1 years (range 23 to 72). The time to conversion of the resurfacing devices was 45.6 months (range 1 to 120). Indications for conversion to Total Hip Replacement included loosening of the femoral component (16), femoral neck fracture (5), acetabular component loosening (2) and sepsis (2). A revision of the femoral component only was performed in 18 hips, and a revision of both components in the remaining 7, including 3 aseptic femoral failures for whom the conversion pre-dated the availability of the large unipolar head to match the pre-existing acetabular shell.

Results: The average follow-up was 72.5 months (range, 1 to 147). Clinical outcomes measures were high with a mean post-operative Harris Hip Score of 92.9 (range 78 to 100) and mean scores of 48.6 and 55.1 for the physical and mental components of the SF-12. The mean UCLA hip scores at last follow-up were 9.5, 9.6, 9.5, and 6.9 for pain, walking, function, and activity, respectively. The operating time and clinical results are comparable to those of primary THR. One well-fixed grit-blasted femoral stem fractured at 41 months and was revised. The patient was a small women and a competitive tennis player. The 6 year K-M survivorship was 92.9%. There have been no cases of aseptic loosening of the femoral or acetabular components, and there have been no dislocations in this series.

Among the 17 hips converted at an outside institution, 3 (2 patients) were femoral failures secondary to high wear of the bearing.In each case a the socket was retained and a Big Femoral Head was used . Clinical and radiographically they are doing well.

followup is short (years) In cases revised for wear it may be desirable to explant the socket .

None of the 42 conversions were associated have been associated with adverse local tissue reaction the so called “pseudotumor”. However, should this occur, prompt conversion is recommended with an alternate choice of bearing and a large femoral head for stability to minimize the risk of dislocation.

Conclusion: Conversion of failed MMRA to a Total Hip Replacement appears to be safe and effective. In all cases, a revision of the femoral component alone should be considered only if the position of the acetabular component is optimal and well fixed.

Prosthesis Head Size Risk Factors: THR vs. Resurfacing – John Antoniou

No difference in ROM, better activity level with resurfacing

Revision for Adverse  local tissue response: Incidence and risk factors contrasted with Oxford Results – Derek McMinn

1996 double heat treatment, caused black tissue even though component was well aligned.96% as opposed to 96% success difference with double heat treated or not.   Heat treatments are bad

Hip Simulators if bad can make results look wrong

Combined cup and femur inclination if higher than if cup angle is fine will still cause excess wear and pseuodotumors.

50% had dysplasia

Impingement can cause pseuodotumors, impingement can cause edge wear where part of the bone gets worn away

1 in 400 pseuodutumors in McMinn

Taken from Syllabus:

Revision for Adverse Local Tissue Response:
Incidence and Risk Factors Contrasted with Oxford Results

Derek McMinn MD FRCS

Pseudotumors have been reported from Oxford and a few other centres in patients with not only different metal-on-metal bearing devices but with conventional hip and knee replacements. Their presentation includes cystic or solid masses and in some cases semiliquid pus-like contents, soft tissue/bony necrosis, pathological fractures and dislocations. In addition the Oxford group estimate that around 5% of those with no current symptoms also have hidden pseudotumors. Patients who were revised for pseudotumors in the Oxford cohort were also reported to have had major complications including nerve palsies, pathological fractures, recurrent dislocations and a high rate of re-revisions. We compare our results with those reported from Oxford.

Methods: Our series of 3014 consecutive BHR implantations between 1997 and 2008 provide the single-centre cohort from which we have analyzed our results. In addition to our own documentation and follow-up, all our patients are independently followed up by two other Outcomes Centres in the UK, and this leads us to believe that we have as far as humanly possible, captured all our revisions.

Results: Out of 58 revisions in the entire cohort, 49 were non-bearing-related (1.6%) and include either infections or femoral failures due to bony insufficiency (fractures or femoral head collapse). Nine were bearing-related failures. Amongst these there were peri-articular fluid collections in 7/3014 (0.2%). Four of these were revised at our centre to non-MM bearing Total Hip Arthroplasty devices. None of these showed extensive necrosis or pathological fractures or dislocations. Current hip function in all the revised hips is good.

Conslusion: Failures in resurfacing are related to 3 different factors: implant factors as we have seen in our 1996 series, surgeon factors such as sub-optimal orientation of components, patient factors – dysplasia with abnormal version of the head and cup etc. Meticulous attention to all these details and good patient selection are critical to obtaining good results in the long-term

Differential Diagnosis and Treatment of Adverse Reactions   Tom Schmalzried

Adverse like tissue reactions (ALTR)

If you get the mechanics right

What doesn’t work  Mis-matched bearings, loose components, Fixation first

Presentation usually pain usually in the groin

May be painless

472 resurfacings , 464 with > 2 year follow up Dr. Schmalzried

Technical Factors Associated with an adverse local tissue response (verified cups)  Koen De Smet

33 failures out of his own 3000 resurfacings, has done over 90 revisions now, others are others, number one is malpositioned cups

Hypersensitivity shows up usually within first 3 years, no men only women has nothing to do with high wear

In Dysplasia women look at cup placement carefully Derek

3051 total resurfacings done Derek

If only doing 5 to 10 a year you will never get over your learning curve

Most hospital look poorly on HSR due to cost of procedure

Coding different in different areas for resurfacing vs. THR so different codes for different criteria like different age groups, etc.

Dr. Gross been doing for 10 years

Get adequate exposure

Correct femoral deformity

Place the acetabular component properly

  Avoid inclination greater than 60 degrees?

  Stay between 30 to 45 degrees

Technical Factors Associated with an Adverse Local Tissue Response – Koen De Smet

Taken from Syllabus:

Technical Factors Associated with an Adverse Local Tissue Response

Koen A. De Smet
ANCA Clinic Gent, Krijgslaan 181, 9000 Ghent, Belgium

One of the reported advantages of hip resurfacing is the easier revision for the femoral part and an overall decreased morbidity at the time of revision. We reviewed our hip resurfacing revision experience to examine the revision options and outcomes.

Between 2001 and 2009, we performed 85 revisions of metal-on-metal resurfacing procedures in 33 men and 52 women at a mean of 28 months [0-101] post-operatively. The primary procedures were done by the senior surgeon in 31 cases and 54 had been performed elsewhere. The mean age of the patient at the time of surgery was 51.6 years [ 18-71 ]. The mean follow-up after revision surgery was 27.5 months [1-100]. Malpositioning of the acetabular component was the main reason for revision (50 revisions, 59%), mostly because of excessive abduction or insufficient or excessive anteversion.

A total hip arthroplasty was done in 70.6% (n=60), cup only exchange was done in 9.4% (n=8), and a femoral procedure with stem and modular head without changing the cup in 20% (n=17).The mean increase in the acetabular component diameter was 1.9 mm [-2 ;+8] when cup exchange was needed (n=68). Post-revision dislocation rates were higher in cases revised with metallosis, because of the need to extensively dissect out metal-stained, enlarged bursae. By contrast, revisions for femoral fracture and loosening had excellent outcomes.

Revision of hip resurfacings can be easy and without a high complication rate if the case is not accompanied by metallosis. In our experience, implant malpositioning was the main cause for metallosis, and our previous studies have correlated malpositioned implants with high wear and elevated serum ion levels. In order to avoid complications at the time of surgery and worse results after surgery, we advise surgeons to monitor the level of serum metal ions, especially when there is malpositioning of the implant.

Techniques of Resurfacing

Taken from Syllabus:

SESSION 8: TECHNIQUES OF RESURFACING
The Uncemented Femoral Component in Hip Surface Replacement

Thomas P. Gross, M.D.

Background: This lecture reviews the 15 year history of modern metal-metal hip surface replacement as it relates to uncemented femoral components. The results of McMinn, Wagner, Villar, Spriggins and Griffin, Fern are reviewed.

The specific types of implants used are highlighted.

Patients with 1-2 year f/u (n=335):               5 revisions (1.5%)

a.         3 femoral neck Fx

b.         1 femoral loosening

c.         1 infection

d.         1 acetabular Loosening

Conclusions: Early results with uncemented femoral components were poor, but are improving. The theoretical basis for uncemented femoral fixation is discussed. The advantages and disadvantages of cemented vs. uncemented fixation are contrasted. Longer term results with modern improved implants are necessary before uncemented femoral fixation can be considered as a proven option in M/M Hip Surface Replacement. However, evidence is mounting for uncemented fixation.

Cementless Update – Thomas Gross

2 years now

Stable initial fixation’Cormet 2000 uncement 2^nd version and now Biomet uncemented

Introduced 3/2007

700 done to date

1^st year follow up 335

Approaches

Posterior Dr. Tom Gross

After about 500 cases Thomas Gross started using mis incisions.  Lots of experience prior to a doctor trying using a smaller incisions First time January 2005.  Uses about a 4 inch incisions  uses Procrit – blood management no transfusions to date

Preserve the neck capsule

Remove lare osteophytes

Place slotted wet towel to contain any debris and prevent Heterotopic ossification

Anterior with Table  Stefan Kreuzer

Smith Petersen approach of Robert Judet  Heiter Approach

Not much visualization

Recovers faster, one guy 7 days pospt op doing deep knee bends, one lady 4 weeks post op doing deep knee bends and full movements

Anterior without Table  John Keggi

Does with partner Kennon

Started in 1983 with THR’s

Visited Ronan Treacy, started using cadaver work

April 2007 started doing Direct anterior approach with hip resurfacing

Prep time short 8 minutes after spinal, starts incision

Curved incision

Does capselotomy

Done about 250 of them, Keggi has done about 150 and Kennon a little over 100

Takes about 85 minutes

Cement Mantle Debate between Amstutz and McMinn

McMinn does not cut away bone to provide more room for cement, he only uses it by pressurizing cement onto the bone, McMinn has NEVER had one loosening of any femoral component EVER.

McMinn stated that Amstutz failure rate at 4 years is higher than McMinn’s is at 12 years.  Amstutz stated that he does much more difficult cases than McMinn does.  Amstutz does osteopenia and AVN and McMinn does not.  The reason to have A ~ One mm mantel is to enable the surgeon to obtain a uniform mantle and pressurization thereby avoiding the tendency to over prssurize the cement.    The thing they both agree on now is that they now both use a inter trochanteric suction, before Amstutz used a dome suction alone.  Interesting to note that there have been a few stems that have fractured or broken (maybe due to the stem size being so thin compared to the BHR for the C+ device?)

Interesting also to note in one of the first panel discussions that McMinn tends to be using a lot of the BMHR device now over BHR’s.  He says that all AVN cases should use a BMHR rather than a BHR.

Joint Preservation for Osteonecrosis  Michael Mont

Trying to avoid Total Hip Replacement’s  but do the most conservative procedure especially for young patients like those in their 20’s.

Core Decompression

Percutaneious drilling

Bone grafting non vascularized or vasularized

Osteotomy – rotational or angular but limited application for 2^nd one.

All able to avoid decapitating the head or major surgery in young patients especially

Pelvic Osteotomies  - John C. Clohisy, MD

Taken from Syllabus:

Pelvic Osteotomies

John C. Clohisy, MD

Background:

The treatment of structural hip deformities has evolved significantly over the past decade. One of the major advances in this field has been the refinement of pelvic osteotomy procedures. In North America, the Bernese periacetabular osteotomy (PAO) has become the preferred surgical technique for reorientation of the dysplastic acetabulum. With the popularization of this technique has become a series of refinements which have expanded the indication for osteotomy surgery and has enhanced the ability to treat hip deformities in a comprehensive manner.

Methods/Results:

In this presentation, the indications and summary of contemporary results of pelvic osteotomy surgery will be discussed. The surgical technique of the periacetabular osteotomy will be briefly reviewed. The expanding role of pelvic osteotomy surgery and the treatment of hip disease will be emphasized. The expanding role of these techniques includes application of pelvic osteotomy to patients with severe acetabular deformities, Perthes-like deformities of the hip and previous osteotomy deformities of the hip. In addition, pelvic osteotomy surgery has now been enhanced by a variety of combined procedures. These combined procedures can add significantly to the comprehensive nature of our treatment for structural hip disease and associated interarticular abnormalities. The role of hip arthroscopy, osteochondroplasty of the femoral head-neck junction, surgical dislocation of the hip and proximal femoral osteotomy will be discussed as adjuncts to modern pelvic osteotomy surgery.

Conclusion:

The combination of these surgical procedures provides a marked improvement in the surgeons’ ability to treat structural hip disease and associated interarticular abnormalities. Pelvic osteotomy surgery should now be viewed as a safe and efficacious intervention for symptomatic, pre-arthritic and early arthritic hip disease. A variety of augmentation procedures can be utilized to optimize osteotomy procedures.

Technical Factors and Ion Levels  Koen De Smet

3003 resurfacing they now do 2 year 5 year and 8 and 10 year ions checks

Rarely find high metal ion levels.  He now has about 1000 patients tested with metals now.  Run in believes it is 1 year

Koen believes if higher than 20 revision needed

Taken from Syllabus:

Technical Factors and Ion Levels
Koen De Smet

Summary: Serum cobalt levels in patients implanted with hip resurfacing greater than 4.1 ug/l have 11 times the odds of developing clinical problems than those with lower levels.

Methods: We measured serum Co and Cr levels (ug/l) of all unilaterally resurfaced patients with no other metallic implant attending follow-up clinics. Patients were categorised as A. Well Functioning (n=358) or B. Clinically Problematic (pain, reduced function, reduced ROM) (n=161); differences in ion levels between these two groups were examined. A variety of implants were used with Birmingham Hip Resurfacing (64%) and Conserve Plus (29%) being the most common. A guideline upper ion level value for well functioning implants was calculated as the upper 75^th percentile ions values for Group A patients having 15mm or more superior cover.

Results: The ion levels were significantly (p<0.001) higher in Group B, (Co 10.2 [95% CI 5.9-14.5], Cr 10.3 [6.7-14.0]) compared to Group A (Co 2.3 [1.7-2.4], Cr 2.8 [2.3-3.4]). The well functioning upper limit for Co was 4.1ug/l and was 5.2ug/l for Cr. Metal ion levels greater than these limits were significantly (p<0.001) associated with the presence of clinical problems; the odds ratio for Co>4.1ug/l was 11.2 [5.7-22.3] and that for Cr>5.2ug/l was 4.3 [2.6-7.0].

Conclusion: There were significantly higher metal ion levels measured in patients with clinical problems after metal-on-metal hip resurfacing than those with well functioning hips. We propose upper acceptable limits for Co (4.1ug/l) and Cr (5.2ug/l) serum levels. Cobalt levels appear to be more reliable in predicting risk of clinical problems; levels greater than our proposed upper limit have 11 times the odds of developing clinical problems and these cases should be followed closely.

Metal Ions: Clinical Consequences  Derek McMinn

Hip Simulators are not accurate

When you take out infections then no difference between men and women

Metal ions do cross the placenta , but the placenta regulates how much passes through

Taken from Syllabus:

Metal ions: Clinical Consequences

Derek McMinn MD FRCS

Results. Longitudinal studies of metal ion output and whole blood metal ion levels show that following resurfacing, there is an early run-in wear followed by a steady state plateau. In terms of bearing diameter we find no difference in metal ion levels between a 28mm metal-metal THR and a 50/54mm diameter resurfacing. Reduced clearance bearings lead to a reduction in metal ion levels in the intermediate phase but have also shown a worrying incidence of progressive radiolucent lines during follow-up.

Being essential elements in the body, the excretory system is adequately geared to handle the excess cobalt and chromium ions generated. This is seen from the fact that renal clearance of cobalt progressively increases with increasing metal ion release from the device. On the key question of transplacental transfer of metal ions, we have demonstrated that both cobalt and chromium ions are transferred across the placenta but the placenta exerts a regulatory role.

Metal ion levels in different cohorts of young patients with BHRs who regularly participate in high quality sport are found to be in the same range as the levels found in a small cohort of patients with historic metal-metal total hip replacements. Epidemiological studies show that historic metal-metal bearings are not associated with carcinogenic effects in the long-term.

Conclusion. It is reasonable to expect that modern resurfacings will also follow the benign clinical history of the historic metal-metal replacements. However, every effort must be made to further improve bearing performance and to reduce bearing wear.

Cancer Risk  James Richardson

Metal metal does not cause cancer

END

There was more but I could never get to it if I had to finish adding all of the details.

Portions taken from the syllabus were approved by the doctors to reprint.

Enjoy reading

Vicky