Dr. Edwin Su Overview of 2nd Annual U.S. Comprehensive Course on Total Hip Resurfacing Arthroplasty
Since I was unable to attend this conference, I asked a couple of doctors to write an overview for the website. Thank you Dr. Su and Dr. Rogerson.
Held in Los Angeles on October 24 & 25, 2008
By Dr. Edwin Su
Dr. Su notes on the Second Annual US Comprehensive Course on Total Hip Resurfacing Arthroplasty
I've typed up some of my notes from the course. In summary, I found that the main topics discussed were: results of hip resurfacing worldwide; technical aspects of hip resurfacing; patient selection; failures of resurfacing; and concerns about metal on metal joints. The overarching theme, however, has become clearer and clearer in these conferences. Namely, that COMPONENT POSITION IS CRITICAL, and experience is paramount to get it right. Surprisingly, a Canadian study found no difference in patient perception, gait, or activity level in a large diameter metal-on-metal THR vs. a hip resurfacing. This caused many attendees to wonder why they would perform a hip resurfacing, given its technical difficulty and additional concerns such as femoral neck fracture. However, I think that the most important aspect of hip resurfacing is its ability to preserve bone, and thus it is still a worthwhile procedure!! Friday, October 24, 2008
Dr. Schmalzried - Evolution of Metal-on-Metal Resufacing
There is a recognized higher risk of short term failure, particularly in certain patients Females Patients with femoral head cysts > 1 cm Shorter patients - perhaps a surrogate for size Implants with varus positioning
Australian Registry has found an increased risk of failures in patients over 65 years old
Increased risk of failures in women Outcomes after hip resurfacing may be better with early intervention in order to preserve function -- no longer advocates "waiting as long as possible before hip surgery" Implant design - he believes there will be a convergence of design; perhaps to a shorter, thinner stem, due to Andrew Shimmin's data that showed more femoral neck remodeling in smaller sizes with a larger, constant thickness stem Material issues: Believes it is important to distinguish between metal reactivity, which is a foreign body response; and metal sensitivity, which is an immunologic response
Dr. Amstutz - History of Materials and Failure Mechanisms
Conserve Plus results are 99.3% survival at 8 years, if femoral component > 46mm Results are also technique dependent: 6% femoral loosening in 1st generation cementing technique 3% in 2nd gen. (removal of cystic tissue, using carbojet) 0% in 3rd gen. (use of femoral suction)
Panel Discussion
In other countries, hip resurfacing arthroplasty (HRA) is 6-10% of all primary THR; where do you believe it will be in the US? Dr. Schmalzried - will depend on FDA approval Give us an idea of your average age patient for THR and HRA, and also the percentage of HRA? Dr. Mont: average age 48 for THR; 44 for HRA 60% resurfacing Dr. Schmalzied: 70 for THR; <50 for HRA 50% resurfacing Dr. Stulberg: 61 for THR; <50 for HRA <5% resurfacing Dr. Amstutz: 70 for THR; 50 for HRA 95% resurfacing
Dr. John Fisher - Metallurgy, Tribology and Hip Resurfacing
Concerns about reaction to nanometer size metallic particles in high concentrations; can cause cytotoxity and tissue necrosis Factors affecting
1) Metallurgy is not a variable as long as high carbide metals are used, which all implants now use No difference between wrought/forged and cast
2) Head diameter - larger diameter has decreased wear because in the initial bedding in phase, there is more conformity
3) Diametrical clearance between cup and head: theoretically, the lower the clearance, the lowere the wear 4) Surgical positioning A 5x increase in wear was noted if cup inclination increased from 45 to 60 degrees, in hip simulator Laxity of tissues may also play a role, microseparation will cause more wear, esp. in a steep cup
Paul Beaule - Femoral Head Blood Flow
Noted decreased blood flow with notching at the head/neck junction Initially notching was viewed as a mechanical problem, but may actually be a vascular problem Another study found that despite using a trochanteric flip approach, there was still a decrease in femoral head blood flow after using the cylindrical reamer. His proposed solution is to either oversize the femoral component or hug the inferomedial neck to preserve superolateral vessels
David Murray (Oxford) - Biomechanics of femoral neck fracture
Oxford experience is 1.6% ( 24/1500) Notes that this is a similar incidence of dislocation after THR, which is often not considered a "failure" after THR. Fractures tended to occur early, with 2/3 occuring in 1st 2 months postop, suggesting they are surgically related In their validated Finite Element model, they did not find any differences in the stresses in the femoral neck in an intact vs. resurfaced hip Neck construct (bone + stem) was actually stronger than the intact, non-operated femur Small notch of 2mm did not have any appreciable effect
Did not find a substantial difference with component position, either
The positioning would have to be markedly different (20 degrees of varus) before there was any effect Therefore, he concluded that fractures are not generally a result of biomechanical considerations Also performed a study that looked at 15 early fractures, and matched each to 2 controls - looked at notching, component overhang, alignment: The only factor that approached significance was that the non-fracture controls had more superior overhang, thus may suggest a vascular issue No significant difference in notching, lengthenigng, varus, co-morbidities
Common failure modes in her retrieved specimens: Fracture - 26% Femoral loosening - 22% Socket loosening - 11% Socket malposition - 11%
Females comprised 69% of socket malpositioning, and 72% of socket loosening
Unexplained pain was a reason for revision also; many of these that are attributed to metal sensitivity may actually be due to impingement, loosening, or fracture There were some cases of metal sensitivity, which can happen in a well-done resurfacing
Dr. Mont - Clinical outcomes of Resurfacing vs. THR
Showed a better gait pattern in resurfacing, but another study by Andrew Shimmin did not Does report a higher activity in resurfacing vs. THR
Martin Lavigne (Montreal) - Comparative studies of HR vs. THR
1) Study HRA vs. 28mm diameter head metal on metal THR Found that 1 year UCLA activity score was 7.3 in HRA vs. 6.1 in THR, but there was no difference at 2 years More patients were doing impact sports in HRA "Hop Test" and "Step Test" were more difficult for THR @ 6 months, but no difference at 2 years Gait lab showed balance was better at 6 months in the HRA.
2) To make the study more comparable, he then used large-diamter metal on metal THR vs. HRA No difference in UCLA score at 1 year 2/3 felt natural in both groups No difference in perception, gait speed, hop/step tests No difference in gait
My most important lessons: Dr. Koen De Smet
1) Component position is extremely important, particularly of the socket
2) There is a difference in component geometry The BHR has a smaller angle (164 degrees) compared to Conserve Plus (170) 3) Metal ions can be a helpful diagnostic tool
Andrew Shimmin (Melbourne Australia)
1) Patient selection is critical - males younger than 65 are preferable; Younger, big boned females are okay AVN will have relatively worse results 2) Exposure is important - make a large incision 3) Always have a THR as backup
John Antoniou (McGill)
1) Avoid femoral neck fracture 2) Understand femoral deformity 3) Understand the factors that may influence metal ion production (positioning)
Martin Lavigne
1) Patient selection is important - rarely does females over 45 years old
2) There is an increase risk of heterotopic ossification in HRA; found 12% vs. 2% in THR Now uses indocin for all patients Graham Isaac - Metal ions Performed a whole blood analysis of metal ions in 40 patients Rapid increase in cobalt and chromium up to 3 months, then plateau Outliers were related to socket position
Mont - Perthes and AVN
Perthes is challenging, may be associated with dysplasia also Short, wide FN may get impingement Reports on 150 patients with AVN; aborted 6 or 7 to THR because of size of lesion Ronan Treacy did 70 patients and found a 7% failure rate
Dr. Amstutz - Rheumatoid arthritis and HRA
challenges include small component size, poor bone quality, higher infection rate Has 14 hips with RA in his first 1000 HRA Mean f/u is 6.8 years, no neck fractures or loosenings in DDH, also a challenge because predominantly women, small sizes Increased anteversion, increased valgus, decreased offset, and joint laxity Inadequate acetabular bone
Andrew Shimmin - Fracture
2.3% Fracture rate Early is 0-3 months - majority are mechanical Later is after 6 months - probably are biological Disagrees with David Murray about the mechanical factors, does believe notching plays a role Found that 52% of fractures had evidence of notching Fracture rate is 2x higher in women
De Smet - Acoustic Phenomena in HRA
1) Popping/clicking - may represent a loose joint, usually from postop to 6 months believes it represents decoaptation of 2 hard on hard surfaces disappears in majority of patients after 6 months; estimates 25% of patients will have it
2) Clicking/clunking - probably from impingement may be femoral neck against cup may occur is insufficient anteversion on cup may occur from failure to correct cam impingement Would believe it is better to remove neck osteophytes and risk fracture of femoral neck rather than have impingement
3) Grinding/clunking - believes this is edge loading and then subluxation Squeaking was noted in 5% of his BHR Shimmin also noted this in 4% of BHR Barrack - Learning curve of HRA US experience looked at 587 cases, 83% with 1 year followup 12 (2.7%) fracture rate Fractures all occured in the 1st 25 cases
Antoniou - Evaluation of painful resurfacing Causes:
1) Femoral neck fracture
2) Loosening/osteolysis
3) Acetabular loosening
4) ALVAL - metal sensitivity
5) Iliopsoas tendinopathy - in THR, this has been reported in up to 5% patients May be addressed by component repositioning or tendon release
6) Hip impingement
7) Heterotopic ossification
8) Infection
Thank you Dr. Su!