Acetabular Revision in Hip Resurfacing

THR= total hip replacement

HRA= hip resurfacing arthroplasty

If an HRA has failed, I try to solve the problem by revising only the acetabular component whenever possible because HRA are functionally better than THR. If only the acetabular component is revised, the patient still has a HRA. If the femoral component is revised, the patient now has a THA.

Currently revising only the acetabular component with a metal/metal (M/M) articulation is only possible with the Biomet Magnum and SNR Birmingham implants. All others have been withdrawn from the market. Wright Conserve can still be revised in this way outside the US, because these perfectly good implants were only withdrawn from the hyper-litigious US market. The failed Depuy ASR and Zimmer Durom can be revised with a custom polyethylene (PE) bearing acetabular component. The only surgeon I know of who has access to these implants is Dr. Pritchett in Seattle. But I am not sure that a PE bearing HRA is better than a THR.

In the past, I preferred revising Biomet femoral failures with a Magnum M/M THR. This is no longer possible because Biomet withdrew the Magnum head because of a fear of inappropriate litigation in the midst of anti-metal hysteria. Now the best option may be a dual mobility head THR  for femoral revisions. Other brands of HRA had poor trunions for their matching femoral stems and were withdrawn from the market for good cause. The Biomet Magnum trunion was unique and was NOT subject to corrosion from strain induced by a large head.

The advantages of hip resurfacing are:

• Longer implant durability (statistically) than THR in young patients:
  • Nordic registry reports a 17% 10 -year revision rate with cemented or uncemented THR in patients under 50
  • 10% of unrevised hips in registries are actually failed but are counted as “successful” because they are unrevised.
  • This means really a 25% failure rate at 10 years for THR in patients under 50
  • My personal 10 -year failure rate with hybrid HRA in over 1000 unselected patients under 50 is 7%.
  • With uncemented HRA my 7-year failure rate is 1%.
• Bone preservation  (sometimes making revision surgery easier)
  • My published 7-year implant survivorship in all HRA revisions is 96%
• Near normal hip stability
  • THR with 28 mm bearings have a 5% rate of dislocation
  • My HRA have a 0.3% rate of dislocation
  • Larger bearing sizes decrease dislocation in THR:  28mm (5%), 32mm (3%), 36mm (1%)
  • There is no 10-year implant survivorship data on 36 mm bearing THR
  • Multiple 10-year papers in HRA indicate survivorship over 90% in younger patients
•  Avoidance of stem related thigh pain
  • 3-5% with uncemented THR stems
  • none with HRA (no stiff metal stem in the femoral canal) 

• Higher functional possibility with HRA
  • 4/5 gait studies show HRA is superior. one shows equivalence. None shows better function with THR.
  • 2/2 functional questionnaire studies indicate higher functional results with HRA
  • 10-year implant survivorship declines much more with THR than hybrid HRA in patients participating in impact sports.
  • No decline in 7- year implant survivorship with uncemented HRA
  • Full unrestricted activity including running and yoga can be allowed 6 -months after HRA
  • But some patients are not able to run longer distances because of residual symptoms even after successful HRA.
•    Patient Longevity
  • 2 studies from the British registry have shown that young patients who have HRA have significantly greater 5 and 10-year survival than similar patients who have THR instead (HRA patients live longer).
  • Previous studies have shown that patients with severe OA live longer if they have their hip replaced than if they try to treat their pain medically.
  • Long-term studies have shown no difference in cancer risk for patients with any joint replacement and the general population
•     Logic:

  The basic problem in an arthritic hip in a young patient is a mild bony deformity resulting in a premature loss of surface cartilage. This exposes the nerve endings in the bone, resulting in activity related pain. Unfortunately we are still unable to resurface with cartilage. It follows, that the best way to correct an arthritic hip is to resurface with artificial parts, making subtle corrections to the underlying bone deformity while preserving the natural biomechanics of the hip as much as possible. Removing more bone and drastically changing the function of the hip only makes sense if resurfacing is not possible. Resurfacing is more complicated to do correctly than THR. Enough surgeons have now demonstrated that resurfacing can be done successfully. The others need to learn or retire. Younger surgeons should let the “old school” surgeons ride into the sunset doing the best that they can, but they should learn the better technique. I am convinced that most can achieve this if they set their mind to it.

The main causes of failure requiring revision in HRA are:

• Acetabular Failure of ingrowth
  • Currently in my series 0.5%
• Adverse Wear Related Failure (AWRF)
  • Currently none since 2009 in > 2000 cases with minimum 2-year follow-up
  • Overall 0.3% in 4000 cases
  • Overall 1% @ 10 years using Kaplan-Meier statistics
• Acetabular Loosening:
  • Biomet acetabular components are out to 9 years without any debonding cases yet
  • 1.5% rate of porous coating debonding from the implant with the Corin brand only at 10 years.
• Femoral neck fracture or head collapse
  • 1.5% and 0.5% prior to instituting postoperative bone protection protocols
  • None since 2009
• Femoral Loosening
  • 3% by 10 years with cemented femoral component (hybrid HRA)
  • None in > 3000 uncemented components since 2007
  •  Deep Infection early postoperative ( < 3 months from surgery)
  • None since 2009
  • Rare prior to that
• Other rare causes for revision:
  • Deep infection Late Hematogenous
  • Recurrent dislocation
  • Impingement pain
  • Instability without dislocation
  • Psoas Irritation

Revising only the Acetabular component:

I can usually perform isolated acetabular revision for the first three causes of failure listed above if we are dealing with Biomet Magnum or SNR Birmingham implants. Some of the other rare causes for revision listed above can sometimes also be solved with isolated acetabular revision. I used to do the same for Corin Cormet or Wright Conserve implants, but these are not available in the US any longer. I never did this with Zimmer Durom and Depuy ASR implants because these were poorly designed. Theoretically all of the last 4 could also instead be revised with custom plastic bearing acetabular components these do not need to be brand matched. As far as I know only Dr. Pritchett has access to these, and I would only do this type of revision with reservation if cross-linked PE were available.

The most controversial acetabular only revision is for AWRF. This requires retaining a possibly abnormally worn femoral component. Both Dr. Pritchett and I have published excellent results in limited numbers of cases using this method. The published results using smaller bearing THR instead have generally been quite poor, notably from the Oxford group (Murray, Kwon etc.).

Generally, surgeons who are opposed to resurfacing believe that AWRF is some type of allergic response and that revision of these cases should entail radical tissue excisions to remove every last bit of metal debris and to implant THR with other bearing types. Unfortunately there is no convincing evidence that allergy to metals is a cause of failure; this is simply an incorrect hypothesis advanced by the Oxford Group. I think that they simply failed to recognize that their AWRF cases had malpositioned acetabular components. Acting based on an incorrect hypothesis has led them to experience disastrous results with revision of these cases. (David Murray is the leader of the Oxford Group; you can search all their papers on pub med if you like).

The cause of HRA failures with extensive metalosis is actually an abnormal wear mechanism called “edge loading”. This is caused by either acetabular component malposition or poor design (ASR low coverage arc). In my opinion the best method to solve this problem entails careful and limited excision of tissue membranes with metalosis staining. There is no need to perform radical tissue excisions that damage muscle, tendons nerves or arteries as others have incorrectly advised. The acetabular component can usually be removed with minimal bone loss. If a well designed implant brand was in place, a new matching component of the same brand can then often be inserted in the correct position solving the problem. Usually, but not always, this requires a slightly thicker walled revision implant with a matching bearing size.

Wear failures with metal bearing THA and modular neck THA often (except the Biomet Magnum) also involve trunion corrosion problems. These problems are more complex to diagnose accurately and deal with than isolated bearing wear in HRA and will not be addressed here. The trunion is the metal connection between the head/neck/stem.

A few words of caution:

Residual unexplained pain after joint replacement:

There is a 10-20% incidence of residual pain after any type of hip or knee arthroplasty. With my experience using all 4 types of operations I find that generally function and satisfaction is greater for HRA> THA> UKA (uni knee) >TKA (total knee). Joint replacements do not create normal joints. Just because there is some residual pain, does not mean that the situation will be improved with a revision surgery. Revision surgery only carries a reasonable chance of success if a specific correctable cause for failure is identified. Revision for unexplained pain is a bad idea. There are several patient groups who are known to have a higher rate of residual unexplained pain after joint replacement surgery. The best thing for a surgeon to do is to recognize the limitations of joint replacement and be more reluctant to implant these patients. Patients at higher risk for residual pain after joint replacement include:

• People with workers comp insurance or those who have an active injury claim. (someone else is to blame for their problem)
• People who are very dissatisfied with their work
• People with less severe pain, but minor x-ray findings. (princess on the pea syndrome)
• People who report more than 4 medicine allergies.
• People with other chronic pain syndromes “requiring” chronic narcotics
• People with extreme anxiety or depression
• Previous major surgery on the joint / revision

Metal Allergy:

In plain English: Allergy to implants does not exist. It is an unproven concept that many people including surgeons believe in. There is no convincing scientific evidence that it is a cause for any described implant related failures. Residual pain has never been linked to skin patch tests or blood allergy test to metals (lymphocyte transformation test). Yet some experts continue to recommend that patients with a history of skin sensitivity to metals not to get certain implants. Many also subscribe to allergy testing before surgery or to diagnose residual pain. This is unscientific thinking and makes absolutely no sense.

Skin sensitivity to Nickel is very common. Trace amounts of Nickel are present in Cobalt chrome alloys used in M/M bearings. Skin sensitivity can be objectively measured by a skin patch test. Numerous studies have shown no correlation between skin patch tests and any implant related problems. At first glance it seems logical to connect skin sensitivity to possible implant rejection in the body and it is certainly a valid question to ask. but skin sensitivity to metals has been shown not to affect outcome of joint replacements. A history of skin sensitivity or a positive skin patch test has no predictive value.

It also makes no sense to order a lymphocyte transformation test (LTT). It costs $500 and gives you a beautiful graphic printout documenting “allergies” that you theoretically have to various metals and even bone cement. The problem is that it is an unvalidated test. The disclaimer says so right on the report. This test has been around for over 10 years but has never been shown to be diagnostic of anything. Basing treatment decisions on this test makes as much sense as consulting a mystic.

About 500,000 TKR (total knee replacements) are done in the US annually. The vast majorities employ a cobalt chrome femoral component. All implants release low levels of artificial particles into the body from wear or corrosion. Measurable ion levels have been recorded for these implants. Metal ion levels from well-functioning M/M HRA are somewhat higher than for TKR. Function is higher and the rate of residual pain and dissatisfaction is lower after HRA than TKR.Yet unexplained pain in HRA is blamed on metal allergy, while no one considers this a viable concept in unsatisfied TKR patients. There seems to be a logical disconnect. Furthermore, most of the 300,000 THR done annually in the US employ a cobalt-chrome head. HRA has been shown to allow higher function than THR. But people are allergic to metal bearings but not metal plastic THR. Again…. a logical disconnect.

The only reason to avoid certain metallic implants is if a patient subscribes to this concept and cannot be convinced otherwise. If a patient believes that they are allergic to Nickel, HRA is not possible. THR and TKR implants employing alumina and zirconia ceramic, polyethylene, and Titanium vanadium alloys can be used. How can one be sure that a patient is not also allergic to these? Perhaps a LTT?

Once someone truly believes this superstition, it is hard to convince them with logic. I have no problem respecting this belief and giving a person a non cobalt-chrome containing implant for their primary surgery. But I do have a problem revising a patient who believes their unexplained pain is caused by metal allergy. I have an even bigger problem revising such a patient if a class action settlement is available.

Revision for unexplained pain:

10-20% of patients after joint replacement have residual unexplained pain. If their joint pain was bad enough before surgery they are still often satisfied with the outcome. 15% of patients with a resurfacing or a standard metal- plastic hip replacement have some fluid collection on MRI. Presence of a small fluid collection and some residual pain is not a good reason for revision surgery. In current orthopedic practice many metal bearings are and most plastic bearings are not revised in this circumstance.

I would generally only recommend revision surgery if a definite correctable cause of failure can be identified. In occasional cases I will explore a hip surgically when I have a suspicion of a rare failure mode.

Unfortunately there are many surgeons who will recommend revisions for any patient with any residual pain if they have a metal bearing device. They will not be operating for a clearly defined cause of failure and will often recommend the surgery for “metal allergy” and then find some “grunge” in the hip joint when they convert the patient to a metal plastic bearing THR. Sometimes they get lucky and the patient gets better, sometimes there are serious complications. The published results for this approach are terrible; but these same surgeons still blame the original metal bearing for causing a “recurrent pseudotumor”

In my view, when surgeons operate without identifying a cause they place their patients at unjustified risk and then have to justify their inappropriate action. This is some of the collateral damage that occurs when a national hysteria develops. Calm, rational thinking is suspended when the media and shady lawyers whip up a storm. Unfortunately many patients get swept up in this, particularly if they are very suggestible or if a large legal settlement is available. I am particularly saddened to see many of my orthopedic colleagues swept up in this nonsense as well.

There are many complexities. There are definitely cases that require revision, there are others that can be observed to see what develops, still others where exploratory surgery can be undertaken if a patient is well informed and is willing to take the risk. But it is a generally a mistake to revise patients with unexplained pain without clear objective findings.

If you have a problem with your hip resurfacing, get a second opinion from an experienced hip-resurfacing surgeon. Be wary of any surgeon who is quick to suggest revision without clearly explaining the cause of failure. Implant allergy is an unproven concept.

 

Thomas Gross MD    1/9/2015