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Examining femoral modularity in THA

Issue: February 2014

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In the second part of a this Round Table, we bring together experienced hip arthroplasty surgeons to provide insight into the pros and cons of modular femoral hip stems for both primary and revision reconstruction.

A. Seth Greenwald, DPhil (Oxon)
Moderator

A. Seth Greenwald, DPhil (Oxon): What are the trigger points for intervention and did the in situ pathology justify the event?

Allan E. Gross, MD, FRCS(C): I have not had to intervene on any modular femoral components in the type we use because of a problem with the junction of the body and the stem.

Wayne G. Paprosky, MD: My trigger point for intervention was pain mostly in the greater trochanter that developed from 6 months to 2.5 years postoperatively. These patients developed elevated serum metal levels and had positive MRIs. All of the tissue pathology was positive for varying degrees of tissue necrosis.

Adolph V. Lombardi, Jr., MD, FACS: Patients who present with a painful total hip should be evaluated for all causes of failure, both intrinsic and extrinsic. When all other causes of failure have been eliminated and one believes the cause of failure is ARMD secondary to corrosion, these patients should be risk-stratified similar to a failed MoM. This involves an evaluation of all factors, including gender, age, track record of the implant, presence of osteolysis, metal ion evaluation and cross-sectional imaging. Symptomatic patients with elevated metal ions and positive cross-sectional imaging should be counseled regarding revision THA.

Thomas P. Schmalzried, MD: My trigger points are pain and/or MRI evidence of an ALTR. There is a range of gross pathology, but the histology is generally consistent with ALVAL.

John J. Callaghan, MD: My trigger point for intervention in symptomatic patients with at-risk components (i.e., the designs we know are at high risk and malpositioned components) is low. I would like to see at least one concerning study (i.e., elevated ions, fluid on ultrasound or MRI). For asymptomatic patients, I have a higher threshold, either bone or soft tissue destruction, large cystic lesions or markedly elevated ion levels.

Michael J. Dunbar, MD, FRCS(C), PhD: The difficulty with our experience with a high fracture rate of modular necks was regarding how to advise patients thought to be at risk. The fractures seemed to have occurred without prodrome or warning. As such, some active patients with long, retroverted modular femoral necks were contacted and advised they were at risk for fracture. Many of these prostheses were well functioning. Subsequently, the patient and physician were left in the dilemma of choosing between the risks associated with revision vs. risk of neck fracture. This is a situation I would like to avoid in the future.

Greenwald: Have you observed that the use of dissimilar materials (cobalt-chrome/titanium alloy) at metal-metal tapered connections has resulted in more or less surface damage? Has this influenced your choice?

Gross: I have not observed this problem. All of our junctions on femoral implants for revisions and primary femoral implants are titanium with a cobalt chrome head. This potential problem has not influenced my choice of implants.

Paprosky: I have observed that the use of dissimilar materials at the metal-metal tapered connections have resulted in significantly more surface damage than with the similar metal-metal connections. I have yet to see any significant surface damage at similar metal-metal connections.

Lombardi: Historically in our practice we have utilized titanium femoral stems with chromium-cobalt femoral heads. We have seen several cases of significant taper corrosion, which has ultimately caused severe osteolysis and ARMD and has required revision arthroplasty. Therefore, I elect to use ceramic femoral heads in my younger higher demand patients.

Schmalzried: I have not.

Callaghan: I can’t say that my experience would support this, but we have never specifically looked up our cases to answer that question. The case series in the literature has led me to use ceramic heads with titanium sleeves to minimize chromium and cobalt in the THA construct in all cases.

Dunbar: No.

Gross: I rarely have done a revision for a femoral head that was greater than 36 mm in diameter, and I have not done a revision for a distal neck-stem taper. Therefore, I have no answer for this question.

Paprosky: Larger femoral heads greater than 36 mm cause much more corrosion when used with distal neck-stem tapers than when used with femoral head-neck connections. We have seen corrosion femoral head-neck connections, but it is less common. Almost every distal neck-stem connection that I have revised with a large head has corrosion.

Lombardi: We have had extensive experience with large diameter femoral heads. We specifically have extensive experience with a 38-mm chromium cobalt head in a MoM articulation. We also have experience with larger anatomic femoral heads. Interestingly, these larger anatomic heads have taper junctions made of titanium alloy. When revisions of the 38-mm heads vs. the large anatomic heads are performed, we routinely see significant corrosion in the 38-mm chromium cobalt heads against the titanium tapered femoral components. This, however, is not seen in the large anatomic femoral head reconstructions which used a titanium sleeve. Therefore, I have restricted utilization of femoral heads larger than 36 mm that are made of chromium cobalt.

Schmalzried: I cannot recall revising a hip with a greater than 36-mm non-metal-metal for a problem due to the taper. I have little experience with modular neck prostheses.

Callaghan: Fortunately, I personally never used large heads, except rarely in a revision to prevent or treat instability. These are usually not high demand patients. I can’t remember seeing taper corrosion at the time of re-revision, yet I am sure I will.

Dunbar: I have not seen a significant difference to date.

Greenwald: In the face of a well-fixed stem where revision is required, will you selectively replace only the femoral head and/or distal neck-stem components given the admonitions of package inserts and the reality that not all taper dimensions and surface finishes are alike even from the same manufacturer?

Gross: When I have a well-fixed stem and there is no indication at all to revise it, we will replace the femoral head from the same manufacturer. I have no experience with distal neck-stem modularity.

Paprosky: When revising a well-fixed stem if there is a distal neck-stem connection, I will revise the entire stem. I do not believe that simply distal neck-stem exchange is the correct treatment of choice. I am assuming that I am revising these stems because of corrosion. The only time I may just exchange the neck-stem segment would be if the reason for revision was for instability or leg length discrepancy and no corrosion was seen.

Lombardi: There is no one generalized answer to this question. Every patient’s treatment must be individualized. If indeed the stem is well-fixed and removal of the stem would cause significant bone destruction and bone loss, then it seems appropriate to selectively replace the femoral head or distal neck-stem component. We must first do no harm. We are all keenly aware that occasionally removal of a well-fixed stem can lead to a difficult and compromised reconstruction.

Schmalzried: In this circumstance, I will replace only the femoral head, but only with a head that was manufactured for that specific taper. In this setting, I currently prefer to use a ceramic head with a titanium taper sleeve.

Callaghan: Concerning femoral heads, I will always leave an intact stem even when there is significant corrosion. Today, I will use ceramic heads with titanium sleeves. In cases with double taper necks, I am revising all stems and leaving no chrome cobalt in the revision THA construct.

Dunbar: No, absolutely not. Firstly, most of the modular titanium neck-body combinations I have revised for nonfracture reasons, such as infection, actually demonstrated cold fusion of the neck to the body. It was impossible to dissociate the taper in some cases. In other cases where it was possible to dissociate, there was obvious damage at the taper junction on the stem. I would be concerned about putting a new neck into such a taper.

Gross: I have observed some corrosion on occasion but not enough that it was an indication to do a revision. I have never measured ions in this particular situation.

Paprosky: Metal-metal tapered connections definitely contribute to hip pathologies. They are responsible for corrosion through particulate generation. This is more common than previously observed. I believe that much of the so-called new pain in components that have not been implanted for a long period of time and do not have MoM bearings are the result of corrosion from metal-metal tapers. This also includes metal head connections.

Lombardi: Recent literature and personal experience has clearly defined the fact that metal-metal taper corrosion can cause significant hip pathology. There have been reports of significant cases of ARMD, including cases of pseudotumor from metal-metal taper corrosion. I have had personal experience with failed metal-metal tapered connections and increased corrosion with reactions that look similar to those reported with ARMD.

Schmalzried: There can be high wear of a metal-metal bearing resulting in ALTR, without any issues at the femoral head-neck taper. However, if there is fretting and corrosion of the head-neck taper, the resultant ALTR will change the characteristics of the fluid around the joint (decreased lubricity) and this will increase the wear of the metal-metal bearing. In other words, if there is a problem with the taper, there will be higher wear of the metal-metal bearing – but not necessarily vice versa.

Callaghan: When corrosion occurs at the metal-metal tapered connections being used today, the patients are at definite risk for symptoms and ALTR. What we don’t know is how many patients have it but are asymptomatic and will stay asymptomatic.

Dunbar: This is difficult to know. It seems that there may be a new issue with associated larger heads leading to increased fretting corrosion. However, this does not seem to be consistent across all stems. Further, other variables changed during this time, such as the actually geometry of the actual taper on the femoral stem, in some cases.

Gross: When we have observed significant adverse tissue reactions, the patient-related outcomes have been compromised usually because of damage to the abductor muscles. This has been limited to MoM articulations in my practice.

Paprosky: When there are ALTR, the patient-related outcomes have been compromised in most cases. This is not limited just to MoM bearings. It is also found in head and neck corrosion cases as well as distal taper connection cases. In some cases, the preoperative symptoms and the postoperative symptoms may be more severe than that of the MoM cases.

Lombardi: Revisions involving catastrophic failure secondary to ARMD have been some of the most difficult and challenging revisions I have had to perform. While there is frequently minimal compromise of bone stock, there is significant compromise of the surrounding soft tissues. Anecdotally, in several cases the acetabular bone stock has appeared necrotic. I have addressed these situations with ultraporous technology and multiple screw fixation. Perhaps the most challenging issue involves the destruction of the abductor mechanism. The only viable solution in these situations is the use of constrained articulations.

Schmalzried: Not necessarily. The revision outcome is related primarily to the extent of the soft tissue disruption and secondarily to any associated bone loss. Evaluations that include blood or serum ion analyses and cross-sectional imaging can identify asymptomatic cases of ALTR and guide the recommendation for revision surgery.

Callaghan: A percentage of patients have definitely been left with a compromising situation. The most compromised patients are those who had deficient or absent abductor muscles at the time of revision. This finding has not been limited to MoM articulations.

Dunbar: Adverse local tissue reaction associated with MoM articulations is a difficult clinical problem. My experience is that even mild cases that undergo successful revisions are often left with residual symptoms, mostly in the form of groin pain. This is pervasive enough that I caution all patients to expect residual groin pain.

Greenwald: Given the seeming abandonment of MoM articulations and recent literature reports indicating that ceramic femoral heads may offer a less reactive taper connection environment, will contemporary ceramic femoral heads articulating against highly crosslinked polyethylene be the bearing selection of choice for all-comers?

Gross: For the time being, we are staying with crosslinked polyethylene and cobalt chrome heads. The ceramic articulations are more expensive with some disadvantages, and for the time being I have seen no significant problems with osteolysis with the new crosslinked polyethylene and cobalt chrome heads. I do not think the combination of a ceramic head articulating against crosslinked polyethylene will be the bearing selection for all-comers and maybe even not for the high-demand patients.

Paprosky: Now that MoM bearings have been mostly abandoned given the taper corrosion seen with metal heads, it certainly appears that ceramic femoral heads against highly crosslinked polyethylene will be a good option moving forward. Given what I have seen with femoral head-taper corrosion with large and small metal heads against chrome or titanium tapers, I have almost exclusively switched to ceramic heads.

Lombardi: Indeed it has been an abandonment of MoM articulations and there has been recent literature indicating that ceramic femoral heads may offer a less reactive taper connection environment. Therefore, I have gravitated to increased utilization of ceramic on highly crosslinked polyethylene. I believe with current knowledge that ceramic on highly crosslinked polyethylene is the preferred articulation.

Schmalzried: A strong argument can be made for that position. However, there is current interest in the Delta ceramic-on-ceramic bearing (DePuy Synthes, Warsaw, Ind.) and it will take experience and time to determine the relative risk-benefit profile of that articulation.

Callaghan: It could be. Today I am using ceramic heads in all patients except the very low-demand patients. However, we still need to study any long-term adverse effects of the alumina zirconia composite components and the titanium taper sleeves.

Dunbar: No. The price is not justified given that this is not present, in my opinion, with all implants. We should focus on the issues associated with specific geometry of tapers and address those specific issues, as opposed to making a wholesale change of the bearing surface yet again. Ceramics are not without problems in their own right.

Greenwald: Recent information from the 2012 Australian Registry indicates that at 10 years, the revision rate for distal neck-stem taper connections is approximately twice that observed when only femoral head-neck modularity is present. Although gathered for a variety of modular femoral stem designs and articulating surfaces, does this suggest that the benefits may not outweigh the risks of their employ?

Gross: We do not use distal neck-stem modularity and we have found no valid indication for its use considering the potential complications. Therefore, there is no question that the risks far outweigh the possible benefits.

Paprosky: Given the information from the 2012 Australian Registry revision rate for distal neck-stem taper connections, it appears that other than extenuating anatomic circumstances the benefits of these devices do not outweigh the risks. In those certain cases such as the exceptional female anatomy, I would only recommend the use of these devices if more standard devices maybe be disadvantageous. If they are used, then similar metal taper connections should only be used.

Lombardi: It is my opinion that the benefits of modular femoral stem designs do not outweigh the risk of their employ. I do not feel these modular junctions add significantly to our performance of THA. While they are attractive to assist in anatomic reconstruction, they have not historically been required. Therefore, I do not believe these types of stems will gain any additional popularity. On the contrary, I believe their utilization will become almost nil.

Schmalzried: That appears to be the case for that generation of components. However, this is an industry that thrives on problem solving. Detailed analyses can shed light on factors associated with failures of modularity. When failure mechanisms are understood, potential solutions can be developed and evaluated. In other words, there is nothing inherently wrong with modularity, but the outcome depends entirely on how it is done.

Callaghan: There are choices and compromises to all designs and techniques employed in total hip replacement today. The problems addressed by double taper necks can readily be addressed today by various offset stems and various head options. As the area of the femoral neck is known to be a high stress area in the total hip construct, and as the track record for these modular necks has been poor, there is no reason to take the risk of using these components today.

Dunbar: Absolutely. In fact, the data is damming. For example, the dislocation rate is actually higher in the same data set for modular necks compared to fixed bearing. Reduction of dislocation rate was a promise of modular necks, one that has not been realized. Further, the rates of aseptic loosening are also higher. To me, this implies that there may be unanticipated adverse biomechanical forces applied to the femoral stem when the version and offset are changed significantly.