Mixing of Head-Stem Components in Total Hip Arthroplasty

Fracture of Contemporary Femoral Stems: Common Trends in This Rare Occurrence

BACKGROUND

Fracture of contemporary femoral stems is a rare occurrence in total hip arthroplasty (THA). A knowledge gap remains regarding manufacturing, patient, and surgeon factors that may contribute to the increased risk of this complication.

METHODS

We analyzed 13 contemporary fractured porous coated femoral stems of various designs to determine cause and contributing factors of mechanical failure. Cases included 12 men and one woman who had an average age at index surgery of 53 years (range, 34 to 76). There were ten of 13 patients who had a body mass index (BMI) greater than 30 (obese); 3 of the 10 had a BMI greater than 40. The mean time to fracture was 7.6 years (range, 7 months to 12 years).

RESULTS

There were four titanium alloy stems that fractured an average of 3.6 years post-revision surgery for head/cup exchange, and had associated iatrogenic mechanical and electrocautery damage to the femoral neck at fracture initiation sites. There were six modular stems that failed at the stem-sleeve or stem-neck interfaces with evidence of fretting corrosion. For two stem-neck fractures, mis-matched head/stem combinations from different manufacturers resulted in untested mechanical offsets and loading. There were two proximal neck fractures and one mid-shaft fracture of coated cobalt-chromium alloy stems that occurred in three obese men. The neck fractures (10 to 12 years) were well-fixed stems. Lack of proximal fixation contributed to the mid-shaft fracture (7 months).

CONCLUSION

While rare, femoral stem fractures pose catastrophic outcomes in primary and revision THA. Manufacturing, patient, and surgical factors contributing to stem failures were identified, including patient obesity, heat-treatment reduction of mechanical properties, iatrogenic implant damage, and mixing of different vendor stems and heads.

Survival rate of total hip replacements with matched and with mixed components with 10.7 years mean follow-up

BACKGROUND

Mixing and matching components from different manufacturers in total hip arthroplasty is a frequently used off-label praxis. The clinical consequences of this procedure have not been studied in detail.

METHODS

860 patients with matched and 1067 patients with mixed primary total hip replacement (THR) components carried out between 1 January 2002 and 31 December 2004, were selected from our Institution registry. The analysis endpoint was set at 1 January 2016. THRs with poorly performing components were excluded from study groups. Kaplan-Meier survival curves for both groups were calculated and compared using the Log-Rank test and the demographic data using the chi-square test. Correlations between demographic data and revisions were calculated using bivariate correlation.

RESULTS

28 revisions were carried out in the matched group and 67 in the mixed group. The 14-year overall survival probability was significantly better in the former (96.0%) than in the mixed group (92.7%) (p = 0.002). Survival, free of aseptic and septic failures, was statistically, significantly higher in the matched group (p = 0.026 and p = 0.007, respectively).The survival of the mixed subgroup with heads and stems from the same manufacturer did not differ statistically from that of the matched group (p = 0.079).

CONCLUSIONS

In contrast to the results listed in the National Joint Registry and the New Zealand Joint Registry, the survival probability in our study was, statistically, significantly higher in total hip replacements using components of the same manufacturer. Importantly, mixing and matching the components of different manufacturers led to similar survival providing the head and the stem were from the same manufacturer.

EFORT recommendations for off-label use, mix & match and mismatch in hip and knee arthroplasty

Off-label use is frequently practiced in primary and revision arthroplasty, as there may be indications for the application of implants for purposes outside the one the manufacturers intended.

Under certain circumstances, patients may benefit from selective application of mix & match. This can refer to primary hip arthroplasty (if evidence suggests that the combination of devices from different manufacturers has superior results) and revision hip or knee arthroplasty (when the exchange of one component only is necessary and the invasiveness of surgery can be reduced).

Within the EFORT ‘Implant and Patient Safety Initiative’, evidence- and consensus-based recommendations have been developed for the safe application of off-label use and mix & match in primary as well as revision hip and knee arthroplasty.

Prior to the application of a medical device for hip or knee arthroplasty off-label and within a mix & match situation, surgeons should balance the risks and benefits to the patient, obtain informed consent, and document the decision process appropriately.

Nevertheless, it is crucial for surgeons to only combine implants that are compatible. Mismatch of components, where their sizes or connections do not fit, may have catastrophic effects and is a surgical mistake.

Surgeons must be fully aware of the features of the components that they use in off-label indications or during mix & match applications, must be appropriately trained and must audit their results.

Considering the frequent practice of off-label and mix & match as well as the potential medico-legal issues, further research is necessary to obtain more data about the appropriate indications and outcomes for those procedures.

Cite this article: EFORT Open Rev 2021;6:982-1005. DOI: 10.1302/2058-5241.6.210080

"Off-label" Usage of an Oxidized Zirconium Femoral Head in Revision of a Total Hip Arthroplasty with Mechanically Assisted Crevice Corrosion and a Legacy Taper

We present a case of a 72-year-old male with a history of a late 1980s metal-on-polyethylene total hip arthroplasty who presented with unilateral leg vascular compromise, joint pain, and stiffness and subsequently underwent revision for adverse local tissue reaction secondary to mechanically assisted crevice corrosion. His stable and extensively porous coated femoral implant had a legacy taper with no currently manufactured option for a non–Co-alloy femoral head. After shared decision-making with the patient, we opted to use an oxidized zirconium femoral head from another manufacturer with a similar taper during his revision surgery and documented that his vascular compromise resolved and his serum Co was undetectable 3 years after the revision.

Femoral prosthesis neck fracture following total hip arthroplasty - a systematic review

PURPOSE

Head-neck modularity was introduced into total hip arthroplasty to provide more intraoperative surgical options. However, modularity led to new problems, such as trunnionosis and fractures of the femoral prosthesis neck. The purpose of this study was to identify risk factors for hip neck fractures and to provide recommendations to prevent damage and fractures of the neck.

METHODS

A systematic review of the literature was performed according to the PRISMA guidelines.

RESULTS

Thirty-three case studies were included. Methodologically, most included studies were of moderate or good quality. The 80 neck fractures included in the review took place, on average, 7 years after stem placement. Male gender, high body weight, obesity, previous revision surgery, mixing components from different manufacturers, use of long skirted heads, cobalt-chromium (large size) heads were identified as potential risk factors.

CONCLUSION

Hip neck fractures occur on average 7 years after stem placement. The etiology of hip neck fractures is multifactorial. This review revealed several preventable implant- and surgeon-related risk factors.

What the Surgeon Can Do to Reduce the Risk of Trunnionosis in Hip Arthroplasty: Recommendations from the Literature

Trunnionosis, defined as wear and corrosion at the head–neck taper connection, is a cause of failure in hip arthroplasty. Trunnionosis is linked to a synergistic combination of factors related to the prosthesis, the patient, and the surgeon. This review presents analytical models that allow for the quantification of the impact of these factors, with the aim of providing practical recommendations to help surgeons minimize the occurrence of this failure mode. A tighter fit reduces micromotion and, consequently, fretting of the taper connection. The paramount parameters controlling the fixation force are the coefficient of friction and the impaction force. The influence of the head diameter, as well as of the diameter and angle of the taper, is comparatively small, but varus alignment of the taper and heads with longer necks are unfavourable under physiologic loads. The trunnion should be rinsed, cleaned, and dried carefully, while avoiding any contamination of the bore—the female counterpart within the head—prior to assembly. Biological debris, and even residual water, might critically reduce the fixation of the taper connection between the head and the neck. The impaction force applied to the components should correspond to at least two strong blows with a 500 g hammer, striking the head with an ad hoc impactor aligned with the axis of the taper. These strong blows should correspond to a minimum impaction force of 4000 N.

Head Taper Corrosion Causing Head Bottoming Out and Consecutive Gross Stem Taper Failure in Total Hip Arthroplasty

BACKGROUND

Taper corrosion in total hip arthroplasty for bearings with metal heads against polyethylene has developed from an anecdotal observation to a clinical problem. Increased taper wear and even gross taper failure have been reported for one particular design. It is hypothesized that corrosion of the female head taper results in taper widening, allowing the cobalt-chromium head to turn on the stem and wear down the softer titanium alloy by abrasive wear, ultimately causing failure. The purpose of this study is to investigate the time course of this process and the general role of taper dimensions and material in this problem.

METHODS

Retrieved cobalt-chromium alloy heads (n = 30, LFIT; Stryker, Mahwah, NJ) and Ti-12Mo-6Zr-2Fe (TMZF) stems (n = 10, Accolade I; Stryker) were available for analysis. Taper material loss was determined using three-dimensional coordinate measurements and scanning. The pristine tip clearance between head and stem was analytically determined. The influence of taper material and taper size on taper deformation and micromotion was investigated using a finite element model.

RESULTS

Material loss at the head taper increased with time in situ up to a volume of 20.8 mm³ (P < .001). A mean linear material loss above 76 μm at the head taper was analytically confirmed to result in bottoming out, which was observed in 12 heads. The finite element calculations showed significantly larger deformations and micromotions for a small 11/13 TMZF taper combined with a distinctly different micromotion pattern compared to other materials and taper designs.

CONCLUSION

A 11/13 TMZF taper design with 36-mm head diameters bears a higher risk for corrosion than larger tapers made from stiffer materials. Failures of this combination are not restricted to the head sizes included in the recall. Patients with this implant combination should be closely monitored.