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. 2012 Jul;470(7):1885-94.
doi: 10.1007/s11999-011-2155-9.

Proximal component modularity in THA--at what cost? An implant retrieval study

A M Kop  1 , C Keogh, E Swarts
Affiliations

Proximal component modularity in THA--at what cost? An implant retrieval study

A M Kop et al. Clin Orthop Relat Res. 2012 Jul.

Abstract

Background: While modular femoral heads have been used in THA for decades, a recent innovation is a second neck-stem taper junction. Clinical advantages include intraoperative adjustment of leg length, femoral anteversion, and easier revision, all providing flexibility to the surgeon; however, there have been reports of catastrophic fracture, cold welding, and corrosion and fretting of the modular junction.

Questions/purposes: We asked whether (1) the neck-stem junction showed the same degradation mechanisms, if any, as the head-neck junction, (2) the junction contributed to THA revision, (3) the alloy affected the degree of degradation, and (4) the trunion machine finish affected the degradation mechanisms.

Methods: We compared 57 retrievals from seven total hip modular designs, three cobalt-chromium-molybdenum and four titanium based: Bionik(®) (four), GMRS(®) (four), Margron(®) (22), Apex(®) (five), M-series(®) (five), ZMR(®) (two), and S-ROM(®) (15). Macroscopic inspection, microscopy, and micro-CT were conducted to determine the effects of materials and design.

Results: The cobalt-chromium-molybdenum components showed crevice corrosion and fretting of the neck-stem taper, whereas the titanium components had less corrosion; however, there were several cases of cold welding where disassembly could not be achieved in theater.

Conclusions: Even with modern taper designs and corrosion-resistant materials, corrosion, fretting, and particulate debris were observed to a greater extent in the second neck-stem junction. Titanium-based modular arthroplasty may lessen the degree of degradation, but cold welding of the components may occur.

Clinical relevance: Degradation of the second junction contributed to 8 cases of metallosis and two cases of aseptic lymphocyte-laminated vascular-associated lesions contributing to revision.

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Figures

Fig. 1A–I
Fig. 1A–I
Co-Cr-Mo modular devices are shown: (A) Bionik®, (B) GMRS®, and (C) Margron®. Macroscopic images are shown of (D) the Bionik® neck-stem trunion, (E) the GMRS® proximal neck-stem and distal trunion, and (F) the Margron® neck-stem trunion. Microscopic images (original magnification, ×10) are shown of (G) the Bionik® neck-stem trunion, (H) the GMRS® neck-stem trunion, and (I) the Margron® neck-stem trunion.
Fig. 2A–L
Fig. 2A–L
Ti modular devices are shown: (A) Apex®, (B) M-series®, (C) S-ROM®, and (D) ZMR®. Macroscopic images are shown of (E) the Apex® neck-stem trunion, (F) the M-series® neck-stem trunion, (G) the S-ROM® collar-stem taper, and (H) the ZMR® neck-stem trunion. Microscopic images (original magnification, ×15) are shown of (I) the Apex® neck-stem trunion, (J) the M-series® neck-stem trunion, (K) the S-ROM® stem, and (L) the ZMR® neck-stem trunion.
Fig. 3
Fig. 3
A graph shows severity of corrosion of Co-Cr-Mo and Ti devices as a function of percentage of devices showing no corrosion (severity of 0) through to severe corrosion (severity of 4). Time in situ for the Co-Cr-Mo and Ti devices is depicted on the second y axis. Despite a shorter implantation time, a greater degree of degradation is seen in the Co-Cr-Mo devices than in the Ti-based devices.
Fig. 4A–F
Fig. 4A–F
Sagittal micro-CT images (original magnification, ×1.4) of the modular devices show proximal sections through the neck-stem junction: (A) Apex®, (B) GMRS®, (C) M-series®, (D) Apex® (higher magnification showing gap of 0.04 mm; original magnification, ×30), (E) Margron®, and (F) ZMR®.
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References

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