[Results of uncemented revision arthroplasty of the hip with the MRP-stem using an intrafemoral approach with vascularized distal fenestration]

Is taper corrosion in modular revision hip stem junctions associated with patient or implant specific factors? A retrieval analysis

Implant modularity within revision total hip arthroplasty (THA) offers multiple implant configurations and allows surgeons a high intraoperative flexibility to restore functionality to the patients joint, even in complex revision cases. However, a rare but devastating complication for patients, clinicians and manufacturers presenting a breakage of the taper junction between the distal stem and the proximal implant part. Aside from implant and patient specific risk factors, corrosion and fretting at the stem junctions have been associated with taper failure. Whether corrosive processes are a precursor of failure or rather an accompaniment of material fatigue is thereby still unclear. Therefore, this study aims to investigate the incidence of taper corrosion in a collection of 17 retrievals from a single type (MRP-Titan, Peter Brehm GmbH) and on the correlation of taper corrosion to implant and patient specific factors. None of the implants was revised for problems related to the taper junction, corrosion or the implant itself. The modular stem junction of all retrievals was visually rated with respect to corrosion, fretting and surface contamination. Additionally, the stability of taper junctions of retrievals where the proximal part with the neck was still assembled to the stem was determined by measuring the loosening moment of the securing screw and the push-out-force for taper dissociation. There was no difference between the mean push-out-force of the retrievals (14 kN ± 1.2 kN) and new reference samples (12.6 kN ± 0.5 kN). Approximately one third of the investigated retrievals showed considerable taper corrosion. The extent of corrosion increased with time in vivo and contamination of the neck piece, while it decreased with the loosening moment of the locking screw. The parameters femoral head offset, neck piece length, lateralized neck pieces, obesity of patients and septic/aseptic revision were not correlated to taper corrosion. Taper corrosion seems to occur regularly in modular taper junctions and is not necessarily connected to taper failure. A correct assembly of the junction and avoiding taper surface contamination during revision surgery is mandatory.

[Modular noncemented femoral stem system in revision total hip arthroplasty]

BACKGROUND

In most cases, loosening of a prosthesis stem is accompanied by periprosthetic osteolysis. This article presents the short-term clinical and radiological results after revision of total hip arthroplasty (THA) with bone substance deficiencies using a modular noncemented femoral stem system (LINK MP).

PATIENTS AND METHODS

Between March 2003 and November 2005, 91 LINK MP modular revision stems were implanted in 90 patients. Eighty-one patients (51 stem revisions, 24 revisions of stem and shell, and six reimplantations after a Girdlestone situation) were available for prospective clinical and radiological evaluation at an average follow-up time of 16.7+/-6.5 (6-36) months. The average patient age at revision was 67.2+/-10.5 (31-87) years.

RESULTS

Bone defects in the proximal femur were evaluated according to the Paprosky classification and showed type 2 in five cases, type 3A in 73 cases, and type 3B in three cases. The Merle d'Aubigné score increased significantly from 10.4+/-2.3 (4-15) preoperatively to 14.7+/-2.2 (9-18) at the latest follow-up (p<0.001). Migration analysis in conventional radiographs revealed an average stem subsidence of 3.4 mm. Thirty-one intraoperative and postoperative complications were noted in 28 (34.5%) patients.

CONCLUSION

After a short-term follow-up, the modular noncemented femoral stem system LINK MP was shown to be a reliable tool for revision of THA with bony defects of the proximal femur. Our results are comparable to those for other modular noncemented revision stems. As expected, complication rates were higher than with primary THA.

[Surface characterization of Al2O3-blasted titanium implants in total hip arthroplasty]

INTRODUCTION

Shot peening and grit blasting techniques are used in several surface modifications for producing hip endoprostheses. Corund blasting techniques using highly pure Al2O3 particles to create a rough surface of titanium implants in cementless total hip arthroplasty achieve better osteointegration. An increasing number of publications in maxillofacial surgery and orthopedic surgery show that there is a significant contamination on corund-blasted surfaces. The latest research studies reported an effect of contaminant particles on early failure of endoprostheses associated with third body wear. The aim of our work was to evaluate the amount and particle size of Al2O3 on the implant surface.

MATERIAL AND METHOD

The surface of four different geometries (five parts each, ARR titanium acetabular reinforcement ring, anisotropic Vektor cup, Vektor titanium stem and modular MRP Titan stem) were analyzed with respect to Al2O3 particles. Grit blasting was performed with Al2O3 particles, Alodur SWSK, Fa. Treibacher. Field emission scanning electron microscopy (LEO 1525) was used for the detection of the Al2O3 particles at the implant surface with a backscattered electron detector. The particle size distribution as well as the average area of the covered surface was calculated with image analyzing software (analySIS, Soft Imaging System GmbH).

RESULTS

The surface of the anisotropic Vektor cup was contaminated at an average of 41.7+/-4.9%, the Vektor titanium stem at an average of 33.3+/-4.7%, the (MRP) Titan stem at an average of 30.6+/-4.2%, and the ARR titanium acetabular reinforcement ring at an average of 23.2+/-1.6 with Al2O3 particles over the whole surface orientated to the bone.

DISCUSSION

The results of this study clearly show that there is contamination of rough titanium surfaces with Al2O3 particles at an unexpectedly high percentage. With respect to third body wear in total hip arthroplasty, further studies are necessary to minimize contamination of roughened surfaces and maintain sufficient roughness for osteointegration.