Use of oxidized zirconium hemiarthroplasty in hip fractures: clinical results and spectrum analysis

Steady state acetabular cartilage wear after bipolar hemiarthroplasty: a case series of 10 patients with radiostereometric analysis

INTRODUCTION

Cartilage wear is a concern after hemiarthroplasty. The precise pattern of the progression of wear has not been evaluated. We previously reported the application of radiostereonetric analysis (RSA) for the measurement of cartilage wear in patients. The purpose of this study was to report the amount and the orientation of the steady state wear of cartilage between 1 and 3 years after bipolar hemiarthroplasty.

METHODS

22 patients with a bipolar hemiarthroplasty for displaced femoral neck fracture were included. 10 patients completed the mean follow up of 37 months. The cartilage wear was evaluated by calculating the migration of the bipolar head in reference to the markers in the acetabulum using RSA.

RESULTS

The mean age of the patients at the final follow-up was 80 (range 67-91) years. The 3-D migration was -0.02 mm (SD 0.30) between 1 and 3 years. The migration in each direction was 0.03 mm (SD 0.49) in medial, 0.03 mm (SD 0.14) in proximal and 0.11 mm (SD 0.29) in posterior directions. 2 patients showed migration of more than 0.2 mm. The large initial migration seen in some patients up to 1 year did not progress further. Total wear after 37 months was 0.43 mm (SD 0.17).

CONCLUSIONS

Cartilage wear progressed slowly in 2 of 10 patients from 1 to 3 years. No pelvic penetration was seen. We believe that RSA will give a basic knowledge about the development and the progression of cartilage wear after hemiarthroplasty.

Articulation of Native Cartilage Against Different Femoral Component Materials. Oxidized Zirconium Damages Cartilage Less Than Cobalt-Chrome

BACKGROUND

Oxidized zirconium (OxZr) is produced by thermally driven oxidization creating an oxidized surface with the properties of a ceramic at the top of the Zr metal substrate. OxZr is much harder and has a lower coefficient of friction than cobalt-chrome (CoCr), both leading to better wear characteristics. We evaluated and compared damage to the cartilage of porcine patella plugs, articulating against OxZr vs CoCr. Our hypothesis was that, owing to its better wear properties, OxZr would damage cartilage less than CoCr. If this is true, OxZr might be a better material for the femoral component during total knee arthroplasty if the patella is not resurfaced.

METHODS

Twenty-one plugs from porcine patellae were prepared and tested in a reciprocating pin-on-disk machine while lubricated with bovine serum and under a constant load. Three different configurations were tested: cartilage-cartilage as the control group, cartilage-OxZr, and cartilage-CoCr. Macroscopic appearance, cartilage thickness, and the modified Mankin score were evaluated after 400,000 wear cycles.

RESULTS

The control group showed statistically significant less damage than plugs articulating against both other materials. Cartilage plugs articulating against OxZr were statistically significantly less damaged than those articulating against CoCr.

CONCLUSION

Although replacing cartilage by an implant always leads to deterioration of the cartilage counterface, OxZr results in less damage than CoCr. The use of OxZr might thus be preferable to CoCr in case of total knee arthroplasty without patella resurfacing.

Articulating Biomaterials

This chapter examines the importance of surface characteristics such as microstructure, composition, crystallographic texture, and surface free energy in achieving desired biocompatibility and tribological properties thereby improving in vivo life of artificial articulating implants. Current implants often fail prematurely due to inadequate mechanical, tribological, biocompatibility, and osseointegration properties, apart from issues related to design and surgical procedures. For long-term in vivo stability, artificial implants intended for articulating joint replacement must exhibit long-term stable articulation surface without stimulating undesirable in vivo effects. Since the implant's surface plays a vital and decisive role in their response to biological environment, and vice versa, surface modification of implants assumes a significant importance. Therefore, overview on important surface modification techniques, their capabilities, properties of modified surfaces/implants are presented in the chapter. The clinical performance of surface modified implants and new surfaces for potential next-generation articulating implant applications are discussed at the end.

Microstructure and magnetic susceptibility of as-cast Zr-Mo alloys

The microstructures and magnetic susceptibilities of Zr-Mo alloys were investigated to develop a Zr alloy with a low magnetic susceptibility for magnetic resonance imaging (MRI). The microstructure was evaluated with an X-ray diffractometer (XRD), an optical microscope (OM) and a transmission electron microscope (TEM), and the magnetic susceptibility was measured with a magnetic susceptibility balance. The alpha' phase with acicular structure was dominant in Zr-1Mo alloys, while the omega and beta phases with the equiaxed and relatively flat (no acicular) microstructure was dominant in Zr-3Mo. The mixed microstructural features of Zr-1Mo and Zr-3Mo were observed in Zr-2Mo, which consists of the alpha', omega and beta phases. The beta phase is stabilized when the Mo content exceeds over 3 mass% Mo. As-cast Zr-Mo alloys showed a minimum value of magnetic susceptibility at 3 mass% Mo, and the value abruptly increased up to 10% Mo before remaining stable up to 15 mass% Mo. XRD, OM and TEM revealed that the minimum value of the susceptibility was closely related to the appearance of the athermal omega phase in the beta phase. As the Mo content decreases from 3 mass%, the alpha' phase appears with the omega and beta phases. On the other hand, as the Mo content increases from 3 mass%, the beta phase increases and the omega phase decreases. Thus the appearance of the alpha' and beta phase leads to an increase in magnetic susceptibility. The magnetic susceptibility of as-cast Zr-3Mo alloy was almost one-third that of Ti-6Al-4V, which is commonly used for medical implant devices. Zr-Mo alloys are useful for medical devices used under MRI.

Dislocation rate after conversion from hip hemiarthroplasty to total hip arthroplasty

BACKGROUND

Revision hip arthroplasty is associated with a dislocation rate that is three to five times greater than the rate following primary hip replacement. Conversion of a hip hemiarthroplasty to a total hip replacement is a revision arthroplasty, but it differs from revisions of total hip arthroplasties because a native acetabulum is replaced and the subsequent prosthetic femoral head is smaller. It was our purpose to determine whether the risk of dislocation following conversion surgery is the same as or greater than that following revision total hip replacement.

METHODS

From 1994 to 2005, eighty-nine hemiarthroplasties were converted to a total hip arthroplasty in seventy-seven patients, and the results were compared with those of 115 first-time revision total hip replacements following a primary total hip replacement in 111 patients. A retrospective chart review was performed, and radiographic measurements were obtained. The patient demographics were similar between the two groups. The percentages of patients who had undergone revision of only the acetabular component as compared with both components as well as the percentages of those who had received a modular femoral stem as compared with a nonmodular stem were also similar between the two groups.

RESULTS

Postoperatively, the femoral head size and the positioning of the acetabular component were similar between the two groups. The acetabular components were significantly larger (p < 0.001) in the group in which a total hip arthroplasty had been revised because they required additional acetabular reaming for placement of a new component. There were significantly more dislocations after the conversion procedures (22%) than after the revisions of the total hip arthroplasties (10%) (p < 0.018). Within both groups, the size of the acetabular component, the intraoperative range of motion, and the positioning of the acetabular component were similar between the hips that dislocated and those that did not. However, smaller femoral head components were at greater risk for dislocation after conversion surgery than after revision of a total hip arthroplasty.

CONCLUSIONS

A substantial reduction of the size of the prosthetic femoral head is unique to conversion arthroplasty and appears to play a role in instability after the revision surgery. While the smallest heads dislocated in the conversion group, a larger femoral head did not ensure stability. The increased dislocation risk with conversion surgery requires emphasis on soft-tissue balance and avoidance of excessive downsizing of the femoral head in an attempt to maximize hip stability.