The skeletal response to matt and polished cemented femoral stems

The twenty-year survivorship of two CDH stems with different design features

Previous studies have shown that anatomical abnormalities of the femur in dislocated hips require the application of special CDH prosthesis for the reconstruction of the proximal femur in total hip arthroplasty (THA). We have retrospectively examined the clinical records and radiographs of 50 patients (67 hips) with low and high dislocations treated with THA in our institution, between January 1987 and December 1994. For the reconstruction of the femur, the stainless steel Charnley CDH stem, with polished surface, monoblock and collarless, was used in 32 hips; the Harris CDH stem, made of CoCr, precoated at the proximal part, modular and with collar was used in 35 hips. At the time of the latest follow-up, 11 Charnley and 6 Harris CDH stems had been revised for aseptic loosening at an average of 14 years (range 6-20) and 13 years (range 2-19), respectively. The survival rate at 20 years, with failure for aseptic loosening as the end point, was 63% for the Charnley and 78% for the Harris CDH stems. These results provide a basis for evaluation of newer techniques and designs.

LEVEL OF EVIDENCE

Therapeutic study, Level IV.

A modified cementing technique using BoneSource to augment fixation of the acetabulum in a sheep model

BACKGROUND AND PURPOSE

Our aim was to assess in an animal model whether the use of HA paste at the cement-bone interface in the acetabulum improves fixation. We examined, in sheep, the effect of interposing a layer of hydroxyapatite cement around the periphery of a polyethylene socket prior to fixing it using polymethylmethacrylate (PMMA).

METHODS

We performed a randomized study involving 22 sheep that had BoneSource hydroxyapatite material applied to the surface of the acetabulum before cementing a polyethylene cup at arthroplasty. We studied the gross radiographic appearance of the implant-bone interface and the histological appearance at the interface.

RESULTS

There were more radiolucencies evident in the control group. Histologically, only sheep randomized into the BoneSource group exhibited a fully osseointegrated interface. Use of the hydroxyapatite material did not give any detrimental effects. In some cases, the material appeared to have been fully resorbed. When the material was evident in histological sections, it was incorporated into an osseointegrated interface. There was no giant cell reaction present. There was no evidence of migration of BoneSource to the articulation.

INTERPRETATION

The application of HA material prior to cementation of a socket produced an improved interface. The technique may be useful in humans, to extend the longevity of the cemented implant by protecting the socket interface from the effect of hydrodynamic fluid flow and particulate debris.

Randomized comparison between 3 surface treatments of a single anteverted stem design: 84 hips followed for 5 years

Eighty patients (84 hips) randomly received an anteverted cobalt-chromium stem (Lubinus SP2; Waldemar Link, Hamburg, Germany) with matte, polymethyl methacrylate-coated, or polished surface (uncollared). Radiostereometry was used to study migration and wear; and the bone mineral density was studied with dual-energy x-ray absorptiometry at 6 months, 1 year, 2 years, and 5 years. The polished stems had subsided 0.1 to 0.2 mm more at 6 months and 0.3 to 0.4 mm more at 5 years than the matte and precoated versions (P < .0001) and subsided mainly inside the cement mantle. The rotations of the stem and the migration and wear of the cemented cup did not differ between the 3 groups. After 1 and 2 years, the polished stems had lost significantly less bone mineral in Gruen zones 1, 2, 6, and 7 (P = .004 to .03); but this difference had disappeared after 5 years. The period of improved bone remodeling around the polished version coincided with the early period of increased subsidence, suggesting that stem motions inside the mantle resulted in a favorable loading of the proximal femur. Our observations suggest that alternative shapes could be possible on future polished femoral stem designs.

Validation of a finite element model of the human metacarpal

Implant loosening and mechanical failure of components are frequently reported following metacarpophalangeal (MCP) joint replacement. Studies of the mechanical environment of the MCP implant-bone construct are rare. The objective of this study was to evaluate the predictive ability of a finite element model of the intact second human metacarpal to provide a validated baseline for further mechanical studies. A right index human metacarpal was subjected to torsion and combined axial/bending loading using strain gauge (SG) and 3D finite element (FE) analysis. Four different representations of bone material properties were considered. Regression analyses were performed comparing maximum and minimum principal surface strains taken from the SG and FE models. Regression slopes close to unity and high correlation coefficients were found when the diaphyseal cortical shell was modelled as anisotropic and cancellous bone properties were derived from quantitative computed tomography. The inclusion of anisotropy for cortical bone was strongly influential in producing high model validity whereas variation in methods of assigning stiffness to cancellous bone had only a minor influence. The validated FE model provides a tool for future investigations of current and novel MCP joint prostheses.

The long-term clinical relevance of calcar atrophy caused by stress shielding in total hip arthroplasty: a 10-year, prospective, randomized study

Eighty osteoarthritic female patients were randomly allocated to 4 equal groups; the Zwey-Muller, the Corail, the Optifix, or Autophor 900S cementless total hip arthroplasties (THAs) were implanted; and bone density changes, at different sites, were prospectively studied. In zone 7, the greatest reduction of bone density values was observed at 2 years (group A: 24%, group B: 8%, group C: 14.8%, and group D: 18.5%). In all groups, a similar pattern of slow but progressive recovery of bone mineral density changes after the third year was observed, approaching baseline values at 10 years, during which all patients showed satisfactory clinical results. We suggest that the clinical and theoretical relevance of the stress-shielding phenomenon in THA has been overestimated in the literature.