[Medium-term results of anatomic straight-shaft IMAGE implantation in primary hip joint endoprosthetics--a...

The IMAGE prosthesis was developed with the objective of proximal load induction to avoid stress shielding and proximal bone resorption. In this study patients were followed clinically and radiologically with a special emphasis on osteointegration of the shaft in the proximal and distal regions. In addition, the reconstruction of the bony geometry of the proximal humerus was investigated.

95 consecutive patients (mean age: 61.1 years) with an IMAGE shaft were followed up prospectively over five years after primary hip arthroplasty. Radiologically, the osteointegration was appraised on the basis of the parameters cortical bone hypertrophy, radiolucent lines, shaft sintering and the position of the rotational centre. The clinical parameters assessed were the Harris hip score (HSS) and the WOMAC score.

In Dorr C configuration no distal cortical bone hypertrophy was visible, in contrast to 19% in types A and B. By means of this criterion in 81% of the cases, a metaphyseal anchoring can be assumed. In 20% of the cases proximal and in 11.1% distal radiolucent lines were found. In only 3.3 % of the patients were the radiolucent lines due to unwanted distal osteointegration. In most cases the reasons were PE wear and metallosis. In 18.8% a distal anchoring was visible. Sintering (in total 18 prostheses) was greatest in Dorr C configuration and high-grade osteoporosis. The difference in offset reconstruction was 4.23 mm on average. In reconstruction of the rotational centre the variability was between 2.0 and 6.9 mm. 94.13 points were attained in the HHS and 10.13 points in the WOMAC score. Specific complications related to the implantation were not observed.

Proximal stress transmission can be supported and the danger of stress shielding can be reduced by means of an appropriate design of a prosthetic stem. Distal corticoid hypertrophy was found in only 19% of the patients with the prosthesis model investigated as compared to 60% having prostheses with distal femoral anchoring. The medium-term clinical results are excellent, so that the shaft appears suitable for primary as well as secondary osteoarthritis of the hip joint.