[Is high-density polyethylene suitable as an implant material in cement-free anchoring of hip endoprostheses? A histomorphologic study of an explanted polyethylene screw-in acetabula]

Morphometric examination of straight, tapered titanium stems: a retrieval study

Cementless straight, tapered rectangular cross section titanium stems have been used by the senior author since 1979. Thirty-four stems retrieved postmortem, after between 10 days and 15.2 years in situ, were studied morphometrically and histologically. Nineteen stems were first generation (1979-1986), with an incomplete sagittal taper and a mean surface roughness of 1 microm (Ra 1.23 +/- 0.3 microm); 15 stems were second generation after 1986, with a full biplane taper and a mean surface roughness of 4 microm (Ra 4.14 +/- 0.36 microm). Implant surface bony coverage was determined morphometrically in 10 segments of the stems, and expressed as a bone implant contact index. Histologically, there were no differences between implants with different levels of roughness. Morphometrically, the first-generation stems showed significant differences in coverage (distal > proximal); second-generation stems had a more uniform pattern. Stems retrieved early after arthroplasty had a mean bone implant contact index of 10%. The mean bone implant contact index showed attainment of maximum coverage by 5 years after arthroplasty, without additional apposition or loss thereafter. Patients younger than 65 years at arthroplasty had similar bone implant contact indices to patients 65 years or older; coverage in the six patients 80 years of age at retrieval did not differ from the rates in the other patients. Morphometry was able to provide objective evidence of design change effects. No differences in coverage were found in terms of times in situ, patient age at arthroplasty and at retrieval, and degree of stem surface roughness.

Implant materials for hip endoprostheses: old proofs and new trends

To judge the significance of a hip joint replacement, the clinical results over 10-20 years must be evaluated. Today, still over half of all hip endoprostheses involves cement fixation. The rest is uncemented, in direct contact with bone. Total hip prostheses with polyethylene cups are equipped either with cobalt-, iron-, surface-hardened titanium-based metal or Al2O3 ceramic ball heads. The pairing Al2O3/Al2O3 and CoCrMoC metal/metal for cups and balls are extremely wear resistant. Most of the cementless cups have spherical or conical cobalt- or titanium-based metal shells with inserts made of polyethylene or CoCrMoC metal. For the fixation stems, high-strength iron-, cobalt- or titanium-based wrought metals are preferred. A taper spigot connection between metallic or ceramic ball heads and stems allows a modular design of hip joint replacements. We have learnt much from the mistakes of the last 40 years in hip endoprosthetics, and there is no excuse to repeat them again.

Long-term reaction of the osseous bed around silicone implants

Between 1970 and 1987, 94 patients received 208 silicone implants at the Department of Orthopaedics, University Hospital, Vienna. Of these, 62.5% were clinically followed up. At follow-up after an average of 116 months, the implant bed was found to be intact in only 41% of cases; in all others we observed lyses around the implant and cysts even in bones at a distance from the operated joint. Histological findings obtained from revision arthroplasty showed a homogeneous picture with foreign-body granulation tissue. These changes were usually clinically inconspicuous and had little effect on patients' subjective well-being. Despite the low discomfort caused, however, the use of such implants in only recommended in critical and severe causes because of the progressive destruction of the osseous bed during the time the implant is in the body.