H�ftgelenk-Oberfl�chenersatzendoprothesen

Metal ion levels and functional results following resurfacing hip arthroplasty versus conventional small-diameter metal-on-metal total hip arthroplasty; a 3 to 5year follow-up of a randomized controlled trial

We present an update of a randomized controlled trial on 71 patients (<65 years) who received either a resurfacing hip arthroplasty (RHA) (n=38) or cementless 28-mm metal-on-metal (MoM) total hip arthroplasty (THA) (n=33). Metal ion levels and functional outcome scores were analyzed with a mean follow-up of 58 months (SD 8.1). No clear shifts in relatively good outcome was encountered between RHA and THA. Metal ion levels appear to equalize between groups after 3 years. Median cobalt and chromium remained below 1.3 μg/L throughout follow-up in both groups. Six revisions were performed, of which three for pseudotumor formation (one THA, two RHA). In conclusion there were no clinical differences between the two groups and metal ion levels were lower than other series remained low, however, pseudotumor formation was not eliminated.

In vivo wear rate of the Birmingham Hip Resurfacing arthroplasty. A review of 10 retrieved components

The wear of 8 femoral and 2 acetabular components of the Birmingham Hip Resurfacing (Midland Medical Technologies Ltd, Birmingham, UK) was measured using a coordinate measuring machine (CMM5; SIP, Geneva, Switzerland). After a median in situ time of 13 months, measurements of the Birmingham Hip Resurfacing femoral heads revealed a median volumetric wear of 2.9 mm(3). In one case with a cup abduction angle of 70 degrees , a significantly higher wear of 17.8 mm(3) was found. The 2 acetabular components showed volumetric wear of 5.4 and 27.6 mm(3) after 14 and 15 months in vivo. The wear rates of the investigated femoral components were somewhat, but not significantly, higher than the previously investigated 28-mm Metasul heads (median, 0.8 mm(3); Zimmer GmbH, Winterthur, Switzerland).

Cementless CUT femoral neck prosthesis: increased rate of aseptic loosening after 5 years

BACKGROUND

Bone-saving hip arthroplasty techniques, which facilitate revision, are gaining importance as the number of hip replacements in younger patients increases.

PATIENTS AND METHODS

123 CUT femoral neck prostheses (ESKA Implants, Lübeck, Germany) were implanted in 113 patients (average age 53 years) between 1999 and 2002. After a mean follow-up of 5 (3-7) years, we determined the state of 120 prostheses; 3 patients could not be located. 97 patients with 107 prostheses, none of which had been revised, were evaluated clinically and radiographically.

RESULTS

The median Harris hip score improved from 51 points to 92 points in the unrevised hips. 13 CUT prostheses (11%) had been revised, 7 because of aseptic loosening, 3 because of persisting thigh pain, 1 because of immediate vertical migration, and 2 because of septic loosening. The 5-year survival rate of the CUT prosthesis was 89%.

INTERPRETATION

The medium-term survival with this type of femoral component is unsatisfactory, with a high rate of aseptic loosening. The surviving prostheses had a good clinical outcome.

Schenkelhalsendoprothesen

The survival rates of cementless femoral neck prostheses are lower than for cementless standard stems. Nevertheless, femoral neck prostheses have the advantage of preserving the femoral neck as well as not opening the diaphyseal marrow cavity. Should the need to change the endoprosthesis arise, a standard stem anchored in the diaphysis can be implanted after resection of the femoral neck. Since there is a relationship between surgical error and the learning curve for a new implant, the surgeon should be experienced in the field of total hip arthroplasty. In addition, the implantation of femoral neck prostheses is technically demanding. Therefore, careful patient selection is necessary and patients have to be informed of the advantages as well as the disadvantages of the different implant models.

Neo-capsule tissue reactions in metal-on-metal hip arthroplasty

BACKGROUND

Modern-generation metal-on-metal articulations have a high wear resistance and may therefore be able to improve the long-term performance of artificial joints. However, the biological effects are still under debate. This study was undertaken to review the histopathological changes in neo-capsule tissues of different metal-on-metal hip arthroplasties.

METHODS

Neo-capsule tissue samples from 46 hips with modern second-generation metal-on-metal articulations (39 hip resurfacings and 7 non-cemented total hip replacements) with a variety of failure mechanisms were examined histopathologically and immunohistochemically.

RESULTS

A distinct lymphocytic infiltration was found in all cases with in situ times of more than 7 months, consisting of CD20-positive B-lymphocytes and CD3-positive T-lymphocytes and sometimes thinly distributed CD138-positive plasma cells without dominant T-cell or plasma cell infiltrates.

INTERPRETATION

This distinct lymphocytic infiltration has not been reported in tissue analyses of metal- or ceramic-on-polyethylene hip replacements, and may therefore be considered to be a characteristic histological pattern of tissue reactions on metal particles and/or ions around metal-on-metal bearings.

Schenkelhalsendoprothese Typ CUT

BACKGROUND

As the number of younger patients undergoing total hip arthroplasty is growing steadily, bone-saving implantation techniques are increasingly gaining in importance.

METHODS

Fifty-six femoral neck prostheses (type CUT, ESKA Implants, Lübeck, Germany) were implanted in 50 patients between 1999 and 2002 (average age 49 years). After a mean follow-up of 4.9 years (min.: 3.2, max.: 6.5), we determined the state of all the prostheses. Forty-four patients with 50 prostheses were examined clinically with the Harris hip score and were assessed radiologically.

RESULTS

The average Harris hip score improved from 48 points preoperatively to 93 points at the most recent follow-up examination. Of the 56 CUT prostheses, 6 (10.7%) had been revised. Four of these six cases (7.1%) required revision because of aseptic loosening. The radiological evaluation of these four cases revealed in three cases progressive horizontal migration with varization of the prosthesis, although the stem had been correctly positioned in primary surgery, with the femoral neck resected too widely or completely. After 4.9 years, the survival rate of the CUT prostheses is 88.4% according to Kaplan-Meier for a necessary exchange of the CUT prostheses as an endpoint.

CONCLUSION

The use of the CUT prosthesis can lead to good clinical and radiological results, but shows a higher loosening rate as compared with cementless standard stems. Further studies are necessary to determine if the CUT prosthesis is a real alternative to cementless standard stems.

Zementfreie Hüftschäfte

Optimal fixation of cementless stems is a precondition for long-lasting stability. Thus, anchorage, stabilizers, material and surface are of essential importance. To achieve primary stability, good rotational, tilting and axial stability is necessary. Stabilizers such as fins and ribs optimize stability. The CCD-angle and length of neck-axis determine the offset (laterality), leg-length and center of rotation. The stem, is responsible for the fixation of the prosthesis and for transmitting forces to the bone. The types of fixation are epiphyseal (the femoral head is covered by a cup prosthesis), metaphyseal and meta-diaphyseal (with straight or anatomically shaped monoblock-prostheses of different lengths, modular and custom-made prostheses) and diaphyseal (using predominantly modular systems). Titanium alloys are the predominate material for cementless stems. The surfaces are generally corundum-blasted or plasma sprayed. For metaphyseal and meta-diaphyseal stems, survival rates from 95 to 98% have been reached after 15 years. Diaphyseal-fixed stems have mid-term survival-rates of 92-99%.