Date Published: August 25, 2012
Publisher: Informa Healthcare
Author(s): Florian Schmidutz, Thomas Graf, Farhad Mazoochian, Andreas Fottner, Andrea Bauer-Melnyk, Volkmar Jansson.
Metaphyseal anchored short-stem hip implants were designed to improve load transmission and preserve femoral bone stock. Until now, only few outcome data have been available and migration studies are one of the few ways of obtaining data that are predictive of implant survival. We therefore evaluated a metaphyseal anchored short-stem hip implant by Ein Bild Roentgen Analyse femoral component analysis (EBRA-FCA).
First, the EBRA-FCA method was validated for the short-stem hip implant. Then 80 of the first 100 consecutive implants were evaluated after at least 2 years. Clinical assessment was performed using the WOMAC and the UCLA score.
After 2.7 (2.0–4.2), years none of the implants had been revised and by that time the stems had subsided by a mean of 0.7 mm (SD 1.8) (95% CI: 0.3–1.1). Of the 80 implants, 78 were stable after 2 years, with 74 being primary stable and 4 showing secondary stabilization after initial subsidence. Continuous migration was seen in only 2 patients. The clinical outcome showed good results with a mean WOMAC of 11 (SD 13) and a mean UCLA score of 7.3 (SD 2.0). [OK?]
The metaphyseal anchored short-stem hip implant showed good functional results and a high degree of stability after 2 years. The outcome is comparable to that of clinically proven conventional hip implants and if the results are confirmed by long-term studies, short-stem hip arthroplasty might be an alternative for young patients requiring hip replacement.
Rotation error. Compared to the neutral position, a flexion of 20° gave a maximum error of –1.5 mm with a mean of –1.5 mm (SD 0.1) (CI: –1.5 to –1.4). An extension of 5° gave a maximum error of +0.9 mm with a mean of +0.8 mm (SD 0.1) (CI: 0.8–0.9). External rotation was conducted at different angles, with 50°, 30°, and 20° being rejected by the software due to detected inaccuracy. The maximum accepted external rotation was 10°, which gave a maximum error of +0.2 mm with a mean of +0.1 mm (SD 0.1) (CI: 0–0.2). Internal rotation with 10° gave a maximum error of –0.2 mm with a mean of –0.1 mm (SD 0.1) (CI: –0.2 to 0) (Table 2).
From the 82 implants, 2 series of radiographs were rejected by the EBRA-FCA software. The remaining 80 implants (73 patients) were analyzed with a mean of 4.5 (SD 1.8) (range 3–9) radiographs for each implant. The numbers of radiographs at defined time points were accepted and measured by EBRA-FCA as follows: n = 80 postoperatively, n = 80 at 3 months, n = 71 at 1 year, n = 68 at 2 years, n = 23 at 3 years, and n = 4 at 4 years.
Although only long-term results in hip arthroplasty should be considered valid, initial evaluation is necessary to identify undesirable results (Baad-Hansen et al. 2011). Early migration analysis allows prediction of implant survival (Krismer et al. 1999, Kroell et al. 2009), which is why we evaluated a metaphyseal anchored short-stem hip implant by EBRA-FCA.