Equally good fixation of cemented and uncemented cups in total trapeziometacarpal joint prostheses. A randomized clinical RSA study with 2-year follow-up

Abstract

Background and purpose: Cup failure is a recognized problem in total trapeziometacarpal (TM) joint prostheses; it may be related to poor fixation, which can be revealed by radiostereometric analysis (RSA). We compared the early implant migration of cemented trapezium cups to that of uncemented screw cups.

Patients and methods: In a prospective, parallel-group, randomized patient-blinded clinical trial, we included 32 hands in 28 patients (5 males) with a mean age of 58 (40-77) years and with Eaton stage-2 or -3 osteoarthritis of the trapeziometacarpal joint. Patients were randomized to surgery with a cemented DLC all-polyethylene cup (C) (n = 16) or an uncemented hydroxyapatite-coated chrome-cobalt Elektra screw cup (UC) (n = 16). Uncemented cups were inserted without threading of the bone. Stereoradiographs for evaluation of cup migration (primary effect size) and DASH and pain scores were obtained during 2 years of follow-up.

Results: The 2-year total translation (TT) was similar (p = 0.2): 0.24 mm (SD 0.10) for the C (n = 11) and 0.19 mm (SD 0.16) for the UC (n = 11). Variances were similar (p = 0.4). Judged by RSA, 2 UC cups and 1 C cup became loose (TT > 1 mm). Both UC cups were found to be loose at revision. Grip strength, pain, and DASH scores were similar between groups at all measurement points.

Interpretation: Early implant fixation and clinical outcome were equally good with both cup designs. This is the first clinical RSA study on trapezium cups, and the method appears to be clinically useful for detection of loose implants.

Figure 1.

The Elektra uncemented chrome-cobalt hydroxyapatite-coated screw cup (UC group) and the cemented DLC all-polyethylene cup (C group).

Figure 2.

Clinical data for all patients, presented as bar charts with mean values and standard deviations (error bars); Mean grip strength, Visual analog scale (VAS) for pain, and DASH score.

Figure 3.

Flow of patients in the study until 2-year follow-up.

Figure 5.

Box-and-whisker plot of the total translations (TTs) showing the sample minimum, lower quartile, median, upper quartile, and the sample maximum. All patients are shown in the graph and 3 outliers are indicated by the dots above 1 mm TT. The numbers of stereo radiographs assessed for each follow-up are given under the lower whiskers.

Figure 4.

Line-and-scatter plot of the total translation (TT) for each individual patient with a screw cup (UC group; n = 13) or a DLC all-polyethylene cup (C group; n = 14). It is clear that 3 patients (all clinically symptomatic with a VAS score at rest of above 7) are outliers with cup migration above 1 mm. 2 of these cups (both UC) were revised and found to be completely loose in the trapezoid bone. One DLC cup seemed to migrate above 1 mm at the 6-month and 1 year follow-up and then return to previous levels at 2 years. The patient was asymptomatic, and RSA analysis in this case was difficult because of occluded markers at these to follow-up visits. We suspected that this was the explanation for the migration curve.

Figure 6.

Subsidence of the cups at 2 years (positive values indicate subsidence). 11 patients per group were available and there was no significant difference between groups (rank sum test; p = 0.5).