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· DOS Abstracts
Increased migration and more revisions of MOTEC
compared with ELECTRA cups. A 2-year RSA study
of trapeziometacarpal prostheses
Maiken Stilling, Torben Bæk-Hansen
Department of Orthopaedics, Regional Hospital Holstebro, Hospital Unit West
Background:
Cup failure is a recognized problem in total trapeziometacarpal
(TM) joint prosthesis. Several cup designs are available but clinical documenta-
tion is sparse. Cementless cups are inserted pressfit and depend on a primary
mechanical and secondary osseous stability, which may be evaluated with ra-
diostereometric analysis (RSA).
Purpose / Aim of Study:
To compare cup stability with two cementless screw
cups and the possible relation to cup revision.
Materials and Methods:
2 consecutive prospective patient cohorts, Eaton
type 2-4, were operated with TM joint prostheses using two differently de-
signed trapezium screw cups: the MOTEC cup with a collar (n=22), and the
ELECTRA bimetal cup without a collar (n=22). Mean age was 60 (45-74) years.
There were 31 female and 13 males. Model-based RSA was used to measure
cup migration with respect to the trapezium, which was marked with 1mm tan-
talum beads during surgery. Stereoradiographs and DASH score was measured
at baseline, 3 and 6 months, and 1 and 2 years postoperative.
Findings / Results:
At 2 years total translation of mean 2.32 (sd 2.4) mm with
MOTEC cups (n=7) was higher (p=0.01) than mean 0.87 (sd 1.61) mm with
ELECTRA cups (n=16). At 3 months total translation was higher in cups that
were revised later on (p=0.03). There was a tendency for more subsidence with
MOTEC cups (1.03 vs 0.22 mm; p=0.053). There was no significant cup migra-
tion between 1 and 2 years (p=0.62). However, at 2 years the revision rate in
the MOTEC group was 41% (9/22), versus 0% (0/22) in the Elektra group (p=
0.02). There were no significant differences in clinical results between the two
groups.
Conclusions:
The MOTEC trapeziometacarpal cup with a collar has higher im-
plant migration and more revisions compared with the ELECTRA collarless bi-
metal cup at 2 years followup. Early migration was higher in cups that were later
revised.
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