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DOS Kongressen 2017 ·
129
SIMILAR PRESS-FIT FIXATION WITH A SPHERICAL AND
A CONICAL CUP DESIGN IN THETRAPEZIOMETACARPAL
JOINT: A RADIOSTEREOMETRIC ANALYSIS WITH A PIG
BONE MODEL
Lene Dremstrup, Sebastian Breddam Mosegaard, Torben Bæk Hansen, Maiken
Stilling
Department of Orthopaedics, University Clinic for Hand, Hip and Knee Surgery,
, Holstebro
Background:
Cup loosening in trapeziometacarpal (TMC) joint arthroplasty is
a problem, and therefore new cup designs have been introduced. We have for-
merly validated a pig bone model for evaluation of TMC cup fixation by use of
radiostereometric analysis (RSA).
Purpose / Aim of Study:
to compare bone fixation of a spherical and a conical
TMC cup.
Materials and Methods:
9 conical Moovis (Stryker) and 10 spherical “Type
T” (Besnoska) cups were inserted into the trapezium equivalent pig bone us-
ing original instruments and surgical technique. Periprosthetic 1mm beads were
inserted, and the bones were fixed with cement in a 20° angle. Static RSA was
performed at baseline, after a low- pressure cyclic test (300 cycles, 150N),
and after push-in loading until visual failure (up to 1100N). Cup subsidence was
evaluated in the length axis of the cup, and double RSA examinations were ob-
tained for assessment of precision by 95% agreement limits.
Findings / Results:
Precision of cup subsidence was 0.1mm, and at 600N
push-in load 9 Type T cups and 3 Moovis cups migrated above the precision
limit (p=0.18). Up to 750N push-in load both cup types migrated (p<0.04),
but similarly between groups (p=0.06), with subsidence of 0.16mm (sd 0.2)
for the T type cup and 0.53mm (sd 0.52) for the Moovis cup. In all, 7 Type T
cups and 4 Moovis cups failed by visual judgement (p=0.18), which coincided
with 1mm cup subsidence. The failure pattern was subsidence of 1mm or more
associated with a cup tilt of 8° -18° for the Type T cup, while the Moovis cup
only subsided.
Conclusions:
Cup subsidence was similar with press- fit fixation of spherical
and conical cup designs. Both cup types sustained failure loads resembling a
forceful pinch (750N). Bone quality is poorer in patients and stresses the impor-
tance of osseointegration prior to loaded hand activities.
No conflicts of interest reported
81.