A pilot trial comparing the tear-out behavior in screw-sockets and cemented polyethylene acetabular components - a cadaveric study.
BACKGROUND
The removal of well-fixed acetabular components following THA (total hip arthroplasty) is a difficult operation and could be accompanied by the loss of acetabular bone stock. The optimal method for fixation is still under debate. The aim of this pilot study was to compare the tear-out resistance and failure behavior between osseo-integrated and non-integrated screw cups. Furthermore, we examined whether there are differences in the properties mentioned between screw sockets and cemented polyethylene cups.


HYPOTHESIS
Tear-out resistance and related mechanical work required for the tear-out of osseo-integrated screw sockets are higher than in non-integrated screw sockets.


PATIENTS AND METHODS
Ten human coxal bones from six cadavers with osseo-integrated screw sockets (n=4), non-integrated (implanted post-mortem, n=3) screw sockets and cemented polyethylene cups (n=3) were used for tear-out testing. The parameters axial failure load and mechanical work for tear-out were introduced as measures for determining the stability of acetabular components following THA.


RESULTS
The osseo-integrated screw sockets yielded slightly higher tear-out resistance (1.61±0.26kN) and related mechanical work compared to the non-integrated screw sockets (1.23±0.39kN, P=0.4). The cemented polyethylene cups yielded the lowest tear-out resistance with a failure load of 1.18±0.24kN. Compared to the screw cups implanted while alive, they also differ on a non-significant level (P=0.1). Osseous failure patterns differed especially for the screw sockets compared to the cemented polyethylene cups.


DISCUSSION
Osseo-integration did not greatly influence the tear-out stability in cementless screw sockets following axial loading. Furthermore, the strength of the bone-implant-interface of cementless screw sockets appears to be similar to cemented polyethylene cups. However, given the high failure load, high mechanical load and because of the related bone failure patterns, removal should not be performed by means of tear-out but rather by osteotomes or other curved cutting devices to preserve the acetabular bone stock.


LEVEL OF EVIDENCE
Level III, case-control-study.
['Möbius|R|R|', 'Schleifenbaum|S|S|', 'Grunert|R|R|', 'Löffler|S|S|', 'Werner|M|M|', 'Prietzel|T|T|', 'Hammer|N|N|']
D000077:Acetabulum D000368:Aged D000369:Aged, 80 and over D019644:Arthroplasty, Replacement, Hip D001843:Bone Cements D001863:Bone Screws D002102:Cadaver D005260:Female D006622:Hip Prosthesis D006801:Humans D008297:Male D008875:Middle Aged D010865:Pilot Projects D020959:Polyethylene D011475:Prosthesis Failure D013314:Stress, Mechanical
Acetabular component THA Osseo-integration Screw socket Acetabular revision Cementless fixation