Criteria for success with threaded cups (design, material and modularity).
OBJECTIVE
Over a period of three generations, threaded cups were developed and have become viable contemporary cementless hip implants. A few implants already have a high success rate over the mid and long term. Aim of this study was to evaluate contemporary threaded cups.


METHODS
30 of the second and third generation cups were systematically analyzed and measured using by a no-touch light section technique. Construction of inner form was determined with half sections.


RESULTS
Approximately 50% have a conical shape, although there is a trend towards a more anatomical shape. 83% of the cups have a height up to 23% smaller than the radius. Only conical threaded cups have a relatively thin and constant wall thickness (1 mm-1.8 mm). Corundum blasted pure titanium, titanium alloys or HA coated implants are considered the standard materials. The insert is pre-assembled in two implants, otherwise the cups have modular inserts. Total ceramic inserts are found in four cups. Ceramic inserts with a sandwich construction are found in six cups. One cup has a full-metal insert. All other cups with metal-metal inserts have a sandwich construction.


CONCLUSIONS
The studies by Kody (6) and our own studies (10) show that the V-cut threads have high values for turning moment and tilting stability.


CONCLUSIONS
The screw-in behavior of threaded cups is largely determined by the design of the threads. Material and surface of threaded cups influence osseointegration and therefore long-term results. Contemporary threaded cups have a narrow V-cut and saw threads or flat threads with depths up to 3 mm, on average 4 turns, and pith values of approximately 4.5 mm. Three generations of threaded cups development were necessary to procure the current form with highly satisfactory mid- and long-term results.
Effenberger
H
H
Orthopaedic University Hospital, Friedrichsheim Foundation, Frankfurt, Germany. Effengerger@implant-atlas.com
Imhof
M
M
Witzel
U
U
D019644:Arthroplasty, Replacement, Hip; D006622:Hip Prosthesis; D006801:Humans; D011474:Prosthesis Design