H Effenberger1, M Imhof, U Witzel. 1. Orthopaedic University Hospital, Friedrichsheim Foundation, Frankfurt, Germany. Effengerger@implant-atlas.com
Abstract
PURPOSE OF THE STUDY: 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. MATERIAL AND 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. DISCUSSION: 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. CONCLUSION: 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.
PURPOSE OF THE STUDY: 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. MATERIAL AND 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. DISCUSSION: 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. CONCLUSION: 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.