Orthopaedic Case Studies
Duke Orthopaedics
presents
Wheeless' Textbook of Orthopaedics

Screw Fixation of Acetabular Components

- See: Acetabular Component Menu

Discussion

  • it is controversial as to whether screws are necessary in THR, and there are relative advantages and disadvantages;
  • cups should be designed with only 2-3 holes so as to maximize the porous coating surface and to minimize conduit for osteolysis;
  • acetabular cup insertion:
  • advantages of screw insertion:
    • theoretically, screw fixation can close any gap created by non congrous reaming;
    • prevents the loss of compressive stresses and resultant shear stresses;
    • may be indicated in osteoporotic bone (when insertion of over-sized components may not be wise) and when additional fixation is required;
    • screw insertion is also indicated in situations in which there is insufficient bony coverage;
  • biomechanical considerations: (design of components)
  • controversies: Do acetabular screws promote osteolysis?
    • although screws may provide excellent initial fixation, later they may be sources of fretting, which could produce wear debris, and provide a conduit for migration of the polyethylene debris;
    • in order to reduce the chance of osteolysis some surgeons insert the least number of screws possible in order to achieve solid fixation;
    • while screws may provide a conduit for wear debris, unfilled screw-holes may also provide access for wear debris from ultra-high molecular weight polyethylene liner to area behind ingrowth cup;
    • ultra-high molecular weight polyethylene may cold-flow (creep) into these holes, resulting in early failure of the polyethylene liner;
    • hence, it remains unclear as to whether screws strongly influence the formation of osteolysis in acetabular components which contain screw holes;
    • Dorr et al 1998 and by Latimer 1996, there is a paucity of evidence to support notion that screw fixation leads to osteolysis;
    • certainly, if a screw does not achieve a rigid bite it should be removed - due to the risk of osteolysis;

Radiographic Evaluation of Screw Position


Screw Placement Considerations

Other Considerations

  • if drill holes are placed eccentrically, then screw insertion may lift cup up out of the bony bed;
  • screw heads left pround wont allow liner to be fully seated

Complications

References:




Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Monday, November 14, 2016 2:18 am

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