Acetabular Cup Insertion

- See: Acetabular Component Menu 
- Acetabular Component: 
    - press fit components 
    - note whether acetabular component is hemispheric or non-hemispheric;
           - non hemispheric components (ie over sized components or components with a peripheral flare) may be more appropriate for
                   protrusio or for situations where acetabulum will be medialized where as hemisperic components may be more appropriate
                   for shallow or osteoporotic acetabuli;
    - acetabular liner / femoral head size:
           - Jasty M, et al (1997): thickness of polyethylene component is especially important in metal backed press fit components;
           - w/ smaller acetabular components consider using a 26 mm rather than a 28 mm head;
           - Uhl RL, et al (2000): a bench top study to evaluate the consquences of mixing different modular THR components;
                   - combination of a skirted neck, smaller femoral head, and a posterior lipped liner can haave effect of causing impingement
                   of the neck on the raised liner (which can cause the femoral head to lever out of socket);
           - references:
                   - Larger diameter femoral heads used in conjunction with a highly cross-linked ultra-high molecular weight polyethylene: a new concept.
                   - Wear of polyethylene acetabular components in total hip arthroplasty. An analysis of one hundred and twenty-eight components retrieved at autopsy or revision operations
                   - A bench-top method for evaluating modular total hip component combinations

    - over-sizing the acetabular component 
- Technical Considerations in Component Insertion:
    - acetabular reaming 
acetabular component position:
           - component is inserted in same direction of reaming; 
    - trial component considerations:
           - insert trial component and note the distance between the end of the prosthesis and the bottom of acetabulum;
           - with firm hand pressure usually this distance is about 5-6 mm;
           - note qualitity of subchondral bone:
                   - hard sclertic bone:
with hard circumferential subchondral bone only 1 mm oversized component may be sufficient;
                          - ensure that the 1 mm undersized component trial can be fully seated (reamer may be used as a trial)
                          - consider re-reaming with 1-2 mm undersized reamer to disrupt the circumferential subcondral rim;
                   - soft bone:
may need to undersize by 2 mm to ensure that the hand pressed trial is about 5-6 mm from the medial edge of the
                                   acetabulum (which means that the real component will advance with good peripheral contact);
    - component insertion;
           - w/ proper acetabular alignment, impact acetabular cup into place; 
           - component impaction
                   - as the component is impacted into place, the component should advance with each blow of mallet;
                   - listen for change in pitch as component seats down;
                   - probe screw holes and if gap is present then impact further; 
                   - references:
                          - Fluctuation of Cup Orientation During Press-Fit Insertion: A Possible Cause of Malpositioning
                          - Periprosthetic Occult Fractures of the Acetabulum Occur Frequently During Primary THA.
           - failure to advance:
if the component fails to properly advance with blows of the mallet, then gentle peripheral reaming is required;
                   - the component is then reinserted;
    - assess component stability:
           - need to determine whether stability is optimal without screw placement;
           - kocher clamp is applied to lip of component - vigorous shaking without component motion indicates component stability;
                   - with inadequate stability, it will be necessary to insert screws or switch to a large component;     
                   - ref: Cup Press Fit in Uncemented THA Depends on Sex, Acetabular Shape, and Surgical Technique
           - acetabular cup insertion without screw insertion: (see components with screws)
                - advantages:
                           - shorter operative time;
                           - ability to adjust cup position if hip instability is found to be present;
                           - absence of screw related vascular complications
                           - easier cup removal at the time of revision (should it be necessary); 
                - technical considerations:
                           - cup should be oversized (or acetabulum should be under-reamed);
                           - note that insertion of oversized cups may result in fracture, especially in over-sized bone
           - component insertion with screws and without forced impaction:
                           - acetabular components can be inserted with use of a line-to-line technique without impaction, relying only on the
                                      screws to obtain the initial fixation;
                           - Craig, et al noted 96% survivorship with technique;
                           - impaction is not a prerequisite for bone ingrowth or for long-term implant fixation
                           - references:
                                  - Primary total hip arthroplasty with a porous-coated acetabular component. A concise follow-up, at a minimum of twenty years, of previous reports.
                                  - Successful long-term fixation and progression of osteolysis associated with first-generation cementless acetabular components retrieved post mortem.
           - references:
                   - Impact biomechanics and pelvic deformation during insertion of press-fit acetabular cups. 
                   - Incomplete seating of press-fit porous-coated acetabular components: the fate of zone 2 lucencies.
                   - Extra-large press-fit cups without screws for acetabular revision.
    - screw placement:
    - anterior & inferior osteophytes;
           - if the acetabulum is retroverted then anterior wall itself will project beyond edges of cup if it is set in anteversion;
           - reflected head of the rectus may be attached to osteophyte;
           - anterio-inferior wall osteophytes must be removed w/ osteotome, cutting along the edge of the cup;
                 - failure to heed this may cause posterior dislocation in flexion and internal rotation; 

    - Polyethylene insertion:

Measuring the Femoral Head Size — An Additional Real-Time Intraoperative Monitoring Tool for the Accuracy of the Preoperative Process and Implant Selection

Load transfer and fixation mode of press-fit acetabular sockets.

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

Last updated by Data Trace Staff on Friday, December 2, 2016 9:15 am