The Hip: Preservation, Replacement and Revision

Acetabular Component Position 

- Discussion:
    - restoration of normal hip center in acetabular reconstruction encourages restoration of normal biomechanics;
    - placing the socket laterally creates increased joint reactive force, and placing it directly superior requires the use of a
             long neck prosthesis to restore abductor moment arm;
    - long neck prosthesis will develop increased lateral bending stresses, adapting to the activities of daily living;
    - acetabular component must be positioned in anatomic position at level of true notch to reduce stresses and increase longevity;
    - acetabular component abduction / inclination: 
    - acetabular component anteversion: 
             - combined anteversion (combined femoral anteversion and acetabular anteversion) has recieved recent attention in several studies;
             - references:
                    - Computed Tomography Measurement of the Accuracy of Component Version in Total Hip Arthroplasty
                    - What is the Fate of Total Hip Arthroplasty (THA) Acetabular Component Orientation When Evaluated in the Standing Position?                                     

    - component dislocation:
           - safe range: prevents impingement and component dislocation;
           - safe range for cup flexion that would allow physiologic ROM w/o impingement w/ cup fixed in 40 deg abduction and 20-40 deg anteversion;
           - position of 45 deg abduction & 30 deg flexion allowed flexion of hip to 90 deg & IR to 90 degrees without impingement; 
           - references:
                    - Dislocation After Total Hip Arthroplasty: Causes and Prevention
                    - Position, orientation and component interaction in dislocation of the total hip prosthesis
                    - Computed tomographic evaluation of component position on dislocation after total hip arthroplasty. 
     - ROM
           - main goal is to avoid impingement which would occur with activities of daily living;
           - references:
                   - The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios.
                   - Compliant positioning of total hip components for optimal range of motion. 
                   - Impingement with Total Hip Replacement
                   - The spatial location of impingement in total hip arthroplasty. 
                   - Guidelines for implant placement to minimize impingement during activities of daily living after total hip arthroplasty.

     - Surgeon Related Error:
           - references:
                   - Comparison of Conventional Versus Computer-Navigated Acetabular Component Insertion.
                   - The accuracy of free-hand cup positioning--a CT based measurement of cup placement in 105 total hip arthroplasties.
                   - Comparison of a mechanical acetabular alignment guide with computer placement of the socket
                   - The definition and measurement of acetabular orientation.  

 



  - Total hip acetabular component position affects component loosening rates.
  - Comparison of two- and three-dimensional methods for assessment of orientation of the total hip prosthesis.
  - Reconstruction of the hip. A mathematical approach to determine optimum geometric relationships.
  - Determination of Acetabular Coverage of the Femoral Head with Use of a Single Anteroposterior Radiograph.  A New Computerized Technique.
  - The relationship between the design, position, and articular wear of acetabular components inserted without cement and development of pelvic osteolysis.
  - Anatomic Referencing of Cup Orientation in Total Hip Arthroplasty.
  - Using Intraoperative Pelvic Landmarks for Acetabular Component Placement in Total Hip Arthroplasty.
  - Does Native Hip Anatomy Fit Recommendations for Safe Component Orientation in THA?

- Case Example:
    - 35-year-old male w/ near anklyosed hip following a GSW to the hip;
    - preoperative films appeared to indicate that little or no medialization was necessary;
    - postoperative films, however, indicate that the cup was lateralized (hence, reaming was inadequate);
    - in retrospect, the radiographs which are rotated externally (like an iliac oblique) tend to falsely minimize the necessary amount of medialization where
            as X-rays which are rotated internally (like an obturator oblique), tend to over-estimate the necessary amount of medialization 

           
             



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

Last updated by Data Trace Staff on Saturday, November 14, 2015 9:40 am