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 received 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.

References

• 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