- See
total hip dislocation:
- Discussion:
- restoration of nl 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;
- orientation of the cemented cup so that it is contained by surrounding bone has significant implications for long-term results;
- safe range: prevents impingement and
component dislocation;
- safe range for cup flexion that would allow physiologic ROM w/o impingement w/ cup fixed in 30 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;
-
Acetabular Component Anteversion:
-
combined anteversion (combined
femoral anteversion and acetabular anteversion) has recieved recent attention in several studies;
- referenences:
-
Compliant positioning of total hip components for optimal range of motion.
- The Effect of the Orientation of the Acetabular and Femoral Components on the ROM of the Hip at Different Head-Neck Ratios.
-
Position, orientation and component interaction in dislocation of the total hip prosthesis.
-
Combined Anteversion Technique for Total Hip Arthroplasty
-
Acetabular Component Abduction / Inclination:
- when cup is abducted < 30 degrees, impingement occurrs in flexion;
- when cup is abducted > 50 deg, head tended to sublux out of acetabulum by "climbing the wall";
- note that the abduction angle of the cup is an important technical factor contributing to the amount of wear;
- cups with an abduction angle of less 40 deg had the lowest annual rates of linear and volumetric wear
- cups with an abduction angle of greater than 50 deg had the highest rates of wear;
-
Pacharapol Udomkiat MD et al, the authors found the abduction angle of the cup to be an important factor contributing to amount of wear;
- cups with an abduction angle of 40° had the lowest annual rates of linear and volumetric wear, and cups with
an abduction angle of >50 deg had the highest rates of wear;
- cups with an abduction angle of >50° had an average volumetric wear rate of 160 mm 3 /yr, which exceeds the critical
rate of 150 mm 3 /yr that can be expected to result in osteolysis and loss of fixation 18;
- this accelerated wear in cups with an abduction angle of >50° was also reported by
Schmalzreid et al;
-
McCollum et al
- safe range for cup abduction that would allow physiologic ROM w/o impingement was 30-50 deg abduction w/ cup in 30 deg flexion;
- note that in lateral position on OR table, superior acetabulum is adducted toward foot of table consistently between 10 deg to 15 deg;
- if cup is placed in position of 45 deg of horizontal abduction to table w/ pelvis in adducted position, when pt stood up cup was
abducted an additional 10-15 deg placing it in 55 degrees -60 degrees of abduction, which is an unstable position;
- references:
-
Cementless Hemispheric Porous-Coated Sockets Implanted with Press-Fit Technique without Screws: Average Ten-Year Follow-up.
-
Dislocation After Total Hip Arthroplasty: Causes and Prevention.
-
The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios.
-
Joint motion and surface contact area related to component position in total hip arthroplasty.
-
The Influence of Acetabular Component Position on Wear in Total Hip Arthroplasty
- 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 xrays which
are rotated internally (like an obturator oblique), tend to over-estimate the necessary amount of medialization;
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 AP Radiograph. A New Computerized Technique.
The relationship between the design, position, and articular wear of acetabular components inserted without cement and the development of pelvic osteolysis.
The spatial location of impingement in total hip arthroplasty.
Dislocation After Total Hip Arthroplasty: Causes and Prevention.
The definition and measurement of acetabular orientation. DW Murray. JBJS. Vol 75(2)-B. 1993. p 228-232.
The effect of the orientation of the acetabular and femoral components on the range of motion of the hip at different head-neck ratios.
Position, orientation and component interaction in dislocation of the total hip prosthesis.
Comparison of a mechanical acetabular alignment guide with computer placement of the socket.
Compliant positioning of total hip components for optimal range of motion.
The accuracy of free-hand cup positioning--a CT based measurement of cup placement in 105 total hip arthroplasties.
Anatomic Referencing of Cup Orientation in Total Hip Arthroplasty.
Computed Tomography Measurement of the Accuracy of Component Version in Total Hip Arthroplasty.
Using Intraoperative Pelvic Landmarks for Acetabular Component Placement in Total Hip Arthroplasty.
Computed tomographic evaluation of component position on dislocation after total hip arthroplasty.
Comparison of Conventional Versus Computer-Navigated Acetabular Component Insertion.
Impingement with Total Hip Replacement
