The target acetabular cup inclination is a 'safe zone' between 30-50° abduction (assessed by AP of hip).Įxcessive inclination (a vertically oriented cup) decreases the surface area of articulation along the superior dome of the cup and therefore increases contact forces causing higher wear rates (known as edge loading). Inclination is the orientation of the cup in the coronal plane. Increasing the acetabular anteversion increases the flexion (decreases extension). The expectation for hip ROM after THA is 110 ° flexion and 30 ° extension. A CT scan gives the best picture of version. True version of pelvis is angle between a) the line from the posterior to anterior wall of acetabulum (essentially the ilioischial line) and b) a line directly from A to P (this is the alpha angle). which corresponds to the the native acetabular positioning within the pelvis.

Studies demonstrate that maximal range of motion before impingement occurs when the acetabular components are placed within this “safe-zone” . The goal of Combined Anteversion is 35° (+/- 10°) . The stem should also be angled slightly forward (anterior), about 15°. It can be assessed postoperatively by cross leg lateral XR (a frog-leg lateral gives lateral view of femur, but an AP of the acetabulum). There is a “safe zone” between 5° and 25° (ie 15° +/- 10°) to match native hip motion and avoid impingement. The target Acetabular Cup version is slight Anteversion. This allows for increased hip AB-duction, but less adduction, and if the hip moves into too much adduction it will impinge on the rim of the cup. In contrast, Retroversion means the cup is opening up slightly posteriorly. Anteversion means the cup is facing slightly anteriorly, this allows for increased hip AD-duction. Neutral version means the cup is facing completely lateral, ie completely in line in the sagittal plane. Femoral neck horizontal plane - femoral neck torsion.Version is the orientation of the implants in the sagittal plane.Femoral neck frontal plane - angle of inclination.However there are some signs on the frontal plane (crossover sign etc). Acetabulum coverage horizontal plane - acetabular version.Acetabulum coverage frontal plane - lateral centre edge etc.Many of the measurements can be conceptualised as follows in the frontal and horizontal plane. It is almost exclusively used in the paediatric population to assess for slipped upper femoral epiphysis (SUFE) and Perthes disease. bilateral examination allows for better visualisation of the hip joints and femoral neck.lateral projection to aid and diagnose femoroacetabular impingement (FAI) due to its increased sensitivity for detecting femoral head-neck asphericity.the ideal projection for bilateral hip or femur trauma.lateral projection demonstrating the neck of the femur without movement of the either limb.

can only be conducted on unilateral hip trauma.lateral projection demonstrating the neck of the femur without movement of the affected limb.standard rolled lateral view demonstrating the femoral neck and acetabular rim can only be performed on non-trauma patients.often only performed in follow up studies.

demonstrates the hip joint in the AP plane, with the limb internally rotated so the neck of the femur is in profile.

Hip radiographs are performed for a variety of indications including

3.2 Acetabular Depth and Coverage Calculations.

3.1 Acetabular Orientation and Morphology.

Normal hip xray frog leg