Cup placement in primary total hip arthroplasty: how to get it right without navigation or robotics

Abstract

Acetabular component orientation and position are important factors in the short- and long-term outcomes of total hip arthroplasty. Different definitions of inclination and anteversion are used in the orthopaedic literature and surgeons should be aware of these differences and understand their relationships. There is no universal safe zone. Preoperative planning should be used to determine the optimum position and orientation of the cup and assess spinopelvic characteristics to adjust cup orientation accordingly. A peripheral reaming technique leads to a more accurate restoration of the centre of rotation with less variability compared with a standard reaming technique. Several intraoperative landmarks can be used to control the version of the cup, the most commonly used and studied is the transverse acetabular ligament. The use of an inclinometer reduces the variability associated with the use of freehand or mechanical alignment guides.

Keywords: cup; orientation; total hip.

Figure 1

Anterior view of a 3D cup model implanted in the lateral decubitus position. The acetabular axis is represented by the thick blue line. OA, operative anteversion; OI, operative inclination; RA, radiographic anteversion; RI, radiographic anteversion.

Figure 2

Relationship between the targeted radiographic anteversion and the operative anteversion with regards to the radiographic inclination. When the radiographic inclination is 40° and the target is a 15° radiographic anteversion angle, the operative anteversion should be 19° (dotted line). RA, radiographic anteversion.

Figure 3

Relationship between the targeted radiographic inclination and the operative inclination with regards to the operative anteversion. RA, radiographic anteversion.

Figure 4

Lateral standing (A) and deep-seated (B) spinopelvic views of a 61 year old patient with Bechterew’s disease prior to his left total hip replacement, having undergone right total hip replacement earlier. The radiographs show all measurements that can be performed as part of pre- and post-op assessments. In this patient the change in LL between positions was 4° and his PI-LL value was 15° indicating that he is at a higher risk of instability post-THA due to a lumbar spine flat-back deformity and stiff lumbar spine. LL, lumbar lordosis angle; PI, pelvic incidence; PT, pelvic tilt; PFA, pelvic femoral angle as a measure of hip flexion; AI, ante-inclination

Figure 5

(A) The centre of the femoral head. (B) When a cup is positioned flush with the true floor of the acetabulum (conventional technique) the centre of rotation is medialized. (C) When a cup is positioned using the anatomical technique the centre of rotation is maintained.

Figure 6

(A) Preoperative and (B) postoperative radiograph of a patient with low acetabular floor depth and (C) preoperative and (D) postoperative radiograph of a patient with high acetabular floor depth.

Figure 7

Intraoperative photographs of the use of the transverse acetabular ligament as a landmark for acetabular component version. TAL, transverse acetabular ligament.