Using acetabular fossa as a guide for anticipated inclination of uncemented cup in total hip replacement

Abstract

Positions of acetabular implant generally are considered to be major causative factors of dislocation. Accurate and consistent achievement of the preoperatively anticipated orientation of the acetabular cup is a great challenge in total hip replacement (THR). In the present study, we investigated the surgical application of acetabular fossa as a guide for anticipated inclination of uncemented cup, and evaluated its accuracy as an anatomic reference for achieving the preoperatively anticipated abduction of the acetabular cup in comparison with traditional device method on cadaveric specimens. Sixteen normal adult pelvic cadaveric specimens were collected. On each of the sixteen normal adult pelvic cadaveric specimens, acetabular fossa related anatomic sites were marked and studied on pelvic radiographs. Our results showed that there is close correlation between most medial aspect of acetabular sourcil and central axis of the acetabular cup at anticipated inclination of 40° ± 5°. And the fossa group can achieve the preoperatively anticipated cup abduction more accurately than the device group. The current results demonstrated that acetabular fossa can be a reasonable alternative, or as a complement to the currently used methods guiding total hip replacement.

Keywords: Acetabular fossa; accuracy; anatomic reference; preoperative assessment; radiographic characteristics; total hip replacement.

Figure 1

Central axis of the acetabular fossa (Z1Z2) extended through the top of fossa (at point T) and rim at point M. Z1 and Z2 were the midway of lineA1A2 and line B1B2 respectively.

Figure 2

Markers were placed at T, M, and T1 which was near to T and at the edge of the fossa.

Figure 3

A hole was Drilled in the direction from midway of MZ1 toward point T, which was along the imaginary central axis of the cup.

Figure 4

Acetabular reaming was performed concentrically along the hole-drilling direction with the diameter of the reamer in line with the central axis of the acetabular fossa.

Figure 5

On anteroposterior pelvic film, abduction angle was determined by the intersection of long axis of cup and inter-teardrop line.

Figure 6

Markers at T and M correspond to most medial and lateral aspect of acetabular sourcil respectively, with T1 being away from the sourcil.

Figure 7

With templating, central axis of cup intersected with medial wall at R1 when the inclinaton angle is 45° (A). With templating, central axis of cup intersected with medial wall at R2 when the inclinaton angle is 35° (B). R lies between R1 and R2.