Does acetabular retroversion affect range of motion after total hip arthroplasty?

Abstract

Background: Increasingly, acetabular retroversion is recognized in patients undergoing hip arthroplasty. Although prosthetic component positioning is not determined solely by native acetabular anatomy, acetabular retroversion presents a dilemma for component positioning if the surgeon implants the device in the anatomic position.

Questions/purposes: We asked (1) whether there is a difference in ROM between surface replacement arthroplasty (SRA) and THA in the retroverted acetabulum, and (2) does increased femoral anteversion improve ROM in the retroverted acetabulum?

Methods: Using a motion analysis tracking system, we determined the ROM of eight cadaveric hips and then created virtual CT-reconstructed bone models of each specimen. ROM was determined with THA and SRA systems virtually implanted with (1) the acetabular component placed in 45° abduction and matching the acetabular anteversion (average 23° ± 4°); (2) virtually retroverting the bony acetabulum 10°; and (3) after anteverting the THA femoral stem 10°.

Results: SRA resulted in ROM deficiencies in four of six maneuvers, averaging 25% to 29% in the normal and retroverted acetabular positions. THA restored ROM in all six positions in the normal acetabulum and in four of the six retroverted acetabula. The two deficient positions averaged 5% deficiency. THA with increased femoral stem anteversion restored ROM in five positions and showed only a 2% deficiency in the sixth position. Compared with the intact hip, ROM deficits were seen after SRA in the normal and retroverted acetabular positions and to a lesser extent for THA which can be improved with increased femoral stem anteversion.

Conclusion: Poor ROM may result after SRA if acetabular retroversion is present.

Fig. 1

A diagram of the intact cadaveric testing apparatus (not to scale) is shown. Using a 3-D motion analysis system, each position of the bone was tracked while applying torque on the femur through a load cell.

Fig. 2

The neutral position, shown here in the anterolateral view, was established using anatomic axes for measurement purposes of the three rotations of the hip. These axes were defined by bony landmarks on the femur and pelvis.

Fig. 3

A ROM simulation is shown. The femur of one typical specimen is first placed in the neutral position after hip resurfacing and then undergoes maximum flexion. (From ORS Transaction #0276: Doherty SD, Thompson MT, Usrey MM, Murihead-Allwood S, Noble PC. Does hip resurfacing restore normal range of motion and provide better joint motion than THR? Trans Orthop Res Soc. 2007;32:paper 0276.)

Fig. 4

Various positions of the femur recreated in the anterior and lateral views are shown. The maneuvers in yellow represent the motion during resurfacing, which, on average, exhibited nearly 25% less motion compared with the intact specimens.

Fig. 5

When compared with the intact specimens, ROM was restored in only two of the six maneuvers after SRA for the normal and retroverted acetabula with an average of 25% to 29% deficiency for the other four maneuvers.

Fig. 6

Compared with the intact specimens, ROM was fully restored using THA in all six maneuvers in the normal acetabulum, but only four of the six maneuvers were in retroverted acetabula.

Fig. 1

An intact reconstructed acetabulum in its anatomic initial position is shown.

Fig. 2

The virtually implanted resurfacing cup in the normal acetabulum (45^o inclination, matched anteversion) is shown.

Fig 3A–C

(A) A large sphere encompassing any impinging portion of the rim is centered in the acetabulum. (B) The portion of the acetabulum in this sphere is disconnected from the rest of the pelvis so that only the acetabulum can be rotated. The two pieces are shown separated here for emphasis, but the acetabulum is actually still centered at the same spot of the pelvis. (C) The acetabulum then is retroverted 10°, shown here separated from the pelvis for emphasis and comparison with Illustration B.

Fig. 4

The virtually implanted resurfacing cup in the retroverted acetabulum (45° inclination with version matched to the retroverted acetabulum) is shown.