Undetected Intraoperative Pelvic Movement Can Lead to Inaccurate Acetabular Cup Component Placement during Total Hip Arthroplasty: A Mathematical Simulation Estimating Change in Cup Position

Abstract

Intraoperative patient movement is a common but underappreciated phenomenon in total hip arthroplasty (THA). Such movement can significantly affect the accuracy with which the acetabular cup component is implanted. To evaluate the effect of intraoperative movement on cup position, we performed a study using mathematical modeling to simulate intraoperative movement. Mathematical simulations were used to simulate pelvic movements during THA. Pelvic axial rotation, tilt, and obliquity were simulated, and the resulting changes in intended cup position were calculated. The rate of change of inclination and anteversion per degree of pelvic movement was calculated, establishing a ratio relating cup angle sensitivity to pelvic movement. These sensitivities were used to construct nomograms showing the per-degree effect of pelvic movement on cup position. The effect of pelvic movement on cup position was multifactorial and dependent on the intended cup orientation. For a cup intended to be inserted at 15° anteversion and 40° inclination, each degree of pelvic rotation induced changes of 0.64° and –0.20°, respectively. For this same cup orientation, each degree of pelvic tilt induced changes of 0.77° for anteversion and 0.17° for inclination. Pelvic obliquity was associated with a 1:1 ratio with inclination, with each degree of obliquity inducing 1° of change in inclination. Anteversion was unaffected by changes in pelvic obliquity. This study demonstrates the consequences of undetected pelvic movement on cup position, including the increased risk of the acetabular component being placed in an orientation that could increase wear or the likelihood of impingement and dislocation.

Accuracy of Acetabular Component Positioning Using Computer-assisted Navigation in Direct Anterior Total Hip Arthroplasty

“…Cup position was reported with intraoperative patient movement taken into consideration, a potentially important feature as previous studies have shown that the pelvis rolls by as much as 9°. prior to cup impaction in the DAA [14] and 1° of pelvic roll can lead to 0.64° and -0.20° changes in anteversion and inclination, respectively [25]. Indeed, the present report demonstrated device accuracy to within 3.4° and 4.0° of postoperative radiographs for anteversion and inclination, respectively.…”

Pelvic Tilt Reduces the Accuracy of Acetabular Component Placement When Using a Portable Navigation System: An In Vitro Study

“…With the use of the PNS, DRI and DRA showed a certain tendency to change with sagittal tilt and axial tilt, whereas with coronal tilt, DRI showed a tendency to change but DRA did not. This result is also consistent with a previous mathematical simulation [16]. In the mathematical simulations, pelvic axial rotation, tilt, and obliquity were simulated, and the resulting changes in the intended cup position were calculated.…”

A Novel Method for Correcting Pelvic Tilt on Anteroposterior Pelvic Radiographs

“…Of specific concern to the THA surgeon is the impact of pelvic tilt (deviation of the anterior pelvic plane (APP) from the coronal plane), as an undetected tilt may contribute to the inaccurate evaluation of cup placement [9][10][11][12][13]. Increasing anterior or posterior pelvic tilt is known to introduce errors in the measurement of acetabular orientation [3,[5][6]11], especially anteversion, which is highly susceptible to changes in pelvic tilt [1,2,8,12], with each degree change in pelvic tilt known to alter anteversion by 0.77-0.80° [14][15]. Various methods of evaluating and correcting pelvic tilt on radiographs have been proposed [3,[16][17][18]; however, none have proven accurate and reliable.…”

“…Anterior pelvic plane tilt represents a significant contributor to inaccuracies in cup position during THA. Studies have shown that for each degree of tilt, anteversion is altered by up to 0.80° [14][15]. Combined with the inherent inaccuracies associated with radiographic imaging, the potential impact of unaccounted-for APPt is substantial.…”