Ultrasound-based computer navigation: An accurate measurement tool for determining combined anteversion?

Variations in pelvic tilt during day-to-day activities after total hip arthroplasty measured with an ultrasound system

INTRODUCTION

The pelvis plays a major role in the orientation of total hip arthroplasty (THA) implants and consequently, on the postoperative stability of the new hip joint. The relationship between the spine and pelvis affects the functional orientation of the acetabular cup, although this relationship differs between individuals and the positions encountered in everyday life. We believe this should be factored in when planning the THA procedure. This led us to conduct an in vivo ultrasound study to document the values of pelvic tilt in standing, sitting and lying positions in patients who have advanced hip osteoarthritis, before and after they undergo THA.

HYPOTHESIS

The pelvic tilt when standing, sitting and lying supine does not change significantly after THA.

MATERIALS AND METHODS

The pelvic tilt, defined as the angle between the anterior pelvic plane and a vertical line was measured using an ultrasound device in 30 patients before the THA procedure and again 6 months later in standing, sitting and lying positions. The measurements were done during an office visit with the patient on an examination table for the lying position, on a chair for the sitting position and with the heels and occiput against the wall for the standing position.

RESULTS

The preoperative and 6-month postoperative pelvic tilt were -5.6̊±10.4̊ [-30.6̊; 11.7̊] and -5.8̊±7.9̊ [-20.6̊; 10.4̊] (p=0.4129) when standing, -44.5̊±6.10 [-53.8̊; -23.9̊] and -43.5̊±6.9̊ [-54.4̊; -17.3̊] (p=0.5760) when sitting, -88.3̊±5.1̊ [-99.3̊; -78.7̊] and -87.9̊±5.9̊ [-97.6̊; -72.4̊] (p=0.6106) when lying supine, respectively. There was no significant difference in the pelvic tilt before and 6 months after THA procedure. Variations of±5̊; ±5-10̊; ±10-15̊ and 15-20̊ were found in 72% (18); 20% (5); 4% (1) and 4% (1) of patients when lying supine, 56% (14); 36% (9); 8% (2); 0% (0) of patients when standing and 76% (19); 24% (6); 0% (0); 0% (0) when sitting. The mean variation for each patient between the preoperative and 6 months postoperative measurement was 4.8±3.4̊ [0.8̊; 10.4̊] (p=0.4129), 3.5±2.3̊ [0.2̊; 9.1̊] (p=0.5760), and 4.6̊±3.2̊ [1.2̊; 15.4̊] (p=0.6106) for the standing, sitting and lying positions respectively.

CONCLUSION

The pelvic tilt does not significantly change 6 months after THA. Taking into account the various positions used in everyday life may help to optimize the implant position. We have described the use of an affordable, accurate and non-irradiating device that provides fast and easy measurements of pelvic tilt in various positions.

LEVEL OF EVIDENCE

IV.

Impingement-free range of movement, acetabular component cover and early clinical results comparing ‘femur-first’ navigation and ‘conventional’ minimally invasive total hip arthroplasty

We report the kinematic and early clinical results of a patient- and observer-blinded randomised controlled trial in which CT scans were used to compare potential impingement-free range of movement (ROM) and acetabular component cover between patients treated with either the navigated ‘femur-first’ total hip arthroplasty (THA) method (n = 66; male/female 29/37, mean age 62.5 years; 50 to 74) or conventional THA (n = 69; male/female 35/34, mean age 62.9 years; 50 to 75). The Hip Osteoarthritis Outcome Score, the Harris hip score, the Euro-Qol-5D and the Mancuso THA patient expectations score were assessed at six weeks, six months and one year after surgery. A total of 48 of the patients (84%) in the navigated ‘femur-first’ group and 43 (65%) in the conventional group reached all the desirable potential ROM boundaries without prosthetic impingement for activities of daily living (ADL) in flexion, extension, abduction, adduction and rotation (p = 0.016). Acetabular component cover and surface contact with the host bone were > 87% in both groups. There was a significant difference between the navigated and the conventional groups’ Harris hip scores six weeks after surgery (p = 0.010). There were no significant differences with respect to any clinical outcome at six months and one year of follow-up. The navigated ‘femur-first’ technique improves the potential ROM for ADL without prosthetic impingement, although there was no observed clinical difference between the two treatment groups.

Cite this article: Bone Joint J 2015; 97-B:890–8.