Reducing variability in apparent operative inclination during total hip arthroplasty: findings of a randomised controlled trial.

AIMS: To determine which of 3 methods of cup insertion most accurately achieved a target apparent operative inclination (AOI) of 35° ± 2.5°: (1) Freehand; (2) Modified Mechanical Alignment Guide (MAG); or (3) Digital Inclinometer assisted. METHODS: Using a cementless cup via a posterior approach in lateral decubitus 270 participants were recruited, with 90 randomised to each method. The primary outcome was the unsigned deviation from target AOI. The digital inclinometer was used to measure AOI in all cases, though the surgeon remained blinded to the reading intraoperatively for both the Freehand and MAG methods. RESULTS: Mean deviation from target AOI for the Freehand, Modified 35° MAG and Digital Inclinometer techniques was 2.9°, 1.8° and 1.3° respectively. When comparing mean deviation from target AOI, statistically significant differences between the Freehand / Inclinometer groups ( p < 0.001), the Freehand / Modified 35° MAG groups ( p < 0.001) and the Digital Inclinometer / Modified 35° MAG groups ( p < 0.023) were evident. The Digital Inclinometer technique enabled the surgeon to achieve a target AOI of 35° ± 2.5° in 88% of cases, compared to 71% of Modified 35° MAG cases and only 51% of Freehand cases. DISCUSSION: The Digital Inclinometer and the Modified 35° MAG techniques were both more accurate than the Freehand technique, with the Digital Inclinometer technique proving most accurate overall. Radiographic inclination (RI) is also influenced by operative anteversion; however, the greatest source of error with respect to RI occurs when the pelvic sagittal plane is not horizontal at the time of acetabular component insertion. Clinical Trial Protocol number: NCT01831401.

Correction of pelvic adduction during total hip arthroplasty reduces variability in radiographic inclination: findings of a randomised controlled trial.

INTRODUCTION: The study aims were to identify the incidence of pelvic adduction during total hip arthroplasty (THA) in lateral decubitus and to determine, when aiming for 35° of apparent operative inclination (AOI), which of 3 operating table positions most accurately obtained a target radiographic inclination (RI) of 42°: (1) horizontal; (2) 7° head-down; (3) patient-specific position based on correction of pelvic adduction. METHODS: With patients seated on a levelled theatre table, a ruler incorporating a spirit level was used to draw transverse pelvic lines (TPLs) on the skin overlying the pelvis and sacrum. Subsequently, when positioned in lateral decubitus these lines provided a measure of pelvic adduction. 270 participants were recruited, with 90 randomised to each group for operating table position. In all cases target AOI was 35°, aiming to achieve a target RI of 42°. The primary outcome measure was absolute (unsigned) deviation from the target RI of 42°. RESULTS: 266/270 patients demonstrated pelvic adduction (overall mean 4.4°, range 0- 9.2°). No patients demonstrated pelvic abduction. There were significant differences in RI between each of the 3 groups. The horizontal table group displayed the highest mean RI. The patient specific table position group achieved the smallest absolute deviation from target RI of 42°. DISCUSSION: In lateral decubitus, unrecognised pelvic adduction is common and is an important contributor to unexpectedly high RI. The use of preoperative TPLs helps identify pelvic adduction and its subsequent correction reduces variability in RI. Clinical Trial Protocol number: NCT01831401.

Acetabular Liner Dissociation following Total Hip Arthroplasty: A Rare but Serious Complication That May Be Easily Misinterpreted in the Emergency Department.

Acetabular liner dissociation is a rare complication of Total Hip Arthroplasty (THA) which requires urgent revision surgery. A case is presented in which the correct diagnosis was not appreciated on two separate Emergency Department attendances. The typical symptoms, signs, and radiological features are outlined and the importance of considering a rare complication following a commonly performed procedure is highlighted.