DOS 2017

DOS Kongressen 2017 ·

163

Diagnostic performance of post-operative inter-

ference gap assessment on plain radiographs after

cementless primary THA.

Maartje Belt, Bjørn Gliese, Omar Muharemovic, Hendrik Husted, Anders Troelsen,

Kirill Gromov

Dept. of Orthopaedic Surgery, Copenhagen University Hospital, Hvidovre

Background:

In clinical settings, implant performance of cementless THA is

often evaluated by radiolucency on plain X-rays. Radiolucency on direct post-

operative radiographs is often classified as interference gaps. Studies use dif-

ferent criteria to define a gap. However, the diagnostic performance of plain

radiographs and the optimal definition for gaps is unknown.

Purpose / Aim of Study:

The aim was to evaluate the diagnostic performance

of radiographic assessment of post-operative interference gaps after primary

THA by comparing it with CT confirmed gaps. The secondary aim was to define

optimal cut-off criteria for assessing interference gaps on plain radiographs.

Materials and Methods:

Patients (N=40) with a primary cementless THA

performed between July 2015 and March 2016 were enrolled in the study.

Acetabular radiolucency was assessed on post-operative AP pelvic digital ra-

diographic images by two observers independently. The maximum width and

percentage of coverage in the three Delee and Charnley zones were reported.

Gap volume was measured by manual segmentation on CT images.

Findings / Results:

95% of patients had a gap on CT. When defining a gap

as a lucency >50% of a zone, the interrater agreement was 0.241. Sensitivity

was 65.8% for observer 1 (Kappa= 0.432), and 86.8% for observer 2 (Kap-

pa=0.383). When defining a gap as a lucency with a width >1mm, the interra-

ter agreement was 0.302. The sensitivity was 55.3% (kappa=0.452) and 50%

(kappa=0.95) for observer 1 and observer 2. The ROC-curve resulted in an

optimal threshold of 0.65mm (AUROC=0.888) and 0.31 mm (AUROC=0.961)

for the two observers.

Conclusions:

The diagnostic performance of plain radiographs to detect inter-

ference gaps is not optimal. Evaluating progression of radiolucency on radio-

graphs should be performed in the light of these findings.

No conflicts of interest reported

115.