ASSESSMENT OF RADIOLUCENT LINES ABOUT THE GLENOID - AN IN-VITRO RADIOGRAPHIC STUDY

A study was undertaken to investigate the precision of plain radiograp hs in the assessment of the width of radiolucent lines and to define p arameters for more accurate measurement. A metal-backed glenoid compon ent was inserted into fourteen cadaveric scapulae; the component had a radiolucent spacer at the central post to provide a gap with a known width at the component-bone interface. The specimens were mounted in a custom-designed jig, and initial radiographs were made with the gleno id in neutral version; sequential radiographs then were made, at 5-deg ree intervals, with the glenoid in 0 to 40 degrees of anteversion and retroversion. Four independent observers with various levels of experi ence measured the width of the radiolucent lines with use of digital m icrocalipers. Osteometric analysis demonstrated that normal glenoid ve rsion ranged from 3 degrees of anteversion to 13 degrees of retroversi on: these values were similar to those reported in previous studies. R adiographic analysis showed that accurate measurement of the width of the gap was dependent on the position of the glenoid. The measured wid ths of the radiolucent lines were significantly smaller than the known width of the gap when retroversion was 10 degrees or more and when an teversion was 15 degrees or more (p less than or equal to 0.05). Radio lucent lines were not consistently observed on radiographs that were m ade with the glenoid in more than 20 degrees of anteversion and retrov ersion. An analysis of interobserver error showed close agreement amon g the measurements made by the different observers when the glenoid wa s in 0 and 5 degrees of rotation, with decreased agreement when the gl enoid was rotated more than 10 degrees from neutral. CLINICAL RELEVANC E: Inaccurate positioning of the patient and anatomical variation in g lenoid version may explain the variability in the reported onsets, pro gressions, and frequencies of radiographic loosening of glenoid compon ents. The findings of the present study also may help to explain the p oor association between clinical and radiographic findings reported fo r patients who have pain at the site of a total shoulder prosthesis. R adiographs made within 10 degrees of neutral should allow accurate ass essment of radiolucent lines about the glenoid.