Humeral head subluxation in Walch type B shoulders varies across imaging modalities

Abstract

Background The Walch type B pattern of glenohumeral osteoarthritis is characterized by posterior humeral head subluxation (PHHS). At present, it is unknown whether the percentage of subluxation measured on axillary radiographs is consistent with measurements on 2-dimensional (2D) axial or 3-dimensional (3D) volumetric computed tomography (CT). The purpose of this study was to evaluate PHHS across imaging modalities (radiographs, 2D CT, and 3D CT). Methods A cohort of 30 patients with Walch type B shoulders underwent radiography and standardized CT scans. The cohort comprised 10 type B1, 10 type B2, and 10 type B3 glenoids. PHHS was measured using the scapulohumeral subluxation method on axillary radiographs and 2D CT. On 3D CT, PHHS was measured volumetrically. PHHS was statistically compared between imaging modalities, with P ≤ .05 considered significant. Results The mean PHHS value for the entire group was 69% ± 24% on radiographs, 65% ± 23% with 2D CT, and 74% ± 24% with 3D volumetric CT. PHHS as measured on complete axillary radiographs was not significantly different than that measured on 2D CT ( P = .941). Additionally, PHHS on 3D volumetric CT was 9.5% greater than that on 2D CT ( P < .001). There were no significant differences in PHHS between the type B1, B2, and B3 groups with 2D or 3D CT measurement techniques ( P > .102). Conclusion Significant differences in PHHS were found between measurement techniques ( P < .035). A 9.5% difference in PHHS between 2D and 3D CT can be mostly accounted for by the linear (2D) vs. volumetric (3D) measurement techniques (a linear 80% PHHS value is mathematically equivalent to a volumetric PHHS value of 89.6%). Surgeons should be aware that subluxation values and therefore thresholds vary across different imaging modalities and measurement techniques.

Serial 3D CT analysis of humeral head alignment in relation to glenoid correction and outcomes after total shoulder arthroplasty

“…The heterogenicity in predictors of clinical outcome between our 3D study and earlier studies using standard radiographs or uncorrected CT might be explained by the applied imaging modality, similarly as previously seen for posterior subluxation of the humeral head. 16 , 22 When assessed in 3D, maximum glenoid erosion in biconcave glenoids is orientated in the posterior-inferior quadrant of the glenoid. 2 As the 3D coordinate system neutralizes the inherent protraction of the scapula to create controlled viewing perspectives, it can be assumed that in the less controlled imaging modalities with inherent scapular protraction the maximum glenoid erosion will be depicted more posteriorly than inferiorly.…”

“… 12 , 34 While follow-up using computed tomography (CT) can improve the assessment of radiolucencies around the implant, three-dimensional (3D) imaging is an important tool to analyze scapular and humeral anatomy. 3 , 16 , 17 , 19 , 22 , 26 , 27 , 28 , 34 The latter provides a standardized viewing perspective, primarily using the plane of the scapula, which allows for a reliable and accurate 3D assessment of humeral head alignment and glenoid parameters. 3 , 16 , 17 , 22 , 28 …”

“… 3 , 16 , 17 , 19 , 22 , 26 , 27 , 28 , 34 The latter provides a standardized viewing perspective, primarily using the plane of the scapula, which allows for a reliable and accurate 3D assessment of humeral head alignment and glenoid parameters. 3 , 16 , 17 , 22 , 28 …”

Quantitative statistical shape model‐based analysis of humeral head migration, Part 2: Shoulder osteoarthritis

“…The more posterior glenoid translation that we found to be associated with B glenoids could be an explanation for this finding. This has implications for HHM correction, as 3D TSA planning software uses different methodologies in determining preoperative HHM 19,24,36 . Shoulder surgeons should be aware that these different methodologies lead to a different appreciation of the amount of HHM 37 .…”

“…This has implications for HHM correction, as 3D TSA planning software uses different methodologies in determining preoperative HHM. 19,24,36 Shoulder surgeons should be aware that these different methodologies lead to a different appreciation of the amount of HHM. 37 Furthermore, the needed amount of HHM correction remains a matter of debate: "normal"…”