A RADIOGRAPHIC ANALYSIS OF PROXIMAL HUMERAL ANATOMY IN PATIENTS WITH PRIMARY GLENOHUMERAL ARTHRITIS…
Figure 1 - Initial two-dimensional multiplanar views for humeral measurements. The frontal view (A) depicts the PD line (solid blue) bisecting the IM canal and the transition point (solid purple line) where the diaphysis becomes parallel. The sagittal view (B) shows the PD line (orange line) bisecting the IM canal.
While short stems in total shoulder arthroplasty (TSA) preserve bone stock and facilitate revision surgery, they have been associated with higher rates of malalignment and loosening in some cases compared to standard length stems. The purpose of this study was to analyze the intramedullary canal in progressive increments distal to the greater tuberosity to provide anatomic information about the optimal length of press-fit short stems for alignment and stability in TSA. We hypothesized that the humeral canal diameter will remain variable for the first 50 to 75 mm distal to the greater tuberosity and will become consistent thereafter. A retrospective review of 99 consecutive patients undergoing TSA with CT scans was performed. Intramedullary anterior-posterior (AP) and medial-lateral (ML) width as well as diameter were analyzed on two-dimensional computed tomography following multiplanar reconstruction. Measurements were taken at consistent distances distal to the greater tuberosity (GT). The transition point was measured at the proximal level of the humerus where endosteal borders of the medial and lateral cortices became parallel. The mean transition point was 73 mm from the GT (range: 53 to 109 mm). ML and AP widths became consistent 80 mm distal to the GT. IM diameter became consistent after 90 mm distal to the GT and a stem length of 90 mm extended past the transition point in 91.9% of cases. In TSA, a humeral stem length of 90 mm is required to predictably reach points at which the humeral canal becomes cylindrical and consistent in diameter. This information may aid data-driven decisions on humeral stem length during press-fit fixation, assuring consistency of alignment and implant stability, while maintaining ease of revision associated with a short stem implant. Level of evidence: III
Figure 2 - Two-dimensional-CT radiographic views depicting the process of measurement technique. Frontal view (A) of segmented humerus demonstrates measurements: greater tuberosity (GT) to metaphysis, Level 1—metaphysis, Level 2—25 mm distal to the metaphysis, Level 3—50 mm distal to the metaphysis, and then succeeding levels of 10 mm segments up to 120 mm distal to the metaphysis. The ML line (purple solid) depicts the cross section where measurements will be taken from the axial view and the PD line (blue solid) formatted to bisect the intramedullary (IM) canal. The axial view (B) depicts example measurements from the respective 25 mm segment from the axial view; ML axis (orange solid), AP axis (blue solid), ML (yellow dotted), AP (red dotted), and IM area (inside green dotted).
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Published May 2022 in the Journal of Clinical Medicine (Volume 11 - Issue 10).