• Patric Raiss, Thomas Wittmann, William Blakeney, Manuel Urvoy, and Gilles Walch.
• OCM (Orthopädische Chirurgie München) Clinic, Steinerstrasse 6, 81369, München, Germany. patric.raiss@ocm-muenchen.de.
• Arch Orthop Trauma Surg. 2023 Apr 1; 143 (4): 183318391833-1839.

IntroductionRadiographic stress shielding is a common finding in uncemented convertible short-stem shoulder arthroplasty (UCSSSA). The distal filling ratio (DFR) has been described as a predictor for the occurrence of stress shielding. A DFR > 70% was mentioned as a risk factor for the occurrence of stress shielding for some UCSSSA. However, measurements were only performed on conventional radiographs and no validation exists for 3D automated planning tools.MethodsDFR was manually measured on postoperative true ap radiographs of 76 shoulder arthroplasties using a standardized protocol and were compared to preoperative CT scans with an automated calculation of the DFR after virtual implantation of the stem.ResultsThe mean DFR measured on X-rays was 75.9% (SD = 8.7; 95% CI = 74-78) vs. 78.9% (SD = 9.1; 95% CI = 76.8-83) automatically measured on CT scans. This difference was significant (p < 0.001). In 7 out of 76 cases (9%) the difference between manual measurement on radiographs and computerized measurement on CT scans was > 10%.ConclusionManual measurement of the DFR is underestimated on conventional radiographs compared to automated calculation on CT scans be a mean of 3%. Therefore, automated measurement of the DFR on CT scans seems to be beneficial, especially in cases with osteopenic cortices. Manual measurement of the DFR on conventional ap radiographs in cases without CT scans, however, is still a viable alternative.Level Of EvidenceLevel IV, retrospective study.© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

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