Evaluation of lengthening in reverse shoulder arthroplasty comparing X-rays and computerised tomography.
OBJECTIVE
The correct amount of arm lengthening in reverse shoulder arthroplasty is crucial to provide joint stability and good results. Determination has been proposed according to radiographs. However, radiographic measurements are error prone in regards to positioning of the arm with regard to the radiographic beam. The purpose of this study was to evaluate the precision of radiographic measurements compared to CT scans of the upper limb following reverse shoulder arthroplasty.


METHODS
Thirty patients undergoing onlay reverse shoulder arthroplasty with comparative radiographs and CT scans of both humeri were included in this study. Arm length, humeral length as well as the arm and humeral lengthening were evaluated on pre- and postoperative radiographs compared to postoperative CT scans following a previously validated protocol.


RESULTS
We found an excellent correlation for arm length and humeral length for radiographic and CT measurements (r > 0.90). The postoperative humeral and arm lengthening compared to the contralateral side was 0.1 (-1.2 to 1.2) cm and 2.8 (0.2 to 5.2) cm for the CT scans, and -0.6 (-4.1 to 2.0) cm and 1.9 (-2.3 to 5.0) cm for the radiographs. For arm lengthening, correlation coefficient was good (r = 0.7) even though radiographs indicated arm shortening in five cases whereas arm lengthening was observed on CT scans.


CONCLUSIONS
Measurements on radiographs and CT scans are comparable in most of the cases. However, we observed some important variations that question the reliability of radiographic measurements in up to 20 % of cases. Therefore, a CT scan appears to be necessary in the event of postoperative complications (e.g., instability, neurological problems).
Générale de Santé, Hôpital Jean Mermoz, Centre Orthopédique Santy, 24 Avenue Paul Santy, 69008, Lyon, France. birgitwerner@hotmail.com.
Birgit S
BS
Werner
Kansas City University of Medicine and Biosciences, Kansas City, MO, USA.
Matthew
M
Daggett
Générale de Santé, Hôpital Jean Mermoz, Centre Orthopédique Santy, 24 Avenue Paul Santy, 69008, Lyon, France.
Yannick
Y
Carrillon
Générale de Santé, Hôpital Jean Mermoz, Centre Orthopédique Santy, 24 Avenue Paul Santy, 69008, Lyon, France.
Gilles
G
Walch
D019643:Arthroplasty, Replacement / Q000379:methods*; D001852:Bone Lengthening / Q000379:methods*; D005260:Female; D006801:Humans; D006811:Humerus / Q000000981:diagnostic imaging* / Q000601:surgery; D008297:Male; D011183:Postoperative Complications / Q000000981:diagnostic imaging; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D014057:Tomography, X-Ray Computed / Q000379:methods; D014965:X-Rays
Arm lengthening; CT scan; Humeral lengthening; Measurement method; Reverse shoulder arthroplasty