Implant design, critical shoulder angle and acromial index should be considered during preoperative planning for reverse shoulder arthroplasty to achieve optimal postoperative distalization and lateralization shoulder angles, new data shows.
Optimum postoperative distalization and lateralization shoulder angles are defined as a between 40˚and 65˚and 75˚and 95˚respectively. The researchers of “Similar optimal distalization and lateralization angles can be achieved with different reverse shoulder arthroplasty implant designs,” however, wrote that it is still unclear whether these values can be reached with different implant designs.
The study, which was published in the November-December 2021 issue of the Journal of Orthopedics, evaluated different reverse shoulder arthroplasty designs to determine if certain implants were more effective at achieving higher values of distilization and lateralization angles.
The researchers also analyzed the connection between preoperative critical shoulder angle and acromial index with the distalization and lateralization shoulder angle.
The retrospective analysis looked at three reverse shoulder arthroplasty designs in particular: group 1 which had 16 patients were given FH Arrow only implants with a 135˚neck-shaft angle, group 2 with 20 patients were given Biomet Comprehensive onlay implants with a 147˚neck-shaft angle and group 3 with 15 patients were given Mathys Affinis inlay implants with a 155˚neck-shaft angle.
According to the data collected, the mean distalization angles were 44˚, 46˚, and 46˚ (p = 0.671) and the mean lateralization angles were 92˚, 91˚, and 82˚for groups 1,2 and 3, respectively.
Group 3 had lower lateralization angles than groups 1 (–10˚; p = 0.005) and 2 (–9˚; p = 0.002).
Overall, optimal distilization and lateralization angles were achieved in 71% and 73% of all arthroplasties, respectively.
The researchers didn’t find any association between implant designs and achieving an optimal distalization angle or lateralization angle. None of the implant designs had a distalization angle greater than 65˚.
The most common cause of failure to reach an optimal lateralization angle in onlay implants was a combination of lateralization angle greater than 95˚and distalization angle less than 40˚. The most common cause of failure in group 3 was distalization angle less than 40˚.
In addition, the distalization angle was negatively correlated with acromial index (–0.384; p = 0.006) and critical shoulder angle (–0.305; p = 0.033). No correlation was observed between the lateralization angle and the acromial index (p = 0.321) or critical shoulder angle (p = 0.137).
“The lateralization angle is lower with the Mathys Affinis implant than with the Biomet Comprehensive and FH Arrow implants; however, most lateralization angles are in the optimal ranges, and no association is observed between different implant designs and optimal distalization and lateralization angles. Implant design, critical shoulder angle and acromial index should be considered during preoperative planning to achieve optimal distalization and lateralization angles,” the researchers wrote.
The authors of the study included Michael Marsalli of the Clinica Universidad del los Andes, Chile, Juan De Dios Errazuriz of the Hospital Del Trabajador, Chile, Marco A. Cartaya of the Hospital Del Trabajador, Chile, Joaquin De La Paz of the Hospital Del Trabajador, Chile, Diego N. Fritis of the Clinica Universidad de los Andes and the Hospital Del Trabajador, Pedro I. Alsua of Hospital Del Trabajador, Nicolas I. Moran of the Hospital Del Trabajador and Hospital San Jose in Chile and Jose T. Rojas of Hospital San Jose in Chile.
