Proximal fixation of a humeral periprosthetic fracture with a stable cemented shoulder prosthesis- a biomechanical assessment of 3 different methods

Objectives Assessing the biomechanical stability of 3 different techniques used to treat a Worland type C periprosthetic fracture after total shoulder arthroplasty (TSA) with cemented anatomical prosthesis.

Methods 27 synthetic left humeri with implanted cemented anatomical shoulder endoprosthesis were cut distally and fixed proximally with LCP and: (1) 1x1.5mm cerclage wire and 2x locking unicortical screws, (2) 3x1.5mm cerclage wires, or (3) 2x supporting plates allowing bicortical fixation by directing offset locking screws tangentially around either side of the prosthesis stem. Torsional stress was assessed after applying 5N force internally then externally and measuring the degrees of rotation at the level of the proximal fixation. Axial stiffness was assessed by applying monotonically increasing sinusoidal and assessing how many mm of mobility did the proximal construct display. Load until failure was measured as the amount of Newtons needed for the proximal stabilization to fail. Relative movements at the plate-humerus interface were registered by motion tracking.

Statistical analysis was performed using SPSS where the statistical differences were detected by Using Mann-Whitney U-Test.

Results and Conclusion Since all our results showed no normal variations we chose to present the results in terms of medians. With regards to internal as well as external rotational stiffness group 1 showed a median stiffness of: 0.5Nm/° (p = 0) and 0.3Nm/° (p = 0) respectively, group 2 had a median stiffness of: 0.33 Nm/° (p = 0) and 0.48 Nm/° (p = 0) respectively, while group 3 had a median stiffness of: 13.81Nm/° (p = 0) and 12.85 Nm/° (p = 0) respectively. Concerning axial stiffness, group 1 showed a median stiffness of 4,464.25 N/mm (p = 0.003), group 2 had a median stiffness of 6,877.5 N/mm (p = 0.003), whereas group 3 had a median stiffness of 6,618.45 N/mm (p = 0.003). Concerning load to failure group 1 had a median of 1400 N (p>0.05), while groups 2 and 3 had median loads of 1675 N (p>0.05) and 1500 N (p>0.05) respectively.

Biomechanically, even though the 2x supporting plates with bicortical fixation displayed a significantly higher torsional stiffness in comparisons to the other groups, the group with only cerclage wires displayed a higher load to failure and a comparable axial stiffness providing an economically cheaper and technically easier alternative.

Stichwörter Periprosthetic Fracture-Shoulder Prosthesis-

Publication History

Article published online:
15 October 2020