BIOMECHANICAL STUDY OF THE TENSIONS THROUGH TUBEROSITY SUTURES PLACING HEMIARTHROPLASTY AT DIFFERENT HEIGHTS AND VERSIONS IN PROXIMAL HUMERAL FRACTURES

Abstract

Introduction: Functional results of hemiarthroplasties in proximal humeral fractures are unpredictable. The correct consolidation of the tuberosities back to the prosthesis seem to be of capital importance in the functional outcome. The objective of the study is to analyze the changes of the tension registered in the sutures passed through the tuberosities when changing the height and version of the prosthesis in a static model and in a dynamic model.

Material and Method: Prosthesis positioning: in both static and dynamic model, the prosthesis was placed in anatomical position, anatomical increasing 20° retroversion, increasing height in 1cm and anatomical version, decreasing height in 1 cm and anatomical version, increasing height in 1cm and increasing 20° retroversion, decreasing height in 1 cm and increasing 20° retroversion,

Static study: a 4-part fracture was reproduced in four fresh-frozen shoulder specimens. Sutures were placed between lesser tuberosity and diafisis (sensor 1) between both tuberosities (sensor 2) and between greater tuberosity and diafisis (sensor 3). Traction was performed through supraspinatus, infraspinatus and subescapularis attachments until the breakage of the suture or 1 cm gap between bony fragments. Tensions registered in a computer model.

Dynamic study: a 4-part fracture was reproduced in a humeral saw bone. Sutures placed in the same position that in the static model. Saw bone fixed at a robotic arm reproducing cycles of 90° anterior elevation, 30° lateral rotation, 30° internal rotation and retropulsion to starting point. Registering of the tensions. Quantitative values studied through t-student and non parametric values studied through U-Mann-Whitney and Kruskal-Wallis test.

Results: In the Static study, the suture placed between the tuberosities is the one that significantly receives more tension. The breakage of the suture happens more frequently when the prosthesis is placed in a lower position and in a lower more retroverted position.

In the dynamic study, the suture placed between the greater tuberosity and the diafisis is the one significantly receives more tension. The breakage of the suture happens more frequently when the prosthesis is placed in a lower position and in a lower more retroverted position.

Conclusions: When planning sutures between tuberosities in proximal humeral fractures treated with hemiarthroplasty postoperative rehabilitation program has to be considered because different sutures are at risk depending on static or dynamic model.

The worst positions of the hemiarthroplasty as far as over tensioning sutures is concerned are the low position and the low more retroverted position.