Modified PHILOS system utilizing a single bone cement calcar screw achieves optimal fixation stability and promotes bone healing: a biomechanical study and corresponding case series.

Backgrounds: The PHILOS system is the most widely utilized device for the treatment of proximal humeral fractures. However, varus deformity of the humeral head, are frequently observed in PHILOS fixed patients. The primary etiology of these complications can be attributed to fixation instability. Consequently, any additional fixation devices that enhance stability may serve as alternative methods to mitigate the complications. Bone cement augmentation is an effective strategy for optimizing fixation stability in osteoporotic patients; however, the size limitation of the calcar screw in the traditional PHILOS plate restricts the volume of and the position bone cement. In response to this challenge, we presents a newly designed PHILOS plate featuring a single cannulated calcar screw. The biomechanical performance of this innovative device has been evaluated. A series of patients treated with this novel fixation device have been enrolled to assess its clinical efficacy.

Methods: A proximal humerus model has been developed, and a simulation of proximal humeral fractures has been conducted using this model. Various operative techniques, including traditional and modified PHILOS fixation methods, as well as additional fixation devices, have been established. The biomechanical performance of these fixation strategies has been compared. Furthermore, a series of patients with proximal humeral fractures were included in this study. Fracture healing and the varus status of the humeral head were assessed to evaluate clinical efficacy during a six-month follow-up period.

Results: In the biomechanical study, a comparison was made between the traditional PHILOS fixed model and three alternative models, revealing that the maximum deformation of the humeral head was significantly reduced in the latter. Notably, the fixation stability of the cement-augmented single calcar screw model surpassed that of the four-screw-augmented model. Furthermore, the maximum stress value observed in the model secured by a single calcar screw PHILOS plate was markedly lower than those recorded for other models. Additionally, 14 patients participated in this clinical series. All enrolled patients achieved optimal bone healing outcomes. The largest varus angle of the humeral head measured at 5°, with no instances of fixation failure reported.

Conclusion: The newly designed PHILOS plate, featuring a cement-augmented single calcar cannulated screw, has demonstrated the ability to significantly reduce the risk of fixation failure and associated complications by optimizing the local biomechanical environment. Given its outstanding clinical outcomes observed in the current patient series, advocating for this fixation device holds considerable clinical significance in enhancing patients’ prognoses.