The stiffness of locking plates provides increased stability for early fracture healing but may limit late interfragmentary motion (IFM) necessary for secondary bone healing. An ideal plating construct would provide early rigidity and late flexibility to optimize bone healing.

A new study published in the Journal of Orthopaedic Trauma assessed the efficiency of a novel screw plate construct, utilizing locking screws with a degradable polymer locking mechanism.

In this study, conventional locked plating constructs (group A) were compared to locking screws with a threaded degradable polymer collar before (group B), and after polymer dissolution (group C). Monotonic axial compression, monotonic torsion, cyclic axial load to failure and IFM at the near and far cortices were tested.

The results showed equivalent axial stiffness in group A and B, but significantly less stiffness in group C. Groups A and B also had similar IFM, but group C had significantly increased IFM, at both, the near and far cortices. Additionally, in cyclic axial load to failure, group A and B were similar, but group C was significantly lower. All failures were above the 500-N threshold seen in typical weight-bearing restrictions for fracture care. On the other hand, torsional stiffness demonstrated significant differences between all groups.

The findings suggested that the use of locking plates with a degradable polymer collar show potential for construct dynamization. It was stated that future in vivo studies are warranted to assess performance under combined loading and the effects of decreasing construct stiffness during the course of bony healing.

Source: Journal of Orthopaedic Trauma. 2020 Mar;34(3):151-157. doi: 10.1097/BOT.0000000000001664