BIOMECHANICS LAB

COMPARING TWO METAL PLATES TO CORRECT “MALUNITED” WRIST FRACTURES

Head of Research: Dr. Jan Herman Kuiper – Orthopaedic Interventions
Collaborators: Mr Andrew Barnett, Dr Kelly Campbell, Ms Taya Chapman, Dr Caroline Dover, Mr Pete Gallacher, Dr Shailesh Naire, Mr Simon Pickard, Dr Nikhil Sharma

Wrist fractures, or to be more precise distal radius fractures, are the commonest fracture in adults, with an incidence rate of over 2000 per million people in a year. Most of these fractures heal well, but in around 10% of cases the bone segments heal in the wrong position, forming a “malunion”. Malunion patients have pain, a smaller range of wrist motion and a lower grip strength. Their treatment involves cutting through the malunited fracture, putting the bones in the correct position and fitting a plate holding the bones in the corrected position until the fracture has healed again. A German company started marketing a service allowing surgeons to send them a CT scan of the malunited wrist. The company used the scan to determine the best way to re-position mal-united bone, the best position of the cut, a customized 3D-printed metal plate and a 3D-printed guide for drilling holes in the bones for the screws holding the plate and for guiding the saw to cut the bone. Although the 3D-printed plate will make the surgery easier and hold the bone in an ideal position, it is not clear how good the fixation is compared to clinically proven standard bone plates.

We therefore performed a laboratory study comparing the movements within the fracture gap of an artificial malunited distal radius specimen, which were cut through, repositioned and fixed by either a standard plate or a 3D-printed custom plate (Figure 1). The distal radius specimens were 3-D printed from a CT scan of a patient who had a malunited fracture. We put the specimens with fixated fractures in our materials testing machine and applied forces replicating the average and peak forces measured in wrist fracture patients who do rehabilitation exercises (Figure 2).

We found that fractures fixated with either plate could withstand 1000 cycles of even the peak measured forces without any permanent change in the bone position. However, the 3-D plate provided a much stiffer fixation, leading to much smaller motions between the bone ends. These smaller motions suggest that patients may be able to start rehabilitating earlier. However, fracture site motion can be beneficial for healing and we don’t know if these smaller motions might affect the healing rate.