Does partial weight bearing unload a healing bone in external ring fixation?

Background. Partial weight bearing is thought to unload and protect the healing bone. Until now, there has been no objective method of assessing the amount of weight placed on the healing zone by the patient. The goal of this study was to determine the effects of partial weight bearing on the loading of the healing bone in tibial osteotomies. Materials and methods. Six patients with complex tibial osteotomies, stabilized with Ilizarov ring fixator constructs, took part in this study. Three-dimensional interfragmentary movements were measured with reflective markers that were attached to the Schanz screws of the fixator. Patients were asked to rest, to co-contract the musculi gastrocnemii, to stand up, to walk slowly and to load partially the affected limb with 20 kg of weight. Results. Compared with co-contraction, ground reaction forces of partial weight bearing, standing up and walking were significantly increased (P<0.05). The interfragmentary movements during partial weight bearing were, however, comparable in partial weight bearing, standing up and walking (P>>0.05). Conclusions. Partial weight bearing did not unload the defect zone. No direct relationship between interfragmentary movement magnitudes and ground reaction forces was identified. Therefore, the concept of partial weight bearing cannot reliably reduce loading of a healing zone. It may, however, help to prevent patients from undergoing critical situations, such as stumbling, by increasing their general awareness.