Patient-specific muscle models for surgical planning

In the Multisense project, several sensorial devices (haptics, speech, visualisation and tracking) are integrated within a virtual reality environment for planning total hip replacement (THR) surgery. In use, a fundamental requirement is the creation of a complete subject-specific model of the lower limb. For THR surgery, the available data is from computed tomography (CT) only. Although CT scans allow accurate extraction of bones and the skin surface, muscles appear as poorly contrasted structures. The challenge is, thus, to produce an intuitive modelling tool that will support interactive deformation of a generic atlas model into a patient-specific model. For this, we first generate synthetic scans along pre-defined slicing axes in patient space. Muscle outlines obtained by an initial mapping of generic atlas models are then superimposed on these slices. These outlines are deformed by simple geometric operations to match the underlying muscle shapes using a novel software tool, the Muscle Modelling Laboratory (MML). The paper presents a shape investigation of the muscles relevant to THR surgery and describes the MML module in operation.