To develop and test the validity of TLEMsafe system, extensive tests are required that couple the predictions of musculo-skeletal models to the actual results of the patients. It is clear that not all patient types can be included in this project, but that a focus is required on certain groups of patients. We have selected two types of patients that challenge the TLEM model and provide the opportunity to adapt and validate the model in different ways. Furthermore, selection of these patient groups was also based on the expertise of the surgeons and availability of the patients at the RUMC:

The Hip Group

The first patient group consists of patients that have a dysplastic hip joint or require a revision of a failed hip prosthesis. In these patients, the centre of rotation of the hip is not placed in the correct anatomical position and needs to be restored (Figure 1). Often, bone grafts are needed to reconstruct the existing bone stock lost. In addition, the muscle balancing is usually inadequate.

Although the survival of these surgeries is satisfying (Somford et al., 2008), the functional results of these patients is sometimes unsatisfying: leg-length discrepancies up to about 25% of the cases have been reported (Argenson et al., 2007), and patients have sometimes an abnormal gait pattern.

For the hip group, patients with congenital hip luxation undergoing larger hip reconstruction or revision hip surgery will be selected. The patients included in this study have to undergo reconstruction (re-balancing) of their muscles/tendons, which will affect the functional ability of the patient. The amount of soft-tissue correction will vary between patients. The first functional measurements will be done at a pre-operative stage. Patients will be radiologically diagnosed before and after surgery.

Figure 1: A patient affected by dysplastic hip joint before (left) and after (right) hip reconstruction.

The Tumor Group

The second patient group consists of patients with oncological musculo-skeletal pathologies around the femur. The surgery usually involves removal of relatively large segments of bone and soft tissue. The bony segments are reconstructed with donor bone or a (massive) prosthesis (Figure 2). These prostheses often contain holes to which muscles can be attached. The optimal location for muscle attachment is often difficult to judge. Quite often, the extensor muscle group is partly resected: to restore its function, the surgeon may use an important kneeflexion muscle (for example the biceps femoris) and re-attach this muscle to the femur so that this muscle becomes an extensor.

These types of reconstructions are very costly (about 100,000 Euros; Georgiadis et al., 1993), are associated with a relatively high complication rates and sometimes its functional outcome is quite disappointing. Therefore an amputation of the lower limb may sometimes be more effective.

For the tumor group, only patients with tumors at the proximal tibia, the distal femur or proximal femur will be selected; about 25% of these patients will get a joint implant. The type of tumor will generally be a high-grade Osteosarcoma, Ewingsarcoma or a Chondrosarcoma. The first functional measurements will be done based on the tumordiagnosis from the MRI images. After this diagnosis, a biopsy is often performed after which the patient is not allowed to apply significant loads. Hence, pre-operative measurements will be done between the imaging-diagnosis and the biopsy moment.

Figure 2: A patient affected by tumor in distal femur before (left) and after (right) reconstruction.

Patient selection is of critical importance. Children under sixteen years of age will not be included as they have been shown not to be able to perform functional activities in a reproducible way. Drug or alcohol addicts, patients with co-morbidities that affect their functional behavior, and patients that cannot execute the functional measurements (for example to due high age) will be excluded from the study. An important inclusion criterion is that the patients have to undergo considerable surgery on their musculo-skeletal system which is highly likely to affect their functional performance.