A protocol for permissive weight bearing during allied health therapy in pelvic and the lower extremities fractures 51 Introduction A plethora of evidence is available about open reduction and internal fixation procedures in trauma patients with (peri)- or intra-articular fractures, as well as about the processes involved in bone healing.1,2 However, the subsequent rehabilitation treatment, or early aftercare, has been less systematically documented and is often based on empirical, implicit knowledge of individual medical or allied health therapists, acquired throughout many years of clinical practice. No formal evidence-based guidelines are available on the aftercare of surgically treated fractures. In view of this lack of evidence, many orthopedic and trauma surgeons tend to advise conservatively in regards to weight bearing in rehabilitation, and hold on to the prevailing dogmas, i.e. recommending time-contingent progression of weight bearing. Besides, even with specific advice from specialists, patients may not always be committed to complying with non-weight bearing advice.3-5 It is remarkable that the recommendations for aftercare in patients surgically treated for fractures are still more or less the same as 60 years ago, without any sources of evidence being given for the advice.2,6 Fracture healing is a physiologically complex process.7 The pace at which bone formation processes take place, together with the aftercare treatment provided, determine what progression of weight bearing may be applied. Weight bearing dosage is often quantified in terms of percentage of body weight, or expressed in more general terms such as non-weight bearing/partial weight bearing/full weight bearing, without the therapist knowing which weight is actually borne at the level of the osteosynthesis and fracture during both rehabilitation training and daily activities. Despite this fairly illdefined terminology, few complications due to overloading seem to occur in clinical practice. Nevertheless, both overloading and underloading may lead to a more complicated and extended recovery. A schematic overview of the consequences of loading for the consolidation process is depicted in Figure 5.1. Weight bearing is necessary to elicit micro-movements between adjacent bony fracture components, stimulating biological processes that enhance fracture consolidation, and to minimize negative effects of immobilization.8,9 To optimize rapid clinical recovery and the restoration of function and functionality, it may be useful to apply a treatment protocol that is near the upper boundary of the therapeutic bandwidth, yet safe enough to avoid overloading. However, no clear evidence on the location of this upper boundary is known from literature. Therapy dosage in the early aftercare treatment of fractures is to a large extent determined by the load bearing capacity of the bone, which in turn depends on the type of fracture, the bone quality, the soft tissue quality, the stabilizing effects of the surrounding soft tissue cuff, the stabilization method used (plaster/nail/plate) as well as the mechanical load bearing capacity, and the point of application and direction