Introduction 9 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 orthopaedic and trauma surgeons tend to advise conservatively with regard to weight bearing in rehabilitation, and hold on to the prevailing dogmas, i.e. recommending time-contingent progression of weight bearing, while physiotherapists and rehabilitation physicians may follow a more progressive approach towards fracture weight bearing. Besides, even with specific advice from specialists, patients may not always be committed to complying with non-weight bearing recommendations.3,4 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.2,5 Furthermore, the lack of individual feedback on the actual weight bearing status causes great differences in weight bearing when the patient is advised restricted weight bearing.3,4,6 These circumstances give rise to a wide range of weight bearing patterns and inconsistent aftercare treatment.7,8 Biomechanical and animal studies indicate that early weight bearing is beneficial.9-11 Little is known about the relationship between fracture weight bearing during daily activities and the progression of consolidation of the fracture parts, the quality and function of the soft tissue, and biomechanical weight bearing capacity during the fracture healing. Fracture healing is an evolutionary well-developed complex process. One of the important factors influencing fracture healing is the amount of weight bearing of the involved limb. The speed with which the bone healing processes take place, together with the (aftercare) treatment provided, govern the progression with which weight bearing can be applied safely. Providing the adequate level of weight bearing on the fracture in a timely fashion during early aftercare treatment is considered essential in the speed towards full mobilisation.12-14 Both over-loading and under-loading may lead to a prolonged and complicated recovery (Figure 1.1). A certain minimum level of loading is necessary to elicit micromovements between adjacent bony fracture components, stimulating biological processes that enhance fracture consolidation and minimizing effects of immobilization. The upper boundary of the therapeutic bandwidth is determined by the mechanical stability of the fracture and the stabilization method used. Under-loading