Rationale: Osteoporotic fractures are associated with high morbidity and mortality. This is why prevention of these fractures is important. The investigators have shown in animal studies that a single treatment with unfocused extracorporeal shock wave therapy leads to highly increased bone mass and improved biomechanical properties. Unfocused extracorporeal shock wave therapy could have important implications for the prevention of osteoporotic fractures.

Objective: To assess the effect of unfocused extracorporeal shock wave therapy on bone mass.

Study design: A clinical pilot study. Study population: Twelve female patients are eligible if they are undergoing elective surgery of the lower extremity or elective spinal surgery under general anesthesia in the investigators hospital.

Intervention: When the patient is under general anaesthesia he/she will receive 3000 unfocused extracorporeal shock waves (energy flux density 0.3mJ/mm2) to one distal forearm. The contra lateral forearm will not be treated and serves as a control.

Main study parameters/endpoints:

The investigators will examine the effect on bone mass with the use of repeated dual energy X-ray absorptiometry measurements. These results are necessary to calculate the number of patients that are needed for larger studies. Furthermore, the investigators will assess patient's discomfort.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: General anaesthesia is performed during treatment and pain after the procedure will be evaluated using pain scales and, if necessary pain medication will be prescribed by the orthopaedic surgeon. The dual energy X-ray absorptiometry-scans and X-rays will cause very low radiation exposure to the patient.

Inclusion Criteria:

• female sex, age 50-80 years, normal dietary intake inclusive calcium and/or milk products and willing to participate

Exclusion Criteria:

• skin disease, systemic corticosteroid use, known systemic disease that interacts with bone (eg. rheumatoid arthritis, multiple myeloma, hyper(para)thyroidism, Paget's disease or Cushing's disease) or a previous wrist fracture