during hip replacement surgery , a practitioner can attach a distal stem to a femur of the patient and can then fixedly attach a proximal body to the distal stem using a bolt . prior to tightening , the bolt can be heated to an elevated temperature greater than average human core body temperature . the practitioner can tighten the bolt to a specified torque while the bolt is at the elevated temperature . after tightening , the bolt cools to average human core body temperature and experiences a tensile stress due to the effects of thermal expansion . the tensile stress in the bolt produces a compressive force between the distal stem and the proximal body . the compressive force can increase the attachment strength of the bolt to the distal stem and the proximal body , beyond what can be achieved by solely torquing the bolt to the specified level during surgery without first heating the bolt .