The purpose of this two-part investigation was to test the feasibility, safety, and efficacy of immediate weight-bearing after treatment of fractures of the shaft of the femur with a statically locked intramedullary nail.

In the first part of the investigation, a biomechanical study was performed to determine the fatigue strength of eleven different statically locked intramedullary nail constructs. Segmentally comminuted midisthmal fractures were simulated with use of sections of polyvinyl chloride pipe; each construct was cyclically loaded in compression with use of physiologically relevant loads in a materials testing machine at eight hertz. The fatigue tests were conducted according to the so-called staircase method, and the construct was considered to have run out (exceeded its anticipated service life) if it had not failed after 500,000 cycles. In the second part of the study, a clinical investigation of immediate weight-bearing after treatment of comminuted fractures of the femoral shaft with a Russell-Taylor (RT-2) construct was performed. Complete follow-up data were available for twenty-eight of the thirty-five patients (thirty-six fractures) entered into the study.

In Part I of the study, two constructs, a statically locked twelve-millimeter-diameter Russell-Taylor femoral nail with two distal locking screws (RT-2) and a statically locked twelve-millimeter-diameter Zimmer femoral nail with two distal locking screws (Z-2), had significantly higher mean fatigue strengths (2171 and 2113 newtons, respectively) than all other constructs tested (p< 0.001), but the strengths of these two constructs were not significantly different from each other. Constructs with only one distal locking screw demonstrated significantly lower (p< 0.05) fatigue strengths than the two-screw constructs. These results suggest that full weight-bearing during the weeks immediately after insertion of the nail may be possible, even for patients who have a comminuted fracture of the femoral shaft. In Part II of the study, twenty-six of the twenty-eight patients were bearing full weight on the fractured limb or limbs at the six-week follow-up visit. All fractures united; only one of these needed an additional procedure (the removal of the screws five months after the insertion of the nail) to stimulate union. No loss of fixation, such as back-out or breakage of a locking screw or breakage or bending of the intramedullary nail, occurred.

We concluded from this two-part investigation that immediate weight-bearing after stabilization of a comminuted fracture of the femoral shaft with a statically locked intramedullary nail is safe when the construct has a relatively high fatigue strength. Immediate weight-bearing after stabilization of a fracture of the femoral shaft permits patients who have multiple fractures of the extremity to walk and to participate in physical therapy earlier, possibly decreasing the duration of the hospital stay or reducing the need for prolonged rehabilitation on an inpatient basis.

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