Session V - Femur

Immediate Weightbearing after Intramedullary Nailing of Comminuted Femoral Shaft Fractures

Robert J. Brumback, MD; Thomas R. Toal, Jr., MD; M. Siobhan Murphy-Zane, MD, Shock Trauma Center; Vincent P. Novak, MS; Stephen M. Belkoff, PhD, Orthopaedic Biomechanics Laboratory, University of Maryland, Baltimore, MD

Purpose: The purpose of this two-part investigation was to test the feas-ibility, safety and efficacy of immediate weightbearing of fractures of the shaft of the femur treated with static interlocking nailing.

Methods: In part I, a biomechanical study was performed to determine the fatigue strength of nine different statically interlocked intramedullary nail constructs. Segmentally comminuted mid-isthmal fractures were simulated using sections of PVC pipe; each construct was cyclically loaded in compression at 8 Hz in a materials-testing machine using physiologically relevant loads. The fatigue tests were conducted according to the "staircase" method with run-out set at 500,000 cycles.

Results: The mean fatigue strengths of two constructs, a statically interlocked 12.0-mm diameter Russell-Taylor femoral nail with two distal interlocking screws (RT-2: 488 pounds) and a statically interlocked 12.0-mm diameter Zimmer femoral nail with two distal interlocking screws (Z-2: 475 pounds), were significantly higher (p<0.001) than that of all other constructs tested but were not significantly different from each other. Constructs with only one distal interlocking screw demonstrated a statistically significant decrease in fatigue strength compared with the two-screw constructs. These results suggest that full weightbearing during the weeks immediately after surgery may be possible, even with comminuted femoral shaft fractures. In part II, a clinical investigation of immediate weightbearing of comminuted femoral shaft fractures treated with the RT-2 construct was performed. Of the 29 patients entered into the study, complete follow-up was available on 23. Twenty of the 23 patients were full weightbearing on the fractured limb at the 6-week follow-up visit. All fractures united; only one required an additional procedure to stimulate fracture union (dynamization at 5 months after surgery). No loss of fixation occurred, including back-out of an interlocking screw, breakage or bending of the intramedullary nail, or breakage of the interlocking screws.

Conclusions: We conclude from this two-part investigation that immediate weightbearing on comminuted fractures of the shaft of the femur stabilized with static interlocking nailing is safe when constructs of relatively high fatigue strengths are inserted. Immediate weightbearing on fractures of the shaft of the femur would permit patients with multiple extremity fractures to ambulate and participate in physical therapy earlier, possibly decreasing their length of hospital stay or their need for prolonged inpatient rehabilitation.