Reaming technique of the femoral diaphysis in cementless total hip arthroplasty.

Distal fixation enhances initial torsional stability of cementless femoral components in primary and revision total hip arthroplasty. Surgical technique affects the quality of distal fixation, and too aggressive a technique can cause femoral fracture during insertion of the stem. Thirty-five adult human cadaveric femoral specimens were implanted with either a standard or long femoral stem. Control specimens were reamed 0.5 mm less than the diameter of the distal cylindrical portion of the stem and were broached line to line proximally. The proximal femur was removed from the remaining specimens to allow assessment of distal fixation. The controls outperformed the distal-only fixation groups in all testing modes, illustrating that proximal and distal fixation work in concert to resist torsional load. The average failure torque in underreamed specimens with only distal fixation was 23.6 Nm for standard length stem specimens and 41.3 Nm for long stem specimens, whereas the average failure torque for specimens with only distal fixation prepared by a line-to-line reaming technique was only 6 Nm. The estimated length of tight distal fit should be 10 to 40 mm to obtain sufficient initial torsional stability of the stem and still avoid intraoperative femoral fracture.