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The Journal of Bone and Joint Surgery (American) 85:1073-1078 (2003)
© 2003 The Journal of Bone and Joint Surgery, Inc.

Scientific Article

Rotational Stability of a Modified Step-Cut for Use in Intercalary Allografts

Drew H. Van Boerum, MD, R. Lor Randall, MD, R. Alexander Mohr, MD, Ernest U. Conrad, MD and Kent N. Bachus, PhD

Investigation performed at the Department of Orthopedics, University of Utah School of Medicine, Salt Lake City, Utah

Drew H. Van Boerum, MD
R. Alexander Mohr, MD
Department of Orthopedics, University of Utah School of Medicine, Salt Lake City, 50 North Medical Drive, UT 84132

R. Lor Randall, MD
Sarcoma Service, Huntsman Cancer Institute, 2000 Circle of Hope, Suite 2100, Salt Lake City, UT 84112. E-mail address: r.lor.randall{at}hsc.utah.edu

Ernest U. Conrad, MD
Department of Orthopaedics, University of Washington Medical Center, Box 356500, 1959 Pacific Street N.E., Seattle, WA 98195

Kent N. Bachus, PhD
Orthopaedic Bioengineering Research Laboratory, Department of Orthopaedics, 20 South 2030 East, Room 190BPR, University of Utah, Salt Lake City, UT 84112

None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated. Biomet, Warsaw, Indiana, and Brett D. Parkin, Med Tech Medical, Salt Lake City, Utah, donated the femoral nails and loaned the insertion instrumentation. In addition, Musculoskeletal Transplant Foundation, Little Silver, New Jersey, donated the cadaver test specimens.

Background: Intercalary allografts are used for the reconstruction of major skeletal defects. Step-cuts help to provide rotational stability when intramedullary fixation is used. A modified step-cut is proposed to reduce rotation at the interface. This study compares the rotational stability of conventional and modified step-cuts.

Methods: In Phase I, seven pairs of human cadaveric femora were divided into a conventional step-cut group (left femora) and a modified step-cut group (right femora). All femora were cut transversely at the mid-diaphysis. In the conventional group, a 1-cm step-cut was created in the exact midsagittal plane in both the proximal and distal segments. In the modified group, a 1-cm step-cut was created in the parasagittal plane, leaving 2 mm of additional bone on both the proximal and the distal fragment. Phase II was identical except that in the modified step-cut group only 1 mm of additional bone was left. Smooth femoral nails were then placed after standard reaming. Specimens were tested by fixing the proximal segment and applying ±2 N-m (17.7 in-lb) of torque to the distal segments with ten oscillation cycles. Maximum rotation was measured. The data were analyzed with the paired Student t test.

Results: The average rotation in Phase I was 23.3° for the conventional step-cut group and 3.0° for the 2-mm modified step-cut group; the difference was significant (p < 0.001). Four femora sustained an incomplete fracture during nail insertion. The average rotation in Phase II was 20.6° for the conventional step-cut group and 0.5° for the 1-mm modified step-cut group without any fractures; the difference was significant (p < 0.001).

Conclusions: Step-cut modification that leaves more bone in the sagittal plane provides rigid fixation and significantly more stability than the conventional step-cut technique.

Clinical Relevance: Such a modification should facilitate osseous incorporation of an intercalary allograft while providing the benefits of intramedullary fixation. Excessive modification (>1 mm) can result in a fracture of the graft.



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