The Effects of Neck Resection Level on the Initial Torsional Stability of Cementless Total Hip Arthroplasty in Dogs

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Title: The Effects of Neck Resection Level on the Initial Torsional Stability of Cementless Total Hip Arthroplasty in Dogs
Author: Brooks, Daniel John
Advisors: Denis J. Marcellin-Little, Committee Member
Ola L.A. Harrysson, Committee Co-Chair
C. Frank Abrams, Committee Member
Peter L. Mente, Committee Co-Chair
Abstract: The initial torsional stability of a cementless total hip arthroplasty (THA) is one of the key factors in determining the biological fixation of the implant. The success of a cementless hip replacement relies on the quantity and quality of bone ingrowth that occurs. This study looked at the effects of femoral neck resection level on the initial torsional stability of cementless THA in the canine population. Twenty paired cadaver femurs were collected from dogs and implanted with canine cementless hip stems. One femur from each pair was prepared with a neck cut with its medial aspect located at the proximal aspect of the lesser trochanter (low neck cut) and the other with a neck cut with its proximo-lateral aspect at the ossum collis femoris isthmus of the greater trochanter and femoral neck (high neck cut). The specimens were then subjected to cyclic torque loads in the caudal direction (Amplitude: -0.1 N-m to set torque) at four torque levels (1 N-m, 2 N-m, 4 N-m, and 6 N-m) and the torsional displacement, axial subsidence, and strain were all recorded. A paired statistical analysis was completed so that specimens from the same dogs could be compared to each other. The low neck cut group was found to have significantly less micromotion than the high neck cut group during the 1 N-m and 4 N-m torque tests (p = 0.02 for both). Because the high neck cut specimens tended to have more micromotion they may be apt to have lower quality bone ingrowth. A significant difference was not found between the torsional displacements of the two groups. The high neck cut specimens were found to have significantly (p = 0.02) more implant rotation at 1.6 N-m of torque, however the average difference was only about 0.22 degrees which most likely does not indicate a clinically significant difference. No statistical difference was found between the axial subsidence of the high and low neck cut specimens other than at the 6 N-m level (p = 0.02). At 6 N-m the stems in the low neck cut specimens had an average upward movement of 255 +⁄- 310 um while the stems in the high neck cuts moved in the opposite direction and had an average downward movement of 280 +⁄- 695 um. The low neck specimens were found to have significantly more canal fill and implant impaction than the high neck cut specimens. This suggests that surgeons need to be mindful that they may not insert stems as deeply in femurs prepared with high neck cuts as they do in femurs with low neck cuts. This study was not able to show that one neck cut level was superior to the other, however the data indicate that the low neck cut group had slightly better stability based on having less micromotion at 1 N-m and 4 N-m and less at rotation at 1.6 N-m.
Date: 2007-06-20
Degree: MS
Discipline: Biomedical Engineering

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