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Journal of Bone and Joint Surgery - British Volume, Vol 89-B, Issue 5, 701-705.
doi: 10.1302/0301-620X.89B5.18504  
Copyright © 2007 by British Editorial Society of Bone and Joint Surgery
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Factors affecting the stability of screws in human cortical osteoporotic bone

A CADAVER STUDY

O. C. Thiele, MD, Research Associate1; C. Eckhardt, MSc, Research Associate1; B. Linke, PhD, Research Associate1; E. Schneider, PhD, Professor and Director1; and C. A. Lill, MD, Orthopaedic Surgeon2

1 AO Research Institute, Clavadelerstrasse CH-7270, Davos Platz, Switzerland.
2 Orthopaedic Clinic, Ganghoferstrasse 31, 80339, Munich, Germany.

Correspondence should be sent to Dr O. C. Thiele at the Department of Oral and Maxillo-Facial Surgery, University Hospital, INF 400, 69120 Heidelberg, Germany; e-mail: oliver.thiele{at}med.uni-heidelberg.de

We investigated several factors which affect the stability of cortical screws in osteoporotic bone using 18 femora from cadavers of women aged between 45 and 96 years (mean 76). We performed bone densitometry to measure the bone mineral density of the cortical and cancellous bone of the shaft and head of the femur, respectively. The thickness and overall bone mass of the cortical layer of the shaft of the femur were measured using a microCT scanner. The force required to pull-out a 3.5 mm titanium cortical bone screw was determined after standardised insertion into specimens of the cortex of the femoral shaft.

A significant correlation was found between the pull-out strength and the overall bone mass of the cortical layer (r2 = 0.867, p < 0.01) and also between its thickness (r2 = 0.826, p < 0.01) and bone mineral density (r2 = 0.861, p < 0.01). There was no statistically significant correlation between the age of the donor and the pull-out force (p = 0.246), the cortical thickness (p = 0.199), the bone mineral density (p = 0.697) or the level of osteoporosis (p = 0.378).

We conclude that the overall bone mass, the thickness and the bone mineral density of the cortical layer, are the main factors which affect the stability of a screw in human female osteoporotic cortical bone.






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Hip, Knee, Trauma, Upper limb, Foot & Ankle, Paediatrics, Oncology, Spine, Arthroplasty, General