TECHNICAL PAPERS: Bone/Orthopedics

A Biomechanical Study of Periacetabular Defects and Cement Filling

[+] Author and Article Information
Zuoping Li, Neha B. Butala, Brandon S. Etheridge, Alan W. Eberhardt

Department of Biomedical Engineering, University of Alabama at Birmingham, Hoehn 370, 1075 13th Street South, Birmingham, AL 35294-4440

Herrick J. Siegel

Division of Orthopaedic Surgery, University of Alabama at Birmingham, Faculty Office Tower 960, 510 20th Street South, Birmingham, AL 35294-4440

Jack E. Lemons

School of Dentistry, University of Alabama at Birmingham, SDB 615, 1919 7th Avenue South, Birmingham, AL 35294-0007

J Biomech Eng 129(2), 129-136 (Sep 21, 2006) (8 pages) doi:10.1115/1.2472367 History: Received February 02, 2006; Revised September 21, 2006

Periacetabular bone metastases cause severe pain and functional disability in cancer patients. Percutaneous acetabuloplasty (PCA) is a minimally invasive, image-guided procedure whereby cement is injected into lesion sites. Pain relief and functional restoration have been observed clinically; however, neither the biomechanical consequences of the lesions nor the effectiveness of the PCA technique are well understood. The objective of this study was to investigate how periacetabular lesion size, cortex involvement, and cement modulus affect pelvic bone stresses and strains under single-legged stance loading. Experiments were performed on a male cadaver pelvis under conditions of intact, periacetabular defect, and cement-filling with surface strains recorded at three strain gage locations. The experimental data were then employed to validate three-dimensional finite element models of the same pelvis, developed using computed tomography data. The models demonstrated that increases in cortical stresses were highest along the posterior column of the acetabulum, adjacent to the defect. Cortical stresses were more profoundly affected in the presence of transcortical defects, as compared to those involving only trabecular bone. Cement filling with a modulus of 2.2GPa was shown to restore cortical stresses to near intact values, while a decrease in cement modulus due to inclusion of BaSO4 reduced the restorative effect. Peak acetabular contact pressures increased less than 15% for all simulated defect conditions; however, the contact stresses were reduced to levels below intact in the presence of either cement filling. These results suggest that periacetabular defects may increase the vulnerability of the pelvis to fracture depending on size and cortical involvement and that PCA filling may lower the risk of periacetabular fractures.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

X-ray of a patient with a large osteolytic metastatic lesion involving the right acetabulum; the head has fractured through the medial wall resulting in protrusion (arrow)

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Figure 2

(left) CT scan of a pelvis showing destruction of the medial wall of the right acetabulum (a) and (right) corresponding X-ray that shows no disruption of the superior acetabulum (b)

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Figure 3

Experimental apparatus for simulating the pelvis in single-legged stance loading (plastic model shown). The pelvis was connected to the load cell through the sacrum via the sacral mount. Abductor forces (three arrows) were generated with a pulley system and hanging weight W.

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Figure 4

Locations of strain gauge rosettes and the transcortical defect on a plastic pelvis; (left) anterior view and (right) posterior view

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Figure 5

FE model of a male pelvis created according to the experimental setting illustrating transcortical defect location as created in the experiments

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Figure 6

Wire frame mesh of the model showing the cemented defect with 100% cortex penetration posterior and superior to the roof of right acetabulum

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Figure 7

Contours of von Mises stress at the surface of the posterior column (position A) and superior rim of the acetabulum (position C) in the vicinity of the simulated periacetabular defect (position B) under (a) intact, (b) defect (15.8cm3), and (c) cement-filled conditions (E=2.2GPa)

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Figure 8

FE predicted von Mises stresses normalized to intact value at posterior column (16.5MPa) and superior rim of the acetabulum (45.8MPa) comparing (a) relative effects of defect size and cortex involvement and (b) relative effects of cement modulus on filling the 15.8cm3 transcortical defect

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Figure 9

FE model predicted joint contact pressure normalized to pre-defect baseline value (4.9MPa) under the intact, defect, and cement-filled conditions



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