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Biomechanical factors in planning of periacetabular osteotomy.

Niknafs N, Murphy RJ, Armiger RS, Lepistö J, Armand M - Front Bioeng Biotechnol (2013)

Bottom Line: For each combination of thickness distribution and compressive properties, the optimal alignment of the acetabulum was found; the resultant geometric and biomechanical characterization of the hip were compared among the optimal alignments.The optimal alignment increased the lateral coverage of the femoral head and decreased the obliqueness of the acetabular roof in all patients.However, in all groups the biomechanically predicted optimal alignment resulted in decreased joint contact pressure and improved acetabular coverage.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Johns Hopkins University , Baltimore, MD , USA.

ABSTRACT

Objective: This study addresses the effects of cartilage thickness distribution and compressive properties in the context of optimal alignment planning for periacetabular osteotomy (PAO).

Background: The Biomechanical Guidance System (BGS) is a computer-assisted surgical suite assisting surgeon's in determining the most beneficial new alignment of a patient's acetabulum. The BGS uses biomechanical analysis of the hip to find this optimal alignment. Articular cartilage is an essential component of this analysis and its physical properties can affect contact pressure outcomes.

Methods: Patient-specific hip joint models created from CT scans of a cohort of 29 dysplastic subjects were tested with four different cartilage thickness profiles (one uniform and three non-uniform) and two sets of compressive characteristics. For each combination of thickness distribution and compressive properties, the optimal alignment of the acetabulum was found; the resultant geometric and biomechanical characterization of the hip were compared among the optimal alignments.

Results: There was an average decrease of 49.2 ± 22.27% in peak contact pressure from the preoperative to the optimal alignment over all patients. We observed an average increase of 19 ± 7.7° in center-edge angle and an average decrease of 19.5 ± 8.4° in acetabular index angle from the preoperative case to the optimized plan. The optimal alignment increased the lateral coverage of the femoral head and decreased the obliqueness of the acetabular roof in all patients. These anatomical observations were independent of the choice for either cartilage thickness profile, or compressive properties.

Conclusion: While patient-specific acetabular morphology is essential for surgeons in planning PAO, the predicted optimal alignment of the acetabulum was not significantly sensitive to the choice of cartilage thickness distribution over the acetabulum. However, in all groups the biomechanically predicted optimal alignment resulted in decreased joint contact pressure and improved acetabular coverage.

No MeSH data available.


Related in: MedlinePlus

The Lunate-Trace segmentation technique selects the lateral and medial edges of the contact surface on (A) the acetabulum and (B) the femoral head. (C) Radial and polar interpolation between the edge points yield arc cross sections of the contact surface.
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Figure 2: The Lunate-Trace segmentation technique selects the lateral and medial edges of the contact surface on (A) the acetabulum and (B) the femoral head. (C) Radial and polar interpolation between the edge points yield arc cross sections of the contact surface.

Mentions: Since bone morphology has been shown to play a significant role in prediction of cartilage stress (Anderson et al., 2008, 2010; Lenaerts et al., 2008, 2009; Chegini et al., 2009; Gu et al., 2010), we manually extracted subject-specific surface models of the femoral head and acetabulum. These subject-specific, non-spherical surface models were created using the Lunate-Trace algorithm (Armiger et al., 2007), which rotates oblique CT reformats of the hip joint about the medio-lateral axis of the hip (Figure 2). Using this procedure, the acetabular and femoral surfaces were specified as triangular surface meshes. The acetabular surface meshes were composed of a set of 1648 ± 150 triangular elements, each 1.49 mm ± 0.74 mm in area. In previous (unpublished) analysis on the Lunate-Trace algorithm, there was an average area difference of 185.6 mm ± 154.5 mm in the acetabular meshes between two trained users corresponding to an average difference in contact pressures of 0.027 ± 0.24 MPa, indicating minor variability in biomechanical analysis between independently segmented acetabulums. The surface meshes used in the present study were generated by a trained user.


Biomechanical factors in planning of periacetabular osteotomy.

Niknafs N, Murphy RJ, Armiger RS, Lepistö J, Armand M - Front Bioeng Biotechnol (2013)

The Lunate-Trace segmentation technique selects the lateral and medial edges of the contact surface on (A) the acetabulum and (B) the femoral head. (C) Radial and polar interpolation between the edge points yield arc cross sections of the contact surface.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126379&req=5

Figure 2: The Lunate-Trace segmentation technique selects the lateral and medial edges of the contact surface on (A) the acetabulum and (B) the femoral head. (C) Radial and polar interpolation between the edge points yield arc cross sections of the contact surface.
Mentions: Since bone morphology has been shown to play a significant role in prediction of cartilage stress (Anderson et al., 2008, 2010; Lenaerts et al., 2008, 2009; Chegini et al., 2009; Gu et al., 2010), we manually extracted subject-specific surface models of the femoral head and acetabulum. These subject-specific, non-spherical surface models were created using the Lunate-Trace algorithm (Armiger et al., 2007), which rotates oblique CT reformats of the hip joint about the medio-lateral axis of the hip (Figure 2). Using this procedure, the acetabular and femoral surfaces were specified as triangular surface meshes. The acetabular surface meshes were composed of a set of 1648 ± 150 triangular elements, each 1.49 mm ± 0.74 mm in area. In previous (unpublished) analysis on the Lunate-Trace algorithm, there was an average area difference of 185.6 mm ± 154.5 mm in the acetabular meshes between two trained users corresponding to an average difference in contact pressures of 0.027 ± 0.24 MPa, indicating minor variability in biomechanical analysis between independently segmented acetabulums. The surface meshes used in the present study were generated by a trained user.

Bottom Line: For each combination of thickness distribution and compressive properties, the optimal alignment of the acetabulum was found; the resultant geometric and biomechanical characterization of the hip were compared among the optimal alignments.The optimal alignment increased the lateral coverage of the femoral head and decreased the obliqueness of the acetabular roof in all patients.However, in all groups the biomechanically predicted optimal alignment resulted in decreased joint contact pressure and improved acetabular coverage.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Johns Hopkins University , Baltimore, MD , USA.

ABSTRACT

Objective: This study addresses the effects of cartilage thickness distribution and compressive properties in the context of optimal alignment planning for periacetabular osteotomy (PAO).

Background: The Biomechanical Guidance System (BGS) is a computer-assisted surgical suite assisting surgeon's in determining the most beneficial new alignment of a patient's acetabulum. The BGS uses biomechanical analysis of the hip to find this optimal alignment. Articular cartilage is an essential component of this analysis and its physical properties can affect contact pressure outcomes.

Methods: Patient-specific hip joint models created from CT scans of a cohort of 29 dysplastic subjects were tested with four different cartilage thickness profiles (one uniform and three non-uniform) and two sets of compressive characteristics. For each combination of thickness distribution and compressive properties, the optimal alignment of the acetabulum was found; the resultant geometric and biomechanical characterization of the hip were compared among the optimal alignments.

Results: There was an average decrease of 49.2 ± 22.27% in peak contact pressure from the preoperative to the optimal alignment over all patients. We observed an average increase of 19 ± 7.7° in center-edge angle and an average decrease of 19.5 ± 8.4° in acetabular index angle from the preoperative case to the optimized plan. The optimal alignment increased the lateral coverage of the femoral head and decreased the obliqueness of the acetabular roof in all patients. These anatomical observations were independent of the choice for either cartilage thickness profile, or compressive properties.

Conclusion: While patient-specific acetabular morphology is essential for surgeons in planning PAO, the predicted optimal alignment of the acetabulum was not significantly sensitive to the choice of cartilage thickness distribution over the acetabulum. However, in all groups the biomechanically predicted optimal alignment resulted in decreased joint contact pressure and improved acetabular coverage.

No MeSH data available.


Related in: MedlinePlus