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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

Cartilage thickness map on weight-bearing area in normal (left) and dysplastic (right) populations. The weight-bearing area is moved out of the joint for better visualization.
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Figure 3: Cartilage thickness map on weight-bearing area in normal (left) and dysplastic (right) populations. The weight-bearing area is moved out of the joint for better visualization.

Mentions: The second and third thickness maps were based on the mean cartilage distribution profile in normal and dysplastic populations (Nishii et al., 2004). The average distribution maps were expressed as the mean cartilage thickness measured over a grid of longitude and latitude across the weight-bearing area (Figure 3). We conducted a two-dimensional Gaussian fit to these data to define models corresponding to the average cartilage thickness maps in dysplastic and normal populations. We aligned the patient-specific acetabular contact surface in a spherical coordinate frame consistent with the Gaussian model. Note that this was not a spherical fit, as the geometries of the dysplastic hips are not spherical. Then, we applied the Gaussian model to the manually segmented contact surface to derive population-based cartilage thickness maps for each patient. Despite the dysplastic nature of the hips in this study, we included both normal and dysplastic population-based cartilage thickness models since recent research has suggested that PAO helps to normalize force distribution (Mechlenburg et al., 2010).


Biomechanical factors in planning of periacetabular osteotomy.

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

Cartilage thickness map on weight-bearing area in normal (left) and dysplastic (right) populations. The weight-bearing area is moved out of the joint for better visualization.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Cartilage thickness map on weight-bearing area in normal (left) and dysplastic (right) populations. The weight-bearing area is moved out of the joint for better visualization.
Mentions: The second and third thickness maps were based on the mean cartilage distribution profile in normal and dysplastic populations (Nishii et al., 2004). The average distribution maps were expressed as the mean cartilage thickness measured over a grid of longitude and latitude across the weight-bearing area (Figure 3). We conducted a two-dimensional Gaussian fit to these data to define models corresponding to the average cartilage thickness maps in dysplastic and normal populations. We aligned the patient-specific acetabular contact surface in a spherical coordinate frame consistent with the Gaussian model. Note that this was not a spherical fit, as the geometries of the dysplastic hips are not spherical. Then, we applied the Gaussian model to the manually segmented contact surface to derive population-based cartilage thickness maps for each patient. Despite the dysplastic nature of the hips in this study, we included both normal and dysplastic population-based cartilage thickness models since recent research has suggested that PAO helps to normalize force distribution (Mechlenburg et al., 2010).

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