TY - JOUR
T1 - DXA Measured Distal Femur Bone Mineral Density in Patients After Total Knee Arthroplasty
T2 - Method Development and Reproducibility
AU - Thomas, B.
AU - Binkley, N.
AU - Anderson, P. A.
AU - Krueger, D.
N1 - Funding Information:
This cross-sectional pilot study evaluated differences in BMD from distal to proximal along the femur in 30 adults with primary TKA 2–5 yr previously. Inclusion criteria limited the study cohort to men or women having a unilateral TKA within the prior 2–5 yr who had no chronic diseases or conditions that might impact bone or use of medications that cause bone loss. To reduce the likelihood of additional conditions confounding these results, further criteria required no use of osteoporosis medications, TKA revision surgery or prosthetics/hardware in the nonreplaced knee or either hip. Participants were recruited from a University-based orthopedic surgery practice of two surgeons specializing in knee and hip joint replacement. Sample size for this exploratory pilot research was selected based upon that required for routine clinical DXA precision assessment. Thus, to allow calculation of precision as recommended by the International Society for Clinical Densitometry (ISCD) ( 23 ), 30 subjects were recruited. Funding for this study was provided by a University of Wisconsin Department of Orthopedics and Rehabilitation award. This study was approved by the University of Wisconsin-Madison Health Sciences Institutional Review Board, and conducted in compliance with local and federal regulations.
Publisher Copyright:
© 2018 The International Society for Clinical Densitometry
PY - 2019/1/1
Y1 - 2019/1/1
N2 - Introduction: Total knee arthroplasty (TKA) is increasingly being performed. Distal femur periprosthetic fracture is a potentially catastrophic complication following TKA and existing data document substantial distal femur bone mineral density (BMD) loss following TKA. However, distal femur BMD is virtually never measured clinically as no consensus approach exists. This pilot study's purpose was to define regional BMD variation throughout the femur, suggest standard dual-energy X-ray absorptiometry (DXA) regions of interest (ROIs) and evaluate BMD reproducibility at these ROIs. Methods: Thirty volunteers 2–5 yr post TKA had both entire femurs imaged twice using a Lunar iDXA with subject repositioning between scans; the atypical femur fracture feature of enCORE software was utilized. To define femoral BMD distribution, custom 1 cm ROIs were stacked one atop the other starting at the intercondylar notch and continuing to the base of the lesser trochanter. Femur length was measured with the ruler tool to calculate distance at 5% increments. ROIs encompassing each 5% increment were utilized to measure BMD at each location. Descriptive statistics were used to determine mean BMD at each ROI and reproducibility at the 15%, 25%, 45%, 60%, and 80% ROIs. Results: The 5 and 10% ROIs included prosthetic and/or patella, causing high BMD values. Distal femur BMD was lowest at the 15% ROI and was higher (p < 0.05) at each more proximal ROI to 45%, then plateaued from 45% to 75%. BMD reproducibility at these regions was excellent; coefficient of variation (CV) from ∼1% to 3.5%. As periprosthetic fractures generally occur in the distal femur, we propose measuring femur BMD using ROIs placed at 15% and 25%. A 60% region could also be used as a highly cortical site. Conclusion: Existing DXA capabilities allow distal femur BMD measurement with good reproducibility. Further research using standardized ROIs to assess distal femur BMD loss after TKA, and interventions to mitigate this loss, is indicated.
AB - Introduction: Total knee arthroplasty (TKA) is increasingly being performed. Distal femur periprosthetic fracture is a potentially catastrophic complication following TKA and existing data document substantial distal femur bone mineral density (BMD) loss following TKA. However, distal femur BMD is virtually never measured clinically as no consensus approach exists. This pilot study's purpose was to define regional BMD variation throughout the femur, suggest standard dual-energy X-ray absorptiometry (DXA) regions of interest (ROIs) and evaluate BMD reproducibility at these ROIs. Methods: Thirty volunteers 2–5 yr post TKA had both entire femurs imaged twice using a Lunar iDXA with subject repositioning between scans; the atypical femur fracture feature of enCORE software was utilized. To define femoral BMD distribution, custom 1 cm ROIs were stacked one atop the other starting at the intercondylar notch and continuing to the base of the lesser trochanter. Femur length was measured with the ruler tool to calculate distance at 5% increments. ROIs encompassing each 5% increment were utilized to measure BMD at each location. Descriptive statistics were used to determine mean BMD at each ROI and reproducibility at the 15%, 25%, 45%, 60%, and 80% ROIs. Results: The 5 and 10% ROIs included prosthetic and/or patella, causing high BMD values. Distal femur BMD was lowest at the 15% ROI and was higher (p < 0.05) at each more proximal ROI to 45%, then plateaued from 45% to 75%. BMD reproducibility at these regions was excellent; coefficient of variation (CV) from ∼1% to 3.5%. As periprosthetic fractures generally occur in the distal femur, we propose measuring femur BMD using ROIs placed at 15% and 25%. A 60% region could also be used as a highly cortical site. Conclusion: Existing DXA capabilities allow distal femur BMD measurement with good reproducibility. Further research using standardized ROIs to assess distal femur BMD loss after TKA, and interventions to mitigate this loss, is indicated.
KW - DXA
KW - bone mineral density
KW - total knee arthroplasty
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U2 - 10.1016/j.jocd.2018.08.003
DO - 10.1016/j.jocd.2018.08.003
M3 - Article
C2 - 30228047
AN - SCOPUS:85053292508
VL - 22
SP - 67
EP - 73
JO - Journal of Clinical Densitometry
JF - Journal of Clinical Densitometry
SN - 1094-6950
IS - 1
ER -