Custom Programming For Evaluation Of Sub-regional Analysis Of Dual-energy X-ray Absorptiometry Scans Of The Knee

Dual-energy X-ray Absorptiometry (DXA) scans are used to determine bone mineral density (BMD) with minimal radiation. Often, these scans are performed on the lumbar spine and hip for osteoporotic risk and bone integrity. Following certain injuries, such as anterior cruciate ligament tears, more specific sub-regional analyses may provide information on regional changes in BMD that may relate to joint health. PURPOSE: To determine the validity, test-retest reliability, and inter-rater reliability of a custom MATLAB program to distinguish sub-regional BMD from DXA scans. METHODS: DXA scans of the knee were acquired using the standard forearm sequence with visualization of both the distal femur and proximal tibia. Four sub-regions of interest (ROI) were analyzed using custom drawing tools to select and define the medial and lateral femoral and tibial condyles from 10 individuals. Validity of the custom MATLAB code was established by comparing BMD values generated from the sub-region analysis to BMD values obtained from the internal DXA software. To determine the test-retest reliability, one rater processed a set of scans twice, one week apart while inter-rater reliability was assessed by having a second rater process the same set of scans. R2 values were calculated between the BMD values obtained from the custom analysis and from the internal DXA software. Intraclass correlation coefficients (ICC), Pearson correlation coefficients (r), and dice coefficients (DC) were determined between each set of raters for each ROI. RESULTS: Validity was high for the custom analysis (R2 > 0.88) (Custom program Avg. BMD = 1.03, 1.14, 0.87, 0.87; DXA Avg. BMD = 1.22, 1.37, 0.95, 0.98). The custom analysis method had high test-retest reliability (ICCs >0.98, r > 0.97, DC > 0.92)) and high inter-rater reliability (ICCs >0.97; r > 0.97, DC > 0.88). CONCLUSIONS: Sub-regional analysis performed with the custom code was highly reliable and repeatable. Sub-regional analysis will allow for more finite assessment of BMD and direct tracking of regional BMD changes due to traumatic injury, providing insights on early degenerative changes to bone with greater processing ease. Future work will apply this MATLAB-based assessment to understand knee joint health across a variety of orthopedic conditions.