Background: There is minimal data on the impact of total knee replacements (TKR) and revisions (rTKR) on post-operative bone mineral density (BMD) in the ipsilateral and contralateral hips. Galgo Medical has developed 3D modelling software which analyses hip Dual Energy X-ray Absorptiometry (DXA) scans reporting on cortical and trabecular bone differences which might allow greater understanding of bone loss and fracture risk.
Method: The testing involved participants from three groups (rTKR (N=27 at baseline), TKR (N=23 at baseline) and controls (N=45 at baseline age) all participants underwent DXA scans prior to their surgery and at post-op intervals (6 weeks, 3, 6, and 12 months). 538 hip scans were then imported into and analysed with 3D SHAPER software that produced patient 3D hip model and measurements (see figure 1). The data were recorded in Excel including: the cortical surface BMD (sBMD), trabecular volumetric BMD (trabecular vBMD), integral volumetric BMD (integral vBMD), Cross Sectional Moment of Inertia (CSMI), and Cross Sectional Area (CSA). Data were then analysed via comparison to their contralateral hip and compared to their pre-op baseline.
Results: All control data recorded showed minimal changes throughout. The rTKR data demonstrated losses of sBMD throughout all visits, and the TKR group showed a similar trend. The trabecular vBMD demonstrated a deficit of -4.055% in the rTKR group at baseline but had increased by 12 months. In the TKR group the opposite was seen with a reduction of -4.206% at 12 months. Integral vBMD demonstrated a deficit of -3.055% compared to the contralateral hip in the rTKR group at baseline, this loss gradually improved throughout resulting in a mean of -1.716% at 12 months. The TKR group had a deficit of -2.461% at 6 weeks, with this deficit increasing to -3.110% at 12 months. The CSMI and CSA showed a similar trend to each other.
Conclusion: Based on the data both TKR and rTKR groups show similar cortical thinning, increasing fracture risk, with the rTKR group showing trabecular vBMD recovery compared to the TKR group. Overall the software’s ability to be applied to hip DXA imaging shows promise, this is reflected in the control participants results showing minimal changes throughout. This is also supported by the trabecular vBMD data from the TKR group data agreeing with current literature, and the CSA and CSMI data showing similar trends, due to their correlation in the femoral strength index.