Quantitative Application of Bone Density Measurements in Pre-and Post-Operative Patients

Introduction:
Change in bone density over time is an expected process in biological processes like bone formation, callus formation in fracture healing, and bone resorption after joint replacement with implants are known in orthopedics. It is challenging to quantify processes over time and determine bone density`s region of Interest (ROI). These changes have clinical implications in decision-making on the effect of bone healing or loosening of implants. In this study, we wanted to quantify changes in bone density over time under the tibial plate after total knee replacement.

Materials and Methods:
Retrospective study, 42 patients after total knee replacement underwent radiological evaluation before and after. ROI was measured in Hounsfield units on the tibia and under the tibial components at 6 defined points by two examiners. Standardization attempt was performed by calculating the ratio between expected bone density change ROI (5 mm under tibial plateau) to unchanged reference density ROI (metal of tibial plate, air) (ref ROI / exp ROI).

Results:
28 patients were evaluated before and after, 17 patients we additionally evaluated for follow-up radiographs. Comparative tests between different time points indicated statistical significance in all categories. At 3 time points, 2 clusters with close accuracy were observed before and after, showing an increase in bone density in the immediate post-operative radiographs. At the follow-up, there was a general decrease with a wider range of results. Moderate agreement was established by two observers (ICC-0.51).

Conclusion:
Our study suggests a new method of quantitative measurement for changes in bone density over time. We showed Immediate post-operative subchondral bone density changes after the surgery and a gradual decrease during the follow-up after 6 weeks. As it was a pilot study, future studies are needed with a wider and longer follow-up period.