Study of bone density according to СT data before and in the remote period after unicondylar knee arthroplasty

Background. Unicondylar knee arthroplasty has become popular among orthopedists in recent years. The main complication of this technology is the instability of the tibial component of the endoprosthesis due to the development of local osteoporosis in the area of arthroplasty. Patients with decreased bone density are at high risk of developing instability of the tibial component of the endoprosthesis. Therefore, determining the levels of bone mineral density in patients with osteopenia before arthroplasty make it possible to calculate the risk of complications in the long term. Objective: to evaluate the bone mineral density according to the computed tomography (CT) of the tibial plateau resection zone for unicondylar arthroplasty in patients at risk. Materials and methods. The state of three cortical layer zones was assessed: anterior, middle, posterior and 4 zones of the plateau cut plane. The optical density of bone tissue was measured on CT images of the tibial plateau of the knee joint using the Hounsfield scale. Changes in bone structures in the area of placing tibial component of the endoprosthesis were studied in 2 groups of patients: group I — ten individuals who had undergone unicondylar knee arthroplasty 3–6 years ago and complained of negative phenomena in the prosthetic knee, group II — ten patients who had undergone unicondylar arthroplasty 1.2–2 years ago. These patients underwent CT densitometry at the follow-up examination. Results. Before arthroplasty, the maximum optical density of bone tissue was statistically the same. The density of the cortical layer was maximal in the anterior part of the bone (~ 720 HU), minimal — in the posterior part (580 HU). For the spongy bone zone, the maximum optical density was observed in the anterior part (~ 470 HU), and in the posterior part, it was lower. In 3–6 years, patients of group I showed a significant decrease in the optical density of the bone, both in its cortical layer and in the cancellous tissue. The greatest losses were detected in the medial zones of the cancellous bone. Patients had areas of cortical layer resorption, and in some individuals, its complete absence. At the same time, the absorption index of the cortical layer in the areas of destruction did not exceed 100 HU. The maximum optical density of the cortical layer in the zones also decreased. In patients of group II, 1.5–2 years after arthroplasty, there were no noticeable changes in the bone structures in the surgery area. Changes occurred in the medial zones of the cancellous bone of the tibial plateau. Patients with osteopenia reported changes in bone optical density already in the first years after arthroplasty, although they do not lead to instability of the tibial component of the endoprosthesis. Conclusions. Patients with decreased bone density (osteopenia) during joint arthroplasty are at risk of developing local osteoporosis in the area of bone resection. The first signs of resorption of the cancellous bone can be observed 1.5–2 years after arthroplasty. Timely treatment measures can slow down the further progression of osteoporosis.