[Occurrence and Progression of Early Radiolucent Lines around Total Knee Arthroplasty]

PURPOSE OF THE STUDY Radiolucent (RL) lines may appear around the total knee arthroplasty (TKA); they occur much more frequently under the tibial component than under the femoral one. The RL lines are gaps between the TKA and the cement, or between the cement and the bone bed. They are clearly visible immediately after the surgery or may appear later. They constitute pathology of the interface and are subject to research mainly due to their potential association with aseptic loosening. The aim of this study was to assess how often they are clearly visible on the first postoperative radiograph in everyday clinical practice, how they develop during the following two years, and to compare the results with the available professional literature. Another aim was to assess the relation between RL lines and the alignment of components, the patient's habitus and clinical outcomes of the surgery. MATERIAL AND METHODS The group included 62 patients with a total number of 69 TKA implants, of which 28 were men (45.2%) and 34 women (54.8%) aged 46 to 79 years of age. The occurrence of RL lines was monitored on the first postoperative radiograph and subsequently at a one-year interval during the following 2 years. The location of RL lines and the placement of components were assessed radiographically in terms of the concept by Meneghini et al. The evaluation of surgical outcomes was done using the Knee Society Score (KSS), and the habitus was assessed with the BMI index. Subjective evaluation of the surgical outcome was done using the 4-point satisfaction scale. RESULTS The first postoperative radiographs showed a RL line at 9 (0.8%) locations in 9 (13.0%) TKAs. The control radiographs made 1 year after the surgery showed a RL line at 42 (3.8%) locations in 29 (42.0%) TKAs. During the last check conducted 2 years after the surgery, a RL line was detected at 60 (5.4%) locations in 33 (47.8%) TKAs. Throughout the follow-up period, progression of the existing RL line occurred at 6 locations in 6 (8.7%) TKAs. On the very contrary, the RL line disappeared at 8 locations in 6 (8.7%) TKAs. An association was found between the RL line occurrence and postoperative limb axis (a higher risk was posed by the varus deformity). Moreover, the frequency of RL lines increased with the growing BMI value. No relation was found between the KSS and satisfaction with the surgery and the occurrence of RL lines. DISCUSSION AND CONCLUSIONS The occurrence of RL lines corresponds roughly with the frequency stated in literature. Some lines show progression, other disappear. So far, we have been unable to distinguish the predictively significant RL lines from the insignificant ones. Important will undoubtedly also be the size of surface of RL lines and their cause. More frequent RL lines were observed in the postoperative varus deformity of TKA and with the growing BMI value. The RL lines under the anterior part of the femoral component showed a tendency to progress. In order to avoid them we recommend modifying the cementing technique. Clinically significant is the fact that the RL lines occurrence correlates neither with subjective nor with clinical outcomes of the surgery. Key words: total knee arthroplasty; total knee replacement; radiolucent lines; progression; alignment; Knee Society Score; BMI.