A modified Radiographic Union Score for Tibia (RUST) scoring system for patella fractures treated with osteosynthesis shows excellent intra und interobserver reliability

Introduction: Patellar fractures are rare at 1% incidence of all fractures. However, they can cause significant functional impairments due to the patella's role in knee joint extension. Current scoring systems lack objectivity in assessing patellar healing. This study aims to validate the Radiographic Union Score for Tibia (RUST) using biplanar radiographs for assessing surgically treated patellar fractures.

Materials and methods: A retrospective analysis of radiological follow-up examinations was conducted on patients undergoing surgical treatment for patellar fractures from January 1st 2013, to June 30th 2023. Thirty patients were randomly selected, yielding 105 postoperative X-rays representing various healing stages. The modified Radiographic Union Score for Tibia (RUST) was applied to these X-rays by three independent trauma surgeons. Radiological follow-up examinations were randomized, pseudonymized, and stored on a hospital server for blinded assessment by three raters. The modified RUST assessed continuity of patellar borders and cortexes, assigning scores based on cortical bridging. Interobserver and intraobserver reliability were evaluated using intraclass correlation coefficients (ICC), adhering to recommended sample size criteria and interpretation guidelines.

Results: The mean modified RUST was 9.1 ± 2.2 points, with scores ranging from 4 to 12 points. The interobserver intraclass correlation coefficient (ICC) was 0.88 (95% CI, 0.81-0.92) and the intraobserver ICC were 0.6 (95% CI, 0.65-0.84), 0.80 (95% CI, 0.71-0.87) and 0.98 (0.98-0.99) respectively, which indicated good to excellent agreement.

Conclusions: This study validated the Radiographic Union Score for Tibia (RUST) for evaluating bone healing in patellar fractures treated with osteosynthesis, demonstrating good intra- and interobserver reliability. The modified RUST can provide a standardized method for assessing healing in patellar fractures, benefiting both clinical practice and clinical trials.