Purpose: to compare the anterior tibial surface curvature, the Akagi's line and the medial third of the tibial tubercle in order to assess which is the most reliable landmark for correct tibial component rotational positioning in total knee arthroplasty. Methods: three independent investigators reviewed 124 knee MRI scans. The most suitable tibial baseplate tracing for the Nexgen Total Knee System (Zimmer, Warsaw, USA) was superimposed on the scan matching the anterior tibial cortex with the anterior aspect of the baseplate. The rotation of the tibial baseplate tracing was calculated with respect to the transepicondylar axis (TEA), the medial third of the tibial tubercle line, Akagi's line and the femoral posterior condylar axis (PCA). Customized software was created and used for analysis of the MRI datasets.The reliability of each measurement was then calculated by using the intraclass correlation coefficient for interobserver agreement. Results: observer agreement on the position of the Akagi's line was within 3° in 64% of the cases and within 5°in 85% of the cases. Agreement on the position of the medial third of the tibial tubercle was within 3°in 29% of the cases and within 5°in 70% of the cases. Agreement on the localization of the anterior tibial surface curvature was within 3°in 89% of the cases and within 5°in 99% of the cases. Component alignment along the anterior cortex guaranteed full matching ± 3° with the epicondylar axis in 75% of the knees. Conclusions: the anterior tibial surface curvature was found to be a more reliable and more easily identifiable landmark for correct tibial component alignment than either Akagi's line or the medial third of the tibialtubercle. Level of evidence: level III, retrospective cohort study.

BackgroundTotal knee arthroplasty (TKA) designs continue to be modified to optimize patient's outcome. This study was designed to compare clinical and radiological results of classic worldwide used TKA posterior-stabilized (PS) design to those of its recent evolution.MethodsA consecutive group of 100 patients undergoing TKA using a classic cemented fixed-bearing PS TKA system was matched by age, gender, body max index to 100 patients having the newer cemented fixed-bearing PS design, both by the same manufacturer. Patients were assessed preoperatively, at 12 months and at 24 months minimum follow-up (range, 24-46) in a standard prospective fashion. The outcome assessments used were the Oxford Knee Score, the Knee Society Score, range of motion, and a satisfaction survey. A 2-sample t test comparing the 2 groups was performed.ResultsNo patients were lost at follow-up. At 2-year follow-up, differences in clinical and radiological Knee Society Score (P = .09), Oxford Score (P = .08), and overall satisfaction rate did not reach statistical significance. Implant group 2 showed a statistically significant decrease in postoperative anterior knee pain (P = .006). At final follow-up, 16% of group 1 knees achieved > 130° flexion compared with 37% in group 2 (P = .0009). There were 2 revisions for any reason in group 1 and none in group 2.ConclusionsDesign modifications applied to the newer TKA system allowed greater flexion and lower patellofemoral complications but did not appear to achieve better overall clinical scores.

This study highlighted that modern femoral designs in TKA allow for a correct reproducibility of a normal patello-femoral conformity. Strict surgical principles are paramount to avoid patello-femoral complications even when modern implants are used.

This study evaluated the influence of modern tibial baseplate designs when using the anterior tibial cortex as a primary rotational landmark for the tibial baseplate in TKA. Eighty patients undergoing TKA were randomized in two groups. Group 1 included 25 females and 15 males receiving a posterior-stabilized (PS) symmetric tibial baseplate while Group 2 included 24 females and 16 males receiving a PS anatomical tibial component. Identical surgical technique, including the use of the surgical transepicondylar femoral axis (sTEA) and the anterior tibial cortex (“Curve-on-Curve”) as rotational alignment landmarks, was used. All patients underwent CT evaluation performed with the knee in full extension. Three observers independently measured the rotational alignment of the tibial component in relation to the sTEA. The rotational alignment of the symmetric baseplate showed an average external rotation of 1.3° (minimum 5°, maximum −1°): 91% of the knees showed 0 ± 3° with respect to the surgical sTEA, being internally rotated in 20%. The rotational alignment of the anatomical baseplate showed an average external rotation of 4.1° (minimum 0.4°, maximum 8.9°): only 47.5% of the knees showed 0 ± 3°, being externally rotated in 100%. The difference between the two groups was statistically significant. This study confirms the reliability of the “Curve-on-Curve” technique as an adequate rotational alignment anatomical landmark in TKA: the use of an asymmetric tibial baseplate might lead to external rotation of the tibial component when this technique is intraoperatively chosen.

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