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Purpose Tibial plateau fractures are serious complications of Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). This study examined where the fracture lines arises and evaluated the keel–cortex distances (KCDs) using three-dimensional computed tomography (3D-CT) and the effects of technical error (assessed by tibial component positions) and proximal tibial morphology on the KCDs. Methods This retrospective study included 217 OUKAs with cementless tibial components. Fifteen patients had tibial fractures after surgery. Anterior and posterior KCDs and fracture line origins were assessed using 3D-CT postoperatively. Proximal tibial morphology was assessed using the medial eminence line (MEL), which runs parallel to the tibial axis and passes through the tip of the medial intercondylar eminence of the tibia on long-leg anteroposterior radiograph. Knees had overhanging medial tibial condyle if the MEL passed medially to the medial tibial cortex. KCDs were compared between patients with/without fractures. Tibial component positions were evaluated, considering effects of tibial morphologies and component positions on fracture prevalence and KCDs. Results Fracture lines were found between the keel and posterior cortex in 12/15 patients. Posterior KCDs were significantly shorter in patients with fractures than in patients without (2.7 ± 1.6 mm vs 5.2 ± 1.7 mm, P  < 0.001). Patients with medial overhanging condyles were more likely to have fracture (10/51 vs 5/166, P  < 0.001) and had significantly shorter posterior KCD than those without (3.6 ± 1.5 mm vs 5.5 ± 1.8 mm, P  < 0.001). Patients with tibial component that was set too medial, low, and valgus had higher rates of fracture than those without (7/39 vs 8/178, P  = 0.008). Medial ( r  = 0.30, P  < 0.001), low ( r  = -0.33, P  < 0.001), and valgus implantations ( r  = 0.35, P  < 0.001) of tibial components were related to shorter posterior KCDs. Conclusion Short posterior KCD after OUKA is a risk factor for postoperative tibial fracture. Patients with either malposition of the tibial component (too medial, low, and valgus) and/or a medial overhanging condyle exhibit a shorter distance of posterior KCD and higher rate of fracture. Level of evidence: Level III.

Purpose The reasons leading to rotational tibial malalignment in total knee arthroplasties (TKAs) remain unclear. A previous cadaver study has shown an increase in internal rotation of the anatomical tibial axis (ATA) after the tibial cut. This study investigates the influence of tibial slope on the ATA and the size of the resected tibial surface. Methods CT scans of 20 cadaver knees were orientated in a standardized coordinate system and used to determine the position of the centres of rotation of the medial and lateral tibial articular surfaces and, hence, of the ATA, after a virtual resection of 6 mm with 0°, 3.5°, 7° and 10° slope, respectively. Furthermore, at each slope, the radii of the medial and lateral tibial articular surfaces after resection were calculated. Results Compared to resection of 6 mm with 0° slope, a slope of 3.5° resulted in a mean external rotation of the ATA of 0.9° (SD, 1.5°; P  = 0.025). A slope of 7° resulted in a mean external rotation of the ATA of 1.0° (SD 2.0°; P  = 0.030) and a slope of 10° had no influence on the rotation of the ATA. The radii of the medial and lateral articular surfaces of the cut tibiae were larger than those of the uncut tibia ( P  < 0.001). Conclusion Differences in the posterior tibial slope should not contribute to a rotational malalignment when using the ATA to align the prosthetic tibial plateau. Although statistically significant, the change in ATA with increasing slope was negligible.

Purpose Total knee arthroplasty (TKA) is frequently performed for obese patients. TKA in this population shows a high rate of complication, particularly tibial component loosening. The aim of this study is to compare the survival rate of tibial components in obese population using TKA with stem versus without stem. Methods From a prospective database of 4216 TKA, obese patients [body mass index (BMI) > 30 kg m²] with primary TKA using a tibial short stem extension (30 mm) at a minimum follow-up of 2 years were retrospectively reviewed and compared to a matched control group (1:3 ratio) with a standard tibial stem. Inclusion criteria were BMI > 30 kg m², first knee surgery and 24 months minimum of follow-up. The primary outcome was revision for tibial aseptic loosening. Secondary outcomes were all-cause revisions and Knee Society Scores (KSS). Results The final study population consisted of 35 TKA with tibial extension stem versus 105 TKA with standard stem. The mean age was 69.2 and 69.5 years, respectively, with a mean follow-up of 52 months. Both groups were comparable before surgery. After 2 years of follow-up, we observed seven tibial loosening in the group without stem (6.6%) versus no tibial loosening in the stemmed group ( p  < 0.001). The difference in KSS knee score (83 versus 86; p  = 0.06) and the KSS function score (73 versus 77; p  = 0.84) were not statistically significant at the final follow-up. Conclusion Using stemmed TKA for obese patients significantly decreased tibial loosening rate at minimum 2 years of follow-up. Level of evidence Case–control study, Level III.

Selective laser melting (SLM) is crucial for fabricating complex geometries, such as the tibial component of an artificial knee joint. However, its inherent high-temperature gradients often induce thermal defects and deformations, compromising product accuracy. This study addressed these challenges by using a multifaceted approach in which finite element method (FEM) simulations, Taguchi method analysis, and deep neural network (DNN) prediction were combined. Initially, a transient thermal model was developed using the FEM to analyze the thermal behavior of a tibial component during and after SLM; the model was then validated through experiments. Subsequently, the Taguchi method was employed to evaluate the thermal influence of various SLM parameters on deformation and stress. Furthermore, a K-means-based exploration method was developed and used to identify critical thermal areas affecting a component’s size and quality. Finally, a DNN model was developed for rapid prediction of thermal deformation by leveraging an FEM proxy modeling methodology to facilitate efficient monitoring in a digital-twin framework. The FEM analysis revealed average deformation errors of 3.26% during SLM and 0.05 mm after SLM. The optimal SLM parameters for minimizing thermal deformation and stress for a tibial component were identified. The DNN model, trained on the proxy database, achieved error margins of only 5.47% and 4.62% in comparison with the FEM and experimental results, respectively, but took substantially less computation time than did the FEM. This study integrated FEM simulations, the Taguchi method, and DNN prediction to enhance the accuracy of SLM manufacturing of tibial components.

BackgroundThis retrospective medium-term follow-up study compares the outcomes of medial fixed-bearing unicompartmental knee arthroplasty (mUKA) using a cemented metal-backed (MB) or an all-polyethylene (AP) tibial component.Materials and methodsThe database of our institution was mined for primary mUKA patients implanted with an MB or an AP tibial component (the MB-UKA and AP-UKA groups, respectively) from 2015 to 2018. We compared patient demographics, patient-reported outcome measures (PROMs), and motion analysis data obtained with the Riablo™ system (CoRehab, Trento, Italy). We conducted propensity-score-matching (PSM) analysis (1:1) using multiple variables.ResultsPSM analysis yielded 77 pairs of MB-UKA and AP-UKA patients. At 5 years, the physical component summary (PCS) score was 52.4 ± 8.3 in MB-UKA and 48.2 ± 8.3 in AP-UKA patients (p < 0.001). The Forgotten Joint Score (FJS-12) was 82.9 ± 18.8 in MB-UKAs and 73.4 ± 22.5 in AP-UKAs (p = 0.015). Tibial pain was reported by 7.8% of the MB-UKA and 35.1% of the AP-UKA patients (p < 0.001). Static postural sway was, respectively, 3.9 ± 2.1 cm and 5.4 ± 2.3 (p = 0.0002), and gait symmetry was, respectively, 92.7% ± 3.7 cm and 90.4% ± 5.4 cm (p = 0.006). Patient satisfaction was 9.2 ± 0.8 in the MB-UKA and 8.3 ± 2.0 in the AP-UKA group (p < 0.003).ConclusionsMB-UKA patients experienced significantly better 5-year static sway and gait symmetry outcomes than AP-UKA patients. Although the PROMs of the two groups overlapped, MB-UKA patients had a lower incidence of tibial pain, better FJS-12 and PCS scores, and were more satisfied.

Purpose The purpose of this retrospective study was to evaluate the effect of varus alignment of the tibial component on the outcomes with a minimum follow-up of 10 years. The hypothesis was that varus alignment of the tibial component might not affect the outcomes and survival of a neutrally aligned primary TKA. Methods A matched case–control study was designed between 66 patients with varus alignment of the tibial component and 66 with neutral alignment with a minimum follow-up of 10 years. Functional outcome was assessed with the knee surgery scores (KSS) and reduced Western Ontario and MacMaster Universities questionnaire (WOMAC). Patient satisfaction was evaluated by a 0–10 visual analog scale. Radiological evaluation was performed at early postoperative and at final follow-up. Results The mean follow-up was 11.9 (SD 2.6) years for both groups. The mean postoperative proximal tibial angle in the varus group was 85.0° (SD 0.9) and 88.8° (SD 0.9) in control group. At the final follow-up, there were no significant differences in KSS, WOMAC, range of motion or patient satisfaction. There were no differences in the coronal anatomical alignment of the TKA between groups. Revision of TKA was performed in four knees in the varus group, and one in control group, due to aseptic loosening of the tibial component in all cases. TKA survival at 10 years was not significantly different between groups. Conclusion The alignment of the tibial component up to 7° varus did not negatively affect implant survival, patient satisfaction, and function of a well-aligned TKA, with a minimum postoperative follow-up of 10 years. Level of evidence III.

Purpose The purpose of this study was to define various anteroposterior axes of the tibial component as references and to evaluate their accuracy and variability using virtual surgery. It was hypothesized that (1) Akagi’s Line could result in high accuracy and low variability in varus osteoarthritic knees; (2) anteroposterior axes defined by using the tibial bony cutting surface as a landmark might be good substitutes for Akagi’s Line; and (3) extra-articular bony landmarks might influence the variability of the anteroposterior axis. Methods Three-dimensional bone models were reconstructed from the preoperative computed tomography data of 111 osteoarthritic knees with varus deformities. Seven different anteroposterior axes of the tibial component were defined: Akagi’s Line, Axis MED, Axis 1/6MED, Axis 1/3MED, Axis of Oval Shape, Axis of Anterior Crest, and Axis Second Metatarsus. The rotational mismatch angle was measured between the tibial anteroposterior axis and the line perpendicular to the transepicondylar axis projected on the cutting surface (positive value: external rotation of the tibial anteroposterior axis). Results The average rotational mismatch angles (referring to the projected anatomical/surgical epicondylar axes) were − 2.7° ± 5.8°/1.0° ± 6.0° (Akagi’s Line), − 4.2° ± 7.7°/− 0.5° ± 7.8°, 2.9° ± 7.2°/6.6° ± 7.2°, 9.8° ± 7.0°/13.5° ± 6.8° (Axis MED, Axis 1/6MED, Axis 1/3MED), − 5.1° ± 7.9°/− 1.4° ± 7.8° (Axis of Oval Shape), and 19.3 ± 9.5°/23.0° ± 9.6°, − 2.0° ± 11.3°/1.7° ± 11.4° (Axis Anterior Crest, Axis Second Metatarsus), respectively. Conclusions Akagi’s Line provided the best accuracy and least variability in varus osteoarthritic knees. Axis 1/6MED and Axis MED are good substitutes for Akagi’s Line due to the difficulty of identifying the attachment site of the posterior cruciate ligament after the proximal tibia has been cut. Extra-articular bony landmarks should not be used for alignment due to their high variability. This study will aid surgeons in choosing the proper anteroposterior axis of the tibial component to reduce rotational mismatch and thus achieve good clinical knee outcomes. Levels of evidence III.

Purpose This study aimed to investigate stress shielding of anatomical tibial components (ATCs) in comparison to conventional symmetric tibial components (STCs) in Korean patients which may be related to medial tibial bone loss. Method 78 knees in 59 patients with ATCs (Persona™) and 74 knees in 58 patients with STCs (NexGen LPS-Flex™) were retrospectively reviewed. Radiographic parameters and clinical outcomes in both groups were compared. Logistic regression analysis was performed to identify risk factors for medial tibial bone loss. Results Medial tibial bone loss was significantly greater in the ATC group (1.6 ± 1.3 mm) than in the STC group (0.4 ± 0.8 mm) ( p  < 0.001). The ATC group showed a shorter distance between the distal metal tip and anteromedial cortex and higher invading into the sclerotic bone lesion (ISBL) than the STC group ( p  = 0.034 and p  = 0.044, respectively). Multiple logistic regression analysis suggested ATC, a shorter distance to the anteromedial cortex, and the presence of ISBL as risk factors for medial tibial bone loss. The odds ratios of medial tibial bone loss according to type of prosthesis, distance to anteromedial cortex, and presence of ISBL were 6.25 (range 2.86–13.63, p  < 0.001), 0.69 (range 0.51–0.93, p  = 0.015), and 3.79 (range 1.56–9.21, p  = 0.003), respectively. Notwithstanding, there was no difference in clinical outcomes between the two groups. Conclusion In Korean patients, ATCs potentially causes greater medial tibial bone loss due to stress shielding than STCs. The design, however, does not yet appear to affect clinical outcomes at mid-term follow-up. Level of evidence Retrospective cohort study, level III.

Purpose Stiffness is a common problem following total knee arthroplasty (TKA). Mal-rotated components have been claimed to be the major cause of pain and limited motion after TKA. The present study investigates whether intra-operative intentional malrotation of the tibial component would change in vivo kinematics. The hypothesis is excessive internal rotation of the tibial component would result in postoperative extension deficit. Methods Thirty-one patients were enrolled in this study. After completing bony cuts and proper soft tissue balancing, the femoral and tibial trials were impacted and fixed using small pins. Lateral radiographs were used to measure and compare intraoperative full knee extension during normal and after intentional internal rotation of the tibial component. The extension deficit angles were also compared between the posterior stabilised (PS) and cruciate retaining (CR) implants. Results For normal tibial component rotation, the median (interquartile range) extension deficit was 0° (4). The mean tibial trial intentional internal rotation was 21.2° (± 4.5). The median (interquartile range) extension deficit significantly increased to 6° (4) after tibial component internal rotation ( p  = 0.001). The use of PS spacers resulted in a significantly greater extension deficit after intentional internal rotation 9° (5) compared to that of the CR implant 1° (4) ( p  = 0.001). Conclusion Internal rotation of the tibial component in total knee arthroplasty can lead to postoperative extension deficit. This could be attributed to interference with “screw home” mechanism that requires full external rotation of the tibia on the femur. Consequently, this deficit may cause pain and knee stiffness following TKA. Level of evidence III.

Purpose The purpose of this study was to compare the clinical results, radiographic loosening and early complications between patients undergoing primary knee arthroplasty (TKA) with tibial short stem extension and those with standard stem for gross varus deformities at minimum two years after surgery. Methods From a prospective TKA database of 4216 patients, patients with a primary TKA with a tibial short stem extension (30 mm) for severe varus deformity (hip-kneeankle angle, HKA < 170°) and a minimum follow-up of 2 years, were reviewed and compared to a matched control group with tibial components with a standard stem, in a 1:3 ratio. Demographics, surgical parameters, pre- and postoperative alignment and outcome parameters were collected for all patients. The primary outcome was aseptic loosening of the tibial component. Secondary outcomes were knee society scores (KSS), postoperative HKA, general postoperative complications and implant survival rates. Results Forty-five patients with tibial short stem extensions (mean HKA 166.2°) were compared in a 1:3 ratio to a matched case–control group of 135 patients with standard stems (mean HKA 167.1°) at a mean follow-up of 57 and 64 months respectively after primary TKA. In the extension stem group, 4 patients encountered complications (8.9%) versus 12 patients in the standard stem group (8.9%). There were no cases of tibial component loosening in the short extension stem versus four cases in the standard stem group (3%). This difference was significant between groups, p  = 0.04. Conclusion In patients with varus deformities > 10°, undergoing primary total knee arthroplasty, prophylactic use of a tibial short extension stem may lead to less loosening of the tibial component. In this study, 3% of patient with big varus deformity without stemmed TKA had a tibial implant loosening versus 0% in the stemmed TKA group. Level of evidence Level III, case–control study