Search

Background: Bicruciate-retaining (BCR) prosthesis has been introduced to recreate normal knee movement by preserving both the anterior and posterior cruciate ligaments. However, the use of BCR total knee arthroplasty (TKA) is still debatable because of several disappointing reports. We have been performing BCR TKAs with personalized alignment (PA). This study aimed to reveal the limb alignment and soft tissue balance of FA-BCR TKAs and compare the clinical outcomes of FA-BCR TKAs with those of unicompartmental knee arthroplasty (UKA)., Methods: Fifty BCR TKAs and 58 UKAs were included in this study. The joint component gaps of BCR TKA were evaluated intraoperatively and the postoperative hip-knee-ankle (HKA) angle, medial proximal tibial angle (MPTA), and lateral distal femoral angle (LDFA) were measured using full-length standing radiography. The short-term clinical outcomes of BCR TKAs were compared with those of UKA using the scoring system of 2011 Knee Society Scoring (KSS) and the knee injury and osteoarthritis outcome score (KOOS) at an average of 2 years postoperatively (1-4yeras)., Results: The coronal alignment values of PA-BCR TKA were as follows: HKA angle, 177.9° ± 2.3°; MPTA, 85.4° ± 1.9°; and LDFA, 87.5° ± 1.9°. The joint component gaps at flexion angles of 10°, 30°, 60°, and 90° were 11.1 ± 1.2, 10.9 ± 1.4, 10.7 ± 1.3, and 11.2 ± 1.4 mm for the medial compartment and 12.9 ± 1.5, 12.6 ± 1.8, 12.5 ± 1.8 and 12.5 ± 1.7 mm for the lateral compartment, respectively. The patient expectation score and maximum extension angle of PA-BCR TKA were significantly better than those of UKAs., Conclusions: The short-term clinical outcomes of PA-BCR TKA were comparable or a slightly superior to those of UKAs., (© 2023. The Author(s).)

Background: Difference in the finite helical axis of the knee joints before and after anterior cruciate ligament-preserving knee arthroplasties such as unicompartmental knee arthroplasty and bi-cruciate-retaining total knee arthroplasty remains unknown. This study compared the knee finite helical axes before and after bi-cruciate-preserving knee arthroplasty., Methods: Patients undergoing medial unicompartmental knee arthroplasty and bi-cruciate-retaining total knee arthroplasty were included. Under fluoroscopy, participants performed a deep knee bend before and after surgery. A two/three-dimensional registration technique was employed to measure tibiofemoral kinematics. Femoral finite helical axis was calculated in a flexion range of 0-120° using 30° windows (early-, mid-, late-, and deep-flexion phases)., Findings: In unicompartmental knee arthroplasty, the preoperative knee vertical angle was larger than the postoperative vertical angle in mid- and deep-flexion phases. The postoperative knee vertical angle was smaller in unicompartmental knee arthroplasty than in bi-cruciate-retaining total knee arthroplasty. In unicompartmental knee arthroplasty, the preoperative horizontal angle was smaller than the postoperative horizontal angle in the early-flexion phase. However, in bi-cruciate-retaining total knee arthroplasty, the preoperative horizontal angle was larger than the postoperative horizontal angle in mid- and deep-flexion phases. The horizontal angle was smaller before unicompartmental knee arthroplasty than that before bi-cruciate-retaining total knee arthroplasty in early-, mid-, and deep-flexion phases. However, the vertical angle was larger after unicompartmental knee arthroplasty than that after bi-cruciate-retaining total knee arthroplasty in the early-flexion phase., Interpretation: The knee finite helical axes before and after unicompartmental knee arthroplasty differed from those before and after bi-cruciate-retaining total knee arthroplasty., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Bi-cruciate stabilized (BCS) total knee arthroplasty (TKA) was developed to approximate normal knee kinematics and is expected to improve clinical outcomes. However, the effects of soft tissue balance at the medial or lateral compartment on patient-reported outcome measures (PROMs) following BCS TKA are unclear. The purpose of this study was to clarify the relationship between the medial or lateral component gaps and PROMs following BCS TKA. One hundred seventeen knees with varus deformities which underwent BCS TKA were included in this study. They were divided into two groups according to the validated Japanese version of the Knee Injury and Osteoarthritis Outcome Score for each subscale of pain, symptoms, and activities of daily living (ADL) at 1 year postoperatively: group H consisted of patients with ≥90 points and group L consisted of patients with <90 points. Intraoperative medial and lateral joint laxities at 0°, 30°, 60°, 90°, and 120° flexion measured using a tensor device were compared between the two groups in each subscale. In the pain subscale, the medial joint laxities at 30° ( p  < 0.05) and 60° flexion ( p  < 0.05) in group H were significantly smaller than those in group L. In the ADL subscale, the medial joint laxity at 60° flexion in group H was significantly smaller than that in group L ( p  < 0.05). In the symptom subscale, the lateral joint laxity at 60° flexion in group H was significantly smaller than that in group L ( p  < 0.05). Surgeons should pay attention to the importance of both medial and lateral joint stabilities to achieve better postoperative PROMs following BCS TKA., Competing Interests: None declared., (Thieme. All rights reserved.)

Background: Medial-pivot type total knee arthroplasty is designed to reproduce physiological femoral rotational kinematics during knee flexion; however, its rotational kinematics in valgus knees remain unknown. This study's hypothesis is that its kinematics show the similar medial pivot motion in valgus knees as in varus knees., Methods: This retrospective study included 50 cases of primary medial-pivot type total knee arthroplasty performed with navigation for knee osteoarthritis. Cases were grouped as valgus (n = 20) or varus (n = 30). In valgus knees, surgeons used preoperative manual testing to confirm that alignment was correctable. They evaluated femoral rotational kinematics at maximum extension, 30°, 60°, 90°, and maximum flexion, using a navigation system, both before and after implantation. Finally, intraoperative rotational kinematics, postoperative patient-reported outcomes, and knee range of motion were compared between the two groups., Findings: Before implantation, both valgus and varus knees displayed external femoral rotation relative to the tibia during knee flexion. The rotation magnitude was significantly larger in varus knees at 60°, 90°, and maximum flexion angles compared to valgus knees (P < 0.05). In contrast, after implantation, both groups displayed external femoral rotation of 12-13° during knee flexion with no significant differences between the two groups at any knee flexion angle tested (P > 0.05). Short-term clinical outcomes were comparable between valgus and varus knees., Interpretation: Postoperatively, medial-pivot type total knee arthroplasty for knee osteoarthritis resulted in external femoral rotation during knee flexion. Notably, this occurred even in valgus knees with good short-term clinical outcomes., Competing Interests: Declaration of Competing Interest Our institute has received donations for research from Medacta Japan KK and Stryker Japan KK. They had no role in the study design, data collection, analysis, or interpretation, or manuscript preparation., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Bicruciate-stabilized total knee arthroplasty (BCS TKA) has been developed to improve TKA kinematic performance. However, the relationship between in vivo kinematics and patient-reported outcomes (PROs) has not been well described. This study was performed to clarify the relationship between in vivo kinematics and PROs in a cohort of patients undergoing BCS TKA. Forty knees were evaluated using a two-dimensional to three-dimensional registration technique obtained from sagittal plane fluoroscopy. In vivo kinematics including anteroposterior (AP) translation and tibiofemoral rotation were evaluated. Knee Society scores (KSSs) and Knee injury and Osteoarthritis Outcome Scores (KOOSs) were assessed before and after surgery. Relationships between tibiofemoral kinematics assessed with the knee in different positions of knee flexion and PROs were evaluated using Spearman's correlation analysis. The study demonstrated a significant negative correlation ( r  =  - 0.33) between medial AP translation from minimum flexion to 30 degrees flexion and postoperative KOOS activities of daily living subscale. A significant positive correlation ( r  = 0.51) was found between the femoral external rotation from minimum flexion to 30 degrees flexion and improvement of the KOOS pain subscale. No correlation was found between the lateral AP translation and PROs. Achieving medial AP and femoral external rotation stability in early flexion may be important in optimizing postoperative PROs., Competing Interests: None declared., (Thieme. All rights reserved.)

Background: Soft tissue balance is important for a good clinical result in total knee arthroplasty. Nevertheless, the appropriate evaluation of the intraoperative gap has not been established. We investigated the relationship between physical characteristics and gap differences due to distraction force, in order to determine whether intraoperative adjustment of the distraction force can be considered based on the physical characteristics of the patient., Methods: A total of 115 varus knees in which primary total knee arthroplasty was performed were retrospectively evaluated. The component gaps were measured under 60 and 80 N. The gap difference under 60 and 80 N was calculated. We performed a linear regression analysis to determine the correlation between the gap differences and patient parameters., Findings: Each gap was significantly larger under 80 N than under 60 N. The component gap difference is larger in the lateral compartment than in the medial compartment at each knee flexion angle. The gap difference negatively correlated with preoperative hip-knee-ankle angle at a knee flexion of 0° and 120° (r = -0.21, -0.19; p = 0.02, 0.05) and positively correlated with BMI in the lateral compartment at a knee flexion of 90° (r = 0.31, p < 0.001)., Interpretation: The difference in the intraoperative gap due to the joint distraction force was affected by the preoperative HKA axis angle and the body mass index in the lateral compartment. Surgeons should consider the effect of preoperative limb alignment and body mass index in interpreting intraoperative gap measurement., Competing Interests: Declaration of Competing Interest None., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Background: A tibial cut with the native posterior tibial slope (PTS) is a theoretical prerequisite in bicruciate-retaining total knee arthroplasty (BCRTKA) to regain physiological knee kinematics. The present study reveals tibial morphological risk factors of trauma to the posteromedial structures of the knee during tibial bone resection in BCRTKA., Methods: Fifty patients undergoing BCRTKA for varus knee osteoarthritis were analyzed. A three-dimensional tibial bone model was reconstructed using a computed tomography-based preoperative planning system, and the coronal tibial slope (CTS) and medial PTS (MPTS) were measured. Then, we set the simulated tibial cutting plane neutral on the coronal plane, posteriorly inclined in accordance with the MPTS on the sagittal plane, and 9 mm below the surface of the subchondral cortical bone (i.e., 11 mm below the surface of the cartilage) of the lateral tibial plateau. The association between the tibial morphology and the distance from the simulated cutting plane to the semimembranosus (SM) insertion (Dsm) was analyzed., Results: Of the 50 patients, 19 (38%) had negative Dsm values, indicating a cut into the SM (namely, below the posterior oblique ligament) insertion. The MPTS was negatively correlated with Dsm (r = -0.396, p = 0.004), whereas the CTS was positively correlated with Dsm (r = 0.619, p < 0.001). On multivariate linear regression analysis, the MPTS and CTS were independent predictors of Dsm., Conclusion: In the setting of tibial cuts reproducing the native MPTS in BCRTKA, patients with larger PTS and smaller CTS had more risk of trauma to the posteromedial structures., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: [Our institute has received donations for research from Smith & Nephew Japan KK. They played no role in the design of this study; in the collection, analysis, or interpretation of the data; or in the writing of this manuscript. The authors declare that they have no personal competing interest.], (Copyright © 2022 Elsevier B.V. All rights reserved.)

Background: The choice of mobile bearing (MB) thickness is essential for obtaining successful results after mobile-bearing Oxford unicompartmental knee arthroplasty (UKA). This study aimed to investigate the effects of a 1-mm difference in bearing thickness on intraoperative MB movement and intraoperative knee kinematics in Oxford UKAs., Methods: We prospectively investigated the effects of a 1-mm difference in bearing thickness on intraoperative MB movement and knee kinematics in 25 patients who underwent Oxford UKAs when surgeons didn't know which bearing thickness to choose with 1-mm difference. A trial tibial component that was scaled every 2 mm was used to measure the intraoperative MB movement, and the tibial internal rotation relative to the femur and the knee varus angle was simultaneously evaluated using the navigation system as the knee kinematics. We separately evaluated sets of two MB thicknesses with 1-mm differences, and we compared the intraoperative parameters at maximum extension; 30º, 45º, 60º, and 90º flexion; and maximum flexion between the thicker MB (thick group) and the thinner MB (thin group)., Results: The MB in the thin group was located significantly posteriorly at 90º flexion compared with that in the thick group; however, there were no differences at the other flexion angles. There was significantly less tibial internal rotation in the thin group at 90º flexion than that in the thick group; however, there were no differences at the other flexion angles. The knee varus angles in the thick group were significantly smaller than those in the thin group by approximately one degree at all angles other than at 30º and 45º flexion., Conclusion: The thicker MB could bring the less posterior MB movement and the more tibial internal rotation at 90º flexion, additionally the valgus correction angle in the thicker MB should be paid attention. These results could help surgeons to decide the thickness of MBs when they wonder the thickness of MB., (© 2022. The Author(s).)

Purpose: The hypothesis of this study was that the kinematics of patients with higher patient-reported outcome measures (PROMs) differ from those of patients with lower PROMs after bicruciate-stabilized total knee arthroplasty (BCS-TKA)., Methods: A total of 32 patients with severe knee osteoarthritis were examined 11.2 ± 3.2 months after BCS-TKA. The patients performed squats under single fluoroscopic surveillance in the sagittal plane. To estimate the spatial position and orientation of the femoral and tibial components, a 2D-to-3D registration technique was used. This technique uses a contour-based registration algorithm, single-view fluoroscopic images and 3D computer-aided design models. Knee range of motion, varus-valgus alignment, axial rotation of the femur relative to the tibial component, anteroposterior translation of the medial and lateral femorotibial contact points, kinematic paths, and anterior and posterior post-cam engagement were measured. The patients were divided into two groups using hierarchical cluster analysis based on the 1-year postoperative Knee Injury and Osteoarthritis Outcome Score and 2011 Knee Society Score., Results: The femoral component had significantly more external rotation in the low-score group than in the high-score group (5.1 ± 1.8° vs. 2.2 ± 2.7°, p = 0.02). The high-score group had a medial pivot pattern from 0 to 20° of flexion, without significant movement from 20 to 70°, and final bicondylar rollback beyond 70°. The low-score group had a medial pivot from 0 to 70° of flexion and bicondylar rollback beyond 70°. There were no significant between-group differences in the varus-valgus angle or post-cam engagement., Conclusion: The higher PROM group had smaller external rotation of the femur after BCS-TKA., Level of Evidence: Level III., (© 2021. European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA).)

Background: Component gap (CG) measurement help surgeons evaluate intraoperative soft-tissue balance. One technique is measuring the CG using tensioner devices with distraction force. Another is to evaluate the laxity under a varus-valgus force using navigation or robotics. The aim was to compare the JL evaluated by CG and varus-valgus force between the different types of total knee arthroplasties., Methods: Forty-three bi-cruciate stabilized (BCS) knees and 33 bi-cruciate retaining (BCR) knees were included. After bone resection and soft tissue balancing, the CG was measured and after the final implantation and capsule closure, JL under a maximum varus-valgus stress was recorded with navigation. JL evaluated by the CG (JLCG) was defined as CG minus selected thickness of the tibial component and JL under varus-valgus force (JLVV) was defined as difference between varus-valgus angles without stress and maximum varus-valgus angles under varus-valgus force. The evaluations were performed at flexions of 10°, 30°, 60° and 90°., Results: Although JLCGs of lateral compartment of BCS were larger than those of BCR, no difference was found between JLVVs of BCS and BCR. Although JLCGs of lateral compartment did not change at each knee flexion angle in both BCS and BCR, JLVVs of lateral compartment increased by 3° from 10° to 90° knee flexion., Conclusion: JLVVs of BCS and BCR were equivalent, whereas BCS showed larger JLCGs of lateral compartment. JLVVs of lateral compartment increased by 3° in the range from 10° to 90° knee flexion whereas JLCGs remained stable., Competing Interests: Declaration of Competing Interest Our institute has received donations for research from Smith & Nephew Japan KK. They played no role in the design of this study; in the collection, analysis, or interpretation of the data; or in the writing of this manuscript. The authors declare that they have no personal competing interests., (Copyright © 2021 Elsevier B.V. All rights reserved.)

This study aims at clarifying implant alignment and other patient factors' influence on clinical outcomes, particularly on patient-reported outcomes (PRO), following Oxford unicompartmental knee arthroplasty (OUKA). A total of 142 patients after OUKA were divided into two groups according to the validated Japanese version of the knee injury and osteoarthritis outcome score (KOOS) for each subscale of pain, symptoms, and activities of daily living (ADL) at postoperative year 1 and 2: group 1 had ≥80 scores and group 2 had <80 scores. Postoperative clinical and radiographical findings were then compared among groups in each subscale. Using postoperative year 1 and 2 data, a multivariable logistic regression analysis was conducted to clarify factors for clinical outcomes' improvement. In the analysis of KOOS subscale of symptoms at postoperative year 1, gender distribution, preoperative body mass index, and postoperative maximum knee flexion angles differed significantly among groups. In the analysis for KOOS subscale of ADL, significant differences were observed in postoperative tibial component varus angles. Multivariable logistic regression analysis revealed that all of these parameters significantly related to ≥80 KOOS scores of each subscale at postoperative year 1. Additionally, at postoperative year 2, larger postoperative knee flexion angles and tibial component varus angles related to ≥80 KOOS subscale of symptoms and ADL were observed. In conclusion, tibial component's larger varus alignment was associated with the better PRO at both 1 and 2 years after OUKA. Importantly, larger postoperative knee flexion angle helped achieve good short-term PRO after OUKA., Competing Interests: None declared., (Thieme. All rights reserved.)

Background: Tibial internal rotation following total knee arthroplasty (TKA) is important in achieving favorable postoperative clinical outcomes. Studies have reported the effect of intraoperative soft tissue balance on tibial internal rotation in conventional TKA, no studies have evaluated the effects of soft tissue balance at medial or lateral compartments separately on tibial internal rotation in bi-cruciate stabilized (BCS) TKA. The purpose of this study was to clarify the relationship between medial or lateral component gaps and rotational knee kinematics in BCS TKA., Methods: One hundred fifty-eight knees that underwent BCS TKA were included in this study. The intraoperative medial and lateral joint laxities which was defined as the value of component gap minus the thickness of the tibial component were firstly divided into two groups, respectively: Group M-stable (medial joint laxity, ≤ 2 mm) or Group M-loose (medial joint laxity, ≥ 3 mm) and Group L-stable (lateral joint laxity, ≤ 3 mm) or Group L-loose (lateral joint laxity, ≥ 4 mm). And finally, the knees enrolled in this study were divided into four groups based on the combination of Group M and Group L: Group A (M-stable and L-stable), Group B (M-stable and L-loose), Group C (M-loose and L-stable), and Group D (M-loose and L-loose). The intraoperative rotational knee kinematics were compared between the four Groups at 0°, 30°, 60°, and 90° flexion, respectively., Results: The rotational angular difference between 0° flexion and maximum flexion in Group B at 30° flexion was significantly larger than that in Group A at 30° flexion (*p < 0.05). The rotational angular difference between 30° flexion and maximum flexion in Group B at 30° flexion was significantly larger than that in Group D at 30° flexion (*p < 0.05). The rotational angular differences between 30° or 90° flexion and maximum flexion in Group B at 60° flexion were significantly larger than those in Group A at 60° flexion (*p < 0.05)., Conclusion: Surgeons should pay attention to the importance of medial joint stability at midflexion and lateral joint laxities at midflexion and 90° flexion on a good tibial internal rotation in BCS TKA., (© 2021. The Author(s).)

Background: One of the causes of dissatisfaction following total knee arthroplasty (TKA) is abnormal knee kinematics. A newly designed bi-cruciate stabilized (BCS) TKA system has been developed to produce close-to-normal kinematics because of its anatomic tibiofemoral articular geometry and cam-post mechanism. Although BCS TKA is expected to improve patient satisfaction, no reports have described the appropriate technique or soft tissue handling required to achieve excellent satisfaction with BCS TKA. This study is to identify preoperative and intraoperative predictors of patient satisfaction after BCS TKA., Methods: Altogether, we studied 113 knees with primary varus knee osteoarthritis that underwent BCS TKA with a navigation system. Preoperative parameters including Knee Society Score and patient-reported scores [the Knee injury and Osteoarthritis Outcome Score (KOOS)] and intraoperative parameters including coronal, sagittal and axial alignment and joint laxity in each compartment that affected patient satisfaction was evaluated. Satisfaction score was evaluated with use of the 2011 Knee Society Scoring system. The multivariate regression analysis included age and preoperative and intraoperative parameters that correlated with satisfaction scores in the univariate analysis ( P < 0.05)., Results: The mean satisfaction score was 28.2 ± 6.1. Multivariate regression analysis showed that the predictors of patient satisfaction were a preoperative high KOOS score for activities of daily living ( P < 0.001), male sex ( P = 0.005), older age ( P = 0.027), and minimal medial joint laxity during flexion ( P = 0.031)., Conclusion: When performing BCS TKA, surgeons should pay attention to maintaining proper stability of the medial compartment, especially during flexion.

Background: This study aims to elucidate and compare the relationship between the knee flexion angle and patient-reported outcome measures (PROM) in both non-weight-bearing (NWB) and weight-bearing (WB) conditions., Methods: This retrospective cohort study included 61 knees (47 patients) who underwent total knee arthroplasty. The knee flexion angle was measured by three conditions: NWB in manual goniometer, NWB in fluoroscopic three-dimensional (3D) analysis and WB in the fluoroscopic 3D analysis. The PROM was evaluated by postoperative 2011 Knee Society Score (2011 KSS) and Knee injury and Osteoarthritis Outcome Score (KOOS). Correlations between the knee flexion angle and PROM was analyzed using Spearman's correlation coefficient. Additionally, whether the angular difference between NWB and WB correlated with the PROM or not was evaluated., Results: The NWB knee flexion angle in a goniometer, NWB in 3D analysis, and WB in 3D analysis were 124.6° ± 8.4°, 118.0° ± 10.5°, and 109.5° ± 13.3°, respectively. The angular difference was 8.5° ± 12.8°. No PROM correlation existed in NWB using a goniometer. Moreover, significant positive correlations in 2011 KSS symptoms (r = 0.35) and 2011 KSS functional activities (r = 0.27) were noted in NWB using 3D analysis. Significant positive correlations existed in 2011 KSS symptoms (r = 0.32), 2011 KSS functional activities (r = 0.57), KOOS pain (r = 0.37), KOOS activity of daily living (ADL; r = 0.45), KOOS sports (r = 0.42), and KOOS quality of life (r = 0.36) in WB using 3D analysis. Significant negative correlations were noted in 2011 KSS functional activities (r = - 0.45), KOOS ADL (r = - 0.30), and KOOS sports (r = - 0.38) in angular difference., Conclusions: The WB knee flexion angle better correlated with PROM compared with NWB by evaluation of 3D analysis. The larger the angular difference existed between NWB and WB, the lower the PROM score., (© 2021. The Author(s).)

Background: To improve the accuracy of tibial cut during unicompartmental knee arthroplasty (UKA), navigation-assisted UKA has been implemented. It has been reported that inexperienced surgeons who use a navigation system achieve better alignment than experienced surgeons who do not use a navigation system. However, there have been no reports comparing the alignments and clinical outcomes of navigation-assisted UKA performed by experienced surgeons in comparison with that by inexperienced surgeons. This study aims to compare these parameters of navigation-assisted UKA performed by experienced and inexperienced surgeons., Methods: A total of 209 UKA procedures using an image-free navigation system were included. One experienced surgeon performed 128 UKAs (E group), and six inexperienced surgeons performed 81 UKAs (I group). The target value in the coronal tibial plane was set at 2.0° in varus. Prosthetic alignments and clinical results were compared between the two groups., Results: No significant differences were found between the two groups for prosthetic alignments and clinical outcomes, except for range of motion. The operation time of the I group was statistically longer than that of the E group (P < .001). The ratio of tibial prosthetic fracture was significantly higher in the I group than that in the E group (P = .022)., Conclusion: Using a navigation system during UKA, inexperienced surgeons achieved accurate alignments and excellent clinical results similar to an experienced surgeon. However, tibial periprosthetic fractures occurred more often in patients of inexperienced surgeons. Even when using a navigation system, inexperienced surgeons need to demonstrate careful and cautious surgical techniques., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: Although Oxford unicompartmental knee arthroplasty (UKA) is used in patients of wide age ranges, there is no clear information regarding the age differences in terms of intraoperative femorotibial rotational kinematics and its influence on clinical outcomes. Therefore, this study was conducted to examine the age differences in terms of intraoperative rotational kinematics and postoperative clinical outcomes and to analyze their relationship with classification according to the age group., Methods: We investigated 111 knees of patients who underwent Oxford UKA using a navigation system and divided them into two groups: elderly (aged ≥75 years; 48 knees) and nonelderly (aged < 75 years; 63 knees). Intraoperative tibial internal rotational angles relative to the femur during passive knee flexion were measured using a navigation system, and clinical outcomes were evaluated using knee range of motion, the Knee Injury and Osteoarthritis Outcome Score (KOOS), and the Knee Society Functional Score at 2 years postoperatively. The relationships between intraoperative tibiofemoral rotational angles and clinical outcomes were also evaluated in the two groups., Results: The intraoperative tibial internal rotational angle relative to the femur during knee flexion was significantly larger in the nonelderly group (13.5°) than in the elderly group (9.0°). The intraoperative tibial internal rotational angle showed a positive correlation with the pain subscale of KOOS only in the nonelderly group., Conclusion: Intraoperative rotational kinematics and its influence on clinical outcomes were different between elderly and nonelderly patients, and the tibial internal rotational angle could be a more important factor for successful UKA in nonelderly patients.

Background: Rotational mismatch between the femoral and tibial components is reported to be a risk factor for unsuccessful total knee arthroplasty (TKA). However, the rotational mismatch can still occur even when each component is aligned within the desired angle. Therefore, there may be other unknown factors. This study aims to investigate a risk factor for component rotational mismatch in TKA. The authors hypothesized a significant correlation between the rotational mismatch angle and not only the rotational alignments of components, but also the preoperative tibiofemoral rotation angle., Method: This retrospective cohort study included 79 knees who underwent TKA. Computed tomography images were obtained preoperatively and 2 weeks after surgery for the component positional measurement. The postoperative component rotational mismatch angle between the tibial and femoral components and the rotational alignment of each tibial and femoral component to anatomical axes was evaluated. In addition, the preoperative rotational angle between the tibia and femur bones and patients' demographics were also investigated. The correlation between the postoperative component rotational mismatch angle and perioperative variables was analyzed to identify risk factors for component rotational mismatch., Results: The mean component rotational mismatch angle was 1.8° of internal rotation of the tibial component relative to the femoral component, and the angle ranged from 11.3° of internal rotation to 7.3° of external rotation of the tibial component. Multivariate regression analysis showed that the preoperative rotational alignment between the tibia and femur and the rotational alignment of each component were influential factors in the postoperative component rotational mismatch angle., Conclusion: The preoperative tibiofemoral rotational alignment and the rotational alignment of each tibial and femoral component and are risk factors for the postoperative component rotational mismatch in TKA., Competing Interests: Declaration of Competing Interest Title: Preoperative Tibiofemoral Rotational Alignment is a Risk Factor for Component Rotational Mismatch in Total Knee Arthroplasty., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Background: One of the causes of dissatisfaction following total knee arthroplasty (TKA) is abnormal knee kinematics. A newly designed bi-cruciate stabilized (BCS) TKA system has been developed to produce close-to-normal kinematics because of its anatomic tibiofemoral articular geometry and cam-post mechanism. Although BCS TKA is expected to improve patient satisfaction, no reports have described the appropriate technique or soft tissue handling required to achieve excellent satisfaction with BCS TKA. This study is to identify intraoperative surgical predictors of patient satisfaction after BCS TKA., Methods: We studied 104 knees with primary varus knee osteoarthritis that underwent BCS TKA with a navigation system retrospectively. Surgical parameters including coronal, sagittal and axial alignment and joint laxity in each compartment that affected patient satisfaction was evaluated. Satisfaction score was evaluated with use of the 2011 Knee Society Scoring system. The multivariate regression analysis included age, gender, body mass index and intraoperative parameters that correlated with satisfaction scores in the univariate analysis (P < 0.05). The current study focused on the patient satisfaction score at 1 year postoperatively and didn't evaluate the long term clinical results nor survivorship., Results: The postoperative satisfaction score was 28.6 ± 8.1. Multivariate analysis showed that medial joint laxity at 30° flexion (P = 0.003), tibial excessive external rotation alignment (P = 0,009) and tibial varus alignment (P = 0.029) were predictors of poor satisfaction score., Conclusions: When performing BCS TKA, surgeons should pay attention to maintaining proper stability of the medial compartment at mid flexion range and should avoid tibial varus and excessive external rotational alignment.

Background: This study aimed to clarify the association between types of knee arthroplasty (KA) (total knee arthroplasty (TKA) or unicompatmental knee arthroplasty (UKA)) and surgical site infection (SSI) with adjustment for various factors, using a Japanese national database., Methods: Data on 181,608 patients who underwent unilateral primary KA for osteoarthritis from 2010 to 2017 were obtained from the Japanese Diagnosis Procedure Combination database. SSI was identified based on International Classification of Diseases 10th Revision codes. Deep SSI (i.e. periprosthetic joint infection (PJI)) was identified as SSI treated with surgical procedures. Multivariable logistic regression analyses for SSI and PJI were performed, in which dependent variables included types of KA, patient backgrounds (sex, age, body mass index (BMI), smoking status, comorbidities), and seasonality., Results: Eight percent of analyzed patients underwent UKA, while 92% underwent TKA. The proportions of SSI and PJI after UKA were 0.9% and 0.3%, respectively, both of which were lower than those after TKA (1.9% and 0.6%) (P < 0.001). Multivariable analyses showed lower proportions of SSI for UKA (adjusted odds ratio, 0.47; 95% confidence interval, 0.37-0.60; P < 0.001) and PJI (adjusted odds ratio, 0.47; 95% confidence interval, 0.34-0.65; P < 0.001) than TKA. Other factors associated with both SSI and PJI included male sex, BMI >30 kg/m 2 , renal dysfunction and summer season., Conclusion: UKA was associated with lower proportions of SSI and PJI than TKA. Surgeons should carefully consider the indication of UKA before performing TKA, especially in patients with knee unicompartmental osteoarthritis who are at a high risk for SSI or PJI., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Background: Of all the intraoperative kinematic parameters recorded using navigation systems, femorotibial rotational alignment is reportedly associated with the clinical outcomes of cruciate retaining and posterior stabilized (PS) total knee arthroplasty (TKA). However, to our knowledge, there are no reports on the relationship of newly designed bi-cruciate stabilized (BCS) TKA and intraoperative rotational kinematics. We aimed to clarify and compare the relationships between the intraoperative kinematics and clinical outcomes of BCS TKA and PS TKA., Methods: We compared the intraoperative rotational kinematics and clinical outcomes at two years postoperatively of 56 BCS TKA patients and 55 PS TKA patients. Further, we evaluated the relationship between the femorotibial rotational kinematics and clinical outcomes., Results: The maximum flexion angle and the pain subscale of the Knee injury and Osteoarthritis Outcome Score (KOOS) in BCS TKA were significantly better than those in PS TKA. The intraoperative kinematic data of BCS TKA showed "screw-home" movement, while that of PS TKA did not show this movement. The rotational angular differences between at maximum flexion angle and at 60° flexion of BCS TKA showed positive correlations with the improvement of KOOS pain, symptom, activity of daily living and sports subscales. The rotational angular differences between at maximum flexion angle and at 30° flexion in PS TKA showed positive correlations with the maximum flexion angle., Conclusion: Intraoperative femorotibial rotational kinematics and its influence on the clinical outcomes were different between BCS and PS TKA. BCS TKA showed more normal-like kinematics and better clinical results than PS TKA., Competing Interests: Declaration of competing interest Our institute has received donations for research from Smith and Nephew and Stryker., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Background: There are no previous reports on the complications around the femoral component of cementless Oxford unicompartmental knee arthroplasty (UKA). However, we experienced two cases of femoral migration to the proximal side, which caused bearing dislocations after cementless Oxford UKA., Case Presentation: Case1. In an 82-year-old woman, bearing dislocation occurred 13 months postoperatively because of femoral migration that was resolved with an revision surgery to cemented component and thicker mobile insert. Case2. In a 52-year-old man, first bearing dislocation occurred 7 months postoperatively. Five months after revising the insert to a thicker one, another dislocation occurred mainly because of the femoral migration. Eventually, a revision to total knee arthroplasty was necessary., Conclusions: The inferred main reasons of femoral migration of cementless Oxford were osteoporosis for the first case and early return to high performance sports activity for the second case. Although several merits of using cementless prosthesis, particularly better fixation and lesser radiolucency than cemented prosthesis, have been reported, surgeons should pay attention to the patient's bone quality and advise a slow return to high-level physical activity.

Background: Femorotibial rotational mismatch has been reported to cause unsatisfactory outcomes after total knee arthroplasty. However, to our knowledge, no previous reports have described the relationship between the femorotibial rotational mismatch and clinical outcomes of Oxford unicompartmental knee arthroplasty (UKA)., Methods: In total, we studied 52 knees with primary varus knee osteoarthritis that underwent Oxford UKA with a navigation system. Tibial component internal rotation angles relative to the femoral component at extension and flexion angle of 90° were measured using a navigation system. We evaluated the relationship between the clinical outcomes and femorotibial rotational mismatch angles. Additionally, we evaluated the relationships between the outcomes and rotational alignments of the femur and tibial components measured by computed tomography (CT)., Results: The tibial component internal rotational angle relative to the femoral component was significantly larger at a flexion angle of 90° than on extension (P < .001) and showed negative correlations with the Knee Society Functional Score and the pain and sports subscales of the Knee Injury and Osteoarthritis Outcome Score. Rotational alignment of the femur and tibial components on computed tomography was not associated with clinical outcomes., Conclusion: The tibial component internal rotational angle relative to the femoral component in the flexion position was negatively correlated with clinical outcome. Surgeons should pay attention to a rotational mismatch between components in the flexion position during the Oxford UKA procedure. Navigation systems will be effective in reducing the femorotibial rotational mismatch and improving clinical outcomes., Competing Interests: Declaration of competing interest The authors confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome., (Copyright © 2020 Elsevier B.V. All rights reserved.)

There have been many reports on the clinical outcomes of Oxford unicompartmental knee arthroplasty (UKA); however, none have investigated the influence of flexion angle after UKA on clinical outcomes. The objective of this study was to clarify the relationship between outcomes and the postoperative maximum flexion angle and reveal the necessary factors for maximum flexion angle ≥ 140 degrees which is considered necessary for Asian populations. We categorized 212 UKA patients into the following three groups based on the postoperative maximum flexion angle: group 1 had flexion angle ≥ 140 degrees in 80 patients (38%), group 2 had 130 degrees ≤ flexion angle < 140 degrees in 80 patients (38%), and group 3 had flexion angle < 130 degrees in 52 patients (24%). Furthermore, we compared the postoperative clinical outcomes between the three groups and conducted multivariable regression analyses to assess parameters affecting the flexion angle. Postoperative Knee Society function scores for group 1 was significantly higher than for group 3. Group 1 had higher mean knee injury and osteoarthritis outcome scores (KOOS) in all subscales and significantly higher KOOS scores in the sports and quality of life subscales compared with group 2 and in all subscales compared with group 3. Multivariable logistic regression showed that preoperative flexion angle and tibial component posterior slope were associated with maximum flexion angle ≥ 140 degrees. Maximum flexion angle ≥ 140 degrees after Oxford UKA improved the clinical results, particularly for patient-reported outcomes. Furthermore, the tibial posterior slope was an important factor in achieving maximum flexion angle ≥ 140 degrees in UKA patients., Competing Interests: None declared., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Background: We evaluated the effect of the anteroposterior (AP) axis of the proximal tibia defined at the cutting surface using an image-free navigation system in total knee arthroplasty., Methods: This prospective study included 68 patients (79 knees) who underwent total knee arthroplasty. The tibial AP axis was registered in the navigation system with reference to Akagi's line, connecting the middle of the posterior cruciate ligament to the medial border of the patellar tendon attachment at the tibial joint surface. After proximal tibial osteotomy, the AP axis was replicated as the AP(O) axis. We measured the difference between the AP axis defined at the joint surface and the AP(O) axis defined at the osteotomy surface., Results: The AP(O) axis at the osteotomy surface internally rotated 2.0° to the AP axis at the joint surface, and the AP(O) axis outlier (difference to AP axis: >3°) occurred in 54% (43 knees). In the >3° malrotation group, internal malrotation occurred in 37% (30 knees) and external malrotation occurred in 17% (13 knees). In the outlier analysis, the left knees were significantly found in the internal outlier group., Conclusion: The tibial AP axis, connecting the middle of the posterior cruciate ligament to the medial border of the patellar tendon attachment defined at the tibial joint surface, could not be replicated at the tibial osteotomy surface. If the tibial components were set depending only on the AP axis defined at the osteotomy surface, the tibial components could internally rotate and have more outliers, especially in the left knees., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Meniscal bearing dislocation while rolling over in sleep has never been reported in Oxford unicompartmental knee arthroplasty (UKA). This study reports two cases of meniscal bearing dislocation into the intercondylar ridge while rolling over in sleep. In the case of one patient, closed reduction of the bearing was performed, and the use of a knee brace was effective in preventing re-dislocation. In the second patient, closed reduction was possible; however, bearing dislocation was repeated. Therefore, revision surgery was performed by replacing the tibial component and using a thicker bearing. The common features in dislocation during rolling over while sleeping in both cases were dislocation into the intercondylar ridge, the combination of small femur and AA-size tibia components, and osteonecrosis. As determined by intraoperative testing, valgus position of the knee while rolling over in sleep could induce bearing dislocation into the intercondylar ridge. LEVEL OF EVIDENCE: Retrospective case series, Level IV., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Computer-assisted surgery is now a common procedure in the field of orthopedics. We present two patients who developed myositis ossificans, a rare complication after navigated knee surgery. Due to careful follow-up and conservative treatment, surgical excision was avoided in both patients with good clinical results. Development of myositis ossificans after navigated knee surgery should be considered in cases of thigh pain and restricted range of motion of the knee., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Background: Bone cutting error can be one of the causes of malalignment in unicompartmental knee arthroplasty (UKA). The amount of cutting error in total knee arthroplasty has been reported. However, none have investigated cutting error in UKA. The purpose of this study was to reveal the amount of cutting error in UKA when open cutting guide was used and clarify whether cutting the tibia horizontally twice using the same cutting guide reduced the cutting errors in UKA., Methods: We measured the alignment of the tibial cutting guides, the first-cut cutting surfaces and the second cut cutting surfaces using the navigation system in 50 UKAs. Cutting error was defined as the angular difference between the cutting guide and cutting surface., Results: The mean absolute first-cut cutting error was 1.9° (1.1° varus) in the coronal plane and 1.1° (0.6° anterior slope) in the sagittal plane, whereas the mean absolute second-cut cutting error was 1.1° (0.6° varus) in the coronal plane and 1.1° (0.4° anterior slope) in the sagittal plane. Cutting the tibia horizontally twice reduced the cutting errors in the coronal plane significantly (P<0.05)., Conclusion: Our study demonstrated that in UKA, cutting the tibia horizontally twice using the same cutting guide reduced cutting error in the coronal plane., (Copyright © 2014 Elsevier B.V. All rights reserved.)