Preoperative Joint Line Convergence Angle as an Indicator of Clinical Outcomes and Accuracy of Alignment Correction After Double-Level Osteotomy.

Background: The relationship between postoperative alignment and clinical outcomes after double-level osteotomy (DLO) has not been clarified. Purpose: To examine the radiological and clinical outcomes after DLO and specifically evaluate the influence of the joint-line convergence angle (JLCA) on the accuracy of alignment correction and surgical outcomes. Study Design: Case-control study; Level of evidence, 3. Methods: Included were 74 knees in 51 patients (mean age, 61.0 years) who underwent DLO for varus osteoarthritic knees and who had a minimum of 2 years of follow-up. The target hip-knee-ankle angle (HKAA) for the intended limb alignment was set to 1° valgus. The lateral distal femoral angle, medial proximal tibial angle, JLCA, and HKAA were measured on preoperative and postoperative radiographs. Outliers in alignment correction were defined as a deviation of ≥3° from the originally intended HKAA. Clinical outcomes were assessed using the Knee injury and Osteoarthritis Outcome Score (KOOS). In the data analysis, the influence of the radiological parameters on the postoperative outcomes was statistically assessed. Results: Radiological and clinical evaluation at 2-year follow-up showed significant improvement from preoperative values (P < .001). The HKAA was corrected from 13.4°± 3.0° varus preoperatively to 0.5°± 2.8° varus at 2 years, indicating a slight undercorrection. Regarding clinical outcomes, significant pre- to postoperative improvement was found on the KOOS (from 185.0 ± 71.2 to 387.9 ± 70.5; P < .001). Overall, 22 of the 74 knees (29.7%) were deemed to be outliers at the 2-year follow-up (19 knees [25.7%] in undercorrection, 3 knees [4.1%] in overcorrection). Postoperative KOOS values were significantly worse in the outliers than in the nonoutliers (344.4 ± 77.7 vs 405.8 ± 59.3; P < .001), and both pre- and postoperative JLCA was significantly larger in the outlier group. The receiver operating characteristic curve analysis indicated a preoperative cutoff JLCA of 6.0° for predicting postoperative alignment outliers. Conclusion: A preoperative JLCA of ≥6° was found to be a significant prognostic factor affecting the radiological and clinical outcomes after DLO for varus osteoarthritic knees by compromising the accuracy of deformity correction, resulting in suboptimal postoperative alignment.

Adjusted planning based on the joint line convergence angle improves correction accuracy in the standing position after opening wedge high tibial osteotomy.

BACKGROUND: Postoperative change of the joint line convergence angle (JLCA) is known to be a factor affecting correction error in opening wedge high tibial osteotomy (OWHTO). The purpose of this study was to assess whether preoperative planning that considers change of the JLCA can achieve accurate correction in the standing position after OWHTO. METHODS: OWHTO was performed for 109 knees with osteoarthritis of the knee. The amount of angular correction was planned aiming to achieve mechanical valgus of 5° in 55 knees (conventional planning), and it was adjusted in 54 knees (adjusted planning) according to the preoperative JLCA as follows: not changed with JLCA ≤ 3°; decreased 1° with JLCA 4-6°; decreased 2° with JLCA 7-8°; and decreased 3° with JLCA ≥ 9°. The hip-knee-ankle (HKA) angle, JLCA, and medial proximal tibial angle (MPTA) were measured on standing long-leg radiographs. Correction error ≤ 2º was defined as the acceptable range, and correction error > 2º was defined as an outlier. RESULTS: The conventional planning group had a significantly greater postoperative HKA angle than the adjusted planning group (6.1º and 4.9º, respectively). The mean JLCA decreased from 4.8º to 2.6º in the conventional planning group and from 4.6º to 2.7º in the adjusted planning group. The conventional planning group had significantly greater postoperative MPTA than the adjusted planning group (96.2º and 94.7º, respectively). The rate of outliers with correction error > 2º was significantly lower in the adjusted planning group (9%) than in the conventional planning group (24%). The rate of the MPTA > 95º was significantly lower in the adjusted planning group (30%) than in the conventional planning group (69%). CONCLUSIONS: This study demonstrated that preoperative planning with adjustment of the correction angle according to the preoperative JLCA improved correction accuracy in the standing position after OWHTO.

Joint line convergence angle is the most associated alignment factor with the severity of medial knee osteoarthritis.

Purpose: The purpose of this study was to evaluate the relationship between the joint line convergence angle (JLCA) and the severity of medial knee osteoarthritis (OA). We hypothesise that JLCA is the most associated factor with the severity of medial knee OA. Methods: This retrospective study included a total of 202 knees that underwent either high tibial osteotomy or medial meniscus repair/partial resection. Kellgren-Lawrence grade and hip-knee-ankle angle (HKAA), mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA) and JLCA were assessed from preoperative radiographs. Medial meniscus extrusion (MME) was measured using preoperative magnetic resonance imaging. The International Cartilage Research Society (ICRS) grade on the medial femoral condyle and medial tibial plateau were also assessed. The relationships between JLCA and Kellgren-Lawrence grades and MME and ICRS grades were analysed using Spearman's correlation test and regression analysis. Results: The JLCA was correlated with the Kellgren-Lawrence grade (R = 0.765, p < 0.001), MME (R = 0.638, p < 0.001), ICRS grade on the MFC (R = 0.586, p < 0.001) and the MTP (R = 0.586, p < 0.001). Regression analysis showed that age (p = 0.002) and JLCA (p < 0.001) were associated with Kellgren-Lawrence grade. Furthermore, JLCA was related to ICRS grade on the MFC (p < 0.001) and MTP (p < 0.001). Conclusion: The JLCA, reflecting radiological severity, meniscus status, and cartilage lesion, was the most associated alignment parameter in the severity of medial knee OA. The JLCA may be beneficial for quantitative assessment of medial knee OA. Level of Evidence: Level III, retrospective cohort study.

Postoperative patient-reported outcome measures after medial open-wedge high tibial osteotomy was improved by decreased joint line convergence angle.

PURPOSE: To evaluate the relationship between pre- and postoperative joint line convergence angle (JLCA) changes and patient-reported outcome measures related to medial open-wedge high tibial osteotomy (MOWHTO). METHODS: Sixty-one patients (71 knees) who underwent MOWHTO were examined. Preoperative and 2-year postoperative radiographic parameters (hip-knee-ankle angle, weight-bearing line ratio, medial proximal tibial angle and JLCA) were measured, and knee injury and osteoarthritis outcome scores (KOOS) were assessed. Patients were divided into two groups: group D (decreased JLCA compared with preoperative status) included 44 knees with a ΔJLCA < 0° and group I (increased JLCA and no-change JLCA compared with preoperative status) included 27 knees with a ΔJLCA ≥ 0°. KOOS sub-scores and the proportion of patients whose improvement exceeded the minimum clinically important difference (MCID) were compared between both groups using Student's t tests, Mann-Whitney U tests and chi-square tests. Multiple regression analysis was performed to determine the factor that had an influential effect on the postoperative KOOS total. RESULTS: Significant differences in 2-year postoperative KOOS were observed between the two groups, including total, symptom, pain and activities of daily living scores. Group D had significantly more patients who achieved MCID for both KOOS symptoms and pain scores than group I did. Multivariate analysis indicated that JLCA change and body mass index were significantly associated with the postoperative KOOS total. CONCLUSION: Patients with decreased JLCA had better 2-year post-MOWHTO KOOS and better symptom and pain improvements. Therefore, strategies that reduce JLCA are crucial to improving clinical outcomes, and efforts should be made to improve JLCA in surgical techniques. LEVEL OF EVIDENCE: Level Ⅳ, Case series.

The posterior tibial slope affects the measurement reliability regarding the radiographic parameter of the knee.

BACKGROUND: Posterior tibial slope (PTS) exhibits considerable variability among individuals and is anticipated to influence the accuracy of radiographic measurements related to the knee. Despite this potential impact, there is a lack of prior research investigating how PTS affects the accuracy of these measurements. Therefore, this study aimed to investigate the effect of PTS on the measurement reliability regarding the radiographic parameter of the knee. METHODS: The medical records of patients who took full-length anteroposterior radiographs of the lower limb between January 2020 and June 2022 were evaluated retrospectively. Radiographic parameters related to the knee joint characteristics such as osteoarthritis grade, hip-knee-ankle angle, weight-bearing line ratio, medial proximal tibial angle (MPTA), lateral distal femoral angle, joint-line convergence angle (JLCA), and PTS were measured. Subjects were classified into 3 groups according to PTS (group A, PTS < 4°; group B, PTS ≥ 4° and < 8°; group C, PTS ≥ 8°), and the measurement reliability for the radiographic variables was compared between groups. The intra- and inter-observer agreements were assessed using the kappa coefficients, intra-class correlation coefficients (ICC), and Bland-Altman plots. RESULTS: A total of 175 limbs (86 patients) were included in this study. As the intra- and inter-observer reliability for PTS ranged over 0.9, grouping was performed based on the average of the measured PTSs. The inter-observer reliability of the MPTA and JLCA decreased as the PTS increased (ICCs for MPTA in Groups A, B, and C: 0.889, 0.796, and 0.790, respectively; ICCs for JLCA in Groups A, B and C: 0.916, 0.859, and 0.843, respectively), whereas there were no remarkable differences in other variables. Similar trends were observed in the comparisons of intra-observer reliability and Bland-Altman plots also showed consistent results. CONCLUSION: The larger the PTS, the lower the measurement reliability regarding the radiographic parameters of the knee that includes the joint line, such as MPTA and JLCA. Given the occasional challenge in accurately identifying the knee joint line in patients with a relatively large PTS, careful measurement of radiographic parameters is crucial and utilizing repetitive measurements for verification may contribute to minimizing measurement errors.

The tipping point in medial opening wedge high tibial osteotomy relates to the shape of the proximal tibia more than to lower limb alignment correction.

PURPOSE: The tipping point (TP) of the knee joint is the centre of rotation of the joint in the coronal plane. This study aimed to define the TP in medial opening wedge high tibial osteotomy (MOWHTO). METHODS: Data from 154 consecutive patients with varus knee malalignment, who underwent MOWHTO between 2017 and 2021, was retrospectively reviewed. The degree of preoperative osteoarthritis (OA), using the Kellgren-Lawrence (KL) grading system, was recorded. Long-leg standing radiographs were used to record the alignment parameters, including the hip-knee-ankle angle (HKA), the mechanical lateral distal femoral angle (mLDFA), the medial proximal tibial angle (MPTA), the joint line convergence angle (JLCA) and the joint line obliquity (JLO) angle. Postoperative Tegner activity scores, Western Ontario and McMaster University Scores and patients' satisfaction were recorded. To define the TP, the relationship of all variables to Δ JLCA (absolute difference between preoperative to postoperative JLCA values) was analysed. Linear regression was employed for Δ JLCA to preoperative JLCA and postoperative and Δ MPTA (absolute difference between preoperative and postoperative values). K-means clustering was used to partition observations into clusters, in which each observation belongs to the cluster with the nearest mean serving as a prototype of the cluster, and analysed if there was any specific threshold influencing Δ JLCA. After defining the TP, further subanalysis of the TP based on the preoperative KL OA grade and analysis of variance of this TP to the KL OA grade was performed. RESULTS: A total of 154 patients (77.9% males and 22.1% females) were included. The mean age was 48.2 ± 11 years, and the mean body mass index was 27.1 ± 4 kg/m2. Preoperatively, 26 (16.9%) patients had KL grade IV OA. The mean preoperative and postoperative JLCA and the significance of their relation to Δ JLCA were 2.6° ± 1.8° (p < 0.0001) and 1.9° ± 1.8° (p = 0.6), respectively. The mean Δ JLCA was 1.4° ± 1.5°. The mean pre- and postoperative MPTA and the significance of their relation to Δ JLCA were 84.6 ± 2.2 (p = 0.005) and 91.8 ± 2.5 (p < 0.0007), respectively. The mean Δ MPTA was 7.2 ± 2.3 (p = 0.3). The mean preoperative and postoperative HKA and the significance of their relation to Δ JLCA were 174.6 ± 2.5 (p = 0.2) and 181.9 ± 2.4 (p = 0.7), respectively. The overall linear regression for Δ JLCA was statistically significant for preoperative JLCA (R2 = 0.3, p < 0.0001) and postoperative MPTA (R2 = 0.09, p = 0.0001) and statistically insignificant for Δ MPTA (R2 = 0.01, p = 0.2) and postoperative HKA (R2 = 0.04, p = 0.7). MPTA > 91.5° was the optimal threshold dividing this series data set between substantial and nonsignificant Δ JLCA. CONCLUSION: In this study, the main predictive factors for intra-articular correction (Δ JLCA) after MOWHTO were the preoperative value of JLCA and the postoperative value of MPTA. A value of 92° for postoperative MPTA is potentially the optimal threshold to predict intra-articular correction. LEVEL OF EVIDENCE: Level IV, retrospective cohort study.

Change of joint line convergence angle and other coronal alignments after total hip arthroplasty.

BACKGROUND: The purpose of this study was to determine the unloading effect of total hip arthroplasty (THA) on the ipsilateral knee joint through the joint line convergence angle (JLCA) change and determine the changes in other coronal radiographic parameters after THA, and evaluate the sensitivity of JLCA. PATIENTS AND METHODS: We retrospectively assessed 70 patients who underwent unilateral THA. Hip parameters such as neck shaft angle (NSA), neck length, and femoral offset and coronal alignment parameters of the lower extremity such as hip-knee-ankle angle (HKA), femur length, mechanical lateral distal femoral angle (mLDFA), JLCA, medial proximal tibial angle (MPTA), lateral distal tibial angle (LDTA), and plafond talus angle (PTA) were measured in the operative and non-operative sides. We compared all hip and coronal alignment parameters between before and 1 year after THA, and the amount of standardized changes (Δ) between all hip and coronal alignment parameters on the operative side, respectively. RESULTS: All mean hip and coronal alignment parameters on the operative side changed significantly 1-year after THA; however, those on the non-operative side did not. On the operative side, mean JLCA and PTA changed in the direction of closing the joint lateral space, from 1.81° and 0.47° to 1.22° and 0.11°, respectively (p<0.001 and 0.046, respectively). Mean NSA, HKA, and mLDFA changed in the valgus direction, from 129.39°, 2.62°, and 86.69° to 133.54°, 1.53°, and 85.91°, respectively (p<0.001). Mean femoral offset, neck length, and femur length increased from 36.45mm, 47.83mm, and 429.20mm to 39.85mm, 55.06mm, and 436.33mm, respectively (p<0.001). Mean MPTA and LDTA increased from 85.43° and 87.50° to 86.73° and 90.38, respectively (p<0.001). JLCA was more vulnerable to change than HKA, femur length, mLDFA, MPTA, and PTA (p<0.05). DISCUSSION: JLCA change on the operative side was more sensitive than changes of other coronal alignments after THA. According to the cohort, THA might have an unloading effect on the medial compartment of the knee joint. LEVEL OF EVIDENCE: IV; retrospective case-control and cohort studies.

Influence of different convergence angles of abutment teeth and cement spaces on internal adaptation of anterior CAD-CAM fixed dental prostheses.

PURPOSE: The aim of this study was to investigate the influence of different convergence angles of abutment teeth and different cement spaces on internal adaptation of anterior fixed dental prostheses (FDPs) fabricated with a computer-aided design-computer-aided manufacturing (CAD-CAM) system. METHODS: Composite resin FDPs for 99 standardized maxillary central incisors were fabricated according to nine parameters: three total convergence angles (4 [DG4], 12 [DG12], and 20 degrees [DG20]) and three cement space settings (10 [CS10], 50 [CS50], and 90 µm [CS90]). Internal space values were measured with a cement space replica technique. The Kruskal-Wallis and Steel-Dwass tests were used to evaluate differences in the total convergence angles and luting agent spaces, respectively (α = 0.05). RESULTS: For all three cement spaces tested, the median marginal gap values between abutment teeth and FDPs decreased significantly as the total convergence angle increased (P < 0.05). For the CS10 and CS50 groups, the internal space values at the axial area increased significantly as the total convergence angles increased (P < 0.05). CONCLUSION: Total convergence angles of the abutment teeth and cement spaces affected the marginal and internal adaptation of anterior FDPs fabricated with a CAD-CAM system.

Preoperative joint line obliquity, a newly identified factor for overcorrection, can be incorporated into a novel preoperative planning method to optimise alignment in high tibial osteotomy.

PURPOSE: The aim of this study was to analyse the factors associated with additional postoperative alignment changes after accurate bony correction by selecting only patients with well-performed bony correction as planned and develop a method of incorporating significant factors into preoperative planning. METHODS: Among 104 consecutive patients who underwent medial open wedge high tibial osteotomy (MOWHTO) between October 2019 and July 2022, 61 with well-performed bony corrections were retrospectively reviewed. The major criterion for well-performed bony correction was a difference of <1° between the simulated medial proximal tibial angle (MPTA) and the actual postoperative MPTA as measured in three dimensions. Radiographic parameters, such as the joint line convergence angle (JLCA) and joint line obliquity (JLO), were measured preoperatively and postoperatively, utilising standing and supine whole lower extremity anteroposterior, valgus and varus stress radiographs. Multiple linear regression analysis identified the factors affecting alignment changes, and a prediction model was developed. A method for applying this prediction model to preoperative planning was proposed. RESULTS: Preoperative JLCA on standing (preJLCAstd ), preoperative JLCA on 0° valgus stress radiograph (vgJLCA0 ), and preoperative JLO (preJLO) were significantly correlated with JLCA change (∆JLCA) (p < 0.001, p < 0.001, p = 0.006). The prediction model was estimated as ∆JLCA = 0.493 × (vgJLCA0 ) - 0.727 × (preJLCAstd ) + 0.189 × (preJLO) - 1.587 in. (R = 0.815, modified R2 = 0.646, p < 0.001). The proposed method resulted in a reduced overcorrection rate (p = 0.003) and an improved proportion of acceptable alignments (p = 0.013). CONCLUSION: PreJLCAstd , vgJLCA0  and preJLO can be used to estimate ∆JLCA. PreJLO was recently identified as a significant factor associated with additional alignment changes. Utilising the proposed preoperative planning and a prediction model with these factors shows promise in calibrating postoperative alignment after MOWHTO. LEVEL OF EVIDENCE: Level III, retrospective cohort study.

The joint line convergence angle (JLCA) correlates with intra-articular arthritis.

PURPOSE: Knees with unicompartmental varus osteoarthritis (OA) usually display a combination of tibiofemoral bony deformity and increased joint line convergence angle (JLCA). The JLCA is a product of intra-articular deformity and lateral soft tissue laxity. This study aims to define the correlation between the JLCA and progression of OA. METHODS: A retrospective radiological analysis of 501 patients, who underwent either high tibial osteotomy (HTO) or unicompartmental knee arthroplasty (UKA), was performed. The preoperative OA grade was reported based on the Ahlbäck and the Kellgren-Lawrence (KL). The hip-knee-ankle angle (HKA), the medial proximal tibial angle (MPTA), the mechanical lateral distal femoral angle (mLDFA) and the joint line convergence angle (JLCA) were recorded. The primary outcome was the relationship between the JLCA values and the OA grade. The secondary outcomes were comparing the JLCA and other alignment parameter values between HTO and UKA groups. RESULTS: A total of 501 (59.3% females n = 297) cases were included, comprising 293 cases of HTO and 208 cases of UKA. Patients had a mean age of 57.63 ± 8.97 years, a mean BMI of 28.37 ± 7.39 kg/m2. Patients with Ahlbäck grade 2 represented 49.3% of all patients (n = 247) and patients with KL grade 3 represented 54.7% of all patients (n = 274). A high JLCA was observed in both groups. The reported mean JLCA in the UKA group was 3.69 ± 2.1°, and in the HTO group was 2.93 ± 1.82. There was a significant association between the increase in the JLCA and the progression of OA based on both the Ahlbäck and KL grades (both p values < 0.001). The mean JLCA in patients with Ahlbäck grades 1 and 4 was 1.48 ± 1.32°, and 7 ± 0.93°, respectively. The mean JLCA in patients with KL grades 1 and 4 was 1.77 ± 1.42°, and 4.89 ± 1.73°, respectively. The mean recorded preoperative HKA angle in the UKA group was 175.06 ± 3.08°, and in the HTO group was 173.26 ± 3.02°, whereas the mean MPTA was 88.63 ± 1.72° for the UKA group and 89.31 ± 2.29° for the HTO group. CONCLUSION: The JLCA progressively increases with osteoarthritis progression in patients with unicompartmental varus knee osteoarthritis. The JLCA can potentially be used as a grading parameter for osteoarthritis progression akin to Ahlbäck and Kellgren-Lawrence grading systems.

Postoperative change in the joint-line convergence angle is associated with inaccurate correction in open-wedge high tibial osteotomy.

OBJECTIVE: Accurate correction is a prerequisite for the favorable outcomes of open-wedge high tibial osteotomy (OWHTO). However, previous studies have reported disappointing results regarding correction accuracy despite the use of intra-operative navigation, which implies that a certain factor other than bony components is involved in the inaccurate correction (mainly overcorrection). The joint-line convergence angle (JLCA) can represent soft tissue effects in OWHTO. This study tried to determine whether the postoperative change in the JLCA (∆JLCA) led to inaccurate correction. METHODS: Medical records of 78 OWHTO patients from 2005 to 2021 were retrospectively reviewed. The hip-knee-ankle angle (HKA) was measured with a positive value indicating varus alignment. Inaccurate correction was defined as postoperative HKA < - 3°. The JLCA was measured before and 6 months after surgery on long-standing hip-to-ankle radiographs, and ∆JLCA was defined as the difference between the preoperative and 6-month postoperative JLCAs. ∆JLCA was compared between the accurate correction group and the inaccurate correction group, and a receiver operating characteristic (ROC) curve was used to obtain the cutoff ∆JLCA at which the sensitivity and the specificity for inaccurate correction were maximized. Clinical outcomes were also compared between the groups using the knee injury and osteoarthritis outcome score (KOOS) at final follow-up (60.9 ± 53.3 months postoperatively). RESULTS: Of the 78 patients, inaccurate correction was noted in 10 patients. The overall preoperative and postoperative HKAs were 7.0 ± 3.1° and - 0.4 ± 1.5°, respectively. The accurate correction group and the inaccurate correction group had a difference in ∆JLCA (p = 0.010). However, no significant difference was found in the preoperative HKA (p = 0.529). An ROC curve showed that the cutoff ∆JLCA was 1.9°. In the patients having ∆JLCA ≥ 1.9°, the mean JLCA was 4.9 ± 1.6° preoperatively and 1.7 ± 1.2° postoperatively. In the other patients having ∆JLCA < 1.9°, the mean preoperative and postoperative JLCA were 2.5 ± 1.8° and 2.3 ± 1.8°, respectively. The difference in the preoperative JLCA was significant (p < 0.001). The postoperative KOOS subscales did not differ according to correction accuracy. CONCLUSION: Inaccurate correction in OWHTO, specifically valgus overcorrection, is associated with large ∆JLCA which represents the postoperative change of soft tissue effects. Overcorrection should be checked in cases of large preoperative JLCAs.

An Angular Radial Extended Interaction Amplifier at the W Band.

In this paper, an angular radial extended interaction amplifier (AREIA) that consists of a pair of angular extended interaction cavities is proposed. Both the convergence angle cavity and the divergence angle cavity, which are designed for the converging beam and diverging beam, respectively, are investigated to present the potential of the proposed AREIA. They are proposed and explored to improve the beam-wave interaction capability of W-band extended interaction klystrons (EIKs). Compared to conventional radial cavities, the angular cavities have greatly decreased the ohmic loss area and increased the characteristic impedance. Compared to the sheet beam (0°) cavity, it has been found that the convergence angle cavity has a higher effective impedance and the diverging beam has a weaker space-charge effect under the same ideal electron beam area; the advantages become more obvious as the propagation distance increases. Particle-in-cell (PIC) results have shown that the diverging beam (8°) EIA performs better at an output power of 94 GHz under the condition of lossless, while the converging beam (-2°) EIA has a higher output power of 6.24 kW under the conditions of ohmic loss, an input power of 0.5 W, and an ideal electron beam of 20.5 kV and 1.5 A. When the loss increases and the beam current decreases, the output power of the -2° EIA can be improved by nearly 30% compared to the 0° EIA, and the -2° EIA has a greatly improved beam-wave interaction capacity than conventional EIAs under those conditions. In addition, an angular radial electron gun is designed.

Deep learning-based landmark recognition and angle measurement of full-leg plain radiographs can be adopted to assess lower extremity alignment.

PURPOSE: Evaluating lower extremity alignment using full-leg plain radiographs is an essential step in diagnosis and treatment of patients with knee osteoarthritis. The study objective was to present a deep learning-based anatomical landmark recognition and angle measurement model, using full-leg radiographs, and validate its performance. METHODS: A total of 11,212 full-leg plain radiographs were used to create the model. To train the data, 15 anatomical landmarks were marked by two orthopaedic surgeons. Mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), joint line convergence angle (JLCA), and hip-knee-ankle angle (HKAA) were then measured. For inter-observer reliability, the inter-observer intraclass correlation coefficient (ICC) was evaluated by comparing measurements from the model, surgeons, and students, to ground truth measurements annotated by an orthopaedic specialist with 14 years of experience. To evaluate test-retest reliability, all measurements were made twice by each measurer. Intra-observer ICCs were then derived. Performance evaluation metrics used in previous studies were also derived for direct comparison of the model's performance. RESULTS: Inter-observer ICCs for all angles of the model were 0.98 or higher (p < 0.001). Intra-observer ICCs for all angles were 1.00, which was higher than that of the orthopaedic specialist (0.97-1.00). Measurements made by the model showed no significant systemic variation. Except for JLCA, angles were precisely measured with absolute error averages under 0.52 degrees and proportion of outliers under 4.26%. CONCLUSIONS: The deep learning model is capable of evaluating lower extremity alignment with performance as accurate as an orthopaedic specialist with 14 years of experience. LEVEL OF EVIDENCE: III, retrospective cohort study.

Effect of bone morphology of the tibia plateau on joint line convergence angle in medial open wedge high tibial osteotomy.

BACKGROUND: Change in the joint line convergence angle (JLCA) of the knee after high tibial osteotomy (HTO) is difficult to predict accurately. Given that any change in JLCA is intra-articular, the shape of the articular surface, including the bone morphology of the proximal tibia, may affect the alignment of the knee joint postoperatively. The purpose of this study was to investigate the relationship between the shape of the tibial plateau and postoperative alignment of the knee joint by focusing on changes in JLCA. METHODS: One hundred and nine knees that underwent HTO were retrospectively reviewed. The shape of the tibial plateau was classified based on the slope of the medial and lateral articular surfaces as depressed, flat (within 3 degrees), or convex (pagoda-like). The relationship between the shape of the tibial plateau and radiological parameters was investigated. RESULTS: The shape of the tibial plateau was depressed in 38 knees, flat in 52 knees, and pagoda-like in 19 knees. There was a moderate correlation between the postoperative change in JLCA and the preoperative hip-knee-ankle angle for knees with a pagoda-shaped tibial plateau (r = 0.56) but not for the other two shapes. CONCLUSIONS: These findings suggest that knees with marked varus deformity before HTO are likely to show more change in JLCA postoperatively if the tibial plateau is pagoda-shaped than if it has a depressed or flat shape. The advantage of focusing on the bone morphology of the proximal tibia is that surgeons can easily perform visual assessment using preoperative radiograph.

Medial meniscus extrusion and varus tilt of joint line convergence angle increase stress in the medial compartment of the knee joint in the knee extension position -finite element analysis.

PURPOSE: Although it has been recognized that the medial meniscus extrusion (MME) leads to progressive cartilage loss and osteoarthritis (OA), about 20% of cases with MME had minor symptoms and poor progression of knee OA. However, it is still unclear which patients will have minimal symptoms or will not progress to degeneration. The purpose of this study is to compare the effect of the relationship between the MME and Joint line convergence angle (JLCA) on knee stress with the finite element (FE) analysis method. METHODS: The 65 year-old female was taken computer tomography (CT) from thigh to ankle. A 3-dimentional nonlinear FE model was constructed from the patient's DICOM data. We made the six models, which was different from JLCA and MME. Contact stresses on the surfaces between femoral and tibial cartilages and both side of meniscus are analyzed. RESULTS: As the JLCA or MME increased, the stress load on the medial compartment increased. The effect of MME was stronger on the femoral side, while the effect of JLCA was stronger for the tibia and meniscus. If the JLCA was tilted valgus, the stress in the medial compartment did not increase even in the presence of MME. CONCLUSIONS: This study revealed that the MME is associated with increased a stress loading on medial compartment structures. Furthermore, this change was enhanced by the varus tilt of the JLCA. In the case of valgus alignment, the contact pressure of the medial compartment did not increase so much even if with the MME. LEVEL OF EVIDENCE: Level V.

Factors Associated with Postoperative Knee Joint Line Obliquity After Medial Open Wedge High Tibial Osteotomy.

BACKGROUND: There are still few reports on factors associated with postoperative knee joint line obliquity (KJLO). PURPOSE: The purpose was to determine preoperative radiographic factors that are associated with KJLO postoperatively after open wedge high tibial osteotomy (OWHTO) using multivariable linear regression analysis and multivariable logistic regression analysis. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: A total of 60 patients with 65 varus knees who underwent OWHTO between December 2012 and June 2018 at a single institution were retrospectively enrolled in this study. The authors evaluated radiologic parameters including the weightbearing line ratio, femorotibial angle, medial proximal tibial angle, mechanical lateral distal femoral angle (LDFA), lateral distal tibial angle, joint line convergence angle (JLCA), KJLO, and ankle joint obliquity. They also categorized these radiographic parameters as preoperative and postoperative and calculated the difference (Δ) between preoperative and postoperative values. To determine which of the radiographic parameters were most associated with postoperative KJLO, multivariable linear regression analysis was performed using the stepwise method. Multivariable logistic regression analysis was used to examine the relative contribution of the preoperative radiographic parameters to an abnormal postoperative KJLO (>4°). RESULTS: In the multivariable linear regression analysis, the preoperative LDFA and JLCA showed a statistically significant correlation. Multivariable logistic regression analysis revealed that the mean preoperative LDFA was significantly larger in the group with abnormal KJLO than in the group with the control group (odds ratio, 1.84; 95% CI, 1.12-3.02; P = .02), while preoperative JLCA tended to be larger in the abnormal KJLO group than the control group but not statistically significantly different. CONCLUSION: KJLO after OWHTO was associated with preoperative LDFA and JLCA in multivariable linear regression analysis, and preoperative LDFA was the most important factor associated with abnormal KJLO after OWHTO in multivariable logistic regression analysis.

Effects of Severe Varus Deformity on Soft Tissue Balancing in Total Knee Arthroplasty.

This study aimed to establish the effect of severe varus deformity on soft tissue balance in total knee arthroplasty (TKA), which is not yet well established. We retrospectively enrolled 205 patients (270 knees) who underwent primary TKA using the measured resection technique. Four intraoperatively measured TKA gaps and gap differences were compared between the severe varus deformity group (Hip-knee-ankle [HKA] varus angle ≥ 10°) and the mild varus deformity group (HKA varus angle < 10°). Pearson's correlation analysis and multiple linear regression analysis were used to investigate the factors affecting flexion and extension gap differences (FGD and EGD). A receiver operating characteristic curve was applied to assess the cut-off value of the HKA varus angle to discriminate the rectangular gap. The FGD (1.42 ± 1.35 mm vs. 1.05 ± 1.16 mm, p = 0.019) and the EGD (1.45 ± 1.32 mm vs. 0.97 ± 1.53 mm, p = 0.006) were significantly larger in severe varus deformity group than in mild varus deformity group. The HKA varus angle was positively correlated with both FGD (r = 0.264, p < 0.001) and EGD (r = 0.319, p < 0.001) and was an influencing factor for FGD (ß = 0.232, p = 0.040) and EGD (ß = 0.229, p = 0.037). A preoperative HKA angle of 12.4° was selected as the cutoff value to discriminate between rectangular and trapezoidal gaps. Thus, the severity of varus deformity (HKA varus angle) was found to be a significant factor affecting the mediolateral gap difference in TKA. When performing TKA in a knee with an HKA varus angle ≥ 12.4°, a trapezoidal gap is more likely to be expected. Level of evidence III, case−control study.

Surgical procedures for the prevention of extension-flexion gap imbalance in total knee arthroplasty.

The purpose of this study was to identify preoperative and intraoperative factors that influence extension-flexion gap imbalance in total knee arthroplasty (TKA). Ninety-three knees undergoing TKA with the modified gap balancing technique were included. Preoperative range of motion, intraoperative extension-flexion gap balance, thickness of the resected bone and radiological parameters were investigated. The preoperative flexion contracture, bone resection thickness in the medial proximal tibia, and the medial distal femur all correlated with the extension-flexion gap balance in TKA. Bone resection thickness in the medial proximal tibia and the medial distal femur were predictive of extension-flexion imbalance.

The effect of preparation taper on the resistance to fracture of monolithic zirconia crowns.

OBJECTIVE: Monolithic zirconia crowns have become a viable alternative to conventional layered restorations. The aim of this study was to evaluate whether the taper, and thus wall thickness, of the abutment or pre-defined cement space affect the fracture resistance or fracture mode of monolithic zirconia crowns. METHODS: A model tooth was prepared with a taper of 15° and a shallow circumferential chamfer preparation (0.5 mm). Two additional models were made based on the master model with a taper of 10° and 30° using computer-aided design software. Twenty monolithic 3rd generation translucent zirconia crowns were produced for each model with pre-defined cement space set to either 30 µm or 60 µm (n = 60). The estimated cement thickness was assessed by the replica method. The cemented crowns were loaded centrally in the occlusal fossa at 0.5 mm/min until fracture. Fractographic analyses were performed on all fractured crowns. RESULTS: The load at fracture was statistically significant different between the groups (p < 0.05). The crowns with 30° taper fractured at lower loads than those with 10° and 15° taper, regardless of the cement space (p < 0.05). The fracture origin for 47/60 crowns (78%) was in the cervical area, close to the top of the curvature in the mesial or distal crown margin. The remaining fractures started at the internal surface of the occlusal area and propagated cervically. SIGNIFICANCE: The fracture resistance of the monolithic zirconia crowns was lower for crowns with very large taper compared to 10 and 15° taper even though the crown walls were thicker.

Open-wedge high tibial osteotomy using intraoperative control of joint line convergence angle with reference to preoperative supine radiograph.

INTRODUCTION: Preoperative supine joint line convergence angle (JLCA) correlates with postoperative standing JLCA. Here, we compared the radiographic and clinical outcomes of knees with preoperative JLCAs of ≥ 4° and < 4° in open-wedge high tibial osteotomy (OWHTO). We hypothesized that the postoperative coronal alignment in both groups would not be affected by a change in JLCA if this change could predict before surgery. MATERIALS AND METHODS: Eighty-four patients with medial knee osteoarthritis who underwent OWHTO were enrolled retrospectively. A weight-bearing line (WBL) ratio of 62% and a JCLA equivalent to the preoperative supine JLCA were anticipated in preoperative planning. These were intraoperatively set using an alignment rod and a radiolucent protractor under fluoroscopy. Soft tissue correction was defined as correction angle minus bone correction. The participants with preoperative JLCAs of < 4° (low-JLCA group) and ≥ 4° (high-JLCA group) were compared. RESULTS: No significant difference in the coronal alignment was found between the groups after OWHTO. No significant differences in correction angle or bone correction were found between the groups, but the soft tissue correction in the high-JLCA group was higher than that in the low-JLCA group after OWHTO (p = 0.013). CONCLUSIONS: When we controlled intraoperative JLCA, the postoperative coronal alignment was not affected by the change in JLCA and the differences in soft tissue correction between the low-JLCA and high-JLCA groups. However, overcorrection compared with the target coronal alignment remained in both groups. LEVEL OF EVIDENCE: Level III, retrospective comparative study.