Muscle characteristics of lower limb in association with physical activity in candidates of total knee arthroplasty with knee osteoarthritis.

BACKGROUND&AIMS: This study aimed to clarify the association between physical activity (PA) and physical functions, including both muscle quantity and quality of ankle plantar flexor muscles in patients with knee osteoarthritis (OA). METHODS: A retrospective cohort study was conducted with ninety-two patients with knee OA. PA, leg muscle cross-sectional area (CSA), knee strength, passive knee angle, and knee pain of the affected side were assessed. PA was assessed by the 2011 Knee Society scoring system. CSA of the quadriceps and ankle plantar flexor muscles on the affected side was measured using a computed tomography image. Based on muscle attenuation assessed with Hounsfield units (HU), the muscle quality of targeted muscle was divided into 4 groups as follows: fat tissue (-190 to -30 HU), very low-density muscle (-29 to -1 HU), low-density muscle (0 to 34 HU), and normal-density muscle (NDM, 35 to 100 HU). The CSA was obtained for each of the 4 groups. Univariate and multivariate linear regression analyses were performed to determine the factors associated with PA. RESULTS: The regression analysis revealed that higher PA was independently associated with the NDM CSA of ankle plantar flexor (ß = 0.51), higher knee extension strength (ß = 0.28), and milder knee pain (ß = -0.29) after adjustment with age, sex, height, weight, and body mass index. CONCLUSION: The present study suggested that NDM CSA of ankle plantar flexor in addition to knee function is one of the factors determining the PA in patients with knee OA.

Medial soft tissue release is also related to the anterior stability of cruciate-retaining total knee arthroplasty: a cadaveric study.

BACKGROUND: Medial soft tissue release is occasionally performed to achieve mediolateral ligament balance in total knee arthroplasty (TKA), whose sequential effect on mediolateral and anteroposterior stability remains unclear. This study aimed to quantitatively evaluate the difference in mediolateral and anteroposterior stability according to a sequential medial soft tissue release in TKA. METHODS: Cruciate-retaining TKA was performed in six cadaveric knees. Medial and lateral joint gaps, varus-valgus angle, and tibial anterior and posterior translations relative to the femur with pulling and pushing forces, respectively, were measured. All measurements were performed at full extension and 45° and 90° flexion after release of the deep medial collateral ligament (MCL) (stage 1), the posteromedial capsule (stage 2), and the superficial MCL (stage 3). Mediolateral and anteroposterior stability were compared between stages, and correlations between mediolateral and anteroposterior stability were analyzed. RESULTS: Medial joint gap significantly increased from stages 1 to 3 by 3.2 mm, 6.8 mm, and 7.2 mm at extension, 45° flexion, and 90° flexion, respectively, and from stages 2 to 3 by 3.5 mm at extension. Varus-valgus angle was varus at stage 2, which turned to valgus at stage 3 (-2.7° to 0.8°, -2.2° to 4.3°, and -5.5° to 2.5° at extension, 45° flexion, and 90° flexion, respectively). Anterior translation at 90° flexion significantly increased from stages 1 and 2 to stage 3 by 11.5 mm and 8.2 mm, respectively, which was significantly correlated with medial gap (r = 0.681) and varus-valgus angle (r = 0.495). CONCLUSIONS: Medial soft tissue release also increased tibial anterior translation as well as medial joint gap, and medial joint gap and tibial anterior translation were significantly correlated. Surgeons should be careful not to create too large medial joint gap and tibial anterior translation in flexion by excessive medial release up to the superficial MCL for achieving an equal mediolateral joint gap in extension.

Association of Undercorrection With Residual Proinflammatory Gene Expressions and Clinical Outcomes After Medial Open Wedge Proximal Tibial Osteotomy.

BACKGROUND: Accumulating evidence suggests that synovial inflammation plays a pivotal role in knee osteoarthritis. Although biomechanical findings have shown that medial open-wedge proximal tibial osteotomy (OWPTO) decreases medial compartment loading by correcting knee alignment, the relationship between knee alignment and synovial inflammation in the biological microenvironment has not yet been elucidated. PURPOSES: To investigate the relationship between preoperative and postoperative knee alignment and synovial gene expression and to determine the cutoff point of postoperative knee alignment at which gene expression of synovial inflammation improves. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: A total of 36 patients with osteoarthritis who underwent OWPTO between June 2018 and May 2020 were enrolled. Synovial tissue was collected from affected knees during initial OWPTO and plate removal surgeries, and gene expression associated with the pathogenesis of osteoarthritis in the synovial tissue was investigated using real-time polymerase chain reaction. The correlation between weightbearing line ratio (WBLR) and synovial gene expression was determined. Receiver operating characteristic curve analysis was used to determine the cutoff values of WBLR for improving gene expression. The participants were divided into 2 groups, according to the cutoff values of their WBLR, and compared according to Knee injury and Osteoarthritis Outcome Score (KOOS) and synovial gene expression. RESULTS: Postoperative WBLR was correlated with gene expression of interleukin 1ß (IL1B) (ρ = -0.43; P = .008) and of interleukin 6 (IL6) (ρ = -0.41; P = .01). The cutoff value to predict improvement of IL6 was postoperative WBLR of 52%, with an area under the curve of 0.74 (P = .03). Patients with WBLR of <52% showed higher postoperative inflammatory gene (IL1B [P = .04] and IL6 [P = .03]) and inferior postoperative KOOS values compared with those with WBLR of >52%. CONCLUSION: The novel cutoff alignment for biological improvement after OWPTO in patients with medial compartment osteoarthritis was determined to be WBLR of 52%, and WBLR of <52% was associated with higher residual intra-articular inflammation and poor clinical outcomes. After accounting for surgical errors, the surgeon should set the target surgical alignment so that the postoperative WBLR does not fall below 52%.

Gap Volume Based on Computed Tomography Measurement Is a Strong Risk Factor for Delayed Gap Healing After Open-Wedge High Tibial Osteotomy.

PURPOSE: To identify factors that affect delayed gap healing after open-wedge high tibial osteotomy (OWHTO) and to determine whether large gap volume is a predictor of delayed gap healing. METHODS: This retrospective study analyzed biplane OWHTO performed between 2019 and 2023 for knee osteoarthritis or osteonecrosis. The minimum follow-up period was 1 year. Delayed gap healing was defined when the medial half of the osteotomy gap area had not reached the consolidation phase by 6 months after surgery based on anteroposterior knee radiographs. Gap volume was calculated from computed tomography images. Logistic regression was performed using body height, smoking, correction angle, hinge fracture, flange thickness, and gap volume. A gap volume cutoff value for delayed gap healing was determined with receiver operating characteristic curve analysis. Gap volume was predicted with multiple linear regression. RESULTS: There were 80 knees in 71 patients (36 men and 44 women). The mean gap volume was 7.6 cm3. Gap healing rates at 3, 6, 9, and 12 months after surgery were 26%, 65%, 89%, and 100%, respectively. There were 25 knees with delayed gap healing. Male sex was not a significant risk factor when adjusted for body height. Multivariate logistic regression revealed that only larger gap volume was a significant risk factor (odds ratio, 1.45; P = .006). The gap volume cutoff value was 7.6 cm3, with an area under the curve of 0.74. Tall body height and a large correction angle (both P < .001) were associated with a significantly larger gap volume (R2 = 0.73). CONCLUSIONS: Large gap volume is the most important risk factor for delayed gap healing after OWHTO. Gap volume can be predicted based on body height and correction angle. When OWHTO with substantial correction is planned for tall men, surgeons should be aware of possibly delayed gap healing. LEVEL OF EVIDENCE: Level IV, retrospective case-control study.

Postoperative function of patients with rheumatoid arthritis after total knee arthroplasty in the last decade was comparable in the unadjusted cohort but inferior in the propensity score matched cohort with that of patients with osteoarthritis.

BACKGROUND: The perioperative pain and function of total knee arthroplasty (TKA) in patients with rheumatoid arthritis (RA) approach those in patients with osteoarthritis (OA). This study aimed to evaluate whether the clinical outcomes, especially functions, of patients with RA reached those of OA, utilizing a background-matched cohort. METHODS: Patients who underwent TKA between 2013 and 2021 were enrolled. Preoperative and minimum 2-year postoperative scores, specifically the Original Knee Society Score (OKSS) and New Knee Society Score (2011KSS), between RA and OA were compared. Clinical assessments were performed on unadjusted and propensity-score matched cohorts, ensuring age, sex, body mass index, and valgus deformity rate parity. RESULTS: In an unadjusted cohort involving 98 patients with RA and 560 patients with OA, patients with RA demonstrated inferior preoperative OKSS-Function Score (FS) but similar postoperative functional scores to OA patients. In the matched cohort of 83, patients with RA displayed lower preoperative OKSS- FS (median difference: 20, P < 0.001) and 2011KSS functional activities (difference: 9, P = 0.01) beyond minimum clinically important differences than patients with OA. Patients with RA improved more in OKSS-FS, yielding no postoperative difference compared with patients with OA. However, postoperative 2011KSS functional activities remained lower in patients with RA (difference: 9.5, P = 0.03), especially in advanced functions, than in those with OA. CONCLUSION: Postoperative function showed no difference between patients with RA and OA in the unadjusted cohort; within the background-matched cohort, postoperative function, especially advanced function, was inferior in patients with RA to those with OA.

Small medial proximal tibial angle is a radiographic finding strongly associated with less coronal alignment correction under valgus stress in medial knee osteoarthritis.

PURPOSE: The degree to which varus knees can be corrected manually is important when considering total versus unicompartmental knee arthroplasty (UKA). The primary aim was to clarify the relationship between the degree of coronal alignment correction and radiographic parameters involved in UKA prognosis using preoperative full-length lower extremity valgus stress radiography. The secondary aim was to identify the factors affecting alignment correction. METHODS: This retrospective observational study included 115 knees with medial osteoarthritis that underwent knee osteotomy or arthroplasty. Percent mechanical axis without valgus stress (%MA: neutral, 50%; varus, <50% and valgus, >50%), mechanical lateral distal femoral angle, lateral bowing femoral angle, medial proximal tibial angle (MPTA), joint line convergence angle, medial and lateral joint space width (LJSW) and medial femoral and tibial joint osteophyte size were measured using preoperative full-length weight-bearing radiographs. Correlation and multiple linear regression analyses were used to assess associations between parameters and %MA with valgus stress or amount of %MA change (%MA with valgus stress minus %MA without valgus stress). RESULTS: %MA with valgus stress was correlated with all radiographic parameters. %MA change was correlated with parameters except for MPTA and LJSW. Multiple regression analyses showed that %MA without valgus stress and MPTA were associated with both %MA with valgus stress and %MA change. When %MA with valgus stress was set at 30%, 40% and 50%, MPTA cutoff values were 81.6°, 83.5° and 84.9°, and cutoffs for %MA without valgus stress were 10.7%, 17.1% and 25.1%, respectively. CONCLUSION: Small MPTA is strongly associated with less alignment correction under valgus stress in varus knees. The finding is useful in surgical planning, especially to avoid undercorrection with UKA when valgus stress radiographs are unavailable. LEVEL OF EVIDENCE: Level III.

Anterior Position of the Femoral Condyle During Mid-Flexion Worsens Knee Activity After Cruciate-Retaining Total Knee Arthroplasty.

BACKGROUND: The effects of kinematics on patient-reported outcome measures (PROMs) after cruciate-retaining (CR) total knee arthroplasty (TKA) remain unclear. This study investigated the effects of kinematic patterns after CR-TKA on PROMs. METHODS: We examined 35 knees (27 patients) undergoing primary CR-TKA. Knee kinematics and 2011 Knee Society Score were evaluated at a mean follow-up of 72.4 (± 28.2) months. Knee kinematics was analyzed using fluoroscopy, and the femoral antero-posterior position relative to the tibial component was assessed separately for medial and lateral compartments during a squat. The correlations between kinematics and PROMs were evaluated. RESULTS: The average amount of posterior femoral translation from full extension to maximum flexion was 0.2 (± 2.6) mm for the medial femoral condyle and 4.1 (± 2.9) mm for the lateral condyle. Medial pivot motion was observed in 24 knees (68.6%) with a low rate (14.3%) of paradoxical anterior translation. The anterior position of the medial femoral condyle at 60° had a negative impact on discretionary activities (ρ = -0.37; P = .039), and at maximum flexion, had a negative impact on total functional activities (ρ = -0.46; P = .005), advanced activities (ρ = -0.45; P = .006), and discretionary activities (ρ = -0.63; P < .001). Anterior position of the lateral femoral condyle at 30° had a negative impact on total functional activities (ρ = -0.48; P = .005), walking and standing (ρ = -0.56; P < .001), and advanced activities (ρ = -0.49; P = .004), and at 60° had a negative impact on walking and standing (ρ = -0.45; P = .010). CONCLUSIONS: The anterior positions of the medial and lateral femoral condyles at mid-flexion and maximum flexion had negative impacts on PROMs. Soft tissue conditions should be carefully managed to achieve medial knee joint stability, which can improve PROMs.

Management and treatment outcomes of rheumatoid arthritis in the era of biologic and targeted synthetic therapies: evaluation of 10-year data from the KURAMA cohort.

BACKGROUND: Advances in rheumatoid arthritis (RA) treatment, highlighted by biological disease-modifying antirheumatic drugs (bDMARDs) and targeted synthetic DMARDs (tsDMARDs), have altered the paradigm of RA treatment in the last decade. Therefore, real-world clinical evidence is needed to understand how treatment strategies and outcomes have changed. METHODS: Using an observational cohort of RA from 2012 to 2021, we collected cross-sectional data of RA patients annually to analyze a trend in RA management. For patients who initiated b/tsDMRDs, we evaluated treatment outcomes between b/tsDMARDs. Mixed-effect models were applied to examine the statistical implications of changes over time in treatment outcomes with a background adjustment. RESULTS: We analyzed annual cross-sectional data from 5070 patients and longitudinal data from 1816 patients in whom b/tsDMARDs were initiated between 2012 and 2021. b/tsDMARD use increased, whereas glucocorticoid use decreased from 2012 to 2021. Disease activity and functional disability measures improved over time. The percentage of tsDMARD prescriptions considerably increased. All b/tsDMARDs showed clinical improvements in disease activity and functional disability. Statistically, TNFi showed better short-term improvements in b/tsDMARD-naïve patients, while IL6Ri demonstrated significant long-term benefits. IL6Ri had better retention rates in switched patients. After adjustment for patient characteristics, the annual change of RA disease activity and functional disability fared significantly better from 2012 to 2021. CONCLUSIONS: With the development of new RA therapeutics, overall treatment outcomes advanced in the past decade.

Predictors for the Knee Extension Strength at 2 Yrs After Total Knee Arthroplasty Using Regression Tree Analysis.

OBJECTIVE: The aim of the study is to clarify the interactive combinations of clinical factors associated with knee extension strength 2 yrs after total knee arthroplasty. DESIGN: A retrospective cohort study was conducted on 264 patients who underwent total knee arthroplasty. Knee extension strength was assessed preoperatively, 3 wks, and 2 yrs after total knee arthroplasty. Physical functions were measured with 10-m walking test, Timed Up and Go test, one-leg standing time, isometric knee flexion strength, knee joint stability, knee pain, femora-tibial angle, and passive knee extension and flexion angle before surgery as a baseline and 3 wks after total knee arthroplasty as acute phase. Regression tree analysis was conducted to clarify the interactive combinations that accurately predict the knee extension strength 2 yrs after total knee arthroplasty. RESULTS: Operational side knee extension strength (>1.00 Nm/kg) at acute phase was the primal predictor for the highest knee extension strength at 2 yrs after total knee arthroplasty. Acute phase Timed Up and Go test (≤10.13 secs) and baseline 10-m walking test (≤11.72 secs) was the second predictor. Acute phase nonoperative side knee extension strength (>0.90 Nm/kg) was also selected as the predictor. CONCLUSIONS: This study demonstrated that knee extension strength or Timed Up and Go test in the acute phase and 10-m walking test before total knee arthroplasty are useful for estimating the knee extension strength after total knee arthroplasty. The results will help determine specific postoperative rehabilitation goals and training options.

Preoperative radiographs underdiagnose the severity of lateral femoral and medial trochlear cartilage damage in varus osteoarthritis knees.

OBJECTIVE: This study evaluated whether preoperative radiographs accurately predicted intra-articular cartilage damage in varus knees. METHODS: The study assessed 181 knees in 156 patients who underwent total knee arthroplasty. Cartilage damage was graded by two examiners with the International Cartilage Repair Society classification; one used knee radiographs and the other used intraoperative photographs. It was then determined if this radiographic cartilage assessment over- or underestimated the actual damage severity. Knee morphological characteristics affecting radiographic misestimation of damage severity were also identified. RESULTS: The concordance rate between radiographic and intraoperative assessments of the medial femoral condyle was high, at around 0.7. Large discrepancies were found for the lateral femoral condyle and medial trochlear groove. Radiographic assessment underestimated cartilage damage on the medial side of the lateral femoral condyle due to a large lateral tibiofemoral joint opening and severe varus alignment {both r = -0.43}. Medial trochlear damage was also underdiagnosed, in cases of residual medial tibiofemoral cartilage and shallow medial tibial slope {r = -0.25 and -0.21, respectively}. CONCLUSIONS: Radiographic evaluation of knee osteoarthritis was moderately practical using International Cartilage Repair Society grades. Lateral femoral condyle and medial trochlear cartilage damage tended to be misestimated, but considering morphologic factors might improve the diagnostic rate.

Comparison of knee kinematics and ligament forces in single and multi-radius cruciate-retaining total knee arthroplasty: A computer simulation study.

BACKGROUND: The single-radius design in total knee arthroplasty has been designed to develop a more fixed flexion-extension axis without mid-flexion instability compared with the multi-radius design. It remains unclear whether differences between the multi-radius and single-radius designs can affect kinematics and collateral ligament forces. This study aimed to simulate knee kinematics and kinetics between single-radius and multi-radius models using a musculoskeletal computer model. METHODS: The single-radius and multi-radius femoral components were virtually implanted in a computer simulation using the same tibial insert. The effects of implant design on kinematics and medial collateral ligament forces during squatting and gait activities were analyzed. RESULTS: During squatting, the multi-radius model exhibited paradoxical anterior translation on both the medial and lateral flexion facet center where peak anterior translation was 2.4 mm for medial flexion facet center and 2.2 mm for the lateral flexion facet center, while the peak anterior translation of the single-radius model was less than 1 mm at early flexion. A rapid decrease in medial collateral ligament tension was observed in the early flexion phase in the multi-radius model, which occurred simultaneously with paradoxical anterior translation, whereas the relatively constant medial collateral ligament tension was observed in the single-radius model. During gait activity, the single-radius model exhibited a more posterior position than the multi-radius model. CONCLUSION: These suggest that abrupt changes in the medial collateral ligament force influence anterior sliding of the femur, and that the single-radius design is a reasonable choice for prevention of mid-flexion instability.

Catastrophic Mid-Flexion Instability After Avulsion Fractures of the Articular Capsule of the Femur and Tibia in a Patient With Posterior-Stabilized Total Knee Arthroplasty: A Case Report.

Mid-flexion instability can be caused by patient-related, implant-related, or technique-specific factors and impairs the activities of daily living after total knee arthroplasty (TKA). In this study, we report a rare case of a patient with severe mid-flexion instability following tibial and femoral avulsion fractures after posterior-stabilized (PS) TKA for knee osteoarthritis. An 82-year-old female with bilateral knee osteoarthritis underwent staged bilateral TKA with a posterior-stabilized prosthesis. The course of the early postoperative period was good, and the patient was able to walk independently with a cane. Two months postoperatively, the patient fell and then experienced left knee pain and instability in the mid-flexion range. Radiographic images showed avulsion fractures of the articular capsule of the femur and tibia, and fluoroscopic examination showed severe posterior subluxation of the tibia between 40° and 60° of flexion. Conservative treatment with a functional knee brace and quadriceps training was initiated due to the patient's hesitation to undergo a second surgery; however, no improvement was observed. Eventually, revision surgery was planned three months after the fall incident (five months after the left primary TKA). At revision surgery, osteosynthesis of the tibial avulsion fracture and thickening of the PS insert did not sufficiently stabilize the instability, and revision TKA with a rotating-hinge prosthesis was needed. The postoperative course was uneventful, and she was able to walk with a cane within two weeks after revision TKA with no complaints of instability. Two years postoperatively, the patient recovered well and had no recurrence of instability, pain, or dysfunction. This case report shows that loss of support by the joint capsules due to avulsion fractures may cause significant anteroposterior instability in the mid-flexion position after posterior-stabilized TKA. In such a case, conservative treatment failed, and the revision of the rotating-hinge prosthesis provided stability and good improvement.

Decreased Elastic Modulus of Knee Articular Cartilage Based on New Macroscopic Methods Accurately Represents Early Histological Findings of Degeneration.

OBJECTIVE: Ex vivo nanoindentation measurement has reported that elastic modulus decreases as cartilage degenerates, but no method has been established to macroscopically evaluate mechanical properties in vivo. The objective of this study was to evaluate the elastic modulus of knee joint cartilage based on macroscopic methods and to compare it with gross and histological findings of degeneration. DESIGN: Osteochondral sections were taken from 50 knees with osteoarthritis (average age, 75 years) undergoing total knee arthroplasty. The elastic modulus of the cartilage was measured with a specialized elasticity tester. Gross findings were recorded as International Cartilage Repair Society (ICRS) grade. Histological findings were graded as Mankin score and microscopic cartilage thickness measurement. RESULTS: In ICRS grades 0 to 2 knees with normal to moderate cartilage abnormalities, the elastic modulus of cartilage decreased significantly as cartilage degeneration progressed. The elastic modulus of cartilage was 12.2 ± 3.8 N/mm for ICRS grade 0, 6.3 ± 2.6 N/mm for ICRS grade 1, and 3.8 ± 2.4 N/mm for ICRS grade 2. Similarly, elastic modulus was correlated with Mankin score (r = -0.51, P < 0.001). Multiple regression analyses showed that increased Mankin score is the most relevant factor associated with decreased elastic modulus of the cartilage (t-value, -4.53; P < 0.001), followed by increased histological thickness of the cartilage (t-value, -3.15; P = 0.002). CONCLUSIONS: Mechanical properties of damaged knee cartilage assessed with new macroscopic methods are strongly correlated with histological findings. The method has potential to become a nondestructive diagnostic modality for early cartilage damage in the clinical setting.

Development of a novel model for intraarticular adhesion in rat knee joint.

In this study, a novel rat model of knee joint adhesion was developed, and its formation was analyzed quantitatively over time. Thirty-nine Wistar rats were randomly divided into intact control (n = 3) and experimental (n = 36) groups. The latter was equally divided into three groups according to the experimental intervention: fixed with deep bending of the knee joint (group I), fixed after incision of the capsule (group II), and fixed after exposure of the patellofemoral joint to artificial patellar subluxation (group III). All rats were subdivided according to their joint immobilization period (1, 2, or 4 weeks). Thereafter, the limited range of motion of the knee joint with (limited knee range of motion) and without (limited knee joint intrinsic range of motion) skin and muscles were measured. The lengths of adhesions of the anterior knee joint and posterior capsules were evaluated histologically. The limited intrinsic range of motion of the knee joint was found to be increased in groups II and III compared to that in group I 4 weeks after immobilization. Adhesions were confirmed within 1 week after immobilization in groups II and III. The length of the adhesions in group III was significantly longer than in other groups at 2 weeks and remained longer than in group I at 4 weeks. This model may contribute to the assessment of the adhesion process and development of new therapeutic avenues following trauma or surgical invasion.

How do symptoms of each joint contribute to global pain, disease activity and functional disability in rheumatoid arthritis?-A comprehensive association study using a large cohort.

BACKGROUND: Established assessment tools for patients with rheumatoid arthritis (RA), including disease activity scores (DASs), disease activity indexes (DAIs), visual analog scales (VASs), and health assessment questionnaires (HAQs), are widely used. However, comparative associations between joint involvement and disease status assessment tools have rarely been investigated. METHODS: We included a dataset of 4016 patients from a large RA cohort from 2012 to 2019. The tenderness and swelling of each joint were counted as a symptom, with 70 and 68 affected joints throughout the body, respectively. The relative contribution of various joints to the disease status assessment tools, VAS scores, and functional disability indexes was analyzed using multiple regression analysis. RESULTS: The wrist showed the most significant contribution overall, especially in DASs and VASs, while the metacarpophalangeal and proximal interphalangeal joints made significant contributions to DASs and DAIs, but not to VASs and HAQs. The shoulder and the elbow significantly contributed to HAQs, but only the shoulder did to the VASs. The knee universally contributed to all of the tools, but the ankle played a minor but important role in most assessment tools, especially in HAQs. Similar but different contribution ratios were found between the sets of DASs, DAIs, VASs, or HAQs. CONCLUSIONS: Each joint makes a unique contribution to these assessment tools. The improvement or aggravation of symptoms in each joint affects the assessment tools in different manners.

Improved genetic prediction of the risk of knee osteoarthritis using the risk factor-based polygenic score.

BACKGROUND: Polygenic risk score (PRS) analysis is used to predict disease risk. Although PRS has been shown to have great potential in improving clinical care, PRS accuracy assessment has been mainly focused on European ancestry. This study aimed to develop an accurate genetic risk score for knee osteoarthritis (OA) using a multi-population PRS and leveraging a multi-trait PRS in the Japanese population. METHODS: We calculated PRS using PRS-CS-auto, derived from genome-wide association study (GWAS) summary statistics for knee OA in the Japanese population (same ancestry) and multi-population. We further identified risk factor traits for which PRS could predict knee OA and subsequently developed an integrated PRS based on multi-trait analysis of GWAS (MTAG), including genetically correlated risk traits. PRS performance was evaluated in participants of the Nagahama cohort study who underwent radiographic evaluation of the knees (n = 3,279). PRSs were incorporated into knee OA integrated risk models along with clinical risk factors. RESULTS: A total of 2,852 genotyped individuals were included in the PRS analysis. The PRS based on Japanese knee OA GWAS was not associated with knee OA (p = 0.228). In contrast, PRS based on multi-population knee OA GWAS showed a significant association with knee OA (p = 6.7 × 10-5, odds ratio (OR) per standard deviation = 1.19), whereas PRS based on MTAG of multi-population knee OA, along with risk factor traits such as body mass index GWAS, displayed an even stronger association with knee OA (p = 5.4 × 10-7, OR = 1.24). Incorporating this PRS into traditional risk factors improved the predictive ability of knee OA (area under the curve, 74.4% to 74.7%; p = 0.029). CONCLUSIONS: This study showed that multi-trait PRS based on MTAG, combined with traditional risk factors, and using large sample size multi-population GWAS, significantly improved predictive accuracy for knee OA in the Japanese population, even when the sample size of GWAS of the same ancestry was small. To the best of our knowledge, this is the first study to show a statistically significant association between the PRS and knee OA in a non-European population. TRIAL REGISTRATION: No. C278.

Excessive flexed position of the femoral component causes abnormal kinematics and joint contact/ ligament forces in total knee arthroplasty.

Poor clinical outcomes are reported in excessive flexion of the femoral component in total knee arthroplasty (TKA), but their mechanisms have not yet been elucidated. This study aimed to investigate the biomechanical effect of flexion of the femoral component. Cruciate-substituting (CS) and posterior-stabilised (PS) TKA were reproduced in a computer simulation. The femoral component was then flexed from 0° to 10° with anterior reference, keeping the implant size and the extension gap. Knee kinematics, joint contact, and ligament forces were evaluated in deep-knee-bend activity. When the femoral component was flexed 10° in CS TKA, paradoxical anterior translation of the medial compartment was observed at mid-flexion. The PS implant was best stabilised with a 4° flexion model in mid-flexion range. The medial compartment contact force and the medial collateral ligament (MCL) force increased with the flexion of the implant. There were no remarkable changes in the patellofemoral contact force or quadriceps in either implant. In conclusions, excessive flexion of the femoral component yielded abnormal kinematics and contact/ligament forces. Avoiding excessive flexion and maintaining mild flexion of the femoral component would provide better kinematics and biomechanical effects in CS and PS TKA.

An electronic force sensor accurately detects increased but not decreased soft tissue tension in total knee arthroplasty.

BACKGROUND: Postoperative knee instability is a leading cause of revision total knee arthroplasty (TKA). This study used a commercially available insert-shaped electronic force sensor to measure joint loads and facilitate ligament balance adjustment, and assessed the ability of this sensor to detect increased or decreased soft tissue tension during primary TKA. METHODS: Changes in medial and lateral tibiofemoral joint loads during knee flexion were evaluated with sensor thicknesses ranging from 10 to 16 mm using six varus osteoarthritis cadaver knees with intact medial collateral ligaments (MCLs), and the measurements were repeated after MCL resection. Correlations between joint loads and maximum knee extension angle were also evaluated. To validate the efficacy of the sensor, the values were compared with those obtained using a conventional tension device. RESULTS: For MCL-intact knees in extension, the medial joint load increased with sensor thickness. The maximum knee extension angle decreased with sensor thickness (ρ = -0.4), resulting in extension restriction up to -20°. Knee flexion contracture was below 5° when the total tibiofemoral joint load was below a cut-off of 42 lb. After the MCL was resected, medial joint loads remained unchanged at low values, even with increased sensor thickness. In contrast, the tension device clearly detected an increased gap as the degree of tension decreased. CONCLUSIONS: The electronic sensor identified increased joint loads associated with increased ligament tension, and could predict knee flexion contracture during TKA. However, unlike the tension device, it did not accurately detect excessively decreased ligament tension.

What is the Optimal Posterior Cruciate Ligament Tension to Achieve Patient Satisfaction in Cruciate-Retaining Total Knee Arthroplasty?

INTRODUCTION: Achieving adequate posterior cruciate ligament (PCL) tension is important during PCL-retaining total knee arthroplasty (CR-TKA), but the effect of PCL release on this tension is unpredictable. This study assessed the relationship between postoperative PCL laxity and patient satisfaction at a 2-year follow-up. METHODS: There were 44 varus osteoarthritis knees undergoing CR-TKA included. The PCL tension was adjusted by resizing the femoral component and modifying the posterior tibial slope, without PCL release. Postoperative PCL laxity at 90° of knee flexion was defined as the difference in radiographic anterior-posterior tibial translation with or without an 80-Newton posterior load at the tibial tubercle measured using a load device. Four subgroups were defined according to the PCL laxity: laxity ≤0 mm (n = 5); 0 mm < laxity ≤2 mm (n = 19); 2 mm < laxity ≤4 mm (n = 10); and laxity >4 mm (n = 10). The effect of PCL laxity on the 2-year postoperative 2011 Knee Society Score was determined. RESULTS: The femoral component was downsized in 27 of 44 knees, while the posterior tibia slope was increased in 6 of 44 knees, but no PCL was released intraoperatively. The 2011 Knee Society Score subscores improved significantly from preoperatively to postoperatively, and patients reported "neutral satisfaction" or better after 96% of operations. The mean PCL laxity was 2.3 mm on postoperative stress radiographs, and postoperative satisfaction scores were significantly highest in the subgroup with 2-4 mm laxity. CONCLUSION: CR-TKA was successfully performed without PCL release. Moderate PCL laxity (2-4 mm) achieved excellent postoperative satisfaction.

Identification of anti-citrullinated osteopontin antibodies and increased inflammatory response by enhancement of osteopontin binding to fibroblast-like synoviocytes in rheumatoid arthritis.

BACKGROUND: Anti-citrullinated protein/peptide antibodies (ACPAs) are present in patients at onset and have important pathogenic roles during the course of rheumatoid arthritis (RA). The characteristics of several molecules recognized by ACPA have been studied in RA, but the positivity rate of autoantibodies against each antigen is not high, and the pathogenic mechanism of each antibody is not fully understood. We investigated the role of anti-citrullinated osteopontin (anti-cit-OPN) antibodies in RA pathogenesis. METHODS: Enzyme-linked immunosorbent assays on RA patients' sera were used to detect autoantibodies against OPN. Fibroblast-like synoviocytes (FLS) isolated from RA patients were used to test the binding activity and inflammatory response of OPN mediated by anti-cit-OPN antibodies, and their effect was tested using an inflammatory arthritis mouse model immunized with cit-OPN. Anti-cit-OPN antibody positivity and clinical characteristics were investigated in the patients as well. RESULTS: Using sera from 224 RA patients, anti-cit-OPN antibodies were positive in approximately 44% of RA patients, while approximately 78% of patients were positive for the cyclic citrullinated peptide (CCP2) assay. IgG from patients with anti-cit-OPN antibody increased the binding activity of OPN to FLSs, which further increased matrix metalloproteinase and interleukin-6 production in TNF-stimulated FLSs. Mice immunized with cit-OPN antibodies experienced severe arthritis. Anti-cit-OPN antibodies in RA patients decreased the drug survival rate of tumor necrosis factor (TNF) inhibitors, while it did not decrease that of CTLA4-Ig. CONCLUSIONS: Anti-cit-OPN antibodies were detected in patients with RA. IgG from patients with anti-cit-OPN antibodies aggravated RA, and anti-cit-OPN antibody was a marker of reduced the survival rate of TNF inhibitors in RA patients.