No differences in long-term clinical outcomes and survival rate of navigation-assisted versus conventional primary mobile-bearing total knee arthroplasty: A minimum 10-year follow-up.

PURPOSE: This study aimed to compare long-term clinical and radiographic outcomes and survival rates between navigation-assisted (NAV) total knee arthroplasty (TKA) and conventional (CON) TKA using a mobile-bearing insert. METHODS: From May 2008 to December 2009, 45 and 63 mobile-bearing TKA patients were enroled in the CON- and NAV-TKA groups with 146.8 months follow-up, respectively. Clinical outcomes (Western Ontario and McMaster University Osteoarthritis Index and Knee Society Scores), radiographic outcomes (hip-knee-ankle [HKA], lateral distal femoral, medial proximal tibial, γ, and δ angles), and survivorship were compared between both groups. RESULTS: The number of HKA angle outliers (more than 3 degrees or less than -3 degree) was significantly lower in the NAV-TKA group (24.4% vs. 9.5%, p = 0.036) than in the CON-TKA group. However, long-term clinical outcomes were similar between both groups. The cumulative survival rate (best-case scenario) was 98.3% in the CON-TKA group and 97.5% in the NAV-TKA group, with no significant difference between the groups (p = 0.883). CONCLUSION: Long-term clinical outcomes and survival rates were similar between the two groups despite fewer outliers of postoperative lower-limb alignment in the NAV-TKA group. Excellent survival rates were observed in both groups using mobile-bearing inserts. LEVEL OF EVIDENCE: Level IV, case series.

Mobile medial pivot (lateral slide)-type total knee arthroplasty exhibited different motion patterns between under anaesthesia and weight-bearing condition.

PURPOSE: Total knee arthroplasty (TKA), which has medial pivot and mobile-bearing mechanisms, has been developed and clinically used. However, the in vivo dynamic kinematics of the mobile medial pivot-type TKA (MMPTKA) is unclear. This study analysed the in vivo kinematics of MMPTKA in weight-bearing and nonweight-bearing conditions. METHODS: The study included 10 knees that underwent primary TKA using MMPTKA. After TKA, lateral view radiographs of the knee in full extension, 90° of flexion and passive full flexion were taken under general anaesthesia in the nonweight-bearing condition. At least 6 months postoperatively, knee motion during squatting from a weight-bearing standing position was observed using a flat-panel detector and analysed using the three-dimensional-to-two-dimensional image registration technique. RESULTS: Under anaesthesia: in passive full flexion, the anteroposterior (AP) locations of the femoral component's medial and lateral distal points were 10.2 and 16.0 mm posterior, and the rotational angles of the femoral component's X-axis (FCX) and insert were 8.1° external rotation and 18.5° internal rotation to full extension, respectively. Squatting: the AP translations of the femoral component's medial and lateral most distal points were 2.2 and 6.4 mm, and the rotational angles of the FCX and insert were 5.7° and 1.6° external rotation, respectively. Significant differences were observed in the AP translation of the femoral component's medial and lateral most distal points and changes in the insert's rotational angle when comparing under anaesthesia and squatting. CONCLUSIONS: The kinematics of the insert in MMPTKA was significantly influenced by loading and muscle contraction. The femoral component exhibited substantial external rotation and posterior translation under anaesthesia, which may contribute to achieving an optimal range of motion. The insert remained relatively stable during squatting and minimal rotation was observed, indicating good stability. MMPTKA was expected to demonstrate rational kinematics by incorporating mobile and medial pivot mechanisms. LEVEL OF EVIDENCE: Level IV, prospective biomechanical case series study.

Femoral Coronal Malalignment is Associated With Failure in Mobile-Bearing Medial Unicompartmental Knee Arthroplasty.

BACKGROUND: Femur-first (FF) technique for mobile-bearing medial unicompartmental knee arthroplasty (UKA) has been described as an alternative to tibia-first (TF) technique. The aim of this study was to compare the radiographic results in UKAs using FF or TF techniques and their influence on failure rates. METHODS: We retrospectively reviewed 288 UKAs with a minimum 2-year follow-up. There were 147 knees in the TF and 141 knees in the FF cohorts. Alignment parameters and overhang were assessed as outliers and far outliers. The mean follow-up was 6 years (range, 2 to 16), the mean age was 63 years (range, 27 to 92), and 45% of patients were women. Univariate and multivariate statistical analyses were carried out with Cox regression models. RESULTS: There were 13 and 6 revisions in the TF and FF cohorts, respectively. The FF had lower rates of femoral coronal alignment (FCA) or femoral sagittal alignment outliers compared to the TF (5.7% versus 19%, P = .011). Tibial coronal alignment and tibial sagittal alignment did not significantly differ between the techniques (22.7% in FF versus 29.9% in TF, P = .119). Overhang outliers did not differ significantly between the groups. Younger age was associated with a higher revision rate (P = .006), while FF versus TF, sex, body mass index, and postoperative mechanical axis did not show statistically significant associations. In multivariate analysis, FCA outliers and younger age were significantly associated with revision. CONCLUSIONS: The FF technique in mobile-bearing UKA resulted in fewer FCA outliers compared to TF. Despite improved knee alignment with the FF technique, FCA outliers and younger age were associated with a higher revision rate, independent of technique.

Propensity of the tight mid-flexion and loose flexion gap despite the adjustment of extension and flexion gaps in Oxford unicompartmental knee arthroplasty: retrospective study.

PURPOSE: A well-balanced joint gap is necessary in Oxford unicompartmental knee arthroplasty (OUKA) to prevent mobile-bearing dislocation. While the gaps between 20° (extension) and 100° (flexion) are precisely adjusted using the incremental mill system, there has been insufficient evaluation of gaps in other angles. We hypothesized that the gap is not always the same in other angles. This retrospective study aimed to evaluate the gap in full-extension (0°), mid-flexion (60°) and deep flexion (130°) for comparison with those in extension and flexion gaps. METHODS: We evaluated 119 knees in 83 patients (51 females, 31 males, aged 71.9 years). The full-extension and mid-flexion gaps were compared with the extension gap, and the deep flexion gap was contrasted with the flexion gap. Each gap was classified into isometric, tight or loose, for evaluation of contributing factors. RESULTS: Although the full-extension gap tended to be isometric (45%), the mid-flexion tended to be tight (48%), whereas the deep-flexion was loose in most knees (84%) (P = 0.002). The tight mid-flexion and loose deep flexion gap pattern accounted for 44% of the total knees, especially so with smaller femoral components (P = 0.004). CONCLUSION: Our results highlight the propensity of tight mid-flexion and loose flexion gap despite the adjustment of extension and flexion gaps in OUKA. Although the effect of such a minor gap imbalance is still unknown, the pattern was more prevalent in patients with smaller-sized femoral components. Use of a larger femoral component may equalize the gap throughout the motion arc.

Comparison of revision rates and epidemiological data of a single total knee arthroplasty system of different designs (cruciate retaining, posterior stabilized, mobile bearing, and fixed bearing): a meta-analysis and systematic review of clinical trials and national arthroplasty registries.

BACKGROUND: This study aimed to meta-analyze epidemiological data, revision rates, and incidences of different designs of a single Total Knee Arthroplasty System and compare these factors across different countries. METHODS: A systematic review was conducted on clinical studies and arthroplasty registries of ATTUNE TKA from 1999 to 2020. The main endpoints analyzed were revision rates and epidemiological data. RESULTS: The average age of patients was 67.8 years, with a gender distribution of 60% female and 40% male. The pooled average BMI was 29.4 kg/m2. Eight clinical studies showed a pooled revision rate per 100 observed CY of 0.5 (n = 1343 cases). Cumulative revision rates after 1, 3, and 5 years varied among registries, with the Swiss registry having the highest revision data (after 5 years: 6.3%) and the American registry having the lowest revision data (after 5 years: 1.7%). A comparison of the revision rates of mobile bearing and fixed bearing (41,200 cases) as well as cruciate retaining and posterior stabilized (n = 123,361 cases) showed no significant advantage in the first 5 years after implantation. CONCLUSION: In conclusion, pooled data from 41,200 cases of TKA with a single Total Knee Arthroplasty System in two arthroplasty registries revealed that there was no significant difference in revision rates between the mobile bearing and fixed bearing design within the first 5 years after implantation. In addition, a comparison of the revision rates in n = 123,361 cases showed no significant advantage for cruciate retaining or posterior stabilized in the first 5 years after implantation.

Wider translations and rotations in posterior-stabilised mobile-bearing total knee arthroplasty compared to fixed-bearing both implanted with mechanical alignment: a dynamic RSA study.

PURPOSE: The purpose of this study was to investigate the in vivo kinematics of the same femoral design mechanically aligned posterior-stabilised (PS) total knee arthroplasty (TKA) with either fixed-bearing (FB) or mobile-bearing (MB) inlay, implanted by the same surgeon, using model-based dynamic radiostereometric analysis (RSA). The hypothesis of the present study was that the MB design would show wider axial rotation than the FB design, without affecting the clinical outcomes. MATERIALS AND METHODS: A cohort of 21 non-randomised patients (21 DePuy Attune PS-FB) was evaluated by dynamic RSA analysis at a minimum 9-month follow-up, while performing differently demanding daily living activities such as sit to stand (STS) and deep knee lunge (DKL). Kinematic data were compared with those of a cohort of 22 patients implanted with the same prosthetic design but with MB inlay. Anterior-posterior (AP) translations, varus-valgus (VV) and internal-external (IE) rotations of the femoral component with respect to the tibial baseplate were investigated. Translation of medial and lateral compartment was analysed using the low point method according to Freeman et al. Questionnaires to calculate objective and subjective clinical scores were administered preoperatively and during follow-up visit by the same investigator. RESULTS: The FB TKA design showed lower AP translation during STS (6.8 ± 3.3 mm in FB vs 9.9 ± 3.7 mm in MB, p = 0.006*), lower VV rotation (1.9 ± 0.8° in FB vs 5.3 ± 3.3° in MB, p = 0.005) and lower IE rotation (2.8 ± 1.1° in FB vs 9.5 ± 4.3° in MB, p = 0.001) during DKL than the mobile-bearing TKA design. Posterior-stabilised FB group showed significant lower translation of the low point of the medial compartment than the MB group (p = 0.008). The percentage of patients performing medial pivot in the FB group was higher compared to MB group in the examined motor tasks. No significant differences in post-operative range of motion (117° ± 16° for FB group and 124° ± 13° for MB group) and in clinical outcomes emerged between the two cohort. CONCLUSIONS: The FB and MB designs differed in AP translations, VV rotations and IE rotations of the femoral component with respect to the tibial component in STS and DKL. Furthermore, FB cohort reported a significant higher percentage of medial pivot with respect to MB cohort. Despite this, no differences in clinical outcomes were detected between groups. Both designs showed stable kinematics and represent a viable option in primary TKA. LEVEL OF EVIDENCE: Prospective cohort study, II.

Less wear in deep-dished mobile compared to fixed bearing total knee arthroplasty of the same design at 5-year follow-up: a randomised controlled model-based Roentgen stereophotogrammetric analysis trial.

PURPOSE: The aim of this prospective randomised controlled study was to compare wear characteristics and functional outcome between deep-dished mobile bearing (MB) and fixed bearing (FB) cemented total knee arthroplasty (TKA). We hypothesised that deep-dished MB reduces polyethylene wear and improves patient-reported outcome measures. METHODS: A total of 50 patients were randomised to receive a MB or FB tibia component of the same cemented TKA design. Patients were evaluated over a 5-year follow-up period. Medial and lateral wear were assessed using model-based Roentgen Stereophotogrammetric Analysis (RSA) and compared with the direct postoperative minimal joint space measurement. Functional outcome was assessed by the clinician-derived KSS and OKS, WOMAC, LEAS, and FJS-12. All data were derived using a general linear mixed model. RESULTS: At 5-year follow-up, decreased wear in the MB compared to the FB group was observed on the lateral side (0.07 ± 0.17 mm, p = 0.026), but not on the medial side (0.31 ± 0.055 mm, p = 0.665). Functional outcomes improved with a statistical significant effect over time, with no significant differences between groups (all p > 0.17). CONCLUSION: This model-based RSA study with 5-year follow-up showed that cemented deep-dished MB reduced lateral polyethylene wear as compared to FB in a single TKA system, whilst clinical outcomes were comparable. Longer follow-up is needed to establish clinical implications of these altered wear patterns and determine type of wear. LEVEL OF EVIDENCE: Level 1 randomised controlled trial.

15-Year Follow-Up of Mobile Bearing Medial Unicompartmental Knee Arthroplasty.

INTRODUCTION: Medial unicompartmental knee arthroplasty (UKA) is a successful treatment for antero-medial osteoarthritis. However, there are few published studies on the long-term survival of this procedure. The purpose of this study was to review the 15-year minimum outcomes and survival of a mobile-bearing medial UKA. METHODS: A retrospective review was performed between July 2004 and December 2006 of all patients who underwent a medial UKA eligible for a minimum of 15-year follow-up. The initial query revealed 299 patients (349 knees). One hundred-seventeen patients died or were lost to follow-up, leaving 182 patients (219 knees) for analyses. Clinical outcomes and survivorship were analyzed. RESULTS: There were 59 implant-related reoperations which occurred at a mean of 10 years (range, 0 to 16 years). The most common reasons for reoperation were arthritic progression (9.1%) and aseptic loosening (9.1%). The 10-year survival with revision to TKA was 89% (95% confidence interval: 86% to 92.4%), and the 15-year survival was 84.1% (95% confidence interval: 80.3% to 88%). There were no statistically significant differences in survival between sex, body mass index, and age. Patients who were not revised had statistically significant improvements in knee range of motion and Knee Society scores. CONCLUSIONS: This study found similar long-term survival of a medial mobile-bearing UKA to published total knee arthroplasty outcomes. The implant evaluated in this study has undergone subsequent improvements in instrumentation and design. Further analyses should be performed on the long-term outcomes of the current implant platform.

Femur-First Technique for Mobile Bearing Unicompartmental Knee Arthroplasty Results in Decreased Implant Variability and Early Improvements in Function and Survivorship.

BACKGROUND: Higher failure rates of unicompartmental knee arthroplasty (UKA) are seen with lower surgical volume. Surgical techniques that introduce less variability improving implant positioning may lead to improved survivorship. A femur-first (FF) technique has been described, but survivorship data compared to traditional tibia-first (TF) technique are under-reported. We report the results of mobile-bearing UKA using the FF technique compared to the TF technique with emphasis on implant position and survivorship. METHODS: A total of 430 UKAs were performed by a single surgeon between 2007 and 2020. After 2012, there were 141 consecutive UKAs performed with the FF technique which were compared with 147 consecutive UKAs prior. Mean follow-up was 6 years (range, 2 to 13 years), average age was 63 years (range, 23 to 92 years), and there were 132 women. Postoperative radiographs were reviewed to determine implant positioning. Survivorship analyses were performed using Kaplan-Meier curves. RESULTS: The FF resulted in significantly thinner polyethylene (3.4 ± 0.7 mm versus 3.7 ± 0.9 mm) (P = .002) and 4 mm or less bearing thickness in 94% of cases. At 5 years, there was an early trend toward improved survivorship free from component revision (98% for the FF group and 94% for the TF [P = .35]). The FF cohort had higher Knee Society Functional scores at final follow-up (P < .001). CONCLUSION: Compared to traditional TF technique, the FF was more bone-preserving and improved radiographic positioning. The FF technique is an alternative method for mobile-bearing UKA and was associated with an improvement in implant survivorship and function.

Mobile-Bearing has no Benefit Over Fixed-Bearing Total Knee Arthroplasty in Joint Awareness and Crepitus: A Randomized Controlled Trial.

BACKGROUND: Given higher component conformity, rotational availability of polyethylene insert, and more physiologic patellofemoral tracking, mobile-bearing (MB) total knee arthroplasty (TKA) is supposed to offer advantages in joint perception and crepitus. The purpose of this study was to investigate whether MB TKA offers superior outcomes over fixed-bearing (FB) TKA in terms of joint awareness and crepitus. METHODS: This prospective, randomized, controlled trial included 49 FB and 49 MB TKAs that shared the same posterior-stabilized femoral component. Primary outcomes included joint awareness assessed with the Forgotten Joint Score and crepitus graded according to severity and sound at 3 years postoperatively. Secondary outcomes were the range of motion, the Knee Society Score, Western Ontario and McMaster Universities Osteoarthritis Index, component position, and joint line level on radiographs. RESULTS: The Forgotten Joint Score showed no significant difference between the FB (67 points; range, 0-100) and MB groups (63 points; range, 13-100) (P = .440). For crepitus, no significant differences were found in the overall incidence rate (FB group, 18%; MB group, 12%; P = .386) and grade (grade 1, 6 versus 5; grade 2, 2 versus 1; grade 3, 1 versus 0, respectively). There were no significant differences in range of motion, Knee Society Score, and Western Ontario and McMaster Universities Osteoarthritis Index, as well as radiographic outcomes between the two groups (all, P > .05). CONCLUSION: MB TKA offers no benefits in terms of joint awareness and crepitus compared with FB TKA at mean 3 years postoperatively. The theoretical advantages of MB TKA have yet to be demonstrated in practice, leaving the selection of bearing type to the surgeon's judgment. LEVEL OF EVIDENCE: Level II.

The James A. Rand Young Investigator's Award: Increased Revision Risk With Mobile Bearings in Total Knee Arthroplasty: An Analysis of the American Joint Replacement Registry.

BACKGROUND: Mobile-bearing (MB) total knee arthroplasty (TKA) may reduce wear and improve patellar tracking but may increase revision risk due to tibial component design, balance complexity, and bearing dislocation. We utilized the American Joint Replacement Registry to examine risk of revision with MB compared to fixed-bearing (FB) designs. METHODS: An analysis of primary TKA in patients over 65 years was performed with American Joint Replacement Registry data linked to Centers for Medicare and Medicaid Services data from 2012 to 2019. Analyses compared MB to FB designs with a subanalysis of implants from a single company. We identified 485,024 TKAs, with 452,199 (93.2%) FB-TKAs and 32,825 (6.8%) MB-TKAs. Cox proportional hazards regression modeling was used for all-cause revision and revision for infection, adjusting for sex, age, and competing risk of mortality. Event-free survival curves evaluated time to all-cause revision and revision for infection. RESULTS: MB-TKAs were at an increased risk for all-cause revision: hazard ratio (HR) 1.36 ([95% confidence interval (CI) 1.24-1.49], P < .0001) but not revision for infection: HR 1.06 ([95% CI 0.90-1.25], P = .52). When comparing implants within a single company, MB-TKAs were at an increased risk of all-cause revision: HR 1.55 ([95% CI 1.38-1.73], P < .0001). Event-free survival curves demonstrated increased risk for all-cause revision for MB-TKA across all time points, with a greater magnitude of risk up to 8 years. CONCLUSION: Although survivorship of both designs was outstanding, MB-TKA designs demonstrated increased risk for all-cause revision. Additional investigation is needed to determine if this is related to patient selection factors, surgical technique, bearing, or implant design.

Approximately 41% of knees have a looser gap in full extension than in 20° flexion after Oxford unicompartmental arthroplasty.

INTRODUCTION: In Oxford unicompartmental knee arthroplasty (OUKA), the flexion and extension gaps should be adjusted to prevent mobile-bearing dislocation. The extension gap is recommended to be evaluated in the 20° flexion position to avoid underestimation due to tension of the posterior capsule. However, we have become aware of a looser gap in full extension than in 20° flexion in some instances. MATERIALS AND METHODS: We retrospectively investigated 83 knees in 60 patients who underwent OUKA between January and June 2020. During surgery, the extension gaps were measured in both full extension and 20° flexion. The knees were classified into two groups: the gap was looser in full extension (0° group), and the gap was equal or looser in 20° flexion than in full extension (20° group). The hip-knee-ankle angle (HKAA), the lateral distal femoral angle (LDFA), the medial proximal tibia angle (MPTA), the posterior tibial slope angle (PTSA), and the last spigot size were also measured and compared between the groups. RESULTS: There was looseness in approximately 41% of knees (34 out of 83 knees) in full extension. In the knees in the 0° group, the last spigot size was significantly smaller (median 1 and 2, P < 0.01). However, there were no significant differences in the HKAA, MPTA, LDFA or PTSA between the groups. CONCLUSIONS: Approximately 41% of knees have a looser gap in full extension than in 20° flexion after OUKA. Further investigation is needed to better understand which extension gap should be used in such cases, and to find the contributing factors in loose full extension gap other than the size of the last spigot.

Mobile-bearing prosthesis suppresses the postoperative rotational mismatch and improves patient-reported outcome measurements better than fixed-bearing prosthesis: rotational analysis by 3D measurement in total knee arthroplasty.

INTRODUCTION: It is preferable to reduce postoperative excessive rotational mismatch between the femur and tibia that causes poor clinical results following total knee arthroplasty (TKA). The aim of this study is to compare postoperative rotational mismatches and clinical outcomes with mobile- and fixed-bearing prostheses. MATERIALS AND METHODS: This study classified 190 TKAs into two groups equally by propensity score matching: mobile-bearing group (n = 95) and fixed-bearing group (n = 95). Computed tomography images of the whole leg were taken at 2 weeks postoperatively. The component alignments, rotational mismatches between the femur and tibia, and rotations among components were measured three-dimensionally. The knee range of motion, New Knee Society Score (KSS) subjective sores, and Forgotten Joint Score (FJS-12) were assessed at the final follow-up. RESULTS: Rotational mismatch between the femur and tibia was significantly less in the mobile- (- 0.8° ± 7.3°) than in the fixed-bearing (3.3° ± 8.5°, p < 0.001) group. New KSS functional activity score was significantly poorer in patients with excessive rotational mismatch (61.3 ± 21.4) than in those without it (49.5 ± 20.6, p = 0.02). Comparing mobile-bearing prosthesis, the use of fixed-bearing prosthesis was a risk factor for postoperative excessive rotational mismatch (odds ratio: 2.32, p = 0.03). CONCLUSION: When compared to a fixed-bearing prosthesis, TKA using a mobile-bearing prosthesis could suppress the postoperative rotational mismatch between the femur and tibia that causes poor subjective functional activity score. However, since this study was conducted for PS-TKA, the results might not be applicable to other models.

Mobile bearing versus fixed bearing medial unicompartmental knee replacement: an independent two center matched-pairs analysis.

INTRODUCTION: The aim of the present study was to compare clinical outcome between patients following fixed-bearing (FB) or mobile-bearing (MB) unicompartmental knee replacement (UKR) for antero-medial knee osteoarthrosis (OA) at two independent orthopedic centers. MATERIALS AND METHODS: Matched-pairs were built between 35 patients receiving FB-UKR and 52 patients following MB-UKR regarding age at time of surgery, body mass index (BMI) and range of motion (ROM) preoperatively. Clinical and functional outcome was measured postoperatively by the American Knee Society Score (AKSS-O/AKSS-F), ROM, Tegner Activity Scale (TAS) as well as the Short Form 36 Health Survey (SF-36). RESULTS: The average treatment effect of the treated (ATT) after propensity score matching showed a significantly superior ROM in patients following MB-UKR (FB: 118°, MB: 124°). All remaining parameters had no statistically significant differences between both groups involving TAS, AKSS and SF-36. CONCLUSIONS: The present study suggests that MB-UKR can provide a greater ROM compared to FB-UKR on comparable patients. The authors believe that both designs are suitable for adequate improvement of clinical outcome and ROM for patients suffering from antero-medial osteoarthrosis of the knee joint. LEVEL OF EVIDENCE: Retrospective cohort study, Level IV.

Minimally invasive Oxford medial unicompartmental knee replacement in patients 50 years of age or younger.

INTRODUCTION: The aim of the present study was to assess clinical outcome and mid-term survivorship of mobile-bearing unicompartmental knee arthroplasty in patients 50 years of age or younger. METHODS: This study reports the results of 119 patients (130 knees) following mobile-bearing medial UKA. Primary indication was advanced osteoarthritis or avascular necrosis of the femoral condyle. The anterior cruciate ligament (ACL) as well as the collateral ligaments were functionally intact, the varus deformity was manually correctable and there was no evidence of osteoarthritis in the lateral compartment. Survivorship analysis was performed with different endpoints and clinical outcome was measured using the Oxford Knee Score (OKS), American Knee Society Score and Functional Score (AKSS-O, AKSS-F), range of motion (ROM), Tegner activity score, University of California Los Angeles score (UCLA) and visual analogue scale for pain (VAS). RESULTS: The survival rate was 96.6% at 6.5 years (95% CI 98.7-91.3%; number at risk: 56) and 91.7% (95% CI 96.7-80%; number at risk: 22) at 10 years for the endpoint device related revisions and 91.5% at 6.5 years (95% CI 95.4-84.5%; number at risk: 56) and 86.8% (95% CI 93-76.2%; number at risk: 22) at 10 years for the endpoint revision for any reason. Outcome scores, VAS and ROM showed significant improvements (p < 0.001). The mean OKS increased from 26.7 (standard deviation (sd): 7.2) preoperatively to 40.9 (sd: 7.6) at final follow-up, the mean AKSS-O from 48.3 (sd: 13.3) to 87.8 (sd: 14.4) and the mean ROM from 118° (sd: 16.7) to 125° (sd: 11.4). The radiological analysis revealed progression of degenerative changes in the lateral compartment in 39.6% of patients without affecting the functional outcome. CONCLUSIONS: Medial mobile-bearing UKA is a viable surgical treatment option in young patients with significant improvements in knee function and pain. Further follow-up is necessary to evaluate the long-term efficacy. LEVEL OF EVIDENCE: Retrospective cohort study, Level III.

Coronal tibiofemoral subluxation under valgus stress force radiography is useful for evaluating postoperative coronal tibiofemoral subluxation in mobile-bearing UKA.

PURPOSE: Coronal tibiofemoral subluxation (CTFS) is considered a controversial and potential contraindication to unicompartmental knee arthroplasty (UKA) but is less discussed. The study aims to observe the CTFS in a cohort of patients before and after mobile-bearing UKA and to investigate the relationship between preoperative variables (preoperative CTFS and preoperative CTFS under valgus stress) and postoperative CTFS after mobile-bearing UKA. METHODS: The study retrospectively analyzed 181 patients (224 knees) undergoing mobile-bearing UKA from September 1 2019 to December 31 2021. By using hip-to-ankle anterior-posterior (AP) standing radiographs and valgus stress force radiographs, preoperative CTFS, preoperative CTFS under valgus stress, and postoperative CTFS were measured. CTFS was defined as the distance between the tangent line to the outermost joint edge of the lateral condyle of the femur and the tangent line of the lateral tibial plateau. All patients were divided into two groups based on postoperative CTFS, group A (postoperative CTFS ≤ 5 mm) and group B (postoperative CTFS > 5 mm). The Student's t-test, one-way ANOVA together with Tukey's post hoc test, the chi-square test, the Fisher's exact test, Pearson correlation analysis, simple and multiple linear regression, and univariate and multiple logistic regression were used in the analyses. RESULTS: The means ± standard deviations (SD) of preoperative CTFS, preoperative CTFS under valgus stress, and postoperative CTFS were 4.96 ± 1.82 mm, 3.06 ± 1.37 mm, and 3.19 ± 1.27 mm. The difference between preoperative CTFS and postoperative CTFS was statistically significant (p < 0.001). The preoperative CTFS (6.35 ± 1.34 mm) in Group B (n = 22) was significantly higher than that (4.81 ± 1.82 mm) in Group A (n = 202) (p < 0.001), so was the variable-preoperative CTFS under valgus stress (5.41 ± 1.00 mm (Group B) > 2.80 ± 1.14 mm (Group A), p < 0.001). In Pearson correlation analysis, there was a correlation between preoperative CTFS and postoperative CTFS (r = 0.493, p < 0.001), while the correlation between preoperative CTFS under valgus stress and postoperative CTFS was stronger (r = 0.842, p < 0.001). In multiple linear regression analysis, preoperative CTFS under valgus stress (ß = 0.798, 95% confidence interval (CI) = 0.714-0.883, p < 0.001) was significantly correlated with postoperative CTFS. In multiple logistic regression analysis, preoperative CTFS under valgus stress (OR = 12.412, 95% CI = 4.757-32.384, and p < 0.001) was expressed as the risk factor of postoperative CTFS (> 5 mm). CONCLUSION: Preoperative CTFS can be improved significantly after mobile-bearing UKA. In addition, postoperative CTFS is correlated with preoperative CTFS under valgus stress and a higher preoperative CTFS under valgus stress will increase the risk of higher postoperative CTFS (> 5 mm). LEVEL OF EVIDENCE: Level III.

Predicting valgus malalignment after mobile-bearing UKA using a new method: the arithmetic HKA of the arthritic knee.

BACKGROUND: Valgus malalignment is one of the most common reasons for the progression of osteoarthritis in the lateral compartment of the knee after mobile-bearing unicompartmental knee arthroplasty (UKA). The arithmetic hip-knee-ankle angle (aHKA) of the Coronal Plane Alignment of the Knee (CPAK) classification could reflect the constitutional alignment of the arthritic knee. The purpose of this study was to observe the relationship between the aHKA and valgus malalignment after mobile-bearing UKA. METHODS: This retrospective study was conducted using 200 knees undergoing UKA from January 1, 2019, to August 1, 2022. These radiographic signs, including preoperative hip-knee-ankle angle (HKA), mechanical proximal tibial angle (MPTA), mechanical lateral distal femoral angle (LDFA), and postoperative HKA, were measured using standardized weight-bearing long-leg radiographs. Patients with postoperative HKA > 180° and postoperative HKA ≤ 180° were classified as the valgus group and non-valgus group, respectively. The aHKA was calculated as 180° + MPTA - LDFA in this study, which had the same meaning as that (aHKA = MPTA - LDFA) in the CPAK classification. The Spearman correlation analysis, the Mann-Whitney U test, the chi-square test, the Fisher's exact test, and multiple logistic regression were used in the study. RESULTS: Of the 200 knees included in our study, 28 knees were classified as the valgus group, while 172 knees were in the non-valgus group. The mean ± standard deviation (SD) of aHKA (all groups) was 177.04 ± 2.58°. In the valgus group, 11 knees (39.3%) had a value of aHKA > 180°, while 17 knees (60.7%) had a value of aHKA ≤ 180°. In the non-valgus group, 12 knees (7.0%) had a value of aHKA > 180°, while 160 knees (93.0%) had a value of aHKA ≤ 180°. In Spearman correlation analysis, aHKA was positively correlated with postoperative HKA (r = 0.693, p < 0.001). In univariate analysis, preoperative HKA (p < 0.001), LDFA (p = 0.02), MPTA (p < 0.001), and aHKA (p < 0.001) showed significant differences between the valgus and non-valgus groups. Variables with p < 0.1 in univariate analysis were further analyzed using multiple logistic regression analysis, and the variable-aHKA (> 180° vs ≤ 180°, odds ratio (OR) = 5.899, 95% confidence interval (CI) = 1.213 to 28.686, and p = 0.028) was expressed as the risk factor of postoperative valgus malalignment. CONCLUSION: The aHKA is correlated with the postoperative alignment of mobile-bearing UKA and a high aHKA (> 180°) will increase the risk of postoperative valgus malalignment. Therefore, mobile-bearing UKA should be performed with caution in patients with preoperative aHKA > 180°.

Comparison of clinical and radiographic results of mobile-bearing total ankle arthroplasty between osteoarthritis and rheumatoid arthritis.

OBJECTIVES: Clinical results of mobile-bearing total ankle arthroplasty (TAA) for rheumatoid arthritis (RA) have been reported, but no studies have compared osteoarthritis (OA) and RA. Clinical and radiographic outcomes after at least 3 years were compared between OA and RA. METHODS: Eleven ankles with OA and 22 ankles with RA were followed after mobile-bearing TAA (FINE total ankle system). Clinical outcomes were assessed by the American Orthopaedic Foot and Ankle Society (AOFAS) score. Radiographic outcomes were evaluated by the angular position of the implant, radiolucent lines, migration, and subsidence. Operative and postoperative complications were assessed. RESULTS: There were no significant differences in clinical outcomes, radiographic outcomes, or complications, except the final follow-up AOFAS total score (OA: 89.4 vs RA: 78.2; p = .044) and pain score (OA: 37.3 vs RA: 30.5; p = .041) at a mean follow-up of 83.4 months. Delayed wound healing occurred in 9.1% in RA and none in OA. Radiolucent lines were observed in 45% of both groups, and implant removal was performed in 9.1% and 18.2% of OA and RA, respectively; there were no significant differences. CONCLUSIONS: The final follow-up AOFAS total score and pain score were significantly higher in OA after the FINE total ankle system. There was a discrepancy between radiographic abnormalities and implant removal in both OA and RA.

No difference in mobile and fixed bearing partial knee arthroplasty in octogenarians: a clinical trial.

BACKGROUND: A clinical trial comparing MB (mobile-bearing) versus FB (fixed-bearing) in medial partial knee arthroplasty (PKA) in octagenarians has been conducted. The focus of the present study was on PROMs, range of motion (ROM), implant positioning and implants survivorship. The hypothesis of the present study was that MB implants performed better than FB in PKA in octogenarians. METHODS: The first group received FB PKA-PPK®; the second received MB PKA-Oxford. Patients were not randomly allocated. The following PROMs were administered at T0 (pre-operatively), T1 (1 year after surgery), and T2 (3 years after surgery): visual analogue scale (VAS), Knee Society Score (KSS) and Oxford Knee Score (OKS). Data regarding the implant survivorship and ROM were also collected. Furthermore, the following radiographic parameters were measured: Femoral component varus/valgus; Tibial component varus/valgus; Anteroposterior slope. RESULTS: At T0, 28 patients were included in the FB and 33 in the MB group. The surgical time was shorter in the FB group (p < 0.001). No difference between FB and MB in ROM, VAS, KSS, and OKS at each follow-up (p > 0.05). No difference was found in implant positioning (p > 0.05). At last follow-up, FB group reported three failures caused by aseptic loosening. Four failures were observed in the MB cohort: two for bearing dislocation and two for aseptic loosening. The Kaplan-Meier Curve found no differences in implant survivorship. CONCLUSIONS: According to the main findings of the present clinical trial, MB implants performed similar to FB in PKA in octogenarians. The FB group demonstrated shorted surgical time. No difference was found in patient reported outcome measures, ROM, implant positioning, and survivorship. LEVEL OF EVIDENCE: Level II, prospective study.

Medium term results of the cementless Oxford mobile bearing medial unicompartmental knee replacement.

BACKGROUND: Medial Unicompartmental Knee Replacement (UKR) has well-documented benefits over Total Knee Replacement in the treatment of anteromedial osteoarthritis of the knee. There has been an increasing move from cemented to cementless UKR over the last decade. This non-design centre study assesses the initial experience using the cementless Oxford medial partial knee replacement and provides medium term revision data, as well as Patient Reported Outcome Measures (PROMs). METHODS: A cohort of 200 consecutive patients undergoing medial UKR using the cementless Oxford were identified from our knee groups prospectively collected database. Cases were performed in a single centre under the care of one of four surgeons. All patients were beyond the 5-year minimum timepoint following UKR surgery in order to produce medium term results, at a mean of 7.9 years. Eligible patients completed a postal questionnaire to collect PROMs: Oxford Knee Score, WOMAC and modified American Knee Society Score questionnaires in January 2020 and had their clinical records reviewed. RESULTS: The survivorship in our cohort was 94.5% at a mean follow up of 7.9 years following surgery. There were 11 re-operations in total with a three percent risk of re-operation within the first 18 months following surgery. There was a sustained improvement in Oxford Knee Score with a near 20 points improvement on pre-operative scores. CONCLUSIONS: Our results provide further evidence that partial knee replacements using the cementless Oxford produce good clinical outcomes. Revision rates are similar to those published in the National Joint Registry. LEVEL OF EVIDENCE: III.