Mobile-bearing Medial Unicompartmental Knee Arthroplasty Research Articles

Outcomes of fixed versus mobile-bearing medial unicompartmental knee arthroplasty.

The optimal bearing surface design for medial unicompartmental knee arthroplasty (UKA) remains controversial. The aim of this study was to compare outcomes of fixed-bearing (FB) and mobile-bearing (MB) UKAs from a single high-volume institution. Prospectively collected data were reviewed for all primary cemented medial UKAs performed by seven surgeons from January 2006 to December 2022. A total of 2,999 UKAs were identified, including 2,315 FB and 684 MB cases. The primary outcome measure was implant survival. Secondary outcomes included 90-day and cumulative complications, reoperations, component revisions, conversion arthroplasties, range of motion, and patient-reported outcome measures. Overall mean age at surgery was 65.7 years (32.9 to 94.3), 53.1% (1,593/2,999) of UKAs were implanted in female patients, and demographics between groups were similar (p > 0.05). The mean follow-up for all UKAs was 3.7 years (0.0 to 15.6). Using revision for any reason as an endpoint, five-year survival for FB UKAs was 97.2% (95% CI 96.4 to 98.1) compared to 96.0% for MB (95% CI 94.1 to 97.9; p = 0.008). The FB group experienced fewer component revisions (14/2,315, 0.6% vs 12/684, 1.8%; p < 0.001) and conversion arthroplasties (38/2315, 1.6% vs 24/684, 3.5%; p < 0.001). A greater number of MB UKAs underwent revision due to osteoarthritis progression (FB = 21/2,315, 0.9% vs MB = 16/684, 2.3%; p = 0.003). In the MB group, 12 (1.8%) subjects experienced bearing dislocations which required revision surgery. There were 15 early periprosthetic tibia fractures (0.6%) in the FB group compared to 0 for MB (p = 0.035). In similar patient populations, FB UKAs demonstrated slightly higher survival than a commonly used MB design. Adverse event profiles differed by bearing type, with an increased risk of bearing dislocation and OA progression with MB designs, and early periprosthetic tibia fractures for FB designs.

Altered dynamic joint space in the lateral condyle compartment following medial unicompartmental knee arthroplasty

PurposeThe progression of osteoarthritis in lateral compartment has been identified as a primary complication in medial unicompartmental knee arthroplasty (UKA) revisions, irrespective of whether employing fixed bearing (FB) or mobile bearing (MB) designs. Compared to the previous contact point analyses, the tibiofemoral contacts during knee movements are comprehended by a more comprehensive understanding of joint spaces. This study aims to dynamically map the joint spaces in the lateral compartment during the single-leg lunge following FB and MB UKA procedures, and compare them with the respective contralateral native knees. It is hypothesized that the significant change in joint space for post-UKA compared to their native knees. MethodsTwelve patients with unilateral medial FB UKA and eleven patients with unilateral medial MB UKA were included and underwent computed tomography scans. The exclusion criteria included anterior cruciate ligament deficiency, postoperative knee pain, any postoperative complications, and musculoskeletal illnesses. A dual fluoroscopic imaging system was utilized to capture the single-leg lunge, and 2D-to-3D registration facilitated the visualization of knee motion. According to the knee motions, joint spaces on tibial and femoral surfaces in the lateral compartments of native, FB, and MB UKA knees were calculated and mapped. ResultsIn comparison to the native knees, FB UKA knees exhibited significant increases in medial, lateral, central, and posterior joint spaces in the lateral compartment (p < 0.05), while MB UKA knees showed significant increases only in central and posterior joint spaces (p < 0.05). Moreover, FB UKA demonstrated greater increases in medial, central, and posterior joint spaces compared to MB UKA. Tibial varus and valgus during lunges, as well as the Oxford Knee Score (OKS) and Hip-Knee-Ankle angle (HKA), correlated with joint spaces. ConclusionsDynamic joint space analysis provided a more comprehensive insight into contact dynamics. FB UKA led to an enlargement of joint spaces, whereas MB UKA resulted in joint spaces closer to native knees. These findings contribute to understanding potential postoperative complication in UKAs.

Prediction of Postoperative Range of Motion after Mobile-Bearing Medial Unicompartmental Knee Arthroplasty from the Preoperative Range of Motion and Other Preoperative Factors.

Postoperative flexion after unicompartmental knee arthroplasty might be predicted from the preoperative range of motion and other preoperative factors, but this has not been sufficiently investigated. Between 2013 and 2017, 198 patients (198 knees) underwent unilateral knee arthroplasty with medial mobile-bearing unicompartmental knee arthroplasty. Range of motion was measured preoperatively and at the time of final follow-up. To investigate the accuracy of the prediction of preoperative to postoperative gain or loss of the flexion angle, we performed receiver operating characteristic analysis. Logistic regression analysis was used to evaluate other predictive factors. Change in flexion angle was significantly strongly and negatively correlated with the preoperative flexion angle (R = - 0.688; 95% confidence interval: -0.755 to -0.607; p < 0.001). Preoperative flexion angle was suggested to be a significant predictor of gain or loss of the flexion angle with the area under the curve of 0.781; the cutoff value calculated using the Youden index was 140 degrees. Logistic regression analysis showed that in addition to the preoperative flexion angle of the operated side, the postoperative flexion range was significantly affected by the patient's height and by the preoperative flexion angle of the contralateral knee. If the preoperative flexion angle in Oxford mobile-bearing medial unicompartmental knee arthroplasty is <140 degrees, the postoperative flexion angle may be improved; if it exceeds 140 degrees, the postoperative flexion angle may worsen. This predictive ability is further improved by consideration of the patient's height and the range of motion on the contralateral side.

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

BackgroundFemur-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. MethodsWe 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. ResultsThere 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. ConclusionsThe 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.

A Comparison of the Periprosthetic Fracture Rate of Cemented and Cementless Mobile Bearing Unicompartmental Knee Arthroplasties: An Analysis of Data From the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man

BackgroundPeriprosthetic fractures are rare but serious complications of unicompartmental knee arthroplasty (UKA). Although cementless UKA has a lower risk of loosening than cemented, there are concerns that tibial fracture risk may be higher given the reliance on interference fit for primary stability. The risk of fracture and the effect of surgical fixation are currently unknown. We compared the periprosthetic fracture rate following cemented and cementless UKA surgery. MethodsA total of 14,122 medial mobile-bearing UKAs (7,061 cemented and 7,061 cementless) from the National Joint Registry and Hospital Episodes Statistics database were propensity score-matched. Cumulative fracture rates were calculated and Cox regressions were used to compare fixation groups. ResultsThe three-month periprosthetic fracture rates were similar (P = .80), being 0.10% in the cemented group and 0.11% in the cementless group. The fracture rates were highest during the first three months postoperatively, but then decreased and remained constant between one and 10 years after surgery. The one-year cumulative fracture rates were 0.2% (confidence interval [CI]: 0.1 to 0.3) for cemented and 0.2% (CI: 0.1 to 0.3) for cementless cases. The 10-year cumulative fracture rates were 0.8% (CI: 0.2 to 1.3) and 0.8% (CI: 0.3 to 1.3), respectively. The hazard ratio during the whole study period was 1.06 (CI: 0.64 to 1.77; P = .79). ConclusionsThe periprosthetic fracture rate following mobile bearing UKA surgery is low, being about 1% at 10 years. There were no significant differences in fracture rates between cemented and cementless implants after matching. We surmise that surgeons are aware of the higher theoretical risk of early fracture with cementless components and take care with tibial preparation. Levels of evidenceIII.

Malposition is main cause of failure of Oxford mobile-bearing medial unicompartmental knee arthroplasty.

Unicompartmental knee arthroplasty (UKA) is the preferred treatment for anterior medial knee osteoarthritis (OA) owing to the rapid postoperative recovery. However, the risk factors for UKA failure remain controversial. The clinical data of Oxford mobile-bearing UKAs performed between 2011 and 2017 with a minimum follow-up of five years were retrospectively analyzed. Demographic, surgical, and follow-up data were collected. The Cox proportional hazards model was used to identify the risk factors that contribute to UKA failure. Kaplan-Meier survival was used to compare the effect of the prosthesis position on UKA survival. A total of 407 patients who underwent UKA were included in the study. The mean age of patients was 61.8 years, and the mean follow-up period of the patients was 91.7 months. The mean Knee Society Score (KSS) preoperatively and at the last follow-up were 64.2 and 89.7, respectively (p = 0.001). Overall, 28 patients (6.9%) with UKA underwent revision due to prosthesis loosening (16 patients), dislocation (eight patients), and persistent pain (four patients). Cox proportional hazards model analysis identified malposition of the prostheses as a high-risk factor for UKA failure (p = 0.007). Kaplan-Meier analysis revealed that the five-year survival rate of the group with malposition was 85.1%, which was significantly lower than that of the group with normal position (96.2%; p < 0.001). UKA constitutes an effective method for treating anteromedial knee OA, with an excellent five-year survival rate. Aseptic loosening caused by prosthesis malposition was identified as the main cause of UKA failure. Surgeons should pay close attention to prevent the potential occurrence of this problem.

The footprint of the anterior horn of medial meniscus: A novel and reliable landmark for the tibial vertical cut in Oxford mobile-bearing medial unicompartmental knee arthroplasty

BackgroundTibial vertical cut is crucial for rotational position and bony coverage in Oxford mobile-bearing medial unicompartmental knee arthroplasty (UKA). This study aimed to determine whether the footprint of the anterior horn of medial meniscus (FAM) is a reliable landmark for tibial vertical cut. MethodsThe FAM and the line through FAM and the edge of anterior cruciate ligament insertion (FAMA line) were identified by dissection five knee joint specimens. The angle between FAMA line and standard Akagi’s line was measured. From 2022 to 2023, 64 patients (74 knees) diagnosed as anteromedial osteoarthritis were included to undergo primary Oxford medial UKA by two surgeons (Group 1 and 2), using FAMA line as a landmark for tibial vertical cut. The anteroposterior (AP) length, mediolateral (ML) length of tibial cut and tibial prothesis were measured by vernier caliper. ML/AP ratio was also calculated, and data were compared intragroup and intergroup. Mediolateral position and external rotation of tibial components were assessed postoperatively. ResultsFAMA line was parallel to standard Akagi’s line. No significant differences were found in AP and ML lengths between tibial cut and tibial component (AP different value = 0.007 ± 0.154 cm, P = 0.674, ML different value = 0.020 ± 0.195 cm, P = 0.155). The ML/AP ratio was similar between the two groups (P = 0.141, 0.646, 0.255, 0.607, 0.384, size AA ∼ D). No significant difference was found in mediolateral position (0.87 ± 0.03 vs. 0.86 ± 0.03, P = 0.156) and external rotation (6.88 ± 2.08 vs. 6.68 ± 2.22, P = 0.746) of the tibial component between the two groups. ConclusionThe FAM is a reliable landmark for tibial vertical cut in Oxford UKA.

Impact of lateral meniscus injury detected by preoperative magnetic resonance imaging on midterm results after unicompartmental knee arthroplasty

BackgroundThe significance of lateral meniscus injury and its impact on success rates with medial unicompartmental knee arthroplasty (UKA) is still debated among scholars. This study aims to investigate whether preoperative magnetic resonance imaging (MRI) findings of lateral meniscus injury influence midterm outcomes following UKA. MethodsThis study recruited 104 patients who underwent medial mobile-bearing UKA. Based on the extent of lateral meniscus injury indicated by the preoperative MRI and Stoller's classification system, patients were divided into two groups: the normal group (grade 0), and the lateral meniscus injury group (grade 3). Further, preoperative demographic and clinical outcome data (Hospital for Special Surgery score, lateral knee pain, squatting, and knee extension ability) were compared at least 2 years postoperatively. ResultsNo statistically significant difference in knee function or clinical outcome was found between the normal group (n = 59) and the lateral meniscus injury group (n = 45). During the 39.2 months (range: 24–64 months), no patient required any reoperation or revision procedures. ConclusionIn summary, the presence of lateral meniscus injury as determined by preoperative MRI does not affect the midterm results after UKA. Without additional treatment for lateral meniscus injury, UKA can yield desired outcomes regardless of the presence of lateral meniscus injury on preoperative MRI.

The impact of preoperative MRI-detected lateral meniscal intra-substance signal abnormalities on mid-term functional outcomes following mobile-bearing unicompartmental knee arthroplasty.

There is a dilemma as to whether the presence of degenerative changes of lateral meniscus is a contraindication to medial unicompartmental knee arthroplasty (UKA). Therefore, the purpose of this study is to assess the influence of preoperative MRI-detected lateral meniscal intra-substance signal abnormalities on mid-term functional outcomes following mobile-bearing UKA. We performed a retrospective review of the record on a consecutive series of patients who have undergone mobile-bearing medial UKA from September 2020 to June 2023. The mean duration of follow-up was 2.34 years. All records were collected from case system. MRI assessment of lateral meniscus was performed with the use of the Stoller's classification system. Patients were categorized into two groups (grade 0 and ≥ grade 1). Patient-reported outcomes were assessed with the use of the American Knee Society functional Score (AKSS-F), American Knee Society Objective Score (AKSS-O), and Oxford Knee Score (OKS) preoperatively and at latest follow-up. Furthermore, range of motion (ROM) and hip-knee-ankle angle (HKA) were measured in preoperative and postoperative periods. A total of 92 patients (101 knees) were included in our study. No differences in AKSS-F, AKSS-O, OKS, HKA, or ROM were found between those who showed normal or abnormal signal change of lateral meniscus preoperatively (P < 0.05). Furthermore, there were also no significant differences between two groups concerning AKSS-F, AKSS-O, OKS, HKA, or ROM at latest postoperative follow-up (P < 0.05). Age and duration of disease were independent predictors of low postoperative AKSS-F and AKSS-O (P < 0.05). Nevertheless, ROM was an independent predictor of high postoperative AKKS-O (P < 0.05). Age and female were independent predictors of high postoperative OKS (P < 0.05). The presence of preoperative MRI-detected lateral meniscal degenerative changes did not affect mid-term functional outcomes in patients who underwent mobile-bearing medial UKA. On the basis of the results of the current study, we believe that the presence of degenerative changes of lateral meniscus is acceptable in mobile-bearing medial UKA.

Influence of patellofemoral joint degeneration on clinical outcomes after medial unicompartmental knee arthroplasty.

Patellofemoral joint (PFJ) degeneration has traditionally been regarded as a contraindication to unicompartmental knee arthroplasty (UKA). More recently, some researchers have proposed that PFJ degeneration can be ignored in medial UKA, and others have proposed that this change should be reviewed in PFJ degenerative facets and severity. This study aimed to systematically evaluate the effect of PFJ degeneration on patient-reported outcome measures (PROMs) and revision rates after medial UKA. Electronic databases (PubMed, Embase, Web of Science, etc.) were searched for studies assessing the influence of PFJ degeneration on medial UKA. A random-effects meta-analysis was conducted for the Oxford knee score (OKS), Knee society score (KSS), and revision rates and stratified by PFJ degenerative facets (medial/lateral/trochlear/unspecified), severe PFJ degeneration (bone exposed), and bearing type (mobile/fixed). Heterogeneity was assessed by the Cochran Q test statistic and chi-squared tests with the I-squared statistic. A total of 34 articles with 7007 knees (2267 with PFJ degeneration) were included (5762 mobile-bearing and 1145 fixed-bearing and 100 unspecified). Slight to moderate degenerative changes in the medial and trochlear facets did not decrease the OKS and KSS, and only lateral facets significantly decreased the OKS (mean difference [MD] = -2.18, P < 0.01) and KSS (MD = -2.61, P < 0.01). The severity degree of PFJ degeneration had no additional adverse effect on the OKS, KSS, or revision rates. For mobile-bearing UKA, only lateral PFJ degeneration significantly decreased the OKS (MD = -2.21, P < 0.01) and KSS (MD = -2.44, P < 0.01). For fixed-bearing UKA, no correlation was found between PROMs/revision rates and PFJ degeneration. For medial mobile-bearing UKA, slight to moderate degenerative changes in the PFJ, except lateral facet, did not compromise PROMs or revision rates. For medial fixed-bearing UKA, although it might not be conclusive enough, PROMs or revision rates were not adversely affected by PFJ degeneration (regardless of the facet).

Valgus Stress Radiograph Can Predict Alignment Change of Medial Mobile-Bearing Unicompartmental Knee Arthroplasty.

Finding reliable tools to predict alignment change after medial mobile-bearing unicompartmental knee arthroplasty (UKA) can help surgeons avoid under- or over-correction. This prospective study aimed to investigate whether the parameters related to medial collateral ligament tension on valgus stress radiograph can predict the alignment change of medial mobile-bearing UKA and establish a prediction model. This study prospectively included the patients undergoing medial mobile-bearing UKA for knee osteoarthritis from November 2018 and April 2021. Patients took valgus stress radiograph and MRI preoperatively and took full-length weight-bearing anterior-posterior radiograph of the lower extremity preoperatively and postoperatively. The medial joint space width (MJSW) on valgus stress radiograph, area of femoral and tibial osteophyte on MRI, medial extrusion distance (MED) of the meniscus on MRI, and the change in hip-knee-ankle angle (∆HKAA) were measured. Factors influencing ∆HKAA were analyzed by correlation analysis. Univariable and multivariable linear regression analysis was performed to establish a prediction model of ∆HKAA. One hundred and seven knees were included. On average, the preoperative HKAA was 170.84° ± 3.73°, and UKA corrected the alignment to 175.16° ± 3.21° postoperatively (p < 0.001), with ∆HKAA of 4.33° ± 1.93°. Correlation analysis showed that ∆HKAA correlated with MJSW (r = 0.628, p < 0.001), MED (r = 0.262, p < 0.001), and tibial osteophyte area (r = 0.235, p < 0.001). The prediction model for ∆HKAA was obtained by multivariable linear regression: ∆HKAA = -2.003 + 0.947 × MJSW(mm) + 1.838 × total osteophyte area(cm2 ). Valgus stress radiographic MJSW and osteophyte area are correlated to the alignment change of medial mobile-bearing UKA. The prediction model for HKAA change is: ∆HKAA = -2.003 + 0.947 × MJSW(mm) + 1.838 × total osteophyte area(cm2 ).

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

IntroductionMedial 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. MethodsA 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. ResultsThere 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. ConclusionsThis 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.

Presence of a Lateral Trochlear Osteophyte Predicts Medial Unicompartmental Arthroplasty Failure at Midterm Follow-up

BackgroundSpecific clinical and radiographic risk factors for medial unicompartmental knee arthroplasty (UKA) failure are incompletely understood. The purpose of this study was to perform a midterm survivorship analysis of medial UKA from a single, nondesigner surgeon. Based on observations from clinical practice, we hypothesized that the presence of a lateral trochlear osteophyte on preoperative Merchant radiographs may be predictive of medial UKA failure secondary to progressive osteoarthritis (OA). MethodsPatients who underwent a mobile-bearing medial UKA by a single surgeon with minimum 24 months of clinical follow-up from 2008 to 2019 were retrospectively identified. Radiographic parameters, including the presence of a lateral trochlear osteophyte, were measured. Kaplan-Meier survivorship analyses were performed. Cox proportional hazards models were used to evaluate variables as risk factors for UKA failure, defined as reoperation or component revision. ResultsA total of 233 UKAs were included. The mean age was 60 years, mean BMI 32 kg/m2, and 53% of patients were male. The mean follow-up duration was 5.7 years (range, 2.0-13.1 years). Using any reoperation as an endpoint, the 10-year survival was 91%. Using any component revision as an endpoint, the 10-year survival was 93%. Using revision due to progressive OA as an endpoint, the 10-year survival was 95%. The presence of a lateral trochlear osteophyte was associated with an increased risk of any reoperation (hazard ratio 3.6; 95% confidence interval 1.3-9.5) and increased risk of revision due to progressive OA (hazard ratio 9.8; 95% confidence interval 2.9-32.7). ConclusionsThe presence of a lateral trochlear osteophyte on preoperative Merchant view radiographs was associated with an increased risk of medial UKA failure.

High tibial osteotomy with an external fixator or unicompartmental knee arthroplasty for varus knee in young patients?

PurposeThis study compares the functional results and survivorship of unicompartmental knee arthroplasty (UKA) and high tibial osteotomy (HTO) with an external fixator for medial compartment osteoarthritis (OA) of the knee. MethodsTwo cohorts of patients aged less than 60 years who had undergone either a cemented medial mobile-bearing UKA or an HTO with an external fixator were included in the study. The first cohort included patients undergoing a series of 197 consecutive medial UKA procedures (UKA group). The second cohort consisted of 60 consecutive patients undergoing HTO with an external fixator (HTO group). Each patient was assessed based on the Oxford Knee Score (OKS), the Knee Injury and Osteoarthritis Outcome Score (KOOS) and the Subjective International Knee Documentation Committee (IKDC) score/questionnaire. A clinical evaluation was conducted on the day of the surgery (T0) and at the follow-up visit (T1) (minimum follow-up time was 60 months). Complications and failures resulting from the surgery were recorded for each patient. ResultsOnly the age of the patients at the pre-operative time differed significantly between the two groups, with the HTO group being significantly younger (47.7 ± 8.0 versus 55.8 ± 2.2).After the final follow-up visit, all scores improved in both groups (p < 0.05).IKDC and Oxford scores were higher for the UKA group (p < 0.05). In the HTO group, three complications occurred (5%), including two superficial infections and one deep infection. On the other hand, the UKA group reported four complications (2%): three aseptic mobilisations and one infection requiring revision surgery. There was no difference in the complication rate between the two groups (p = 0.208). ConclusionsIn young patients (<60 years) with an isolated medial knee OA, both HTO and UKA led to good to excellent clinical results with a low rate of complications at mid-term follow-up; both surgical procedures may be considered in this patient population. Level of evidenceLevel III.

Effect of tibial component overhang on survivorship in medial mobile-bearing unicompartmental knee arthroplasty

BackgroundSome studies have shown that the position of the tibial component in Oxford unicompartmental knee arthroplasty with a mobile bearing will affect the clinical outcome of patients. Hence, our study aimed to investigate the relationship between the overhang distance of the tibial component and the survival of the implant. MethodsA retrospective analysis of patients who underwent unicompartmental knee arthroplasty at the same institution from 2014 to 2018 was presented. The study was divided into three groups: minor underhang group (underhang between −3 and 0 mm); minor overhang group (overhang 0–3 mm); and major overhang group (overhang ≥ 3 mm). Demographic and clinical profile characteristics of each group were compared, and survival curves of each group were also compared using Kaplan–Meier and modeled using multivariate Cox regression. ResultsA total of 351 knees were included in this study with a minimum follow up of three years and a mean follow up of 4.8 ± 1.5 years. The revision rates in each group were 3.6% (minor underhang group), 2.7% (minor overhang group), and 20.9% (major overhang group) (P < 0.001). From the three groups’ cumulative survival rates, the major overhang group was significantly lower than the other two groups (log rank P < 0.001). Multivariate Cox regression showed an association between the major overhang group and implant survival rate (hazard ratio = 7.515, 95% confidence interval = 2.500–22.593, P < 0.001) ConclusionThe risk of revision will increase if the tibial component overhangs more than 3 mm medially. Moreover, the reasons for revision are generally bearing dislocation and aseptic loosening.

Assessment of in vivo bone activity patterns in medial mobile-bearing unicompartmental knee arthroplasty : a prospective SPECT/CT study.

Higher osteoblastic bone activity is expected in aseptic loosening and painful unicompartmental knee arthroplasty (UKA). However, insights into normal bone activity patterns after medial UKAs are lacking. The aim of this study was to identify the evolution in bone activity pattern in well-functioning medial mobile-bearing UKAs. In total, 34 patients (13 female, 21 male; mean age 62 years (41 to 79); BMI 29.7 kg/m2 (23.6 to 42.1)) with 38 medial Oxford partial UKAs (20 left, 18 right; 19 cementless, 14 cemented, and five hybrid) were prospectively followed with sequential 99mTc-hydroxymethane diphosphonate single photon emission CT (SPECT)/CT preoperatively, and at one and two years postoperatively. Changes in mean osteoblastic activity were investigated using a tracer localization scheme with volumes of interest (VOIs), reported by normalized mean tracer values. A SPECT/CT registration platform additionally explored cortical tracer evolution in zones of interest identified by previous experimental research. Significant reduction of tracer activity from the preoperative situation was found in femoral and anteromedial tibial VOIs adjacent to the UKA components. Temporarily increased osteoblastic bone activity was observed in VOIs comprising the UKA keel structure at one year postoperatively compared to the preoperative activity. Persistent higher tracer uptake was found in the posterior tibial cortex at final follow-up. Multivariate analysis showed no statistical difference in osteoblastic bone activity underneath cemented or cementless components. Well-functioning medial mobile-bearing UKAs showed distinct changes in patterns of normalized bone tracer activity in the different VOIs adjacent to the prosthetic components, regardless of their type of fixation. Compared to the preoperative situation, persistent high bone activity was found underneath the keel and the posterior tibial cortex at final follow-up, with significant reduced activity only being identified in femoral and anteromedial tibial VOIs. Cite this article: Bone Joint J2022;104-B(1):34-44.

Return to physical activity and change in body mass index after hypoallergenic medial mobile-bearing unicompartmental knee arthroplasty

BackgroundThe primary purpose of the present prospective study was to consecutively analyse the outcomes of the return to sports activity of patients with positive patch tests undergoing a medial mobile-bearing titanium niobium nitride (TiNbN) unicompartmental knee arthroplasty (UKA). The secondary purpose was to ascertain if a higher grade of physical activity leads to a reduction in the body mass index (BMI) of the patients.Material and methodsForty-one patients with positive skin patch tests were included in this prospective study. The clinical evaluation consisted of the University of California, Los Angeles (UCLA) activity scale and the High-Activity Arthroplasty Score (HAAS). Each patient was evaluated the day before surgery (T0), after 12.37 ± 0.70 months (T1), and on the day of the final follow-up, after 67.03 ± 18.2 months (T2). Furthermore, the BMI of each patient was analysed before surgery and during the final follow-up.ResultsThe UCLA and HAAS mean preoperative values ranged from 3.68 ± 1.1.7 and 6.15 ± 0.76 to 6.1 ± 0.76 and 10.34 ± 1.3, respectively, at T1 (p < 0.0001) and to the final values of 6.34 ± 0.62 and 11.0 ± 8.9, respectively, at T2 (UCLA: T2 versus T1: p = 0.132; T2 versus T0: p < 0.0001; HAAS: T2 versus T1: p = 0.0027; T2 versus T0: p < 0.001). BMI ranged from a preoperative value of 27.97 ± 3.63 to a final value of 26.84 ± 3.11 (p < 0.0001). The only differences within the subgroups concerned patients with BMI ≥ 28, showing a superior HAAS at each follow-up (p < 0.05). A positive correlation was found between BMI and HAAS at T0 and T2 (p < 0.05).ConclusionsThis is the first study to evaluate the rate of the return to sports activities and change in BMI following hypoallergenic UKA. The majority of patients reduced their weight following UKA and improved their physical activity, showing outcomes that were comparable to the standard cobalt–chrome (CoCr) prostheses, regardless of gender, age, BMI and implant size.Level of evidenceIV – Prospective Cohort Study.Trial registration researchregistry5978—Research Registry www.researchregistry.com

Sensor and machine learning-based assessment of gap balancing in cadaveric unicompartmental knee arthroplasty surgical training.

The aim of this study was to assess the difference between flexion and extension contact forces-gap balance-after Oxford mobile-bearing medial unicompartmental knee arthroplasty (UKA) performed by surgeons with varying levels of experience. Surgeons in a training programme performed UKAs on fresh frozen cadaveric specimens (n = 60). Contact force in the medial compartment of the knee was measured after UKA during extension and flexion using a force sensor, and values were clustered using an unsupervised machine learning (k-means algorithm). Univariate analysis was performed with general linear regression models to identify the explanatory variable. The level of experience was predictive of gap balance; surgeons were clustered into beginner, mid-level and experienced groups. Experienced surgeons' mean difference between flexion and extension contact force was 83N, which was significantly lower (p < 0.05) than that achieved by mid-level (215N) or beginner (346N) surgeons. We found that the lowest mean difference between flexion and extension contact force after UKA was 83N, which was achieved by surgeons with the most experience; this value can be considered the optimal value. Beginner and mid-level surgeons achieved values that were significantly lower. This study also demonstrates that machine learning can be used in combination with sensor technology for improving gap balancing judgement in UKA.

Similar rates of return to sports and BMI reduction regardless of age, gender and preoperative BMI as seen in matched cohort of hypoallergenic and standard Cobalt Chromium medial unicompartmental knee arthroplasty.

To compare the rate of return to sports and body mass index (BMI) reduction in patients who underwent surgery for unicompartmental knee arthroplasty (UKA) with either Cobalt-Chromium (CoCr) alloy UKA or with hypoallergenic UKA, stratified by age, gender and BMI. Two consecutive cohorts of patients with a total of 172 UKA and a minimum 2-year follow-up period were prospectively included in this comparative study. The first cohort consisted of 136 consecutive series of standard Cobalt-Chromium (CoCr Group). The second cohort consisted of 36 consecutive mobile-bearing hypoallergenic Titanium Niobium Nitride UKA, (TiNbN Group). The clinical evaluation was based on the University of California, Los Angeles (UCLA) activity scores and the High-Activity Arthroplasty Score (HAAS) evaluated on the day before surgery (T0) and after a minimum follow-up of 12months (T1) and 24months (T2). Radiographic evaluation performed at T2 included the femoral component position in varus/valgus, the tibial component in varus/valgus and the anteroposterior slope. No statistical differences were found between the groups at each follow-up, as shown by the UCLA and HAAS score (n.s.). Both groups showed a statistically significant improvement (p < 0.05) at each follow-up.. Both groups showed a statistically significant BMI reduction between T0 and T2 (p < 0.05). Radiographicanalysis revealed no statistical differences between the two groups in terms of the three measures after the final follow-up (n.s.). All the subgroups showed a significant (p < 0.05) rate of return to sport if compared with the preoperative value (T2 versus T0), except for male in TiNbN group. Both TiNbN and CoCr medial mobile-bearing UKA enabled patients to return to sports after the final follow-up, regardless of age, BMI, gender and metal sensitivity. These findings inform shared decision making and can help to manage patient expectations after surgery, in particular, in active patients with an overt metal allergy, a specific hypoallergenic implant should be considered the gold standard implant in partial knee replacement surgery. Cohort Study, Level III. researchregistry6250- www.researchregistry.com .

Cemented medial mobile-bearing Unicompartmental Knee Arthroplasty: Effects of compliance with current indications on functional outcomes and long-term survival rates

BackgroundUnicompartmental knee arthroplasty (UKA) is a surgical option for patients with medial compartment osteoarthritis (OA). The objective of this study was to describe the functional outcomes and long-term survival rates of cemented medial mobile-bearing UKA according to the compliance with current indications. MethodsRetrospective study of 78 patients with medial unicompartimental knee OA treated with mobile-bearing cemented UKA (Oxford phase-III) between 2002 and 2012, with an average follow-up of 10.4 ± 3.4 years. Preoperative radiographs and clinical records were reviewed to assess the compliance with current indications (isolated medial compartment OA, flexion ≥ 90°, integrity of all ligaments, varus deformity<15°). Patients who met all criteria were classified with appropriate indication. The function was measured using the knee society score (KSS). ResultsNineteen (24.3%) patients did not meet the current indications for UKA. Non-isolated OA of the medial compartment was the most frequent inappropriate indication (16 patients), followed by range of flexion<90° (2 patients) and lack of integrity of the ligaments (1 patient). A significant improvement was found on the KSS after surgery [preoperative KSS: 50.0 (Interquartile range-IQR: (35.0–60.0); postoperative KSS: 70.0 (IQR:60.0–70.0), p < 0.05]. Survival after 15 years of follow-up in cases without and with appropriate indication was 55.8% and 89.7%, respectively. A higher risk of revision surgery was found in cases with inappropriate indication (hazard ratio: 4.87, 95% Confidence Interval: 1.54–15.38, p:0.007). ConclusionWhen proper patient selection is carried out, cemented medial mobile-bearing UKA offers good functional outcomes with a survival rate of 89.7% at 15 years of follow-up.