Impact of Proximal Tibial Varus Anatomy on Survivorship After Medial Unicondylar Knee Arthroplasty

BackgroundPrecise indications for medial unicondylar knee arthroplasty (UKA) continue to be defined. It is unclear if patients who have proximal tibia vara should be considered candidates for UKA. The purpose of this study was to evaluate the impact of proximal tibial varus alignment on outcomes after UKA.MethodsA retrospective review identified 2,416 patients (3,029 knees) who underwent mobile-bearing medial UKA with 2-year minimum follow-up or revision. Preoperative radiographs were evaluated, and medial proximal tibial angle (mPTA) was measured. Patients were grouped into two groups as follows: mPTA <80 degrees and mPTA ≥80 degrees. Analyses were performed on the impact of mPTA on clinical outcomes, all-cause revisions, and tibial failures.ResultsAt a mean follow-up of 5 years (range, 0.5 years to 12.8 years), there was not a statistically significant difference in clinical outcomes nor increased risk for all-cause revision or tibial failure in patients who had an mPTA <80°. Mean mPTA in patients who had tibial failures was 82.5° and not significantly different than those who did not have a tibial failure (82.9°) (P = .289). Tibial failure rate in knees with an mPTA <80° was 2.2% and not significantly different than knees with an mPTA ≥80° at 1.4% (P = .211). The all-cause revision rate in knees with an mPTA <80° was 5.8% and was not significantly different than knees with an mPTA ≥80° at 4.9% (P = .492).ConclusionPatients who have tibia vara are not at increased risk for tibial related or all-cause failure in medial UKA. This data may allow surgeons to increase their indications for medial UKA.     

Is Mobile-Bearing Medial Unicompartmental Knee Arthroplasty Appropriate for Asian Patients With the Risk of Bearing Dislocation?

BackgroundMobile-bearing unicompartmental knee arthroplasty (UKA) is an attractive operation for medial unicompartmental knee arthritis, but unexpected bearing dislocation is a drawback. Bearing dislocation occurs more frequently in Asians, whose lifestyle involves deeper knee flexion than Westerners. This study investigated whether mobile-bearing medial UKA is appropriate for Asians by analyzing (1) the rate of bearing dislocation and (2) the results of patients with bearing dislocation.MethodsWe retrospectively reviewed 531 consecutive mobile-bearing medial UKA in the previous 15 years, including 22 patients with bearing dislocation who had at least 2 years of follow-up. The entire patient cohort was divided into 2 groups: the symmetrical bearing (187 knees) and the anatomic bearing (344 knees) groups. In the anatomic bearing group, patients who underwent surgery using the conventional phase III (283 knees) vs the Microplasty (61 knees) instrumentation systems were compared.ResultsThe overall incidence of bearing dislocation was 4.1% (22/531). Patients with the symmetrical bearing displayed a relatively high dislocation rate of 9.6% (18/187), which significantly decreased to 1.1% (4/344) after changing to the anatomic bearing (P < .001). In the anatomic bearing group, the dislocation rate with the conventional phase III system was 1.4% (4/283). There were no bearing dislocations in the Microplasty system group (0%, 0/61) after at least 2 years of follow-up.ConclusionAlthough mobile-bearing medial UKA was reported to have a high incidence of bearing dislocation in Asians, this frequency of dislocation is drastically decreased by bearing design and implantation system improvements. We consider mobile-bearing medial UKA appropriate for Asians.     

Varus-Valgus Constrained Implants With a Mobile-Bearing Articulation: Results of 367 Revision Total Knee Arthroplasties

BackgroundVarus-valgus constrained (VVC) implants are used for compromised ligamentous stability in revision total knee arthroplasties (TKAs). Mobile-bearing VVC implants may reduce rotational forces; yet, limited clinical data exist. The purpose of this study is to report mid-term risk of re-revision, complications, and clinical outcomes with a mobile-bearing VVC implant.MethodsThree hundred thirty-seven patients (367 TKAs) who underwent revision TKA with a mobile-bearing VVC implant between 1999 and 2013 at a single institution were reviewed. Mean age at revision was 67 years. Mean follow-up was 4 years. The main indications for revision were aseptic loosening in 158 cases (43%), reimplantation after 2-stage exchange arthroplasty in 120 (33%), instability in 61 (17%), and other in 28 (7%). Clinical outcomes were assessed by Knee Society Scores, and survivorship was analyzed with death as the competing risk.ResultsThe 5-year cumulative incidences of any re-revision or re-revision for aseptic loosening were 9% and 3%, respectively. Twenty-six knees (7%) were re-revised: 15 for infection, 6 for aseptic loosening, and 5 for other causes. There were 17 cases of irrigation and debridement, 10 cases of manipulations under anesthesia, and 9 cases of periprosthetic fractures. There were no bearing “spin-outs.” The mean Knee Society Scores improved from 45 preoperatively to 77 at most recent follow-up (P < .001).ConclusionThe functional improvement and 5-year cumulative incidence of revision of a mobile-bearing VVC implant demonstrated acceptable outcomes with no unique complications related to the mobile-bearing construct. Additional follow-up will be needed to determine long-term implant survivorship.     

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.     

Anterior Cruciate Ligament Deficiency is Not Always a Contraindication for Medial Unicompartmental Knee Arthroplasty: A Retrospective Study in Nondesigner’s Japanese Hospital

BackgroundAn intact anterior cruciate ligament (ACL) is thought to be prerequisite for successful unicompartmental knee arthroplasty (UKA), but recent studies reported successful midterm results of UKA in ACL-deficient (ACLD) knees. We hypothesized that ACLD is not always a contraindication for medial UKA when preoperative radiographs showed typical anteromedial knee patterns.MethodsFrom April 2012 to March 2016, 401 Oxford mobile-bearing UKAs in 282 patients were retrospectively identified from our database. Patients whose ACL was severely damaged, but preoperative X-rays showed typical anteromedial osteoarthritis patterns, were categorized into the ACLD group. From intraoperative data, those whose ACL was intact were categorized into the ACL functional (ACLF) group. There were 32 and 369 knees in the ACLD and ACLF groups, respectively, and mean follow-up periods were 66.1 and 63.8 months for the ACLD and ACLF groups, respectively. We compared the postoperative clinical outcome and component survivorship, with an endpoint of component revision, between ACLD groups and ACLF groups.ResultsIn both groups, the Oxford knee score, Knee Society score, Tegner activity score, and knee range of motion in extension were improved after surgery. The UKA component survival rate at five years was 100% in the ACLD group and 98.9% in the ACLF group. There were no significant differences between the groups.ConclusionMid-term clinical outcomes of Oxford mobile-bearing UKA in ACLD knees were similar to those in ACLF knees. ACL deficiency is not always a contraindication for medial unicompartmental knee arthroplasty in patients with typical anteromedial osteoarthritis radiographs.     

Valgus Subsidence of the Tibial Component Caused by Tibial Component Malpositioning in Cementless Oxford Mobile-Bearing Unicompartmental Knee Arthroplasty

BackgroundValgus subsidence (VS) of the tibial component is a rare complication of unicompartmental knee arthroplasty (UKA), and surgeons might consider revision surgery. The present study aimed to identify the factors related to VS of the tibial component after cementless Oxford mobile-bearing UKA.MethodsThe study included 120 patients who underwent Oxford mobile-bearing UKA using a cementless tibial component in our center between September 2015 and September 2016. Six showed VS of >2° after surgery. Patients were stratified into 2 groups according to the occurrence of VS of the tibial component (VS group, n = 6; no-subsidence group, n = 114). Postoperative radiographic evaluations were conducted to assess the varus/valgus alignment, rotation, and mediolateral position of the tibial and femoral components. The Oxford Knee Score (OKS) was assessed at 3, 6, and 12 months postoperatively. Positional parameters and sequential change in OKS were compared between the two groups using unpaired t-test (P < .05, statistically significant).ResultsAt 3 months postoperatively, an average VS of 3.4° in the VS group was observed, with a significant decrease in OKS. VS was associated with a significantly more medial position and external rotation of the tibial component. After 3 months, VS stopped, and the OKS gradually improved without revision surgery.ConclusionsVS might be caused by the malpositioning of the tibial component. VS of the tibial component after UKA appears to stop, with simultaneous pain relief, even without revision after 3 months postoperatively.     

Satisfactory Outcomes of All-Poly Fixed Bearing Unicompartmental Knee Arthroplasty for Avascular Osteonecrosis Versus Osteoarthritis: A Comparative Study With 10 to 22 Years of Follow-up

BackgroundWhile good mid-term results for treating spontaneous knee osteonecrosis (SPONK) with unicompartmental knee arthroplasty (UKA) have been reported, concerns remain about implant survival at long-term. This study aimed to compare outcomes and survivorship of UKA for SPONK vs osteoarthritis at a minimum of 10 years.MethodsThis case-control study included medial UKA for femoral SPONK operated between 1996 and 2010 with a minimum 10-year follow-up (n = 47). Each case was matched with a medial UKA for osteoarthritis based on body mass index (BMI), gender, and age. Knee Society Score (KSS), complications and radiological (loosening) data were collected at the last follow-up. Kaplan-Meier survivorship analysis was performed using revision implant removal as endpoint.ResultsThe mean follow-up was 13.2 years (range 10 to 21 years). Mean age and BMI were 72.9 ± 8.4 years and 25.5 ± 3.6 Kg/m² in SPONK group. At last follow-up, knee and function KSS were 89.5 ± 12 and 79 ± 18 in SPONK group vs 90 ± 15 (P = .85) and 81.7 ± 17 (P = .47) in control group. Complications and radiological results showed no significant differences. The survival rate free from any revision was 85.1% at last follow-up in SPONK group and 93.6% in control group (P = .23). The leading cause for revision was aseptic tibial loosening (57.1%) in SPONK group. The 15-year survival estimate was 83% in SPONK group.ConclusionSatisfactory clinical outcomes at long-term after UKA for femoral SPONK were observed, similar to those after UKA for osteoarthritis, despite a higher risk of tibial loosening in the SPONK group. No symptomatic femoral loosening leading to a revision was observed.Level of EvidenceIV.     

A Comprehensive Evaluation of Lateral Unicompartmental Knee Arthroplasty Short to Mid-Term Survivorship,and the Effect of Patient and Implant Characteristics: An Analysis of Data From the Dutch Arthroplasty Register

BackgroundThe rarity of lateral unicompartmental knee arthroplasty (UKA) results in a lack of large cohort studies and understanding. The aim of this study is to comprehensively evaluate survivorship of lateral UKA with registry data and compare this to medial UKA.MethodsLateral (n = 537) and medial UKAs (n = 19,295) in 2007-2017 were selected from the Dutch Arthroplasty Register. Survival analyses were performed with revision for any reason as primary endpoint. Adjustments were made for patient and implant characteristics. Stratified analyses according to patient and implant characteristics were performed. Reasons and type of revision were grouped according to laterality and bearing design.ResultsThe 5-year revision rate was 12.9% for lateral UKA and 9.3% for medial UKA. Multivariable regression analyses showed no significant increased risk for revision for lateral UKA (hazard ratio 0.87, 95% confidence interval 0.66-1.15). Stratified analyses showed that the effect of patient characteristics on revision was comparable between lateral and medial UKA; however, the use of mobile-bearing design for lateral UKA was associated with increased revision rate. Progression of osteoarthritis was the main reason for revision on both sides accompanied by tibia component loosening for medial UKA. Reasons and type of revision varied depending on bearing design.ConclusionSimilar survivorship of lateral and medial UKA was reported. Specifically, there is a notable risk for revision when using mobile-bearing designs for lateral UKA. Failure modes and type of revision depends on laterality and bearing design. These findings emphasize that surgical challenges related to anatomy and kinematics of the lateral and medial knee compartment need to be considered.     

High Survival Rate and Very Low Wear of Lateral Unicompartmental Arthroplasty at Long Term: A Case Series of 54 Cases at a Mean Follow-Up of 17 Years

BackgroundSurvivorship of lateral unicompartmental knee arthroplasty (UKA) has progressively improved. However, there are few studies describing long-term results, and no study reports on polyethylene (PE) wear in lateral unicompartmental arthroplasty.The aims of this study are to determine the survival rate of lateral UKA with a fixed, all-PE bearing, and the PE wear of the tibial implant at a minimum of 15 years follow-up.MethodsFrom January 1988 to October 2003, we performed 54 lateral UKAs in 52 patients. All patients had isolated lateral osteoarthritis (OA). The mean age at the index procedure was 65.4 ± 11 years. Thirty-nine UKAs were available for follow-up (30 alive and 9 dead after 15 years). Twelve patients had died before 15 years and 3 patients were lost to follow-up. The mean follow-up was 17.9 years (range, 15-23 years).ResultsAt the final follow-up, 8 knees of 39 (20.5%) had a surgical revision. The cumulative survival rate was 82.1% at 15 years and 79.4% at 20 years. The main reason of revision was progression of OA (87.5%), followed by aseptic loosening of the tibial component (12.5%). With a mean follow-up of 17.9 years, the mean PE wear was 0.061 mm/y. There was no radiographic loosening in the surviving implants and no revisions for wear. The mean functional International Knee Society score was 66.5 ± 26.8, with a mean objective score of 84.4 points ± 13.2. In the population without revision, 90.5% were satisfied or very satisfied at the latest follow-up.ConclusionLateral UKA with a fixed, all-PE tibial bearing and a femoral resurfacing implant presents a high survivorship at long term, with very low PE wear.     

Fixed-Bearing Medial Unicompartmental Knee Arthroplasty in Patients Younger Than 55 Years of Age at 4-19 Years of Follow-Up: A Concise Follow-Up of a Previous Report

BackgroundUnicompartmental knee arthroplasty (UKA) is an effective alternative to total knee arthroplasty (TKA) in isolated unicompartmental disease; however, mid-term to long-term results in young patients are unknown. The purpose of this study is to determine the mid-term outcomes of fixed-bearing medial UKA in patients less than 55 years of age.MethodsSeventy-seven fixed-bearing medial UKAs in patients less than 55 years of age (mean 49.9, range 38-55) from a previously published report were retrospectively reviewed at a mean follow-up of 11.2 years (range 4.1-19.2).ResultsEleven knees were converted to TKA (14.3%) at 0.7-13.8 years postoperatively. The indications for revision included 7 for unexplained pain (9.1%), 2 for grade 4 arthritic progression (1 isolated lateral and 1 lateral and patellofemoral compartments; 2.6%), 1 for polyethylene wear (1.3%), and 1 for femoral component loosening (1.3%). Predicted survivorship free from component revision was 90.4% (95% confidence interval 86.9-93.9) at 10 years and 75.1% (95% confidence interval 66.2-84.0) at 19 years. The mean Knee Society Score improved from a mean of 51.9-88.6 points (P < .001). Of the 52 knees with 4-year minimum radiographs, 3 (5.8%) developed isolated grade 4 patellofemoral arthritis that was asymptomatic, and no knees had evidence of component loosening or osteolysis.ConclusionFixed-bearing medial UKA is a durable option for young patients with unicompartmental arthritis, with good clinical outcomes at mid-term follow-up. Unexplained pain was the most common reason for revision to TKA.     

Seventeen to Twenty Years of Follow-Up of the Low Contact Stress Rotating-Platform Total Knee Arthroplasty With a Cementless Tibia in All Cases

Background

Total knee arthroplasty designs can be categorized by bearing design and fixation method. The mobile-bearing concept was developed with the aim of increasing longevity and improving function by reduced polyethylene wear and closer replication of physiological knee motion. Cementless fixation has the goal of achieving a long-lasting “biological” fixation between prosthesis and bone.

High Failure Rates for Unicompartmental Knee Arthroplasty in Morbidly Obese Patients: A Two-Year Minimum Follow-Up Study

BackgroundSeveral recent studies have recommended offering unicompartmental knee arthroplasty (UKA) to all patients regardless of body mass index (BMI). The aim of this investigation was to evaluate the proposition that UKA can indeed be offered to the morbidly-obese and super-obese (morbidly-obese, BMI ≥ 40 kg/m²) without compromising results or survivorship.MethodsWe retrospectively reviewed mobile-bearing medial UKA procedures performed at our facility from January 2012 to May 2015 with a minimum of 2-year follow-up. The study cohort was divided into patients with morbid obesity (BMI ≥ 40 kg/m²) and those without morbid obesity (BMI < 40 kg/m²). A detailed medical record review was performed. Extracted outcome data included the frequency of (1) major revision procedures (components revised), (2) minor secondary procedures (components not revised), (3) infection procedures, and (4) recommendations for revision.ResultsWe found 152 patients (190 knees) who met criteria for inclusion. Mean follow-up duration was 3.4 years (range: 2.0-6.8 years). Major revision surgery occurred more frequently in the morbid-obesity UKA group (15.7% vs 3.0%, P < .01). Rates of minor secondary surgery and infection were comparable for both groups. Most failures in the morbid-obesity UKA group (85.7%) were due to disease progression involving other compartments or mobile-bearing instability.ConclusionWe found the rate of early major revision surgery in morbidly-obese patients undergoing UKA to be over 5-times greater than that of other patients. Failure was predominantly due to disease progression in other compartments or mobile-bearing instability. Further study is warranted and needed before expanding UKA indications to the morbidly-obese population.     

High Incidence of Tibial Component Loosening After Total Knee Arthroplasty Using Ceramic Titanium-Nitride-Coated Mobile Bearing Prosthesis in Moderate to Severe Varus Deformity: A Matched-Pair Study Between Ceramic-Coated Mobile Bearing and Fixed Bearing Prostheses

BackgroundWe compared the incidence of aseptic component loosening and subsequent revision, and the survival rate between ceramic titanium-nitride-coated mobile bearing (MB) and fixed bearing total knee arthroplasties (TKAs) performed in patients with moderate to severe varus deformities.MethodsIn total, 200 TKAs using advanced coated system posterior stabilized prostheses in varus deformity of mechanical axis >8° between 2012 and 2016 were retrospectively reviewed. One hundred MB (ceramic-m group) and 100 fixed bearing (ceramic-f group) prostheses were included. The matches were made according to preoperative demographics, range of motion, and severity of deformity. The mean follow-up period was not different (ceramic-m vs ceramic-f = 4.8 vs 5.1 years; P = .104). The incidence of revision TKA due to aseptic component loosening and the survival rate (failure: revision due to aseptic loosening) was investigated.ResultsThe incidence of revision TKA due to aseptic component loosening was 7 (7%) in the ceramic-m group and 1 (1%) in the ceramic-f group (P = .032). All cases of aseptic loosening occurred at the tibial component. The overall survival rate was 91.3% in the ceramic-m group and 98.9% in the ceramic-f group (P = .025).ConclusionConsidering the higher revision incidence and lower survival rate due to tibial component loosening, caution should be taken in tibial component fixation when using advanced coated system MB prosthesis in moderate to severe varus deformity.Level of EvidenceIII     

Central Implantation of the Femoral Component Relative to the Tibial Insert Improves Clinical Outcomes in Fixed-Bearing Unicompartmental Knee Arthroplasty

BackgroundThe direct relationship between clinical outcomes and femoral component positioning relative to a tibial insert remains unknown. We determined whether the femoral component position relative to the tibial insert could affect clinical outcomes after fixed-bearing unicompartmental knee arthroplasty (UKA).MethodsThe femoral component position relative to the tibial insert of 66 patients with anteromedial osteoarthritis and osteonecrosis of the knee who underwent fixed-bearing UKA was assessed at 2 weeks postoperatively. We classified patients according to the contact point of the femoral component with the tibial component: group M (medial), 18 knees; group C (central), 30 knees; and group L (lateral), 18 knees. Patient-derived clinical scores using the 2011 Knee Society Score were also assessed preoperatively and at 2 years postoperatively and compared among the 3 groups using the analysis of variance.ResultsThe average 2-year postoperative “symptom” and “patient satisfaction” scores based on the 2011 Knee Society Score were significantly higher in group C than in group M or group L.ConclusionCentral implantation of the femoral component relative to the tibial insert plays an important role in decreasing pain and could result in better patient satisfaction after fixed-bearing UKA at 2 years postoperatively. Surgeons should set the femoral component at the center relative to the tibial insert for better patient satisfaction and higher active knee flexion after fixed-bearing UKA.     

Midterm Outcomes and Survivorship of Anterior Stabilized Versus Cruciate Retaining Bearing in Primary Total Knee Arthroplasty

BackgroundThere has been increasing utilization of ultracongruent bearings with a cruciate retaining (CR) femoral component in primary total knee arthroplasty. The purpose of this study is to compare outcomes and survivorship between an ultracongruent anterior stabilized (AS) and CR bearing.MethodsA retrospective review was performed from 2010 through 2014 of all primary total knee arthroplasties with a single knee systems identical CR femur and AS or CR bearing with minimum 2-year follow-up yielding a study cohort of 3323 patients (4164 knees). Knee range of motion, Knee Society pain scores, Knee Society clinical scores, Knee Society functional scores, and University of California Los Angeles activity scores were evaluated. The need for manipulation under anesthesia (MUA), nonrevision surgery and revisions were assessed.ResultsAS bearing was used in 1471 knees (35%) and CR bearing used in 2693 knees (65%). Mean follow-up was 5.4 years. The AS group had significantly higher improvements in knee range of motion, Knee Society clinical, Knee Society functional, and Knee Society pain scores. MUAs were performed on 120 knees (8.2%) in the AS group compared with 158 knees (5.9%) in the CR group (P = .005). The AS group had significantly less all-cause failure, aseptic failures, revisions for instability, and revisions for isolated polyethylene wear. The 10-year aseptic survival for AS was 98.3% and for 92.3% for the CR group (P = .002).ConclusionThese mid-term results demonstrate the AS bearing had significantly higher improvements in clinical and functional outcomes as well as greater survivorship. Knees in which an AS bearing was used did have a higher incidence of MUA.     

Treatment and Outcome of Periprosthetic Joint Infection in Unicompartmental Knee Arthroplasty

BackgroundPeriprosthetic joint infection (PJI) after unicompartmental knee arthroplasty (UKA) is a devastating but poorly understood complication, with a paucity of published data regarding treatment and outcomes. This study analyzes the largest cohort of UKA PJIs to date comparing treatment outcome, septic and aseptic reoperation rates, and risk factors for treatment failure.MethodsTwenty-one UKAs in 21 patients treated for PJI, as defined by Musculoskeletal Infection Society criteria, were retrospectively reviewed. Minimum and mean follow-up was 1 and 3.5 years, respectively. Fourteen (67%) patients had acute postoperative PJIs. Surgical treatment included 16 debridement, antibiotics, and implant retentions (DAIRs) (76%), 4 two-stage revisions (19%), and 1 one-stage revision (5%). Twenty (95%) PJIs were culture positive with Staphylococcus species identified in 15 cases (71%).ResultsSurvivorship free from reoperation for infection at 1 year was 76% (95% confidence interval, 58%-93%). Overall survival from all-cause reoperation was 57% (95% confidence interval, 27%-87%) at 5 years. Two additional patients (10%) underwent aseptic revision total knee arthroplasty for lateral compartment degeneration 1 year after DAIR and tibial aseptic loosening 2.5 years after 2-stage revision. All patients who initially failed PJI UKA treatment presented with acute postoperative PJIs (5 of 14; 36%).ConclusionSurvivorship free from persistent PJI at 1 year is low at 76% but is consistent with similar reports of DAIRs for total knee arthroplasties. Furthermore, there is low survivorship free from all-cause reoperation of 71% and 57% at 2 and 5 years, respectively. Surgeons should be aware of these poorer outcomes and consider treating UKA PJI early and aggressively.     

Increased risk of aseptic loosening for 43,525 rotating-platform vs. fixed-bearing total knee replacements

Background and purpose — Given similar functional outcomes with mobile and fixed bearings, a difference in survivorship may favor either. This study investigated the risk of aseptic loosening for the most used subtypes of mobile-bearing rotating-platform knees, in Norway and Australia.

Patients and methods — Primary TKRs reported to the Norwegian and Australian joint registries, between 2003 and 2014, were analyzed with aseptic loosening as primary end-point and all revisions as secondary end-point. We hypothesized that no difference would be found in the rate of revision between rotating-platform and the most used fixed-bearing TKRs, or between keeled and non-keeled tibia. Kaplan–Meier estimates and curves, and Cox regression relative risk estimates adjusted for age, sex, and diagnosis were used for comparison.

Results — The rotating-platform TKRs had an increased risk of revision for aseptic loosening compared with the most used fixed-bearing knees, in Norway (RR =6, 95% CI 4–8) and Australia (RR =2.1, 95% CI 1.8–2.5). The risk of aseptic loosening as a reason for revision was highest in Norway compared with Australia (RR =1.7, 95% CI 1.4–2.0). The keeled tibial component had the same risk of aseptic loosening as the non-keeled tibia (Australia). Fixation method and subtypes of the tibial components had no impact on the risk of aseptic loosening in these mobile-bearing knees.

Interpretation — The rotating-platform TKRs in this study appeared to have a higher risk of revision for aseptic loosening than the most used fixed-bearing TKRs.     

Do Fixed or Mobile Bearing Implants Have Better Survivorship in Medial Unicompartmental Knee Arthroplasty? A Study From the Australian Orthopaedic Association National Joint Replacement Registry

BackgroundDuring the last 5 years, there has been an increase in the use of unicompartmental knee arthroplasty (UKA) to treat knee osteoarthritis in Australia, and these account for almost 6% of annual knee replacement procedures. However, there is debate as to whether a fixed bearing or a mobile bearing design is best for decreasing revision for loosening and disease progression as well as improving survivorship. Small sample sizes and possible confounding in the studies on the topic may have masked differences between fixed and mobile bearing designs.Questions/purposesUsing data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), we selected the four contemporary designs of medial compartment UKA: mobile bearing, fixed modular, all-polyethylene, and fixed molded metal-backed used for the treatment of osteoarthritis to ask: (1) How do the different designs of unicompartmental knees compare with survivorship as measured by cumulative percentage revision (CPR)? (2) Is there a difference in the revision rate between designs as a function of patient sex or age? (3) Do the reasons for revision differ, and what types of revision procedures are performed when these UKA are revised?MethodsThe AOANJRR longitudinally maintains data on all primary and revision joint arthroplasties, with nearly 100% capture. The study population included all UKA procedures undertaken for osteoarthritis between September 1999 and December 2018. Of 56,628 unicompartmental knees recorded during the study period, 50,380 medial UKA procedures undertaken for osteoarthritis were included in the analysis after exclusion of procedures with unknown bearing types (31 of 56,628), lateral or patellofemoral compartment UKA procedures (5657 of 56,628), and those performed for a primary diagnosis other than osteoarthritis (560 of 56,628). There were 50,380 UKA procedures available for analysis. The study group consisted of 40% (20,208 of 50,380) mobile bearing UKA, 35% (17,822 of 50,380) fixed modular UKA, 23% (11,461 of 50,380) all-polyethylene UKA, and 2% (889 of 50,380) fixed molded metal-backed UKA. There were similar sex proportions and age distributions for each bearing group. The overall mean age of patients was 65 ± 9.4 years, and 55% (27,496 of 50,380) of patients were males. The outcome measure was the CPR, which was defined using Kaplan-Meier estimates of survivorship to describe the time to the first revision. Hazard ratios from Cox proportional hazards models, adjusted for sex and age, were performed to compare the revision rates among groups. The cohort was stratified into age groups of younger than 65 years and 65 years and older to compare revision rates as a function of age. Differences among bearing groups for the major causes and modes of revision were assessed using hazard ratios.ResultsAt 15 years, fixed modular UKA had a CPR of 16% (95% CI 15% to 17%). In comparison, the CPR was 23% (95% CI 22% to 24%) for mobile bearing UKA, 26% (95% CI 24% to 27%) for all-polyethylene UKA, and 20% (95% CI 16% to 24%) for fixed molded metal-backed UKA. The lower revision rate for fixed modular UKA was seen through the entire period compared with mobile bearing UKA (hazard ratio 1.5 [95% CI 1.4 to 1.6]; p < 0.001) and fixed molded metal-backed UKA (HR 1.3 [95% CI 1.1 to 1.6]; p = 0.003), but it varied with time compared with all-polyethylene UKA. The findings were consistent when stratified by sex or age. Although all-polyethylene UKA had the highest revision rate overall and for patients younger than 65 years, for patients aged 65 years and older, there was no difference between all-polyethylene and mobile bearing UKA. When compared with fixed modular UKA, a higher revision risk for loosening was shown in both mobile bearing UKA (HR 1.7 [95% CI 1.5 to 1.9]; p < 0.001) and all-polyethylene UKA (HR 2.4 [95% CI 2.1 to 2.7]; p < 0.001). The revision risk for disease progression was higher for all-polyethylene UKA at all time points (HR 1.4 [95% CI 1.3 to 1.6]; p < 0.001) and for mobile bearing UKA after 8 years when each were compared with fixed modular UKA (8 to 12 years: HR 1.4 [95% CI 1.2 to 1.7]; p < 0.001; 12 or more years: HR 1.9 [95% CI 1.5 to 2.3]; p < 0.001). The risk of revision to TKA was higher for mobile bearing UKA compared with fixed modular UKA (HR 1.4 [95% CI 1.3 to 1.5]; p < 0.001).ConclusionIf UKA is to be considered for the treatment of isolated medial compartment osteoarthritis, the fixed modular UKA bearing has the best survivorship of the current UKA designs.Level of EvidenceLevel III, therapeutic study.