Finite Element Analysis of Mobile-bearing Unicompartmental Knee Arthroplasty： The Influence of Tibial Component Coronal Alignment

Background： Controversies about the rational positioning of the tibial component in unicompartmental knee arthroplasty （UKA） still exist. Previous finite element （FE） studies were rare, and the results varied. This FE study aimed to analyze the influence of the tibial component coronal alignment on knee biomechanics in mobile-bearing UKA and find a ration range of inclination angles. Methods： A three-dimensional FE model of the intact knee was constructed from image data of one normal subject. A 1000 N compressive load was applied to the intact knee model for validating. Then a set of eleven UKA FE models was developed with the coronal inclination angles of the tibial tray ranging from 10° valgus to 10° varus. Tibial bone stresses and strains, contact pressures and load distribution in all UKA models were calculated and analyzed under the unified loading and boundary conditions. Results： Load distribution, contact pressures, and contact areas in intact knee model were validated. In UKA models, von Mises stress and compressive strain at proximal medial cortical bone increased significantly as the tibial tray was in valgus inclination 〉4°, which may increase the risk of residual pain. Compressive strains at tibial keel slot were above the high threshold with varus inclination 〉4°, which may result in greater risk of component migration. Tibial bone resection comer acted as a strain-raiser regardless of the inclination angles. Compressive strains at the resected surface slightly changed with the varying inclinations and were not supposed to induce bone resorption and component loosening. Contact pressures and load percentage in lateral compartment increased with the more varus inclination, which may lead to osteoarthritis progression. Conclusions： Static knee biomechanics after UKA can be greatly affected by tibial component coronal alignment. A rauge from 4° valgus to 4° varus inclination oftibial component can be recommended in mobile-bearing UKA.

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

Background: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.Methods: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.Results: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.Conclusion: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).