All-polyethylene Research Articles

Mid-term outcomes of medial metal backed and all-polyethylene unicompartmental knee arthroplasty in obese patients: a retrospective propensity-matched analysis

BackgroundThis retrospective study compares the outcomes of unicompartmental medial fixed-bearing knee arthroplasty (mUKA), involving a cemented metal-backed (MB) or an all-polyethylene (AP) tibial component, performed in obese patients with a body mass index (BMI) > 30 with a follow-up of at least 5 years.MethodsThe institutional database was mined for primary mUKAs involving an MB or an AP tibial component (MB-UKA and AP-UKA groups, respectively) performed from January 2015 to August 2019. Patient demographics and patient-reported outcome measures (PROMs) were compared and a propensity score matching (PSM) analysis (1:1) using multiple variables was conducted.ResultsPSM analysis yielded 37 pairs of obese MB-UKA and AP-UKA patients. At 5 years, the Knee Society Function Score (KSFS) was 75.1 ± 10.6 in MB-UKA and 79.4 ± 9.1 in AP-UKA patients (p = 0.029), and the Oxford Knee Score (OKS) was 38.1 ± 4.4 in MB-UKA and 40.6 ± 5.7 in AP-UKA patients (p = 0.011).ConclusionAt five-year follow-up, in a matched group of obese MB-UKA and AP-UKA patients, the AP-UKA group achieved better KSFSs and OKSs. Both the AP and the MB tibial components were able to bring about a significant improvement of the most widely used PROMs.

All-Polyethylene Tibial Component in Unicompartmental Knee Arthroplasty Offers Excellent Survivorship and Clinical Outcomes at Short-Term Follow-Up: A Multicenter Retrospective Clinical Study.

Background and Objectives: The ten-year survivorship of unicompartmental knee arthroplasty (UKA) is up to 96%, varying from implants and hospitals; however, most of registry studies do not distinguish between metal-back (MB) tibial implants and all-polyethylene (AP) tibial implants. The aim of the present retrospective clinical study was to analyze the clinical outcomes and survivorship of medial and lateral UKA with a newly designed all-polyethylene tibial plateau at short-term follow-up. Materials and Methods: A retrospective analysis of prospectively collected consecutive patients who underwent medial or lateral UKA with AP tibial plateau was conducted, with a minimum follow-up of 1 year. Primary outcomes were clinical score (VAS, OKS, and KOOS) variations from baseline up to the latest follow-up. Secondary outcomes were Likert scale variations from baseline to the follow-up, evaluation of the influence of demographic factors (age and BMI) at the time of surgery on the clinical outcomes, and evaluation of revision rate up to the last follow-up. Results: The final study population included 99 knees. The mean VAS score for the medial group significantly decreased from 7.61 ± 1.65 (pre-intervention) to 2.74 ± 2.26 (post-intervention). Similar improvements were registered for the OKS as well, for both the medial group (from 22.5 ± 12.6 to 36.6 ± 10.6, with a delta of 14.11 (10.05 to 18.17)) and the lateral group (from 22.6 ± 12.6 to 36.9 ± 11.8, with a delta of 14.24 (8.65 to 19.83)). Moreover, all the KOOS subscales reported an amelioration, both in medial UKA and lateral UKA. Furthermore, a logistic regression of delta VAS was performed in relation to the other clinical questionnaires and the demographic factors. For both medial and lateral UKAs, no statistically significant correlation was found between the VAS scale regression and the demographic factors. The survival rate free from any revision of the cohort at the latest follow-up was 96.32%. Conclusions: All-polyethylene tibial component in unicompartmental knee arthroplasty demonstrates significant improvements in clinical scores and a low failure rate at short-term follow-up.

Metal-backed or all-poly tibial components: which are better for medial unicompartmental knee arthroplasty? A propensity-score-matching retrospective study at the 5-year follow-up

BackgroundThis retrospective medium-term follow-up study compares the outcomes of medial fixed-bearing unicompartmental knee arthroplasty (mUKA) using a cemented metal-backed (MB) or an all-polyethylene (AP) tibial component.Materials and methodsThe database of our institution was mined for primary mUKA patients implanted with an MB or an AP tibial component (the MB-UKA and AP-UKA groups, respectively) from 2015 to 2018. We compared patient demographics, patient-reported outcome measures (PROMs), and motion analysis data obtained with the Riablo™ system (CoRehab, Trento, Italy). We conducted propensity-score-matching (PSM) analysis (1:1) using multiple variables.ResultsPSM analysis yielded 77 pairs of MB-UKA and AP-UKA patients. At 5 years, the physical component summary (PCS) score was 52.4 ± 8.3 in MB-UKA and 48.2 ± 8.3 in AP-UKA patients (p < 0.001). The Forgotten Joint Score (FJS-12) was 82.9 ± 18.8 in MB-UKAs and 73.4 ± 22.5 in AP-UKAs (p = 0.015). Tibial pain was reported by 7.8% of the MB-UKA and 35.1% of the AP-UKA patients (p < 0.001). Static postural sway was, respectively, 3.9 ± 2.1 cm and 5.4 ± 2.3 (p = 0.0002), and gait symmetry was, respectively, 92.7% ± 3.7 cm and 90.4% ± 5.4 cm (p = 0.006). Patient satisfaction was 9.2 ± 0.8 in the MB-UKA and 8.3 ± 2.0 in the AP-UKA group (p < 0.003).ConclusionsMB-UKA patients experienced significantly better 5-year static sway and gait symmetry outcomes than AP-UKA patients. Although the PROMs of the two groups overlapped, MB-UKA patients had a lower incidence of tibial pain, better FJS-12 and PCS scores, and were more satisfied.

Outcomes of Revision Unlinked Total Elbow Arthroplasty for Rheumatoid Elbow.

Background: Although unlinked total elbow arthroplasty (TEA) is a treatment option for end-stage rheumatoid arthritis (RA) of the elbow, its long-term outcomes were inferior. Moreover, revision TEA could be technically challenging. The unlinked TEA procedure comprises the ease of implant removal at revision and advantage of bone preservation. This study evaluated the clinical outcomes in patients who underwent revision TEA using primary unlinked TEA for rheumatoid elbows. It also aimed to determine whether selecting the unlinked prosthesis for the primary TEA would make revision more accessible and successful. Methods: We retrospectively reviewed data of 13 consecutive patients (14 elbows) who underwent revision TEAs for implant failure due to different aetiologies, excluding septic loosening. Three different unlinked TEA implants were used: the Kudo type-5 with all-polyethylene (AP) ulnar component, Kudo type-5 with metal-backed (MB) ulnar component and K-Now TEA. We evaluated the patients' pre- and postoperative outcomes, including the range of motion, pain score and Mayo Elbow Performance Index (MEPI). Results: Among the 14 elbows, 11 were revised using the Kudo type-5 ulnar component (nine and two with AP and MB ulnar component, respectively), and three using the K-Now. We found that each model of TEA had different tendencies to indication for revision surgery. Three more resulted in further failure. The clinical outcomes were assessed in the 11 surviving elbows. Eight of the 11 elbows showed no pain at the final follow-up. However, the remaining three showed only mild pain. The MEPI revealed that seven cases were excellent, two were good and two were fair. Conclusions: The mode of implant failure was largely dependent on the implant design. Furthermore, partial revision with the same implant design was sufficient in managing implant failure in the early phase. However, conversion from unlinked to linked design could be recommended in patients with progressive failure or instability. Level of Evidence: Level IV (Therapeutic).

COMPARATIVE STUDY OF TOTAL KNEE REPLACEMENT USING ALL POLYETHYLENE AND METAL BACKED TIBIAL PROSTHESIS

Introduction: Osteoarthritis is the result of mechanical and biological events that destabilize the normal processes of degradation and synthesis of articular cartilage chondrocytes, extracellular matrix, and subchondral bone. All-polyethylene (AP) tibial components were largely abandoned in favour of metal-backed (MB) components in the 1980s. metal backing is now the predominant design in total knee arthroplasty (TKA). The present study aimed to assess and compare the functional outcome, in patient with total knee replacement using all polyethylene and metal backed tibial prosthesis in Primary Total Knee Replacement. Material And Methods: Our is an analytical cross-sectional study in which we have included 36 patients with primary knee osteoarthritis kellgren –lawrence grade III, IV 18 patients in all poly group and 18 patients in metal backed group. In which during follow up X-rays and functional outcome was evaluated using the American Knee Society Score at 1, 3, and 6-month follow-ups for patients of both the groups and compared. Result: In all polyethylene groups the functional score at 1, 3 and 6 months were 51.39 + 8.1, 76.67 + 8.1 and 89.72 + 4.6 respectively. While in metal group, the mean functional scores were 50.28 + 5.8, 77.22 + 5.7 and 988.61 + 4.1 at 1 month, 3 months and 6 months respectively. The most common complication was stiffness in 13.9% of patients of both the groups followed by extension leg (5.6%), infection (2.8%) and proximal tibial fracture (2.8%) in both groups. In present study, 75% of the patient did not have any post operative complications among all study subjects. Conclusion: There is no statistically significant difference in clinical outcome between all polyethylene and metal backed, improved values in terms of functional and clinical scores preferably in both the group metal backed and all polyethylene group. This study is not without limitations. Even though it is prospective study, patients were followed for shorter duration only. Hence, a study with elegant methodology and long follow up period can accurately assess the efficacy of all polyethylene and metal backed prosthesis used in knee replacement surgery.

COMPARATIVE STUDY OF TOTAL KNEE REPLACEMENT USING ALL POLYETHYLENE AND METAL BACKED TIBIAL PROSTHESIS

COMPARATIVE STUDY OF TOTAL KNEE REPLACEMENT USING ALL POLYETHYLENE AND METAL BACKED TIBIAL PROSTHESIS

Comparison of All-Polyethylene Tibial Versus Metal-Backed Tibial Component in Total Knee Replacement Surgery

Introduction: Total knee replacement (TKR) is the most successful procedure in Orthopedics. The selection of an ideal implant relies on better survivorship, restoration of functional activities and cost-effectiveness. This study compared the effectiveness of all-polyethylene (AP) versus metal-backed tibial (MTB) implant in TKR patients in terms of objective and subjective patient related outcomes. Objectives: To compare the effectiveness of all-polyethylene tibial implants versus metal-backed tibial implants in total knee replacement patients in terms of improvement in the American Knee Society Score (AKSS). Methodology: It was a nonrandomized controlled trial done in the Orthopaedic Department of the Sharif Medical City Hospital, Lahore, after approval by the institutional ethical committee. Fifty patients of grade IV knee joint osteoarthritis for greater than six months were included by nonprobability convenient sampling technique. The patients were allocated equally into standard treatment and intervention groups; patients underwent TKR with MTB implants in the standard group and AP implants in the intervention group after taking informed written consent. The AKSS score was calculated pre-operatively, 3 months and 6 months after surgery by the team member not involved in surgical planning. Results: A statistically significant improvement was observed in pre-operative to post-operative knee scores (p-value = 0.004) and functional scores (p-value = 0.001) with TKR. When the means of knee scores were compared between AP and MTB implants, there was no significant difference between the two groups between pre-operative and post-operative knee scores and functional scores. Practical implication Conclusion: There is no significant difference in knee score between the all-polyethylene and metal-backed implants regarding pain and functional status. All-polyethylene implants are a better substitute for MTB implants due to their cost-effectiveness, particularly in countries with financial constraints. The most practical implication of the current study is health economics. In a developing country with a low per capita income, expensive implants can be swapped with low cost implants to bring the cost of the procedure down. Keywords: All-polyethylene tibial, Metal-backed tibial, Total knee replacement, American Knee Society Score, AKSS.

All-polyethylene tibia components have the same functional outcomes and survival, and are more cost-effective than metal-backed components in patients 70 years and older undergoing total knee arthroplasty

The tibial component of total knee arthroplasty can either be an all-polyethylene (AP) implant or a metal-backed (MB) implant. This study aims to compare the five-year functional outcomes of AP tibial components to MB components in patients aged over 70 years. Secondary aims are to compare quality of life, implant survivorship, and cost-effectiveness. A group of 130 patients who had received an AP tibial component were matched for demographic factors of age, BMI, American Society of Anesthesiologists (ASA) grade, sex, and preoperative Knee Society Score (KSS) to create a comparison group of 130 patients who received a MB tibial component. Functional outcome was assessed prospectively by KSS, quality of life by 12-Item Short-Form Health Survey questionnaire (SF-12), and range of motion (ROM), and implant survivorships were compared. The SF six-dimension (6D) was used to calculate the incremental cost effectiveness ratio (ICER) for AP compared to MB tibial components using quality-adjusted life year methodology. The AP group had a mean KSS-Knee of 83.4 (standard deviation (SD) 19.2) and the MB group a mean of 84.9 (SD 18.2; p = 0.631), while mean KSS-Function was 75.4 (SD 15.3) and 73.2 (SD 16.2 p = 0.472), respectively. The mental (44.3 vs 45.1; p = 0.464) and physical (44.8 vs 44.9; p = 0.893) dimensions of the SF-12 and ROM (97.9° vs 99.7°; p = 0.444) were not different between the groups. Implant survivorship at five years were 99.2% and 97.7% (p = 0.321). The AP group had a greater SF-6D gain of 0.145 compared to the MB group, with an associated cost saving of £406, which resulted in a negative ICER of -£406/0.145 = -£2,800. Therefore, the AP tibial component was dominant, being a more effective and less expensive intervention. There were no differences in functional outcomes or survivorship at five years between AP and MB tibial components in patients aged 70 years and older, however the AP component was shown to be more cost-effective. In the UK, only 1.4% of all total knee arthroplasties use an AP component; even a modest increase in usage nationally could lead to significant financial savings.Cite this article: Bone Jt Open2022;3(12):969-976.

All-polyethylene unicompartmental knee arthroplasty is associated with increased risks of poorer knee society knee score and lower satisfaction in obese patients.

Although metal-backed tibial component (MB) is biomechanically superior to all-polyethylene (AP) implants in fixed-bearing unicompartmental knee arthroplasty (UKA), recent studies have shown comparable functional outcomes between the two. However, no study has examined this comparison in obese patients (BMI ≥ 30kg/m2). We investigated whether functional outcomes between the two implants differ among obese patients, and whether the extent of obesity influences these outcomes. Four hundred twenty-two UKA implants from 347 obese patients were reviewed retrospectively. Patients were assessed using the Knee Society Knee Score (KSKS) and Function Score (KSFS), the original Oxford Knee Score (OKS), and SF-36 Physical Component Summary (PCS) and Mental Component Summary (MCS). Minimal clinically important difference (MCID) attainment was recorded. Patients' fulfillment of expectations and satisfaction with the surgery outcome was also graded. Patients were further divided into lower obesity (BMI 30-34.9kg/m2) and higher obesity (BMI ≥ 35kg/m2) to examine effect modification. There were no differences in functional outcomes and quality-of-life scores, MCID attainment of functional scores, as well as satisfaction and expectation fulfillment between AP and MB. Among higher obesity patients, AP was associated with a poorer KSKS (p = 0.031) and lower proportion of satisfaction fulfillment (p = 0.041) 2years postoperatively compared to MB. We found no differences in functional and quality-of-life outcomes between fixed-bearing AP and MB tibial components among obese patients who underwent UKA. However, among higher obesity patients (BMI ≥ 35kg/m2), patients with AP tibial component were associated with lower KSKS score and a lower proportion of attaining satisfaction fulfillment 2years postoperatively.

Late stabilization after initial migration in patients undergoing cemented total knee arthroplasty: a 5-year followup of 2 randomized controlled trials using radiostereometric analysis.

Background and purposeIn total knee arthroplasty (TKA), metal-backed (MBT) and all-polyethylene (APT) designs have shown comparable implant migration up to 2 years postoperatively using radiostereometric analysis (RSA). However, studies comparing mid-term migration of both designs are lacking. Furthermore, continuously migrating TKAs up to 2 years may continue to migrate or stabilize thereafter. Therefore, we compared 5-year migration of MBT and APT using either cruciate-stabilizing (CS) or posteriorstabilizing (PS) designs and specifically assessed migration profiles of continuously migrating TKAs beyond 2 years.Patients and methodsThe present study includes results from 2 randomized trials comparing migration of cemented MBT with APT of either CS (CS study, n = 59) or PS (PS study, n = 56) design. 2 surgeons performed all surgeries. We used a linear mixed model for the analyses.ResultsThe overall migration between MBT and APT TKAs was similar for either the CS or PS design over a 5-year period. In both studies combined, 9 implants showed continuous migration in the second postoperative year, of which 1 (APT-CS) was revised for instability, 4 (2 MBT-CS, MBT-PS, APT-PS) stabilized, and 4 (2 MBT-CS, APT-CS, MBT-PS) lacked 5-year data.InterpretationOverall migration was similar between MBT and APT TKAs up to 5 years, for both the CS and PS design. 4 initially migrating TKAs stabilized between 2- and 5-year follow-up, stressing the need for longer-term followup to determine whether second-year continuous migration correctly predicts loosening.

Early failure of all polyethylene tibial components in bilateral total knee arthroplasty: A case report

Introduction: Outcomes of Total Knee Arthroplasty (TKA) performed with modern all polyethylene (AP) tibial components have been reported to be comparable with or better than those TKAs performed using metal-backed modular (MBM) tibial components in several medium and long term studies. As AP components also provide substantial cost savings, there has been increase in their use in primary TKA. In spite of such good results, failure of AP tibial components has been reported.Case Presentation: A sixty three year old lady operated for bilateral cruciate retaining PFC Sigma TKA utilizing AP tibial components without patellar resurfacing in 2011 presented to us in December 2014 with two-year history of severe pain in both knees and inability to walk or stand. She had marked varus deformity of both knees. Radiological examination revealed fracture of the medial tibial plateau with failure of AP tibial component and marked varus deformity. She was treated with bilateral staged revision TKA which resulted in a satisfactory outcome. Conclusion: This case report describes previously unreported complication of AP tibial component following cruciate retaining bilateral AP tibia PFC Sigma TKA in a patient of varus osteoarthritis of knee joint. Early collapse of medial tibial plateau leading to failure of bilateral TKA, which could be attributed to under correction of varus deformity and instability, was managed with bilateral revision TKA using tibial metaphyseal sleeves which led to a very satisfactory outcome and excellent five year follow up.

Unicompartmental knee arthroplasty: all-poly versus metal-backed tibial component-a long-term follow-up study.

While considered a satisfactory solution, unicompartmental knee arthroplasty (UKA) still raises concerns in regard to its durability. These concerns particularly focus on the tibial component. This study aims to compare two different cemented tibial components belonging to the same UKA design: all polyethylene (AP) versus metal backed (MB), at a long-term follow-up. We retrospectively reviewed 143 successive patients, 83 of which underwent surgery with AP tibial component UKA (37 males, 46 females), and 67 with MB ones (17 males, 50 females). All implants had the same prosthetic design (Accuris UKA, Smith e Nephew) with identical femoral oxinium component but different tibial component, AP or MB. The KSS and KOOS were assessed at a mean of 11.5-year follow-up and compared to pre-operative, post-operative, and oneyear evaluation. Statistical analysis was performed with SPSS for Mac (version 17.0). To assess potential statistically significant differences, t test was used and significance was set at P< 0.05. Final KSS at a mean of 11.5-year follow-up was 94.27 for the AP group and 96.12 for the MB ones. The final KOOS was 87 for AP components and 89.67 for the MB group. These results demonstrated, in all cases, statistically significant better results for MB tibial components compared to AP regarding KSS (P= 0.048), KOOS (P= 0.000), and pain (P= 0.014) at the 11.5-year follow-up. Survivorship for AP tibial component implants was 97.6%, while it was 89.5% for MB ones. While the survivorship rate has been found to be greater for AP implants compared to MB tibial components, this study reveals statistically better functional results according to KSS and KOOS, and pain, at a long-term follow-up for MB implants.

The effect of malalignment on proximal tibial strain in fixed-bearing unicompartmental knee arthroplasty: A comparison between metal-backed and all-polyethylene components using a validated finite element model.

ObjectivesElevated proximal tibial bone strain may cause unexplained pain, an important cause of unicompartmental knee arthroplasty (UKA) revision. This study investigates the effect of tibial component alignment in metal-backed (MB) and all-polyethylene (AP) fixed-bearing medial UKAs on bone strain, using an experimentally validated finite element model (FEM).MethodsA previously experimentally validated FEM of a composite tibia implanted with a cemented fixed-bearing UKA (MB and AP) was used. Standard alignment (medial proximal tibial angle 90°, 6° posterior slope), coronal malalignment (3°, 5°, 10° varus; 3°, 5° valgus), and sagittal malalignment (0°, 3°, 6°, 9°, 12°) were analyzed. The primary outcome measure was the volume of compressively overstrained cancellous bone (VOCB) < -3000 µε. The secondary outcome measure was maximum von Mises stress in cortical bone (MSCB) over a medial region of interest.ResultsVarus malalignment decreased VOCB but increased MSCB in both implants, more so in the AP implant. Varus malalignment of 10° reduced the VOCB by 10% and 3% in AP and MB implants but increased the MSCB by 14% and 13%, respectively. Valgus malalignment of 5° increased the VOCB by 8% and 4% in AP and MB implants, with reductions in MSCB of 7% and 10%, respectively. Sagittal malalignment displayed negligible effects. Well-aligned AP implants displayed greater VOCB than malaligned MB implants.ConclusionAll-polyethylene implants are more sensitive to coronal plane malalignments than MB implants are; varus malalignment reduced cancellous bone strain but increased anteromedial cortical bone stress. Sagittal plane malalignment has a negligible effect on bone strain.Cite this article: I. Danese, P. Pankaj, C. E. H. Scott. The effect of malalignment on proximal tibial strain in fixed-bearing unicompartmental knee arthroplasty: A comparison between metal-backed and all-polyethylene components using a validated finite element model. Bone Joint Res 2019;8:55–64. DOI: 10.1302/2046-3758.82.BJR-2018-0186.R2.

Revision of Unicompartmental to Total Knee Arthroplasty: Does the Unicompartmental Implant (Metal-Backed vs All-Polyethylene) Impact the Total Knee Arthroplasty?

BackgroundThe aim of this study is to investigate differences in implant requirement, outcomes, and re-revision when total knee arthroplasty (TKA) was performed following unicompartmental knee arthroplasties (UKAs) with metal-backed (MB) compared to all-polyethylene (AP) tibial components. MethodsRetrospective study of 60 UKAs converted to 60 TKAs at mean 7.3 years (0.1 to 17) after implantation in 55 patients (mean age, 64 [49-83]; 44% male): 44 MB and 16 AP. TKA implant requirement was investigated in addition to mode of failure, Oxford Knee Score, and TKA survival at mean 5.4 years (0.5 to 17). ResultsProgression of osteoarthritis was the commonest mode of failure in MB UKAs (P = .03) and unexplained pain in AP (P = .011) where revisions were performed earlier (4.8 ± 3.2 vs 8.2 ± 4.5, P = .012). In 56 of 60 (93%) cases, unconstrained TKA implants were used. The use of standard cruciate-retaining TKAs without augments or stems was less likely following MB UKA compared to AP (12 of 38 [32%] vs 10/14 [71%], P = .013). Specifically MB UKA implants were associated with more tibial stem use (P = .04) and more use of cruciate-substituting polyethylene (P = .05). There was no difference in the use of constrained implants. Multivariate analysis showed tibial resection depth to predict stem requirement. Seven were re-revised giving 7-year TKA survival: from MB UKA 70.3 (95% CI, 47.0 to 93.6) and from AP UKA 87.5 (95% CI, 64.6 to 100; P = .191). ConclusionMB UKA implants increase the chances of a complex revision requiring tibial stems and cruciate substitution but reduce the chances of early revision compared to AP UKA which often fail early with pain.

Metal-backed versus all-polyethylene unicompartmental knee arthroplasty: Proximal tibial strain in an experimentally validated finite element model.

ObjectivesUp to 40% of unicompartmental knee arthroplasty (UKA) revisions are performed for unexplained pain which may be caused by elevated proximal tibial bone strain. This study investigates the effect of tibial component metal backing and polyethylene thickness on bone strain in a cemented fixed-bearing medial UKA using a finite element model (FEM) validated experimentally by digital image correlation (DIC) and acoustic emission (AE).Materials and MethodsA total of ten composite tibias implanted with all-polyethylene (AP) and metal-backed (MB) tibial components were loaded to 2500 N. Cortical strain was measured using DIC and cancellous microdamage using AE. FEMs were created and validated and polyethylene thickness varied from 6 mm to 10 mm. The volume of cancellous bone exposed to < -3000 µε (pathological loading) and < -7000 µε (yield point) minimum principal (compressive) microstrain and > 3000 µε and > 7000 µε maximum principal (tensile) microstrain was computed.ResultsExperimental AE data and the FEM volume of cancellous bone with compressive strain < -3000 µε correlated strongly: R = 0.947, R2 = 0.847, percentage error 12.5% (p < 0.001). DIC and FEM data correlated: R = 0.838, R2 = 0.702, percentage error 4.5% (p < 0.001). FEM strain patterns included MB lateral edge concentrations; AP concentrations at keel, peg and at the region of load application. Cancellous strains were higher in AP implants at all loads: 2.2- (10 mm) to 3.2-times (6 mm) the volume of cancellous bone compressively strained < -7000 µε.ConclusionAP tibial components display greater volumes of pathologically overstrained cancellous bone than MB implants of the same geometry. Increasing AP thickness does not overcome these pathological forces and comes at the cost of greater bone resection.Cite this article: C. E. H. Scott, M. J. Eaton, R. W. Nutton, F. A. Wade, S. L. Evans, P. Pankaj. Metal-backed versus all-polyethylene unicompartmental knee arthroplasty: Proximal tibial strain in an experimentally validated finite element model. Bone Joint Res 2017;6:22–30. DOI:10.1302/2046-3758.61.BJR-2016-0142.R1

Stress shielding in periprosthetic bone following a total knee replacement: Effects of implant material, design and alignment

Periprosthetic bone strain distributions in some of the typical cases of total knee replacement (TKR) were studied with regard to the selection of material, design and the alignments of tibial components to examine which conditions are more forgiving than the others to stress shielding post a TKR. Four tibial components with two implant designs (cruciate sacrificing and cruciate retaining) and material properties (metal-backed (MB) and all-polyethylene (AP)) were considered in a specimen-specific finite element tibia bone model loaded in a neutral position. The influence of tibial material and design on the periprosthetic bone strain response was investigated under the peak loads of walking and stair descending/ascending. Two of the models were also modified to examine the effect of selected implant malalignment conditions (7° posterior, 5° valgus and 5° varus) on stress shielding in the bone, where the medio-lateral load share ratios were adjusted accordingly. The predicted increases of bone density due to implantation for the selected cases studied were also presented.For the cases examined, the effect of stress shielding on the periprosthetic bone seems to be more significantly influenced by the implant material than by the implant geometry. Significant stress shielding is found in MB cases, as opposed to increase in bone density found in AP cases, particularly in the bones immediately beneath the baseplate. The effect of stress shielding is reduced somewhat for the MB components in the malaligned positions compared with the neutral case. In AP cases, the effect of stress shielding is mostly low except in the varus position, possibly due to off-loading of lateral condyle. Increases in bone density are found in both MB and AP cases for the malaligned conditions.

Metal or Modularity: Why Do Metal-Backed Tibias Have Inferior Outcomes to All-Polyethylene Tibial Components in Patients With Osteoarthritis

BackgroundBiomechanical studies have suggested improved stress distribution in metal-backed (MB) compared to all-polyethylene (AP) tibias, but such potential benefits have not been realized clinically. The purpose of this investigation was to analyze the outcomes of AP components in patients with primary osteoarthritis and compare the results to those obtained with MB tibial components in total knee arthroplasty (TKA). MethodsWe reviewed 11,653 patients undergoing primary TKA for osteoarthritis. There were 9999 (86%) MB (8470 modular and 1529 monoblock) and 1654 (14%) AP tibial components. All patients had at least 2 years of clinical follow-up with mean follow-up of 8 years (range, 2-30 years). ResultsMean survivorship for all primary TKAs at the 5-year, 10-year, 15-year, and 20-year time points was 97%, 92%, 86%, and 78%. AP tibial components were found to have improved survivorship when compared to modular and monoblock MB counterparts (P < .0001). Likewise, AP tibial components were found to have lower rates of tibial component loosening (P < .0001), tibial osteolysis, and component fracture. Furthermore, the AP group had improved survival rates in most age-groups except <55 years where there was no difference. AP tibial components demonstrated improved survival for all body mass index (BMI) groups except in patients with a BMI ≤25 kg/m2 where there was no difference. ConclusionAP tibial components had significantly improved implant survival across all age-groups and most BMI categories in patients who underwent TKA for osteoarthritis. Given these outcomes, AP tibias are a reasonable option, regardless of patient age and BMI.

A Finite-Element Study of Metal Backing and Tibial Resection Depth in a Composite Tibia Following Total Knee Arthroplasty.

Prosthetic alignment, patient characteristics, and implant design are all factors in long-term survival of total knee arthroplasty (TKA), yet the level at which each of these factors contribute to implant loosening has not been fully described. Prior clinical and biomechanical studies have indicated tibial overload as a cause of early TKA revision. The purpose of this study was to determine the relationship between tibial component design and bone resection on tibial loading. Finite-element analysis (FEA) was performed after simulated implantation of metal backed (MB) and all-polyethylene (AP) TKA components in 5 and 15 mm of tibial resection into a validated intact tibia model. Proximal tibial strains significantly increased between 13% and 199% when implanted with AP components (p < 0.05). Strain significantly increased between 12% and 209% in the posterior tibial compartment with increased bone resection (p < 0.05). This study indicates elevated strains in AP implanted tibias across the entirety of the proximal tibial cortex, as well as a posterior shift in tibial loading in instances of increased resection depth. These results are consistent with trends observed in prior biomechanical studies and may associate the documented device history of tibial collapse in AP components with increased bone strain and overload beneath the prosthesis.

Modular versus all‐polyethylene tibial components: comparison of pre‐ and early post‐operative patient scores in total knee replacement

All-polyethylene (AP) tibial components of total knee replacement (TKR) are substantially cheaper than their modular counterparts. It is well established that their survivorship and radiographic outcomes are comparable. In this study, patient-derived outcome measures were used to compare these two implant types. A cohort of 456 primary TKRs (142 AP, 314 modular) were assessed with preoperative and 1-year post-operative Oxford Knee Score, Western Ontario and McMaster Universities Arthritis Index and Short Form - 12 scores. Both groups performed well with no significant difference in improvement and final scores at 1 year. Although there was a significant difference in mean age among the groups (P < 0.001) age-adjusted scores continued to show no significant difference between the two groups. Our results support the more frequent use of AP tibial components for uncomplicated TKR.

Metal-backed versus all-polyethylene tibial components in primary total knee arthroplasty

Background and purpose The choice of either all-polyethylene (AP) tibial components or metal-backed (MB) tibial components in total knee arthroplasty (TKA) remains controversial. We therefore performed a meta-analysis and systematic review of randomized controlled trials that have evaluated MB and AP tibial components in primary TKA.Methods The search strategy included a computerized literature search (Medline, EMBASE, Scopus, and the Cochrane Central Register of Controlled Trials) and a manual search of major orthopedic journals. A meta-analysis and systematic review of randomized or quasi-randomized trials that compared the performance of tibial components in primary TKA was performed using a fixed or random effects model. We assessed the methodological quality of studies using Detsky quality scale.Results 9 randomized controlled trials (RCTs) published between 2000 and 2009 met the inclusion quality standards for the systematic review. The mean standardized Detsky score was 14 (SD 3). We found that the frequency of radiolucent lines in the MB group was significantly higher than that in the AP group. There were no statistically significant differences between the MB and AP tibial components regarding component positioning, knee score, knee range of motion, quality of life, and postoperative complications.Interpretation Based on evidence obtained from this study, the AP tibial component was comparable with or better than the MB tibial component in TKA. However, high-quality RCTs are required to validate the results.