BACKGROUND AND OBJECTIVE: Total knee arthroplasty (TKA) with modern all-polyethylene tibial (APT) components has shown high long-term survival rates and comparable results to those with metal-backed tibial components. Nevertheless, APT components are primarily recommended for older and low-demand patients. There are no evidence-based biomechanical guidelines for orthopaedic surgeons to determine the appropriate lower age limit for implantation of APT components. A biomechanical analysis was assumed to be suitable to evaluate the clinical results in patients under 70 years. The scope of this study was to determine biomechanically the appropriate lower age limit for implantation of APT components. METHODS: To generate data of the highest possible quality, the geometry of the computational models was created based on computed tomography (CT) images of a representative patient. The cortical bone tissue model distinguishes the change in mechanical properties described in three parts from the tibial cut. The cancellous bone material model has a heterogeneous distribution of mechanical properties. The values used to determine the material properties of the tissues were obtained from measurements of a CT dataset comprising 45 patients. RESULTS: Computational modeling showed that in the majority of the periprosthetic volume, the von Mises strain equivalent ranges from 200 to 2700 με; these strain values induce bone modeling and remodeling. The highest measured deformation value was 2910 με. There was no significant difference in the induced mechanical response between bone models of the 60-year and 70-year age groups, and there was <3% difference from the 65-year age group. CONCLUSIONS: Considering in silico limitations, we suggest that APT components could be conveniently used on a bone with mechanical properties of the examined age categories. Under defined loading conditions, implantation of TKA with APT components is expected to induce modeling and remodeling of the periprosthetic tibia. Following clinical validation, the results of our study could modify the indication criteria of the procedure, and lead to more frequent implantation of all-polyethylene TKA in younger patients.

• MeSH
• analýza metodou konečných prvků MeSH
• biomechanika MeSH
• kovy MeSH
• lidé MeSH
• mechanický stres MeSH
• polyethylen MeSH
• protézy - design MeSH
• protézy kolene * MeSH
• tibie diagnostické zobrazování   chirurgie   MeSH
• totální endoprotéza kolene * metody   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH

BACKGROUND: Total knee arthroplasty (TKA) with all-polyethylene tibial (APT) components has shown comparable survivorship and clinical outcomes to that with metal-backed tibial (MBT). Although MBT is more frequently implanted, APT equivalents are considered a low-cost variant for elderly patients. A biomechanical analysis was assumed to be suitable to compare the response of the periprosthetic tibia after implantation of TKA NexGen APT and MBT equivalent. METHODS: A standardised load model was used representing the highest load achieved during level walking. The geometry and material models were created using computed tomography data. In the analysis, a material model was created that represents a patient with osteopenia. RESULTS: The equivalent strain distribution in the models of cancellous bone with an APT component showed values above 1000 με in the area below the medial tibial section, with MBT component were primarily localised in the stem tip area. For APT variants, the microstrain values in more than 80% of the volume were in the range from 300 to 1500 με, MBT only in less than 64% of the volume. CONCLUSION: The effect of APT implantation on the periprosthetic tibia was shown as equal or even superior to that of MBT despite maximum strain values occurring in different locations. On the basis of the strain distribution, the state of the bone tissue was analysed to determine whether bone tissue remodelling or remodelling would occur. Following clinical validation, outcomes could eventually modify the implant selection criteria and lead to more frequent implantation of APT components.

• MeSH
• analýza metodou konečných prvků MeSH
• kovy MeSH
• lidé MeSH
• polyethylen MeSH
• protézy - design MeSH
• protézy kolene * MeSH
• senioři MeSH
• tibie diagnostické zobrazování   chirurgie   MeSH
• totální endoprotéza kolene * MeSH
• Check Tag
• lidé MeSH
• senioři MeSH
• Publikační typ
• časopisecké články MeSH

PURPOSE OF THE STUDY Use of an all-polyethylene (all-poly, AP) tibial component in primary total knee arthroplasty is still an attractive option considering the durability of replacement, the elimination of backside wear and the lower cost compared to modular metalbacked tibia. The purpose of the study was to evaluate the long-term results of the total knee replacement using the P.F.C. Sigma system with a monoblock all-polyethylene tibial component implanted at the 1st Orthopedic Department of the St. Anne's University Hospital and Masaryk University Brno in the period 1999-2010. MATERIAL AND METHODS In the monitored period, 911 total knee replacements using P.F.C. Sigma with an all-polyethylene tibial component were performed. This cohort of patients was evaluated at least 10 years after the primary replacement surgery. Altogether 323 knee replacements in 289 patients were evaluated. The clinical outcomes were assessed according to the Knee Society Clinical Rating System (KSS) and the Total Knee Arthroplasty Roentgenographic Evaluation and Scoring System. The replacement survival was evaluated using the Kaplan-Meier survival analysis. RESULTS In the evaluated group, the average KS was 82.6 points and the average functional score was 74.7 points. Excellent results were recorded in 213 cases, good results in 78 and satisfactory in 23 replacements. Poor clinical results were reported in 9 patients. The average range of motion was 105.8°. In 5 knees (1.5%) revision surgery was performed for infection complications, 3 cases were complicated due to periprosthetic fractures, 4 replacements were revised due to anterior knee pain and 8 knees showed a limited range of motion. Only 1 replacement was revised for aseptic loosening, with no need for reimplantation of the component. The survivorship of the implant was 98.5 % at the follow-up of 12.8 years, including the reasons of reimplantation. DISCUSSION Total knee replacement with an all-polyethylene tibial component is not so popular as the metal-backed modular implants. The all-polyethylene tibial component has certain advantages: lower unit costs, no backside wear, no liner dislocation, possibility of conservative bone resection. On the other hand, this type of implant is not modular and augmentations or longer stems cannot be used. Even though this type of endoprosthesis is recommended exclusively for elderly patients with a lower level of activity, the current mid- and long-term results show that indications for all-poly implants are much broader. CONCLUSIONS The total knee replacement with an all-polyethylene tibial component shows very good long-term clinical outcomes with an excellent survival rate. The all-poly design is cost-effective and may be used not only in elderly patients. Key words: total knee replacement, all-polyethylene tibial component, long-term results.

• MeSH
• lidé MeSH
• následné studie MeSH
• polyethylen MeSH
• protézy - design MeSH
• protézy kolene * MeSH
• reoperace MeSH
• selhání protézy MeSH
• senioři MeSH
• tibie chirurgie   MeSH
• totální endoprotéza kolene * škodlivé účinky   MeSH
• Check Tag
• lidé MeSH
• senioři MeSH
• Publikační typ
• časopisecké články MeSH

The kinematics of an intact knee joint and that of a knee replacement have been studied in many research centres. In the 1987 radiographic study, Bradley, Goodfellow and O'Connor reported the movement of a polyethylene insert in patients with unicompartmental Oxford knee replacement. Views with the knee at full extension and 90° of flexion were obtained and the movement of the meniscal bearings over this range of flexion was measured. The bearings were found to move backwards on the tibia through an average distance of 4.4 mm in all 16 patients. This measurement was in agreement with the then valid concept of knee biomechanics and a roll-back phenomenon. However, our observations had not always agreed with the results of these authors, but gave an impetus for a detailed evaluation of our own patient group. The aim of the study was to evaluate the dynamic relationship between the components of a unicompartmental Oxford knee replacement and elucidate it with the use of recent information from the field of biomechanics. A relationship of the obtained kinematic values to clinical outcomes was also investigated. Answers to the following hypotheses were sought: Would our results be in agreement with the British authors' findings? Would clinical outcomes depend on the kinematic properties of knee replacements? MATERIAL AND METHODS The group comprised 33 patients, 23 women and 10 men. They all had replacement of the medial compartment of the knee. The construction of the unicompartmental Oxford Phase III knee replacement enabled us to locate the centre of rotation of the medial femoral condyle in relation to the tibial component at flexion and extension of the knee, using radiography. The patients were examined in a supine position with the knee at full extension, and subsequently views of the knee were obtained at 80°-90° flexion in accordance with the method used by the British authors. The clinical findings of knee joints were assessed using the American Knee Society (AKS) scoring system (Insall et al.). Pain was rated on the Visual Analogue Scale (VAS). The results were statistically evaluated with the t-test and Chi-square test. RESULTS On moving the knee from extension to flexion, movement of the polyethylene insert ventrally by an average of 3.4 mm in relation to the tibia was recorded, i.e., "paradoxical" ventral translocation. In the patients with insert movement less than or equal to 3 mm, the average AKS score was 89 points, in those with movement over 3 mm it was 87 points. The average functional scores were 87 and 83 points in the patients with movement less than 3 mm and more than 3 mm, respectively. The average VAS score was 1.55 in the former and 1.18 in the latter. DISCUSSION The unicompartmental Oxford Phase III knee replacement substitutes a flexion femoral facet and eliminates the role of an extension femoral facet. This is the reason why, at knee extension between -5° and +20°, the centre of rotation of the medial femoral condyle is in the centre of the flexion facet and not in that of the extension facet. When the stabilising functions of the extension tibial facet in the ventral direction and of the dorsal part of the insert in the dorsal direction are missing, the position of the contact surface centre becomes much dependent also on the strength and direction of external forces acting in the knee joint vicinity. CONCLUSIONS The kinematic parameters of the unicompartmental Oxford Phase III knee replacement investigated in our group differed from the findings of the British authors. However, neither the magnitude nor the direction of movement had any effect on the clinical outcome of knee arthroplasty.

• MeSH
• biomechanika MeSH
• kolenní kloub patofyziologie   MeSH
• lidé středního věku MeSH
• lidé MeSH
• protézy kolene MeSH
• senioři nad 80 let MeSH
• senioři MeSH
• totální endoprotéza kolene MeSH
• Check Tag
• lidé středního věku MeSH
• lidé MeSH
• mužské pohlaví MeSH
• senioři nad 80 let MeSH
• senioři MeSH
• ženské pohlaví MeSH

• MeSH
• chirurgie operační MeSH
• ortopedické výkony MeSH
• ortopedie MeSH

• Konspekt
• Ortopedie. Chirurgie. Oftalmologie
• NLK Obory
• ortopedie
• chirurgie
• NLK Publikační typ
• kolektivní monografie