Comparative retrieval analysis of antioxidant polyethylene: bonding of vitamin-E does not reduce in-vivo surface damage

Background With the Persona® knee system a new polyethylene formulation incorporating vitamin-E which aims to reduce oxidation and maintain wear resistance was introduced. Although in-vitro studies have demonstrated positive effects of the vitamin-E antioxidants on UHMWPE, no retrieval study has looked at polyethylene damage of this system yet. It was the aim to investigate the in-vivo performance of this new design, by comparing it with its predecessor in retrieval analysis. Methods 15 NexGen® and 8 Persona® fixed-bearing implants from the same manufacturer (Zimmer Biomet) were retrieved from two knee revision centres. For retrieval analysis, a macroscopic analysis of polyethylene using a peer-reviewed damage grading method was used (Hood-score). The roughness of all articulating metal components was measured using a contact profilometer. The reason(s) for TKA revision were recorded. Statistical analyses (t-test) were performed to investigate differences between the two designs. Results The mean Hood score for Persona® inserts was 109.3 and for NexGen® 115.1 without significant differences between the two designs. Results from the profilometer revealed that Persona® and NexGen® femoral implants showed an identical mean surface roughness of 0.14 μm. The Persona® tibial tray showed a significantly smoother surface (0.06 μm) compared to the NexGen® (0.2 μm; p < 0.001). Both Hood score and surface roughness were influenced by the reasons for revision (p < 0.01). Conclusions The bonding of the antioxidant vitamin-E to the PE chain used in the novel Persona® knee system does not reduce in-vivo surface damage compared to highly crosslinked PE without supplemented vitamin-E used in its predecessor knee system NexGen®. However, the Persona® titanium alloy tibial tray showed a significantly smoother surface in comparison to the NexGen® titanium alloy tibial tray. This study provides first retrieval findings of a novel TKA design and may help to understand how the new Persona® anatomic knee system performs in vivo.

Polymethyl methacrylate cure time in simulated in vivo total knee arthroplasty versus in vitro conditions

Background The present means of confirming the cure of intra-operative polymethyl methacrylate (PMMA) cement are to wait for the remainder cement to harden. To our knowledge, there is no available technique to determine the precise moment of cure for in-vivo cement beneath the tibial tray. This study uses a novel means to determine cement curing time in two environments. One environment represents the operating theater, and the other environment attempts to model cement conditions under the tibial tray during surgery. Materials and methods We determined the temperature-versus-time plot of cement curing using the following two temperature sensors: one in a simulated implanted tibial tray and another in the remainder cement. We performed 55 tests using dental methyl methacrylate cement mixed in the same ratio as the orthopedic cement. To simulate in vivo conditions, a simulated stainless-steel tibial tray was implanted on a cancellous bone substitute (Sawbones, Vashon Island, WA, USA) using standard cement technique and subsequently placed in a 90°F (32.2 °C) circulating water bath. We positioned a temperature sensor in the cement mantel and positioned a second sensor in a portion of the remaining cement. The temperature from both sensors was measured simultaneously, beginning at 5 min after mixing and continuing for 20 min. The first derivative of the temperature provided the precise curing time for each condition. We analyzed the results of 55 repeated experiments with an independent samples t-test. Results With the described technique, we were able to accurately determine the moment of cure of the cement beneath the simulated tray. There was a mean difference between cure time of 5 min and 26 s (p value < 0.001) between the two conditions. Conclusions We validated that our technique was successful in determining the precise time to cure in two different environments. Level of evidence This was not a clinical trial and did not involve patients as such the level of evidence was Grade A: Consistent 1 and 2.

Polymethyl Methacrylate Cure Time in Simulated In Vivo Total Knee Arthroplasty Versus In Vitro Conditions

Background: The present means of confirming the cure of intra-operative polymethyl methacrylate (PMMA) cement is to wait for the remainder cement to harden. To our knowledge, there is no available technique to determine the precise moment of cure for in-vivo cement beneath the tibial tray. This study uses a novel means to determine cement curing time in two environments. One environment represents the operating theater, and the other environment attempts to model cement conditions under the tibial tray during surgery.Materials and Methods: We determined the temperature-versus-time plot of cement curing using the following two temperature sensors: one in a simulated implanted tibial tray and another in the remainder cement. We performed 55 tests using dental methyl methacrylate cement mixed in the same ratio as the orthopedic cement. To simulate in vivo conditions, a simulated stainless-steel tibial tray was implanted on a cancellous bone substitute (Sawbones, Vashon Island, WA, USA) using standard cement technique and subsequently placed in a 90°F (32.2 °C) circulating water bath. We positioned a temperature sensor in the cement mantel and positioned a second sensor in a portion of the remaining cement. The temperature from both sensors was measured simultaneously, beginning at 5 mins after mixing and continuing for 20 mins. The first derivative of the temperature provided the precise curing time for each condition. We analyzed the results of 55 repeated experiments with an independent samples t-test. Results: With the described technique, we were able to accurately determine the moment of cure of the cement beneath the simulated tray. There was a mean difference between cure time of 5 mins and 26 s (p-value<0.001) between the two conditions. Conclusions: We validated that our technique was successful in determining the precise time to cure in two different environments.Level of Evidence: This was not a clinical trial and did not involve patients as such the level of evidence was Grade A: Consistent 1 and 2

Improving the cementation of the tibial component in knee arthroplasty

Aims The main objective of this study is to analyze the penetration of bone cement in four different full cementation techniques of the tibial tray. Methods In order to determine the best tibial tray cementation technique, we applied cement to 40 cryopreserved donor tibiae by four different techniques: 1) double-layer cementation of the tibial component and tibial bone with bone restrictor; 2) metallic cementation of the tibial component without bone restrictor; 3) bone cementation of the tibia with bone restrictor; and 4) superficial bone cementation of the tibia and metallic keel cementation of the tibial component without bone restrictor. We performed CT exams of all 40 subjects, and measured cement layer thickness at both levels of the resected surface of the epiphysis and the endomedular metaphyseal level. Results At the epiphyseal level, Technique 2 gave the greatest depth compared to the other investigated techniques. At the endomedular metaphyseal level, Technique 1 showed greater cement penetration than the other techniques. Conclusion The best metaphyseal cementation technique of the tibial component is bone cementation with cement restrictor. Additionally, if full tibial component cementation is to be done, the cement volume used should be about 40 g of cement, and not the usual 20 g. Cite this article: Bone Joint Res 2021;10(8):467–473.

Cementless Highly Porous Titanium Tibial Base Plate in Total Knee Arthroplasty – Midterm Outcomes.

Introduction & Aims TKA in more active and young patients has prompted the interest in more durable and biological methods of Osteo-integration with cementless components. With the emergence of improved biomaterials like porous titanium and the success, search for a cementless TKA with long-term durability and survivorship may have ended. This is a retrospective study of 492 consecutive TKAs using Cementless tibial fixation, reporting on the early 4 years clinical and radiological outcomes. Method We studied 492 TKAs performed consecutively by a single surgeon between 1stJan. 2010 and 31stDec. 2015 using a cementless, fixed bearing tibial tray (porous–Regenerex, Vanguard, Zimmer-Biomet) and a cementless femoral component (Vanguard) with no exclusion criteria. Clinical and radiological follow-up was done on these patients and in addition a comprehensive joint registry review was performed on the whole cohort (Level II evidence). Results The average Knee Society Score at final follow-up was 89.33, average pre-op being 42.06. Average post-op WOMAC score was 43.45 and average pre-op was 77.78. On radiological examination, no patients had osteolysis around tibial base plate. In our series 9 patients were revised, out of which only 4 patients had the tibial tray and femoral component revised and 5 patients had patella resurfacing or liner exchange. Overall survivorship of the cementless tibial component is excellent with a survivorship of 99.4% at 5.9 years based on a comprehensive AOANJRR data. Conclusions Cementless tibial fixation using a porous titanium construct can provide stable bone ingrowth fixation on the tibial side with excellent and predictable early 4 to 5 year clinical and radiological outcomes.

Multi-energy spectral photon-counting computed tomography (MARS) for detection of arthroplasty implant failure

To determine whether state-of-the-art multi-energy spectral photon-counting computed tomography (MARS) can detect knee arthroplasty implant failure not detected by standard pre-operative imaging techniques. A total knee arthroplasty (TKA) removed from a patient was reviewed. The extracted prosthesis [NexGen Legacy Posterior Stabilized (LPS) TKA] was analyzed as were pre-operative imaging examination and compared with a MARS-CT examination obtained of the extracted TKA prosthesis. Radiographs, fluoroscopy, ultrasound and MRI preoperatively did not reveal the cause of the implant failure. MARS CT images of the extracted prosthesis clearly showed the presence of posteromedial polyethylene and tibial tray wear which is compatible with the clinical appearance of the extracted TKA. MARS can identify polyethylene insert and metallic tibial tray wear as a cause of TKA failure, that could not be identified with on standard pre-operative imaging. Although clinical MARS CT system is still under development, this case does illustrate its potential clinical usefulness. This is the first study to document how MARS CT imaging can detect orthopedic implant failure not detected by standard current imaging techniques. This system has a potential clinical application in orthopedic patients.

Tibial tray rotation and posterior slope increase risk for outliers in coronal alignment

Aims The extensive variation in axial rotation of tibial components can lead to coronal plane malalignment. We analyzed the change in coronal alignment induced by tray malrotation. Methods We constructed a computer model of knee arthroplasty and used a virtual cutting guide to cut the tibia at 90° to the coronal plane. The virtual guide was rotated axially (15° medial to 15° lateral) and with posterior slopes (0° to 7°). To assess the effect of axial malrotation, we measured the coronal plane alignment of a tibial tray that was axially rotated (25° internal to 15° external), as viewed on a standard anteroposterior (AP) radiograph. Results Axial rotation of the cutting guide induced a varus-valgus malalignment up to 1.8° (for 15° of axial rotation combined with 7° of posterior slope). Axial malrotation of tibial tray induced a substantially higher risk of coronal plane malalignment ranging from 1.9° valgus with 15° external rotation, to over 3° varus with 25° of internal rotation. Coronal alignment of the tibial cut changed by 0.07° per degree of axial rotation and 0.22° per degree of posterior slope (linear regression, R2 > 0.99). Conclusion While the effect of axial malalignment has been studied, the impact on coronal alignment is not known. Our results indicate that the direction of the cutting guide and malalignment in axial rotation alter coronal plane alignment and can increase the incidence of outliers. Cite this article: Bone Joint J 2020;102-B(6 Supple A):43–48.