Knee Implants Research Articles

Successful medial unicompartmental knee arthroplasty-What are the most important surgical tricks?

Unicompartmental knee arthroplasty (UKA) is an established surgical treatment option for end-stage anteromedial osteoarthritis with excellent functional outcomes and implant survival. Routine preoperative varus and valgus stress views are crucial for the selection of patients for unicompartmental or total knee arthroplasty. UKA is asoft-tissue based operation that aims to reconstruct the individual joint line and pre-arthritic alignment by restoring the physiological tension of the medial collateral and the cruciate ligaments. Current data for medial UKA show excellent results for both mobile and fixed bearing implant designs with the correct indication and surgical technique. Cementless fixation offers potential advantages over cemented implants. Registry data demonstrate that institutions and surgeons specializing in partial knee replacement (> 30cases/year per surgeon, > 100/year per institution) with ahigh percentage of UKA relative to the total number of knee implants (> 20%) have significantly lower revision rates.

Antibiotic prophylaxis prior to colonoscopy with biopsy does not decrease risk of prosthetic joint infection in total knee arthroplasty recipients

IntroductionProsthetic joint infection (PJI) risk continues to receive much attention given its associated morbidity and costs to patients and healthcare systems. It has been hypothesized that invasive colonoscopies may increase the risk of PJI. However, the decision to administer antibiotic prophylaxis lacks clinical guidance. In this study we aimed to compare PJI rates in patients undergoing colonoscopies with and without antibiotic prophylaxis against a control group, analyzing PJI occurrences at 90 days, 6 months, 9 months, and 1-year post-procedure and (2) assess the impact of antibiotic prophylaxis on PJI rates to inform clinical guidelines. MethodsWe queried a national, all-payer database to identify all primary total knee arthroplasty procedures without prior history of PJI between January 2010 and October 2020 (n = 1.9 million). All patients who had a diagnosis of PJI within one year of index procedure were excluded. There were three cohorts identified: colonoscopy with biopsy without antibiotic prophylaxis; colonoscopy with biopsy with antibiotic prophylaxis; and a control of no prior colonoscopy. Both colonoscopy cohorts were slightly younger and had higher comorbidities than the controls. The PJI diagnoses were identified at four separate time intervals within one-year after colonoscopy: 90-days; 6-months; 9-months; and 1-year. Chi-square analyses with odds ratios (ORs) and 95% confidence intervals were conducted for PJI rates between groups at all time-points. ResultsAmong all cohorts, no significant differences in PJI rates were found at 90-days (P = 0.459), 6-months (P = 0.608), 9-months (P = 0.598), and 1-year (P = 0.330). Similarly, direct comparison of both colonoscopy groups, with and without antibiotic prophylaxis, demonstrated no PJI rate differences at 90-day (P = 0.540), 6-months (P = 0.812), 9-months (P = 0.958), and 1-year (P = 0.207). Ranges of ORs between the colonoscopy cohorts were 1.07–1.43. ConclusionInvasive colonoscopy does not increase the risk of PJI in patients who have pre-existing knee implants. Furthermore, antibiotic prophylaxis may not be warranted in patients undergoing colonoscopy who have a planned biopsy.

Minimum 19-Year Clinical Results and Patient Satisfaction After Total Knee Arthroplasty

BackgroundLong-term (minimum 19-year) outcome data on clinical results and patient satisfaction after posterior-stabilized total knee arthroplasties (TKAs) are missing in the literature. The purpose of the study was to evaluate the clinical and radiographic results as well as patient satisfaction at a mean of 21.2 years after posterior-stabilized TKAs. MethodsThis study included 756 patients (1,350 knees) who had undergone TKAs. There were 96 men and 660 women (mean age, 58 years; range, 40 to 84). The mean follow-up was 21.2 years (range, 19 to 23). At each follow-up visit, the patients were assessed radiographically and clinically. Furthermore, patient satisfaction was determined. ResultsThe Knee Society total, pain, function, and deformity scores were 42, 18, 33, and 5 points, respectively, at the final follow-up. The mean Western Ontario and McMaster Universities Arthritis Index score was 25 points at the final follow-up. With revision or aseptic loosening as the end point, the 23-year intimated survival for the implant was 96% (95% confidence interval, 91 to 100%). The overall patient satisfaction score at the final follow-up was 83.3 points (range, 81 to 86). Patient satisfaction scores with regard to pain, housework, recreation, and surgery were 84, 81, 82, and 86 points, respectively. ConclusionsThe findings of the present, mean 21-year follow-up clinical study suggest excellent results with regard to the revision rates and survivorship of the posterior-stabilized total knee implants. However, consistent with the literature, we found that about 80% of patients expressed overall satisfaction with their primary TKAs. About 8% of patients were either somewhat or very dissatisfied with the procedure.

Saw-box osteotomy versus reamer-box osteotomy in posterior stabilized total knee arthroplasty: a retrospective study of an average fiveyear follow-up.

The purpose of this study is to compare the difference of results between two methods of femoral box osteotomy adopted by two designs of posterior stabilized total knee prostheses. Retrospective analysis of the results of two groups of patients operatedupon using two primary PS TKA systems, PFC Sigma (DePuy Synthes, Johnson and Johnson®) and Genesis II prosthesis (Smith and Nephew®), with an average of fiveyear follow-up was done. Group 1 included 152 knees in 121 patients and group 2 included 122 knees in 111 patients. The average follow-up period in both groups was fiveyears. The box osteotomy method depends on bone saw in group 1, and bone reamer in group 2. The KSS score of group 2 was better in the first sixmonths postoperatively. Then, no significant differences were seen in the remaining follow-up visits. The risk of periprosthetic fractures was significantly higher in group 1 (p-value 0.040). Survival analysis showed a significantly shorter time for reoperation in group 1 than in group 2 as described by log-rank test, (p < 0.006). The method of box cutting has an impact on the function and longevity of posterior stabilized primary knee implants. The risk of periprosthetic fractures can be reduced by proper patient selection, decreasing the box sizes, and development of more "controlled" box osteotomy instruments.

Morphometric analysis of distal femur through MRI in Turkish population and review of the literature

Measurements of the distal femur are highly variable among different subjects. To obtain the best stability and longevity of the knee implants, anthropometric data of the distal femur is required. The aim of this study was to investigate the anatomical structure of the distal femur according to age and gender and to determine the changes in the groups, of the patients with meniscopathy and controls. A total of 488 patients were included in the study according to age groups (0-15, 16-30, 31-45, 46-60, 61 and above). Intercondylar width, intercondylar anteroposterior distance, medial condylar width, lateral condylar width, bicondylar width, medial condyle anteroposterior distance, and lateral condyle anteroposterior distance were measured on axial Magnetic Resonance Imaging (MRI). Intercondylar width, medial condylar width, lateral condylar width and bicondylar width were significantly higher in men in all age groups compared to women (p &lt; 0.05). Intercondylar anteroposterior distance, medial condyle anteroposterior distance and lateral condyle anteroposterior distance were statistically significantly higher in males than in females except 0-15 age group (p &lt; 0.05). There was no significant difference in medial and lateral anteroposterior distance values in men (p &gt; 0.05), and found to be statistically significant (p &lt; 0.05) on the right and left side in women. Although personalized implant production is expensive compared to today’s conditions, we think that age and gender changes should be considered in the selection of prosthesis, since the dimensions of the distal femur will affect the stability and duration of use of knee implants.

CONCEPTION, IMPLEMENTATION, AND PRE-CLINICAL TESTING OF 3D-PRINTED CUSTOM-MADE ORTHOPAEDIC IMPLANTS IN COMPLEX KNEE AND HIP REVISION ARTHROPLASTY: CHALLENGES IN TREATMENT OF PERIPROSTHETIC FRACTURES AND SEVERE BONE DEFECT SITUATIONS

In severe cases of total knee &amp; hip arthroplasty, where off-the-shelf implants are not suitable (i.e., in cases with extended bone defects or periprosthetic fractures), 3D-printed custom-made knee &amp; hip revision implants out of titanium or cobalt-chromium alloy represent one of the few remaining clinical treatment options. Design verification and validation of such custom-made implants is very challenging. Therefore, a methodology was developed to support surgeons and engineers in their decision on whether a developed design is suitable for the specific case. A novel method for the pre-clinical testing of 3D-printed custom-made knee implants has been established, which relies on the biomechanical test and finite element analysis (FEA) of a comparable clinically established reference implant. The method comprises different steps, such as identification of the main potential failure mechanism, reproduction of the biomechanical test of the reference implant via FEA, identification of the maximum value of the corresponding FEA quantity of interest at the required load level, definition of this value as the acceptance criterion for the FEA of the custom-made implant, reproduction of the biomechanical test with the custom-made implant via FEA, decision making for realization or re-design based on the acceptance criterion is fulfilled or not. Exemplary cases of custom-made knee &amp; hip implants were evaluated with this new methodology. The FEA acceptance criterion derived from the reference implants was fulfilled in both custom-made implants and subsequent biomechanical tests verified the FEA results. The suggested method allows a quantitative evaluation of the biomechanical properties of custom-made knee &amp; hip implant without performing physical bench testing. This represents an important contribution to achieve a sustainable patient treatment in complex revision total knee &amp; hip arthroplasty with custom-made 3D printed implants in a safe and timely manner.

A Brief Review on PEEK as biomaterial, Importance of Implant Design, 3D Printing and FEA in Dental Implant

The present research study seeks to provide a thorough literature evaluation on implant-based materials, implant design and application of FEA approach (Finite Element Analysis). PEEK biomaterial is the primary subject of this article. Implant design and the significance of PEEK material in future clinical applications are significant subtopics in this study. Due to its excellent physical qualities, titanium plays an essential part in the implant business. PEEK and zirconia materials appear to have promise for the future. Biomedical uses of PEEK and its composite materials in a number of different fields, including dentistry, hip implant, anterior plate fixation, crainoplasticity, knee implants, spine implants, and so forth. The implant's impact and success are greatly impacted by the prudent selection of implant biomaterial. Before the PEEK implant can replace titanium and zirconium, further research and well-controlled clinical studies are required. In this study, a number of biomaterials that were used in the implant industry will be finalized.

A Comparative Study of Morphometric Parameters of Knee Using Magnetic Resonance Imaging in Different Population Groups

Abstract Background: The design of majority of commercially available knee implants has their basis on data obtained from the European population. Anthropometric research has demonstrated a difference in the shape and size of proximal tibia and distal femur between the genders and ethnic groups. Underfit or overhang of prosthetic components can result in poor clinical and functional outcomes with need for revision. This study compares the dimensions of the knee in multiple racial groups to observe if significant racial and gender differences occur. Methodology: Morphometric parameters of the knee of adult patients (&gt;18 years) in four population groups (Native Emirati, East Asian, Indian, and Caucasian) were measured using magnetic resonance imaging. Knee parameters were obtained from 368 patients (179 females and 189 males). Results: Males have larger femoral and tibial parameters compared to females (P &lt; 0.01). For any specified anteroposterior length of knee, females demonstrate narrower mediolateral widths compared to males. Significant differences exist in knee parameters between the racial groups in both genders (P &lt; 0.01). Conclusion: Adult knee parameters show significant variation between the genders and racial groups showing strong evidence for a race- and gender-specific knee arthroplasty system.

Strains on the human femur after revision total knee arthroplasty: An in vitro study using digital image correlation.

Pain at the tip of the stem of a knee prosthesis (End-of-Stem Pain) is a common problem in revision total knee arthroplasty (TKA). It may be caused by a problematic interaction between stem and bone, but the exact biomechanical correlate is still unknown. On top of this, there is no biomechanical study investigating End-of-Stem Pain at the distal femur using human specimens. Aim of this study was to find out whether the implantation of a revision total knee implant leads to high femoral surface strains at the tip of the stem, which the authors expect to be the biomechanical correlate of End-of-Stem Pain. We implanted 16 rotating hinge knee implants into 16 fresh-frozen human femora using the hybrid fixation technique and comparing two reaming protocols. Afterwards, surface strains on these femora were measured under dynamic load in two different load scenarios (climbing stairs and chair rising) using digital image correlation (DIC) and fracture patterns after overcritical load were analysed. Peak surface strains were found at the tip of the stem in several measurements in both load scenarios. There were no significant differences between the two compared groups (different trial sizes) regarding surface strains and fracture patterns. We conclude that implantation of a long intramedullary stem in revision TKA can lead to high surface strains at the tip of the stem that may be the correlate of femoral End-of-Stem Pain. This finding might allow for a targeted development of future stem designs that can lead to lower surface strains and therefore might reduce End-of-Stem Pain. Digital Image Correlation proved valid for the measurement of surface strains and can be used in the future to test new stem designs in vitro.

Sustainable material for knee replacement using topsis method

Sustainable materials are required for providing good design to products and proper application. It is economical, environmentally friendly and is widely accepted in society. The demand for knee replacement can be fulfilled with fulfilling aesthetic design and bio-compatibility of knee replacement. As the knee is the most important part of the body and the mobility of a person depends on its proper surgery and sustainable knee implants, in this paper an effort is made to design the knee implants using solid work design and the best implant material is selected Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method. The selection criteria of sustainable implant materials are dependent on properties like mechanical property, bio-compatibility ness and cost of the material , which helps in selection of best material, where as solid work helps in designing, optimizing and simulating sustainable knee implant design before manufacturing. For analyzing the material selection process, durability, performance and patients ' requirements are taken care of. Case studies and examples demonstrate the effectiveness of this approach in advancing orthopedic implant design and material selection, ultimately contributing to the improvement of patient care in the field of orthopedic surgery.

Progressive Late-Onset Genu Recurvatum Post-Total Knee Arthroplasty: Insights from a Spinal Stenosis-Related Case Series.

Knee osteoarthritis is common among older individuals, necessitating Total Knee Arthroplasty (TKA) for end-stage cases. The aging population has increased TKA demand, leading to a rise in revision surgeries. Genu recurvatum, a rare complication, often requires surgical intervention, with late-onset cases linked to neuromuscular conditions. This case series focuses on the infrequent occurrence of late-onset genu recurvatum resulting from spinal stenosis in patients without other predisposing conditions. A retrospective case series of 10 patients (11 knees) referred between February 2016 and August 2020 due to late recurvatum instability. Exclusion criteria encompassed neuromuscular diseases other than spinal stenosis, prosthetic joint infection, and pre-existing recurvatum deformity. Data, including demographics, medical history, imaging findings, and surgical details, were collected retrospectively. Patient performance was assessed using the Knee Society Score (KSS) at specified postoperative intervals. The study cohort, exhibiting hyperextension ranging from 11 to 30 degrees, underwent successful revision surgery using rotating hinge knee (RHK) implants after failed conservative measures. Follow-up assessments at 6, 18, and 24 months showed no recurrence of genu recurvatum. Late-onset genu recurvatum poses a challenge, necessitating surgical intervention. Identifying predisposing factors is crucial, with spinal stenosis emerging as a rare cause. The use of posterior stabilized (PS) implants in primary surgery aligns with higher revision rates, possibly linked to PCL removal. Limited literature explores the spinal-genu recurvatum relationship. A stepwise screening protocol is proposed for high-risk patients, emphasizing history, physical examination, and imaging. Strategic considerations include lower constraining, a tighter extension gap, and potential use of Hinge implants.

Distal Femoral Osteotomy for the Management of Coronal Deformity Following Total Knee Arthroplasty: A Report of 2 Cases.

We present 2 cases demonstrating the management of coronal malalignment with an existing total knee arthroplasty using opening wedge distal femur osteotomy. The mechanical axis was corrected, and the primary total knee implants were maintained. Patients resumed full activity 3 to 4 months after surgery. In certain cases, opening wedge distal femoral osteotomy is an option to correct coronal malalignment with an existing total knee arthroplasty without revising the implant.

Enhanced corrosion resistance of CoCrMo by laser-based surface modification

Biomedical grade cobalt–chromium–molybdenum (CoCrMo) alloys are extensively used for load-bearing biomedical applications such as hip and knee implants due to their exceptional biocompatible and biomechanical properties. However, the strain-induced martensite ε-phase development during contact loading results in thin oxide layers that are prone to fracture leading to corrosion. The formation of thin oxide layers is undesirable for long-term deployment. We employed laser-texturing to enhance the corrosion resistance of the material in simulated body fluid by the formation of hcp ε-phase martensite and via the formation of oxide layers. However, partial formation of hcp ε-phase martensite was observed. By means of central composite design-based response surface methodology, three laser parameters such as average laser power, texture density and the number of passes were optimised for maximal open circuit potential, an indicator for minimal corrosion. The textured surfaces were found to assist in the cellular proliferation of fibroblasts and inhibit bacterial growth.

Development of patient-specific 3D printed implants for total knee arthroplasty

Aim: Arthritis is a degenerative condition characterized by the progressive deterioration of the knee joint, leading to aches, rigidity, and decreased mobility. Total knee arthroplasty (TKA) surgery is performed to alleviate pain for restoring activity in these patients. TKA is carried out due to natural wear of the cartilage and meniscus or by sudden impact at the knee joint area. The surgical procedure involves careful planning, precise bone cuts, and insertion of artificial components made of metal alloys and high-density polyethylene. However, conventional manufacturing of customized knee implants involves time and cost. This work aims to present the application of three-dimensional (3D) printing for developing individualized knee implants for TKA and the challenges faced during it. Methods: Morphometry of the knee joint varies among different populations, including Indian and Western, which pose challenges during the surgery as accurate alignment and implant sizing are crucial for optimal outcomes. A female patient’s pre-surgery computed tomography (CT) scan is considered to identify the disease and to find region of interest (ROI) such as knee joint. Process involves converting scanned data to a file format for 3D printing via computer-aided design (CAD). Results: The patient’s CT scan data is processed to obtain the CAD models of knee joint and standard triangulation language (STL) file. Additional geometries and noise present near the region are removed to get ROI. Open loops and overlapping triangles are rectified in the STL file. Based on the morphometry of the bone, resection is done to obtain the CAD models of knee implants. 3D printing of the knee joint and implant prototypes is then obtained using fused deposition modelling (FDM). Line layers on the printed implant prototype are seen. Conclusions: Patient-specific 3D printed knee joint implant prototypes are successfully obtained using FDM. Challenges faced during the work are successfully worked out.

Improved postoperative kneeling ability in posterior stabilized total knee arthroplasty with medialized dome-patella resurfacing: A retrospective comparative outcome analysis

ObjectivesThis investigation aimed to evaluate if the modifications to prosthesis designs improve patients' clinical and functional outcomes after total knee arthroplasty (TKA), with a special focus on pain and kneeling ability. MethodsRetrospective and comparative analysis of consecutive patients who were treated with posterior stabilized TKA using two different prostheses designs (single surgeon, single vendor). Group 1 received a traditional design TKA (PFC Sigma; DePuy, Inc., Warsaw, IN) with conventional dome-patella resurfacing, and group 2 received a modern design implant (Attune; DePuy, Inc., Warsaw, IN) with medialized dome-patella resurfacing. Functional outcome (range of motion: ROM) and the Oxford Knee Score (OKS) were collected preoperatively, at 4–6 weeks and 12 months following surgery. ResultsNinety-nine participants were included. Of these, 30 received traditional-design implants and 69 received modern-design knee implants. The comparison between the two implants showed a statistically significant increase in total OKS and kneeling ability in the modern design cohort at 1-year follow-up compared to the traditional design cohort (p ​< ​0.01). In the modern design group, 53% (N ​= ​37) could kneel easily or with little difficulty, compared to 30% (N ​= ​9) in the traditional design group. No statistically significant differences in ROM or the OKS pain component were seen. ConclusionThe incorporation of a medialized dome-patella in modern knee implant design may offer advantages over traditional designs, as seen in improved total OKS and kneeling ability at one-year follow-up. Further research with larger cohorts is needed to confirm these findings and explore the broader impact of implant design changes on patient outcomes. Level of evidenceClinical Study, Level III.

Satisfactory Short‑Term Outcomes of Condylar‑Constrained Knee Implants in Primary Total Knee Arthroplasty

Background: This research set out to assess the functional prognosis of constrained condylar knee (CCK) in patients with severe intraoperative instability and/or coronal deformity undergoing primary total knee arthroplasty (TKA). Materials and methods: A prospective cohort study including 25 knees (21 cases) who underwent primary TKA using CCK implants. Senior surgeon operated all patients during 2020/2021 and followed clinically and radiographically at three, six and 12 months and 2 years postoperative. All cases were implanted with a single-design, second-generation CCK implant with a mean follow-up of 2 years. Results: The current research involved 25 knees (21 patients) with mean age 62.8 ± 12.2 years and most of the included patients were females (19; 76%). Preoperatively, valgus was demonstrated in six patients (24%) while varus was reported in 19 patients (76%) with mean preoperative Valgus/Varus angle 24.4 ± 9.9. Mean preoperative Knee Society Score (KSS) was 13.2 ± 2.7, mean preoperative functional KSS was 23.8 ± 19.2 and mean preoperative range of movement (ROM) was 107 ± 19.2. After 6 months, mean values of KSS was 86.2 ± 7.59. After 1 year, 2 years &amp; over 2 years, mean values of KSS were 86.2 ± 7.6, 86.2 ± 7.5, 86.3 ± 7.7 respectively. Degree of change in KSS before and after the operation was 69.1 ± 20.9. Mean values of late functional KSS was 62.5 ± 23.3. Degree of change in functional KSS before and after the operation was 36.8 ± 19.1. Postoperative ROM mean value was 120 ± 6.9 with degree of change 12.8 ± 6.3. Three cases reported postoperative complications; one cellulitis, one anterior femoral notching and one peroneal nerve injury. KSS increased from baseline to early postoperative with statistically significant variances (p&lt; 0.001) however, no statistically significant changes were discovered in KSS from early postoperatively to 2 years of follow up. Conclusion: Primary TKA utilizing CCK implants in cases with severe coronal abnormalities and/or intraoperative instability had a good short-term survival rate, on par with less limited implants. With positive clinical and radiological results, CCK implants can be thought of as a good alternative in some instances. It is important to exercise caution while utilizing an elevated level of restraint, since less restricted implants should be preferred.

Effects of arc current and travel speed on the processing of stainless steel via wire arc additive manufacturing (WAAM) process

Wire Arc Additive Manufacturing (WAAM) is an additive manufacturing process that uses an electric arc as the heat source to melt the feed metal wire and deposit it as per the desired 3D shapes. The current study investigates the influence of critical process parameters, namely welding current and travel speed, on the bead geometry and microstructure of deposits of stainless steel (308L). The results reveal that higher welding currents lead to increased bead width, while travel speed inversely affects bead height. Moreover, contact angles between the deposited material and the substrate increase with the welding current. An analysis of the liquid-to-vapor transition (δ) highlights its correlation with travel speed, impacting the spreadability of the deposited material. Notably, among all tested combinations of current and travel speed, 120 A and 25 mm/min yield uniform layer deposition of 308L stainless steel wire, an ideal outcome for WAAM applications. Additionally, it was observed that the percentage of the ferrite phase within the deposited material’s microstructure exhibits an intriguing relationship, increasing with travel speed while decreasing with rising current and layer number. These findings offer valuable insights into process optimization for WAAM-based orthopedic applications, emphasizing the potential for customized orthopedic knee implants with improved quality and performance.

Design, Simulations and Tests of a Novel Force and Moments Sensor for Instrumented Knee Implants.

Early identification of mechanical complications of total knee arthroplasties is of great importance to minimize the complexity and iatrogenicity of revision surgeries. There is therefore a critical need to use smart knee implants during intra or postoperative phases. Nevertheless, these devices are absent from commercialized orthopaedic implants, mainly due to their manufacturing complexity. We report the design, simulations and tests of a force and moments sensor integrated inside the tibial tray of a knee implant. By means of a "tray-pillar-membrane" arrangement, strain gauges and metal additive technology, our device facilitates the manufacturing and assembly steps of the complete system. We used finite element simulations to optimize the sensor and we compared the simulation results to mechanical measurements performed on a real instrumented tibial tray. With a low power acquisition electronics, the measurements corroborate with simulations for low vertical input forces. Additionally, we performed ISO fatigue testings and high force measurements, with a good agreement compared to simulations but high non-linearities for positions far from the tray centre. In order to estimate the center of pressure coordinates and the normal force applied on the tray, we also implemented a small-size artificial neural network. This work shows that relevant mechanical components acting on a tibial tray of a knee implant can be measured in an easy to assemble, leak-proof and mechanically robust design while offering relevant data usable by clinicians during the surgical or rehabilitation procedures. This work contributes to increase the technological readiness of smart orthopaedic implants.

A comparison of joint line height after revision total knee replacement using a rotating hinge versus a condylar revision knee system

PurposeThis retrospective study aimed to assess the effects of two differing revision total knee implants designs (condylar and rotating hinge) on joint line height. MethodThe use of distal augmentation and pre and post revision radiographic joint line heights were compared in 19 condylar type knee replacements (Zimmer NexGen Legacy Constrained Condylar Knee - LCCK) and 40 LINK-Endo-rotating hinge knee replacements. Joint line and patellar heights were determined for each implant using four validated methods. For comparison within a group a two tailed paired Student's t-test was used, for comparison between the groups an unpaired, two tailed Student's t-test was used. A p value of less than 0.05 was deemed statistically significant. ResultsIn 15 of 19 NexGen revision knee replacements distal augments were used. No distal augments were used in the LINK-Endo RHK group. In both systems there was no tendency to elevate the joint line relative to the tibia. The joint line was distalised relative to the femur in the NexGen group and proximalised in the rotating hinge knee group. Measurements using antero-posterior radiographs were found to be the most reliable method of assessing joint line height when compared to lateral radiographs. ConclusionBoth revision knee implant systems adequately restored joint line height. In condylar type knee revision implants elevation of the joint line height may be avoided through the use of distal augmentation. We found AP radiographs to be the most reliable method of accurately assessing joint line height.

The influence of implant design and limb alignment on in vivo wear rates of fixed-bearing and rotating-platform knee implant retrievals.

Analysis of polyethylene (PE) wear in knee implants is crucial for understanding the factors leading to revision in total knee arthroplasty. Importantly, current experimental and computational methods for predicting insert wear can only be validated against true in vivo measurements from retrievals. This study quantitatively investigated in vivo PE wear rates in fixed-bearing (FB) (n = 21) and rotating-platform (n = 53) implant retrievals. 3D surface geometry of the retrievals was measured using a structured light scanner. Then, a reference surface that included the deformation, but not the wear that the retrievals had experienced in vivo, was constructed using a fully automatic surface reconstruction algorithm. Finally, wear volume was calculated from the deviation between the worn and reconstructed surfaces. The measurement and analysis techniques were validated and the algorithm was found to produce errors of only 0.2% relative to the component volumes. In addition to quantifying cohort-level wear rates, the effect of mechanical axis limb alignment on mediolateral wear distribution was examined for a subset of the retrievals (n = 14 + 26). Our results show that FB implants produce significantly (p = 0.04) higher topside wear rates (24.6 ± 10.1 mm3/year) than rotating-platform implants (15.3 ± 8.0 mm3/year). This effect was larger than that of limb alignment, which had a smaller and nonsignificant influence on overall wear rates (+4.5 ± 11.6 mm3/year, p = 0.43). However, increased varus alignment was associated significantly with greater medial compartment wear in both the FB and rotating-platform designs (+1.7 ± 1.3%/° and +1.8 ± 1.6%/°). Our findings emphasize the importance of implant design and limb alignment on wear outcomes, providing reference data for improving implant performance and longevity.