Unicompartmental Knee Prosthesis Research Articles

Finite element analysis of sagittal angles of unicompartmental knee arthroplasty

BackgroundUnicompartmental knee arthroplasty is an effective treatment for knee osteoarthritis, but it has the risk of failure, and the installation position of the prosthesis is one of the factors affecting the failure. There are few biomechanical studies on the installation angle of unicompartmental knee prosthesis. MethodsConstructed a finite element model of a normal human knee joint, and the validity of the model was verified by stress and front anterior methods. The mobile-bearing unicompartmental knee arthroplasty femoral prosthesis was placed at 3° intervals from 0° sagittal plane to 15° flexion, and − 2° and 17°were established, and observing the biomechanical changes of components. FindingsMaximum peak stresses occurred at a sagittal mounting angle of −2° for the insert and the contralateral meniscus, with the tibia showing a maximum at 17° sagittal and the tibial prosthesis stress maximum occurring at 6° sagittal. As the sagittal plane angle of the femoral prosthesis increases and the osteotomy distance extends posteriorly, more bone is amputated during the osteotomy. The ratio of the distance from the tip of the anterior intramedullary nail to the anterior end of the osteotomy to the total anteroposterior length of the sagittal osteotomy ranged from 43.2% to 44.6%. InterpretationIn this paper, the more appropriate sagittal mounting position for the femoral prosthesis is between 9 and 12°, based on the amount of osteotomy and the peak stress of each component in a standing position.

CORR Insights®: Did a New Design of the Oxford Unicompartmental Knee Prosthesis Result in Improved Survival? A Study From the Norwegian Arthroplasty Register 2012-2021.

1Clinical Assistant Professor, Department of Orthopaedic Surgery, University of Michigan Health System, Ann Arbor, MI, USA B. R. Hallstrom, University of Michigan Health System, Department of Orthopaedic Surgery, 2912 Taubman Center, Box 5328, 1500 East Medical Center Drive, Ann Arbor, MI 48109-5328, USA, Email: [email protected] This CORR Insights® is a commentary on the article “Did a New Design of the Oxford Unicompartmental Knee Prosthesis Result in Improved Survival? A Study From the Norwegian Arthroplasty Register 2012-2021” by Skåden and colleagues available at: DOI: 10.1097/CORR.0000000000002671. The author certifies that there are no funding or commercial associations (consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article related to the author or any immediate family members. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request. The opinions expressed are those of the writer, and do not reflect the opinion or policy of CORR® or The Association of Bone and Joint Surgeons®.

Treatment of Acute Anterior Cruciate Ligament Tear in a Patient with Unicompartmental Knee Prosthesis

Treatment of Acute Anterior Cruciate Ligament Tear in a Patient with Unicompartmental Knee Prosthesis

Early migration in unicompartmental knee arthroplasty: a radiostereometric study of 26 patients with 24 months of follow-up.

Aseptic loosening, mainly caused by migration, is one of the most common indications for revisions in unicompartmental knee arthroplasty (UKA). In this study, we investigated the early migration of the Persona Partial Knee (PPK, Zimmer Biomet, Warsaw, IN), a cemented medial fixed-bearing unicompartmental knee prosthesis, and evaluated the clinical results. 26 primary PPKs were implanted. Radiographs were obtained direct postoperatively, at 6 weeks, 6, 12 and 24 months postoperatively. Migration of the femoral and tibial component was calculated using model-based radiostereophotogrammetric analysis (mRSA) in terms of translations and rotations. Patient-reported outcome measures (PROMs) were also registered. At 24 months postoperatively, we found low migration of both the femoral and tibial component in the first 6 months, after which both components stabilized. Only the rotation of the tibial component about the z-axis did not stabilize. All PROMs improved after 24 months compared with preoperative PROMs. The Persona Partial Knee shows low migration of both the femoral and tibial component and PROMs were improved at 24 months follow-up. Long-term follow-up is needed to investigate the performance of the prosthesis compared with other prostheses.

A prospective study of 93 unicompartmental knee prosthesis emphasises the appearance of radiolucencies under the tibial component

Here, we report the presence of radiolucent lines in a consecutive group of 93 partial knee replacements (UKA). The prospective study was conducted from 2011 to 2019 with a minimum follow-up of two years. Clinical data and radiographs were recorded. Of the 93 UKA, 65 were cemented. The Oxford Knee Score was recorded before and two years after surgery. In 75 cases, the follow-up was conducted at > 2 years. A lateral knee replacement was performed in 12 cases. In one case, a medial UKA with patellofemoral prosthesis was performed. In eight patients (8.6%), a radiolucent line (RLL) underneath the tibia component was observed. In four of these eight patients, RLLs were non-progressive, without clinical implications. In two cemented UKAs, RLLs were progressive and were revised with total knee arthroplasty. Early severe osteopenia of the tibia (zone 1 to 7) in the frontal view was observed in two cementless medial UKA cases. The demineralisation occurred spontaneously five months after surgery. We diagnosed two early deep infections, one of which was treated locally. RLLs were present in 8.6% of the patients. Even in severe cases of osteopenia, spontaneous recovery of RLLs is possible with cementless UKAs.

Contribution of Minimally Invasive Bone Augmentation With PMMA Cement in Primary Fixation of Schatzker Type II Tibial Plateau Fractures.

Background: The most common type of fracture of the lateral tibial plateau is the Schatzker type II split-depressed fracture. Minimally invasive surgery using balloon reduction appears to be very promising compared to the gold standard using a bone tamp. This surgery aims to have the best reduction and stabilization to benefit from an early passive and active rehabilitation to avoid stiffening and muscle wasting. Using a balloon for fracture reduction has allowed the use of semi-liquid Injectable Bone Cement (IBC) fillers. These fillers can be phosphocalcic or polymethyl methacrylate (PMMA). The latest recommendations on these IBCs in spinal surgery increasingly rule out phosphocalcic fillers because of their low mechanical strength. Questions/purposes: 1) What is the mechanical influence of IBC filling (PMMA) regarding the split and depression components of a Schatzker type II fracture? 2) What is the mechanical influence of osteosynthesis regarding the split and depression components of a Schatzker type II fracture with or without PMMA filing in three different kinds of percutaneous fixations? Methods: This biomechanical study was performed on 36 fresh frozen tibia/fibula specimens. Six groups were formed according to the type of percutaneous osteosynthesis or possible PMMA filling. Mechanical strength tests were carried out using a Unicompartmental Knee prosthesis and displacement components were measured on either side of the separation on the anterolateral facet by optical method. Results: We found a significant difference between cementless and cemented osteosynthesis for depression fracture stabilization (difference −507.56N with 95% confidence interval [−904.17; −110.94] (p-value = 0.026)). The differences between the different types of osteosynthesis were not significant (p-value = 0.58). There was a significant difference between osteosynthesis without cement and osteosynthesis with cement on separation (difference −477.72N [−878.52; −76.93] (p-value = 0.03)). The differences between the different types of fixations were not significant regarding separation (p-value = 0.99). Conclusion: PMMA cement significantly improves primary stability, regardless of the type of osteosynthesis for a Schatzker type II plateau fracture. Filling with PMMA cement during tuberoplasty seems to be a very promising strategy in association with percutaneous osteosynthesis to allow rapid recovery after surgery.

Does hip or knee joint replacement decrease chances to complete an ultra-trail race? Study in participants at the Ultra-Trail du Mont Blanc®

IntroductionThe number of patients with hip or knee joint replacements is increasing. Some of these patients want to practice sport, including in high-impact sports such as ultra-trails. Is the proportion of drop-out higher among runners after a hip or knee replacement? What are the symptoms of these patients? HypothesisHip or knee joint replacements are associated with a higher drop-out rate during an ultra-trail. Material and methodsWe conducted a monocentric retrospective epidemiological study. A questionnaire translated into French, English and Spanish were sent to all runners registered for one or more of the 5 races of the 2015 to 2017 Ultra-Trail du Mont-Blanc® (UTMB®) editions. There were no exclusion criteria. The drop-out rate of patients who responded to the questionnaire was calculated among patients with and without hip or knee joint replacement. Specific symptoms related to these joint replacements were identified before, during and after the race. ResultsOut of the 24,855 participants having run at least one of the 3 editions, 2,469 responded. Some of them ran several races: these 2469 runners were on 3171 start lines and 2548 finish lines (drop-out rate of 19.6%). Among these 2469 runners, 18 had hip and/or knee replacement and were on 27 start lines and 17 finish lines (drop-out rate of 37%). The race was finished by 3 of the 6 runners with a total hip arthroplasty (THA), all of the 8 runners with a hip resurfacing arthroplasty (HRA) and 3 of the 4 runners with a total knee arthroplasty (TKA). Among runners with THA, pubalgia or groin pain was described by one of them before the race, 3 during the race and 2 after the race. Among runners with HRA, pygalgia or groin pain was described by 2 of them during the race. As for the TKA, there was no specific symptom. No answering runner had a unicompartmental knee prosthesis. DiscussionRunning ultra-trail is possible after a hip or knee joint replacement. All of the 8 runners with HRA finished the race. We may remain cautious about the long-term survival of prostheses. Level of proofIV; monocentric retrospective epidemiological study.

Varus or valgus positioning of the tibial component of a unicompartmental fixed-bearing knee arthroplasty does not increase wear.

Higher revision rates were shown in varus- or valgus-positioned tibias in unicompartmental knee arthroplasty (UKA), but more than 15% of UKA prostheses are implanted with more than 5° of varus or valgus. This study aimed to analyze the wear rate in UKA when implanting the tibial component in either varus or valgus position versus a neutral placement at 90° to the tibial anatomical axis. The study hypothesized that a 5° varus or valgus positioning of the tibial plateau will generate less wear compared to a neutral alignment. Wear was experimentally analyzed on a medial anatomical fixed-bearing unicompartmental knee prosthesis (Univation, Aesculap, Germany) in vitro with a customized, four-station, servohydraulic knee wear simulator, reproducing the walking cycle. The forces, loading and range of motion were applied as specified in the ISO 14243-1:2002, 5 million cycles were analyzed. The tibial components of the medial prostheses were inserted in a neutral position, with 5° varus, and 5° valgus (n = 3, each group). The wear rate decreased significantly with a 5° varus positioning (6.30 ± 1.38mg/million cycles) and a 5° valgus positioning (4.96 ± 2.47mg/million cycles) compared to the neutral position (12.16 ± 1.26mg/million cycles) (p < 0.01 for the varus and the valgus position). The wear area on the inlay was slightly reduced in the varus and valgus group. A varus or valgus "malpositioning" up to 5° will not lead to an increased wear. Wear was even less because of the reduced articulating contact area between the inlay and the femur. A slight varus positioning of the tibial component (parallel to the anatomical joint line) positioning can be advocated from a point of wear. Experimental study.

Progression of osteoarthritis and reoperation in unicompartmental knee arthroplasty: A comparison of national joint registries

Unicompartmental knee arthroplasty remains a challenge for orthopaedic surgeons because of its higher revision rate compare with the total knee arthroplasty. The hypothesis of this work is that the progression of osteoarthritis in unicompartmental knee prostheses is the natural history of the degenerative disease and a reason for reoperation. Most international joint registries consider this fact as a failure of the implant and a cause of revision. Annual joint registries were searched for progression of osteoarthritis in unicompartmental knee arthroplasty and reasons for their revisions. Current data from registries for unicompartmental knee indicate that the revision rate of such prostheses is overestimated. Considering osteoarthritis progression as the development of the existing disease and not as a failure of the implant, revision rate will be reduced. Registries, reports, and studies are needed to evaluate the progression of osteoarthritis as a cause of reoperation instead of a reason for revision, reducing unicompartmental revision rate and encouraging surgeons to implant more of them.

Does the body mass index influence the long-term survival of unicompartmental knee prostheses? A retrospective multi-centre study

The effect of being obese on the long-term survival of total joint arthroplasty is persistently discussed. Considering only studies with large cohort of patients and meta-analysis, a high body mass index has been correlated with a higher incidence of complication but not univocally with a lower survival rate. In this study, we analyzed, retrospectively, the data of patients that received unicompartmental knee prostheses in order to examine if obesity has an effect on clinical outcomes. A retrospective multi-centre study was carried out on 4964 unicompartmental knee replacements between July 2000 and December 2016, the patients involved were 3976, with 988 bilateral cases. The patients were categorized into three groups: non-obese with a body mass index (BMI) < 30kg/m2, obese with BMI ranged between 30 and 39kg/m2, and morbidly obese (BMI ≥ 40kg/m2). The outcome was measured using the Cox proportional hazards model with end point UKA revision for any reasons. Results were stratified for sex, age, weight, and bi-laterality. The morbidly obese group was significantly younger and required a significantly longer operating time. No statistical significant differences were observed considering the BMI groups in terms of type of insert, type of tibial component, prosthetic condyle, and prosthesis fixation (p > 0.05; chi-square test). Obese and morbidly obese patients have as much to gain from total knee replacement as non-obese patients.

Clinical Results of Lateral Unicompartmental Knee Arthroplasty: Minimum 2-Year Follow-up.

BackgroundWe investigated the clinical results and early complications after lateral unicompartmental knee arthroplasty (UKA) using the Zimmer unicompartmental high-flex knee (ZUK) prosthesis with a minimum follow-up of 2 years.MethodsTwenty-seven patients (30 cases) who underwent lateral UKA with the ZUK prosthesis between January 2011 and February 2014 were selected for this study. The mean age of the patients was 63.3 years at the time of surgery, and the mean followup was 3 years and 2 months (range, 24 to 48 months). A retrospective investigation method was used to evaluate the clinical and radiographic results with use of the Knee Society (KS) clinical rating system and plain radiography.ResultsThe mean KS pain score was improved from 17.9 points (range, 10 to 30 points) preoperatively to 40.5 points (range, 30 to 45 points) at the final follow-up (p < 0.001). The mean KS knee score and function score significantly increased from 63.2 points (range, 48 to 70 points) and 68.6 points (range, 35 to 80 points), respectively, preoperatively to 86.0 points (range, 74 to 95 points) and 92.4 points (range, 60 to 100 points), respectively, at the final follow-up (p < 0.001). The mean range of motion of the knee was recovered from 127.1° (range, 110° to 135°) preoperatively to 131.6° (range, 120° to 135°) at the final follow-up. The mean tibiofemoral angle changed from 6.2° of valgus (range, 0.1° to 11.4° of valgus) preoperatively to 3.4°of valgus (range, 0.2° to 9.5° of valgus) at the final follow-up. The overall results classified based on the KS knee score were "excellent" in 21 cases and "good" in 8 cases. Revision total knee arthroplasty was required in one case because of consistent pain on the medial side of the knee after surgery.ConclusionsThe early clinical results of lateral UKA using the ZUK prosthesis were satisfactory for improvement of pain, knee score, function score, and recovery of knee motion. Therefore, the lateral UKA could be a useful method in the treatment of osteoarthritis in the lateral compartment of the knee. Long-term survivorship remains to be confirmed through ongoing follow-up.

Unicompartmental knee arthroplasty is effective: ten year results.

Unicompartmental knee arthroplasty (UKA) presents low morbidity and complication risk and provides excellent outcomes and fast recovery. Despite these facts, knee-replacement registries have shown high failure rates for UKA, especially when compared with traditional TKA. The purpose of this study was therefore to report outcomes, complications, and ten year survivorship rate of medial ZUK unicompartmental knee prosthesis. We retrospectively analysed 136 medial UKAs in 124 patients, with a maximum follow-up of ten years. Patients were assessed through the International Knee Society (IKS) scores and range of motion (ROM). A complete X-ray study was performed in all patients. Limb alignment was assessed by measuring the femorotibial mechanical alignment. At surgery, bone resections were performed according to proximal tibial epiphyseal axis. Mean IKS knee score improved from 45.7 (range 35-63) points preoperatively to 87.2 (range 71-100) points at the latest follow-up. Mean IKS function score improved from 50.9 (range 40-70) points to 89.1 (range 75-100) points (p < 0.05). Mean ROM increased from 106.1° (range 98-123°) to 128.6° (range 116-139°) (p < 0.01). Four cases (2.9 %) were revised due to failure for any cause, so that survivorship was 97.1 % at the latest follow-up. This study demonstrates excellent outcomes and survivorship for the ZUK unicompartmental knee prosthesis. Based on our findings, we believe that the ZUK prosthesis offers an effective and durable solution for treating medial degeneration of the knee. Level of Evidence IV - Retrospective case series study.

Increase in the tibial slope reduces wear after medial unicompartmental fixed-bearing arthroplasty of the knee.

Introduction. Unicompartmental arthroplasty of the knee in patients with isolated medial osteoarthritis gives good results, but survival is inferior to that of total knee prosthesis. Knees may fail because positioning of the prosthesis has been suboptimal. The aim of this study was to investigate the influence of the tibial slope on the rate of wear of a medial fixed-bearing unicompartmental knee arthroplasty. Materials and Methods. We simulated wear on a medial fixed-bearing unicompartmental knee prosthesis (Univation) in vitro with a customised, four-station, and servohydraulic knee wear simulator, which exactly reproduced the walking cycle (International Organisation for Standardisation (ISO) 14243-1:2002(E)). The medial prostheses were inserted with 3 different posterior tibial slopes: 0°, 4°, and 8° (n = 3 in each group). Results. The wear rate decreased significantly between 0° and 4° slope from 10.4 (SD 0.62) mg/million cycles to 3.22 (SD 1.71) mg/million cycles. Increasing the tibial slope to 8° did not significantly change the wear rate. Discussion. As an increase in the tibial slope reduced the wear rate in a fixed-bearing prosthesis, a higher tibial slope should be recommended. However, other factors that are influenced by the tibial slope (e.g., the tension of the ligament) must also be considered.

Clinical results of unicompartmental arthroplasty for knee osteoarthritis using a tibial component with screw fixation

Unicompartmental knee prostheses with screw fixation into the proximal tibia were employed and postoperative clinical results for osteoarthritis of the knee, especially regarding relief of pain, range of motion and satisfactory limb alignment are reported and discussed. A total of 140 knees (131 medial and 9 lateral) of 85 patients (21 men and 64 women) were followed up for two to 17 years with an average of 7.0 ± 3.0 years. In spite of loss to follow-up in three knees of two patients and revision to total knee arthroplasty in one knee of one patient, in the remaining 136 knees (82 patients) the mean knee score of the Knee Society Clinical Rating System was 41.0 ± 14.7 pre-operatively, which improved to 93.1 ± 5.7 at follow-up, while the mean functional score similarly improved from 36.9 ± 8.1 to 88.5 ± 6.3 (p < 0.001 respectively). One knee developed a fracture in the medial proximal part of the tibia, but no knee developed loosening of the prosthesis or infection. The mean pre-operative knee flexion was 122.6 ± 15.9°, which improved to 132.9 ± 13.4° (p < 0.001) at follow-up. The limb alignment showed 4.8 ± 4.5° anatomical varus angulation pre-operatively, which was corrected to 5.8 ± 3.3° valgus at follow-up in the medial unicompartmental replacement group (127 knees), and 19 ± 6.1° valgus pre-operatively, which was corrected to 6.7 ± 3.0° valgus at follow-up in the lateral unicompartmental replacement group (nine knees). The clinical results of arthroplasty with screw fixation were concluded to be promising.

Ten year survivorship after cemented and uncemented medial Uniglide® unicompartmental knee arthroplasties

BackgroundResults of knee replacement registries have shown that unicompartmental knee arthroplasty (UKA) has a significantly higher revision and failure rate than current state-of-the-art TKA. The aim of this prospective study is to evaluate the long-term outcomes and to calculate the 10year survival of knees with medial osteoarthritis treated with Uniglide® UKA. MethodsTwo hundred thirty-four patients were assessed by an independent clinical observer using the American Knee Society Clinical Rating System, a validated outcome measure. Kaplan–Meier analysis was used to calculate the 10year survival rates using revision surgery for any cause as the end point. ResultsThere were no revisions due to progression of lateral osteoarthritis or polyethylene failure. There were one traumatic and three non-traumatic bearing dislocations and two revisions due to aseptic loosening of the tibial component. One joint was revised for traumatic ligament rupture, one for synovitis from bearing impingement, one due to femoral component mal-positioning and one for infection.A total of 10 cases were revised due to failures for any cause in the 61 patients withdrawn because they had died, thus giving a cumulative survival rate at 10years of 95.57%. The knee (function) score showed an increase from 33.4 (54.7) pre-operatively to 94 (83.4) points post-operatively. The average range of motion increased from 107 to 122° (p<0.01). ConclusionBased on our findings we believe that the Uniglide® unicompartmental knee prosthesis offers a safe and effective solution for the treatment of medial compartment osteoarthritis.

Patient-Specific Design and Biomechanical Evaluation of a Novel Bipolar Femoral Hemi-Knee Prosthesis

AbstractWhile total knee replacement is successful, hemiarthroplasty is necessary for some young, obese and active patients who are especially not suitable for unicompartmental or total knee prostheses. Hemiarthroplasty also provides an opportunity for children with bone tumors. The design of hemiarthroplasty should be patient-specific to reduce contact stress and friction as well as instability, compared to conventional hemi-knee prosthesis. A novel bipolar hemi-knee prosthesis with two flexion stages was developed according to a healthy male's knee morphological profile. The motion mode of the bipolar hemi-knee prosthesis was observed through roentgenoscopy in vitro experiment. The biomechanical properties in one gait cycle were evaluated though finite element simulation. The bipolar hemi-knee prosthesis was found to produce knee flexion at two stages through X-ray images. The first stage is the motion from upright posture to a specified 60° flexion, followed by the second stage of motion subsequently to deep flexion. The finite element simulation results also show that the designed hemi-knee prosthesis has the ability to reduce stresses on the joint contact surfaces. Therefore, it is possible for the bipolar hemi-knee prosthesis to provide better biotribological performances because it can reduce stresses and potentially wear on the opposing contacting surface during a gait cycle, providing a promising treatment strategy in future joint repair and replacement.

Quantification of Wear Rates and Plastic Deformation on Mobile Unicompartmental UHMWPE Tibial Knee Inserts

Experimental wear testing is an essential step in the evaluation of unicompartmental knee prostheses; the major mechanisms that dominate the wear of conventional ultra high molecular weight polyethylene tibial knee menisci are the sub-surface cracking and delamination that induce particle release by abrasion/adhesion and subsequently periprosthetic osteolysis. The aim of this study was to determine whether plastic deformation affects the wear of the polymer and to measure the magnitude of these effects. Wear test was performed using a displacement-control knee wear simulator with “three-plus-one” stations, in accordance with the ISO 14243-3/2. A state-of-the-art coordinate measuring machine was used to quantify the volumetric mass loss of the mobile knee polyethylene menisci as well as creep/plastic deformations. The volumetric wear measured by this method was compared to that measured by the gravimetric method. Raman spectroscopy showed morphology changes induced by mechanical stress in both the upper and lower surfaces of the menisci. The amorphous content increased at expenses of the crystalline orthorhombic content, which generally decreased in all menisci. A slight orthorhombic → monoclinic phase transformation occurred upon mechanical stress. Plastic deformation appeared as the main factor affecting the trend of the spectroscopic markers and thus the morphology degradation.

Joint registry approach for identification of outlier prostheses

Background and purpose Joint Replacement Registries play a significant role in monitoring arthroplasty outcomes by publishing data on survivorship of individual prostheses or combinations of prostheses. The difference in outcomes can be device- or non-device-related, and these factors can be analyzed separately. Although registry data indicate that most prostheses have similar outcomes, some have a higher than anticipated rate of revision when compared to all other prostheses in their class. This report outlines how the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) has developed a method to report prostheses with a higher than expected rate of revision. These are referred to as “outlier” prostheses.Material and methods Since 2004, the AOANJRR has developed a standardized process for identifying outliers. This is based on a 3-stage process consisting of an automated algorithm, an extensive analysis of individual prostheses or combinations by registry staff, and finally a meeting involving a panel from the Australian Orthopaedic Association Arthroplasty Society. Outlier prostheses are listed in the Annual Report as (1) identified but no longer used in Australia, (2) those that have been re-identified and that are still used, and (3) those that are being identified for the first time.Results 78 prostheses or prosthesis combinations have been identified as being outliers using this approach (AOANJRR 2011 Annual Report). In addition, 5 conventional hip prostheses were initially identified, but after further analysis no longer met the defined criteria. 1 resurfacing hip prosthesis was initially identified, subsequently removed from the list, and then re-identified the following year when further data were available. All unicompartmental and primary total knee prostheses identified as having a higher than expected rate of revision have continued to be re-identified.Interpretation It is important that registries use a transparent and accountable process to identify an outlier prosthesis. This paper describes the development, implementation, assessment, and impact of the approach used by the Australian Registry.

Do bone loss and reconstruction procedures differ at revision of cemented unicompartmental knee prostheses according to the use of metal-back or all-polyethylene tibial component?

Results of unicompartmental knee arthroplasty (UKA) revision are known but the severity of bone loss and the need for reconstruction are not detailed for different tibial implants. Metal-backing UKA revision exposes the patient to more severe tibial bone loss and requires more substantial reconstruction procedures than cemented polyethylene UKA revision. This retrospective series of 23 revisions of UKA to total knee arthroplasty (TKA) compared 11 all-polyethylene UKAs with 12 metal-backing UKAs. Factors that contributed to failure were aseptic loosening (n=12) and osteoarthritis evolution (n=11). Both groups were similar regarding the demographic and clinical features. We reported bone loss and the reconstruction procedure to fill it according to the initially used tibial implant. The results were evaluated with the IKS score to a follow-up of 37 months (range, 24-67 months). There were more tibial segmental bone loss (10 versus 3) and more metal wedges (8/12 versus 2/11) in metal-backing UKA revision (P<0.05). Tibial stems were more often used in metal-backing UKA revision (12/12 versus 7/11) (P=0.04). The results of TKA at follow-up did not differ according to whether the revised tibial implant was all polyethylene (IKS=155 [range, 107-195]) or metal-back (IKS=155 [range, 127-172]). This study suggests that metal-backing UKA revision exposes the patient to more severe tibial bone loss requiring more substantial reconstruction. These results must be confirmed on a larger population, but surgeons should be alerted to this kind of revision surgery, which warrants having available a revision knee prothesis. Level III, case-control study.

The influence of third-body particles on wear rate in unicondylar knee arthroplasty: a wear simulator study with bone and cement debris

The reduced intraoperative visibility of minimally invasive implanted unicondylar knee arthroplasty makes it difficult to remove bone and cement debris, which have been reported on the surface of damaged and retrieved bearings. Therefore, the aim of this study was to analyze the influence of bone and cement particles on the wear rate of unicompartmental knee prostheses in vitro. Fixed bearing unicompartmental knee prostheses were tested using a knee-wear-simulator according to the ISO standard 14243-1:2002(E) for 5.0 million cycles. Afterwards bone debris (particle size 671 ± 262 μm) were added to the test fluid in a concentration of 5 g/l for 1.5 million cycles, followed by 1.5 million cycles blended with cement debris (particle size 644 ± 186 μm) in the same concentration. Wear rate, knee-kinematics and wear-pattern were analyzed. The wear rate reached 12.5 ± 1.0 mm³/million cycles in the running-in and decreased during the steady state phase to 4.4 ± 0.91 mm³/million cycles. Bone particles resulted in a wear rate of 3.0 ± 1.27 mm³/million cycles with no influence on the wear rate compared to the steady state phase. Cement particles, however, lead to a significantly higher wear rate (25.0 ± 16.93 mm³/million cycles) compared to the steady state phase. The careful removal of extruded cement debris during implantation may help in reducing wear rate. Bone debris are suggested to have less critical influence on the prostheses wear rate.