Background. Obesity has been linked with increased rates of knee osteoarthritis. Limited information is available on the survival and functional outcome results of rTKR in the obese patients. This registry-based study aimed to identify whether BMI is an independent risk factor for poorer functional outcomes and /or implant survival in rTKA. Methods. New Zealand Joint Registry (NZJR) data of patients who underwent rTKA from 1st January 2010 to January 2023 was performed. Demographics, American Society of Anesthesiologists (ASA), BMI, Operative time, indications for revision and components revised of the patients undergoing rTKA was collected. Oxford knee score (OKS) at 6 months and rates of second revision (re- revision) were stratified based on standardised BMI categories. Results. Of the 2687 revisions, functional outcome scores were available for 1261 patients. Oxford knee scores following rTKA are significantly inferior in higher BMI patients (36.5 vs 31.5 p<0.001). This held true when adjusted for age (35.7 vs 30.9 p<0.001). Tibial component loosening was a more common indication for revision in patients with BMI >40 (31.1% vs 21% for BMI <25), whereas periprosthetic femoral fracture was significantly more commonly seen in patients with BMI <25. Re-revision rates displayed no significant differences between any pairs of BMI groups (2.18/100 component years) and adjusting for age and sex did not alter this (p= 0.462). Indications for re-revision were also not different between BMI categories. Over 50% of the rTKA patients were obese. Significantly more obese patients were ASA grade 3,4 and more were <75 years. Operative time was longer in the obese patients (p<0.001). Conclusions. Although overall re-revision rates are similar between all BMI categories, the functional outcomes favour those with lower BMI. Patients with higher BMI are younger, more comorbid and carry potentially higher perioperative risks. The registry data provides valuable information when providing counsel to patients undergoing rTKA and lends further support to optimising patients prior to pTKA

Introduction. In the lower extremity, lymphedema is characterized by fluid buildup and swelling which can lead to fibrosis of the skin and recurring soft-tissue infections. Risk factors include obesity, older age, lower extremity surgery, and radiotherapy. There is currently a paucity of data examining the impact of lymphedema in primary total knee arthroplasty (TKA). The purpose of this study was to review outcomes following primary TKA performed in patients with lymphedema compared to a matched cohort with primary osteoarthritis. Methods. Over a 19-year period (1998–2016), 144 patients underwent primary TKA with a preceding diagnosis of ipsilateral lymphedema (Table 1). There were 114 (79%) females, a mean age of 69 years, and mean BMI of 37.1 kg/m2. Mean follow-up was 7-years (range 2–17 years). A blinded analyst completed a 1:2 match of patients with lymphedema to a group of patients without lymphedema undergoing primary TKA for osteoarthritis during the same period. Matching criteria included sex, age, date of surgery, and BMI. Matched controls included 228 (79%) females along with a mean age and BMI of 69 and 36.4 kg/m2. The mean follow-up for the comparison cohort was 8 years (range 2–18 years). There were no significant differences between groups on the evaluated baseline parameters. Results: Patients with a history of lymphedema were at a significantly increased risk of revision TKA (HR 7.60, P<0.001), reoperation for any cause (HR 2.87, P<0.001), and postoperative infection (HR 6.19, P<0.001). Patients with lymphedema were also at increased risk for periprosthetic fracture (p=0.04) and tibial component loosening (p=0.01). Morbid obesity increased the risk of reoperation (HR 2.11, p=0.02) and trended toward increased risk of revision TKA (HR 2.29, p=0.059) and infection (HR 2.37, p=0.06). Discussion: Patients with lymphedema are at significantly increased risk of revision, reoperation, and infection following primary TKA. This data highlights the need for appropriate patient counseling in this population and optimization of lymphedema management before and after TKA. Results. Patients with a history of lymphedema were at a significantly increased risk of revision TKA (HR 7.60, P<0.001), reoperation for any cause (HR 2.87, P<0.001), and postoperative infection (HR 6.19, P<0.001). Patients with lymphedema were also at increased risk for periprosthetic fracture (p=0.04) and tibial component loosening (p=0.01). Morbid obesity increased the risk of reoperation (HR 2.11, p=0.02) and trended toward increased risk of revision TKA (HR 2.29, p=0.059) and infection (HR 2.37, p=0.06). Discussion. Patients with lymphedema are at significantly increased risk of revision, reoperation, and infection following primary TKA. This data highlights the need for appropriate patient counseling in this population and optimization of lymphedema management before and after TKA. For any figures or tables, please contact authors directly

Answering the question of what the patient can teach us about the future of joint replacement starts with a look to the past. The modern era of total joint replacement began in the late 1950's with the pioneering work of John Charnley that established the fundamental structure of a total joint replacement with a metal component bearing against polyethylene and provided many disabled patients with a substantial improvement in function. As the application of joint replacement expanded to a broader patient population it became apparent that a better understanding of the mechanics of patient function was needed to provide more rigorous design criteria and objective assessment of design changes. This presentation will examine how improvements in total knee replacement has been aided by objective measures of ambulatory function and the potential for future improvements in joint replacement that can be based on information from testing patients. Specifically, from a historical viewpoint one of the major problems limiting the use of total knee replacement in the 1970's was tibial component loosening. The problem of tibial component loosening could be related to the load imbalance between the medial and lateral surface of the tibia. The load asymmetry at the knee resulting from the adduction moment during gait provided a strong rationale for maintaining proper limb alignment following total knee arthroplasty. The analysis clearly showed that knees with a varus alignment of the mechanical axis were more likely to have a substantial load imbalance creating the type of stresses that would eventually lead to tibial component loosening. When the information from gait studies was combined with both clinical and biomechanical studies, tibial component designs were modified using metal backing of the polyethylene articulating surface and instrumentation was modified to allow for proper alignment of the mechanical axis and avoid residual varus deformity following total knee replacement. Similarly, knee kinematics and moments have been used to differentiate the functional characteristics of different types of designs during stair climbing. Patients with cruciate-sacrificing knee replacements had a tendency to reduce the moment sustained by the quadriceps by leaning forward during the portion of the support phase of ascending stairs when the quadriceps moment would reach a peak value, while patients with a posterior cruciate retaining design were able to sustain normal quadriceps function. The functional differences between the PCL-retaining and sacrificing designs were associated with the normal posterior movement of the femur on the tibia (rollback), with flexion. This finding indicated that TKR design must permit rollback in the early phases of knee flexion to sustain normal stair climbing. This presentation will conclude with a review of the functional performance of patients with an anterior cruciate deficient knee as a basis for addressing the future needs of a knee replacement to permit natural knee movement. Specifically the role of the anterior cruciate ligament will be discussed in the context of the interaction of the curvature of the articulating surfaces in maintaining a functional envelope of movement that is consistent with retaining both cruciate ligaments

Background. There are case series of debonding of the ATTUNE® tibial component introduced in 2013. We studied the early clinical results of this total knee arthroplasty (TKA) and compared it to other designs at one hospital. Methods. This is a retrospective study of 223 consecutive, non-randomized, cemented fixed-bearing posterior-stabilized ATTUNE® TKAs at one hospital by 5 surgeons from 2013 through 2017. We excluded 4 knees with early infection and 53 with follow-up less than 6 months. Of 166 TKAs reviewed, the mean patient age was 63.8 years, mean BMI 32, and mean follow-up 25 months. We compared this to a “control” cohort of 511 TKAs of other manufacturers performed at the same hospital. The endpoints were revision performed and revision pending. Results. Nineteen (11.5%) ATTUNE® knees have been revised and revision is pending in 12 (7%) knees, at a mean of 30 months. Tibial component loosening was seen in 17 (90%) revised knees. There was no difference between knees revised or revision pending and unrevised knees in patient demographics, cement used (p=0.84), or attending surgeon (p=0.55). In the “control” cohort, there were 13 (2.6%) knees revised (p<0.0001) and revision pending in 8 (1.5%) (p<0.0001), and only 2 had tibial loosening as the reason for revision. Conclusion. This cemented TKA design had an unexpected high early rate of revision. Debonding of the tibial component was the most common reason for failure. Additional longer-term follow-up studies of this component and techniques for implantation are warranted

Abstract. Introduction. Medial fix bearing unicompartmental knee replacement (UKR) designs are consider safe and effective implants with many registries data and big cohort series showing excellent survivorship and clinical outcome comparable to that reported for the most expensive and surgically challenging medial UKR mobile bearing designs. However, whether all polyethylene tibial components (all-poly) provided comparable results to metal-backed modular components during medial fix bearing UKR remains unclear. There have been previous suggestions that all-poly tibia UKR implants might show unacceptable higher rates of early failure due to tibial component early loosening especially in high body max index (BMI) patients. This study aims to find out the short and long-term survival rate of all-poly tibia UKR and its relationship with implant thickness and patient demographics including sex, age, ASA and BMI. Material and Methods. we present the results of a series of 388 medial fixed bearing all-polly tibia UKR done in our institution by a single surgeon between 2007–2019. Results. We found out excellent implant survival with this all-poly tibia UKR design with 5 years survival rate: 96.42%, 7 years survival rate: 95.33%, and 10 years survival rate: 91.87%. Only 1.28% had early revision within 2 years. Conclusion. Fixed bearing medial all-poly tibia UKR shows excellent survivor rate at 2, 5, 7 and 10 years follow up and the survival rate is not related with sex, age, BMI, ASA grade or implant thickness. Contrary to the popular belief, we found out that only 1.71% of all implants was revised due to implant loosening

Introduction. Beneath infection, instability and malalignment, aseptic tibial component loosening remains a major cause of failure in total knee arthroplasty (TKA) [1]. This emphasizes the need for stable primary and long-term secondary fixation of tibial baseplates. To evaluate the primary stability of cemented tibial baseplates, different pre-clinical test methods have been undergone: finite element analysis [2], static push-out [3,4] or dynamic compression-shear loading [5] until interface failure. However, these test conditions do not reflect the long-term endurance under in vivo loading modes, where the tibial baseplate is predominantly subjected to compression and shear forces in a cyclic profile [5,6]. To distinguish between design parameters the aim of our study was to develop suitable pre-clinical test methods to evaluate the endurance of the implant-cement-bone interface fixation for tibial baseplates under severe anterior (method I) and internal-external torsional (method II) shear test conditions. Materials & Methods. To create a clinically relevant cement penetration pattern a 4. th. generation composite bone model was customised with a cancellous core (12.5 PCF cellular rigid PU foam) to enable for high cycle endurance testing. VEGA System. ®. PS & Columbus. ®. CRA/PSA ZrN-multilayer coated tibial baseplates (2×12) were implanted in the customised bone model using Palacos. ®. R HV bone cement (Figure 1). An anterior compression-shear test (method II) was conducted at 2500 N for 10 million cycles and continued at 3000 N & 3500 N for each 1 million cycles (total: 12 million cycles) simulating post-cam engagement at 45° flexion. An internal-external torsional shear test (method II) was executed in an exaggeration of clinically relevant rotations [7,8] with ±17.2° for 1 million cycles at 3000 N tibio-femoral load in extension. After endurance testing either under anterior shear or internal-external torsion each tibial baseplate was mounted into a testing frame and maximum push-out strength was determined [3]. Results. The cement penetration depth and characteristic pattern were comparable to 3D-CT scans of 24 cemented human tibiae from a previous study [5]. From the final push-out testing, no statistical significant differences could be found for anterior compression-shear testing (method I) with VEGA System. ®. PS (2674 ± 754 N) and Columbus. ®. CRA/PSA (2177 ± 429 N) (p = 0.191), as well as internal-external torsional shear testing (method II) between VEGA System. ®. PS (2561 ± 519 N) and Columbus. ®. CRA/PSA (2825 ± 515 N) tibial baseplates (p = 0.399). Discussion. The newly developed methods allow the evaluation of the endurance behaviour of the implant-cement-bone interface fixation for tibial baseplates in comparison to clinically long-term established knee systems, based on a combination of a suitable artificial bone model and severe anterior and internal-external torsional high cycle shear test conditions

Background. To evaluate the causes and modes of complications after unicompartmental knee arthroplasty (UKA), and to identify its prevention and treatment method by analyzing the complications after UKA. Materials and Methods. A total of 1,576 UKAs were performed between January 2002 and December 2014 at a single-institution. Postoperative complications occurred in 89 knees (83 patients, 5.6%), and 86 of them were found in females and 3 in males. Their mean age was 61 years (range, 46 to 81 years) at the time of initial UKA and 66 years (range, 46 to 82 years) at the time of revision surgery. We analyzed the complications after UKA retrospectively andinvestigated the proper methods of treatment (Table 1). Results. A total of 89 complications (5.6%) occurred afterUKA. Regarding the type of complications after UKA, there were bearing dislocation (n=42), component loosening (n=23), 11 cases of femoral component loosening, 8 cases of tibial component loosening, and 4 cases of both femoral and tibial component loosening, periprosthetic fracture (n=6), polyethylene wear/ destruction (n=3), progression of arthritis to the other compartment (n=3), medial collateral ligament (MCL) injury (n=2), impingement (n=2), infection (n=5), ankylosis (n=1), and unexplained pain (n=2) (Table 2). The most common complication after UKA was mobile bearing dislocation in mobile-bearing type and loosening of prosthesis in fixed-bearing type, but polyethylene wear and progression of arthritis were relatively rare. The mean interval from UKA to the occurrence of complications was 4 years and 6 months (range, 0 [during operation] to 12 years). Of those complications following UKA, 58 knees were treated with conversion TKA, 1 with revision UKA, and 21 with simple bearing change. Complications in the remaining knees were treated with arthroscopic management (n=2), open reduction and internal fixation (n=3), closed reduction and internal fixation (n=1), manipulation (n=1), and MCL repair (n=2) (Table 3). Discussion. In this single-center study, we reviewed the causes and types of complications (n=89) that occurred following UKA (n=1,576) and investigated optimal treatment methods. The incidence and type of complications were also compared among patients classified according to gender, medial/lateral UKA, and implant design and type. The strengths of this study include that all the patients were enrolled from the same institution and the sample size (UKA cases and complication cases) was relatively large compared to that in previous publications. The most common complication following UKA was bearing dislocation in the mobile-bearing knees and component loosening in the fixed-bearing knees. The incidence of polyethylene wear and progression of arthritis to the other compartment was relatively low. The results of our study are in some discrepancy with those of studies involving Western patients. This can be attributed to the differences in patient characteristics such as lifestyle and in the type and design of implant used. Conclusion. Thorough understanding of UKA, proper patient selection, appropriate implant choice are essential to reduce complications following UKA and obtain satisfactory outcomes. We suggest that complications following UKA should be treated differently according to the type and cause of complication and conversion TKA can be the most effective treatment when revision operation is determined necessary

Introduction. The precise indications for tibial component metal backing and modularity remain controversial in routine primary total knee arthroplasty. This is particularly true in elderly patients where the perceived benefits of metal backing such as load redistribution and the reduction of polyethylene strain may be clinically less relevant. The cost implications for choosing a metal-backed design over an all-polyethylene design may exceed USD500 per primary knee arthroplasty case. Methods. A prospective randomised clinical trial was carried out at the QEII Health Sciences Centre, Halifax, Nova Scotia, to compare modular metal-backed versus an all-polyethylene tibial component. Outcome measures included clinical range of motion, radiographs, survivorship, Knee Society Clinical Rating System, WOMAC and SF-12. Results. 116 patients requesting primary knee arthroplasty were recruited and randomised between the Smith & Nephew Genesis I non-modular (57) and modular (59) tibial designs between September 1995 and August 1997. At 10 years clinical follow-up, 4 implant revisions or intention-to-revise decisions were recorded in the metal-tray/modular group of which 2 were for aseptic tibial component loosening. 2 implant revisions in the all-polyethylene non-modular group were recorded, neither of which were for tibial component loosening. At 5, 7 and 10 year review; the KSCRS, WOMAC and SF12 scores were similar in both groups. As most patients randomised were over seventy years of age, this impacted significantly on the numbers available for longer term review and data was analysed by comparing pre- and post-operative scores for individual patients. Conclusion. There was no difference in performance between the all-polyethylene tibial component and the metal-backed tibial component. The case for using the all-polyethylene tibia in elderly patients is justified on both clinical efficacy and cost-containment grounds

Background. Use of a robotic tool to perform surgery introduces a risk of unexpected soft tissue damage due to the uncommon tactile feedback for the surgeon. Early experience with robotics in total hip and knee replacement surgery reported having to abort the procedure in 18–34 percent of cases due to inability to complete preoperative planning, hardware and soft tissue issues, registration issues, as well as concerns over actual and potential soft tissue damage. These can result in significant morbidity to the patient, negating all the desired advantages of precision and reproducibility with robotic assisted surgery. The risk of soft tissue damage can be mitigated by haptic software prohibiting the cutting tip from striking vital soft tissues and by the surgeon making sure there is a clear workspace path for the cutting tool. This robotic total knee system with a semi-active haptic guided technique was approved by the FDA on 8/5/2015 and commercialized in August of 2016. Two year clinical results have not been reported to date. Objective. To review an initial and consecutive series of robotic total knee arthroplasties for safety in regard to avoidance of known or delayed soft tissue injuries and the necessity to abort the using the robot to complete the procedure. Report the clinical outcomes with robotic total knee replacement at or beyond two years to demonstrate no delayed effect on expected outcome. Methods. The initial consecutive series of 65 Triathlon. TM. total knee replacements using a semi-active haptic guided system that were performed after commercialization that would be eligible for two year follow-up were reviewed. Pre-operative planning utilizing CT determined the implant placement and boundaries and thus the limit of excursion from any part of the end effector saw tip. Self-retaining retractors were also utilized. Operative reports, 2, 6, and 12 week, and yearly follow-up visit reports were reviewed for any evidence of inadvertent injury to the medial collateral ligament, patellar tendon, or a neurovascular structure from the cutting tool. Operative notes were also reviewed to determine if the robotic procedure was partially or completely aborted due to any issue. Knee Society Knee Scores (KS-KS) and Functional Scores (KS-FS) were recorded from pre-operative and yearly. Any complications were recorded. Results. 40 cases had two year follow-up. The average follow-up for this series was 1.51 years. No cases were unable to be completed robotically. No case had evidence for acute or delayed injury to the medial collateral ligament, patellar tendon, or neurovascular structure. The only complication was a revision total knee for tibial component loosening after a fall induced periprosthetic tibial fracture. Average pre-operative KS-KS and KS-FS improved from 46.9 and 52.1 to 99.2 and 88.6 at one year follow-up, 100.5 and 86.9 at two year follow-up. Conclusions. A semi-active haptic guided robotic system is a safe and reliable method to perform total knee replacement surgery. This series of initial robotic arm assisted surgery had no intraoperative or delayed soft tissue injuries. Preliminary short-term outcomes at up to two years show excellent outcomes

Introduction. Tibial component loosening is a frequent cause of failure in primary total knee arthroplasty (TKA). Management options include isolated tibial component revision or full component revision. A full component revision is frequently selected by surgeons who are unfamiliar with the existing implant or have a “let's just start over attitude.” This option adds morbidity versus isolated tibial exchange. While isolated tibial exchange has lower morbidity, it is technically more challenging with regard to exposure and maintaining prosthetic stability. This study was designed to compare these two reconstructive options. Methods. Patients revised for isolated aseptic tibial loosening were identified from 2012–2017. Patients with revision implants, or those revised for infection, instability, osteolysis, or femoral component loosening were excluded. 161 patients met these criteria, 85 patients had an isolated tibial revision and 76 had revision of both components despite having only a loose tibial component. Patient demographics as well as clinical and radiographic outcomes were recorded for each cohort. Results. Patient demographical information, including age, gender, and BMI were statistically similar between the two cohorts. Median follow-up was 3.5 years. Supplemental metaphyseal fixation was used in 22 patients in the isolated tibial cohort and 19 of the full revision cohort. There was a higher incidence of radiographic loosening in the full component revision cohort (10.5% vs. 6.0%; p=0.28). There were five failures requiring revision in the isolated tibial cohort, two for sepsis, one for repeat isolated tibial loosening, one for femoral aseptic loosening, and one for an extensor mechanism disruption. There were eight failures in the full component cohort, three for patellar avascular necrosis, two for sepsis, one for repeat tibial loosening, one for arthrofibrosis, and one for a postoperative wound dehiscence. Conclusion. Isolated tibial revision for aseptic tibial loosening has similar clinical and radiographic results when compared to full component revision. Although no intraoperative complications were identified when revising the femur, there is the potential for complications unique to femoral revision. Femoral component revision for isolated tibial loosening is unnecessary and should be avoided provided adequate ligamentous stability can be obtained. Keywords: Aseptic loosening, Tibial loosening, revision total knee replacement, total knee replacement. For figures, tables, or references, please contact authors directly

Loosening is generally the most common reason for revision TKA. In the AOA NJR, the rate of revision varies depending on fixation. Cemented fixation has a lower rate of revision than cementless fixation; 6.7% vs. 8.2% at 14 years. Loosening does occur more frequently in younger patients and in males. Tibial component loosening is the most common. There is an opportunity for improvement. More durable fixation can be achieved through improved cement technique, rather than going cementless. De-bonding of the tibial baseplate from the cement is the mechanism of failure in up to 2.9% of total knee arthroplasties. Among seven surgeons at one center, there was a 6.4 fold range (0.7%-4.5%) in the occurrence of such loosening with the same prosthesis. This surgeon-related variability in tibial component de-bonding indicates that surgical technique influences loosening. In a laboratory study, earlier application of cement to metal increases bond strength (p<0.01) while later application reduces bond strength (p<0.05). Fat contamination of the tibial tray-cement interface reduces bond strength, but application of cement to the underside of the tibial tray prior to insertion substantially mitigates this (p<0.05)

Introduction. Cementless Total Knee Replacement (TKR) was introduced to improve the longevity of implant; but has yet to be widely adopted because of reports of higher earlier failures in some series. The cementless TKR design has evolved recently and we have been using cementless component – both femoral and tibial on our patients. The long follow-up for fully TKR has been scarce in the literature. The purpose of this study isto investigate the minimum of ten years clinical and radiographic result of cementless titanium component and cementless tantalum component in primary TKR. Material & method. From 2008 to 2010 317 TKR underwent primary total knee with cementless femoral component titanium based (Zimmer Nexgen) and cementless tantalum component monoblock tibial component, The surgery was performed mainly on younger patients - average age was 48 yrs old ranging from 26 yrs old to 62 yrs old. All surgeries were performed by single surgeon. All patients were followed clinically and radiographically for a minimum of 8 yrs. Mean 7.8 years and range from 7 to 9 years. The underlying diagnosis for majority of the cases were degenerative arthritis in 97 of the cases and rheumatoid arthritis on the 3%. Result. We have revised 6 cases − 3 cases were for sepsis. They were revised in 2 stages. And we also revised 5 cases for loosening of femoral component. The tibial component revision for aseptic loosening or osteolysis for an end point for survivorship was a 100% for the tibia monoblock design. There was no radiographic evidence of tibial component loosening or subsidence, or migration at the time of the latest follow-up for tibia monoblock. On the femoral part we documented 16 cases other than those 4 revision for osteolysis, where limited osteolysis happened in some area of the tibial component but it did not affect stability and those has been followed up for a longer term. There was interesting phenomena in some of those cases where bone growth happened around the anterior cortex where it sealed the component entirely. Knee society scores improved from 51 pre-operatively to 94 pre-operatively on the last clinical visit. We had 32 cases where the patientswere able to regain their full mobility flexion of over 150 degrees. Conclusion. Our data clearly shows that the cementless TKR has excellent result as compared to the cemented with a good survival ship at 10 years. The tantalum tibial component shows an excellent survivorship. The femoral component also present reasonably good result but we still faced a few cases of loosening. The functional outcome for the implant with the surgery was satisfactory. With this result we strongly recommend using the cementless implant in young patients. We believe that cementless tibial is totally safe at this point as well as the femoral cementless prosthesis. However, we expect some improvement with the outcome with the femoral component when using the tantalum

Introduction. The revision rate of unicompartmental knee replacement (UKR) in national joint registries is much higher than that of total knee replacements and that of UKR in cohort studies from multiple high-volume centres. The reasons for this are unclear but may be due to incorrect patient selection, inadequate surgical technique, and inappropriate indications for revision. Meniscal bearing UKR has well defined evidence based indications based on preoperative radiographs, the surgical technique can be assessed from post-operative radiographs and the reason for revision from pre-revision radiographs. However, for an accurate assessment aligned radiographs are required. The aim of the study was to determine why the revision rate of UKR in registries is so high by undertaking a radiographic review of revised UKR identified by the United Kingdom's (UK) National Joint Registry (NJR). Methods. A novel cross-sectional study was designed. Revised medial meniscal bearing UKR with primary operation registered with the NJR between 2006 and 2010 were identified. Participating centres from all over the country provided blinded pre-operative, post-operative, and pre-revision radiographs. Two observers reviewed the radiographs. Results. Radiographs were provided for 107 revised UKR from multiple centres. The recommended indications were not satisfied in 30%. The most common reason was the absence of bone-on-bone arthritis, and in 16 (19%) the medial joint space was normal or nearly normal. Post-operative films were mal-aligned in 50%. Significant surgical errors were seen in 50%, with most errors attributable to tibial component placement and orientation. No definite reason for revision was identified in 67%. Reasons for revision included disease progression (10%), tibial component loosening (7%), dislocation of the bearing (7%), infection (6%) femoral component loosening (3%), and peri-prosthetic fracture (2% - one femur, one tibia). Discussion and Conclusion. This study found that improper patient selection, inadequate surgical technique, inappropriate revisions and poorly taken radiographs all contributed to the high revision rate. There is a misconception that UKR should be used for early OA. Bone-on-bone arthritis is a requirement and was definitely not present in about 20%. There were many surgical errors, particularly related to the tibial cut: The new instrumentation should reduce this. There was a high prevalence of mal-aligned radiographs. Revisions should be avoided unless there is a definite problem, as the outcome of revision is usually poor in this situation. 80% of UKR revisions could potentially be avoided if surgeons adhered to the recommended indications for primary and revision surgery, and used the recommended surgical techniques. This study therefore suggests that if UKR was used appropriately the revision rate would be substantially lower and probably similar to that of TKR

Loosening is generally the most common reason for revision TKA. In the AOA NJR, the rate of revision varies depending on fixation. Cemented fixation has a lower rate of revision than cementless fixation; 6.7% vs. 8.2% at 14 years. Loosening does occur more frequently in younger patients and in males. Tibial component loosening is the most common. There is an opportunity for improvement. More durable fixation can be achieved through improved cement technique. De-bonding of the tibial baseplate from the cement is the mechanism of failure in up to 2.9% of total knee prostheses. Among seven surgeons at one center, there was a 6.4-fold range (0.7%-4.5%) in the occurrence of such loosening with the same prosthesis. This surgeon-related variability in tibial component de-bonding suggests that surgical technique influences loosening rates. In a laboratory study, earlier application of cement to metal increases bond strength (p<0.01) while later application reduces bond strength (p<0.05). Fat contamination of the tibial tray-cement interface reduces bond strength, but application of cement to the underside of the tibial tray prior to insertion substantially mitigates this (p<0.05)

Background. There are limited data on the complication rates and risk of periprosthetic joint infection (PJI) in patients who have an acute wound dehiscence after total knee arthroplasty (TKA). Methods. From 2002 to 2018, 16,134 primary TKAs were performed at a single institution. Twenty-six patients (0.1%) had a traumatic wound dehiscence within the first 30 days. Mean age was 68, 38% were female, and mean BMI was 33 kg/m2. Median time to dehiscence was 13 days. The dehiscence resulted from a fall in 22 cases, including 4 in-hospital falls (3 with femoral nerve blocks), and sudden flexion after staple removal in 4 cases. The arthrotomy was disrupted in 58%, including a complete extensor mechanism disruption in 4 knees. A surgical debridement was performed within 48 hours in 19 of 26 knees. Two-thirds were discharged on antibiotic therapy. Results. Only two knees were complicated by PJI (cumulative incidence of 11% vs. 1% in all other primary TKAs, HR 6.5, p <0.01). One patient who developed a PJI was initially treated with a bedside closure in the ER rather than surgical debridement. The second patient had a complete extensor mechanism disruption at the time of dehiscence and was treated with surgical debridement, but did not receive a subsequent course of antibiotics. There were no PJIs in any of the cases that were treated with surgical debridement and a course of antibiotics. Three knees required reoperation (cumulative incidence of reoperation was 16% at 2 years, compared to 6% in all other primary TKAs, p=0.32) including 1 two-stage exchange for PJI, 1 irrigation and debridement with component retention for PJI, and 1 revision for tibial component aseptic loosening. Conclusion. Despite having a traumatic wound dehiscence, with nearly 60% resulting in arthrotomies that exposed implants, the risk of PJI was low but significantly higher than not having a traumatic arthrotomy. We recommend urgent surgical irrigation and debridement, inspection of arthrotomy integrity, and antibiotic treatment to decrease the risk of PJI. Summary. An acute, traumatic wound dehiscence with in the first 30 days after primary TKA results in a 11% risk of infection at 2 years

Aims

The mean age of patients undergoing total knee arthroplasty (TKA) has reduced with time. Younger patients have increased expectations following TKA. Aseptic loosening of the tibial component is the most common cause of failure of TKA in the UK. Interest in cementless TKA has re-emerged due to its encouraging results in the younger patient population. We review a large series of tantalum trabecular metal cementless implants in patients who are at the highest risk of revision surgery.

Tibial component loosening is an important failure mode in unicompartmental knee arthroplasty (UKA) which may be due to the 6–8 mm of bone resection required or the limited surface area. To address component loosening and fixation, a new Early Intervention (EI) design is proposed which reverses the traditional material scheme between femoral and tibial components. That is, the EI design consists of a plastic inlay component for the distal femur and a thin metal plate for the proximal tibia. With this reversed materials scheme, the EI design requires minimal tibial bone resection compared to traditional UKA to preserve the dense and stiff bone in the proximal tibia. This study investigated, by means of finite element (FE) simulations, the potential advantages of a thin metal tibial component compared with traditional UKA tibial components, such as an all-plastic inlay or a metal-backed onlay. We hypothesized that an EI component would produce comparable stress, strain, and strain energy density characteristics to an intact knee and more favorable values than UKA components. Indeed, the finite element results showed that an EI design reduced stresses, strains and strain energy density in the underlying support bone compared to an all-plastic UKA component. Analyzed parameters were similar for an EI and a metal-backed onlay, but the EI component had the advantage of minimal resection of the stiffest bone

Aims

The primary objective of this registry-based study was to compare patient-reported outcomes of cementless and cemented medial unicompartmental knee arthroplasty (UKA) during the first postoperative year. The secondary objective was to assess one- and three-year implant survival of both fixation techniques.

There is a report that higher failure rate in uncemented total knee replacement components due to loosening. However, uncemented fixation has been an attractive concept because of bone preservation and revision surgery, potential improved load transfer, and decreased surgical time. “Regenerex” is a porous titanium layer with excellent initial fixation, and the promise of providing favourable biological fixation. This is used with the Biomet Vanguard total knee replacement. 14 patients had undergone total knee replacement surgery comprising 11 men and three women with an average age of 63.07 years, and a body mass index of 30.33. Three of these patients required revision, because of tibial component loosening within 12 months of surgery. There were two men and one woman with an average age of 63.33 and BMI of 34.55. Clinically, patients developed pain and a gradual deformity as a result of a symmetrical collapse of the proximal tibial bony support surface. Histopathology on the removed specimens shows the development of fibre cartilaginous metaplasia with evidence of necrotic bone. This was similar in all patients. There was no foreign body giant cell reaction, and no evidence of infection. The appearance was suggested of osteonecrosis, occurring gradually. The incidence of frequency of this complication with this component in our experience is of concern, and the aim of this presentation is to determine whether this is a more widespread phenomenon

Introduction. High BMI has been classically regarded as a contraindication for unicompartmental knee arthroplasty (UKA) as it can potentially lead to poor clinical outcomes and a higher risk of failure. In recent years, UKA has increased in popularity and, as a result, patient selection criteria are beginning to broaden. However, UKA performed manually continues to be technically challenging and surgical technique errors may result in suboptimal implant positioning. UKA performed with robotic assistance has been shown to improve component positioning, overall limb alignment, and ligament balancing, resulting in overall improved clinical outcomes. The purpose of this study is to examine the effect of high BMI in patients receiving UKA with robotic assistance. Methods. 1007 patients (1135 knees) were identified in an initial and consecutive multi-surgeon multi-center series receiving robotically assisted medial UKA, with a fixed bearing metal backed onlay tibial component. As part of an IRB approved study, every patient in the series was contacted at a minimum two year (±2 months) follow up and asked a series of questions to determine implant survivorship and satisfaction. 160 patients were lost to follow up, 35 patients declined to participate, and 15 patients were deceased. 797 patients (909 knees) at a minimum two year follow up enrolled in the study for an enrollment rate of 80%. 45% of the patients were female. The average age at time of surgery was 69.0 ± 9.5 (range: 39–93). BMI data was available for 887 knees; the average BMI at time of surgery was 29.4 ± 4.9. Patients were stratified in to five categories based on their BMI: normal (< 25; 16%), overweight (25–30; 46%), obese class I (30–35; 25%), obese class II (35–40; 11%) and obese class III (>40; 2%). Results. Across all BMI groups, nine knees were reported as revised at two years post-operative yielding a two year revision rate of 0.99%, 4 in the overweight group, 2 in the obese class I group and 3 in the obese class II group. There was no significant difference in the rate of revision between the BMI groups (c. 2. (4, N = 887) = 6.04, p = 0.20). Of the 3 revisions for tibial component loosening, one occurred in the overweight group, one in the obese group and one in the morbidly obese group. The overall patient satisfaction rate for the entire population was 92% with the following distribution: normal: 92%, overweight: 93%, obese class I: 92%, obese class II: 87% and obese class III: 83%. While the most severely obese patients tended to be less satisfied, this was not statistically significant between the groups (c. 2. (4, N = 887) = 5.12, p = 0.27). Conclusion. These results suggest that BMI does not effect the survivorship or the satisfaction of patients undergoing robotically assisted UKA. Advancement in UKA implant designs and improvements in surgical technique may help to broaden indications and patient selection for UKA. This study will continue to track patients mid to long term to determine the longer term effect of robotically assisted UKA on high BMI patients