Tibial Polyethylene Research Articles

Isolated revision of the polyethylene component at revision total knee arthroplasty has excellent survivorship at ten years.

The aim of this study was to establish the results of isolated exchange of the tibial polyethylene insert in revision total knee arthroplasty (RTKA) in patients with well-fixed femoral or tibial components. We report on a series of RTKAs where only the polyethylene was replaced, and the patients were followed for a mean of 13.2 years (10.0 to 19.1). Our study group consisted of 64 non-infected, grossly stable TKA patients revised over an eight-year period (1998 to 2006). The mean age of the patients at time of revision was 72.2 years (48 to 88). There were 36 females (56%) and 28 males (44%) in the cohort. All patients had received the same cemented, cruciate-retaining patella resurfaced primary TKA. All subsequently underwent an isolated polyethylene insert exchange. The mean time from the primary TKA to RTKA was 9.1 years (2.2 to 16.1). At final follow-up, 13 patients had died, leaving 51 patients for study. Only seven of these patients had required re-operation. Knee Society scores (KSS) prior to RTKA were a mean of 78.4 (24 to 100). By six weeks post-revision, the mean total KSS was 93.5 (38 to 100) and at final follow-up, they had a mean of 91.6 (36 to 100). In appropriate circumstances, where the femoral and tibial components are satisfactorily aligned and well fixed, and where the soft tissues can be balanced, a polyethylene exchange alone can provide a durable solution for these RTKA patients. Cite this article: Bone Joint J 2019;101-B(7 Supple C):104-107.

Prospective randomized trial of standard versus highly crosslinked tibial polyethylene in primary posterior-stabilized total knee arthroplasty: clinical and radiological follow-up at 2 to 11 years.

There is insufficient evidence to recommend the use of alternative polyethylene bearings in modular, fixed-bearing total knee arthroplasty (TKA). The purpose of this study was to compare standard polyethylene (SP) and highly crosslinked polyethylene (XLP) tibial liners in posterior-stabilized TKA, with osteolysis as the primary outcome and clinical results and the rate of re-operation as the secondary outcomes. This is a single-surgeon, prospective randomized study involving one design of modular posterior-stabilized TKA. An analysis of 122 TKAs with an SP compression moulded liner and 123 with an XLP liner was performed, with a mean follow-up of six years (2 to 11). Patients were evaluated clinically using the Knee Society score, Lower Extremity Activity Score (LEAS), and the presence of an effusion, and standard radiographs were assessed for radiolucent lines and osteolytic lesions. Osteolysis was present in four TKAs (3.3%) in the SP group, and no knees in the XLP group (p = 0.06). There were no significant differences between the Knee Society total score, change in total score, knee function score, change in function score, LEAS, and change in LEAS in the two groups. There was a significant difference in the presence of an effusion (10/122 with SP liners, 1/123 with XLP liners; p = 0.02). There was no significant difference in the rate of re-operation between the two groups (p = 0.36). There were no complications related to the XLP liner. At this length of follow-up, there were no advantages and no complications related to the use of this XLP tibial liner. The presence of effusion and small osteolytic lesions was more frequent with SP than XLP liners, but of unknown clinical significance. Cite this article: Bone Joint J 2019;101-B(7 Supple C):33-39.

Influence of friction on knee internal rotation in patients with knee arthroplasties during activities of daily living

Aims and Objectives: In recent decades, knee arthroplasty (KA) succeeded to improve patients’ clinical scores and gait patterns [1]. However, to date, studies primary focused on biomechanical analysis of level walking with total knee arthroplasty (TKA) patients. The investigation of neuromuscular more challenging activities of daily living (ADL) like stair climbing and especially ramp negotiation was partly neglected [2]. Furthermore, non-sagittal plane parameters have mostly not been considered, whereby the evaluation of e.g. transverse plane kinematics and kinetics may reveal potential differences between various endoprosthetic designs. Additionally, frictional forces transmit appreciable shear between the femoral component and the tibial polyethylene insert, potentially contributing to axial knee rotational constraints and implant loosening [3]. The aim of this study was to investigate transverse plane kinematics and kinetics in connection with the force of friction (FOF) during ADL in patients after TKA and unicondylar knee arthroplasty (UKA) surgery. Materials and Methods: - Motion analysis was performed using a ten-camera 3D- motion capture system (100 Hz, Vicon). - Ground reaction forces were measured utilizing in a total five force plates (1000 Hz, Kistler) - Kinematics and inverse dynamics were calculated with AnyBody Modeling SystemTM (AnyBody Technology). - FOF was estimated of the two articulating artificial surfaces (#CHR: mu_LOWER# =0.12) compared with the cartilage on cartilage friction (#CHR: mu_LOWER# =0.01). The Coulomb model of friction was applied to calculate FOF (Ff=Fn* #CHR: mu_LOWER#). - Completed ADL: level and decline walking, stair descent. - Participants: TKA (n=11), UKA (n=13), controls (CG, n=13). - Statistics: Statistical non-Parametric Mapping (SnPM). Results: No statistically significant differences were detected between the TKA and UKA group, regardless of the locomotion task. Each motor task revealed impaired knee internal rotation angles in the TKA group compared with the CG (Fig. 1, a-c). Fig. 1 (d) clarifies the determining role of the coefficient of friction regarding FOF which showed the highest values during stair ascent and decline walking in all groups. Interestingly, the mentioned tasks exposed lower knee internal moment time series compared with level walking. Lower internal rotation moments might contribute in connection with high friction to the constraint knee internal rotation motion, particularly during ADL including greater normal force values, such as stair climbing and ramp negotiation. Conclusion: Apart from implant congruency in the TKA group, FOF could represent a mechanical resistance, which contributes to the impaired knee motion in the transverse plane. References Smith A, et al., J Orthop Res. 22:260-266, 2004. Komnik I, et al., Gait Posture. 41:370-377, 2015. Wolterbeek N, et al., Gait Posture. 36:394-398, 2012

Risk of Reinfection after Irrigation and Debridement of Acute Periprosthetic Joint Infection following TKA.

The purpose of this study was to determine the risk factors associated with reinfection in patients treated with irrigation and debridement (I&D) with liner exchange for an acute (less than 3 months) prosthetic joint infection following the index primary total knee arthroplasty (TKA). Medicare claims database was queried to identify patients with periprosthetic joint infection within 3 months of their index TKA who underwent I&D with tibial polyethylene liner exchange. Exclusion criteria included age < 65 years and < 1 year of claims prior to TKA. A total of 341 patients met our criteria and were analyzed by age, sex, diabetes, obesity, Charlson comorbidity score, and time between TKA and I&D with liner exchange. Average time to I&D with liner exchange following primary TKA was 38.5 ± 21.3 days and multivariate analysis showed a significantly higher risk of reinfection within 1 year in patients > 85 years old (p < 0.001) and diabetes (p < 0.02). The risk of reinfection was lowest for patients treated with I&D with liner exchange within 14 days after TKA (p = 0.028). The incidence of reinfection was 223% greater if I&D with liner exchange was performed 2 to 4 weeks after primary TKA (p < 0.03), and 277% higher if performed > 6 weeks after index procedure compared with those performed within 2 weeks. Patients older than 85 years, diabetics, or treated with I&D with liner exchange > 14 days following the primary TKA had a significantly higher risk of reinfection within 1 year. Patients should be cautioned on the risk of reinfection prior to proceeding with I&D with liner exchange > 2 weeks following the index procedure.

Screw Track Osteolysis in the Cementless Total Knee Replacement Design

BackgroundThere is a paucity of reports on osteolysis associated with tibial screw fixation in cementless total knee arthroplasty (TKA), and the pathophysiology is not clear. This study aimed to describe the pathology related to screw track osteolysis around the tibia in cementless TKA. MethodsThe study cohort comprised 100 revised cementless TKAs with tibial screw fixation. Screw track osteolysis and various screw angles were analyzed radiologically. Tissue samples from the joint capsule and the osteolytic cavity were investigated for metal/polyethylene wear. The type of tissue response was determined using immunohistochemistry. Retrieved tibial polyethylene inserts were analyzed for screw hole impression and mode of wear. Tissue metal content was measured by inductively coupled plasma optical emission spectrometry. Electrochemical reactions between the tibial tray and the cancellous screws were investigated. ResultsRadiological analysis showed screw track osteolysis predominantly at the medial aspect of the tibial component, and the severity of osteolysis positively correlated with smaller medial proximal tibial screw angles. Osteolysis was associated with high titanium concentrations but not with polyethylene particles. An open circuit potential between the screw and the tibial base plate was measured. Necrosis, osteolytic cyst formation and macrophages, T and B cells, and dendritic cells were present. ConclusionThe present study highlights the risk for screw track osteolysis in cementless TKA with screw fixation. Our data collectively suggest that titanium wear may contribute to screw track osteolysis in the cementless TKA design. The contribution of screw angles is difficult to prove.

Literature review of acquired patella baja

Patella baja is one of the complications after total knee arthroplasty (TKA). It refers to an abnormal location of patella occurred secondary to shortening of the patellar tendon or distal positioning of the patella relative to the femoral trochlea. Clinically, it can be classified into congenital, acquired, and a combination of the above two types. Acquired patella baja is the most common type and usually occur as a result of trauma or surgery. Acquired patella baja is also caused by elevation of the joint line after TKA, which refers to pseudo-patella baja. Presently, its etiology is still uncertain. Some studies report the following causes of patella baja, including extending of quadriceps femoris, contracture of patella tendon or patellar fat pad, and fibrosis of joint. The diagnosis is mostly based on the lateral roentgenogram. The following parameters, including Insall-Salvati ratio, Modified Insall-Salvati ratio, Blackburne-Peel ratio, Caton-Deschamps ratio and Plateau-Patella angle, are used to assist diagnosis for patella baja. With the progress of imageology, some literatures describe several methods based on magnetic resonance imaging (MRI). However, the diagnostic methods of patella baja are not entirely precise. Patella baja can lead to decreased range of motion (ROM), a decreased lever arm, impingement of the patella against the tibial polyethylene or tibial plate, which may result in anterior knee pain, rupture of the patellar or quadriceps tendons. The treatment of patella baja depends on determining the cause and distinguishing between patella baja and pseudo-patella baja. Patients with severe symptom or failed for conservative treatment should receive surgery. The corrective measures for patella baja include lengthening of the patellar tendon and proximalize osteotomy of tibial tuberosity. In addition, the therapies for pseudo-patella baja include reestablishing the joint line by use of distal femoral augment, replacement of the patellar implant or polyethylene insert.

Five cases of tibial post fracture in posterior stabilized total knee arthroplasty using Prolong highly cross-linked polyethylene

BackgroundFracture of a polyethylene tibial post after a posterior stabilized total knee arthroplasty (PS-TKA) is an uncommon but severe complication. We report five cases of non-traumatic fracture of a tibial polyethylene post that occurred with Prolong highly cross-linked polyethylene with the NexGen LPS-Flex total knee prosthesis. MethodsA Joint Reconstruction database for a high volume arthroplasty unit was used to identify all cases of revision of Prolong polyethylene used in PS-TKA. Five cases were identified as being revised because of a broken tibial post. ResultsAll five cases presented with a combination of sudden and increasing pain, instability and giving way, in previously well-functioning TKAs. There was no history of trauma or precipitating incident. Mean time from primary TKA to presentation and diagnosis of post fracture was 67.7 months (range 24–108). All five cases were successfully treated by revision, in the form of a liner exchange to a standard ultra-high molecular weight polyethylene (UHMWPE) bearing of the same thickness. The five cases occurred from a consecutive series of 955 total PS-TKAs with Prolong. This gives a conservative estimate of the frequency of this complication of 0.52%. This would give a risk of a tibial post fracture in approximately one in every 200 TKAs with this specific implant and bearing combination. ConclusionsTo our knowledge, this is the first report of a non-traumatic fracture to the tibial post with this bearing type. We would advocate against the routine use of Prolong highly crosslinked polyethylene in PS-TKA.

Isolated Polyethylene Exchange With Increased Constraint Is Comparable to Component Revision TKA for Instability in Properly Selected Patients

BackgroundSymptomatic instability following total knee arthroplasty (TKA) is a leading cause of early failure. Most reports recommend component revision as the preferred treatment because of poor outcomes and high failure rates with isolated tibial polyethylene insert exchange (ITPIE). However, these ideas have not been tested in modern implant systems that allow insert constraint to be increased. MethodsWe retrospectively reviewed 90 consecutive patients with minimum 2-year (mean 3.7 years) follow-up who underwent revision TKA for instability at a single institution. Mean age was 62.0 years (range, 41 to 83 years), and 73% of patients were women. Forty percent of patients were treated with ITPIE when standardized preoperative and intraoperative criteria were met; 60% underwent revision of one or both components when these criteria were not met. ResultsPatients experienced significant improvements in Knee Society (KS) knee (48.4 to 82.6; P < .001) and function (49.0 to 81.0; P < .001) scores. There were no significant differences in improvements in KS knee scores (38.1 vs 33.1; P = .18), KS function scores (36.0 vs 34.0; P = .63), or arc of motion (5° vs 6°; P = .88) between those treated with ITPIE and component revision. Failure rates were 19.4% in the ITPIE group vs 18.5% in the component revision group (odds ratio, 1.06; P = .91). Re-revision rates were significantly lower (6.3% vs 30.8%; odds ratio, 0.15; P = .004) when polyethylene insert constraint was increased. ConclusionIn selected patients, ITPIE is not inferior to component revision at addressing symptomatic instability following TKA. Degree of constraint should be increased whenever possible during revision surgery for instability.

Evaluation of the Tibiofemoral Contact Characteristics of a Customized Surface-Guided Knee Implant

A surface-guided total knee replacement (TKR) aims to achieve close to normal kinematics through specially shaped tibiofemoral articulating surfaces. The resulting geometry of the TKR components affects the tibiofemoral contact mechanics. Therefore, evaluation of the contact characteristics of the implant is critical, as the tibiofemoral contact stress influences the short-term and long-term performance and durability of the implants. In this study, the contact behavior at the tibiofemoral articulating interface for a customized surface-guided TKR was studied. The contact area and mean contact stress at specific flexion angles were measured mechanically by pressure sensitive films to validate the outcomes from finite element analysis (FEA) under similar load conditions. Two activities of daily living were studied; lunging and squatting. As expected, FEA predicted larger contact areas at various flexion angles due to the limited sensitivity range of the pressure sensitive films. During lunging and squatting, the contact area increased as the flexion angle reached 90°, and decreased as the knee was flexed to higher angles. The mean contact pressure was less than 10 MPa at 120 degrees of flexion under squatting load. The outcomes revealed that a high range of motion can be achieved, while the mean contact pressure remains below the material limits of the tibial polyethylene insert.

Why All Tibial Polyethylene Bearings are Not the Same?

Important differences exist in both the materials and geometric forms of tibial bearings across total knee implant systems on the market. The extent of crosslinking, sterilization methods, mechanical/thermal treatment methods used for management of free radicals, the amount of incorporated antioxidants, and the methods for incorporation of antioxidants, are some of the material variables, which may affect bearing clinical performance. Despite initial concerns about increased fatigue damage and failure with crosslinked ultra high molecular weight polyethylene developed to reduce the incidence of osteolysis, their utilization now constitutes close to 50% of tibial bearings in primary operations. This is based on long-term clinical data, which show equivalent or better performance in revisions due to aseptic loosening compared with conventional materials. Similarly, bearing conformity, modularity and mobility, are important geometric elements influencing polyethylene wear and failure. With regard to conformity, conventional wisdom has favored more conforming designs. However, growing body of evidence suggests potential for improved wear performance with less conforming designs enabled by modern polyethylene processing techniques. Long-term clinical data show excellent outcomes for all-polyethylene bearings, which may assume an enhanced role in total knee replacement in the future. In contrast, modern fixed-bearing designs seem to outperform mobile-bearing designs in the long run. Consequently, the use of the mobile bearings has declined over time, and currently they account for about 7% of primary knee replacements.

Medial Pivot in Total Knee Arthroplasty: Literature Review and Our First Experience.

Background:Traditional total knee implants designs, usually, are not able to reproduce the physiological kinematics of the knee, leaving almost 20% of the patients, those who underwent a total knee arthroplasty (TKA), not fully satisfied. Modern inserts are nowadays designed with a fully congruent medial compartment to reproduce the normal medial pivoting biomechanics of the knee. The aim of this article was to evaluate preliminary clinical improvement using the Medial Congruent (MC) insert as specific level of constraint.Materials and methods:A total of 10 consecutive patients have been enrolled in this study and treated using an MC tibial polyethylene insert. The Oxford Knee Score (OKS) and the Knee Society Score (KSS) have been assessed preoperatively and at 3-month, 6-month, and 1-year follow-up (FU) and used as validated measurements to evaluate early clinical improvements. Postoperative radiological examination was reviewed looking for radiolucent lines or loosening of the components.Results:Average improvement in OKS was from 19.5 to 41.2, whereas KSS improved with an average score from 64.7 preoperatively to 167.5 at the final FU showing good to excellent results in 95% of the treated knees. Evaluating the range of motion, the average maximum active movement was 124° and none of the patients needing for a revision surgery or manipulation under anesthesia. No complications were observed at the final FU as septic or aseptic loosening or vascular or neurologic injury.Discussion and conclusions:Medial Congruent insert showed good to excellent clinical results at 1-year FU. Range of motion and subjective outcomes were satisfying and comparable with results obtained in literature using traditional TKA design.

The role of isolated polyethylene exchange in total knee arthroplasty.

The use of modular total knee arthroplasty (TKA) implants allows surgeons to perform isolated tibial polyethylene insert exchange (IPE) while retaining well-fixed and stable components.The purported advantages of IPE include preservation of bone stock, shorter operating time, less blood loss, faster rehabilitation and lower cost. However, the indications for IPE are limited.IPE for wear and osteolysis has moderate success in the medium term but should be avoided in cases of accelerated wear. In selected cases, debridement and IPE for early infection can result in low morbidity with high success rates in the short term. IPE for arthrofibrosis has poor results.IPE should be undertaken with caution and an institutional algorithm should be followed.Cite this article: EFORT Open Rev 2017;2:66–71 DOI: 10.1302/2058-5241.2.160049

Damage estimator, a possible way to predict the failure of hip and knee endoprosthesis

PurposeThe purpose of this study was to realize finite element simulation in order to dynamically determine the area of the contact, the contact pressure and the strain energy density (identified as a damage function) for three different activities – normal walking, ascending stairs and descending stairs – that could be considered to define the level of the activity of the patient.Design/methodology/approachThe finite element model uses a modern contact mechanism that includes friction between the metallic femoral condyles or femoral head (considered rigid) and the tibial polyethylene insert or acetabular cup (considering a non-linear behaviour).FindingsFor all three activities, the finite element analyses were performed, and a damage score was computed. Finally, a cumulative damage score (that accounts for all three activities) was determined, and the areas where the fatigue wear is likely to occur were identified.Originality/valueA closer look at the distribution of the damage score reveals that the maximum damage is likely to occur not at the contact surface, but in the subsurface.

A Numerical Investigation into the Effects of Overweight and Obesity on Total Knee Arthroplasty

Overweight and obesity increase risks of knee osteoarthritis, which is a major cause of disability. Severe knee osteoarthritis can be treated by knee arthroplasty. Total knee arthroplasty has been used in overweight and obese patients; however, clinical reports showed that the outcome of this group of patients was not good as normal-weight patients. Two computer models were created in this paper to simulate the effect of excess loads on the distal femoral bone and contact pressures in total knee arthroplasty during a gait cycle. The numerical results showed increased stress in periprosthetic distal femoral bones and higher contact pressure on tibial polyethylene insert during the stance phase. Based on the computer simulation results and published research work, cementless total knee arthroplasty with thicker tibial polyethylene insert may be a better option for overweight patients.

An Approach to Developing Customized Total Knee Replacement Implants.

Total knee replacement (TKR) has been performed for patients with end-stage knee joint arthritis to relieve pain and gain functions. Most knee replacement patients can gain satisfactory knee functions; however, the range of motion of the implanted knee is variable. There are many designs of TKR implants; it has been suggested by some researchers that customized implants could offer a better option for patients. Currently, the 3-dimensional knee model of a patient can be created from magnetic resonance imaging (MRI) or computed tomography (CT) data using image processing techniques. The knee models can be used for patient-specific implant design, biomechanical analysis, and creating bone cutting guide blocks. Researchers have developed patient-specific musculoskeletal lower limb model with total knee replacement, and the models can be used to predict muscle forces, joint forces on knee condyles, and wear of tibial polyethylene insert. These available techniques make it feasible to create customized implants for individual patients. Methods and a workflow of creating a customized total knee replacement implant for improving TKR kinematics and functions are discussed and presented in this paper.

Femoral Component Survival in Hybrid Total Knee Arthroplasty.

Although the majority of North American surgeons perform total knee arthroplasty by cementing both the femoral and the tibial components, hybrid fixation with a press-fit femur and cemented tibia is an alternative form of total knee arthroplasty performed by some. Currently, there is a paucity of literature evaluating long-term outcomes after hybrid total knee arthroplasty. As such, the purpose of the current study was to describe the long-term results of total knee arthroplasty performed using the hybrid technique. The authors retrospectively reviewed a total of 77 hybrid total knee arthroplasties with at least 12 years of follow-up. Clinical and radiographic evaluations were performed to determine patient function and the incidence of femoral component failure after hybrid total knee arthroplasty. At the time of last follow-up, 76 of 77 (99%) of the femoral components remained in place without evidence of loosening. One femoral component failed due to aseptic loosening and was ultimately revised to a cemented femoral component without further complication. In addition, 1 tibial component and 2 patellar components failed due to aseptic loosening. Four tibial polyethylene liners were revised for polyethylene wear. In conclusion, press-fit fixation of the femoral component is a reliable and durable alternative to cemented fixation. [Orthopedics. 2016; 39(3):181-186.].

Total Knee Post-Cam Design Variations and Their Effects on Kinematics and Wear Patterns.

Post-cam designs for posterior-stabilized total knee arthroplasy (TKA) implants have evolved over the last 2 decades. These designs have evolved from symmetric post and cam to asymmetric designs that include anterior post interactions to affect a kinematic change in full extension. All design changes have consequences on the resulting femorotibial contact kinematics and, depending on the amount of constraint built into the design, these changes may have significant consequences on the wear patterns on the tibial polyethylene insert. The current authors review the kinematic effects of symmetric and asymmetric cam designs and use a retrieval database of TKA implants obtained at the time of necropsy to show how different design variables may affect polyethylene wear patterns after 10 or more years of implantation or from modeled wear in simulators. More modern designs seem to have moved the post posteriorly and sloped the anterior aspect to avoid impingement of the anterior post in terminal flexion on the inferior aspect of the patella button. [Orthopedics. 2016; 39(3):S45-S49.].

Cross-linked versus conventional polyethylene for total knee arthroplasty: a meta-analysis.

BackgroundHighly cross-linked polyethylene (HXLPE) has been reported as an effective material for decreasing polyethylene wear and osteolysis in total knee arthroplasty (TKA). Because no single study to date has been large enough to definitively determine the benefit of HXLPE in TKA, we conducted a meta-analysis to pool the results from randomized controlled trials (RCTs) and non-RCTs to make such a determination.MethodsPotential candidate articles were identified by searching the Cochrane Library, Medline (1966-2015.10), PubMed (1966-2015.10), Embase (1980-2015.10), ScienceDirect (1985-2015.10), and other databases. “Gray studies” were identified from the included articles’ reference lists. Pooled data were analyzed using RevMan 5.1.ResultsThree RCTs and three non-RCTs were included in the meta-analysis. There were no significant differences between the groups in the total number of reoperations (P = 0.11), reoperations for prosthesis loosening (P = 0.08), radiolucent line (P = 0.20), osteolysis (P = 0.38), prosthesis loosening (P = 0.10), and mechanical failures related to the tibial polyethylene (P = 1.00). Similarly, no significant differences between the two groups were found in postoperative total knee score (P = 0.18) or functional score (P = 0.23).ConclusionsThe meta-analysis showed that compared with conventional polyethylene, HXLPE did not improve the clinical and radiographic outcomes in mid-term follow-up after TKA. Additional high-quality multicenter prospective RCTs with good design, large study populations and long-term follow-up will be necessary to further clarify the effect of HXLPE in TKA.

Use of Technetium Bone Scan to Help Predict Whether Patella Resurfacing Will Be Successful in Treating Pain Following Primary TKR

Objectives:Anterior knee pain is not uncommon following primary TKR. The AOANJRR (2014) reports that 12.1% of revisions of primary TKR are for patellofemoral pain. Patella resurfacing does not always relieve this pain. The objective of this study is to investigate whether a technetium bone scan after TKR will predict success of a subsequent patella resurfacing.Methods:Observational Case Series. This is a retrospective review of patients of a single orthopaedic surgeon over a 22 year period. Patients who had subsequent isolated patella resurfacing (or patella resurfacing plus tibial insert exchange) of a primary TKR were identified and contacted by telephone. All had bone scans performed in their workup to patella resurfacing. Bone scan was considered positive if the radiologist reported greater uptake in the patella than elsewhere in the knee. Three patient outcome measures were used: Satisfaction (very satisfied, satisfied, dissatisfied, very dissatisfied); Pain relief (excellent, good, no improvement, worse); “Would you have the surgery again?” (yes, no). Correlation was made between results of bone scans and patient outcome measures.Results:35 patients were identified who underwent subsequent patella resurfacing of a primary TKR. 22 were contactable and eligible for the study. The average time from primary knee replacement to patella resurfacing was 6 years, 4 months. The average time from the patella resurfacing to interview was 3 years, 8 months. 17 of the patients did not have their patella resurfaced at the primary procedure. 5 had loose patella buttons. 3 had replacement of their tibial polyethylene insert at the same time as patella resurfacing. There were 15(68%) positive bone scans. Of these, 14(93%) were very satisfied or satisfied. There was a single case (7%) who was dissatisfied. 14(93%) had excellent or good pain relief, 1(7%) had no improvement. 14 patients said that they would have the surgery again, 1 would not. There were 7(32%) negative bone scans. Of these, 2(29%) were very satisfied or satisfied and 5(71%) were dissatisfied. 2(29%) had excellent or good pain relief, 5(71%) had no improvement. 4 patients said that they would have the surgery again, 3 would not.Conclusions:In patients with a painful primary TKR, technetium bone scan may be a useful additional tool to help predict which patients will benefit from subsequent patella resurfacing

Posterior Tibial Polyethylene Fracture in Cruciate-Retaining Total Knee Arthroplasty

Introduction One of the common prostheses for primary total knee arthroplasty (TKA) is a cruciate-retaining (CR) design. The tibial polyethylene inserts commonly used in TKA are made of ultra-high molecular weight polyethylene (UHMWPE). The CR TKA design retains the posterior cruciate ligament (PCL), which is believed to provide increased stability, promote femoral roll back, improve proprioception, and enhance stair-climbing ability. Delamination, adhesive wear, and abrasive wear of the polyethylene component are common mechanisms of failure, but fracture of the component at the posterior side in a CR TKA is rare. The cause of this type of failure is often multifactorial. This case report presents a case of posteromedial polyethylene fracture in a CR TKA.