Tibial Liner Research Articles

Robotic-assisted differential total knee arthroplasty with patient-specific implants: surgical techniques and preliminary results

ObjectiveIn total knee arthroplasty (TKA), achieving soft-tissue balance while retaining acceptable lower limb alignment is sometimes difficult and may lead to patient dissatisfaction. Theoretically, patient-specific implants can bring great benefits, while the lack of precise surgical tools may hinder the improvement of outcomes. The objective of this study was to illustrate surgical techniques and evaluate kinematics and early clinical outcomes of robotic-assisted TKA using patient-specific implants.MethodsBased on preoperative CT scan, femoral and tibial components were 3D printed. Medial and lateral tibial liners were separate with different thicknesses, posterior slopes and conformity. TiRobot Recon Robot was used for surgery, and was armed with smart tools that quantify gap, force and femoral-tibial track. We collected data on demographics, intraoperative gap balance and femoral-tibial motion. In the follow-up, we evaluated the range of motion, Visual Analogue Scale (VAS), forgotten joint score (FJS), Knee injury and Osteoarthritis Outcome Score, Joint Replacement (KOOS, JR) score. Radiological data were also harvested.ResultsFifteen patients (17 knees) were enrolled with a mean age of 64.6 ± 6.4 (53–76) years. In 5 knees, we used symmetric tibial liners, the rest were asymmetric. After surgery, the average alignment was 1.6 ± 2.0 (-3–5) degrees varus. The average follow-up lasted 6.7 ± 4.2 (1–14) months. The mean visual analogue scale was 0.8 ± 0.7 (0–2), FJS was 62.4 ± 25.3 (0–87), KOOS was 86.5 ± 9.4 (57–97). 11 patients were “very satisfied”, 3 were “satisfied" with the result, and one patient was neutral due to restricted extension and unsatisfactory rehabilitation at five months’ follow-up.ConclusionsWith patient-specific implants and robotics, TKA could be performed by a mathematical way, which was dubbed a “differential” TKA. Intraoperative kinematics was excellent in terms of gap-force balancing and femoral-tibial relative motion. Preliminary clinical outcomes were overall satisfactory.

Joint line elevation and tibial slope are associated with increased polyethylene wear in cruciate-retaining total knee replacement.

The purpose of this retrieval study was to determine the effect of implant positioning on wear, taking patient-related factors into account. Therefore, the volumetric material loss of 59 retrieved tibial liners was quantitatively determined using a coordinate measuring-machine. All retrievals were made of the same polyethylene and design by a single manufacturer. Using time in-situ and linear regression, a wear rate for each liner was determined and corrected for bedding-in. Backside damage was qualitatively scored. The following implant positioning parameters were obtained from radiographs: anatomical lateral-distal femoral angle, anatomical medial-proximal tibial angle, femoral tilt angle, and posterior tibial slope. The patella position was assessed by the Blackburne-Peel index and the Insall-Salvati ratio. Unlike the Insall-Salvati ratio, the Blackburne-Peel index is known to detect surgical joint line elevation. Using general linear modeling the most impactful factors on wear rate and backside damage was determined, thereby taking patient demographic factors into account. The mean volumetric wear rate was 11.6 mm3 /y. Wear decreased with older age (P = .021) and female sex (P = .001). The wear rate increased with joint line elevation as indicated from a decreased Blackburne-Peel index (P = .019), and increased with increased posterior tibial slope (P = .026). The backside damage score also increased with joint line elevation (P = .036). A Blackburne-Peel index decrease of 0.1, signifying joint line elevation, was found to increase the wear rate by 1.8 mm3 /y and increase back-sided wear. A high tibial slope (>7°) led to a 9.3 mm3 /y increase in wear rate compared with a low tibial slope (<3°). The results of this study demonstrate that tibial liner positioning has a significant impact on polyethylene wear with potential implications on osteolysis over time.

New method for acquiring the expected extension gap in total knee arthroplasty.

Adjusting the soft-tissue balance during surgery is crucial in total knee arthroplasty (TKA). However, even using the gap technique, the expected tibial gap is sometimes not achievable. We developed a new method of proximal tibial cutting to acquire the expected tibial gap and insert a tibial liner of appropriate thickness. This study included 128 patients who underwent medial pivot-type TKA for varus knee osteoarthrosis. After completion of the femoral cut using and removal of the bony spur at the medial tibia according to the preoperative plan, we inserted a trial femoral component to the distal femur. Applying valgus manual stress on the knee in extension, we measured the medial gap between the femoral trial and tibial plateau using calipers, defining this medial gap as "pre-gap". A proximal tibial cut was made referring to the pre-gap in the pre-gap group (n = 64). We defined Δgap as the difference between the expected tibial liner thickness and the final tibial liner thickness during surgery. We compared Δgap between the pre-gap group and a control group with conventional tibial cutting without pre-gap measurement (n = 64). The frequency of an ideal tibial cut (Δgap = 0) was 82% in the pre-gap group and 61% in the control group. The frequency of outliers (Δgap ≥ 2mm) was 4% and 18%, respectively. The expected tibial liner was selected more frequently in the pre-gap group than in the control group. Our method was beneficial for acquiring the expected gap in extension to avoid an inadequate gap. Case-control study.

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.

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.

Marker-based technique for visualizing radiolucent implant components in radiographic imaging.

Radiography is the predominant imaging modality used for the in-vivo analysis of orthopaedic implants. A major disadvantage of radiography is that the articulating joint components that are composed of radiolucent polyethylene cannot be directly visualized. Current strategies attempt to circumvent this limitation by estimating component positions and simplifying the joint system, however, these approaches lead to a number of associated errors. Thus, this study provides a method to enable the visualization of the polyethylene component of total knee replacements in radiographic images. This was achieved through the repeatable insertion of markers and accompanying registration process, which were evaluated in this study for reproducibility and accuracy. An insertion guide was developed to insert tantalum beads into polyethylene tibial surface liners. The bead-inserted liners were micro-CT scanned to obtain 3D surface geometries. An in-vivo mimicking phantom RSA experiment was then used to test the 3D to 2D registration process. The guide positioned the beads consistently to ±0.21 mm. The 3D to 2D registration demonstrated a repeatability of -0.014 ± 0.008 mm. Registration of different bead-inserted tibial liners to the phantom revealed an average error of 0.026 ± 0.047 mm for this visualization method. This visualization approach provides greatly improved registration and inter-component measurements than current alternative strategies. This process is suitable for a number of other joints and would greatly benefit procedures that analyze component interactions and implant performance over time. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2017-2022, 2017.

Greater Medial Compartment Forces During Total Knee Arthroplasty Associated With Improved Patient Satisfaction and Ability to Navigate Stairs

BackgroundThe purpose of this study was to determine if postoperative patient satisfaction, subjective outcomes, and functional force testing differed between those with symmetric or asymmetric intraoperative mediolateral (ML) compressive forces. We hypothesized that the threshold would be similar to the previously reported valued of 15 lbf and that a significantly greater proportion of those with more symmetrical medial and lateral compressive forces would be satisfied with their total knee arthroplasty. MethodsA commercially available instrumented trial tibial liner was used to measure ML compressive force differences with the knee at 0°, 20°, and 90°. Patient satisfaction and Knee Society Scores were compared between patients with ML asymmetries above and below the calculated optimal threshold. ResultsSurprisingly, lower ML asymmetries in extension were associated with a greater risk of being dissatisfied. Of the 50 total knee arthroplasties, 6 of 23 (26%) with ML force asymmetries <10 lbf were dissatisfied compared with 0 of 27 with ML asymmetries >10 lbf (P = .01). Greater asymmetry was associated with significantly greater gains in EQ-5D scores (P = .05) and pain scores (P = .03) and greater pain relief (P = .006) and reduced impact forces when navigating stairs (P = .05). ConclusionContrary to our hypotheses, the results of this study support the concept that recreating greater forces in the medial compartment much like that of the native knee may yield improved patient-reported outcomes and increased patient satisfaction. The current results further suggest that recreating greater medial compartment forces may have the greatest affect on more demanding activities such as navigating stairs.

Arthroscopic Treatment of Popliteal Tendon Impingement Following Total Knee Arthroplasty: A Case Report

The popliteal tendon has been known to catch over a femoral osteophyte or the overhanging edge of the femoral component very occasionally following total knee arthroplasty (TKA). However, impingement of the popliteal tendon against the posterior edge of the tibial liner is rare. Although its pathological mechanism is simple, this complication cannot be definitively diagnosed unless posterior arthroscopic examination is performed. In this report, we describe the diagnostic and treatment challenges of using arthroscopy via posteromedial and posterolateral portals.

Joint gap measurement in total knee arthroplasty using a tensor device with the same articulating surface as the prosthesis

We developed a new tensor to measure the joint gap throughout knee flexion during total knee arthroplasty (TKA). This tensor has the same articular shape as that of the tibial liner, including the post structure and the curvature of femorotibial articular surface, to measure the gap intraoperatively under the same conditions as after TKA. The present study aimed to examine the precision of the new tensor for gap measurement after implantation. We performed TKA using the modified gap technique in four cadaveric knees and measured the gaps using the new tensor. The intra-observer and inter-observer error of the tensor was analyzed using 168 measurements of the gaps as determined at least twice by two surgeons. In addition, the gaps in rotating-platform posterior-stabilized TKA were measured at seven positions with the knee bending from extension to full flexion. The inter-observer and intra-observer errors were 0.8 and 0.3mm, respectively, indicating precise and reproducible gap measurement. The gaps before implantation in reduced patellar position were 12.1mm at extension and 12.5mm at 90° flexion. The gaps after implantation were 9.1, 12.9, 13.1, 13.5, 13.8, 13.3, and 10.1mm at 0°, 30°, 45°, 60°, 90°, 120°, and full flexion, respectively. The new tensor provides precise and reproducible measurements. Although the joint gap before implantation was parallel and equal at extension and 90° flexion, the joint gap after implantation was variable throughout knee flexion. This feature of the gap should be considered during the operation.

Increased risk of revision for high flexion total knee replacement with thicker tibial liners

The outcome of total knee replacement (TKR) using components designed to increase the range of flexion is not fully understood. The short- to mid-term risk of aseptic revision in high flexion TKR was evaluated. The endpoint of the study was aseptic revision and the following variables were investigated: implant design (high flexion vs non-high flexion), the thickness of the tibial insert (≤ 14 mm vs > 14 mm), cruciate ligament (posterior stabilised (PS) vs cruciate retaining), mobility (fixed vs rotating), and the manufacturer (Zimmer, Smith & Nephew and DePuy). Covariates included patient, implant, surgeon and hospital factors. Marginal Cox proportional hazard models were used. In a cohort of 64 000 TKRs, high flexion components were used in 8035 (12.5%). The high flexion knees with tibial liners of thickness > 14 mm had a density of revision of 1.45/100 years of observation, compared with 0.37/100 in non-high flexion TKR with liners ≤ 14 mm thick. Relative to a standard fixed PS TKR, the NexGen (Zimmer, Warsaw, Indiana) Gender Specific Female high flexion fixed PS TKR had an increased risk of revision (hazard ratio (HR) 2.27 (95% confidence interval (CI) 1.48 to 3.50)), an effect that was magnified when a thicker tibial insert was used (HR 8.10 (95% CI 4.41 to 14.89)). Surgeons should be cautious when choosing high flexion TKRs, particularly when thicker tibial liners might be required.

Retrieval Analysis of an Early Fracture of a Vitamin E-Stabilized Tibial Liner in Total Knee Arthroplasty

1Department of Orthopaedic Surgery, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8233, St. Louis, MO 63110. E-mail address: [email protected]

Errors in visual estimation of flexion contractures during total knee arthroplasty

To quantify and reduce the errors in visual estimation of knee flexion contractures during total knee arthroplasty (TKA). This study was divided into two parts: Quantification of error and reduction of error. To quantify error, 3 orthopedic surgeons visually estimated preoperative knee flexion contractures from lateral digital images of 23 patients prior to and after surgical draping. A repeated-measure analysis of variance was used to compare the estimated angles prior to and following the placement of the surgical drapes with the true knee angle measured with a long-arm goniometer. In an effort to reduce the error of visual estimation, a dual set of inclinometers was developed to improve intra-operative measurement of knee flexion contracture during TKA. A single surgeon performed 6 knee extension measurements with the device during 146 consecutive TKA cases. Three measurements were taken with the desired tibial liner trial thickness, and 3 were taken with a trial that was 2 mm thicker. An intraclass correlation coefficient (ICC) was calculated to assess the test-retest reliability for the 3 measurements taken with the desired liner thickness, and a paired t test was used to determine if the knee extension measurements differed when a thicker tibial trial liner was placed. The surgeons significantly overestimated flexion contractures in 23 TKAs prior to draping and significantly underestimated the contractures after draping (actual knee angle = 6.1° ± 6.4°, pre-drape estimate = 6.9° ± 6.8°, post-drape estimate = 4.3° ± 6.1°, P = 0.003). Following the development and application of the measurement devices, the measurements were highly reliable (ICC = 0.98), and the device indicated that 2.7° ± 2.2° of knee extension was lost with the insertion of a 2 mm thicker tibial liner. The device failed to detect a difference in knee extension angle with the insertion of the 2 mm thicker liner in 9/146 cases (6.2%). We determined the amount of error associated with visual estimation of knee flexion contractures, and developed a simple, reliable device and method to improve feedback related to sagittal alignment during TKA.

Liner Exchange in Total Knee Arthroplasty

Exchange of the tibial liner in revision knee arthroplasty for wear and other indications is controversial. The purpose of the study was to determine the clinical success and reoperation rate for liner exchange performed for four groups of patients. Thirty-nine revisions were identified in which modular liner exchange was performed: polyethylene wear (12 knees), acute infection (11 knees), instability (4 knees), and a variety of other diagnoses (12 knees). The knees were evaluated using the systems of the Knee Society. The mean follow-up time was 4.3 years. Liner exchange for wear was successful in all 12 patients: for acute infection, in 9 of 11 patients; for instability, in 3 of 4 patients; for other diagnoses, in 10 of 12 patients. There were significant improvements in the pain score in all four groups and significant improvement in the function score in the infection and other diagnoses groups. With the use of six criteria, these observations suggest that liner exchange for wear is successful.

Are undesirable contact kinematics minimized after kinematically aligned total knee arthroplasty? An intersurgeon analysis of consecutive patients

Tibiofemoral contact kinematics or knee implant motions have a direct influence on patient function and implant longevity and should be evaluated for any new alignment technique such as kinematically aligned total knee arthroplasty (TKA). Edge loading of the tibial liner and external rotation (reverse of normal) and adduction of the tibial component on the femoral component are undesirable contact kinematics that should be minimized. Accordingly, this study determined whether the overall prevalence of undesirable contact kinematics during standing, mid kneeling near 90 degrees and full kneeling with kinematically aligned TKA are minimal and not different between groups of consecutive patients treated by different surgeons. Three surgeons were asked to perform cemented, kinematically aligned TKA with patient-specific guides in a consecutive series of patients with their preferred cruciate-retaining (CR) implant. In vivo tibiofemoral contact positions were obtained using a 3- to 2-dimensional image registration technique in 69 subjects (Vanguard CR-TKA N = 22, and Triathlon CR-TKA N = 47). Anterior or posterior edge loading of the tibial liner was not observed. The overall prevalence of external rotation of the tibial component on the femoral component of 6 % was low and not different between surgeons (n.s.). The overall prevalence of adduction of the tibial component on the femoral component of 4 % was low and not different between surgeons (n.s.). Kinematically aligned TKA minimized the undesirable contact kinematics of edge loading of the tibial liner, and external rotation and adduction of the tibial component on the femoral component during standing and kneeling, which suggests an optimistic prognosis for durable long-term function. III.

Can Microcomputed Tomography Measure Retrieved Polyethylene Wear? Comparing Fixed-bearing and Rotating-platform Knees

Wear of total knee polyethylene has been quantified gravimetrically with thickness measurements and evaluation of surface wear modes. However, these techniques do not localize volumetric wear. We used micro-CT scans of retrieved total knee liners and unworn, new liners to determine the volume and location of wear. We retrieved 12 fixed and 12 rotating-platform bearings after a mean 52months of use. Inserts were weighed and thickness was measured. Micro-CT scans of retrieved and matched new liners were superimposed to compare the location and magnitude of wear. The average total wear was 254±248mm(3). The average wear rate was 58±41mm(3)/year. Wear was 69% of penetration, demonstrating the contribution of deformation to knee wear. Rotating-platform wear rate was 43±25mm(3)/year and the fixed-bearing rate was 74±49mm(3)/year. Five percent of the rotating-platform wear rate came from the backside compared with 14% of the fixed-bearing wear rate. Micro-CT can determine the volume and location of wear of retrieved tibial liners. Because the magnitude of the manufacturing tolerances was approximately half the magnitude of the total wear on average, accounting for the potential influence of tolerances is important to accurately measure volumetric wear if the unworn (preimplantation) geometry of the insert is unknown. Without accounting for tolerances, this technique may not be applicable for retrievals with a short followup that have low wear. However, application of micro-CT could be of value in determining the exact location of wear in knee simulator studies in which the same insert is measured repeatedly and manufacturing tolerances are not a concern.

The Use of Highly Cross-linked Polyethylene in Total Knee Arthroplasty

Polyethylene wear, with resultant particle-induced osteolysis, is a cause of late failure of total knee arthroplasty. The causes of both wear and osteolysis are multifactorial; still, improvements in the polyethylene liner have been investigated. Available highly cross-linked polyethylene tibial liners and patellar prostheses differ greatly in the amount and method of irradiation, thermal treatments, and sterilization techniques they undergo. Several varieties of highly cross-linked polyethylene reduce the gravimetric and volumetric wear of tibial liners in knee simulator studies. However, reduced fracture toughness and the generation of smaller and possibly more reactive particles also have been reported with some varieties of polyethylene. Clinical studies of the use of highly cross-linked polyethylene in total knee arthroplasty are limited. Two nonrandomized trials of highly cross-linked polyethylene in total knee arthroplasty have reported a nonsignificant decrease in radiolucent lines at 2 and 5 years, respectively. The risks of using highly cross-linked polyethylene include fracture of the liner or of a posterior-stabilized tibial post, liner dislodgement or locking mechanism disruption, and possibly more osteolysis. Highly cross-linked polyethylene tibial liners may be considered for younger, more active patients. However, until additional clinical results are available, a cautious approach is warranted to the widespread use of highly cross-linked polyethylene in total knee arthroplasty.

The role of the cemented all-polyethylene tibial component in total knee replacement: A 30-year patient follow-up and review of the literature

Use of an all-polyethylene tibial component in primary total knee arthroplasty remains an attractive option considering the reported durability of the construct, the lowered cost compared to modular metal-backed tibia, and the elimination of backside wear. The two major intra-operative disadvantages include the inability to alter the tibial component thickness after permanent implant placement and the inability to use varus-valgus constrained designs. The long-term disadvantage is the inability to perform a modular insert exchange should this be required. We report the 30-year outcome of a single patient using the duopatellar total knee replacement system. Based on a critical review of the literature we would recommend use in patients 80 years of age or older, consideration in patients 75 to 79 years, and possibly in younger yet less active patients. These three groups would be the least likely to require a modular tibial liner exchange in their lifetime.

In Vivo Adduction and Reverse Axial Rotation (External) of the Tibial Component Can Be Minimized

Mechanical alignment with conventional total knee arthroplasty (TKA) instruments often requires collateral ligament releases, which result in a high prevalence of adduction and reverse axial rotation (external rotation) of the tibial component during knee flexion with a variety of component designs. We used a radiographic image-matching technique to determine the contact kinematics during standing and kneeling at 90 degrees and maximum flexion in a series of 35 patients in which a new image-guided, custom cutting block system was used to kinematically align a cruciate-retaining prosthesis with the intent of restoring the 3 kinematic axes of the knee. The kinematically aligned prosthesis had a minimal prevalence of adduction (3%) and reverse axial rotation (8.5%). The anteroposterior contact positions of the lateral and medial femoral condyles did not edge load the tibial liner. The moderate association between abduction and internal rotation, the degree of knee flexion, and the contact position of the medial femoral condyle suggest that abduction was not a sign of lift-off of the medial femoral condyle, but the result of the medial femoral condyle moving up the anterior slope of the tibial liner. These more normal contact kinematics were achieved without release of the collateral ligaments or lateral retinaculum. In contrast to mechanical alignment with conventional surgical techniques, the use of kinematic alignment with custom-fit cutting guides and a cruciate-retaining, symmetric medial and lateral femoral-tibial bearing surface minimizes the undesirable consequences of adduction and reverse axial rotation (external rotation).

Osteolysis After Unidirectional and Multidirectional Mobile-Bearing Total Knee Arthroplasty in Young Patients

We questioned whether a difference exists between multidirectional and unidirectional mobile-bearing total knee arthroplasties in terms of clinical results and the prevalence of polyethylene wear and periprosthetic osteolysis. We studied 62 patients who underwent simultaneous bilateral total knee arthroplasties, with a unidirectional prosthesis implanted in 1 knee and a multidirectional one in the other. Of the patients, 9 were men and 53 were women, with a mean age of 57.6 years (35-60 years). The minimum follow-up was 11 years (mean, 11.8 years; range, 11-13 years). Preoperative and postoperative knee and functional scores were not different between the 2 groups. No knee in either group had detectable tibial polyethylene liner wear or osteolysis on radiographs or on computed tomography scans. Two (3%) knees in each group were revised.

Unilateral Tibial Polyethylene Liner Failure in Bilateral Total Knee Arthroplasty—Bilateral Retrieval Analysis at 8 Years

This is a report of a unique case of bilateral simultaneous total knee arthroplasties in which one tibial liner failed dramatically, whereas the other liner showed minimal evidence of wear. This unique case allows isolation of component factors as the primary contributing etiology to failure. The differentiating characteristic was the method of sterilization and the shelf life of the polyethylene liner. The insert that showed minimal wear was sterilized with γ radiation in a barrier package and had a shelf life of less than 1 year, whereas the insert that failed dramatically was sterilized in air and had a shelf life of more than 5 years. This case provides a dramatic example of the potential detrimental effects of manufacturing details on the performance of orthopedic implants, particularly polyethylene inserts.