Femoral Component In Total Knee Arthroplasty Research Articles

Osteometric Dimension of Lower End of Femoral Bone among Bangladeshi Population

Introduction: The osteometric dimensions of the lower end of the femur have significant clinical implications, particularly in the context of total knee arthroplasty (TKA). Accurate measurements are crucial for the design of femoral components in TKA, which can influence surgical outcomes. This study aims to determine the measurements of different variables of the lower end of the femur, including femoral condylar width, intercondylar width and depth, and the depth of the medial and lateral condyles, in a Bangladeshi population. Methods: This cross-sectional study was conducted on 50 dried femurs collected from three medical colleges in Dhaka, Bangladesh. Measurements were obtained using digital sliding calipers and were rounded to two decimal places. Data analysis was performed using SPSS. Result: Statistical analysis revealed that 56% of the femurs were right-sided and 44% were left-sided. The mean femoral bicondylar width was 69.78 ± 5.38 mm, falling mostly in the "Above Average" range (30%). The mean intercondylar width was 23.77 ± 1.55 mm, with 50% falling in the "Medium" range. Other variables like femur medial condylar width had a mean of 31.05 ± 1.74 mm. Conclusion: Observationally, the study successfully delineates the osteometric dimensions of the lower end of the femur in a Bangladeshi cohort. The statistical results not only fulfill the study's initial aim but also provide a nuanced understanding of the osteometric variations. These findings are instrumental for clinicians in the design and customization of femoral components in TKA, thereby potentially enhancing surgical outcomes and patient satisfaction. The data also lay the groundwork for future research in this area.

Femoral Valgus Correction Angle for the Intramedullary Alignment Rod Is Strongly Associated with Femoral Lateral Bowing in Japanese Patients with Varus Knee Osteoarthritis Undergoing Total Knee Arthroplasty

Background This study aimed to investigate factors, such as differences in femoral shape, that could affect the femoral valgus correction angle (VCA) for the intramedullary alignment rod (IM rod) by using a three-dimensional (3D) measurement system in patients with varus knee osteoarthritis undergoing total knee arthroplasty (TKA). Methods A total of 305 knees in 233 Japanese patients with varus knee osteoarthritis who underwent primary TKA by using Jig Engaged 3D Pre-Operative Planning Software for the TKA operation support system was examined. We retrospectively analysed factors, such as the shape of the proximal, middle, and distal femur in the coronal plane, all of which could affect the VCA for the IM rod, by multiple linear regression analyses. Results The VCA for the IM rod was 5.9° ± 1.6° (range: 1.7° to 10.7°), and the femoral lateral bowing angle (FBA) was 3.5° ± 3.2°. Major factors independently associated with the VCA for the IM rod were the FBA (β: 0.75), femoral offset (β: 0.38), and the medial angle between the mechanical femoral axis and the line that connects the distal margins of the medial and lateral femoral condyles (β: −0.16). The model was created by stepwise multiple linear regression (F = 266.6, p < 0.001, and estimated effect size = 4.4) explained 85% of the variance in the VCA for the IM rod (R2 = 0.85). Conclusions The VCA for the IM rod was most strongly associated with femoral lateral bowing in patients with varus knee osteoarthritis undergoing TKA. Our findings suggest that preoperatively measuring the VCA for the IM rod in patients with femoral lateral bowing by using a 3D measurement system could be useful for accurate coronal alignment of the femoral component in TKA.

Higher Pelvic Incidence Was Associated with a Higher Risk of Sagittal Malposition of Femoral Component and Poor Outcomes of Primary Total Knee Arthroplasty: A Retrospective Cohort Analysis.

Spine-pelvis-lower extremity sagittal alignment is regarded as a global sagittal balance. Currently, there are few studies evaluating the pelvic and femoral sagittal alignment during total knee arthroplasty (TKA). This retrospective study aims to elucidate how pelvic and femoral sagittal alignment affect clinical outcomes of primary TKA for osteoarthritis (OA) and determine the proper range of femoral sagittal alignment. Patient-reported outcome measures (PROMs), including the Knee Society Score (KSS), Western Ontario and McMaster Universities (WOMAC), and patient satisfaction scores, and clinician-reported outcomes (CROs), including range of motion (ROM) and pelvic and femoral sagittal parameters, of 67 cases were evaluated (89 knees) before and 1 year after TKA. The angle between the distal femur anterior cortex line and flange of the femoral component (FC) was defined as the α angle. Correlations between the α angle and PROM and CRO were investigated using multivariate and secondary regression analyses. Patients were further divided into four cohorts (A, B, C, and D) according to the α angle, and comparisons of their postoperative PROM and ROM scores were performed. Postoperative PROM and ROM scores improved significantly compared with the preoperative scores (p < 0.01). Only the α angle was significantly associated with postoperative knee extension among all PROM and CRO indexes (p = 0.001). Secondary regression demonstrated a convex upward function, and the scores were the highest at α angles of 0.57, 0.96, and -1.42 degrees for postoperative KSS, satisfaction, and range of knee extension, respectively (p < 0.01). However, the concave upward degree was the lowest at an α angle of 0.33 degrees for pelvic incidence (p < 0.001). Bonferroni's paired comparisons indicated that postoperative KSS and satisfaction of the cohort B (0 degrees ≤ α angle ≤ 3 degrees) were better than those of other cohorts (p < 0.0125). The results indicate that surgeons should pay more attention to the sagittal alignment of FC in patients with increased pelvic incidence, the distal femoral anterior cortex is recommended as an anatomic landmark, and 0 to 3 degrees might be "safe zones" of the sagittal flexion of FC in TKA. This study reflects the level of evidence III.

Stability with a Constrained Posterior Stabilized Primary Total Knee Arthroplasty Does Not Compromise Durability.

Total knee arthroplasty (TKA) in cases of complex deformity (e.g., ligamentous laxity, posttraumatic arthritis) may require prostheses with inherent varus-valgus stability greater than that of traditional posterior stabilized or cruciate-retaining implants. Here, we investigate the clinical and radiographic outcomes of TKA using a midlevel constraint (MLC) prosthesis. A retrospective review of 53 patients (62 knees) who underwent primary TKA with an MLC implant was performed. Short tibial stem extensions were utilized in 49 knees, and 13 knees received no stem extension. Mean follow-up time was 31.6 months (standard deviation [SD] = 10.0, range = 24-53). Preoperative and postoperative range of motion (ROM) were assessed. Plain radiographs were reviewed for alignment, radiolucent lines, component loosening, and osteolysis. Patients who developed postoperative arthrofibrosis underwent manipulation under anesthesia (MUA). Failure was defined as instability, component loosening, or need for revision surgery. Mean ROM significantly improved from 114.1 degrees (SD = 19.7 degrees) preoperatively to 123.5 degrees (SD = 12.2 degrees) at final follow-up (t = -3.43, p = 0.001). Thirty-seven knees initially presented with varus deformity (mean = 7.5 degrees, SD = 4.8 degrees), whereas 23 had valgus deformity (mean = 10.6 degrees, SD = 6.5 degrees), and 2 knees had neutral alignment. Following surgery, mean alignment was 4.3 degrees valgus (SD = 1.7 degrees, range = 0-8 degrees), representing a statistically significant improvement (t = 5.29, p < 0.001). Six patients (9.7%) developed arthrofibrosis requiring MUA, which was irrespective of baseline ROM (p = 0.92) and consistent with 12% incidence reported in the literature. There were no significant differences in postoperative ROM (t = 0.38, p = 0.71), alignment (t = -0.22, p = 0.83), or incidence of arthrofibrosis (χ2 = 0.07, p = 0.79) between short-stemmed and nonstemmed implants. There was no radiographic evidence of radiolucent lines, component loosening, or osteolysis in any patients. No patients required revision surgery. Use of an MLC prosthesis with primary femoral component in TKA resulted in satisfactory clinical and radiographic results with no evidence of component loosening, osteolysis, instability, or need for revision at minimum 2-year follow-up.

Preoperative rotational assessment of the distal femur with CT may cause femoral component malrotation in TKA

BackgroundBefore total knee arthroplasty (TKA), rotational assessment of the distal femur can be performed using either magnetic resonance imaging (MRI) or computed tomography (CT). Until now, there has been no study comparing the two modalities regarding rotational assessment of the distal femur in the same patients. MethodsWe retrospectively reviewed the preoperative CT and MRI images of 110 knees in 110 patients who underwent TKA. In the axial planes of CT and MRI scan, the posterior condylar axis (PCA), anatomical transepicondylar axis (aTEA), and perpendicular line to anteroposterior axis (pAPA) were identified; the angles between these studied lines were calculated. During TKA, the angles measured on the preoperative CT and MRI were compared with the measurements obtained in the intraoperative field. ResultsThe mean aTEA-PCA angle was 6.2 ± 1.9° with CT and 5.1 ± 1.8° with MRI. The mean pAPA-PCA angle was 4.7 ± 2.1° with CT and 3.5 ± 2.0° with MRI. The mean aTEA-PCA (1.1 ± 1.3°, p = 0.001) and pAPA-PCA (1.2 ± 1.2°, p = 0.012) angles significantly differed between CT and MRI. Intra-operatively, the mean aTEA-PCA angle was 4.7 ± 1.1° and the mean pAPA-PCA angle was 3.2 ± 0.9°. Reliability analysis between the preoperative CT/MRI and the intraoperative measurements gave kappa values of 0.72 for aTEA-PCA and 0.66 for pAPA-PCA with CT, and 0.82 for aTEA-PCA and 0.84 for pAPA-PCA with MRI. ConclusionsPreoperative rotational assessment of the distal femur with CT may cause higher external rotation of femoral component in TKA.

Preoperative planning of total knee arthroplasty: reliability of axial alignment using a three-dimensional planning approach.

Preoperative templating of total knee arthroplasty (TKA) can nowadays be performed three-dimensionally with software solutions using computed tomography (CT) datasets. Currently there is no consensus concerning the axial orientation of TKA components in three-dimensional (3D) planning. To assess intra-/inter-observer reliability of detection of different bony landmarks in planning axial component alignment using axial CT images and 3D reconstructions. Intra- and inter-observer reliability of determination of four predefined axial femoral and tibial axes was calculated using data from CT scans. Axes determination was performed on the axial slices and on the 3D reconstruction using preoperative planning software. In summary, 61 datasets were analyzed by one medical student (intra-observer reliability) and 15 datasets were analyzed by four different observers independently (inter-observer reliability). For the femur, clinical epicondylar axis and posterior condylar axis showed the best reliability with an inter-observer variability of 0.7° and 0.5°, respectively. For the tibia, posterior condylar axis provided best reliability (inter-observer variability: 1.7°). Overall variability was greater for tibial than for femoral axes. Reliability of axis determination was more accurate using axial CT slices rather than 3D reconstructions. The femoral clinical epicondylar axis is highly reliable. Landmarks for the tibia are not as easily identifiable as for the femur. The tibial posterior condylar axis presents the axis with highest reliability. Based on these results, clinical epicondylar axis for orientation of the femoral TKA component and posterior condylar axis for the tibial implant, both defined on axial slices can be recommended.

Evaluation of an operation support system using the femoral anterior tangent line to determine intraoperative femoral component rotation in total knee arthroplasty

BackgroundThe femoral anterior tangent (FAT) line refers to a line parallel to the anterior surface of the distal femur in the axial plane. This study aimed to evaluate the effectiveness of a new operation support system which uses the FAT line to set the femoral component rotational alignment in total knee arthroplasty (TKA). MethodsA total of 170 consecutive knees in 139 patients undergoing primary TKA with the JIGEN (Jig Engaged Three-dimensional (3D) Pre-Operative Planning Software for TKA) operation support system was examined. The JIGEN system creates 3D models of bones using computed tomography data, allowing for surgical simulations such as positioning of implants while calculating positions of the intramedullary alignment rod (IM rod) and surgical jig. We retrospectively analyzed the FAT line angle relative to the surgical epicondylar axis (SEA) on the axis plane perpendicular to the IM rod and evaluated the accuracy of the femoral component alignment after TKA with the 3D measurement system. ResultsThe FAT line was 9.6° ± 3.7° (range, 1.4°–20.4°) internally rotated relative to the SEA. The average absolute error was 1.4° ± 1.1° in the coronal plane, 2.0° ± 1.5° in the sagittal plane, and 1.6° ± 1.3° in the axial plane. The femoral component outliers (i.e., >3° away from the goal alignment) were 7.7% in the coronal plane, 20.6% in the sagittal plane, and 10.3% in the axial plane. ConclusionsOur findings suggest that the FAT line is a reliable and reproducibly identifiable axis for the accurate determination of proper rotational alignment in TKA. An operation support system which uses the FAT line for determining intraoperative femoral component rotation can effectively achieve highly accurate positioning of the femoral component in TKA.

The effect of different interference fits on the primary fixation of a cementless femoral component during experimental testing

Cementless femoral total knee arthroplasty (TKA) components use a press-fit (referred to as interference fit) to achieve initial fixation. A higher interference fit could lead to a superior fixation, but it could also introduce more damage to the bone during implantation. The purpose of the current study was to investigate the effect of interference fit on the micromotions and gap opening/closing at the bone-implant interface. Experimental tests were performed in six pairs of cadaveric femurs implanted with femoral components using a low interference fit of 350 μm and a high interference fit of 700 μm. The specimens were subjected to the peak loads of gait and squat, based on the Orthoload dataset. Digital Image Correlation (DIC) was used to measure the micromotions and opening/closing in different regions of interest (ROIs). Two linear mixed-effect statistical models were created with micromotions and gap opening/closing as dependent variables. ROIs, loading conditions, and implant designs as independent variables, and cadaver specimens as random intercepts. The results revealed no significant difference between the two interference fit implants for micromotions (p = 0.837 for gait and p = 0.065 for squat), nor for the gap opening/closing (p = 0.748 for gait and p = 0.561 for squat). In contrast, significant differences were found between loading and most of the ROIs in both dependent variables (p < 0.0001). Additionally, no difference in bone deformation was found between low and high interference fit. Changing interference between either 350 μm or 700 μm did not affect the primary stability of a femoral TKA component. There could be an interference fit threshold beyond which fixation does not further improve.

Flexible versus standard intramedullary rod in posterior stabilized primary total knee arthroplasty: protocol for a randomized controlled trial

BackgroundIn total knee arthroplasty (TKA) a flexible intramedullary rod can be used to account for sagittal bowing of the distal femur. Although patients report better post-operative functional outcome when the flexible rod was used, it is unknown how the use of the flexible rod affects the placement of the femoral TKA component, and how this relates to activities of daily living. It is expected that the use of the flexible rod will result in a more flexed femoral component, a larger patellar tendon moment arm, and consequently in better functional outcome. The goal of this study is to compare the flexible rod to the standard intramedullary rod in primary TKA in terms of fit of the TKA, functional outcome, and sizing of the femoral component.MethodsA single-blind randomized controlled trial with two groups (flexible vs standard rod), with patients blinded for group allocation, and 2 years post-operative follow-up. The fit of the TKA is quantified by two parameters: (1) the flexion angle of the TKA in the sagittal plane and (2) the sagittal profile of the distal femur compared between the pre-operative bone and the TKA. Both parameters are calculated in 3D volume images obtained using fluoroscopy. Functional outcome will be measured using (1) the timed Get-up and Go test (2), the stair climbing test (3), knee power output, and (4) patient and clinician reported outcomes. Different parameters will be measured during the TKA procedure to account for the invisibility of cartilage in the 3D volumes and to study if the amount of bone removed during the procedure is affected by group allocation.DiscussionThe sagittal fit of TKA is not a standardized outcome measure. We discuss our choice of parameters to define the sagittal fit (i.e., flexion angle and sagittal profile), our choice for the parameters we measure during the TKA procedure to account for the lack of cartilage thickness in fluoroscopy, and our choice for the parameters to study if the amount of bone removed during the procedure is affected by group allocation. Lastly, we discuss the merits of this planned trial.Trial registrationNetherlands Trial Register, 4888, registered 30 March 2015. https://www.trialregister.nl/trial/4888

Intra- and postoperative assessment of femoral component rotation in total knee arthroplasty: an EKA knee expert group clinical review.

Malrotation of the femoral component after primary total knee arthroplasty (TKA) is one of the most important problems leading to painful TKA requiring revision surgery. A comprehensive systematic review of the literature was performed to present current evidence on how to optimally place the femoral component in TKA. Several landmarks and techniques for intraoperative determination of femoral component placement and examination of their reliability were analyzed. 2806 articles were identified and 21 met the inclusion criteria. As there is no unquestioned gold standard, numerous approaches are possible which come along with specific advantages and disadvantages. In addition, imaging modalities and measurements regarding postoperative femoral component rotation were also investigated. Femoral component rotation measurements on three-dimensional (3D) reconstructed computerised tomography (CT) images displayed intraclass correlation coefficients (ICC) above 0.85, significantly better than those performed in radiographics or two-dimensional (2D) CT images. Thus, 3D CT images to accurately evaluate the femoral prosthetic component rotation are recommended, especially in unsatisfied patients after TKA. The EKA Femoral Rotation Focus Group has not identified a single best reference method to determine femoral component rotation, but surgeons mostly prefer the measured resection technique using at least two landmarks for cross-checking the rotation. III.

Roles of sagittal anatomical parameters in femoral component alignment of primary posterior stabilized total knee arthroplasty for osteoarthritis

Purpose: Total knee arthroplasty (TKA) is one of the important methods to treat severe osteoarthritis (OA) of knee joint. The alignments of the knee joint are pivotal in ensuring patient satisfaction and functional ability after TKA. Compared with the balance of coronal plane, more attention is paid to the balance of sagittal plane. Moreover, the probability for sagittal malposition of the femoral component is higher than that of tibial component. Normal sagittal spine-pelvis-lower extremity alignment is crucial in humans for maintaining a balance of motion, including the motion of spine, hip, knee and ankle joints. There has been little study on balance of pelvis-knee joint alignment with regard to the sagittal alignment of the femoral component. The objective of our study is to determine the role of the impact of pelvis-knee joint sagittal alignment parameters on the femoral component in primary posterior stabilized (PS) TKA for OA. Methods: This retrospective study was approved by the First Affiliated Hospital of Sun Yat-sen University Clinical Research Ethics Committee (Guangzhou, China). The Knee Society Score (KSS), the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index and patient satisfaction were evaluated before surgery and 1 years after surgery, respectively. Surgimap® software (Nemaris, Inc) was applied to investigated the following parameters: pre-operation:pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), pelvic femoral angle (PFA), sacrum femoral angle (SFA), femoral inclination(FI), femoral anterior bowing angle (FABA), distal femoral flexion angle(DFFA), distal femoral anterior cortex angle (DFACA, Figure 1); post-operation: femoral prosthesis flexion angle (FPFA),αangle ( the angle between the distal femur anterior cortex line and flange of femoral component, βangle (the angle between a line parallel to the distal cement interface of the femoral component and the femoral machanical axis),γangle (the proximal angle between a line drawn perpendicular to the distal cement interface of the femoral component and the femoral anatomical axis, , Figure 2) , rang of knee flexion and extension. Data were analyzed using SPSS version 20.0 (IBM Co., Armonk, NY, USA). Multivariate regression analysis, Pearson correlation analysis, χ2 tests and t-tests were used to compare differences between groups and means. Cohorts were checked for statistical homogeneity at baseline. Results: The study comprised a total of 54 Chinese patients (73 knees) who received TKA surgery (Smith &Nephew, PS) during January to July 2018, including 13 men and 41 women with a mean age of 69.1 years (range, 57-87 years). The mean BMI of all patients was 25.8 (range, 17.6-34.5 years). The results of function scales are as follow:pre-operation:KSS:61.3±14.7 (37⁓92), functional scores:38.6±12.5(15⁓95), WOMAC:48.9±7.2(37⁓65); post-operation:KSS:86.3±10.0 (40⁓100), functional scores:62.2±13.9(35⁓90), WOMAC:29.3±5.5(21⁓40), patient satisfaction: 7.6±1.1(5⁓10). Sagittal anatomical parameters was evaluated before surgery as follows: PI:56.1±14.1°(30.2⁓94.6°), PT:17.7±10.2°(0.3⁓45.5°), SS:38.8±10.5°(10.4⁓61.2°), PFA:11.1±9.2°(0.4⁓35.2°), SFA:58.6±14.2°(17.9⁓102.0°), FI:15.7±9.1°(1.2⁓62.2°), FABA:10.9±4.0°(3.2⁓20.7°), DFFA: 3.3±1.9°(0.3⁓8.5°), DFACA:2.8±2.1°(0.1⁓10.2°). The parameters was assessed one year after surgery as follows: FPFA:6.0±4.9°(0.4⁓20.7°),α angle:2.5±5.4°(-13.7⁓20.0°), β angle:86.4±10.3°(63.8⁓113.3°),γangle:6.3±5.2°(0.0⁓19.0°), rang of knee flexion: 109.2±12.0 (85.0 ⁓125.0), rang of knee extension: 3.2±3.5(-5.0⁓10.0).(Table 1) It was found that PI=PT+SS,t tests revealed that the scale scores of KSS and WOMAC after surgery improved significantly than that of pre-surgery(p<0.001), which indicated most patients gained a good clinical outcome after surgery. Pearson correlation analysis showed that PI was positively related with the absolute value of α angle (r=-0.5696, p=0.0001, Figure 3A), which suggested that increased PI would probably lead to a greater α angle.Moreover, the absolute value of α angle was found negatively related with the KSS and patient satisfaction, respectively( r= -0.4906, -0.5204; p=0.0001,p=0.0002, respectively, Figure 3B, C). However, multivariate regression analysis and Pearson correlation analysis didn`t show significance relationship among functional scales , WOMAC and other sagittal anatomical parameters(p>0.05). Furthermore, the patients was divided into four cohorts according the α angle: A:α angle extension >0°;B:0°≤α angle flexion≤3°; C:3°≤α angle flexion≤7°; D: α angle flexion>7°(Figure 5). Bonferroni paired comparison showed KSS, functional scales and rang of knee flexion in B cohort were highest (p=0.025) while these above scales both in A and D cohorts were lower (p=0.033, p=0.005) among these four cohorts. Conclusions: Increased PI would probably lead to a greater α angle, which suggested that older patients with greater PI might have greater probability for femoral malposition. The distal femur anterior cortex and α angle might be useful index for sagittal alignment of femoral component in TKA. The patients with neutral-to-mild flexion of femoral component( 0°≤α angle flexion≤3°) would possibly gain a good clinical outcome.

Femoral component malrotation is not correlated with poor clinical outcomes after total knee arthroplasty.

Proper rotational alignment of the femoral component is critical for a successful total knee arthroplasty (TKA). The aim of this systematic review was to analyse the available literature to examine the effect of the TKA femoral component malrotation on clinical outcomes and assess a cut-off value for femoral rotation leading to revision surgery. A detailed and systematic search from 1996 to 2019 of the PUBMED, Medline, Cochrane Reviews and Google Scholar databases had been performed using the keyword terms "total knee arthroplasty OR replacement" AND "femoral alignment OR malalignment OR femoral rotation OR malrotation" AND "clinical outcome". We used the methodological index for non-randomized studies (MINORS) to identify scientifically sound articles in a reproducible format. Eleven articles met inclusion criteria. A total of 896 arthroplasties were included in this review; 409 were unexplained painful TKA patients, while 487 were painless TKA patients. The mean age of patients was 67.5 (± 2.1) years. The mean post-operative follow-up delay was 46.8 (± 32.2) months. The mean of MINORS score was 21 points indicating good methodological quality in the included studies. The present review confirms that the malrotation of the femoral component in TKA does not correlate automatically to poor clinical and functional outcome. The clinical relevance of this study was that, to improve accuracy in femoral component rotation, surgeons should consider the anatomical variability of femur in each knee and perform additional measurements pre- and intra-operatively. Taking a more accurate approach will shed light on unanswered questions in unhappy TKA. III.

Fatigue failure of the femoral component of a total knee arthroplasty: a case report and review of the literature

ABSTRACT INTRODUCTION: Reports of fatigue failure of the femoral component of a total knee arthroplasty (TKA) is scanty in the literature. As a result, there are no clearly defined risk factors to aid us in predicting fatigue failure of an implant. Furthermore, these patients may present with non-specific knee pain, which may or may not be well tolerated, depending on the stability of the implant. We report a case of fatigue failure of a poorly cemented femoral component of a TKA in a 72-year-old female, approximately seven years after the initial surgery CASE REPORT: A 72-year-old female presented to our tertiary level arthroplasty unit with new-onset knee pain approximately seven years after undergoing a TKA at our unit. She reported hearing a crack six months earlier, while standing up from a seated position. She had initially presented to her local clinic, but the pathology was missed. She received revision surgery at our institution and was doing well at early follow-up. DISCUSSION: We reviewed the literature on fatigue failure of femoral components in TKA in an attempt to define risk factors. We also summarised all cases of femoral component fatigue failure in the English literature. CONCLUSION: Although femoral component fatigue failure in TKA is rare, the majority of cases have attributed the failure to poor surgical technique. Despite this, certain implants have been failing more often than others, and proposed mechanisms for this exist. Orthopaedic surgeons need to be aware of which implant designs are prone to failure, as well as how meticulous surgical technique can reduce the chances of fatigue failure. Level of evidence: Level 5 Keywords: femoral component, total knee arthroplasty, fatigue failure, stress fracture

Different femoral rotation with navigated flexion-gap balanced or measured resection in total knee arthroplasty does not lead to different clinical outcomes.

Femoral rotation in total knee arthroplasty (TKA) is hypothesized to vary in the same knee depending on the method used to establish it. Thirty-eight patients who underwent TKA surgery using a measured resection technique (RT) were compared with 40 patients who underwent a flexion-gap balancing technique with computer-assisted (for navigation) surgery (FB-CAS) to assess clinical and radiographic alignment differences at two years postoperatively. In 36 of the 40 patients in the FB-CAS group, both methods were used. Intraoperatively, the transepicondylar femoral rotation (TEFR) in reference to the transepicondylar axis was established as the rotation that balanced the flexion gap. Once the TEFR was obtained, an analogous rotation as measured by a posterior reference femoral rotation (PRFR) cutting guide was determined. Femoral component rotation determined by the TEFR and PRFR methods differed in each of the knees. The median TEFR was 0.08°±0.6° (range - 1.5°, 1.5°), and the median PRFR was 0.06°±2.8° (range - 6°, 5°). The mean difference in the rotational alignment between the TEFR and PRFR techniques was 0.01° ± 3.1°. The 95% limits of agreement between the mean differences in measurements were between 6.2° external rotation and - 6.1° internal rotation. At 2 years postoperatively, we found no differences in the radiographic or clinical American Knee Society score between the two groups. Rotation of the femoral component in TKA can vary in the same knee depending on the surgical method used to establish it. This variation in femoral rotation is sufficiently small enough to have no apparent effect on the 2-year clinical outcome score. II.

An accelerometer-based navigation did not improve the femoral component positioning compared to a modified conventional technique of pre-operatively planned placement of intramedullary rod in total knee arthroplasty.

Although the most commonly used method of femoral component alignment in total knee arthroplasty (TKA) is intramedullary (IM) guides, this method demonstrated a limited degree of accuracy. Because of the femoral anterior bowing, the tip of the guide rod will impinge on the anterior cortex if a long rod is inserted. We hypothesized that the pre-operative planned insertion depth of the rod could increase the accuracy of the femoral component positioning in conventional TKA (modified conventional technique). Accelerometer-based, portable navigation device has been postulated to have better accuracy than conventional TKA in component positioning. The purpose of this study was to compare the post-operative femoral component alignment of TKA using the modified conventional technique with the accelerometer-based navigation. Fifty-five knees underwent TKA using the modified conventional technique and femoral component positioning was compared with 55 knees performed using the accelerometer-based navigation device. The femoral component alignment was evaluated with a CT-based three-dimensional software. The mean absolute deviation from targeted alignment in the sagittal plane was significantly less in the modified conventional cohort than in the accelerometer-based navigation cohort (1.1° vs 2.6°, P < 0.001). In the modified conventional cohort, 96.4% had an alignment within 3° of a targeted angle in the coronal plane (vs 89.1% with the accelerometer-based navigation, P = 0.14), and 96.4% in the sagittal plane (vs 74.5% with the accelerometer-based navigation, P < 0.001). The modified conventional technique is a simple and equal to or more accurate method than the accelerometer-based navigation in positioning the femoral component in TKA at a mid-volume hospital.

Optimization of parameters for femoral component implantation during TKA using finite element analysis and orthogonal array testing

BackgroundIndividualized and accurate implantation of a femoral component during total knee arthroplasty (TKA) is essential in achieving equal distribution of intra-articular stress and long-term survival of the prosthesis. However, individualized component implantation remains challenging. This study aimed to optimize and individualize the positioning parameters of a femoral component in order to facilitate its accurate implantation.MethodsUsing computer-simulated TKA, the positioning parameters of a femoral component were optimized individually by finite element analysis in combination with orthogonal array testing. Flexion angle, valgus angle, and external rotation angle were optimized in order to reduce the peak value of the pressure on the polyethylene liner of the prosthesis.ResultsThe optimal implantation parameters of the femoral component were as follows: 1° flexion, 5° valgus angle, and 4° external rotation. Under these conditions, the peak value of the pressure on the polyethylene liner surface was minimized to 16.46 MPa. Among the three parameters, the external rotation angle had the greatest effect on the pressure, followed by the valgus angle and the flexion angle.ConclusionFinite element analysis in combination with orthogonal array testing can optimize the implantation parameters of a femoral component for TKA. This approach would possibly reduce the wear of the polyethylene liner and prolong the survival of the TKA prosthesis, due to its capacity to minimize stress. This technique represents a new method for preoperative optimization of the implantation parameters that can achieve the best possible TKA outcome.

Fixation strength of a polyetheretherketone femoral component in total knee arthroplasty

IntroductionIntroducing polyetheretherketone (PEEK) polymer as a material for femoral components in total knee arthroplasty (TKA) could potentially lead to a reduction of the cemented fixation strength. A PEEK implant is more likely to deform under high loads, rendering geometrical locking features less effective. Fixation strength may be enhanced by adding more undercuts or specific surface treatments. The aim of this study is to measure the initial fixation strength and investigate the associated failure patterns of three different iterations of PEEK-OPTIMA® implants compared with a Cobalt–Chromium (CoCr) component. MethodsFemoral components were cemented onto trabecular bone analogue foam blocks and preconditioned with 86,400 cycles of compressive loading (2600 N–260 N at 1 Hz). They were then extracted while the force was measured and the initial failure mechanism was recorded. Four groups were compared: CoCr, regular PEEK, PEEK with an enhanced cement-bonding surface and the latter with additional surface primer. ResultsThe mean pull-off forces for the four groups were 3814 N, 688 N, 2525 N and 2552 N, respectively. The initial failure patterns for groups 1, 3 and 4 were the same; posterior condylar foam fracture and cement–bone debonding. Implants from group 2 failed at the cement–implant interface. ConclusionsThis study has shown that a PEEK-OPTIMA® femoral TKA component with enhanced macro- and microtexture is able to replicate the main failure mechanism of a conventional CoCr femoral implant. The fixation strength is lower than for a CoCr implant, but substantially higher than loads occurring under in-vivo conditions.

Wear predictions for UHMWPE material with various surface properties used on the femoral component in total knee arthroplasty: a computational simulation study.

The wear of ultrahigh-molecular weight polyethylene (UHMWPE) tibial inserts in total knee arthroplasty (TKA) remains a major limitation that hinders the longevity of clinically successful devices. Surface properties significantly affect the overall performance of TKA, and surface modification with mechanically and chemically stable materials is an effective method for overcoming the wear of TKA. However, wear tests are not cost-efficient or time-efficient; thus, the effects of geometric, loading, and alignment perturbations are often evaluated via parametric studies. Computational wear prediction using a finite element (FE) model followed by validation through comparison with experimental data is effective for assessing new prosthetic designs or surface change methods prior to functional testing and surgical implementation. The aim of this study was to evaluate the weight loss, wear depth, and kinematics for different surface properties, including nanostructured diamond (NSD), diamond-like carbon (DLC), titanium-nitride (TiN), and oxidized zirconium (OxZr) on femoral components in TKA using FE analysis under gait-cycle loading conditions. Weight loss and wear depth were lowest with OxZr followed by TiN, NSD, and DLC. However, the DLC femoral component did not show any improvement in wear rate compared to an uncoated cobalt-chromium (Co-Cr) femoral component. Not all surface changes applied in this study did lead to improvement in wear performance. However, this study demonstrates the potential of OxZr and TiN for reducing UHMWPE wear and offers new insights into the effects of wear on TKA.

Long-Term Durability of Ceramic Tri-Condylar Knee Implants: A Minimum 15-Year Follow-Up

BackgroundCeramic bearings are not commonly used in total knee arthroplasty (TKA). So far, little information is available about whether long-term survivorship and good clinical outcomes can be ensured with ceramic knee implants. The purposes of the present study were to evaluate the clinical and radiological outcomes, and to assess the long-term durability of a ceramic tri-condylar implant. MethodsA total of 507 consecutive TKAs were carried out using a ceramic tri-condylar femoral implant. The posterior cruciate ligament was sacrificed, and all components were fixed with bone cement. Clinical outcomes were assessed retrospectively with the Knee Society scoring system. Kaplan-Meier survivorship was calculated to determine the cumulative survival rate. ResultsOne hundred sixty-seven knees (114 patients) were available for clinical outcomes. The average range of flexion improved from 118.1° preoperatively to 123.7° at a minimum 15-year follow-up (P < .001). The average Knee Society knee score improved from 39.1 to 92.8 (P < .001). The functional score also improved from 36.0 to 47.0 (P < .001). With revision for any surgery or radiographic failure as the end point, Kaplan-Meier survivorship at 15 years was 94.0%. With revision of any component as the end point, the corresponding survivorship was 96.2%. ConclusionClinically, the postoperative knee flexion range and Knee Society scores were good after long-term follow-up. The survivorship of the ceramic knee implant was excellent over the 15-year follow-up, and long-term durability was achieved, making ceramic a promising alternative material for the femoral component in TKA.

The Posterior Condylar Cartilage Affects Rotational Alignment of the Femoral Component in Varus Knee Osteoarthritis.

Rotational alignment of the femoral component in total knee arthroplasty (TKA) is important for patellar tracking and ligament balance. Preoperative planning based on radiography might have a potential risk for over-rotation because these X-ray based measurements can not detect asymmetric cartilage wear on posterior condyle. The purpose of this study is to evaluate the effect of the posterior condylar cartilage of varus osteoarthritic knee on rotational alignment of the femoral component in TKA. We established two different condylar twist angles (CTA) from intraoperative multiplanar reconstruction (MPR) images and intraoperative information of navigation system. The CTA measured by a navigation system that includes the cartilage (4.8±2.0°) was smaller than those measured by MPR images, which does not include the cartilage (6.6±2.1°) (p<0.05). The difference between these two angles that corresponds to the remaining posterior condylar cartilage was 1.7±1.2°. This result demonstrated that the posterior condylar cartilage might lead to over-rotational of the femoral component in varus osteoarthritic knee. Therefore, when determining rotational alignment of the femoral component, surgeons should consider the effect of the remaining posterior condylar cartilage to avoid the over-rotation of the femoral component, especially in severe varus knees. J. Med. Invest. 64: 24-29, February, 2016.