Polyethylene contact stresses, articular congruity, and knee alignment

Why Kinematic Alignment Makes Little Sense in Valgus Osteoarthritis of the Knee: A Narrative Review

There is a debate about the best alignment strategies in total knee arthroplasty (TKA). Mechanical alignment (MA) targets in combination with necessary soft tissue releases are the gold standard for TKA in end-stage valgus osteoarthritis. Some authors propagate kinematic alignment (KA) with the aim of restoring the patient's native alignment and minimizing the need for soft tissue releases. Our previous studies showed that MA with standardized soft tissue release produces reproducible results, and that the preoperative phenotype does not influence the results of patients with valgus osteoarthritis. These data suggest that there is no functional advantage to preserving valgus alignment in patients with valgus osteoarthritis. Many patients with valgus osteoarthritis present with a compromised medial collateral ligament and leaving the knee in valgus could increase the risk of secondary instability. The current literature supports MA TKA with soft tissue release as the gold standard. While using more sophisticated enabling technologies like robotic surgery might allow for aiming for very slight (1-2°) valgus alignment on the femoral side, any valgus alignment outside this range should be avoided. This review paper summarizes our current knowledge on the surgical techniques of TKA in patients with valgus osteoarthritis.

The influence of cross shear and contact pressure on the wear of UHMWPE-on-PEEK-OPTIMA™ for use in total knee replacement

PEEK-OPTIMA™ polymer is being considered as an alternative material to cobalt chrome in the femoral component of total knee arthroplasty to give a metal-free knee replacement system. Simple geometry pin-on-plate wear simulation can be used to systematically investigate and understand the wear of materials under many different conditions. The aim of this study was to investigate the wear of UHMWPE-on-PEEK-OPTIMA™ under a range of contact pressure (2.1-80 MPa) and cross-shear ratio (0-0.18) conditions. With increasing contact pressure, there was a trend of decreasing UHMWPE wear factor with a significant difference (p<0.001) in the wear factor of UHMWPE under the different contact pressure conditions of interest. Under uniaxial motion (cross-shear ratio = 0), the wear of UHMWPE was low, introducing multi-axial motion increased the wear of the UHMWPE. There was a significant difference (p<0.01) in the wear factor at different cross-shear ratios however, post hoc analysis showed only the study carried out under unidirectional motion to be significantly different from the other conditions. With varying contact pressure and cross-shear ratio, the wear of UHMWPE against PEEK-OPTIMA™ polymer showed similar trends to previous studies of UHMWPE-on-cobalt chrome.

Effects of Unrestricted Kinematically Aligned Total Knee Arthroplasty with a Modified Soft-Tissue Respecting Technique on the Deformity of Limb Alignment in Japanese Patients

Background and Objectives: Unrestricted kinematic alignment total knee arthroplasty (KA-TKA) with a soft-tissue respecting technique (STRT) is a soft-tissue-dependent tibial resection entailing the restoration of the original soft-tissue tension using ligamentotaxis after resurfacing the femur, based on the concept of restoring the native or pre-osteoarthritis alignment in each patient. However, there is no consensus on the indications of unrestricted KA-TKA with the STRT. We modified the STRT, followed by an investigation of the effects of surgery on the postoperative hip-knee-ankle angle (HKAA). Materials and Methods: We retrospectively analyzed the clinical background data, including the preoperative and postoperative HKAA, of 87 patients who underwent unrestricted KA-TKA with the modified STRT. Univariate and multivariate analyses were performed to determine the factors affecting the postoperative HKAA. A receiver operating characteristic (ROC) curve was plotted to investigate the change in the cut-off values of preoperative HKAA with respect to the safe zone of the postoperative HKAA. We generated two regression models, the linear regression model and generalized additive model (GAM) using machine learning, to predict the postoperative HKAA. Results: Univariate and multivariate analyses revealed the preoperative HKAA as the factor most relevant to the postoperative HKAA. ROC analysis revealed that the preoperative HKAA exhibited a high predictive utility, with a cut-off value of -10°, when the safe range of postoperative HKAA was set at ±5°. The GAM was the superior machine learning model, indicating a non-linear association between the preoperative and postoperative HKAA. Patients with preoperative HKAAs ranging from -18° to 4° were more likely to fall within the ±5° safe range of the postoperative HKAA. Conclusions: The preoperative HKAA influences the postoperative HKAA in unrestricted KA-TKA with the modified STRT. Machine learning using the GAM may contribute to the selection of patients eligible for the surgical approach.

Static Baropodometry for Assessing Short-Term Functional Outcome after Unilateral Total Knee Arthroplasty: Exploring Correlation between Static Plantar Pressure Measurements and Self-Reported Outcomes

This study aimed to investigate the association between objective baropodometric and radiological measurements and patient self-reported functional outcomes, assessed through the Knee Injury and Osteoarthritis Outcome Score (KOOS). Additionally, it sought to evaluate the effectiveness of static baropodometry in predicting short-term KOOS results following unilateral total knee arthroplasty (TKA). We conducted a prospective single-center study involving 32 patients who underwent unilateral TKA for knee osteoarthritis (KOA). Patients were evaluated both preoperatively and six months postoperatively, utilizing objective measurements derived from static baropodometric analysis in a normal, relaxed, bipedal standing position using a multi-platform Plantar Pressure Analysis System (PPAS) and radiographic measurements of the femorotibial angle (FTA) and subjective assessments through the national validated version of the KOOS. The study found an insignificant average correction of -0.69° ± 4.12° in the preoperative FTA at the sixth month after TKA. Moreover, there were no significant differences in the KOOS based on different types of knee alignment (KA) both pre- and postoperatively (p > 0.05). No significant correlations were observed between the KOOS, and total average affected and unaffected plantar pressures (TAAPP and TAUPP) pre- and postoperatively, as well as KA pre- and postoperatively. However, significant changes were observed in TAAPP and TAUPP measurements after unilateral TKA. TAAPP demonstrated a significant increase postoperatively (mean change (SD) = 18.60 (47.71); p = 0.035). In conclusion, this study found no significant correlation between KA, static baropodometric measurements, including pre- and postoperative differences, and KOOS outcomes. Therefore, static plantar pressure measurements alone might not serve as a reliable predictor of short-term clinical outcomes after unilateral TKA, as reported by patients.

Individual Phenotype Does Not Impact the Outcome of Mechanical Aligned Total Knee Arthroplasties for Valgus Osteoarthritis

Background and Objectives: There is an ongoing discussion about the best alignment targets in total knee arthroplasty (TKA). Mechanical alignment has been the standard in TKA for years. Alongside the development of various classification systems to describe the native alignment of the knee (knee phenotype), kinematic alignment restoring the individual phenotype of the knee has been advocated more recently. Alignment in TKA becomes even more challenging in knees with preoperative deformities such as valgus osteoarthritis. Materials and Methods: The study retrospectively evaluated 158 knees in 135 patients who underwent TKA with a mechanical alignment target for valgus osteoarthritis. Pre- and postoperative hip knee angle, lateral distal femur angle, and medial proximal tibial angle/tibial plate angle (pre-/postoperative) were measured on standing hip-to-ankle radiographs. Knees were grouped according to the coronal plane alignment of the knee (CPAK) classification. Preoperative and postoperative range of motion and patient-related outcome measures (WOMAC, UCLA, SF-12, pain) were assessed. Results: There was no difference in outcome for mechanically aligned TKA between the different CPAK phenotypes, suggesting that mechanical alignment is an appropriate target for the different phenotypes analyzed in the study. Remaining valgus alignment was associated with decreased postoperative UCLA scores and decreased improvement in SF-12 scores (p = 0.011/p = 0.028). Within CPAK III, mechanical aligned TKA showed better postoperative UCLA Scores than TKA with valgus alignment (p = 0.015). The individual knee phenotype in patients with valgus osteoarthritis did not influence the outcome of mechanical aligned TKA operated with standardized soft-tissue release.

Valgus alignment of the femoral component is associated with higher revision rates 10 years after TKA

PURPOSE

Appropriate positioning and alignment of tibial and femoral component in primary total knee arthroplasty (TKA) are factors of major importance directly related to patient satisfaction and implant survival. Most literature works elaborate on overall post-operative alignment and its correlation to implant survival. However, less is known about the impact of individual component alignment. The purpose of this study was to investigate the effect of undercorrection of overall alignment as well as the effect of individual tibial and femoral component alignment on the post-operative failure rate after total knee arthroplasty.

METHODS

Clinical and radiographic data of primary TKA cases from 2002 to 2004, with a minimum of 10-year follow-up, were retrospectively reviewed. The pre- and post-operative hip-knee-ankle angle (HKA), mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA) were measured on weight-bearing, full-length antero-posterior lower limb radiographs. Statistical analysis was performed to establish the correlation between both overall and implant alignment and revision rate.

RESULTS

In total, 379 primary TKA cases were evaluated. The mean time of follow-up was 12.9 years (range 10.3-15.9 years, SD = 1.8). Nine out of 379 cases were revised due to aseptic loosening; the mean time to revision was 5.5 years (range 1.0-15.5 years, SD = 4.6). Varus undercorrection of overall alignment was not associated with a higher rate of revision (p = 0.316). Post-operative valgus femoral alignment (mLDFA < 87°) contributed to a significant decreased prosthesis survival in contrast to neutral femoral alignment (revision rate valgus group: 10.7% and neutral group: 1.7%; p = 0.003). Post-operative tibial mechanical alignment was not identified as a significant predictor for implant survival (revision rate varus group: 2.9% and neutral group: 2.4%; p = 0.855).

CONCLUSIONS

Primary TKA showed significantly higher revision rates when the femoral component was placed in > 3° of valgus (mLDFA < 87°). In contrast, postoperative overall residual varus alignment (HKA) and varus alignment of the tibial component were not related to higher revision rates at a minimum 10-year follow-up after TKA. These findings should be considered when choosing component position in individualised TKA.

LEVEL OF EVIDENCE

III.

Validation of a Robotic Testbench for Evaluating Biomechanical Effects of Implant Rotation in Total Knee Arthroplasty on a Cadaveric Specimen

In this study, we developed and validated a robotic testbench to investigate the biomechanical compatibility of three total knee arthroplasty (TKA) configurations under different loading conditions, including varus-valgus and internal-external loading across defined flexion angles. The testbench captured force-torque data, position, and quaternion information of the knee joint. A cadaver study was conducted, encompassing a native knee joint assessment and successive TKA testing, featuring femoral component rotations at -5°, 0°, and +5° relative to the transepicondylar axis of the femur. The native knee showed enhanced stability in varus-valgus loading, with the +5° external rotation TKA displaying the smallest deviation, indicating biomechanical compatibility. The robotic testbench consistently demonstrated high precision across all loading conditions. The findings demonstrated that the TKA configuration with a +5° external rotation displayed the minimal mean deviation under internal-external loading, indicating superior joint stability. These results contribute meaningful understanding regarding the influence of different TKA configurations on knee joint biomechanics, potentially influencing surgical planning and implant positioning. We are making the collected dataset available for further biomechanical model development and plan to explore the 6 Degrees of Freedom (DOF) robotic platform for additional biomechanical analysis. This study highlights the versatility and usefulness of the robotic testbench as an instrumental tool for expanding our understanding of knee joint biomechanics.

Do Interlimb Knee Joint Loading Asymmetries Persist throughout Stance during Uphill Walking Following Total Knee Arthroplasty?

The purpose of this study was to determine differences in total (TCF), medial compartment (MCF), and lateral compartment (LCF) tibiofemoral joint compressive forces and related muscle forces between replaced and non-replaced limbs during level and uphill walking at an incline of 10°. A musculoskeletal modeling and simulation approach using static optimization was used to determine the muscle forces and TCF, MCF, and LCF for 25 patients with primary TKA. A statistical parametric mapping repeated-measures ANOVA was conducted on knee compressive forces and muscle forces using statistical parametric mapping. Greater TCF, MCF, and LCF values were observed throughout the loading response, mid-stance, and late stance during uphill walking. During level walking, knee extensor muscle forces were greater throughout the first 50% of the stance during level walking, yet greater during uphill walking during the last 50% of the stance. Conversely, knee flexor muscle forces were greater through the loading response and push-off phases of the stance. No between-limb differences were observed for compressive or muscle forces, suggesting that uphill walking may promote a more balanced loading of replaced and non-replaced limbs. Additionally, patients with TKA appear to rely on the hamstrings muscle group during the late stance for knee joint control, thus supporting uphill walking as an effective exercise modality to improve posterior chain muscle strength.

Current Concepts in Alignment in Total Knee Arthroplasty

BACKGROUND

In an effort to increase satisfaction among total knee arthroplasty (TKA) patients, emphasis has been placed on implant positioning and limb alignment. Traditionally, the aim for TKA has been to achieve a neutral mechanical alignment (MA) to maximize implant longevity. However, with the recent spike in interest in individualized alignment techniques and with the advent of new technologies, surgeons are slowly evolving away from classical MA.

METHODS

This review elucidates the differences in alignment techniques for TKA, describes the concept of knee phenotypes, summarizes comparative studies between MA and individualized alignment, and provides a simple way to incorporate the latter into surgeons' practice.

RESULTS

In order to manage patients by applying these strategies in day-to-day practice, a basic understanding of the aforementioned concepts is essential. Transition to an individualized alignment technique should be done gradually with caution in a stepwise approach.

CONCLUSION

Alignment and implant positioning are now at the heart of the debate and surgeons are investigating a more personalized approach to TKA.

Anatomical variations of the equine femur and tibia using statistical shape modeling

The objective of this study was to provide an overarching description of the inter-subject variability of the equine femur and tibia morphology using statistical shape modeling. Fifteen femora and fourteen tibiae were used for building the femur and tibia statistical shape models, respectively. Geometric variations in each mode were explained by biometrics measured on ±3 standard deviation instances generated by the shape models. Approximately 95% of shape variations within the population were described by 6 and 3 modes in the femur and tibia shape models, respectively. In the femur shape model, the first mode of variation was scaling, followed by notable variation in the femoral mechanical-anatomical angle and femoral neck angle in mode 2. Orientation of the femoral trochlear tubercle and femoral version angle were described in mode 3 and mode 4, respectively. In the tibia shape model, the main mode of variation was also scaling. In mode 2 and mode 3, the angles of the coronal tibial plateau and the medial and lateral caudal tibial slope were described, showing the lateral caudal tibial slope angle being significantly larger than the medial. The presented femur and tibia shape models with quantified biometrics, such as femoral version angle and posterior tibial slope, could serve as a baseline for future investigations on correlation between the equine stifle morphology and joint disorders due to altered biomechanics, as well as facilitate the development of novel surgical treatment and implant design. By generating instances matching patient-specific femorotibial joint anatomy with radiographs, the shape model could assist virtual surgical planning and provide clinicians with opportunities to practice on 3D printed models.

Joint awareness after fixed and mobile-bearing total knee arthroplasty with minimum 12 years of follow-up: A propensity matched-pair analysis

BACKGROUND

Many comparative articles studied mobile-bearing (MB) and fixed-bearing (FB) total knee arthroplasties (TKAs). Meta-analyses found no difference in survival or biomechanical outcome. This study aimed to compare long-term clinical results between fixed-bearing (FB) and mobile-bearing (MB) total knee arthroplasty (TKA) as well as patients' adaptation to their artificial joints.

METHOD

TKAs performed with the same surgical protocol divided into categories according to the insert design preferred. 70 MB design TKAs were compared with 70 FB design TKAs utilizing propensity matching for parameters; gender, age, body mass index, coronal plane deformity, range of motion (ROM) and appropriateness criteria. Forgotten Joint Score-12 (FJS-12) was used to assess patients' ability to forget their artificial joints in daily life.

RESULTS

Patients had a mean follow-up of 15.6 (±2.2) years. No difference was observed between groups for post-operative ROM, WOMAC, Knee Society Knee and Function Scores. The FJS-12 in the MB and FB groups were 66.1 and 72.8, respectively (P = 0.026). There was no significant difference in survival between both designs.

CONCLUSION

This study suggests that in TKA, joint awareness is higher in MB compared to FB design. FJS-12 appears to be a sensitive measuring tool when comparing two designs and should be implemented in long-term follow-up.

Mid-Term Clinical and Radiological Results at a Tertiary Care Hospital in Türkiye: Is Residual Varus Really Important After Mechanically-Aligned Total Knee Arthroplasty?

INTRODUCTION

 Traditionally, in total knee arthroplasty (TKA), it is aimed to keep the mechanical axis of the lower extremity neutral (mechanical alignment: 3° varus-valgus in the coronal plane) to improve long-term outcomes. This study aimed to assess the mid-term radiological and clinical results of patients with postoperative residual varus (more than 3° of varus) after mechanically-aligned TKA.

METHODS

A total of 616 individuals who had undergone TKA for primary knee osteoarthritis between 2008 and 2013 in our tertiary care hospital were retrospectively examined. All TKAs were performed with the mechanical alignment strategy. For radiological evaluation, hip-knee-ankle (HKA) angle, knee alignment angle (KAA), mechanical medial proximal tibial angle (mMPTA), knee inclination (KI), joint line orientation angle relative to ground (JLOA-G), posterior tibial slope (PS), joint line convergence angle (JLCA) were measured. Besides, patients' latest radiographs were screened for any clue of aseptic loosening or mechanical failure. Knee Society Score (KSS) (knee and functional subgroups), and Lysholm, Oxford, and Tegner scores were used for clinical evaluation. In addition, knee flexion and extension limitations were assessed.

RESULTS

After applying the exclusion criteria, a minimum of five-year follow-up result of 110 patients was demonstrated. There were 101 females (92%) and nine males (8%). The mean follow-up time was 65.8 ± 6.3 months (range: 60.8-75.8 years). The mean age was 65.9 ± 7.7 years (range: 39 to 89 years). The preoperative mean mechanical axis angle of the lower extremity was 17.3° ± 7.8° (range: 13.4-43.9°), whereas it was 8.3° ± 3.6° (range: 3.2-19.8°) postoperatively. The preoperative mean flexion angle was 90.7° ± 23.8° (range: 40-130°), and the extension limitation was -2.5° ± 7.4° (range: -40-0°), whereas, postoperatively, they were 102.8° ± 15.4° (range from 40° to 150°) and -3.7° ± 7.5° (range from -40° to 0°), respectively. The latest follow-up's mean KSS knee subgroup was 67 ± 18.4 (range: 12-93), the mean KSS functional subgroup was 74 ± 23.6 (range: 20-100), the mean Lysholm score was 81.7 ± 15.7 (range:25-100), the mean Tegner score was 3.65 ± 0.99 (range: 1-5), the mean Oxford score was 37.4 ± 6.5 (range: 9-48). There was no patient with aseptic loosening or mechanical failure.

CONCLUSIONS

In the mid-term follow-up of patients with residual varus after mechanically-aligned TKA, satisfactory clinical and radiological results were obtained without aseptic loosening or implant failure.

Correlation of short knee and full-length X-rays in evaluating coronal plane alignment in total knee arthroplasty

Background

Coronal alignment after total knee arthroplasty (TKA) would influence the implant survival. Coronal alignment could be measured on short and full-length X-rays. The goal of the current study was to assess the correlation of short and full-length X-rays to accurate prediction of the true Hip-Knee-Ankle alignment after TKA in the Iranian population.

Methods

Lateral distal femoral and medial proximal tibial angles, FTA, HKA, in 180 Iranian patients (243 knees without extra-articular deformities) were measured and compared on short and full-length standing X-rays of primary TKA pre/postoperatively.

Results

The correlation between the preoperative FTA-short and FTA-long, FTA-short and HKA, and FTA-long and HKA values in degrees were fair, good and good (r = 0.64) (r = 0.73), (r = 0.76), respectively. This correlation for postoperative aMPTA and mMPTA (r = 0.73), and FTA-short and HKA (r = 0.76) values were good and significant (P = 0.001). Also, assessing coronal alignment based on short and full-length measurements would result in varying pre/postoperative alignments (varus, neutral and valgus).

Conclusion

Full length X-rays could not be replaced by short knee X-rays to asses true coronal alignment in TKA; considerable portion of our cases were missorted as varus, neutral or valgus based on the FTA versus the HKA. Intraoperative fixed 5° valgus angle cut of distal femur did not result in postoperative favorable neutral alignment in all cases.

Level of evidence

IV.

Influence of the angle between tibial and prosthesis mechanical axes on tibial bone remodeling in total knee arthroplasty

Osteoarthritis of the knee is one of the most common diseases that affect the quality of life in the elderly population, and Total Knee Arthroplasty is considered the only real treatment for it, and as with any other surgery, a suboptimal technique may lead to an undesirable outcome. This paper aims to investigate the effects of the angle between mechanical axes of the tibia and the implant on the bone remodeling process. A 3D model was reconstructed using CT images, which was then used in an ABAQUS model with a USDFLD subroutine to simulate bone remodeling post TKA. The USDFLD subroutine compares the strain energy density from each increment to that of the previous increment to determine how the bone density will change. Simulation results suggest that when the prosthesis is inclined to one side, stress and density distribution increase, whereas stress and bone density decrease substantially on the opposite side. This decrease in bone density can be as much as 35% in the coronal plane. Sagittal malalignment results suggest that the effect would be relatively localized to the vicinity of the cutting plane. Results suggest uniform load distribution may be achieved when the two mechanical axes are kept parallel, which in turn can lead to decreased prosthesis loosening and bone fractures.

Knee biomechanics of patients with total knee replacement during downhill walking on different slopes

PURPOSE

The purpose of this study was to compare knee biomechanics of the replaced limb to the non-replaced limb of total knee replacement (TKR) patients and healthy controls during walking on level ground and on decline surfaces of 5°, 10°, and 15°.

METHODS

Twenty-five TKR patients and 10 healthy controls performed 5 walking trials on different decline slopes on a force platform and an instrumented ramp system. Two analyses of variance, 2 × 2 (limb × group) and 2 × 4 (limb × decline slope), were used to examine selected biomechanics variables.

RESULTS

The replaced limb of TKR patients had lower peak loading-response and push-off knee extension moment than the non-replaced and the matched limb of healthy controls. No differences were found in loading-response and push-off knee internal abduction moments among replaced, non-replaced, and matched limb of healthy controls. The knee flexion range of motion, peak loading-response vertical ground reaction force, and peak knee extension moment increased across all slope comparisons between 0° and 15° in both the replaced and non-replaced limb of TKR patients.

CONCLUSION

Downhill walking may not be appropriate to include in early stage rehabilitation exercise protocols for TKR patients.

Optimal Conformity Design of Tibial Insert Component Based on ISO Standard Wear Test Using Finite Element Analysis and Surrogate Model

Total knee replacement is a standard surgical treatment used to treat osteoarthritis in the knee. The implant is complicated, requiring expensive designs and testing as well as a surgical intervention. This research proposes a technique concerning the optimal conformity design of the symmetric polyethylene tibial insert component for fixed-bearing total knee arthroplasty. The Latin Hypercube Sampling (LHS) design of the experiment was used to create 30 cases of the varied tibial insert conformity that influenced the total knee replacement wear volume. The combination of finite element analysis and a surrogate model was performed to predict wear volume according to the standard of ISO-14243:2014 wear test and to determine the optimal conformity. In the first step, the results could predict wear volume between 5.50 to 72.92 mm3/106 cycle. The Kriging method of a surrogate model has then created the increased design based on the efficient global optimization (EGO) method with improving data 10 design points. The result revealed that the optimum design of tibial insert conformity in a coronal and sagittal plane was 0.70 and 0.59, respectively, with a minimizing wear volume of 3.07 mm3/106 cycle. The verification results revealed that the area surface scrape and wear volume are similar to those predicted by the experiment. The wear behavior on the tibial insert surface was asymmetry of both sides. From this study it can be concluded that the optimal conformity design of the tibial insert component can be by using a finite element and surrogate model combined with the design of conformity to the minimized wear volume.

Biomechanical Analysis of Non-Metallic Biomaterial in the Manufacture of a New Knee Prosthesis

The increase in the number of revision surgeries after a total knee replacement surgery reaches 19%. One of the reasons for the majority of revisions relates to the debris of the ultra-high molecular weight polyethylene that serves to facilitate the sliding between the femoral and tibial components. This paper addresses the biomechanical properties of ULTEM^TM 1010 in a totally new knee replacement design, based on one of the commercial models of the Stryker manufacturer. It is designed and produced through additive manufacturing that replaces the tibial component and the polyethylene in such a way as to reduce the pieces that are part of the prosthetic assembly to only two: the femoral and the tibial (the so-called “two-component knee prosthesis”). The cytotoxicity as well as the live/dead tests carried out on a series of biomaterials guarantee the best osteointegration of the studied material. The finite element simulation method guarantees the stability of the material before a load of 2000 N is applied in the bending angles 0°, 30°, 60°, 90°, and 120°. Thus, the non-metallic prosthetic material and approach represent a promising alternative for metal-allergic patients.

Tibial Mechanical Axis Is Nonorthogonal to the Floor in Varus Knee Alignment

Background

Classical models of the knee assume the joint line is parallel to the floor and the tibial mechanical axis (TMA) is orthogonal to the floor. Our study characterizes the angle subtended by the TMA and floor during bipedal stance, called the tibial axis orientation angle (TAOA), and tests the assumption that the TMA should be orthogonal to the floor.

Methods

We reviewed the nonoperative knee on full-length, standing radiographs in patients undergoing total knee arthroplasty between 2013 and 2017. Radiographic measurements were obtained for hip-knee-ankle axis, medial proximal tibial angle (MPTA), joint line orientation angle, and TAOA and correlated by regression analysis. The cohort was stratified by hip-knee-ankle axis alignment to determine statistical differences in knee angle values. Demographic data were collected to assess associations with knee angles.

Results

Our cohort included 68 patients, with 56% female and average age of 62.3 years. Varus knees comprised 56% of the cohort, with 7% neutral and 37% valgus. The cohort demonstrated an MPTA of 3.06°, TAOA of 2.67°, and joint line orientation angle of 0.36°. Varus knees had a higher MPTA (4.26°) and TAOA (4.74°) than valgus knees (P < .001). MPTA and TAOA were correlated on regression analysis (r² = 0.465), and all angles were statistically different between sexes.

Conclusion

The angle between the TMA and floor, called TAOA, is not orthogonal in normal knees, contrary to assumptions in classical biomechanics. Knee angles vary significantly between varus and valgus cohorts, and the distinction between these cohorts should be noted when evaluating normal joint line angles.

Spherical center axial hinge knee prosthesis causes lower contact stress on tibial insert and bushing compared with biaxial hinge knee prosthesis

BACKGROUND

Motion axial system may affect contact stress of hinge knee prosthesis. However, it is unclear which axial system provides the better biomechanical effect. Therefore, the aim of this study was to compare the contact stress and stress distribution on the tibial insert and the bushing of hinge knee prostheses with a biaxial (BA) system and a spherical center axial (SA) system during a gait cycle.

METHODS

Three-dimensional finite-element (FE) models of the prostheses with different motion systems were included. The comparisons between experimental tests and FE analyses were performed to verify the models. Dynamic implicit FE analyses were performed to investigate the peak contact stresses and stress distributions on the tibial insert and the bushing.

RESULTS

The peak contact stresses on the tibial insert and the bushing of the BA prosthesis were higher than those of the SA prosthesis during most gait cycles. The contact time on the bushing is short in the SA prosthesis. The stress distributions on the superior surface of the tibial insert in the BA prosthesis were at the posterior side, but of the SA prosthesis were not fixed.

CONCLUSION

The SA prosthesis has a lower peak contact stress on tibial insert and bushing than the BA prosthesis; in addition, the SA prosthesis has a 'self-adjustment' mechanism which could disperse high stress on the tibial insert to decrease the risk of wear and damage. The comparison could help designers and surgeons to better understand the future design of rotating hinge knee prostheses which should be able to achieve multiaxial motion and complete weight bearing by the tibial condylar to transmit the axial force better.

Comparative assessment of biomechanics induced by hinge knee prostheses with two different motion axial system

We aimed to evaluate the biomechanical contact characteristics of rotating hinge knee (RHK) prostheses with different motion axial systems. We performed finite element (FE) analyses to investigate and compare the peak contact stress and contact location on tibial insert and bushing during a gait cycle. The biaxial (BA) system and spherical center axial (SA) system RHK prostheses were included in this study. The comparisons between experimental tests and FE analyses were performed to verify the validation of FE models. Decreased ISO loadings were then applied to the validated FE models to investigate the peak contact stress and contact location on tibial insert and bushing. The contact areas obtained from experimental tests and FE analyses were in a good agreement. The peak contact stresses on tibial insert and bushing of BA prosthesis were higher than those of SA prosthesis. The contact locations on the superior surface of tibial insert in SA and BA prostheses were at the middle-posterior and posterior side, while those on the rotating axial surface were at the medial and lateral sides, respectively. This study indicate that the tibial insert and bushing of an SA prosthesis have lower peak contact stresses and better contact locations than those of a BA prosthesis during a gait cycle, which may decrease the risk of long-term complications of RHK prostheses. Future studies should be performed to confirm the relationship between the contact characteristics and wear in RHK prostheses.

The tibial cut influences the patellofemoral knee kinematics and pressure distribution in total knee arthroplasty with constitutional varus alignment

PURPOSE

The current literature suggests that kinematic total knee arthroplasty (kTKA) may be associated with better outcome scores in patients with constitutional varus alignment. The underlying patellofemoral kinematic changes (patella tilting and patella tracking) and patellofemoral pressure distribution have not yet been described. The present study compared the effects of different tibial cuts, as used in kTKA, on patellofemoral knee kinematics and the pressure distribution, in addition to comparisons with the natural constitutional varus knee.

METHODS

Seven cadaveric knee joints with constitutional varus alignment were examined in the native state and after 0°, 3°, or 6° tibial cut cruciate-retaining (CR)-TKA using an established knee joint simulator. The effects on patella rotation/patella tilting, patellofemoral pressure, and patellofemoral length ratios (= patella tracking) were determined. In addition, the natural knee joint and different tibial cuts in CR-TKA were compared (Student's t test).

RESULTS

In the patellofemoral joint, 6° CR-TKA was associated with the greatest similarity with the natural constitutional varus knee. By contrast, knees subjected to 0° CR-TKA exhibited the largest deviations of patellar kinematics. The smallest difference compared with the natural knee joint concerning patella tilting was found for 6° CR-TKA (mean 0.4°, p < 0.001), and the largest difference was noted for 0° CR-TKA (mean 1.7°, p < 0.001). Concerning patellofemoral pressure, 6° CR-TKA resulted in outcomes most similar to the natural knee joint, featuring a mean difference of 3 MPa. The largest difference from the natural knee joint was identified for 0° CR-TKA, with an average difference of 8.1 MPa (p < 0.001; total mean 17.7 MPa). Meanwhile, 3° and 6° CR-TKA induced medialization of the patella, with the latter inducing the largest medialization value of 4.5 mm at 90° flexion.

CONCLUSIONS

The improved outcome parameters in kTKA described in the literature could be attributable to the similar kinematics of the patellofemoral joint relative to the normal state. The current study confirmed the similar kinematics between the native constitutional varus knee joint and knee joints subjected to 3° or 6° CR-TKA (patellofemoral rotation/patella tilting and patella pressure). Conversely, there was pronounced medialization of the patella following 6° CR-TKA. Patella pressure and patella tilting are described in the literature as possible causes of anterior knee pain after TKA, whereas medialization of the patella, which is also influenced by other causes, might play a subordinate role.

LEVEL OF EVIDENCE

V, Biomechanical study.

Effect of the Extent of Release for Knee Balancing on Post-Operative Limb Coronal Alignment After Primary Total Knee Arthroplasty

Introduction

Outcomes and longevity of total knee arthroplasty (TKA) depend mainly on restoring knee function, through precise bony resection and appropriate soft tissue balancing. The current literature lacks evidence regarding the degree of radiographic change after intra-operative knee balancing. The purpose of our study was to assess the degree of change in coronal lower extremity alignment by comparing pre-operative to post-operative full-length radiographs (FLR) after quantifying the degree of intra-operative knee balancing and correlate patient-reported outcomes to the extent of balancing required.

Patients and Methods

One hundred and fifty-four patients undergoing primary TKA for varus knee osteoarthritis were included in the study. The performed soft tissue releases and bony adjustments to obtain a balanced TKA intra-operatively were prospectively documented and were grouped into minimal, moderate and extensive release groups. Hip-knee-ankle angle (HKA), anatomical femoral-tibial angle (FTA), condylar hip angle (CH), medial proximal tibial angle (MPTA) and condylar plateau angle (CPA) were measured on full-length radiographs both pre-operatively and post-operatively. Frequencies of the soft tissue releases and bony resections in addition to descriptive statistics of the measured angles on the radiographs were recorded. In addition, patient-reported outcome scores (PROMs) were compared between the grouped patients.

Results

Of those that were included in the study, 66 knees (42.9%) required minimal release to adequately balance the knee, while 70 (45.5%) required moderate release and 18 (11.7%) required extensive release. No statistically significant differences were found in change of alignment between the groups for all the measured angles. In addition, no difference in PROMs was seen between the groups both pre- and post-operatively.

Conclusion

Although we found no association between post-operative coronal alignment of a TKA and the degree of soft tissue release and bony resection, this likely represents the fact that a balanced TKA is dynamic and not dependent on change of single radiographic parameters. Patient-reported outcomes were not impacted by the extent of releases.

Clinical outcomes of kinematic alignment versus mechanical alignment in total knee arthroplasty: a systematic review

Although mechanical alignment (MA) has traditionally been considered the gold standard, the optimal alignment strategy for total knee arthroplasty (TKA) is still debated.

Kinematic alignment (KA) aims to restore native alignment by respecting the three axes of rotation of the knee and thereby producing knee motion more akin to the native knee.

Designer surgeon case series and case control studies have demonstrated excellent subjective and objective clinical outcomes as well as survivorship for KA TKA with up to 10 years follow up, but these results have not been reproduced in high-quality randomized clinical trials.

Gait analyses have demonstrated differences in parameters such as knee adduction, extension and external rotation moments, the relevance of which needs further evaluation.

Objective improvements in soft tissue balance using KA have not been shown to result in improvements in patient-reported outcomes measures.

Technologies that permit accurate reproduction of implant positioning and objective measurement of soft tissue balance, such as robotic-assisted TKA and compartmental pressure sensors, may play an important role in improving our understanding of the optimum alignment strategy and implant position.

Cite this article: EFORT Open Rev 2020;5:486-497. DOI: 10.1302/2058-5241.5.190093

The biomechanical effect of different posterior tibial slopes on the tibiofemoral joint after posterior-stabilized total knee arthroplasty

Background

Different posterior tibial slopes (PTS) after posterior-stabilized total knee arthroplasty (PS-TKA) may lead to different biomechanical characteristics of knee joint. This cadaveric study was designed to investigate the tibiofemoral kinematics and contact pressures after PS-TKA with different PTS.

Methods

Nine human cadaveric knee specimens were used for PS-TKA with the PTS of 3°, 6°, and 9°. The tibiofemoral kinematics and contact pressures were measured during knee flexion angle changing from 0 to 120° (with an increment of 10°) with an axial load of 1000 N at each angle.

Results

The root mean square (RMS) of the tibiofemoral contact area and the mean and peak contact pressures during knee flexion were 586.2 mm², 1.85 MPa, and 5.39 MPa before TKA and changed to 130.2 mm², 7.56 MPa, and 17.98 MPa after TKA, respectively. Larger contact area and smaller mean and peak contact pressures were found in the joints with the larger PTS after TKA. The RMS differences of femoral rotation before and after TKA were more than 9.9°. The posterior translation of the lateral condyle with larger PTS was more than that with smaller PTS, while overall, the RMS differences before and after TKA were more than 11.4 mm.

Conclusion

After TKA, the tibiofemoral contact area is reduced, and the contact pressure is increased greatly. Approximately 80% of the femoral rotation is lost, and only about 60% of the femoral translation of lateral condyle is recovered. TKA with larger PTS results in more posterior femoral translation, larger contact area, and smaller contact pressure, indicating that with caution, it may be beneficial to properly increase PTS for PS-TKA.

Angular limit for coronal joint deformity correction using intramedullary guidance in total knee arthroplasty. A pilot study

INTRODUCTION

Post-operative misalignment of the lower limb mechanical axis following total knee arthroplasty (TKA) is thought to be associated with clinical failure. In a balanced knee, a neutral global mechanical axis following the use of intra-medullary (IM) guidance does not necessarily imply a horizontal TKA joint line. Using femoral and tibial axes separately would be more accurate in evaluating TKA alignment. Thus, the aim of the study is to define a pre-operative mechanical tibial and/or femoral angle threshold value for post-operative optimal alignment correction using IM guides.

METHODS

This single-center prospective continuous pilot study included 50 patients treated with a TKA for primitive osteoarthritis. Femoral and tibial cuts were performed using intramedullary (IM) guide. Three angles were calculated and analyzed pre and post-operatively on standing antero-posterior views using long-leg radiographs: femorotibial angle (FTA), mechanical femoral angle (MFA), and mechanical tibial angle (MTA). Statistical analysis was performed for the whole sample and for the three following FTA subgroups; normo-axial, varus and valgus.

RESULTS

The pre-operative MTA is the only parameter for which a threshold value was observed; when pre-operative MTA exceeded the value of 94°, an optimal correction might not be obtained post-operatively.

DISCUSSION

Our results suggest that the bony correction obtained via IM guiding depends exclusively on the primary deformation of the tibia. In cases of a varus of more than 94°, the IM guide was found to yield sub-optimal corrections. Thus, other solutions need to be investigated.

Current evidence base for kinematic alignment

BACKGROUND

Kinematic alignment recently became an alternative alignment option for total knee arthroplasty (TKA). Beside previous studies assessing mechanical alignment in comparison to unintentional malalignment of TKA in terms of implant survival and clinical outcome, more and more studies have focused on the direct comparison of intentional kinematic alignment with mechanical alignment of the prosthesis. In the past 5 years the number of studies with respect to kinematic alignment has risen from 11 to 91 studies.

AIM

The aim of this review article is to give a narrative overview of the current literature in the debate concerning kinematic and mechanical alignment in TKA.

Influence of Congruency Design on the Contact Stress of a Novel Hinged Knee Prosthesis Using Finite Element Analysis

Objectives

To investigate the contact stress and the contact area o tibial inserts and bushings with respect to different congruency designs in a spherical center axis and rotating bearing hinge knee prosthesis under gait cycle loading conditions using finite element analysis.

Methods

Nine prostheses with different congruency (different degrees of tibiofemoral conformity and different distances between the spherical center and the bushing) designs were developed with the same femoral and tibial components. The models were transferred to finite element software. The peak contact stresses and contact areas on tibial inserts and bushings under the gait cycle loading conditions were investigated and compared.

Results

For tibial insert, the peak contact stress was the highest in the low conformity‐long group (61.4486 MPa), and it was 1.88 times higher than that in the group with the lowest stress (moderate conformity‐short group, 32.754 MPa). The contact area was the largest in the low conformity‐long group (420.485 mm²), and it was 1.19 times larger than that in the group with the smallest area (moderate conformity‐middle group, 352.332 mm²). For bushing, the peak contact stress was the highest in the high conformity‐long group (72.8093 MPa), and it was 3.21 times higher than that in the group with the lowest stress (high conformity‐short group, 22.6928 MPa). The contact area was the largest in the low conformity‐short group (2.41 mm²), and it was 2.27 times larger than that in the group with the smallest area (high conformity‐middle group, 1.063 mm²).

Conclusion

The results of our study showed that the congruency of the tibiofemoral surface and bushing surface should be considered carefully in the design of the spherical center axis and rotating bearing hinge knee prosthesis. Different levels of contact performance were observed with different congruency designs. In addition, the influence of contact stress and contact area on the polyethylene wear of rotating hinge knee prostheses should be confirmed with additional laboratory tests.

Computational wear prediction of insert conformity and material on mobile-bearing unicompartmental knee arthroplasty

Objectives

Unicompartmental knee arthroplasty (UKA) is an alternative to total knee arthroplasty with isolated medial or lateral compartment osteoarthritis. However, polyethylene wear can significantly reduce the lifespan of UKA. Different bearing designs and materials for UKA have been developed to change the rate of polyethylene wear. Therefore, the objective of this study is to investigate the effect of insert conformity and material on the predicted wear in mobile-bearing UKA using a previously developed computational wear method.

Methods

Two different designs were tested with the same femoral component under identical kinematic input: anatomy mimetic design (AMD) and conforming design inserts with different conformity levels. The insert materials were standard or crosslinked ultra-high-molecular-weight polyethylene (UHMWPE). We evaluated the contact pressure, contact area, wear rate, wear depth, and volumetric wear under gait cycle loading conditions.

Results

Conforming design inserts had the lower contact pressure and larger contact area. However, they also had the higher wear rate and volumetric wear. The improved wear performance was found with AMD inserts. In addition, the computationally predicted volumetric wear of crosslinked UHMWPE inserts was less than half that of standard UHMWPE inserts.

Conclusion

Our results showed that increasing conformity may not be the sole predictor of wear performance; highly crosslinked mobile-bearing polyethylene inserts can also provide improvement in wear performance. These results provide improvements in design and materials to reduce wear in mobile-bearing UKA.

Cite this article: Bone Joint Res 2019;8:563–569.

Flexion gap stabilization by oversizing posterior condylar offset in deep-dished total knee replacement does not compromise flexion: A single-surgeon, retrospective, observational, mid-term series

INTRODUCTION

In total knee replacement surgery, medio-lateral knee balancing is recognized as the key to achieving satisfactory functional results. But it may not be enough to stabilize the flexion gap using deep-dished implants. We achieved flexion gap balance by oversizing the femoral component, thus increasing the posterior condylar offset (PCO). The purpose of this study was to describe the applicability of this technique and to test whether it produced adverse effects on medium-term outcomes. We hypothesized that it would not compromise the results if used properly. We therefore asked: (1) at how many cases of flexion gap balance would require oversizing the femoral component; (2) if femoral components oversizing would modify the mid-term results as per forgotten joint score (FJS) scores and whether flexion gain would be comparable to patients in whom it was not increased.

MATERIALS AND METHODS

Ninety-four patients (120 knees) were operated between September 2009 and 2011 (age 68±9 years) using the cementless Hyperflex version of the Natural Knees (Zimmer, Warsaw, IN, USA). Postero stabilization was achieved using deep-dished inserts. The Gender configuration has provided narrow inserts to better adapt the female anatomy. A special navigation system measured the displacement of the lateral and medial femoro-tibial contact points with infra-millimetric precision. Adopting a tibial cut first, gap-balancing technique with anterior referencing, the decision to oversize the femoral component relied on the 90° flexion drawer test, which showed more than 6mm sagittal laxity before the femoral bone cuts. Eighty-one (105 knees) patients were reviewed with average 63±27-month follow-up.

RESULTS

Femoral components were augmented by 1 size in 60 cases and by 2 sizes in 7 cases. At final review, knees with an oversized femoral component (60) achieved the same results as those implanted with a non-oversized femoral component (n=45) in terms of mean flexion gain (-5°±34 versus -4°±23, p=0.78), mean FJS (63±26 versus 61±23; p=0.56).

CONCLUSION

Balancing the Flexion gap by oversizing the femoral component did not compromise flexion range and functional results.

LEVEL OF EVIDENCE

IV, Retrospective cohort study.

Minimal under-correction gives better outcomes following total knee arthroplasty in severe varus knees-myth or reality?-analysis of one hundred sixty two knees with varus greater than fifteen degrees

PURPOSE OF THE STUDY

To document and compare the functional outcome of neutral alignment and under-correction after total knee arthroplasty (TKA) in severe varus knees of more than 15° at three and 12 months post-surgery.

MATERIALS AND METHODS

One hundred twenty-four consecutive patients (163 TKAs) of an average age of 61.9 years (52-79) with a pre-operative varus more than 15° were managed with jig-based TKA. Based on the post-operative mechanical femorotibial alignment (FTMA), they were categorised into three groups, namely neutral (180 + 3^°), mild varus (173° to 176°) and severe varus (172° and below). The outcomes of these three groups were assessed at three and 12 months by the Oxford knee score and the WOMAC score were calculated and co-related to the extent of correction.

RESULTS

At three months, knees in the mild varus group (n = 88) had the best results with an Oxford knee score of 41.76 + 1.44 and a WOMAC score of 19.29 + 2.93 compared to the severe varus group and the neutral alignment group which had Oxford knee scores (OKS) of 37.43 + 2.51 and 31.91 + 3.51 and WOMAC scores of 22.57 + 1.51 and 24.46 + 4.15 respectively. However at 12 months, knees in all the groups (neutral, mild varus, severe varus) had similar good functional outcomes with OKS of 39.08 + 1.68, 39.24 + 1.88, 39.29 + 1.11 and WOMAC scores of 17.42 + 2.15, 16.48 + 2.11, 16.14 + 1.21 respectively. A scatter plot done for post-operative FTMA and the functional outcome score for both scores showed a bell curve with the best outcome corresponding to a FTMA of 175° at 3 months and equal distribution for both scores at 12 months.

CONCLUSION

The results of our study showed that minimal under-correction gave superior functional outcomes at three months. But this advantage was temporary and both, under-correction and neutral alignment achieved equally good outcomes at one year. Considering the increased prosthesis longevity associated with neutral alignment, we propose that neutral alignment must be aimed for during TKA for knees with severe varus.

STUDY DESIGN

Prospective study.

Under-corrected knees do not fail more than aligned knees at 8 years in fixed severe valgus total knee replacement

PURPOSES

A fixed severe valgus knee is a surgical challenge. A safe post-operative Hip-Knee-Ankle angle (HKA) range of 180° ± 4 was recommended, but recent studies mentioned equal results from outliers of this range. Nevertheless, no distinction was made between varus and valgus knees, as well as over-corrected or under-corrected knees. Did post-operative nonaligned total knee replacements (TKR) from fixed severe valgus knees behave differently from the properly aligned population? Did over-corrected knees behave differently from under-corrected knees?

METHODS

Through a multi-center retrospective cohort study, we provided 557 knees of at least 10° of minimal pre-operative valgus; in this population 75 presented a post-operative Hip-Knee-Ankle angle (HKA) outside of the 180° ± 4 range; 23 of them had at least 5° of varus; 52 of them had at least 5° of valgus. Median pre-operative HKA of the entire cohort was 194° (range 190-198). Median follow-up was 8 years (range 5-11); Knee Society Score (KSS) results, HKA, Femoral and Tibial Mechanical Angles (FMA, TMA) and complication rates were obtained. The outlier group (HKA ≤ 175 or ≥ 185) was compared to the control group (HKA 180 ± 4); over-corrected (HKA ≤ 175) and under-corrected (HKA ≥ 185) sub-groups were individually tested against the control group.

RESULTS

The outlier group had a lower Final Knee Score than the aligned group (p = 0.023). In the over-corrected sub-group, median post-operative FMA was 88° (SD 4°) and median TMA was 87° (SD 4°). The complication rate was higher (p = 0.019). Knee (p = 0.018), Function (p = 0.034) and Final Knee Scores (p = 0.03) were statistically lower than in the control group. In the under-corrected sub-group, mean post-operative FMA was 93° (SD 2°) and mean TMA was 91° (SD 2°). The complication rate was lower (p = 0.019) and there was no difference with the control group concerning KSS.

CONCLUSIONS

In case of pre-operative fixed severe valgus knee, one should avoid over-correcting HKA angle and especially the TMA. Over-correction of a severe preoperative valgus in a post-operative varus was prejudicial for TKA survival. Keeping a severe valgus knee in low valgus to avoid using a more constrained implant and/or ligament releases will not decrease the 5-10 year implant survival and functional scores.

LEVEL OF EVIDENCE

Level IV-Case series.

A randomized prospective study comparing mobile-bearing against fixed-bearing PFC Sigma cruciate-retaining total knee arthroplasties with ten-year minimum follow-up

AIMS

This study compares the PFC total knee arthroplasty (TKA) system in a prospective randomized control trial (RCT) of the mobile-bearing rotating-platform (RP) TKA against the fixed-bearing (FB) TKA. This is the largest RCT with the longest follow-up where cruciate-retaining PFC total knee arthroplasties are compared in a non-bilateral TKA study.

PATIENTS AND METHODS

A total of 167 patients (190 knees with 23 bilateral cases), were recruited prospectively and randomly assigned, with 91 knees receiving the RP and 99 knees receiving FB. The mean age was 65.5 years (48 to 82), the mean body mass index (BMI) was 29.7 kg/m² (20 to 52) and 73 patients were female. The Knee Society Score (KSS), Knee Society Functional Score (KSFS), Oxford Knee Score (OKS), Western Ontario and McMaster Universities Arthritis Index (WOMAC), and 12-Item Short-Form Health Survey Physical and Mental Component Scores (SF-12 PCS, SF-12 MCS) were gathered and recorded preoperatively, at five-years' follow-up, and at ten years' follow-up. Additionally, Knee Injury and Osteoarthritis Outcome Scores (KOOS) were collected at five- and ten-year follow-ups. The prevalence of radiolucent lines (RL) on radiographs and implant survival were recorded at five- and ten-year follow-ups.

RESULTS

At the ten-year follow-up, the RP group (n = 39) had a statistically significant superior score in the OKS (p = 0.001), WOMAC (p = 0.023), SF-12 PCS (p = 0.019), KOOS Activities of Daily Living (ADL) (p = 0.010), and KOOS Sport and Recreation (Sport/Rec) (p = 0.006) compared with the FB group (n = 46). The OKS, SF-12 PCS, and KOOS Sport/Rec at ten years had mean scores above the minimal clinically important difference (MCID) threshold. There was no significant difference in prevalence of radiolucency between groups at five-years' follow-up (p = 0.449), nor at ten-years' follow-up (p = 0.08). Implant survival rate at 14 years postoperative was 95.2 (95% CI 90.7 to 99.8) and 94.7 (95% CI 86.8 to 100.0) for the RP and FB TKAs, respectively.

CONCLUSION

At ten-year follow-up, the mobile-bearing knee joint arthroplasty had statistically and clinically relevant superior OKS, SF-12 PCS, and KOOS (Sport/Rec) than the fixed-bearing platform. No difference was seen in prevalence of radiolucent lines. There was a greater than 94% implant survival rate for both cohorts at 14 years. Cite this article: Bone Joint J 2018;100-B:1336-44.

Influence of the post-operative axis on the clinical results of total knee replacement for severe varus deformities: does a slight residual varus improve the results?

PURPOSE

Some recent articles have suggested that in the case of large varus deformity, it may be advantageous to leave some residual post-operative varus as a means of improving functional outcome. The objective of this study is to compare the results of total knee replacement (TKR) performed for significant varus deformity (HKA < 170°) where there is a residual post-operative varus (HKA < 180°) to the results of TKR for significant varus deformity with either neutral post-operative (HKA = 180°) or mild valgus post-operative alignment (HKA > 180°).

METHODS

This series was made up of 208 knees. The mean pre-operative HKA angle was 166 ± 3° (154-169°), of which 150 were followed up for a mean 8.5 years (58 lost to follow-up). Based on post-operative radiographs, two groups were formed: group 1 (88 knees) in which post-operative alignment was 177.8 ± 1° (175-179°) and group 2 (62 knees) in which post-operative alignment was 181 ± 1° (180-184°).

RESULTS

The mean international knee society (IKS) score for group 1 was 178.8 ± 22 points (113-200) and 181.7 ± 22 points (95-200) for group 2. Oxford knee score was 20.4 ± 9 points (12-45) in group 1 and 19.2 ± 9 (12-50) in group 2. The results were slightly better in group 2 (in slight valgus) but this difference was not statistically significant (p = 0.44 and 0.4).

CONCLUSION

The results of knee replacement performed for severe varus deformity are not adversely affected by post-operative valgus alignment. There is in fact a trend towards superior results for neutral or valgus alignment than slight residual varus, but this difference was not statistically significant.

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

Background

Individualized 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.

Methods

Using 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.

Results

The 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.

Conclusion

Finite 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.

Neutral alignment leads to higher knee society scores after total knee arthroplasty in preoperatively non-varus patients: a prospective clinical study using 3D-CT

PURPOSE

The optimal coronal alignment is still under debate. However, in most of the studies, alignment was only assessed using radiographs, which are not accurate enough for assessment of tibial and femoral TKA position. The primary purpose of this study was to assess the relationship between coronal TKA alignment using 3D-reconstructed CTs and clinical outcome in patients with preoperative varus in comparison with patients with natural or valgus deformity. It was the hypothesis that neutral limb alignment shows a better outcome after TKA.

METHODS

Prospectively collected data of 38 patients were included. The clinical and radiological follow-up was 24 months. The patients were grouped into two groups with regard to their preoperative limb alignment. Group A (varus) consisted of 21 patients with preoperative varus of 3° or more, while group B (non-varus) consisted of 17 patients with neutral (- 3 < 0 > + 3) or valgus alignment (> + 3). For assessment of TKA component position and orientation, 3D-reconstructed CT was used. The measurements of the deviation from the whole limb mechanical axis (HKA angle) and the joint line alignment in the femoral (mLDFA) and the tibial side (MPTA) were assessed in the preoperative leg as well as during follow-up after TKA. For clinical outcome assessment, the Knee Society Score (KSS) was used at 1 and 2 years postoperatively. Correlation between KSS score and each variable was done using a linear and quadratic regression model (p < 0.05).

RESULTS

The mean postoperative HKA angle was - 1.3 (varus) in the varus group and + 1.4 (valgus) in the non-varus group. Overall, significant correlations between the preoperative and postoperative alignments were found. In the preoperatively non-varus group, a highly significant correlation was found between neutral limb alignment (HKA = 0° ± 3°) and higher KSS (r ² = 0.74, p = 0.00). In the varus group, no correlation was found between the postoperative whole limb alignment and the components' position in the coronal plane to KSS score.

CONCLUSION

A significant correlation was found between neutral limb alignment and higher KSS only in patients with preoperative non-varus alignment. The concept of constitutional varus alignment is still under debate. Moreover, it appears that one should aim for a more individualized, alignment target based on the individual knee morphotype.

LEVEL OF EVIDENCE

Diagnostic study, Level II.

Is Immediate Postoperative Mechanical Axis Associated with the Revision Rate of Primary Total Knee Arthroplasty? A 10-Year Follow-up Study

Background

Achieving neutral limb alignment during total knee arthroplasty (TKA) has been considered an important determinant in the long-term prosthesis survival. The purpose of this study was to evaluate the association between the immediate postoperative mechanical alignment of the lower limb and the rate of revision TKA by comparing an acceptable mechanical axis group (within ± 3° from neutral alignment) and an outlier group (> 3° deviation from neutral alignment).

Methods

Between 2000 and 2006, clinical and radiographic data of 334 primary TKAs were retrospectively reviewed to determine the 10-year Kaplan-Meier survival rate. Patients were divided into acceptable and outlier groups according to the mechanical axis checked postoperatively within a month. Clinical outcomes were assessed using Hospital for Special Surgery, Knee Society Score, and Western Ontario and McMaster Universities Osteoarthritis Index score preoperatively and at the final follow-up. Postoperative complications and revision rates were also evaluated.

Results

The mean change in mechanical axis between the immediate postoperative examination and the last follow-up was greater in the outlier group (1.6 ± 2.7) than in the acceptable group (0.8 ± 2.4). The revision rates were significantly different between the two groups (p = 0.04). At the last follow-up, clinical scores were all improved in both groups compared to each preoperative condition. There were no significant differences in clinical scores between the two groups at the last follow-up. The 10-year Kaplan-Meier survival analysis showed a tendency towards better survival with restoration of neutral mechanical axis. However, the difference was not statistically significant (p = 0.25).

Conclusions

Restoration of neutral limb alignment is a factor that can result in a lower revision rate and higher longevity in TKA. However, there were no significant differences in clinical outcomes between the two groups.

Is there a relationship between the load distribution on the tibial plateau and hip knee ankle angle after TKA?

INTRODUCTION

This study asked whether differences in coronal alignment after total knee arthroplasty (TKA) affect the load distribution on the tibial plateau. The aim of this study was to investigate the correlation between coronal alignment and the load distribution on the tibial plateau after TKA, using three-dimensional multi-detector-row-computed tomography (3D-MDCT).

MATERIALS AND METHODS

In this study, we performed 84 cementless TKA with porous tantalum modular tibial component (PTMT) and divided into three groups based on post-operative hip-knee-ankle (HKA) angle: varus alignment group (n = 22), (176° ≧) neutral alignment group (n = 45), (180° ± 3°), and valgus alignment group (n = 17) (184° ≦).The changes in bone quality parameters of trabecular patterns under peg of PTMT were interpreted as load distribution due to changes in alignment. The relationship between HKA angle and load distribution on the tibial plateau was analyzed every 6 months for 4.5 years by measuring Bone marrow contents/tissue volumes (mg/cm³) and bone volumes/tissue volumes (%) under peg of porous tantalum modular tibial component by visualizing three dimensionally with 3D-osteo-morphometry software.

RESULTS

There were no correlations between HKA angle and the load distribution on the tibial plateau after TKA at all periods. There was a significantly higher increase in the medial region than the lateral about the BMC/TV and BV/TV values, regardless of the post-operative alignment after TKA for all periods. The relative BMC/TV and BV/TV changes at medial region in varus alignment group were significantly lower than the neutral and the valgus alignment groups of pre-operative medial osteoarthritis of the knee.

CONCLUSIONS

As far, it can be concluded by the study and the methods used therein that there were no relationships between the load distribution on the tibial plateau and HKA angle after TKA.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

Extra-articular deformities in arthritic knees-a grueling challenge for arthroplasty surgeons: An evidence-based update

Critical to the success of a total knee arthroplasty (TKA) is the anatomical alignment. This may appear as a challenge in an extra-articular deformity (EAD) that may be inherent in certain people or result from fracture malunion, congenital disorders, nutritional, metabolic and infective causes. This appraisal aimed at providing the reader with an up-todate overview of the research carried out on, and existent evidence of EAD correction while planning a TKA. We reviewed the current English literature on TKA in extra-articular knee deformities. Among the published data, a common initial approach of mandatory clinical and radiological assessment emerges as an obligatory step while handling cases with EAD. While several methods of managing the deformity and arthritis have been described, a broad division into intra-articular and extra-articular means can be deciphered. The relatively old-school, yet reliable thought process of extra-articular correction allows an all-inclusive restoration of alignment with the inherent complications related to the necessary osteotomy. A cohort of younger and more venturesome surgeons seem inclined towards performing navigated, intra-articular correction for mild to moderate and sometimes, severe deformities. The crux of the matter lies is obtaining a well-balanced knee without violating the all-important cruciates. Restoring the patient’s ambulatory status seems sooner with the intra-articular methods which are also more precise in determining the axes and while removing minimum bone. Greatest satisfaction is accomplished in those with less grotesque, rotationallyaligned knees while meticulously balancing soft-tissues and encouraging earlier weightbearing.

Physiological joint line total knee arthroplasty designs are especially sensitive to rotational placement - A finite element analysis

Mechanical and kinematical aligning techniques are the usual positioning methods during total knee arthroplasty. However, alteration of the physiological joint line and unbalanced medio-lateral load distribution are considered disadvantages in the mechanical and kinematical techniques, respectively. The aim of this study was to analyse the influence of the joint line on the strain and stress distributions in an implanted knee and their sensitivity to rotational mal-alignment. Finite element calculations were conducted to analyse the stresses in the PE-Inlay and the mechanical strains at the bone side of the tibia component-tibia bone interface during normal positioning of the components and internal and external mal-rotation of the tibial component. Two designs were included, a horizontal and a physiological implant. The loading conditions are based on internal knee joint loads during walking. A medialization of the stresses on the PE-Inlay was observed in the physiological implant in a normal position, accompanied by higher stresses in the mal-rotated positions. Within the tibia component-tibia bone interface, similar strain distributions were observed in both implant geometries in the normal position. However, a medialization of the strains was observed in the physiological implant in both mal-rotated conditions with greater bone volume affected by higher strains. Although evident changes due to mal-rotation were observed, the stresses do not suggest a local plastic deformation of the PE-Inlay. The strains values within most of the tibia component-tibia bone interface were in the physiological strain zone and no significant bone changes would be expected. The physiological cut on the articular aspect showed no detrimental effect compared to the horizontal implant.

Patient Variation Limits Use of Fixed References for Femoral Rotation Component Alignment in Total Knee Arthroplasty

BACKGROUND

Optimal rotational alignment of the femoral component is a common goal during total knee arthroplasty. The posterior condylar axis (PCA) is thought to be the most reproducible reference in surgery, while the transepicondylar axis (TEA) seems to better approximate the native kinematic flexion axis. This study sought to determine if rules based on patient gender or coronal alignment could allow reliable reproduction of the TEA from the PCA.

METHODS

Three-dimensional models based on preoperative computed tomography were made representing a patient's arthritic knee joint. The landmarks were defined and angular relationships determined.

RESULTS

The population group of 726 patients contained large anatomic variation. When applying the standard reference rule of 3° external rotation from the PCA, 36.9% of patients would have a rotational target greater than ±2° from their TEA. When applying the mean external rotation of the TEA from the PCA (1.85°) from this population, this proportion dropped to 26.0% of patients. The use of statistically significant gender and coronal alignment relationships to define the femoral rotation did not reduce the proportion of patients in ±2° error.

CONCLUSION

This study shows that gender and coronal alignment relationships to the TEA to PCA angle are not clinically significant as a quarter of patients would still have a target for rotation greater than ±2° from the TEA using these relationships. Superior tools for orienting rotational cuts directly to the TEA in surgery or preoperative identification of relevant patient-specific angles might capture the proportion of patients for whom standard reference angles are not appropriate.

No correlation between coronal alignment of total knee arthroplasty and clinical outcomes: a prospective clinical study using 3D-CT

PURPOSE

The aim of this study was to evaluate femoral and tibial as well as whole leg coronal TKA alignment using 3D-reconstructed CTs and to assess the relationship of coronal TKA alignment and clinical outcome in a large prospective series of patients. It was hypothesized that a coronal deviation of TKA position and leg alignment from the mechanical axis is correlated with poorer patients' outcome after TKA.

METHODS

A total of 81 consecutive patients who underwent primary TKA were prospectively included. The patient's demographics such as age, gender and time from primary TKA were noted. All patients underwent clinical and radiological examination including standardized radiographs (anteroposterior and lateral weight-bearing, patellar skyline view) and CT as part of their postoperative follow-up. For assessment of TKA component position and orientation 3D-reconstructed CT was used. For clinical outcome scoring the Knee Society Score (KSS) was used at 1 and 2 years postoperatively. Linear and quadratic regression models were used to test for correlations between alignment variables and KSS (p < .05).

RESULTS

The mean Knee Society Score was 181 ± 28 (range 52-200) 2 years postoperatively, while 78% of the patients were completely pain free and 22% had some persisting pain interfering with their daily activities. The mean mechanical whole limb alignment (HKA angle), femoral component alignment and tibial component alignment were 0°, 0.1° and -0.7°, respectively. The component position parameters, as well as the whole limb alignment measurements, did not show any statistically significant correlation with the KSS, after 1 and 2 years postoperatively.

CONCLUSION

In this prospective study, using 3D-CT to measure the component position, the postoperative outcome was not influenced by coronal TKA component position as well as the whole leg alignment. The findings challenge the current target of neutral coronal alignment and point towards a more individualized mechanical alignment target.

LEVEL OF EVIDENCE

Prognostic study, Level I.

Polyethylene Damage Increases With Varus Implant Alignment in Posterior-stabilized and Constrained Condylar Knee Arthroplasty

BACKGROUND

Implant malalignment in primary TKA has been reported to increase stresses placed on the bearing surfaces of implant components. We used a longitudinally maintained registry coupled with an implant retrieval program to consider whether preoperative, postoperative, or prerevision malalignment was associated with increased risk of revision surgery after TKA.

QUESTIONS/PURPOSES

(1) What is the relative polyethylene damage on medial and lateral compartments of the tibial plateaus from revised TKAs? (2) Does coronal TKA alignment affect implant performance, such that TKAs aligned in varus are predisposed to experience increased polyethylene damage? (3) Does TKA alignment differ between postoperative and prerevision radiographs, and if so, what does this difference suggest about the mechanical contact load placed on a knee with a TKA?

METHODS

Between 2007 and 2012, we performed 18,065 primary TKAs at our institution. By March 2016, 178 of those TKAs (1%) were revised at our center at least 2 years after primary surgery at our institution. Eighteen of those TKAs were excluded from this analysis because the tibial insert was not explanted during revision surgery, and four more were excluded because the inserts were lost or returned to the patient before the study was initiated, leaving 156 retrieved polyethylene tibial inserts (in 153 patients) revised at greater than 2 years after the primary TKA for this retrospective study. Patients who underwent revision surgery elsewhere were not considered here, since this study depended on having retrieved components. Polyethylene damage modes of burnishing, pitting, scratching, delamination, surface deformation, abrasion, and third-body debris were subjectively graded on a scale of 0 to 3 to reflect the extent and severity of each damage mode. On preoperative, postoperative, and prerevision radiographs, overall alignment, femoral alignment, and tibial alignment in the coronal plane were measured according to the protocol recommended by the Knee Society.

RESULTS

Knees with more overall varus alignment after TKA had increased total damage on the retrieved tibial inserts (Spearman's rank correlation coefficients of -0.3 [95% CI, -0.4 to -0.1; p = 0.001]). We also found revised TKAs tended to drift back into greater varus before revision surgery, with a mean (SD) of 3.6° ± 4.0° valgus for postoperative alignment compared with 1.7° ± 6.4° prerevision (p = 0.04).

CONCLUSIONS

Despite surgical efforts to achieve neutral mechanical alignment, remaining varus alignment places an increased contact load on the polyethylene articular surfaces. The drift toward further varus alignment postoperatively is consistent with the knee adduction moment remaining high after surgery.

CLINICAL RELEVANCE

While we found a predisposition toward recurrence of the preoperative varus deformity, we did not find increased medial as opposed to lateral polyethylene damage, which may be explained by the curve-on-curve toroidal design of the articulating surfaces of the TKA implants in this study.

Customized surface-guided knee implant: Contact analysis and experimental test

Contact pressure and stresses on the articulating surface of the tibial component of a total knee replacement are directly related to the joint contact forces and the contact area. These stresses can result in wear and fatigue damage of the ultra-high-molecular-weight polyethylene. Therefore, conducting stress analysis on a newly designed surface-guided knee implant is necessary to evaluate the design with respect to the polyethylene wear. Finite element modeling is used to analyze the design’s performance in level walking, stair ascending and squatting. Two different constitutive material models have been used for the tibia component to evaluate the effect of material properties on the stress distribution. The contact pressure results of the finite element analysis are compared with the results of contact pressure using pressure-sensitive film tests. In both analyses, the average contact pressure remains below the material limits of ultra-high-molecular-weight polyethylene insert. The peak von Mises stresses in 90° of flexion and 120° of flexion (squatting) are 16.28 and 29.55 MPa, respectively. All the peak stresses are less than the fatigue failure limit of ultra-high-molecular-weight polyethylene which is 32 MPa. The average contact pressure during 90° and 120° of flexion in squatting are 5.51 and 5.46 MPa according to finite element analysis and 5.67 and 8.14 MPa according to pressure-sensitive film experiment. Surface-guided knee implants are aimed to resolve the limitations in activities of daily living after total knee replacement by providing close to normal kinematics. The proposed knee implant model provides patterns of motion much closer to the natural target, especially as the knee flexes to higher degrees during squatting.

Extramedullary Tibial Bone Cutting Using Medial Cortical Line in Total Knee Arthroplasty

Purpose

This study aims to identify the effectiveness of the medial cortical line for attaining a more accurate tibial component alignment in proximal tibial resection using an extramedullary alignment rod.

Materials and Methods

The study examined 100 cases of total knee arthroplasty performed from December 2013 to February 2014 in a retrospective manner. On a preoperative anteroposterior (AP) radiograph of the entire tibia, we identified the medial cortical line that runs parallel to the tibial anatomical axis and passes the medial tibial spine, and measured the point where the medial cortical line crosses between the medial malleolus and the lateral malleolus in the ankle joint.

Results

The preoperative AP radiograph of the tibia showed the medial cortical line passing the point 40.4%±0.8% medial to the distance from the medial malleolus to the lateral malleolus including the skin thickness in the ankle joint. When the proximal tibial resection was performed with the extramedullary tibial cutting guide aligned with the medial cortical line, the tibial component angle averaged 0.7°±0.3° varus and the alignment accuracy of the tibial component within 0°±3° varus amounted to 97.0%.

Conclusions

The use of the medial cortical line in proximal tibial resection with an extramedullary tibial cutting guide allowed for relatively accurate alignment of the tibial component.