Biomechanical effects of fixed-bearing femoral prostheses with different coronal positions in medial unicompartmental knee arthroplasty

[Biomechanical effects of medial and lateral translation deviations of femoral components in unicompartmental knee arthroplasty on tibial prosthesis fixation]

Prosthesis loosening is the leading cause of postoperative revision in unicompartmental knee arthroplasty (UKA). The deviation of medial and lateral translational installation of the prosthesis during surgery is a common clinical phenomenon and an important factor in increasing the risk of prosthesis loosening. This study established a UKA finite element model and a bone-prosthesis fixation interface micromotion prediction model. The predicted medial contact force and joint motion of the knee joint from a patient-specific lower extremity musculoskeletal multibody dynamics model of UKA were used as boundary conditions. The effects of 9 femoral component medial and lateral translational installation deviations on the Von Mises stress of the proximal tibia, the contact stress, and the micro-motion of the bone prosthesis fixation interface were quantitatively studied. It was found that compared with the neutral position (a/A of 0.492), the lateral translational deviation of the femoral component significantly increased the tibial Von Mises stress and the bone-prosthesis fixation interface contact stress. The maximum Von Mises stress and the maximum contact stress of the fixation interface increased by 14.08% and 143.15%, respectively, when a/A was 0.361. The medial translational deviation of the femoral component significantly increased the bone-prosthesis fixation interface micro-motion. The maximum value of micromotion under the conditions of femoral neutral and medial translation deviation was in the range of 20-50 μm, which is suitable for osseointegration. Therefore, based on considerations such as the micromotion range suitable for osseointegration reported in the literature, the risk of reducing prosthesis loosening, and factors that may induce pain, it is recommended that clinicians control the mounting position of the femoral component during surgery within the safe range of 0-4 mm medial translation deviation.

Finite element study of stress distribution in medial UKA under varied lower limb alignment

Knee osteoarthritis (KOA) has a high incidence among the elderly, significantly impacting their quality of life and overall health. Medial unicompartmental knee arthroplasty (UKA) is an excellent choice for treating knee single-compartment lesions, and lower limb alignment has a profound impact on medial UKA. To explore the influence of different lower limb alignments on medial UKA. In this study, we selected MR and CT data of healthy adult male knee joints to establish a complete finite element analysis (FEA) model of the knee joint. After validation, we established a finite element model of medial UKA. Subsequently, we created 60 sets of FEA models with different lower limb alignments to analyze the impact of different lower limb alignments on medial UKA. A vertical load of 1000 N was applied to the FEA models with different lower limb alignments. During the process of shifting the Mikulicz line from the midpoint of the knee joint towards the medial side, the lower limb load was primarily concentrated on the medial compartment. The stress values of the lateral meniscus, tibial cartilage, and femoral cartilage gradually decreased. ROI (region of interest) 1 and ROI 2 showed the maximum principal strain changes, while ROI 3 and ROI 4 exhibited less pronounced fluctuations, with the maximum principal strain roughly proportionally increased. During the process of shifting the Mikulicz line towards the lateral side from the midpoint of the knee joint, the stress on the lateral compartment increased observably. ROI 1, ROI 2, ROI 3, and ROI 4 showed decreased maximum principal strains, approximately inversely proportional changes, but the overall reduction was relatively small. Different lower limb alignments have a profound impact on the short- and long-term joint function after UKA. When the Mikulicz line is 10 mm inside the midpoint of the knee joint or slightly outside, there is a relatively lower risk of tibial component fractures, lower stress on the lateral compartment, and lower load on the prosthesis. During medial UKA, measures such as bone resection and prosthesis selection should be taken to ensure that the Mikulicz line is in the ideal position.

China-made robot-assisted unicompartmental knee arthroplasty can enhance the precision of prosthesis placement and yield better short-term efficacy

BACKGROUND

The purpose of this study was to assess whether China-made robot-assisted medial UKA can improve prosthesis placement accuracy and yield superior short-term outcomes compared with conventional UKA.

METHODS

50 patients who underwent initial medial UKA were included in this single-center, prospective, parallel, randomized, controlled trial. Preoperatively, patients were randomly categorized the robot-assisted UKA group and conventional UKA group. The operation time, intraoperative blood loss, postoperative pain scores (VAS scores at 24 h, 72 h, and 3 months post-surgery), KSS scores (clinical and functional scores), and knee range of motion (ROM) were compared between the two groups. The coronal deviation values of the femoral component, tibial component, and knee joint line height change were also compared between the two groups.

RESULTS

The deviations in tibial component coronal plane alignment, femoral component coronal plane alignment, and joint line height change were significantly smaller in the robot-assisted group compared to those in the conventional group (p < 0.05). The operation time of the robot-assisted group was longer than that of the conventional group (p < 0.05). At 24 h and 72 h postoperatively, patients in the robot-assisted group reported lower VAS scores compared to those in the conventional group (p < 0.05). No significant differences were observed between the two groups regarding intraoperative bloodloss, the VAS scores at 3 months postoperatively, the KSS scores (clinical scores and functional scores) at 3 months postoperatively, and the Knee range of motion at 3 months postoperatively.

CONCLUSIONS

The China-made UKA robot can enhance the precision of prosthesis placement, yielding favorable short-term therapeutic outcomes.

Biomechanical effects of femoral prosthesis misalignment on the structure of the lateral compartment during medial unicompartmental knee arthroplasty in osteoporotic patients

BACKGROUND

This study aims to investigate the impact of varying coronal alignments of femoral prostheses on stress and strain distributions within the lateral compartment following unicompartmental knee arthroplasty (UKA) in patients with normal bone density and osteoporosis using finite element analysis. Additionally, it examines the relationship between osteoporosis and the progression of osteoarthritis in the lateral compartment postoperatively.

METHODS

UKA models were developed for both normal bone and osteoporotic conditions using a validated finite element model of the knee. Seven alignment conditions for the femoral prosthesis were simulated: 0° (neutral alignment), varus angles of 3°, 6°, and 9°, and valgus angles of 3°, 6°, and 9°, resulting in a total of 14 scenarios. Stress and strain distributions in the meniscus, tibial cartilage, and femoral cartilage of the lateral compartment were evaluated.

RESULTS

The results indicated that stress and strain in the meniscus, tibial cartilage, and femoral cartilage of the lateral compartment increased with greater varus alignment and decreased with greater valgus alignment in both normal and osteoporotic models. At equivalent alignment angles, stress and strain were consistently higher in the osteoporotic model (M2) compared to the normal bone model (M1), although the peak equivalent stress in the tibial cartilage was lower in the M2 model than in the M1 model.

CONCLUSIONS

In patients with osteoporosis undergoing fixed-bearing medial UKA, varus malalignment of the femoral prosthesis can lead to increased stress and strain in the lateral compartment's meniscus, tibial cartilage, and femoral cartilage. These findings suggest that osteoporosis may contribute to abnormal stress and strain distributions in the lateral compartment following UKA, potentially accelerating the progression of osteoarthritis in this region postoperatively.

Finite element analysis of sagittal angles of unicompartmental knee arthroplasty

BACKGROUND

Unicompartmental knee arthroplasty is an effective treatment for knee osteoarthritis, but it has the risk of failure, and the installation position of the prosthesis is one of the factors affecting the failure. There are few biomechanical studies on the installation angle of unicompartmental knee prosthesis.

METHODS

Constructed a finite element model of a normal human knee joint, and the validity of the model was verified by stress and front anterior methods. The mobile-bearing unicompartmental knee arthroplasty femoral prosthesis was placed at 3° intervals from 0° sagittal plane to 15° flexion, and - 2° and 17°were established, and observing the biomechanical changes of components.

FINDINGS

Maximum peak stresses occurred at a sagittal mounting angle of -2° for the insert and the contralateral meniscus, with the tibia showing a maximum at 17° sagittal and the tibial prosthesis stress maximum occurring at 6° sagittal. As the sagittal plane angle of the femoral prosthesis increases and the osteotomy distance extends posteriorly, more bone is amputated during the osteotomy. The ratio of the distance from the tip of the anterior intramedullary nail to the anterior end of the osteotomy to the total anteroposterior length of the sagittal osteotomy ranged from 43.2% to 44.6%.

INTERPRETATION

In this paper, the more appropriate sagittal mounting position for the femoral prosthesis is between 9 and 12°, based on the amount of osteotomy and the peak stress of each component in a standing position.

Anterior cruciate ligament injury should not be considered a contraindication for medial unicompartmental knee arthroplasty: Finite element analysis

PURPOSE

The research objective of this study is to use finite element analysis to investigate the impact of anterior cruciate ligament (ACL) injury on medial unicompartmental knee arthroplasty (UKA) and explore whether patients with ACL injuries can undergo UKA.

METHODS

Based on the morphology of the ACL, models of ACL with diameters ranging from 1 to 10mm are created. Finite element models of UKA include ACL absence and ACLs with different diameters. After creating a complete finite element model and validating it, four different types of loads are applied to the knee joint. Statistical analysis is conducted to assess the stress variations in the knee joint structure.

RESULTS

A total of 11 finite element models of UKA were established. Regarding the stress on the ACL, as the diameter of the ACL increased, when a vertical load of 750N was applied to the femur, combined with an anterior tibial load of 105N, the stress on the ACL increased from 2.61 MPa to 4.62 MPa, representing a 77.05% increase. Regarding the equivalent stress on the polyethylene gasket, a notable high stress change was observed. The stress on the gasket remained between 12.68 MPa and 14.33 MPa in all models. the stress on the gasket demonstrated a decreasing trend. The equivalent stress in the lateral meniscus and lateral femoral cartilage decreases, reducing from the maximum stress of 4.71 MPa to 2.61 MPa, with a mean value of 3.73 MPa. This represents a reduction of 44.72%, and the statistical significance is (P < 0.05). However, under the other three loads, there was no significant statistical significance (P > 0.05).

CONCLUSION

This study suggests that the integrity of the ACL plays a protective role in performing medial UKA. However, this protective effect is limited when performing medial UKA. When the knee joint only has varying degrees of ACL injury, even ACL rupture, and the remaining structures of the knee joint are intact with anterior-posterior stability in the knee joint, it should not be considered a contraindication for medial UKA.

The efficacy and safety of patient-specific instrumentation versus conventional instrumentation for unicompartmental knee arthroplasty: Evidence from a meta-analysis

BACKGROUND

The aim of this study was to compare the efficacy and safety of patient-specific instrumentation (PSI) and conventional instrumentation (CI) for unicompartmental knee arthroplasty. Our hypothesis was that the PSI would be superior to CI in improving implant positioning and clinical function.

METHODS

We searched electronic databases (PubMed, Web of Science, Embase, and Cochrane) to identify relevant studies published before July 1, 2023 that met our inclusion criteria. The identified reports at least included one of the following outcome variables: coronal component alignment, sagittal component alignment, number of outliers, hip-knee-ankle angle, postoperative complications, operative time and knee joint functional evaluation. For dichotomous variables, we calculated the risk ratio and its 95% confidence interval (CI). For continuous variables, we calculated the mean difference (MD) and its 95% CI. Heterogeneity of the included studies was assessed using the standard chi-square test. Meta-analyses were performed using RevMan 5.4. software. The meta-analysis was registered with PROSPERO (No. CRD42023454160).

RESULTS

A total of 9 articles were included in the analysis, consisting of 4 randomized controlled trials and 5 cohort studies. The study population comprised 494 patients, with 262 in the PSI group and 232 in the CI group. Our findings demonstrate that the PSI group exhibits superior tibial component coronal alignment compared to the CI group (MD = -0.66, 95% CI: -1.21 to -0.12, P = .02). Conversely, the CI group demonstrates better femoral component coronal alignment than the PSI group (MD = 0.89, 95% CI: 0.17-1.60, P = .01). No significant between 2 groups differences were observed in tibial component sagittal alignment, femoral component sagittal alignment, tibial coronal axis outliers, tibial sagittal axis outliers, femoral coronal axis outliers, femoral sagittal axis outliers, postoperative complications, operative time, hip-knee-ankle angle, and postoperative knee joint function score.

CONCLUSIONS

Our study findings suggest that the PSI confer an advantage in achieving superior tibial component coronal alignment, whereas the CI associated with better femoral component coronal alignment. However, no significant differences were observed between the groups in terms of other parameters. Future studies with larger sample sizes are needed to validate these findings.

Application strategy of finite element analysis in artificial knee arthroplasty

Artificial knee arthroplasty, as the most effective method for the treatment of end-stage joint diseases such as knee osteoarthritis and rheumatoid arthritis, is widely used in the field of joint surgery. At present, Finite element analysis (FEA) has been widely used in artificial knee replacement biomechanical research. This review presents the current hotspots for the application of FEA in the field of artificial knee replacement by reviewing the existing research literature and, by comparison, summarizes guidance and recommendations for artificial knee replacement surgery. We believe that lower contact stress can produce less wear and complications when components move against each other, in the process of total knee arthroplasty (TKA), mobile-bearing prostheses reduce the contact surface stress of the tibial-femoral joint compared with fixed-bearing prostheses, thus reducing the wear of the polyethylene insert. Compared with mechanical alignment, kinematic alignment reduces the maximum stress and maximum strain of the femoral component and polyethylene insert in TKA, and the lower stress reduces the wear of the joint contact surface and prolongs the life of the prosthesis. In the unicompartmental knee arthroplasty (UKA), the femoral and tibial components of mobile-bearing prostheses have better conformity, which can reduce the wear of the components, while local stress concentration caused by excessive overconformity of fixed-bearing prostheses should be avoided in UKA to prevent accelerated wear of the components, the mobile-bearing prosthesis maintained in the coronal position from 4° varus to 4° valgus and the fixed-bearing prosthesis implanted in the neutral position (0°) are recommended. In revision total knee arthroplasty (RTKA), the stem implant design should maintain the best balance between preserving bone and reducing stress around the prosthesis after implantation. Compared with cemented stems, cementless press-fit femoral stems show higher fretting, for tibial plateau bone defects, porous metal blocks are more effective in stress dispersion. Finally, compared with traditional mechanical research methods, FEA methods can yield relatively accurate simulations, which could compensate for the deficiencies of traditional mechanics in knee joint research. Thus, FEA has great potential for applications in the field of medicine.