Contact stress on polyethylene components of a new rotating hinge with a spherical contact surface

Assessing the impact of distal femoral morphology using Citak's ratio: an independent risk factor for aseptic loosening in rotating hinge knee prosthesis

BACKGROUND

Aseptic loosening (AL) is a frequent complication after rotating hinge knee (RHK) prosthesis. Citak's ratio has recently been developed to describe and classify distal femoral morphology into 3 groups (A, B, C). It consists in a ratio between the diameters of the femoral canal at 20 cm from the knee joint line and at 2 cm from the adductor tubercle. The objective of the study was to identify whether the femoral distal anatomical shape described with this ratio represents a risk factor for AL in RHK prosthesis.

METHODS

Retrospective study of patients who had undergone primary or revision RHK prosthesis, with a follow-up of minimum 4 years. Citak's ratio was calculated, and patients were classified depending on its value. Univariate and bivariate statistical analysis was performed to identify AL risk factors. Receiver Operating Characteristics (ROC) analyses were conducted to examine diagnostic quality of the parameters of interest.

RESULTS

Thirty-three patients were included. Most of them females (ratio 26:7), with a mean age of 78.2 (SD 6.9). Three patients presented AL (rate of 9%), all of them classified into group C (100%). Citak's ratio was significantly related to the AL rate (p < 0.001), and so was the femoral canal diameter at 20 cm from the knee joint (p 0.010). The ROC curve analysis yielded an Area Under the Curve (AUC) of 0.922 (CI 95% 0.819-1.000) for the Citak´s ratio.

CONCLUSION

The inner femoral diameter at 20 cm proximal to the knee joint line and Citak's ratio help indentify patients at risk of AL after RHK prosthesis, and thus a better planning of the surgery.

Assessing the influence of gastrocnemius reconstruction on stress distribution of femoral tumor rotating hinge knee prosthesis via finite element analysis

Background

After femoral oncological knee arthroplasty, some patients suffer from rotating axis fracture, which significantly impacts the life span of the rotating hinge knee (RHK) prosthesis. This research aimed to analyze the biomechanical response of anatomical gastrocnemius reconstruction and assess whether it could reduce the risk of rotating axis breakage by finite element (FE) analysis.

Methods

A femur-prosthesis-tibia FE model was established using the data from CT scans. The mechanical properties of the RHK implant were quantitatively compared before and after gastrocnemius reconstruction at 6 angles: 10°, 20°, 30°, 40°, 50°, and 60°.

Results

Our results showed that gastrocnemius reconstruction effectively altered the stress distribution around the rotating axis, considerably relieving the stress in the fracture-prone region. In addition, the peak stress in the rotating axis, bending axis, prosthesis stem, and femoral condyles decreased variably.

Conclusion

In distal femoral resection knee arthroplasty, the rebuilding of gastrocnemius substantially improved the stress distribution within the prosthesis, thereby having the potential to reduce the risk of prosthetic fracture and prolong the overall durability of the prosthesis.

Risk Factors for Aseptic Loosening After Total Knee Arthroplasty with a Rotating-Hinge Implant: A Case-Control Study

BACKGROUND

Successful results have been reported in association with the use of a rotating-hinge prosthesis for primary total knee arthroplasty (TKA). The objective of the present study was to identify risk factors for aseptic loosening in patients who underwent primary TKA with rotating-hinge knee prostheses.

METHODS

The records of 1,235 patients who underwent primary TKA with a rotating-hinge prosthesis at our center were evaluated. A total of 125 patients who underwent revision were further evaluated according to the inclusion and exclusion criteria, and 33 patients who underwent revision because of aseptic loosening were then compared with a group of 30 patients who did not require revision surgery. All data, including radiographic measurements, were obtained from records prior to the primary TKA.

RESULTS

On the basis of our review of demographic, anthropometric, clinical, surgical, and radiographic findings, we found that higher body mass index (BMI) was associated with revision. The majority of patients with aseptic loosening had loosening of the femoral component. Furthermore, the inner femoral diameter at 20 cm proximal to the knee joint (on both anteroposterior and lateral images) was found to be predictive of revision among those with aseptic loosening. Receiver operating characteristic curve analysis showed that an inner diameter of the femur of >19 mm on anteroposterior images had a sensitivity of 91% and specificity of 87% for predicting the need for revision surgery in patients with aseptic loosening.

CONCLUSIONS

This is one of few studies that has focused on determining risk factors for the failure of rotating-hinge prostheses following TKA surgery. Our findings indicate that a novel variable, the inner (diaphyseal) diameter of the femur at the point 20 cm proximal to the knee joint, is an extremely reliable predictor of revision surgery in patients with aseptic loosening.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Spherical center and rotating platform hinged knee prosthesis: Finite-element model establishment, verification and contact analysis

BACKGROUND

Biomechanical study is fundamental for the preclinical evaluation of knee prostheses. However, there are few reports on the contact characteristic investigation in the hinged knee prosthesis. The purpose of this study was to investigate the contact characteristics of a novel hinged knee prosthesis.

METHODS

All of the component models were designed and assembled using Solidworks. A comparison of the contact area and ultra-high-molecular-weight polyethylene (UHMWPE) deformation using the experimental method (EM) and finite-element analysis (FEA) under 3000 N with the prosthesis at different flexions was performed. The peak contact pressure and von Mises stress on tibial insert and bushing were investigated under nine specific samples that were extracted from a gait cycle using FEA (according to ISO 14243-1: 2009).

RESULTS

The largest contact area and UHMWPE deformation were 100.78 ± 8.71 mm² and 0.085 ± 0.015 mm in the EM, and 96.68 mm² and 0.096 mm in FEA. The peak contact pressure and von Mises stress on the tibial insert were 26.3071 MPa and 10.5115 MPa at 13% of the gait cycle and on bushing were consistently 0 MPa. The contact pressures were distributed at the posterior of the insert.

CONCLUSION

The finite-element model was validated to be applicable for predicting the real prosthesis behavior based on the good correlation of the results using the EM and FEA. The model can help to identify contact characteristics and be can used in optimization studies of this novel prosthesis during the design phase.

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.

A 3D finite element model to investigate prosthetic interface stresses of different posterior tibial slope

PURPOSE

Posterior tibial slope that is created during proximal tibial resection in total knee arthroplasty has emerged as an important factor in the mechanics of the knee joint and the surgical outcome. But the ideal degree of posterior tibial slope for recovery of the knee joint function and preventions of complications remains controversial and should vary in different racial groups. The objective of this paper is to investigate the effects of posterior tibial slope on contact stresses in the tibial polyethylene component of total knee prostheses.

METHODS

Three-dimensional finite element analysis was used to calculate contact stresses in tibial polyethylene component of total knee prostheses subjected to a compressive load. The 3D finite element model of total knee prosthesis was constructed from the images produced by 3D scanning technology. Stresses in tibial polyethylene component were calculated with four different posterior tibial slopes (0°, 3°, 6° and 9°).

RESULTS

The 3D finite element model of total knee prosthesis we presented was well validated. We found that the stress distribution in the polythene as evaluated by the distributions of the von Mises stress, the maximum principle stress, the minimum principle stress and the Cpress were more uniform with 3° and 6° posterior tibial slopes than with 0° and 9° posterior tibial slopes. Moreover, the peaks of the above stresses and trends of changes with increasing degree of knee flexion were more ideal with 3° and 6° posterior slopes.

CONCLUSIONS

The results suggested that the tibial component inclination might be favourable to 7°-10° so far as the stress distribution is concerned. The range of the tibial component inclination also can decrease the wear of polyethylene. Chinese posterior tibial slope is bigger than in the West, and the current domestic use of prostheses is imported from the West, so their demands to tilt back bone cutting can lead to shorten the service life of prostheses; this experiment result is of important clinical significance, guiding orthopaedic surgeon after the best angle to cut bone.

ENDOPROSTHESIS-RELATED COMPLICATIONS AFTER LIMB-SALVAGE OPERATION OF MALIGNANT BONE TUMORS AROUND THE KNEE

Endoprosthetic reconstruction using a custom-made metallic megaendoprosthesis is one of the common modalities for the limb salvage operation. The new promising advance of material science, design and fabrication of the endoprosthesis enable an immediate rehabilitation program and provide a durable and functional limb. Thus a successful limb reconstruction is possible in the well-selected patients. In addition to the endoprosthesis-related increased stress, a limited soft tissue support and constraint after limb salvage procedure usually results in an increased incidence of complications, especially in the long term survivors. Some patients may even need revision of the endoprosthesis and, at times, amputation.

The complications after oncological endoprosthectic reconstructions usually occur more frequent than the conventional primary total joint arthroplasty. Considering the characteristics of the surgical procedure and the high demands on the implants, such a relatively high frequency of complications is not unexpected. The common complications include wound necrosis, aseptic loosening, fatigue fracture, local osteolysis, joint contracture, dislodgement/dislocation, nerve or vascular injury, rotational deformity, leg length discrepancy, infection, periprosthectic fracture, etc. Some complications are encountered with other modality of limb salvage procedure, whereas the other endoprosthesis-related complications are endoprosthetic-unique and not uncommon. The major causes of such a relatively high endoprosthesis-related complications include (1) extensive excision of soft tissue, leading to change of biomechanical ergonomics, little soft tissue constraints or support for a long replacement segments, and decreased local defense to infection, (2) increased stress on the implants due to higher activity level in the youthful active individuals, relatively narrower medullary canals with less cancellous bone for fixation, (3) special needs for the stability resulting an increased mechanical constraints placed directly within the endoprosthesis, thus raising the local stress transferred to the prosthesis, and to the prosthesis-bone interface, (4) poor immunological, hematological, or nutritional status resulting from chronic oncologic diseases or chemotherapy. It in turn accelerates the wear processes of the components, induces the wear particulate disease and local osteolysis, as well as to cause the aseptic loosening eventually. Early detection and early correction of minor complications has an important role of preventing the major complications, thus reduces the necessity of reoperation, and at times, amputation. We will review these complications in this article.

Functional outcomes after endoprosthetic knee reconstruction following resection of osteosarcoma near the knee

PURPOSE

The aims of this study were to evaluate outcomes of osteosarcoma patients who underwent wide resection and endoprosthetic knee reconstruction, to compare with their own sound sides and controls, and to assess the interrelationships among these parameters.

METHOD

Twenty patients and 20 matched controls were recruited. Strength and range of motion (ROM) of the knee, gait and Enneking functional score were measured.

RESULTS

The results revealed the operated knees were significantly weaker than sound knees and controls (p < 0.05). The ROM of operated knees, sound knees and controls were 106.2 degrees +/- 13.0 degrees, 134.1 degrees +/- 7.5 degrees, and 137.7 degrees +/- 7.0 degrees respectively (p < 0.05). Patients' and controls' walking velocity were 54 +/- 12 m/min, and 72 +/- 6 m/min (p < 0.05). Their Enneking score was 21.6 +/- 2.8 (72% of total score, 30). The ratio of extensor strength of operated/sound knee and isometric hamstring/quadriceps ratio of operated knee were significantly correlated to the difference of stance-phase duration of bilateral sides (p < 0.05). In addition, the ratio of isometric flexor strength was significantly correlated to Enneking score (p < 0.05).

CONCLUSIONS

The patients achieved an acceptable recovery in strength and gait in spite of some functional limitation.

Contact stresses and fatigue life in a knee prosthesis: comparison between in vitro measurements and computational simulations

The evaluation of contact areas and pressures in total knee prosthesis is a key issue to prevent early failure. The first part of this study is based on the hypothesis that the patterns of contact stresses on the tibial insert of a knee prosthesis at different stages of the gait cycle could be an indicator of the wear performances of a knee prosthesis. Contact stresses were calculated for a mobile bearing knee prosthesis by means of finite element method (FEM). Contact areas and stresses were also measured through in vitro tests using Fuji Prescale film in order to support the FEM findings. The second part of this study addresses the long-term structural integrity of metal tibial components in terms of fatigue life by means of experimental tests and FEM simulations. Fatigue experimental evaluations were performed on Cr-Co alloy tibial tray, based on ISO standards. FEM models were used to calculate the stress patterns. The failure risk was estimated with a standard fatigue criterion on the basis of the results obtained from the FEM calculations. Experimental and computational results showed a positive matching.