Yung-Chang Lu

The effect of the design of the femoral component on the conformity of the patellofemoral joint in total knee replacement

One of the most controversial issues in total knee replacement is whether or not to resurface the patella. In order to determine the effects of different designs of femoral component on the conformity of the patellofemoral joint, five different knee prostheses were investigated. These were Low Contact Stress, the Miller-Galante II, the NexGen, the Porous-Coated Anatomic, and the Total Condylar prostheses. Three-dimensional models of the prostheses and a native patella were developed and assessed by computer. The conformity of the curvature of the five different prosthetic femoral components to their corresponding patellar implants and to the native patella at different angles of flexion was assessed by measuring the angles of intersection of tangential lines. The Total Condylar prosthesis had the lowest conformity with the native patella (mean 8.58 degrees ; 0.14 degrees to 29.9 degrees ) and with its own patellar component (mean 11.36 degrees ; 0.55 degrees to 39.19 degrees ). In the other four prostheses, the conformity was better (mean 2.25 degrees ; 0.02 degrees to 10.52 degrees ) when articulated with the corresponding patellar component. The Porous-Coated Anatomic femoral component showed better conformity (mean 6.51 degrees ; 0.07 degrees to 9.89 degrees ) than the Miller-Galante II prosthesis (mean 11.20 degrees ; 5.80 degrees to 16.72 degrees ) when tested with the native patella. Although the Nexgen prosthesis had less conformity with the native patella at a low angle of flexion, this improved at mid (mean 3.57 degrees ; 1.40 degrees to 4.56 degrees ) or high angles of flexion (mean 4.54 degrees ; 0.91 degrees to 9.39 degrees ), respectively. The Low Contact Stress femoral component had the best conformity with the native patella (mean 2.39 degrees ; 0.04 degrees to 4.56 degrees ). There was no significant difference (p > 0.208) between the conformity when tested with the native patella or its own patellar component at any angle of flexion. The geometry of the anterior flange of a femoral component affects the conformity of the patellofemoral joint when articulating with the native patella. A more anatomical design of femoral component is preferable if the surgeon decides not to resurface the patella at the time of operation.

Biomechanical evaluation of proximal tibial behavior following unicondylar knee arthroplasty: Modified resected surface with corresponding surgical technique

Persistent pain and periprosthetic fracture of the proximal tibia are troublesome complications in modern unicondylar knee arthroplasty (UKA). Surgical errors and acute corners on the resected surface can place excessive strains on the bone, leading to bone degeneration. This study attempted to lower strains by altering the orthogonal geometry and avoiding extended vertical saw cuts. Finite element models were utilized to predict biomechanical behavior and were subsequently compared against experimental data. On the resected surface of the extended saw cut model, the greatest strains showed a 50% increase over a standard implant; conversely, the strains decreased by 40% for the radial-corner shaped model. For all UKA models, the peak strains below the resection level increased by 40% relative to an intact tibia. There was no significant difference among the implanted models. This study demonstrated that a large increase in strains arises on the tibial plateau to resist a cantilever-like bending moment following UKA. Surgical errors generally weaken the tibial support and increase the risk of fractures. This study provides guidance on altering the orthogonal geometry into a radial-shape to reduce strains and avoid degenerative remodeling. Furthermore, it could be expected that predrilling a posteriorly sloped tunnel through the tibia prior to cutting could achieve greater accuracy in surgical preparations.

Wear-pattern analysis in retrieved tibial inserts of mobile-bearing and fixed-bearing total knee prostheses

Components from 73 failed knee replacements (TKRs) consisting of rotating-platform, mobile-bearing and fixed-bearing implants were examined to assess the patterns of wear. The patterns were divided into low-grade (burnishing, abrasion and cold flow) and high-grade (scratching, pitting/metal embedding and delamination) to assess the severity of the wear of polyethylene. The rotating-platform group had a higher incidence of low-grade wear on the upper surface compared with the fixed-bearing group. By contrast, high-grade wear comprising scratching, pitting and third-body embedding was seen on the lower surface. Linear regression analysis showed a significant correlation of the wear scores between the upper and lower surfaces of the tibial insert (R(2) = 0.29, p = 0.04) for the rotating-platform group, but no significant correlation was found for the fixed-bearing counterpart. This suggests that high-grade wear patterns on the upper surface are reduced with the rotating-platform design. However, the incidence of burnishing, pitting/third-body embedding and scratching wear patterns on the lower surface was higher compared with that in the fixed-bearing knee.

Morphometrical measurement of resected surface of medial and lateral proximal tibia for Chinese population

PurposeThe objective of this study was to analyze the morphology of the medial tibial plateau and lateral tibial plateau in Chinese knees and compared these measurements and features with those of commercial unicondylar tibial baseplates.MethodsThree-dimensional knee models were reconstructed from computed tomography slices of 81 subjects. Among the series, 27 knees were from male subjects and 54 knees from female subjects. The dimensions and shape of the medial and lateral tibial plateaus were measured and compared with six commercially available unicondylar tibial baseplates.ResultsThe results showed significant differences between the shapes of the medial and lateral tibial plateaus. For the lateral tibial plateau, the shape was symmetric about the mediolateral axis. The medial plateaus presented their widest mediolateral width in an obviously more posterior position than the lateral compartment. Additionally, the plateau aspect ratio decreased with increasing mediolateral dimensions, in contrast to the constant aspect ratio shown by conventional unicondylar knee prostheses.ConclusionCompartment-specific designs may optimize coverage between the prosthesis and resected tibial surface. The morphometrical measurements presented may allow manufacturers to design tibial baseplates that accommodate the structural variability between different ethnic groups.Level of evidenceProspective comparative study, Level II.

Elastoplastic behavior of highly cross-linked and vitamin E-stabilized polyethylene – A biomechanical study

Background: Vitamin E‐stabilized cross‐linked polyethylene has been touted to alleviate the negative effects of oxidation. Although it has demonstrated significant improvements in wear resistance, bio‐tribology, and oxidative resistance, little is known about the effect of antioxidants and dosage of cross‐linking on the mechanical strength. This study aimed to evaluate the mechanical properties of these novel materials, which are commonly used in orthopedic implants. Methods: Samples of different polymers were prepared with various levels of cross‐linking and with or without vitamin E‐stabilization and then tested according to ASTM D695 and D638. The elastoplastic characteristics under compression and tension were compared between the groups. Findings: Vitamin E‐stabilized cross‐linked polyethylene showed a significant increase in elastic modulus over other groups, with a maximum increase of 26% in compression and 40% in tension when compared to the highly cross‐linked group without vitamin E stabilization. The elastoplastic behavior under compression differed to that in tension for all polymers, demonstrating the anisotropic characteristics of these polymers. Interpretation: The lower mechanical strength of highly cross‐linked polyethylene has been a complication with the use of this polymer in orthopedic liners. This current study suggests that vitamin E‐stabilized cross‐linked polyethylene could be a suitable alternative material for knee implants because of its improved strength in resisting external forces.

Topical Tranexamic Acid Reduces Drainage Blood Loss in Primary Total Knee Arthroplasty: A Retrospective Study

Introduction: Total knee arthroplasty (TKA) surgery is associated with significant bleeding and commonly requires allogeneic blood transfusion. Although tranexamic acid (TXA) is reported to reduce post-operative bleeding, concerns on the safety of systemic TXA and of patients with higher risk of deep-vein thrombosis or pulmonary embolism have hindered its wider use. This retrospective study aimed to assess the safety and efficacy of topical TXA in patients undergoing primary TKA. Patients and methods: Between January 2008 and December 2011, a consecutive series of 271 patients who underwent TKAs in hospital single medical center were reviewed. The TXA group received topical tranexamic acid at the end of surgery while the control group did not. Drainage blood loss was measured and the need for blood transfusion was noted. Results: Drainage blood loss was significantly lower in the topical TXA group (304.9 ± 151.2 ml) than in the control group (520.2 ± 251.2 ml) (p ＜ 0.001). Blood transfusion rate was apparently lower in the TXA-treat group (14.3%) when compared to the group without TXA (44.4%) (p=0.013). There was no increase in deep vein thrombosis or wound complication. Conclusions: In this study, topical TXA can effectively reduce blood loss and transfusion rate, and is not associated with any increase in surgical complications.

Medial Unicompartmental Knee Arthroplasty in Chinese Population: Mid-term follow-up Results

Background: Mismatch between the component and resected bone surface can result in poor clinical outcomes after unicompartmental knee arthroplasty (UKA). Although many studies have reported that UKA is a suitable procedure with reliable results in Caucasians, few studies have reported the clinical outcomes in Asians. This study reports our experience of the use of imported knee prostheses in a Chinese population. Methods: Forty-five patients with medial compartmental osteoarthritis who had undergone UKA 6 to 10 years previously were retrospectively followed up. All of the cases received Zimmer high flex system UKA. Pain score of Knee Society Score (KSS), KSS functional score and anatomic tibiofemoral angle, was recorded pre-operatively and post-operatively. The satisfaction rate and radiolucent line beneath the tibial component were also recorded at last follow-up. Results: The average KSS pain score was 13.7 pre-operatively and 43.4 post-operatively. The average KSS functional score was 45.7 pre-operatively and 78.3 post-operatively. The average anatomic tibiofemoral angle was 0° pre-operatively, 3° immediately postoperatively, and 4.6° at last follow-up. Radiolucent lines beneath the tibial component were observed in 40% of the cases and not correlated with poor functional outcomes or pain scores. Only one patient felt unsatisfied with the surgery. Conclusions: The patients who received UKA had good pain relief and acceptable functional performance in this study. The imported knee prostheses provided satisfactory results in this Chinese population, however not as good as those reported in Caucasians. Strict patient selection and good knee alignment are the crucial factors for UKA.