Finite element analysis of cemented prostheses for hip replacement in elderly patients with comminuted intertrochanteric fracture.

BACKGROUND: To determine postoperative stress distribution after cemented arthroplasty in elderly patients with comminuted intertrochanteric fracture, and assist in determining a rational prosthetic stem length. METHODS: A three-dimensional (3D) model of intertrochanteric fracture was established using the Mimics and Unigraphics modeling software, which included the 3D model of comminuted intertrochanteric fracture, two long-stem(#4,#5) and one short stem(#3) prostheses, and the mantle layer of cement. The bone defect of the calcar femorale was replaced with a 5-mm thick cement. Then, the 3D finite element model of those materials was established, boundary conditions of force were imposed, and material parameters were set. Accordingly, a finite element analysis was performed to this model in stress. RESULTS: (1) The stress of the femur in the three-stem replacement prosthesis models increased from proximal end to distal end in the same pattern, while a stress concentration region was found at 5 mm from within the distal tip of the short-stem prosthesis (#3), which had a peak value of 67.85 MPa. However, no stress concentration was found on the long-stem prosthesis model. (2) For the short-stem prosthesis, the stress distribution of the cement-prosthesis interface was significantly concentrated in the distal region around the prosthesis end, in which the peak value of the lateral interface exceeded the fatigue strength of the bone cement. However, the biomechanics for the long prosthesis was better appreciated. CONCLUSION: Long prosthesis stems may theoretically be a better option for comminuted intertrochanteric fractures in elderly patients. However, the application of exceedingly long prosthesis stems would not be a better option. KEY WORDS: Comminuted intertrochanteric fracture, Elderly patients Finite element analysis, Prosthetic replacement.

Effect of Cross-Linked Hyaluronate Scaffold on Cartilage Repair: An In Vivo Study.

OBJECTIVE: To determine the safety and effectiveness of a cross-linked sodium hyaluronate (CHA) scaffold in cartilage repair. METHODS: Physicochemical properties of the scaffold were determined. The safety and effectiveness of the scaffold for cartilage repair were evaluated in a minipig model of a full-thickness cartilage defect with microfracture surgery. Postoperative observation and hematological examination were used to evaluate the safety of the CHA scaffold implantation. Pathological examination as well as biomechanical testing, including Young's modulus, stress relaxation time, and creep time, were conducted at 6 and 12 months postsurgery to assess the effectiveness of the scaffold for cartilage repair. Furthermore, type II collagen and glycosaminoglycan content were determined to confirm the influence of the scaffold in the damaged cartilage tissue. RESULTS: The results showed that the routine hematological indexes of the experimental animals were within the normal physiological ranges, which confirmed the safety of CHA scaffold implantation. Based on macroscopic observation, it was evident that repair of the defective cartilage in the animal knee joint began during the 6 months postoperation and was gradually enhanced from the central to the surrounding region. The repair smoothness and color of the 12-month cartilage samples from the operation area were better than those of the 6-month samples, and the results for the CHA scaffold implantation group were better than the control group. Greater cell degeneration and degeneration of the adjacent cartilage was found in the implantation group compared with the control group at both 6 and 12 months postoperation, evaluated by O'Driscoll Articular Cartilage Histology Scoring. Implantation with the CHA scaffold matrix promoted cartilage repair and improved its compression capacity. The type II collagen level in the CHA scaffold implantation group tended to be higher than that in the control group at 6 months (2.33 ± 1.50 vs 1.68 ± 0.56) and 12 months postsurgery (3.37 ± 1.70 vs 2.06 ± 0.63). The GAG content in the cartilage of the control group was significantly lower than that of the experimental group (2.17 ± 0.43 vs 3.64 ± 1.17, P = 0.002 at 6 months and 2.27 ± 0.38 vs 4.12 ± 1.02, P = 0.002 at 12 months). Type II collagen and glycosaminoglycan content also demonstrated that CHA was beneficial for the accumulation of both these vital substances in the cartilage tissue. CONCLUSIONS: The CHA scaffold displayed the ability to promote cartilage repair when applied in microfracture surgery, which makes it a promising material for application in the area of cartilage tissue engineering.

[Biomechanical characteristics of hip prosthesis in hip arthroplasty treating elderly patients with Evans I-III intertrochanteric fracture of femur].

OBJECTIVE: To investigate the feasibility of hip arthroplasty in the treatment of elderly patients with Evans I-III intertrochanteric fracture of femur by analyzing its biomechanics characters. METHODS: We solved the CT digital image files with the graphics processing software Mimics at DICOM 3.0 standard, and reconstructed the three-dimensional entity of femur with CAD modeling software Unigraphics. Then the fracture line was defined in the model as the line between the tip of greater trochanter and inferior margin of small trochanter, above which the upper bone was removed. Afterwards the two prosthesises with different stem lengths (120 mm and 170 mm) were implanted into the fracture model respectively as hip arthroplasty with 3 mm bone cement layer between prosthesis and femur, and the bone defect was repatched with 5 mm bone cement layer. A three-dimensional finite element model was established with finite element analysis software ABAQUS 6.5. We formulated different material parameters under the stress condition standing with single leg to build the stress distribution map of the femur prosthesis, and took 5 loci of region of stress concentration to calculate the mean value of stress. RESULTS: The stress distribution maps of the short and long stem length prothesises were similar. And there were two areas of stress concentration, including the upper portion and the lower portion close to the joint of the prosthesis stem, and the stress concentration in the junction part was obviously between the lower portion and the upper area of the small trachanter. The stress reached the first concentration area at the junction and then gradually reached the second concentration area at the interior terminal of the stem. While the stress gradually increased along the lateral prosthesis stem, and reached the stress concentration area at the end. CONCLUSIONS: The stress distribution maps in the femur prosthesises are similar between hip arthroplasty in the treatment of intertrochanteric fracture of femur and the traditional hip arthroplasty surgery. The peak stress values are higher in the long stem prosthesis in the treatment of intertrochanteric fracture of femur than the short type, while they are under the rupture value of the metal.

Clinical application of extracorporeal membrane oxygenation for treatment of adult refractory cardiogenic shock / 中华心血管病杂志

<p><b>OBJECTIVE</b>To summarize the clinical experience of extracorporeal membrane oxygenation (ECMO) treatment for adult refractory cardiogenic shock.</p><p><b>METHODS</b>From January 2003 to January 2011, patients with refractory cardiogenic shock required veno-arterial ECMO by failure of conventional therapy and intra-aortic balloon pump counterpulsation therapy were retrospectively studied. Patients with severe traumatic brain injury, advanced malignancies and multiple organ failure were excluded. Patients were divided into weaned group (n = 31) and not weaned group (n = 23) according to the ECMO weaning.</p><p><b>RESULTS</b>The duration of ECMO was 24.16 (14.12, 56.75) hours. Twenty-two out of 31 patients in the weaned group survived and were discharged, 9 patients died after successfully weaned from ECMO (5 due to multisystem organ failure, 2 due to reoccurred cardiogenic shock, 1 due to infectious shock and 1 due to disseminated or diffuse intravascular coagulation). Pre-ECMO mean arterial pressure, ejection fraction, the duration of ECMO were significantly higher while pre-ECMO blood lactate [(8.64 ± 3.17) vs. (14.44 ± 2.52) , P < 0.01], the duration of ROSC [ (16.70 ± 5.29) vs. (35.64 ± 5.89), P < 0.01] and multisystem organ failure [0 vs. 17.4% (4/23) , P < 0.05] were lower in weaned group than in not wean group.</p><p><b>CONCLUSIONS</b>ECMO is an effective mechanical assistant therapy strategy for adult refractory cardiogenic shock patients. Timely applying this strategy on suitable patients is crucial for the success of ECMO. Cardiac function and reversibility of heart failure are key factors determine the fate of weaned or not weaned ECMO in adult refractory cardiogenic shock patients.</p>

Biomechanical supporting effect of tantalum rods for the femoral head with various sized lesions: a finite-element analysis.

BACKGROUND: Features of necrotic lesions and various interventions could affect the biomechanics of the femoral head. A three-dimensional finite-element analysis was designed to demonstrate necrotic femoral head stress changes with various sizes of necrotic lesions, and evaluate the effect of tantalum rods on preventing femoral head cracking. METHODS: Femoral computed tomography scans were used to build a normal three-dimensional finite-element femoral head model in a computer. Based on the normal model, necrotic models of different lesion diameters (15 mm, 20 mm and 30 mm) were created, as were the repaired models with tantalum rods for each diameter. After a series of meshing and force loading, the von Mises stress distributions, simulating single-legged stance, and stresses on specific points under loaded conditions were determined for each model. RESULTS: Deep exploration into the burdened area of the femoral head indicated that higher stresses to the femoral head were observed with a larger necrotic lesion; the largest stress concentration, 91.3 MPa, was found on the femoral head with a lesion diameter of 30 mm. By contrast, topical stress on the surface of the necrotic regions was lowered following implantation of a tantalum rod, and the changes in stress were significant in models with lesions of 15 mm and 30 mm in diameter, with the best biomechanical benefit from the tantalum rod found with a lesion diameter of 15 mm. CONCLUSIONS: Femoral heads with larger necrotic lesions usually have a higher stress concentration and a higher risk of collapse. Various sized lesions on the femoral head can benefit from the mechanical support offered by the implantation of a tantalum rod; however, femoral heads with smaller sized lesions may benefit more. A thorough evaluation of the lesion size should be conducted prior to the use of tantalum rod implants in the treatment of femoral head necrosis.

Therapeutic effect of an injectable sustained-release sinomenine hydrochloride and sodium hyaluronate compound in a rabbit model of osteoarthritis.

BACKGROUND: While intra-articular injection of sinomenine hydrochloride has a therapeutic effect on osteoarthritis, it has a short half-life, and is thermolabile and photolabile. The aim of this research was to evaluate the sustained-release of sinomenine hydrochloride from an injectable sinomenine hydrochloride and sodium hyaluronate compound (CSSSI) and its therapeutic effect in a rabbit model of osteoarthritis following intra-articular injection. METHODS: An injectable compound consisting of 1% sodium hyaluronate and 2.5% sinomenine hydrochloride was prepared and kept as the experiment group, and 2.5% sinomenine hydrochloride was prepared and kept as the control group. The cumulative mass release was measured at different time points in each group in vitro. Sixty-five male Zelanian rabbits were randomly divided into five groups: 15 (30 knees) each for the control, sodium hyaluronate, sinomenine hydrochloride, and CSSSI groups respectively, and five (10 knees) for the modeling group. Papain was injected into both knees of each rabbit for model establishment. Subsequently, 0.2 ml of the corresponding drugs was injected into the articular cavities of the remaining experiment groups, while the control group was treated with 0.2 ml normal saline. All groups were treated once a week for 4 weeks. Seven days after the last treatment, knees were anatomized to perform pathological observations and Mankin's evaluation of the synovium. Four groups were compared using the SPSS 13.0 software package. RESULTS: In the in vitro sustained-release experiments, 90% of the drug was released in the experiment group 360 minutes following the injection. Comparison of the Mankin's evaluations of the four groups illustrated statistical discrepancies (P < 0.05). In further paired comparisons of the CSSSI group vs. modeling control/sodium hyaluronate/sinomenine hydrochloride groups, statistical significance was uniformly obtained. Moreover, sodium hyaluronate and sinomenine hydrochloride treatments showed significant improvement over the modeling control (P < 0.05), whereas sodium hyaluronate vs. sinomenine hydrochloride comparison failed to reach significance (P > 0.05). CONCLUSIONS: CSSSI has a sustained-release effect on sinomenine hydrochloride. Intra-articular injection of CSSSI was significantly better than the sole sodium hyaluronate or sinomenine hydrochloride for the treatment of osteoarthritis in a rabbit model.