Rina Sakai

Hammering sound frequency analysis and prevention of intraoperative periprosthetic fractures during total hip arthroplasty.

Adequate fixation at the time of cementless stem implantation depends on the operators experience. An objective evaluation method to determine whether the stem has been appropriately implanted may be helpful. We studied the relationship between the hammering sound frequency during stem implantation and internal stress in a femoral model, and evaluated the possible usefulness of hammering sound frequency analysis for preventing intraoperative fracture. Three types of cementless stem (BiCONTACT®, SL-PLUS®, and AI-Hip®) were used. Surgeons performed stem insertion using a procedure similar to that employed in a routine operation. Stress was estimated by finite element analysis, the hammering force was measured, and frequency analysis of hammering sound data obtained using a microphone. Finite element analysis showed a decrease in the hammering sound frequency with an increase in the estimated maximum stress. When a decrease in frequency was observed, adequate hammering had occurred, and the continuation of hammering risked fracture. Based on the relationship between stress and frequency, the evaluation of changes in frequency may be useful for preventing the development of intraoperative fractures. Using our method, when a decrease in frequency is observed, the hammering force should be reduced. Hammering sound frequency analysis may allow the prediction of bone fractures that can be visually confirmed, and may be a useful objective evaluation method for the prevention of intraoperative periprosthetic fractures during stem insertion.

Should we use cortical bone screws for cortical bone trajectory

OBJECT In 2009, Santoni et al. reported cortical bone trajectory (CBT) as a method of inserting pedicle screws to obtain more solid fixation, and proposed the use of cortical trajectory screws with a more closely placed thread (cortical screws) for CBT. Since the entry trajectory in CBT differs from that in the traditional trajectory, it is unclear whether the increased strength derives from the specific trajectory or the shape of the screw thread in contact with the cortical bone. Whether the use of cortical screws is always required with CBT thus remains unclear. The authors therefore investigated the relationship between screw entry trajectory and screw thread characteristics and pullout strength in animal experiments. METHODS Lumbar vertebrae (L1-L4) from 4-month-old female pigs were randomly assigned to one of 4 groups, with cancellous screws or cortical screws inserted via the traditional trajectory or CBT. For pullout strength testing, the screw was pulled out vertically against the direction of insertion. Rod pullout testing (toggle testing) was also performed, and the peak breaking strength was measured. RESULTS The maximum pullout strength was significantly greater for CBT using cortical screws than for the traditional trajectory using cancellous screws. Pullout strength tended to be higher when cortical screws were used in both CBT and the traditional trajectory, although the difference was not significant. Toggle testing showed no significant differences among the 4 groups. CONCLUSIONS The specific unconventional trajectory seemed to have a major impact on the increased strength obtained with CBT.

Initial fixation of a finite element model of an AI-Hip cementless stem evaluated by micromotion and stress

BackgroundThis study investigated issues related to initial stability after stem fixation. Finite element models of the AI-Hip cementless stem were constructed for computer simulation.MethodsAnalysis was performed after implantation of two types of cementless hip stem for clinical use; and micromotion and stress were then calculated. Boundary and initial conditions were (1) rigid contact of the distal end of the model femur with a rigid base; (2) a stepping load of 1800 N was applied to the proximal top of the stem; (3) a load of 1440 N was pulled from the greater trochanter of the femur as muscle force; (4) a torsion load of 18.9 Nm was applied to the proximal femur as the intrarotation.ResultsRelative micromotion of the AI-Hip cementless stem showed a value as low as that of a conventional stem. The calculated von Mises stress was below the level that would cause destruction of the femur and stem.ConclusionsBased on the relative micromotion and von Mises stress level, the AI-Hip cementless stem showed initial stability. The present experimental results should be compared with those obtained in clinical practice.

Two-Stage Revision Total Hip Arthroplasty for Periprosthetic Infections Using Antibiotic-Impregnated Cement Spacers of Various Types and Materials

Antibiotic-impregnated hip cement spacers of various types and materials have been used in the treatment of periprosthetic hip infections. We developed a handmade spacer by using polymethylmethacrylate (PMMA) and/or α-tricalcium phosphate (α-TCP). In this study, we retrospectively reviewed the surgical outcomes in 36 consecutive patients treated with 2-stage revision total hip arthroplasty by using our antibiotic-impregnated hip cement spacers. We aimed to analyze the infection control and reinfection rates after revision surgery. Moreover, we analyzed the possible predictors of postoperative reinfection. After exclusion of 1 patient who died immediately after the first-stage surgery, infection was controlled in 33 of the 36 hips (success rate, 91.7%). Two of these 33 hips underwent resection arthroplasty. Of the 36 hips that had been treated with the antibiotic-cement spacer, 31 hips (86.1%) were eligible for the second-stage prosthesis re-implantation. The 31 protocol hip joints of patients followed up for >6 months (mean, 48.6 months). Ten of these 31 hips (32.3%) became reinfected. No possible predictor examined differed significantly between the reinfection-positive and reinfection-negative groups. However, spacers consisting of PMMA cement alone were associated with the highest risk of reinfection. Therefore, α-TCP-containing antibiotic-impregnated hip cement spacers might decrease the reinfection rate in patients undergoing re-implantation.

Finite element analysis of the effect of proximal interlocking on primary fixation of the Intra-Medullary Cruciate stem

BackgroundThe primary fixation of cementless hip prostheses is related to the shape of the stem. When there is a complication of loading in the rotational direction, the mechanical fixation of a hip stem is considered to provide good primary fixation. The purpose of this study was to evaluate whether the Intra-Medullary Cruciate stem with a characteristic fixation method, which was developed by a group at Kitasato University, contributes to primary fixation by finite element analysis.MethodsAnalysis was performed at a friction coefficient of 0.1 with automatic contact, under the restriction of the distal femoral end. The following three loading conditions were applied: (1) step loading of the joint resultant force in the region around the hip stem; (2) loading in the rotational direction, simulating torsion; and (3) loading of the femoral head equivalent to that during walking. Displacement of an Intra-Medullary Cruciate stem and a reference stem along the x-, y-, and z-axes and rotational direction was calculated by simulation, and the stress distributed on the stem and femur was determined.ResultsRelative displacement along the z-axis of distal parts, which is a clinical problem with hip prosthesis stems, was lower for the Intra-Medullary Cruciate stem than for the reference stem. Displacement of the stem along the z-axis direction was low, indicating a low risk of sinking. The interlocking mechanism, which is a characteristic of the Intra-Medullary Cruciate stem, functioned to suppress its displacement, indicating that the locking method of this stem contributed to its stability. Because no stress concentration was detected in certain regions, it was thought that there are no risks of breakage of the Intra-Medullary Cruciate stem and femur.ConclusionsIt was suggested that effective fixation of the Intra-Medullary Cruciate stem can be achieved because its displacement is lower than that of the reference stem and displacement of the stress level is appropriate for primary fixation.

Revision total hip replacement using a cementless interlocking distal femoral stem with allograft-cemented composite and the application of intramedullary and onlay cortical strut allografts: two case reports.

Abstract It is often difficult to perform repeated revision total hip replacement (re-THR) after prosthesis loosening stemming from infection, mechanical loosening, and osteolysis. Reasons for this include the size of the bone defect and poor quality of the remaining bone. We have previously performed revision surgery using a cementless interlocking distal femoral stem with segmental cortical allograft-cemented composite for reconstruction in the presence of circumferential bone loss of the proximal femur according to Gustilo classification type IV [1]. However, in the case where the distal femur had a stovepipe canal due to osteoporosis, osteolysis, and infection, it was difficult to achieve stable fixation to the distal femoral cortical bone using a cementless interlocking distal femoral stem. Therefore, a cortical strut allograft is inserted into the femoral bone canal on the medial side, followed by the insertion of an interlocking stem. A further cortical strut allograft is inserted on the lateral side of the distal femur. In addition, the distal onlay allograft should pass over the allograft–host bone junction. The two allografts are finally secured with interlocking screws. The bone allografting to augment femoral bone deficiency was performed using mainly cadaveric bone allografts obtained from our bone bank [2, 3]. In this report, we describe two cases of re-THR involving the use of intramedullary and onlay cortical strut allografts with a cementless interlocking distal femoral long stem to achieve favorable fixation stability. The two patients were asked if the data from the case could be submitted for publication, and both gave their consent

Comparison of Internal Fixations for Distal Clavicular Fractures Based on Loading Tests and Finite Element Analyses

It is difficult to apply strong and stable internal fixation to a fracture of the distal end of the clavicle because it is unstable, the distal clavicle fragment is small, and the fractured region is near the acromioclavicular joint. In this study, to identify a superior internal fixation method for unstable distal clavicular fracture, we compared three types of internal fixation (tension band wiring, scorpion, and LCP clavicle hook plate). Firstly, loading tests were performed, in which fixations were evaluated using bending stiffness and torsional stiffness as indices, followed by finite element analysis to evaluate fixability using the stress and strain as indices. The bending and torsional stiffness were significantly higher in the artificial clavicles fixed with the two types of plate than in that fixed by tension band wiring (P < 0.05). No marked stress concentration on the clavicle was noted in the scorpion because the arm plate did not interfere with the acromioclavicular joint, suggesting that favorable shoulder joint function can be achieved. The stability of fixation with the LCP clavicle hook plate and the scorpion was similar, and plate fixations were stronger than fixation by tension band wiring.

Hydrogen Supplementation of Preservation Solution Improves Viability of Osteochondral Grafts

Allogenic osteochondral tissue (OCT) is used for the treatment of large cartilage defects. Typically, OCTs collected during the disease-screening period are preserved at 4°C; however, the gradual reduction in cell viability during cold preservation adversely affects transplantation outcomes. Therefore, improved storage methods that maintain the cell viability of OCTs are needed to increase the availability of high-quality OCTs and improve treatment outcomes. Here, we evaluated whether long-term hydrogen delivery to preservation solution improved the viability of rat OCTs during cold preservation. Hydrogen-supplemented Dulbeccos Modified Eagles Medium (DMEM) and University of Wisconsin (UW) solution both significantly improved the cell viability of OCTs during preservation at 4°C for 21 days compared to nonsupplemented media. However, the long-term cold preservation of OCTs in DMEM containing hydrogen was associated with the most optimal maintenance of chondrocytes with respect to viability and morphology. Our findings demonstrate that OCTs preserved in DMEM supplemented with hydrogen are a promising material for the repair of large cartilage defects in the clinical setting.

Influence of hooks and a lag screw on internal fixation plates for lateral malleolar fracture: a biomechanical and ergonomic study

BackgroundFor internal fixation of AO classification Type B lateral malleolar fracture, insertion of lag screws into the fracture plane and fixation with a one-third tubular plate as a neutralization plate are the standard treatment procedures. The one-third tubular plate is processed to a hook shape and hung on the distal end of the fibula. In this study, to compare the function of the hook and lag screws of a one-third tubular plate and LCP for osteosynthesis of lateral malleolar fracture, mechanical indices of internal fixation were compared among the one-third tubular plates with lag screws with and without the hook and a locking compression plate.MethodsAs mechanical tests, a compression test was performed in which compression in the bone axis direction produced by supporting the body weight was simulated, and a torsion test was performed in which external rotation of the bone axis caused by plantar flexion of the ankle joint was simulated. Muscle strength during walking and the force and torque acting on the ankle and knee joints were determined using inverse dynamic analysis. Finite element analysis was performed to analyze the function of hooks and lag screws. The joint reaction force determined by inverse dynamic analysis was adopted as the loading condition of finite element analysis.ResultsA stiffness equivalent to that of healthy bone could be achieved by all three internal fixations. It was clarified that the presence of the hook does not make a difference in stiffness. Displacement of the one-third tubular plate was small regardless of the presence or absence of the hook compared with those of locking compression plates.ConclusionsThe presence of the hook did not make any difference in stiffness, suggesting that active preparation of the hook is unnecessary. We also clarified that lag screws inhibit displacement.

Evaluation of digital tomosynthesis reconstruction algorithms used to reduce metal artifacts for arthroplasty: A phantom study

To investigate methods to reduce metal artifacts during digital tomosynthesis for arthroplasty, we evaluated five algorithms with and without metal artifact reduction (MAR)-processing tested under different radiation doses (0.54, 0.47, and 0.33mSv): adaptive steepest descent projection onto convex sets (ASD-POCS), simultaneous algebraic reconstruction technique total variation (SART-TV), filtered back projection (FBP), maximum likelihood expectation maximization (MLEM), and SART. The algorithms were assessed by determining the artifact index (AI) and artifact spread function (ASF) on a prosthesis phantom. The AI data were statistically analyzed by two-way analysis of variance. Without MAR-processing, the greatest degree of effectiveness of the MLEM algorithm for reducing prosthetic phantom-related metal artifacts was achieved by quantification using the AI (MLEM vs. ASD-POCS, SART-TV, SART, and FBP; all P<0.05). With MAR-processing, the greatest degree of effectiveness of the MLEM, ASD-POCS, SART-TV, and SART algorithms for reducing prosthetic phantom-related metal artifacts was achieved by quantification using the AI (MLEM, ASD-POCS, SART-TV, and SART vs. FBP; all P<0.05). When assessed by ASF, metal artifact reduction was largest for the MLEM algorithm without MAR-processing and ASD-POCS, SART-TV, and SART algorithm with MAR-processing. In ASF, the effect of metal artifact reduction was always greater at reduced radiation doses, regardless of which reconstruction algorithm with and without MAR-processing was used. In this phantom study, the MLEM algorithm without MAR-processing and ASD-POCS, SART-TV, and SART algorithm with MAR-processing gave improved metal artifact reduction.