Kosuke Kubo

Mechanisms of plastic deformation in highly cross-linked UHMWPE for total hip components--the molecular physics viewpoint.

Plastic deformation is an unavoidable event in biomedical polymeric implants for load-bearing application during long-term in-vivo service life, which involves a mass transfer process, irreversible chain motion, and molecular reorganization. Deformation-induced microstructural alterations greatly affect mechanical properties and durability of implant devices. The present research focused on evaluating, from a molecular physics viewpoint, the impact of externally applied strain (or stress) in ultra-high molecular weight polyethylene (UHMWPE) prostheses, subjected to radiation cross-linking and subsequent remelting for application in total hip arthroplasty (THA). Two different types of commercial acetabular liners, which belong to the first-generation highly cross-linked UHMWPE (HXLPE), were investigated by means of confocal/polarized Raman microprobe spectroscopy. The amount of crystalline region and the spatial distribution of molecular chain orientation were quantitatively analyzed according to a combined theory including Raman selection rules for the polyethylene orthorhombic structure and the orientation distribution function (ODF) statistical approach. The structurally important finding was that pronounced recrystallization and molecular reorientation increasingly appeared in the near-surface regions of HXLPE liners with increasing the amount of plastic (compressive) deformation stored in the microstructure. Such molecular rearrangements, occurred in response to external strains, locally increase surface cross-shear (CS) stresses, which in turn trigger microscopic wear processes in HXLPE acetabular liners. Thus, on the basis of the results obtained at the molecular scale, we emphasize here the importance of minimizing the development of irrecoverable deformation strain in order to retain the pristine and intrinsically high wear performance of HXLPE components.

Size and thickness effect on creep behavior in conventional and vitamin E-diffused highly crosslinked polyethylene for total hip arthroplasty.

Since the early 2000s, the use of large femoral heads is becoming increasingly popular in total hip arthroplasty (THA), which provides an improved range of motion and joint stability. Large femoral heads commonly necessitate to be coupled with thinner acetabular liners than the conventionally used because of the limited sizes of outer shells (especially for patients with small pelvic size). However, the influence of the liner thinning on the mechanical performance is still not clearly understood. The objective of this study was to experimentally clarify the size and thickness effect on the rates of compressive creep strain in conventional (virgin low-crosslinked) and vitamin E-diffused highly crosslinked, ultra-high molecular weight polyethylene (UHMWPE) acetabular liners. We applied uniaxial compression to these liners of various internal diameters (28, 32 and 36mm) and thicknesses (4.8, 6.8 and 8.9mm) up to 4320min under the constant load of 3000N. Vitamin E-diffused highly crosslinked UHMWPE components showed significantly greater creep resistance than the conventional ones. In the both types of UHMWPE, the rates of creep strain significantly decreased by increasing the internal diameter and thickness. Varying the component thickness contributed more largely to the creep behavior rather than the internal diameter. Our results suggest the positive mechanical advantage of using large femoral heads, but at the same time, a considerable liner thinning is not recommended for minimizing creep strain. Therefore, the further in-vitro as well as in-vivo research are necessary to conclude the optimal balance of head diameter and liner thickness within the limited sizes of outer shells.

Highly Cross-Linked Polyethylene in Total Hip and Knee Replacement: Spatial Distribution of Molecular Orientation and Shape Recovery Behavior

The present study investigated effects of processing procedures on morphology of highly cross-linked and re-melted UHMWPE (XLPE) in total hip and knee arthroplasty (THA, TKA). The shape recovery behavior was also monitored via uniaxial compression test at room temperature after non-destructive characterizations of the in-depth microstructure by confocal/polarized Raman spectroscopy. The goal of this study was to relate the manufacturing-induced morphology to the in vivo micromechanical performance, and ultimately to explore an optimal structure in each alternative joint bearing. It was clearly confirmed that the investigated XLPE hip and knee implants, which were produced from different orthopaedic grade resins (GUR 1050 and GUR 1020), consisted of two structural regions in the as-received states: the near-surface transitional anisotropic layer (≈100 μm thickness) and the bulk isotropic structural region. These XLPEs exhibited a different crystalline anisotropy and molecular texture within the near-surface layers. In addition, the knee insert showed a slightly higher efficiency of shape recovery against the applied strain over the hip liner owing to a markedly higher percentage of the bulk amorphous phase with intermolecular cross-linking. The quantitative data presented in this study might contribute to construct manufacturing strategies for further rationalized structures as alternative bearings in THA and TKA.

Acute suppurative oligoarthritis and osteomyelitis: A differential diagnosis that overlaps with acute rheumatic fever

BACKGROUND Acute rheumatic fever (ARF) is an illness caused by group A streptococcus (GAS) infection, and remains the leading cause of acquired heart disease in worldwide. Distinguishing between ARF and septic arthritis may be difficult. This report describes a case of suppurative arthritis overlapping with ARF. CASE PRESENTATION A 4-year-old, previously healthy boy presented with fever and left leg pain. The level of anti-streptolysin O (ASO) was elevated. His throat swab cultures grew GAS, but none were detected in his synovial fluid. Magnetic resonance imaging revealed suspected arthritis and osteomyelitis. The patient was treated for septic arthritis, but was subsequently diagnosed with ARF, after the development of carditis. CONCLUSION The clinical and laboratory features of ARF and suppurative arthritis demonstrate substantial overlap. Patients with an elevated ASO should undergo a careful cardiac examination for carditis associated with ARF by an echocardiogram.

Vitamin-E blended and infused highly cross-linked polyethylene for total hip arthroplasty: A comparison of three-dimensional crystalline morphology and strain recovery behavior

Vitamin-E (α-tocopherol) is now recognized worldwide as one of the most promising antioxidant agents for highly cross-linked polyethylene (HXLPE) used in total joint replacements. In the contemporary manufacturing processes, two alternative methods are currently accepted to incorporate this antioxidant into polyethylene microstructure: (i) blending vitamin-E before consolidation and radiation crosslinking; (ii) infusing vitamin-E via a homogenizing heat treatment after radiation crosslinking. However, the effects of these technological differences on crystalline morphology and mechanical behavior of polyethylene remains to be fully elucidated. The aim of this paper is to quantitatively evaluate the microstructural differences of commercially available vitamin-E blended and infused HXLPE liner (referred to as Liner BL and IF, respectively). For this purpose, confocal/polarized Raman spectroscopy was used to systematically examine the three-phase percentages (amorphous (αa), crystalline (αc), and intermediate third phase (αt)), preferential molecular orientation (θp), and degree of crystalline anisotropy (〈P2(cosβ)〉). Additionally, we compared the time-dependent deformation of Liner BL and IF as obtained by uniaxial stress relaxation tests followed by strain recovery. Distinctive features of the near-surface αc, θp, and〈P2(cosβ)〉 were clearly observed within the first 35μm in the two studied liners. Despite the equivalent level of the bulk αc and 〈P2(cosβ)〉, higher restoring force against a uniaxial strain was observed in Liner IF, which reflects a higher crosslink density in its amorphous phase. On the other hands, a higher degree of surface orientational randomness was detected in Liner BL, which is structurally more beneficial for minimizing the in-vivo occurrence of strain-softening-assisted wear.

Post-deformation shape-recovery behavior of vitamin E-diffused, radiation crosslinked polyethylene acetabular components

The in-vivo progression of creep and wear in ultra-high molecular weight polyethylene (UHMWPE) acetabular liners has been clinically evaluated by measuring radiographic penetration of femoral heads. In such clinical assessments, however, viscoelastic strain relaxation has been rarely considered after a removal of hip joint loading, potentially leading to an underestimation of the penetrated thickness. The objective of this study was to investigate shape-recovery behavior of pre-compressed, radiation crosslinked and antioxidant vitamin E-diffused UHMWPE acetabular liners, and also to characterize the effects of varying their internal diameter (ID) and wall thickness (WT). We applied uniaxial compression to the UHMWPE specimens of various ID (28, 32, 36mm) and WT (4.8, 6.8, 8.9mm) for 4320min under the constant load of 3000N, and subsequently monitored the strain-relaxation behavior as a function of time after unloading. It was observed that there was a considerable shape recovery of the components after removal of the external static load. Reducing ID and WT significantly accelerated the rate of creep strain recovery, and varying WT was more sensitive to the recovery behavior than ID. Creep deformation of the tested liners recovered mostly within the first 300min after unloading. Note that approximately half of the total recovery amount proceeded just within 5min after unloading. These results suggest a remarkably high capability of shape recovery of vitamin E-diffused highly crosslinked UHMWPE. In conclusion, the time-dependent shape recovering and the diameter-thickness effect on its behavior should be carefully considered when the postoperative penetration is quantified in highly crosslinked UHMWPE acetabular liners (especially on the non-weight bearing radiographs).

Perioperative management of hemophilia patients receiving total hip and knee arthroplasty: a complication report of two cases

It has been recognized that perioperative hemostasis management after joint-replacement surgery for hemophilia patients is complicated and cumbersome, due to the necessity of rigorous monitoring for clotting-factor levels throughout the infusion. Between 2005 and 2014, we examined seven patients with hemophilia A (ten joints: six hips and four knees) receiving total hip or knee arthroplasty (THA or TKA) for hemophilic arthropathy. One male patient (31 years old) showed an intra-articular hematoma formation after THA (case 1). In another male patient (46 years old) receiving TKA, the postoperative trough factor VIII level became lower significantly than reference levels (80%–100% for the 5–10 postoperative days) recommended by the guidelines from the Japanese Society on Thrombosis and Hemostasis, despite sufficient coagulant based on the guidelines being administered (case 2). In the latter patient, deep infection and hematoma formation were observed postoperatively. In this article, we provide a detailed clinical report regarding these two complication cases at the early postoperative periods, and the management of bleeding control for hemophilia patients is discussed.

Radiographic Determination of Hip Rotation Center and Femoral Offset in Japanese Adults: A Preliminary Investigation toward the Preoperative Implications in Total Hip Arthroplasty

The values of hip rotation center (HRC) and femoral offset (FO) evaluated according to Caucasian anatomical landmarks have been regarded as a useful reference also for Japanese patients in total hip arthroplasty (THA). In a strict sense, however, since there can be racial differences among their anatomical morphologies, it is clinically important to reconsider those parameters for the Japanese. In the present study, in order to investigate correlations among hip and pelvic morphometric parameters, frontal radiographs were taken from 98 Japanese adults (60 males and 38 females) without acetabular dysplasia and arthropathy in the standing position. Their mean age was 62.0 ± 16.7 years. The horizontal position of HRC was significantly correlated with the pelvic width in both genders (P = 0.0026 and 0.0010 for the males and the females, resp.). The vertical position of HRC was significantly correlated with the teardrop-sacroiliac distance in the males (P = 0.0003) and with the pelvic cavity height in the females (P = 0.0067). However, in both genders, there were no correlations among FO and the other parameters analyzed in this study. Our present findings might contribute to theoretical implications of an appropriate HRC position for Japanese OA patients in THA.

Study of Ligament Ossification and Abnormal Glucose Tolerance in the Zucker Fatty Rat

Significant expression of insulin-sensitive cells and the IGF-I-binding protein CTGF was observed in the cellular hyperplasia areas of the spinal ligament sites and Achilles tendon ectopic ossifi cation sites of Zucker fatty rats. We prepared MSG-treated rats, which exhibit hyperleptinemia and hyperinsulinemia from 6 months of age onward, as in ZFRs; however, as in other rats with dietary obesity, no ligament ossifi cation changes were seen at the spinal ligament sites.