The tram track sign: a characteristic sonographic feature of polyethylene liner dissociation after total-hip arthroplasty

OBJECTIVES

Polyethylene liner dissociation from an acetabular component is a complication of total-hip arthroplasty (THA) caused by slippage of the liner, which causes pain and requires a revision. The aim of this study was to evaluate sonographic features of liner dissociation and detect useful sonographic findings compared to conventional radiography and computed tomography (CT).

METHODS

Among a total of 226 patients who underwent revision THA at our institution between September 2008 and June 2012, 10 patients (6 male and 4 female; mean age, 56.2 years) who showed severe narrowing of the superior joint space on the THA side and underwent sonography were retrospectively reviewed by evaluating radiographic, CT, and sonographic findings. In evaluation of the images, we put more emphasis on the "radiographic crescent sign," "CT crescent sign," and "sonographic tram track sign."

RESULTS

At surgery, 7 patients showed liner dissociation, and 3 showed severe liner wear. On radiography, 8 of 10 patients (80%) had a correct diagnosis of the presence or absence of liner dissociation; on sonography, all 10 patients (100%) had a correct diagnosis. The sensitivity, specificity, and accuracy for diagnosis of liner dissociation by pelvic radiography and sonography were 100% (7 of 7), 33% (1 of 3), and 80% (8 of 10) and 100% (7 of 7), 100% (3 of 3), and 100% (10 of 10), respectively.

CONCLUSIONS

Liner dissociation can be easily and well visualized by sonography, especially compared to pelvic radiography and CT. The sonographic tram track sign should be a very useful feature in the early diagnosis of liner dissociation.

[Expressions of bone morphogenetic protein 2 and runt-related transcription factor 2 and microarchitecture of trabecular bone periacetabula in adult patients with developmental dysplasia of hip]

OBJECTIVE

To explore the expressions of bone morphogenetic protein 2 (BMP-2) and runt-related transcription facotr 2 (Runx2) and microarchitecture of trabecular bone periacetabula in adult patients with developmental dysplasia of the hip (DDH).

METHODS

Between March and September 2008, the trabecular bone periacetabulum was collected from 8 patients with DDH who were scheduled for total hip arthroplasty (aged 37-55 years, 3 males and 5 females, trial group) and from 8 patients with avascular necrosis of the femoral head (Ficat stage II) who were scheduled for hip resurfacing arthroplasty (aged 36-55 years, 3 males and 5 females, control group). The expressions of BMP-2 and Runx2 in the trabecular bone were determined by real-time quantitative PCR, and the microarchitecture was observed by micro-CT and the following parameters were determined: bone volume/total volume (BV/TV), connectivity density (Conn.Dens), trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), and structure model index (SMI).

RESULTS

The expressions of BMP-2 and Runx2 were significantly lower in trial group than in control group (P < 0.05). The micro-CT showed sparse trabecular bone in trial group and dense trabecular bone in control group. BV/TV and Tb.N in trial group were significantly lower than those in control group, and SMI and Tb.Sp in trial group were significantly higher than those in control group (P < 0.05); there was no significant difference in Conn.Dens and Tb.Th between 2 groups (P > 0.05).

CONCLUSION

The trabecular bone is in a low metabolism condition and its microarchitecture is tendency to be osteoporosis trabecualr bone in adult patients with DDH. It may be related with the acetabular component loosening after total hip arthroplasty.

Increasing thickness and fibrosis of the cartilage in acetabular dysplasia: a rabbit model research

BACKGROUND

The order and mechanism of pathological changes in acetabular dysplasia are still unclear. This study investigated cartilage changes in rabbit acetabular dysplasia models at different ages.

METHODS

Twenty-seven 1-month-old New Zealand rabbits underwent cast immobilization of the left hind limb in knee extension. Serial acetabular dysplasia models were established by assessment of the acetabular index and Sharp's angle on radiographs. The thickness of the acetabular cartilage was measured under a microscope, and fibrosis was observed. Ultrastructural changes were investigated with scanning electron microscopy and transmission electron microscopy. The messenger RNA expression of collagen I and II, β1 integrin, and caspase-9 were measured by real-time fluorescence quantitative polymerase chain reaction.

RESULTS

In an immature group of rabbits, the acetabular index of the treated hip increased with animal growth. The cartilage on the brim of the left acetabulum was significantly thicker than that on the right side. The collagen fibrils on the surface of the cartilage became gross, and the chondrocytes in the enlargement layer underwent necrosis. In a mature group of rabbits, the left Sharp's angle increased in the rabbits with 6-week casting. The cartilage on the brim of the left acetabulum underwent fibrosis. The chondrocytes were weakly stained, and the number of lysosomes was much larger than normal. The messenger RNA expression of collagen I and II, β1 integrin, and caspase-9 in the cartilage differed significantly at different ages.

CONCLUSIONS

Increasing thickness followed by fibrosis may be the order of pathological cartilage changes in acetabular dysplasia, with changes in ultrastructure and collagen expression contributing to the process.

The significance of metal staining on alumina femoral heads in total hip arthroplasty

Metallic transfer to alumina can occur intraoperatively and while reducing a dislocated total hip, when the femoral head contacts the rim of the metal acetabular shell. To see if metal discoloration is associated with changes to the alumina, we examined 14 metal-stained alumina femoral heads retrieved from ceramic-on-ceramic articulations using electron microscopy and noncontact profilometry. Metal staining was associated with surface damage to alumina on the femoral heads removed from unstable total hips. The surface roughness of metal-stained alumina heads was significantly greater than that of unused alumina heads. Alumina femoral heads should be protected against contact with the metal cup during total hip implantation. Dislocations in ceramic-on-ceramic total hips should be addressed early because of possible damage to the surface.

Effect of oral diacerein (DAR) in an experimental hip chondrolysis model

We aimed to reproduce the articular cartilage structural changes in a joint exposed to a metallic implant as in the adolescent pinned hip with persistent joint penetration and secondly, to test the effect of an interleukin inhibitor, diacerein (DAR) in the ensuing articular cartilage lesion. Twenty immature beagles were submitted to a surgical K-wire implantation in the hip with the material left in the joint space for 6 months. Twelve animals were sacrificed for histological and biochemical tests. Eight animals were sacrificed at 10 months (half of them treated with DAR) and analyzed by scanning electron microscopy (SEM) and biochemistry of the articular cartilage. Preoperative and monthly C3 and C4 complement and immunoglobulins serum levels were determined. The histological and the electrophoretic profile changes were significative at 6 months. At 10 months the migration profile (CaCl2) recovered to normal levels in the operated hip and the SEM scores for the acetabulum were similar to the non operated control hip after treatment. The serum level of IgA was elevated at the 4th and 6th month postoperatively. The persistence of a metallic implant resulted in degenerative changes parallel to that described for hip chondrolysis as a complication of in-situ pinning; and the cartilage lesion improved with DAR treatment.

Effect of hip hemiarthroplasty on articular cartilage and bone in a canine model

The purpose of this study was to determine if acetabular articular cartilage damage occurs in the presence or absence of changes in subchondral plate thickness or porosity and trabecular bone architecture after hip hemiarthroplasty. Eight canines were sacrificed 6 months after receiving unilateral hemiarthroplasties in which a cobalt chrome alloy femoral head was used. The acetabular cartilage, subchondral plate, and trabecular bone were quantitatively evaluated. Although the articular cartilage in the treated hip showed gross and histologic degenerative changes, there were no differences in the treated and contralateral hips in any of the trabecular bone parameters or subchondral plate thickness. However, the subchondral plate porosity was increased 2.6-fold in the treated hip. Therefore, degradation of cartilage can occur in the absence of thickening of the subchondral plate or alterations in the supporting trabecular bone architecture. These observations provide a better understanding of the role that periarticular bone has in the degenerative process after hemiarthoplasty.

Structure and vascularization of the acetabular labrum with regard to the pathogenesis and healing of labral lesions

INTRODUCTION

The aim of this study is to examine the structure and vascularization of the acetabular labrum with regard to the pathogenesis and healing of labral tears.

MATERIALS AND METHODS

The labral tissue was characterized immunohistochemically and under light microscopy; the collagen fibril texture was demonstrated by scanning electron microscopy after temporary staggered maceration of the tissue; and the vascularization of the acetabular labrum was studied immunohistochemically using antibodies against laminin.

RESULTS

The peripheral aspect of the acetabular labrum consists of dense connective tissue. The internal layer consists of type II collagen-positive fibrocartilage. Scanning electron microscopy revealed three distinct layers in the acetabular labrum: (1) the articular surface was covered by a meshwork of thin fibrils; (2) beneath the superficial network, there is a layer of lamella-like collagen fibrils; (3) the majority of the collagen fibrils are oriented in a circular manner. Blood vessels enter the labrum from the adjacent joint capsule. The distribution of vessels within the labrum is not homogenous. Blood vessels can be detected only in the peripheral one-third of the labrum. The internal part is avascular.

CONCLUSION

The result of this study demonstrates that the structure of the acetabular labrum is highly significant for the direction of traumatic and dysplastic labral lesions. The biomechanical analysis of the structure suggests that the labrum is stressed by compressive load. Therefore, excision or removal of the labrum may alter physiological functions such as enhancing joint stability and load distribution. The vascular pattern identified should encourage surgeons to develop repair strategies of peripheral labral tears to maintain its functions in the hip.

Quantitative analysis of UHMWPE wear debris isolated from the periprosthetic femoral tissues from a series of Charnley total hip arthroplasties

Submicrometer and micrometer-sized UHMWPE wear particles have been associated with osteolysis and failure of total hip replacements. A previous study by Tipper et al. examined the wear debris isolated from the acetabular periprosthetic tissues from 18 Charnley total hip replacements, and compared this data to the tribological variables of the prostheses. The present study aimed to isolate the UHMWPE wear debris from the femoral periprosthetic tissues from 10 of the same cohort of patients, and compare it with the debris isolated from the corresponding acetabular tissues. A variety of particle morphologies were observed, discrete submicrometer particles, along with flakes and fibrils. The particle size distributions ranged from 0.1 to >250 microm, however, the largest particles were only found in samples when the femoral head damage was characterised as low (R(pm) < 0.2 microm). The mode of the frequency distribution of particles was in the range of 0.1-0.5 microm for all the femoral tissues. Considerable variations were found in the mass distributions of the wear particles as a function of size for different patients. The net mass of debris isolated from the femoral tissues was significantly lower (p < 0.05, Student's t-test) than from the corresponding acetabular tissues. This along with considerable spatial variation in the net mass of debris isolated from the different regions of the same sample of acetabular tissue, indicates that the transportation of the debris has a marked effect on the net mass of debris accumulated in different tissues.

Tissue response to porous tantalum acetabular cups: a canine model

This study evaluated the osseous tissue response to a noncemented metal-backed acetabular component made of a new porous tantalum biomaterial. Eleven dogs with bilateral total hip arthroplasties (22 acetabular implants) were studied for a period of 6 months. Thin section histology, high-resolution radiography, and backscattered scanning electron microscopy revealed that all 22 implants had stable bone-implant interfaces. Regions of bone ingrowth were present in all histologic sections. The depth of bone ingrowth varied from 0.2 mm to the maximal limit of 2 mm. Analyzing contiguous regions of interest across the full bone-implant interface, the mean bone ingrowth for all sections was 16.8% +/- 5.7%. In the peripheral regions of the cup where bone-implant contact was most consistent, bone ingrowth averaged 25.1% +/- 10.1%. The data indicate that the porous tantalum material is effective for biologic fixation in the dog and may provide a suitable alternative to other porous materials used in acetabular cup design.

Wear analysis of a retrieved hip implant with titanium nitride coating

There is increasing interest in using surface modification technology to improve the wear properties of titanium alloy and limit articular surface wear of metal and polyethylene components. This report details the in vivo wear performance of titanium nitride coating on a retrieved hip implant obtained postmortem from a low demand patient 1 year after total hip arthroplasty. Analysis of the well-functioning implant revealed that wear debris can originate from a titanium nitride coated femoral head, as delaminated surface asperities, and manifest as adhesive wear on the articular surface. The wear observed on this implant indicates that rigorous testing and evaluation of titanium nitride coating technology should be conducted prior to widespread use on total joint implants.

Role of cyclic plastic deformation in the wear of UHMWPE acetabular cups

The mechanisms of wear in ultra-high-molecular-weight polyethylene (UHMWPE) acetabular cups were investigated on both laboratory simulator-tested cups and a clinically retrieved component. Two different levels of wear process were identified: one characterized by the formation and detachment of platelet-like flakes from initial machining marks, and the other by the formation of fine ripple and fibrils by repeated passes of microscopic asperities on the femoral head. Both wear processes could be described by a criterion of critical plastic strain. A theoretical model was developed to account for the generation of the microscopic wear particles based on such a critical strain criterion. Its predictions of the dependence of the UHMWPE wear rate on surface roughness and applied load were in excellent agreement with previously published experimental correlations.

Glass ceramic augmentation of the acetabulum. Total hip arthroplasties in 24 dogs

Implants made of glass-ceramic containing apatite and wollastonite were used for reconstruction of large bone defects of the weight-bearing acetabulum in canine total hip arthroplasties. 24 dogs underwent replacements and were killed after 3, 6, and 12 months. The interface between the prosthesis and bone was examined radiographically, histologically, and mechanically. Bone bonding with the prosthesis occurred in all the implants. Glass ceramic containing apatite and wollastonite implants seem promising for use in total hip arthroplasty as filling materials for large defects in weight-bearing bone.

Comparison of bone ingrowth into cobalt chrome sphere and titanium fiber mesh porous coated cementless canine acetabular components

Bone ingrowth into uncemented hemispherical canine acetabular components porous-coated with cobalt chrome spheres was compared to those porous-coated with titanium fiber mesh. While good bone ingrowth was noted in both types of porous coatings at 6 weeks after surgery with no difference in the histologic quality of the ingrown bone, quantitation of bone ingrowth showed that significantly more bone grew into titanium fiber mesh porous-coated components. The mean amount of bone ingrowth measured 10.5% of the area of the porous coating with fiber mesh coatings and only 5.5% of the area of the porous coating with spherical coatings (significant difference at P < .0005). The mean area density of the ingrown bone inside the pores measured 21.5% of the pore area with fiber mesh coatings, also significantly greater than 13.4% of the pore area with sphere coatings (P < .025). The ingrown bone penetrated a mean 66% of the depth of the porous layer with fiber mesh coatings compared to 32% of the depth of the porous layer with spherical coating (significant difference at P < .0005). The mean extent of the periphery of the porous layer with bone ingrowth was 88% for the mesh coatings and 55% for the spherical coatings (also a significant difference at P < .01).

[Aging process of the acetabular labrum--an electron-microscopic study]

We have studied the aging process of the labrum of the hip using scanning and transmission electron-microscopes. The materials consisted of 22 human hip joint acetabula. Disruption and irregular ridges were evident on the uppermost superficial layer and the superficial layer of the labrum in their fifties of age. Collagen fibers composing the labrum increased in density and sectional area in the specimens of subjects up to their twenties, but decreased in those of subjects in their thirties. At the joint of the labrum and articular cartilage, a bundle of fibers approximately 20 microns in diameter was observed to extend from the labrum to the cartilage, reinforcing the bond of these components. Disruption of this area starting on the acetabular side and leaving fibers of the labrum of about 400 to 500 microns on the cartilage side was more frequent in the specimens of subjects in their fifties of age. The changes with aging in the collagen fibers along with concentration of the stress of weight bearing at the point where the labrum meets the cartilage, may have some effect on the well-fitting of the acetabulum and femoral head.

Measuring the volume fraction of bone ingrowth: a comparison of three techniques

The need for quick, accurate, and reproducible methods to measure the amount of bone within porous metals has increased as the use of these materials has become more common within orthopedics. The purpose of this paper is to compare measurements of bone ingrowth using microradiography, stained histology, and backscattered electron imaging-scanning electron microscopy (BEI-SEM) in cementless, porous-coated acetabular components retrieved from human patients. BEI-SEM of bone ingrowth into porous metal provided excellent images for quantitative analysis. The stained sections and BEI-SEM images provided very comparable results, while microradiography consistently underestimated the porosity of the porous coating and overestimated the amount of bone ingrowth.

[Scanning electron microscopic study of the coxofemoral articular surfaces in the human fetus]

A scanning electron microscopic study of the coxo-femoral articular cartilage was performed in ten human fetuses aged from 15 to 40 weeks. An irregular surface was observed at the level of both femoral head and acetabulum. These surface irregularities are modified during development.

The response of articular cartilage to weight-bearing against metal. A study of hemiarthroplasty of the hip in the dog

Hemiarthroplasty of the hip and some other joints has been used for many years with satisfactory results, but the fate of articular cartilage when weight-bearing against metal has not been reported. Replacement of the head of the femur was carried out in one hip of each of 26 dogs, and the changes in acetabular cartilage studied at intervals of up to 24 weeks. There was early loss of proteoglycan, followed by surface damage to the cartilage, progressive degenerative changes, and growth of pannus from the articular margins. At 24 weeks after operation there was little remaining articular cartilage, while intense subchondral activity suggested that the bony skeleton was being remodelled to conform to the shape of the prosthesis. This study is not intended to suggest that hemiarthroplasty does not help patients.

A method for the postmortem evaluation of an in situ total hip replacement

A method was developed for the post-mortem evaluation of a total hip replacement retrieved in situ. The hip replacement had been implanted for six years. The evaluation procedure employed existing techniques in a logical sequence such that earlier tests would not compromise results from subsequent ones. These techniques included the measurement of range of motion, aspiration of the joint for analysis of debris, radionuclide arthrograms for determination of looseness of the components, gross and histological inspection of the capsule and synovial tissue, serial sectioning of the femoral component, determination of some mechanical properties of the bone and femoral stem, and scanning electron microscopy of the articulating surfaces of the prosthetic components. Positive findings in the specimen studied were: excessive wear of the articulating surface of the acetabular component, and associated polyethylene debris in the aspirate and surrounding synovial and granulation tissue.