Cell sheet injection as a technique of osteogenic supply.

We previously reported a new cell transplantation method utilizing injections of mesenchymal stem cell (MSC) sheets that have osteogenic potential. After subcutaneous transplantation without any scaffold, the sheet demonstrated in vivo bone formation. In the present study, we transplanted such sheets by injection into implanted ceramics and assessed whether the injectable MSC sheets could stimulate osteogenic integration of the ceramics. To fabricate MSC sheets, bone marrow cells cultured from femur shafts of 7-week-old rats were subcultured in regular 10-cm dishes containing dexamethasone and ascorbic acid phosphate until confluent. Each cell sheet was then lifted using a scraper. Porous ß-tricalcium phosphate (ß-TCP) disks (5 mm Φ×2 mm) were transplanted subcutaneously into the backs of the rats. Immediately following implantation, the sheets were injected around the disks via a 16G needle (immediate group). Cell sheets were also injected into the remaining implanted disks 1 week after disk implantation (1-wk group). Four weeks following sheet injection, radiography and histology revealed calcification and bone tissue around the harvested disks of the immediate group (eight disks exhibited bone formation/eight implanted disks), whereas calcification and bone tissue were observed in 50% of the samples in the 1-wk group (four disks exhibited bone formation/eight implanted disks). The present study indicates that injected cell sheets can supply osteogenic potential to implanted ceramics. Owing to the usage of a needle for cell sheet transplantation, such an injection method can be applied as a minimally invasive technique of osteogenic supply to implanted ceramics.

Distal cement mantle thickness with a triangular distal centralizer inserted into the stem tip in cemented total hip arthroplasty.

Fifty-seven hips undergoing a primary cemented total hip arthroplasty with use of a triangular distal centralizer inserted into the stem tip were investigated, with a special focus on distal cement mantle thickness. The subjects were 43 women and 3 men. When evaluated on conventional anteroposterior and lateral radiographs, the relative incidence of thin cement mantles in zones 3 or 5 owing to the distal centralizer was 15.8% (9 hips). Unsatisfactory findings were that the distal centralizer and distal part of the stem shifted to the cortex in 7 hips and bent or failed at the inserted site in 2 hips. There is risk of generating a thin cement mantle with use of the triangular centralizer and its insertion into the stem tip.

Thin cement mantle and osteolysis with a precoated stem.

The radiographic and clinical results of 55 hips (52 patients) implanted with the Harris precoat hip prosthesis using second generation cementing technique were investigated in this study. All metal backed sockets were fixed with cement. The preoperative diagnoses were osteoarthritis secondary to dysplastic hips in 42 patients, primary osteoarthritis in six, rapidly destructive coxarthrosis in five, and osteonecrosis of the femoral head in two. The average age of patients at the time of surgery was 67 years. The average duration of followup was 8 years. The rates of aseptic loosening and osteolysis in the femoral side were 5.5% (three hips) and 12.7% (seven hips), respectively. Three sockets were loosened, and no osteolysis was detected in the acetabular side. The mantle of cement in the femur was graded using the criteria described by Mulroy et al. Twenty-seven of 55 (49%) hips had regions with a thin cement mantle less than 1 mm in thickness or a defect in the cement mantle. Osteolysis was detected in seven of the 27 (26%) hips. Locations of osteolysis were coincidental with those of thin cement mantle or defect with the exception of one hip. This study clearly shows that a thin cement mantle less than 1 mm in thickness and a defect in the cement mantle lead to osteolysis.

Importance of a thin cement mantle. Autopsy studies of eight hips.

The question whether thin cement mantles around cemented femoral components led to an increased frequency of cracks in the cement was asked. Microscopically, multiple cross sections of eight femurs retrieved at autopsy from clinically successful total hip replacements after prolonged in vivo service containing well fixed Harris Design 2 cemented femoral components were studied. None of the components were loose by radiographic criteria. All were fixed solidly when loaded in vitro in simulated stair climbing and gait, as assessed by high resolution micromotion sensors. The specimens were sectioned transversely at 5-mm increments. The cross sections were examined under a dissecting microscope at x 100. A thin mantle arbitrarily was defined as a mantle of less than 1 mm in thickness. The analysis of the contact radiographs showed that the routine anteroposterior and lateral radiographs underestimated the prevalence of thin cement mantles and mantle defects. Although overall on all the cross sections 9% of the aggregated cement mantles was classified as having thin cement, 92 of the 101 cement cracks occurred in areas of the mantles that were less than 1 mm thick.

Wear of retrieved cemented polyethylene acetabula with alumina femoral heads.

Four yttrium-stabilized alumina ceramic-on-polyethylene articulations obtained from patients who were undergoing revision surgery for sepsis (3) or recurrent dislocation (I) between 34 and 73 months were evaluated to assess their in vivo wear performance. The annual volumetric wear of the acetabular components determined directly by a fluid displacement method ranged from 58 to 140 mm3/y. Scanning electron microscope examination of these four ceramic heads revealed similar surface damage in all cases from a variety of causes. These included differential granular wear (alumina grains and yttrium-stabilized alumina grains at different depths), multidirectional scratches with heaped up boundaries, and incompletely sintered grains, as well as the formation of craters and separation of grain boundaries. The femoral heads in this small series of revision cases show that yttrium-stabilized alumina ceramic heads may develop surface irregularities from either manufacturing processes or in vivo use. The wear rates of this type of alumina-on-polyethylene articulation up to the time of revision were not substantially different from those found in other metal-on-polyethylene articulations retrieved at revision surgery.

[Assessment of limp in patients with coxarthrosis--three-dimensional measurement of the pelvic rotation].

To assess the gait characteristics of the patients with coxarthrosis objectively, the rotation of the pelvis during ambulation was measured on the frontal, sagittal and horizontal planes using 3 gas-rate-sensors(Rotational Angle Measurement System G-2210, Anima Inc., Tokyo). In the normal subjects, the waveforms of the rotational angle on the frontal plane were symmetrical, highly reproducible and had 2 peaks. In contrast, the waveforms of the patients were asymmetrical and poorly reproducible. This was shown objectively using Fourier transform technique. The mean rotational angle of the patients was smaller than that of the normal subjects on the frontal plane, and larger on the sagittal plane. We can distinguish the patients from the normal subjects by observation of the waveform on the frontal plane and the ratio of the rotational angle on the sagittal plane to that on the frontal plane.