Thigh pain appears often after THA used of the cement-less femoral components, but the appearance mechanism of thigh pain does not have been elucidated. As one factor of manifestation of thigh pain, it has been guessed that the pressure from the inside of medullary cavity of bone by the stem. The purpose of this study is confirming whether the flexor reflex is caused, by using the femur of a rabbit that applied the pressure from the inside of medullary cavity of bone.

Japanese white rabbits with weight of about 3kg were used. Evaluation of the appearance of the pain by the pressure was performed by measurement of the hind leg flexor activity produced by the flexor reflex. After confirming that appearance of the muscles activity by the pain reflex from adding the pain stimulus to the hind leg skin of rabbits, we loaded of the pressure into the inside of medullary cavity of bone and observed whether the muscles activity appears. As the laboratory animals model, we prepared two kinds of rabbits by the difference in the amount of reaming. And we tested how the differences show up between these two kinds of rabbits.

In the rabbits with few amounts of reaming, the flexor reflex appeared in low pressure. But, in the rabbits with many amounts of reaming, the flexor reflex did not appear in high pressure, either.

It is known that the somatic sensory nerves are distributed in the bone, and it is known that the sensory nerve ends exist in the medullary cavity of bone. It was suggested that the pain is induced, when the sensory nerve ends remained in the inside of medullary cavity of bone and the pressure in whicha reaction is possible was carried out there.

We evaluated intermediate-term results of primary cementless Omniflex prostheses.

Forty-nine patients (57 hips) with a mean age of 44 years were observed for an average of 8.6 years.

These results were inferior to those using other recent cementless total hip systems. The increasing prevalence of loosening and osteolysis with time are problems related to this Omniflex femoral component. Although the implant design is unique, the authors no longer use this system.

Prosthetic impingement after THA is to different for the angle and shape of the implant. Purpose of this study is examine the range of motion(ROM) on a computer when angle and shape of the implant are changed.

The 3D implant models were created on a computer. The angle was measured in the flexion, extension, adduction direction byevery 0.1 degrees. There are three kinds of acetabular abduction angle, two kinds of acetabular anteversion angle and two kinds of femoral anteversion angle. There are three kinds of the radius of neck and the neck shaft angle. All 324 patterns of the above model were measured.

When the radius of neck decreased, the ROM increased in all cases. When the neck shaft angle decreased, the ROM increased by almost all cases. When the acetabular anteversion angle increased, the ROM of flexion direction increased and adduction direction decreased, and as for the extension direction, all the factors had influenced the change in the ROM. When the acetabular angle increased, the ROM of the extension direction increased and the flexion directions decreased. As for adduction direction, femoral anteversion angle, acetabular anteversion angles, and the radius of neck had influenced the ROM. When the femoral anteversion angle increased, the ROM of flexion direction increased and extension, adduction direction decreased.

The clinical ROM is affected by the impingement of non-implant and the strain of the soft tissue. Therefore, It’ s considered that the clinical ROM is smaller than the ROM which was investigated in this study in many cases. When the radius of neck and the neck shaft angle decrease, the increase of the ROM expected. However the radius of the neck should not be decreased too much to avoid the decrease of the neck strength.

Introduction: This study evaluated the sphericity of bearing surfaces in total hip arthroplasty.

Methods: All the prosthetic metal femoral heads and the UHMWPE liners evaluated in this study were obtained straight from manufacturers (DePuy Johnson and Johnson, Howmedica Osteonics, Kyocera, Smith and Nephew, Zimmer). Out-of-roundness was assessed as an indicator representing sphericity. A total of 50 femoral heads and 22 UHMWPE liners were evaluated in 1995. Out-of-roundness of ball bearings were measured for the control study. A total of 43 femoral heads and 40 UHMWPE liners were evaluated in 1999 and 2000.

Results: The out-of-roundness of the femoral heads and the UHMWPE liners were significantly inferior to those of ball bearings. The out-of-roundness of the UHMWPE liners was significantly inferior to that of the femoral heads. The out-of-roundness of the femoral head on the sagittal plane was significantly inferior to that on the transverse plane. Several significant differences were found among different manufacturers. Overall, the out-of-roundness of the femoral head on the sagittal plane and UHMWPE liners had improved significantly in 1999/2000 compared to that in 1995.

Discussion: We previously reported that UHMWPE wear in poor out-of-roundness coupling (femoral head: 9.5 μm, socket: 36 μm) was 148% greater compared to those in good out-of-roundness coupling (femoral head: 0.5 μm, socket: 0.6 μm) at 1 million cycle experiments (J Arthroplasty 15:332, 2000). Some prosthetic femoral heads indicated more than 9.5 μm out-of-roundness in the present study, and these femoral heads with poor sphericity might be unfavorable to wear if implanted. We consider that sphericity of UHMWPE liners should be also improved to reduce initial UHMWPE wear. The sphericity of bearing surfaces can be improved by appropriate changes in manufacturing technique. Further improvement is desirable, since this is expected to prolong the functional performance of the prosthesis after total hip arthroplasty.

The use of prostheses with porous surfaces in cementless total hip arthroplasty now predominates. Beads are popular for use as a porous coating, but their mechanical strength may be insufficient because of displacement of some of the beads from the coating. In this study, we propose a new porous surface, created by making direct holes in the metal surface using a YAG laser. A titanium-alloy (Ti-6Al-4V) rod was used. A Bead-type prosthesis was made by diffusion bonding pure titanium beads to the rod; it was 5 mm in diameter and 35% in porosity. A Laser type was made by directly creating holes in the same rod surface using a YAG laser; it was 5 mm in diameter and 33.7% in porosity. Both implants were evaluated in vivo using the hemitranscortical cylindrical model in two beagle dogs. Four prostheses were implanted into each femur through the lateral cortex, for a total of eight of each type, and remained in place for 12 weeks. Except for the proximal implant, push-out tests were performed to measure the shear strength of fixation of the implants to the cortical bone. For observations of the implant-bone interface, decalcified specimens of the proximal femur were stained with toluidine blue and observed with an optical microscope. The mean push-out strength of the Laser type was approximately 10.2 MPa and that of the Beads type was approximately 10.7 MPa. There was no significant difference in interface push-out strength between the groups. Bone ingrowth into both types was sufficient, however, some specimens of the Beads type demonstrated displacement of some of the beads from the rod surface. This study indicates that a porous surface created with a YAG laser might be useful not only for its shear strength, but also for the strength of the surface itself.

Lumbar Degenerative Kyphosis (LDK) is a clinical entity showing kyphosis in the lumbar spine in elderly with multilevel disc narrowing and a varied degree of osteoporosis. LDK patient complains of stooped gait with persistent low back pain and weakness. Purpose of this paper is to study the lumbar muscle in LDK patients with histopathologic and biophysical evaluations to investigate the pathogenesis.

Materials and Methods: 1. Intramuscular pressure (IMP) (a) of the lumbar extensor compartment and hemoglobin content (Hb)□@(b) of 25 young volunteers were also investigated comparing in standing upright and flexion positions using (a)□@pressure monitoring kits and an non-invasive oxygenation monitor. 2.Muscle biopsy specimens obtained from the lumbar extensors of 9 LDK patients were histopathologically examined with HE, cytochrome c oxidase and other methods. These data were compared with muscles taken from age-match controls. Mitochondria function was also examined on biochemistry.

1. IMP of the extensors markedly increased in the flexion position (130.0□}45.4 in males and 86.3 mmHg in fem.) comparing to straight upright□@(22.8□}14.4, 17.0□}6.0). Oxy-Hb concentration decreased from 100% to 92.9, 95.5 % respectively in flexion, which was a sign of ischemia. 2. Both multifidus and sacrospinalis m. showed moderate to marked interstitial fibrosis, decreased number of muscle fibers and decreased stain intensity of cytochrome c oxidase. These finding were similar to those seen in repeatedly compressed muscles of an animal model of the chronic compartment syndrome. In comparison the rectus abd. and psoas muscles in the patients showed almost normal except for some aging changes. Conclusion: There appeared to be definite atrophy of the lumbar extensor muscles with histochemical and biochemical methods in LDK patients, whereas the flexors showed no change. This extensor atrophy is limited in the lumbar region in LDK. These localized atrophy of the lumbar extensors would suggest a result of high IMP during working in deep bending position of the spine for many years and may play important role in etiology of this disease condition.