Objective

This paper aims to analyze the kinetics of the over-ground wheel-type body weight supporting system (BWS); tendency changes of low extremity joint moment (hip, knee, ankle), 3 axis accelerations of a trunk, cadence and gait velocity as weight bearing level changes.

Typical navigation system to insert hip implants in the accurate position consists of a 3D position measurement device and a computer. These navigation systems are classified into two categories according to the method of identifying the anterior pelvic plane that works as the reference of the orientation of the acetabulum cup. The preparation process for imageless navigation system is very easy because it uses three anatomical bony markers to define the anterior pelvic plane. When these anatomical bony markers are hard to locate, especially at the pubic symphysis due to the thick soft tissue, the accurate direction of the cup cannot be secured. The aim of this study is to estimate the soft tissue thickness without using the patient’s specific data such as the A-mode ultrasound image or C-arm image.

In our previous study, it was pointed out that the thickness of the hypodermic fat obtained through an ultrasound image could be estimated using the patient’s BMI and the displacement created by a specific force. Considering the probe shape, the soft-tissue thickness estimation formula is expressed as follows:

\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[Y_{estimated_thickness}\ =\ k(b_{0}\ +\ b_{1}\ {\times}\ BMI\ +\ b_{2}{\times}\ {\delta})\] \end{document}

k: constant for the shape of the probe end

Only two kinds of the probe end shapes (flat-ended probe and spherical-ended probe) were considered, and the change in the k value corresponding to the radius was calculated using the FE model of the soft tissue for each subject. The finite-element model was constructed as axisymmetric.

The simulation result of the initially assumed variables and the measured result were compared, and the optimization method was used to minimize the error: The RMS difference between the result of the experiment and that of the analysis was taken as the objective function. With the FE analysis for the two kinds of probe shapes with one subject, we determined the shape variable (k).

From the formula composed by a model with data from 28 people, the average error was 3 mm equivalent to the angle error of less than 1°. Therefore, the use of the method suggested in this study will help to improve the acetabulum cup navigation in THA, when we use only the surface points on the soft tissue. In addition, it seems that the soft-tissue thickness estimation formula suggested in this study may be generally used.

We evaluated the effects on infection control and clinical feasibility of a prosthesis with antibiotic-loaded acrylic cement(PROSTALAC) which was designed for treatment of infected total hip arthroplasty.

Thirty patients underwent two-staged exchange arthroplasty using the PROSTALAC for treatment of the infected total hip arthroplasty were analysed from March 1995 to February 2007. For shaping of the stem spacer, cement containing antibiotics were appropriately coated on stem spacer and push and pull movement was carried out within the medullary cavity of proximal femur until cement hardened. Also, for prevent of post surgical dislocation, a specially designed polyethylene liner was used. Postoperatively, antibiotics were administered for at least 6 weeks according to the results of erythrocyte sedimentation rate and C-reactive protein assessment.

Infection cure rated 83.3% (20 cases) and C-reactive protein normalized in an average of 5.6weeks (2wks~26wks) but ESR showed very variable score. Partial weight bearing with crutch was possible after 2 weeks postoperatively and lower-limb shortening averaged to 1.43 cm (0.5~3) with a mean bending range of 63.6 degrees (40~90). There were neither dislocations nor fractures during patient mobilization and 5 cases, especially in old age showed satisfactory results even without second staged revision. Recurred infection after PROSTALAC insertion occurred in 5 cases (15%).

Appropriate techniques of PROSTALAC insertion for stability allows us to adjust the reimplantation timing to the course of infection control.

The congenital or acquired contracture of gluteus maximus is relatively rare, and its clinical feature of chronic lower back pain and extension contracture of the hip joint had been confused with herniations of lumbar disc disease or sequelae of cerebral palsy. The authors successfully treated these contracture of gluteus maximus, so report these cases and results. 9 patients suffering from Difficulty in squatting position or gait disturbance were surgically treated in our department from 1979 to 2000. There were eight men and a woman, mean age was 17.3 years old, and seven patients were bilateral. Four patients revealed past medical history of multiple intramuscular injection at gluteal region, but five patients revealed unremarkable history. Preoperative mean further flexion, internal rotation and external rotation of hip joint were 42°, 15°, and −5°. These patients revealed specific features of frog leg position in squatting position. Intraoperatively, the authors released the fibrotic band of the gluteus maximus, the short external rotators, the gluteal attachment of the iliotibial band and the joint capsule. After anesthesiologic recovery, active and passive joint motion exercise of flexion and rotation was started to prevent recurrence of contracture. Postoperatively, mean further flexion of hip joint were increased to 105°, and no Difficulty in sitting or squatting position, but slight limitation in rotation was remained. In follow up visit, no decrease of articular motion were observed. Conclusively, severe limitation of joint motion due to contracture of gluteus maximus can be successfully treated with surgical maneuver accompanied with postoperative aggressive physical therapy.