The use of cementless expansion acetabular component and an alumina-polyethylene bearing in total hip arthroplasty for osteonecrosis.

We performed 114 consecutive primary total hip arthroplasties with a cementless expansion acetabular component in 101 patients for advanced osteonecrosis of the femoral head. The mean age of the patients at surgery was 51 years (36 to 62) and the mean length of follow-up was 110 months (84 to 129). The mean pre-operative Harris hip score of 47 points improved to 93 points at final follow-up. The polyethylene liner was exchanged in two hips during this period and one broken acetabular component was revised. The mean linear wear rate of polyethylene was 0.07 mm/year and peri-acetabular osteolysis was seen in two hips (1.9%). Kaplan-Meier analysis indicated that the survival of the acetabular component without revision was 97.8% (95% confidence interval 0.956 to 1.000) at ten years. Our study has shown that the results of THA with a cementless expansion acetabular component and an alumina-polyethylene bearing surface are good.

High bifurcation of median nerve at the wrist causing common digital nerve injury in endoscopic carpal tunnel release.

A 45-year-old right-handed woman was treated by endoscopic carpal tunnel release under local anaesthetic. When cutting the proximal half of the flexor retinaculum with the retrograde blade, she complained of an electric shock-like pain in her middle and ring fingers. Open exploration of the carpal tunnel was performed and a laceration of the middle/ring common digital nerve, which bifurcated at the unusually high level of the wrist crease, was found.

Biomechanical properties after pre-twist of canine patellar tendon.

We studied what effect a rotational pre-twist of the patellar tendon had on its mechanical properties. We used the central strip of canine patellar tendons. The length, width and thickness of each specimen were measured and the specimens were mounted in custom-made aluminum pots. Five groups of 10 specimens each were measured with neutral rotation, 90 degrees external rotation, 180 degrees external rotation, 270 degrees external rotation and 360 degrees external rotation. The ultimate stress, ultimate strain, average elastic modulus, and strain energy density were measured. There were no statistically significant differences among the five groups. Twisting the graft up to 360 degrees did not decrease the biomechanical properties of the graft.

Primary unreamed intramedullary nailing for open fractures of the tibia.

Forty-six open tibial fractures (42 patients) were treated by primary unreamed intramedullary nailing, with debridement of open wounds and treatment of soft tissue. According to Gustilo-Anderson classification there were 18 grade I cases, 18 grade II cases and 10 grade III cases. The incidence of infection was low with two cases of superficial infection and one of deep infection. The mean time for union was 21.9 weeks and the rate of nonunion was 10.8%. There was no significant difference in the mean time to union, infection rate and rate of nonunion with different site and grade of fracture, but there was a longer union time and a higher rate of nonunion in complex and comminuted fractures. Unreamed intramedullary nailing, with appropriate soft tissue treatment, gives good results in the treatment of open tibial fractures including grade III.

Fracture separation of the distal humeral epiphysis in children younger than three years old.

This study evaluated the change of carrying angle and the causes of cubitus varus after the fracture separation of the distal humeral epiphysis in young children. Twelve cases of fracture separation of distal humeral epiphysis were treated from January 1995 to July 1997. The age of all patients was younger than 3 years old. A metaphyseal fragment was seen in all cases (Salter-Harris type II), but the size of the metaphyseal fragment was either a very small flake or a large Thurston-Holland fragment. Posteromedial displacement was seen in all cases. There were three treatment groups: closed reduction with percutaneous pinning, closed reduction with cast, and cast without reduction. Follow-up period averaged 23.5 months (range, 12-40). Cubitus varus deformity was seen in seven cases, and six of them had a partial defect of the medial condyle that was avascular necrosis. The methods of treatment, age of injury, and the type of epiphyseal injury had no influence on the development of cubitus varus, but avascular necrosis of the medial condyle was related to the cubitus varus deformity (p<0.05). The results of this study suggest that fracture separation of distal humeral epiphysis in young children is likely to produce cubitus varus deformity with the development of avascular necrosis of the medial humeral condyle.

Three dimensional shape reconstruction and finite element analysis of femur before and after the cementless type of total hip replacement.

Computerized tomography was used to reconstruct a shape, and stresses in three-dimensional objects were analysed. The human femur, which has a very irregular shape, was chosen as an object. CT image data of a cadaver femur were transferred to a computer, and an edge extraction program generated the cross-section of bone by specifying a range of CT values for each slice. Pixel data from the CT scan are converted into a vector of points (x, y, z) which can specify the boundaries of bone. Lateral surfaces are defined by stacking up the slices and making use of the vectorized data. Intermediate and oblique cross-sections can be obtained by an interpolation technique. The constructed model was used as input data for the finite element analysis. To understand the stress distributions before and after the cementless type of total hip replacement, a three-dimensional finite element stress analysis of the bone-implant system was carried out, assuming micromotions between the stem and the femur. The analysis was done for both frictionless and friction cases, modelling the contact point with a gap element having isotropic friction. The analysis shows that the stress is not concentrated on the femoral calcar when the friction coefficient is large.

In vitro study of contact area and pressure distribution in the human knee after partial and total meniscectomy.

Many investigators have attempted to find the cause of the osteoarthritic changes after meniscectomy. Alteration of the mechanical factors resulting in stress concentration, is now thought to be one of the most important causes but few experimental studies have reported the differences in contact area and pressure distribution after partial or total meniscectomy. By using pressure sensitive film, we have calculated the contact area and the pattern of weight distribution in three different situations; intact meniscus, partial and total meniscectomy. The experimental materials were obtained from 5 above knee amputation specimens. The knee joint was fixed in full extension to an Instron machine using an aluminium box and mounting resin. Load was transmitted to the tibiofemoral joint containing the special film, within a physiological range. Analysis of the contact area for each situation (intact meniscus, partial and total meniscectomy) was made by reviewing the film. By measuring the contact area after meniscectomy, we showed that the meniscus performs a load transmitting function in the knee joint. The medial contact area of the tibiofemoral joint with an intact meniscus is always larger than the lateral compartment (1.36:1), but in partial and total meniscectomy the difference between them gradually decreased. There was a minor decrease in contact area after partial meniscectomy and a much greater decrease after total meniscectomy. The degree of stress concentration in the contact area was increased when part or all the meniscus was excised. There was little change of contact area in the opposite, intact side of the joint after partial meniscectomy, but marked change after total meniscectomy.

Photoelastic analysis of stress distribution on the tibiofemoral joint after meniscectomy.

Three-dimensional photoelasticity models of the knee joints were made of epoxy to observe the change in the status of stresses according to the size of defect in the meniscus. Three kinds of meniscus models were made of rubber. Through axial application of a vertical compressive load of 8 kg, equivalent to the joint reaction of 3000 N in the human knee joint, the patterns of the isochromatic fringes were observed and stresses around the knee joint were analyzed according to the size of the defect in the medial meniscus. Stress was increased in magnitude according to the size of the defect of the meniscus, and was focalized after meniscectomy. In the partial meniscectomy model, the maximum stress concentration point of the removed side migrated to the margin of the same side of the joint. But, in the total meniscectomy model, stresses were markedly increased in magnitude on both sides of joints, and maximum stress concentration points were more centralized. This centralization effect would contribute to the degenerative process of the knee joint after meniscectomy.