In order to study the joint contact and joint space of statically loaded human knee and hip joints, observations of serial slices of joint specimens which were frozen during the application of a load were carried out. In the intact joints, the articular cartilage surfaces did not come into direct contact with each other even under a load of more than twice that of the body weight. The minimum distance between cartilage surfaces in each specimen ranged from 0.2 to 0.6 mm. The Indian ink whish was injected into the joints before the load application was squeezed out of some areas of the remaining joint space, but a dye-free fluid apparently remained in this space.Based on our findings, the definition of joint contact and the lubrication mechanism in the intact human joint have been discussed.

In uncemented total hip arthroplasty, a complete filling of the gap between femoral prosthesis and the host bone is difficult and defects would remain, because the anatomy of the reamed intramedullary canal cannot fit the prosthesis. Therefore, it seems practical to fill the gap with a clay containing hydroxyapatite (HA), which has an osteoconductive character. The clay (HA clay) is made by mixing HA granules (size 0.1 mm or more) having a homogeneous pore distribution and a porosity of 35-48 vol%, and a viscous substance such as a saline solution of sodium alginate (SSSA). In the first experiment, the ratio of HA granules and sodium alginate in SSSA is set for the same handling properties of HA clay and polymethylmethacrylate bone cement (standard viscosity) before hardening. As a result, the ratio is set for 55 wt% of HA in the clay and 12.5 wt% of sodium alginate in SSSA (i.e., HA:sodium alginate:saline solution = 9.8:1:7). In the second study, the gap between the femoral stem and bone model is completely filled with HA clay. However, the gap is not filled only with HA granules or HA granules mixed with saline solution. In the third animal experiment, using an unloaded model, histology shows that HA clay has an osteoconductive property bridging the gap between the implant and the cortical bone without any adverse reaction. HA clay is considered a useful biomaterial to fill the gap with adequate bone ingrowth.

A 34-year-old man developed a nonfatal venous air embolism during arthrography of his post-traumatically contractured knee joint. From the arthrographic findings, injected air was assumed to have entered the great saphenous vein via the venous opening in the knee joint. Venous air embolism is an extremely rare complication of knee arthrography, but can occur. As it is potentially fatal, prompt recognition and appropriate positional and supportive therapy are essential.

Once the opportunity for primary repair of injured knee ligaments after traumatic dislocation has been lost, ligamentous reconstruction is difficult using only autogenic tissues because of the risk of loss of function at the donor site, so other substitutes are needed. The four major ligaments in the unstable knee of a 35-year-old man were reconstructed by solvent-preserved human fascia lata three months after traumatic open dislocation. The clinical results were satisfactory. Arthroscopic examination one year later showed that the reconstructed ligaments had good thickness and tension and were composed of autologous connective tissue without evidence of rejection. The literature on dislocation of the knee and on cruciate ligament reconstruction by allograft was reviewed, and a brief introduction to solvent-preserved human fascia lata was presented. The commercialization of this material has solved some common problems concerned with using allogenic tissues.

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