The spontaneous development of chondroblastoma was seen clinically and demonstrated radiologically in the talus of a 5.5-year-old boy. It was followed for 9.5 years before surgery was performed. Histological examination revealed typical features. This suggests that chondroblastomas may undergo very slow growth and development. The case is compared with 31 other chondroblastomas of the foot.

In March, 1981, development of a hip socket for implantation without the use of bone cement was begun in the Biomechanics Research Laboratory of the Department of Orthopaedic Surgery of the University of Zurich, Balgrist. Already in March, 1982, the first artificial socket with selflocking action, the Balgrist Hip Socket, was successfully implanted in a patient. Following some design modifications, a series of 287 hip sockets were implanted before April, 1986; all of them being made entirely of high density polyethylene. In an attempt to improve the anchoring of the prosthesis within the bone, the outer surface of polyethylene that faced the bone was furnished with a thin coating of titanium and in this form the socket was used 63 times. In the meantime, a model with the outer split shell made of titanium was designed so that in this presently used form, from November, 1987, up to August, 1989, 133 of these hip sockets have been implanted. With the removal or replacement of only 29 sockets, which amounts to 6% (2.7% aseptic and 0.8% septic loosenings, 1.3% removed because of technical mistakes made in the early stages, and 1.3% removed because of suspected low grade infection) the results up to now might well be considered most encouraging.

From September 1980 to March 1985, 123 cementless, polyethylene Endler acetabular sockets of the threaded, tapered type were implanted in 115 patients at the department of orthopaedic surgery, Balgrist, University of Zurich. The first 102 Endler sockets, in combination with a Zweymüller femoral prosthesis, have been followed up till April 1988, this corresponding to an average observation period of 57.4 months. 12.8% of the total number of qualitative criteria and the Sutherland method, and further 20.6% of the cases were suspected of having loosened, so that a figure of 33.3% (34 loosened sockets) resulted. A definite correlation between loosening and the following factors were determined: females, limping, Trendelenburg sign, period of implantation and severe, continuous pain. No correlation was found between either tolerable pain, age, weight, or para-articular ossification, and loosening. The cementless artificial hip joint of Endler/Zweymüller combination led to a definite improvement of independency and living quality through increase in mobility and reduction of pain.

Since introduction of the prosthetic joint replacement numerous design modifications have taken place. Some were successful other were given up after short time. During almost twenty years now in joint arthroplasty of the hip components made of A12 03-ceramics--ball and/or socket--are used. Many papers have reported about the results of these implants. One of the possible complications described in the literature is the breakage of the ceramic component(s). Since April 1981 we have implanted over 500 cementless prosthesis of the hip in combination with a ceramic ball. In one patients we observed a breakage of the head two years after implantation. We will describe the story of this case and discuss possible reasons for this complication in reference to the literature.