The trunnion bearing (Figure 2, Figure 3a) was a well-known mechanical device that could be designed for the large forces that act on the hip joint. In Christiansen’s hemiprosthesis, the angle between the cylindrical trunnion and the stem of the prosthesis was empirically set to 115°, which permitted a sufficient bearing for movements in the sagittal plane – flexion and extension. Thereby, most of the movements in the hip joint between the artificial femoral head and the acetabulum were transferred to the trunnion bearing.
Figure 2 Christiansen’s hemiprosthesis in 1967. Femoral heads made of polyethylene, diameter 44 mm and 52 mm, without a steel coating. Stems of varying sizes, a file and a punch to drive them into the femoral shaft. During the surgery, a sterile slide caliper was needed to find the diameter of the caput femoris that had been removed by the surgeon. Photo: Einar Sudmann
Figure 3 a) Christiansen’s hemiprosthesis as used in the period 1965 – 67. A loose femoral head articulates with a cylindrical trunnion on the stem of the prosthesis, the trunnion bearing. To achieve a lasting fixation in the femoral canal, the stem of the prosthesis had several perforations, similar to the stem of an Austin Moore hemiprosthesis. The perforations were intended to permit ingrowth of bone tissue to fixate the stem permanently to the bone. The angle between the head and the stem is 115°. The femoral head was initially made of Teflon, from 1967 of polyethylene. b) Christiansen’s hemiprosthesis as used from 1968. The loose femoral head, with a steel coating added by the Polaris factory in Sandnes, was initially made of polyethylene, later of Delrin. The stem is smooth for fixation with cement. c) Christiansen’s total prosthesis as used from 1970. The relatively large metal femoral head articulates on the inside against a sleeve of Delrin and on the outside against a relatively thin-walled artificial acetabular cup made of Delrin. The acetabular cup has small indentations on the outside to enable adherence of the cement. The stem is smooth for fixation with cement. d) A modern Charnley-Hastings hemiprosthesis with a loose femoral head of polyethylene with a steel coating. The femoral head articulates against a standard Charnley stem with a small head, and the steel coating – as in all other hemiprostheses – against the joint cartilage in the acetabulum. In 1969, Christiansen was granted a US patent for this kind of «ball-and-socket joint», bipolar hemiprosthesis in 1969.
With the aid of radiological function imaging using a small metal marker in the plastic femoral head, it could be shown that the latter stayed immobile during flexion/extension of the hip joint
(6). These findings were later verified by cineradiography (7). During abduction, adduction and rotation, however, the prosthesis functioned as a regular hemiprosthesis with a fixed femoral head.
Christiansen obtained a Norwegian and US patent for his hemiprosthesis, with 26 May 1965 and 24 May 1966 as priority dates, respectively. The first prototypes were made by the Fadum mechanical factory in Drammen by the engineers Robert Johansen and Knut Nilsen. According to a front-page article in the
Fædrelandsvennen daily, the prosthesis came into production in the autumn of 1968 at the AS Nymo factory, which mostly manufactured maritime equipment (8). To ensure production and distribution, the company AS Joni was registered on 13 September 1966.
In 1965, Christiansen’s hemiprostheses were first used in Drammen for dislocated medial collum fractures in patients over 70 years. The artificial femoral head was made of polytetrafluorethylene (Teflon), a material that later proved to be unsuitable. Christiansen, one of the authors (Ramstad) and engineer Nilsen therefore visited John Charnley (1911 – 1982) at Wrightington Hospital near Wigan in England on 19 September 1966. Charnley had used Teflon for an artificial hip joint socket in his first total prostheses
(9). These patients had to undergo revision surgery, however, since the acetabular sockets wore out quickly (Figure 4) and the Teflon particles caused a massive tissue reaction. Charnley therefore stopped using Teflon in November 1962 (10, 11). After that, he used a cemented stem with a small, fixed femoral head against a thick, cemented hip socket made of high molecular-weight polyethylene (HMWP) (Figure 4). In his book Low friction arthroplasty of the hip (12) he showed that this produced very positive long-term results, and this prosthesis later became the gold standard against which all total prostheses were later measured.
Figure 4 Two samples from autopsies. On the left, a Teflon acetabular cup worn out after some years of use. Note vertical direction of wear track. On the right, the future-oriented prosthesis with an acetabular cup made of ultra-high molecular-weight polyethylene first used by Charnley in 1962. The picture was taken in 1967 when Sudmann visited Charnley. Photo: Einar Sudmann
When the Norwegian delegation visited Charnley, Christiansen was only interested in hemiprostheses, not total prostheses. In addition, at the time they were sceptical of fixing the femoral stem in the femoral shaft with cement, although not of the choice of steel on polyethylene.
In 1967 Christiansen accordingly exchanged the Teflon femoral head for a corresponding one made of high molecular-weight polyethylene (Figure 2, Figure 3a)
(5). However, recalling the tissue reaction caused by the Teflon femoral heads, one of us (Ramstad) suggested applying a two-millimetre stainless steel coating on the polyethylene ball. This was done by the Polaris factory in Sandnes (Figure 3b). For financial reasons, no patent for the steel coating was applied for. The first 150 of a total order of 500 artificial femoral heads with a stainless steel coating and an outer diameter of 44 – 54 mm were dispatched by Polaris to Joni on 21 September 1968. These femoral heads produced much better results than those made of polyethylene with no steel coating (13).
Ramstad used Christiansen’s hemiprosthesis over a ten-year period from 1968 in 200 patients at Bodø Central Hospital. In a follow-up examination of this material with a median observation time of 14 years, altogether 42 patients with a total of 44 hip operations were still alive and able to come to the examination. 25 % of the prosthesis stems had become loose
(14). All had an artificial femoral head made of polyethylene with a steel coating, with the exception of seven, which had a femoral head made of polyoxymethylene (Delrin) manufactured by Benoist Girard & Co. This was a French company in the Howmedica Inc. group that had taken over the production of Christiansen’s hemiprosthesis in 1971.