Erich Weidenhammer, PhD
With the substantial collection of artifacts gathered by orthopedic surgeon Robert W. Jackson are a number of knee prostheses that document a decades-long project at Toronto General Hospital (TGH) and the University of Toronto. The MacIntosh tibial plateau was first implanted in 1954 at TGH by its namesake, orthopedic surgeon David L. MacIntosh (1914 – 2013). Development work continued in this area for several decades, with the tibial prosthesis eventually developing into a two-part knee hemiarthroplasty that, while patented, was never offered commercially. The original MacIntosh knee plateau was well studied and widely used. However, the Jackson collection likely offers some of the only surviving evidence about this later development .
Initial development
The origin story of the MacIntosh implant is familiar within a small community with ties to Toronto orthopedics. The orthopedic team at TGH has come into possession of an acrylic tibia surface replacement, developed by Drs. Sven Kiær (1894-1955) and Knud Jansen (1913- 1982) at the Orthopaedic Hospital of Copenhagen. This had likely been brought back to TGH by surgeon W. Robert Harris (1922 – 2005), who had visited Sweden as an ABC Travelling Fellow.
An opportunity to try the implant emerged as the team considered whether to fuse the knee of a seventy-three-year-old woman with severe valgus deformity in one knee due to arthritis. MacIntosh reportedly inspected the prosthesis before cutting it in half with a surgical saw. He then implanted it into the patient, correcting the valgus deformity while preserving the mobility of her knee. (MacIntosh and Hunter 1972, 244). This success inspired further experimentation.
Design and materials
The MacIntosh knee plateau that emerged was designed to be used in cases of valgus and varus deformity of the knee due to osteoarthritis or rheumatoid arthritis. A shelf was cut into a condyle of the knee, and a prosthesis installed to provide a new bearing surface of the appropriate height, replacing a damaged and collapsed surface and straightening the knee. In cases of severe rheumatoid arthritis, it was common to replace both condyles.
In both official advertising and private correspondence, the MacIntosh implant is invariably referred to as the “ashtray” design. This was a cementless implant that relied on its textured bottom surface to stay in place. This design decision due to the recent experience of the eventual breakdown of polymethyl methacrylate (PMMA) bone cement in hip implants that led to foreign body reaction, prosthetic loosening, bone resorption, and collapse. Initial versions were of acrylic. These original acrylic models were likely produced by Down Bros. and Meyer & Phelps (usually called Down Brothers), which had a Canadian subsidiary at 70 Granville St. in Toronto. These facilities had a workshop where the prostheses were “… polished down from an acrylic block.” (UTARMS, MacIntosh fonds, MacIntosh to Frank. Sept 9, 1958, B2013-0036/14(01)) .
As the design gained popularity over the 1960s, acrylic was abandoned. This was due to concerns about the eventual breakdown of acrylic raised by the failure of early acrylic hip implants. (See these examples of such acrylic hip implants in the Robert W. Jackson collection.) The group then tried other materials available through Down Brothers, first titanium, then Teflon. Teflon “… wore badly and promoted an acute foreign body reaction.” Over half of the sixteen patients involved in this trial required knee fusion. (MacIntosh and Hunter 1972, 244). The collection includes several examples of, what may be, early Teflon MacIntosh knee plateaus. Titanium was also found to be too soft for long-term wear. Around 1965, Down Brothers conducted a metallurgical study into the failure of its titanium implants and proposed a stronger alloy. However, after 1964, only Vitallium implants were used.
Vitalium is a biocompatible cobalt alloy first developed in England in the 1930s. The switch to this material required a change of manufacturer; Vitallium MacIntosh Implants were manufactured by the Austenal company, a division of the Howe Sound Company that was based in New York. (Down Brothers may have distributed these Vitallium implants in the UK). Austenal Vitallium implants likely first became available around 1963. The collection includes several such implants in various sizes and in two slightly different formats that likely indicate evolution in design and manufacture.
An alternative to the MacIntosh plateau did exist in the McKeever prosthesis, a slightly earlier contemporary invented by Duncan C. McKeever (1905 – 1959) of Valley Falls, Kansas. Also made of Vitallium, the McKeever tibial plateau prosthesis was manufactured by Zimmer (see Potter 1969). Unlike the friction fit of the MacIntosh Implant, the McKeever implant required the cutting of a t-shaped slot into the prepared surface of the tibia. A useful study comparing the two devices was published by surgeon Theodore A. Potter in 1969.
Widespread adoption
The design seems to have taken off around 1965. Growing buzz generated by initial reports, conference presentations, and the accounts of early adopters, resulted in a growing number of inquiries from interested surgeons. These appear among MacIntosh’s papers in the University of Toronto archive. In 1965, the MacIntosh implant was featured on the long-running d CBC television show “Take Thirty”, hosted by Anna Cameron. This prompted a number of inquiries from Canadians with relatives afflicted by arthritis.
This attention created pressure on the TGH group and Austenal to provide clinical evidence of the design’s efficacy. MacIntosh’s first substantial publication on the matter appeared in the Journal of Bone and Joint Surgery in 1972, though others had published in the design before this. In the mid-1960s Austenal notably sponsored a series of films showing the TGH group implanting the prosthesis that were shown at various orthopedic conferences.
The MacIntosh Implant as represented in the Austenal Catalogue. (UTARMS Archive B2013-0036/ 014/ 02)
The design evolves
Given its evident success, researchers at TGH and the University of Toronto continued to develop the prosthesis, eventually creating a two-part hemiarthroplasty consisting of a plastic (likely high density polyethylene, or HDPE) femoral component. The best evidence for this later work, which never reached production, is a 1977 patent (US patent 4,034,418), assigned to the University of Toronto, with Robert W. Jackson listed as the lead inventor. David L. MacIntosh was also listed among the inventors. The patent shows a highly modified, and significantly thinner, version of MacIntosh implant. This is likely meant as a general purpose tibial bearing rather than a spacer meant to correct lateral deformities of the knee. The femoral implant is of plastic and consequently features an element that is cemented into a groove cut into a condyle of the knee joint.
This arrangement is the opposite of the standard that has subsequently emerged for the artificial knee joint, which typically uses an HDPE tibial bearing surface and a metal femoral implant. Given the experience of decades, most orthopedic surgeons would likely see the 1977 University of Toronto Hemiarthroplasty (for lack of a better name) as unworkable. However, it should be appreciated that, when this prosthesis was developed, the current consensus had not yet emerged.
The collection gathered by Robert W. Jackson is practically undocumented. However, it contains many items that are clearly related to the developmental process behind the 1977 patent. This seems to indicate that Dr. Jackson was keen to represent this research. For instance, both components shown in the patent are represented in this catalogue entry. Interestingly, the collection also includes an example, removed from a patient, that combines the earlier form of the MacIntosh plateau with a later plastic femoral implant that has obviously failed. Whether this is representative of fundamental problems with the design is plausible though unclear.
The collection also includes examples of a ceramic tibial plateaus that were likely tested later in the developmental process. One artifact includes two ceramic plateaus and two plastic femoral implants sent new from to Dr. Jackson from OSTEO, AG, an medical manufacturer based in Switzerland. The package is dated April 1979. Interestingly, experiments with uncemented ceramic tibial plateaus based on the MacIntosh design began in 1972 at the Rudolf-Elle-Hospital in Eisenberg, Germany and the Orthopedic Clinic of the University of Jena, Germany (see Heimke, Leyen, and Willmann 2002, 1542; and Mittelmeier et al. 2007). However, it is unclear whether there is a substantive relationship between the work done in Germany and the later Swiss-based manufacture of ceramic components. The Swiss components are substantially thinner, more closely resembling the thin plateau shown in the 1977 patent.
Finally, the collection includes a number of tools and and prototype items that are challenging to situate chronologically within the development process. These include, for instance, a plastic femoral component as well as a plastinated and sectioned human femoral condyle that may point to early experiments aimed at securing a plastic femoral component using a threaded mount. The collection also includes a tool that was likely created to test fit the femoral component as well as to assist in applying bone cement prior to the placement of the implant.
In summary, little has been written about this later phase of the development of knee prostheses at the University of Toronto and Toronto General Hospital. However, continued study of these artifacts may produce new insights into this research.
An ongoing bibliography of sources related to this research is available here.