Innovation & Evolution in Hip Replacement Surgery: Highlights from the Keggi–Rubin Hip Implant Collection at Yale University
Charnley’s Impact, Cemented in Time
Surgeons’ efforts before the 1960s laid the groundwork for Sir John Charnley to develop his revolutionary low-friction arthroplasty of the hip. His procedure was the first to consistently achieve predictable and positive outcomes due to the incorporation of a reliable socket replacement. Dr. Charnley’s novel total hip replacement combined a small femoral head in a molded plastic socket with both of these prosthetic components secured in position by fast-setting bone cement. The immediate clinical success of his arthroplasty rapidly became the new gold standard for hip replacement surgery. Many companies and surgeons subsequently adopted and modified Charnley’s original design to continue the advancement of total hip arthroplasty.
While working in Manchester, England, Dr. Charnley began to observe prosthetic hip joint squeaking in patients who had previously undergone partial hip replacement surgery. He suspected that the squeaking was a result of high frictional resistance and reasoned that this could be fixed by placing a femoral head with a smaller diameter within an acetabular socket. Dr. Charnley searched for a durable socket material and discovered the plastic known as ultra-high-molecular-weight polyethylene (UHMWPE), an extremely strong plastic with high abrasion and wear resistance. Then, to securely fasten the plastic cup and femoral prosthetic, Dr. Charnley turned to cement. The idea of using fast-setting cement to secure implants had recently occurred to surgeon Edward Haboush after observing its use at the dentist. With all of these ideas in mind, Dr. Charnley introduced his low-friction arthroplasty, which he would continue to refine as it became celebrated as the gold standard for total hip arthroplasty.
Charnley's major text , Low Friction Arthoplasty of the Hip, describing his techniques.
McKee-Farrar Prosthesis
In the 1960s, G. K. McKee and J. Watson-Farrar designed a metal-on-metal, cemented total hip prosthesis. The implant’s unique cup used its pegs on the reverse side for additional cement stabilization in the pelvic socket. Original fragments of bone cement still cling to the pegs and rim of the acetabulum on this prosthesis.
Ring Prosthesis
The first metal-on-metal total joint replacement was designed by Dr. P.A. Ring in the 1950s. This implant used an unusual acetabular component with a long central screw driven into the ilium to serve as the socket for the hip bearing. His design used a femoral stem very similar to the Austin Moore prosthesis. Both implant components were uncemented; the Ring prosthesis failed due to both implant loosening and reactions from metal debris (metallosis).
Bechtol Total Hip System
Dr. Charles O. Bechtol, a former professor of orthopaedic surgery at Yale, moved to UCLA where he designed one of the first cemented hips manufactured in the United States. Unfortunately, this implant construct experienced a significant rate of early femoral stem fractures.
Cement Process and the Early Acetabular Shell Evolution
Dr. Charnley felt that surgeons should have some training on how to mix and use bone cement prior to performing cemented total hip replacements. The American Academy of Orthopaedic Surgeons (AAOS) sponsored educational seminars on how to properly mix the cement’s powder and polymer and how to then insert it into the acetabulum and femur. Once the seminars were completed, the era of cemented hip replacements was launched in the United States. The cement was originally mixed by hand in a simple bowl in the 1970s, but now, in 2022, this bowl has a vacuum suction seal and mixing beaters to improve the mechanical strength of the final cement. A femur is shown in cross section to demonstrate the cemented stem construct seated within the proximal femoral canal.
Early Polyethylene Acetabular Sockets
Over time, there were also modifications of the polyethylene acetabulum, such as the addition of beads on the outer surface to ensure an even thickness of the cement mantle. Various ridges and grooves were also added on the reverse side of these sockets to help further improve the cement fixation of the implant.
Early Cemented Implant Failures
The Zimmer DF80 and T28 femoral implants each proved to be unsuccessful cemented femoral implant designs. The titanium DF80 femoral implant failed because its stem loosened frequently. The T28 femoral implant was initially very promising because of its variety of stem sizes and neck lengths; unfortunately, it was made of cast stainless steel, which had a high fracture rate. Later on, when the material was switched to a stronger forged steel, the second generation TR28 became a useful and successful implant.
T28 (1)
T28 (2)
Case 2 photograph of physical exhibition in Cushing Rotunda, Cushing/Whitney Medical Library-Charnley’s Impact, Cemented in Time