Innovation & Evolution in Hip Replacement Surgery: Highlights from the Keggi–Rubin Hip Implant Collection at Yale University
Modular Implant Development & Failures
The concept of implant modularity first arose in the early 1970s to address the recurring issue of implant instability, gaining traction later on. Modular implants were originally designed to give surgeons the freedom to adjust an implant’s position, angle, offset, and size. The surgeon could combine different femoral stems, neck length or lateral offset, and head sizes to best fit the patient’s anatomy. Another benefit of modular implants was that they simplified revision surgeries by allowing a surgeon to treat a wide range of femur sizes with a single comprehensive implant system. If an implant failed, the surgeon would theoretically be able to change one component piece instead of removing the whole implant, but this was not always the case. Some modular implants also failed due to fatigue fracture of the metal itself, metal corrosion between the modular parts, or loosening from the bone.
The modern S-Rom total hip system originally evolved from the Sivash prosthesis (displayed in the adjacent case) in the 1970s. In 1975, Engineer Doug Noiles began to modify the Sivash stem to reduce stem rotation, and others worked towards improving its overall performance. The S-Rom modular femoral component evolved, consisting of a titanium alloy stem that locks into a titanium alloy sleeve. The inoperative adaptability of the implant’s stem, sleeve, and neck allowed the surgeon to choose components that best fit the patient’s anatomy, with more than 10,398 configurations possible. The S-Rom SuperCup featured pads of stabilizing fins, a porous coating, and screw holes to help lock the shell into place. While the fins and optional screws mechanically fixed the shell in place, the porous titanium coating supported long-term bone ongrowth. Overall, the S-Rom system has performed well in both primary and revision surgeries. This implant was originally licensed for use in the United States by the U.S. Surgical Corporation (North Haven, Connecticut) in 1971 then acquired, modified, and renamed as the S-Rom by the Joint Medical Products Corporation in 1982, with the first clinical implantation of the modern S-Rom by Dr. Hugh Cameron in 1984. In 1995, DePuy acquired Joint Medical Products Corporation and has marketed the stem since 1998. As of 2021, the system is owned by DePuy-Synthes (Warsaw, Indiana) and is still used in the U.S. today.
Omni Life Science: Apex K1 and K2
Omni Life Science’s first- and second-generation Apex modular systems provided surgeons with a wide range of femoral head, neck, and stem combinations to restore joint function. The femoral components were a titanium alloy stem and neck that connected by fitting the base of the neck into a corresponding hole in the top of the stem. The precise fit of these modular components made leg length more predictable and intended to spare the neck from overwhelming pressure. The Apex K1 and K2 implants share a unique rectangular femoral stem modeled after the Zweymüller prosthesis, and had a dual-press modular design. In the Apex K2 system, the locking mechanism for the neck was improved to strengthen the junction, and a titanium coating was later added to the lateral neck section to improve bony ongrowth to the prosthesis. Unfortunately, production and implantation of the Apex K1 and K2 systems were ultimately halted due to implant failures leading to a higher than expected revision rates.
Osteoimplany Technology, Inc. (OTI) R-120
The OTI R-120 modular implant was a cemented Vitallium device developed in the 1980s, and a bead coated press-fit uncemented stem later became an option. The trapezoid-shaped femoral stem had a thick collar to compress cement in the femoral canal. The collar had an imprinted clock face to help the surgeon select the neck rotation (anteversion) position of the final construct. The surgeon would consult a chart of angle measurements corresponding to the collar’s clock face and lock the modular neck by impacting it into the selected position. The R-120 implants were intended to improve the accuracy of implant positioning and reduce the difficulty of revision surgeries. Unfortunately, the R-120 implants failed due to fatigue failure of the modular femoral neck, metal abrasion, or dissociation of the modular implant segments.
Case 5 photograph of physical exhibition in Cushing Rotunda, Cushing/Whitney Medical Library- Modular Implant Development & Failures