Innovation & Evolution in Hip Replacement Surgery: Highlights from the Keggi–Rubin Hip Implant Collection at Yale University
Rare and Unusual Implants
Over the years, orthopaedic surgeons have witnessed the evolution and innovation of hip replacement surgery firsthand. The history of this evolution not only documents the well-known failures, alterations, impacts, and successes of popular implants, but also must recognize uncommon implant designs that each represented an effort to improve upon their predecessors. After decades of performing hip replacement and hip revision surgeries, this group of rare and unusual implants have been collected by orthopaedic surgeons Dr. Keggi and Dr. Rubin, and each implant has an interesting story.
While the world struggled to achieve long-term implant stabilization through bone ingrowth, several doctors began exploring alternative ways to secure implants. Two of these doctors were Dr. Homsy and Dr. Tullos, who developed this Proplast coated stem implant while working at Houston Methodist Hospital in the 1970s. This femoral stem is coated in Proplast, a highly porous Teflon fiber. The pair had hoped the stem’s Proplast coating would achieve cementless fibrous fixation, similar to that of human teeth. Unfortunately, the Proplast provided insufficient stabilization that led to disastrous patient outcomes and hefty lawsuits. A salesman gave Dr. Keggi this device, hoping that he would start implanting it; however, luckily, Dr. Keggi never inserted a Proplast coated stem implant.
Russian orthopaedic surgeon Konstantin Sivash developed the design of the original Sivash metal-on-metal hip implant in 1956 (modified designs eventually followed). His designs feature a constrained cup with metal fins on the backside. The constrained cup mechanically locks in the metal femoral head so that the implant’s stem, head, and cup are all linked. Dr. Sivash believed that constraining the femoral head in the cup would significantly reduce the rate of post-op dislocation. When surgeons inserted these implants, the reverse fins were hammered by a mallet deep into the bone of the patient’s hip socket. Once the reverse fins were pounded into place, they “Russian cemented” the cup in position, which gave surgeons only one chance to properly insert the implant. Though the constrained design did lower dislocation rates, the implant suffered from metal-on-metal debris, stem loosening, and surgeon hesitancy. Dr. Keggi received these implants during one of his teaching visits to the Soviet Union in 1986.
In the early 1980s, the Link ribbed stem was developed by Hans Lubinus to minimize stress shielding, which had become a recurring issue in chrome cobalt designs. The stem was manufactured from a titanium alloy to better mimic the elastic nature of bone. The deep ribs of the stem served to reduce bone stiffness compared to similarly designed solid stems. These ribs also provided more surface area for bony ingrowth. During surgery, once the prosthesis was properly positioned, the collar could be removed so that additional bone graft material could be packed into the spaces between the ribs. Then, the collar could be secured again with the assistance of a screw. The lateral shoulder had an anchoring screw hole option that could be used to further secure the stem to the lateral femoral bone cortex.
Handmade Chinese "Dimpled" Tripolar Implant
In 1989, Dr. Keggi extracted this implant during a hip revision surgery he performed in Riga, Latvia. The patient was a 50-year-old diamond miner from the far east of Siberia. Two years prior, he had undergone hip replacement surgery at the First Army Hospital in Shanghai, China. Chinese metalsmiths had apparently handcrafted the implant’s irregular dimples on the stem surface, presumably to help provide a roughened surface for bone healing to the implant. This likely showcases a very early attempt to create a personalized implant, though this was never confirmed. The stem was paired with a common Western head and socket. Unfortunately, the handcrafted stem offered and achieved very little bony fixation, which caused the implant’s failure. This led to the miner’s journey to Riga, Latvia, where Dr. Keggi revised his original replacement at the Soviet-Latvian Institute of Orthopaedics and Traumatology.
These custom-made IdentiFit hip implants were products of DePuy’s X-Press Patient Specific Hip Service program from the early 1990s. The system advertised implants customized to fit a patient’s exact femoral dimensions. Prior to surgery, scaled x-rays of the patient’s femur were taken and sent to DePuy Orthogenesis engineers in Warsaw, Indiana. The DePuy engineers would send a metal blank stem corresponding to the size of the patient’s femur. During surgery, the surgeon would then cast a model of the patient’s femoral canal using bone cement. The mold would then be taken down to a truck parked near the hospital. There, an engineer would forge the blank to correspond to the cement mold, and the final implant would then be quickly returned back to the surgeon in the OR for sterilization and implantation. Very few of these devices were ever manufactured. Sometimes, these customized implants would not fit and the surgeon then had to use a standard, “off the shelf ” implant. Although the IdentiFit program was short-lived and discontinued, the information DePuy collected from this program went into designing other implant styles (e.g. Express and Stability Stem Designs) that were later used in standard lines of femoral implants.
After years of meticulous research and data collection in the 1970s, including on bearing-rib prostheses implanted into dogs, German professor Dr. H. Mittelmeier presented his uncemented ceramic-on-ceramic total hip system in the 1980s. His implant features a ceramic head and matching ceramic threaded cup, which displayed excellent wear resistance and had no notable tissue reactions. The metal femoral stem displays unique fenestrations and grooves, which were intended to allow bone growth and packing to help secure the implant. While surgeons struggled to properly insert this device via the posterior or lateral approaches, Dr. Keggi was able to accurately insert many Mittelmeier implants with few complications using the Anterior Approach due to the accuracy of cup positioning when using this technique. Dr. Keggi even has a number of living patients who are still thriving with this exact implant from their original hip replacement surgeries performed in the early 1980s.
Cover of text edited by Mittelmeier describing 10 years experience with ceramic hip prostheses
Case 4 photograph of physical exhibition in Cushing Rotunda, Cushing/Whitney Medical Library- Rare and Unusual Implants