Jonathan-Week 3

I had a very interesting last week. Since my mentor, Dr. Bostrom, was away for the week, I spent a day shadowing Dr. Jerabeck in the clinic, a additional day shadowing him in the OR, and three days working on my summer research project. In the clinic, Dr. Jerabeck had two cases I found particularly interesting. In the first case, a young woman came in experiencing severe knee pain with some swelling. She had been battling cancer for years and appears to be in remission. The cancer damaged the bone quality in both her femur and tibia, leaving necrotic bone voids in each. These bone voids have the potential to cause her tibio-femoral joint to collapse. The case was complicated because the young woman did not want to have new X-rays taken due to all of the radiation exposure she experienced during her cancer treatments. Dr. Jerabeck could not know how bad the situation was without up to date X-rays. If the severity of the bone voids was still low, she could be helped with bone filling surgical techniques from Dr. Joseph Lane, but if the situation had worsened to joint collapse, she would need a knee replacement. The patient was recommended to Dr. Lane and encouraged to receive up to date X-rays.

For the next case, a elderly woman with a hip replacement came in with severe pain. Her previous doctors could not explain the pain. Dr. Jerabeck identified that her pain likely was a result of problems associated with metal-on-metal total hip replacement. The problem with these hip replacement designs is the generation of metallic wear. All hip and knee replacement systems wear; however, in most designs, the wear in polyethylene wear, which is much less harmful to the body. Cobalt of chromium wear causes a more severe inflammatory and allergic response from the body. The previous doctor likely did not know what was wrong with her because he did not run thorough enough tests on her to determine the metal content in her blood. Dr. Jerabeck prescribed her to have additional tests; based on the outcomes of those tests, Dr. Jerabeck will decide if a revision THR is necessary.

In the OR, the case I found most interesting was the use of the MAKO-plasty robotic assistant device in a unicondylar knee replacement. Uniconylar knee replacements (UKRs) are sometimes used in place of TKRs because their kinematic behavior more closely resembles the natural knee joint or only one of the sides of the knee is experiencing arthritis. For the MAKO-plasty robot, the surgeon first uses a specially designed set of tools and a camera to recreate the 3D position of femur and tibia in the computer. To do this, the surgeon places a fine-tipped tool only approximately 100 points across the tibia and femur matching points on the computer. Using these coordinates, the computer can recreate the two bone surfaces with an accuracy around 0.5 mm. A microscopic cutting tool equipped to the robot is then used to cut away the cartilage for the tibia and femur of the side of the knee they are installing the UKR. The cartilage must be cut away so that the implant can be fixated with bone and so that the new implant surface is properly aligned with the cartilage surfaces of the other side of the knee. Using this system, Dr. Jerabeck was able to install the UKR with precise alignment and with minimal destruction of the surrounding bone.

My research project is going very well. I am researching about why cementless knee replacements are not more widely used and about how recent technological developments (trabecular metal, bioactive coatings) may make cementless TKRs a more attractive design option in the future. I am planning to present my findings to the Bostrom lab near near the end of my summer immersion term.