Advanced Techniques
Knee Replacement Technology
Dr. Assini pairs medial-pivot implant design with computer navigation and robotic assistance in total knee replacement — technology he has helped design, teach, and study.
Advanced Alignment — Medial-Pivot Total Knee Replacement
The medial-pivot philosophy is based on the observation that a normal knee does not function like a simple hinge. During flexion, the medial compartment remains relatively stable and acts as a pivot, while the lateral femoral condyle translates posteriorly. This creates a combination of stability and rotational motion that is fundamentally different from the sliding motion seen in many traditional knee replacement designs.
MicroPort Orthopedics has been the pioneer of this concept. Its original Advance® medial-pivot knee was introduced in 1998, following research by surgeons and engineers including Dr. J. David Blaha, Michael Freeman, and Richard Komistek examining the kinematics of the native knee. The technology subsequently evolved into the Evolution® Medial-Pivot Knee, which has more than 25 years of clinical experience and more than one million implants worldwide.
The Evolution design uses a highly conforming medial “ball-and-socket” articulation and a mobile lateral compartment. This is intended to reproduce the stability and rotational behavior of the normal knee, minimize unwanted anterior-posterior translation, and provide stability throughout the range of motion. MicroPort also emphasizes potential improvements in quadriceps efficiency, proprioception, flexion stability, and a more natural-feeling knee.
The philosophy fits particularly well with kinematic alignment, where the goal is to restore the patient's individual joint line and native anatomy rather than applying a uniform mechanical alignment target. MicroPort has specifically developed a Kinematic Alignment technique around the Evolution Medial-Pivot implant.
Dr. Joseph Assini has a direct connection to this technology. He is featured by MicroPort as an Evolution Medial-Pivot surgeon and consultant, describing faster recovery, improved motion, greater stability, and a more natural knee. MicroPort specifically quotes Dr. Assini describing the goal as recreating knee kinematics so accurately that the procedure approaches a “resurfacing” concept rather than simply replacing the knee.
Robotic-Assisted Knee Replacement
Robotic total knee arthroplasty (TKA) is an advanced approach to knee replacement that uses computer-assisted technology to help the surgeon plan and execute the procedure. Before surgery, a CT scan or other imaging is used to create a three-dimensional model of the patient's knee. This allows the surgeon to develop a personalized surgical plan, including the size and position of the implants and the desired alignment of the knee.
During surgery, a robotic system helps the surgeon make precise bone cuts and position the implants according to the preoperative plan. The technology can also provide real-time information about the knee's alignment, stability, and soft-tissue balance. Importantly, the robot does not perform the surgery independently—the surgeon remains fully responsible for all decisions and uses the robotic system as a precision tool.
The potential advantages of robotic TKA include improved accuracy and reproducibility of bone cuts, more precise implant positioning, and the ability to tailor alignment and soft-tissue balance to an individual patient. These technologies may be particularly useful when employing modern alignment strategies such as kinematic or functional alignment, rather than relying on a single “one-size-fits-all” mechanical alignment target.
However, robotic assistance does not automatically guarantee a better clinical outcome. Patient selection, surgical technique, implant design, alignment philosophy, and the experience of the surgeon remain critical factors. Current evidence suggests that robotic TKA can improve the accuracy of implant positioning, while the long-term clinical advantages over well-performed conventional TKA continue to evolve.
Patient Specific Navigation
In patient-specific navigation, advanced imaging—typically a CT scan—is obtained before total knee replacement to create a detailed three-dimensional model of the patient's knee. This allows the surgeon to develop an individualized surgical plan based on the patient's unique anatomy, including implant sizing, positioning, bone cuts, and the desired overall alignment of the knee.
The CT-based model is then used to 3D print customized cutting blocks or surgical guides specifically for that patient. During surgery, these patient-specific guides are positioned directly onto the patient's anatomy. They help guide the surgeon's bone cuts so that the procedure closely reproduces the preoperative plan and desired alignment.
This approach allows knee replacement to be tailored to the individual patient rather than relying solely on standardized anatomical landmarks and conventional instrumentation. It can be particularly useful when the surgeon is using personalized alignment strategies, such as kinematic alignment, where the goal is to more closely reproduce the patient's natural knee anatomy and joint orientation.
Potential advantages include improved accuracy and reproducibility of bone cuts and implant positioning, less reliance on conventional instrumentation, and the ability to plan the operation in detail before entering the operating room.
As with robotic technology, patient-specific navigation is a tool that assists the surgeon rather than replacing surgical expertise. Successful knee replacement still depends on appropriate patient selection, implant choice, surgical technique, alignment philosophy, and the experience and judgment of the surgeon.
Next Generation Design & Implementation
Now that robotics are becoming a more common tool in TKA, Dr. Assini is involved in the next evolution of knee replacement technology.
First is Kinomatic pre-operative planning. Kinomatic is a patient-specific, CT-based preoperative planning system designed to personalize total knee replacement around the individual patient's anatomy and biomechanics. Rather than relying primarily on standardized alignment targets and 2D X-rays, Kinomatic uses a low-dose CT scan from the hip through the ankle to create a detailed 3D model of the patient's entire lower extremity.
The CT data are converted into a 3D anatomical model using AI-assisted segmentation and then analyzed by biomedical engineers. Hundreds of anatomical measurements can be obtained, allowing the surgeon to evaluate the patient's native alignment, bone anatomy, deformity, and overall lower-extremity biomechanics.
The surgeon can then virtually test different implant sizes, positions, and orientations to develop a personalized surgical plan. Particular emphasis is placed on restoring the patient's individual biomechanical alignment rather than applying a generic alignment target. This makes the technology particularly relevant to kinematic and personalized alignment philosophies.
A key feature is that the surgeon can review and virtually rehearse the planned procedure in 3D/VR before surgery, making adjustments before entering the operating room. Kinomatic emphasizes that the plan is a guide—the surgeon retains complete control and can modify the plan based on intraoperative findings.
Importantly, Kinomatic is not a robot. Its primary role is sophisticated preoperative planning and 3D visualization, although the resulting plan can be used in conjunction with robotic or other intraoperative technologies.
Dr. Assini is also on the Advisory Board for the TiRobot. This robotics platform is a step forward over previous generation robotics such as Rosa and Mako. Not only is the system CT based, it also features improved accuracy, active registration, enhanced arm movements and safety features that are surgeon controlled and patient specific.
Teaching & Research
Each year, as a member of Colorado Joint Replacement, Dr. Assini has the privilege to help educate 2 fellows from the US or Canada in hip and knee replacement technology/techniques.
Dr. Assini lectures internationally on robotic-assisted knee replacement — most recently “My Journey to Robotics,” on the SkyWalker robotic platform with the Evolution® medial-pivot knee, at the CBCJ knee surgery congress in Brazil. He also leads a randomized controlled trial examining a novel drug to reduce narcotic use in total knee replacement patients.
Ready to take the next step?
Ask about an appointment with Dr. Assini — his team will guide you from there.