Orthopedic Surgery

July 22, 2025

Orthopedic surgeons have used mechanical alignment for many years to place patients who require total knee arthroplasty (TKA) in a neutrally aligned knee. Yet, over time in the field of orthopedics, U.S. knee specialists, including those at Mayo Clinic, have developed increasing interest in alternative knee alignment for TKA. This type of alignment is currently a hot topic in the field, says Kevin I. Perry, M.D., an orthopedic surgeon at Mayo Clinic's campus in Minnesota.

"Using robotics in a total knee replacement, orthopedic surgeons now have the tools to individualize alignment," says Dr. Perry. "Now, we don't have to box all patients who undergo this surgery into the same neutral alignment."

Patient outcomes and satisfaction post-TKA are impacted by ensuring the knee alignment is correct, he says.

The evolution of TKA alignment

Before robotic surgery was widely used in TKA, ensuring greater reliability than a nonrobotic approach, the environment in which these replacements occurred was different than today, says Cody C. Wyles, M.D., also a Mayo Clinic orthopedic surgeon. Robotic surgery allows for more democratized outcomes with better results and tools to make the procedure reproducible, he says. As implants have improved over time, patient expectations have correspondingly increased, and younger, more-active individuals seek TKA.

"Now patients are coming in as weekend warriors, and just making the knee straight with a TKA has not been the best outcome for all patients," says Dr. Wyles. "In the first few decades of knee replacement, by contrast, we were used to devastating cases with primarily wheelchair-bound, arthritic patients. In that era, if patients went from wheelchairs to walking, they thought of their results as a home run."

According to a 2010 publication in Clinical Orthopaedics and Related Research, 15% to 20% of patients undergoing a TKA conveyed some level of dissatisfaction. By comparison, > 95% of patients who have a hip replacement were satisfied, according to a publication in Journal of Physical Therapy Science.

Bridging the patient satisfaction gap after decades of TKA experience, the rise of robotic TKA offers a means of alternative alignment, says Dr. Wyles.

"Prior to the advent of robotic surgery, orthopedic surgeons tried alternative alignment philosophies, but this was mainly surgeons making one-off tools according to their individual alignment philosophies," says Dr. Wyles. "The problem is that these attempts were not replicable, and there was not a significant amount of data available."

Over time, as orthopedic surgeons used robotic surgery more frequently, he says that prominent voices in the TKA field found success with alternative alignment philosophies.

Today, to accurately customize a patient's TKA, the orthopedic surgeon determines the patient's knee phenotype presurgically by X-ray, using the coronal plane alignment of the knee classification, including:

• Neutral knee alignment.
• Bowlegged, called varus, alignment.
• Knock-kneed, called valgus, alignment.

Dr. Perry says that he and knee specialist colleagues also can look at and help restore a patient's native joint line obliquity.

He also says a certain percentage of patients do well with neutral mechanical alignment, the traditional alignment philosophy that he calls "tried-and-true."

The knee phenotype helps the surgeon determine if an alternative alignment might best suit patients' native knee alignments upon arrival at a presurgical appointment. The phenotype also aids in accurate planning for a given patient's surgery to reduce pain and improve function and range of motion.

Alternative alignments used in Mayo Clinic TKA: kinematic and inverse kinematic

Dr. Perry favors kinematic alignment (KA), while others at Mayo Clinic, including Dr. Wyles, favor inverse kinematic alignment (IKA) for TKA.

"The reason I've adopted kinematic knee alignment is that it inherently makes sense to look at a patient as an individual and use the patient's natural knee alignment," says Dr. Perry.

The key difference between these two types of alternative alignment is the method used to balance the patient's knee during the TKA. In a KA, modifying the tibial cut balances the knee; in IKA, modifying femoral cuts balances the knee.

These two types of alignment also differ in what gets prioritized. In IKA, the priority is balance of the knee in flexion and extension. In KA, the priority is resurfacing the knee back to its prearthritic state.

"With kinematic alignment, the surgeon puts the knee back in space where it was prearthritically, but perfectly balancing the gaps is not the priority," he says. With IKA, the surgeon uses gap balancers to position the knee's flexion and extension, leading to a well-balanced knee with ideal ligament tension.

The high priority on gap balancing and pressure exerted on soft tissue in IKA is similar to functional alignment, says Dr. Perry.

"IKA tends to be the approach focused on ligament, balance and the gaps," says Dr. Wyles. "KA is more of a bony procedure focused on resurfacing the anatomy where it is. In contrast, KA takes the philosophy of using the native anatomy and playing it as it lies — not realigning, but assuming that the patient was put in that position for a reason."

Dr. Perry notes the type of alignment a surgeon uses in a TKA is irrelevant for insurers, who do not dictate this choice. However, the type of alternative alignment that surgeons favor typically fits some aspect of their personalities, says Dr. Wyles.

Dr. Wyles says that while both KA and IKA work well, it is possible one of them will rise to the fore or that with more data in the future, certain patient phenotypes may benefit from one strategy more than another.

"We as orthopedic surgeons need to hold alternative knee alignment philosophies we favor with an open palm, not a clenched fist," says Dr. Wyles.

Data behind alternative alignment in TKA

Dr. Perry says the field of alternative alignment has spread slowly. Many publications are yet up-and-coming. He has been working with current data on kinematic alignment and is nearing the point of writing and publishing a paper. Dr. Perry says that while 16-year data is available from the work of Stephen Howell, M.D., demonstrating the efficacy of KA, no gold standard, definitive data show that this alignment is superior to other alignment philosophies. Part of the dearth of sufficient data now relates to the fact that, to date, orthopedic surgeons have not widely adopted KA or any alternative knee alignment.

"Anecdotally, I am seeing better outcomes with KA than with mechanical alignment," says Dr. Perry.

Meanwhile, as robotic TKAs using alternative alignment proceed, the robot itself serves as a data collection instrument, says Dr. Wyles. Data collected points to the factor orthopedic surgeons care about most: outcomes.

"I'm seeing increasing evidence that the early adopters of alternative knee alignment techniques are achieving improved outcomes on some metrics compared with traditional mechanical alignment," he says. "Alternative alignment is using good science and theory to push toward a better way to perform a TKA in 2025 and beyond. Both alternative alignment processes are viable, and we will see how things come out over time with data from the robot we will feed into an AI algorithm," says Dr. Wyles.

For more information

Bourne RB, et al. Patient satisfaction after total knee arthroplasty: Who is satisfied and who is not? Clinical Orthopaedics and Related Research. 2010;468:57.

Fujita T, et al. Analysis of factors influencing patient satisfaction after total hip arthroplasty in a Japanese cohort: The significant effect of postoperative physical activity. Journal of Physical Therapy Science. 2022;34:76.

Refer a patient to Mayo Clinic.