When performing knee replacement surgery, also called total knee arthroplasty, doctors traditionally attempt to align the hip, knee, and ankle in a straight line, forming a neutral alignment, rather than replicating the patient’s original alignment. Now, in an effort to understand which approach is best, researchers at Kyushu University have compiled compelling evidence in favor of preserving the patient’s native alignment. The study was published in The Bone and Joint Journal on October 1, 2024.
When the knee is damaged due to injury or arthritis, performing daily activities such as walking, sitting, and running becomes difficult due to extreme pain. In cases of severe damage, orthopedic surgeons recommend knee replacement surgery to reshape the damaged parts of the knee and relieve pain by achieving neutral alignment.
However, this neutral alignment is not always the patient’s original alignment and there is some debate within the orthopedic community as to whether restoring the patient’s original alignment can lead to better patient-reported outcomes. In the present study, the researchers attempted to resolve this debate and create a comprehensive guide on preoperative planning and execution of knee replacement surgery.
This study primarily focuses on a classification system called Coronal Plane Alignment of the Knee (CPAK). It classifies possible knee joint alignments based on two main characteristics. The first is the hip-knee-ankle angle; Large negative angles cause the knees to point outward, while large positive angles cause the knees to point inward. Meanwhile, the second characteristic is the joint line angle, which refers to the angle between a line at ground level and an imaginary line passing through the points where the femur meets the tibia.
The research team, which included MD Toshiki Konishi and Associate Professor Satoshi Hamai of the Department of Orthopedic Surgery at Kyushu University Hospital, sought to determine whether changes in CPAK categorization before and after knee replacement surgery were associated with notable differences in the results. To do this, they collected data from 231 patients who received knee replacement surgery for osteoarthritis at Kyushu University Hospital between 2013 and 2019. Using X-ray images, the team determined the CPAK classification and alignment variables of the patients before and after surgery. They also sent a questionnaire to the patients, from which they derived a series of standardized scores related to symptoms, overall satisfaction, activity levels, and quality of life after the operation.
After statistical analysis, the researchers revealed that patients who underwent changes in knee alignment after knee replacement surgery, as determined by CPAK classification, had significantly worse long-term outcomes. Interestingly, they also found that patients whose joint line angle was tilted toward the outside of the knee after surgery (away from the other leg) also reported worse outcomes overall.
This study demonstrates that accurately replicating a patient’s native alignment during surgery is crucial to ensuring optimal recovery and increased quality of life. These results could have important implications for how knee replacement surgeries are performed around the world.
“In future clinical practice, our findings can guide surgeons in the preoperative planning and execution of total knee arthroplasty. By attempting to restore the patient’s inherent alignment, patients can achieve superior postoperative results,” explains Konishi. He adds: “This could help address the challenge of variability in patient outcomes after total knee arthroplasty by providing a more personalized approach to knee alignment, which could become a new standard in orthopedic surgery.” “.
Highlighting the fact that this was a retrospective study, the research team now intends to take a prospective approach in their next work. “We plan to incorporate the CPAK classification into preoperative planning, establishing each patient’s native knee alignment as the surgical goal. Using the robot-assisted technology implemented at our institution, we can now perform total knee arthroplasty with high precision, ensuring the exact reproduction of the preoperative plan,” says Konishi.
The researchers believe these efforts will help improve the gold standard of knee replacement surgery, leading to a healthier, pain-free, and more active post-operative life for patients.