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Fig. 1 TKA patient completing stair ascent task during motion capture gait analysis, 1 year following surgery. Images
courtesy of christopher Wendt and Cory Alcon

AAOS Now

Published 5/1/2015
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Catherine Rategan

Which Knee Implant Design Is Better?

OREF-funded study compares posterior cruciate ligament retaining and posterior-substituting designs

Osteoarthritis (OA) is one of the most prevalent health conditions worldwide. It causes chronic pain, loss of mobility and loss of function among an estimated 27 million adults in the United States, and as the population ages, the number of people affected is expected to increase to almost 67 million adults by 2030. One of the most prevalent forms affects the knees; among those 55 and older, OA of the knee is three times more prevalent than hip OA.

For many patients, when conservative interventions cease to adequately address the symptoms of progressing arthritis, total knee arthroplasty (TKA) becomes an excellent treatment option. And once the decision to have a TKA is made, the patient and physician are often faced with another dilemma: Which type of TKA implant is “best”—one that retains the posterior cruciate ligament or one that substitutes for it? With funding from the Orthopaedic Research and Education Foundation (OREF), Jason E. Lang, MD, associate professor of orthopaedic surgery at Wake Forest University Health Sciences in Winston-Salem, N.C., is studying this question.

Which design is better?
Since the first TKA was performed in 1968, many improvements have occurred in surgical techniques, implant designs, ligament balancing, and fixation principles. Many mid- and long-term studies have shown good outcomes and long-term durability of the prostheses, with most patients regaining mobility and improving their health-related quality of life.

Proponents of the posterior cruciate ligament retaining (CR) design believe that preservation of the posterior cruciate ligament maintains normal joint sensorimotor function, especially proprioception and kinematics. Other advantages include bone preservation and prevention of anterior femoral translation on the tibia. However, the surgical technique for the CR implant design requires precise ligament balancing to recreate natural joint motion.

Those who support posterior cruciate ligament substituting (PS) designs point out that the surgery is less complex than for CR designs. In addition, some studies have shown that the PS designs result in greater knee range of motion and a more stable component interface.

The results of previous studies comparing outcomes in patients receiving either CR or PS designs have been equivocal, and the question of whether one design has any advantage over the other is unresolved. Dr. Lang and his research team are evaluating the differences in proprioception and gait between patients who received the two types of total knee prostheses to determine whether proprioception plays a role in patient outcomes following TKA.

Patient study
Dr. Lang hypothesized that the CR design would maintain proprioception to a greater degree than the PS design. Further, the study proposed that the use of the CR TKA design would facilitate earlier functional outcomes in gait and balance when compared with PS TKA.

Dr. Lang explained, “Literature supports both designs, based on pain scores and fluoroscopic data. With this study, we wanted to learn whether one design is superior to the other in terms of ‘real-world’ functionality. We did this by recruiting patients to come in for a gait analysis before surgery and then again at 6 months and a year after their operation.”

Members of Dr. Lang’s research team—Judy Foxworth, PT, PhD, OCS, and Christopher Wendt, MS—coordinate the motion analysis studies through a partnership between the department of orthopaedic surgery at Wake Forest University Health Sciences and the Human Performance and Biodynamics Laboratory at Winston-Salem State University. Patients recruited for the study were randomized to receive either a CR or a PS TKA design.

At each study time point, the research team placed motion markers along both of the patients’ lower extremities. As patients performed common daily activities, such as stepping over small obstacles, walking up and down varying degrees of inclines and declines and climbing up and down stairs (Fig.1), their movements were recorded by motion-capture cameras. Drs. Lang and Foxworth then analyzed the data to determine how the patient’s preoperative arthritic state varied from the postoperative state and how it varied between the two TKA designs.

Dr. Lang said that he has had little trouble recruiting patients for this study. “We coordinated it with other preoperative visits to make it convenient for patients, and, after I explained that they would be doing this to help advance orthopaedics for other patients, they were usually receptive and happy to participate.”

Opportunities for advancing orthopaedics
Although recruiting patients was not a problem, finding funding was difficult—until Dr. Lang received the OREF grant. “The grant has been extraordinarily important. It allowed the pieces to fall together and the wheels to turn. It was truly the key to moving this forward.”

Dr. Lang said that OREF also gave him the opportunity to be a mentor. “I’m fortunate to have an opportunity through OREF to involve and mentor resident physicians. The (AAOS/OREF/Orthopaedic Research Society) Clinician Scholar Career Development Program for residents and early-on graduates is tailored to those in their first 3 years.”

Dr. Lang also pointed out that supporting OREF gives orthopaedic surgeons who don’t conduct research of their own a way to be involved in advancing the specialty. “In such cases,” Dr. Lang said, “supporting OREF gives others the opportunity to ask questions and get some answers. That’s their way of contributing to the community of orthopaedic surgeons.”

Catherine Rategan is a contributing writer for the OREF and can be reached at communications@oref.org.

References:

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