What, in Fact, Is a Successful Total Knee Arthroplasty?

What, in fact, is a successful total knee arthroplasty? Poll 100 surgeons and you might get 150 opinions. But a new study from Australia, using HOOS-12 and KOOS-12 scores for more than 3,400 patients, found THE scores that surgeons can use to define clinically relevant changes in joint-specific pain, function, or quality of life.

Details and results are available in the full study, “Minimal Clinically Important Changes in HOOS-12 and KOOS-12 Scores Following Joint Replacement,” which appears in the June 1, 2022 edition of The Journal of Bone and Joint Surgery.

The research team began by collecting 12-item Hip disability and Osteoarthritis Outcome Scores (HOOS-12) and Knee injury and Osteoarthritis Outcome (KOOS-12) scores for 3,421 patients receiving joint replacement surgery for osteoarthritis (OA)—1,490 total hips and 1,931 total knees.

Ilana Ackerman, Ph.D., co-deputy director of the Monash-Cabrini Department of Musculoskeletal Health and Clinical Epidemiology at the School of Public Health and Preventive Medicine at Monash University in Melbourne, Australia, described to OTW the basic objective and methodology of the study: “The 12-item HOOS-12 and KOOS-12 instruments are relatively new measures of joint-specific pain, function, and quality of life that can be used to assess outcomes after joint replacement surgery from the patient’s perspective. They were developed from the longer HOOS and KOOS instruments.”

“We have previously investigated some of the important measurement properties for these new instruments (for example, how valid and reliable the instruments are, and whether they are responsive to change after joint replacement surgery) but what represents a meaningful or ‘clinically important improvement’ in HOOS-12 or KOOS-12 score has not yet been established.”

Using patient-level data from the Australian Orthopaedic Association National Joint Replacement Registry, the researchers collected preoperative and 6-month postoperative HOOS-12 and KOOS-12 domain and summary impact scores plus a rating of patient-perceived change after surgery (on a 5-point scale—”much worse” to “much better”).

According to Dr. Ackerman, the team used an anchor-based approach, “Where we related patient-perceived improvement after joint replacement surgery (the ‘anchor’) to the change in HOOS-12 or KOOS-12 score after surgery.”

“We also adjusted for the proportion of improved patients, given that most patients report improvement after joint replacement. Depending on the specific scale, we found that an increase of at least 16-19 HOOS-12 points can be considered a clinically important improvement in hip-related outcomes, and an increase of at least 14-17 KOOS-12 points can be considered an important improvement in knee-related outcomes.”

The team found that the minimal clinically important changes ranged from 24.0 to 27.5 points for the HOOS-12 and 17.5 to 21.8 points for the KOOS-12. They wrote, “The ROC analyses generated comparable MCIC values (28.1 for HOOS-12 and a range of 15.6 to 21.9 for KOOS-12) with high sensitivity and specificity. Lower estimates were derived from predictive modeling following adjustment for the proportion of improved patients (range, 15.7 to 19.2 for HOOS-12 and 14.2 to 16.5 for KOOS-12).”

“By defining thresholds for clinically important change,” said Dr. Ackerman to OTW, “our study provides practical information for clinicians and researchers. Changes in patient’s HOOS-12 or KOOS-12 scores that exceed these thresholds can be interpreted as meaningful changes in joint-specific pain, function, or quality of life. Our estimates can also be used by researchers for sample size calculations when planning future studies. We do note that our estimates are specific to joint replacement outcomes, and meaningful changes after other types of osteoarthritis treatments will likely vary.”