Skip to content

Benchmark Values Facilitate Evaluation of Patient-Reported Recovery After TKA

Key findings

  • To interpret scores on patient-reported outcome measures (PROMs), clinicians can use the patient acceptable symptom state (PASS)—the cutoff value on a PROM scale beyond which patients consider themselves to be in a satisfactory state
  • Using prospective data on 499 patients, orthopedic surgeons at Massachusetts General Hospital have established PASS thresholds for the knee injury and osteoarthritis outcome score and four other PROMs for use after total knee arthroplasty (TKA)
  • When applied to validation cohorts, nearly all PASS thresholds demonstrated acceptable or excellent ability to predict patient satisfaction
  • Surgeons can use the PASS thresholds as benchmarks to assess a patient's recovery progress one year and three years after TKA

Patient-reported outcome measures (PROM) are increasingly being used to evaluate the results of medical and surgical interventions. PROMs temper some of the biases inherent in outcomes that are judged by physicians, and they incorporate the patient's perspective when quantifying the impact of treatment.

To facilitate interpretation of PROM scores, the concept of the patient acceptable symptom state (PASS) has been developed. The PASS represents the threshold value on a PROM scale beyond which patients consider themselves well or in a satisfactory state.

Henrik Malchau, MD, PhD, director emeritus of the Harris Orthopaedic Laboratory at Massachusetts General Hospital, and colleagues are the first to establish PASS thresholds for the knee injury and osteoarthritis outcome score (KOOS) after total knee arthroplasty (TKA). They also determined PASS thresholds for four other PROMs, as they report in The Journal of Bone & Joint Surgery.

Study Participants and Design

The researchers retrospectively analyzed 499 patients from 11 centers who underwent TKA between 2011 and 2014 from a prospective international, multicenter study (not yet published) of a TKA system. Preoperatively and at each postoperative follow-up visit (1, 3, 5, 7 and 10 years), patients completed:

  • The KOOS, on which each subscale is rated from 0 (extreme knee problems) to 100 (no problems)
  • The EuroQol five-dimension, three-level questionnaire (EQ-5D-3L) about quality of life, for which an index value from 1 (best health state) to 0 is calculated on the basis of mobility, self-care, usual activities, pain/discomfort and anxiety/depression
  • The EuroQol visual analog scale (EQ-VAS), with which the patient rates their current general health state from 0 (worst imaginable) to 100 (best imaginable)
  • Two numeric rating scales (NRS): knee-related pain and satisfaction with the results of the procedure, each rated from 0 to 10

PASS thresholds are calculated by comparing PROM ratings to the answers to an anchor question. In this study, the researchers used the NRS about satisfaction as the anchor. Based on the distribution of responses, patients assigning ratings of ≤2.5 were considered satisfied and the others were considered dissatisfied.

Satisfaction Scores

  • At both 1-year and 3-year, correlations between the anchor question and PROM scores were higher than 0.40 for all PROMs except EQ-VAS.
  • All PROMs were either acceptable or excellent predictors of satisfaction at the 1-year and 3-year follow-ups.

PASS Thresholds for PROMs

At 1-year, PASS thresholds were calculated to be:

  • 84.5 points : KOOS pain subscale
  • 83.0 points: KOOS activities of daily living
  • 80.5 points: KOOS symptoms
  • 66.0 points: KOOS quality of life
  • 83.0 points: EQ-VAS
  • 0.80 point: EQ-5D-3L
  • 1.8 points: NRS about pain

At 3-year, the thresholds were:

  • 87.5 points: KOOS pain
  • 87.5 points: KOOS activities of daily living
  • 84.0 points: KOOS symptoms
  • 66.0 points: KOOS quality of life
  • 90.5 points: EQ-VAS
  • 0.80 point: EQ-5D-3L
  • 1.8 points: NRS about pain

Change Over Time

Thus, the changes in PASS thresholds between the 1-year and 3-year follow-ups were:

  • Increases in KOOS pain (+3.0 points), KOOS symptoms (+3.5), KOOS activities of daily living (+4.5) and EQ-VAS (+7.5)
  • No change in KOOS quality of life, EQ-5D-3L or NRS pain

The change in each PROM was smaller than its minimal clinically important difference, and 95% confidence intervals (CIs) overlapped between 1- and 3-year. Therefore, there were no significantly or clinically important changes over time in PROM PASS thresholds.

Furthermore, the proportion of patients who were satisfied did not change between 1-year (79%) and 3-year (80%). The researchers speculate that 1-year follow-up of PROMs may be adequate to predict results.

Validity of PASS Thresholds

When the PASS threshold values were applied to validation cohorts, all except those for EQ-VAS demonstrated acceptable or excellent ability to predict patient satisfaction.

Using the Results in Practice

The patients in this study came from six countries on four continents. Thus, the results may be generalizable to a broad range of patient demographic characteristics, cultures and hospital settings. Surgeons can use the PASS cutoff values as benchmarks to assess recovery progress at 1 and 3 years after TKA and discuss it with patients.

Learn more about the Center for Hip and Knee Replacement

Refer a patient to the Center for Hip and Knee Replacement

Related topics

Related

The first systematic study of customized knee implants suggests that greater adoption could reduce costs for patients, hospitals and insurers, but better insurance coverage would be required.

Related

Orthopedic surgeons at Massachusetts General Hospital became the first to investigate how the recently introduced bicruciate-retaining total knee arthroplasty affects in vivo kinematics, articular contact position and pivot point location during gait.