Minimal Clinically Important Differences for Lower Extremity Metastatic Surgery

Patient-centric outcome measures, such as quality-of-life questionnaires, are now considered key to the definition of a successful orthopedic surgery. This is particularly true for terminally ill patients with metastatic bone disease who are undergoing palliative/prophylactic surgery.

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Three questionnaires in the Patient-Reported Outcomes Measurement Information System (PROMIS)—Global, Cancer-specific Physical Function and Pain Interference—are used for patients with a wide variety of oncologic conditions. The minimal clinically important differences (MCIDs) on these questionnaires are the changes in score that patients perceive as beneficial, which can differ from the small changes that might be statistically significant in a large clinical trial.

Michiel E.R. Bongers, MD, Olivier Q. Groot, MD, and Quirina Thio, MD, research fellows at Massachusetts General Hospital, Kevin Raskin, MD, acting chief of Orthopaedic Oncology, Erik Newman, MD, and Santiago Lozano-Calderon, MD, PhD, orthopaedic oncology surgeons, and Joseph H. Schwab MD, chief of the Orthopaedic Spine Center and director of Spine Oncology & co-director of the Stephan L. Harris Chordoma Center at Mass General Cancer Center, and their colleagues in the Netherlands recently became the first to determine MCIDs on these three questionnaires for patients treated surgically for metastatic bone disease of lower extremities. Their report appears in Acta Oncologica.

Study Methods

This prospective study evaluated 33 adults that attended the orthopaedic oncology clinic at Mass General between April 1, 2017, and December 18, 2018, for metastatic disease of the femur, tibia or fibula and were scheduled for surgery for a pathologic fracture or impending fracture.

The subjects completed the PROMIS Global, Cancer-specific Physical Function and Pain Interference questionnaires before surgery, and then again one to three months afterward. Postoperatively, they also rated their overall response to surgery on a seven-point Likert scale. The answers to this "anchor" question were used to calculate MCIDs.

Results

The average pre- to postoperative changes in scores were:

• PROMIS Pain Interference, −7.4
• PROMIS Cancer-specific Physical Function, +4.5
• PROMIS Global–Physical Health, +4.4
• PROMIS Global–Mental Health, −1.0

In response to the anchor question, 31 patients (94%) said they were "a little better," "somewhat better" or "much better" after surgery. Anchor-based MCIDs were calculated as:

• PROMIS Pain Interference, 7.5 points (95% CI, 3.4–12)
• PROMIS Cancer-specific Physical Function, 4.1 (0.6–7.6)
• PROMIS Global–Physical Health, 4.3 (2.0–6.6)

The anchor-based analysis did not yield a usable estimate for the MCID of PROMIS Global–Mental Health. Many patients adapt to a disease over time, which can contribute to the stabilization of mental health scores regardless of whether a particular treatment is received.

Counseling Patients

Patients—and clinicians—who understand these MCID values should be better prepared to manage their expectations about the quality of life after palliative/prophylactic surgery for lower-extremity metastases. A large, multicenter trial might be able to define narrower ranges of values.

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