Predicting Which Patients Are Unlikely to Improve After THA

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A variety of patient-reported outcome measures (PROMs) are used after total hip arthroplasty (THA) to assess whether the goals of surgery have been met. These tools can also be helpful preoperatively, as they make it easier for the patient's input to be considered during shared decision-making about whether to proceed with THA.

Unfortunately, PROMs can be difficult to interpret because statistically significant results are often clinically irrelevant. To correct for this, clinicians can use the minimum clinically important difference (MCID) for each PROM to assess improvement after an intervention. An MCID is the smallest improvement in a given PROM that has been determined to be important to patients.

In a retrospective study of prospectively collected data, Pakdee Rojanasopondist, BA, clinical research coordinator, Charles R. Bragdon, PhD, associate director of clinical studies, and Henrik Malchau, MD, PhD, director emeritus of the Harris Orthopaedics Laboratory at Massachusetts General Hospital, and colleagues have identified preoperative factors associated with not achieving MCIDs in pain and function one year after THA. They published their findings in Clinical Orthopaedics and Related Research.

Study Design

The researchers studied 594 participants from an international, multicenter study that evaluated the long-term performance of several widely used implant systems. It involved a wide array of countries, surgeons and practice settings. These patients underwent THA between 2007 and 2012.

Both preoperatively and one year after surgery, patients completed general health and disease-specific PROMs:

• Short-form 36 (SF-36), a quality-of-life instrument that covers eight domains, including physical function. It yields two summary scores: Physical Component Summary (PCS) and Mental Component Summary (MCS)
• EuroQol five-dimension three-level (EQ-5D), another quality-of-life instrument
• University of California Los Angeles (UCLA) activity score — classifies patients' physical activity (0–10)
• Harris hip score (HHS) — composite measure of pain and physical function (0–100)
• Numerical rating scale (NRS) of hip-related pain (0–10)

Outcomes

The outcomes considered in the current study were the achievement of the following at one year after THA:

• MCID in pain — either a reduction of two points on the NRS or a one-year NRS score of 0
• MCID in physical function — either an increase ≥8.3 on the SF-36 physical function subscore or a one-year SF-36 physical function subscore ≥57.2 (the cutoff for being within the 95th percentile of scores)

54 (9%) did not achieve the MCID in pain and 146 (25%) did not achieve the MCID in physical function.

Preoperative Predictors of Inadequate Improvement

Predictors of Not Achieving the MCID in Pain:

• Higher joint space width (OR, 2.19; 95% CI, 1.49–3.22; P < .001)
• Female gender (OR, 2.04; 95% CI, 1.08–3.82; P = 0.03)
• Lower SF-36 MCS (OR, 0.95; 95% CI, 0.929–0.980; P = .001)

Predictors of Not Achieving the MCID in Function:

• Higher joint space width (OR, 1.54; 95% CI, 1.18–2.02; P = .002)
• Higher HHS (OR, 1.01; 95% CI, 1.00–1.03; P = .02)

Each one-millimeter increase in joint space width increased the odds of not achieving the MCID in pain by 119% and increased the odds of not achieving the MCID in physical function by 54%.

Implications for Patient Counseling

The researchers caution that their findings should not be used as selection criteria for THA. Rather, the study results can guide surgeons' conversations with patients when helping them evaluate their likelihood of improvement. The authors emphasized that since THA is a significant surgical procedure with serious risks and costs, patients deserve more than a slight decrease in pain or minor gains in physical function.

With regard to the implications of specific risk factors, the findings on joint space width provide evidence that multiple patients in the cohort may have undergone the procedure prematurely. When patients have less radiographically severe osteoarthritis, it is absolutely critical to:

• Counsel patients on their significantly increased risk of experiencing only a minor increase, if not a decrease, in pain and function postoperatively
• Discuss alternative treatment options with the patient, such as delaying surgery or pursuing more conservative treatment options until their disease progresses further

Patients with low preoperative SF-36 MCS scores may be more likely than most to use catastrophizing coping mechanisms and have a difficult time with pain control after surgery. Surgeons may wish to discuss delaying surgery, to allow these patients to receive counseling to improve their mental and emotional health first.

The research on how gender affects post-THA outcomes is mixed. Unlike this study, several others have reported no relationship between female gender and worse postoperative pain, function or quality of life. Still, surgeons may wish to counsel women that they are at increased risk of failure to experience relief of pain.

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