Study Links OA Severity to Young THA Patients’ Outcomes

Young total hip arthroplasty (THA) patients with less severe radiographic joint space narrowing have less predictable clinical improvement in terms of function, pain relief, and activity, according to the results of a study to be presented Thursday by Jeffrey B. Stambough, MD. These findings indicate that by directly quantifying anticipated gains based on baseline clinical scores, young patients with joint space width (JSW) of >1.5 mm may have suboptimal THA clinical outcomes.

Previous studies have established that patient satisfaction after THA strongly correlates to postoperative pain, function, activity level, and success in meeting patient expectations. There is a need to better understand predictors of THA outcomes in an era of healthcare reform that places more emphasis on patient satisfaction scores, asserted Dr. Stambough.

As Dr. Stambough explained, the study aimed to determine the association between preoperative radiographic disease—as measured quantitatively by JSW—and patient-reported function, activity, pain, and quality of life scores after THA. The investigators hypothesized that individuals with more advanced radiographic osteoarthritis experience consistent and greater magnitudes of improvement in clinical outcomes after THA.

“We chose to focus on this study question because a similar paper looking at the outcomes of TKA and preoperative radiographic disease found that those with Kellgren-Lawrence Grade 1 or 2 disease—hence, more preserved joint space width on X-ray—were associated with higher levels of dissatisfaction (approximately 50 percent) at 1-year follow-up,” said Dr. Stambough. “We wanted to test a similar hypothesis with young patients receiving THAs since little had been published regarding this issue. We thought that in 2016, a question like this is most important because surgeons are partly assessed, reimbursed, and penalized according to patient satisfaction scales.”

Retrospective analysis
The researchers retrospectively analyzed 146 patients (≤55 years of age; 146 hips) with a diagnosis of primary osteoarthritis (OA) from their institution’s joint registry who underwent cementless THA between January 2009 and December 2010. The cohort consisted of 54 percent females (n = 79) and 46 percent (n = 67) males, with a median age of 47 years and a median body mass index (BMI) of 27.5 kg/m2. Preoperative anteroposterior (AP) digitized pelvic radiographs were measured by one author blinded to clinical outcomes and not involved in clinical care to establish JSW, defined as the minimal joint space (ie, the shortest distance between the femoral head margin and the acetabulum) in the superolateral weight-bearing zone (Fig. 1). Measurements on the same patient were made at least 2 weeks apart, averaged, and then adjusted by a factor of 1.2 to correct for magnification.

 AND-2016-03-02-018-fig01

Fig. 1 An anteroposterior pelvis radiograph with neutral tilt and rotation obtained by the investigators to measure JSW in the study participants. The radiograph uses a coned-in view to focus on the superolateral weight-bearing region of the joint.
Courtesy of Jeffrey B. Stambough, MD

Investigators treated the JSW as a continuous variable when applied to statistical modeling. The relationship between the width of joint space and the improvement of clinical outcome was examined via a general linear modeling approach with the adjustment for patients’ age, BMI, and gender. The average pre-arthroplasty JSW for the cohort was 1.14 mm.

Assessing results
Findings indicated a significant improvement in all patient-reported outcomes after THA for the cohort (P < 0.001) the researchers found an inverse relationship between preoperative radiographic disease, as measured by JSW when treated as a continuous variable, and improvements in postoperative patient-reported functional, activity, pain, and quality of life scores. The generalized linear model (Fig.1) demonstrated that as JSW decreased by 1 mm, the following outcome measures experienced predicted improvements: modified Harris Hip Score (mhhs): 6.3 (P < 0.001); SF-12 physical: 2.1 (P = 0.027); Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)-pain: 4.8 (P  = 0.01); and UCLA Activity score: 0.44 (P = 0.02). Minimal clinically important thresholds, when available, were surpassed in all cases when the JSW change was noted to be 2 mm or more.

“What was most surprising was that the improvement in some patient-reported scores—namely, the mHHS—was more exaggerated once the joint space width was less than 1.5 mm,” stated Dr. Stambough. “Thus, those with the most severe disease radiographically had the greatest improvements in outcome scores.”                          

Dr. Stambough’s coauthors of Paper 588 “Does Radiographic Severity of Osteoarthritis Predict Outcomes in Young Hip Arthroplasty Patients?” are Ao Xiong, MD; John J. Callaghan, MD; and primary investigator/senior author John C. Clohisy, MD.

Details of the authors’ disclosures as submitted to the Orthopaedic Disclosure Program can be found in the Final Program; the most current disclosure information may be accessed electronically at www.aaos.org/disclosure

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