Quantification of progressive joint space narrowing in osteoarthritis of the hip: longitudinal analysis of the contralateral hip after total hip arthroplasty.

OBJECTIVE: The rate of progressive joint space narrowing in the contralateral hip after total hip arthroplasty (THA) for osteoarthritis (OA) and the factors which may predispose patients to more aggressive joint space narrowing remain undefined. The current study sought to evaluate the rate and pattern of, and risk factors for, progressive joint space narrowing in the contralateral hip after THA for OA.

METHODS: Each patient who underwent THA for OA in 1984-1985 was followed up longitudinally, and annual anteroposterior (AP) pelvis radiographs were obtained. The radiographic joint space width (JSW) of each contralateral hip joint was quantified, and the rates of JSW narrowing were determined. Evaluation of potential risk factors for accelerated progression of joint space narrowing included age, sex, side of surgery, weight, height, body mass index (BMI), hip pain, etiology of OA, and Kellgren/Lawrence radiographic grade.

RESULTS: Ninety-nine patients and 619 AP pelvis radiographs were evaluated. The median initial JSW was 3.48 mm (interquartile range 1.55). JSW declined in a linear manner at a median rate of 0.10 mm/year. The rate of decline between baseline and followup in 20 months was predictive of the overall slope. Two subpopulations were identified. Eighty-five percent of patients maintained a slow decline in JSW (< or =0.2 mm/year), and 15% exhibited an accelerated decline in JSW (>0.2 mm/year). Kellgren/ Lawrence radiographic grade > or =2 and a diagnosis of primary OA were each associated with a more rapid decline in JSW (P = 0.006 and P = 0.02, respectively). Initial JSW, age, sex, weight, height, BMI, and hip pain were not risk factors for rapid decline in JSW.

CONCLUSION: Radiographic hip JSW may be reliably quantified and followed up longitudinally using standard AP radiographs. Progression of JSW narrowing in the contralateral hip after THA for OA proceeds in a linear manner over several years. A subpopulation of patients with accelerated narrowing of contralateral JSW may be identified within 20 months, and may represent a suitable population with which to assess the potential efficacy of new disease-modifying agents.