Background Hip joints are the most commonly affected part of locomotor system in ankylosing spondylitis (AS) patients, imposing serious functional limitations. Hip joints involvement is diagnosed in 56% of AS patients in Russia, being the cause of 7% total hip replacement surgeries.

Objectives To study ultrasound features of AS coxitis in hospitalized patients.

Methods The study included 220 consecutive AS patients (criteria 1984), hospitalized to V. A. Nasonova Research Institute of Rheumatology during the period 2012-13 yy. Mean patients' age was 36,3±10,2. Mean age at disease onset - -30,6±11,0 y. 82% of patients were HLA-B27-positive, disease activity by BASDAI - 4,5±2,1, ASDAS - 3,3±1,2. Functional BASFI index was 4,4±2,6. All patients were subjected to routine clinical examination. Hip joints ultrasound examination was performed with Sono Diagnost 360 (Philips) using linear (7,5 MHz) and convex (5,0 MHz) transducers. Transudation in the joint space was registered when the distance between signals from the capsule and medial aspect of femoral neck was ≥7 mm [1].

Results Transudation in the joint space based on established US ≥7 mm distance was found in 119 (54%) patients, 104 (83%) out of them also had clinical signs and symptoms of coxitis (pain and functional limitations). Patients' clinical data of both subgroups – with and without US coxitis criteria - are presented in the Table. Both subgroups were comparable by demographic parameters. Higher disease activity, CRP levels and BASFI scores (i.e. functional impairment) are evident in patients with US diagnosed transudation. 15 patients with US symptoms of sinoviitis had no clinical manifestations of coxitis. In these patients the capsular-neck distance did not exceed 8 mm.

Conclusions Clinical manifestations accompany US-diagnosed coxitis only when capsular-neck distance is ≥8 mm. More studies are warranted to establish upper limit of the normal US-measured distance between the capsule and femoral neck for US final diagnosis of coxitis.

References

1. Koski J.M., Antilla P.J., Isomaki H.A. Ultrasonography of the adult hip joint. Scand. J. Rheumatol., 1989, 18, 113-119.

Disclosure of Interest None declared