Ultrasonography of entheseal insertions in the lower limb in spondyloarthropathy

To compare ultrasonography (US) with clinical examination in the detection of entheseal abnormality of the lower limb in patients with spondyloarthropathy (SpA).

35 patients with SpA (ankylosing spondylitis 27; psoriatic arthritis 7; reactive arthritis 1) underwent independent clinical and ultrasonographic examination of both lower limbs at five entheseal sites-superior pole and inferior pole of patella, tibial tuberosity, Achilles tendon, and plantar aponeurosis. US was performed using an ATL (Advanced Technology Laboratories, Bothell, Washington, USA) high definition imaging 3000 machine with linear 7-4 MHz and compact linear 10-5 MHz probes to detect bursitis, structure thickness, bony erosion, and enthesophyte (bony spur). An enthesitis score was formulated from these US findings giving a possible maximum total score of 36.

On clinical examination 75/348 (22%) entheseal sites were abnormal and on US examination 195/348 (56%) sites were abnormal. In 19 entheseal sites with bursitis on US, only five were detected by clinical examination. Compared with US, clinical examination had a low sensitivity (22.6%) and moderate specificity (79.7%) for the detection of enthesitis of the lower limbs. There was no significant correlation between the US score of enthesitis and acute phase parameters such as erythrocyte sedimentation rate (ESR) or C reactive protein (CRP). The intraobserver kappa value for analysis of all sites was 0.9.

Most entheseal abnormality in SpA is not detected at clinical examination. US is better than clinical examination in the detection of entheseal abnormality of the lower limbs in SpA. A quantitative US score of lower limb enthesitis is proposed but further studies are required to validate it in SpA.