Ultrasonography of entheseal insertions in the lower limb in spondyloarthropathy

Abstract

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

Methods: 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.

Results: 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.

Conclusions: 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.

Figure 1

Normal ultrasonographic appearance on lower limb entheseal insertions. (A) Quadriceps tendon enthesis: PR, proximal; DI, distal; S, skin; Q, quadriceps tendon; P, patella; *, tendon attachment. (B) Proximal patellar ligament enthesis: PR, proximal; DI, distal; S, skin; L, patellar ligament; P, patella; H, Hoffa fat pad; F, femur; *, ligament attachment. (C) Distal patellar ligament enthesis: PR, proximal; DI, distal; S, skin; L, patellar ligament; H, Hoffa fat pad; T, tibia; *, ligament attachment. (D) Achilles enthesis: PR, proximal; DI, distal; S, skin; A, Achilles tendon; C, calcaneus; K, Kager fat pad; *, tendon attachment. (E) Plantar aponeurosis enthesis: PO, posterior; AN, anterior; S, skin; A, plantar aponeurosis; C, calcaneus; H, heel fat pad; *, aponeurosis attachment.

Figure 2

Ultrasonographic appearances of lower limb enthesitis. (A) Posterior calcaneal erosions: PR, proximal; DI, distal; S, skin; A, Achilles tendon; K, Kager fat pad; C, calcaneus; E, erosion. For comparison with the normal image see fig 1D. (B) Infrapatellar bursitis: PR, proximal; DI, distal; S, skin; L, patellar ligament; T, tibia; H, Hoffa fat pad; the crosses mark infrapatellar bursa. For comparison with the normal image see fig 1C. (C) Inferior patella enthesophyte: PR, proximal; DI, distal; S, skin; L, patellar ligament; P, patella; H, Hoffa fat pad; E, enthesophyte. For comparison with the normal image see fig 1B. (D) Suprapatellar bursitis: PR, proximal; DI, distal; S, skin; Q, quadriceps tendon; F, fluid collection in the suprapatellar bursa; P, patella; PF, perifemoral fat. For comparison with the normal image see fig 1A. (E) Inferior calcaneal spur: PO, posterior; AN, anterior; S, skin; P, plantar aponeurosis; C, calcaneus; H, heel fat pad; BP, bony spur. For comparison with the normal image see fig 1E.

Figure 3

Correlation of clinical abnormality (either swollen or tender) with any US abnormality at entheseal sites in the lower limbs. SP, superior pole of the patella; IP, inferior pole of the patella; TT, tibial tuberosity; SC, superior pole of the calcaneus; IC, inferior pole of the calcaneus.