Background Hip involvement is the most frequent extra spinal arthritic manifestation of Axial Spondyloarthrities (AS) and a common cause of disability.

Objectives To assess the progression of radiological forms of hip disease in AS Tunisian patients and to evaluate the effect of TNF inhibitors on this progression.

Methods AS patients (satisfying ASAS criteria 2009) with hip disease and with at least two sets of Anteroposterior X-rays of the pelvis at a minimum gap of 2 years were included. Radiographic forms of hip disease were assessed according to Netter classification (early, condensing, destructive, combined and synostosis forms) at baseline, at 2 years and at an average of 5 years of treatment. Bath AS Disease Activity Index (BASDAI), BASFI, ESR, CRP, HLA-B27, age of onset were included in the model.

Results 84 patients were evaluated, The median age of onset of the disease was 25 years [16-54ans], HLA B27 was positive in 50% of cases. The median BASDAI and BASFI scores were respectively 5,4 and 5,5. The average ESR and CRP were respectively 47 and 33. 46 patients received TNF inhibitors (infliximab 48%, Adalimumab 14% and Etanercept 36%), 27 patients received csDMARDs and 46 NSAID. Sixty four patients had bilateral hip involvement. At baseline: 139 hips were evaluated; patients had an early form in 38 hips, condensing form in 4 hips and destructive form in 72 hips. After 2years, 74 hips were evaluated, 16 hips with an early form, four with a condensing form, 33 with destructive form, and 20 had combined form. After an average of 5 years, 96 hips were evaluated; hip involvement was debutant in 14 cases, condensing in 3 cases, destructive in 48 cases, combined in 27 cases and synostosis in 2 cases. Early forms evolved to destructives forms in 8 cases (1 at 2years and 7 at 5years). Destructive forms progressed to combined forms in 8 cases (5 at 2years and 3 at 5years),combined forms progressed to destructives forms in 2 cases and to synostosis forms in 2cases. There was no progression in condensing forms. When we compare patients with TNF inhibitors versus patients TNFnaïf, there were no significant differences between the two groups for the mean age of onset, the mean CRP and VS level and in forms of hips involvement at baseline, however BASDAI and BASFI scores at baseline were significantly higher in TNF inhibitors. When we compare the radiological forms progression between the two groups we found that there is no significant difference in radiographic progression of destructive, condensing and combined forms however there were significantly higher progression in beginning forms in TNF- naïf patients

Conclusions The destructive form is the most common radiographic form of hip disease in AS Tunisian patient and TNF inhibitors seem have a protective effect on the hip, especially on the beginning form.

Disclosure of Interest None declared