Background: The entheses are a primary target organ in the seronegative spondylarthropathies, including psoriatic
arthritis (PsA) . Susceptibility to damage is multifactorial but inflammatory and mechanical factors may be important. In patients with non insertional chronic Achilles tendinopathy (AT) a relationship has been found between clinical symptoms,
ultrasonographic features, such as power Doppler signal, and abnormal foot function . These relationship have not been investigated for the AT enthesis in patients with PsA.
Objectives: To investigate the relationship between clinical and ultrasound features and mechanical foot function at the
AT enthesis in PsA patients.
Methods: Twenty nine PsA patients (10 male, 19 female) with a mean ±SD age of 47.6 ±12.3 years and disease duration
11.3 ±9.7 years were recruited from rheumatology outpatient clinics at Glasgow Royal Infirmary. The AT enthesis site
was clinically examined for spontaneous pain, tenderness elicited by pressure, mobilization or contraction of the tendon
against resistance and localised swelling at the enthesis. B-Mode and power Doppler ultrasound (PDUS) (Esaote
MyLab70, 10-18MHz, using a linear array probe) was used to detect the presence/absence of PDUS, retrocalcaneal
bursitis, erosion, and enthesophyte. AT thickness and the GUESS score were also measured. 3-D gait analysis was
undertaken using a multi-segmented foot model to derive rotational movement at the ankle joint complex and ankle joint
moments and power. Chi-square, student t-tests and Spearman correlation coefficients statistical tests were used.
Results: PsA patients with painful AT enthesis walked significantly slower (1.05 m/s ±0.24 m/s Vs 1.29 m/s ±0.18 m/s, p=
0.01) and had reduced ankle dorsiflexion (16.4° ±3.2° Vs 20.6° ±4.1°, p= 0.006) in comparison to asymptomatic patients.
There were no statistically significant differences in ankle joint complex inversion/eversion (p=0.30) and internal/external rotation (p=0.24) rotations or ankle joint moments (p=0.16) and power (p=0.61). On ultrasound examination no subjects had PDUS signal. The AT thickness was not significantly different between symptomatic and non-symptomatic patients (40.7mm ±13.8mm Vs 38.4mm ±5.7mm, p=0.54). There was no statistically significant difference in the proportion of PsA
patients with and without AT pain who exhibited US evidence of retrocalcaneal bursitis (p=0.15), erosion (p=0.97),
enthesophyte (p=0.71) or GUESS score (p=0.97). AT thickness was positively correlated with body-mass index (rho 0.41,
p=0.03), tendon loading (peak ankle joint moment) (rho 0.53, p=0.003), and GUESS score (rho 0.42, p=0.02). US detected AT erosions were positively correlated with ankle rotational movement (rho 0.39, p=0.04) and enthesophytes negatively correlated with ankle joint dorsiflexion (rho 0.43, p=0.02).
Conclusions: In this cohort of PsA patients, associations were found between clinically detected entheseal pain, AT
thickness and mechanical foot function.