de Jonge (2011) analysed the records of 50000 general practice patients in the Netherlands and found an incidence of 2.35/1000 adult patients, so this is a reasonably common condition.
Most studies describe non-insertional tendonopathy in athletic populations, commonly in their 30s and 40s. In such populations
- prevalence is about 5-15%
- the condition is twice as common in men
- paratendonitis is common
Other series look at older less athletic populations in their 40s and over, in whom peritendonitis is less common and non-insertional tendonopathy more frequent.
Nicol et al (2006) found ultrasound evidence of tendonopathy in 59% of the tendons of 126 asymptomatic subjects with a mean age of 33y.
There are associations with (Holmes and Lin 2006, Corrao et al 2006):
- quinolone antibiotics
- oral steroids
- hormone replacement therapy
- oral contraceptive pill
- hypertension (in women)
- diabetes (in men <44y)
Gaida (2010) studied fasting seum lipids in 60 patients with non-insertional Achilles tendonopathy and 60 matched controls. They found a pattern of dyslipidaemia consistent with insulin resistance and a possible association with the metabolic syndrome. Gaida suggested that cardiovascular disease research may shed light on tendonopathy.
There is only one long-term outcome study. Paavola (2000) reported 83 patients followed up for 8 years after non-surgical treatment:
- 60% were pain-free and only 5% had disabling pain
- 40% had tender tendons and 20% nodules in the tendon
- 40% had developed problems with the other Achilles tendon
- 30% had had tendon surgery
- Only one had ruptured
On the basis of Paavola's series it appears that Achilles tendonopathy is a relatively benign condition, which may progress slowly but rarely leads to rupture in those who present initially with pain. About 30% of patients fail non-operative treatment and are offered surgery.