Rupture of a popliteal cyst causes pain in the proximal calf. Examination shows tenderness, swelling, and bruising of the calf but again no definite weakness of ankle plantar flexion or tenderness of the Achilles tendon. Rupture of a popliteal cyst may be diagnosed by ultrasonography; however, the definitive diagnosis is made by knee arthrography.
Achilles tendinopathy most commonly occurs in athletes, especially runners. Patients report pain and swelling of the tendon, as well as morning stiffness and decreased function of the leg. The diagnosis is best made by physical examination, which shows tenderness and thickening of the Achilles tendon but no gap or significant weakness. MRI and ultrasonography can confirm the diagnosis if necessary. Achilles tendinopathy is characterized by disorganization of the collagen fibers and tenocytes, which makes the tendon more susceptible to rupture.
The retrocalcaneal bursa is located between the Achilles tendon posteriorly and the calcaneus anteriorly. Thus, retrocalcaneal bursitis causes tenderness at the back of the heel rather than in the midportion of the Achilles tendon.
Achilles tendons usually rupture during sporting events, particularly running and jumping events that involve eccentric loading and explosive calf contraction. The typical patient is a 40-year-old man; women are affected less often. Less commonly, ruptures occur in older patients who have degenerated Achilles tendons. Their risk for Achilles tendon rupture is increased not only by age but also in about 10% of cases by other factors, including a Haglund deformity (a protuberance at the superior corner of the calcaneus), systemic corticosteroid use, corticosteroid injections into the Achilles tendon, inability to bear weight on the opposite extremity, and use of fluoroquinolone antibiotics. Figure 2 shows an example of a swollen ankle several days after an Achilles tendon rupture.
Although fluoroquinolones are generally as well tolerated as other antibiotics, they do have some adverse effects, including central nervous system problems, arthropathy, and tendon rupture, particularly Achilles tendon rupture. The risk is higher in patients who take corticosteroids. Cases of Achilles tendon rupture after the use of other antibiotics have been reported, but the association is less well established. Other drugs, including statins and corticosteroids, may more rarely be associated with Achilles tendon rupture.
A systematic review and meta-analysis found that fluoroquinolone treatment increases the risk for Achilles tendon rupture by a factor of 2.5. The risk for such rupture is increased in patients older than 60 years and by the concomitant use of corticosteroids. Although tendon ruptures associated with fluoroquinolone treatment are more common in older adults, they can occur occasionally even in adolescents.
Another systematic review concluded that, in addition to fluoroquinolone treatment, risk factors for Achilles tendon rupture include a lower limb fracture, alcohol use, training in cold weather, and an abnormal gait. A population-based cohort study reported that fluoroquinolone use triples the risk for Achilles tendon rupture. Even so, the incidence is only about 1 in 5000 users. The mechanism by which fluoroquinolones increase the risk for Achilles tendon rupture is unknown.
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