Causes of Tenosynovitis

What Causes Tenosynovitis?

Tenosynovitis develops when the delicate synovial lining that surrounds certain tendons becomes irritated and inflamed. Most cases are still linked to work patterns that load the same tissues day after day, but infection, systemic illness and even some medicines can all play a part.

Over-use and repetitive tasks

Typing, barcode scanning, playing the violin or tightening bolts on a production line all involve thousands of identical movements. Each cycle compresses the sheath, produces heat and, over time, stimulates thickening of the lining. Once space inside the tunnel is reduced, the tendon begins to stick and pain follows. The Health and Safety Executive (HSE) continues to cite repetitive force as the single biggest occupational risk factor for upper limb tenosynovitis.

Static postures

Remaining in one position sounds harmless, yet holding a steering wheel or standing rigidly at a checkout for example stalls blood flow to the tendon sheaths. Without that circulation the lubricating fluid becomes syrupy, friction rises and inflammation sets in. Regular breaks and gentle stretches are proven to lower risk but are still overlooked in many workplaces.

Awkward reach and poor workstation design

Tasks performed above shoulder height or just out of comfortable reach place tendons on a prolonged stretch. The resulting tension, particularly across the wrist and forearm, accelerates micro-trauma. Updated HSE guidance (2024) stresses that keyboards, scanners and component trays should sit within a forearm’s length to cut incidence rates.

Forceful lifting and manual handling

Shifting heavy boxes, rolling barrels or even manoeuvring obese patients forces tendons to transmit high loads. If manual handling technique, handle design or team lift policies are inadequate the tendon sheath can fray and swell. Cold environments magnify the effect because muscles lose elasticity.

Hand–arm vibration and cold exposure

Operating high-vibration machinery such as pneumatic needle scalers, rotary hammer drills or plate compactors repeatedly bathes the tendons in tiny shock waves. Over months this bruises the synovial lining and narrows its space, rather like grit under a bicycle chain. The Control of Vibration at Work Regulations 2005 set daily exposure limits, yet HSE inspections continue to find construction and grounds maintenance crews regularly exceed them on busy shifts. Cold weather magnifies the problem because blood vessels tighten and the lubricant inside the sheath thickens. If you notice tingling, numbness or stiffness whilst using this type of equipment on a frosty morning, your body is signalling that damage may already be under way.

Physical conditioning and previous injury

Tendons respond to gradual loading, yet an untrained or de-conditioned muscle-tendon unit fatigues quickly and loses its shock-absorbing capacity. Old strains, fractures or lacerations may also focus stress on the sheath.

Infection after trauma

An animal bite, thorn puncture or contaminated laceration can seed bacteria directly into the synovial sheath. As the sheath is a closed compartment, pressure builds rapidly, risking tendon necrosis within 24–48 hours. Urgent surgical washout and intravenous antibiotics are essential. Infections can also spread from distant sites via the bloodstream, so pain in the hand after, for example, a foot ulcer, should never be ignored.

Systemic diseases and medicines

Certain long-term illnesses can inflame tendon sheaths from within, so even everyday tasks can become painful.

Rheumatoid arthritis and psoriatic arthritis are autoimmune disorders in which the body’s defence system attacks the synovial lining. The sheath thickens, joints feel warm and stiff – especially first thing in the morning – and tendons start to creak or catch.

Diabetes changes the chemistry of collagen and narrows the small blood vessels that feed the sheath. High glucose leaves tendons less elastic while slower circulation delays repair, so tiny strains build into full-blown inflammation.

Gout is famous for tormenting the big toe, yet the same urate crystals can settle in the flexor sheaths of the wrist or ankle. The result is sudden swelling, redness and tenderness that may be mistaken for infection.

Hypothyroidism slows metabolism; the resulting build-up of mucopolysaccharides makes tendons waterlogged and irritable.

Less common connective tissue diseases such as systemic lupus erythematosus and scleroderma can also announce themselves with tenosynovitis early in their course.

The Medicines and Healthcare products Regulatory Agency (MHRA) also cautions that, on rare occasions, tendon-sheath inflammation can appear within a few weeks of starting certain fluoroquinolone antibiotics or the hormone-blocking medicines prescribed after breast cancer surgery. Bringing the underlying condition under control cuts flare ups dramatically and coupled with a physiotherapist-designed graded exercise plan, it’s the best defence against recurring tendon sheath inflammation.

When no cause is found

Doctors cannot always work out why tenosynovitis starts. In around one in ten people, even after scans and blood tests, no trigger is found; these are called “idiopathic” cases, which simply means the cause is unknown.

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