The Science of De Quervain's Tenosynovitis

De Quervain's tenosynovitis is a stenosing tenosynovitis affecting the first dorsal compartment of the wrist, specifically involving the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) tendons. These tendons pass through a fibro-osseous tunnel bordered by the radial styloid process and overlying extensor retinaculum. The condition represents inflammation and thickening of the tendon sheath (tenosynovium) that creates a progressive stenosis (narrowing) of the compartment, mechanically restricting tendon glide and causing friction-induced inflammation. The pathophysiological cascade begins with repetitive mechanical irritation from thumb movements combined with wrist deviation. This creates microtrauma to the tendon sheath lining, triggering an inflammatory response with synovial thickening, edema, and fibrous tissue deposition. As the sheath thickens, the space available for tendon excursion diminishes, creating a vicious cycle where normal movements cause progressively more friction and inflammation. Histologically, the sheath shows chronic inflammatory changes, fibrocartilaginous metaplasia, and myxoid degeneration rather than acute inflammation, explaining why anti-inflammatory medications have limited efficacy. Anatomical variations significantly influence susceptibility. Studies show 20-30% of individuals have multiple APL tendon slips (up to 4-5 separate slips), and approximately 50% have septations subdividing the first compartment into separate subcompartments for APL and EPB. These septations create additional friction points and explain why some cases respond poorly to injection therapy - the medication doesn't reach all affected compartments. The EPB may also have its own separate compartment in 10-20% of people, creating a variant anatomy that requires modified treatment approaches. The condition shows strong demographic patterns: women are affected 6-10 times more frequently than men, with peak incidence in the 4th-6th decades. Pregnancy and early postpartum period represent particularly high-risk times due to hormonal influences on tendon and ligament laxity combined with new repetitive infant care activities. Estrogen and relaxin affect collagen metabolism and tendon material properties, potentially predisposing to inflammatory conditions. Risk factors include diabetes mellitus (2-3 times higher prevalence), rheumatoid arthritis, hypothyroidism, and previous wrist trauma or fracture. The condition frequently coexists with other thumb pathology including carpometacarpal (CMC) arthritis, intersection syndrome (inflammation where APL/EPB cross over wrist extensors), and carpal tunnel syndrome. Differential diagnosis requires careful assessment as these conditions can produce overlapping symptoms but require different management approaches.