(See also Overview and Evaluation of Hand Disorders Overview and Evaluation of Hand Disorders Common hand disorders include a variety of deformities, ganglia, infections, Kienböck disease, nerve compression syndromes, noninfectious tenosynovitis, and osteoarthritis. (See also complex... read more 
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The usual cause of infectious flexor tenosynovitis is a penetration and bacterial inoculation of the sheath.
Diagnosis of Infectious Flexor Tenosynovitis
Kanavel signs
X-rays
Culture of drainage or surgical sample
Infectious flexor tenosynovitis causes Kanavel signs:
Flexed resting position of the digit
Fusiform swelling
Tenderness along the flexor tendon sheath
Pain with passive extension of the digit
X-rays should be taken to detect occult foreign bodies. Acute calcific tendinitis and rheumatoid arthritis can restrict motion and cause pain in the tendon sheath but can usually be differentiated from infectious flexor tenosynovitis by a more gradual onset and the absence of some Kanavel signs. Disseminated gonococcal infection Symptoms and Signs 
can cause tenosynovitis but often involves multiple joints (particularly those of the wrists, fingers, ankles, and toes), and patients often have recent fever, rash, polyarthralgias, and often risk factors for a sexually transmitted disease. Infection of the tendon sheath may involve nontuberculous mycobacteria, but these infections are usually more indolent, especially in immunocompromised patients (1 Diagnosis reference Infectious flexor tenosynovitis is an acute infection within the flexor tendon sheath. Diagnosis is suggested by Kanavel signs and confirmed with x-rays. Treatment is surgical drainage and antibiotics... read more ).
Diagnosis reference
1. Kazmers NH, Fryhofer GW, Gittings D, et al: Acute deep infections of the upper extremity: The utility of obtaining atypical cultures in the presence of purulence. J Hand Surg Am 42(8):663.e1-663.e8, 2017. doi: 10.1016/j.jhsa.2017.05.004. Epub 2017 May 25. PMID: 28550986.
Treatment of Infectious Flexor Tenosynovitis
Surgical drainage and antibiotics
Treatment of infectious flexor tenosynovitis is surgical drainage (eg, irrigation of the tendon sheath by inserting a cannula into one end and allowing the irrigating fluid to pass along the tendon sheath to the other end, or an extensive open incision for more serious infections).
Antibiotic therapy (beginning empirically with a cephalosporin) and cultures are also required. In areas where methicillin-resistant Staphylococcus aureus (MRSA) is prevalent, trimethoprim/sulfamethoxazole, clindamycin, doxycycline, or linezolid should be used instead of a cephalosporin.
