Introduction

• Flexor sheath infection is an infection of the synovial sheath surrounding flexor tendon in the hand .
• This is a surgical emergency that can result in significant morbidity.
• Flexor sheath is a closed compartment that releases synovial fluid that contributes nutrients to the tendons and allows smooth and efficient tendon glide. Raised pressure from infection can impair blood flow, leading to tendon necrosis and loss of the finger.
• Patient should be referred to the hand surgery team urgently as the majority will require surgical washout within 24 hours¹.

Epidemiology

Flexor sheath infections prevalence ranges from 2.5% to 9.4% of hand infections².

Pathophysiology

• Direct inoculation following penetrating trauma
  • E.g. thorn pricks, animal / human bites.
• Contiguous spread from nearby soft tissue infections e.g. felon, septic joint.
• Haematogenous spread of infection.
  • Neisseria gonorrhea, mycobacterium tuberculosis³.
• Common causative organisms include:
  • Staphylococcus aureus (most common).
  • MRSA.
  • Skin commensals e.g. Staphylococcus epidermidis, Pseudomonas aeruginosa, beta-haemolytic streptococcus⁴.
• Risk factors include: diabetes mellitus, immunocompromised patients, intravenous drug use⁴.

Clinical Features

• Four cardinal features – Kanavel signs:
  • pain on passive extension of the finger. This is often earliest sign
  • Fusiform swelling of the finger or ‘sausage finger’
  • Tenderness on palpation over flexor sheath.
  • Finger held in partial flexion.

Differential Diagnosis

Infectious: felon, herpetic whitlow cellulitis, septic arthritis, collar button abscess, deep space infections⁵.

Noninfectious: gout, autoimmune e.g. rheumatoid arthritis, overuse tenosynovitis⁵.

Investigation

• Flexor sheath infection is a clinical diagnosis.
• Blood tests: FBC (leukocytosis), CRP, serum urate if suspecting gout as differential .
• Hand Xray: identify foreign bodies, osteomyelitis/bone changes.

Management

Immediate management:

• Consider ABCDE approach and Sepsis 6 pathway including early empirical IV antibiotics.
• Consider tetanus booster if applicable.
• Remove all rings!
• Elevate.
• Splint in a Position of Safe immobilisation (POSI).
• Urgent referral to the hand surgery department.

Operative management:

• Surgical washout of the flexor sheath within 24 hours of the decision to operate.
• Washout using high volumes of normal saline +/- antibiotics from proximal to distal aspect of the finger.
• Wound swab should be sent and purulent infections will require a relook and repeat washout at 48 hours.

Non-operative management:

• An experienced hand surgeon should make the decision for non-operative management.
• Close monitoring with elevation, hand splinting and IV antibiotics.
• If there is no improvement or it clinically deteriorates within 24 hours, then surgery would be indicated.

Complications

Complication rates can reach as high as 38% in association with flexor sheath infections and may include the following:

• Finger stiffness.
• Boutonniere deformity.
• Deep space infection including horseshoe abscess
  • Horseshoe abscess – the contiguous spread of infection via a connection between the little finger and thumb flexor sheath called space of Parona (see image below).
  • This is also a surgical emergency and requires prompt referral to the hand surgery team.
• Tendon necrosis.
• Adhesions.
• Persistent infection.
• Need for amputation.

References

1. British Society for Surgery of the Hand – Flexor Sheath Infection Document
2. Pang H-N, Teoh L-C, Yam AK, et al. (2007) Factors affecting the prognosis of pyogenic flexor tenosynovitis. J Bone Joint Surg Am 89(8):1742–1748
3. Nikkhah D, Rodrigues J, Osman K, Dejager L. Pyogenic flexor tenosynovitis: one year’s experience at a UK hand unit and a review of the current literature. Hand Surg. 2012;17(2):199–203.
4. Hermena S, Tiwari V. (2024). Pyogenic Flexor Tenosynovitis. [Online]. National Library of Medicine. Last Updated: 8 January 2024.
5. Ray G, Sandean DP, Tall MA. Tenosynovitis. StatPearls Publishing; 2023.
6. Giladi AM, Malay S, Chung KC. A systematic review of the management of acute pyogenic flexor tenosynovitis. J Hand Surg Eur Vol. 2015 Sep;40(7):720-8. doi: 10.1177/1753193415570248. Epub 2015 Feb 10. PMID: 25670687; PMCID: PMC4804717.

Figures:

• Picture 1: Brent M. Egeland, Sandeep J. Sebastin, Kevin C. Chung. Drainage of Purulent Flexor Tenosynovitis. Plastic Surgery Key. Available at: https://plasticsurgerykey.com/4-drainage-of-purulent-flexor-tenosynovitis/. Permission obtained 05/07/24.
• Figure 1: “Position of Safe Immobilisation”, Van J. M. T., 2024.
• Figure 2: “Horseshoe Abscess”, Lam Y. J. Z., 2024.

Written by Dr Kantida Koysombat (CT1) & reviewed by Jonathan Van (Plastic Surgery Registrar)