M65.18 Other infective (teno)synovitis, other site

ICD-10-CM Code M65.18: Other infective (teno)synovitis, other site

ICD-10-CM code M65.18 designates other infective (teno)synovitis at an other site. Infective tenosynovitis involves pathogens proliferating within the tendon sheath, and prompt treatment is essential. This code is listed in billing and coding articles alongside more specific site codes, but its presence in such documents does not establish payer coverage. 1 3 4 5 6

Plain-language overview

Tenosynovitis is an inflammatory condition affecting the lining of the sheath that surrounds a tendon, and infective tenosynovitis is caused by infective pathogens proliferating within these tendon sheaths. 1 3

What this code represents

In the ICD-10-CM Section M65-M67, code M65.18 represents the diagnosis of other infective (teno)synovitis at an other site. 6

Coding details

Within the ICD-10-CM coding structure, M65.18 is listed alongside M65.19 for other infective (teno)synovitis at multiple sites, and M65.10 for an unspecified site. 6

The code M65.18 is listed in Medicare billing and coding articles for pain management procedures, appearing alongside M65.19 for other infective (teno)synovitis at multiple sites. 4 5

Clinical context

Pyogenic flexor tenosynovitis is a serious bacterial infection within the closed space of the digital flexor tendon sheaths that can result in tendon necrosis and marked loss of digit movements. 2

An infected cut to the hands or wrists that causes infectious tenosynovitis may be an emergency requiring surgery, and tenosynovitis caused by infection needs to be treated right away. 3

Documentation considerations

A detailed history focusing on possible etiologies is essential for tenosynovitis, as the cause actively directs treatment, and infectious tenosynovitis treatment can vary based on the offending agent when known. 1

What the sources add

The clinical literature from the National Center for Biotechnology Information describes tenosynovitis as an inflammatory condition with infective and non-infective causes, while the Medicare billing articles list M65.18 within pain management coding contexts. 1 4 5

The clinical sources describe the diagnosis and treatment of infective tenosynovitis, whereas the coding sources establish the specific alphanumeric structure and billing article inclusion of code M65.18. 1 2 6

Sources

1. Bookshelf — ncbi.nlm.nih.gov; accessed 2026-07-25.
2. Bookshelf — ncbi.nlm.nih.gov; accessed 2026-07-25.
3. Tenosynovitis: MedlinePlus Medical Encyclopedia — medlineplus.gov; accessed 2026-07-25.
4. Article - Billing and Coding: Pain Management - injection of tendon sheaths, ligaments, ganglion cysts, carpal and tarsal tunnels (A52863) — cms.gov; accessed 2026-07-25.
5. Article - Billing and Coding: Pain Management - injection of tendon sheaths, ligaments, ganglion cysts, carpal and tarsal tunnels (A52863) — cms.gov; accessed 2026-07-25.
6. Coding: ICD-10-CM Section M65-M67 — imedicalcode.com; accessed 2026-07-25.