Written and maintained by CASRAI Editorial Board
Last updated
General product and regulatory information only, not medical advice. Questions about use belong with a treating clinician.
Short answer
A knee immobilizer is a brace that supports the knee and limits its movement. In US regulation it is not a separate device type: it falls under the limb orthosis (brace) definition in 21 CFR 890.3475, a Class I device that is exempt from premarket notification.
Definition and scope
Patient-education material from ECU Health (StayWell content) describes a knee immobilizer as a type of brace used to provide support and limit movement of the knee, with a hook-and-loop closure. That is the everyday meaning, and it is what most people searching this phrase want to know.
The regulatory wording is broader. Under 21 CFR 890.3475, a limb orthosis (brace) is “a device intended for medical purposes that is worn on the upper or lower extremities to support, to correct, or to prevent deformities or to align body structures for functional improvement.” The regulation lists a “knee cage” among its examples, alongside a whole limb and joint brace, a hand splint, an elastic stocking and a corrective shoe.
FDA’s product classification database lists “cage, knee” under product code ITM, regulation number 890.3475, Device Class 1, 510(k) exempt, with the definition “Limb orthosis.” FDA does not publish a product code literally named “knee immobilizer,” so this page does not claim that knee immobilizers are code ITM; it reports what FDA lists for the knee cage and the limb orthosis.
Related terms and what each source says
The terms below overlap but come from different sources. The table keeps each definition attached to the document that states it.
| Term | What the source says | Source |
|---|---|---|
| Knee immobilizer | A type of brace used to provide support and limit movement of the knee | ECU Health patient education |
| Limb orthosis (brace) | A device worn on the upper or lower extremities to support, to correct, or to prevent deformities or to align body structures for functional improvement | 21 CFR 890.3475(a) |
| Knee cage | Named as an example of a limb orthosis in the regulation; listed by FDA as “cage, knee,” product code ITM, Class 1, 510(k) exempt | 21 CFR 890.3475(a); FDA product classification database |
| Class I (general controls) | Exempt from premarket notification (subject to the limitations in 21 CFR 890.9) and from the quality management system regulation (part 820) except records and complaint files | 21 CFR 890.3475(b) |
For other braces and supports, see the CASRAI guides on the ROM brace, the cervical collar, the hip brace and the splint.
Where it matters for clinics and supply decisions
The regulatory status gives a clinic or lab supply team a few concrete questions to ask about any knee immobilizer it stocks, each tied to the sources above.
- Classification. Ask which regulation the supplier places the product under. The limb orthosis regulation is 21 CFR 890.3475, and its classification is Class I (general controls).
- Premarket status. Class I limb orthoses are exempt from premarket notification. The exemption is subject to the limitations in 21 CFR 890.9.
- Records. The quality management system exemption keeps records and complaint-file requirements in place.
- Sterile labeling. FDA’s classification page states the partial exemption from GMP applies “as long as the device is not labeled or otherwise represented as sterile.”
Related supply planning is covered in the sports medicine clinic supply checklist and the physical therapy clinic supply checklist. For how 510(k) works in general, see the guide to FDA 510(k) premarket notification.
Common misunderstandings
“Class I means unregulated”
Class I devices are subject to general controls. The regulation exempts them from premarket notification and, apart from records and complaint files, from the quality management system regulation. That is a lighter pathway, not an absence of rules.
“FDA has a product code for knee immobilizers”
FDA lists “cage, knee” (ITM) under limb orthosis. There is no product code with the name “knee immobilizer,” so a supplier’s marketing name and FDA’s listed name can differ.
“A brace and an immobilizer are different regulated products”
The regulation defines a limb orthosis as a brace and names a knee cage as an example. The “limits movement” wording comes from patient-education material, not from a separate regulatory category.
Frequently asked questions
What is a knee immobilizer?
A type of brace used to provide support and limit movement of the knee (ECU Health patient education, last reviewed 02/01/2025).
Is a knee immobilizer an FDA Class I device?
FDA lists the knee cage as a Class 1 limb orthosis under 21 CFR 890.3475. FDA has no product code named “knee immobilizer,” so classification is stated for the limb orthosis and knee cage entries.
Does a knee immobilizer need a 510(k)?
Limb orthoses under 21 CFR 890.3475 are exempt from premarket notification, subject to the limitations in 21 CFR 890.9.
Who decides how a knee immobilizer is used?
That is a clinical decision for the treating provider. This page covers product and regulatory information only.
Sources
- 21 CFR 890.3475, Limb orthosis, eCFR, checked 2026-10-30.
- FDA Product Classification database, product code ITM (“cage, knee”), accessdata.fda.gov, checked 2026-10-30.
- ECU Health HealthHub, “Knee Immobilizer” (StayWell patient education; last reviewed 02/01/2025), healthlibrary.ecuhealth.org, checked 2026-10-30.
