Zero G has a functional 'joint' at the ankle, if you will. The L1971 includes the product, fitting, and adjustment. The other products which would be referred to by most as 'ankle braces' fit the functional description for L1971, though both are used to different purposes and have different covered diagnoses.

2019/2020 HCPCS Code L1971
"Ankle foot orthosis, plastic or other material with ankle joint, prefabricated, includes fitting and adjustment"

The other codes in parenthesis range from an off the shelf device to custom fabricated products of varying materials.

Others may have more :specific information.

I meant to clarify the range of products coded as L1971 may be used for very different diagnoses (I.e. acute injury versus chronic condition), etc.

Thank you, very helpful

Samantha already provided a great answer. Just jotting down an excerpt of the CMS LCA (A52457) that supports what she mentioned.

"For prefabricated orthoses (L1902, L1906, L1910, L1930, L1932, L1951, L1971, L2035, L2112, L2114, L2116, L2132, L2134, L2136, L4350, L4360, L4361, L4370, L4386, L4387, L4396, L4397, L4398), there is no physical difference between orthoses coded as custom fitted versus those coded as off-the-shelf. The differentiating factor for proper coding (see definitions in Coding Guidelines below) is the need for “minimal self-adjustment” at the time of fitting by the beneficiary, caretaker for the beneficiary, or supplier. This minimal self-adjustment does not require the services of a certified orthotist or an individual who has specialized training. Items requiring minimal self-adjustment are coded as off-the-shelf orthoses. For example, adjustment of straps and closures, bending or trimming for final fit or comfort (not all-inclusive) fall into this category."
...
"Items requiring more than minimal self-adjustment by a qualified practitioner (as defined in the Coding Guidelines below) are coded as custom fitted (L1910, L1930, L1932, L1951, L1971, L2035, L2112, L2114, L2116, L2132, L2134, L2136, L4360, L4386, L4396). Documentation must be sufficiently detailed to include, but is not limited to, a detailed description of the modifications necessary at the time of fitting the orthosis to the beneficiary. This information must be available upon request.

Local Coverage Article: Ankle-Foot/Knee-Ankle-Foot Orthoses - Policy Article (A52457)

thank you; appreciate it

Do you have the number of DFUs that occur annually in the USA and globally? I have % but not an actual number.

Hi Marsha
These 2 papers show data on the prevalence of DFU among Medicare beneficiaries in 2008 and 2014.
 - Margolis et al, 2011: DFU prevalence was 8% of the 2008 Medicare beneficiaries, in 2008 there were 31.89 million beneficiaries (calculated based on their numbers) -> DFU prevalence in 2008: 2.55 million (8%) Medicare beneficiaries
- Nussbaum et al, 2018: DFU prevalence was 4.1% of the 2014 Medicare beneficiaries, in 2014 there were 56.55 million beneficiaries (calculated based on their numbers) -> DFU prevalence in 2014: 2.31 million (4.1%) Medicare beneficiariesNote that the number of beneficiaries may differ depending on how each author defined DFU (which ICD codes they used, etc). 

>Margolis: https://effectivehealthcare.ahrq.gov/sites/default/files/pdf/diabetes-foot-ulcer-amputation-prevalence_research.pdf
>Nussbaum: https://www.valueinhealthjournal.com/article/S1098-3015(17)30329-7/pdf