The Brace Is Identical. What Happened in the Fitting Room Decides the Code.

An orthotic fitter delivers a prefabricated walking boot to a 74-year-old with a stable fifth metatarsal fracture. The boot comes out of the box, the straps get pulled to fit, and the patient walks out. The claim goes out as L4360, the custom-fitted code, because that is what the practice has always billed for that product and the fee schedule is better.

Nothing about that delivery was clinically wrong. The boot suited the fracture and the patient did well. The claim is still denied as incorrect coding, because pulling straps to fit is the textbook example of minimal self-adjustment, and minimal self-adjustment is L4361.

L4360 and L4361 can be the exact same physical product, and so can L4386 and L4387, or L4396 and L4397. The policy says so outright.

Two codes, one product, and the fitting room decides

Policy Article A52457 has a sentence worth taping above the fitting bench:

"For prefabricated orthoses — there is no physical difference between orthoses coded as custom fitted versus those coded as OTS."

Off-the-shelf and custom-fit items are both prefabricated braces for Medicare coding. The line between them is drawn at 42 CFR §414.402, and it turns on one question: did the final fitting at the time of delivery require more than minimal self-adjustment?

Minimal self-adjustment is an adjustment the beneficiary, the caregiver or the supplier can perform without the services of a certified orthotist or someone with equivalent specialized training. The policy gives examples: adjusting straps and closures, bending or trimming for final fit or comfort. If that is what happened, the item is off-the-shelf.

More than minimal self-adjustment means changes made to achieve an individualized fit at delivery that require the expertise of a certified orthotist, or an individual with equivalent specialized training, in compliance with applicable federal and state licensure requirements, which puts the item on the custom-fitted side.

Enforcement runs in both directions: if a custom fit code is billed when only minimal self-adjustment was provided, or an OTS code is billed when more than minimal adjustment was made, the claim is denied as incorrect coding. The paired codes work like this:

• L4360 / L4361 — pneumatic or vacuum walking boot
• L4386 / L4387 — non-pneumatic walking boot
• L4396 / L4397 — static or dynamic positioning AFO
• L1932 / L1933 and L1951 / L1952 — prefabricated AFOs

Two more rules sit underneath. Assembling an item, installing add-on components or using some basic materials in preparation does not turn an off-the-shelf item into a custom-fitted one. And to bill a custom-fitted code, the documentation has to be "sufficiently detailed to include… a detailed description of why the modifications are necessary and what modifications were performed at the time of fitting the orthosis to the beneficiary," available on request. A fitter's initials on a delivery ticket is not that description.

There is also a trap for the codes with no off-the-shelf twin. Several prefabricated codes are written as "prefabricated, includes fitting and adjustment" and have no OTS partner, including L1910, L1930, L1971 and L2035. If one of those products goes out with only strap adjustment, the catalog code is wrong. Bill L2999, the miscellaneous orthosis code, with a description and a breakdown of charges in the narrative.

The word the chart usually skips: ambulatory

Before any coding question matters, L33686 sets the entry condition. AFOs described by L1900 through L1990, the L2100 series, L4350, L4360, L4361, L4386, L4387 and L4631 are covered for ambulatory beneficiaries with weakness or deformity of the foot and ankle who require stabilization for medical reasons and have the potential to benefit functionally.

KAFOs, coded L2000 through L2038, the L2126 series and L4370, are covered for ambulatory beneficiaries for whom an AFO is covered and for whom additional knee stability is required. The KAFO criterion is borrowed. A chart that documents knee instability beautifully and says nothing about the foot and ankle has not established the predicate, so the denial comes back on an AFO criterion the chart never addressed.

If the basic criteria are not met, the orthosis is denied as not reasonable and necessary. That sentence covers a large share of the 26.5% "no documentation" bucket, because the qualifying facts live in a physical therapy note or a surgeon's op report that the supplier never requested.

Five criteria stand between custom fabrication and a takeback

A custom fabricated orthosis is individually made for one patient from clinically derived castings, tracings, measurements or images, with substantial work such as vacuum forming, cutting, bending, molding, sewing, drilling and finishing before it ever touches the patient. It also costs several times what a prefabricated brace costs, which is why reviewers look at it closely.

L33686 covers custom fabricated AFOs and KAFOs for ambulatory beneficiaries who meet the basic criteria and one of the following:

• The beneficiary could not be fit with a prefabricated AFO.
• The condition necessitating the orthosis is expected to be permanent or of longstanding duration, meaning more than six months.
• There is a need to control the knee, ankle or foot in more than one plane.
• The beneficiary has a documented neurological, circulatory or orthopedic status that requires custom fabricating to prevent tissue injury.
• The beneficiary has a healing fracture which lacks normal anatomical integrity or anthropometric proportions.

That list comes with two caveats. The fourth criterion used to read "requires custom fabricating over a modelto prevent tissue injury," and the words "over a model" were removed effective 23 January 2024. Plenty of internal checklists and vendor templates still carry the old wording, which sends staff hunting for a fact the policy no longer asks for.

The second caveat matters more. The policy says the justification for custom fabrication rather than prefabrication must be in the treating practitioner's records, and that it "will be corroborated by the functional evaluation in the orthotist's records." Section 1834(h)(5) of the Social Security Act makes the orthotist's documentation part of the medical record, which is a genuine help, but it makes that documentation supporting evidence. When the only narrative explaining why an off-the-shelf brace would not work is the one the orthotist wrote, the file is corroboration without anything to corroborate. That gap is the most common insufficient-documentation finding in this policy family.

The non-ambulatory path is narrow, and it is measured with a goniometer

There is one route for a beneficiary who does not walk, and it is tightly written. L4396 and L4397, the static or dynamic positioning AFO, are covered if all of criteria 1 through 4 are met, or if criterion 5 is met on its own:

• A plantar flexion contracture of the ankle with dorsiflexion on passive range of motion testing of at least 10 degrees, which is to say a nonfixed contracture; and
• A reasonable expectation of the ability to correct the contracture; and
• The contracture is interfering or expected to interfere significantly with functional abilities; and
• The device is used as a component of a therapy program that includes active stretching of the involved muscles or tendons.
• Or, standing alone: the beneficiary has plantar fasciitis.

When the indication is a contracture, the pre-treatment passive range of motion has to be measured with a goniometer and written in the chart in degrees before treatment starts, and the record has to show an appropriate stretching program carried out by nursing facility staff or by a caregiver at home. "Tight heel cords" is not a measurement.

The denials clustered around this code are worth knowing by heart, because they arrive in volume from long-term care referrals:

• A fixed contracture denies the splint and the replacement interface as not reasonable and necessary.
• Foot drop without an ankle flexion contracture denies L4396, L4397 and L4392.
• A component of a static or dynamic AFO addressing knee or hip positioning is denied, because effectiveness is not established.
• L4398, the foot drop splint or recumbent positioning device, and its interface L4394 are not reimbursed at all for a nonambulatory beneficiary with foot drop.
• The replacement interface L4392 is limited to one per six months. Additional interfaces are denied.

One more rule decides the modifier as well as the payment. When L4396, L4397 or L4392 are used solely for prevention or treatment of a heel pressure ulcer, they are denied as noncovered, no Medicare benefit, because in that use they are not supporting a weak or deformed body member. That is a statutory exclusion, not a medical necessity denial. Walking boots used solely for offloading or pressure reduction are coded A9283 for the same reason, and A9283 is also a statutory no-benefit item. Suppliers routinely attach GA or GZ to these lines when the correct answer sits in a different family altogether.

Boots that cannot carry add-ons, and the one CROW code

Prefabricated walking boots coded L4360, L4361, L4386 and L4387 describe complete products. Claims for add-on codes billed with them are denied as unbundling. The same principle applies more strictly to L4631, the Charcot restraint orthotic walker: code L4631 includes all additions including straps and closures, and no additional codes may be billed with it.

L4631 has seven product characteristics, all of which must be true, and the fifth is the one that gets missed. The orthosis has to maintain the foot at a fixed 0 degree position, allow varus or valgus deformity correction, contain a rocker bottom sole with a custom arch support, incorporate a rigid anterior tibial shell, be used by a beneficiary who is ambulatory, have a soft interface and be totally encapsulated. A nonambulatory Charcot patient has no L4631 route. And because L4631 is custom fabricated, it has to clear one of the five custom fabrication criteria independently.

Two smaller rules travel with these codes. The supplier must include the diagnosis code on the claim line for L4396, L4397, L4392 and L4631, and the covered diagnosis lists are short. For L4631 there are seven ICD-10 codes; for the positioning splints there are five. Second, additions to AFOs and KAFOs, the long L2180 through L2830 series, are denied when either the base orthosis is not reasonable and necessary or the addition itself is not. An addition cannot outperform the brace it is attached to.