CPT code 77073 – Bone length studies

Key takeaways

CPT code 77073 covers bone length studies by orthoroentgenogram or CT scanogram, reported once per study rather than once per limb.

Modifier -50 does not apply, because Medicare’s bilateral indicator for 77073 is 0.

Medicare Advantage and many commercial plans can require prior authorization through radiology benefit managers such as eviCore.

Pabau’s claims management software links imaging orders to coded encounters and tracks each claim from submission to payment.

CPT code 77073: Official descriptor and quick-reference data

CPT code 77073 is defined by the American Medical Association’s CPT code set as: Bone length studies (orthoroentgenogram, scanogram). It sits in the Radiology section, Bone/Joint Studies subsection (77071-77086). The code measures limb length discrepancy and is reported once per study.

Procedure overview: What bone length studies involve

Bone length studies measure limb length discrepancy by capturing a calibrated radiographic series across the full extremity. CPT code 77073 covers two techniques, the orthoroentgenogram and the CT scanogram. The choice between them depends on patient size, radiation dose, and the equipment available.

Orthoroentgenogram

The orthoroentgenogram uses three separate plain-film exposures on a single long cassette: Hip, knee, and ankle. A calibrated ruler is placed alongside the limb. The technologist measures segment lengths from the exposures. Orthopedic surgeons and musculoskeletal imaging departments order this study for scoliosis follow-up, leg length inequality workup, and post-surgical alignment assessment.

CT scanogram

The CT scanogram uses scout images from a CT acquisition rather than plain film. Both techniques produce the same clinical output: Segment-by-segment length measurements with a calculated discrepancy. Documentation must specify which technique was used, as payers audit this detail.

Unilateral or bilateral: How CPT code 77073 is reported

CPT code 77073 is reported once per study, regardless of how many limbs are measured. The study captures a comparative measurement across both legs to quantify the discrepancy. Medicare’s bilateral indicator for 77073 is 0 (no bilateral adjustment), so do not append -50 or report two units.

• Correct: One unit of 77073 per encounter, even when both legs are imaged
• Incorrect: Two units of 77073 with modifier -50 to represent bilateral imaging
• Incorrect: Modifier -LT or -RT appended to 77073 (these laterality modifiers do not apply to a study that is bilateral by design)

Bilateral reporting errors commonly cause denials and overpayment findings on 77073 claims. Train billing staff that the code already describes a study capturing both limbs.

CPT 77073 vs 77072, 77074, and 77075: Choosing the right code

The 770xx bone study family covers four distinct clinical scenarios, and picking the wrong one commonly causes denials. An order that asks for skeletal maturity rather than limb length belongs under 77072, not 77073.

Billing 77073 with a same-session knee series: This is a contested coding question. The AMA CPT Knowledge Base has addressed whether 77073 can be co-billed with a same-session 73562. That answer is subscription-gated. Before submitting both codes on one claim, consult the Knowledge Base directly or contact your MAC for policy guidance. Do not assume bundling is permissible or prohibited until you confirm the answer for your payer.

Modifiers for CPT code 77073

CPT code 77073 has a PC/TC split, so the professional and technical components can be billed separately. That happens in split-billing arrangements, such as a radiologist employed by a group reading on hospital-owned equipment.

ICD-10 codes commonly paired with CPT code 77073

Medical necessity for CPT code 77073 must be established through a linked ICD-10-CM diagnosis code. Payers audit the diagnosis-to-procedure pairing, and a missing or unsupported diagnosis code commonly causes denials.

Always use the most specific ICD-10 code available. Submitting M21.70 (unequal limb lengths, unspecified site) can trigger a medical necessity review when the referral clearly documents the femur or tibia.

Medicare coverage and fee schedule for CPT code 77073

Medicare covers CPT code 77073 when medical necessity is established. Coverage is governed by the Medicare Physician Fee Schedule (MPFS). Payment varies by place of service and by whether the global, professional, or technical component is billed. Use the CMS Physician Fee Schedule lookup for current national rates, as figures change annually. The 2026 non-facility rate (POS 11 – office) is higher than the facility rate (POS 19/22 – outpatient hospital). That’s because the practice expense component is paid separately in a non-facility setting.

No national coverage determination (NCD) exclusively governs bone length studies. MAC-specific local coverage determinations (LCDs) may apply, so check your MAC’s LCD database before submitting. Some LCDs restrict 77073 to specific diagnoses or clinical thresholds.

Pabau, the practice management platform we build, submits claims electronically through Claim.MD, which connects to thousands of US payers. Eligibility checks run before the claim is submitted.

Prior authorization requirements for CPT 77073

Traditional Medicare (Parts A and B) does not require prior authorization for CPT code 77073 at the national level. Medicare Advantage plans are a different matter. eviCore by Evernorth manages radiology benefits for many Medicare Advantage plans, including HCSC Medicare Advantage. CPT code 77073 appears on the HCSC Medicare Advantage radiology prior authorization code list effective January 1, 2026.

Confirming insurance eligibility verification at scheduling is the first step. The authorization process then typically requires:

1. The ordering physician’s clinical indication, including current measured leg length discrepancy (in centimeters)
2. Relevant diagnosis codes (ICD-10-CM) supporting medical necessity
3. History of prior studies or treatments attempted
4. Expected clinical decision based on study results (surgical correction, shoe lift, observation)

Commercial payers not using eviCore may have their own radiology management programs. Always check the specific plan before scheduling the study.

Documentation requirements for a 77073 claim

Insufficient documentation commonly causes 77073 claims to fail post-submission audits. The referral and the radiology report together must establish medical necessity and technique. Submitting a clean claim starts with verifying these elements before the claim leaves the practice.

• Ordering physician referral: Must document the clinical indication, the relevant diagnosis code, and any relevant surgical or treatment history. An example indication is “right leg shorter than left by approximately 2 cm on clinical exam, requesting quantification.”
• Radiology report: Must state the technique (orthoroentgenogram or CT scanogram) and the number of exposures. It also lists segment-by-segment measurements (femur, tibia, foot), the calculated total discrepancy, and comparison with any prior studies.
• Technique documentation: Payers distinguish between orthoroentgenogram and scanogram, so the report must name the method rather than just state “bone length study.”
• Physician interpretation: The professional component requires a signed, dated interpretation report. An unsigned or undated report is an immediate denial trigger.
• Prior study comparison: Not mandatory, but payers may request it during medical necessity review for established patients.

Common claim denial reasons for CPT code 77073 and how to fix them

CPT code 77073 denials cluster around five root causes. Structured denial management workflows should track each reason code separately so patterns surface quickly. Review medical billing denial codes alongside the specific reason your MAC or payer uses to categorize each rejection.

Each of those denials has a matching check you can run before submission. The sequence below follows the order a 77073 claim passes them, from authorization to the signed report.

Place of service and facility vs non-facility rates

Where 77073 is performed directly affects Medicare payment. The MPFS pays a higher allowed amount in non-facility settings (POS 11 – physician office). There, the practice expense component of the RVU is not shared with a facility. In hospital outpatient departments (POS 19 off-campus, POS 22 on-campus), the facility receives a separate payment under the OPPS. The physician fee schedule then pays only the reduced professional component, even without modifier -26.

Use the FastRVU 2026 RVU lookup to retrieve current Work, Practice Expense, and Malpractice RVU values for 77073 by facility status. Current rates are not reproduced here, because the MPFS is updated annually and a stated figure would soon go stale.

How Pabau supports 77073 billing workflows

Billing 77073 slows down when the imaging order, the diagnosis, and the claim sit in separate systems. Coders re-key ICD-10 codes, call payers to confirm coverage, and track claim progress in spreadsheets.

Pabau’s claims management software keeps the clinical record and the claim in one place. The diagnosis on the encounter carries through to the claim, and every claim shows its current status.

• Order-to-code linking: The imaging order and the coded encounter share one patient record, so the ICD-10 diagnosis reaches the claim without re-entry.
• Eligibility checks: Coverage is checked before the study date, so an inactive policy surfaces before the patient is imaged.
• Claim status tracking: Each claim shows as Pending, Submitted, Processing, Paid, or Error on the claims dashboard.
• Clearinghouse and remittance: Claims route through Claim.MD, Pabau’s US clearinghouse partner. Electronic remittance advice (ERA) then comes back against each claim, supporting a broader revenue cycle management approach.

Manage 77073 billing from order to payment

Pabau links imaging orders to coded encounters, checks eligibility before the study, and tracks every claim from submission to payment. See each claim’s status and remittance on one dashboard.

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Conclusion

Most of the rules for CPT code 77073 follow from one fact: The study already covers both legs. Bill one unit, choose the modifier by place of service, and link the most specific diagnosis the referral supports.

Prior authorization is the check to move earliest. Confirm it with Medicare Advantage and commercial plans when the order arrives, rather than after a denial comes back.

Want the order, the diagnosis, and the claim status in one record for your radiology or orthopedic billing? Book a demo to see how Pabau handles it.

Continue your research

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