Glossary · Anatomy

Bursa

A bursa is a small, fluid-filled sac lined with synovial membrane that reduces friction between adjacent bones, tendons, muscles, or skin. There are roughly 160 bursae in the human body; in orthopedics, the subacromial, trochanteric, olecranon, prepatellar, and retrocalcaneal bursae are the most clinically and procedurally significant.

Verified May 8, 2026 · 7 sources ↓

Drawn from CMSICD10DataAAPCMedicotechllcBenchmarksystems

Definition

Source · Editorial summary grounded in 7 cited references ↓

Bursae are closed, saclike structures whose inner lining secretes a thin layer of synovial fluid. That fluid acts as a lubricant, allowing neighboring tissues—most commonly a tendon or muscle gliding over a bony prominence—to move without generating destructive friction. In a healthy joint, the bursa is nearly invisible on imaging and produces no symptoms. Structurally, bursae are classified as either native (present from birth) or adventitious (formed in response to chronic mechanical stress, such as the bursa that develops over a bunion).

When a bursa becomes inflamed—a condition called bursitis—its lining proliferates and produces excess fluid, causing the sac to swell, compress surrounding structures, and generate pain with movement or direct pressure. Inflammation can stem from acute trauma, repetitive mechanical overload, crystalline deposits (gout, pseudogout), septic infection, or systemic inflammatory disease such as rheumatoid arthritis. The distinction between septic and aseptic bursitis is clinically urgent because each demands a fundamentally different treatment pathway.

From a procedural standpoint, the bursa is the direct anatomic target of aspiration and injection procedures coded under CPT 20610 (major bursa, no ultrasound guidance) and CPT 20611 (with ultrasound guidance and permanent image documentation). Correct identification of the specific bursa in the operative or procedure note drives accurate ICD-10-CM diagnosis coding and supports medical necessity for the intervention billed.

Why it matters

Failing to specify the exact bursa treated—and whether ultrasound guidance was used—creates two concrete billing risks. First, CPT 20610 and 20611 reimburse at meaningfully different rates because 20611 requires separate documentation of the ultrasound image; billing 20610 when guidance was used (or vice versa) invites both underpayment and audit exposure. Second, vague documentation such as 'shoulder injection' without identifying the subacromial bursa versus the glenohumeral joint can trigger claim denial, because payers map the diagnosis code (e.g., M75.51 for bursitis of the right shoulder) to a specific anatomic site—and a mismatch between the diagnosis code, the procedure note, and the CPT code is a top reason orthopedic injection claims are rejected or recouped on post-payment review.

Common mistakes

Where people most often go wrong with this concept.

Source · Editorial brief grounded in cited references ↓

Documenting 'shoulder injection' without specifying the target bursa (e.g., subacromial vs. subdeltoid vs. glenohumeral joint), which breaks the link between the ICD-10-CM site-specific bursitis code and the CPT code billed.
Billing CPT 20610 when real-time ultrasound guidance with permanent image storage was used; the correct code is 20611, and the image must be retained in the medical record.
Assigning M71.9 (Bursopathy, unspecified) when the site is documented in the note—site-specific codes such as M71.51 (subacromial bursitis, right shoulder) are required when the location is known and are essential for medical-necessity review.
Billing a separate injection code for aspiration and injection of the same bursa during the same encounter; both activities are captured by a single unit of CPT 20610 or 20611.
Missing laterality in the diagnosis code (e.g., using M75.5 instead of M75.51 or M75.52) when the operative note clearly documents right or left side, which can trigger payer edits and delay adjudication.

Related codes

Codes commonly involved when this concept appears in practice.

CPT

ICD-10

M71.9 M75.51 M75.52 M70.60

Modifiers

RT Right side LT Left side 50 Bilateral procedure 59 Distinct procedural service XS Separate structure

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 7 cited references ↓

01What is the difference between a bursa and a joint capsule?

A joint capsule is a continuous sleeve of connective tissue that encloses an entire synovial joint and defines its cavity. A bursa is a distinct, separate sac that exists outside—or only loosely communicates with—the joint; its sole role is friction reduction between specific moving structures near, but not necessarily inside, the joint space. Aspiration of a bursa and aspiration of a joint cavity are different procedures that may require different CPT codes and diagnosis codes.

02Does bursitis always require an injection, and does that affect coding?

No. Many bursitis cases resolve with rest, ice, NSAIDs, and physical therapy—no injection is performed and no procedural CPT code is billed. An injection code (20610 or 20611) is only appropriate when the provider actually performs an aspiration or injection during that encounter. Billing an injection code on the basis of a bursitis diagnosis alone, without a documented procedure, constitutes a coding error and creates audit risk.

03When is CPT 20611 used instead of 20610 for a bursa procedure?

CPT 20611 applies when the provider uses real-time ultrasound to guide needle placement into a major joint or bursa AND permanently stores an image documenting needle positioning. Both elements—real-time guidance and image retention in the record—must be present. If either is absent, CPT 20610 is the correct code. The two codes must not be billed together for the same bursa at the same encounter.

04What ICD-10-CM code should be used for unspecified bursitis when the site is not documented?

M71.9 (Bursopathy, unspecified) is the fallback code when the site genuinely cannot be determined. However, coders should query the provider before defaulting to an unspecified code, because site-specific codes—such as M71.51 for right subacromial bursitis—are almost always available from the procedure note and are required by most payers for medical-necessity review.

05Can adventitious bursae (those caused by pressure or overuse) be coded separately from inflammatory bursitis?

Yes. ICD-10-CM category M70 covers bursitis and related soft-tissue disorders arising from use, overuse, or pressure—for example, M70.60 for trochanteric bursitis. These are distinct from the M71 'other bursopathies' category. Selecting the correct parent category depends on whether the documented etiology is mechanical/occupational (M70) or inflammatory or unspecified (M71), so provider documentation of cause directly affects code selection.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

Mira AI Scribe

When a bursa injection or aspiration is documented, Mira flags the following for the coder before claim submission: 1. SITE SPECIFICITY — The note must name the exact bursa (e.g., subacromial, trochanteric, olecranon, prepatellar, retrocalcaneal). If the provider wrote only 'shoulder injection,' Mira queues a clarification request before a diagnosis code is assigned. 2. LATERALITY — Mira auto-populates the laterality modifier (RT/LT) and selects the lateralized ICD-10-CM code (e.g., M71.51 right, M71.52 left) based on side documented in the procedure note. If laterality is absent, the claim is held. 3. ULTRASOUND GUIDANCE — Mira reads imaging references in the note. If real-time ultrasound with image documentation is confirmed, it substitutes CPT 20611 for 20610 and flags the need to attach the saved image to the record. If guidance is mentioned but no image retention is documented, Mira alerts the provider before submission. 4. SAME-ENCOUNTER BUNDLING — If aspiration and injection of the same bursa at the same encounter are billed as two line items, Mira collapses them to one unit of the appropriate code and logs the edit. 5. SEPTIC VS. ASEPTIC — If the note contains terms such as 'infected bursa,' 'septic bursitis,' or documents a culture being sent, Mira surfaces an alert to consider an infectious etiology code (e.g., M71.0x for abscess of bursa) and flags the case for potential antibiotic documentation review, since payer medical-necessity criteria differ between septic and non-septic bursitis.

See Mira's approach

Related terms

Bursitis Clinical

Bursitis is inflammation of a bursa—a fluid-filled sac that cushions bones, tendons, and muscles near joints—most commonly caused by repetitive motion, acute trauma, infection, or underlying inflammatory disease. Accurate site, laterality, and etiology documentation is essential for selecting the correct ICD-10-CM code and supporting medical necessity for injection or surgical procedures.