Bursa is a small, closed, fluid-filled synovial sac interposed between anatomical structures — most commonly between tendons, muscles, skin, and underlying bony prominences — that functions as a mechanical buffer to reduce friction and absorb compressive forces during movement. Unlike a joint capsule, which encloses an articular space between two bones, a bursa is an independent, extrasynovial structure that does not communicate with the joint cavity unless pathologically ruptured or congenitally connected. The sac is lined by a specialized synovial membrane that secretes and reabsorbs a small volume of lubricating fluid (synovial fluid), maintaining near-frictionless gliding between adjacent structures. Bursae exist as either anatomic bursae (present at birth, constant across individuals — e.g., subacromial, olecranon, prepatellar) or adventitious bursae (acquired in response to chronic external pressure or friction at atypical sites — e.g., over a bunion or bony prominence in an amputee’s residual limb). When the synovial lining becomes inflamed — from trauma, overuse, infection, gout, or systemic inflammatory disease — the condition is termed bursitis, characterized by excessive fluid accumulation, pain, swelling, and restricted range of motion (ICD-10-CM M70-M71 range). Bursa is commonly confused with ganglion cyst, which arises from joint or tendon sheath connective tissue and lacks a true synovial lining, and with synovial cyst, which communicates directly with an adjacent joint space.
Noun-forming suffix — denotes a singular feminine noun in the first declension; plural becomes bursae
The word entered English in the 1690s as bursa (noun), borrowed directly from Medieval Latin bursa (“pouch, purse”), from Greek byrsa (“hide, wine-skin, pouch”) — literally “a little purse or pouch.” The anatomical use was adopted by early anatomists who noted the structural resemblance of the fluid-filled sac to a drawstring purse. The root burs- (“pouch”) connects bursa to the entire -burs- ROOT FAMILY: bursitis (burs- + -itis → inflammation of the bursa), bursar (burs- → treasurer, keeper of the purse), and bursa of Fabricius (lymphoid organ in birds, named by Hieronymus Fabricius, 1621). The suffix -a marks this as a Latin first-declension feminine noun; its plural bursae is the form used in anatomical nomenclature and should be recognized when encountered in operative and pathology reports.
🔀 ALIASES / ALTERNATE TERMS
Bursal(adjective form — appears clinically as “bursal fluid,” “bursal inflammation,” “bursal injection,” “bursal thickening” on imaging reports)
Synovial bursa(anatomically precise synonym emphasizing the synovial lining; distinguishes true bursae from adventitious or non-synovial sacs)
Bursal sac(descriptive lay/clinical term used in operative notes and patient education; coded under the same M70-M71 range depending on site and etiology)
Bursae(Latin plural form; used in anatomical nomenclature, pathology reports, and imaging — e.g., “bilateral subacromial bursae”)
Adventitious bursa(acquired bursa that forms at sites of chronic pressure or friction not typically containing a bursa; common in amputee residual limbs, bunion sites, and pressure injury-prone bony prominences; coded as other bursitis NEC — M71.3x)
Retrocalcaneal bursa(anatomic bursa located between the Achilles tendon and the calcaneus; inflammation coded as M77.3x — retrocalcaneal bursitis)
Subacromial bursa(largest and most clinically significant bursa in the shoulder, located between the rotator cuff and the acromion; inflammation coded as M75.5x — subacromial bursitis)
Olecranon bursa(anatomic bursa overlying the olecranon process of the ulna at the elbow; inflammation coded as M70.2x — olecranon bursitis)
Prepatellar bursa(anatomic bursa anterior to the patella; classic occupational bursitis — “housemaid’s knee”; coded as M70.4x)
Infrapatellar bursa(anatomic bursa inferior to the patella, superficial or deep; inflammation coded as M70.5x — infrapatellar bursitis)
Trochanteric bursa(anatomic bursa overlying the greater trochanter of the femur; inflammation coded as M70.6x — trochanteric bursitis; high-frequency code in PM&R)
Ischial bursa(anatomic bursa over the ischial tuberosity; inflammation coded as M70.7x — other bursitis of hip; relevant in wheelchair-dependent patients)
🔗 RELATED TERMS
Bursitis — the pathological state of bursa; inflammation of the synovial lining resulting in excessive fluid production, pain, warmth, and swelling; principal ICD-10-CM codes in the M70-M71 range with site-specific and laterality subcategories
Synovium — shares the synovi- root with synovial cyst and synovial fluid; the specialized secretory lining membrane common to both bursae and joint capsules; its inflammation (synovitis) may coexist with bursitis
Synovial cyst — closely related fluid-filled structure, but communicates directly with an adjacent joint space, distinguishing it from a true bursa; common sites include the popliteal fossa (Baker’s cyst, M71.2x) and wrist
Ganglion cyst — a mucinous cyst arising from joint or tendon sheath connective tissue, lacking a true synovial lining; frequently confused with bursal pathology on clinical exam; coded M67.4x
Bursectomy — surgical excision of an inflamed or chronically thickened bursa; performed when conservative management fails; relevant CPT codes include 27060 (ischial) and 27062 (trochanteric)
Tendon — the primary anatomical neighbor of most bursae; bursae exist specifically to reduce friction between tendons and underlying bony surfaces; concurrent tendinitis and bursitis frequently coexist and may both require coding
Synovial fluid — the lubricating secretion produced by the synovial lining of the bursa; aspiration and laboratory analysis of bursal fluid is used to differentiate septic bursitis, gout, pseudogout, and inflammatory arthritis
Septic bursitis — infectious bursitis most commonly caused by Staphylococcus aureus; coded M71.0x (right) or M71.02 (elbow); requires specific documentation of organism for most specific coding and CC/MCC capture
Gout — systemic purine metabolism disorder causing urate crystal deposition within bursae and joint spaces; acute gouty bursitis is a high-frequency coding scenario in inpatient PM&R and orthopedics (M10.0x-M10.9x)
Calcific bursitis — bursitis complicated by calcium hydroxyapatite crystal deposition within the bursal sac; associated with rotator cuff calcific tendinopathy; coded M71.4x (calcium deposit in bursa)
Aspiration/injection, bursa — key diagnostic and therapeutic procedure; bursal aspiration yields fluid for culture and crystal analysis; corticosteroid injection is first-line treatment for non-infectious bursitis; CPT 20610-20611
CODING CORNER
🏥 ICD-10-CM CODES
Soft Tissue Disorders Related to Use, Overuse, and Pressure — Bursitis (M70.x)
Arthroscopy, shoulder, surgical; with decompression of subacromial space with partial acromioplasty, with coracoacromial ligament (e.g., arch) release, when performed (includes bursectomy)
Ultrasonic guidance for needle placement, imaging supervision and interpretation (use with 20610/20611 when billed separately — check bundling)
⚠️ Coding Note: Site specificity and laterality are required for all M70-M71 codes — unspecified laterality codes (e.g., M70.60) should be queried if documentation supports a specific side, as payers including UnitedHealthcare and Aetna increasingly flag unspecified laterality on professional claims. Sequence the underlying condition first when bursitis is a manifestation of gout (M10.0x), rheumatoid arthritis (M05-M06), or infection (M71.0x-M71.1x), with the bursal code as an additional diagnosis. A common undercoding alert in PM&R inpatient stays: trochanteric bursitis (M70.6x) is frequently documented only as “hip pain” or “greater trochanter tenderness” — both phrases should trigger a physician query to clarify whether bursitis has been diagnosed, as M70.61/M70.62 are significantly more specific and support stronger DRG coding than R10 or M25.55x pain codes. For septic bursitis, always append the causative organism code (B95-B97 range) per ICD-10-CM instructional note at M71.0x; MRSA bursitis (M71.1x + B95.62) captures an MCC in most MS-DRG groupings. CPT 20611 (ultrasound-guided major bursa injection) is increasingly required by BCBS of Wisconsin and UMR for shoulder and hip bursal injections — confirm that permanent imaging documentation exists before billing, as this is a common audit trigger.