tendinitis

DEFINITION of tendinitis

Tendinitis (also spelled tendonitis) is the acute or subacute inflammatory condition of a tendon characterized by localized pain, tenderness, swelling, and functional limitation — most commonly resulting from repetitive mechanical overload, sudden unaccustomed exertion, or direct microtrauma to tendon fibers, which triggers a classical inflammatory cascade involving prostaglandins, cytokines, and vascular hyperemia at the affected site. It must be distinguished from tendinosis, which is a non-inflammatory, chronic degenerative condition characterized by collagen disorganization and mucoid degeneration without significant inflammatory infiltrate — a distinction that is not yet consistently reflected in ICD-10-CM coding, where “tendinitis” terminology is applied to codes that may in practice represent either condition. The underlying pathophysiological mechanism of true tendinitis involves repetitive strain exceeding the tendon’s intrinsic repair capacity, causing collagen microtears that, if acutely symptomatic, produce the classic inflammatory response; if left unresolved, this process progresses to tendinosis (chronic degeneration) or tendinopathy (the umbrella term for any tendon disorder regardless of mechanism). Clinically, tendinitis is classified by anatomic location — the most common sites include the rotator cuff (M75.31/M75.32), bicipital tendon (M75.21/M75.22), lateral epicondyle (M77.11/M77.12), Achilles tendon (M76.61/M76.62), patellar tendon (M76.51/M76.52), and the de Quervain (radial styloid) tenosynovitis variant (M65.4). A key diagnostic distinction: tendinitis differs from tenosynovitis (inflammation of the tendon and its surrounding synovial sheath — e.g., M65.x) and from enthesopathy (pathology specifically at the tendon’s bony attachment — e.g., M77.x), both of which have their own distinct ICD-10-CM code families.

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ETYMOLOGY of tendinitis

latin | greek

Component	Origin	Meaning
tendin- / tendo-	Latin tendo (TEN-doh), genitive tendinis (TEN-din-is), from Greek teinein (TAY-nein)	“tendon,” “sinew” — from the verb meaning “to stretch” or “to strain”; anatomical Latin term for the fibrous cord connecting muscle to bone
-itis	Greek -itis (-EYE-tis), feminine of adjective suffix -itēs	Noun-forming suffix indicating “inflammation of” or “disease of” — originally a Greek adjective suffix applied to diseases of specific organs or tissues

The word entered English in the 1840s as tendinitis (noun), formed from Neo-Latin tendo (tendon) + the Greek suffix -itis (inflammation) — literally “inflammation of the tendon.” The alternate spelling tendonitis (from the nominative form tendon rather than the genitive stem tendin-) entered popular use in the 20th century and is now accepted in clinical documentation, though tendinitis is the preferred anatomical spelling per most medical style guides and the ICD-10-CM index. The Latin root tendo ultimately descends from the Greek verb teinein (“to stretch”), connecting tendinitis to the broader ten- root family: tendon (the structure itself), tenosynovitis (tendon + synovial sheath inflammation), tenotomy (surgical tendon division), tensor (a muscle that stretches or tightens), and tonic (pertaining to sustained muscle tension). The suffix -itis is among the most productive suffixes in all of medical terminology, appearing in arthritis, bursitis, fasciitis, periostitis, and hundreds of other terms denoting tissue inflammation.

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🔀 ALIASES / ALTERNATE TERMS

• Tendonitis (alternate spelling using nominative “tendon” stem rather than genitive “tendin-” stem; both spellings accepted in clinical documentation and payer submissions)
• Tendinopathy (broad umbrella term for any tendon disorder regardless of mechanism — encompasses both tendinitis and tendinosis; preferred in current sports medicine literature)
• Inflammatory tendinopathy (clinical descriptor specifying the acute/subacute inflammatory subtype; used to distinguish from degenerative tendinopathy/tendinosis in documentation)
• Tendinosis (the chronic, non-inflammatory degenerative form of tendon pathology — collagen disorganization without active inflammation; frequently miscoded as tendinitis; distinct pathophysiology and treatment)
• Tenosynovitis (inflammation of the tendon AND its surrounding synovial sheath — coded under M65.x; distinct from pure tendinitis; examples: de Quervain M65.4, trigger finger M65.3x)
• Enthesopathy (tendon/ligament pathology specifically at the bony insertion/origin — coded under M77.x; tennis elbow M77.11/M77.12 and golfer’s elbow M77.01/M77.02 are technically enthesopathies)
• Calcific tendinitis (subtype with calcium hydroxyapatite crystal deposition within the tendon substance; coded under M65.2x by site or M75.31/M75.32 for shoulder)
• Rotator cuff tendinitis (shoulder-specific; common clinical entry point for M75.x codes; distinguish from rotator cuff tear M75.121/M75.122)
• Bicipital tendinitis (tendinitis of the biceps tendon at the shoulder — M75.21/M75.22; clinically presents with anterior shoulder pain with Speed’s test provocation)
• Patellar tendinitis (“jumper’s knee” — M76.51/M76.52; common in basketball/volleyball athletes; affects infrapatellar tendon at patellar apex)
• Achilles tendinitis (inflammation of the Achilles tendon — M76.61/M76.62; distinguish from Achilles tendon rupture S86.0x)
• De Quervain tenosynovitis (radial styloid tenosynovitis involving APL and EPB tendons — M65.4; confirmed clinically with Finkelstein test)

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🔗 RELATED TERMS

• tendinosis — the chronic, non-inflammatory degenerative tendon condition distinguished by collagen disorganization, mucoid degeneration, and absence of active inflammatory infiltrate on histopathology; often miscoded as tendinitis in clinical documentation — the key distinction is chronicity and mechanism, not symptom severity
• tenosynovitis — inflammation of the tendon and its surrounding synovial sheath (tendon + synovial envelope); coded separately under M65.x; clinical examples include de Quervain (M65.4) and trigger finger (M65.3x) — both tendinitis AND tenosynovitis involve pain along a tendon, but tenosynovitis also involves the sheath
• enthesopathy — pathology specifically at the tendon’s or ligament’s bony attachment (enthesis); coded under M77.x; lateral epicondylitis (tennis elbow — M77.11/M77.12) and plantar fasciitis (M72.2) are enthesopathies, though colloquially called “tendinitis”
• bursitis — inflammation of the synovial bursa, which frequently co-exists with tendinitis at the same anatomic site (e.g., subacromial bursitis + rotator cuff tendinitis); coded separately under M70.x or M75.5 for shoulder
• tendon rupture — complete or partial structural failure of the tendon; the end-stage complication of chronic tendinopathy; coded under M66.x (spontaneous) or S-codes (traumatic) — distinct from tendinitis, which involves inflammation without structural discontinuity
• tendinopathy — the modern umbrella term preferred in sports medicine and physical therapy literature to describe any painful tendon disorder without implying a specific pathological mechanism; encompasses tendinitis, tendinosis, and paratendinitis
• calcific tendinitis — subtype involving deposition of calcium hydroxyapatite crystals within the tendon substance, most commonly at the supraspinatus tendon; associated with acute severe pain episodes (M65.2x, M75.31/M75.32)
• paratendinitis — inflammation of the paratenon (loose connective tissue surrounding tendons without a synovial sheath, such as the Achilles); distinct from tenosynovitis; associated with Achilles tendon region pain
• overuse syndrome — the biomechanical precondition for most tendinitis; repetitive microtrauma exceeding the tendon’s repair rate; often associated with occupational exposure codes (Z57.x)
• NSAIDs — non-steroidal anti-inflammatory drugs; first-line pharmacological treatment for acute tendinitis; relevant when coding for associated GI complications (e.g., K29.70)
• Ultrasound / musculoskeletal ultrasound (76881, 76882) — primary diagnostic and injection-guidance imaging tool for tendinitis evaluation and treatment; assess for tendon thickening, hyperemia, calcification, and partial tears

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CODING CORNER

🏥 ICD-10-CM CODES

Calcific Tendinitis by Site (M65.2x — Site and Laterality Required; Excludes Shoulder → Use M75.31/M75.32)

Code	Description
M65.211	Calcific tendinitis, right shoulder (Note: per Excludes1, use M75.31 for shoulder — M65.211 is technically valid but review payer preference)
M65.212	Calcific tendinitis, left shoulder
M65.219	Calcific tendinitis, unspecified shoulder
M65.221	Calcific tendinitis, right upper arm
M65.222	Calcific tendinitis, left upper arm
M65.229	Calcific tendinitis, unspecified upper arm
M65.231	Calcific tendinitis, right forearm
M65.232	Calcific tendinitis, left forearm
M65.239	Calcific tendinitis, unspecified forearm
M65.241	Calcific tendinitis, right hand
M65.242	Calcific tendinitis, left hand
M65.249	Calcific tendinitis, unspecified hand
M65.251	Calcific tendinitis, right thigh
M65.252	Calcific tendinitis, left thigh
M65.259	Calcific tendinitis, unspecified thigh
M65.261	Calcific tendinitis, right lower leg
M65.262	Calcific tendinitis, left lower leg
M65.269	Calcific tendinitis, unspecified lower leg
M65.271	Calcific tendinitis, right ankle and foot
M65.272	Calcific tendinitis, left ankle and foot
M65.279	Calcific tendinitis, unspecified ankle and foot
M65.28	Calcific tendinitis, other site
M65.29	Calcific tendinitis, multiple sites

Shoulder Tendinitis (M75.x — Laterality Required)

Code	Description
M75.21	Bicipital tendinitis, right shoulder
M75.22	Bicipital tendinitis, left shoulder
M75.20	Bicipital tendinitis, unspecified shoulder
M75.31	Calcific tendinitis of right shoulder
M75.32	Calcific tendinitis of left shoulder
M75.30	Calcific tendinitis of unspecified shoulder
M75.81	Other shoulder lesions, right shoulder (use when tendinitis NOS at shoulder, not otherwise specified)
M75.82	Other shoulder lesions, left shoulder
M75.80	Other shoulder lesions, unspecified shoulder

Enthesopathy / Tendinitis at Elbow (M77.x — Laterality Required)

Code	Description
M77.11	Lateral epicondylitis, right elbow (tennis elbow)
M77.12	Lateral epicondylitis, left elbow
M77.10	Lateral epicondylitis, unspecified elbow
M77.01	Medial epicondylitis, right elbow (golfer’s elbow)
M77.02	Medial epicondylitis, left elbow
M77.00	Medial epicondylitis, unspecified elbow

Lower Extremity Tendinitis by Site (M76.x — Laterality Required)

Code	Description
M76.01	Gluteal tendinitis, right hip
M76.02	Gluteal tendinitis, left hip
M76.00	Gluteal tendinitis, unspecified hip
M76.11	Psoas tendinitis, right hip
M76.12	Psoas tendinitis, left hip
M76.10	Psoas tendinitis, unspecified hip
M76.21	Iliac crest spur, right hip
M76.22	Iliac crest spur, left hip
M76.20	Iliac crest spur, unspecified hip
M76.31	Iliotibial band syndrome, right leg
M76.32	Iliotibial band syndrome, left leg
M76.30	Iliotibial band syndrome, unspecified leg
M76.51	Patellar tendinitis, right knee (jumper’s knee)
M76.52	Patellar tendinitis, left knee
M76.50	Patellar tendinitis, unspecified knee
M76.61	Achilles tendinitis, right leg
M76.62	Achilles tendinitis, left leg
M76.60	Achilles tendinitis, unspecified leg
M76.71	Peroneal tendinitis, right leg
M76.72	Peroneal tendinitis, left leg
M76.70	Peroneal tendinitis, unspecified leg
M76.891	Other specified enthesopathies of right lower limb, excluding foot
M76.892	Other specified enthesopathies of left lower limb, excluding foot
M76.899	Other specified enthesopathies of unspecified lower limb, excluding foot

De Quervain / Trigger Finger Tenosynovitis (M65.x)

Code	Description
M65.4	Radial styloid tenosynovitis (de Quervain)
M65.311	Trigger thumb, right thumb
M65.312	Trigger thumb, left thumb
M65.319	Trigger thumb, unspecified thumb
M65.321	Trigger finger, right index finger
M65.322	Trigger finger, left index finger
M65.331	Trigger finger, right middle finger
M65.332	Trigger finger, left middle finger
M65.341	Trigger finger, right ring finger
M65.342	Trigger finger, left ring finger
M65.351	Trigger finger, right little finger
M65.352	Trigger finger, left little finger

Plantar Fasciitis / Foot Enthesopathy (M77.x)

Code	Description
M72.2	Plantar fascial fibromatosis (plantar fasciitis — note: coded under M72, not M77)
M77.31	Calcaneal spur, right foot
M77.32	Calcaneal spur, left foot
M77.30	Calcaneal spur, unspecified foot
M77.51	Other enthesopathy of right foot and ankle
M77.52	Other enthesopathy of left foot and ankle
M77.50	Other enthesopathy of unspecified foot and ankle

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🔧 COMMON CPT CODES (Tendinitis-Related Diagnosis & Treatment)

CPT Code	Description
20550	Injection(s); single tendon sheath, or ligament, aponeurosis (e.g., plantar fascia) — use for sheath injection; modifier 59 for each additional site; modifier 50 permitted for bilateral
20551	Injection(s); single tendon origin/insertion — use for enthesis-level injection; modifier 59 for multiple sites; modifier 50 NOT reportable per CMS A52863
20526	Injection, therapeutic (e.g., local anesthetic, corticosteroid), carpal tunnel
29826	Arthroscopy, shoulder, surgical; decompression of subacromial space with partial acromioplasty, with or without coracoacromial release (used in rotator cuff tendinitis with impingement)
29822	Arthroscopy, shoulder, surgical; debridement, limited, one or two discrete structures (e.g., biceps tendon, rotator cuff, bursa)
29823	Arthroscopy, shoulder, surgical; debridement, extensive, three or more discrete structures
23412	Repair of ruptured musculotendinous cuff (e.g., rotator cuff), open; chronic
27605	Tenotomy, percutaneous, Achilles tendon (separate procedure); local anesthesia
27606	Tenotomy, percutaneous, Achilles tendon (separate procedure); general anesthesia
26060	Tenotomy, percutaneous, single, flexor or extensor tendon; finger (used in trigger finger release)
26055	Tendon sheath incision (e.g., trigger finger) — open release of tendon sheath; finger
97110	Therapeutic procedure, 1 or more areas, each 15 min; therapeutic exercises to develop strength and endurance (PT — used with tendinitis rehab, time-based)
97014	Application of a modality to one or more areas; electrical stimulation (unattended) — e-stim for pain/inflammation in tendinitis
97012	Application of a modality to one or more areas; traction, mechanical — used in cervical/lumbar tendinitis-adjacent conditions
76881	Ultrasound, extremity, non-vascular, real time with image documentation; complete — diagnostic MSK ultrasound for tendon evaluation
76882	Ultrasound, extremity, non-vascular, real time with image documentation; limited, anatomic specific structure — targeted tendon exam
76942	Ultrasonic guidance for needle placement (e.g., injection), imaging supervision and interpretation — add-on to 20550 or 20551; requires permanent image documentation; never bill alongside bundled ultrasound-inclusive codes

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⚠️ Coding Note: For inpatient profee claims involving tendinitis, laterality and site-specificity are non-negotiable — parent-level codes such as M76.5 (Patellar tendinitis), M76.6 (Achilles tendinitis), and M77.1 (Lateral epicondylitis) are non-billable and will reject; always drill to the 5th or 6th character level (e.g., M76.51, M76.61, M77.11). Coding sequencing note: When tendinitis is the documented reason for a corticosteroid injection encounter, the tendinitis code leads and the injection CPT code follows — do not sequence the drug administration code first unless the payer’s policy specifically requires it. Undercoding alert: Providers frequently document “shoulder pain” or “elbow pain” in the assessment when imaging confirms rotator cuff tendinitis, bicipital tendinitis, or epicondylitis — trigger a documentation clarification query whenever a specific tendon structure is named in the HPI, physical exam, or imaging report but only generic pain codes appear in the assessment. Per CMS Article A52863, CPT 20551 (tendon origin/insertion injection) cannot be reported with modifier 50; if bilateral injections at the origin/insertion are performed, report 20551 on two separate lines with modifier -59 appended to the second line — failure to do this correctly is one of the most common NCCI edit violations in orthopedic and sports medicine profee billing. For ultrasound-guided injections, note that 76942 is a separate add-on reportable with 20550 and [[20551]], but must NOT be reported separately when using joint injection codes that already include ultrasound guidance in their descriptor (e.g., 20611 — see CPT bundling rules).

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DERIVATIONS of tendinitis

TABLE definition AS Definition
FROM #medterm 
WHERE length(filter(roots, (word) => econtains([[tendinitis]].roots, word))) > 0 AND file.name != [[tendinitis]].file.name
SORT file.name ASC

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Query functionality

TABLE definition AS Definition
FROM #medterm 
WHERE length(filter(definition, (word) => econtains([[tendinitis]].definition, word))) > 0 AND file.name != [[tendinitis]].file.name

Med roots dictionary Appendix A Prefixes Appendix B Combining Forms Appendix C Suffixes Appendix D Suffix forms