A tendon is a tough, inelastic cord or band of dense regular connective tissue — composed almost entirely of type I collagen fibers arranged in parallel fascicles — that serves as the mechanical link between a skeletal muscle and its bony attachment, transmitting the contractile force of the muscle to move or stabilize the joint. Tendons are distinguished from ligaments, which connect bone to bone, and from aponeuroses, which are flat, sheet-like fibrous expansions that serve the same muscle-to-bone anchoring function but over a broad surface area rather than a focal point. The structural organization of a tendon follows a hierarchical pattern: individual collagen fibrils bundle into fascicles, fascicles are surrounded by endotenon, and the entire structure is enclosed by the epitenon and, in high-friction zones, by a synovial tendon sheath that secretes lubricating fluid to reduce friction during movement. Tendons have limited vascularity — particularly in their mid-substance — making them slow to heal; injury to the mid-tendon region characteristically produces tendinosis (degenerative collagen disorganization without significant inflammation) rather than classic inflammatory tendinitis, a distinction with direct coding implications since most chronic tendon pain maps to the degenerative end of the spectrum. The largest tendon in the human body is the Achilles tendon (tendo calcaneus), connecting the gastrocnemius and soleus to the calcaneus, while the most clinically coded tendon complex in inpatient profee is the rotator cuff — a four-tendon structure (supraspinatus, infraspinatus, teres minor, subscapularis) whose pathology dominates the M75 code family.
Ancient Greek τένων (ténōn), genitive ténontos; from τείνειν (teínein)
“tendon,” “sinew,” “that which is stretched” — root noun directly naming the structure; from PIE root *ten- “to stretch, extend”
tendo-(Latin form)
Medieval Latin tendo (nominative), tendonem (accusative), altered from Late Latin tenon
”tendon” — Latin anatomical term shaped by association with Latin tendere (“to stretch, extend”); the Medieval Latin form introduced the spelling preserved in modern English
-on(Greek nominal suffix)
Ancient Greek nominal suffix
Noun-forming ending commonly applied to names of anatomical structures and instruments in Greek medical terminology
The word tendon entered English in the 1540s from Medieval Latin tendonem (nominative tendo), which was itself an alteration of Late Latin tenon, borrowed from Greek ténōn (genitive ténontos) — literally “that which is stretched” or “sinew.” The Medieval Latin spelling was reshaped by association with the verb tendere (“to stretch”), which shares the same Proto-Indo-European root *ten- (“to stretch, extend”). An earlier English form, tenoun, appears in the late 14th century directly from the unaltered Latin tenon. The word entered French as tendon (17th century), and English adopted the modern spelling from this French intermediary. The Greek root τείνειν (teínein, “to stretch”) generates one of the broadest root families in anatomy and medicine: tension (state of being stretched), tenotomy (cutting of a tendon), tenodesis (fixation of a tendon to bone), tenolysis (release of tendon adhesions), tenorrhaphy (suture repair of a tendon), and hypertension (excessive vascular tension). The combining forms teno-, tenont-, and tend- are all active in clinical terminology and appear across orthopaedic, podiatric, and hand surgery nomenclature.
🔀 ALIASES / ALTERNATE TERMS
Tendinous(adjective form — appears clinically as “tendinous insertion,” “tendinous cuff,” “tendinous avulsion”; describes structures composed of or relating to tendon tissue)
Sinew(lay and archaic clinical synonym for tendon; still used colloquially and occasionally in older clinical records; not an indexed ICD-10-CM term)
Tendo(Latin anatomical form; used in formal anatomical nomenclature — e.g., “tendo calcaneus” for the Achilles tendon, “tendo Achillis”; appears in surgical operative notes and anatomy texts)
Tendinopathy(umbrella clinical term for any pathological condition of a tendon regardless of mechanism — includes both inflammatory and degenerative forms; preferred over “tendinitis” in modern evidence-based literature; coded by site under M65.x, M66.x, M67.x, M75.x, M76.x families)
Tendinosis(degenerative, non-inflammatory tendon disorder characterized by collagen disorganization, mucoid degeneration, and neovascularization without significant inflammatory infiltrate; the underlying pathology in most “chronic tendinitis” cases; coded as tendinopathy under the appropriate site-specific code)
tendinitis / Tendonitis(inflammatory tendon condition; acute irritation with nociceptive and inflammatory cell infiltrate; the distinction from tendinosis is clinically important but does not change the ICD-10-CM code — both map to the same site-specific M-code family; the spelling “tendinitis” is preferred in current ICD-10-CM)
Rotator cuff(the four-tendon complex of the shoulder — supraspinatus, infraspinatus, teres minor, subscapularis — whose collective function is glenohumeral stabilization and rotation; the most commonly coded tendon complex in orthopaedic profee billing; coded under M75.1xx-M75.3xx family)
Achilles tendon / Tendo calcaneus(the largest tendon in the body; connects gastrocnemius and soleus to the calcaneus; prone to spontaneous rupture (M66.361/M66.362) and insertional/mid-substance tendinopathy (M76.60-M76.62))
Patellar tendon / Patellar ligament(the distal continuation of the quadriceps mechanism from patella to tibial tuberosity; prone to tendinopathy “jumper’s knee” coded M76.50-M76.52; technically classified as a ligament anatomically despite being called a tendon clinically)
Aponeurosis(flat, broad sheet of dense connective tissue performing the same function as a tendon over a wide area; e.g., plantar fascia/aponeurosis; distinction from tendon is important for injection coding — plantar fascia injections use 20550, not 20551)
🔗 RELATED TERMS
Ligament — fibrous connective tissue connecting bone to bone across a joint; shares the same dense collagen I structure as tendons but serves a joint stabilization rather than muscle-force-transmission function; coded in the M series by site; a key distinction for injection coding (20550 covers both tendon sheaths and ligaments)
tendinitis — inflammatory condition of a tendon; acute; coded by anatomic site under M65.2x (calcific tendinitis) or site-specific codes in M75.x/M76.x; distinguished from tendinosis by the presence of inflammatory cells on histology, though clinically and for coding purposes the codes overlap
Tendinosis — degenerative, non-inflammatory tendon pathology; the predominant finding in chronic overuse tendinopathy; histologically characterized by mucoid degeneration and failed tendon healing; coded under the same site-specific M-code as tendinitis in ICD-10-CM
Tenosynovitis — inflammation of the synovial tendon sheath surrounding a tendon; coded under M65.x family by site (e.g., M65.811-M65.819 other synovitis/tenosynovitis); distinct from tendinitis, which involves the tendon body itself; requires the sheath to be present (only tendons enclosed in synovial sheaths can develop tenosynovitis)
Trigger finger (stenosing tenosynovitis) — thickening of the tendon sheath of a digital flexor tendon causing the tendon to catch or lock when flexing; coded M65.311-M65.319 (right), M65.321-M65.329 (left), by digit; injection coded 20550; surgical release coded 26055
De Quervain tenosynovitis — stenosing tenosynovitis of the first dorsal compartment (abductor pollicis longus and extensor pollicis brevis); coded M65.4 (without laterality specification in ICD-10-CM); treated with 20550 injection or surgical release (26145)
Rotator cuff tear — partial or complete disruption of one or more of the four rotator cuff tendons; non-traumatic coded M75.1xx; traumatic coded S46.0xx; the most commonly repaired tendon lesion in orthopaedic surgery (arthroscopic repair CPT 29827)
Collagen type I — the primary structural protein of tendon; organized in parallel fibril bundles aligned along the axis of tensile stress; reduced cross-linking, aging, and repetitive microtrauma reduce type I collagen integrity, leading to tendinosis
Enthesopathy — pathology at the tendon-bone insertion (enthesis); distinct from mid-substance tendinopathy; coded M77.x (enthesopathies) by site; e.g., lateral epicondylitis (M77.11/M77.12), medial epicondylitis (M77.01/M77.02), plantar fasciitis (M72.2); injection at insertion site coded 20551
Tenodesis — surgical procedure anchoring a tendon to bone, typically to restore function after rupture or transfer; CPT coded by site and technique (e.g., biceps tenodesis 23430)
Tenotomy — surgical or percutaneous cutting of a tendon to release contracture or correct deformity; CPT coded by site and approach (e.g., percutaneous Achilles 27605, open finger flexor 26060)
Tenorrhaphy — suture repair of a lacerated or ruptured tendon; the root operative procedure in most tendon repair CPT codes (e.g., 27650 Achilles repair, 26410 extensor tendon hand repair)
Calcific tendinitis — deposition of calcium hydroxyapatite crystals within tendon substance, most commonly the supraspinatus; coded M65.20-M65.29 by site; produces acute inflammatory pain episodes superimposed on chronic tendinopathy
Other synovitis and tenosynovitis, unspecified shoulder
M65.851
Other synovitis and tenosynovitis, right hip
M65.852
Other synovitis and tenosynovitis, left hip
M65.871
Other synovitis and tenosynovitis, right ankle and foot
M65.872
Other synovitis and tenosynovitis, left ankle and foot
Shoulder Tendon Pathology — Rotator Cuff (M75.x)
Code
Description
M75.100
Unspecified rotator cuff tear or rupture, not specified as traumatic, unspecified shoulder
M75.101
Unspecified rotator cuff tear or rupture, not specified as traumatic, right shoulder
M75.102
Unspecified rotator cuff tear or rupture, not specified as traumatic, left shoulder
M75.111
Incomplete rotator cuff tear or rupture of right shoulder, not specified as traumatic
M75.112
Incomplete rotator cuff tear or rupture of left shoulder, not specified as traumatic
M75.121
Complete rotator cuff tear or rupture of right shoulder, not specified as traumatic
M75.122
Complete rotator cuff tear or rupture of left shoulder, not specified as traumatic
M75.20
Bicipital tendinitis, unspecified shoulder
M75.21
Bicipital tendinitis, right shoulder
M75.22
Bicipital tendinitis, left shoulder
Lower Extremity Tendon Pathology (M76.x — Enthesopathies/Tendinitis by Site)
Code
Description
M76.00
Gluteal tendinitis, unspecified hip
M76.01
Gluteal tendinitis, right hip
M76.02
Gluteal tendinitis, left hip
M76.10
Psoas tendinitis, unspecified hip
M76.11
Psoas tendinitis, right hip
M76.12
Psoas tendinitis, left hip
M76.50
Patellar tendinitis, unspecified knee
M76.51
Patellar tendinitis, right knee
M76.52
Patellar tendinitis, left knee
M76.60
Achilles tendinitis, unspecified leg
M76.61
Achilles tendinitis, right leg
M76.62
Achilles tendinitis, left leg
M76.70
Peroneal tendinitis, unspecified leg
M76.71
Peroneal tendinitis, right leg
M76.72
Peroneal tendinitis, left leg
Elbow & Wrist Enthesopathies (M77.x)
Code
Description
M77.00
Medial epicondylitis, unspecified elbow
M77.01
Medial epicondylitis, right elbow
M77.02
Medial epicondylitis, left elbow
M77.10
Lateral epicondylitis, unspecified elbow
M77.11
Lateral epicondylitis, right elbow (tennis elbow)
M77.12
Lateral epicondylitis, left elbow (tennis elbow)
M72.2
Plantar fascial fibromatosis (plantar fasciitis)
🔧 COMMON CPT CODES (Tendon-Related Procedures)
CPT Code
Description
20550
Injection(s); single tendon sheath, or ligament, aponeurosis (e.g., trigger finger, De Quervain’s, plantar fascia) — one injection site; use modifier -59 or -XS for additional separate sites on same date
20551
Injection(s); single tendon origin/insertion (e.g., lateral epicondylitis, gluteal tendinitis) — distinct from 20550; do NOT use 20551 for plantar fascia or trigger finger
Ultrasonic guidance for needle placement, imaging supervision and interpretation (add-on when ultrasound guidance is used with 20550 or 20551; requires separate image documentation)
27650
Repair, primary, open or percutaneous, ruptured Achilles tendon — traumatic or acute non-traumatic rupture; unilateral
27652
Repair, primary, ruptured Achilles tendon; with graft (includes obtaining graft)
29827
Arthroscopy, shoulder; with rotator cuff repair (most common shoulder tendon procedure billed in orthopedic profee)
23430
Tenodesis of long tendon of biceps (open biceps tenodesis; frequently paired with 29827 when performed concurrently)
26410
Repair, extensor tendon, hand; primary or secondary, each tendon, without free graft, each tendon
26418
Repair, extensor tendon, finger, primary or secondary; with free graft, each tendon (includes obtaining graft)
26356
Repair or advancement, flexor tendon, in digital sheath; primary, without free graft, each tendon
27605
Tenotomy, percutaneous, Achilles tendon; local anesthesia
27606
Tenotomy, percutaneous, Achilles tendon; requiring general anesthesia
Synovectomy, tendon sheath, radical (tenosynovectomy), each tendon; wrist (De Quervain surgical release)
⚠️ Coding Note: The single most critical distinction in tendon injection coding is 20550 vs. 20551: 20550 applies to injections into a tendon sheath, ligament, or aponeurosis (e.g., trigger finger flexor sheath, plantar fascia, De Quervain’s first dorsal compartment), while 20551 applies to injections at a tendon origin or insertion (e.g., lateral epicondyle, gluteal insertion) — these codes are commonly miscoded interchangeably, but payers audit the distinction; when ultrasound guidance is performed and documented with image archival, add 76942 separately as it is not bundled. For inpatient profee, a critical undercoding alert: when a provider documents “tendon rupture” without specifying traumatic vs. non-traumatic mechanism, query before assigning — non-traumatic (spontaneous) ruptures map to the M66.x family, while traumatic ruptures map to the injury code families (S-codes by body region); the difference affects MS-DRG grouping and external cause code requirements. When rotator cuff repair (29827) is performed arthroscopicallywith concurrent biceps tenodesis (23430), both codes are reportable — 23430 is not bundled into 29827 per CPT and CCI edits — but documentation must clearly support the tenodesis as a separately performed and indicated procedure. For bilateral tendon procedures, most tendon repair and tenotomy CPT codes are unilateral by descriptor — append modifier -50 for bilateral same-session procedures, or bill the code twice with modifiers -RT and -LT per payer-specific preference; however, 20550 modifier -50 is payer-specific and CMS does not recognize -50 for injection codes — review payer policy individually.
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