Nonunion is the permanent cessation of the bone healing process following a fracture, distinguished from delayed union (which implies slowed but ongoing healing) by the complete absence of progressive radiographic repair. The most widely used clinical and regulatory standard — established by the U.S. FDA — defines nonunion as a fracture that is at least 9 months old and has shown no visible progressive signs of healing on serial radiographs for a minimum of 3 consecutive months. Nonunion is classified by the degree of biological reactivity at the fracture site using the Weber and Cêch classification system: hypertrophic nonunion demonstrates exuberant callus formation at the bone ends, indicating intact vascularity but inadequate mechanical stability; atrophic nonunion shows no callus whatsoever, indicating insufficient blood supply or biological failure to mount a healing response; and oligotrophic nonunion falls between, with minimal callus and intermediate vascularity. A separate subtype, pseudarthrosis (literally “false joint”), develops when the fracture site forms a fibrocartilaginous false joint with a synovial-like fluid-filled cavity, representing the endpoint of untreated nonunion. Clinical Indicators: In ICD-10-CM, nonunion is encoded via the 7th character “K” appended to the original fracture code representing the specific anatomical site and fracture type. There is NO standalone nonunion category in ICD-10-CM — the coder must always build the full fracture code first, then apply the 7th character K to confirm it is a subsequent encounter for fracture with nonunion. M84.3x-M84.9x codes are for stress/pathological fractures, not traumatic nonunions. For traumatic fracture nonunion, use the original fracture code series (S-codes) with 7th character K.
”Not, absence of” — a simple Latin negation prefix indicating the failure of the expected process to occur; appears in noncompliance, nonhealing, noninvasive
uni-
Latin ūnus / ūniō
”One, to unite” — from the Latin unio, meaning a uniting or joining together into a single whole; the root captures the expected biological outcome (osseous union) that has failed
pseudo-
Ancient Greek ψευδής (pseudḗs)
“False, spurious” — the prefix in the synonym pseudarthrosis; indicates the false resemblance of the nonunion site to a functional joint
-arthrosis
Ancient Greek ἄρθρον (árthron) + -ōsis
”Joint” + “abnormal condition” — the suffix in pseudarthrosis, together denoting an abnormal false-joint state; appears in arthritis, arthroscopy, arthroplasty
Literally: “Non-union” = “absence of joining” — a compound term that is medically self-explanatory. Its Greek synonym pseudarthrosis translates as “false joint abnormal condition,” a historically evocative term first used in the nineteenth century to describe the fibrocartilaginous false joint that forms at the ends of chronically nonunited bone fragments. Both terms remain in active ICD-10-CM use: nonunion through the 7th character K extension on fracture codes, and pseudarthrosis explicitly in M96.0 (pseudarthrosis after failed fusion or arthrodesis).
🔀 ALIASES / ALTERNATE TERMS
Term
Context
Fracture nonunion
The full clinical descriptor used in operative notes and radiologic reports; the form most recognizable for coding purposes.
Pseudarthrosis
The formal anatomical/pathological synonym; refers to the false-joint stage of established nonunion; also has its own ICD-10-CM code M96.0 specifically for failed arthrodesis/fusion context.
False joint
The layperson translation of pseudarthrosis; acceptable in patient education but not as a sole coding descriptor.
Fibrous nonunion
A descriptive subtype in which fibrous tissue — rather than bone — bridges the fracture gap; generally corresponds to atrophic or oligotrophic classifications.
Delayed union
A related but distinct diagnosis — healing is occurring but more slowly than expected; use 7th character G (delayed healing) rather than K (nonunion) when the physician documents delayed but progressive healing.
Malunion
A separate complication in which the fracture healed but in a malpositioned/angulated alignment; code with 7th character P rather than K; requires documentation of improper healing, not failure to heal.
🔗 RELATED TERMS
Delayed union — 7th character G on the original fracture code (e.g., S52.001G for right radial fracture with delayed healing); distinct from nonunion — healing is occurring but slowly; treatment is more conservative before escalating to operative management.
Malunion — 7th character P on the original fracture code; the fracture healed but in incorrect position/angulation; managed with corrective osteotomy rather than nonunion repair; a critical ICD-10-CM distinction from nonunion (K).
Pseudarthrosis after fusion/arthrodesis — M96.0; a specific standalone ICD-10-CM code for failed spinal or appendicular fusion — where the intended surgical arthrodesis has failed to achieve bony union; distinct from traumatic fracture nonunion coding.
Osteomyelitis — M86.9 (unspecified) / site-specific M86.x codes; chronic bone infection that may be the underlying cause of atrophic or septic nonunion, particularly in open fractures; code as an additional diagnosis when documented.
osteoporosis — M81.0 (age-related); reduced bone mineral density is a major risk factor for nonunion, particularly in fragility fractures of the hip, vertebra, and distal radius; code additionally when documented as a contributing condition.
Implant failure / mechanical complication — T84.01xA - T84.298x (range); internal fixation hardware failure (broken nail, loose screws) contributing to or resulting from nonunion; code additionally with T84.- mechanical complication codes when documented.
Bone loss, not elsewhere classified — M89.70 - M89.78x (site-specific); significant cortical or cancellous bone loss at the nonunion site requiring structural grafting; code as an additional diagnosis when documented to support medical necessity for bone graft procedures.
CODING CORNER
🏥 ICD-10-CM CODES
7th Character K — The Nonunion Extender
⚠️ ICD-10-CM / Chapter Nuances: There is NO standalone ICD-10-CM category for traumatic fracture nonunion. Nonunion is captured by appending 7th character “K” to the appropriate site-specific fracture code. Coders must first identify the fracture site, fracture type (displaced/nondisplaced, open/closed), and laterality from the medical record, build the full fracture code, and replace the 7th character with K to indicate the encounter is for a subsequent encounter for fracture with nonunion. 7th character G = delayed healing (healing slowly, not yet nonunion); 7th character K = nonunion (healing has completely arrested); 7th character P = malunion (healed in wrong position). These are mutually exclusive — use only the one supported by documentation.
Code
Description
S52.001K
Fracture of upper end of right radius, unspecified type, subsequent encounter for closed fracture with nonunion (Example: radial head nonunion, right — always verify the specific fracture subtype from the original injury record for full specificity)
S52.201K
Fracture of shaft of right radius, unspecified, subsequent encounter for closed fracture with nonunion
S42.201K
Fracture of upper end of right humerus, unspecified, subsequent encounter for closed fracture with nonunion (Proximal humerus nonunion; commonly treated with revision ORIF or arthroplasty in elderly patients)
S72.001K
Fracture of unspecified part of neck of right femur, subsequent encounter for closed fracture with nonunion (Femoral neck nonunion; high-risk due to avascular necrosis potential; often requires hemiarthroplasty or total hip replacement)
S82.201K
Fracture of upper end of right tibia, unspecified, subsequent encounter for closed fracture with nonunion (Tibial nonunion is the most studied long bone nonunion type in FDA evidence supporting electrical bone stimulation)
S82.001K
Fracture of patella, unspecified, right knee, subsequent encounter for closed fracture with nonunion
S62.001K
Fracture of distal pole of navicular (scaphoid) bone of right wrist, subsequent encounter for fracture with nonunion (Scaphoid nonunion is a distinct, high-prevalence entity in young active patients with missed or untreated scaphoid fractures; specific repair codes exist — see CPT section)
M96.0
Pseudarthrosis after fusion or arthrodesis (STANDALONE billable code; use specifically when a surgically intended spinal or appendicular arthrodesis has FAILED to achieve union — NOT for traumatic fracture nonunion)
Age-related osteoporosis without current pathological fracture (Code additionally when osteoporosis is documented as a contributing biological factor in the nonunion)
Osteomyelitis, unspecified (Code additionally when septic/infected nonunion is documented; drives surgical debridement in addition to nonunion repair)
T84.01xA
Broken internal right hip prosthesis, initial encounter (When implant failure has contributed to the nonunion; the T84.- mechanical complication series is the appropriate family)
Personal history of other musculoskeletal disorders (Secondary code for prior fracture or bone conditions relevant to the nonunion clinical picture)
🔧 COMMON CPT CODES (Evaluation, Repair & Stimulation)
Nonunion Repair — Upper Extremity
⚠️ CPT Nuance: Nonunion repair codes are organized by anatomical site and by whether a bone graft is included in the code descriptor. When the descriptor states “includes obtaining graft,” do NOT separately report bone graft harvest codes 20900 or 20902 — they are already bundled. Only report 20900/20902 when the harvest is through a separate incision for a primary procedure whose descriptor does NOT include graft harvesting.
CPT Code
Description
23485
Osteotomy, clavicle, with or without internal fixation; with bone graft for nonunion or malunion (Includes obtaining graft and/or necessary fixation — do NOT separately bill graft harvest)
24430
Repair of nonunion or malunion, humerus; without graft (e.g., compression technique) (Use when the nonunion is mechanically addressed via compression fixation without adding bone graft material)
24435
Repair of nonunion or malunion, humerus; with iliac or other autograft (Includes obtaining graft — do NOT separately report 20900/20902)
25400
Repair of nonunion or malunion, radius OR ulna; without graft (e.g., compression technique)
25405
Repair of nonunion or malunion, radius OR ulna; with autograft (includes obtaining graft)
25415
Repair of nonunion or malunion, radius AND ulna; without graft (e.g., compression technique)
25420
Repair of nonunion or malunion, radius AND ulna; with autograft (includes obtaining graft)
25430
Insertion of vascular pedicle into carpal bone (e.g., Hori procedure) (Used for vascularized bone grafting of the proximal pole of the scaphoid in avascular nonunion — a technically distinct procedure)
25431
Repair of nonunion of carpal bone (excluding carpal scaphoid/navicular) (includes obtaining graft and necessary fixation), each bone
25440
Repair of nonunion, scaphoid carpal (navicular) bone, with or without radial styloidectomy (The dedicated scaphoid nonunion repair code; includes graft obtaining and fixation)
Nonunion Repair — Lower Extremity
CPT Code
Description
27470
Repair, nonunion or malunion, femur, distal to head and neck; without graft (e.g., compression technique)
27472
Repair, nonunion or malunion, femur, distal to head and neck; with iliac or other bone graft (includes obtaining graft)
27720
Repair of nonunion or malunion, tibia; without graft (e.g., compression technique) (Tibial nonunion without graft — typically revision intramedullary nailing or exchange nailing with compression)
27722
Repair of nonunion or malunion, tibia; with iliac or other bone graft (includes obtaining graft) (Use when structural or cancellous graft is added to the tibial nonunion repair site — graft harvest bundled)
27724
Repair of nonunion or malunion, tibia; with sliding graft (Cortical sliding graft technique; a less common procedure reserved for specific biomechanical configurations)
27726
Repair of nonunion or malunion, tibia; with fibula, with or without bone graft
Bone Graft Harvest — Separately Reportable When NOT Bundled
⚠️ Only report these codes when the primary procedure’s descriptor does NOT state “includes obtaining graft.” Do NOT append modifier -62 to bone graft codes 20900-20938.
CPT Code
Description
20900
Bone graft, any donor area; minor or small (e.g., dowel or button) (Report separately only when bone graft harvest is through a distinct incision for a primary procedure that does not bundle graft harvest in its descriptor)
Bone graft, any donor area; major or large (Report for large structural or cancellous graft harvests — e.g., iliac crest — when not already included in the primary repair code)
20930
Allograft, morselized, or placement of osteopromotive material, for spine surgery only (Spinal arthrodesis context; distinct from appendicular nonunion repair)
20936
Autograft for spine surgery only; local (e.g., ribs, spinous process, or laminar fragments) obtained from same incision (Spinal context only)
Bone Growth Stimulation (Non-Surgical / Electrical)
⚠️ Coverage Nuance: Medicare and most commercial payers require documented evidence of fracture nonunion via two sets of radiographs separated by at least 90 days confirming no progressive healing before authorizing electrical stimulation. Electrical stimulation is generally considered an alternative to surgery — not an adjunct. Do NOT bill stimulation codes simultaneously with active surgical repair claims for the same fracture site.
CPT Code
Description
20974
Electrical stimulation to aid bone healing; noninvasive (nonoperative) (The primary CPT code for external bone growth stimulators — both pulsed electromagnetic field [PEMF] and capacitively coupled devices; report with HCPCS E0747 for the device supply when applicable)
20975
Electrical stimulation to aid bone healing; invasive (operative) (Use when the bone stimulator electrodes are surgically implanted directly at the nonunion site intraoperatively — a less common approach)
HCPCS Codes — Devices
HCPCS Code
Description
E0747
Osteogenesis stimulator; electrical, noninvasive, other than spinal applications (DME code for the external electrical bone stimulator device; report in addition to 20974 when billing the device supply separately)
E0748
Osteogenesis stimulator; electrical, noninvasive, spinal applications (For spinal pseudarthrosis/failed fusion context — use with M96.0 as the supporting diagnosis)
E0749
Osteogenesis stimulator; electrical, surgically implanted (DME code for implanted stimulator device; report with 20975 for the surgical placement procedure)
Unplanned return to the operating room by the same physician following initial procedure for a related procedure during the postoperative period — Append to nonunion repair CPT codes when the nonunion develops and requires surgery within the global period of the original fracture fixation surgery
Unrelated procedure or service by the same physician during the postoperative period — Append when treating nonunion at a separate, unrelated fracture site during another fracture’s global period
Increased procedural services — Append to the primary nonunion repair code when the procedure is substantially more complex than typical (e.g., extensive adhesion lysis, scarring from prior hardware, vascularized graft required); must be supported by a detailed operative note with specific documentation of the increased complexity
Multiple procedures — Append to secondary procedures when multiple anatomical nonunion sites are repaired at the same operative session (e.g., radius AND ulna each coded individually at the same encounter)
Right side / Left side — Append laterality modifiers to all nonunion repair codes when applicable for right vs. left extremity identification
⚠️ Coding Note: The most pervasive compliance error in nonunion coding is using M84.3x codes for traumatic fracture nonunion. M84.3x is specifically for stress fractures — not traumatic fracture nonunion. Traumatic fracture nonunion is always coded using the original fracture S-code with 7th character K. To locate the correct code, reference the original fracture documentation (site, type, open vs. closed, laterality) and replace the 7th character with K. A second critical billing rule involves bone graft bundling: surgeons frequently document graft harvesting in their operative notes alongside nonunion repair codes that already include harvesting in their descriptor (e.g., 24435, 27722) — separately billing 20900 or 20902 in that scenario constitutes duplicate billing. Reserve 20900/20902 strictly for primary procedures whose descriptors are silent on graft inclusion. For modifier -78 vs. -79, the key question is always: Is the nonunion at the same site as the original surgery, within its global period? If yes → -78. If it’s a different site or outside the global → -79. Modifier -22 for increased complexity should never be appended without a supporting attestation paragraph in the operative note explaining specifically why the work exceeded the typical procedure — claims with -22 but without supporting documentation are a top OIG audit target in orthopedic surgery.
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