Impingement syndrome of the left shoulder, classifying mechanical compression of soft tissue structures within the left subacromial space — distinct from right-side (M75.41) and unspecified-side (M75.40) variants.

Documentation tips

What should appear in the chart to support M75.42.

Source · Editorial brief grounded in 6 cited references ↓

• Explicitly state 'left shoulder' in the assessment — avoid 'shoulder impingement' without laterality, which forces a drop to M75.40.
• Record results of provocative tests by name: positive Hawkins-Kennedy or Neer sign directly supports M75.42 over a generic pain code.
• Summarize imaging findings that confirm subacromial narrowing, acromial morphology (Bigliani type), or rotator cuff tendinopathy — Kellgren or outlet view detail strengthens medical necessity.
• Document range-of-motion deficits and pain arc (typically 60–120 degrees of abduction) to support both the diagnosis and any associated physical therapy or injection claim.
• If conservative care preceded a surgical referral, list the treatments tried (PT, corticosteroid injection, NSAIDs) and their outcomes — this chain supports medical necessity for arthroscopic subacromial decompression (CPT 29826).
• Update the diagnosis code at each encounter if findings evolve; if MRI confirms a rotator cuff tear after M75.42 was assigned, transition to the appropriate M75.1x2 code.

Related CPT procedures

Procedure codes commonly billed with M75.42. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

Common coding pitfalls

The recurring mistakes coders make with M75.42 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

• Leaving M25.512 (left shoulder pain) on the claim after impingement is clinically confirmed — once the specific diagnosis is established, the symptom code must be replaced with M75.42.
• Using M75.40 (unspecified shoulder) when the note clearly states 'left' — this is both a specificity failure and a denial risk.
• Continuing to bill M75.42 after imaging or arthroscopy reveals a discrete rotator cuff tear — the correct code shifts to M75.102 (unspecified), M75.112 (incomplete), or M75.122 (complete) for the left shoulder.
• Coding only shoulder pain (M25.512) alongside a procedure like CPT 29826 — payers expect a structural diagnosis code, not a symptom code, to justify subacromial decompression.
• Conflating subacromial bursitis (M75.52) with impingement syndrome (M75.42) — both may coexist and can be coded together when independently documented, but they are not interchangeable.

Clinical context

Source · Editorial summary grounded in 6 cited references ↓

Sibling codes

Other billable codes under M75.4 (laterality / anatomic variants).