Inflammation of the bursa at the tibial collateral ligament on the left knee, classified under Pellegrini-Stieda syndrome — a condition involving calcification or bursitis at the medial femoral condyle insertion of the tibial collateral ligament.
Verified May 8, 2026 · 4 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 9
- Region
- Knee
Documentation tips
What should appear in the chart to support M76.42.
Source · Editorial brief grounded in 4 cited references ↓
- Explicitly document 'left' laterality in the assessment — 'tibial collateral bursitis, left knee' maps directly to M76.42 and prevents fallback to the unspecified M76.40.
- Record whether a prior medial knee sprain or contusion is present; Pellegrini-Stieda is post-traumatic in character, and noting the mechanism strengthens medical necessity.
- Include imaging findings that support the diagnosis — medial compartment soft-tissue calcification on plain radiograph or bursal fluid on MRI correlates to the Pellegrini-Stieda pattern.
- Document conservative care tried (NSAIDs, physical therapy, corticosteroid injection) before any procedural referral; payers require this history for authorization of advanced imaging or surgery.
- If both knees are affected, add M76.41 (right leg) as a secondary code; M76.42 covers left only and there is no bilateral code in this subcategory.
Related CPT procedures
Procedure codes commonly billed with M76.42. 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 M76.42 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Using M76.40 (unspecified leg) when the provider has clearly documented 'left knee' — always assign the laterality-specific code M76.42 when the side is documented.
- Confusing Pellegrini-Stieda bursitis with general medial knee overuse bursitis and routing to M70.52 (left knee bursitis); M76.42 is the correct code when the diagnosis is specifically Pellegrini-Stieda or tibial collateral ligament bursitis.
- Billing amniotic or placental-derived injection CPT codes with M76.42 — CMS LCD A59764 lists M76.42 as a non-supporting diagnosis for those procedures, guaranteeing denial.
- Omitting a separate code for any concurrent MCL sprain or medial knee pathology when both conditions are documented and treated at the same encounter.
Clinical context
Source · Editorial summary grounded in 4 cited references ↓
M76.42 applies when a patient presents with left-sided tibial collateral bursitis confirmed as Pellegrini-Stieda disease or syndrome. Pellegrini-Stieda involves heterotopic calcification or reactive bursitis at the proximal tibial collateral ligament (MCL), typically following a medial knee sprain or contusion. The bursa between the tibial collateral ligament and the medial knee joint capsule becomes inflamed, producing medial knee pain, swelling, and restricted flexion. Confirm left-side laterality is explicitly documented before using M76.42; use M76.41 for the right leg or M76.40 when the side is unspecified.
M76.42 sits within the M76 enthesopathy block, so it codes the structural/inflammatory process rather than an acute injury. If bursitis is directly attributable to repetitive use, overuse, or pressure, the Excludes2 note at the M76 category level directs you to the M70 range instead — but Pellegrini-Stieda is a distinct post-traumatic calcific/bursitis entity, not a generic overuse bursitis, so M76.42 is the correct home when that specific diagnosis is documented. Enthesopathies of the ankle and foot are separately coded under M77.5-.
This code groups to MS-DRG 557 (Tendonitis, Myositis and Bursitis with MCC) or 558 (without MCC). Per CMS LCD A59764, M76.42 does not support medical necessity for amniotic or placental-derived product injections — flag this before ordering those procedures to avoid denial.
Sibling codes
Other billable codes under M76.4 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 4 cited references ↓
01What is the difference between M76.42 and M70.52?
02Is there a bilateral code for tibial collateral bursitis?
03Can M76.42 be used to support amniotic injection procedures?
04Which MS-DRGs does M76.42 map to?
05Does M76.42 require a 7th-character extension?
06What imaging is most useful for supporting an M76.42 diagnosis?
07When should I use M76.40 (unspecified) instead of M76.42?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
Mira AI Scribe
The Mira AI Scribe captures left-side laterality, symptom onset, history of prior medial knee trauma, imaging findings (calcification on X-ray or bursal effusion on MRI), and documentation of conservative treatments already attempted. This prevents fallback to the unspecified M76.40 and eliminates the audit risk of missing laterality on a billable enthesopathy claim.
See how Mira captures M76.42 documentation