Erin Farrelly, M.D., M.S.
Erin Farrelly, M.D., M.S. is an Orthopaedic Surgery Physician in San Marcos, CA, registered under NPI 1922354422. This provider registers 2 separate taxonomy codes, which usually means they practise across more than one recognised specialty.
Getting there
The practice address on file is 277 RANCHEROS DR STE 101, San Marcos, CA 92069. We have not yet mapped what surrounds this office — parking, transit, and nearby pharmacies are added as our data collection reaches each location.
Credentials and Medicare
| Licence | State | Specialty |
|---|---|---|
| A121731 | CA | Orthopaedic Surgery Physician primary |
| A121731 | CA | Orthopaedic Trauma Physician |
This provider holds licence A121731 issued in CA. A licence number in NPPES reflects what was filed at registration — it does not confirm the licence is still active today.
- Status
- Approved
- Provider type
- Practitioner - Orthopedic Surgery
- PAC ID
- 4284888546
Enrolled in Medicare 3 times, across 3 states:
| State | Enrollment ID | Provider type |
|---|---|---|
| California | I20130214000173 | Practitioner - Orthopedic Surgery |
| Maryland | I20240620003877 | Practitioner - Orthopedic Surgery |
| District of Columbia | I20251210001998 | Practitioner - Orthopedic Surgery |
Medicare enrolment is recorded as approved under the provider type Practitioner - Orthopedic Surgery. There are 3 separate enrolment records across 3 states (CA, MD, DC). Multiple enrolments usually mean the provider bills Medicare from more than one practice location, or has kept an earlier enrolment after moving. Each record carries its own enrolment ID, listed above. Being enrolled means the provider can bill Medicare; it does not tell you whether they are currently accepting new Medicare patients. Call the office to confirm.
What Orthopaedic Surgery covers
An orthopaedic surgeon is trained in the preservation, investigation and restoration of the form and function of the extremities, spine and associated structures by medical, surgical and physical means. An orthopaedic surgeon is involved with the care of patients whose musculoskeletal problems include congenital deformities, trauma, infections, tumors, metabolic disturbances of the musculoskeletal system, deformities, injuries and degenerative diseases of the spine, hands, feet, knee, hip, shoulder and elbow in children and adults. An orthopaedic surgeon is also concerned with primary and secondary muscular problems and the effects of central or peripheral nervous system lesions of the musculoskeletal system. NUCC Health Care Provider Taxonomy, code 207X00000X
All registered taxonomy codes
This provider registers 2 taxonomy codes. The primary code is what appears on most claims; the others record additional recognised specialties.
| Code | Specialty | Licence | State | |
|---|---|---|---|---|
| 207X00000X | Orthopaedic Surgery Physician | A121731 | CA | primary |
| 207XX0801X | Orthopaedic Trauma Physician Orthopaedic Trauma | A121731 | CA |
The taxonomy records how the provider classifies their own practice. It does not confirm which conditions they currently treat, whether they are accepting new patients, or which insurance they take — call the office for that.
Full NPPES record
An NPI-1 identifies a single person. It stays with the clinician for life, even if they move practice or change state, which is why the address on file can lag behind where they actually work today.
| NPI | 1922354422 valid check digit |
|---|---|
| Entity type | Individual (NPI-1) |
| Enumeration date | Aug 2, 2012 |
| Last updated | Jan 6, 2021 |
| Status | Active |
| Sole proprietor | No |
| Credential | M.D., M.S. |
| Practice address |
277 RANCHEROS DR STE 101 San Marcos, CA 92069 (760) 750-1902 Fax (760) 750-1906 |
Number check
How the check works, step by step
Every NPI carries a Luhn check digit — the same scheme used on credit cards. CMS prefixes the number with 80840 before computing it, which marks it as a US health identifier.
| Digit | 8 | 0 | 8 | 4 | 0 | 1 | 9 | 2 | 2 | 3 | 5 | 4 | 4 | 2 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Doubled? | — | ×2 | — | ×2 | — | ×2 | — | ×2 | — | ×2 | — | ×2 | — | ×2 |
| Value | 8 | 0 | 8 | 8 | 0 | 2 | 9 | 4 | 2 | 6 | 5 | 8 | 4 | 4 |
Sum = 68 · next multiple of 10 = 70 · check digit = 2 · actual last digit = 2
A valid check digit only means the number is well-formed. It does not mean the provider is licensed, active, or in good standing — those are separate questions answered by the sections above.