Glossary · Anatomy
Patella
The patella is the largest sesamoid bone in the body, embedded within the quadriceps tendon and sitting anterior to the knee joint. It protects the femoral condyles and increases the mechanical advantage of the quadriceps during knee extension.
Verified May 8, 2026 · 9 sources ↓
Definition
Source · Editorial summary grounded in 9 cited references ↓
The patella is a triangular, flat bone that forms the anterior wall of the knee joint. Its posterior surface is covered by the thickest articular cartilage in the human body, divided into medial and lateral facets that articulate with the corresponding femoral trochlea. The proximal pole receives the quadriceps tendon, while the distal pole gives origin to the patellar ligament, which inserts on the tibial tubercle. This arrangement converts the patella into a pulley, amplifying extensor force by up to 50% at certain angles of flexion.
Vascularity is supplied by a periarticular anastomotic ring derived from the geniculate branches of the popliteal artery. Because the central third of the bone is relatively avascular, certain fracture patterns and surgical approaches carry a risk of avascular necrosis. The patella tracks within the trochlear groove; malalignment—whether from dysplasia, muscle imbalance, or soft-tissue tightness—produces the spectrum of patellofemoral disorders coded under M22.
Clinically relevant anatomic variants include bipartite patella (a developmental accessory ossification center, most often superolateral) and patella alta or baja (abnormally high or low patellar position). Both variants can mimic fracture on imaging and affect how surgeons approach implant sizing during total knee arthroplasty, particularly when patellar resurfacing is planned.
Why it matters
Accurate identification of the patella as the anatomic site drives the entire coding chain: the wrong body-part selection in ICD-10-PCS changes reimbursement, and failing to distinguish a patellar fracture (S82.0xx) from a patellofemoral disorder (M22) or a bipartite patella can trigger a medical-necessity denial or an NCCI edit conflict. In total knee arthroplasty, the decision to resurface the patella determines whether CPT 27447 (with or without patella resurfacing) is the complete descriptor or whether a separate patella arthroplasty code applies—an error that auditors flag routinely.
Common mistakes
Where people most often go wrong with this concept.
Source · Editorial brief grounded in cited references ↓
- Coding a bipartite patella as a fracture (S82.0xx) instead of a congenital variant, which misrepresents acuity and can trigger inappropriate fracture-care reimbursement.
- Selecting unspecified-laterality codes (e.g., M22.2X9 or S82.009x) when the operative report clearly documents right or left knee, resulting in avoidable specificity-based denials.
- Reporting a separate patellar arthroplasty code alongside CPT 27447 when patellar resurfacing is already included in the total knee arthroplasty descriptor, creating an unbundling vulnerability.
- Using M22 disorder codes for acute traumatic patellar dislocation—acute injuries require S-series codes (e.g., S83.0xx), while M22.0 applies only to recurrent dislocation.
- Failing to append the correct 7th-character encounter qualifier (A = initial, D = subsequent, S = sequela) to patellar fracture codes, which renders the ICD-10-CM code technically invalid and delays payment.
Related codes
Codes commonly involved when this concept appears in practice.
CPT
- 27520 $369.75Closed treatment of a patellar fracture without manipulation — immobilization only, no bone repositioning or surgical fixation.
- 27524 $705.09Open surgical repair of a patellar fracture involving internal fixation hardware, with optional partial or complete removal of the kneecap and repair of the surrounding soft tissue structures.
- 27438 $781.92Patellar arthroplasty with insertion of a prosthetic implant to resurface the kneecap.
- 27447 $1,159.35Knee replacement surgery addressing both the medial and lateral tibiofemoral compartments, with or without resurfacing of the patella.
- 27486 $1,274.91Revision of a total knee arthroplasty involving a single component, performed with or without the use of donor bone graft material.
- 27487 $1,574.52Revision total knee arthroplasty with replacement of both the femoral and tibial components, with or without the use of allograft tissue.
- 27488 $1,099.89Removal of a knee prosthesis — including total knee components and methylmethacrylate cement — with or without insertion of a spacer at the same operative session.
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 9 cited references ↓
01What is the difference between M22 and S82.0xx codes for the patella?
02Does patellar resurfacing require a separate CPT code when reported with a total knee arthroplasty?
03How should a bipartite patella be coded if it is asymptomatic and found incidentally on imaging?
04Which ICD-10-PCS code applies to open surgical repair of a patellar fracture with internal fixation?
05When should modifier 50 be used for bilateral patellar procedures?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01jnjmedtech.comhttps://www.jnjmedtech.com/system/files/pdf/163477-201222%20DSUS%20Depuy%20Patella%20Fracture%20Coding%20Guide.pdf
- 02aapc.comhttps://www.aapc.com/codes/icd-10-codes/M22
- 03aapc.comhttps://www.aapc.com/codes/cpt-codes/27520
- 04outsourcestrategies.comhttps://www.outsourcestrategies.com/blog/patellofemoral-syndrome-coding-and-billing-guidelines/
- 05aapc.comhttps://www.aapc.com/blog/35663-combat-common-denials-in-orthopedic-coding/
- 06icdcodes.aihttps://icdcodes.ai/diagnosis/patella-pain/documentation
- 07findacode.comhttps://www.findacode.com/newsletters/aha-coding-clinic/icd/patella-resurfacing-tibial-liner-exchange-I103028.html
- 08CMS ICD-10-PCS Official Guidelines for Coding and Reporting
- 09AAOS Musculoskeletal Coding Resource
Mira AI Scribe
When Mira's scribe layer captures documentation involving the patella, it flags several downstream coding decisions in real time. **Laterality lock:** Any mention of 'right' or 'left' knee locks the laterality digit and prevents unspecified-laterality defaults (e.g., forces M22.2X1 or M22.2X2 rather than M22.2X9). **Acute vs. chronic differentiation:** Language such as 'acute dislocation,' 'fell,' or 'trauma' routes to S-series codes with a 7th-character encounter qualifier prompt. Language such as 'recurrent,' 'chronic,' or 'history of' routes to M22.0x or M22.1x. **Resurfacing flag in TKA notes:** When the operative note contains 'patellar resurfacing' or 'patella cemented,' the scribe surfaces a reminder that CPT 27447 already encompasses patellar resurfacing and that a separate arthroplasty code would create an unbundling conflict. **Fracture specificity prompt:** For patellar fracture documentation, the scribe checks for fracture pattern (comminuted, transverse, etc.), open vs. closed status, and encounter type to populate the full S82.0xx code to the required digit length—incomplete codes are flagged before claim submission. **Bipartite patella alert:** If imaging findings reference 'bipartite' or 'accessory ossification,' the scribe flags the risk of miscoding as fracture and suggests clinical correlation documentation to support a congenital-variant classification.
See Mira's approach