Summary & Overview

HCPCS M1046: Knee Replacement Functional Outcome Below Threshold

HCPCS Level II code M1046 identifies patients with suboptimal functional outcomes one year (9–15 months) after knee joint replacement, defined as an Oxford Knee Score below 37 or a KOOS, JR. below 71. The code is used to flag postoperative patients with clinically relevant limitations in knee function and may be recorded in outpatient orthopedic follow-up or quality reporting contexts. Nationally, documenting patient-reported outcome measures (PROMs) like OKS and KOOS, JR. is increasingly important for quality measurement, value-based contracting, and benchmarking of joint replacement programs.

Key payers in this discussion include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will learn the clinical intent of the code, typical service setting, and the role of PROM thresholds represented by the code. The publication outlines how the code fits into postoperative outcome tracking and quality programs, summarizes likely payer interest, and presents context for interpreting the specified score cutoffs.

This summary covers the clinical definition and implications of the code, what types of services and sites commonly document it, and the national relevance for quality measurement and payer reporting. Data not available in the input: specific payer coverage policies, associated taxonomies, ICD-10 diagnoses, related codes, and service line details.

AetnaBlue Cross Blue ShieldCigna HealthUnitedHealthcareMedicareM1046HCPCS Level IIknee replacementOxford Knee ScoreKOOS JR.patient-reported outcomespostoperative assessmentorthopedicsquality measurement

Billing Code Overview

HCPCS Level II code M1046 indicates postoperative functional status measured at one year (9 to 15 months) after knee joint replacement, specifically when the Oxford Knee Score (OKS) is less than 37 or the Knee injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS, JR.) is less than 71. This code captures a clinical outcome metric reflecting suboptimal patient-reported function following knee arthroplasty.

Service type: Postoperative functional outcome assessment

Typical site of service: Orthopedic clinic or postoperative follow-up setting (outpatient)

Clinical & Coding Specifications

Clinical Context

A 67-year-old patient presents to the orthopedic joint replacement clinic for a one-year postoperative outcomes assessment following a primary total knee arthroplasty. The clinic visit falls within the 9–15 month postoperative window. The patient completes the Oxford Knee Score (OKS) and the Knee injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS, JR.) questionnaires as part of routine outcomes tracking. Results show an OKS < 37 or a KOOS, JR. < 71, indicating suboptimal functional recovery. The clinical workflow includes review of patient-reported outcome measures (PROMs), focused history for pain, stiffness, wound or neurovascular concerns, targeted physical examination of the operated knee, comparison with baseline and preoperative PROMs, and documentation of functional limitations. Based on findings, the orthopedic surgeon may order radiographs, evaluate for prosthetic complications (loosening, malalignment, infection), adjust postoperative rehabilitation plans, or refer to physical therapy or pain management. Billing for the outcomes threshold is reported with the HCPCS Level II code M1046 when the specified PROM thresholds are met at the one-year assessment.

Coding Specifications

Modifier	Description	When to Use
`22`	Increased Procedural Services	Use when documentation supports substantially greater work than typical for the service, for example extended visit to address complex postoperative complications.
`23`	Unusual Anesthesia	Use when general anesthesia is required for an otherwise non-anesthesia procedure; rarely applicable to PROM reporting but included for completeness.
`52`	Reduced Services	Use when the service was partially reduced or not fully performed.
`53`	Discontinued Procedure	Use when the procedure was started but discontinued due to extenuating circumstances.
`54`	Surgical Care Only	Use when only the surgical portion is billed by the surgeon and subsequent care is billed separately.
`55`	Postoperative Management Only	Use when only postoperative care (eg, follow-up PROM assessment and management) is billed by the provider.
`56`	Preoperative Management Only	Use when only preoperative management is billed by the provider.
`62`	Two Surgeons	Use when two surgeons work together as primary surgeons on complex cases.
`AS`	Ambulatory Surgery Center	Use to indicate services provided in an ambulatory surgery center setting when applicable.
`QK`	Medical Direction of Two, Three, or Four Individuals	Use for anesthesia reporting when the physician medically directs multiple individuals.

Taxonomy Code	Specialty	Notes
`207L00000X`	Orthopaedic Surgery	Primary specialty performing knee arthroplasty and postoperative follow-up.
`208800000X`	Physical Medicine & Rehabilitation	Specialists who evaluate functional outcomes and coordinate rehabilitation.
`2084P0800X`	Pain Medicine	Consultants for persistent postoperative pain management.
`207R00000X`	Sports Medicine	Providers managing postoperative mobility, activity resumption, and functional assessment.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`M17.0`	Bilateral primary osteoarthritis of knee	Common indication for total knee arthroplasty; postoperative PROMs assess residual functional limitation.
`M17.11`	Unilateral primary osteoarthritis, right knee	Typical preoperative diagnosis leading to knee replacement and subsequent 1-year outcome measurement.
`M17.12`	Unilateral primary osteoarthritis, left knee	As above for the contralateral side.
`T84.0X5A`	Infection and inflammatory reaction due to internal joint prosthesis, initial encounter	A postoperative complication that can lower PROM scores and trigger further evaluation.
`T84.02XA`	Mechanical complication of prosthetic joint, initial encounter	Includes loosening or wear that can cause poor functional outcomes reflected in OKS/KOOS, JR.
`M25.561`	Pain in right knee	Symptom commonly documented when PROMs are below threshold; guides clinical evaluation.
`M25.562`	Pain in left knee	As above for the left knee.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`27447`	Arthroplasty, knee, condyle and plateau; medial and lateral compartments with or without patellar resurfacing (total knee arthroplasty)	Primary surgical procedure whose outcomes are measured by the OKS and KOOS, JR. at one year.
`73562`	Radiologic examination, knee; without contrast, 3 views	Common imaging ordered during follow-up to evaluate prosthesis position, loosening, or periprosthetic changes when PROMs indicate problems.
`99213`	Office or other outpatient visit for the evaluation and management of an established patient, typically 15 minutes	Typical visit level for focused postoperative assessment and PROM review.
`99304`	Nursing facility admission services, init. hospital care (example of extended evaluation)	Used when patients in institutional settings require PROM collection and follow-up assessments.
`97110`	Therapeutic exercises to develop strength, endurance, range of motion and flexibility (15 minutes)	Frequently used in postoperative rehabilitation when functional scores are below expected thresholds.