M1045 HCPCS: Reimbursement & Policy Benchmarks

HCPCS Level II code M1045 designates a standardized functional outcome measure for patients roughly one year after knee replacement. It reports achievement of a threshold Oxford Knee Score (OKS ≥ 37) or KOOS, JR. score (≥ 71) between 9 and 15 months postoperatively. Nationally, such patient-reported outcome metrics are increasingly used to evaluate surgical quality, inform value-based contracting, and support performance reporting across hospitals and orthopedics practices.

Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find context on the clinical intent of the measure, implications for postoperative outcome monitoring, and how the code is used in payer reporting and quality programs. The publication outlines common benchmarking uses, policy considerations relevant to coverage and performance measurement, and the clinical context behind OKS and KOOS, JR. scoring thresholds.

This summary is intended for clinicians, billing professionals, and policy analysts seeking a concise national overview of HCPCS Level II code M1045, including practical context for its role in outcome tracking and quality measurement.

Billing Code Overview

HCPCS Level II code M1045 indicates a postoperative functional status assessment for knee replacement patients, defined as an Oxford Knee Score (OKS) at one year (9 to 15 months) of greater than or equal to 37, or a Knee injury and Osteoarthritis Outcome Score Joint Replacement (KOOS, JR.) greater than or equal to 71.

Service type: Postoperative functional outcome measurement
Typical site of service: Orthopedic clinic or outpatient surgical follow-up (assessment conducted in a clinical outpatient setting)

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Clinical Context

A typical patient is a 65-year-old who underwent primary total knee arthroplasty (TKA) for end-stage osteoarthritis 12 months prior and presents for a routine one-year postoperative outcome assessment. The orthopedic clinic schedules the patient for a focused follow-up visit to document functional outcome measures required for quality reporting and registry submission. During the visit the clinician or trained staff administers the Oxford Knee Score (OKS) or the Knee injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS, Jr.). The patient completes the validated questionnaire in clinic or via a secure patient portal between 9 and 15 months postoperatively. A score of OKS ≥ 37 or KOOS, Jr. ≥ 71 documents an acceptable functional outcome at one year and is recorded in the medical record. The encounter includes review of wound healing, range of motion, pain level, and any complications (infection, instability, stiffness). Results are entered into the patient’s chart and, if applicable, submitted to registries or payors for performance measurement. Typical site of service is an outpatient orthopedic clinic or ambulatory surgery follow-up clinic. Common modifiers that may accompany the billing for related services include 22, 23, 52, 53, 54, 55, 56, 62, AS, CO, CQ, , , , , depending on payer and circumstance.

Coding Specifications

Modifier	Description	When to Use
`22`	Increased procedural services	Use when documentation supports substantially greater work during an associated service (e.g., complex assessment or protracted counseling during the follow-up visit).
`23`	Unusual anesthesia	Use if the patient required general anesthesia for an associated procedure during the encounter (rare for this assessment alone).
`52`	Reduced services	Use when the assessment was partially performed or truncated (e.g., incomplete questionnaire due to patient inability).
`53`	Discontinued procedure	Use if the visit or planned assessment was started but terminated before completion for unforeseen circumstances.
`54`	Surgical care only	Use when the billing relates only to the surgeon’s intraoperative care and postoperative evaluation is billed separately.
`55`	Postoperative management only	Use when only postoperative follow-up was provided by a different clinician who bills separately.
`56`	Preoperative management only	Use when only preoperative evaluation was provided by another clinician.
`62`	Two surgeons	Use when two surgeons with different specialties share the procedure and documentation supports distinct roles for the encounter.
`AS`	Ambulatory surgical center facility	Use to designate services provided in an ASC setting when required by payor.
`CQ`	Service furnished under a structured data collection platform	Use when outcomes are collected under a qualified clinical data registry or CMS-approved program.
`QK`	Medical direction of two, three, or four assistants	Use when the surgeon medically directs multiple assistants during an associated surgical episode.
`QX`	Assistant surgeon, assistant at surgery	Use to indicate a qualified assistant at surgery for the associated operative episode.
`QY`	Surgical assistant who is a physician assistant	Use when a physician assistant served as the surgical assistant.

Taxonomy Code	Specialty	Notes
`208800000X`	Orthopaedic Surgery	Primary specialty performing TKA and postoperative outcome assessment.
`207L00000X`	Physical Medicine & Rehabilitation	Performs functional assessments and coordinates PROMs-based rehabilitation.
`2084P0800X`	Orthopaedic Surgery, Knee	Subspecialty focus on knee arthroplasty and outcomes.
`261QM0800X`	Physical Therapist	Often administers and documents PROMs such as OKS/KOOS, Jr. during rehabilitation visits.
`3336C0003X`	Nurse Practitioner	Provides postoperative clinic follow-up and documents outcome scores.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`M17.11`	Unilateral primary osteoarthritis, right knee	Primary indication for total knee arthroplasty and subsequent one-year functional outcome assessment.
`M17.12`	Unilateral primary osteoarthritis, left knee	Same clinical relevance for left-sided primary TKA outcome measurement.
`M17.0`	Bilateral primary osteoarthritis of knee	Indicates patients with bilateral disease who may have staged or simultaneous TKAs and require outcome tracking.
`M17.9`	Osteoarthritis of knee, unspecified	Used when laterality is not specified but the patient underwent knee arthroplasty.
`Z96.651`	Presence of right artificial knee joint	Postoperative code indicating an artificial knee joint present, relevant for registry and outcome documentation.
`Z96.652`	Presence of left artificial knee joint	Same relevance for the left knee.
`T84.02XA`	Dislocation of prosthetic joint, initial encounter	Relevant as a complication that would prompt outcome assessment and potentially lower OKS/KOOS, Jr. scores.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`99213`	Office or other outpatient visit for the evaluation and management of an established patient, typically 15 minutes	Common E/M code used for routine one-year postoperative follow-up where PROMs are reviewed and documented.
`99214`	Office or other outpatient visit for the evaluation and management of an established patient, typically 25 minutes	Used when the visit requires moderate to high complexity medical decision making or prolonged counseling related to postoperative care and outcome assessment.
`99024`	Postoperative follow-up visit, normally included in the global service, related to the recovery from the procedure	Used when the visit is considered routine postoperative global care and not separately billable by some payors; documentation must support separate billing if submitted.
`99070`	Supplies and materials (e.g., for remote or electronic PROMs collection)	Used when additional non-covered supplies or materials are provided to collect outcome measures if the payer allows.
`96127`	Brief emotional/behavioral assessment (e.g., depression inventory)	Occasionally used adjunctively when brief standardized questionnaires relevant to recovery are administered during the visit.

OpenPayer

Summary & Overview

HCPCS M1045: Postoperative Knee Replacement Functional Outcome Assessment