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MS-DRG 400 · MDC 08 · Surgical

MS-DRG 400: Knee Procedures with Principal Diagnosis of Infection

Reviewed by QuickIntell RCM Editorial Team · Last reviewed

Data effective
Data currency: IPPS Table 5 FY2027 final rule (effective October 1, 2026); Definitions Manual v44 (effective October 1, 2026). Next CMS release: April 1, 2027 (v44.1 mid-year update), then the FY2028 final rule in August 2027.

Key facts for DRG 400

FY2027 relative weight
2.0250
Higher than 63% of all MS-DRGs
Change vs FY2026
New DRG
No FY2026 weight
Geometric mean LOS
5.8 days
Arithmetic mean 6.9 days
MDC
08
Diseases and Disorders of the Musculoskeletal System and Connective Tissue
Severity level
single severity level
Transfer policy
Post-acute transfer DRG
Special-pay DRG

TL;DR

MS-DRG 400 is a surgical group in MDC 08 (Diseases and Disorders of the Musculoskeletal System and Connective Tissue) at a single-severity group of its family. CMS assigns it a FY2027 relative weight of 2.0250 with a geometric mean length of stay of 5.8 days and an arithmetic mean of 6.9. It is new for FY2027, so there is no prior-year weight to compare. That weight is higher than 63% of all surgical and medical MS-DRGs. CMS does not split this group by severity. The v44 Definitions Manual assigns it through 270 operating room procedures codes and 56 principal diagnosis codes.

What changed from FY2026 to FY2027

DRG 400 is new in the v44 grouper effective October 1, 2026, so there is no FY2026 weight to compare. Review the FY2027 final rule Table 6 series for the code moves that created it and confirm that your encoder and contract modeling have loaded v44.

CC and MCC family

DRG 400 stands alone: CMS does not split this base group by CC or MCC severity, so complication documentation does not move the assignment, although it still affects quality and risk-adjustment reporting.

Grouper logic (v44 Definitions Manual)

Operating Room Procedures: 270 ICD-10 codes drive assignment to this group; the first 12 are shown.

Operating Room Procedures codes assigned to DRG 400 (sample)
ICD-10 codeDescription
0M9N40ZDrainage of Right Knee Bursa and Ligament with Drainage Device, Percutaneous Endoscopic Approach
0M9P40ZDrainage of Left Knee Bursa and Ligament with Drainage Device, Percutaneous Endoscopic Approach
0MQN0ZZRepair Right Knee Bursa and Ligament, Open Approach
0MQN3ZZRepair Right Knee Bursa and Ligament, Percutaneous Approach
0MQN4ZZRepair Right Knee Bursa and Ligament, Percutaneous Endoscopic Approach
0MQP0ZZRepair Left Knee Bursa and Ligament, Open Approach
0MQP3ZZRepair Left Knee Bursa and Ligament, Percutaneous Approach
0MQP4ZZRepair Left Knee Bursa and Ligament, Percutaneous Endoscopic Approach
0MRN07ZReplacement of Right Knee Bursa and Ligament with Autologous Tissue Substitute, Open Approach
0MRN0JZReplacement of Right Knee Bursa and Ligament with Synthetic Substitute, Open Approach
0MRN0KZReplacement of Right Knee Bursa and Ligament with Nonautologous Tissue Substitute, Open Approach
0MRN47ZReplacement of Right Knee Bursa and Ligament with Autologous Tissue Substitute, Percutaneous Endoscopic Approach

Principal Diagnosis: 56 ICD-10 codes drive assignment to this group; the first 12 are shown.

Principal Diagnosis codes assigned to DRG 400 (sample)
ICD-10 codeDescription
A1802Tuberculous arthritis of other joints
A5442Gonococcal arthritis
M00061Staphylococcal arthritis, right knee
M00062Staphylococcal arthritis, left knee
M00069Staphylococcal arthritis, unspecified knee
M00161Pneumococcal arthritis, right knee
M00162Pneumococcal arthritis, left knee
M00169Pneumococcal arthritis, unspecified knee
M00261Other streptococcal arthritis, right knee
M00262Other streptococcal arthritis, left knee
M00269Other streptococcal arthritis, unspecified knee
M00861Arthritis due to other bacteria, right knee

Documentation and denial exposure

As a surgical DRG, assignment depends on a qualifying operating-room procedure being coded from the operative report; a missing or non-OR procedure code drops the stay into a medical DRG in MDC 08 with a lower weight. Because this family has no severity split, review risk concentrates on medical-necessity of the admission itself and on the two-midnight benchmark. Typical inpatient denial codes for this group: CARC 16 (claim lacks information needed to group the stay), CARC 50 (the admission or procedure is judged not medically necessary), CARC 97 (a service is bundled into the DRG payment).

How QuickIntell uses DRG 400 data

QuickCode groups inpatient encounters against the current v44 logic, flags CC and MCC candidates that lack supporting documentation, and shows the weight difference across the family before the claim drops. QuickScribe captures the attending's language that supports severity, and QuickRCM works DRG-validation denials with the grouper evidence attached.

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Frequently asked questions — DRG 400

What is MS-DRG 400?

MS-DRG 400 is "Knee Procedures with Principal Diagnosis of Infection", a surgical Medicare Severity Diagnosis-Related Group in MDC 08, Diseases and Disorders of the Musculoskeletal System and Connective Tissue. Medicare pays inpatient stays grouped here at the hospital's base rate multiplied by the DRG relative weight.

What is the FY2027 relative weight for DRG 400?

The FY2027 relative weight is 2.0250 (IPPS final rule Table 5, effective October 1, 2026). The DRG is new for FY2027.

What is the average length of stay for DRG 400?

CMS reports a geometric mean length of stay of 5.8 days and an arithmetic mean of 6.9 days for FY2027. The geometric mean is used for transfer-payment calculations.

What documentation supports the severity level of DRG 400?

DRG 400 has no CC or MCC sibling, so secondary-diagnosis capture does not change the group or its weight. Review effort belongs instead on the principal diagnosis sequencing and the procedure codes that place the stay in this group, and on medical necessity of the inpatient admission itself under the two-midnight benchmark, which is where denials for single-severity groups concentrate.

Which codes group to DRG 400?

The v44 Definitions Manual lists 270 operating room procedures codes and 56 principal diagnosis codes for this group. Examples from the operating room procedures list: 0M9N40Z (Drainage of Right Knee Bursa and Ligament with Drainage Device, Percutaneous Endoscopic Approach); 0M9P40Z (Drainage of Left Knee Bursa and Ligament with Drainage Device, Percutaneous Endoscopic Approach); 0MQN0ZZ (Repair Right Knee Bursa and Ligament, Open Approach); 0MQN3ZZ (Repair Right Knee Bursa and Ligament, Percutaneous Approach).

Is DRG 400 a post-acute transfer DRG?

Yes. CMS flags DRG 400 under the post-acute care transfer policy, so a discharge to a qualifying post-acute setting before the geometric mean length of stay is paid a per-diem amount rather than the full DRG payment. It is also a special-pay DRG.

Sources

Every figure on this page is taken from the CMS publications below, as released by the Centers for Medicare & Medicaid Services. Projection built 2026-10-01. Verify against the primary file before billing or contracting decisions.

Disclaimer

This page is an operational reference compiled from the CMS IPPS FY2027 final rule (Table 5) and the v44 ICD-10 MS-DRG Definitions Manual. Relative weights are national factors; actual payment depends on each hospital's wage-adjusted base rate, add-ons, outliers and transfer adjustments. Nothing here is legal, clinical or billing advice; verify grouping against your encoder and the published CMS files.