Retain the observation method. Apply the original diameter and bone-exposure boundaries only when supported, label MRI adaptations, and never turn this macroscopic grade into autonomous treatment or prognosis.
{
"categories": [
{
"outcome_code": "0",
"state": "normal_intact_articular_cartilage",
"role": "conventional_normal_state"
},
{
"outcome_code": "I",
"state": "softening_and_swelling",
"surface": "may_appear_intact",
"tactile_probe": "usually_required_for_confident_original_grade"
},
{
"outcome_code": "II",
"state": "partial_thickness_fragmentation_or_fissuring",
"maximum_surface_diameter": "not_greater_than_0.5_inch_approximately_12.7_mm",
"subchondral_bone": "not_reached_or_exposed"
},
{
"outcome_code": "III",
"state": "deep_fragmentation_or_fissuring",
"maximum_surface_diameter": "greater_than_0.5_inch_approximately_12.7_mm",
"subchondral_bone": "extends_down_to_but_does_not_expose"
},
{
"outcome_code": "IV",
"state": "full_thickness_cartilage_erosion",
"subchondral_bone": "exposed",
"size_rule": "bone_exposure_overrides_the_II_III_diameter_boundary"
}
],
"applicability": {
"use_for": "Macroscopic severity description of one focal articular-cartilage lesion, originally by direct open or arthroscopic visualization and probing.",
"classification_unit": "one_named_articular_surface_lesion",
"required_inputs": [
"joint_and_side",
"articular_surface_and_location",
"assessment_modality",
"surface_integrity",
"softening_or_swelling_when_directly_probed",
"fissuring_or_fragmentation",
"maximum_lesion_diameter",
"subchondral_bone_exposure"
],
"outside_scope": [
"whole_joint_osteoarthritis_stage",
"symptom_or_pain_source",
"cartilage_repair_selection",
"lesion_stability",
"bone_marrow_or_meniscal_grading",
"calibrated_prognosis"
]
},
"modality_and_quality_gate": {
"original_reference_method": "Direct visualization with tactile probing. Grade I depends on softening and swelling that may not be visible without probe feedback.",
"MRI_rule": "When grading MRI, label the result modified Outerbridge on MRI and state the sequence and image quality. MRI can depict contour, depth and bone exposure but cannot directly reproduce tactile softening.",
"MRI_grade_I_guard": "Do not present Grade I as an original arthroscopic observation when only MRI signal alteration with an intact contour is available; return a low-confidence modified-MRI Grade I or describe the signal change without a definitive original grade.",
"adequacy_rule": "If cartilage thickness, surface, lesion diameter or the cartilage-bone interface is not adequately shown, preserve the unresolved adjacent grades rather than force a label.",
"joint_transfer_guard": "The original study concerned patellar chondromalacia. Later use across the knee and other joints is an adaptation; always retain joint, surface and method."
},
"original_classification_algorithm": [
{
"if": "intact_normal_cartilage_without_softening_swelling_fissure_or_erosion",
"output_code": "0"
},
{
"if": "softening_and_swelling_without_fragmentation_fissuring_or_bone_exposure",
"output_code": "I"
},
{
"if": "partial_thickness_fragmentation_or_fissuring_not_greater_than_12.7_mm_and_without_bone_exposure",
"output_code": "II"
},
{
"if": "deep_fragmentation_or_fissuring_greater_than_12.7_mm_reaching_toward_subchondral_bone_without_exposure",
"output_code": "III"
},
{
"if": "full_thickness_erosion_with_exposed_subchondral_bone",
"output_code": "IV"
}
],
"measurement_and_boundary_rules": {
"diameter_definition": "Use the maximum surface diameter of the chondral lesion. The original 0.5-inch boundary is approximately 12.7 mm; record the measured value and do not round solely to cross the boundary.",
"II_versus_III": "The original distinction is lesion surface diameter around 0.5 inch together with depth toward subchondral bone, not a generic 50-percent cartilage-depth threshold.",
"III_versus_IV": "Grade III reaches down to subchondral bone without exposing it; any unequivocal exposed subchondral bone is Grade IV regardless of lesion diameter.",
"worst_component_rule": "For a heterogeneous lesion, report the maximum supported grade and also record the area or diameter of each full-thickness component rather than allowing a tiny Grade IV focus to erase lesion extent.",
"multiple_lesion_rule": "Grade each anatomically separate lesion independently or explicitly state the aggregation rule; do not average Roman grades across surfaces."
},
"version_and_terminology_boundary": {
"original_outerbridge": "The original macroscopic system uses Grades I-IV; Grade 0 is the conventional normal state used in later descriptions.",
"modified_MRI_outerbridge": "Common MRI adaptations replace direct tactile findings with signal, contour and depth surrogates and may use percentage-depth bands. These thresholds are not identical to the original diameter-based II-III boundary and must be labeled as modified MRI criteria.",
"ICRS_guard": "ICRS cartilage grades are a separate depth-based framework with subgrades. Do not translate ICRS and Outerbridge numbers one-to-one without an explicit validated mapping.",
"no_ordinal_arithmetic": "Roman grades are categories. Do not average grades or treat a one-grade difference as a fixed biological interval."
},
"required_companion_report": [
"joint_side_and_exact_articular_surface",
"lesion_focal_or_diffuse_distribution",
"maximum_surface_diameter_and_estimated_area",
"cartilage_depth_or_full_thickness_component",
"subchondral_bone_exposure_and_reactive_change",
"unstable_flap_delamination_loose_body_or_opposing_kissing_lesion",
"associated_meniscal_ligamentous_alignment_or_osteoarthritic_findings",
"assessment_modality_and_whether_the_grade_is_original_arthroscopic_or_modified_MRI"
],
"management_and_risk_context": {
"management_rule": "Outerbridge grade does not prescribe debridement, marrow stimulation, grafting, cell implantation, osteotomy or arthroplasty. Treatment depends on symptoms, lesion size and containment, location, subchondral bone, alignment, meniscus, age, activity and the whole joint.",
"risk_rule": "Some cohorts associate Grades III-IV with worse outcomes after specific arthroscopic procedures, but the system has no validated per-grade probability of pain, progression or treatment success.",
"reliability_rule": "Published interobserver agreement is variable, especially around tactile Grade I and the II-III diameter boundary. Preserve uncertainty and the raw morphology."
},
"output_contract": [
"joint_side_surface_and_location",
"arthroscopy_open_visualization_or_modified_MRI",
"technical_adequacy",
"softening_swelling_surface_fissuring_fragmentation_and_depth",
"maximum_diameter_in_mm_and_area_when_available",
"subchondral_bone_exposure",
"Outerbridge_0_I_II_III_IV_or_adjacent_grade_uncertainty",
"associated_cartilage_and_joint_findings",
"no_treatment_or_numeric_prognosis_from_grade_alone"
],
"missing_input_behavior": [
"If tactile probing is unavailable, do not assert original Grade I from imaging alone.",
"If lesion diameter is unknown near the II-III boundary, return II-versus-III uncertainty and report depth and surface morphology.",
"If the cartilage-bone interface is obscured, do not distinguish III from IV with confidence.",
"If the MRI adaptation and its thresholds are unspecified, retain the observed morphology instead of silently applying an assumed modified scale."
],
"interpretation_limits": [
"Outerbridge is a macroscopic cartilage-lesion description, not a whole-joint osteoarthritis score or symptom attribution tool.",
"The classification has inconsistent reader reliability and limited prognostic evidence and does not guide treatment by itself.",
"MRI, arthroscopy and open inspection are not interchangeable observations; apparent grade changes across modalities may reflect method rather than biology."
],
"supporting_sources": [
{
"role": "original_classification",
"citation": "Outerbridge RE. J Bone Joint Surg Br. 1961;43-B:752-757",
"doi": "10.1302/0301-620X.43B4.752",
"pmid": "14038135"
},
{
"role": "classification_review_and_limits",
"citation": "Slattery and Kweon. Clin Orthop Relat Res. 2018;476:2101-2104",
"doi": "10.1007/s11999.0000000000000255",
"pmcid": "PMC6259817"
},
{
"role": "MRI_arthroscopy_validation",
"citation": "Potter et al. J Bone Joint Surg Am. 1998;80:1276-1284",
"doi": "10.2106/00004623-199809000-00005",
"pmid": "9759811"
}
],
"source_locator": "Outerbridge 1961, DOI 10.1302/0301-620X.43B4.752, original patellar chondromalacia series; Slattery and Kweon 2018, PMC6259817, History, Description, Validation, Limitations and Conclusions; Potter et al. 1998, PMID 9759811, prospective MRI-to-arthroscopy comparison."
}