Herring Modified Herring lateral pillar classification of Legg-Calve-Perthes disease

{
  "categories": [
    {
      "outcome_code": "A",
      "lateral_pillar_involvement": "none",
      "retained_height": "full",
      "density_or_ossification_change": "none_required"
    },
    {
      "outcome_code": "B",
      "lateral_pillar_involvement": "present",
      "retained_height": "greater_than_50_percent",
      "border_features": "absent"
    },
    {
      "outcome_code": "B/C",
      "lateral_pillar_involvement": "present",
      "retained_height": "borderline_at_or_above_50_percent",
      "border_features": "at_least_one_modified_2004_border_morphology"
    },
    {
      "outcome_code": "C",
      "lateral_pillar_involvement": "present",
      "retained_height": "less_than_50_percent"
    }
  ],
  "applicability": {
    "use_for": "Radiographic prognostic classification of a hip with confirmed Legg-Calve-Perthes disease when the capital femoral epiphysis is in the fragmentation stage.",
    "classification_unit": "one_affected_hip",
    "required_inputs": [
      "side",
      "true_AP_pelvis_or_hip_radiograph",
      "fragmentation_stage_confirmed",
      "lateral_pillar_height_relative_to_its_expected_or_central_pillar_height",
      "lateral_pillar_width_and_ossification_quality",
      "age_at_symptom_onset"
    ],
    "useful_companion_inputs": [
      "disease_stage_and_duration",
      "femoral_head_extrusion",
      "hip_range_of_motion",
      "containment_status",
      "contralateral_hip_if_usable",
      "prior_treatment"
    ],
    "outside_scope": [
      "initial_or_necrotic_stage_before_fragmentation",
      "reossification_or_healed_stage",
      "other_causes_of_femoral_head_osteonecrosis",
      "treatment_selection_from_grade_alone",
      "prediction_in_children_older_than_the_validated_age_range_without_explicit_caution"
    ]
  },
  "anatomic_and_measurement_model": {
    "epiphyseal_partition": "On the true AP view, conceptualize medial, central and lateral pillars; the lateral pillar is approximately the lateral 15-30 percent of the capital femoral epiphysis.",
    "comparison_rule": "Assess the maximum retained height of the lateral pillar during fragmentation against its expected height and the central pillar, using the complete contour rather than a single convenient pixel column.",
    "percent_rule": "Record the estimated retained-height percentage and the image on which it was judged. Preserve the raw observation because the 50-percent boundary and B/C morphology can change the output.",
    "unit_guard": "The modified primary description uses thin or narrow pillar morphology. Do not hard-code a numeric width from secondary renderings whose millimetre/centimetre units conflict."
  },
  "stage_and_quality_gate": {
    "valid_stage": "Assign the lateral-pillar group only once fragmentation permits stable assessment; earlier radiographs can underestimate final involvement.",
    "projection": "Require a true AP projection without rotation or foreshortening sufficient to compare pillar height. Frog-leg views may add morphology but do not replace the true AP classification view.",
    "temporal_instability": "Initial films underestimate severity in a substantial minority and the category may evolve over months. Record study date and disease stage; when not yet stable, report provisional or unclassifiable and recommend interval specialist reassessment rather than false certainty.",
    "bilateral_rule": "Classify each hip separately. A contralateral hip is not a dependable internal control when disease is bilateral or the comparison is otherwise abnormal."
  },
  "modified_2004_border_morphologies": [
    {
      "phenotype": "thin_or_narrow_but_relatively_tall",
      "rule": "more_than_50_percent_height_is_retained_but_the_lateral_pillar_is_unusually_thin_or_narrow"
    },
    {
      "phenotype": "poorly_ossified",
      "rule": "at_least_about_50_percent_height_is_present_but_ossification_is_poor_or_indistinct"
    },
    {
      "phenotype": "exactly_half_height",
      "rule": "the_lateral_pillar_is_depressed_to_about_exactly_50_percent_of_the_central_pillar_height"
    }
  ],
  "classification_order": [
    {
      "step": 1,
      "if": "lateral_pillar_uninvolved_with_full_height",
      "output_code": "A"
    },
    {
      "step": 2,
      "if": "retained_height_less_than_50_percent",
      "output_code": "C"
    },
    {
      "step": 3,
      "if": "retained_height_at_or_above_50_percent_and_any_modified_border_morphology_is_present",
      "output_code": "B/C"
    },
    {
      "step": 4,
      "if": "retained_height_greater_than_50_percent_without_a_border_morphology",
      "output_code": "B"
    }
  ],
  "decisive_boundaries": {
    "exact_50_percent": "About exactly 50 percent retained height belongs to the B/C border group when the pillar is depressed to the central-pillar half-height boundary; B requires more than 50 percent without a B/C feature, while C requires less than 50 percent.",
    "height_versus_ossification": "Height alone does not separate B from B/C. Thin width or poor ossification can move an otherwise greater-than-half pillar into B/C.",
    "A_versus_B": "Any genuine lateral-pillar involvement or height loss excludes A; A has full preserved height and no required density change.",
    "uncertain_boundary": "If the study cannot distinguish just above, approximately equal to, or just below one-half height, return the competing B, B/C or C states with the missing measurement instead of rounding into a definitive label."
  },
  "prognostic_evidence": {
    "endpoint": "Stulberg femoral-head sphericity and congruence at skeletal maturity in the multicenter outcome cohort, not immediate symptoms or guaranteed individual disability.",
    "group_distributions": [
      {
        "outcome_code": "A",
        "Stulberg_I_or_II": "100_percent"
      },
      {
        "outcome_code": "B",
        "Stulberg_I_or_II": "67_percent",
        "Stulberg_III": "27_percent",
        "Stulberg_IV_or_V": "6_percent"
      },
      {
        "outcome_code": "B/C",
        "Stulberg_I_or_II": "28_percent",
        "Stulberg_III": "43_percent",
        "Stulberg_IV_or_V": "30_percent",
        "rounding_note": "published_percentages_round_to_approximately_101_percent"
      },
      {
        "outcome_code": "C",
        "Stulberg_II": "13_percent",
        "Stulberg_III": "52_percent",
        "Stulberg_IV_or_V": "35_percent"
      }
    ],
    "interpretation_guard": "These are cohort distributions from historical treatment-era data. They are not calibrated personal probabilities and must not be presented as certainty for an individual hip."
  },
  "age_and_treatment_context": {
    "independent_prognostic_inputs": [
      "age_at_onset",
      "modified_Herring_group"
    ],
    "multicenter_2004_findings": "Among children with onset after age 8 years, groups B and B/C had better outcomes after operative containment in the study; group B at age 8 or younger had similarly favorable outcomes with operative and nonoperative care. Group C had the least favorable results and no demonstrated operative-versus-nonoperative difference in that cohort.",
    "younger_age_guard": "The prospective study found no significant treatment effect for onset at 8 years or younger or skeletal age 6 years or younger; this is a group-level result, not permission to ignore extrusion, motion loss or disease evolution.",
    "current_POSNA_boundary": "Current care integrates chronological and skeletal age, stage, radiographic severity, extrusion, range of motion and containment feasibility. Containment is generally considered early, sometimes before a stable lateral-pillar category can yet be assigned.",
    "safety_rule": "Never generate or withhold bracing, osteotomy, activity restriction, follow-up timing or salvage treatment from the Herring code alone. Group C is not an automatic no-treatment label, and group A is not an automatic discharge rule."
  },
  "reliability_and_limits": {
    "modified_system_results": "In the 2004 reliability study, interobserver agreement was 81 percent then 85 percent with weighted kappa 0.71 then 0.79; intraobserver exact agreement was 77 percent with weighted kappa 0.81 and generalizability coefficient 0.91.",
    "maturation_limit": "The category can worsen as fragmentation progresses; the final stable classification may require repeated imaging, with roughly one-third changing category in reported review data.",
    "age_limit": "Evidence is centered on childhood LCP disease and the system may not be valid after age 12; explicitly flag extrapolation.",
    "scope_limit": "The code captures lateral-pillar preservation, not whole-head extrusion, hinge abduction, range of motion, skeletal maturity, symptoms or patient goals."
  },
  "agent_output_contract": [
    "system_name_and_modified_2004_version",
    "right_or_left_hip",
    "study_date_and_disease_stage",
    "true_AP_technical_adequacy",
    "lateral_pillar_retained_height_and_comparator",
    "thin_width_or_poor_ossification_border_features",
    "definitive_or_provisional_A_B_BC_C_output",
    "age_at_onset_and_current_age",
    "prognostic_context_as_group_level_not_personal_probability",
    "extrusion_range_of_motion_and_containment_inputs_if_known",
    "uncertainty_and_next_required_input",
    "no_grade_only_management_warning"
  ],
  "missing_input_behavior": [
    "If fragmentation is not confirmed, do not assign A, B, B/C or C; return stage not yet classifiable.",
    "If the AP view is not technically adequate, return unclassifiable and request an adequate true AP study.",
    "If height is near 50 percent but width and ossification are not evaluable, preserve B/B-C/C uncertainty and request the missing morphology rather than forcing a grade.",
    "If age at onset is unknown, report morphology but withhold age-stratified prognosis and treatment-context statements.",
    "If serial imaging shows progression, retain dates and supersede the provisional category explicitly rather than overwriting its history."
  ],
  "supporting_sources": [
    {
      "role": "modified_classification_and_reliability",
      "citation": "Herring et al. JBJS Am. 2004;86:2103-2120",
      "doi": "10.2106/00004623-200410000-00001",
      "pmid": "15466719"
    },
    {
      "role": "prospective_treatment_and_outcome_context",
      "citation": "Herring et al. JBJS Am. 2004;86:2121-2134",
      "doi": "10.2106/00004623-200410000-00002",
      "pmid": "15466720"
    },
    {
      "role": "open_classification_review",
      "citation": "Kollitz and Gee. Clin Orthop Relat Res. 2013",
      "pmcid": "PMC3676599"
    },
    {
      "role": "current_specialty_context",
      "citation": "POSNA Legg-Calve-Perthes Disease Study Guide",
      "url": "https://posna.org/physician-education/study-guide/legg-calve-perthes-disease"
    }
  ],
  "source_locator": "Herring et al. JBJS Am 2004 Part I, PMID 15466719 and DOI 10.2106/00004623-200410000-00001, modified groups and reliability; Part II, PMID 15466720 and DOI 10.2106/00004623-200410000-00002, age-treatment-outcome interaction; Kollitz and Gee 2013, PMC3676599, Tables 1-2 and limitations; current POSNA LCP Study Guide, treatment principles and timing caveat."
}