- The Herring lateral pillar classification assesses the height of the lateral third of the femoral capital epiphysis on the true AP pelvis radiograph during the fragmentation stage. It is the most widely used and validated radiographic prognostic tool in Legg-Calvé-Perthes disease.
- Group A: lateral pillar fully preserved (no loss of height). Group B: lateral pillar maintains at least 50 percent of original height. Group B-C border: lateral pillar is very narrow (less than 50 percent but not fully collapsed) or is exactly 50 percent with other risk factors. Group C: lateral pillar collapsed to less than 50 percent or completely obliterated.
- Age at onset and lateral pillar group together drive prognosis. A child under six in group A or B has a good prognosis without surgical containment. A child over eight in group B or worse warrants consideration of containment surgery (femoral varus osteotomy or Salter innominate osteotomy).
- The classification must be applied during the fragmentation phase, not the initial or reossification phase, because lateral pillar height changes as the disease progresses. Serial radiographs are essential.
The Herring lateral pillar classification (also called the lateral pillar classification of Herring) is applied to the AP radiograph of the pelvis during the fragmentation stage of Perthes disease. It grades the lateral pillar (the lateral third of the epiphysis) by height preservation: A = no collapse, B = at least 50 percent preserved, B-C border = very narrow or exactly 50 percent, C = less than 50 percent or absent. Examiners expect you to classify a case from an AP radiograph, state the prognosis by age group, and explain how it guides containment decisions. Do not confuse it with Catterall (which assesses the whole head involvement in four groups) — Herring is more reproducible and prognostically superior.
The lateral pillar is the last part of the epiphysis to collapse in Perthes disease because it receives the most robust residual blood supply from the lateral circumflex artery anastomoses. This is why its preservation correlates so strongly with a good outcome — an intact lateral pillar mechanically supports the central and medial segments during reossification.
The Herring Lateral Pillar Classification
The classification is based on the height of the lateral pillar (the lateral one-third of the femoral capital epiphysis) on a true anteroposterior pelvic radiograph taken during the fragmentation stage of Legg-Calvé-Perthes disease.
| Group | Lateral Pillar Height | Prognosis (Stulberg I/II) | Typical Management |
|---|---|---|---|
| A | No loss of height; lateral pillar fully preserved | Excellent — near-universal Stulberg I or II | Observation; no containment needed |
| B | At least 50 percent of original lateral pillar height maintained | Good if under age 6; guarded if over age 8 | Observation under 6; consider containment over 8 |
| B-C border | Very narrow lateral pillar (less than 50 percent but not fully collapsed), or exactly 50 percent with lateral calcification or Gage sign | Intermediate — outcome between B and C | Treat as B or C based on age and clinical factors; usually manage as C |
| C | Less than 50 percent of original height, or complete collapse of the lateral pillar | Poor — high risk of Stulberg III, IV, or V | Early containment (osteotomy); consider older surgical options |
A B C — All Better CourseThe lateral pillar groups — A, B, B-C, C
Fragment — Fix — FollowWhen to apply the classification
Gage sign — a radiolucent V-shaped defect in the lateral epiphysis — is an early sign of Perthes that may accompany lateral pillar involvement. It does not define the Herring group but supports the diagnosis when seen alongside pillar changes.
Prognosis by Age and Lateral Pillar Group
The interaction between age at onset and lateral pillar group is the critical prognostic determinant. The same lateral pillar group carries a very different prognosis in a four-year-old versus a ten-year-old.
| Lateral Pillar Group | Under 6 years at onset | 6 to 8 years at onset | Over 8 years at onset |
|---|---|---|---|
| A | Excellent — observe | Excellent — observe | Excellent — observe |
| B | Good — observe | Guarded — consider containment | Poor — containment recommended |
| B-C border | Good to guarded | Guarded — lean toward containment | Poor — containment recommended |
| C | Guarded — consider containment | Poor — containment recommended | Poor — containment strongly recommended; outcome often unsatisfactory |
Children over age eight at onset with lateral pillar group B or worse have a significantly increased risk of aspherical healing (Stulberg III or higher). Even with containment surgery, outcomes in this age group are less predictable. Early recognition and prompt referral to a paediatric orthopaedic surgeon are essential — the window for effective containment is during the fragmentation and early reossification phases and closes as the child approaches skeletal maturity.
Lateral Pillar versus Other Perthes Classifications
Several classification systems exist for Perthes disease. The Herring lateral pillar system has largely superseded earlier systems in clinical practice because of its superior inter-observer reliability and prognostic accuracy.
| Classification | What It Assesses | Number of Groups | Key Strength | Key Limitation |
|---|---|---|---|---|
| Herring (Lateral Pillar) | Height of lateral pillar on AP in fragmentation phase | 4 (A, B, B-C, C) | Best reproducibility and prognostic accuracy; validated multi-centre | Must be applied during fragmentation phase only |
| Catterall | Extent of head involvement (all three pillars) on AP and lateral | 4 (Groups I–IV) | First widely used classification; intuitive anatomical concept | Moderate inter-observer reliability; less prognostically accurate than Herring |
| Salter-Thompson | Width of radiolucent crescent (subchondral fracture line) on early films | 2 (A = less than half, B = more than half) | Simple; can be applied very early in disease | Crescent sign often not visible; only two groups limit granularity |
| Stulberg (Outcome) | Sphericity of the healed femoral head at maturity | 5 (I–V) | Gold-standard outcome measure; correlates with late arthritis | Outcome measure only — cannot be used to guide acute treatment |
Pillar Predicts Prognosis PreciselyWhy lateral pillar is the exam favourite
Containment Decision-Making
The lateral pillar classification directly guides the decision to pursue containment — the principle of keeping the femoral head covered by the acetabulum during the fragmentation and reossification phases to promote spherical healing.
- Group A: No containment needed. The lateral pillar is intact and the prognosis is excellent with observation and activity modification alone.
- Group B (under age 6): Observation is reasonable. Good remodelling potential supports a non-operative approach.
- Group B (over age 8): Containment is recommended. Options include femoral varus derotational osteotomy, Salter innominate osteotomy, or a combination (shelf acetabuloplasty in selected cases). The choice depends on surgeon expertise, concomitant acetabular dysplasia, and range of motion.
- Group B-C border: Treat as C if over age 6. The risk of aspherical healing is high enough to justify intervention.
- Group C: Containment strongly recommended at any age. Even with containment, the prognosis is guarded, particularly in older children. Some surgeons advocate for more aggressive approaches including Petrie cast or broomstick cast as adjuncts.
Containment methods: Non-operative (Petrie casts, broomstick casts, abduction bracing) and operative (femoral varus derotational osteotomy, Salter innominate osteotomy, double-level osteotomy, shelf acetabuloplasty). The principle is the same: maintain femoral head coverage within the acetabulum during the vulnerable reossification phase. Operative containment is preferred in children over age 6 with lateral pillar B or worse because it provides more reliable and durable coverage.
Radiographic Technique and Pitfalls
Accurate lateral pillar classification depends on proper radiographic technique:
- True AP pelvis: The radiograph must be a true anteroposterior view of the pelvis, not a frog lateral or oblique. Internal or external rotation of the limb distorts the apparent pillar height.
- Timing during fragmentation: The classification is valid only during the fragmentation phase (typically 6 to 12 months after onset). Applying it too early (initial avascular phase) underestimates involvement; applying it too late (reossification) overestimates recovery.
- Serial radiographs: Because pillar height can change, the classification should be reassessed on sequential AP pelvic radiographs at 3 to 4-month intervals during fragmentation.
- Identify the lateral pillar correctly: The lateral pillar is the lateral one-third of the epiphysis, bordered medially by a vertical line from the junction of the middle and lateral thirds. The central and medial pillars are not assessed.
- Do not use the frog lateral for classification: The lateral pillar is assessed on the AP view only. The frog lateral is complementary for assessing head-at-risk signs and hinge abduction but does not provide the pillar measurement.
Hinge abduction is a critical concept in Perthes management. If the enlarged femoral head hinges on the lateral acetabular margin during abduction (visible on dynamic arthrogram or frog lateral), containment procedures will fail because the head cannot be reduced under the acetabular roof. Hinge abduction must be excluded before proceeding with containment surgery — an arthrogram under anaesthesia is the gold standard to assess this.
Guidelines, Registries and Global Practice
- No single international guideline governs Perthes management. Treatment decisions are individualised based on age, lateral pillar group, range of motion, and surgeon preference. The evidence base consists primarily of retrospective cohort studies and expert consensus.
- POSNA (Pediatric Orthopaedic Society of North America) and EPOS (European Paediatric Orthopaedic Society) broadly endorse the lateral pillar classification as the preferred radiographic prognostic tool. Containment decisions follow the age-and-pillar framework described above.
- Global practice variation: North American surgeons more commonly use femoral varus osteotomy for containment. European surgeons, particularly in the UK and Scandinavia, more often favour Salter innominate osteotomy or non-operative containment (Petrie casts). Japanese centres have reported good results with prolonged bed rest and traction in younger children. These differences reflect training tradition rather than definitive evidence of superiority.
- The lateral pillar classification has been validated across multiple ethnic populations and healthcare settings, supporting its use as a global prognostic tool.
- Long-term follow-up to skeletal maturity is universally recommended regardless of treatment approach, because the Stulberg outcome cannot be reliably predicted before growth plate closure.
Evidence Base
Legg-Calve-Perthes disease. Part II: prospective multicenter study of the effect of treatment on outcome
- 451 hips classified by the modified lateral pillar classification; lateral pillar group and age at onset were both strong independent prognostic factors (p under 0.0001)
- Lateral pillar B and B/C-border hips in children over 8 years at onset did significantly better with surgery than non-operatively
- Group C hips had the worst outcomes regardless of treatment; group B under 8 years did well irrespective of treatment
Radiographic classifications in Perthes disease
- The original lateral pillar classification was strongly associated with 5-year femoral head sphericity (gamma 0.75)
- Adding the modified B/C-border group did not improve interobserver agreement or prognostic value over the original
- Original lateral pillar and Catterall classifications both had sufficient reliability for clinical use
Exam Viva
Practise clinical reasoning and management decisions out loud
“A 7-year-old boy presents with a 4-month history of a limp and right hip pain. An AP pelvic radiograph shows Perthes disease in the fragmentation phase. The lateral pillar of the right femoral head has lost approximately 40 percent of its height. How would you classify this, what is the prognosis, and how would you manage him?”
“A 10-year-old girl presents with left hip Perthes disease. The AP radiograph in fragmentation shows complete collapse of the lateral pillar with lateral subluxation of the femoral head. She has limited abduction to 20 degrees. Classify, prognosticate, and outline your management.”
The four lateral pillar groups
- Group A: no lateral pillar height loss — excellent prognosis
- Group B: at least 50 percent of lateral pillar height preserved — good under 6, guarded over 8
- Group B-C border: very narrow pillar or exactly 50 percent with risk factors — treat as C
- Group C: less than 50 percent height or complete collapse — poor prognosis
Classification essentials
- Apply on true AP pelvis radiograph during the fragmentation phase only
- Assess the lateral one-third of the epiphysis (the lateral pillar)
- Age at onset and lateral pillar group together determine prognosis
- Serial radiographs at 3 to 4-month intervals — pillar height can change
Management by group and age
- Group A (any age): observe — no containment needed
- Group B under 6: observe; Group B over 8: containment surgery recommended
- Group C (any age): containment strongly recommended; prognosis still guarded
- Always exclude hinge abduction with arthrogram before containment surgery
Key distinctions for the exam
- Herring (lateral pillar) is more reproducible and prognostic than Catterall
- Containment options: femoral varus osteotomy, Salter osteotomy, or combined double-level
- Stulberg classification is the outcome measure at skeletal maturity, not a treatment guide
- The lateral pillar is the last to collapse because of robust lateral circumflex blood supply