# Physeal Injuries: Salter-Harris Classification and Growth Arrest

## Introduction

Physeal (growth plate) injuries account for approximately 15 to 30% of all pediatric fractures. The physis is the weakest link in the pediatric musculoskeletal system, making it vulnerable to traumatic forces that would cause ligamentous injury in adults. Accurate classification, appropriate management, and vigilant follow-up are essential to minimize the risk of growth disturbance and long-term deformity.

## Anatomy of the Physis

The physis is organized into four histologic zones from epiphysis to metaphysis. The reserve (resting) zone stores nutrients and provides structural support. The proliferative zone is responsible for active chondrocyte division and longitudinal growth. The hypertrophic zone is where chondrocyte enlargement and matrix calcification occur, and it is the weakest zone mechanically. The zone of provisional calcification is the interface with the metaphysis where vascular invasion and ossification occur. The germinal cells of the proliferative zone are critical for continued growth, and their disruption leads to growth arrest. The perichondrial ring of LaCroix and the periosteum provide peripheral stability to the physis.

## Salter-Harris Classification

| Type | Fracture Pattern | Frequency | Growth Arrest Risk | Treatment |
|------|-----------------|-----------|-------------------|-----------|
| I | Through physis only (hypertrophic zone) | ~6% | Rare | Immobilization 3-4 weeks |
| II | Through physis + metaphyseal fragment (Thurston-Holland) | ~75% | Uncommon | Closed reduction + casting |
| III | Through physis + into epiphysis (intra-articular) | ~8% | Higher | Anatomic reduction; ORIF if > 2 mm displacement |
| IV | Metaphysis → physis → epiphysis | ~10% | Highest (common types) | Anatomic ORIF required |
| V | Crush injury to physis (no visible fracture) | ~1% | Near certain | Observation; treat resulting deformity |

### Type I

Type I fractures pass through the physis only, transversely through the hypertrophic zone. Radiographs may appear normal, and the diagnosis is made by tenderness over the physis and soft tissue swelling. Widening of the physis or subtle epiphyseal displacement may be seen. The prognosis is excellent with rare growth arrest, and treatment consists of immobilization for 3 to 4 weeks.

### Type II

Type II fractures pass through the physis with a metaphyseal fragment (the Thurston-Holland fragment). This is the most common type, accounting for approximately 75% of physeal fractures. The periosteum is intact on the side of the metaphyseal fragment, aiding reduction. The prognosis is excellent with uncommon growth disturbance. Treatment involves closed reduction and casting, with anatomic reduction desirable though slight displacement tolerated.

### Type III

Type III fractures pass through the physis and extend into the epiphysis, making them intra-articular. They disrupt both the articular surface and the germinal layer. The risk of growth arrest and articular incongruity is higher. Treatment requires anatomic reduction, with ORIF indicated if displacement exceeds 2 mm.

### Type IV

Type IV fractures cross the metaphysis, physis, and epiphysis. If not anatomically reduced, a bony bridge forms across the physis. This type carries the highest risk of growth arrest among the common types. Anatomic ORIF is required to restore the articular surface and physeal alignment.

### Type V

Type V fractures are crush injuries to the physis with no visible fracture line on initial radiographs. They are diagnosed retrospectively when growth arrest becomes apparent. The prognosis is poor with near-certain growth disturbance. Treatment is observation with close follow-up and management directed at the resulting deformity.

## Additional Classification Considerations

Peterson Type VI is an open physeal injury with loss of a portion of the physis, such as from lawnmower injuries. Rang Type VI involves injury to the perichondrial ring. Both carry very high risks of growth disturbance and angular deformity.

## Epidemiology

Peak incidence occurs during adolescence when the physis is most vulnerable due to rapid growth and a thicker hypertrophic zone. The distal radius is the most common location overall, with other common sites including the distal fibula, distal tibia, phalanges, and distal humerus. Boys are affected approximately twice as often as girls.

## Growth Arrest

### Mechanisms

A physeal bar (bony bridge) forms across the physis from fracture malreduction, crush injury, or ischemia. Bars may be central, peripheral, or linear in orientation. A bar involving less than 50% of the physeal cross-sectional area with more than 2 years of growth remaining is potentially amenable to bar resection.

### Clinical Manifestations

Peripheral or eccentric bars cause angular deformity from asymmetric growth. Central bars cause limb length discrepancy from symmetric growth inhibition. Combined deformity involves both angular and length abnormalities.

### Evaluation

Serial radiographs at 3 to 6 month intervals for at least 12 months after injury are essential. MRI is the gold standard for identifying physeal bars and mapping their extent. Harris growth arrest lines are transverse sclerotic lines in the metaphysis that should be parallel to the physis; angulation indicates asymmetric growth.

### Treatment of Growth Arrest

Observation is appropriate for bars involving more than 50% of the physis or with less than 2 years of growth remaining. Physeal bar resection (Langenskiold procedure) involves excision of the bony bridge and interposition of fat, cement, or silastic to prevent reformation, and is indicated when the bar is less than 50% with adequate growth remaining. Corrective osteotomy addresses established angular deformity. Contralateral epiphysiodesis equalizes limb lengths when growth arrest is complete and discrepancy is significant. Limb lengthening is used for significant leg length discrepancy, typically greater than 2.5 cm at maturity.

## Site-Specific Considerations

### Distal Femur

The distal femoral physis is the fastest-growing physis in the body, contributing approximately 70% of femoral growth. It has a high rate of growth disturbance even with anatomic reduction (up to 40 to 50% of Salter-Harris types III and IV). Meticulous anatomic reduction and long-term follow-up are required.

### Distal Tibia

The Tillaux fracture is a Salter-Harris III of the anterolateral distal tibial epiphysis, occurring during asymmetric physeal closure in adolescence. The triplane fracture is a complex fracture with components in three planes (sagittal epiphyseal, axial physeal, coronal metaphyseal), and CT is essential for surgical planning. Both require ORIF if articular step-off exceeds 2 mm.

### Proximal Tibia

Proximal tibial physeal fractures are rare but dangerous because of the proximity to the popliteal artery, requiring vascular assessment. There is risk of vascular injury and subsequent compartment syndrome.

## Clinical Pearls

Salter-Harris Type II is by far the most common physeal fracture and has an excellent prognosis; Types III and IV require anatomic reduction to minimize the risk of growth arrest and articular incongruity. A normal radiograph does not exclude a physeal injury; clinical tenderness over the physis should be treated as a Salter-Harris Type I until proven otherwise. The distal femoral physis has the highest growth rate and the highest rate of growth disturbance, so all distal femoral physeal injuries should be followed closely for at least one year. MRI is the best modality for identifying and mapping physeal bars; bar resection is only effective when the bar involves less than 50% of the physeal area with significant growth remaining.

## References
1. Salter RB, Harris WR. Injuries involving the epiphyseal plate. *J Bone Joint Surg Am*. 1963;45(3):587-622.
2. Peterson HA. Physeal fractures: Part 3. Classification. *J Pediatr Orthop*. 1994;14(4):439-448.
3. Langenskiold A. An operation for partial closure of an epiphyseal plate in children, and its experimental basis. *J Bone Joint Surg Br*. 1975;57(3):325-330.
4. Barmada A, Gaynor T, Mubarak SJ. Premature physeal closure following distal tibia physeal fractures: a new radiographic predictor. *J Pediatr Orthop*. 2003;23(6):733-739.