# Salter-Harris Fractures: Types I-V Explained

A Salter-Harris fracture is a fracture that crosses the growth plate (physis) of a young dog or cat, and the five types are classified by which tissue layers the fracture line passes through. The Salter-Harris system is the standard language used to describe these injuries, predict how the growth plate will behave afterward, and choose treatment in juvenile animals whose bones are still growing.

Why it matters: damage to a growth plate can stop or slow the growth of that segment of bone, or allow the remaining growth to push the limb into an angular or rotational deformity. A fracture that looks minor on the first radiograph can still leave a puppy or kitten with a crooked leg months later. Understanding the five types, and knowing when the plain view is not enough, is the difference between a limb that grows straight and one that needs a corrective surgery the animal's family did not expect.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

## The Growth Plate in Plain Language

A physis (plural physes), commonly called the growth plate, is a disc of cartilage between the epiphysis and the metaphysis of a long bone. The epiphysis is the rounded end of the bone that forms the joint surface and, in a growing animal, is separated from the bone shaft by the physis. The metaphysis is the flared region of the shaft immediately next to the physis. Cartilage here produces new bone in a controlled sequence, lengthening the bone until the physis closes and is replaced by solid bone.

Four zones matter for fracture behavior, from the epiphyseal side outward:

1. **Resting (reserve) zone**, small cartilage cells that act as a reserve source.
2. **Proliferative zone**, cells divide and line up in columns, this is the true growth engine and it is fragile.
3. **Hypertrophic zone**, enlarged cells in a calcified matrix, the weakest plane mechanically.
4. **Zone of provisional calcification / primary spongiosa**, where cartilage is replaced by woven bone.

The hypertrophic zone is where most experimental physeal fractures separate. That mechanical fact explains why type I and II injuries look clean on a radiograph. But a clean radiographic line does not mean the proliferative zone survived. In a histologic study of naturally occurring physeal fractures in dogs, ten of thirteen fractures disrupted cells in the proliferative zone, a finding that correlates more closely with the clinical observation of growth retardation than experimental models of fracture through the hypertrophic zone [1]. That single finding is the reason a veterinarian cannot promise normal growth based on fracture type alone.

## The Salter-Harris Classification: Five Types

<figure class="article-figure">
  <img src="https://thumb.wikimedia.org/wikipedia/commons/thumb/1/10/Salter_Harris_Fracture_Types.svg/1280px-Salter_Harris_Fracture_Types.svg.png" alt="Diagram of Salter-Harris fracture types I through V at the growth plate" loading="lazy" decoding="async" width="1000" height="801" />
  <figcaption>The five Salter-Harris types shown at the physis, from a pure physeal separation (I) to a physeal crush (V). Image: Llywelyn2000, CC BY-SA 4.0, via <a href="https://commons.wikimedia.org/wiki/File:Salter_Harris_Fracture_Types.svg" rel="noopener noreferrer">Wikimedia Commons</a>.</figcaption>
</figure>

The original classification was developed from experimentally induced fractures in animals, then applied clinically. Salter and Harris described five patterns, I through V, numbered roughly by how much of the physis and adjacent bone each pattern crosses.

### Type I

The fracture line runs entirely through the physis itself, usually through the hypertrophic zone. There is no metaphyseal or epiphyseal component. The epiphysis separates from the metaphysis, an injury sometimes called epiphysiolysis or a slipped epiphysis. On a radiograph, the physis simply appears widened, or the epiphysis is displaced relative to the metaphysis. In a young animal before the physis calcifies enough to fracture cleanly through bone, this is essentially a shearing injury of cartilage, and it may be radiographically silent except for displacement.

### Type II

The fracture line passes through the physis and exits into the metaphysis, creating a triangular metaphyseal fragment. That triangular piece is called the Thurston-Holland sign, and it is the most reliable radiographic marker of a type II injury [2]. Because the fragment is attached to the epiphysis, the periosteum on that side remains intact, which is one mechanical reason type II fractures tend to reduce and stabilize more predictably than types III through V.

### Type III

The fracture line runs through the physis and into the epiphysis, producing an intra-articular fracture that splits the joint surface. The physis is involved and the joint is involved. The epiphyseal fragment can be displaced, and because it carries articular cartilage, reconstruction must restore both the joint surface and physeal alignment. Type III injuries are much less common in dogs and cats than types I and II.

### Type IV

The fracture line passes through the metaphysis, the physis, and the epiphysis, and it is also intra-articular. All three layers are involved. This is the most anatomically complete injury short of a crush, and in dogs the most common physeal fracture reported was a type IV fracture of the distal femur [2]. Because growth occurs on both sides of the fracture line in relation to the displaced epiphyseal segment, even small residual steps can lead to disproportionate growth and angular deformity.

### Type V

Type V is a compression or crush injury of the physis. There is no visible fracture line in the classic description. The physis is damaged by axial load and may show only subtle loss of height or increased opacity on the radiograph. Because there is no displacement, type V is frequently diagnosed retrospectively, when the animal later develops a growth disturbance or a focal physeal closure that was not visible at the time of injury. In practice, a type V is often a working diagnosis made after the fact.

## Frequency in Dogs and Cats

A retrospective review of 288 fractures in 245 dogs and cats with suspected growth-plate injuries in the appendicular skeleton found the following distribution [2]:

- Type I: 39.9%
- Type II: 37.8%
- Type III: 3.1%
- Type IV: 19.1%

The femur was the bone most often affected at 46.5%, followed by the humerus at 19.8%, the tibia at 13.5%, and the radius at 11.8%. The distal growth plate was involved more often than the proximal growth plate in every bone, at 79.5% versus 20.5% [2]. That last point is clinically useful because the distal physis of the femur, tibia, and radius are common sites for growth disturbance, and they are the plates most likely to need recheck radiographs.

A separate review of 36 physeal fractures in 34 cats found the distal femur most commonly affected at 17 fractures, followed by the distal tibia and fibula at 11, the distal radius and ulna at five, the proximal tibia at two, and the distal humerus at one. Classification in that series was type I in 14, type II in 16, type III in two, and type IV in four [3]. The cat data reinforce that types I and II dominate clinically, but that the less common types III and IV are over-represented in the growth disturbance cases that return for follow-up.

## Summary Comparison Table

| Type | Anatomic layers involved | Typical prognosis | Representative example |
|--|--|--|--|
| I | Physis only (epiphysiolysis) | Generally good with prompt anatomical reduction, but the proliferative zone can still be damaged [1] | Distal femoral physeal separation in a young cat [4][3] |
| II | Physis plus metaphysis (Thurston-Holland fragment) | Generally good, similar to type I [4][2] | Distal femoral physeal fracture in a cat treated with modified intramedullary pinning [4] |
| III | Physis plus epiphysis, intra-articular | Guarded, joint surface and physis both affected, growth disturbance more likely | Uncommon, often distal femur or distal tibia [2][3] |
| IV | Metaphysis, physis, and epiphysis, intra-articular | Guarded to poor, most common pattern in the distal femur of dogs [2] | Distal femoral type IV in a dog [2] |
| V | Crush of the physis, no visible fracture line | Poor, often diagnosed retrospectively after growth disturbance appears | Focal physeal closure found on later recheck radiographs |

## Why Types I and II Usually Do Better Than III, IV, and V

Three anatomical reasons explain the prognosis gap.

First, in types I and II the fracture line stays in the physis and, for type II, exits through the metaphysis. The periosteum on the metaphyseal side is often preserved, which provides a natural hinge for reduction and a source of stability while healing occurs. In types III and IV the line violates the epiphysis and the articular surface, so the surgeon must restore a joint surface rather than simply reduce a physeal separation.

Second, in types III and IV the epiphyseal fragment carries a true growth plate plus articular cartilage. If the fragment heals in even slight malalignment, the growth plate on either side of the fracture line can continue to grow at different rates, feeding directly into angular deformity.

Third, mechanical damage to the proliferative zone tends to be more extensive when the fracture line travels through the epiphysis and metaphysis, because the region of the physis that stays attached to the epiphysis is at risk of vascular disruption. In the canine histologic review, ten of thirteen naturally occurring fractures disrupted proliferative zone cells, and the appearance correlated with clinical growth retardation rather than continued growth [1]. Prognosis therefore tracks the anatomy of the fracture line and the biology of the physis together, not the type number alone.

## Diagnosis: How These Fractures Are Found

### Radiography

Standard orthogonal radiographs are the first step. The telltale signs of a physeal fracture are at least two of the following: a change in opacity, displacement of the epiphysis, and the Thurston-Holland sign [2]. A widened physis may be the only finding in a type I injury, and a subtle metaphyseal triangle may be the only evidence of a type II.

The same retrospective review found that original radiographic reports were erroneous about Salter-Harris grouping in 44 of 288 fractures. Five of those 44 had technical deficiencies that may have contributed, including three cases with oblique projections, and minimal variation in projection was evident in most of the reviewed cases [2]. That is a strong argument for good positioning, orthogonal views, and honest uncertainty when the physis is partially open.

### Stress Radiography and Comparison Views

When a fracture line is not visible, stress radiography applies a controlled load to the limb to see if the physis opens. Comparison views of the contralateral limb are useful because physeal width varies with age and between individuals, so the opposite side provides a reference. In a growing animal, the physis is normally radiolucent, which makes subtle widening easy to miss on a single view.

### Advanced Imaging

Cross-sectional imaging and three-dimensional reconstructions are increasingly used for planning and teaching. A study describing three-dimensional printed models of canine femoral physeal fractures reported that radiographs of the models clearly demonstrated the Salter-Harris classification, and the models replicated bone length, width, and thickness closely [5]. These models are teaching and planning tools, not a replacement for imaging the patient.

## Treatment Principles for Physeal Fractures

Treatment is aimed at restoring anatomical alignment with the least possible trauma to the physis and the surrounding soft tissue. The choice of technique depends on the type, location, displacement, and the age and size of the animal.

Minimally invasive osteosynthesis (MIO), which stabilizes a fracture through small incisions using fluoroscopic or radiographic guidance, has been reported across long bone, physeal, and articular fractures in dogs and cats. A review of more than 40 MIO studies found it feasible with low complication rates, but the available evidence did not show superior bone healing or functional outcomes compared with standard methods, and the authors noted that good results depend on careful case selection and surgical experience [6].

Two clinically relevant techniques appear repeatedly in the physeal fracture literature.

**Modified intramedullary pinning for distal femoral physeal fractures.** In a retrospective study of 31 cats with distal femoral Salter-Harris type I and II fractures treated with an intramedullary pin plus one antirotational pin in the lateral femoral condyle, bone healing was radiographically confirmed at 6 to 8 weeks postoperatively in all cases. Thirty of 31 cats were classified as having full functional outcomes at mid-term follow-up, and the overall mid-term complication rate was 3% (1 of 31). Implant migration was not observed and implant removal was not needed in any case [4]. An earlier report of a similar modified technique in dogs and cats found no fixation failures in 11 animals, compared with 2 failures in 13 animals treated with a multiple pin technique [7].

**Fluoroscopic-assisted percutaneous pinning (FAPP).** A retrospective study of 42 physeal fractures in 37 dogs and 4 cats treated with FAPP reported full functional outcome in 92% of animals, an overall complication rate of 15% (6 animals), and elective pin removal in 41% (17 animals). In dogs where measurements were obtained, goniometry and limb circumference did not differ significantly between the affected and contralateral limbs. In 17 of 18 animals measured, bone length changes were seen on follow-up radiographs [8].

**Percutaneous tibial physeal repair.** A case series of 14 dogs and 3 cats described percutaneous tibial physeal fracture repair using intra-operative fluoroscopy or digital radiography, including a "spiking" technique for tibial tuberosity avulsion fractures. Surgery times ranged from 8 to 54 minutes, return to function averaged 1.9 weeks, and long-term follow-up was available for all 17 cases at a mean of 40.6 months. Final outcome was excellent in most cases and good in the remainder [9].

**Capital physeal fractures and slipped epiphysis.** Fractures of the femoral head and neck, including physeal separations, are common in growing dogs and cats, and prognosis is favorable with early anatomical reduction, gentle tissue handling to preserve blood supply, and stable internal fixation [10]. Avascular necrosis of the femoral head, a feared complication in human patients, does not appear to be a complication in small animals [10]. Where the femoral head cannot be salvaged, total hip replacement has been reported as a successful treatment for capital physeal fractures in dogs and cats, with force plate gait analysis showing no significant difference between the operated limb and the normal contralateral limb in the dogs measured [11], and a feline case series reporting subjectively good outcomes [12]. For atraumatic slipped femoral capital epiphysis (SCFE) in dogs, a review of 15 cases treated with total hip replacement found improvement in lameness and pain scores in all cases at four weeks, and at a median of 22 months all owners reported good quality of life [13]. In cats, slipped capital femoral epiphysis has been described as an idiopathic condition, including a report of five feline total hip replacements [12], a case of bilateral idiopathic slipped capital femoral epiphysis [14], and a series of 17 Maine Coon cats in which 8.17% of Maine Coons presented were diagnosed with SCFE, compared with 0.67% of all cats in the same practice population [15].

## Clinical Relevance, Limitations and Common Mistakes

**Follow-up radiographs are not optional.** A young dog or cat with a physeal fracture should be rechecked radiographically as it grows. The cat series found premature physeal closure in 23 fractures at radiographic follow-up, of which 15 were considered premature [3]. That level of closure cannot be predicted from the initial film alone. Rechecks at healing and again during the growth period catch angular deformity early enough to plan correction.

**Type V is a retrospective diagnosis.** Because there is no visible fracture line, a type V injury is often recognized only when a growth disturbance appears later. A young animal with a history of axial trauma and a painful, swollen limb but a normal-looking physis on radiographs deserves close follow-up.

**Stress radiography and comparison views catch what a single view misses.** A physis that looks normal on a neutral view can open under stress. Always image the opposite limb for reference when the diagnosis is not clear.

**Reporting errors are common.** Original radiographic reports disagreed with the final Salter-Harris grouping in 44 of 288 fractures in one review, and technical factors such as oblique projections contributed in some cases [2]. If a physeal fracture is suspected but not seen, repeat the study with proper orthogonal positioning rather than accepting an equivocal report.

**Type alone does not determine outcome.** A type I fracture with extensive proliferative zone damage can still cause growth retardation [1], and the histologic study of naturally occurring fractures showed physeal cartilage damage is often more severe than the experimental classification predicts [1]. Treat the animal, not the number.

**Not every physeal lesion is traumatic.** Polyostotic lymphoma in a 6-month-old cat produced lysis and proliferative change within multiple physes and pathological physeal fractures of the distal radii, metacarpal, and metatarsal bones [16]. A physeal fracture without a believable trauma history deserves a broader diagnostic workup.

## Quick Review

1. Type I runs through the physis only (epiphysiolysis), type II through physis and metaphysis with a Thurston-Holland fragment, type III through physis and epiphysis (intra-articular), type IV through metaphysis, physis, and epiphysis (intra-articular), type V is a crush of the physis with no visible fracture line.
2. Types I and II generally carry a better prognosis than types III, IV, and V because the periosteum is often preserved and the articular surface is spared.
3. Type V is usually diagnosed retrospectively, after a growth disturbance appears.
4. In dogs and cats, types I and II account for the large majority of physeal fractures, and the distal physis is involved far more often than the proximal physis [2].
5. Growth-plate injury in a young dog or cat can produce angular limb deformity, so follow-up radiographs during growth are part of standard care [3].
6. Stress radiography and comparison views of the opposite limb help when the initial radiograph is equivocal.
7. Traumatic damage to the proliferative zone is common in naturally occurring fractures and explains why some type I and II injuries still grow abnormally [1].

## Frequently Asked Questions

### What are the five Salter-Harris fracture types?

Type I crosses the physis only. Type II crosses the physis and metaphysis and leaves a triangular metaphyseal fragment. Type III crosses the physis and epiphysis and enters the joint. Type IV crosses the metaphysis, physis, and epiphysis and also enters the joint. Type V is a compression or crush injury of the physis with no visible fracture line.

### Which Salter-Harris types have the best prognosis?

Types I and II generally have the better prognosis because the fracture line stays out of the joint surface and the periosteum is often intact, allowing more predictable reduction and healing. Types III, IV, and V carry a higher risk of growth disturbance and angular deformity.

### Why is a type V Salter-Harris fracture often diagnosed late?

A type V injury crushes the physis without creating a visible fracture line, so the initial radiograph may look normal. The diagnosis is often made retrospectively when the animal returns with a growth abnormality or a focal physeal closure.

### Can a puppy or kitten with a growth-plate fracture develop a crooked leg?

Yes. Physeal injury can slow or stop growth in part of the plate, and the remaining growth can push the limb into an angular or rotational deformity. Follow-up radiographs during the growth period are how these changes are caught early.

### Do all physeal fractures need surgery?

No. Treatment depends on the type, location, displacement, and the age and size of the animal. Some minimally displaced fractures can be managed with closed reduction and percutaneous pinning, and the choice of technique is a case-by-case decision made by the attending veterinarian.

### Are stress radiographs and comparison views necessary?

They are often helpful when the initial radiograph does not clearly show a fracture. Stress radiography can open a physis that looks normal at rest, and imaging the opposite limb gives a reference for normal physeal width at that age.

<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "FAQPage",
  "mainEntity": [
    {
      "@type": "Question",
      "name": "What are the five Salter-Harris fracture types?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Type I crosses the physis only. Type II crosses the physis and metaphysis and leaves a triangular metaphyseal fragment. Type III crosses the physis and epiphysis and enters the joint. Type IV crosses the metaphysis, physis, and epiphysis and also enters the joint. Type V is a compression or crush injury of the physis with no visible fracture line."
      }
    },
    {
      "@type": "Question",
      "name": "Which Salter-Harris types have the best prognosis?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Types I and II generally have the better prognosis because the fracture line stays out of the joint surface and the periosteum is often intact, allowing more predictable reduction and healing. Types III, IV, and V carry a higher risk of growth disturbance and angular deformity."
      }
    },
    {
      "@type": "Question",
      "name": "Why is a type V Salter-Harris fracture often diagnosed late?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "A type V injury crushes the physis without creating a visible fracture line, so the initial radiograph may look normal. The diagnosis is often made retrospectively when the animal returns with a growth abnormality or a focal physeal closure."
      }
    },
    {
      "@type": "Question",
      "name": "Can a puppy or kitten with a growth-plate fracture develop a crooked leg?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Yes. Physeal injury can slow or stop growth in part of the plate, and the remaining growth can push the limb into an angular or rotational deformity. Follow-up radiographs during the growth period are how these changes are caught early."
      }
    },
    {
      "@type": "Question",
      "name": "Do all physeal fractures need surgery?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "No. Treatment depends on the type, location, displacement, and the age and size of the animal. Some minimally displaced fractures can be managed with closed reduction and percutaneous pinning, and the choice of technique is a case-by-case decision made by the attending veterinarian."
      }
    },
    {
      "@type": "Question",
      "name": "Are stress radiographs and comparison views necessary?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "They are often helpful when the initial radiograph does not clearly show a fracture. Stress radiography can open a physis that looks normal at rest, and imaging the opposite limb gives a reference for normal physeal width at that age."
      }
    }
  ]
}
</script>

## Related Articles

- [Fracture Repair in Exotic Pets](/knowledge/veterinary-medicine/exotic-animal-medicine/fracture-repair-in-exotic-pets-selecting-the-right-fixation-method-for-reptiles-birds-and-small-mamm)
- [Radiographic Assessment of Fracture Healing in Dogs and Cats](/knowledge/veterinary-medicine/diagnostic-imaging/radiographic-assessment-fracture-healing-dogs-cats)
- [Avian Orthopedics: Fracture Repair and Management in Birds](/knowledge/veterinary-medicine/backyard-poultry/avian-orthopedics-fracture-repair-management-birds)
- [Surgical Approaches to the Femur and Stifle](/knowledge/veterinary-medicine/veterinary-surgery/surgical-approaches-femur-stifle)
- [Fracture Healing Assessment: Radiographic and Clinical Evaluation](/knowledge/veterinary-medicine/veterinary-surgery/fracture-healing-assessment-radiographic-clinical)
- [Surgical Approaches to the Humerus and Elbow](/knowledge/veterinary-medicine/veterinary-surgery/surgical-approaches-humerus-elbow)
- [IV Fluids: Types, Rates, and Vet Calculations](/knowledge/veterinary-medicine/emergency-and-first-aid/iv-fluids-types-rates-and-vet-calculations)
- [Mange in Cats: Symptoms, Types, and Treatment](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/mange-in-cats-symptoms-types-and-treatment)

## Sources

1. [Histological appearance of naturally occurring canine physeal fractures.](https://pubmed.ncbi.nlm.nih.gov/8191677/)
2. [[Salter-harris fractures in dogs and cats considering problems in radiological reports--a retrospective analysis of 245 cases between 1997 and 2012].](https://pubmed.ncbi.nlm.nih.gov/24490347/)
3. [Traumatic physeal fractures in cats: a review of 36 cases (2010-2020).](https://pubmed.ncbi.nlm.nih.gov/33847538/)
4. [Use of a Modified Intramedullary Pinning Technique for Distal Femoral Physeal Salter-Harris Type I and II Fracture Management: A Retrospective Study of 31 Cats.](https://pubmed.ncbi.nlm.nih.gov/37907243/)
5. [Three-dimensional models of physeal fractures in the femur for the teaching of veterinary medicine.](https://pubmed.ncbi.nlm.nih.gov/39109784/)
6. [A review of minimally invasive fracture stabilization in dogs and cats.](https://pubmed.ncbi.nlm.nih.gov/34309048/)
7. [Modified intramedullary pin technique for repair of distal femoral physeal fractures in the dog and cat.](https://pubmed.ncbi.nlm.nih.gov/6735844/)
8. [Closed reduction and fluoroscopic-assisted percutaneous pinning of 42 physeal fractures in 37 dogs and 4 cats.](https://pubmed.ncbi.nlm.nih.gov/27925240/)
9. [Percutaneous tibial physeal fracture repair in small animals: technique and 17 cases.](https://pubmed.ncbi.nlm.nih.gov/28636058/)
10. [[Proximal femoral fractures in cats and dogs].](https://pubmed.ncbi.nlm.nih.gov/4012774/)
11. [Total hip replacement as a treatment option for capital physeal fractures in dogs and cats.](https://pubmed.ncbi.nlm.nih.gov/22103440/)
12. [Preliminary results of five feline total hip replacements.](https://pubmed.ncbi.nlm.nih.gov/20553374/)
13. [Total hip replacement for the treatment of atraumatic slipped femoral capital epiphysis in dogs.](https://pubmed.ncbi.nlm.nih.gov/22784332/)
14. [[Bilateral idiopathic femur head epiphyseolysis ("slipped epiphysis") in cats: literature review and case description].](https://pubmed.ncbi.nlm.nih.gov/10028226/)
15. [Slipped capital femoral epiphysis in 17 Maine Coon cats.](https://pubmed.ncbi.nlm.nih.gov/26265738/)
16. [Polyostotic lymphoma with multiple pathological fractures in a six-month-old cat.](https://pubmed.ncbi.nlm.nih.gov/22334622/)