Physeal Fractures

Introduction

The physis consists of four zones:

1. Reserve zone: adjacent to the epiphysis, where the chondrocytes divide and produce matrix
2. Proliferating zone: chondrocyte division produces organised columns extending away from the epiphysis. The true germinal cells of the physis are closest to the epiphysis.
3. Hypertrophic zone: chondrocytes increase in volume (80%) a,d ùatrox decreases and undergoes biochemical changes in preparation for calcification.
4. Provisional calcification zone: matrix becomes seeded with calcium phosphate.

The physis is weaker than the surrounding ligaments and bone, and therefore most susceptible to injury.

The physis is weakest at the junction between the proliferative and hypertrophic zones, and the hypertrophic zone itself is structurally weak due to the large cell:matrix ratio.

Physeal fractures involve the growth plate in all animals, and are classified according to the system described by Salter-Harris.

Salter-Harris Classification

Type I: separation through the hypertrophic zone

Type II: fracture-separation through part of the hypertrophic zone and part of the metaphysis

Type III: fracture-separation through part of the hypertrophic zone and part of the epiphysis involving the joint surface. There is an intra-articular component.

Type IV: fracture-separation involving the hypertrophic zone, metaphysis and epiphysis. There is an intra-articular component.

Type V: crushing injury of the physis

Type VI: crushing injury of the physis with new bone bridging across one side of the physis

This classification is most usefuly in describing fractures, and is not accurate at providing a prognosis for continued growth at the physis.

Pathophysiology

In most physeal fractures, both the hypertrophipc and germinal zones are involved and therefore all types have the potential to produce altered growth and limb deformities.

Compression of the physis is more detrimental than shearing, and this is determined partly by the shape of the growth plate. For example, the distal ulnar physis can easily become compressed.

In most cases, the physis is subject to a combination of forces that will produce permanent damage resulting in cessation of growth, i.e. closure of the physis.

Depending upon the physis involved, the effects may be clinically important or insignificant. (cessation of growth of a paired bone like the ulna can have major consequences).

Treatment

Treatment should be aimed at minimising further damage to the physis, although in most cases irreversible damaged will have occurred at the time of the injury.

Implants that create compression across the physis, rather than the fracture, should be avoided wherever possible.

Salter-Harris type I and II

These fractures do not have an intra-articular component. They are generally stable when reduced, with good resistance to compression and moderate resistance to bending and rotation.

Bending forces tend to be less than for diaphyseal fractures, and therefore smaller, less rigid implants can often be used, compared to those required for stabilisation of diaphyseal fractures.

K-wire fixation is used in most cases in a variety of ways:

rush pins: theoretically allowed continued growth as the pins run along the endosteal surface of the cortex rather than penetrating it.

cross pins: two wires are placed from the medial and lateral surface of the epiphysis to cross the fracture line, and then each other just proximal to the fracture line, before penetration the opposite cortex in the metaphysis. These prevent further growth unless they are removed.

parallel wires: theoretically will allow continued growth.

Salter-Harris type III and IV

These are intra-articular fractures, and therefore repair should follow certain principles:

Anatomic reduction and alignement: avoid steps in the joint surface and exposure of the fracture to synovial fluid

Rigid stabilisation with compression: to achieve direct bone healing. A lag screw is the idea method of fixation, as it will compress and provide rigid stability. A second point of fixation such as a K-wire or a second screw will add rotational stability. Rigid fixation also allow early limb use and helps maintain joint function and range of motion

Post-operative management: cold compresses, good analgesia, exercise restriction and physiotherapy

Avoid prolonged immobilisation of the joint.

Post-traumatic osteoarthritis is inevitable even with a perfect repair. Areas of damage tend to be replaced by biomechanically inferior fibrocartilage.

In general, as these are young growing animals, fracture healing is rapid and often complete within 3-4 weeks. Although removal of the implants when fracture healing is complete would facilitate further growth where the potential exists, in most cases they are left in-situ unless they are expected to cause problems.

Physeal Fractures Learning Resources
Flashcards Test your knowledge using flashcard type questions	Small Animal Orthopaedics Q&A 07

References

Corr, S. (2009) Physeal fractures RVC student notes

Slatter, D. (2002) Textbook of small animal surgery Elsevier Health Sciences

Denny, H. (2008) A guide to canine and feline orthpaedic surgery John Wiley and Sons