The Physis and Skeletal Injury

Dennis Wenger

James Bomar

INTRODUCTION

Many simple fractures in children would heal well, whether they were looked after by a professor in a university hospital or by an aborigine on an undiscovered island. Fractures through the physis (growth plate) are a different story.

EPIPHYSEAL FRACTURES

Fractures of the true epiphysis usually involve the growth plate but occasionally occur in isolation. They may be classified as follows (Fig. 2-1):

Avulsion at the site of ligamentous attachment
Comminuted compression fracture
Displaced osteochondral fragment

“The physician is only nature’s assistant”

—Galen

Figure 2-1 Epiphyseal fractures not involving the growth plate.

Figure 2-2 Anterior tibial spine fracture (arrow).

Figure 2-3 Osteochondral fracture of the lateral femoral condyle secondary to acute traumatic patellar dislocation. The fragment was large enough that it could be surgically repositioned.

Avulsion at the Site of Ligamentous Attachment

The common sites of this injury are the tibial spine (Fig. 2-2), the ulnar styloid, the base of phalanges, and the secondary ossification centers of the pelvis (see Chapter 12). The bony fragment retains an adequate blood supply and does not undergo avascular necrosis. If the fragment is displaced, union is rare because synovial fluid inhibits callus formation. The displaced fragment may block joint movement or may leave the joint unstable because of functional ligamentous lengthening. These problems justify accurate reduction and may require open reduction.

Osteochondral Fragments

Osteochondral fragments are most commonly sheared off the distal femur, the patella, the capitellum (humerus), and the radial head. A displaced fragment produces the problems of a loose body and articular cartilage injury. If the fragment is large and from an important part of the joint, it should be replaced and fixed anatomically (Fig. 2-3). If small, it should be removed. Often the fragment has little bone attached and is difficult to see on x-ray (especially radial head and capitellum).

PHYSEAL (GROWTH PLATE) INJURIES

Growth plate injuries can cause significant distress to worried mothers. These mothers often immediately Google the term “growth plate” on their phone while in clinic. Such searches produce over two million results and these mothers often zero in on the most alarming search results. Be prepared to explain that injuries to the growth plate make up approximately one-third of skeletal trauma in children. Possible consequences of such injuries include progressive angular deformity, progressive limb-length discrepancy, and joint incongruity. It is important to note that although damage to the growth plate has the potential for causing many disastrous problems, in fact the area repairs well, and problems after injury are uncommon when treated well. When growth is disturbed, the reason is one of the following:

Avascular necrosis of the physis
Crushing or infection of the physis
Formation of a bone bridge between the bony epiphysis and the metaphysis
Hyperemia producing local overgrowth

The problems and the means of their prevention can only be understood by an appreciation of the anatomy and the healing reactions in the growth plate area.

Anatomy

The growth plate is a cartilaginous disc situated between the epiphysis and the metaphysis, with germinal cells attached to the epiphysis and a blood supply from epiphyseal vessels (Fig. 2-4). Repeated multiplication of these germinal cells provides the cell population for the rest of the physis. The daughter cells multiply further, secreting a cartilage matrix, and increase in size, thereby producing growth. The matrix calcifies. Metaphyseal vessels enter the cell columns, remove a little matrix, and lay down bone upon the cartilage matrix to form metaphyseal bone.

With a fracture, the plane of separation is most frequently the junction between calcified and uncalcified cartilage. A transverse section through the growth plate in this region demonstrates the small amount of structural matrix present, which probably accounts for the relative weakness of the area. The important germinal part of the plate—indeed the greater thickness of the plate—remains mostly with the epiphysis. This plane of separation is relatively bloodless, so that an epiphyseal separation often has little associated swelling.

However, when the plane of fracture separation has been examined carefully, the anatomic fracture line is often less “pure.” Johnston and Jones performed biopsies of fractures requiring open reduction and found that the fracture line often passes between the epiphysis and the germinal layer.

This is commonly seen in fractures through physes that have significant natural undulations (a “hilly terrain”) such as the distal femur and distal tibia (Fig. 2-5). These undulations may be evolutionary design features that prevent easy disruption of the physis but when it finally is forced to give, the shearing action often disrupts the germinal layer. If reduction is not anatomic, there will be epiphyseal to metaphyseal bone contact, which with healing, may form a bar across the physis. Obviously, if much of the germinal layer is disturbed, there is a chance for growth arrest.

Figure 2-4 Blood supply of the growth plate. Damage to the epiphyseal artery can destroy the plate. Damage to the metaphyseal artery is less important.

Figure 2-5 The irregularity and undulations in certain physes may increase the risk for physeal closure with fracture (e.g., “Kump’s bump”—distal tibial physes).

Figure 2-6 The blood supply of two types of epiphyses. A. Vessels to the femoral head track in the periosteum under the synovium. A periosteal tear or a high-pressure effusion may cause AVN. B. Vessels to the distal femur pass through a thick wad of soft tissues and are rarely disrupted with a fracture.

Blood Supply to the Epiphysis

The blood supply of the epiphysis is important. Dale and Harris showed that there are two fundamental types of epiphyses (Fig. 2-6) according to how they receive their blood supply. The prognosis after physeal injury is greatly determined by this factor.

Epiphyses Totally Clad with Cartilage (such as head of femur, head of radius). Total interruption of the blood supply to the germinal cells may follow fracture separation. Avascular necrosis of the plate and epiphysis, and arrest of longitudinal growth naturally follow (Fig. 2-7). Ganz et al. after a study of femoral head blood supply clarified how conditions such as acute SCFE (slipped capital femoral epiphysis), a type of acute physeal separation, so readily lead to AVN.

Epiphyses with Soft-Tissue Attachments (most physeal injuries—distal radius, distal tibia, distal femur, etc.). When these are separated, the soft-tissue hinge will remain attached to the epiphysis, so that the circulation to the epiphysis remains intact. The germinal cells are not injured, and longitudinal growth continues unscathed.

Figure 2-7 This 13-year-old boy fractured his femoral neck. Although promptly and anatomically reduced, he developed AVN of the femoral head because of disruption of the vessels that ascend the femoral neck.

HEALING REACTIONS OF THE PHYSIS AND EPIPHYSIS

Dale and Harris have published the most credible description of growth plate separation. The plate separates mostly between the calcified and uncalcified layers of the growth plate. For a week or 2, the hiatus is filled by fibrin. Initially the physis becomes wider, because growth
cartilage continues to be produced without invasion by metaphyseal vessels. After about 2 weeks, the vessels begin to invade the cartilage columns again with the physis becoming narrower once more, and healing occurs without leaving a scar. In this way, the growth plate heals more quickly than a fracture through bone (Fig. 2-8). The repair of an injury at right angles to the plane of the growth plate shows more variation (Fig. 2-9).

Cartilaginous Epiphysis. If they remain displaced, both portions of the epiphysis continue to grow separately, producing a double-ended bone.

Ossified Epiphysis. If the fracture surfaces are not in contact, both fragments continue to grow for some time. Eventually, premature arrest of growth adjacent to the fracture line takes place.

If the fracture surfaces are approximated but without anatomic reduction of the growth plate, a bridge of callus will form between the epiphysis on one side and the metaphysis on the other. This bony bridge produces a brake on growth. When the bridge is at the center of the epiphysis, the two outside edges will continue to grow, resulting in tenting of the end of the bone. When the bridge is toward one margin of the growth plate, a progressive, angular deformity develops.

Figure 2-8 Healing after growth plate separation occurs by means of new bone formed by the growth plate and by the periosteum. This can be seen clearly 3 weeks after the initial injury.

Figure 2-9 Healing patterns of Type IV injuries.

If the fracture is accurately reduced so that there is coaptation of the growth plate, there will be a small scar at the site of growth plate injury, but this is not sufficient to disturb growth. If there is no reduction and there is poor apposition of the fragments, the result is non-union.

Effect of Internal Fixation. Small Kirschner wires passed through the center of the plate do not interfere with growth. If they are passed near the margin of the plate, growth is occasionally disturbed. Threaded pins or screws across the plate act as effectively as Blount staples in inhibiting growth.

Repair of Articular Surfaces. Cartilage defects in a joint invite intra-articular adhesions. Salter and associates have shown that continuous passive motion (CPM) not only discourages adhesions but also stimulates more rapid and complete healing of full-thickness defects in rabbits. Motion—not immobilization—for injured joint surfaces would seem wise; however, often early motion will increase the chance for pseudarthrosis. Finding a happy medium is the art. CPM is rarely required following primary treatment of children’s joint fractures (as opposed to adults who are much more likely to become stiff).

SALTER-HARRIS CLASSIFICATION

The Salter-Harris classification of growth plate injuries remains the most practical and commonly used. Founded on the pathology of injury, the classification is well suited to an accurate verbal description of a fracture and provides an excellent guide to rational treatment (Table 2-1). Most growth plate injuries can be easily classified, leaving very
few fracture patterns that produce arguments at fracture rounds. The classification should be studied in the original, as it is one of the classic papers in orthopedics.

Table 2-1 Salter Harris Classification

S.H. I	S.H. II	S.H. III	S.H. IV	S.H. V

Fracture through physis	Fracture through physis extending through metaphysis (with resulting triangular Thurston-Holland fragment)	Fracture through physis extending through epiphysis	Fracture through epiphysis and metaphysis crossing the physis	Compression fracture through physis not extending to epiphysis of metaphysis