Salter-Harris Distal Femur and Proximal Tibia Fractures



Salter-Harris Distal Femur and Proximal Tibia Fractures


Lauren E. Lamont

Matthew R. Garner

Roger F. Widmann



INTRODUCTION

Knee injuries in adolescents commonly result in fractures of either the distal femoral or proximal tibial physis. When abnormal loads are sustained by maturing bone, the weaker physis fails more commonly than the surrounding ligaments and musculotendinous units. The Salter-Harris classification describes these patterns of injury. The severity of injury and the Salter-Harris classification often correlate with the risk of growth arrest. Resultant growth arrest may result in either leg length discrepancy or angular deformity of the knee due to the large contribution of these physes to lower limb growth.

The Salter-Harris classification ranges from types I to V (Fig. 34.1). Salter-Harris I is a transphyseal fracture involving the hypertrophic and calcified zones that tends to have a good prognosis when nondisplaced. When the transphyseal component of the fracture exits through the metaphysis, it is classified as a Salter-Harris II. The metaphyseal fragment is called the Thurston-Holland fragment; the periosteum is usually intact on the metaphyseal side and these fractures tend to heal well. A Salter-Harris III fracture is an intra-articular fracture as the transphyseal fracture exits the epiphysis. The reserve and proliferative zones of the physis are usually involved. These fractures usually need operative intervention to ensure an anatomic reduction of the joint surface. When the transphyseal fracture traverses the epiphysis, the physis, and exits in the metaphysis, it is a Salter-Harris IV. In these fractures, all four zones of the physis are disrupted. As with Salter-Harris III fractures, these fractures must be anatomically reduced to prevent bony bridge formation. Salter-Harris IV fractures have a worse prognosis if there is unreduced articular displacement. Last, a Salter-Harris V is a crush injury to the physis; this diagnosis is generally made retrospectively after growth arrest is seen. Here we review the physeal fractures of the distal femur and proximal tibia.


DISTAL FEMUR FRACTURES

Distal femoral physeal fractures in children may be difficult to treat and are associated with a high rate of complications including growth arrest.1 Close follow-up is necessary to detect early angular deformity that may result from a partial growth arrest. The greater the severity of fracture and displacement across the physis, the higher the risk of growth arrest.2 There should be a low threshold for obtaining computed tomography (CT) or magnetic resonance imaging (MRI) of the affected physis when a bony bridge is suspected in order to allow early intervention.


Anatomy

The distal femur is the most rapidly growing physis in the human body and the first epiphysis to ossify. In a full-term infant, the distal femoral ossification center is usually present at birth. The distal femur contributes approximately 70% of the growth of the femur and 40% of the overall limb.3,4 The distal femur’s average growth is 1 cm a year until closure between 14 and 16 years of age in girls and 16 to 18 years of age in boys.5

The majority of the distal femoral epiphysis is covered by the articular cartilage and articulates with the patella and proximal tibia. The distal femoral physis is an extra-articular structure; the capsule originates distal to the physis from the epiphysis. The undulating contour of the physis may be more resistant to shear forces; however, when shearing injury does occur, there is greater risk of growth arrest. Liu et al.6 described the lateral and anteromedial peripheral notches located at the metaphyseal- epiphyseal junction of the distal femur. Additionally, three major undulations within the epiphysis were identified across cadaveric specimens. These ridges were identified centrally, laterally, and medially and found to decrease with age especially in the central ridge.

The stabilizing medial and lateral collateral ligaments originate from the distal femoral epiphysis. The gastrocnemius takes its origin from the posterior surface of the epiphysis. Whereas in adults the ligaments may be injured due to varus and valgus stress on the knee, in skeletally immature patients, the distal femoral physis is more commonly injured.

Multiple neurovascular structures are at risk with injury to the distal femur. Most vulnerable are the popliteal artery and peroneal and posterior tibial nerves. The popliteal artery may be injured by the metaphyseal spike of distal femoral fracture. This vulnerability is in part due to the tethering of the artery
above at the adductor hiatus and distally by the fibrous tissue over the soleus muscle. Injuries may lead to thrombosis or bleeding from intimal tears. Displaced physeal fractures also have a risk of compartment syndrome, as arterial injury is more likely to occur. In a series of distal femoral physeal fractures, compartment syndrome occurred in 1.3% of patients.7 Injury to nervous structures may also occur with displacement. The posterior tibial and peroneal nerves form after the sciatic nerve branches in the popliteal space. Both are subject to traction injuries with displaced fractures. The incidence of peroneal nerve injuries was 7.3% in the same clinical series.7






Figure 34.1. Illustration showing the Salter-Harris classification for physeal fractures.


Classification

The Salter-Harris classification is commonly used and easily applied to these fractures. This classification can help dictate treatment as well as predict outcomes and rate of complications associated with individual fracture. The classification for distal femur fractures can be seen in Figure 34.1 and is defined as follows8:

A Salter-Harris I fracture is defined as a separation through the distal femoral physis with no involvement of either the metaphysis or the epiphysis. Salter-Harris II fractures are a separation through the distal femoral physis fracture exiting through the metaphysis. The resulting metaphyseal fragment is called the Thurston-Holland fragment. The portion of the physis that is “unprotected” by the Thurston-Holland fragment is at risk of growth arrest.

A Salter-Harris III is a physeal fracture in which the fracture line exits through the epiphysis and into the knee joint. Fractures of the medial femoral condyle that originate at the medial physis and exit into the notch have been compared to transitional fractures of the ankle given their relation to physeal closure.9 Coronal shear fractures of the lateral condyles have also been described.10 Salter-Harris IV injuries originate in the physis and the fracture exits through both the metaphysis (with a Thurston-Holland fragment) and the epiphysis. Salter-Harris V injuries are a crush injury to the physis and are unable to be definitively identified until resulting growth arrest manifests.


Epidemiology

Classification and displacement of distal femur physeal fractures has been shown to be predictive of overall outcome.1 Overall, these fractures account for between 1.4% and 5.5% of all physeal injuries in children.11,12,13 Of all fractures in children, these represent little more than 1%.11


Mechanism of Injury

Epidemiologic studies have shown that when physeal fractures of the distal femur occur in younger children, they are usually due to severe trauma or a high-energy injury.13 However, Salter-Harris I and II fractures in older children and adolescents are generally related to lower energy injuries or sports-related activities.2 For Salter-Harris I and II injuries, the knee is generally in a position of hyperextension with or without varus or valgus strain (Fig. 34.2).5 Patients will usually present complaints of significant knee pain and have associated knee swelling.

A Salter-Harris II fracture is more likely when both compression and distraction forces occur across the knee. This simultaneously creates tension and compression sides to the fracture and metaphyseal failure occurs due to compressive shear.14

Salter-Harris type III fractures are relatively rare injuries compared with the more common Salter-Harris I and II. They can lead to poor outcomes but have similar mechanisms of injury. Fractures of the medial femoral condyle result from a valgus force on the knee. These fractures will demonstrate valgus laxity on presenting exam; this has been shown to resolve after fracture healing.9 Coronal fractures involving the lateral femoral condyles result from a shear-type mechanism. The fracture types with an epiphyseal component such as a Salter-Harris III usually result in a larger effusion than types I and II injuries. Sports-related twisting or high-energy motor vehicle trauma can be the cause of a Salter-Harris IV. Similar to a Salter-Harris III, the patient will likely have a knee effusion due to the intra-articular component. The mechanism of a Salter-Harris V is unclear, but trauma causes a crush injury to the physis.



Imaging

Careful inspection of the physis on plain radiographs is necessary in order to identify minimally displaced fractures. At presentation, Salter-Harris I radiographs may demonstrate a
widening or irregularity of the physis (Fig. 34.3). Sometimes a small fleck of bone may be evident adjacent to the physis. In nondisplaced fractures, the only sign of fracture may be periosteal reaction 2 to 3 weeks after the injury. Plain radiographs including anteroposterior, lateral, and oblique views of the knee are usually adequate for diagnosis. Although historically stress radiographs were used to document Salter-Harris I fractures, this has largely been abandoned. The impetus behind this shift in thinking is that given the nonoperative management of these injuries, the risk of stressing the physis and potentially causing additional injury to an already damaged physis is not indicated.16 MRI has largely replaced stress radiographs and should be considered in any case of knee trauma, pain and swelling, and negative plain radiographs in order to confirm the diagnosis of a nondisplaced Salter-Harris I fracture.






Figure 34.2. A,B. Valgus load causing injury to distal femoral physis.






Figure 34.3. Asymmetrical physeal widening of the distal femoral physis representing a Salter-Harris I fracture.

For Salter-Harris II fractures, it is important to identify the metaphyseal component of these injuries, the size of which may influence surgical planning. MRI has been used to identify the frequency of posterior periosteal disruption in seemingly mild injuries. This posterior periosteal disruption was associated with a hyperextension mechanism of injury.17

Plain radiographs may not be sufficient for Salter-Harris III or IV fractures due to their intra-articular nature. The overlying patella may hide the epiphyseal component of the fracture, the displacement of which may not be adequately visualized on lateral imaging. Oblique radiographs will improve the sensitivity of assessing these fractures; however, radiographs have been shown to significantly underestimate displacement of Salter-Harris III fractures.18,19 To most accurately determine the amount of articular step-off, a CT scan or MRI should be obtained. Advanced imaging has been shown to change surgical plan and is important given that many of these minimally displaced injuries are initially missed.15

Salter-Harris V fractures, as noted, are difficult to diagnose on imaging at time of initial presentation. These injuries are
distinguished from their nondisplaced Salter-Harris I counterparts only in hindsight with growth arrest. It has been suggested that blurring of the bone structure around the physis may demonstrate a Salter-Harris V.20 MRI may be helpful to identify physeal injury in the setting of negative plain films at the time of injury.

Mar 7, 2021 | Posted by in ORTHOPEDIC | Comments Off on Salter-Harris Distal Femur and Proximal Tibia Fractures
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