- Distal femur fractures in children commonly involve the physis
- Salter Harris II fractures are the most common distal femoral physeal injury
- Reduction and fixation is typically required for distal femoral physeal injuries
- Growth arrest (up to 50% incidence) is the most common complication following distal femoral physeal injuries
Description:Distal femur fractures in children can have various fracture patterns, including supracondylar fractures, T-condylar fractures, or fractures of any pattern from the Salter-Harris classification. Salter-Harris II fractures of the distal femur are the most common pattern in children, and will be the focus of this review. (Arkader, 2007; Riseborough 1983; Thompson 1995). Even though distal femur fractures are relatively uncommon injuries, they can have significant implications for limb alignment and future growth (Arkader, 2007; Basener, 2009; Eid, 2002). Restoration of normal limb alignment requires fracture reduction and fixation in a near-anatomic position, without risking further damage to the growing physis (Czitrom, 1981). Because of the undulating nature of the distal femoral physis, and the propensity for Salter-Harris II fractures in this location to cross different zones of the growing physis, these fractures are among the most likely to lead to permanent physeal arrest (Thomson, 1995).
Epidemiology:Distal femur fractures in children are typically related to significant trauma, such as falls, motor vehicle accidents, or contact sports. They are rare injuries comprising only 7% of all pediatric lower extremity fractures. (Azar, 2017).
Clinical Findings:Patients typically have pain, swelling about the knee, possible deformity, and an inability to bear weight on the affected leg (Azar, 2017). Severe deformity or displacement of the distal fragment should raise concern for possible vascular injury prompting ABIs or vascular consult as indicated.
Imaging Studies:X-Rays (AP and lateral views) of the affected knee are the standard modality for diagnosing distal femur fractures. Imaging of the entire femur should be considered in most cases, especially in incidences of high energy trauma, to ensure the absence of segmental fractures including femoral neck fractures, or other associated injuries. In rare cases, patients can have distal femoral physeal injuries without displacement, which can be difficult to appreciate on plain radiographs. In the past, stress radiographs have been recommended to visualize physeal displacement. However, this remains controversial as most injuries can be seen on regular x-rays. When there is a concern for a subtle physeal injury, it may be more prudent to obtain an MRI. MRI is becoming more accessible and inexpensive, and has the advantage of avoiding further damage or displacement to the physis (Segal, 2011).
Treatment:Treatment options for Salter-Harris II distal femur fractures include closed manipulation and casting, percutaneous fixation, external fixation, or open reduction with internal fixation.
- Observation is not indicated for displaced fractures (Graham, 1990).
- Closed manipulation and casting is an option, although Salter-Harris II fractures of the distal femur have significant potential for instability, which could lead to malunion, and continued micromotion at the fracture site may encourage physeal arrest (Lombardo, 1977).
- External fixation is an option, but is technically difficult, as it requires placing multiple percutaneous pins in the relatively small distal femoral epiphysis or spanning the knee for stability. It is therefore typically reserved for cases where temporary fixation is needed, such as severe open injuries or multitrauma.
- Internal fixation using cannulated screws, or percutaneous fixation with smooth wires are the most commonly chosen treatments, and the choice between the two depends on the fracture pattern.
- Salter II fractures with large metaphyseal Thurstan-Holland fragments can be fixed with transverse screws across the fragment, entirely within the metaphysis.
- Fractures with smaller metaphyseal fragments, which are more similar to Salter I injuries, require fixation that crosses the physis for stability. To minimize further physeal damage, most surgeons choose small-diameter K-wires or Steinman Pins, placed in a crossed pattern, and removed several weeks later after sufficient healing (Dahl, 2014; Garrett, 2011). Guidelines for choosing transverse, metaphyseal fixation versus crossed transphyseal fixation are not well defined. Similarly, there is no standard or significant guidance from the literature regarding whether smooth K-wires should be started proximally or distally, buried or left percutaneous, or removed in an outpatient setting or under a second anesthetic.
Complications:Malunion is a concern for distal femur fractures, and appropriate reduction with internal fixation is typically used to avoid this complication. Permanent physeal arrest is a major concern with Salter Harris injuries to the distal femoral physis. The incidence of physeal arrest following distal femur fractures has been reported as high as 50% (Basener, 2009). If patients have significant remaining growth, partial physeal arrest may cause a leg length discrepancy or angular deformity, depending on the location and extent of the arrest. Leg length discrepancies or angular deformities may require other procedures to maintain appropriate limb lengths and alignment, including physeal bar resection (Khoshhal, 2005), guided growth, corrective angular osteotomies, femoral lengthening, or contralateral femoral epiphysiodesis or shortening.
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