Marcus is a 13-year-old boy who sustained an injury to his right leg during a rugby match, describing a hyperextension injury at the knee during a tackle. He is brought to your ED via ambulance. He is complaining of a significantly painful right leg which is quite swollen and exquisitely tender at the distal thigh and knee. Marcus is treated using advanced paediatric trauma protocols and no other injuries are identified. The injury to his leg is a closed injury and his distal neurovascular status is intact. An IV cannula is inserted. IV Morphine is administered for pain and an above knee back-slab is applied to splint the injury. An X-ray is suspicious for a Salter Harris type III fracture to his distal femur. Marcus is kept nil by mouth and referred to the orthopaedic team for urgent review.
Epidemiology
Distal femoral physeal injuries are uncommon. They represent approximately 7% of lower extremity injuries in children and less than 1% of all paediatric fractures. Although rare, distal femoral physeal fractures have a high incidence of long-term complications. These injuries must be considered in patients with open physes to avoid misdiagnosis as collateral ligament injuries and minimise the risk of complications.
Anatomy
Bones
The epiphysis of the distal femur is the first epiphysis to ossify and is present at birth. From birth to skeletal maturity the distal femoral physis contributes 70% of the growth of the femur and 37% of the growth of the lower extremity. The distal femoral physis has an average growth of 1.0 cm/year, making it the fastest growing physis. Growth ceases at a mean skeletal age of fourteen years old in girls and sixteen years old in boys. Compared with ligamentous structures, the physis is generally considered weaker within joints of children, therefore most periarticular injuries involve the growth plate.
Muscles
Both heads of the gastrocnemius and plantaris muscles originate just proximal to the physis of the distal femur.
Ligaments
The collateral ligaments of the knee attach distal to the physis at the level of the epiphysis of the distal femur. The ACL and PCL attach to epiphysis at the intercondylar notch and can be injured.
Blood supply
The popliteal artery is an important vessel in this area and can be prone to injury. It is important to undertake a careful neurovascular exam in children with confirmed or suspected distal femur fractures. Although rare, injury to the popliteal artery can result in loss of lower limb viability.
Nerves
The sciatic nerve divides into the peroneal and tibial nerves proximal to the popliteal space.
Mechanism of injury
Distal femoral physeal injuries can be caused by hyperextension of the knee, with or without varus or valgus strain, or can occur by direct impact to the area. In the days of horse drawn wagons, this injury was coined ‘wagon-wheel injury’ or ‘cartwheel injury’ because it occurred when children attempted to jump onto a moving wagon and the leg became entrapped between the spoke of the moving wheel. Nowadays, most distal femur fractures are as a result of significant trauma such as motor vehicle accidents or sports related trauma. This is especially true for children between the ages of 2-11 years old, however less force is required for physeal disruption in infants and adolescents.
Children with underlying conditions such as neuromuscular disorders, joint contractures, difficult deliveries, or nutritional deficiencies can be more predisposed to distal femur physeal injuries.
Evaluation
Children with distal femur fractures will have significant pain and may be quite anxious, especially if assessment is undertaken in a resus situation. Make sure to follow advanced trauma protocols and ensure the child has had adequate analgesia.
Children with distal femoral physeal fractures generally present with pain, swelling and tenderness to the distal femur or knee and an inability to weight bear. Displaced separation of the distal femoral epiphysis may produce clinical deformity. Abrasions or lacerations of the overlying soft tissues may be a clue to the mechanism of injury or to an open fracture. Children with distal femur fractures may hold the knee in a flexed position due to hamstring muscle spasm. There may be varus or valgus knee instability on exam also.
A careful neurovascular exam of the lower limb including pulses, colour, temperature and motor and sensory status should be undertaken. Swelling in the popliteal space may be a sign of a vascular injury which requires urgent orthopaedic intervention. Although rare, injury to the popliteal artery is most commonly associated with an anterior displacement of the epiphysis or a posterior spike at the fracture site. The use of doppler ultrasound may be helpful in evaluating circulation distal to the injury but one of the most important screening tools for a vascular injury is measurement of the ankle-brachial index ratio.
The ankle-brachial index ratio involves comparing differences in systolic BP between the lower and upper limb. The cuff systolic blood pressure of the ankle should be >90% of the arm’s (brachial) systolic blood pressure. If the ankle’s cuff systolic blood pressure is <80-90% of the arm’s cuff systolic pressure, further investigation with a flow doppler ultrasound or arteriogram may be indicated.
If either the ankle-brachial index ratio or clinical exam suggest a vascular injury, then formal imaging with CT angiography should be carried out as soon as possible and repair of any defect to revascularize the distal limb must be undertaken as soon as possible but certainly within 6 hours of the initial injury. Urgent referral to orthopaedics is essential.
Evaluate the patient for signs and symptoms of compartment syndrome.
Assessing for compartment syndrome – the 5 Ps
- Pain – the most important indicator. Often diffuse and progressive, not resolved by analgesia, worsened by passive flexion of the injury.
- Pallor – assess distal to the injury. Dusky or cool skin (compared to the other side) or delayed capillary return.
- Pulse – weak or absent pulse indicates poor perfusion,
- Paralysis – assess active movement of the toes and foot. This may cause pain, but the purpose is to assess ability to move.
- Paraesthesia – ask about pins and needles or a feeling of the leg/foot “falling asleep”. Assess sensation with light touch or using an object such as a pen lid.
Any concerns about potential compartment syndrome must be escalated to an ED or orthopaedic senior without delay as this is a time-critical situation.
Injury to the peroneal nerve can be caused by anterior or medial displacement of the femoral epiphysis. The nerve can become stretched resulting in neurapraxia. Spontaneous recovery can be expected following reduction or fixation of the fracture. The exception to this is a transected nerve in association with an open injury which requires urgent orthopaedic input.
Testing motor and sensory function of the lower limb
Radiology
Most distal femur fractures can be identified on plain X-ray. AP, lateral and oblique views are recommended. Stress radiographs for suspected physeal injury are no longer routinely performed, MRI or ultrasound have replaced stress views in this setting. CT may be necessary for evaluation of intra-articular extension and to define fracture fragments to plan fixation.
Classification
The standard Salter Harris (SH) classification is used to describe distal femoral physeal fractures.
Salter Harris Type I (SHI)
A SHI fracture is a separation through the distal femoral physis. A non-displaced SHI fracture may be difficult to diagnose on X-Ray. A slight fleck of bone adjacent to the physis, a slight widening of the growth plate, or other irregularities of the physis can indicate a SHI fracture of the distal femur. Sometimes diagnosis is only made or confirmed during follow up when subperiosteal new bone formation along the adjacent metaphysis is identified on subsequent X-rays.
Non-displaced SHI fractures should be suspected when knee tenderness is localised circumferentially to the distal femoral physis. To help guide examation it is helpful to know that when the knee is in extension the waist of the patella overlies the distal femoral physis. Gentle varus/valgus stress to the knee may elicit pain.
Patients who have tenderness of the growth plate and are unable to weight bear should be treated as having a presumptive physeal fracture and should be casted and referred to a fracture clinic for follow up. If in doubt, seek advice by discussing your clinical findings with orthopaedics.
Salter Harris Type II (SHII)
Distal femoral physeal fractures are most commonly SHII fractures. This fracture pattern is characterised by an oblique fracture that extends across the metaphysis of the distal femur. The metaphyseal corner that remains attached to the epiphysis is called a Thurston-Holland fragment.
Salter Harris Type III (SHIII)
A SHIII fracture involves the physis and extends vertically through the epiphysis. These injuries can be produced by valgus stress during sports activities and may have an associated injury to the cruciate ligaments.
Salter Harris Type IV (SHIV)
SHIV fractures of the distal femur are uncommon. This injury pattern involves a fracture that extends vertically through the distal femoral metaphysis, physis and exits through the articular surface of the epiphysis.
Salter Harris Type V (SHV)
SHV fractures occur when the physis is crushed. This injury is rare and similar to SHI fractures in that they are often diagnosed retrospectively, when growth disturbance is observed following injury to the knee.
Management
Non-operative
Non-operative management may be considered in the case of non-displaced fractures. The injured leg is immobilised in a long leg cast for 4-6 weeks. Close clinical follow up by orthopaedics is essential to minimise complications.
Operative: closed technique
Closed reduction and percutaneous fixation followed by casting is used in cases of displaced SHI or SHII fractures. Some SHIII and SHIV fractures may be treated in this manner if anatomical reduction can be achieved. Again, the patient is followed closely post-operatively by orthopaedics to monitor for complications.
Operative: open technique
Open reduction internal fixation (ORIF) is indicated in the case of SHIII and SHIV fractures with weightbearing articular involvement or in the case of irreducible SHI or SHII fractures.
Complications
Growth arrest and arthritis
Any physeal fractures of the distal femur can be complicated by growth arrest. SHI and SH II fractures in other areas of the body usually have a low risk of growth arrest but in the case of distal femoral physeal fractures even minimally displaced SHI and SHII type fractures should be followed closely for physeal injury leading to growth arrest.
A complete growth arrest can lead to limb length discrepancies. A partial growth arrest can lead to angular deformities at the knee. SHIII and SHIV fractures that heal with displacement can produce post-traumatic arthritis because of their joint surface involvement. The risk of these complications can be minimised by maintaining anatomical physeal alignment and close follow up following non-operative and operative treatment.
Popliteal artery injury, peroneal nerve palsy and compartment syndrome
Although rare, vascular injuries can be associated with anterior displacement of the epiphysis or a posterior spike at the fracture site. Some studies have suggested that peroneal nerve palsy is observed in approximately 7.3% of distal femoral physeal fractures and compartment syndrome is noted in approximately 1.3% of these injuries.
Classic metaphyseal lesions
While discussing distal femur fracture patterns, it is important to mention classic metaphyseal lesions (CML). These fractures, also known as ‘bucket handle fractures’ or ‘corner fractures’, are highly specific for non-accidental injury (NAI) in children <1 year old. CMLs are most common in the tibia, femur and proximal humerus and can result from shearing forces applied to these long bones, which causes avulsion of the metaphysis. Shearing forces can be produced by holding a child by their trunk and shaking them causing their limbs to move back and forth. Any fracture in a non-mobile child should raise suspicion for NAI but be vigilant for the subtle findings of CMLs on X-ray. If you have concerns regarding NAI, escalate your concerns to the most senior clinician, contact the relevant social work / safeguarding department and discuss fracture management with the orthopaedic team. Refer to local hospital guidelines to give you an idea of what teams the child should be admitted under and what investigations should be carried out. See these DFTB resources related to child safeguarding for more information: skeletal surveys and NAI and safeguarding module facilitator guide.
The orthopaedic team review Marcus and a CT of his distal femur and knee is ordered to evaluate the degree of intra-articular extension and to define fracture fragments to plan fixation. Following CT he undergoes open reduction and internal fixation (ORIF) of the SH III fracture to distal femur and he is discharged home after a couple of days in a long leg cast. He will be closely monitored in fracture clinic during his recovery to minimise the risk of complications.
References
Amick A. (2019, Oct 7). Non-Accidental Trauma. [NUEM Blog. Expert Commentary by Riney C]. Retrieved from: http://www.nuemblog.com/blog/nonaccidental-trauma.
Ilharreborde, B., Raquillet, C., Morel, E., Fitoussi, F., Bensahel, H., Penneçot, G.F. and Mazda, K. (2006). Long-term prognosis of Salter–Harris type 2 injuries of the distal femoral physis. Journal of Pediatric Orthopaedics B, 15(6), pp.433-438.
Kareem, S., Shirley, E. and Skaggs, D. (2020). Distal Femoral Physeal Fractures- Pediatrics. Retrieved from: https://www.orthobullets.com/pediatrics/4020/distal-femoral-physeal-fractures–pediatric
McKenna, S.M., Hamilton, S.W. and Barker, S.L. (2013). Salter Harris fractures of the distal femur: Learning points from two cases compared. Journal of investigative medicine high impact case reports, 1(3), p.2324709613500238.
Price, C.T (2020). Extra-Articular Injuries of the Knee. Retrieved from: https://teachmeorthopedics.info/extra-articular-injuries-of-the-knee/
Wall, E.J. and May, M.M. (2012). Growth plate fractures of the distal femur. Journal of Pediatric Orthopaedics, 32, pp.S40-S46.
