Clinical History
A 12-year-old boy who had sustained a twisting injury to his right knee while racing on a scrambler was presented to us. Clinically, his knee was found to be swollen and bruised with a gross swelling
of the thigh. AP and lateral radiographs were obtained to assess the boy's condition.
Imaging Findings
A 12-year-old boy presented to the Accident and Emergency department after having sustained a twisting injury to his right knee while racing on a scrambler. He described that his right foot became
lodged into the ground, with his knee in the extended position, as the motorcycle turned sharply to the right. Clinically, it was found that he had a swollen and bruised right knee. The foot was
internally rotated with respect to the knee and the thigh. The knee motion was grossly restricted, and the patient could not raise his leg straight. There was localised tenderness over the proximal
tibia. It was not possible to accurately assess the status of the collateral and cruciate ligaments. There was no evidence of neurological or vascular compromise, although the calf was very swollen.
An X-ray examination demonstrated a fracture involving the proximal physis of the tibia. In the lateral view, the epiphysis was seen to have been displaced anteriorly with respect to the tibial
metaphysis. There were no fractures of the epiphysis or metaphysis. This was therefore diagnosed as a Salter Harris type I injury (i.e. a fracture through the physis without any involvement of the
epiphysis or the metaphysis). It was treated by closed reduction and K-wiring, with plaster immobilisation. Post-operatively, it was found that the right lower limb remained neuro-vascularly intact
and an X-ray scan anatomically demonstrated correct reduction. He remained in cast for six weeks, and the pins were removed when he was put in the outpatient ward. He was reviewed clinically and by
taking standard radiographs for six months: initially, at two-week intervals for two months, and then at four-week intervals. The fracture healed in anatomical position and a full range of knee
movements could be performed. There was also full ligamentous stability. There was no evidence of a premature bony fusion of the physis as the Harris growth lines remained parallel to the growth
plate. These lines are dense, trabecular and transversely orientated within the metaphysis, commonly seen on radiographs in children of all ages, and which typically follow a period of
immobilisation. They relate to a temporary slowdown of normal longitudinal growth during the period of illness and become radiographically visible following a period of normal growth. A line that
converges towards the physis suggests localised growth damage, and may predict a growth deformity.
Discussion
Injuries of the proximal tibial epiphysis are known to be rare, accounting for approximately 0.5%–3.1% of all epiphyseal injuries. They usually involve a Salter Harris Type II, III or IV
injury, and are associated with a high incidence of growth disturbance. There are a number of anatomical factors which may account for the irrelatively low incidence. The proximal tibial epiphysis
does not receive attachments from the medial or lateral collateral ligaments. Hence, varus and valgus forces are transmitted directly to the metaphysis, and not to the epiphysis. This is in contrast
to the lower femoral epiphysis which does receive attachments of these ligaments, and which has a higher incidence of injury. Laterally, the proximal tibial epiphysis is buttressed by the upper end
of the fibula, anteriorly and the tubercle projects inferiorly to overhang the metaphysis. The epiphyseal attachment to the shaft is irregular; hence, any fracture at this level will shear across
different levels within the physeal plate. This fact may explain the high association of proximal tibial physeal fractures and growth disturbance. Additionally, the insertion of the semimembranous
tendon extends into the metaphysis and the patellar tendon inserts into a separate centre of ossification, protecting the epiphysis from avulsion strains. The peak incidence of injury is found in
those who are 12–14 years of age and is more common in males. This probably reflects a greater exposure to trauma and the relative skeletal maturity found in females, rather than to any
intrinsic physeal difference. Clinical features include the inability to lift the leg because of the presenceof pain and hamstring spasm. There may be a haemarthrosis present with a soft tissue
swelling of the leg and tenderness at the level of the growth plate 1–1.5 cm distal to the joint line. In 40% of the cases, there is an injury to the ipsilateral lower limb. X-ray images may be
difficult to interpret, and when an epiphyseal injury is suspected, stress views and views of the unaffected leg may be required. Hyperextension of the knee should be avoided because of the
possibility of there being a popliteal artery injury. Where a physeal injury is suspected, but is radiographically occult, MRI provides an improved delineation of non-displaced growth plate fractures
of the knee, while simultaneously allowing for evaluation of soft tissue structures. Cross sectional imaging is of value in monitoring the development of a premature physeal closure. Anatomical
reduction may be achieved by a closed reduction and cast immobilisation, K-wiring, or open reduction with screw fixation. Associated problems include ligamentous injuries, vascular complications
including the compartment syndrome, knee instability, and growth disturbance (in up to 25% of the cases).
Differential Diagnosis List
Salter Harris type I fracture of the proximal tibial epiphysis.
Final Diagnosis
Salter Harris type I fracture of the proximal tibial epiphysis.
