AJR 2003; 181:1397-1399
© American Roentgen Ray Society
MRI of Trapped Periosteum in a Proximal Tibial Physeal Injury of a Pediatric Patient
Andrew Whan1,2,
William Breidahl1 and
Gregory Janes3
1 Perth Radiological Clinic, Magnetic Resonance Imaging Centre, 127 Hamersley
Rd., Subiaco, Western Australia, 6008 Australia.
2 Present address: Barwon Medical Imaging, The Geelong Hospital, PO Box 281,
Geelong, Victoria, 3220 Australia.
3 Perth Orthopaedic and Sports Medicine Centre, 31 Outram St., West Perth,
Western Australia, 6005 Australia.
Received October 21, 2002;
accepted after revision April 17, 2003.
Address correspondence to A. Whan.
Introduction
Proximal tibial physeal injuries are rare, accounting for 0.5% of all
physeal injuries [1] and
usually occurring in adolescents. Irreducible fractures of the proximal tibial
physis due to interposed soft tissues have been reported in the orthopedics
literature but are unusual [1,
2]. The diagnosis is usually
made only at open surgery after a failed closed reduction. We report the
preoperative MRI diagnosis of a Salter-Harris type 1 proximal tibial physeal
injury with interposition of periosteum in the posterior growth plate, which
required open surgical reduction.
Case Report
A 16-year-old male gymnast competing at the international level suffered a
severe hyperextension injury to both knees on landing from a rings-routine
apparatus. Initial radiographs of both knees showed bilateral knee joint
effusions and bilateral widening of the posterior proximal tibial physeal
plate (Fig. 1A). Clinically,
there was also suspicion of cruciate ligament, medial collateral ligament,
posterolateral corner, and gastrocnemius muscle injuries. However, clinical
assessment was difficult because of severe pain. MRI performed 12 days after
the injury showed a similar pattern of injury in both knees. The findings were
bilateral Salter-Harris type 1 proximal tibial physeal injuries with anterior
compression and posterior distraction of the growth plate
(Fig. 1B) and bilateral
gastrocnemius and soleus muscle injuries. In the right knee, an elongated
focus of low signal intensity on all sequences extended 10 mm into the
posterior aspect of the proximal tibial growth plate, both medial and lateral
to the posterior cruciate ligament insertion (Figs.
1C and
1D). This focus was interpreted
as an enfolded periosteum. The relatively thick appearance of the periosteum
(Fig. 1C) may have been caused
by the combination of the low-signal periosteum and adjacent compact bone on
either side of the physeal plate or a degree of buckling and edema of the
periosteum or both. As a result of this finding, surgery was performed 2 days
after MRI and confirmed trapped periosteum insinuated in the posterior growth
plate, which was released with some difficulty through a posteromedial and
posterolateral approach. The flap was 10 mm in length, corresponding with the
MRI appearance.
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Fig. 1A. —16-year-old male gymnast who sustained bilateral
hyperextension knee injury 12 days earlier. Lateral radiograph of right knee
shows widening (arrow) of posterior proximal tibial physeal
plate.
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Fig. 1B. —16-year-old male gymnast who sustained bilateral
hyperextension knee injury 12 days earlier. Sagittal proton
density–weighted image shows posterior widening (solid arrow)
of medial part of proximal tibial physis. Note large joint effusion (open
arrow) anteriorly.
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Fig. 1C. —16-year-old male gymnast who sustained bilateral
hyperextension knee injury 12 days earlier. Sagittal proton
density–weighted image obtained lateral to B reveals enfolded
periosteum (arrow) in widened posterior aspect of medial tibial
physis.
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Fig. 1D. —16-year-old male gymnast who sustained bilateral
hyperextension knee injury 12 days earlier. Axial fat-saturated proton
density–weighted image obtained at level of physis shows lower signal
periosteum (between arrows) trapped in medial growth plate.
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Discussion
Physeal injuries are common in children less than 16 years old. The
mainstay for imaging these injuries, as is true for all fractures, is
radiography. CT, particularly helical CT with multiplanar reformatting, is
useful to more fully evaluate and classify physeal injuries. CT is most
commonly used in the ankle and knee and for Salter-Harris type 4 fractures to
assess articular surface displacement and growth arrest
[3].
The role of MRI in revealing physeal injuries is still evolving. It has
advantages such as visualization of cartilage (including nonossified
epiphyses) and soft tissues, multiplanar capability, and absence of ionizing
radiation. It is the best modality to depict avascular necrosis complicating
epiphyseal injury and bony bridges across growth plates that cause growth
disturbances as sequelae of some physeal injuries
[3]. MRI is not required for
most physeal injuries but may be useful in the assessment of acute physeal
injuries of the elbow, knee, and sometimes the ankle
[3]. MRI can be used to confirm
or exclude physeal injuries that may be difficult or impossible to depict on
radiography, particularly Salter-Harris types 1 and 5 fractures. It is also
helpful to reveal associated ligamentous injuries, which occur in half of
patients with physeal separations around the knee
[3].
Although knee injuries are relatively common in children and adolescents,
proximal tibial physeal injuries are rare, representing less than 1% of all
physeal injuries; two thirds of these are Salter-Harris types 1 and 2
fractures [1,
4]. The physis is relatively
protected by ligamentous attachments on the proximal tibia distal to the
physis and by the buttressing effect of the proximal tibiofibular joint
[4]. The most common mechanism
of injury is an indirect valgus force. Hyperextension injuries, such as in
this case, can be associated with popliteal artery injury, particularly
intimal tears [4].
The usual management of Salter-Harris types 1 and 2 fractures of the
proximal tibial physis is closed manipulation and a long leg cast.
Salter-Harris types 3 and 4 fractures are usually treated with open reduction
and internal fixation. Failed closed reduction of displaced types 1 and 2
fractures is an indication for open reduction and is recognized in the
orthopedics literature as most often due to an interposed periosteal flap
[4,
5]. Several case reports
describe nonreducible proximal tibial physeal fractures due to interposition
of the pes anserinus and periosteum in one case
[2] and periosteum interposed
in the medial physis in another
[1]. The periosteum tears on
the tension or distraction side of the fracture and typically tears distal to
the separated proximal tibial physis
[5]. Entrapped periosteum has
been described as a cause for irreducible fractures in a number of other sites
including the distal radius
[6], proximal humerus
[7], and distal tibia
[8]. Other soft tissues such as
muscles, tendons, ligaments, and neurovascular bundles may also become
interposed in the fracture site, resulting in irreducibility
[5,
7,
8]. Roberts
[5] has described a case of an
entrapped distal medial collateral ligament in the proximal tibial growth
plate seen on MRI in the setting of a valgus deformity of the tibia 1 year
after a proximal tibial physeal injury.
The detection of interposed periosteum in association with a physeal injury
using MRI or other imaging techniques has not been described in the
literature, despite being recognized as the commonest cause of irreducibility.
Close and Strouse [9] reviewed
nine physeal fractures around the knee seen on MRI and described periosteal
elevation in six cases, none of which showed the periosteum interposed at the
fracture site. The case that we have described includes an important diagnosis
that can be made noninvasively on MRI, allowing prompt appropriate surgical
treatment, which may prevent potential complications such as nonunion and
growth disturbance.
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Introduction
Case Report
