AJR 2005; 184:1495-1498
© American Roentgen Ray Society
Plastic Deformation of the Femur: Cross-Sectional Imaging
James F. Griffith1,
Mei Po Tong1,
Hiu Yee Hung1 and
Shekhar Madhukar Kumta2
1 Department of Diagnostic Radiology & Organ Imaging, Prince of Wales
Hospital, Chinese University of Hong Kong, Shatin, N. T., Hong Kong.
2 Department of Orthopedics and Traumatology, Prince of Wales Hospital, Chinese
University of Hong Kong, Shatin, N. T., Hong Kong.
Received May 20, 2004;
accepted after revision July 22, 2004.
Address correspondence to J. F. Griffith
(griffith{at}ruby.edu.cuhk.edu.hk).
Introduction
Immature bone possesses greater elasticity than mature bone does. When
excessive force is applied, immature bone undergoes deformation that returns
to normal when the force is removed (elastic deformation), persists when the
force is removed (plastic deformation), or proceeds to fracture
[1,
2]. Plastic deformation
usually, though not invariably, occurs in children and most commonly affects
the radius and ulna [3,
4]. Less frequently, the
fibula, femur, clavicle, rib, and tibia are affected
[2].
Plastic deformation has two components: longitudinal and axial. Radiographs
allow ready visualization of longitudinal deformation
[2,
4]. Axial deformation is best
seen on cross-sectional imaging. To our knowledge, this is the first report
illustrating cross-sectional imaging of plastic deformation.
Case Report
A 7-year-old boy, otherwise in good past health, was climbing to the top of
his bedroom doorframe when he fell from a height of about 5 ft (150 cm). He
developed severe pain in the right thigh that resolved over the next few
hours. However, during the ensuing weeks and months he intermittently
complained of right thigh pain. These painful episodes were infrequent and
short-lived so medical attention was not sought. Three months after the
initial injury, he was sitting on a sofa with his legs extended when his
younger brother fell, apparently quite lightly, against his right thigh. This
precipitated severe thigh pain, which prompted a consultation with the family
practitioner. A muscular injury was considered most likely and rest was
advised. However, pain persisted over the next few days, during which time the
boy's parents also noticed a hard lump in his thigh. Radiographs (Figs.
1A and
1B) and MR images (Figs.
1C and
1D) were obtained at a private
clinic, and the patient was referred to the hospital with a suspected bone
tumor.
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Fig. 1A. —7-year-old boy with plastic deformation of femur. Frontal
radiograph (A) of both femurs and lateral radiograph (B) of
right femur at presentation show anteromedial bowing and apparent anteromedial
cortical thickening of distal right femoral diaphysis (arrows).
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Fig. 1B. —7-year-old boy with plastic deformation of femur. Frontal
radiograph (A) of both femurs and lateral radiograph (B) of
right femur at presentation show anteromedial bowing and apparent anteromedial
cortical thickening of distal right femoral diaphysis (arrows).
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Fig. 1C. —7-year-old boy with plastic deformation of femur. Axial
(C) and sagittal (D) T2-weighted fat-suppressed images (TR/TE,
5,236/70) of right femur show that the femoral diaphysis has a curved oblong
contour. Note moderately severe medullary edema involving most of femoral
diaphysis. Focal T2 hyperintensity (arrow, C) and T1
intermediate intensity (not shown) are present at apex of deformed cortex.
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Fig. 1D. —7-year-old boy with plastic deformation of femur. Axial
(C) and sagittal (D) T2-weighted fat-suppressed images (TR/TE,
5,236/70) of right femur show that the femoral diaphysis has a curved oblong
contour. Note moderately severe medullary edema involving most of femoral
diaphysis. Focal T2 hyperintensity (arrow, C) and T1
intermediate intensity (not shown) are present at apex of deformed cortex.
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The radiographs and MR images were reviewed, and CT examination of the
right femur was undertaken (Figs.
1E and
1F). A diagnosis of
posttraumatic plastic deformation of the femur was made. The patient was
treated conservatively with 1 week of bed rest followed by the gradual
resumption of normal activity. Thigh pain settled completely over the next 2
weeks and did not recur. He continues to be followed up in the orthopedic
clinic yearly. Repeated radiography (Figs.
1G and
1H) and MRI (Fig.
1I) examination 5 years after
the initial injury (i.e., when the boy was 12 years old) revealed marked
improvement in the degree of longitudinal bowing and axial deformation.
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Fig. 1E. —7-year-old boy with plastic deformation of femur. Axial
(E) and oblique coronal (F) CT reformations at same location as
C show microfractures (arrows) extending obliquely along
deformed cortex.
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Fig. 1F. —7-year-old boy with plastic deformation of femur. Axial
(E) and oblique coronal (F) CT reformations at same location as
C show microfractures (arrows) extending obliquely along
deformed cortex.
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Fig. 1G. —7-year-old boy with plastic deformation of femur. Frontal
radiograph (G) of both femurs and lateral radiograph (H) of
right femur 5 years after initial presentation show that degree of femoral
bowing has returned to almost normal. The apparent anteromedial cortical
thickening of distal femoral diaphysis (arrow, G) is now much
less than previously (A and B). Thickening
("buttressing") of posterior mid diaphyseal cortex
(arrows, H) has occurred.
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Fig. 1H. —7-year-old boy with plastic deformation of femur. Frontal
radiograph (G) of both femurs and lateral radiograph (H) of
right femur 5 years after initial presentation show that degree of femoral
bowing has returned to almost normal. The apparent anteromedial cortical
thickening of distal femoral diaphysis (arrow, G) is now much
less than previously (A and B). Thickening
("buttressing") of posterior mid diaphyseal cortex
(arrows, H) has occurred.
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Fig. 1I. —7-year-old boy with plastic deformation of femur. Axial
T1-weighted image (425/12) 5 years after initial presentation at same location
as C shows that femoral diaphysis is now much more rounded in contour.
Note small residual anteromedial cortical protrusion (long arrow) and
new thickening of posterior cortex (short arrow). Medullary canal is
normal.
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Discussion
Plastic deformation occurs in that narrow stress–strain zone when
bone exceeds its elastic limit, although not to a sufficient degree to
fracture [1,
5]. Most cases of plastic
deformation result from longitudinal compression of long tubular bones
[3]. A histologic study of
animal bones has shown that although elastic deformation does not cause
detectable change in bone microstructure, plastic deformation is characterized
by longitudinal microfractures or "slip lines" in the injured
cortex [5]. These
microfractures transverse the cortex at an angle of about 30°, comparable
to the degree of bowing [5].
Increasing severity of force results in increasing frequency of microfracture,
further bone weakening, and eventual fracture
[1,
5].
Three imaging techniques combined to reveal the diagnosis and provide a
better understanding of the pathophysiology of plastic deformation in this
patient. The degree of plastic deformation was such that it simulated a
sessile osteochondroma on initial radiographs. However, several features
(longitudinal bowing, diaphyseal location, and lesional length) did not favor
this diagnosis. The severity of axial deformation of the femoral diaphysis
could not be fully appreciated on radiographs, but it was fully seen on
cross-sectional imaging. CT also revealed linear longitudinal microfractures
extending along the deformed cortex on the convex aspect of the femur. These
microfractures were analogous histologically to the microfractures previously
described as an integral part of plastic deformation
[5]. MRI revealed diffuse
medullary canal edema with additional signal change at the apex of the
deformed cortex, comparable to the microfractures seen on CT
[2].
Plastic deformation probably resulted from the first (most severe) trauma
and was aggravated by the second (less severe) trauma 3 months later. Symptoms
and signs resolved fully with conservative treatment. Follow-up radiography 5
years after initial presentation revealed partial resolution of the femoral
bowing and increased posterior cortical buttressing. Follow-up MRI examination
revealed marked improvement in the degree of diaphyseal axial deformation.
In summary, this case illustrates the severe degree of axial deformation
that can occur with plastic deformation of bone, how characteristic cortical
microfractures can be visualized on CT, and how axial and longitudinal
deformation can largely resolve with time.
References
- Mabrey JD, Fitch RD. Plastic deformation in pediatric fractures:
mechanism and treatment. J Pediatr Orthop1989; 9:310
–314[Medline]
- Resnick D. Diagnosis of bone and joint
disorders, 4th ed. Philadelphia, PA: Saunders, 2002:2682
–2683
- Borden S 4th. Roentgen recognition of acute plastic bowing of the
forearm in children. AJR1975; 125:524
–530[Abstract]
- Sclamberg J, Sonin AH, Sclamberg E, D'Sonza N. Acute plastic bowing
deformation of the forearm in an adult. AJR1998; 170:1259
–1260[Free Full Text]
- Chamay A. Mechanical and morphological aspects of experimental
overload and fatigue in bone. J Biomech1970; 3:263
–270[Medline]
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Introduction
Case Report
