Hawkins sign of the knee: Imaging appearance and clinical implication of an unusual pattern of disuse osteopenia

Abstract

Disuse osteopenia (DO) is a disorder due to reduced weight-bearing often following immobilization injuries. It is most commonly observed in the ankles and knees and is believed to be due primarily to increased bone reabsorption associated with disuse. Both traditional radiography and magnetic resonance (MR) imaging are useful in identifying abnormalities associated with DO. Specifically, linear subchondral osteopenia has been given the term "Hawkins sign" when seen in the talus, but this finding may also be seen elsewhere. When present, it not only is an indication of DO but also indicates the presence of sufficient vascular flow, and the unlikely development of avascular necrosis. We report a case of Hawkins sign of the knee demonstrated on radiography and MR and demonstrate the clinical importance of recognizing this sign, outside its usual setting, in assessing the prognosis of a healing fracture.

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Journal of Clinical Imaging Science • 2022 • 12(51) | 1
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Musculoskeletal Imaging Case Report
Hawkins sign of the knee: Imaging appearance and
clinical implication of an unusual pattern of disuse
osteopenia
Nicholas C. Adams1, Robin L. Alonge1, Lance D. Edmonds1
1Department of Radiology, David Grant Medical Center, Faireld, California, United States.
*Corresponding author:
Nicholas C. Adams,
Department of Radiology,
David Grant Medical
Center, Faireld, California,
UnitedStates.
nadams04@gmail.com
Received : 27March 2022
Accepted : 09August 2022
Published : 22 August 2022
DOI
10.25259/JCIS_33_2022
Quick Response Code:
INTRODUCTION
Although the pathogenesis is not entirely understood, disuse osteopenia (DO) is a known
phenomenon associated with reduced weight-bearing as seen in the setting following a
fracture.[1] Linear subchondral DO is a characteristic pattern commonly observed following
a talus fracture.[2] is presents on radiographs as a subchondral radiolucent line, known as
“Hawkins sign,” and is the result of active bone resorption which is dependent on a hyperemic
state in the disused bone.[1,2] is hyperemia appears on magnetic resonance (MR) imaging as
T2 hyperintense signal.[3] Seen approximately 6–8weeks aer trauma, it is an indicator of an
intact vascular supply and an unlikely progression to avascular necrosis.[4] is pattern of DO
is reported less frequently outside the talar dome. We report a case of isolated subchondral DO
seen within the knee, a “Hawkins sign” of the knee.
CASE REPORT
A 22-year-old otherwise healthy male military member sustained a severe right knee injury
including knee dislocation and subsequent relocation. e patient ambulated only with crutches
for the following 6weeks. On presentation to the orthopedic surgeon, he reported pain with
ABSTRACT
Disuse osteopenia (DO) is a disorder due to reduced weight-bearing oen following immobilization injuries.
It is most commonly observed in the ankles and knees and is believed to be due primarily to increased bone
reabsorption associated with disuse. Both traditional radiography and magnetic resonance (MR) imaging are
useful in identifying abnormalities associated with DO. Specically, linear subchondral osteopenia has been given
the term “Hawkins sign” when seen in the talus, but this nding may also be seen elsewhere. When present,
it not only is an indication of DO but also indicates the presence of sucient vascular ow, and the unlikely
development of avascular necrosis. We report a case of Hawkins sign of the knee demonstrated on radiography
and MR and demonstrate the clinical importance of recognizing this sign, outside its usual setting, in assessing
the prognosis of a healing fracture.
Keywords: Hawkins sign, Disuse osteopenia, Knee
www.clinicalimagingscience.org
Journal of Clinical Imaging Science

Adams, et al.: Hawkins sign of the knee
Journal of Clinical Imaging Science • 2022 • 12(51) | 2
ambulation and inability to bear full weight secondary to
pain and instability. Physical examination demonstrated a
large right knee eusion, diuse joint line tenderness, limited
range of motion in exion and extension, varus laxity, a
positive anterior drawer sign, and positive pivot shi.
Knee radiographs revealed a knee eusion and sequelae
of impaction injury involving the medial femoral condyle.
In addition, faint linear demineralization was observed
involving the medial femoral condyle, lateral femoral
condyle, and lateral tibial plateau [Figure 1]. Subsequent
MR imaging demonstrated ndings consistent with severe
posterolateral corner injury, sequelae of knee dislocation
including impaction fracture of the medial femoral condyle,
complete tearing of the anterior and posterior cruciate
ligaments, and partial tearing of the medial collateral
ligament. Additionally seen was linear increased T2
signal underlying the cartilage in all three compartments,
suggestive of hyperemia in the setting of disuse osteopenia
[Figure2].
DISCUSSION
DO may manifest in any setting of reduced weight-
bearing, including fractures, inactivity, neuromuscular,
and arthritic diseases. Although the exact pathogenesis
is not entirely understood, some studies have indicated it
likely begins with a hyperemic state in the disused bone
and are followed by active bone resorption accompanied
by inhibition of bone formation.[1,5-7] is has caused
it to be considered a “high turnover osteoporosis.”[3]
DO changes rst become evident aer approximately
6–8 weeks of disuse, with earlier observations noted in
younger populations.[3] Although, peak bone mass decit
has been reported to occur as long as 4months aer the
immobilizing injury occurred.[1,3] Very commonly, bone
mass may be recovered if the patient resumes activity
within the active phase of DO. However, there may be no
regeneration of bone for as long as 1 year following the
original period of immobilization.[3]
Leland Hawkins rst described three patterns of talar
neck injury in 1970.[8] He described a band-like pattern
of subchondral osteopenia involving the talar dome aer
talar fractures, which has been subsequently referred to
as “Hawkins sign.” Hawkins noted that this pattern of DO
was most evident on AP radiographs and could be missed
on lateral lms.[9] e development of the subchondral
osteopenia is dependent on active hyperemia in the
immobilized joint and its high prevalence within the ankle is
believed to be due to the nature of the high vascularity of the
ankle.[2,9] us, the “Hawkins sign” has clinical signicance as
its presence indicates sucient vascularity within the injured
osseous structure and subsequently a decreased risk of the
development of avascular necrosis.[8]
Traditional radiography and MR imaging have both
proved useful in visualizing DO. Visualization of DO is
most commonly seen in the ankle and knee, though it has
also been described in other locations to include the wrist,
shoulder, and spine.[3,6-7] Within the knee, the most common
sites include the femur and patella.[1] A common radiographic
appearance of DO is band-like subchondral osteopenia,
which is classically seen in the talar dome following a talar
neck fracture.[2] MR ndings of DO include accentuation
of vertical trabecular lines, presence of subchondral lobules
of fat, presence of horizontal trabecular lines, prominence
of bone vessels, and presence of dotted areas of high signal
intensity on T2-weighted fat-suppressed sequences.[1,3] One
study of patients with clinical and radiographic evidence
of DO found 100% of patients (16/16) showed evidence of
osseous demineralization on MR imaging.[3] Increased T2
signal seen in a linear, subchondral distribution reects
hyperemia secondary to prominent vasculature and acts as
the corresponding MR nding to a subchondral lucency seen
on radiographs.[3]
The patient discussed in this case sustained a severe
knee injury, resulting in inability to bear weight on his
right knee over the 6-week period between injury and
imaging. During this time, DO developed in an isolated
subchondral distribution. Both radiography and MR
imaging revealed this unexpected yet reassuring sign.
The patient later underwent arthroscopy with orthopedic
surgery, with reconstruction of the cruciate ligaments and
Figure 1: A22-year-old male aer
6 weeks inability to bear full weight,
subsequent to knee dislocation. Frontal
radiograph of the right knee shows
impaction fracture of the medial femoral
condyle. Linear demineralization is seen
involving the medial femoral condyle,
lateral femoral condyle, and lateral tibial
plateau (red arrows).

Adams, et al.: Hawkins sign of the knee
Journal of Clinical Imaging Science • 2022 • 12(51) | 3
posterolateral corner using allograft, and is following an
expected postoperative course.
CONCLUSION
DO is commonly seen in the setting of prolonged
immobilization aer a traumatic injury and can present
in a variety of distributions. A band-like subchondral
distribution is frequently described involving the talar dome,
but can also be found elsewhere in the body. is nding
reects increased bone resorption dependent on intact
vasculature and therefore a lower risk for the development
of avascular necrosis. is case demonstrates the importance
for awareness among radiologists and orthopedic surgeons to
recognize this sign in determination of prognosis following a
fracture with a period of prolonged immobility.
Disclaimer
e views expressed in this manuscript are those of the
authors and do not reect the ocial policy or position of the
Department of the Air Force, Department of Defense, or the
US Government.
Declaration of patient consent
Patient’s consent not required as patient’s identity is not
disclosed or compromised.
Financial support and sponsorship
Nil.
Conicts of interest
ere are no conicts of interest.
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How to cite this article: Adams NC, Alonge RL, Edmonds LD. Hawkins
sign of the knee: Imaging appearance and clinical implication of an
unusual pattern of disuse osteopenia. JClin Imaging Sci 2022;12:51.
Figure 2: Same patient as above. Images from non-contrast knee magnetic resonance imaging.
(a)Coronal T2 fat-saturated imaging shows band-like subchondral T2 hyperintensity involving the
femoral condyles and tibial plateau (yellow arrows). Also demonstrated was complete tearing of the
ACL and PCL, partial tearing of the MCL, and an impaction fracture of the medial femoral condyle,
(b) sagittal proton-density fat-saturated imaging shows band-like subchondral T2 hyperintensity
involving the patella and lateral tibial plateau (blue arrows), (c) axial proton-density fat-saturated
imaging shows band-like subchondral T2 hyperintensity involving the patella and trochlear groove
(white arrows). Additionally there is an impaction fracture of the anterior medial femoral condyle
with subperiosteal hematoma formation.
c
b
a