the role of bone scan in heterotropic classifications

1. Heterotrophic
Ossifications
Geetha Subrahamaniam
07/05/2021

2. Introduction
 Heterotopic ossification(HO) is the presence of bone in soft tissue
where bone normally does not exist.
 Acquired form of HO most frequently is seen with either
musculosketletal trauma, spinal cord injru or central nervous
system injury.
 Fever, swelling, erythema and occasional joint tenderness seen in
early HO, can be difficult to distinguish from cellulitis, OM or
thrombhophlebitis.
 Bone scanning and other imaging test frequently are used to
distinguish between these diagnostic possibilities.
 As prophylaxis/treatment, NSAIDs, diphosphonate or local
radiation theraphy is recommended.
 Before theraphy bone scanning maybe requested to
confirm diagnosis of HO.

3.  HO likely to recur and possibly progress if resection is undertaken
before the lesion had become mature.
 To avoid recurrent HO and other operative complications, serial of
quantitative bone scans are used as an aid to
time surgical intervention.

4. This articles reviews the current concepts of HO
a. Classification
b. Etiology
c. Pathophysiology
d. Diagnosis
e. Treatment of HO

5. Classfications
Two version of HO
A) Acquired form
Incidence
 Spinal cord injuries ranges 20 to 30% and up to 35% will have limited
joint mobility
 Closed head injuries , HO develops in 10-20% and 10 % will have limited
joint mobility
 AfterTHA ranges o.6% to 90%, the HA forms is minor and not clinically
significant
 Precipitated by
I. Trauma (any types of musculoskeltal trauma) ,includes variant
myositis ossificans, patients often have soft tissue ossifications at
sites of trauma adjacent to long bones
II. Neurogenic causes ( traumatic form after injury to nervous system)
a. Often occurs among patients with recent spincal cord injury
b. Develops in sites distal to the level of spinal cord injury
c. Head injuries, strokes and brain tumors may lead to HO

6. B) Hereditary form (autosomal dominant)
 Known as myositis ossificans progressiva , extremely rare
 a/w skeletal abnormalities including malformation (including great
toes/shortening of digits).
 This diagnosis is usually missed out during childhood.
 Progression to severely impaired joint mobility and ankylosis by
early adulthood is the hallmark of disease
 Tx: options is limited, surgery may aggravated the conditons

7. Clinical
Presentation
 Symptoms of HO appear as early as 3 weeks, or as late as 12
weeks
 Initial stage early inflammatory disease
 Pain
 Fever
 Erythema
 Swelling
 Stiffening hip joint
Later stage (principal complications) about 10-20%
 Reduce range of motion and ankylosis.
 Loss of joint mobility and resulting loss of function.
 Peripheral nerve entrapment and pressure ulcer
*

8. Role of bone
scan
 Clinicians often turn to conventional radiography followed by 3
phase bone scanning to confirm the diagnosis of HO and establish
both the extent and metabolic activity of this ossifying lesion

9. Pathophysiology
HO
 3 conditions needed for HO: osteogenic precursor cells, inducing
agents, and a permissive environment.
 Demineralized bone matrix could invoke bone formation
ectopically and postulated a small, hydrophobic bone
morphogenetic protein as a causative agent .
 This protein capable of changing the development of
mesenchymal cells in the muscle from fibrous tissue into bone
when respiratory and nutritional requirements are also fulfilled.
 Postulated that bone morphology genetic protein is
liberated from normal bone in response to venous
stasis, inflammation, or disease of connective tissue attachments
to bone, conditions that often accompany immobilization or
trauma.
 Some investigators proposed the presence of a centrally mediated
factors, PGE2(progenitor cells)
 Heterotropic bone may begin some distance from normal bone,
later moving toward it.

10.  Other contributing factors: hypercalcemia, tissue hypoxia,
changes in sympathetic nerve activity, prolonged immobilization
 In early course, edema with exudative cellular infiltrate is
present, followed fibroblastic proliferation and osteoid formation.
 Myositis ossificans shows ossification principally in the periphery ,
an ossified and radiopaque peripheral rim surrounds a non-
oosified and radiolucent center, differentiates from
osteosarcoma/malignant tumors which forms dense central
ossification.

11.  The periphery of myositis ossificans shows mature lamellar bone
surrounded by a capsule of compressed muscle fibers and fibrous
tissue.
 A radiolucent cleft can be identified around myositis ossificans.
 The development of HO is extraarticular and occurs outside the
joint capsule. Bone forms in the connective tissue between the
muscles planes and not within the muscle itself.
 Mature HO shows cancellous bone and mature lammellar bone,
vessels and bone marrow with minor amount of hematopoiesis.

12. Laboratory
 Useful screening tool
 Alkaline phosphatase increases (3x more than normal), 10week
after trauma.
 But cannot be used to assess the maturity or recurrence of HO
 24 hours PGE urinary excretion as indicator for early HO
 Sudden increase in PGE excretion points to the need for bone scan
to qualify the process

13. Imaging
studies
 Radiologic appearance: is circumferential ossification with a lucent
centre.
 Conventional radiographs usually shows the evalution of HO
lesion, with detectable calcific density present only 4-6 week after
results of the 3phase bone scan have become positive.
 Conventional radiograph have been used to classify HO that
develops afterTHA. It may progress to ankylosis with bony
bridging from femur to the pelvis.

14. Classification
ofSchmidt and
Hackenbroch
for HO

15. Imaging
studies
 Three phase bone scintigraphy is the most sensitive for early
detection of HO.
 Flow studies and blood-pool images will detect incipient HO
approximately 2.5 wk after injury, with findings on delayed
scintigrams becoming positive approximately one week later.
 Radiography findings will not become positive in HO for at least
another 1-4 wk.
 Most bone scan findings return to baseline within 12 month. In
some cases, remains slightly elevated even though the underlying
HO has become mature.
 During the course of HO, the delayed bone scan may show
increased activity even after flow study and blood-pool
returned to normal.
 Serial bone scan used successfully to monitor the metabolic
activity of HO and determine the appropriate time for surgical
resection, if needed and to predict post operative recurrence.

16.  MRI also has been used in the evaluation of HO (One study
showed that a rim of low signal intensity is the most common
finding and is a typical appearance of HO).
 Tumor, infection, inflammation and DVT are major entities from
which HO must distinguish on imaging studies
 3phase bone scans, the proximal joints typically involved(more
than single joints involved often bilateral joints), region of the
knee is seldom present in brain traumatic injuries.
 If its affects the knee region, most common site of involvement is
the medial aspect of the joint.

19. Treatment HO
Complications of HO
 Peripheral nerve entrapment
 Pressure ulcers
 Functional impairments if joint ankylosis develops.
Early HO
 Passive range of motion exercise to maintain joint mobility
 Aggressive joint manipulation
 NSAID(indomethacin/ibuprofen) or diphosphonates
 Radiation theraphy to prevent and treat.
 Postoperative irradiation in preventing HO afterTHA
 Surgery to increase joint mobility, the duration of surgery depends
on the stage of maturity HO

20.  Radiographic depictions of maturity, consisting of lesion with
distinct margins and well defined trabeculation.
 Serial of Preoperative bone scans, quantify the ratio of
heterotropic to normal bone activity, predict the
intraoperative/postoperative complications.

22. Conclusion
 Presents multiple diagnostic and therapeutic challenged.
 Labaratory investigations such as ALP, PGE2 and bone
scintigraphy permits early detection and more successful mx
 Many patient at risk of HO, either NSAIDs or local radiation
theraphy is recommended.
 Clinicians, may request bone scanning to confirm the diagnosis of
HO, to determine the medical tx is warranted and choose
appropriate time for surgical resection of HO.

23. Recommendations
for serial
quantitative bone
scans to assess
maturity of HO
 This technique is used to time surgical resection
 Obtain a baseline quantitative bone scan as soon as possible after
the onset of clinical symptoms of HO.
 Obtain serial scans at between 1- and 6month intervals.
 More frequent serial scans improves the accuracy of technique
 2-3 months are the most reliable scintigraphy parameter for
determining whether HO has reached maturity.

24. Indications:
Assessment ofbone
metastasis.
ScanAcquisition:
Delayed whole body
planar bone scan
anteriorly and
posteriorly.
SPECT view ofpelvis.
15 years old boy, diagnosed with neuroblastoma at the age of 1 year
old. He undergone laminectomy (T5-T10) and chemotherapy in 2007
which complicated with neurogenic bladder.
He had history of left thigh swelling in June 2020.
Biopsy(07/07/2020) : mild chronic inflammation.
Currently had right femur fracture since March 2021. Denied any
pain, history of fall or trauma. Previously had history of right femur
pathological fracture secondary toTB osteomyelitis.

26. Findings:
There is lumbar scoliosis with convexity to the left.
There are photon deficient area seen alongT5-T10 vertebrae.
There are 2 separated foci of intense tracer uptake seen at the enlarged
bony lesion of right proximal femur with soft tissue uptake posterior to
it.
Prominent left knee uptake could be due to improper positioning.
Tracer distribution elsewhere is physiological.
Both kidneys are visualized.
Impression:
1. Scan changes at right proximal femur is consistent with pathological
fracture likely secondary to metastasis.The uptake at the adjacent soft
tissue may represent heterotropic ossification secondary to
fracture/prolonged immobilization.
2.The photon deficient area atT5-T10 vertebrae is due to post
laminectomy changes.