rare case of patellar osteoblastoma with anterior knee pain

1. A rare case of Patellar
Osteoblastoma with anterior
knee pain
Dr P. ROHIT RAJ
MBBS MS ORTHO
ASSISTANT PROFESSOR
ORTHOPAEDIC DEPARTMENT
VISHWABHARATHI MEDICAL COLLEGE

2. ABSTRACT
• Tumors of the patella are rare and most of them are benign. With
Osteoblastoma being an uncommon primary bone tumor, it is even
rarer in the patella. This is a case report of a 21 year old male patient
with a history of knee pain of 6 months duration. Imaging
characteristics suggested a benign lesion
• Histopathological diagnosis was consistent with Benign
Osteoblastoma. With the advent of improved diagnostic modalities
and treatment options, more number of patellar neoplasms are being
identified and should be considered as a cause of knee pain despite
the rarity of occurrence.

3. INTRODUCTION
• Patella is an uncommon location for development of neoplasms,
majority of which are benign [3]. Patella is a sesamoid bone that
develops in quadriceps tendon. Due to similarities in its ossification to
a long bone’s epiphysis or apophysis, it is a potential site for bony
lesions, most common benign lesions are Giant Cell Tumor (GCT),
second benign chondroblastoma [1-3].
• Tumors of patella clinically present as anterior knee pain and/or
swelling. Osteoblastoma is a benign primary bone tumor which is rare
and occurs more frequently in vertebral column, and long bones,
especially, femur and tibia. Very few cases of osteoblastoma of the
patella have been reported [8-11].

4. CLINICAL CASE
• A 21 year old male patient presented with pain in the left knee for 6
months and difficulty in squatting. No history of any other joint
involvement was present
• On examination anterior knee pain

5. Pre op x ray -
• well defined round lucency in the patella

7. Mri-
• Showed focal hypointense lesion in the patella with peripheral
hypointense margin and extensive edema involving the entire patella
.Edema also noted in the adjacent Hof'fás fat pad -likely
chondroblastoma

11. Intra op photo- before curettage

17. After curettage

18. Bone grafting

20. Post op x ray

22. Follow up x ray proper consolidation of the bone
graft

25. Differential diagnosis---
• Chondroblastoma

26. • Surgery details intra operative window made anterior aspect of
patella and currettage of material done and after thorough lavage
iliac bone graft is harvested in the defect

27. Histopathological report
• Gross description of the surgical specimen - Multiple grey brown
friable soft tissue and bony bits
• Histopathological characteristics-
• 1) sections show spicules and trabeculae of woven bone lined by
plump osteoblasts
• 2) The cells have round to ovoid nuclei with nucleoli and moderate
dense cytoplasm
• 3)also seen are numerous osteoclast type giant cells though out the
lesion
• 4) focally sclerotic woven bone and focal chondroid matrix seen

28. Diagnosis
• Osteoblastoma
• The patient had improvement in symptoms after the surgery.
• The patient is on follow up and there has been no recurrence and
remains asymptomatic till date with good range of movements

29. DISCUSSION
• Primary tumors of the patella are rare, and most are benign, GCT being the
commonest, followed by Chondroblastoma [1-3]. They present as persisting
anterior knee pain with or without swelling
• J. Singh et al in their case series of 59 patients with patellar lesions,
reported 39% to be benign tumors, about 15% malignant and nearly 46%
pseudotumors [4].
• Bhagat et al in their analysis of 7 patients found 5 to be benign and, 2 as
non-neoplastic [5]. Most studies show a male predilection [2-5].
• Osteoblastoma is a rare benign osteoid-forming tumor and is histologically
the same as osteoid osteoma but, is greater than 2 cm in size. Whereas,
Osteoid osteoma tends to regress, osteoblastoma may progress.

30. • Jackson et al reported 35% percent of osteoblastomas in the spine,
10% in the femur, 5% in the tibia and 9% in the bones of the foot and
ankle in a series of 184 patients [6]. The age at presentation is in first,
second or third decades of life, most of them presenting between 10-
20 years of age.
• Osteoblastoma of the patella is very rare, is less than 1% of all
primary bone tumors. And, it accounts for about 2% of all patellar
tumors [1,2]. Clinically, it manifests as dull and aching anterior knee
pain of few months to about 2 years in duration, and not relieved by
aspirin. May present as local tenderness and a palpable mass on
examination. The range of motion is usually maintained [1].

31. • The lesion maybe cortical (most common) [7], intramedullary or
subperiosteal. Radiographically it may present as a giant osteoid
osteoma: >2cm in diameter, lytic lesion with reactive sclerosis, more
prominent periosteal response relative to osteoid osteoma. A
pathological fracture could be present.
• Other presentations are a blow-out expansile lesion similar to an
aneurysmal bone cyst (ABC), especially in the spine; an aggressive
lesion with a large soft tissue mass; a periosteal lesion a thin shell of
newly formed periosteal bone.

32. • CT scan can reveal a well-defined lesion of patella with calcifications. Bone
scintigraphy can show a hotspot in the affected patella. MRI is helpful to
determine the extent of lesion or involvement of surrounding soft tissues and
evidence of cortical destruction and in pre-op planning.
• Certain characteristics are useful to differentiate benign from malignant lesions
like pattern of bone destruction, tumor margins, cortical involvement, rim of
sclerosis, calcifications, presence of pathological fracture, surrounding tissue
invasion and joint involvement [1]. Benign lesions may have lobulated or sharp or
rounded margins; thinned, expanded cortex; sclerotic rim; septa and rarely,
calcifications, reactive bone formation, surrounding tissue invasion, pathological
fracture. Malignant tumors may have permeative or moth-eaten pattern of bone
destruction, ill-defined margins; cortical destruction; septation; pathological
fracture; invasion of surrounding tissue; articular involvement; and rarely,
periosteal reaction, reactive bone formation. Both types of lesions can involve an
eccentric area or entire patella

33. • Radiological differential diagnosis of osteoblastoma should include
osteoid osteoma, bone abscess, aneurysmal bone cyst, enchondroma,
osteosarcoma. Osteoid osteoma is usually less than 1.5 cm in size,
may have a sclerotic center. A bone abscess can cross the growth
plate which is never seen in osteoblastoma. ABC is an expansile lesion
with thin sclerotic rim, lacks central radiopacities and may have soft
tissue extension. Enchondroma is a radiolucent lesion with central
calcification in the form of rings, dots or arcs, amd no periosteal
reaction. Osteosarcoma displays permeative or moth-eaten bone
destruction, wide zone of transition, cloud-like opacities, aggressive
periosteal reaction, soft-tissue mass

34. • Grossly, it appears as well demarcated from adjacent bone, expansile
and hemorrhagic, and often contains a central osseous nidus. A
curetted specimen appears red and gritty. Histopathologically, the
lesion shows irregular broad and long trabeculae of immature woven
bone, lined by osteoblasts within a loosely packed fibrovascular
stroma and contains numerous osteoclasts. Intralesional hemorrhage
and secondary ABC areas can be seen. The mitotic activity is low.
• Aggressive osteoblastoma shows features similar to benign
osteoblastoma except that the osteoblasts are large and have
epitheloid appearance. Cytoplasm is abundantly eosinophilic with
eccentric vescicular nuclei and prominent nucleoli

35. • Treatment options include conservative surgery, marginal or wide en
bloc resection. Intralesional curettage is associated with a high rate of
recurrence. For local recurrences wide en bloc resection should be
done. Patellectomy could be done if there is a failure after wide
curettage.[1]

36. CONCLUSION
• Patellar tumors are uncommon and vast majority are benign. With
increased identification as a cause of knee pain in young adults, these
should not be overlooked. In case of suspicion, dedicated imaging for
the patella should be incorporated and biopsy of the lesion should be
done for definitive diagnosis and an integrated approach has to be
followed for low recurrence, better treatment and prognosis.

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