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\begin{document}

\title{Rare retro-patellar unilateral multiple osteochondroma in patellar
tendon: a case report}



\author[1]{Hosein  Pirmohamadi}%
\author[1]{Mohsen  Rahimi}%
\author[1]{Mohammad Kazem  Emami Meibodi}%
\author[2]{mohsen Akbaribazm}%
\affil[1]{Baqiyatallah University of Medical Sciences}%
\affil[2]{Torbat Heydarieh University of Medical Sciences}%


\vspace{-1em}



  
  \date{May 15, 2024}


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\textbf{1. INTRODUCTION}

Osteochondromas (OC) are benign tumors that account for 20-50\% of
benign and 10\% of all bone tumors. The incidence rate of OC in males is
twice that of females and its peak is usually in the second decade of
life (1). These lesions are inherited in an autosomal dominant manner
and cause the formation of isolated lesions or multiple exostoses during
the development of bones in the process of enchondral ossification in
the long bones (2). Also, OC is associated with the mutation of some
tumor suppressor genes, including EXT1 or EXT2 genes. OC have a
periosteal origin and are formed in the active parts of bones, including
the metaphysis of long bones and the cartilage at their ends. Studies
show that OC can be caused after surgery/radiation-induced injury and
hematopoietic stem cell transplantation (3).

Osteocartilaginous exostosis is mainly detected in childhood and in the
form of palpable masses, with chronic pain and sometimes with edema (4).
The presence of misplaced bone masses in the joint capsule and sometimes
with cartilaginous coating in radiographic images is one of its common
manifestations. The most common joints involved in OC are the hip and
knee joints. Patellar OC is rare and mostly affects the patellar bursa.
Moraes et al. (2014) reported a patellar OC measuring 8 \selectlanguage{ngerman}× 6 × 3 cm
anterior to the patella in a 60-year-old man who was painless and
without limitation of flexion-extension in the knee joint (5). In the
present case, rare retro-patellar OC was observed in the area of the
patellar ligament.

\textbf{2. CASE REPORT}

A 19-year-old male presented with swelling, chronic pain and a palpable
mass in the anteroinferior region of the left knee, and after
examination with the help of lateral radiography of the left knee
(Figure 1), with irregularities in the inferior of patella joint surface
and multiple exostosis was observed in the patellar tendon region. The
tumor lesion had sharp borders and a hyper-dense appearance, and no
signs of fracture or dislocation were observed in the tibiofemoral and
patellofemoral joints.

After surgery of the left knee joint, radical resection of the mass and
proximal osteotomy of the left tibia, 3 irregular bone masses with total
dimensions of 7 × 5 × 1 cm were sent for histopathological examination.
In histopathological evaluation, well-differentiated trabeculae-spongy
bone tissue, containing proliferated chondroid and osteoid areas in
hypodense lacunae which covered with fibro-fatty tissue and thick
hyaline cartilage was observed (Figure 2). This evaluation also
confirmed multiple exostosis in the patellar tendon. After 3 months of
follow-up, the patient had no movement disorders related to flexion and
extension of the knee joint, pain and tumor lesion.

\textbf{3. DISCUSSION}

OC is a benign tumor of bone tissue that occurs mainly during
endochondral ossification of growth plates of long bones. OC is often
caused by hereditary multiple exostoses in the areas of the tibiofemoral
and patellofemoral joints (6). Of course, this lesion is rarely observed
in the patellar ligament and usually causes stiffness of the knee joint
(joint locking), dysfunction of the anatomic function of the quadriceps
femoris muscle tendon and loss of knee joint extension, edema, chronic
pain, ossification of the ligament, formation of fibro- fatty tissue,
degenerative arthritis and finally neurovascular compression (7).

In the present case, the patient presented with common symptoms of OC,
including edema, chronic pain and stiffness in the knee joint and
palpation of solid masses in the patellar ligament. These symptoms could
be due to the inflammatory processes involved in the degeneration of
dense connective tissue around the mass of exostoses in the lacunae of
the patellar ligament. Studies show that OC is associated with good
prognosis and low risk of metastasis, but due to the disturbance in the
anatomical alignment of the knee joint, the masses are removed by
radical resection and the patellar ligament is fixed and stabilized at
the connection to the tibial tuberosity (5). In the report of Pandian et
al. (2016), in a 22-year-old man, bilateral OC masses in the patella and
patellar ligament caused severe arthritis, chronic pain, edema, and
impaired flexion-extension knee movements (8). In 15\% of cases, the
mass is surrounded by a calcified cartilage cap around the bony lacuna,
and its thickness even reaches \textgreater{}15 mm (4). Studies show
that the incidence ranges of OC are 0.9 - 1.4\% per 100,000, which is
rare in the patellar ligament. If there is no intervention, valgus
deformity in the ankle, knee and pelvic joints is expected in the third
decade of life. However, vascular compression and/or nerve compression
along with acute pain, extensive edema and tissue degeneration are
observed in OC of the hip (sacroiliac-iliofemoral) and shoulder
(glenohumerus) joints (9 and 10).

\textbf{4. CONCLUSION}

OC is a benign tumor of the articular-metaphysic areas of long bones
that rarely causes intra-articular and intra-ligamentous lesions. OC
patellofemoral joint is rare and mainly causes limitation of
flexion/extension movements of the knee joint along with stiffness and
chronic pain in the area, which can be treated with radical resection of
the mass.

\textbf{AUTHOR CONTRIBUTIONS}

\textbf{Mohsen Akbaribazm} : Conceptualization; writing -- original
draft; writing -- review and editing. \textbf{Hossein Pirmohamadi} :
Conceptualization, supervision, writing -- review and
editing.\textbf{Mohsen Rahimi} and \textbf{Mohammad Kazem Emami Meibodi}
: Supervision, writing -- review and editing.

\textbf{ACKNOWLEDGEMENTS}

None.

\textbf{CONFLICT OF INTEREST STATEMENT}

The authors declare that there is no conflict of interest.

\textbf{CONSENT}

Written informed consent was obtained from the patient to publish this
report in accordance with the journal's patient consent policy.

\textbf{REFERENCES}

\begin{enumerate}
\tightlist
\item
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  Bhatnagar AS, Malhan K, Mehta S. A rare case report of patellar
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  Vijayakumar S. A rare case of osteochondroma of Patella-Case Report.
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\item
  Pandian S, Jayaraman T, Rajendiran C. Osteochondromatosis and
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\item
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\item
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\end{enumerate}

\textbf{Figure legends:}

\textbf{Figure 1:} X-ray image of the left knee joint. F: Femur, P:
Patella, PL: Patellar ligament, Fi: Fibula, T: Tibia, TT: Tibial
tuberosity and OC: Osteochondromas masses.

\textbf{Figure 2:} Histopathology of osteochondromas masses. FFT: Fibro-
fatty tissue, T: Bone trabeculae (bone matrix-calcified region), L:
Osteocytic lacunae. (H\&E staining × 100, Scale bar = 200 \selectlanguage{greek}μ\selectlanguage{english}m).\selectlanguage{english}
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