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CASE REPORT
Spontaneous Resolution Of Unicameral Bone Cyst Of The Patella – A Case Report

* Sanjay Purushothamdas, #David JS Anderson

*Clinical Research Fellow, Department of Orthopaedics, North Tyneside General Hospital, North Shields
#Consultant, Department of Orthopaedics, Dr. Gray’s Hospital, Elgin

Address for Correspondence

Mr. Sanjay Purushothamdas,
No. 1 Beech Court, North Tyneside General Hospital,
Rake Lane, North Shields, NE29 8NH
Email: sanjaydhiran@yahoo.com

Abstract

Unicameral bone cysts in the patella are uncommon. They are mostly asymptomatic and are detected as an incidental finding during radiological examination of the knee. Symptomatic cases present as anterior knee pain or as a pathological fracture after a trivial injury. The authors present a case of Unicameral Bone Cyst in the patella which had resolved spontaneously following simple fracture management of a pathological fracture of the patella.

J.Orthopaedics 2006;3(2)e8

Introduction :

Tumours of the patella are uncommon. An extensive review of the literature by Mercuri etal [7] had revealed only 384 cases of patellar tumours in the last one hundred years. The common tumours are benign and include Giant cell tumour and Chondroblastoma. Secondary metastases and Osteosarcoma are the most frequent malignant tumours.

Unicameral bone cysts in the patella are uncommon. Symptomatic presenting features include anterior knee pain and pathological fracture after a trivial injury. The management guidelines for the bone cyst in the patella are not clearly specified in the literature. Incidentally discovered bone cyst and that causing anterior knee pain are managed based on bone tumour principles such as further radiological evaluation with bone scan or magnetic resonance imaging, biopsy for tissue diagnosis and usually undergo surgical treatment. Operative intervention can be divided into open and percutaneous procedures. Open methods include curettage only, curettage combined with chemical adjuvant and bone grafting, subtotal resection with and without bone grafting. Percutaneous treatment technique of injecting methylprednisolone acetate in the cyst cavity has been in vogue over the last two decades.

Patients presenting with a pathological fracture are usually conservatively treated based on the principles of fracture management with immobilisation. Such treatment results in spontaneous resolution of the cyst with fracture healing in about 25% of the cases.

The authors present a case of a Unicameral bone cyst of the patella presenting as a pathological fracture which was treated successfully with simple fracture management. 

Case Report:

A 21 year old man presented to the accident and emergency department with complaints of pain in the right knee following an injury when he slipped on ice. He was able to weight bear partially after the injury. Clinical examination of the knee showed an effusion and restricted range of movements. Straight leg raise was painful to perform. Radiograph of the knee showed an undisplaced pathological fracture of the patella through a multiloculated cystic lesion. Radiological opinion confirmed the diagnosis of the cystic lesion to be a simple bone cyst (Figure 1).

The fracture was treated conservatively with a cylinder cast for a period of six weeks. The patient was allowed partial weight bearing during this period. Check radiographs of the knee showed healing of the fracture with spontaneous resolution of the cyst. A one-year follow-up showed complete resolution of the cyst (Figure 2) and full range of motion of the knee joint.

Discussion :

Tumours of the patella are uncommon [3, 7]. The literature on primary tumours of patella is very scant and majority of them are in the form of scattered case reports and case series. Mercuri etal collected 384 cases from a literature search from 1900 to 2000 [7]. Benign patellar tumours are more frequent than malignant tumours. The most common tumours included giant cell tumour and chondroblastoma, the majority of the malignant lesions included secondary metastasis and osteosarcoma.

Unicameral bone cyst (UBC) was initially described by Jaffe and Liechtenstein. It is seen predominantly during the first two decades of life, although not necessarily limited to these age groups. It is characterised pathologically by a thin-walled cavity developing most often within the metaphysis of a long tubular bone, closely adjacent to the growth plate and appearing to migrate away from the growth plate as it matures. A UBC may appear in virtually any bone, but typically, it is found in either the proximal humerus or proximal femur. Most of the patients with a UBC are asymptomatic and diagnosed as an incidental finding during radiological examination. Symptomatic presentation is usually due to a pathological fracture following a trivial incident.  Anterior knee pain has been recognised as a presenting feature [6].

Radiologically, the lesion is characterized by a large, well-localized radiolucent expansile lesion which may be multiloculated. The differential diagnosis includes aneurysmal bone cyst, giant cell tumour, fibrous dysplasia and enchondroma [5].

The treatment of unicameral bone cyst is variable. Nonoperative treatment is usually followed for presentation with pathological fracture when fracture immobilisation and watchful waiting results in obliteration of the cyst. The success rates of such treatment have been variable and reports of approximately 25% of cases resulting in spontaneous healing have been quoted, although not all authors recommend this treatment option [6].

Surgical treatment can be divided into open and percutaneous procedures. Open methods of treatment include curettage only, curettage combined with chemical adjuvants and bone grafting, subtotal resection with and without bone grafting. Percutaneous treatment technique of injecting methylprednisolone acetate in the cyst cavity has been in vogue over the last two decades.  Other reported percuataneous injections include alcohol based fibrosing agent, autologous bone marrow and injection of demineralised bone matrix.

Bone cyst in the patella is uncommon. Only anecdotal case reports could be found in the literature [1,2,4,8,9 and 10]. The treatment of patellar bone cyst has been variable [1, 6]. Non operative in the form of fracture management and watchful waiting was followed for pathological fracture and operative methods of curettage and autologous bone grafting or patellectomy were performed for presentations with anterior knee pain with or without swelling.

In the present case, a conservative approach of management was adopted which resulted in the spontaneous obliteration of the cyst cavity with healing of the fracture.

 

Reference :

  1. Cole WH. Primary Tumours of Patella. J Bone Joint Surg 1925; 23: 637-654.

  2. Deepak Chaudhary, Naval Bhatia, Abrar Ahmed, Chopra R K. Unicameral bone cyst of the Patella. Orthopaedics 2000; 12: 1285-1286.

  3. Ferguson PC, Griffin AM, Bell RS. Primary Patellar Tumours. Clin Orthop 1997; 336: 199-204.

  4. Jucker C, Cuneo L. Juvenile solitary bone cysts of the patella. Presentation of a case report. Ann Radiol Diagn (Bologna). 1962; 35: 192-194.

  5. Linda M Parman, Mark D Murphey. Alphabet Soup: Cystic Lesions of Bone. Seminars in Musculoskeletal Radiology 2000; 4(1): 89-101

  6. Masaki Chigira, Susumu Maehara, Satoru Arita, Ehchi Udagawa. The aetiology and treatment of simple bone cysts. J Bone Joint Surg [Br] 1983; 65B:  633-636.

  7. Mercuri M, Casadei R. Patellar Tumours. Clin Orthop 2001; 389: 35-46.

  8. Saglik Y, Ucar DH, Yildiz HY, Dogan M. Unicameral bone cyst of the patella. A case report.  Int Orthop 1995; 19(5): 280.281.

  9. Schultz E, Greenspan A. Case report 378: Simple bone cyst. Skeletal Radiol 1986; 15(5): 405-407.

  10. Weintroub S, Salama R, Baratz M, Papo I, Weissman SL. Unicameral bone cyst of the Patella. Clin Orthop 1979; 140: 158-161.

 

This is a peer reviewed paper 

Please cite as : Sanjay Purushothamdas: Spontaneous Resolution Of Unicameral Bone Cyst Of The Patella – A Case Report

J.Orthopaedics 2006;3(2)e8

URL: http://www.jortho.org/2006/3/2/e8

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