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An atypically located large subchondral cyst in an osteoarthritic hip joint: a case report
© Güven et al.; licensee BioMed Central Ltd. 2013
Received: 31 December 2012
Accepted: 15 May 2013
Published: 5 July 2013
Osteoarthritic subchondral cysts within or around the hip joint can sometimes be difficult to distinguish from primary osseous and soft tissue tumors due to their radiological appearance and uncommon location.
We report the case of a 74-year-old Turkish man with a subchondral cyst arising from the hip joint, eroding the acetabulum and located on the medial side of the iliac bone, which imitated a soft tissue tumor. This cystic lesion was resected and the results of histopathological analysis of tissue samples were found to be consistent with an osteoarthritic cyst.
The present case illustrates how an osteoarthritic subchondral cyst can grow into the soft tissue planes in the presence of destruction of the articular cartilage and subchondral bone continuity, and present as an apparent soft tissue tumor.
Osteoarthritis (OA) is a degenerative joint disease with some radiological characteristics including the presence of multiple, small cysts (geodes) with subchondral sclerosis, marginal osteophytes, intra-articular osteochondral bodies and narrowing or loss of joint space [1, 2]. Osteoarthritic subchondral cysts frequently occur in weight-bearing joints such as the hip. The etiology of these cysts in hip OA remains uncertain. Theories on their pathogenesis include that they originate from intrusion of synovial fluid into the bone at the joint surface, initiate in areas of bone necrosis, or are confined to pressure segments in the femoral head and acetabulum [3–8]. Regardless of their etiology, subchondral cysts are generally thought to develop in bone adjacent to highly degenerated joint surfaces and, as a result, are frequently found in weight-bearing areas of the osteoarthritic hip joint at the time of total hip arthroplasty . However, large symptomatic subchondral cysts in the hip joint can sometimes be difficult to distinguish from primary osseous and soft tissue tumors due to their radiological appearance and uncommon location [9–11].
In the present work, we report the case of a patient with an atypically located osteoarthritic cyst arising from the hip joint, eroding the acetabulum and located on the medial side of the iliac bone, which imitated a soft tissue tumor on radiological imaging studies.
A 74-year-old Turkish man was referred to our out-patient clinic because of right hip pain without a history of trauma. He had experienced severe pain in the groin on weight bearing, with variable degree of pain at rest, over the last 45 days. He was able to walk only with the assistance of crutches. His medical history was unremarkable.
On physical examination, he was afebrile and had a blood pressure of 120/80mmHg. His active ranges of motion (ROM) for both hips were restricted in all directions and the passive ROM of right hip was painful in flexion, abduction and internal rotation. The result of a Thomas test was positive for the right hip.
Surgery for excision of the cystic lesion was recommended, and was performed under general anesthesia. Our patient lay in a supine position and an anterior ilioinguinal incision was made in the right hip. The interval between the tensor fascia lata and sartorius muscle was identified. The lateral femoral cutaneous nerve was retracted laterally. The dissection was extended proximally to expose the medial surface of the iliac bone. The rectus femoris muscle was not incised from its attachment to the upper part of the acetabular rim, but was instead retracted laterally. The iliacus muscle was identified and stripped from the medial surface of the iliac bone. The cystic lesion was identified. There were no adhesions between the cyst membrane and surrounding soft tissue. However, it was associated with the antero-medial acetabular wall and had eroded the adjacent acetabulum. The cystic lesion was resected en bloc and examined in the operating room on the surgical table. Calcified necrotic material was exposed in the cyst.
There were no complications such as infection and skin necrosis during the follow-up period. At the final follow-up (4 months post-operatively), our patient was assessed clinically. The active ROM for both hips were restricted as had been the case pre-operatively. However, he had only slight pain in his right hip and was able to walk without support. Primary total hip replacement surgery for both hips was recommended in view of the radiological findings.
Tumors and tumor-like lesions located in the pelvis have some specific differences from those tumors arising in other parts of the body. The main difference is that pelvic tumors are located deep in the body, while tumors located in the extremities are relatively superficial. Patients with pelvic tumors are usually older and their tumors larger relative to patients diagnosed as having tumors in the extremities. The clinical presentation is therefore often several years later compared to the same tumor type located in an extremity . The number of benign and malignant soft tissue tumors is much larger than the number of osseous lesions in the pelvic region. However, synovial diseases such as osteoarthritis, rheumatoid arthritis and pigmented villonodular synovitis are common in the hip joint and large subchondral cysts occurring primarily or secondarily to these diseases may raise suspicion of a neoplasm on radiological examination. They can cause massive osseous destruction simultaneously in the femur and acetabulum .
Subchondral cysts in degenerative osteoarthritis are often multiple and variable in size, whereas solitary and large cysts are unusual. It has been shown previously that nearly two-thirds of osteoarthritic cysts completely disappear radiographically or become smaller with no additional treatment . However, it is also possible for an osteoarthritic cyst to progress with time if a pathway to the joint space exists.
Some theories have been described to explain the pathophysiology of subchondral cysts in OA. Intrusion of synovial fluid through the articular cartilage secondary to elevated pressure of intra-articular fluid, which results in hydraulic destruction of subchondral bone, has been proposed as a possible etiology . This theory is supported by the presence of defects in the articular cartilage over cysts, of fragments of articular cartilage within cysts, and the similarity of cyst fluid to synovial fluid. However, this theory cannot explain cases where subchondral cysts are not in continuity with the joint space. An alternative hypothesis is that stress-induced micro-fractures lead to secondary effects such as localized areas of bone necrosis, osteoclast resorption and thus cyst formation, with the articular cartilage being left intact [3, 5]. This is based on evidence of bony contusions, trabecular fractures and primary subchondral osteolysis, which may, subsequently, communicate with the joint if the overlying articular cartilage and subchondral bone plate cracks.
Our patient’s case illustrates how an osteoarthritic subchondral cyst can grow into the soft tissue planes in the presence of destruction of the articular cartilage and subchondral bone continuity, and present as a soft tissue tumor.
Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
No funding was received for this study.
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