Anterior knee pain is a frequently encountered condition in orthopedic practice. The common causes of this pain include degenerative or inflammatory conditions, trauma, and tendonitis. In addition, however, anterior knee pain may occasionally arise from a tumor of the patella or the extensor mechanism. Although osteosarcoma is the most common primary malignancy of bone, it has only been reported to arise from the patella in a handful of cases. Careful physical examination of the knee and evaluation of radiographs are essential to detect this rare and devastating condition.
| || |Figure 1:
Patient presented with marked knee swelling.
Osteosarcoma is the most common malignant bone tumor of children and young adults, with a predilection for the metaphysis of long bones, particularly the tibia, femur, and humerus.1-4 Flat bones are less commonly involved. Osteosarcomas can be classified by either their radiographic or their histologic subtype of which multiple types have been described. Osteogenic osteosarcomas account for 50% of all osteosarcomas, another 25% consist of chondroblastic osteosarcomas, and less common is the fibroblastic variant. Telangiectatic osteosarcoma accounts for <5% of all osteosarcomas, and it is distinguished histologically by spaces, often blood filled, separated by septa containing highly malignant cells and radiographically by a predominately lytic and/or expansile component.5,6 Similar to other osteosarcomas, the telangiectatic variant is diagnosed by radiographic evaluation and biopsy. Telangiectatic osteosarcoma can be radiologically confused with aneurysmal bone cyst or giant cell tumor.1,2
Primary tumors of the patella are rare and the majority of these tumors are benign. In some series, osteosarcomas constitute approximately 6% of all patellar tumors1; however, no cases of telangiectatic osteosarcoma have been reported.1-4,7-11 We report a case of patellar telangiectatic osteosarcoma, an extremely rare and unusual anatomical site for malignant bone neoplasms. We report the clinical presentation, radiologic and pathologic findings, and surgical and medical management, along with a review of the literature.
A 22-year-old otherwise healthy man was referred with a history of anterior knee pain for 6 months. He had been originally diagnosed with chondromalacia patellae based on history alone and had been referred to physical therapy for treatment. Because of persistent and progressive pain, including pain at rest, radiographs and magnetic resonance images were obtained, demonstrating an abnormality of the patellar mechanism.
The patient presented with swelling of the right knee (Figure 1), pain at rest and with activity, and significant limitation of flexion. On physical examination, marked swelling anterior to the patella, significant tenderness to palpation, and moderate knee effusion were noted. The patient was able to perform a straight leg raise, but he had significant pain with passive or active flexion of the knee.
Review of anteroposterior and lateral radiographs of the knee obtained several weeks prior to referral demonstrated a diffuse destructive process involving the majority of the patella, particularly the inferior pole. A soft tissue mass was also visible, with apparent osteoid matrix visible in the soft tissue component along the inferior pole of the patella. Repeated radiographs at the time of our initial evaluation demonstrated significant progression of the destructive changes, with loss of the inferior patellar cortex, as well as a lytic lesion of the proximal tibia (Figure 2).
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| Figure 2: Lateral radiograph of the knee showing complete destruction of the patella, with a lytic lesion in the proximal portion of the tibia. Figure 3: Sagital cut MRI shows the patella eaten by the tumor, with extension to the proximal tibia, and multiple foci of the tumor in the distal femur. |
Magnetic resonance imaging demonstrated a large tumor involving the patella and extending along the patellar tendon. A second, noncontiguous lesion (skip lesion) involving the proximal tibia was also observed, with signal characteristics similar to that of the patellar lesion (Figure 3). Additionally, two small 2- to 3-mm lesions were present in the distal femoral epiphysis with signal characteristics identical to the main lesion. A moderate knee effusion was present, along with some small (<1 cm) lesions of the distal femur. Staging studies included a Tc-99m MDP bone scan, showing increased uptake of radiotracer about the knee, with one focal area of increased activity involving the patella and another involving the proximal tibia. The lesions of the distal femur were presumably not large enough to produce a focal area of uptake. A computed tomography scan of the chest showed 2 pulmonary nodules in the right lung consistent with metastatic disease. Core needle biopsy was performed through a midline approach into the patellar mass under local anesthetic with intravenous conscious sedation. Histologic evaluation of the tumor showed osteosarcoma with telangiectatic features.
Based on the histologic findings and imaging studies, the patient was classified as having an Enneking stage III (American Joint Committee on Cancer stage IV) metastatic telangiectatic osteosarcoma with both skip metastases and lung metastases. Given that the majority of the tumor involved the patella and extensor mechanism and that the patients symptoms began with anterior knee pain, it was clear that the tumor originated in the patella. Following confirmation of the diagnosis, the patient was enrolled on Childrens Oncology Group (COG) protocol AOST 0121 for induction chemotherapy. This treatment protocol includes the standard COG protocol P9450 and examines the addition of trastuzumab for patients with metastatic osteosarcoma that over-expresses human epidermal growth factor receptor 2.12 He received 5 cycles of induction chemotherapy, including doxorubicin, cisplatin, and methotrexate, with surgery performed after his counts recovered. During induction chemotherapy, he was kept in an adjustable and removable knee immobilizer for comfort and for prevention of patellar fracture while weight-bearing ambulation without supports was permitted.
Repeat staging following induction chemotherapy showed evidence of disease progression in the patella, without any significant change in the lung nodules. Surgical options were reviewed with the patient at this point. The decision to proceed with an attempted limb-sparing procedure was made because amputation offered no survival advantage in the presence of pulmonary metastases, and a palliative limb-sparing approach would maximize function while providing local control of his disease. Given the presence of disease involving the distal femur and proximal tibia as well as the extensor mechanism, an extra-articular resection of the knee was planned. A modified endoprosthesis, featuring a constrained hinged knee mechanism, was selected for skeletal reconstruction on the basis of complete loss of all primary and secondary constraints of the knee as well as an active extensor mechanism following surgical resection.
Through an extensile, transadductor approach to the knee13, a true extra-articular resection of the knee joint was performed excising the distal femur, proximal tibia, and extensor mechanism en bloc (Figure 4). The anterior skin incision was made, ellipsing out the prior biopsy tract along with some of the anterior skin overlying the prominent patellar mass. Medial and lateral fasciocutaneous flaps were elevated, leaving the patella, patellar tendon, knee capsule, and collateral ligaments intact with the resection specimen.
| || |Figure 4:
Intraoperative photograph showing the extra-articular resection of the knee joint.
The proximal resection margin was taken through the quadriceps muscle approximately 15 cm (6 inches) above the joint line in conjunction with the distal femoral osteotomy. The popliteal exploration was uneventful, with all geniculate branches arising from the popliteal artery ligated and divided. The proximal tibial osteotomy was performed 5 cm (2 inches) below the tibial tubercle, with preservation of the anterior tibial artery. The proximal tibial fibular joint was opened and disarticulated, with release of the lateral collateral ligament from the fibular head. Intraoperative frozen sections were used to confirm clear margins at the resection margins.
Skeletal reconstruction was performed using the Global Modular Replacement System (Stryker Howmedica Osteonics, Rutherford, New Jersey), consisting of modular components for the distal femur and proximal tibia (Figure 5). Given the need to resect the extensor mechanism, which is critical to the control of a standard rotating hinge knee prosthesis, a custom modification was created by manufacturing a 1-piece proximal tibial component that incorporated the metallic tibial bearing component. This eliminated all axial and rotational translation associated with the rotating hinge knee, effectively converting the knee into a constrained hinged knee design that would not require an intact extensor mechanism for rotational or axial control. Because no constrained hinge prostheses for adults are currently available in the US market, this modification was justified as a simple, cost-effective solution in this patient with metastatic disease and overall poor prognosis. Cemented femoral and tibial stems were used to permit immediate stability and weight bearing.
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| Figure 5: Another intraoperative photograph shows the implanted prosthesis, consisting of the hinged distal femur and proximal tibia prostheses. Figure 6: Gore-Tex aortic graft with Dacron tape was used for reconstruction of the extensor mechanism. |
Reconstruction of the extensor mechanism was performed using a 40-mm Gore-Tex aortic vascular graft (Gore, Newark, Delaware) that was directly attached to the proximal tibial prosthesis using 5-mm Dacron tapes (Deknatel, Coventry, Connecticut) woven through the provided holes in the prosthesis and then though the distal portion of the aortic graft in a modified Kessler stitch pattern (Figure 6). The proximal graft was then secured directly to the remnants of the quadriceps muscles in a similar fashion after tensioning of the quads by advancing them as distally as possible. This reconstruction was augmented using a medial gastrocnemius muscle rotational flap which covered the entire extensor reconstruction as well as the prosthesis. The skin flaps were then closed over drains, completing the reconstruction. A skin graft was not required.
Postoperatively, the patients limb was kept in extension, first using a posterior splint and then a knee immobilizer. He was permitted to be out of bed, weight bearing as tolerated, by postoperative day 3. Following gait training with physical therapy, he was discharged home on postoperative day 5. Resumption of chemotherapy began 3 weeks postoperatively following uneventful wound healing. By 6 weeks, the patient could perform a straight leg raise without evidence of extensor lag. He was kept in extension for the first 12 weeks, using the knee immobilizer, to protect the extensor reconstruction. Passive, gravity-assisted flexion was then permitted, with the patient achieving 80° of flexion, along with a 30° extensor lag. His reconstruction remained intact, however, with full active extension possible with gravity eliminated in the lateral position. The extensor strength is sufficient to allow him to ambulate without braces or assistive devices.
The postoperative chemotherapy was composed of 12 cycles, as follows: week 13, ifosfamide and etoposide; week 16, methotrexate; week 17, doxorubicin and cisplatin; week 20, methotrexate; week 21, ifosfamide and etoposide; week 24, methotrexate; week 25, doxorubicin and cisplatin; week 28, methotrexate; week 29, doxorubicin; week 32, methotrexate; week 33, methotrexate; and week 34, ifosfamide and etoposide.
Osteosarcoma is the most common malignant bone tumor in children and young adults, with a predilection for the metaphysis of long bones, particularly the tibia, femur, and humerus.5,6 Flat bones are less commonly involved. Osteosarcoma is by definition a malignant tumor that produces osteoid matrix.6 Osteosarcoma is divided into several subtypes according to clinical, roentgenographic, and microscopic features.
The primary types of osteosarcoma include conventional (high-grade) medullary osteosarcoma, low-grade central osteosarcoma, parosteal osteosarcoma, periosteal osteosarcoma, and telangiectatic osteosarcoma. The secondary osteosarcomas include those associated with Pagets disease, postirradiation sarcomas, and those that originate as a benign precursor, such as fibrous dysplasia and bone infarcts.5,6
Multiple histologic subtypes of osteosarcoma have been identified. Osteogenic osteosarcoma accounts for 50% of cases, chondroblastic osteosarcoma for 25%, and less common is the fibroblastic variant. Telangiectatic osteosarcoma accounts for <5% of all cases.6
The resection specimen in our case showed an enlarged patella measuring 10 cm in diameter. On cut section, there were multiple blood-filled spaces separated by septa (Figure 7). A similar isolated lesion measuring 4 cm in diameter was present in the proximal tibial metaphysis. The articular surface between the tibia and the patella was intact. Microscopic examination revealed cyst-like spaces divided by septa composed of highly atypical cells (Figure 8A). There was a high degree of nuclear atypia, cellular pleomorphisim, and mitotic activity with numerous atypical mitoses (Figure 8B). Foci of neoplastic osteoid production were present. The diagnosis rendered was telangiectatic osteosarcoma extensively involving the patella, with a separate identical tumor in the head of the tibia. The criteria used to make the diagnosis of telangiectatic osteosarcoma are radiographic evidence of a lytic or destructive lesion and a gross appearance of blood-filled spaces separated by septa, which on microscopic examination contain highly malignant cells.
| |Figure 7:
Telangiectatic osteosarcoma of the patella.
Telangiectatic osteosarcoma does not differ prognostically from conventional osteosarcoma; it should, however, be separated as a distinct entity because it can mimic aneurysmal bone cyst, giant cell tumor, and conventional osteosarcoma with focal telangiectatic features.6
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| Figure 8: A low-power microscopic image of the resection specimen demonstrates the cyst-like spaces divided by septa composed of highly atypical cells (A). A high-power microscopic view reveals a high degree of nuclear atypia, cellular pleomorphisim, and mitotic activity with numerous atypical mitoses (B). |
The clinical behavior of telangiectatic osteosarcoma was originally thought to be worse than that of conventional osteosarcoma. More recent reports have indicated that with modern combined modality treatment, the particularly bad prognosis formerly associated with telangiectatic osteosarcoma no longer applies.5,6
According to Mercuri AND Casadei,7 there have been 384 reported cases of patellar bone tumors in the literature since 1900; the most common diagnosis in these cases was benign giant cell tumor of bone (33%), followed by chondroblastoma (16%). Osteosarcoma of the patella is extremely uncommon, with an estimated 25 cases in the literature since 1900.7 Ferguson et al9 suggested that the number is even less, having found only 10 reports of primary patellar osteosarcoma in the literature, all of the conventional subtype. The majority of reported cases were in patients with underlying syndromes increasing the vulnerability to osteosarcoma, such as Werner syndrome (adult progeria).10 A detailed review of the literature showed no previously reported cases of telangiectatic osteosarcoma of the patella. Given the distinctive radiographic and histologic features of this unusual variant of osteosarcoma, it is reasonable to expect that this would have been mentioned in these reports of patellar osteosarcoma. We conclude that this is the first reported case of telangiectatic osteosarcoma involving the patella.
The treatment protocol for extremity osteosarcoma includes preoperative chemotherapy ranging from 6 to 8 cycles, followed by limb-sparing surgery and postoperative chemotherapy. The cure rate may be as high as 70% to 80% in patients treated with modern chemotherapy protocols. Limb-sparing surgery can be performed in lieu of amputation in 90% to 95% of patients.
The percentage of necrosis of tumor cells is the most important guide for tumor response to chemotherapy and the subsequent possibility of cure. Those tumors with necrosis of ≥90% are associated with a good prognosis, those with necrosis of 70% to 90% are associated with a fair prognosis, and those with necrosis of <70% are associated with a poor prognosis. Necrosis in our patient was between 20% and 30%.
Our patient presented with a large lesion arising from the patella and smaller lesions of the proximal tibia and distal femur, representing possible regional metastases (skip mets) or, alternatively, multifocal osteosarcoma. Although this may simply represent a debate about semantics, it generally is agreed that these correlate with a poor prognosis compared with a solitary conventional extremity osteosarcoma. Surgical options considered included above-knee amputation versus limb-sparing surgery. As the goal of surgical resection was the complete removal of the entire area involved with a wide margin, and given the lack of popliteal involvement, we judged that limb-sparing, extraarticular resection of the knee and extensor mechanism was clearly feasible.
Although several choices for reconstruction exist, we opted to perform a customized endoprosthetic reconstruction. A simple hinge for the knee mechanism was selected to reduce torsional forces on the extensor reconstruction while noting that fixed hinged prostheses are associated with an increased risk of prosthetic loosening. We elected not to perform an allograft patellar replacement given the significant amount of skin loss due to the large anterior tumor mass. As an alternative, we used an aortic graft spanning the gap between the quadriceps and the proximal tibial component. In addition to providing a low profile, thus facilitating wound closure, the graft material permits ingrowth of fibroblasts and the development of a tight fibrous attachment to the surrounding tissue. Reinforcement of the reconstruction by advancement of the quadriceps and medial gastrocnemius rotation flap then permitted complete muscular coverage of the prosthetic joint, reducing the potential risk of secondary infection due to wound breakdown.
- Roger DJ, Uhl RL, Carl A. Malignant fibrous histiocytoma of the patella. Orthopedics. 1994; 17(2):189-193.
- Kransdorf M, Moser R Jr, Vinh T, Aoki J, Callaghan J. Primary tumors of the patella: A Review of 42 Cases. Skeletal Radiol. 1989;18(5):365-371.
- Linscheid RL, Dahlin D. Unusual lesions of the patella. J Bone Joint Surg Am. 1966; 48(7):1359-1366.
- Gibbs P, Weber K, Scarborough M. Malignant bone tumors. J Bone Joint Surg Am. 2001; 83 (11):1727-1745.
- Dorfman H, Bogdan C. Bone Tumors. St. Louis, MO: Mosby, Inc; 1998.
- Sternberg S. Diagnostic Surgical Pathology. Philadelphia, PA: Lippincott, Williams, & Wilkins; 1999.
- Mercuri M, Casadei R. Patellar tumors. Clin Orthop Relat Res. 2001; (389):35-46.
- Cooper ME, Mess D. Isolated skeletal metastasis to the patella. Am J Orthop. 2000; 29(3):210-212.
- Ferguson PC, Griffin AM, Bell RS. Primary patellar tumors. Clin Orthop Relat Res. 1997; (336):199-204.
- Ishikawa Y, Miller R, Machinami R, Sugano H, Goto M. Atypical osteosarcomas in Werner Syndrome (adult progeria). Jpn J Cancer Res. 2000; 91(12):1345-1349.
- Mohadjer Y, Wilson M, Fuller C, Haik B. Primary pelvic telangiectatic osteosarcoma metastatic to both orbits. Ophthal Plast Reconstr Surg. 2004; 20(1):77-79.
- National Cancer Institute. Phase II Study of chemotherapy with or without Trastuzumab (Herceptin) in patients with metastatic osteosarcoma. http://www.cancer.gov/clinicaltrials/COG-AOST0121. Accessed July 18, 2008.
- Malawer M, Kellar-Graney K. Soft tissue reconstruction after limb-sparing surgery for tumors of the upper and lower extremities. Operative Techniques in Orthopaedics. 2003; 14(4):276-287.
Dr Shehadeh is from the Department of Surgery, King Hussein Cancer Center, Amman, Jordan; and Drs Haiba and Lack are from the Department of Pathology and Laboratory Services, and Dr Henshaw is from the Department of Orthopedic Oncology, Washington Cancer Institute, Washington Hospital Center, Washington, District of Columbia.
Drs Shehadeh, Haiba, Henshaw, and Lack have no relevant financial relationships to disclose.
Correspondence should be addressed to: Robert M. Henshaw, MD, Orthopedic Oncology, C-2173, Washington Cancer Institute, 110 Irving St, NW, Washington, DC 20010.