CT scan of a chondroblastoma of the proximal tibial epiphysis. (a) It was treated by means of percutaneous radiofrequency ablation. (b) Electrode in place
Osteochondroma, or osteocartilaginous exostosis, is the most common skeletal neoplasm. The cartilage-capped subperiosteal bone projection accounts for 35 % of benign and 8 % of all bone tumors, which is probably an underestimate as the majority are asymptomatic and not clinically apparent. Osteochondroma is a benign tumor of young people, 10–30 years of age, with no known sex predilection. Osteochondromas appear in a juxta-epiphyseal location, frequently around the knee. Approximately 15 % of patients have multiple lesions. Hereditary multiple osteochondromatosis is an autosomal dominant condition that can lead to both sessile and pedunculated lesions [1–4].
Many, if not most lesions, are asymptomatic and found incidentally. In symptomatic cases, the most common presentation is that of a hard mass of long-standing duration. Some cases present with symptoms related to secondary complications such as mechanical obstruction, nerve impingement, bursa forming over the osteochondroma, pseudoaneurysm of an overlying vessel, infarction of the osteochondroma or fracture of the stalk of the lesion . After closure of the growth plate in late adolescence, there is normally no further growth of the osteochondroma, so an enlarging tumor in an adult should raise concern of malignant transformation. This occurs in less than 1 % of patients with solitary and approximately 1–3 % of patients with hereditary multiple osteochondromatosis .
Plain radiographs are normally enough to diagnose an osteochondroma. It is a metaphyseal lesion, appearing as a sessile or pedunculated osseous mass, typically growing away from the adjacent joint. This lesion is in continuity with the medullary cavity and cortex of the bone and is covered by a cap of hyaline cartilage. Computed tomography (CT) is helpful in determining if the marrow and cortices of the lesion are continuous with the bone. Magnetic resonance imaging (MRI) can delineate the relationship of the lesion to other structures and can allow measurement of the thickness of the cartilage cap, which assists in predicting the risk of malignant transformation .
Osteochondromas do not always need surgery; only if the symptoms are significant, marginal resection is indicated. Patients with multiple osteochondromatosis should have regular screening exams and radiographs to detect malignant transformation early.
Enchondroma is a benign hyaline cartilage neoplasm of medullary bone. Most tumors are solitary; however, they occasionally involve more than one bone or more than one site in a single bone. Enchondromas are relatively common, accounting for 10–25 % of all benign bone tumors. Again, the true incidence is much higher since many tumors are detected incidentally and never biopsied. The peak incidence is in the third decade and is equal between men and women. Enchondroma occurs most commonly in the hands and feet; the long bones, especially proximal humerus and proximal and distal femur, are next in frequency [1–4].
Most patients have no symptoms and many cases are detected incidentally in radiographs, MRI or bone scans taken for other reasons. The presence of pain is suspicious for malignant transformation to chondrosarcoma or for the presence of pathological fracture. Multiple enchondromatosis is a non-heritable condition also known as Ollier’s disease; multiple enchondromas and soft tissue hemangiomas constitute a condition known as Maffucci’s Syndrome. Change in symptoms and extension beyond the bony cortex into the adjacent soft tissue herald the development of chondrosarcoma. Malignant transformation occurs by 40 years of age in approximately 25–30 % of cases of multiple enchondromatosis [4, 9].
Radiographically, enchondromas form well marginated tumors that vary from radiolucent to heavily mineralized. Calcifications throughout the lesion can range from punctate to rings. In larger lesions, the lucent defect has endosteal scalloping and the cortex is expanded and thinned; in long bones, this is considered suspicious for low grade chondrosarcoma. More extensive endosteal erosion, cortical destruction and soft tissue invasion should never be seen in enchondromas. Long bone tumors are usually centrally located within the metaphysis which may extend to the diaphyseal or subarticular region of the bone. CT, MRI and bone scan allow differentiation between an enchondroma and a low grade chondrosarcoma .
A solitary painless enchondroma may be observed. Painful or worrisome lesions suspicious for low grade chondrosarcoma should be treated.
13.2.4 Chondromixoid Fibroma
Chondromyxoid fibroma is a benign cartilage tumor that also has myxoid and fibrous elements. It is extremely rare and accounts for less that 1 % of all bone tumors . It presents in the second to third decade and has a male to female ratio of 2:1. It is most frequent in the long bones, most often the proximal tibia (the most common site) and the distal femur. The clinical presentation is usually chronic pain, swelling and possibly a palpable soft tissue mass or restriction of movement, but it can be an incidental finding [2, 3].
The appearance on imaging studies is of a lytic lesion with well defined usually sclerotic margins, eccentrically placed and located near the end of long bones. Most lesions are entirely lucent; approximately 10 % may show focal calcified matrix, more often detectable with CT scans . Treatment is intralesional resection and bone grafting.
13.2.5 Osteoid Osteoma
Osteoid osteoma is a small and disproportionately painful benign bone-forming tumor. This lesion accounts for approximately 10 % of benign bone tumors, and usually affects children and adolescents. It is more common in males. It can occur anywhere in the body but is most commonly located in the diaphysis and occasionally in metaphysis of femur or tibia [1–4].
Patients will have pain during the day but also pain that wakes them at night. In many cases, they will have discovered that use of aspirin or ibuprofen provides rapid but temporary relief of the symptoms. When lesions are located at the very end of a long bone, patients may present with swelling and effusion of the nearest joint. Generally, the diagnosis is clear enough from imaging studies that biopsy is not required. On plain films, the lesion is characterized by dense cortical sclerosis surrounding a radiolucent nidus. The best imaging study to demonstrate osteoid osteoma is a CT scan.
13.2.6 Giant Cell Tumor
Giant cell tumor (GCT) is a benign, locally aggressive neoplasm which is composed of sheets of neoplastic ovoid mononuclear cells interspersed with uniformly distributed large, osteoclast-like giant cells. GCT represents around 4–5 % of all primary bone tumors, and approximately 20 % of benign primary bone tumors. The peak incidence is between the ages of 20 and 45. GCTs have a predilection for the epiphysis and adjacent metaphysis; frequently, there is extension up to the subchondral plate, sometimes with joint involvement. GCT occurs around the knee in 50–65 % of cases [1–4].
Clinical presentation includes pain, swelling, and limitation of motion. Pathological fracture occurs in up to 10 % of cases. These tumors are considered locally aggressive. They tend to continue to enlarge, destroy bone, and may eventually erode the rest of the bone and extend into the soft tissues. These tumors are notorious for their tendency to recur. Radiographs demonstrate a subarticular and metaphyseal lytic lesion. The lesion is typically eccentric and elongated, and it may appear multiloculated and expansile. CT and MRI allow evaluation of the extraosseous and intraosseous extent of tumor. In very rare instances, this lesion has the potential for metastasis to the lungs, and in these cases, the lung lesions may behave in an indolent fashion and even require no treatment .
Treatment of giant cell tumors is surgical. Extended intralesional resection is the treatment of choice, because curettage alone is thought to lead to high rate of local recurrence. Multiply recurrent GCTs, those with extensive bone destruction or pathological fracture are also treated with wide resection . In recent years, clinical results using denosumab, a highly effective and specific antagonist of RANKL, have shown that it reduces bony destruction and therefore may offer an option for unresectable tumors or in cases with severe surgical morbidity. The role of denosumab in curative treatment is the subject of ongoing studies .
13.3 Tumor-Like Lesions of Bone
13.3.1 Nonossifying Fibroma
Nonossifying fibroma is a well circumscribed, solitary fibrous proliferation. A very small nonossifying fibroma is called a fibrous cortical defect. These lesions are developmental defects in which parts of bone that normally ossify are instead filled with fibrous tissue. They commonly affect the metaphyses, and the most commonly affected sites are, in order, the distal femur, distal tibia, and proximal tibia. Nonossifying fibromas are common among children. The lesion is found in males more commonly than in females. Most lesions eventually ossify and undergo remodeling, often resulting in dense, sclerotic areas in adults [1–3].
Small nonossifying fibromas are asymptomatic, they are generally first noted incidentally on imaging studies. However, lesions that involve nearly 50 % of the bone diameter tend to cause pain and increase the risk of pathologic fracture. Plain film radiography demonstrates a well-circumscribed, eccentric, multiloculated osteolytic lesion, arising from the metaphyseal cortex. Serial X-rays will show the lesion migrating away from the epiphyseal plate with time.
For most patients, lesions will heal as they reach their 20s and thus they are typically simply observed. In the rare cases where the lesion is large enough to weaken the bone and threaten fracture, surgery can be performed to remove the tumor and fill the bone defect with bone graft alongside internal fixation of the fracture if necessary. The only definite indication to treat nonossifying fibromas is a pathologic fracture.
13.3.2 Aneurismal Bone Cyst
Aneurysmal bone cyst is a benign lesion that contains blood-filled cavities and is seen in young people, 10–30 years of age. It is not a neoplastic lesion that should be considered in the differential diagnosis of lytic neoplasms around the knee joint. Aneurismal bone cyst may arise de novo as a primary lesion, or secondarily complicate other benign and malignant bone tumors that have undergone haemorrhagic cystic change. It occurs in the metaphysis of the long bones, including the tibia and the femur [1–4].
The most common signs and symptoms are pain and swelling, which are rarely secondary to fracture. Radiographically it presents as a lytic, eccentric, expansile mass with well defined margins. Most tumors contain a thin shell of subperiosteal reactive bone. CT and MRI studies show internal septa and characteristic fluid-fluid levels created by the different densities of the cyst fluid caused by the settling of red blood cells. In secondary lesions, CT and MRI may show evidence of an underlying primary lesion. A careful search for radiological signs of the precursor lesion, if any, is recommended. Some of these precursor lesions may have a flocculent chondroid matrix that may be a clue to their pathogenesis .
Aneurismal bone cyst is a benign, potentially locally recurrent lesion. Extended intralesional resection is normally used. Large lesions may require other treatments, such as embolization. The cyst can be packed with bone chips or polymethylmethacrylate cement .
13.4 Malignant Bone Tumors
Osteosarcoma is a primary malignant mesenchymal tumor in which the neoplastic cells produce osteoid, even if only in small amounts. There are many types of osteosarcomas. The most common type, conventional osteosarcoma, which is intramedullary and high grade, represents approximately 75 % of all osteosarcomas. Osteosarcoma is the most common, nonhaematopoietic, primary malignant tumor of bone, with an estimated incidence of 4–5 per million population.
It most frequently occurs in the second decade and 60 % of patients are under the age of 25. Although 30 % of osteosarcomas occur in patients over 40 years of age, the possibility of a secondary osteosarcoma should always be considered in older patients. Secondary osteosarcomas are bone forming sarcomas occurring in bones that are affected by preexisting abnormalities, the most common being Paget disease and following radiotherapy. Osteosarcoma is slightly more common in males than females possibly due to longer period of male skeletal growth. The most common sites are the distal femur and proximal tibia. Most (90 %) arise from the metaphysis of the bone, thus in most instances, the tumor arises next to the knee joint [1–4].
Symptoms generally develop over a period of weeks to a few months. The most common presentation is pain and a mass, which occurs near a joint. Pain gradually becomes more severe and is accompanied by swelling and limitation of motion. On radiographs, conventional osteosarcoma occurs predominantly in the metaphysis, and appears as a mixed sclerotic and lytic lesion, that may permeate the bone and the nearby cortex, causing a soft tissue mass and a periosteal reaction. Bone formation within the tumor is characteristic of osteosarcoma and is usually visible on the X-rays .
Although rare, parosteal osteosarcoma is the most common type of osteosarcoma of the surface of bone. Patients in their 20s and 30s are most commonly affected. About 70 % involve the surface of the distal posterior femur [2, 4]. Patients generally complain of a painless swelling; inability to flex the knee may be the initial symptom. Some patients complain of a painful swelling. Radiographs show a heavily mineralised mass attached to the cortex with a broad base. Other variants of osteosarcoma are commonly located around the knee.
High grade osteosarcoma is treated with neoadjuvant chemotherapy, surgical resection with a wide margin and adjuvant chemotherapy. The vast majority of patients do not require amputation but rather can be treated with limb salvage surgery.
Chondrosarcoma is a malignant mesenchymal tumor that produces cartilage matrix. There are several subtypes of chondrosarcoma, which vary in terms of location, appearance, treatment, and prognosis. Primary chondrosarcoma accounts for approximately 20 % of malignant bone tumors in one large series. It is the third most common primary malignancy of bone after multiple myeloma and osteosarcoma. In the total group of chondrosarcomas, more than 90 % are primary (conventional) type. Chondrosarcoma most commonly occurs in adults aged 30–70 years. The most common skeletal site is the pelvis; approximately 25 % occur in the femur but rarely in the distal part [1–4].
Clinically, chondrosarcoma presents with pain, a soft tissue mass, warmth, and erythema, and may present with pathological fracture. Chondrosarcoma is classified as central or peripheral, with the peripheral form arising from a preexisting osteochondroma. It is difficult to prove malignant transformation in enchondromas. Patients with Ollier’s disease or Maffucci’s syndrome are at much higher risk (25–30 %) of developing chondrosarcoma than the normal population and often present in the third and fourth decade [4, 9]. Local swelling and pain, alone or in combination, are significant presenting symptoms. The symptoms are usually of long duration.
In the long bones, primary chondrosarcomas occur in the metaphysis or diaphysis where they produce fusiform expansion with cortical thickening of the bone. They present as an area of radiolucency with variably distributed punctate or ring-like opacities (mineralization). Cortical erosion or destruction is usually present. The cortex is often thickened but periosteal reaction is scant or absent. MRI can be helpful in delineating the extent of the tumor and establishing the presence of soft tissue extension. CT scans aid in demonstrating matrix calcification .
Treatment of chondrosarcoma is wide surgical excision. In most cases, surgery is the only treatment. The role for chemotherapy or radiation is currently unknown. However, for high grade dedifferentiated and mesenchymal chondrosarcoma, chemotherapy is indicated. Extended intralesional resection is safe and effective in the treatment in low grade chondrosarcomas of the appendicular skeleton .
13.4.3 Ewing Sarcoma
Ewing sarcoma is a primary osseous neoplasm composed of uniform, monotonous, small round blue cells without any matrix production.
It is the fourth most common primary malignancy of bone and the second most common sarcoma in bone and soft tissue in children. Nearly 80 % of patients are younger than 20 years. Ewing sarcoma tends to arise in the diaphysis or metaphyseal-diaphyseal portion of long bones, but its location around the knee is rare [1–4].
Pain and a mass in the involved area are the most common clinical symptoms. Fever (low grade, about 38 °C), anemia, leukocytosis and increase in sedimentation rate are often seen. Radiographically, an ill defined osteolytic lesion involving the diaphysis of a long bone or flat bone is the most common feature. Permeative or moth-eaten bone destruction is characteristic, often associated with “onion-skin” multilayered periosteal reaction. The cortex overlying the tumor is irregularly thinned or thickened. A large, ill defined soft tissue mass is a frequent association in Ewing tumor. Expansile bone destruction with soap-bubble appearance might be seen. CT is helpful in defining bone destruction. MRI is essential to elucidate the soft tissue involvement .
Treatment for Ewing sarcoma includes neoadjuvant chemotherapy, surgery with wide margins and adjuvant chemotherapy. Radiotherapy also has a role.
13.4.4 Undifferentiated/Unclassified Sarcoma of Bone
Undifferentiated sarcoma of bone is a malignant neoplasm composed of fibroblasts and pleomorphic cells with a prominent storiform pattern. It represents less than 2 % of all primary malignant bone lesions. It can occur in patients ranging from 10 to 60 years, with a higher incidence in adults over 40 years of age. The knee is a common location, with concurrent involvement of the distal femur and proximal tibia. Undifferentiated sarcoma of bone can arise as a primary bone tumor or may develop secondary to preexisting bone conditions such as Paget disease or bone infarct, or at the site of bone which has been irradiated .
Clinically, most patients complain of pain. Radiographically, there are osteolytic lesions, but sclerotic areas may be present. The margins are usually ill-defined and a moth-eaten or permeative pattern of bone destruction can be observed.
Treatment is the same as conventional osteosarcoma, including chemotherapy and wide surgical resection.
13.4.5 Bone Metastases
Skeletal metastases are the most common malignant tumors of bone, typically seen in patients over 40 years of age. Cancers that most frequently spread to bone include; breast, lung, thyroid, kidney, and prostate. Metastases are most commonly seen in the axial skeleton and proximal femur and humerus, with rare occurrence about the knee. Pain is the most common presenting symptom, pathological fracture typically occurs after a few weeks or months of pain. Radiographically, metastases may appear purely lytic, blastic, or with a mixed pattern depending on the primary tumor.
Metastatic tumors are treated according to the prognosis of the patient. When palliative surgery is performed, which is the most common situation, metastatic lesions are treated in case of impending or pathologic fracture by internal fixation and if necessary an intralesional resection (Fig. 13.2). If a curative procedure is performed, in the case of solitary breast metastasis, for example, the lesion is treated as if it was a primary bone sarcoma, with en bloc resection and endoprosthetic replacement.
A 64 years old woman with metastatic breast cancer, complaining of knee pain. Anteroposterior radiograph showing a lytic lesion in the metaphysis of the distal femur in risk of impending pathologic fracture. (a) Postoperative radiograph after prophylactic surgery (b)
Treatment for bone tumors depends on the histological grade, the size and location of the tumor and the age of the patient. Both benign and malignant tumors of bone should be staged according to the Enneking staging system, adapted by the Musculoskeletal Tumor Society, prior to planning treatment . The surgical treatment of tumors and tumor-like lesions of bone involves a multidisciplinary team approach. Work-up begins with a detailed history, physical exam, and imaging. Biopsy to obtain a histological diagnosis is an important step prior to treatment. The principle of full surgical resection with maintenance of adequate margins is important to obtain local control. Tumors around the knee represent a difficult reconstructive challenge given their juxta-articular nature.
There are four basic types of resection; each is based on the relationship of the dissection plane to the tumor and its pseudocapsule. Margins can be defined as intralesional, marginal, wide, and radical. An intralesional margin is created if the tumor is entered or cut into at any point during surgery. A marginal margin is created when the surgical dissection extends into the abnormal, reactive tissues that surround the tumor. A wide margin is created when the dissection is through entirely normal tissues, and a cuff of normal tissue is left on all sides of the tumor. A radical margin is created if the surgeon resects the entire bony or myofascial compartment or compartments containing the tumor.
Tumor grade and location dictate the type of excision required. In general, benign bone tumors are adequately treated by either an intralesional procedure or by marginal resection and mechanical, chemical, and thermal adjuncts can be employed to further reduce the risk of recurrence. Primary bone sarcomas and some aggressive benign tumors require a wide excision. It is important to emphasize that a wide margin may be accomplished by a limb salvage procedure or by amputation. Staging studies are used to assess local tumor extent and relevant local anatomy, and thereby determine how a desired surgical margin may be achieved. Various reconstruction options can be used to help restore function.
Tumors around the knee are a difficult reconstructive challenge; limb salvage principles are largely employed if neurovascular structures can be preserved and a level of function maintained. Ultimately the surgical treatment of bone tumors provides unique challenges for surgeons, and advances in imaging, surgical techniques, prosthetic design, and adjuvant treatments have continued to assist surgeons in improving functional outcomes.
13.5.1 Benign Tumors
The indications for surgical treatment of benign bone tumors and tumor-like lesions depend on the biological activity, clinical symptoms and anatomic location of the lesion. The staging system for benign tumors is useful for determining which tumors are most likely to require treatment and which can be safely observed. Benign bone tumors are staged according to their radiographic appearance and apparent clinical behavior. Stage 1 lesions are static, latent lesions, which are typically self-healing. Stage 2 lesions are active but remain within the confines of the bone and are associated with bone destruction or remodeling. Stage 3 lesions are active and locally aggressive and tend to extend beyond the cortex into surrounding soft tissue.