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 [4]. 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 [8].

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 [8].

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 [10].

A solitary painless enchondroma may be observed. Painful or worrisome lesions suspicious for low grade chondrosarcoma should be treated.

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 [1]. 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 [5]. Treatment is intralesional resection and bone grafting.

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.

Most osteoid osteomas are treated by an interventional musculoskeletal radiologists using percutaneous radiofrequency ablation. Less often, osteoid osteomas are surgically curetted or excised [7, 11].

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 [12].

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 [13]. 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 [14].

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 [17]. 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.