Primary bone malignancies such as osteosarcoma and Ewing sarcoma commonly occur in the distal femur. Before the advent of modern chemotherapy protocols and reconstruction options, the mainstay of surgical treatment of these malignancies was transfemoral amputation. Currently, with advances in multimodal treatment, limb-sparing surgery and reconstruction with curative intent has become the standard of practice. Local recurrence rates after neoadjuvant chemotherapy and oncologic resection of distal femoral osteosarcoma with endoprosthetic reconstruction have been reported in the literature to be up to 10%. Adequate surgical margins and good response to chemotherapy are essential in minimizing local recurrence. Reconstruction is commonly achieved with the use of a modular replacement system or, in highly specific populations, an allograft-prosthetic composite. Although the primary indication for distal femoral resection and reconstruction is primary bone sarcoma, other indications include metastatic disease, trauma, and revision total knee arthroplasty in the setting of massive bone loss. Distal femoral resection and endoprosthetic or allograft reconstruction should be considered in all cases where the oncologic and functional outcomes are preferable to transfemoral amputation or rotationplasty. Although a viable option to restore function after an oncologic resection of the distal femur, rotationplasty is not discussed in this chapter. The reader
should, however, be aware of rotationplasty as a surgical option when conventional limb salvage is not feasible. The perioperative considerations, reconstruction options, and observed outcomes of distal femoral resection and reconstruction are described with a focus on the population with primary bone sarcoma.

Indications for distal femoral resection and reconstruction are (1) primary bone sarcoma, (2) benign aggressive bone tumors or disease associated with distal femoral compromise where other treatment options are not feasible or would yield inferior oncologic and functional results (ie, circumferential bone loss), (3) metastatic disease limited to the distal femur where overall patient survival and function may be improved with an oncologic resection (ie, solitary bone metastasis from renal cell carcinoma),¹ (4) revision total knee arthroplasty in the setting of massive bone loss without infection, and (5) trauma in the setting of massive bone loss (Figures 1 and 2). Immediate reconstruction with an endoprosthetic device should not be attempted in a contaminated field; however, delayed reconstruction remains a useful salvage option if the distal femoral fragments are not amenable to repair.

When sarcoma is suspected based on radiography and local cross-section imaging (including bone scintigraphy), systemic staging should be completed per existing guidelines, and a biopsy should be performed in accordance with the oncologic principles of biopsy, preferably by an orthopaedic oncologist. The tumor volume and extent of systemic disease should be evaluated both before and after neoadjuvant chemotherapy. With limb salvage as the current standard of care, patients who undergo transfemoral amputation generally are those who have more extensive infiltrative neurovascular and/or muscular tumors such that the reconstructed limb would have inferior function to a prosthesis or, rarely, prefer amputation. To provide further context and consideration, a meta-analysis found that limb-sparing surgery had both a significantly lower metastatic occurrence and higher 5-year overall survival rate, albeit no significant difference in recurrence rate when compared with amputation in patients with lower extremity osteosarcoma.²

Whether a pathologic fracture necessitated immediate amputation in the setting of a primary bone sarcoma was previously controversial. Primary bone tumors with pathologic femur fracture were found to have a poor prognosis with a 38% local recurrence rate in a population-based study.³ In this study, the patients who underwent resection and reconstruction had an overall prognosis similar to those who underwent limb salvage. Although pathologic fractures were previously thought to be poor prognostic signs of survivorship, a study that controlled for other established prognostic factors (ie, advanced Musculoskeletal Tumor Society stage, a curbed response to chemotherapy, proximal location of tumors in long bones) found that pathologic fractures were not associated with decreased overall or disease-free survival.⁴ A 2022 meta-analysis including 3,839 patients with surgically treated osteosarcoma complicated by pathologic fracture found no difference between limb salvage and amputation in either local recurrence rate or metastasis.⁵ Nonetheless, the final surgical decision should be made after induction chemotherapy, and in the interim, fracture stability can be achieved with external immobilization. If radiographs show ossification of the fracture site after induction chemotherapy, it is reasonable to consider limb salvage. In the setting of benign aggressive tumors, a pathologic fracture does not necessitate wide resection and endoprosthetic reconstruction. One study reported similar functional and recurrence outcomes for patients with intra-articular pathologic fractures from giant cell tumor of bone treated with intralesional curettage versus wide resection and reconstruction.⁶

The femur may be resected via a lateral, anterior, or medial approach. A medial approach is most commonly used and is performed as follows. The patient should be positioned supine with a sandbag positioning device under the ipsilateral hip and the entire leg including the hip prepped and draped in a sterile manner. The planned excision should be considered on a patient-by-patient basis but classically begins at the medial thigh and extends past the knee using a medial parapatellar approach to below the pes anserinus. The approach begins with exploration of the fossa and demarcation of the tumor mass from the popliteal neurovascular structures. Distal femoral sarcoma resection should be performed in accordance with strict oncologic principles. The tumor should be removed en bloc with adequate soft-tissue and bony margins on the basis of postchemotherapy imaging, with care taken to include the biopsy tract and other potentially contaminated tissues in the resection specimen. Intraoperative frozen sections of the proximal femoral margin should be sent for pathologic analysis to ensure a negative proximal margin before proceeding with skeletal reconstruction. Distal femoral reconstruction is then performed. Adequate soft-tissue coverage is ensured by medial gastrocnemius flap and/or sartorius flap reconstruction in selected patients if primary closure is not feasible. Rarely, free tissue transfers may be considered to ensure coverage.

Infection is the most common postoperative complication of endoprosthetic reconstruction, with multiple systematic reviews of retrospective data suggesting an approximately 10% incidence of deep infection.^7,8 Despite the magnitude of this problem, a survey of musculoskeletal oncologists identified widely disparate treatment patterns in terms of postoperative antibiotic prophylaxis.⁹ The Prophylactic Antibiotic Regimens in Tumor Surgery trial was a multicenter randomized clinical trial published in 2022 that included 604 patients to investigate antibiotic prophylaxis after endoprosthetic reconstruction.¹⁰ The trial compared a 5-day regimen of postoperative prophylactic antibiotics with a 24-hour regimen and found a 15.9% overall infection rate with no difference in surgical site infection (deep, superficial, or organ space) between the groups at 1 year but found significantly greater antibiotic-related complications in the 5-day antibiotic group.

Available reconstruction options vary by extent of resection, soft-tissue loss, and skeletal maturity. Appropriate reconstruction should be considered on a patient-by-patient basis.