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Osteosarcomas are the most common primary malignant bone tumour of children and young adults. These aggressive mesenchymal tumours most commonly arise in the metaphyseal regions of the distal and proximal femur, proximal tibia, proximal humerus and pelvis.
The oncological principle is to widely resect the tumour with the biopsy tract in-situ with adequate surgical margins in all planes to minimise the risk of local recurrence and reconstruct the segmental osseous defect with endoprosthesis, allograft or autograft. In our centre we most frequently use custom ‘growing’ endoprostheses in younger (<13 years) children that can be lengthened as a child grows to avoid significant limb length discrepancy. These ‘growing’ endoprostheses might be non-invasive (using an internal gearbox which lengthens when an external electromagnetic field is applied) or minimally invasive (involves a small incision and manually lengthening the prosthesis with a hexagonal key) which are intermittently extended to keep pace with growth (http://www.stanmoreimplants.com/jts-non-invasive-extendible-prostheses.php).
In some cases the tumour extension has involved the joint cavity of the knee which would lead or compromised surgical margins if the joint capsule were exposed peri-operatively. This may be clear on pre-operative imaging or be suspected with subtle effusions radiologically. Consequently a demanding ‘extra-articular’ excision is undertaken to excise the distal femur and proximal tibial epiphysis en-bloc without compromising the proximal tibial growth plate or exposing the tumour.
Indications:
The indication for an extra-articular resection of the distal femur is when pre-operative imaging shows tumour involvement of the joint such that an intra-articular approach would compromise an en-bloc curative resection of the tumour. In order to achieve and oncologically sound wide en-bloc resection of the tumour we assess the the pre-operative imaging particularly the axial T1-weighted images to ensure we can excise the tumour in one piece, without leaving tumour cells behind whilst also preserving the neurovascular structures necessary to achieve limb-salvage. According to the Birmingham classification (https://link.springer.com/article/10.1007/s11999-016-4851-y) a minimum 2mm margin of normal soft-tissues around osteosarcomas is a predictor for local recurrence.
Symptoms and examination:
Patients with osteosarcoma usually present with pain and swelling around the the metaphyseal regions of the distal and proximal femur, proximal tibia, proximal humerus and pelvis. Patients are evaluated to determine the length of symptom duration and severity, limitation of motion, effusion around the knee (which may indicate intra-articular extension) and distal neuromuscular status. Warmth and tenderness may be noted on examination and numbness if peripheral nerves are involved. Other sites of skeletal pain must also be excluded.
Investigation:
All patients must undergo local and distal staging. The local staging should include measured radiographs and MRI of the whole bone and adjacent joint involved (e.g. whole femur including the knee in a distal femoral tumour). Biopsies are performed using fluoroscopic or CT guidance adhering to the principles of biopsy which mandates that only one compartment is contaminated by the biopsy tract which should be sited appropriately to facilitate en-nbloc excision of the tract at the time of definitive resection. Distal staging must include CT chest and whole skeletal imaging (i.e. bone scintigraphy/whole body PET-CT) to exclude metastasis at diagnosis which confers a worse prognosis.
Non-operative management:
Neo-adjuvant (pre-operative) chemotherapy is the standard of treatment prior to en-bloc excision of the tumour followed by post-operative chemotherapy in accordance with international protocols.
Alternative operative management:
After the first two cycles of chemotherapy the MRI scan is repeated to confirm that the tumour is resectable. Most osteosarcomas will have soft-tissue extension at diagnosis, but if the extension involves the neurovascular structures posteriorly at the popliteal fossa then limb-salvage may not be possible. If deemed non-resectable then amputation or even rotationplasty may be considered in approximately 10% of cases in the distal femur. Rotationplasty involves resection of the tumour around the knee preserving the sciatic nerve +/- vessels and rotating the tibia which is osteosynthesised to the femur such that the ankle joint forms a new knee joint permitting a below ‘knee’ prosthesis to be worn (https://journals.lww.com/jbjsjournal/subjects/Oncology/Abstract/1999/04000/Malignant_Tumor_of_the_Distal_Part_of_the_Femur_or.3.aspx).
Contraindications:
Contraindications to en-bloc excision and reconstruction surgery might include medical comorbidity which prevents major surgery, infection or non-resectable tumours.
The patient is positioned supine after IV antibiotic prophylaxis prior to general anaesthesia and epidural anaesthesia. A clear plastic exclusion drape is applied around the proximal thigh. After chlorhexidine skin prep, Ioban exclusion drapes are applied to the isolated limb with a clear plastic bowel bag over the foot for intra-operative assessment of vascular status. The WHO check is completed prior to skin incision.
Heel pressure area protection until epidural removed
Removable soft-cast to be applied when comfortable for 2-3 weeks
Wound check 14 days
3 post-operative doses of IV antibiotics (flucloxacillin)
X-rays when safe, AP/lateral right femur and knee
Protected weight bearing with crutches until safely independent of walking aids
Readmission for inpatient hydrotherapy after chemotherapy
Sarcoma surveillance: all patients with primary bone sarcomas undergo post-operative surveillance to monitor for local recurrence and metastasis. International guidelines mandate that patients are seen 3-monthly for the first two years, then 6-monthly until year five, then annually until year ten. At our institution we do chest radiographs at each visit plus radiographs of the femur and endoprosthesis.
Te results after extra-articular resection of the knee and endoprosthetic reconstruction are reportedly worse than for resections utilising an arthotomy. Ieguchi et al. reported that their extra-articular excision group developed more complications than the intra-articular excision group, as a result of extensive bone and muscle excision, but that the limb survival rates were similar in both groups.(https://academic.oup.com/jjco/article/44/9/812/882656).
In a series of 59 patients, Hardes et al. reported failure of the prosthesis due to deep infection in 22 patients (37%), aseptic loosening in ten patients (17%), and peri-prosthetic fracture in six patients (10%) (https://online.boneandjoint.org.uk/doi/pdf/10.1302/0301-620x.95b10.31740?journalCode=bjj). Survival of the prosthesis without revision was 48% at two years and 25% at five years post-operatively, which is significantly worse than with more routine distal femoral endoprosthetic replacements for bone sarcomas.
Both Hardes et al. and Zwolak et al. reported functional outcomes to be comparable to those for patients having intraarticular resections (https://link.springer.com/article/10.1007/s11999-010-1359-8), although an extensor lag or up to 20% has been reported. By contrast, Kendall et al. reported a significantly greater functional deficit that was primarily due to a compromised extensor mechanism inherent in this type of surgical resection necessary to achieve adequate removal of the tumour (https://www.arthroplastyjournal.org/article/S0883-5403(00)58614-8/abstract).
‘Growing’ endoprostheses ave been available for more than 30 years and have become more sophisticated with time. The latest generation is ‘non-invasive’ and can be lengthened with an external magnetic force. In a series of 51 children (mean age 10 years), revision-free implant survival was 62% at five years: Deep infection occurred in 20% of implants at a mean of 12.5 months (0 to 55). Other complications were a failure of the lengthening mechanism in five prostheses (10%) and breakage of the implant in two (4%). Overall, there were 53 additional operations for 51 prostheses. A total of seven patients (14%) underwent amputation, three for local recurrence and four for infection (https://online.boneandjoint.org.uk/doi/abs/10.1302/0301-620x.98b12.bjj-2016-0467?journalCode=bjj).
Sporting activities that are non- or low impact such as cycling are permissible with these implants but running is avoided.
Reference
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