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Osteosarcoma is the commonest primary bone sarcoma arising in the young adult population, with a peak incidence in the second and third decade. Treatment following diagnosis comprises neo-adjuant chemotherapy followed by surgical resection of the tumour, either by limb salvage or limb sacrifice. Reconstruction following tumour resection most commonly comprises either biological reconstruction or reconstruction using an endo prosthetic replacement (EPR). The most common sites for osteosarcoma are the distal femur and proximal tibia, followed by the proximal humerus and distal radius. The most common histological variant of osteosarcoma is a high grade osteoblastic variant.
The commonest endo prosthetic reconstruction used in the UK is that available from Stanmore Implants Worldwide (Stryker). This is available as a modular or custom made option with either fixed or rotating hinge options for reconstruction of the knee. Fixation is usually with cement and for high risk body sites, including the proximal tibia, surface treatment with a silver coating is often used in an attempt to reduce the risk of infection.
INDICATIONS
Proximal tibial replacement is indicated for primary tumours of bone arising from the proximal tibia without compromise of the knee joint itself. A conventional intra articular resection of the proximal tibia is indicated for tumours following neo-adjuvant chemotherapy where the margins achieved at en bloc resection are not compromised by intra articular resection, or where the neurovascular bundle is clear of tumour and limb salvage is not contraindicated.
SYMPTOMS & EXAMINATION
Patients often present with an insidious onset of pain. Given the age of the population affected, this is often attributed to muscle strains or growing pains. However, the pain invariably follows a progressive course from functional pain to rest pain and finally, night pain. If not identified at this stage, the pain is often followed by development of a mass which often extends laterally into the buttock and medially into the distensible pelvic space. In extreme cases, the patient may present with constitutional symptoms of fever and weight loss. A low threshold for malignancy should be taken for any child with pain around the pelvis, particularly night pain.
IMAGING
Radiographs are generally diagnostic showing an ill-defined, permeative bone forming lesion causing cortical destruction, periosteal reaction and expansion into the soft tissues. The tumours can be variably mineralised, there may be a Codman’s triangle where new bone forms in response to periosteal elevation and a ‘sunburst’ appearance when the periosteum does not have enough time to lay down a new layer and instead the sharpey’s fibres stretch perpendicular to the periosteum. Classically 80% are extra compartmental at presentation i.e. extending through the cortex. MRI of the whole bone will delineate the medullary and extra-osseous extent of the tumour. Nuclear medicine bone scintigraphy is intensively hot and may identify bone skip lesions, distant bone metastases or bone producing chest metastases. CT chest is mandatory as lung metastases are common (up to 15%).
ALTERNATIVE OPERATIVE TREATMENT
Limb salvage is always the aim of surgical resection following neo-adjuvant treatment where it does not compromise the principles of orthopaedic oncology whereby the resection must not compromise the oncological outcome by compromising the margin at the time of resection, must be acceptable to the patient and their family, and must result in an acceptable level of function for the patient. Alternatives to limb salvage surgery include amputation and rotationplasty.
Alternatives to endoprosthetic replacement for limb salvage include biological reconstruction options, either utilising the patients own bone or donated bone. The autologous fibula can be used as a graft for diaphyseal reconstructions, or for reconstruction of joints such as the proximal humerus or distal radius in the growing skeleton. Allogenic bone can be used for larger reconstructions including osteo-articular reconstructions.
NON-OPERATIVE MANAGEMENT
Non-operative management may be considered in the presence of advanced metastatic disease. This presents a very challenging problem however, as in the absence of chemotherapy and surgery, osteosarcoma are resistant to many conventional oncological treatments. However, where highly morbid surgery is contemplated, such as amputation, this must be offset by the knowledge that this will not result in cure.
CONTRAINDICATIONS
Contraindications to surgical resection and endoprosthetic replacement include significant cytopaenia secondary to neo-adjuvant chemotherapy, or active infection. As the largest complication of endoprosthetic replacement, infection must be avoided at all costs as the consequences can be devastating. Therefore, patients must be optimised prior to surgery, often a challenge for young patients undergoing high dose cytotoxic chemotherapy.
Following full, informed consent, the patient is anaesthetised. A combined spinal/epidural anaesthetic is often used to allow adequate post operative analgesia. Intravenous antibiotics are given prior to skin incision in line with the hospital policies. A urinary catheter is inserted to allow close monitoring of urine output post op. The patient is positioned supine with a side support at the level of the proximal thigh and a knee role distally to support the leg in flexion. A tourniquet is applied and protected using a clear plastic exclusion drape. A pre-prep is completed in the anaesthetic room before transfer to the operating theatre. A WHO check list is completed before starting the procedure.
The patient receives 24 hours of post operative prophylactic antibiotics as per the hospital protocol.
Foot pumps are used until mobile but no chemical anti thromboembolic prophylaxis is given.
The patient is rested in bed for 5 days.
The wound is inspected at 5 days post operation and if all is well, the vacuum dressing is removed.
The patient has an x-ray within 48 hours of the procedure.
Once the x-ray and wound have been reviewed, mobilisation under the guidance of a physiotherapist can begin. The patient can weight bear in the cricket pad splint but the extensor mechanism repair must be protected for a period of 6 weels. Bending of the knee is resisted for the first 6 weeks. At 6 weeks, the patient is re-admitted for a week of intensive physiotherapy including hydrotherapy where the knee is progressively bent.
The patient can recommence chemotherapy once the wound has healed.
The resection specimen is assessed by a specialist musculoskeletal pathologist and details of the tumour response to neo adjuvant chemotherapy and the margins achieved at resection are recorded. The case must be discussed in a specialist sarcoma multi-disciplinary team meeting.
The patient will be reviewed at standard intervals in line with national guidelines for the surveillance of osteosarcoma. The reconstruction is reviewed regularly for the lifetime of the patient.
The proximal tibia is the second commonest site for osteosarcoma. Improvements in diagnostics and the use of multi agent chemotherapy have dramatically improved survival for osteosarcoma over the last 30 years. Improvements in engineering and implant design have also improved the survival of implants for patients undergoing limb salvage surgery, particularly around the proximal tibia. Older designs utilised a fixed hinge at the knee which resulted in high rates of failure at short time intervals due to aseptic loosening at the implant bone interface. The advent of rotating hinge designs and the introduction of HA collars, which effectively act as a purse string around the implant bone interface, have dramatically improved implant survival. Myers et al (Myers et al, JBJS Br, 2007) demonstrated a reduction in revision rates from 47% for fixed hinge designs at 10 years to 3% using a rotating hinge.
The benefits of endoprosthetic replacement include early weight bearing and a low level of early complications. Overall implant survival has been reported to be good in the long term (Grimer et al, BJJ, 2016) though further operations are required for the lifetime of the implant. Infection remains the biggest cause of failure, particularly around the proximal tibia, and this can be devastating to treat, on occasion requiring amputation to eradicate the infection (Jeys et al., JBJS Am, 2008; Grimer et al., BJJ, 2016).
In an attempt to reduce the risk of infection, several novel surface coatings have been introduced to implants with a view to reducing the formation of biofilm. Most widely adopted is the addition of a silver coating either in the form of ionic silver stitched onto the implant (as is the case in the Stanmore system, Stryker) or a silver layer annealed onto the implant (as is the case in the Implantcast system). Whilst initial results would support the use os such adjuncts in terms of a reduction in infection (Hardes et al., JSO, 2010; Wafa et al, BJJ, 2015), this should not be seen as a compensation for surgical technique and theatre discipline. The risk of infection in the proximal tibia remains very high, in the order of 23% in some series (Jeys et al, JBJS Am 2005),
Reference
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