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Computer navigated Hemi-pelvectomy for Ewings sarcoma

    Overview

    Learn the Computer navigated Hemi-pelvectomy for Ewings sarcoma surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Computer navigated Hemi-pelvectomy for Ewings sarcoma surgical procedure.
    Malignant bone tumours account for only 4% to 6% of all cancers in children under 14 years of age. Although these tumours can arise anywhere in the skeleton, tumours arising from the pelvis are rare. The principle tumour types arising from the pelvis in those under 16 years of age are osteosarcoma and Ewing’s sarcoma, with the remainder constituting rare histologic subtypes. Ewing’s sarcoma is composed of primitive, undifferentiated, small round blue cells with large nuclei and scant cytoplasm that bears no resemblance to normal tissue. The characteristic translocation between chromosomes 11 and 22 results in a fusion gene, EWSR1-FL11, which is present in 90% of cases. Other translocations have been discovered, most frequently t(21:22).
    Pre-operative chemotherapy frequently results in extensive tumour necrosis and shrinkage. Wide excision is often combined with radiotherapy to improve disease free survival. Definitive radiotherapy rather than surgical excision, although associated with worse overall survival, may be advocated if non-resectable or metastasis has occurred during chemotherapy, to spare the surgical morbidity.
    Computer navigation surgery allows linking between the patient’s imaging information and anatomy through the use of tracking and registration of the preoperative and/or intraoperative acquired images. The use of computer navigation for tumour resections has found favour for resection of pelvic lesions. Navigation allows accurate pre operative planning of resections with accurate placement of planned osteotomies to allow adequate margins to be achieved without compromising vital structures.

    Indications

    INDICATIONS
    Primary tumours of bone are a rare group of tumours which, even when considered as a single group, account for only 0.2% of all cancer diagnoses in the UK, an incidence of only 8.2 cases per million of the population. Of the three most recognisable primary bone tumours, Ewings sarcoma is the least frequent with only 2 new cases per million of the population. Ewings sarcoma tends to occur in children and has a particular preponderance for the pelvis. Ewing’s sarcoma is believed to arise from mesenchymal stem cells in the bone marrow. Ewings sarcoma occurs more frequently in males, typically between 10 to 20 years of age. Pain is the earliest symptom, followed by swelling (although soft-tissue masses may not be apparent in pelvic sites) and a low-grade fever.
    Recent evidence has highlighted the potential survival advantage in terms of disease free survival for combined chemotherapy, radiotherapy and surgery for Ewings sarcoma of the pelvis. Resection of pelvic sarcomas confers a high degree of complexity and the potential for significant morbidity due to the proximity of nearby critical structures. Adequate margins at surgery are more difficult to achieve when compared to appendicular resections again due to the proximity of these critical structures.
    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 pian 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
    Radiographically, an aggressive, permeative, poorly defined, osteolytic lesion with cortical destruction, periosteal reaction and large, radiolucent soft-tissue mass could be found. Periosteal reaction is common in young patients with the lamellar ‘onion-skin’ appearance causing fusiform bone enlargement. Local staging in the form of magnetic resonance imaging (MRI) is required to assess the extra osseous component of the tumour. It is mandatory that this presentation volume of tumour is treated either in the form of excision at the time of resection or by including this volume in the target volume for radiotherapy. Routine local and distal staging includes bone scintigraphy and chest CT.
    ALTERNATIVE OPERATIVE TREATMENT
    Treatment of pelvic tumours arising from bone includes chemotherapy with the addition of radiotherapy in the case of Ewings sarcoma. Surgery for tumours of the pelvis is often difficult due to the large size at presentation and the proximity of vital structures within the pelvis, which often produces difficulty in achieving adequate margins of resection. Although limb salvage is often the aim of surgical resection of pelvic tumours, there is still a role for hindquarter amputation, particularly for tumours where margin or function will be compromised by attempted limb salvage. Advances in treatment of these tumours, particularly improvements in imaging, multimodal chemotherapy, and targeted radiotherapy, have translated into an improvement in rates of local recurrence, disease free, and overall survival. However, despite these advances, tumours arising from the pelvis continue to have a poor prognosis when compared with those at other sites.
    NON-OPERATIVE MANAGEMENT
    Ewings sarcoma are invariably very sensitive to multi agent chemotherapy. There is often a dramatic reduction in the volume of tumour following commencement of chemotherapy with a reciprocal improvement in symptoms. In the case of Ewings sarcoma, radiotherapy is often added either by photon radiotherapy or more recently, with the use of proton radiotherapy. In cases of advanced disease with pulmonary and osseous metastases, surgery may not be used for treatment of the primary tumour and in these cases, local treatment may be in the form of radiotherapy alone. In the case of very large tumours or where the projected morbidity from pelvic resection is deemed unacceptable, radiotherapy may be considered to the primary tumour without subsequent surgical excision.
    CONTRAINDICATIONS
    Surgical resection with limb salvage surgery should not be attempted if this will compromise the surgical margin achieved on removal of the tumour. Relative contraindications to limb salvage surgery around the pelvis include involvement by tumour or its resection, of the external iliac vessels anteriorly, or the sciatic nerve posteriorly. In such cases, limb sacrifice by means of a hindquarter amputation may need to be considered. In many cases, this may be considered unacceptable to the patient or their family in which case, consideration may be given to radiotherapy alone for local control.

    Setup

    Excision of pelvic tumours represents one of the most challenging aspects of orthopaedic oncology surgery. The procedure should be performed by a specialist surgical team under the guidance of the regional sarcoma multidisciplinary team (MDT).
    To ensure the accuracy of the navigation system, a CT scan and MRI scan of the pelvis is obtained as close to the time of surgery as possible, ideally within the preceding 48 hours. The navigation setup can be completed prior to the day of surgery. This navigation system (in this case, Stryker Orthomap) allows the fusion of CT and MRI images to allow the creation of a 3D model of the pelvis. To this can be mapped the exact position and outline of the tumour. The osteotomy planes can then be added taking into consideration the expected margin of resection. Prior to the operation, the surgeon manually maps out the tumour n the overlaid CT and MRI images to produce the 3D image of the tumour. The registration process is then completed to map out fixed anatomical structures that can be found during the operation (eg the anterior superior iliac spine) and which the navigation system can use as reference points to orientate the 3D model.
    At the time of surgery, the procedure is performed in a laminar flow theatre.
    Pre operative prophylactic antibiotics are given in accordance with the hospital protocol.
    The patient is positioned in a floppy lateral position free draping the ipsilateral leg to allow free movement of the limb and pelvis. This allows the pelvis to be pushed forward to allow access to the posterior iliac spine and sacrum, and retracted posteriorly to allow access to the abdominal wall and pelvic contents.
    The ipsilateral leg is fully draped to allow harvest of the mid portion of the fibula which will be used as a free autograft for reconstruction.
    The anaesthetic should be performed by a specialist anaesthetist experienced in the management of pelvic resections. The preferred method has been reported and utilises a combined spinal epidural technique resulting in a hypotensive epidural anaesthetic (Freeman et al., CORR, 2017).
    The instrument sets should include an orthopaedic oncology set, instruments for the navigation system, vascular instruments, abdominal retractors, osteotomes and saws. Appropriate sized suture material should be available to allow the safe dissection and tying off of vessels as required.

    Operation – 1

    Pre operative coronal T2 fat saturation MRI scan after completion of neo adjuvant chemotherapy. The tumour can be seen in the posterior ilium with evidence of a small effusion within the ipsilateral sacroiliac joint.

    Pre operative axial T2 fat saturation MRI of the pelvis. The tumour can be seen lying within the posterior ilium. There is oedema within the ipsilateral sacroiliac joint but no evidence os tumour within the sacral ala. There has been complete resolution of the very small extra-osseous soft tissue component seen on the pre chemotherapy imaging.

    Following anaesthesia and antibiotics, the patient is positioned in a floppy lateral position. The posterior support should be placed at the level of the low thoracic/high lumber vertebrae and the drapes placed posteriorly below the midline. Marks should be placed on the skin overlying the spinous processes of the lumber and sacral vertebrae. The posterior superior and posterior inferior iliac spines should be marked. Anteriorly, support can be provided by placing a sandbag under the abdomen to prevent the body rolling forward. The drapes ar placed below the midline, marked by the umbilicus and symphysis pubis. The anterior superior iliac spine and pelvis brim should be marked before draping. The draping should include the whole limb including the foot which is protected in a bowel back. This will allow access to the fibula as well as allowing visualisation of the foot throughout to monitor vascularity in the limb.

    The approach is centred over the posterior ilium. The biopsy site (1) has been marked pre incision to allow excision of the biopsy tract with the specimen. The skin and subcutaneous fascia is incised just above the pelvic brim.

    The incision is extended deep to the fascia. Again, the biopsy tract can be seen in continuity with the underlying pelvis.

    The biopsy tract (1) can be seen dissected with the underlying bone. The fascia overlying the gluteal compartment (2) inserts onto the outer table of the pelvis at the iliac brim. This plane must be identified to allow the fascia to be elevated off the underlying muscles. The fascia is incised away from the insertion to allow a finger to be passed beneath the fascia developing this plane.

    Having mobilised the fascia over the gluteal compartment, the posterior insertion of the abdominal wall and erector spinae muscles can now be mobilised. The posterior abdominal wall muscles (transversus abdominus, internal and external obliques) insert onto the posterior extent of the ilium. The erector spinae muscles are in two groups, those inserting onto the posterior superior iliac outside the pelvis and those inserting on the inner table of the posterior ilium. Having created a window in the muscles, a pair of forceps can be seen under this muscle insertion at a safe distance from the posterior ilium. This distance is based on the location of the tumour and should prevent contamination of the margin.

    The abdominal wall can now be incised away from the ilium (1). The fascia (2) can be opened by cutting down onto an instrument to prevent inadvertent damage to underlying structures (including iliac vessels and L5 nerve root). The biopsy tract can be seen retracted anteriorly but still in continuity with the underlying specimen (3).

    Having mobilised the abdominal wall (1) off the pelvis, the gluteal dissection can continue elevating gluteus maximus and the overlying fascia (2) off the outer table of the pelvis but leaving gluteus medius on the ilium.

    The posterior dissection elevates the muscle and fascia off the subcutaneous structures and developing the plane between the posterior superior iliac spine (1) and the gluteus maximus origin.

    Having mobilised the posterior muscle flap off the outer table of the ilium, the anterior dissection can now begin. The abdominal wall is elevated from the pelvic brim but dividing each of the three layers of the abdominal wall (external oblique, transversus abdominus and internal oblique) in turn.
    The pelvis is entered through the inguinal canal and the retroperitoneal space opened to expose the external iliac vessels (1). The retroperitoneal approach utilises the iliacus fascia overlying the iliacus muscle (2). This can be swept away towards the midline to expose the vessels. The vessels are mobilised by developing the perivascular plane overlying the vessels. Non-toothed forceps are used when manipulating the vessels to prevent inadvertent injury.

    The ilium is now exposed (1). The iliacus is seen in continuity overlying the inner table of the ilium. The anterior abdominal wall can be seen retracted medially (2). The external iliac artery and vein have been mobilised to allow their retraction medially away from the tumour (3).

    At this stage, the iliolumber ligament (1) can be divided under direct vision by passing an instrument beneath the ligament and dividing using electrocautery. Deep to this ligament lie the iliolumber veins which should be identified, tied and divided under control to prevent excessive blood loss.

    Further anterior dissection involves elevating psoas (1) to expose the femoral nerve (2). This must be preserved to prevent loss of quadriceps function following resection.

    Having completed the anterior dissection and elevated the posterior gluteal muscle group (1), leaving gluteus medius overlying the section of pelvis to be resected, the navigation tracker (2) can now be placed. The pins to hold the tracker (3) are placed in the anterior ilium, away from the section of bone to be removed. The tracker should be positioned to allow it to be seen by the navigation detector. The pins for the tracker can either be placed away from the section of bone to be removed (as in this case), or into the tumour itself as this section will subsequently be removed. If the pins are to be placed in the tumour, great care must be taken to prevent contamination or tumour spillage.

    The accuracy of the registration for the navigation is checked using the navigated probe (1) to ensure that the computer and the surgeon are in agreement with the registration. Any margins of error should be corrected at this stage to ensure that no more than 1mm discrepancy between the registration and the patient is seen.

    Posterior view demonstrating the elevated posterior abdominal wall (1), the navigation tracker (2), the elevated glutei (3), and the area of bone to be resected (4).

    A navigated osteotome (1) can now be placed in position to commence the posterior osteotomy. The navigated osteotome allows the user to plan and monitor the trajectory of the osteotomy as well as observing in real time the depth of the osteotomy. For this case, the osteotomy will pass just medial to the sacroiliac joint taking a sliver of sacral ala with the tumour. The biopsy tract (2), can still be seen in continuity with the specimen.

    The osteotomy can now proceed. A finger is placed at the projected exit point of the osteotomy as a fail safe to prevent over-penetration. The operator is however, watching the osteotome on the navigation screen to see in real time the passage of the osterotome.

    The position of the osteotomies through the ilium can be checked using the navigation probe. The trajectory and position of the these osteotomies can be checked and then osteotomes (1) placed to mirror this position.

    Having completed the osteotomies, the tumour can be delivered en masse by dividing the final soft tissue attachments.

    Following delivery of the tumour, haemostasis is achieved. The blood pressure can be normalised at this stage to allow any bleeding vessels to be identified. The resection area is washed with normal saline pulsed lavage.

    The resection area can now be seen. The apex of the osteotomies can be seen in the sciatic notch (1). Great care has been taken to protect the superior gluteal pedicle which will give blood supply to the gluteal flap. The lateral margin of the resection is through the ilium (2) with the medial margin extending through the sacral ala (3). The superior gluteal pedicle passes underneath the apex of the greater sciatic notch. This must be preserved to maintain the blood supply to the gluteal compartment.

    At this stage, the harvest of the free fibula autograft can begin. The position of the fibula head is marked (1) and the lateral malleolus. The incision is through a direct lateral incision. Note, all gowns and gloves have been changed prior to commencing the fibula harvest and all instruments have been changed to prevent the potential risk of seeding tumour to the fibula harvest site.

    Meticulous dissection between the anterior compartment and the peroneal compartment onto the fibula is completed to expose the fibula. This utilises the intermusculous plane between the anterior and peroneal muscle groups.

    Operation – 2

    Once onto the fibula, the periosteum is elevated to allow a subperiosteal dissection of the length of fibula required. The proximal 5 cm which contribute to the proximal tibiofibular joint and attachment of the lateral colateral ligament, should not be sacrificed. Equally, the distal 5-7 cm which contributes to the ankle syndesmosis and ankle stability, should be preserved.

    The desired length of fibula has been fully exposed. At this stage, a small bone elevator retractor can be placed around the osteotomy site to protect the underlying peroneal vessels during the osteotomy.

    The proximal extent of the resection is again identified and protected with bone elevators.

    An oblique osteotomy is completed at either end to give a chevron cut to the end of the fibula autograft.

    The resected fibula is denuded of soft tissue and measured to fit the defect in the pelvis.

    The fibula is the cut to length.

    The fibula autograft can now be placed into the defect. The pelvis can be distracted at this stage to allow compression of the graft. The fibula autograft acts to bridge the defect in the pelvic ring and prevent proximal migration of the acetabular segment on the symphysis pubis. The forceps can be seen protecting the superior gluteal pedicle in the sciatic notch.

    Follwoing release of the distraction on the pelvis, the chevron cuts at either end of the fibula bury into the sacral ala and the ilium. No fixation is required in this case as the graft is stable under compression.
    Following placement of the graft, the cavity is further washed with normal saline.
    The wound over the pelvis can now be closed. The abdominal wall is reattached to the pelvic brim through drill holes anteriorly, Posteriorly, the abdominal wall is reattached to the fascia overlying the glutei. The repair uses vicryl over 2 suction drains. Further layered closure is with vicryl. The skin is closed using clips or subcutaneous absorbable sutures. A vacuum assisted dressing is applied over the wound only and low negative pressure applied.

    Post Operative

    The patient is given prophylactic antibiotics in keeping with the hospital protocol.
    The patient is managed with bed rest for the first 5 days. At this stage, the vacuum dressing is removed and a simple adherent dressing applied.
    The mobilised non weight bearing for the first 6 weeks using crutches. This allows the fibula autograft to incorporate with the host bone. At 6 weeks post operation, the patient is admitted for 5 days of intensive physiotherapy using both gym based physiotherapy and hydrotherapy. This allows the patient to progress up to full weight bearing at this stage.
    The patient recommences adjuvant chemotherapy in line with nationally agreed standards as soon as the wound has healed. The chemotherapy regimen and the use of adjuvant radiotherapy is based on the margin achieved at resection and the post resection necrosis seen after neo-adjuvant chemotherapy. This is a marker of the sensitivity of the tumour to the chemotherapy and is a vital prognostic indicator for relapse of disease.
    The patient embarks on sarcoma surveillance which comprises routine chest imaging with plain radiography every 3 months for the first 2 years, every 6 months up to 5 years and annually thereafter up to 10 years. In addition, for pelvic sarcoma resections, an MRI of the primary tumour site is undertaken every 6 months for the first 3 years.

    Recommended Reading

    Malignant tumours of bone are rare. They constitute only 4-6% of all malignancies in those under 14years of age (Arndt & Crist, NEJM, 1999). The principle tumour types arising from the pelvis and sacrum in children are osteosarcoma and Ewings sarcoma, with the remainder constituting rare histological variants. There has been a great deal of advancement in the management of these tumours, particularly around the initial imaging and histological diagnosis as well as vast advances in the oncological management of these rare tumours. This has resulted in increasing rates of limb salvage for pelvic tumours. Despite these advances, tumours of the pelvis still confer a poor prognosis, when compared to other anatomical sites (Bacci et al., J Paed Haem Oncol, 2003).
    The overall survival for paediatric patients treated for Ewings sarcoma of the pelvis is estimated at 37% at 5 years and 33% at 10 years (Laitinen et al., J Paed Ortho. 2016). This survival is poor in comparison to Ewings sarcoma at other locations and may well reflect the volume of tumours arising from the pelvis at the time of presentation. Survival is affected by the intention to treat. For patients with unresectable tumours, either due to the tumour volume or the presence of metastases, have a significantly worse prognosis. The presence of metastases at diagnosis, tumour location, and tumour size are associated with overall survival.
    The response to chemotherapy has a significant effect on overall survival (Albergo et al., BJJ, 2016). A number of studies have demonstrated tan association between improved survival and a high response rate to neo adjuvant chemotherapy. Exactly what constitutes a good response remains an area for debate.
    Where surgery is undertaken, the aim should be to excise the tumour with a clear margin. There is a significant association between marginal or intra-lesional resection margins and event free survival (Gaspar et al., Eur J Canc, 2012). Patients who undergo surgery for local control, have a survival advantage to those who do not undergo surgery (Foulon et al., Eur J Canc, 2012). Patients treated with radiotherapy alone have a worse overall survival than those who have combined radiotherapy and surgery, whilst those who have pre operative radiotherapy in combination with surgery, particularly around the pelvis, have improved event free survival (Foulon et al., Eur J Canc, 2016).
    The role of navigation on achieving clear surgical margins has been extensively investigated. Wong and Kumpta (CORR, 2012), reported clear margins in all cases of pelvic resections and reduced the local recurrence rate from 70% to 25%. Jeys et al., reported a reduction in intralesional resection rates for all pelvic resection from 29% to 8.7% with the addition of navigation assistance (BJJ, 2013).
    In conclusion, the aim of surgery for primary tumours of the pelvic bones in children should be removal of the tumour with a clear margin. This can be very difficult to achieve given the size of tumours at this location and the proximity of nearby vital structures. The addition of computer navigation is a vital addition to the surgeons armoury and has already translated to an improvement in the margins seen at resection of pelvic tumours. Despite these improvements, overall survival following resection of Ewings sarcoma of the pelvis, remains largely affected by the response of the tumour to neo adjuvant chemotherapy.

    Reference

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