Metastatic Bone Disease: Pelvis


Pelvic resection classification system

Type I

Ilium

Type II

Periacetabular

Type III

Pubis

Type IV

Ilium

Resections including the femoral head

H1

Femoral head

H2

Peritrochanteric area

H3

Subtrochanteric area

Spinopelvic resections

Type 1

Total sacrectomy

Type 2

Hemisacrectomy

Type 3

Partial sacrectomy with hemipelvectomy

Type 4

Total sacrectomy with hemipelvectomy


Lesions in multiple areas named by combining numbers



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Fig. 23.1
Anatomic zones of the pelvis as described by Enneking [1]


Other vital non-musculoskeletal structures in the pelvis may also be involved or require protection when addressing metastatic pelvic tumors. These include the urethra, prostate and corpus of the penis in males; uterus, ovaries and vagina in females; and rectum and bowel. This underscores the multidisciplinary approach, involving colleagues from urology, general surgery, vascular surgery, colorectal surgery, plastic surgery, neurosurgery, and spine surgery that may be required for these tumors.



Exposure


The incision commonly used for most types of pelvic metastatic disease is the ilioinguinal approach. This approach extends from the pubic tubercle along the inguinal ligament to the anterior superior iliac spine and along the iliac crest to the posterior superior iliac spine. Anterior lesions may require an extension to the contralateral pubic ramus and an additional perpendicular T-incision for good visualization. Posterior lesions may require extension to the midline of the spine with or without a perpendicular midline extension. For periacetabular lesions, the ilioinguinal approach can be extended laterally to the thigh. In addition, if the hip is involved, an anterolateral approach to the hip can be used and a supra-acetabular window can be made. A standard posterior approach to the hip can also be utilized, depending on the location and visualization requirements of the tumor being removed.


Curettage, Cementation, and Adjuvant Therapy


Multiple methods exist for the intralesional treatment of pelvic metastatic disease, including percutaneous cementoplasty and traditional open curettage and cementation. These intralesional procedures are much more commonly performed than extralesional resections in the pelvis due to the fact that they are less invasive and thus less morbid methods of treatment.

Percutaneous cementoplasty is the percutaneous, image-guided application of cement to treat or prevent pathologic fractures and pain. Cement is used to describe a wide variety of viscous materials that are injected for stabilization and consolidation of osteolytic lesions. The relief of pain is believed to be from the consolidation of weakened and pathological cancellous bone as well as a thermal and chemical cytotoxic effect produced during the polymerization of the cement. Polymethylmethacrylate (PMMA) is the most commonly used cement and polymerizes at a temperature of 80–120 °C [15]. This exothermic reaction has a penetration of 1.5–2 mm in cancellous bone and 0.5 mm in cortical bone [16]. Other materials, such as dimethacrylate resins and calcium phosphate based cements are also used. It is recommended that iodinated contrast be injected into the defect prior to cement injection to predict cement distribution and possible pathways of extravasation. Due to the high temperatures PMMA reaches during polymerization, extravasation adjacent to important neurovascular structures such as the obturator or pudendal nerves can cause substantial damage and should be avoided.

Open curettage and cementation requires the creation of a large cortical window corresponding to the location of the lesion. The tumor is then carefully and fully curetted out. A high-speed burr can then be used to create a single concentric cavity and remove any microscopic disease, as well as expand the margins of the cavity. After this is complete, adjuvants such as phenol, liquid nitrogen, or argon are often used to maximize tumor kill in the cavity. Phenol is a chemical agent that induces necrosis by protein coagulation with an infiltration depth estimated at 0.2 mm [16]. Cryoablation with liquid nitrogen induces necrosis through intracellular ice crystal formation and membrane disruption. Repetitive rapid freeze and slow thaw cycles can increase margins by up to 2 cm. Argon is a plasma gas that is ionized by a high voltage spark at the tip of a probe, distributing thermal energy on the cavity surface that penetrates roughly 2–3 mm [17]. Any adjuvant can be used to good effect, depending on surgeon preference, as none have proven to be superior in the literature. Finally, PMMA is inserted for consolidation and structural stabilization similar to percutaneous cementoplasty. In addition, cement will allow for easier determination of tumor extent on postoperative imaging and radiation field planning as well as early detection of local recurrence at the cement bone interface.


Type I Lesions


Type I metastatic pelvic lesions are those that involve the ilium. Positioning for surgical treatment of these lesions is typically supine with the ipsilateral hip slightly elevated. Exposure to the appropriate area of the ilium can usually be obtained using the posterior aspect of the standard ilioinguinal approach. The glutei and iliacus muscles are detached and reflected from the outer and inner tables respectively. At the superomedial aspect of the posterior iliac crest, the iliolumbar ligament is identified. This ligament is a good landmark for the L5 nerve root, which runs just inferomedial to it. This ligament can also be released to enhance exposure if necessary.

Due to the fact that iliac resections generally do not impair sacroiliac or acetabular joint integrity, they rarely have an impact on function. This, combined with the difficulty of curettage of iliac tumors, makes resections for type I lesions the preferred treatment [13]. Osteotomies of the ilium around the lesion are performed. The anterior osteotomy is typically through the sciatic notch or just superior to the acetabulum, while the posterior osteotomy is through or adjacent to the sacroiliac joint. These resections are often left unreconstructed, except when the sciatic buttress is resected, which leads to disruption of pelvic ring continuity and resultant limb length discrepancy. This can be restored with autograft, allograft, or a metallic prosthesis. A small case control study looking at patients with either iliosacral repair or no reconstruction showed similar functional scores and survival rates in both groups. Yet patients who did not undergo reconstruction needed a lesser degree of chronic pain medication and assistive ambulatory devices, demonstrating that leaving these resections unreconstructed is a reasonable option [18]. The preference of the authors’ is to leave Type I lesions unreconstructed.


Type II Lesions


Periacetabular lesions are called type II lesions, and are the lesions for which surgical intervention is most common. Positioning is dependent on the approach used. If the ilioinguinal approach will be utilized, the patient can be positioned supine with the ipsilateral hip slightly elevated. If the anterolateral or posterior approach to the hip is used, the patient should be positioned true lateral with the affected side facing up. With the ilioinguinal approach, the middle component of the incision is used. For lesions with medial cortical destruction, the incision can be extended 5 cm along the inguinal arm of the incision. The iliacus can then be detached and reflected from the inner table exposing the medial acetabulum. For lesions with lateral cortical destruction, a 5 cm extension is made along the lateral thigh. The glutei are then detached and reflected from the outer table, exposing the lateral acetabulum. For lesions with equivalent destruction, this lateral approach is used due to its ease. If reconstruction of the hip is required for weight bearing stability or there is concurrent femoral disease (the majority of surgical cases in the authors’ practice), a standard posterior approach to the hip can be utilized and is preferred over an anterior approach because of its extensile nature.

Whenever feasible, a cortical window is then made above the lesion and curettage with high speed burr drilling, adjuvant therapy and cementation is performed. Metastatic disease typically does not invade cartilage, so these lesions normally spare acetabular cartilage [19]. When there are no cortices left to contain an internal fixation device, formal resection is done. This requires three osteotomies. The first is the superior osteotomy, made superior to the posterior iliac spine through the greater sciatic notch [12]. The second is the anterior osteotomy, through the anterior column of the acetabulum at the base of the superior pubic ramus. The final osteotomy is the posterior osteotomy, through the posterior acetabular column or ischium.

There are a large variety of reconstructive options for peri-acetabular lesions. The most commonly used reconstructive option in the authors’ practice is the arthroplasty reconstruction . After initial reaming of the acetabulum, the periacetabular tumor is often encountered just deep to the cartilage. This lesion can be curetted and burred out, and adjuvant therapy used. If adequate ilium and pubis are remaining, implants can be attached and cement may be used to fill any residual defects and increase stability. Options for reconstruction include allograft or prosthetic composites such as cup-cage and porous tantalum reconstructions. The authors’ preferred method of reconstruction is the Harrington reconstruction [20]. This is a cement-rebar reconstruction technique that involves placing screws in either an antegrade or retrograde manner through the ilium and into the acetabular defect (Fig. 23.2 and 23.3). Bone cement is then placed into the defect to create the cement-rebar construct. The acetabular component is placed into the cement and the femur is prepared using a cemented long-stemmed implant. This reconstruction results in good cosmesis and limb length equality. A retrospective series from the author’s institution showed good outcomes, including a failure rate of 9.6 %, and 96 % of patients able to ambulate after surgery. However, the authors have experienced higher than expected failure rates in patients with significant tumor burden in the ischium and prolonged life expectancy. In this patient population, the authors express caution.

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Fig. 23.2
Harrington technique with (a) antegrade Steinmann pins placed through the iliac wing proud into the defect, followed by (b) cementation to fill the defect and create a rebar receptor for the acetabular component, and (c) placement of the acetabular component


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Fig. 23.3
Harrington technique with (a) retrograde screws placed from the defect in the posterior column (authors’ preferred technique), followed by (b) cementation to fill the defect and create a rebar receptor for the acetabular component, and (c) placement of the acetabular component

Other reconstructive prosthetic options include pedestal cup endoprostheses, saddle prostheses, and custom implants. The saddle prosthesis was previously used due to its ease of insertion, maintenance of limb length equality, and good cosmesis. This implant is anchored in the femur and hinges over an articulating notch made in the ilium. Yet due to an extremely high reported failure rate of 41.1 %, they are now off the market [21]. Failures were reported due to infection, nerve palsy, fracture, loosening, lateral shift, heterotopic ossification, and dislocation. In addition, the eccentric position of the new hip center resulted in reduced range of motion. Custom devices require Food and Drug Administration (FDA) approval prior to the procedure, limiting their use due to the lengthy approval process. Further details about the resection and reconstruction of tumors involving the femur can be found in the chapter about surgical management of metastatic disease to the femur.

When limited bone stock is available and anatomic hip reconstruction is not viable, alternatives include hip arthrodesis and leaving a non-reconstructed flail hip. The goal of a hip arthrodesis or pseudoarthrodesis is to establish a fibrous or solid union between the proximal femur and remaining pelvis (iliofemoral, ischiofemoral, or sacrofemoral), using hardware [22, 23]. This procedure is currently rarely used, as arthrodesis requires hip spica cast immobilization for 3 months to obtain potential union. Even then, union rates are less than 50 % and most patients end up developing a stable and painless pseudoarthrosis [24, 25]. In addition to the long consolidation time, which consequently requires prolonged rehabilitation, the disadvantages of arthrodesis include loss of hip joint function, limb length discrepancy, and lack of mobility.

A final option that should not be overlooked is the Friedman–Eilber resection arthroplasty , or flail hip, which requires only a soft tissue closure with a hip transposition. The hip transposition consists of anchoring or tying the proximal femur or femoral head to the remaining ilium or sacrum. The suspension and stabilization of the residual limb is important to maximize function and provide stability. This procedure can be performed without any prerequisite amount of bone available on the pelvic side and is used by the authors when resection includes an internal hemipelvectomy. The benefits of the Friedman–Eilber resection arthroplasty are its shorter surgical time, reduced blood loss, and decreased hospital stays in comparison to a more complex reconstruction, although it has a long recovery time of up to 2 years [26].


Type III Lesions


Lesions involving the pubis are considered type III metastatic pelvic lesions. Positioning for these lesions is supine with the ipsilateral hip slightly elevated. For exposure, the anterior aspect of the standard ilioinguinal approach is used, from the anterior superior iliac spine to 2 cm across the pubic symphysis. During the exposure, the femoral neurovascular bundle is isolated, marked with vessel loops and mobilized. The retropubic space is exposed, and a pad is inserted between the bladder and pubis. Lastly, the muscle attachments on the inferior aspect of the pubis can be removed if necessary.

Whenever possible, the preferred treatment of type III lesions is curettage with high speed burr drilling, adjuvant therapy and cementation through a cortical window above the lesion. Occasionally, the pubis will be destroyed, and no cortices will be left to permit curettage. In these situations, the incision should be extended to expose intact cortices on both sides of the lesion [12]. A medial osteotomy can then be done as far as the pubic symphysis or beyond at the opposite pubic ramus, and the lateral osteotomy just medial to or through the acetabulum, attempting to preserve as much intact bone as possible. It is important to be aware that the obturator neurovascular bundle may need to be sacrificed due to its proximity to the tumor. Aside from filling a defect created by curettage with cement, no formal bony reconstruction is required for these lesions. A critical component of these surgeries is the soft tissue reconstruction, to prevent bladder or soft tissue herniation into the soft tissue defect. These are typically reconstructed with a synthetic mesh or fascial allograft. The inguinal floor should also be reconstructed from the pubic tubercle to the lateral ilium to prevent peritoneal hernias. Care should be taken to appropriately reposition the femoral vessels, as well as the spermatic cord and its contents in men.

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Jun 4, 2017 | Posted by in ORTHOPEDIC | Comments Off on Metastatic Bone Disease: Pelvis
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