Masterclass: Extra-Articular Resection and Reconstruction of Supra-acetabular Metastatic Lesions

Welcome, fellows, to the operating theater. Today, we're tackling a challenging yet incredibly rewarding procedure: the extra-articular resection and reconstruction of a supra-acetabular metastatic lesion. Our primary goal is to alleviate pain, restore structural integrity, and facilitate immediate ambulation for our patient, all while preserving the native hip joint. This approach is specifically tailored for Harrington Class I lesions – those with extensive tumor invasion but without significant loss of structural integrity of the acetabulum itself, and crucially, minimal medial wall disease. It's a testament to preserving function and minimizing morbidity.

Preoperative Planning: The Blueprint for Success

Before we even consider making an incision, meticulous preoperative planning is paramount. This isn't just about identifying the tumor; it's about understanding its exact three-dimensional relationship to critical neurovascular structures and the hip joint.

Imaging and Staging Studies

Our patient today presents with a supra-acetabular lesion, which falls under Harrington's Class I classification. This means the tumor is confined to the supra-acetabular region, sparing the medial wall and, critically, the ipsilateral femoral head. If the femoral head were involved, this extra-articular approach would be contraindicated, and we'd be looking at a total hip replacement.

1. Plain Radiographs: We always start with plain AP and lateral radiographs of the pelvis and hip. These provide our initial assessment of the lesion's lytic or blastic nature and its general extent.
2. Computed Tomography (CT) Scans: This is our workhorse for defining the precise extent of the lesion and the remaining bone stock. We utilize both standard axial and coronal views, but increasingly, three-dimensional CT reconstructions are invaluable. They allow us to visualize the tumor in relation to the acetabular dome, the iliac crest, and the sciatic notch with incredible accuracy. This helps us template our resection margins and plan our reconstruction.
   

   
   
   

FIG 1 • A. Supra-acetabular metastatic lytic lesion. Joint contour is preserved.

Biopsy and Indications

For metastatic disease, a definitive biopsy is performed at the time of surgery. A frozen section typically provides adequate diagnostic information, allowing us to proceed with confidence.

Our patient is experiencing significant pain on weight-bearing, which has been resistant to radiation therapy. This, coupled with the risk of an impending pathological fracture, makes surgical intervention the treatment of choice. Remember, radiation therapy is often the first line for many metastatic lesions, but for structural instability or intractable pain, surgery becomes necessary.

Comprehensive Surgical Anatomy: Navigating the Posterior Hip

Understanding the regional anatomy is paramount for a safe and effective approach. We're using a posterior approach to the hip, which provides excellent access to the supra-acetabular region while minimizing disruption to the joint.

Muscular Intervals and Dissection Planes

• Gluteus Maximus: This is the most superficial and largest muscle. We'll detach its anterior portion from the iliotibial band and retract it superiorly and anteriorly. This exposes the retrogluteal space.
• Gluteus Medius and Minimus: These muscles lie deep to the gluteus maximus. We'll retract them anteriorly to expose the iliac bone superior to the acetabulum. This interval is critical.

Neurovascular Structures: The "No-Touch" Zones

• Sciatic Nerve: This is the most critical structure in this approach. It exits the pelvis below the piriformis muscle, passing inferior to the sciatic notch. We must meticulously identify it and protect it throughout the procedure. Injury to the sciatic nerve can lead to devastating motor and sensory deficits.
• Superior Gluteal Artery and Nerve: These emerge from the greater sciatic foramen, superior to the piriformis, and supply the gluteus medius and minimus. They are vulnerable during retraction of these muscles.
• Inferior Gluteal Artery and Nerve: These emerge inferior to the piriformis, along with the sciatic nerve, and supply the gluteus maximus. While less directly in our field for supra-acetabular lesions, awareness is key.

Osteology

We'll be working around the iliac crest, the supra-acetabular region of the ilium, and the greater trochanter. The sciatic notch serves as a key landmark for identifying and protecting the sciatic nerve.

Patient Positioning and Setup: The Foundation

With our preoperative plan firmly in mind, let's get our patient positioned.

1. Lateral Decubitus Position: The patient is carefully placed in a true lateral decubitus position on the operating table, with the affected hip superior.
2. Padding and Support: We use a beanbag to secure the torso, ensuring it doesn't roll anteriorly or posteriorly. All pressure points – especially the dependent arm, leg, and peroneal nerve at the fibular head – are meticulously padded to prevent iatrogenic nerve compression injuries. A bolster is placed between the knees to prevent adduction of the superior leg, which can tension the sciatic nerve.
3. Fluoroscopy Setup: The C-arm is brought in and draped. We ensure it can obtain clear AP and lateral oblique views of the hip and supra-acetabular region without repositioning the patient. This is crucial for intraoperative guidance during curettage and hardware placement.
4. Sterile Prep and Drape: The surgical field extends from the ipsilateral iliac crest to the mid-thigh, encompassing the entire gluteal region and hip joint.

Step-by-Step Intraoperative Execution: The Operating Surgeon's Viewpoint

Alright, fellows, let's scrub in. We've got our patient positioned perfectly, and our imaging is loaded.

Incision and Superficial Dissection

"Scalpel, please. We'll make our incision from the posterior third of the iliac crest, extending distally towards the greater trochanter. This curvilinear incision, typically 15-20 cm, provides excellent access to the posterior gluteal region."

1. Skin Incision: "Let's make a clean incision through the skin and subcutaneous tissues. We'll use electrocautery for hemostasis, meticulously controlling any bleeders."
2. Fascia Lata: "Now, we incise the fascia lata longitudinally, just posterior to the tensor fasciae latae. This exposes the underlying gluteus maximus."

Deep Dissection and Neurovascular Protection

"Next, we need to access the retrogluteal space. This requires careful dissection to protect our vital neurovascular structures."

1. Gluteus Maximus Mobilization: "Identify the anterior border of the gluteus maximus. We'll detach its origin from the iliotibial band using electrocautery. As we do this, we're careful to stay superficial to the muscle belly itself."

2. Retraction of Gluteus Maximus: "Now, we can retract the gluteus maximus superiorly and anteriorly. This exposes the deeper structures."

   Surgical Warning: As you retract the gluteus maximus, be acutely aware of the underlying sciatic nerve. Excessive or uncontrolled retraction can cause neuropraxia or even transection.

3. Sciatic Nerve Identification: "This is a critical step. Look for the sciatic nerve as it emerges from beneath the piriformis muscle, just inferior to the sciatic notch. It's usually a large, whitish cord. Once identified, gently lift it and secure it with a vessel loop."

   • "We'll place the vessel loop around the nerve, ensuring it's free from tension and clearly visible throughout the case. This tag serves as a constant reminder of its location and allows us to gently mobilize it if needed, always under direct visualization."

4. Exposure of Supra-acetabular Ilium: "With the sciatic nerve safely protected and tagged, we can now focus on exposing the iliac bone superior to the acetabulum. We'll achieve this by carefully retracting the gluteus medius and minimus muscles anteriorly."

   • "Use broad, smooth retractors, such as Hohmanns or specific gluteal retractors, to gently pull these muscles forward. Ensure the retractors are placed on bone to avoid soft tissue damage."

   Surgical Warning: As we retract the gluteus medius and minimus, we must be extremely cautious of the superior and inferior gluteal vessels and nerves. These structures are vulnerable in this interval. Identify them early. If necessary, small branches can be cauterized or ligated, but the main trunks of the superior gluteal vessels must be preserved to maintain muscle viability.

Lesion Unroofing and Curettage

"Now that we have excellent exposure, we can directly visualize the supra-acetabular metastatic lesion. Our goal is to unroof it and meticulously curette out all visible tumor."

1. Unroofing the Lesion: "Using an osteotome and a mallet, or a high-speed burr, we'll carefully unroof the cortical bone overlying the metastatic lesion. The goal is to create a wide opening to allow for thorough tumor removal."
   • "Be precise here. We want to remove enough bone to access the tumor, but preserve as much healthy bone as possible, especially the subchondral bone supporting the acetabular cartilage."
   • "For lytic lesions, the bone might be quite soft, so gentle rongeurs can also be effective."
     

     
     
     

TECH FIG 1 • A. The metastatic lesion is unroofed and curetted. In this patient, the subchondral bone supporting the joint cartilage is preserved.
2. Meticulous Curettage: "Once unroofed, we'll use sharp curettes of various sizes to meticulously scoop out all gross tumor. Work systematically, ensuring you scrape the walls of the cavity until you feel firm, healthy bone."
* "We are aiming for a clean cavity. If there are areas of dense tumor or sclerotic bone, a high-speed burr can be used to further debride the lesion, always under constant irrigation to prevent thermal necrosis."
* "Crucially, we are vigilant about the integrity of the acetabular cartilage. As you can see, the metastatic disease has respected the cartilage, and the subchondral bone is largely preserved. This is key to our extra-articular approach."
3. Intraoperative Biopsy: "Once we've curetted the bulk of the tumor, we'll send a sample to pathology for frozen section analysis. This confirms the metastatic nature of the lesion and ensures we haven't encountered an unexpected primary bone tumor."
4. Cavity Preparation: "After curettage, thoroughly irrigate the cavity to remove any remaining tumor cells or debris. Ensure the cavity is dry before proceeding to reconstruction."

Reconstruction: Restoring Structural Integrity

"Now for the reconstruction phase. Our aim is to provide immediate structural support to the subchondral bone and fill the defect, allowing for early weight-bearing."

1. Additional Support with Steinmann Pins (If Needed): "In cases where the inner wall of the ilium has been significantly compromised or destroyed by the tumor, we may need to augment our reconstruction with Steinmann pins. These can be inserted in an antegrade fashion from the iliac crest down into the lesion, or in a retrograde fashion from within the cavity, extending into healthy bone."
   • "Use fluoroscopic guidance for precise pin placement, ensuring they are well-seated in healthy bone and do not violate the joint or impinge on neurovascular structures."
2. Polyethylene Tibial Liner Application: "The next step is to provide direct support to the acetabular cartilage and remaining subchondral bone. For this, we use a highly cross-linked polyethylene tibial liner, typically sourced from a total knee replacement system."
   • "Why a tibial liner? Because its concave shape perfectly mimics the contour of the hip joint. We'll carefully cut this liner to size, ensuring it fits snugly within the unroofed defect, with its concave side facing the hip joint."
   • "This acts as a buttress, distributing forces across the preserved subchondral plate and preventing collapse."
     

     
     
     

TECH FIG 1 • B. Highly cross-linked polyethylene is cut to fit the defect. The concave side of the polyethylene, taken from a tibial total knee replacement insert, is placed facing the hip joint.
3. Polymethylmethacrylate (PMMA) Packing: "With the polyethylene liner in place, we'll now fill the remaining bone defect with polymethylmethacrylate (PMMA) bone cement."
* "Prepare the cement according to the manufacturer's instructions. As it reaches a doughy consistency, pack it firmly around and behind the polyethylene liner, ensuring all voids are filled. This provides a rigid, immediate load-bearing construct."
* "Ensure the cement doesn't extravasate into the joint or excessively compress surrounding soft tissues or nerves. We want a contained, stable fill."

Postoperative Pain Management Catheter

"Before closing, we'll address postoperative pain management. This is crucial for early mobilization."

1. Perineural Catheter Insertion: "We'll carefully insert a perineural catheter into the sciatic nerve sheath, adjacent to our protected sciatic nerve. This allows for continuous regional analgesia."
   • "Confirm its placement under direct vision. Through this catheter, we can administer a continuous infusion of 0.25% bupivacaine for up to 72 hours postoperatively, providing excellent pain control and facilitating early physical therapy."

Wound Closure

"With our reconstruction complete and stable, and the perineural catheter in place, we'll now proceed with a meticulous layered closure."

1. Irrigation and Hemostasis: "Thoroughly irrigate the wound and ensure complete hemostasis. Any residual bleeding should be addressed with electrocautery or ligatures."
2. Drain Placement: "We'll place a suction drain (e.g., a JP drain) deep to the gluteus maximus to evacuate any postoperative seroma or hematoma. Secure it to the skin with a suture."
3. Muscle and Fascial Closure: "Reapproximate the gluteus maximus to the iliotibial band. Close the fascia lata with strong, absorbable sutures. This restores anatomical layers and provides structural integrity."
4. Subcutaneous and Skin Closure: "Close the subcutaneous layer to obliterate dead space and then approximate the skin edges with staples or sutures, ensuring a clean, tension-free closure."
   

   
   
   

TECH FIG 1 • D. Postoperative radiograph showing the defect filled with the polyethylene and cement. The patient ambulates painlessly with a cane after postoperative radiation.

💡 Pearls and Pitfalls

Here are some critical points to remember, fellows:

• Sciatic Nerve Protection is Paramount: This nerve is the most vulnerable structure. Early identification, gentle tagging with a vessel loop, and constant vigilance against excessive retraction are non-negotiable. If a neurological deficit is noted postoperatively, immediate investigation (e.g., nerve conduction studies, MRI) is warranted, and in severe cases, exploration may be necessary.
• Superior Gluteal Vessels and Nerves: These are at risk during anterior retraction of the gluteus medius and minimus. Identify them and protect them. Injury can lead to abductor weakness and a Trendelenburg gait. If bleeding occurs, direct pressure, cautery, or ligation of smaller branches is appropriate.
• Joint Violation: The beauty of this technique is preserving the hip joint. If, during tumor resection, the acetabular cartilage is violated or the subchondral bone is completely destroyed, the plan may need to be revised, potentially converting to a total hip replacement. This is why thorough preoperative MRI is so important.
• Inadequate Tumor Resection: While we aim for gross total resection, microscopic margins may be positive in metastatic disease. The goal is pain relief and stability. If residual tumor is suspected, postoperative radiation therapy is typically indicated.
• Cement Extravasation: Ensure the bone cavity is dry and the polyethylene liner creates a good seal. Cement extravasation into the joint or onto the sciatic nerve can cause pain, stiffness, or nerve irritation.
• Blood Loss: While less than a THR, significant blood loss can still occur, especially with vascular tumors. Have blood products readily available. Preoperative embolization is key for high-risk lesions.
• Infection: As with any orthopedic surgery involving implants, infection is a risk. Strict sterile technique, prophylactic antibiotics, and meticulous wound closure are essential.

Postoperative Care: The Road to Recovery

Our work isn't done until the patient is ambulating comfortably.

1. Weight-Bearing Status: A significant advantage of this stable reconstruction is that immediate weight-bearing is allowed. The structure is designed to be stable and virtually pain-free from day one. We encourage protected weight-bearing with crutches or a cane initially, progressing as tolerated.
2. Pain Management: The perineural catheter will be utilized for continuous bupivacaine infusion for up to 72 hours. This, combined with a multimodal oral analgesic regimen, ensures optimal pain control, facilitating early participation in physical therapy.
3. Rehabilitation Protocol:
   • Day 0-3: Focus on pain control, gentle ankle pumps, quadriceps sets, and gluteal sets. Initiate out-of-bed activity for transfers and short walking distances with assistive devices.
   • Week 1-6: Gradually increase ambulation distance and duration. Begin gentle active and passive range of motion exercises for the hip within comfortable limits. Avoid extreme hip flexion, adduction, and internal rotation initially, though the risk of dislocation is minimal since the joint wasn't violated.
   • Beyond 6 Weeks: Progress to strengthening exercises for hip abductors, extensors, and core musculature. Full weight-bearing and return to activities of daily living as tolerated.
4. DVT Prophylaxis: Standard DVT prophylaxis protocols will be initiated, including chemical prophylaxis (e.g., low molecular weight heparin) and mechanical prophylaxis (e.g., sequential compression devices).
5. Wound Care: The wound drain will typically be removed when output is minimal (e.g., <30 mL over 8 hours). Staples or sutures are usually removed at 2-3 weeks post-op. Monitor closely for signs of infection (redness, swelling, purulent discharge) or wound dehiscence.
6. Adjuvant Therapy: Postoperative radiation therapy is almost universally indicated for metastatic lesions to address any microscopic residual disease and improve local control. This typically begins a few weeks after surgery, once the wound has healed.

Complication Management

• Wound Dehiscence/Infection: Manage with local wound care, antibiotics, and if severe, surgical debridement.
• Hardware Failure: While rare with this robust construct, any loosening of Steinmann pins or cement fracture would necessitate revision surgery.
• Neurological Deficits: If a sciatic nerve palsy persists, further evaluation and potential neurolysis may be considered.

This extra-articular approach to supra-acetabular metastatic lesions is a powerful tool in our armamentarium, offering significant pain relief and functional restoration with minimal morbidity. By adhering to meticulous preoperative planning, precise surgical technique, and comprehensive postoperative care, we can achieve excellent outcomes for our patients. Any questions, fellows?

REFERENCES

OUTCOMES
- Full weight bearing permitted

• Minimal blood loss ( 300 mL)

• No infections to date

• Avoids the possible complications of total hip replacement

• Rare tumor progression

COMPLICATIONS
- Risk of postoperative infection is minimal due to the minimal extent of the surgery.

1. Harrington KD. The management of acetabular insufficiency secondary to metastatic malignant disease. J Bone Joint Surg Am 1981;63A:654–664.

2. Malawer M, Sugarbaker PH. Musculoskeletal Cancer Surgery: Treatment of Sarcomas and Allied Diseases. Dordrecht, The Netherlands: Kluwer Academic Publishers, 2001.

3. Marco R, Sheth D, Boland P, et al. Functional and oncological outcome of acetabular reconstruction for the treatment of metastatic disease. J Bone Joint Surg Am 2000;82A:642–651.