INBONE Total Ankle Arthroplasty: An Intraoperative Masterclass

Welcome, fellows, to the operating theater. Today, we're tackling an end-stage ankle arthrosis case using the INBONE™ Total Ankle System. This system stands apart from many others due to its unique intramedullary referencing, a technique that, while initially demanding, offers unparalleled precision in deformity correction. Our goal is to restore a pain-free, functional ankle joint, and we'll walk through every critical step to achieve that.

Indications and Pathogenesis: Understanding the "Why"

Before we even make an incision, we must understand why we are here. The INBONE™ total ankle system, much like its counterparts, is indicated for end-stage ankle arthritis that has failed exhaustive nonoperative interventions.

Common Etiologies:

• Post-traumatic arthrosis: This is, by far, the most prevalent cause we encounter. A history of ankle trauma – be it an intra-articular fracture, a fracture-dislocation with malunion, or chronic ankle instability leading to recurrent sprains – often culminates in progressive articular cartilage wear. This can manifest as relative anterior subluxation of the talus, varus tilt within the ankle mortise, or a hindfoot varus position.
• Primary osteoarthrosis: Relatively rare in the ankle compared to the hip and knee, and often poorly understood.
• Inflammatory arthropathy: Conditions like rheumatoid arthritis, hemochromatosis, or pigmented villonodular synovitis can lead to progressive and proliferative synovial erosive changes. These cases often present with chronic posterior tibial tendinopathy, progressive valgus hindfoot deformity, eventual valgus tilt of the talus, potential lateral malleolar stress fracture, and compensatory forefoot varus.
• Other less common causes: Charcot neuroarthropathy or septic arthritis (once resolved) may also lead to end-stage changes requiring arthroplasty.

Patient Presentation: Clinical Clues

Patients typically present with a history of chronic anterior ankle pain, predominantly with activity and weight-bearing. They often report ankle stiffness, particularly limited dorsiflexion, and swelling. On examination, you'll observe a limp, often with compensatory external rotation of the hip to externally rotate the ankle, avoiding painful push-off. Painful and limited ankle range of motion (ROM) is characteristic, along with mild ankle edema and potential associated foot deformities. Post-traumatic cases with chronic instability often show varus ankle and hindfoot, while inflammatory arthritis may present with progressive flatfoot, valgus ankle/hindfoot, and equinus.

Comprehensive Surgical Anatomy: Navigating the Landscape

Understanding the intricate anatomy of the ankle joint is paramount. We're operating in a confined space, rich with vital neurovascular structures.

The Ankle Mortise: Bones and Articulations

• Tibial Plafond: The distal articular surface of the tibia, forming the roof of the ankle joint.
  • It possesses a slight posterior slope in the sagittal plane.
  • In the coronal plane, its articular surface is typically 88 to 92 degrees relative to the lateral tibial shaft axis.
  • It articulates with the dorsal and medial aspects of the talus.
  • The medial malleolus extends distally, forming the medial wall of the mortise.
• Fibula: The lateral malleolus, articulating with the lateral talus. It bears approximately one-sixth of the axial load distribution of the ankle. Its integrity is crucial for ankle stability.
• Talus: A unique bone, 60% of its surface area is covered by articular cartilage. Its dual radius of curvature allows for dorsiflexion and plantarflexion.
• Distal Tibiofibular Syndesmosis: This critical fibrous joint, composed of the anterior inferior tibiofibular ligament, the interosseous membrane, and the posterior tibiofibular ligament, maintains the integrity of the ankle mortise. Any compromise here can lead to instability.

Neurovascular Structures: The "No-Touch" Zones

• Superficial Peroneal Nerve (SPN): This sensory nerve runs just deep to the skin in the anterior leg, typically piercing the deep fascia in the distal third of the leg. It then branches to supply sensation to the dorsum of the foot, except for the first web space.
  • CRITICAL PEARL: In our experience, there is a consistent branch of the superficial peroneal nerve that crosses directly over or immediately proximal to the tibiotalar joint. This nerve is extremely vulnerable during an anterior approach and must be identified and protected. Injury can lead to distressing numbness or neuropathic pain.
• Deep Peroneal Nerve: This motor and sensory nerve runs with the anterior tibial artery. It innervates the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and peroneus tertius muscles, and provides sensation to the first web space.
• Anterior Tibial Artery (distal continuation as Dorsalis Pedis Artery): This major artery supplies the anterior compartment of the leg and the dorsum of the foot. It runs alongside the deep peroneal nerve.
• Posterior Tibial Artery (and its Deltoid Branch): While not directly in our anterior field, the deltoid branch of the posterior tibial artery is crucial for the perfusion of the medial talar dome. Aggressive medial talar dissection during soft tissue balancing can compromise this supply, risking avascular necrosis of the talus.

Muscular Intervals and Tendons: Our Surgical Corridor

We utilize an anterior approach, specifically the interval between the tibialis anterior (TA) tendon and the extensor hallucis longus (EHL) tendon.
* Tibialis Anterior (TA): Lies medially, responsible for dorsiflexion and inversion.
* Extensor Hallucis Longus (EHL): Lies laterally, responsible for great toe extension and ankle dorsiflexion.
* Extensor Digitorum Longus (EDL): Further lateral, extending the lesser toes.

Preoperative Planning: The Blueprint for Success

Thorough preoperative planning is the cornerstone of a successful total ankle arthroplasty, especially with the INBONE™ system's intramedullary referencing.

Imaging and Deformity Analysis:

• Weight-bearing Radiographs:
  • AP, Lateral, and Mortise views of the ankle: Crucial for assessing joint space narrowing, osteophyte formation, alignment, and bone quality. We routinely include the contralateral ankle for comparison.
  • AP, Lateral, and Oblique views of the foot: Essential, particularly with associated foot deformities, to assess hindfoot and forefoot alignment.
  • Weight-bearing AP and Lateral Tibia-Fibula views: Routinely obtained for the lower leg to identify any proximal deformities that could influence ankle alignment.
  • Weight-bearing Mechanical Axis (Hip-to-Ankle) views: Occasionally obtained for both extremities if a complex lower extremity deformity is suspected, providing a global perspective on limb alignment.
• CT Scans: For complex or ill-defined ankle-hindfoot arthritis patterns, especially with significant deformity, a CT scan provides detailed bony anatomy, allowing for precise measurement of bone loss and osteophyte burden.
• MRI: Indicated if avascular necrosis of the talus or distal tibia is suspected, to assess vascularity and cartilage status.
• Ankle ROM Assessment: Crucial to quantify stiffness, particularly lack of dorsiflexion, which often requires soft tissue releases or osteophyte removal.

Vascular Assessment: Ensuring Healing Potential

• Satisfactory perfusion is non-negotiable for wound healing. We routinely perform noninvasive vascular studies. If any concerns arise, a vascular surgery consultation is immediately obtained. Neuropathic patients require heightened vigilance.

Deformity Correction Strategy: Anticipating the Intraoperative Challenge

• Coronal Plane Alignment: Determine if the deformity is passively correctable. This provides insight into the extent of ligamentous release required.
• Sagittal Plane Stiffness: Address lack of dorsiflexion. This often necessitates:
  • Anterior tibiotalar exostectomy (removal of anterior osteophytes).
  • Posterior capsular release.
  • Occasionally, a formal tendo Achilles lengthening.
• Associated Deformities: Be prepared for concomitant procedures such as corrective osteotomies of the distal tibia or foot, hindfoot arthrodesis, ligament releases or stabilization, and tendon transfers. The durability of the INBONE™ implants, particularly the broad talar component and tibial stem extensions, allows us to maintain correction of coronal and sagittal plane deformities achieved through soft tissue balancing and osteotomies.

Anesthesia and Tourniquet:

• We routinely use a thigh tourniquet for a bloodless field, which is critical for precise dissection and bone cuts.
• Regional anesthesia (popliteal block) is our preference, offering excellent postoperative pain relief, especially with a regional catheter. This also preserves hip and knee flexion-extension, facilitating early postoperative mobilization.
• CRITICAL PITFALL: If a popliteal block is combined with a thigh tourniquet, a supplemental femoral nerve block (temporarily forfeiting knee extension) or general anesthesia may be necessary to manage tourniquet pain.

Operating Room Setup and Patient Positioning: Precision from the Start

• Patient Position: Supine on the operating table.
• Operated Foot Placement: The plantar aspect of the operated foot is positioned at the very end of the operating table. This allows for full range of motion and unimpeded access for the intramedullary frame.
• Hip Bolster: A bolster is placed under the ipsilateral hip to prevent undesired external rotation of the hip, ensuring the foot and ankle are well balanced with the toes directed towards the ceiling.
• Opposite Extremity: Ensure the opposite extremity is not secured too close to the operative extremity, allowing ample space for the INBONE™ leg holder and fluoroscopy unit.
• Fluoroscopy: A large fluoroscopic scanner is essential. It must be capable of straddling the leg and the bulky INBONE™ leg holder, and allow fluoroscopy through the operating table. A small C-arm is inadequate for this system. Foot pedals to make subtle adjustments to the table position are invaluable for fine-tuning alignment.

Instrumentation: The Surgeon's Toolbox

• Saws: Small oscillating and reciprocating saws for fine cuts and precise resection of prominences. A larger oscillating saw for broad bone cuts. The smaller saws are excellent for morselizing large bone fragments for evacuation.
• Rasp: For final preparation and smoothing of cut bony surfaces.
• 90-degree Angled Curette: Particularly useful for separating bone from the posterior capsule.
• Lamina Spreaders:
  • Toothed Lamina Spreader: Used to distract the joint and aid in realignment of preoperative ankle deformity. With the INBONE™ prosthesis using a monoblock cutting guide, an intra-articular lamina spreader helps limit excessive bone resection. Placing it on the concave side of a deformed joint assists in realignment.
  • Toothless Lamina Spreader: For judicious distraction of the ankle to improve exposure, even after initial surface preparation.
• INBONE™ Leg Holder: This specialized holder maintains the leg in position relative to the alignment guides and reference drill, crucial for intramedullary referencing.

Step-by-Step Intraoperative Execution: The Scrubbed-In View

Alright, team, let's get scrubbed in. We've completed our planning; now, let's execute.

I. Surgical Approach: The Anterior Corridor

We will use a standard anterior approach to the ankle, meticulously navigating the interval between the tibialis anterior (TA) and extensor hallucis longus (EHL) tendons.

1. Incision:

   • Surgeon's Directive: "Scalpel, please. We'll make a longitudinal midline incision over the anterior ankle. Start approximately 10 cm proximal to the tibiotalar joint, about 1 cm lateral to the tibial crest, and extend it distally just beyond the talonavicular joint."
   • This length ensures adequate exposure for instrumentation and soft tissue retraction.
   • Surgical Warning:
     > At no point should direct tension be placed on the skin margins. We perform deep, full-thickness retraction as soon as possible to limit the risk of skin complications, which can be devastating in ankle arthroplasty.

2. Subcutaneous Dissection and Nerve Protection:

   • Surgeon's Directive: "Let's carefully dissect through the subcutaneous tissue. Identify and protect the superficial peroneal nerve. Dr. Smith, can you gently retract it laterally with a Senn retractor?"
   • Clinical Pearl: Remember, there's a consistent branch of the superficial peroneal nerve that often crosses directly over or immediately proximal to the tibiotalar joint. Be vigilant for this. Injury can lead to persistent numbness or painful neuroma.
   • We want to ensure this nerve is safely retracted laterally throughout the procedure.

3. Retinacular Incision:

   • Surgeon's Directive: "Now, we expose the extensor retinaculum. Identify the course of the EHL tendon. We'll sharply, but carefully, divide the retinaculum directly over the EHL tendon."
   • We always attempt to maintain the TA tendon in its dedicated sheath if present. Preserving the retinaculum over the TA tendon prevents bowstringing and reduces stress on the anterior wound. In the event of wound dehiscence, the TA tendon is not directly exposed.
   • However, sometimes the retinaculum over the TA tendon is absent or confluent with the EHL retinaculum.

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TECH FIG 1 • In this case there is no separate sheath for the tibialis anterior (TA) tendon. Nonetheless, the retinaculum was opened lateral to the tendon, and upon closure the TA will not be immediately up against the suture line.
* Surgeon's Directive: "We'll use the interval between the TA and EHL tendons. Retract the TA medially and the EHL laterally."

1. Deep Neurovascular Bundle Protection:

   • Surgeon's Directive: "Now, identify the deep neurovascular bundle – that's your anterior tibial artery and deep peroneal nerve. Carefully retract it laterally throughout the remainder of the procedure. We'll use a narrow Hohmann for this, ensuring no direct pressure."
   • Surgical Warning:
     > The deep neurovascular bundle is highly susceptible to injury from direct trauma or prolonged retraction. Ensure gentle, intermittent retraction to prevent nerve neuropraxia or vascular compromise.

2. Capsulotomy and Periosteal Elevation:

   • Surgeon's Directive: "Perform an anterior capsulotomy. Then, elevate the tibial and dorsal talar periosteum approximately 6 to 8 cm proximally to the tibial plafond and distally to the talonavicular joint, respectively. This separated capsule and periosteum will be elevated medially and laterally to expose the ankle joint fully, access the medial and lateral gutters, and visualize the medial and lateral malleoli."

3. Osteophyte Removal:

   • Surgeon's Directive: "Observe the anterior tibial and talar osteophytes. We need to remove these now. Use a small oscillating saw and a curette to meticulously resect them. This is critical for achieving adequate exposure and preventing interference with our instrumentation later."
   • Clinical Pearl: Thorough osteophyte removal is key to regaining dorsiflexion and ensuring the intramedullary alignment guides can be seated properly.

II. Tibiotalar Alignment and Soft Tissue Balancing

Before we introduce any hardware, we must achieve optimal ankle soft tissue balance and alignment. This is where we correct preoperative deformities.

1. Varus Malalignment Correction:
   • Surgeon's Directive: "For this moderate to severe varus malalignment, we will perform a comprehensive medial release. The concept here is similar to balancing a varus knee in total knee arthroplasty."
   • Subperiosteal Soft Tissue Sleeve Elevation: "We will subperiosteally raise a continuous soft tissue sleeve from the distal medial tibia down to the medial talus. Use a Cobb elevator for this, staying tight to the bone."
   • Surgical Warning:
     > Be careful not to be overly aggressive on the medial talus. This area is supplied by the deltoid branch of the posterior tibial artery, and excessive dissection can compromise the vascularity of the medial talar dome, risking avascular necrosis.
   • Deltoid Ligament Release: "The superficial deltoid (medial collateral) ligament will be elevated but left intact proximally and attached distally. The release of these fibers is complete when the posterior tibial tendon can be visualized."
   • "Next, the deep deltoid (medial collateral) ligament may need to be peeled off the medial malleolus to balance the ankle appropriately. In severe varus deformity, the entire deep deltoid ligament must be released to achieve tibiotalar balance. Observe how the ankle now opens up with a lamina spreader."

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TECH FIG 2 • A. In this varus ankle a complete medial peel of the deltoid ligament has been performed and the ankle can be opened up with the lamina spreader.
* Clinical Pearl: Over-release of the deltoid ligament in severe varus deformity is theoretically possible, but in our extensive experience, the ankle will not collapse into valgus even with a complete release, given the inherent stability provided by the bony anatomy and the lateral structures.
* Surgeon's Directive: "Once the release is complete, place a toothed lamina spreader in the medial tibiotalar joint to maintain the correction and facilitate exposure."

1. Valgus Malalignment Correction:
   • Surgeon's Directive: "Now, let's consider valgus malalignment. This also must be rebalanced, but our approach is often different."
   • Clinical Pearl: In our experience, we rarely need to perform a formal lateral ligament release for valgus deformity. Often, valgus is secondary to lateral ankle joint collapse and some medial (deltoid) ligament attenuation, which may involve a component of lateral ankle ligament instability. This seems counterintuitive, but lateral release in such situations may paradoxically lead to increased lateral instability.
   • Surgeon's Directive: "Instead, we use a lateral lamina spreader placed on the concave side of the joint to realign the ankle and regain functional tension in the medial ligaments."

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TECH FIG 2 • E. Valgus ankle with AP alignment guide properly rotated. However, the talus is not orthogonal to the guide or the tibia.
*

III. Intramedullary Alignment: The INBONE™ Advantage

This is the core of the INBONE™ system. It requires meticulous attention to detail and reliance on fluoroscopy.

1. Frame Assembly and Calibration:
   • Surgeon's Directive: "Before we secure the leg, ensure the INBONE™ foot and ankle frame is properly assembled and the alignment drill guide trajectory is calibrated. If there's any doubt, assemble the cannula into the holder, insert the drill, and take a fluoroscopic view to confirm they coincide."

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TECH FIG 3 • A. Be sure the foot and ankle frame is properly assembled and the alignment drill guide trajectory is calibrated. If unsure, you can assemble the cannula into the holder, put the drill in, and take a fluoroscopic view to make sure they coincide.

1. Securing the Leg in the Holder:
   • Surgeon's Directive: "Now that we've balanced the soft tissues and corrected the deformity, we will transfer the leg into the foot and ankle holder. Ensure the lamina spreader, if used for correction, remains in place as we secure the foot and lower leg."
   • Clinical Pearl: Securing the foot and ankle first can make it difficult to effectively position the lamina spreader for initial deformity correction. Always correct first, then secure.

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TECH FIG 3 • B. The foot and lower leg are secured in the leg holder. With correction of the preoperative deformity, we transfer the leg into the foot and ankle holder with the lamina spreader in place.

1. Achieving Proper Rotation:

   • Surgeon's Directive: "For proper rotation, we'll use a small straight osteotome in the medial gutter as our reference. Rotate the entire foot and leg holder assembly until this osteotome is perfectly parallel with the leg holder foot plate. Dr. Lee, can you confirm this with fluoroscopy, please?"
   • Clinical Pearl: Subtle adjustments to the table's rotation, combined with the leg holder, allow us to confirm ideal alignment relative to the alignment guides.

2. Ensuring a Plantigrade Foot:

   • Surgeon's Directive: "Crucially, the heel must be flush with the foot plate of the guide. Confirm this visually and with lateral fluoroscopy."
   • Surgical Warning:
     > If the heel is not flush, the talar cut will have an undesirable posterior slope. This removes an excessive amount of the talar body, significantly increasing the risk of posterior talar component subsidence and potential catastrophic failure. Ensure all anterior tibiotalar exostoses are fully resected to allow the talus to sit flush.

3. Tibial Intramedullary Rod Insertion:

   • Surgeon's Directive: "Now, we will insert the tibial intramedullary rod. This rod serves as our central axis for tibial component alignment. Advance it carefully under constant fluoroscopic guidance to ensure it remains within the medullary canal and does not perforate the cortex."

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* Clinical Pearl: The INBONE™ system's intramedullary alignment guide passes through the plantar foot, calcaneus, talus, and tibia. Importantly, it does so anterior to the posterior facet of the calcaneus, thus not violating any articulations of the subtalar joint.

1. Drilling the Tibial Pilot Hole:
   • Surgeon's Directive: "With the intramedullary rod securely positioned and confirmed by fluoroscopy in both AP and lateral views, we will now drill the tibial pilot hole. Use the appropriate drill bit through the guide. Maintain constant irrigation to prevent thermal necrosis."

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* Surgical Warning:
> Drill under constant fluoroscopic guidance to prevent eccentric drilling or cortical perforation, which can compromise implant stability.

1. Tibial Cutting Guide Placement:
   • Surgeon's Directive: "Once the pilot hole is established, remove the drill and insert the tibial cutting guide over the intramedullary rod. Ensure it seats flush against the anterior tibia. Confirm its position and rotation with AP and lateral fluoroscopy. We can make subtle adjustments to the alignment guides relative to the ankle to fine-tune the reference drill trajectory."

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*

1. Tibial Resection:
   • Surgeon's Directive: "Now, using a large oscillating saw, perform the initial tibial resection through the cutting guide. Take your time, ensure the saw blade is fully engaged, and make a clean, flat cut. We'll start with the anterior cut, then the posterior, and finally the medial and lateral facets."

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* Clinical Pearl: The INBONE™ system often uses a monoblock cutting guide for tibial and talar resection, which helps ensure parallel cuts and limits

Additional Intraoperative Imaging & Surgical Steps

REFERENCES

1. Bonnin M, Judet T, Colombier JA, et al. Mid-term results of the Salto total ankle prosthesis: report of 98 cases with minimum two years follow up. Clin Orthop Relat Res 2004;424:6–18.

2. Gougoulias N, Khanna A, Maffulli N. How successful are current ankle replacements? A systematic review of the literature. Clin Orthop Relat Res 2010;468:199–208.

3. Haddad SL, Coetzee JC, Estok R, et al. Intermediate and long-term outcomes of total ankle arthroplasty and ankle arthrodesis: a systematic review of the literature. J Bone Joint Surg Am 2007;89A:1899–1905.

4. Patient satisfaction rates for total ankle arthroplasty exceed 90%, although follow-up data for patient satisfaction often do not exceed 5 years.

5. Overall survivorship analysis for currently available implants, designating removal of a metal component or conversion to arthrodesis as the endpoint, ranges from about 90% to 95% at 5 to 6 years and 80% to 92% at 10 to 12 years.