Isolated Subtalar or Talonavicular Fusion Has Failed. Now What?

Isolated Subtalar or Talonavicular Fusion Has Failed. Now What? Anish R. Kadakia MD Associate Professor Northwestern University: Feinberg School of Medicine Northwestern Memorial Hospital Department of Orthopedic Surgery

Subtalar Arthrodesis Reported Nonunion Rates 0%-16% Difficult to assess fusion on plain radiographs CT is method of choice

Ultimate Arthrodesis Rate Isolated Subtalar Fusion 83% Part of Triple Arthrodesis 100%

What s s the Problem with Isolated Subtalar? 184 subtalar fusions (46% smoker) 159 in situ 148 available for final F/U to determine union Surgical Technique Summary Sinus Tarsi Approach Graft Cancellous autograft 94 Cancellous allograft 17 None 39 Fixation 1 or 2 screws

Overall Union Rate 84% Risk Factor for Nonunion Smoking 73% vs. 92% (non-smoker) >2mm avascular bone 62% overall union rate if present All nonunions occurred in this population Revision 71% vs. 86% (primary) Prior Ankle Fusion 33% nonunion rate No determined effect of bone graft use No determined effect of number of screws

Analysis Evaluate Patient Factors Smoker? Cessation required Non-compliance early WB? Long-term care facility Long-term cast 3 months Avascular Necrosis MRI? Evaluated extent of non-viable bone to plan resection May require bone-block block to maintain height

Analysis Evaluate Mechanical Factors Fixation Although no evidence that 2 screws > 1 screw CT Missed Calcaneus? Too medial? Threads not fully crossed fusion site 2 screws for revision Biomechanically superior Prior Ankle Fusion Possibly secondary increased stress on arthrodesis site Increased fixation More than 1 screw Screws into Tibia Prolonged NWB? 3 months

Screw Fixation Screw Fixation

Lag Screw Fixation at Time 0 Lag Screw Fixation at Time 0 Bone on Bone apposition Compression No motion Stability

Initial Bone Resorption Initial Bone Resorption

Initial Bone Resorption Initial Bone Resorption Lose Stability given loss of bone on bone apposition => Micromotion

Overdrilled Fully Threaded Overdrilled Fully Threaded Screw? Can Still Piston along gliding hole

Screw Fixation Screw Fixation

What is ideal? Better Screw? Compression Fully Threaded for stability No Gliding Hole Headless? Decreases skin irritation Does not solely on cortex for fixation Better for cancellous bone in hindfoot and ankle

Divergent Screw Fixation Divergent Screw Fixation Placing 2 nd Screw within Talar Neck minimizes risk of talar body fracture. Rarely reported, devastating when occurs

Symptomatic? Not all radiographic nonunion are symptomatic 42 radiographic nonunions 30 symptomatic => 71%

Bone Stimulator No objective data to support use in the setting of a hindfoot nonunion Good Candidate Logical principles Partial Union Evidence of trabecular continuity Potential for healing is present Intact fixation Mechanical stability is still present for healing Maximize biology/mechanics Smoking cessation Assess Vit. D level Ensure NWB

Preop Planning Hardware Revision Removal of prior screw will leave large void fixation concern Choices Multiple smaller screws Large 8.0 mm screws Plate? never seen it done Fill void with Calcium Phosphate Fill void Fixation is improved

Additional Joint Involvement Consider when Bone loss is severe that stability may be compromised TN fusion 75% reduction of ST motion 91-92% 92% reduction of ST motion

Preop Planning Bone Preparation Revision Possible void after debridement Structural Autograft/Allograft Biologic Supplementation Cancellous Autograft BMP? Stem Cell? Trinity Bone Marrow Aspirate PRP?

Revision Invasive Supplementation Implantable Bone Stimulator Effective Costly Non-invasive PO No data to demonstrate improved efficacy Postop Regimen NWB 3 months

Revision Involvement of other joints? TN fixation Eliminate ST motion => Minimize stress on fusion site 13 ST revisions 3 part of triple 100% mean union (bony trabeculation) on CT 9 isolated 1 nonunion 77.3% mean union (trabeculation) in 8

Case Example Case Example

Patient Factor Analysis Non-smoker Non-neuropathic neuropathic Inadequate bony preparation? Mechanical Factors Fixation Single screw dorsal to plantar Inability to achieve compression Compliance Unknown 100% complaint per patient Always seems to be the case

Biology Adjuvant Trinity Bone Graft Mechanical 2 screws Preop Plan Stem Cell with cancellous allograft Fully threaded with gliding hole 2 nd Maximal purchase nd divergent screw Maximal stability

Case Example Case Example

Talonavicular Arthrodesis Reported Nonunion Rates 5% - Inflammatory Arthritis (Chiodo CP, Martin T, Wilson M. Foot Ankle Int. 2000) 6% - Traumatic/OA/SLE (Chen, C. et. Al. Foot Ankle Int. 2001) 4% - PTTD (Harper MC. Clin Orthop Relat Res. 1999)

CT assessment CT assessment

Plate vs. Screw TN fixation (Jarrell S, et. al. Biomechanical comparison of screw versus plate/screw construct for talonavicular fusion. Foot Ankle Int,, 2009) No significant difference Bending stiffness Plate/screw (recon) 363 N/mm Screw only (3) 380 N/mm Load to Failure Plate/screw (recon) 946 N Screw only (3) 1099 N

Additional Joint Involvement Very little increased functional loss with addition of Subtalar Fusion TN fusion 75% reduction of ST motion 91-92% 92% reduction of ST motion Subtalar fusion 26% reduction of TN motion

Additional ST fusion Preop Planning Limited functional detriment Increased rigidity decreased stress on TN joint Fixation One medial screw One lateral screw Naviculo Calcaneal screw Biologic augment as discussed previously

Dorsolateral screw T-N N fixation (Campbell et. al. AOFAS Summer Meeting 2010) Superior compression with 1 medial screw and 1 dorsolateral screw

N-C C screw increased rigidity to dorsal/plantar and medio-lateral stress

Case Presentation Case Presentation

TN gone very bad Disruption of TN stability Nonunion Evans Calc Ost

PO Clinical PO Clinical

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