CHAPTER SYNOPSIS:

This chapter will address the complicated problem of revising an ankle arthroplasty that has become a valgus deformity following implantation. The implications of a sustained valgus deformity following total ankle arthroplasty are grave for the implant, as eccentric loads about the prosthesis may cause further failure through subsidence and polyethylene wear. Thus, recognition of the problem and the knowledge base to successfully correct it are critical to survival of the implant.

IMPORTANT POINTS:

• •
  

  Determine if the valgus deformity is coming from ligament instability, bone defects/subsidence, or mechanical alignment of the tibia/foot.

  
  
  
  
  • ○
    

    Weight-bearing radiographs of the length of the tibia, the mechanical axis of the hip–knee–ankle, the ankle, and the foot are required, in addition to a Cobey view of the calcaneus.

  
  
  
  
• •
  

  Determine the potential to salvage the implant, versus removal and arthrodesis.

  
  
  
  
  • ○
    

    A computed tomography scan is used to estimate the amount of residual bone present following implant removal/revision.

    
    
  • ○
    

    Stress radiographs and reverse-stress radiographs are used to evaluate the ability to correct the implant to neutral.

  
  
  
  
• •
  

  Determine the best method to salvage the implant (if applicable).

  
  
  
  
  • ○
    

    Ligament instability.

    
    
    
    
    • ▪
      

      Revision to a custom implant will increase height (making up for bone loss) and improve ligamentotaxis.

      
      
    • ▪
      

      Reconstruct the deficient ligaments via a tendon transfer procedure.

      
      
    • ▪
      

      Alter the alignment of the foot and/or tibia to improve the mechanical axis and balance the load on the implant.

    
    
    
    
  • ○
    

    Subsidence.

    
    
    
    
    • ▪
      

      Revision to a custom implant will make up for bone loss and provide better coverage and fixation.

      
      
    • ▪
      

      Add reinforcement to stabilize the implant (bone graft versus polymethylmethacrylate).

    
    

  
  

VIDEO AVAILABLE:

None

HISTORY/INTRODUCTION/SCOPE OF THE PROBLEM

As noted in the Chapter Preview, the implications of a sustained valgus deformity following total ankle arthroplasty are grave for the implant, as eccentric loads about the prosthesis may cause further failure through subsidence and polyethylene wear. Thus, recognition of the problem and the knowledge base to successfully correct it are critical to survival of the implant. Fukuda, Haddad, and colleagues (Impact of Talar Component Rotation on Contact Pressure after Total Ankle Arthroplasty: A Cadaveric Study. Fukuda T, Haddad SL, Ren Y, Zhang L. Unpublished manuscript, 2009.) found that malrotation of the talar component prosthesis with respect to the tibial component leads to a statistically significant decreased contact area and subsequent increased peak pressure and rotational torque. This imbalance is similar to that seen with edge loading from angular deformity, and thus congruence between the tibial and talar components is paramount to a successful arthroplasty.

INDICATIONS

Valgus deformity about a previously placed ankle prosthesis may arise from a variety of circumstances. Ligament imbalance is often the primary culprit, and in the case of valgus, a persistent, deficient deltoid ligament in combination with a persistent tight lateral collateral ligament complex allows deformity progression ( Fig. 15-1 ). This is rarely the sole component to recurrent valgus deformity but must be considered during any attempt at revising the prosthesis. Failure to adequately stabilize the deltoid ligament in any implant with a tendency toward valgus will result in repetitive failure. To assess ligament balance, the examiner may incorporate stress radiographs done manually. The examiner must also perform “reverse” stress radiographs to determine the capability of deformity correction. If the prosthesis does not correct to neutral alignment under these circumstances, then clearly there are other factors (i.e., bone impingement or significant scar tissue) compounding the valgus deformity, and isolated ligament reconstruction will fail.

Valgus deformity following total ankle arthroplasty due to deltoid insufficiency.

A second and equally important factor is the mechanical alignment of the extremity, which may not have been addressed sufficiently in the primary arthroplasty. If the patient sustained a prior tibia fracture with varus deformity (or if they have congenital genu varum), alignment of the hip–knee–ankle axis invariably places a valgus thrust about the ankle ( Fig. 15-2 ). Under these circumstances, patients with an existing implant fail through either subsidence of the prosthesis into valgus by the weakened anterolateral tibial cortex, insufficient fibular bone structural support (lack of fibula coverage of the lateral implant), or attenuation of the deltoid ligament with repetitive impact. Revision in this case thus involves either a custom prosthesis to restore height in the deficient bone or the ligament reconstruction mentioned earlier. In either case, it is critical to address the tibial deformity through osteotomy to prevent recurrence following revision. Discussion of these methods is beyond the scope of this text. Techniques range from opening or closing wedge osteotomies and, more recently, distraction osteogenesis to provide more fluid and adjustable correction. Needless to say, the goal is to establish a neutral mechanical axis to prevent aberrant prosthesis overload into valgus. Finally, these techniques are used well in advance of any revisions applied to the prosthesis itself. I stage these operations, correcting all mechanical deformity surrounding the prosthesis first. After successful healing of both bone and ligament pathology, revision of the prosthesis itself is performed (at a minimum of 3 months later), which then becomes a straightforward ankle revision without compounding deformity. Timing is critical, and allowing the edema about the skin and subcutaneous tissues to dissipate over the 3- to 5-month period has the added benefit of minimizing surgical incision complications through the repeat anterior approach in revision ankle arthroplasty.

Genu varum creating valgus vector force, creating subsidence and failure of prosthesis into valgus.

Along the line of tibial deformity creating valgus, residual pes planovalgus or acquired flatfoot deformity in the foot will place increased structural demands on the prosthesis, allowing it to fail by one of the methods mentioned. Under these circumstances, the examiner must perceive the foot deformity through weight-bearing inspection and correct said deformity through a medial slide calcaneal osteotomy, a Cotton opening wedge medial cuneiform osteotomy (or a plantarflexion first metatarsocuneiform arthrodesis if laxity is present about that joint), and/or an Evans procedure/lateral column lengthening to balance structural deformity. In cases where hindfoot arthritis prevails, a corrective triple arthrodesis is more appropriate in comparison to joint-preserving operations. It is critical that the surgeon recognize this problem, as it is often the most unrecognized issue that leads to valgus in an already implanted prosthesis. Again, correction of the foot deformities is beyond the scope of this publication, although this is not to underemphasize their importance in obtaining a balanced ankle prosthesis. The surgeon must be certain that the foot is plantigrade, and this must be done simultaneously with component revision, as there is no better time to appreciate the foot forces creating imbalance and valgus deformity. As with tibial deformity, I prefer to stage this correction, performing the revision arthroplasty at a later date.

Following failure of the prosthesis into the supportive bone, the surgeon must consider osteolysis. Osteolysis occurs from shed polyethylene particles, creating a macrophage reaction and autodestruction of bone through osteoclasts. This weakened, cystic bone allows the prosthesis to subside through the resection margin, creating deformity and failure. A preoperative computed tomography (CT) scan is important in making this assessment. All osteolytic cysts must be targeted for bone grafting following recognition.

Interesting compounding factors in revision for deformity revolve around the character of the bone (tibia and talus) following implant removal. This in and of itself is not a contraindication for surgical revision, but it must be respected and planned for during the reconstruction. This problem is more often noted on the talar side of the prosthesis, as tilt and subsidence erode the softer talar bone, leading to a void that must be considered when addressing fixation of the revised talar component. Stemmed implants are one option, of course, but this author has used polymethylmethacrylate in combination with bone grafting to allow increased accuracy with talar component placement. The longevity and reviseability of either construct, however, remain in question.