Management of the Unstable Total Knee Arthroplasty


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Management of the Unstable Total Knee Arthroplasty


John Esposito MD FRCSC, and James L. Howard MD MSc FRCSC1


London Health Sciences Centre, Western University, ON, Canada


Top three questions



  1. In patients who have undergone total knee arthroplasty (TKA), which risk factors, compared to others, predict instability?
  2. Among patients with instability who undergo revision TKA, how do functional outcomes compare to primary TKA?
  3. In patients undergoing revision TKA for instability, which surgical techniques, compared to others, produce optimal outcomes?

Question 1: In patients who have undergone total knee arthroplasty (TKA), which risk factors, compared to others, predict instability?


Rationale


Identifying the causes of instability prior to revision surgery is imperative for the treating surgeon so that the subsequent revision can be appropriately directed to the underlying cause. Failure to do this could contribute to ongoing instability following revision TKA.


Clinical comment


Instability following TKA is not uncommon, the etiology of which may be multifactorial. Elucidating the causes of instability after TKA may help prevent their incidence, as well as allow the treating surgeon to specifically look for these underlying causes and correct them through subsequent revision surgery.


Available literature and quality of the evidence



  • Level IV.

Findings


The unstable TKA may result from a variety of distinct etiologies,1 and the identification and treatment of these etiologies at the time of revision is crucial in order to restore stability. The causes of instability that have been described include, flexion/extension gap mismatch, component malposition, isolated ligament insufficiency, extensor mechanism insufficiency, component loosening, and global instability.1 Calliess et al. in a survey of 1449 TK revisions remarks the evolving etiology of TKA failure.2 Low‐grade infection and instability are two major causes that have increased over the years. To our knowledge, this study represents the largest published series evaluating the specific failure mechanisms in revision TKA.


Surgical treatment for instability may encompass a variety of procedures, especially when the instability results from more than one etiological factor. Technical errors such as flexion/extension gap mismatch and component malpositioning tend to present early. Other causes tend to present late and result in attenuation of the soft tissue around the knee.1 Isolated ligament insufficiency may be persistent or iatrogenic. Extensor mechanism insufficiency causing TKA instability may be categorized into patellar component problems, tendinous and patellar bone integrity problems, and soft tissue imbalance or instability of the patellofemoral joint.3 Component loosening is often identified preoperatively and confirmed at the time of revision surgery. Knees with component loosening may progress to multidirectional instability.4 Global instability has been subcategorized into soft tissue attenuation (due to chronic synovitis, recurrent hemarthrosis, or undersizing of the polyethylene [PE] insert), direct negative effects of the PE insert (post fracture or wear) and knee dislocation.1 Knee dislocation after TKA has been attributed to severe flexion/extension gap mismatch and extensor mechanism insufficiency.1


Resolution of clinical scenario



  • The unstable TKA may arise from one or more etiologies and identification of these etiologies is integral to the restoration of stability.
  • Instability is a major cause of the need for revision. Often, increased constraint is needed to supplement or perform the function of incompetent ligament and soft tissue structures.5
  • Revision TKA for instability should specifically address the causes of the instability.

Question 2: Among patients with instability who undergo revision TKA, how do functional outcomes compare to primary TKA?


Rationale


As the number of primary TKAs performed continues to increase annually, it is reasonable to expect an increase in revision TKAs performed. Outcome data on revision TKA for instability will presumably support it as a reliable pursuit and have the potential to identify predictors of success and failure.


Clinical comment

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Nov 28, 2021 | Posted by in ORTHOPEDIC | Comments Off on Management of the Unstable Total Knee Arthroplasty

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