Evaluation and treatment of flexion, midflexion, and global instability

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As we have seen in Part 1 and Part 2  of this series of articles on instability after total knee arthroplasty (TKA), instability is a common cause of dissatisfaction after TKA and is also one of the main reasons that patients undergo a revision TKA. One of the best described forms of instability is flexion instability, which is well known as a cause of revision TKA [1]. Midflexion instability is, however, a relatively poorly understood clinical entity, undergoing much analysis in the literature within the last decade [1, 2]. While flexion instability is challenging to diagnose and midflexion instability has a vague clinical presentation, global instability on the contrary is clearly detectable in multiple planes, yet it presents the surgeon with a complex-to-treat clinical situation.

In this part, Sam Oussedik from the University College Hospital in London, UK walks us through the presentation and evaluation of flexion, midflexion, and global instability and examines the current methods of treatment available for these complex forms of instability after TKA.

Sam Oussedik

AO Recon Joint Preservation Knee Curriculum Taskforce
University College Hospital London
London, UK

Flexion instability

Flexion instability is caused when the flexion gap exceeds the extension gap [3]. This situation can occur, for example, in poorly executed TKA stabilized posteriorly; because these do not provide a varus-valgus constraint, sacrifice of the posterior cruciate ligament (PCL) can increase the flexion gap and lead to collateral ligament laxity [4].

In contrast to extension instability, where the knee can become unstable during activities such as walking [5], flexion instability occurs when the knee is bent and loaded and thus becomes symptomatic as the patient ascends or descends stairs, or transfers from sitting to standing [5]. Flexion instability is associated with a cluster of additional symptoms; aside from the instability when getting up from a sitting position or when using stairs, whereby a patient may feel anterior knee pain, the patient may have recurrent serosanguinous effusions [6] or synovitis and hemarthroses [3]; more than 60% of patients with flexion instability had a serosanguinous aspirate in one study [7]. Additionally, patients have tendinopathy at the pes anserinus and iliotibial band, periarticular bursitis of the knee [8], and on examination will test positive on the anterior drawer test [6]. In a study by Abdel et al [4], the clinical findings of patients with flexion instability were well described.

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  • Flexion instability
  • Stepwise technique for revision total knee arthroplasty in patients with flexion instability
  • Increasing constrain in rerevisions for recurrent instability
  • Polyethylene insert exchange may be successful in carefully selected patients
  • Evolving surgical techniques
  • Midflexion instability
  • Global instability
  • Future directions

Part 1 | Etiology and classification of the unstable total knee arthroplasty

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Part 2 | Evaluation and treatment of extension and recurvatum instability

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Contributing experts

This series of articles was created with the support of the following specialists (in alphabetical order):

Dario E Garin

Hospital Ángeles
Tijuana, Mexico

Beatriz Montoya-Ortiz

Clínica El Rosario
Medellín, Colombia

Sam Oussedik

AO Recon Joint Preservation Knee Curriculum Taskforce
University College Hospital London
London, UK

This issue was written by Lyndsey Kostadinov, AO Innovation Translation Center, Clinical Science, Switzerland.

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