Timothy S. Brown
Matthew P. Abdel
Instability accounts for approximately 10 to 25% of revision total knee arthroplasties (TKAs).
Types of tibiofemoral instability include:
Sagittal (anteroposterior) instability (Figure 67.1) due to flexion-extension mismatch such as flexion instability (Figure 67.2).
Coronal (varus-valgus) instability
Condylar fracture (Figure 67.3)
Attritional damage to ligaments, such as from
Polyethylene wear synovitis (Figure 67.4)
Cement synovitis from debonded tibial component (Figure 67.5A and B)
Periprosthetic joint infection
Global instability (Figure 67.6)
Hyperextension (recurvatum) instability (Figure 67.7)
Accurate diagnosis of the etiology causing instability is essential to appropriately manage this complication.
Sterile Instruments and Implants
Routine revision TKA instruments
Large and small sagittal saws
Large and small flexible osteotomes
High-speed 6.5-mm and pencil-tip burrs
Square tip impactor
Implants with varying levels of constraint should be available during all cases, from posterior-stabilized to varus-valgus constraint (VVC) to rotating-hinge constructs.
In most cases, a medial parapatellar approach can be used. Occasionally, an extensile exposure may be required, such as a quadriceps snip.
Figure 67.1 ▪ Lateral radiograph of a 55-year-old man with a dislocated knee after a revision TKA completed at an outside institution.
A full complement of knee radiographs are recommended, including a long-leg hip-knee-ankle radiograph, standing anteroposterior (AP) radiograph, standing posteroanterior flexion radiograph, lateral radiograph, and patellar view.
Prior radiographs for comparison are often very helpful.
As with any revision TKA, periprosthetic joint infection (PJI) should be excluded with inflammatory markers (erythrocyte sedimentation rate and C-reactive protein) and a joint aspiration.
Figure 67.4 ▪ Intraoperative picture of a 25-year-old man with marked polyethylene wear 8 years after a distal femoral replacement for oncologic purposes. Even with a hinged construct, this resulted in instability.
Bone, Implant, and Soft Tissue Techniques
The patient should be positioned supine.
The knee should be examined under anesthesia to determine the true form and extent of instability (Figure 67.8).
Figure 67.6 ▪ Lateral radiograph of a 61-year-old woman with global instability related to her extensor mechanism disruption.Premium Wordpress Themes by UFO Themes
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