Instability is equal to infection as the most common cause of revision in the first 5 years after total knee arthroplasty (TKA).

Additionally, instability accounts for one-fifth of TKAs revised after 5 years.

The spectrum of implant constraint in the revision setting typically includes posterior stabilized (PS) implants, varus-valgus constrained (VVC) implants, and hinged implants.

Remember that constraint varies between different implant designs and between manufacturers. Not all PS or VVC implants offer the same inherent knee stability.

With increasing constraint there is a theoretical trade-off between reducing instability of the knee and increasing forces at the implant-cement-bone interfaces.

VVC implants should be considered when deformity exists but the collateral ligaments are intact, when there is substantial ligament imbalance between the medial and lateral structures, or if there is an intraoperative medial collateral ligament (MCL) injury that can be repaired.

Indications for rotating-hinge TKA implants include true ligament incompetence from major bone loss (from infection (Figure 66.1), trauma, osteolysis (Figure 66.2), or iatrogenic (Figure 66.3) damaged, uncorrectable severe flexion/extension space mismatch, oncologic cases that violate the collateral ligaments, distal femur fractures that are not amenable to fixation (Figures 66.4 and 66.5), and uncorrectable recurvatum.

With all constrained implants it is wise to add stems and/or metaphyseal cones or sleeves to offload the implant-cement-bone interfaces.

Supine position