Design
• Constrained prosthesis without axle connecting tibial and femoral components (nonhinged)
• Large tibial post and deep femoral box provide
– Varus/valgus stability
– Rotational stability
Indications
• LCL attenuation or deficiency
• MCL attenuation or deficiency
• Flexion gap laxity
• Moderate bone loss in the setting of neuropathic arthropathy
Modularity
• Definition
– The ability to augment a standard prosthesis to balance soft tissues and/or restore bone loss
• Options include
– Metal tibial baseplate with modular polyethylene insert
– Metal augmentation for bone loss
– Modular femoral and tibial stems
Advantages
• Prosthesis allows stability in the face of soft tissue (ligamentous) or bony deficiency
• Ability to customize implant intraoperatively
Disadvantages
• More femoral bone resection
– Necessary to accommodate large box
• Aseptic loosening
– As a result of increased constraint
• Increased rates of osteolysis in modular components