Review Question - QID 219989

The implant in Figure A is a condylar constrained knee (CCK) (or constrained nonhinged or varus-valgus constrained) implant. Indications for this implant include varus-valgus laxity greater than 5 mm, neuropathic arthropathy, or collateral ligament attenuation (Answer 4).

Various designs exist for total knee arthroplasty with various levels of constraint. The lowest constraint implant is a simple cruciate-retaining (CR) knee. CR implants are used in patients with minimal deformity (varus < 10 degrees, valgus < 15 degrees) and historically intact PCL. Newer, ultra-congruent bearings allow for the sacrifice of the PCL without diminishing functional outcomes. Posterior-stabilized (PS) implants provide a slightly greater level of constraint than CR implants. PS implants feature a polyethylene post that engages the femoral box to allow rollback. PS implants require sacrificing the PCL and are indicated in larger coronal deformity cases with intact and balanced collateral ligaments. A modification of the PS bearings is the more constrained varus-valgus constrained bearings. The varus-valgus constrained bearings (or constrained non-hinged or constrained condylar) are similar to PS implants but feature a larger tibial post that further engages the femoral box to provide additional constraint in the coronal plane and rotationally. The indications for a varus-valgus-constrained implant include varus-valgus laxity greater than 5 mm, collateral ligament attenuation or deficiency, flexion gap laxity, and neuropathic arthropathy. At this level of constraint, increased stress is placed at the implant-bone interface and therefore consideration of intramedullary stems is warranted. The highest level of constraint exists in a constrained hinged prosthesis. In this implant, the joint's femoral and tibial components are linked to constrain coronal and sagittal motion. Rotation in the axial plane can occur when using rotating hinged prostheses. Hinged prostheses can be employed for global ligamentous deficiency, hyperextension instability, severe deformity, or significant bone loss.

Kim et al. published a retrospective study on the long-term clinical outcomes and survivorship of CCK prosthesis in revision total knee arthroplasty (rTKA). The study featured 99 rTKAs with a mean follow-up of 12.6 years. The results of the study demonstrated an overall improvement in Knee Society Scores (KSS), range of motion, and implant survivorship. Specifically, CCK implants demonstrated an overall implant survivorship of 94.5% and 92.8% at 10 and 15 years, respectively. The authors concluded that the CCK implants provide a reliable and durable knee in complex rTKAs.

Maynard et al. also published a retrospective analysis of the outcomes of CCK implants in the primary setting. The author's indication for primary CCK was varus/valgus laxity over 5 mm after appropriate balancing. With a mean follow-up of 8.6 years, 78 primary CCKs were performed and evaluated using KSS, radiographic evaluation, and survivorship analysis. This study found improved clinical scores and patient-reported outcomes with implant survivorship, which was 94.9% at the final follow-up. The authors concluded that using primary CCK provides a reliable option with adequate outcomes in the setting of ligamentous instability and deformity.

Figure A demonstrates a constrained nonhinged (or CCK) implant in a right knee.

Incorrect Answers:
Answer 1: Hyperextension instability is an indication for a hinged prosthesis.
Answer 2: This level of valgus deformity and intraoperative laxity could be treated with a CR implant and appropriate balancing. A CCK implant is not indicated in this scenario.
Answer 3: Unresurfaced patella is not an indication for a varus-valgus-constrained implant. In the absence of patellectomy, resurfacing or not resurfacing the patella does not impact implant constraint choice.
Answer 5: This is not an indication for a CCK implant. In the setting of over-resection of the PCL intraoperatively, options include increasing constraint to ultra-congruent bearings in a CR implant or a PS implant.