What is the preferred choice between hinge total knee replacement (TKR) and constrained total knee replacement (TKR) for patients with knee instability or deformity?

Hinge vs Constrained TKR

For patients requiring increased constraint in total knee replacement, use a constrained condylar knee (CCK) prosthesis as the first-line option, reserving rotating hinge (RTH) designs only for cases with severe deformity or instability that cannot be managed with a CCK implant. 1

Clinical Decision Algorithm

First-Line: Constrained Condylar Knee (CCK)

• CCK prostheses should be used for patients with substantial coronal plane instability that is difficult to balance with standard posterior-stabilized or cruciate-retaining implants alone 1
• CCK designs are appropriate for severe knee deformities with significant instability in primary TKA, particularly in elderly patients over 75 years old 2
• Second-generation semi-constrained CCK prostheses demonstrate excellent functional outcomes, with mean Knee Society Scores improving from 30 preoperatively to 92.1 points at follow-up 2
• CCK implants show good survival rates with no radiolucent lines, deep infections, or periprosthetic fractures in primary cases 2

Reserve for Severe Cases: Rotating Hinge (RTH)

• Rotating-hinge knee implants should be reserved exclusively for patients with severe deformity or instability that cannot be managed with a CCK implant 1
• RTH designs are typically indicated when ligaments and muscles cannot provide adequate stability for less constrained prostheses 3

Key Clinical Considerations

Constraint Selection Rationale

• Increasing component constraint reduces instability but transmits increased forces to fixation and implant interfaces, potentially causing premature aseptic loosening 1
• The goal is to use the minimum constraint necessary to achieve stability while minimizing stress on bone-implant interfaces 1

Specific Indications for CCK Over Standard Implants

• Prior patellectomy 1
• Rheumatoid arthritis 1
• Substantial preoperative deformities 1
• Severe coronal plane instability unresponsive to soft tissue balancing 1

Evidence Quality Limitations

• A critical caveat: there is limited high-level comparative evidence directly comparing CCK and RTH designs 4
• An ongoing randomized controlled trial is investigating whether RTH and CCK designs yield similar outcomes, but results are not yet available 5
• Most existing evidence consists of case series and observational studies rather than head-to-head comparisons 4

Outcomes Data

CCK Performance

• CCK prostheses demonstrate excellent and very good results in both primary and revision cases 4
• Full extension recovery is achieved in all patients during follow-up 2
• No radiographic evidence of loosening at medium-term follow-up (mean 31 months) 2

Common Pitfall to Avoid

• Do not routinely use RTH designs when CCK would suffice—the increased constraint of hinged implants may lead to higher interface stresses and potential complications without providing additional clinical benefit in cases manageable with CCK 1, 4