THE ROLE OF HINGES: NO ROLE AT ALL – OPPOSES

Abstract

Non- or semi-constraint TKA implants do have their limitations in the absence of collateral ligaments, severe deformity, large osseous defects and gross flexion - extension instability or mismatch, even in primary TKA. Additionally instability is increasingly recognised as a major failure factor in primary and revision TKA.

Historically most of the first pure hinged TKA implants have shown disappointing results, due to early loosening based on excessive force transmission from the hinge mechanism to the bone-cement interface, used the use of all metal articulation, suboptimal instrumentation or design. Consequently a hinged design was abandoned by most US surgeons. However, some European centres continued with the use of some early European designed pure- and rotating hinged implants.

Although most indication in primary TKA can be solved with modular non- or semi-constrained implants, an adequate balancing might require a relevant soft tissue release or reconstruction with allografts. This consequently increases the complexity and operative time with less predictable results in the elderly patient with principal less healing potential, desirable early post-operative full weightbearing and full range of motion.

Thus potential indications in the elderly for a rotating- or pure hinged implant in primary TKA include:

1. –

   Complete MCL instability

2. –

   Severe varus or valgus deformity (>25°) with necessary relevant soft tissue release

3. –

   Relevant bone loss with insertions of collaterals

4. –

   Gross flexion-extension in balance

5. –

   Post-traumatic with distal femur or proximal tibia fracture

6. –

   Stiff knee

7. –

   Severe osteoporosis in the old patient

8. –

   Post infectious for a one staged implantation with specific antibiotics in cement

While some authors showed excellent survival rates in of 96% after 15 years in primary TKA, some recent studies revealed high complication rates of up to 25%, including a high infection rate of 2.9%. This remains inconsistent with our clinical results in primary TKA, which revealed an overall survival rate in patients over 60 years of 94% after 13 years, while patients < 60 years revealed a survival rate of only 77%. Correlation between survival rate and deformity revealed in varus alignment a survival rate of 97%, whereas in valgus only a rate of 79%. Consequently we strictly reserve a rotational hinge for patients > 60 years with a combined varus alignment, whereas in severe valgus deformities a pure hinged should be used for our implant design.

Limitations of most hinged implants are relatively rare. In our hands the main limitation is hyperextension and weak extensor mechanism, because this leads to early loosenings.