Similar outcomes with usage of varus valgus constrained and a rotating hinge knee: A review of 108 cases

Abstract

ObjectiveConstraint is defined as the effect of elements knee implant designs that provide the stability needed in the presence of a deficient soft tissue envelope. The prosthesis with the minimal acceptable constraint generates maximal functional outcome is the general dictum. Varus valgus constrained (VVC) and rotating hinge knees(RHK) are implants which comprise the constraint group with later having higher constraint. However there are no clearcut guidelines of usage of each of the above implant group and literature is sparse in comparison of outcomes of the above 2 groups. This study was done with aim to better delineate indications and compare outcomes of the VVC and RHK implants. MethodsWe evaluated 56 varus valgus constrained and 52 rotating hinge total knee arthroplasties. The indication of usage and basic demographic data was collected. Clinical and functional outcomes were calculated and compared between the implant groups. ResultThe mean final range of motion (ROM) was 104.58° in RHK group and 108.75 in the VVC group. The final mean Oxford knee score (OKS) was 31.23 in the RHK group and 32 .44 in the VVC group. The final mean Knee society score (KSS) was 81.69 in RHK group and 83.79 in the VVC group. There was no statistically significant difference in the 2 groups when final mean ROM, OKS and KSS were compared. Thus the two implant groups gave similar clinical and functional outcomes. The number of revision were similar in RHK (4/52) and VVC (4/56) group. ConclusionThus similar outcomes were reported in our study when both implant groups were compared. We recommend usage of RHK in revision of infected Total knee arthroplasty, in cases with any amount of flexion extension mismatch and in cases where there is doubt regarding partial or full incompetence of collaterals. The use of VVC should be restricted to Osteoarthritis (OA) with gross deformities. However long term randomised clinical trial is needed to better define longevity and complications in the 2 implant groups.