Introduction

Revision implants with long stem extensions are routinely implanted in revision TKAs, but they involve more bone loss. The present study was designed to evaluate the possibility of implanting routinely primary implants instead of revision implants during revision TKAs.
The hypothesis of this study will be that the survival rate of primary TKAs implanted for revision cases will not be negatively impacted in comparison to revision implants.

Material And Methods

All patients undergoing a TKA exchange for any reason between January 2013 and December 2017 were included. All patients were operated on by two senior surgeons experienced with revision TKA. The target for reimplantation was: neutral mechanical alignment, orthogonal position of both implants in anteroposterior and lateral planes, restoration of the joint line within 2 mm of the native one, medial and lateral gaps in flexion and in extension less than 5 mm. All these parameters were controlled by a navigation system. Bone loss was filled by bone allografting and/or metal augments without increasing bone defects by additional resection. The smallest implant was chosen, which allowed primary fixation of both implants and graft/augment.
Information about follow-up was collected from the individual patient files. All patients were recalled for clinical and radiological examination. The survival curve was plotted.

Results

158 patients were included: 96 women and 62 men, with a mean age at surgery of 71 ± 10 years. The mean body mass index was 31.6 ± 6.72 kg/m². Reasons for revision were infection (65%), aseptic loosening (13%), implant malposition (10%), and instability (6%).
11 cases were reimplanted with a smaller implant than the implant removed (Group A). 37 cases were reimplanted with the same size of implant than the implant removed (Group B). 31 cases were reimplanted with a longer implant than the implant removed for only one tibial or femoral component (Group C), and 79 cases were reimplanted with a longer implant than the implant removed for both components (Group D). There was no significant difference between all groups for demographic data: age, gender, body mass index, ASA score. Bone defects were significantly larger in group D than in all other groups.
The survival rate of the group A was 100% at 5 years. The survival rate of the group B was 96% at 5 years. The survival rate of the group C was 94% at 5 years. The survival rate of the group D was 92% at 5 years. The differences were not statistically significant.

Discussion

Reimplantation of a TKA smaller or with the same size than the removed implant was possible in 30% of the cases, without a negative impact on the survival rate after 5 years. Both tibial and femoral extension stems were necessary only in 48% of the cases. Navigation offers the possibility to decrease significantly the size of the implants during TKA revision. This might allow preserving bone stock for a possible repeat revision, especially in cases of infected TKA where the failure rate is significantly higher.