BACKGROUND

Certain clinical or adverse intraoperative situations require the use of increased constraint in primary total knee arthroplasty (TKA). These include significant angular deformities causing incompetent collateral ligaments, or inadvertent intraoperative injury to collateral structures as well as the inability to achieve a balanced flexion and extension gap. Clinical success has been described with the use of constrained condylar knee arthroplasty in the primary setting in these situations. Traditionally, increasing constraint has been in conjunction with intramedullary stems, referred to as stemmed constrained condylar knees (SCCK); however, some devices provide an intermediary option by increasing constraint without the use of stems, herein referred to as nonstemmed constrained condylar knees (NSCCK). The aim of this study was to compare the clinical outcomes of both these devices in primary TKA in terms of revision rates and change in outcome measures over the follow-up period.

METHODS

Between 2007 and 2012, 85 SCCKs and 354 NSCCKs were identified in our institutional registry database performed in the primary TKA setting with minimum 2-year clinical outcome measure follow-up. Baseline demographic information, as well as Western Ontario and McMaster Universities Arthritis Index (WOMAC) and Lower Extremity Activity Scale (LEAS) were collected preoperatively at 2-year follow-up. Revision data were also collected.

RESULTS

Both groups showed substantial improvement in WOMAC scores (pain, stiffness, and function), and LEAS at 2 years postoperatively compared with baseline, although the changes in scores were not statistically significant. One of 85 SCCKs (1.17%) was revised for infection, whereas 9 of 354 NSCCKs (2.54%) were revised (6 for mechanical complications, eg, loosening, 2 for periprosthetic fracture, and 1 for infection).

CONCLUSION

Both cohorts demonstrated improvement in clinical outcome measures at 2-year follow-up. None of the SCCKs performed in the primary setting were revised for a mechanical complication. Although both groups had overall low revision rates, there was trend toward a higher revision rate with NSCCKs. Many of these were revised for component loosening. In summary, when necessary, constrained options in the primary TKA setting provide excellent clinical outcome at short-term follow-up. However, constrained constructs with stemmed fixation may provide more rigid fixation and be less susceptible to mechanical failure.