What’s the Claim?
A case series from a large institutional registry found that among patients who had a history of polio and who underwent TKA either in the affected or the unaffected limb, periprosthetic fractures and knee stiffness were the most-common complications, the latter often being severe — only 69% of patients achieved ≥90° of flexion. Instability also was a problem, despite 25% of the patients receiving either a varus-valgus constrained knee or a rotating hinge implant.
Survivorship free from reoperation at 10 years was 83% (95% CI 74% to 93%), with no difference between the affected and unaffected limbs. We’ll come back to the importance of those wide 95% CIs in a moment.
How’s It Stack Up?
This is by far the largest single-center experience on the topic. A pooled analysis in a systematic review of six other studies found similar-looking survivorship percentages and a similar proportion of TKAs that were performed using constrained implants. That these studies reinforced one another increases our confidence in the generalizability of their findings.
Interestingly, in that systematic review, hyperextension was common before surgery (observed in 44% of patients). Of those, it recurred postoperatively in 36%. As you know, hyperextension is hell on TKA implants. The current series doesn’t mention that complication, other than to caution readers to avoid it by increasing implant constraint and decreasing the distal femoral resection (recommendations the systematic review also made). Hyperextension, stiffness, and fractures make a tough needle to thread.
And as sobering as these findings were, they’re probably a best-case scenario — 7% of the patients were lost to follow-up before two years, but the series was accumulated over a 20-year span going back to 2000. Someone who had surgery in 2000 and had two years of follow-up — but no more — hadn’t been seen in 17 years when the authors here tallied things up. It’s fair to say that patient is lost, and it’s reasonable to assume that missing patients are more likely to have had complications. For this reason, the large 95% CIs are important — don’t just look at the point estimate, but also at the lower bound of the 95% CI range.