The effects of over- and under-stuffing the anterior knee compartment in primary TKA: A systematic review

Up to 20% of patients remain dissatisfied following total knee arthroplasty (TKA), often due to anterior knee pain (AKP) and other patellofemoral complications. Several studies highlighted risks of over- or under-stuffing within the patellofemoral compartment, yet there are no standardised methods for their assessment, and their effects on patient-reported outcome measures (PROMs) remain unclear. The aim of this review was to synthesise and critically appraise all published studies that investigated effects of over- and under-stuffing the anterior compartment on PROMs following primary TKA.

The protocol for this systematic review followed PRISMA guidelines was registered on PROSPERO (July 2024), before electronic searches by two readers (C.K. and V.G.) using Medline and Scopus. The authors included clinical studies published in English, reporting a quantifiable method to assess the anterior compartment in TKA, with clinical and/or radiographic outcomes. The authors excluded in vitro or ex vivo studies, reviews or editorials, studies on revision TKA and studies with follow-up <1 year.

Searches returned 160 records, of which 14 met the eligibility criteria (10 retrospective and 4 prospective), representing 4404 knees in 3718 patients. The primary outcome was over-stuffing in five studies, which investigated its correlation with PROMs and/or AKP, while the primary outcome was under-stuffing in two studies. The PROMs reported were Western Ontario and McMaster Universities Osteoarthritis Index (eight studies), knee society score (six studies), knee injury and osteoarthritis outcome score (two studies), as well as Oxford knee score, forgotten joint score and Kujala scores (each one study). Only two studies used dynamic assessments, while 12 used static assessments. Only 3 of the 14 studies found significant effects of over-stuffing (by >5 mm) on PROMs.

Changes in anterior offset, particularly over-stuffing, may cause patellofemoral complications. Although it would be ideal to restore the anterior compartment, small deviations do not affect clinical outcomes. A threshold of 5 mm could represent the 'safe zone' for change in anterior offset in patients undergoing TKA.

Level III.