Functional Limb Length Preservation and Coronal Alignment Categories in Revision Total Knee Arthroplasty.

BACKGROUND: This study evaluated functional limb-length (LL) and coronal-alignment preservation after revision total knee arthroplasty (rTKA) relative to contralateral and pre-rTKA baselines, examining their association with patient-reported outcome measures (PROMs).

METHODS: We retrospectively reviewed 70 rTKA patients with pre- and post-rTKA full-length radiographs. Functional LL preservation was defined as ± 10 mm of the target. Patient-reported outcomes-including Knee injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS, JR) and Patient-Reported Outcomes Measurement Information System (PROMIS) Pain Intensity and Pain Interference-were compared across LL (shortened/preserved/over-lengthened) relative to contralateral/pre-rTKA baselines and coronal alignment (preserved/changed) categories. Indications included aseptic loosening (31.4%), instability (30.0%), arthrofibrosis (14.3%), periprosthetic joint infection (12.9%), and insert wear (11.4%).

RESULTS: The post-rTKA LL was preserved relative to the contralateral LL in 68.6% of the patients and pre-rTKA LL in 47.1%. Coronal alignment was preserved in 64.3%. PROM improvements were comparable across categories (P > 0.05). When referencing the contralateral limb, only the over-lengthened cohort achieved the minimal clinically important difference (MCID) across all PROMs at three months; at one year, all cohorts achieved MCID for KOOS, JR, and pain intensity, but missed the pain interference threshold. When referencing the pre-rTKA state, preserved and over-lengthened cohorts achieved MCID across all PROMs at three months; at one year, all cohorts sustained the MCID across all three outcome domains. The preserved alignment cohort achieved MCID across all PROMs, while the changed alignment cohort missed the threshold for pain interference.

CONCLUSIONS: Revision TKA preserved functional LL and coronal alignment in approximately two-thirds of cases. Although PROMs were comparable among categories, early MCID achievement was associated with over-lengthening relative to the contralateral limb and avoiding shortening relative to the pre-rTKA state. At one year, preserving pre-rTKA coronal alignment provided superior pain interference relief, sustained only when evaluated relative to the pre-rTKA baseline.