Incidence of Leg-Length Discrepancy After Index Hinge Total Knee Arthroplasty.

BACKGROUND: Leg-length discrepancies are not commonly associated with total knee arthroplasty (TKA); however, hinge TKA is a complex form of knee reconstruction where functionality of all knee ligaments is replaced by the TKA construct. The purpose of this study is to evaluate the incidence of leg-length discrepancies after unilateral index hinge TKA and association with patient outcomes. METHODS: A retrospective review was performed of all patients who underwent unilateral index hinge TKA at a single academic institution from 1999 to 2019. Among 671 patients who underwent index hinge TKA, 188 (28%) had full-length standing anteroposterior hip-to-ankle radiographs available for review both preoperatively and postoperatively. All patients with a leg-length change ≥2 cm were also contacted with a standardized questionnaire to assess for complications. The mean age was 65 years, the mean body mass index was 33 kg/m2, and 52% were female. The mean number of prior surgeries was 2 (range, 0-12). RESULTS: The absolute mean and median change in leg lengths was 20 mm and 13 mm, respectively (range, 0-130 mm). Lengthening occurred in 119 (63%) patients compared with shortening in 69 (37%) patients. An absolute change in leg lengths ≥1 cm was observed in 109 (58%) patients, ≥2 cm in 63 (34%) patients, and ≥5 cm in 15 (8%) patients. CONCLUSION: Large changes in the leg length are common after hinge TKA, likely secondary to altered soft-tissue constraints. Surgeons should be cognizant of potential changes in the leg length in the setting of hinge TKA and incorporate this into preoperative planning and patient counseling. LEVEL OF EVIDENCE: Level IV, therapeutic.