Can Treatment of Periprosthetic Distal Femur Fractures Result in Iatrogenic Flexion Instability in Previously Stable Total Knee Arthroplasty? A Single-Center Retrospective Review of 73 patients.

Abstract

To describe outcomes in patients with periprosthetic distal femur fractures (PPDFF) who underwent retrograde intramedullary nailing (rIMN), including subsequent revision total knee arthroplasty (TKA) and subjective and/or objective evidence of flexion instability (FI). The hypothesis of this study is flexion instability can occur following rIMN in cruciate-retaining total knee arthroplasty (CR-TKA), possibly due to iatrogenic PCL damage. Design: Retrospective review. Single academic Level-I trauma center. All patients who sustained a PPDFF, OTA/AO 33A, between 2008-2022 who were treated with a rIMN by a trauma fellowship trained orthopedic surgeon with >3 months follow-up were included. Patients with < 3 months follow-up, treated with locked plating, nail-plate combinations or whose surgery was not performed by a trauma fellowship trained orthopedic surgeon were excluded. The primary outcome was rate of revision TKA for instability. Secondary outcomes included radiographic measurements (posterior tibial translation, femoral component ratio, and final coronal and sagittal alignment) and complications. 73 patients (61, 83.6% female) were included. Average age was 73.8 ± 12.3 years and median length of follow-up was 294 days (IQR: 156, 411 days). There were 4 (6.2%) revision TKA, performed; 3 CR-TKAs and 1 PS-TKA. All three CR-TKA knees revised were for instability. There were 16 (20.5%) complications requiring return to the OR. Median time to return to OR was 204.5 days (IQR of 135-390.25 days). The most common indication was irritable hardware (n=4, 5.5%) and nonunion (n=4, 5.5%) followed by primary instability (n=3, 4.1%). All 3 nonunions underwent revision ORIF. Five (6.8%) patients reported symptoms and 7 (9.6%) had positive physical exam findings suggestive of FI. There were 22 (30.1%) patients with radiographic posterior tibial translation. This retrospective review suggests that flexion instability secondary to damage of the posterior cruciate ligament is a potential complication following retrograde intramedullary of periprosthetic distal femur fractures. Level III.