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

OBJECTIVES: 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. METHODS: Design : Retrospective review Setting: Single academic Level-I trauma center Patient Selection Criteria: 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. Outcome Measures and Comparisons: 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. RESULTS: 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. CONCLUSIONS: 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 OF EVIDENCE: Level III