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Objectives and questions: The posterolateral corner (PLC) of the knee is a key stabilizer of varus, rotational, and posterior knee stability. Open anatomic reconstruction is an established treatment for high-grade PLC injuries, whereas clinical data on the all-arthroscopic anatomic reconstruction remain limited. The purpose of this prospective study was to compare clinical, functional, and radiological outcomes after all-arthroscopic versus open anatomic PLC reconstruction at a minimum of 36 months follow up.

Material and methods: This prospective cohort study included patients with chronic (>6 weeks) combined PLC and posterior cruciate ligament (PCL) injuries classified as Fanelli type B/PoLIS LI-B treated between January 2019 and December 2021. Patients were block-randomized to arthroscopic anatomic PLC reconstruction or open reconstruction. Standardized clinical follow-up was performed at a minimum of 36 months. Primary outcomes included Lysholm and subjective International Knee Documentation Committee (IKDC) scores and objective posterior stability assessed by posterior drawer and stress radiography (side-to-side difference). Continuous variables are reported as median and interquartile range (IQR). Statistical analysis used Welch’s t-tests or Mann–Whitney U tests (p<0.05). Continuous variables are reported as median and interquartile range (IQR).

Results: Twenty-four patients (arthroscopic n=13, open n=11) were evaluated at a median follow-up of 49.9 months. Arthroscopic reconstruction required shorter operative time (134 [120–144] vs. 170 [142.5–194.5] minutes; p=0.024). At 36 months, functional outcomes were comparable between groups, with similar Lysholm scores (93.0 [81.0–94.0] vs. 94.0 [83.5–94.5]; p>0.05) and IKDC scores (80.5 [63.2–90.8] vs. 80.5 [71.9–91.4]; p>0.05). Posterior stability was equally restored, with comparable posterior drawer side-to-side differences (2.0 [1.7–2.7] vs. 1.0 [0.5–2.5] mm) and stress radiography values (2.7 [1.3–3.4] vs. 3.3 [2.0–5.2] mm; all p>0.05). No perioperative complications occurred.

Discussion and conclusions: Both all-arthroscopic and open anatomic PLC reconstruction provide durable restoration of knee stability with comparable clinical and functional outcomes at 36-month follow-up in chronic Fanelli B injuries. When performed by experienced surgeons, the all-arthroscopic technique represents a safe minimally invasive alternative and is associated with shorter operative time.