The Ultrasound Verification of Compression Ischemic Neuropathy of the Infrapatellar Nerve in Patients with Grade II–III Knee Osteoarthritis

Abstract

Background / Objective. To perform a detailed ultrasound (US) analysis of pathologically altered periarticular soft tissue structures in the medial compartments of the knee in patients with grade II–III knee osteoarthritis (OA) and to assess the relationship of these changes with anterior medial knee pain. Materials and Methods. A prospective randomized single‑center study enrolled 82 patients. The main group (n=42) included patients with grade II–III OA, varus/valgus deformity and anterior medial knee pain; the control group (n=40) comprised patients with grade 0–I OA without pain. All participants underwent physical examination (Tinel sign), US assessment of superior femoral ligament (SFL) protrusion and anteroposterior dimension of the interfascial space (APDIFS) in the infrapatellar nerve (IPN) projection, numeric pain rating scale (NRS), and PainDetect questionnaire. Results. The two groups did not differ significantly in age or sex; women predominated (>98%). SFL protrusion was significantly higher in the main group (7.2–13.8 mm vs. 2.5–6.8 mm, p≤0.05), while APDIFS was significantly lower (0–0.8 mm vs. 1.2–2.1 mm, p≤0.05). Based on SFL protrusion, a practical classification was proposed: type 0 (<7.0 mm) – minimal/no CIN symptoms; type 1 (7.0–10 mm) – episodic symptoms; type 2 (>10 mm) – persistent severe manifestations. Severe CIN was confirmed in 90.4% of type 2 patients (n=38). In 23 type 2 patients not responding to conservative treatment, US‑guided saphenous nerve block and subsequent radiofrequency ablation provided pain regression to 2–3 NRS points in 21 patients; 15 patients underwent total knee arthroplasty with complete pain resolution. Conclusion. Anterior medial knee pain in OA has a neuropathic origin due to IPN compression caused by SFL protrusion and interfascial space narrowing. US allows reliable verification of these changes, expands clinical interpretation of patient complaints, and helps to choose optimal diagnostic and therapeutic strategies.