The relationship between real-time ultrasound-detected extra-articular soft tissue pathologies and knee pain in osteoarthritis: a cross-sectional study

Objective Extra-articular soft tissue pathologies are relatively understudied in osteoarthritis (OA). We aimed to explore the relationship between structural pathology, sites of knee pain and knee pain severity, as determined using real-time ultrasound (US).

Methods Patients with painful knee OA received an US scan assessing a range of soft tissue structures at four quadrants (anterior, medial, lateral and posterior). US probe site tenderness (sono-palpation) was also assessed at each structure. Participants’ reported outcome measures were recorded, including sites of knee pain using the Knee Pain Map (using the same quadrant locations as structural pathology) and average numeric rating scale (NRS) for pain severity in the past week.

Results Fifty-four knees (26 men, BMI 31.5, mean NRS pain 5.4, 96% Kellgren–Lawrence 2/3) were included. Medial pain was the most frequently reported location. Semimembranosus tendon (SMT) hypoechogenicity, indicating tendinopathy, was the most frequent US finding (53%). However, there was no clear pattern between SMT pathology and knee pain location. Medial collateral ligament (MCL) and lateral collateral ligament (LCL) sono-palpation (reflecting clinical enthesitis) was more frequently observed in medial and lateral knee pain, respectively (43.2% and 52.9%). Higher NRS pain was significantly associated with MCL sono-palpation (1.41 NRS points; CI 0.47–2.36, p = 0.004) and Baker’s cyst sono-palpation (1.78 NRS points; CI 0.35–3.20, p = 0.016). A trend toward greater NRS pain was associated with US-detected patellar tendon pathology (1.1 NRS points; CI − 0.14–2.35, p = 0.08).

Conclusion This exploratory study highlighted the potential importance of extra-articular knee pathologies, particularly the collateral ligaments, in understanding OA knee pain location and severity.