MR imaging of intra- and periarticular cyst-like lesions of the knee joint in workers with occupational kneeling

Introduction
The knee joint is affected by a significant impact during activity and biomechanical studies have showed that contact forces increase considerably during deep knee flexion with a significant stress concentration located in the postero-medial part of the joint. Direct and indirect loading during kneeling work could therefore be a predisposing factor in the development of both intra- and periarticular disorders. The objective of the study was to determine the risk of intra- and periarticular cyst-like lesions including bursitides of the knee joint in occupational kneeling.

Methods
MR imaging (1.5 Tesla) of both knees (n=282) was conducted in 92 male floor layers and 49 male graphic designers (referents), with a mean age of 55.6 years (range 42-70 years). Associations between cyst-like lesions and occupation were analysed by logistic regression, adjusted for age, body mass index, knee injuries, and knee-straining sports. Additionally, the relationship between cyst-like lesions and knee complaints, and trade seniority were analysed.

Results
Floor layers had a significantly higher prevalence of cyst-like lesions in the posterior part of the knee (subgastrocnemius, semimembranosus-gastrocnemius bursitides, femoral metaphysis cysts) compared to graphic designers (OR 2.70, 95% CI 1.50-4.84), and a higher prevalence of cystic lesions along the popliteus tendon (OR 2.17, 95% CI 0.99-4.77). The prevalence of cystic lesions in the anterior part of the knee (prepatellar, infrapatellar, anserine bursitides) was low among floor layers (8.7%) and there were no significant difference between the trade groups. Knee complaints were most frequently associated with cysts along the anterior cruciate ligament, and there were no clear dose-response relationship between cyst-like lesions and trade seniority.

Discussion
This is the first MRI study to assess the relationship between occupational kneeling and intra- and periarticular cyst-like lesions of the knee joint. Results indicate that occupational kneeling increases the risk of cyst-like lesions in the posterior part of the knee joint.