The lateral joint space width can be measured reliably with Telos valgus stress radiography in medial knee osteoarthritis.

To examine the reproducibility of valgus stress radiographs with the Telos stress device for assessment of lateral compartment degenerative changes in patients with medial osteoarthritis of the knee. A prospective reliability study was performed. Seventy-nine patients (80 knees) were included, and standardized valgus stress radiographs were obtained using the Telos stress device. Osteophytes and joint space narrowing (JSN) were graded using the OARSI (Osteoarthritis Research Society International) classification, and the joint space width (JSW) was measured in millimeters. Reproducibility was determined as intra-and inter-rater reliability and test-retest reliability. Weighted kappa was used to determine the reliability of osteophyte and JSN grading, and the intra-class correlation coefficient for JSW. Grading of osteophytes had an intra- and inter-rater reliability ranging from 0.40 to 0.83 on the medial side and ranging from 0.39 to 0.87 on the lateral side. Grading of medial JSN had an intra- and inter-rater reliability ranging from 0.62 to 0.84, and grading of lateral JSN had an intra- and inter-rater reliability ranging from 0.32 to 0.65. Intra- and inter-rater reliability of JSW ranged from 0.84 to 0.98 on the medial side, and from 0.59 to 0.89 on the lateral side. Test-retest reliability of JSW of the medial and lateral side ranged from 0.69 to 0.92. Standardized valgus stress radiographs taken with the Telos stress device are a reliable supplement in the assessment of medial OA of the knee. Evaluation of the lateral compartment on valgus stress radiographs is most reliable with measurement of the lateral JSW.