This observational study will compare the clinical value of weight-bearing CT arthrography (WBCTa) with that for MRI in evaluating meniscal and cartilage lesions of the knee joint. The MRI Osteoarthritis Knee Score (MOAKS) and modified MOAKS for WBCTa will be used to compare findings between MRI and WBCTa of the knee while comparing with surgical measurements using the ICRS scoring system.

The study hypothesis is that meniscal and cartilage lesions may be missed by non-weight-bearing MRI, but detected by WBCTa.

Study Objectives:

Aim 1 Establish the accuracy of WBCTa and MRI for diagnosing knee cartilage and meniscal lesions in both surgical and non-surgical participants.

Hypothesis 1: Pre-operative cartilage and meniscal scoring on WBCTa is more accurate than MRI, in comparison with arthroscopic assessment.

Aim 2 Establish the accuracy of WBCTa for detecting persistent and recurrent meniscal root and radial tears not detected by MRI 6 months after meniscal repair (defined by diastasis of the repair or meniscal extrusion ≥3mm).

Hypothesis 2: Six months following meniscal repair, WBCTa detects persistent and recurrent meniscal root and radial re-tears not detected by MRI.

Study Type and Design: This cross-sectional, observational study will compare WBCTa with MRI to evaluate rate of detection of meniscal and cartilage lesions. The inter-rater reliability of WBCTa readings also will be assessed.

Inclusion Criteria:

• Male or female over 18 years of age with a knee MRI acquired in the previous 10 days to evaluate for suspected meniscal or cartilage pathology.
• Body mass index (BMI) ≤ 45 kg/m2
• Ability to stand with support without moving for at least 2 minutes.

Exclusion Criteria:

• End stage kidney disease
• Allergic to iodinated contrast material.
• Pregnancy
• Skin breakdown or rash at the knee joint which would prevent injection of the contrast.
• Any clinically significant degree of cognitive impairment or other condition, finding, or psychiatric illness at screening which, in the opinion of the investigator, affects their ability to ambulate to a sufficient degree and could compromise patient safety or interfere with the assessment of the safety of the study injection.
• Superficial or deep infection in or around the index knee joint or allergy to iodinated contrast media.
• History of inflammatory arthritis, meniscectomy, or end-stage OA

Participants will be recruited from orthopedic clinics as well as other musculoskeletal clinics that request knee MRI. Special efforts will be made to recruit the majority from orthopedic sports medicine clinical practices to include patients who are scheduled for arthroscopic meniscal repair of full-thickness radial tears of the posterior horn or body or root tears of the posterior horn after clinical MRI. There will be no exclusions based on sex or ethnic group.