**3.3 Clinical presentation**

Patients with focal chondral defects of the knee may be asymptomatic. Articular cartilage is an aneural tissue. Thus, the presence of a defect does not necessarily produce pain. However, patients with full-thickness chondral defects may demonstrate major limitations in pain and function, according to the Knee Injury and Osteoarthritis Outcomes Score (KOOS)(Heir, Nerhus et al. 2010). In fact, the KOOS quality of life subscore for patients with focal cartilage defects were not significantly different from those patients with OA enrolled for knee osteotomy or arthroplasty. Further, patients with cartilage defects had significantly worse overall KOOS and all KOOS subscores versus patients with anterior cruciate ligament (ACL) deficiency. Patients with chondral defects may also have other concurrent extra- and intra-articular confounders, which make the diagnosis of chondral pathology difficult. Nevertheless, patients with symptomatic chondral defects generally complain of activityrelated pain located in a region that correlates with the intra-articular location of the defect for tibiofemoral defects. Patellofemoral lesions generally cause anterior knee pain, worse with prolonged knee flexion or stair climbing. The exact mechanism to account for pain due to pathology in an aneural tissue is not completely understood. However, stimulation of nociceptive fibers in the subchondral bone is one current accepted theory(Mach, Rogers et al. 2002). Further, inflammatory cartilage breakdown products may cause joint effusion with capsular distension in conjunction with synovitis, both leading to joint pain. Patients with chondral flaps may also present with mechanical symptoms such as catching or clicking. Clearly, diagnosis of chondral pathology is complex and requires a thorough history and physical examination, with imaging and arthroscopic examination often required.
