**4. Articular cartilage imaging**

Advances in technology have allowed improved imaging of articular cartilage. These include more sensitive and specific magnetic resonance imaging (MRI) sequences. Further, the ability to both directly and indirectly analyze cartilage qualitatively and quantitatively and its biochemical composition has been enhanced with MRI techniques like dGEMRIC (delayed gadolinium-enhanced MRI of cartilage), T1-rho, T2 mapping, sodium imaging, and diffusion-weighted imaging.

#### **4.1 X-ray**

Standard radiographs should always be included in the workup of articular cartilage pathology. Generally speaking, the presence of diffuse arthritic change precludes most cartilage repair or restoration procedures. The 45 degree weight-bearing posteroanterior xray (Rosenberg view) (Figure 8) is the most accurate, sensitive and specific for detection of major degenerative changes in the tibiofemoral joint(Rosenberg, Paulos et al. 1988). However, x-ray is extremely important in analysis of the weight-bearing mechanical axis (Figure 8) of the lower extremity for those patients that are enrolled for cartilage surgery.

Articular cartilage defects in the medial compartment are at higher risk for progression if varus malalignment exists (and lateral compartment for valgus, as well)(Linden 1977; Hughston, Hergenroeder et al. 1984; Messner and Maletius 1996; Sharma, Song et al. 2001).

accounts not only for lesion area (cm2), but also depth, while Outerbridge does not. Osteochondritis dissecans lesions can also be classified according to a similar ICRS-OCD

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

system(Brittberg and Winalski 2003). This classification is based on lesion stability.

physical examination, with imaging and arthroscopic examination often required.

Advances in technology have allowed improved imaging of articular cartilage. These include more sensitive and specific magnetic resonance imaging (MRI) sequences. Further, the ability to both directly and indirectly analyze cartilage qualitatively and quantitatively and its biochemical composition has been enhanced with MRI techniques like dGEMRIC (delayed gadolinium-enhanced MRI of cartilage), T1-rho, T2 mapping, sodium imaging, and

Standard radiographs should always be included in the workup of articular cartilage pathology. Generally speaking, the presence of diffuse arthritic change precludes most cartilage repair or restoration procedures. The 45 degree weight-bearing posteroanterior xray (Rosenberg view) (Figure 8) is the most accurate, sensitive and specific for detection of major degenerative changes in the tibiofemoral joint(Rosenberg, Paulos et al. 1988). However, x-ray is extremely important in analysis of the weight-bearing mechanical axis (Figure 8) of the lower extremity for those patients that are enrolled for cartilage surgery. Articular cartilage defects in the medial compartment are at higher risk for progression if varus malalignment exists (and lateral compartment for valgus, as well)(Linden 1977; Hughston, Hergenroeder et al. 1984; Messner and Maletius 1996; Sharma, Song et al. 2001).

**3.3 Clinical presentation** 

**4. Articular cartilage imaging** 

diffusion-weighted imaging.

**4.1 X-ray** 

Therefore, surgical correction of tibiofemoral malalignment to neutral or overcorrection is recommended in conjunction with most cartilage surgery (Figure 8). Thus, in addition to standard radiographic workup (extension standing anteroposterior [AP], Rosenberg view, lateral, and Mercer Merchant views), the full-length bilateral hip-to-ankle x-ray allows calculation of mechanical axis of the limb and the necessary alignment correction.

Fig. 8. Left) Standing hip-to-ankle x-ray demonstrating mechanical axis of lower extremity (in medial compartment); Right upper) Rosenberg view (no evidence of OA); Right lower) Rosenberg view after high tibial osteotomy.
