Articular cartilage injury can be caused by an acute injury that results in a focal chondral or osteochondral injury or chronic/subacute injuries or conditions that result in degenerative lesions. Damage to the chondral surfaces can occur in isolation or, as is often the case, in association with other intra-articular injury. The evaluating physician should maintain a high index of suspicion for chondral injury when evaluating the knee for any causes of pain, effusion, instability, or mechanical symptoms.

A thorough history should include details related to the onset of symptoms (traumatic or insidious), mechanism of injury, previous injuries and surgery, and symptom-provoking activities.

A thorough physical examination should evaluate formal alignment, abnormal gait, swelling, effusions, instability, meniscal symptoms, range of motion, strength, and neurovascular abnormalities. Crepitus, catching, locking, or grinding can occur with focal irregularities of the articular surfaces. Diagnosis of all concomitant pathology is critical to formulate a successful, global treatment plan.

Radiographic workup should include posterior-anterior, weight-bearing, 45-degree plain films and patellofemoral, and non-weight-bearing lateral projections. Evaluation on plain films for joint space narrowing, subchondral sclerosis, osteophytes, and cysts should be performed. History and physical examination, along with these radiographs, are often all that is needed to make the appropriate diagnosis. Magnetic resonance imaging (MRI) can be valuable to assess the status of the knee ligaments and menisci but can underestimate the degree of cartilage abnormalities seen during arthroscopy (36). Use of 3.0-tesla magnets, cartilage imaging sequence techniques including fat-suppressed or fat-suppressed spoiled gradient-echo imaging, and balanced free precession steady-state sequences have improved detection and characterization of chondral injuries using MRI (6). Routine MRI sequences are typically sufficient to evaluate for subchondral abnormalities that may become useful findings during definitive decision making.

Arthroscopic debridement and lavage is a consideration for a first-line surgical intervention in a patient with a symptomatic articular cartilage injury. This treatment modality allows the surgeon to perform diagnostic arthroscopy to assess the chondral injury and the remainder of the joint. Patient expectations must be managed in that the results of this procedure can range from diagnostic to therapeutic due to the removal of degenerative debris, loose nonviable chondral fragments, and lavage of the associated inflammatory cytokines such as interleukin-1 and tumor necrosis factor-α (1). Care is taken to preserve intact, healthy articular cartilage. Arthroscopic lavage alone has been proven to provide at least short-term benefits in 50%-70% of patients (1,24). In a select group of highly active individuals, especially in season when return-to-sport time lines are critical, arthroscopic debridement may prove to be beneficial in the short term. In general, however, the results of arthroscopic debridement and lavage are often not durable and deteriorate over time, and the primary benefit that remains is the diagnostic information obtained to help guide future treatment decisions (Table 6.2) (10,32,33,54,58).

Fixation of a chondral lesion is predicated on the condition, size, shape, defect location, and adequacy of subchondral bone attached to the osteochondral fragment. Radiographic and MRI evaluation can help with the determination of many of these factors and appropriateness of this surgical option. Prior to fixation of the osteochondral fragment, both the fragment and defect must be prepared to create an adequate
healing milieu. The fragment must be reduced anatomically into its bed, and fixation may then be completed using either absorbable or nonabsorbable implants. Occasionally, bone graft augmentation is required for deeper cavitating lesions. Treating osteochondral lesions with the same considerations as a fracture nonunion will lead to more predictable healing. These factors include debriding fibrocartilage at the base of the lesion, microfracture augmentation of the base to promote bleeding, and rigid fixation with compression. Resorbable fixation placed without the intention to remove the implant should be buried to or beneath the level of the subchondral bone because these lesions can subside over time. Metallic implants removed at 6 to 8 weeks allow the opportunity to verify fragment healing and prevent the untoward effects of prominent hardware that can develop over time. Successful healing of the osteochondral fragment with the use of headless metallic cannulated screws has been reported in up to 90% of patients (1).

The goal of marrow stimulation techniques is the delivery of mesenchymal stem cell progenitors to the defect bed and the subsequent formation of a fibrocartilage-like repair tissue from these cells. This technique can be performed in a number of ways to include drilling, abrasion, and microfracture and always involves penetration of the calcified cartilage layer into the subchondral bone to allow the migration of progenitor cells to the articular surface. Because of the limited fill that may occur in some lesions, particularly larger ones greater than 2 cm², and the different structural and biomechanical properties of this fibrocartilage-like repair tissue (see earlier Basic Science section), the best results are typically achieved with relatively small defects in a low-demand patient population (1). Results of microfracture technique are summarized in Table 6.3.