Many of these injuries will include the medial or lateral femoral condyle, in both OCD and acute cartilage injury.

The etiology of OCD is not known, although many theories have been suggested, including trauma, vascular anomaly/injury, overuse or repetitive stress injury, genetic predisposition, etc.

Acute traumatic injuries can cause displacement of preexisting OCD lesions or the development of acutely displaced cartilage fragment on otherwise normal bone and cartilage structures.

The natural history of OCD runs a variable course.

Many patients, especially those who are skeletally immature, with significant growth remaining, have good potential for healing with appropriate activity modification, and in select cases, subchondral bone drilling.

Patients close to or beyond skeletal maturity have a worse prognosis for healing with activity modifications.

The older patients may not respond to less invasive surgeries such as subchondral bone drilling.

Patients with acute, traumatic cartilage injury with displaced fragments may be candidates for surgery.

Cases in which the cartilage damage is so severe that the fragment is unsalvageable, osteochondral defects may be addressed with a variety of cartilage restoration procedures.

Review of previous imaging studies (typically radiographs and/or magnetic resonance imaging [MRI]), operative reports, and arthroscopic imaging is critical in the evaluation of these patients. In many of these patients, previous surgery and arthroscopic imaging have been performed. Reviewing these studies can provide useful information about the location, depth, and perimeter of the lesion (FIG 1).

The presence of a “kissing lesion” on the opposite articular surface is important, as its presence may alter or preclude certain allograft approaches. Significant osteoarthritis, especially if more diffuse, rather than focal, may be a contraindication to osteochondral allograft use.

Patient factors: Individual patient factors, including patient preferences, alignment of the lower extremities, social resources, work/job demands, and medical comorbidities must be considered when evaluating these patients. Some research has also shown factors such as age older than 30 years and a history of two or more previous surgeries on the joint are associated with poorer outcomes.¹⁴

In patients with more advanced osteochondral pathology, the history frequently includes episodes of pain, mechanical symptoms, giving way, and swelling. Both traumatic injuries and patients with OCD may present after months or years of milder symptoms.

The most valuable tools for evaluating osteochondral lesions are high-quality imaging studies, the most basic of which is the weight bearing, plain radiograph of the knee. The authors prefer standing anteroposterior, tunnel, lateral, and Merchant views.

A wealth of information can be gleaned from properly performed radiographs, including the approximate dimensions and location of the lesion and the precedence of diffuse osteoarthritis. Long-standing radiographs are valuable in assessing limb length discrepancy and malalignment.

MRI provides a more detailed look at the condition of the lesion and surrounding cartilage. The MRI may also reveal kissing lesions, in which there is chondral injury on opposing articular surfaces. Careful inspection for malalignment, kissing lesions, or signs of more diffuse cartilage injury is essential, as these factors may change the surgical management of the patient.¹⁴ The lesions are less common in younger patients but may increase in frequency in older patients or those with a prolonged history of symptoms.

Nonoperative management may consist of activity modifications, maintenance of ideal body weight, and low-impact conditioning programs.

Significant mechanical symptoms may not be addressed with this approach.

With regard to stable OCD lesions, many procedures are designed to promote healing, including subchondral drilling, both antegrade^{11, 15, 24} and retrograde.^{26, 28} For unstable lesions, drilling in combination with internal fixation, bone grafting, and other procedures may promote healing. Excision of loose fragments may provide reasonable short-term results, but long-term outcomes are generally poor.^{17, 18} Although less invasive procedures may improve mechanical symptoms, they may not address the long-term impact of the cartilage or bone defect in a weight-bearing region of the joint.

For patients in whom native cartilage and bone cannot be successfully repaired, or those that have failed previous attempts at repair of native tissue, osteochondral allograft is one option to be considered. Other options to be considered for cartilage loss are outlined in the following text, although some of them may have limitations especially in larger lesions and those with deep subchondral bone loss.

For patients that have focal, full-thickness cartilage defects, several techniques can be used to restore the joint cartilage surface. These techniques include the following: