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The dynamic structure and function of articular cartilage is explored in detail in this chapter. Emphasis is placed on the ultrastructure of cartilage and how this provides for its remarkable physical properties.

Many factors influence the evaluation of outcome following cartilage procedures. The outcome is influenced by the patient, the nature of the lesion, the procedure performed, and the outcome measure utilized. All of these factors must be independently considered in great detail to appropriately evaluate any treatment or procedure for a cartilage lesion. Each of these is reviewed in this chapter.

The ability of noninvasive magnetic resonance imaging (MRI) to obtain reproducible, accurate images of cartilage has enabled early detection of cartilage lesions and provides clinically relevant information when planning cartilage repair. With appropriate pulse sequencing, MRI depicts not only the integrity of the surface cartilage, which would be seen at arthroscopy, but also that of the subchondral bone, which would not be visualized at arthroscopic inspection. This information is vital when planning for complex, sometimes multistage, techniques that require careful size delineation of the cartilage lesion and evaluation of the surrounding subchondral bone. In addition to aiding in preoperative planning, these techniques offer an important objective evaluation of cartilage repair to be correlated with the more subjective clinical outcome instruments and provide insight into the biology of the repair process. Finally, newer matrix assessment techniques will disclose information about the ultrastructure of these individual cartilage repair procedures.

The treatment of isolated articular cartilage lesions remains a difficult clinical problem. Cartilage has a poor intrinsic capacity for repair. Untreated lesions persist indefinitely and can predispose affected joints to pain and dysfunction. Fortunately, the treatment options for these lesions continue to evolve and expand. However, a validated approach to the treatment of such lesions remains elusive. Decision making in these circumstances is highly variable between practitioners. We describe an approach to the patient with a symptomatic articular cartilage lesion. Consideration of certain parameters, including lesion size, lesion location, patient demand, body mass index, limb alignment, and treatment history should be considered when selecting a surgical approach. In addition, surgeons should understand the physiology of the cartilage repair method employed and how this relates to the postoperative rehabilitation program. Cartilage repair strategies are classified into the following: enhancement intrinsic repair response, cell-based, scaffold-based, cell plus scaffold-based, and whole tissue transplantation. A treatment algorithm based on lesion size, patient demand, and treatment (primary vs secondary) is presented.

Chondral injuries represent a spectrum of disorders that include both partial and full-thickness defects. The natural history of full-thickness cartilage lesions remains unclear. Repair or regeneration of normal functioning hyaline cartilage, in the mature adult, has yet to be confirmed following known cartilage restoration procedures and treatments. As such, the initial management of these lesions is largely nonoperative. Those nonoperative treatment modalities that are available to clinicians include physical therapy, activity modification, bracing, patient education, topical medications, systemic medications, and intra-articular medications. However, it is important to consider that patient responses to these initial treatment modalities are often unpredictable and idiosyncratic. Evidence-based treatment protocols and reliable predictors for identifying efficacious treatment strategies have yet to be established in this group of patients. Given this lack of data, the goals of therapy should be focused on reducing pain and inflammation, increasing flexibility, increasing strength, and optimizing function for a timely return to activities of daily living. This chapter discusses each of these interventions in detail. Current literature and controversies are explored. Ultimately, nonoperative modalities can be effective at relieving pain and improving function in affected patients and as such should be a first-line approach in the management of these lesions.

Small full-thickness chondral injuries of the knee can be treated by marrow stimulation techniques. In the United States, the technique used most frequently to address posttraumatic femoral cartilage defects is microfracture arthroplasty. This chapter reviews the history, underlying theory, technique, and outcomes of microfracture and other marrow stimulation techniques.

A new biomaterial for cartilage repair has been developed and investigated in animal studies and in a clinical cohort. The biomaterial is a physiological solution of chitosan (a natural polysaccharide containing glucosamine residues) in a buffer containing glycerol phosphate (GP). The soluble and physiological characteristics of this polymer solution permit its combination with freshly drawn autologous whole blood to form a hybrid polymer-blood mixture that can be applied to cartilage and bone surfaces, to which it adheres and solidifies as a polymer-stabilized clot. Histology and electron microscopy analysis of in vitro-generated chitosan-GP/blood clots revealed the chitosan component to be dispersed among the blood components, to interact closely with platelets, and to impede platelet-mediated clot contraction, thereby maintaining a voluminous bioactive and adhesive clot at the site of application. Experiments in microdrilled cartilage lesions in adult rabbits comparing chitosan-GP/blood clots to controls (microdrilled only) highlighted the ability of chitosan-GP/blood clots to recruit more host cells and to increase subchondral vascularization and bone-remodeling activity during acute and intermediate stages of repair. This led to the establishment of more hyaline repair cartilage that was integrated with a porous subchondral bone plate. Microfractured cartilage defects in adult sheep treated with chitosan-GP/blood clots resulted in a statistically significant increase in tissue fill with a greater proportion of hyaline cartilage compared to controls (microfracture only). Patients with femoral condyle cartilage lesions have received chitosan-GP/blood implants to resurface articular cartilage as part of a compassionate use program for medical devices. Results to date suggest safety and clinical benefit of this approach that is free from both donor site morbidity and suture damage to healthy adjacent cartilage. This single-intervention approach is now the subject of a multicenter, randomized comparative clinical trial designed and initiated to investigate cartilage repair resulting from treatment with chitosan-GP and microfracture vs microfracture alone.

Focal cartilage defects of knee constitute a challenging clinical problem for the orthopedic surgeon. These injuries typically occur in active patients, can result in debilitating pain, and have a limited capacity for spontaneous healing. Autologous osteochondral transplantation has been advocated as a treatment for focal cartilage defects, as this surgical technique can restore hyaline cartilage architecture and, to some degree, the structural support of underlying subchondral bone. The short- and intermediate-term outcomes following this procedure are encouraging. This chapter serves to review the indications, surgical technique, and rehabilitation protocol for autologous osteochondral transplantation of the knee and provide a comparison of its clinical results to other cartilage restoration procedures.

Cartilage repair is a challenging clinical problem because once adult cartilage sustains damage, whether traumatic or pathological, an irreversible, degenerative process can occur (1) . The resulting defects may lead to osteoarthritis (2–4) . Attempts to repair articular cartilage have included implantation of artificial matrices, growth factors, perichondrium, periosteum, and transplanted cells (5) , but to date no reliable, reproducible approach has been identified. Furthermore, repair tissue frequently lacks the physical structure and mechanical properties necessary to ensure long-term efficacy (6) . It is reasonable to hypothesize that the inferior mechanical properties of the repair tissue are partially caused by inadequate support during healing.

Currently, autologous chondrocyte implantation (ACI) is ideally indicated for symptomatic ICRS grade III-IV lesions greater than 2 cm^2 along the femoral condyle or trochlear regions. High-demand patients between the ages of 15 to 55 years of age with excellent motivation and compliance potential should be chosen. Lars Peterson assessed his first 101 patients at intermediate to long-term follow-up. Good to excellent clinical results were seen in 92% of the isolated femoral condylar lesions, while these results decreased to 67% in patients with multiple lesions. Osteochondritis dissecans lesions demostrated 89% good-to-excellent results, and in contrast to the initial series patellar lesions did relatively well with 65% good-to-excellent results. Histologic analysis of the matrix in 37 biopsy specimens assessing for type II collagen showed a correlation between hyaline-like repair tissue and good-to-excellent clinical results. Scott Gillogly evaluated 112 patients with 139 defects treated with the ACI procedure over a 5-year period of time. Average size of the defect was 5.7 cm^2 with over 60% of patients having failed at least one prior procedure. According to the clinician evaluation portion of the Modified Cincinnati Scale 93% demonstrated good-to-excellent outcomes, while the patient evaluation portion demonstrated 89% good-to-excellent outcomes. This chapter will describe the technique of ACI first reported by the senior author (LP) in 1994, as well as additional methods to deal with the various complex problems that can arise during these demanding procedures. A further review of the current literature supporting this techique as well as those studies that compare ACI to other accepted treatment options will be undertaken as well. In addition, we will review and discuss developing literature supporting current use of various matrices in combination with autologous chondrocytes to treat this difficult patient population.