summary Articular cartilage defects of the knee comprise of a spectrum of disease entities from single, focal defects to advanced degenerative disease of articular (hyaline) cartilage. Diagnosis generally requires an MRI to accurately assess the location of specific defects. Treatment can be nonoperative or operative depending on patient age, degree of symptoms and the size of the lesion. Epidemiology Incidence 5-10% of people > 40 years old have high grade chondral lesions Anatomic location chronic ACL tear anterior aspect of lateral femoral chondyle and posterolateral tibial plateau osteochondritis dissecans 70% of lesions found in posterolateral aspect of medial femoral condyle Etiology Pathophysiology mechanism of injury acute trauma or chronic repetitive overload impaction resulting in cartilage softening; fissuring; flap tears; or delamination the cause of OCD is unknown pathomechanics impaction forces greater than 24 MPa will disrupt normal cartilage cellular biology cartilage injuries have limited spontaneous healing and propensity to worsen over time Anatomy See Articular Cartilage Basic Science Classification Outerbridge Arthroscopic Grading System Grade 0 Normal cartilage Grade I Softening and swelling (noted with tactile feedback with probe) Grade II Partial-thickness defect with surface fissures (do not reach subchondral bone or exceed 1.5 cm in diameter) Grade III Deep fissures at the level of subchondral bone with a diameter more than 1.5 cm Grade IV Exposed subchondral bone ICRS (International Cartilage Repair Society) Grading System Grade 0 Normal cartilage Grade 1 Nearly normal (superficial lesions) Grade 2 Abnormal (lesions extend < 50% of cartilage depth) Grade 3 Severely abnormal (>50% of cartilage depth) Grade 4 Severely abnormal (through the subchondral bone) Presentation History commonly present with history of precipitating trauma some defects found incidentally on MRI or arthroscopy Symptoms asymptomatic vs. localized knee pain may complain of effusion, motion deficits, mechanical symptoms (e.g., catching, instability) Physical exam inspection look for background factors that predispose to the formation of articular defects joint laxity malalignment compartment overload motion assess range of motion, ligamentous stability, gait Imaging Radiographs indications used to rule out arthritis, bony defects, and check alignment recommended views standing AP, lateral, merchant views optional views semiflexed 45 deg PA views most sensitive for early joint space narrowing long-leg alignment views determine the mechanical axis CT scan indications better evaluation of bone loss findings used to measure TT-TG when evaluating the patello-femoral joint MRI indication most sensitive for evaluating focal defects views Fat-suppressed T2, proton density, T2 fast spin-echo (FSE) offer improved sensitivity and specificity over standard sequences dGEMRIC (delayed gadolinium-enhanced MRI for cartilage) and T2-mapping are evolving techniques to evaluate cartilage defects and repair Studies Laboratory may be used to rule out inflammatory disease Treatment Nonoperative rest, NSAIDs, physiotherapy, weight loss indications first line of treatment when symptoms are mild viscosupplementatoin, corticosteroid injections, unloader brace indications controversial may provide symptomatic relief but healing of defect is unlikely Operative debridement/chondroplasty vs. reconstruction techniques indications failure of nonoperative management acute osteochondral fractures resulting in full-thickness loss of cartilage technique treatment is individualized, there is no one best technique for all defects decision-making algorithm is based on several factors patient factors age skeletal maturity low vs. high demand activities ability to tolerate extended rehabilitation defect factors size of defect location contained vs. uncontained presence or absence of subchondral bone involvement basic algorithm (may vary depending on published data) femoral condyle defect correct malaligment, ligament instability, meniscal deficiency measure size < 4 cm2 = microfracture or osteochondral autograft transfer (pallative if older/low demand) > 4 cm2 = osteochondral allograft transplantation or autologous chondrocyte implantation patellofemoral defect address patellofemoral maltracking and malalignment measure size < 4 cm2 = microfracture or osteochondral autograft transfer > 4 cm2 = autologous chondrocyte implantation (microfracture if older/low demand) Surgical Techniques Debridement / Chondroplasty overview goal is to debride loose flaps of cartilage removal of loose chondral fragments may relieve mechanical symptoms short-term benefit in 50-70% of patients benefits include simple arthroscopic procedure, faster rehabilitation limitations problem is exposed subchondral bone or layers of injured cartilage unknown natural history of progression after treatment Fixation of Unstable Fragments overview need osteochondral fragment with adequate subchondral bone technique debride underlying nonviable tissue consider drilling subchondral bone or adding local bone graft fix with absorbable or nonabsorbable screws or devices benefits best results for unstable osteochondritis dissecans (OCD) fragments in patients with open physis limitations lower healing rates in skeletally mature patients nonabsorbable fixation (headless screws) should be removed at 3-6 months Marrow Stimulation Techniques overview goal is to allow access of marrow elements into defect to stimulate the formation of reparative tissue includes microfracture, abrasion chondroplasty, osteochondral drilling microfracture technique defect is prepared with stable vertical walls and the calcified cartilage layer is removed aggressive debridement with removal of subchondral plate may lead to osseous overgrowth awls are used to make multiple perforations through the subchondral bone 3 - 4 mm apart relies on formation of type 1 and 2 cartilage type 1 > type 2 cartilage protected weight bearing and continuous passive motion (CPM) are used while mesenchymal stem cells mature into mainly fibrocartilage benefits include cost-effectiveness, single-stage, arthroscopic best results for acute, contained cartilage lesions less than 2 cm x 2cm limitations poor results for larger defects >2 cm x 2cm does not address bone defects requires limitation of weight bearing for 6 - 8 weeks Osteochondral autograft / Mosaicplasty overview goal is to replace a cartilage defect in a high weight bearing area with normal autologous cartilage and bone plug(s) from a lower weight bearing area chondrocytes remain viable, bone graft is incorporated into subchondral bone and overlying cartilage layer heals. technique a recipient socket is drilled at the site of the defect a single or multiple small cylinders of normal articular cartilage with underlying bone are cored out from lesser weight bearing areas (periphery of trochlea or notch) plugs are then press-fit into the defect limitations size constraints and donor site morbidity limit usage of this technique matching the size and radius of curvature of cartilage defect is difficult fixation strength of graft initially decreases with initial healing response weight bearing should be delayed 3 months benefits include autologous tissue, cost-effectiveness, single-stage, may be performed arthroscopically Osteochondral allograft transplantation overview goal is to replace cartilage defect with live chondrocytes in mature matrix along with underlying bone fresh, refrigerated grafts are used which retain chondrocyte viability may be performed as a bulk graft (fixed with screws) or shell (dowels) grafts technique match the size and radius of curvature of articular cartilage with donor tissue a recipient socket is drilled at the site of the defect an osteochondral dowel of the appropriate size is cored out of the donor the dowel is press-fit into place benefits include ability to address larger defects, can correct significant bone loss/edema, useful in revision of other techniques limitations limited availability and high cost of donor tissue live allograft tissue carries potential risk of infection Autologous chondrocyte implantation (ACI) overview cell therapy with goal of forming autologous "hyaline-like" cartilage technique arthroscopic harvest of cartilage from a lesser weight bearing area in the lab, chondrocytes are released from matrix and are expanded in culture defect is prepared, and chondrocytes are then injected under a periosteal patch sewn over the defect during a second surgery benefits may provide better histologic tissue than marrow stimulation long term results comparable to microfracture in most series include regeneration of autologous tissue, can address larger defects limitations must have full-thickness cartilage margins around the defect open surgery 2-stage procedure prolonged protection necessary to allow for maturation Patellar cartilage unloading procedures Maquet (tibia tubercle anteriorization) indicated only for distal pole lesions only elevate 1 cm or else risk of skin necrosis contraindications superior patellar arthrosis (scope before you perform the surgery) Fulkerson alignment surgery (tibia tubercle anteriorization and medialization indications (controversial) lateral and distal pole lesions increased Q angle contraindications superior medial patellar arthrosis (scope before you perform the surgery) skeletal immaturity Matrix-associated autologous chondrocyte implantation overview example is "MACI" cells are cultured and embedded in a matrix or scaffold matrix is secured with fibrin glue or sutures results in Type I and Type II collagen benefits only FDA approved cell therapy for cartilage in the USA include ability to perform without suturing, may be performed arthroscopically limitations 2-stage procedure Expense