Michael J. Angel, MD *Nicholas A. Sgaglione, MD Christian Lattermann, MD
Articular Cartilage Lesions
Recent trends indicate that a rise in physical activity among adult patients of all ages has led to an increase in symptomatic osteochondrol lesions that require treatment. In one study, cartilage damage was noted in approximately 63% of patients undergoing knee ar- throscopy.1Similarly, chondral or osteochondral defects
were found in 610 of 1,000 patients undergoing knee arthroscopy, most often in the medial femoral condyle.2
Because of the reported frequency of this injury, the practicing orthopaedist should be comfortable with treatment.
Basic Science
Structure/Function
Articular cartilage is a complex viscoelastic structure that provides a smooth, low-friction surface that trans- mits variable loads across the joint while minimizing peak stress on the underlying subchondral bone. In the knee, these load-bearing characteristics are shared with the meniscus. The medial and lateral meniscus trans- mits 50% and 70% of the load, respectively. Thus, par- tial or complete injury to the meniscus dramatically transmits loads to the articular surface, rendering it more vulnerable to substantial injury and degeneration. Response to Damages
The healing response in articular cartilage is poor, largely because of its limited vascular supply and ca- pacity for chondrocyte division and migration. Superfi- cial or partial-thickness cartilage injury will result in a cellular insult with decreased matrix production by the underlying chondrocytes with little healing. Full- thickness defects will respond in similar fashion. A de- fect that penetrates the subchondral plate, an osteo- chondral lesion, results in an influx of marrow contents including inflammatory cells, undifferentiated mesen-
chymal cells, cytokines, and growth factors.3,4This will
result in a healing response that more closely mimics normal healing; however, the resultant repair typically resembles fibrocartilage instead of hyaline cartilage. Natural History
The natural history of chondral injury is not completely understood. The process begins with the disruption of the integrity of articular cartilage, resulting in volume loss and leading to pathologic edge loading of the sur- rounding perimeter. The elevated contact pressures on the surrounding surfaces can result in joint degrada- tion. Although the literature often does not make a dis- tinction between partial-thickness and full-thickness chondral defects because of their similar healing re- sponse, a full-thickness defect is more likely to expand. An osteochondral defect will result in a healing re- sponse filling the defect with fibrocartilage, a substance biomechanically inferior to hyaline. Although fibrocar- tilaginous healing may be tolerated clinically in smaller defects, larger insults are more likely to lead to signifi- cant degeneration and osteoarthritis.
Clinical Evaluation and Presentation
History
Clinical evaluation begins with a precise history. A pa- tient who recalls a single injury or series of injuries is likely to have incurred a focal chondral or osteochon- dral lesion, whereas a patient who may not recall an event is likely to have a degenerative chondral lesion. If the patient recalls an injury, details surrounding the in- jury may help in determining the extent of the lesion. With a history that is suspicious for injury to the liga- ments (the classic “pop” associated with anterior cruci- ate ligament injury or reports of instability), an associ- ated chondral lesion is likely present. In addition, mechanical symptoms such as locking or catching may be associated with a pathologic chondral or osteochon- dral defect.
Physical Examination
Inspection of the knee begins with an evaluation of gait and alignment of the limb. Antalgia and precise evalu- ation of varus/valgus alignment are key elements of the
*Nicholas A. Sgaglione, MD or the department with which he is affiliated holds stock or stock options in Arthrocare and is a consultant for or an employee of Smith & Nephew Endoscopy, ConMed Linvatec, Arthrocare, and Musculoskeletal Tissue Foun- dation.
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examination. Range of motion is tested, evaluating for mechanical symptoms such as locking, popping, or crepitus. The Wilson sign is performed with the knee flexed to 90° and the tibia internally rotated; gradual extension of the joint leads to pain at approximately 30° of flexion.5 External rotation of the tibia at this
point relieves the pain. The symptoms result from im- pingement of the tibial eminence on the chondral lesion on the medial femoral condyle. An effusion may also be detected. A thorough examination of the knee should assess for instability or pinpoint other associated inju- ries.
Radiologic Studies
Radiographic examination includes a standing AP, lat- eral, Merchant, and 45° flexion PA views. In addition to a focal osteochondral defect, the radiographs may show associated pathology such as osteophytes, joint space narrowing, fractures, or signs of ligamentous in- jury. The identification of associated degenerative joint disease is essential because it may affect decisions about surgical treatment options.
MRI can be used for evaluation of cartilage lesions and concomitant pathology or osteochondritis disse- cans lesions. The presence of edema tracking around the cartilage defect is a significant radiographic sign that indicates the presence of an unstable cartilage le- sion that may require surgical fixation (Figure 1). Al-
though there is no consensus on the best pulse se- quence, fat-suppressed T2, proton density, and T2- weighted fast spin-echo sequences appear to result in improved sensitivity and specificity of cartilage lesions over standard sequences.
Bone scintigraphy may also be useful but has been supplanted in recent years by MRI. Bone scan has a sig- nificant advantage over MRI as a prognostic indicator because of its higher degree of osseous uptake, correlat- ing with healing potential of an osteochondral lesion. Arthroscopic Grading
The most accurate assessment of location, size, depth, shape, and stability of articular cartilage is obtained ar- throscopically. The Outerbridge classification is a widely used classification system for grading chondral lesions. This classification of chondral wear was ini- tially described as four grades: grade I, softening and swelling of the cartilage; grade 2, fragmentation and fissuring in an area half an inch or less in diameter; grade 3, same as grade 2, but involving greater than half an inch of cartilage; grade 4, erosion of cartilage down to bone.6 This classification was later modified
(Table 1). More recently, however, the International Cartilage Repair Society has proposed a universal grad- ing system that offers a more precise description of chondral and osteochondral lesions, including size, depth, and location of injured cartilage7(Figure 2).
Figure 1 T1- and T2-weighted sequence MRI images of osteochondral lesions of the knee showing “fluid tracking” indicative of an unstable lesion.
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Nonsurgical Treatment
The initial management of articular cartilage lesions should consist of rest, analgesics to control pain, and anti-inflammatory medications. Although physical ther- apy is often used for strengthening and conditioning, it is often less effective in reducing symptoms. The use of steroid injections, hyaluronic acid, and glucosamine and chondroitin sulfate remains controversial. Al- though they may provide temporary pain relief, healing of cartilage is not likely. Although hyaluronic acid in- jections are used to treat early stages of degenerative ar- thritis, there are no current data to support its applica- tion with isolated focal articular cartilage lesions. Bracing can be used to treat an associated malalign- ment. Although an unloader brace may improve symp- toms by decreasing the load incurred by the affected compartment, symptom relief is typically unsatisfactory in younger and more active patients.
Surgical Techniques
Débridement
Arthroscopic débridement and lavage is a temporizing first-line arthroscopic treatment of chondral lesions used in an attempt to reduce pain, inflammation, and mechanical symptoms caused by loose chondral fragments and inflammatory cytokines such as interleukin-1 and tumor necrosis factor-α.8 Arthro-
scopic lavage alone has shown to provide short-term benefits in 50% to 70% of patients.8-10 Although pa-
tients have improved results when arthroscopic lavage is combined with a formal chondroplasty, the studies to date have usually focused on patients with more degen- erative conditions of the knee. Arthroscopic débride- ment remains a viable surgical alternative for a subset of patients with advanced degenerative conditions in the knee and for patients who cannot readily comply with the strict postoperative protocols required for car- tilage restoration procedures. Chondroplasty is done using an arthroscopic shaver and meniscal biter, débrid- ing loose chondral fragments while carefully preserving the intact surrounding cartilage.11
Fixation Techniques
Fixation of an osteochondral defect is a decision that depends on many characteristics of the lesion, including size, shape, and location along with the condition of the remaining fragment. Fixation is generally recom- mended for symptomatic, unstable fragments with ade- quate subchondral bone. MRI allows an accurate eval- uation of the fragment and its stability in determining its suitability for fixation.
Osteochondral fixation begins with precise prepara- tion. The nonviable or necrotic tissue underneath the fragment is débrided with a rasp, shaver, or curet. De- pending on the condition of the underlying subchon- dral defect, bone graft may be used and obtained from Gerdy’s tubercle or (less preferably) the intercondylar notch. The fragment must be reduced anatomically for effective fixation. Accessory portals are often needed to
improve exposure, reduction, and fixation. After prep- aration and reduction, drilling or passage of a small Kirschner wire may help obtain subchondral bleeding and promote healing. Care must be taken during drill- ing and placement of the fixation devices to avoid open physis and penetration of and damage to normal artic- ular cartilage.
Fixation may be achieved with both absorbable and nonabsorbable devices. Although nonabsorbable fixa- tion devices provide optimal compression, they must be removed at a later date, requiring a second surgery. Successful healing has been achieved in 80% to 90% of patients with the use of headless metallic cannulated screws.8This device may be countersunk and provides
excellent compression across the fracture site. Staple fixation, on the other hand, has had poor results, with 50% healing and 30% staple breakage.8 The biosorb-
able devices, such as SmartNail (ConMed Linvatec, Largo, FL) or Biotrak resorbable screws (Acumed, Sports Medicine, Hillsboro, OR) are a lower profile and require smaller perforations in the articular sur- face; however, fixation and compression strength re- main a concern for many surgeons. In addition, the rapid breakdown of the polymers has led to localized inflammatory reactions and joint irritation.
Marrow Stimulation Techniques
Marrow stimulation techniques include osteochondral drilling, abrasion arthroplasty, and microfracture. The goal of marrow stimulation is the delivery of progeni- tor cells from the marrow below the subchondral plate to the articular surfaces, which differentiate and form fibrocartilage tissue. Fibrocartilage consists primarily of type I collagen, whereas native hyaline cartilage con- sists of type II collagen, a biomechanically superior ma- trix. This is typically used as a first-line treatment of small, focal lesions with grade III or IV changes.
The technique involves débriding the damaged and unstable cartilage on the surface, removing the calcified cartilage below with a shaver or curet and creating a well-contained lesion to optimize clot adhesion.12,13The
awls are then placed perpendicular to the surface, ap- proximately 2 to 3 mm apart, and driven in with a mal-
Table 1
Description of Outerbridge Classification
Grade Description
0 Normal cartilage I Softening and swelling
II Partial thickness defect, fissures less than 1.5 cm diameter
III Fissures that reach subchondral bone, diameter greater than 1.5 cm IV Exposed subchondral bone
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let to a level of 2 to 4 mm (Figure 3). Fat droplets or blood typically are seen when the appropriate depth has been reached. Younger patients with smaller lesions have shown the potential for optimal outcomes. In carefully selected patients, microfracture is a cost- effective procedure that can provide symptomatic relief and improve function without making other restoration procedures infeasible.
Osteochondral Autograft Transplantation
This procedure involves the transfer of an osteochon- dral plug from a non–weight-bearing region to the symptomatic cartilage lesion. The typical harvest sites include the lateral or medial trochlea or the perimeter of the intercondylar notch14 (Figure 4). The goal is to
provide a structure that grossly and histologically matches the native tissue; the use of an autograft has a higher probability of healing to the surrounding recipi- ent tissue. The preservation of chondrocyte viability, found in an autograft, is of paramount importance to the success of this surgery. Donor site availability and morbidity dictate the limitations of autologous trans- plantation. Focal, symptomatic grade IV lesions of the distal femoral condyle between 1 to 4 cm2represent the
ideal lesion to treat using this technique; defects up to 2.5 cm2in size also can be treated. When lesions are of
significant size, multiple small osteochondral cylinders will be transferred to the recipient site(Figure 5). The lack of appropriate donor sites and lesions greater than 2 cm2 are absolute contraindications to autologous
transplantation.
The surgery is performed arthroscopically or arthro- scopically assisted with an arthrotomy. A medial or lat- eral parapatellar miniarthrotomy is used to expose and assess the lesion. Assessment of the lesion determines the location, size, and shape of the defect. The lesion site is then prepared by drilling and shaping to provide a clean cylindrical recipient site with no loose frag- ments of cartilage or subchondral bone. Selection of the autograft site is based on tissue that will match the shape, contour, and size of the recipient site. Procure- ment of the autograft is then performed; several propri- etary equipment systems have been developed to assist in this technique including MosaicPlasty (Smith & Nephew, Andover, MA), Osteochondral Autograft Transfer System (OATS, Arthrex, Naples, FL), and the COR Osteochondral Cartilage Repair System (DePuy Mitek, Westwood, MA).14The grafts are then placed in
press-fit fashion into the recipient site. Each system has its own method of transferring the graft in a manner that retains the graft shape and limits significant impac- tion on the articular surface, a technique that sustains
Figure 2 Classification system as described by the International Cartilage Repair Society. (Reprinted with permission from the
International Cartilage Repair Society, Switzerland.)
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chondrocyte viability. Graft height is positioned to sit flush with the native tissue. Grafts that are placed proud or countersunk lead to poor results.
TruFit Bone Graft Substitute Plugs (Smith and Nephew, Andover, MA) are porous polygraft mate- rial composed of a patented blend of polylactide-co- glycolide, calcium sulfate and polyglycolide fibers which may be used to backfill the bony defect at the harvest site. TruFit plugs are biomechanically stable scaffolds that allow ingrowth of new surface healing tissue and underlying subchondral bone, which may re- duce donor site morbidity.
Osteochondral Allografts
Osteochondral allograft transplantation is a valuable treatment alternative for osteochondral lesions larger
than 2.5 cm2. The use of fresh or cold-stored allograft
is preferred over fresh-frozen grafts because both carti- lage cells and matrix are preserved. Significant de- creases in chondrocyte viability are appreciated 14 to 21 days after storage in physiologic culture media; however, recent studies have shown that the chondro- cyte cell appearance and biomechanical properties of the allograft persist even at 4 weeks.15
The procedure is performed in a manner similar to autologous transplantation, either arthroscopically or arthroscopically assisted with a miniarthrotomy. Using specialized proprietary instrumentation, a cylindrical dowel graft is obtained from the donor tissue that matches the defect at the lesion site(Figure 6). Ideally, the donor graft is of the same joint (that is, hemi- condyle for weightbearing surfaces of the knee); more important, the shape and contour of the allograft should match the native site. The graft is similarly placed in press-fit fashion with no need for further in- ternal fixation.16,17
Osteochondral allograft transplantation may pro- vide fully formed articular cartilage and bone without size limitation or concern for donor site morbidity. Sev- eral concerns include graft availability, chondrocyte vi- ability at the time of implantation, disease transmis- sion, and graft rejection. The advantage of using an autologous graft is its low cost, availability, and ab- sence of disease transmission. Clinical outcomes have suggested that patients with unipolar, isolated lesions secondary to trauma can expect the greatest improve- ment in symptoms. Patients with ligament instability, tibiofemoral malalignment, or meniscal pathology have had limited clinical success with this procedure. There- fore, osteochondral allograft transplantation remains a viable treatment option in carefully selected patients with lesions larger than 2.5 cm.
Figure 3 Arthroscopic image of microfracture of an articu- lar cartilage lesion.
Figure 4 Illustration depicting the possible donor sites to be used for autologous chondrocyte transplan- tation. (Reproduced with permission from Simo-
nian PT, Sussman PS, Wickiewicz TL, Paletta GA, Warren RF: Contact pressures at osteochondral donor sites in the knee. Am J Sports Med 1998;26:491-494.)
Figure 5 Intraoperative image of a mosaicplasty being per- formed with multiple osteochodnral plugs of
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Autologous Chondrocyte Implantation
Autologous chondrocyte implantation (ACI) is a cell- based procedure that attempts to repair the damaged chondral tissue by replacing it with viable autogenous chondrocytes. The first stage of the procedure involves arthroscopically obtaining a biopsy specimen of the ar- ticular cartilage to be implanted. This specimen typi- cally is taken from the superomedial edge of the troch- lea or the lateral side of the intercondylar notch and then sent for processing and cellular expansion. During the second stage of the procedure, the chondrocytes are reimplanted into the lesion underneath a periosteal patch approximately 6 to 8 weeks after the index har- vest procedure. The chondrocytes can be preserved for up to 18 months, with cryopreservation limits up to 4 years.18
ACI can be used to treat lesions that are 2 to 10 cm2.
The ideal candidate has a focal, symptomatic, and uni- polar defect with minimal subchondral bone loss. Mar- row stimulation with an adequate amount of time for
recovery usually is unsuccessful in these patients. A bi- polar kissing lesion is a relative contraindication to the ACI procedure. Ligamentous instability, malalignment, and meniscus pathology are not contraindications to the procedure as long as all of the pathology is treated during the index surgery.
Postoperative Management
The postoperative treatment of chondral lesions is fun- damental to the success of the surgery. Each of these techniques requires a motivated and compliant patient who understands the significance of the treatment regi- men.
The patient who undergoes a débridement and chon- droplasty does not require a significant amount of re- strictions. Full weight bearing is allowed immediately after surgery. Continuous passive motion (CPM) or physical therapy with active or active-assisted motion exercises begins early, and progression to low-impact strengthening protocols occurs after the swelling and
Figure 6 A, Image showing the harvesting of osteochondral allograft from donor tissue. B, Image of preparation of the lesion
site by placement of a guidewire and reaming of the lesion. C, Image of the allograft after procurement from the donor tissue. D, Image of the graft after placement in the lesion.
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pain subside, with a return to activities in 3 months or less.
In patients who undergo fixation of the lesion, weight bearing is restricted initially, with toe touch or partial weight bearing implemented with more strin-