Update on advanced surgical techniques in the treatment of traumatic focal articular cartilage lesions in the knee

Update on Advanced Surgical Techniques in the Treatment of Traumatic Focal Articular Cartilage Lesions in the Knee Nicholas A. Sgaglione, M.D., Anthony Miniaci, M.D., Scott D. Gillogly, M.D., and Thomas R. Carter, M.D.

Abstract: Considerable interest has been developed over the past several years in expanding the treatment of symptomatic femoral condylar articular cartilage lesions in active patients. Multiple surgical techniques have been reported and evolving technologies, equipment and approaches continue to expand. The purpose of this paper is to review the presentation of focal articular cartilage lesions including treatment indications, current surgical options and postoperative protocols emphasizing advanced techniques used to preserve or restore hyaline cartilage tissue. The various surgical options are discussed and the advantages and disadvantages are reviewed and highlighted in a clinical practice guideline algorithm.

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he treatment of symptomatic focal traumatic articular cartilage lesions of the knee in active individuals remains a significant challenge. The marked increase in sports participation and increased emphasis on physical fitness across all age groups contribute to greater expectations regarding outcome on the part of active individuals. Nonsurgical treatment for many patients remains effective, particularly in the short term, however recent advances in the surgical approach to knee chondral pathology as well as a greater understanding of the long term natural history of these lesions to go on to degenerative arthritis, has heightened the interest in operative solutions to this problem.1 Articular cartilage lesions are difficult to treat in part due to the distinctive structure and remarkable

From the Division of Sports Medicine, North Shore University Hospital, Manhasset, New York, U.S.A. Presented at the 20th Annual Meeting of the Arthroscopy Association of North America, Instructional Course 303, April 21, 2001, Seattle, Washington, U.S.A. Address correspondence to Nicholas A. Sgaglione, M.D., Division of Sports Medicine, North Shore University Hospital. 800 Community Dr, Manhasset, NY 11030, U.S.A. E-mail: Nas@ Optonline.Net © 2002 by the Arthroscopy Association of North America 0749-8063/02/1802-0102$35.00/0 doi:10.1053/jars.2002.31783

function of hyaline cartilage.2-6 The unique architecture and ultrastructure is based upon the elaborate interaction of water, chondrocytes, negatively charged matrix proteoglycan macromolecules and type 2 collagen fibril meshwork. Metabolically active chondrocytes are unique in that they have a relatively low turnover rate and are sparsely distributed within the surrounding matrix maintaining minimal cell to cell contact. The interaction between the cells, collagen framework, aggrecan, and retained fluid is responsible for the complex biomechanical profile and superior loading characteristics of hyaline cartilage making it difficult to replace or reproduce. Furthermore, controversies remain regarding the unpredictable natural history of these lesions after injury and risk factors for progression over time. It is often unclear which lesions will go on to become symptomatic not only in the early subacute period but also over the course of the patient’s lifetime. This is in part due to the fact that chondral trauma frequently presents in association with other knee pathology (anterior cruciate ligament and meniscal tears) making it difficult to determine which tissue injury is responsible for which symptom and to what extent. In addition, the tendency for articular cartilage to respond to injury with a limited or disordered repair response and as well the biological latency of chondrocytes contribute to highly variable pathophysio-

Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 2 (February, Suppl 1), 2002: pp 9 –32

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logical patterns.7-9 Furthermore, the wide spectrum of actual chondral lesions and variable pathoetiology, lead to imprecise comparisons of chondral trauma with osteochondritis dissecans and early degenerative wear. Despite these issues, multiple techniques and opinions abound in the face of limited peer reviewed, controlled, longer term, valid outcome data.10-12 Our goals, nonetheless, remain high in that most would agree that the “Holy Grail” will be a method that restores hyaline cartilage through a practical and minimally invasive approach preferably arthroscopic and associated with minimal morbidity not only perioperatively but over an extended period of time. In particular, that relates to not compromising the ability to effectively perform established procedures such as knee arthroplasty if resurfacing attempts fail. In addition, optimal treatment should be cost effective, ultimately reimbursable and most importantly, successful not only in the short term, but also in the long term and as far as the development of osteoarthritis is concerned. Advances in arthroscopy and the introduction of techniques designed to restore knee articular function through resurfacing have generated considerable interest and research in recent years. Traditional surgical methods such as debridement and drilling have come under greater scrutiny as the recognition that optimal outcome may be associated with restoration of hyaline or hyaline-like articular cartilage. This concept has challenged the clinician to strive for a more complex histologic tissue to repair chondral lesions that may be associated with a more durable response to loading over time.13 The purpose of this article is to address several of these existing challenges and controversies by reviewing current techniques and approaches and posing several questions regarding the presentation, surgical indications, treatment options and outcome of knee articular cartilage surgery. In an attempt to clarify the approach to this problem, we will work to get answers to the following questions. Firstly, how can the diagnosis of focal articular lesions in the knee be more precise? Who needs surgery? Which lesions should be treated? Which procedures should be selected? How do we accurately and validly analyze results? Finally, where are we heading over the next ten years as far as future directions in treatment are concerned? HOW CAN DIAGNOSIS BE MORE PRECISE? Diagnosis of chondral lesions in the knee requires a thorough assessment of the symptomatic patient,

including history, review of prior trauma or overuse mechanisms, as well as evaluation of any prior operative records, photographs and arthroscopic video. Physical examination must include documentation of body mass index, lower extremity alignment and gait patterns, patellofemoral joint, meniscal, and ligamentous evaluation as well as sites of point tenderness, crepitus and catching and effusion. Radiographs including patellar skyline, notch or tunnel, 45° flexion weight-bearing posteroanterior views and when appropriate full length mechanical and anatomic assessment views, should be reviewed. The use of high resolution scans can be useful and radionuclide technetium bone scanning may be particularly helpful in the evaluation of ill-defined more diffuse chondral pathology as seen in degenerative processes and patellofemoral pain syndrome and also in documenting the activity of osteochondritis dissecans (OCD) lesion fragments.14-18 Diagnosis of articular cartilage pathology can be more precise through the use of noninvasive cartilagespecific magnetic resonance imaging. Although sensitivity and specificity is currently not routinely reliable in all settings, evolving work by Potter et al. has shown a significant degree of accuracy using high resolution modified echo time fast spin echo sequence techniques to evaluate and predict lesion site, size and depth.18 In addition, imaging techniques using T1weighted fat-suppressed three-dimensional spoiled gradient-echo and T2-weighted fast spin echo with fat saturation have been also been shown to be useful in visualizing articular cartilage pathology.19 Newer techniques have been reported using ionic gadolinium diethylene triamine penta-acetic acid (Gd-DTPA) contrast as well as sodium imaging which can detect early biochemical and biomechanical changes and matrix degeneration.19,20 These techniques represent useful methods for detecting occult chondral lesions prior to arthroscopy as well as for postoperative assessment of repair tissue integrity and quality. The ability to use high resolution MR scanning to correlate actual glycosaminoglycan content and thereby interpret and extrapolate biomechanical profile and mechanical function has significant potential. The grading of articular surface lesions has traditionally been based upon visual assessment techniques. These grading methods are not only potentially inaccurate due to interobserver variability but numerous classification systems exist and are frequently cited in the literature including those described by Outerbridge, Insall, Bauer and Jackson, and Noyes.21-24 More recently the International Cartilage

TRAUMATIC FOCAL ARTICULAR CARTILAGE LESIONS TABLE 1. ICRS Articular Cartilage Grading System Grade 0–Normal Grade I–Nearly normal Superficial lesions. Soft indentation (A) and/or superficial fissures and cracks (B) Grade II–Abnormal Lesions extending down to ⬍50% of cartilage depth Grade III–Severely abnormal Cartilage defects extending down ⬎50% of cartilage depth (A) as well as down to calcified layer (B) and down to but not through the subchondral bone (C). Blisters are included in this Grade (D) Grade IV–Severely abnormal Subchondral bone exposure ICRS Classification of OCD Lesions ICRS OCD I–Stable, continuity: softened area covered by intact cartilage. ICRS OCD II–Partial discontinuity, stable on probing. ICRS OCD III–Complete discontinuity, “dead in situ,” not displaced. ICRS OCD IV–Displaced fragment, loose within the bed or empty defect If lesion is ⬍10 mm deep (IVA) If lesion is ⬎10 mm deep (IVB)

Repair Society (ICRS) has proposed an articular cartilage surface grading system in the interest of improving precise mapping and description of chondral lesions including OCD lesions and to promote a more universal language for reporting on and communicating about cartilage pathology25 (Table 1). WHO NEEDS SURGERY AND WHICH LESIONS SHOULD BE TREATED? Which lesions should be treated? The 19-year-old skier who presents with a well-defined history of trauma and an osteochondral fracture and associated anterior cruciate ligament tear is quite different (from a pathophysiologic as well as etiologic standpoint) from a 45-year-old recreational basketball player who presents with a history of overuse and an irreparable meniscus tear with a focal full thickness medial femoral condyle “degenerative” lesion. Precise surgical indications are essential in order to formulate sound decisions regarding which lesions to treat, when and with which procedures (Table 2). WHICH PROCEDURES SHOULD BE SELECTED? Technique Overview Various articular cartilage surgical procedures can be considered primary versus secondary in their

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TABLE 2. Overall Indications for Surgery 1. Acute traumatic lesions ⱖ1 cm in diameter 2. Focal nondegenerative lesions and cases without history of gout, rheumatoid disease, sepsis and systemic disease 3. Distal femoral condyle lesions 4. Symptomatic grade IV lesions and grade 2, 3 and 4 OCD lesions (ICRS classification) 5. Asymptomatic lesions in active patients undergoing associated procedures (ACL, high tibial osteotomy, or meniscal allograft replacement) 6. Symptomatic patients after a failed prior cartilage resurfacing procedure 7. Aligned, stable and meniscal intact knee 8. Body mass index (weight/height in m2) ⬍25-30 9. Rehabilitation compliance

application. Primary or simple procedures include arthroscopic lavage with or without debridement, fixation techniques addressing chondral and osteochondral fractures as well as osteochondritis dissecans lesions and marrow stimulation techniques including drilling, arthroscopic abrasion arthroplasty and microfracture. These techniques can usually be carried out arthroscopically as a first line of treatment. Secondary or complex procedures include those procedures that strive to restore type 2 hyaline cartilage tissue such as osteochondral autografting or allograft transfer or autologous chondrocyte implantation (Table 3). Primary Procedures Lavage and Debridement: Arthroscopic joint lavage has been reported to result in good to excellent results in 50% to 70% of patients. Debridement chondroplasty in addition to lavage appears to improve results and provide a more durable outcome.26-30 However, most studies evaluating the effectiveness of joint debridement and lavage include patients with degenerative lesions rather than focal traumatic lesions. Furthermore, satisfactory results at least in the short term tend to be associated with patients who have symptoms less than one year, have a specific history of trauma, have minimal malalignment and low body mass index.27

TABLE 3. Primary Versus Secondary Procedures Primary

Secondary Procedures

Debridement and lavage Osteochondral autograft transplantation Fixation techniques Osteochondral allograft transplantation Marrow stimulation techniques Autologous chondrocyte implantation

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Marrow Stimulation Techniques: Perforation of eburnated bone to evoke a vascular “healing response” was reported in 1959 by Pridie and subsequent investigators observed a fibrous tissue and fibrocartilaginous mosaic after drilling of the subchondral bone.31,32 Insall reported on success in 60% of patients treated with a similar technique.33 Arthroscopic drilling techniques including abrasion arthroplasty using arthroscopic motorized shavers as introduced by Johnson, resulted in satisfactory outcome in select cases.34 However, since most cases were in degenerative knees with the average patient age being 60 years, it was unclear as to whether drilling or abrasion techniques were any more optimal than debridement alone.35-38 Published results indicated that in a subset of patients, abrasion arthroplasty may not be associated with a satisfactory result and could in certain cases result in a worse clinical outcome.35 More recently, Steadman introduced the technique of microfracture chondroplasty using arthroscopic angled awls to perforate the subchondral bone of focal articular cartilage surface lesions.39-43 This technique proposes that by avoiding power drilling (thereby reducing the chance of thermal necrosis), a more controlled and precise subchondral bone perforation could be obtained arthroscopically. Theoretically, the perforations would access the underlying cancellous bone and marrow cavity resulting in release of blood and “mesenchymal stem cells” which would result in a reparative granulation superclot. The superclot would then under protected loading conditions and continuous passive motion proliferate and differentiate into a fibrous or fibrocartilage mosaic repair tissue. Important technique considerations include meticulous debridement of the calcified cartilage layer and perimeter junction with more normal hyaline host tissue as well as postoperative use of continuous passive motion and 8 weeks of restricted weight-bearing. Indications Indications would include focal as well as degenerative grade 4 articular surface lesions. Contraindications are subchondral bone loss, significant compartment malalignment and noncompliance with postoperative rehabilitation protocols including restricted weight-bearing. Optimal outcome has been noted in younger patients with smaller lesions and a welldefined history of trauma.39 One of the disadvantages of marrow stimulation is that stem cells and undifferentiated cells are found in greater numbers in the marrow cavity of younger patients and with increasing

age the pluripotential cell count drops off precipitously. Another disadvantage is that the repair tissue response can be unpredictable and variable and it is unclear whether the tissue will respond optimally to compression and shear loads in the knee or whether it will be durable over time. Fixation Techniques Articular cartilage trauma can result in multiple patterns of damage depending on the type and direction of injury force, position of the knee, age of the patient, and associated injury and pathology.44-46 Traumatic fracture and separation of the osteochondral surface is age dependent and in skeletally mature individuals tends to be along the lines of the tidemark resulting in isolated chondral shear fractures without attached underlying bone fragments. In adolescent athletes, the failure tends to be along the deeper subchondral cancellous bone resulting in an osteochondral fracture. OCD, which should be considered a distinct clinical entity separate from traumatic chondral or osteochondral fractures, can present as a nondisplaced lesion in-situ, a separated but nondisplaced fragment, a partially displaced fragment, or a displaced fragment with loose body.47-52 OCD lesions, which can be associated with a history of trauma, can be approached in a fashion similar to pure articular cartilage traumatic fractures in that every attempt to repair the fragment should be made. It is essential to preserve native hyaline cartilage and its corresponding and underlying bony tissue base since long term follow-up after excision has yielded poor results particularly in lesions greater than 2 cm2.53,54 Indications Decision making regarding fixation will be dependent on articular cartilage and underlying bone size, shape, thickness, viability (extent of necrosis and measure of chronicity), and site of the lesion in the knee. It is important to carefully inspect the underlying surface of the actual fragment, since it may, in chronic cases, have fibrous or nonviable scar tissue interposed which can impede healing. In cases in which comminuted fragmentation of the fracture or OCD lesion occurs with a irreparable loose body or where significant necrosis and fragment deformation occurs, then excision and debridement may be needed. In all other cases significant effort should be made to replace, stabilize and optimally fixate the articular surface fracture or fragment.

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Fixation Methods

Surgical Technique

Removal of all nonviable or necrotic debris with arthroscopic shaving of the base is carried out. The lesion should be approached as if it is a “fracture nonunion” associated with altered biological properties. If fragment excision is required then in addition to debridement, marrow stimulation techniques may be carried out to address the potential incompletely covered areas of the lesion. If drilling is selected rather than microfracture, a 0.062 inch diameter smooth Kirshner wire can be used with either a retrograde (drilling from proximal to distal into the bony base of the lesion) or transarticular antegrade technique (drilling arthroscopically from the joint from distal to proximal.54,55 Retrograde drilling can be technically more difficult than antegrade drilling and particular care needs to be exercised in the skeletally immature patient population in order to angle the drill wires away from the distal femoral physis so as to not violate the growth plate. An arthroscopic anterior cruciate ligament vector drill guide can be useful in optimizing retrograde drilling and precisely accessing the lesion base. Antegrade drilling, although easier, is associated in nondisplaced lesions, with the disadvantage of drilling through and perforating areas of otherwise intact cartilage.55 Fixation remains the treatment of choice in chondral or osteochondral fractures in which the fracture fragment remains viable, nondeformed and reducible.56-58 Fixation for OCD lesions is recommended in those lesions that are noted to be unstable, partially detached, or completely detached and nondisplaced or displaced and loose in the joint. Intact OCD fragments that demonstrate motion upon probing should be stabilized, particularly if preoperative magnetic resonance imaging reveals a fluid signal on T2-weighted images indicating synovial fluid dissection through the base of the lesion. Partially detached lesions, detached but nondisplaced lesions as well as viable displaced fragments should be fixed. Open and arthroscopic techniques may be used to stabilize OCD lesions and the decision to use one method over another is dependent on the size and site of the OCD lesion, fixation device chosen and surgeon’s technical preference. Posterior condyle lesions and the less common patella and tibial plateau lesions are particularly difficult to fix arthroscopically and an arthrotomy should be used in order to ensure precise access, exposure, reduction and fixation of the lesion.

The fixation technique for complete or partially detached fragments includes evaluation of the geometry of the lesion as far as restoring of surface congruence eliminating or reducing any mismatch. Debridement of the lesion and underlying bone bed is then carried out followed by reduction of the fragment. It is important to utilize accessory arthroscopic portals in order to insert the fixation device as perpendicular to the articular surface as possible. Provisional fixation using a fine Kirschner wire or corresponding wire device included as part of the numerous fixation equipment systems is used to hold the fragment in optimal position prior to obtaining definitive fixation and preferably compression. Alternatively, an absorbable suture may be used for provisional fixation. Intraoperative fluoroscopic imaging may be useful to ensure proper fragment reduction. Usually two points of fixation are required to ensure stability and limit fragment rotation. Numerous fixation devices and methods have been described to repair symptomatic chondral, osteochondral and OCD lesions including bone pegs and metallic and bioabsorbable screws and wires.56-58 Metallic devices include smooth Steinman pins, Kirschner wires, and AO small fragment screws. The use of lower profile cannulated screws has facilitated more rigid fixation through improved pullout strength and compression as well as ease of insertion. The advantages of metallic fixation devices include optimal fixation strength and superior compression. The disadvantages are the potential need for removal of hardware even with some of the headless lower profile devices, a large bore perforation of the articular surface (larger than the bioabsorbable implants) and potential risk of further fragmentation of the lesion. More recently, bioabsorbable fixation implants have been introduced. These devices are composed both of polylactic acid and/or polyglycolic acid polymers. The advantages of bioabsorbable fixation devices include lower profile implants, smaller bore perforation of the articular surface, no need for removal of hardware and facilitated arthroscopic delivery. The disadvantages of these devices include potentially inferior fixation strength and suboptimal fixation in compression compared to metallic devices as well as higher implant costs and the potential for biological reactions to the polymer material. Furthermore, there is scant clinical outcome data yet to be published demonstrating success using these devices. The decision to utilize metallic fixation devices is

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dependent on the fragment geometry, site of the lesion and surgeon preference. In general, metallic devices are more optimal in cases where the lesion is larger (⬎2 cm2) and deeper where bone grafting is needed, where an OCD lesion appears less viable and possibly deformed or if the osteochondral fragment has a larger attached bone wafer to it. Bioabsorbable devices may perform better in smaller lesions (⬍2 cm2) not requiring bone grafting with a more viable appearing fracture or OCD fragment, and if the lesion has more chondral tissue and surface with less attached underlying bone.

Clinical Outcome Prognosis after fixation of osteochondral fractures and OCD lesions is dependent on the age at presentation, extent of surface restoration, underlying healing and perimeter integration. Lateral femoral condyle lesions may be associated with a poorer prognosis. Optimal outcome is usually associated with adequate debridement, appropriate bone grafting and achieving secure fixation and compression across the fixation site. Results have been reported with success noted in 80 to 90% of patients treated with fragment stabilization.51,56,57,61

Bone Grafting When bone loss is noted, specifically greater than 6 to 8 mm below the adjacent subchondral plate, then bone grafting of the lesion should be performed. Autogenous cancellous bone graft is preferable and can be harvested from the proximal tibial metaphysis. Allograft bone graft substitutes can also be utilized. The bone graft can be introduced and placed either in a retrograde (open) or antegrade (miniarthrotomy or arthroscopic) and is tamped into place flush to the subchondral bone surface not the articular cartilage surface. Hybrid Techniques When lesion fragmentation, necrosis, size, depth and site (posterior condyles, patella and plateau) limit the ability to treat the entire lesion with one uniform technique, then hybrid techniques may be used. This can include fixation of part of a viable fragment and drilling, osteochondral autograft transfer, autologous chondrocyte implantation and allografts in various application in order to resurface as much of the joint as possible.58-61 Postoperative Rehabilitation Immediate range of motion including use of a continuous passive motion machine is started with limited or non-weight bearing for up to 6 to 8 weeks depending on the size, site and security of fixation achieved. If a metallic fixation device is used, then limited weight-bearing may be delayed until the hardware is removed which should be following clinical and radiographic signs of healing are confirmed or at least 8 to 12 weeks postoperatively. Chronic OCD lesions or lesions requiring bone grafting may require a more extended healing time for chondral and bony consolidation.

SECONDARY PROCEDURES Osteochondral Autograft Transplantation Osteochondral autogenous transfer refers to the transfer of a plug of osteochondral tissue with overlying normal intact articular cartilage with viable chondrocytes and underlying attached subchondral bone into an articular cartilage defect. Various procedural terms based upon several proprietary equipment systems have been used to describe the technique of transferring autologous osteochondral grafts including mosaicplasty.62-65 The whole tissue graft which is obtained from condylar surfaces that are associated with less weightbearing and presumably less loading, can then be implanted to restore the joint contour at the site of the articular surface lesion. The autogenous procedure involves the open and/or arthroscopic harvesting of cylindrical plugs ranging from 4.5 to 12 mm in diameter from the superolateral ridge of the femoral condyles above the sulcus terminalis or in the perimeter of the intercondylar notch particularly in the region of where a notchplasty is performed during anterior cruciate ligament reconstruction. The grafts are then transferred to the lesion providing immediate hyaline cartilage coverage and a bone base restoration. The autograft plug insertion can be through an existing intact OCD lesion thereby contributing a “fixation peg” or as stand alone grafts. Osteochondral autograft transplantation is a technically demanding procedure and the location of the donor site and the size of the harvested osteochondral grafts play a key role. At the recipient site, the coverage of the defect, mechanical stability and positioning of the grafts and the method of graft delivery are critical. The size of the grafts, the method by which they are harvested and the healing environment including applied biomechanical loading

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are important for articular cartilage survival. Also the length, support, positioning and sequence of insertion of the grafts differs according to the type of defect treated. The advantages of osteochondral autograft transfer techniques include the availability of tissue grafts, potential for a single stage arthroscopic procedure and immediate reliable three dimensional whole tissue transfer of viable hyaline cartilage, intact tidemark, subchondral plate and bone. Disadvantages are the significant limitation of graft availability particularly in attempting to treat larger lesions greater than 2 cm2, concerns over donor site insult or morbidity,66 the technical challenge of restoring a congruent bevel to the convex condylar surface and the concave trochlea surface and levering and shear stresses that the grafts can be subjected to when placed in deeper OCD lesions with more than 8 mm of bone loss. Indications The indications for osteochondral autograft transfer include symptomatic nondegenerative, unipolar grade IV distal femoral condyle articular cartilage lesions that are greater than 1 to 2 cm in diameter. Lesions up to 3 to 4 cm in diameter can be treated, although graft limitations tend to reduce optimal indications to treating lesions 1 to 3 cm in size. The treatment of patella or tibial surface lesions as well as intact but loose ICRS grade II OCD lesions would be relative indications.63-65,67-70 Donor Site: Graft Size Work has been carried out to study the effects of differing graft sizes taken from the outer edge femoral trochlear donor site on the healing of the defect that is left and the development of degenerative arthritis in an ovine model71 (See Fig 1). Small 2.7-mm diameter grafts left a defect that was able to heal with congruent fibrocartilage and without focal evidence of significant degenerative changes at the patellofemoral joint. The defects left after intermediate 4.5 mm diameter graft harvesting healed fully with a continuous fibrocartilaginous tissue with no patellofemoral joint degenerative changes. However, the defects left at the donor site following large 6.5 mm diameter graft harvests were noted to be incompletely healed and at 3 months there was evidence of significant osteoarthritic changes at both the harvest site and on the reciprocal patella articular surface.

FIGURE 1. Donor site healing (ovine model). (A) 4.5-mm donor sites have fully healed with fibrocartilaginous tissue and no degenerative change at 3 months. (B) 6.5-mm donor sites have not healed and there are degenerative changes on both the femoral trochlea and patella at 3 months.

Recipient Site: Graft Insertion The congruence of a graft compared to the surrounding articular cartilage has been demonstrated in a recent study72 (Fig 2). Grafts were inserted into recipient holes that were deeper than the length of the graft. Half of the grafts were inserted flush with the joint surface and half were inserted 2 mm proud and allowed to “float” with weight bearing. The grafts delivered proud appeared to be damaged by weight bearing and underwent micromotion that interfered with the graft/recipient bone interface producing fibrous tissue interfaces and subchondral cysts. Autografts delivered flush with the joint surface resulted in a more optimal hyaline tissue surface. Countersinking the grafts below the level of the surrounding

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FIGURE 2. The effect of congruence on graft performance at 3 months. (A) Gross and histologic specimens of flush grafts demonstrating bony healing with good intrinsic articular cartilage repair and peripheral cartilage flow. (B) Gross and histologic specimens of proud grafts demonstrating subchondral cyst formation at the base of the graft and articular cartilage breakdown.

articular surface appears to also have a detrimental effect and preliminary results have shown that a layer of fibrous tissue covers the recessed grafts so that they effectively become non-functional. The results of grafts positioned flush to the surrounding articular surface that were either inserted into holes drilled to the same depth as the graft, so that the base of the graft was supported, or into holes that were deeper than the graft, so that the base of the graft was unsupported have been compared. Preliminary results demonstrate that the supported grafts heal well but that the unsupported grafts tend to subside becoming covered by fibrous tissue. Graft Size Small grafts have the potential advantage of reconstructing defects and curved surfaces more accurately,

whereas larger grafts require less time to harvest and transplant71 (Fig 3). The effect of differing graft diameter on survival and healing has been studied. Small 2.7-mm diameter grafts were too fragile and difficult to harvest and handle and the multiple graft/ recipient interfaces proved to be a serious liability as the interstices between grafts had inadequate extrinsic repair. Intermediate 4.5-mm grafts were easy to harvest and deliver and provided good results at the recipient site. Large 6.5-mm grafts were the easiest to handle and produced good recipient site healing and repair. Some investigators have recommended using fewer but larger diameter osteochondral grafts measuring 8 to 10 mm. The advantages would include a more confluent uninterrupted grafted hyaline surface with less interface surface area between native and transferred hyaline cartilage. Disadvantages include

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potential problem with a conical shaped graft is that the peripheral edges of the articular cap are unsupported and may collapse after insertion.

FIGURE 3. Healing of osteochondral grafts of differing sizes (ovine model). (A) Gross and histologic specimens of articular cartilage and bony healing of 4.5-mm and 6.5-mm grafts. (B) Gross and histologic specimens of articular failure and bony biomechanical collapse in 2.7-mm grafts.

Defect Reconstruction Chondral: For focal chondral defects where there is no subchondral bone loss or loss of joint contour, standard 4.5 mm diameter by 15 mm length grafts can be used. The number of grafts required is determined by marking out the recipient site using the end of the 4.5 mm insertion tube. The grafts can be inserted into their recipient holes in any sequence. Osteochondral: Osteochondral defects are usually crater shaped with the cavity being deeper in the center. This can sometimes make it difficult to appreciate the loss of joint contour and there is a tendency to align the tops of the inserted grafts flat rather than restoring the apical crown thereby recreating the joint curvature. The grafts in the center of the defect need to be more prominent than those at the periphery and will consequently have a longer length of graft protruding from the recipient bed which is unsupported. When reconstructing larger defects, grafts should be inserted into the periphery first to provide peripheral support

harvest site morbidity and healing concerns. It appears that optimal graft diameter may be in the 4.5 to 10 mm diameter range. Harvesting Method The effects of power trephination compared to manual punch harvesting on the survival of a graft have been investigated. Histology and cell viability studies of the articular cartilage of grafts harvested manually or by power were compared to normal articular cartilage (Fig 4). There was a 20% decrease in chondrocyte viability of the articular cartilage around the peripheral rim of grafts harvested using a manual punch and a 60% to 70% decrease in grafts harvested by power trephination due to thermal necrosis. In addition, the larger the diameter of the graft, the greater the percentage of undamaged to damaged articular cartilage. It was also noted on gross histology that the grafts harvested by manual punch had a uniform diameter along their length, while the power trephination grafts were slightly conical with a larger diameter at the articular end than at the base. The

FIGURE 4. The effects on articular cartilage survival following either manual punch and power trephination harvesting. Perivital staining of articular chondrocytes showing predominantly dead cells in the power harvested grafts and predominantly live cells in the manually harvested grafts.

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for the more prominent central grafts at the time of their insertion (Fig 5). The depth to which a graft should be inserted into the bone at the base of the

defect should be at least the same as the length of the graft that will be left exposed. Fragment In Situ: When an osteochondral graft is inserted into recipient bone, a very tight interference fit can be obtained. This provides biological fixation, stimulation of the subchondral blood supply, bone grafting and bridging at the lesion interface in addition to restoring a congruent articular surface at the site of the osteochondritis dissecans lesion (OCD) or large osteochondral fracture. This technique has resulted in good results at clinical and magnetic resonance imaging follow-up (Figs 6 and 7).61 Surgical Technique Based on the results of earlier studies, 4.5 mm osteochondral grafts are currently used and harvested by a manual punch from the non-articulating superior edges of the femoral trochlea. It is important that the harvesting chisel is perpendicular to the articular surface at the time of graft harvest. If this is being performed arthroscopically an accessory portal is required. Also, a mini-arthrotomy can be made to facilitate exposure and access to the harvest site. It is essential that the grafts are inserted congruently, that they are not proud or recessed and they are supported at the base of the bone tunnels. When reconstructing larger osteochondral defects, the peripheral grafts are inserted first; 4.5 mm osteochondral grafts are harvested from the medial and lateral edges of the trochlea. Postoperative Rehabilitation The patient is encouraged to move the knee in a hinged brace through an unrestricted range of motion but is strictly non-weight bearing for the first 6 weeks after surgery. After satisfactory assessment the patient can begin to gradually weight bear as tolerated. Graft healing is assessed both clinically and by 3 monthly serial cartilage specific MRI scans. Patients are only allowed to return to full sporting activities after MRI evidence of full healing has been obtained. Clinical Results

FIGURE 5. (A) Osteochondral lesion. (B) Lesion filled with osteochondral grafts inserted flat not recreating joint curvature. (C) Lesion filled with central osteochondral grafts inserted more prominently than the peripheral grafts to better recreate the joint contour

Osteochondral grafting has the advantage over other repair methods of transplanting a fully formed articular cartilage matrix with its subchondral bone. Autogenous osteochondral grafts have the benefit of transferring viable chondrocytes thereby providing hyaline cartilage resurfacing of the chondral lesion without potential for an immunogenic reaction using a costeffective single staged arthroscopically assisted pro-

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FIGURE 6. Stabilization of in situ osteochondritis dissecans fragments. (A) Loose fragment identified. (B) Fragment stabilized with a central graft. (C) Additional grafts inserted until fragment fully stable

cedure. Published clinical outcomes documenting treatment of focal articular cartilage lesions with osteochondral autografts have been limited although several investigators have reported preliminary data suggesting successful results in up to 91% of patients and minimal associated harvest site morbidity.61-65 AUTOLOGOUS CHONDROCYTE IMPLANTATION In larger lesions, surgical resurfacing using autograft transfer can be a significant challenge. Restoration of articular surface in lesions greater than 2.5 to 3 cm2 and up to 10 to 15 cm2 can be accomplished by autologous chondrocyte implantation (ACI).73-77 The procedure requires a two stage approach in which the

articular cartilage cells are first arthroscopically harvested and expanded ex vivo in cell culture. Then via arthrotomy, the cultured chondrocytes are implanted under an autologous periosteal tissue flap. The advantages of autologous chondrocyte implantation include the potential to treat larger lesions, use of autologous tissue and reliability of obtaining hyaline-like tissue at outcome. Disadvantages are the high cost of the procedure, difficulty in obtaining third party insurance approval for reimbursement, the need for staged surgeries and an arthrotomy for reimplantation as well as the possibility that the repair tissue is at best a rather unpredictable and inconsistent mosaic of bone, fibrous, fibrocartilaginous and hyaline tissue. ACI represents one of the first clinical applications of tissue engineering used in orthopaedics and re-

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N. A. SGAGLIONE ET AL. Indications Autologous chondrocyte implantation is indicated for symptomatic, large (2.5 to 10 cm2) full-thickness chondral lesions located on the femoral condyles and trochlear groove, including OCD lesions in patients from age 15 to 35 years. Patients should demonstrate the ability to be compliant with the postoperative rehabilitation protocol. ACI is not indicated as a treatment option for osteoarthritis, or in cases where bipolar corresponding tibial plateau bone on femoral condyle bone lesions are noted.78,79 The presence of coexisting pathology such as ongoing ligamentous instability, bony malalignment, or complete meniscal deficiency remain contraindications to performing the procedure.80 Radiographs and MRI are useful to determine status of the underlying subchondral bone. Any bony loss of greater than 7 to 8 mm in depth requires bone grafting prior to cell implantation. The definitive decision to determine the suitability of a chondral lesion for ACI is made at the time of arthroscopic assessment. The size and degree of the defect, the status of the surrounding articular cartilage and underlying bone, as well as the status of the opposing chondral surfaces are all evaluated. The ideal chondral lesion for repair with ACI is one that has full thickness involvement with exposed subchondral bone and is well shouldered on all sides by normal appearing articular cartilage in an otherwise stable and aligned knee. In general, the defects treated by this technique are larger than 2 cm.79 Surgical Technique

FIGURE 7. (A) Medial femoral condyle defect in a 32-year-old man during ACI procedure. (B) Same MFC defect during secondlook arthroscopy 8 months after ACI.

quires that a small biopsy of healthy chondral tissue to be obtained arthroscopically when the lesion is identified. The biopsy tissue is then processed ex vivo and then undergoes in vitro cell culture returning a 12-fold increase in autologous chondrocyte cells available for implantation into the defect at the second stage of the procedure. This method results in a repair tissue that has a morphological structure similar to hyaline cartilage. The concept behind using autologous chondrocytes is to produce a durable repair tissue more closely resembling the characteristics of hyaline cartilage.

The surgical technique for ACI has been well defined and published in numerous articles.75-77 The essential steps include an initial chondral biopsy for autologous chondrocyte cell culture followed by a separate implantation procedure consisting of arthrotomy, defect preparation, periosteal procurement, fixation of the periosteal tissue, securing a watertight seal with fibrin glue, implanting the chondrocytes and wound closure. Although an arthrotomy is necessary for the implant procedure, the size and location of the defect determine the amount of exposure necessary. The most important aspect of exposure is that the full extent of the defect is exposed facilitating all the technical aspects of the implantation. During debridement of the defect all damaged cartilage and fibrocartilage is removed leaving exposed subchondral bone with a rim of stable cartilage around the circumference of the defect. The subchondral bone should not be violated, and hemostasis of the defect must be ob-

TRAUMATIC FOCAL ARTICULAR CARTILAGE LESIONS tained prior to implantation of the cultured chondrocytes. In cases where the defect is not fully contained by a rim of healthy cartilage, special techniques including the use of transosseous drill tunnels or suture anchors are necessary to secure the periosteum and still establish a watertight seal. A slightly, 1 to 2 mm, oversized periosteal graft is then harvested from a separate small incision over the proximal medial tibia, distal to the pes anserine insertion on the subcutaneous border of the tibia. The periosteal graft is then aligned over the defect with the cambium layer facing the defect. The periosteum is then sutured to the cartilage rim with multiple 6-0 vicryl interrupted sutures spaced every 2 to 3 mm. The periosteum is sutured and trimmed so as to create a secure, tight drum-like appearance over the defect. Once all the sutures are in place with only a small opening remaining, the graftdefect interface is sealed with fibrin glue to assure a watertight seal. The autologous chondrocytes are then aspirated (maintaining sterile technique) from their shipping vial into a tuberculin syringe using an 18gauge angiocatheter and injected under the periosteal graft into the defect. The injection site is then closed with one or two additional sutures and sealed with fibrin glue. At this point the knee is brought back to full extension and no further manipulation of the knee is performed. Any concomitant procedures that were necessary should be completed prior to injecting the cells so that no disruption of the periosteal flap or underlying implanted cells occurs. After completion of the ACI, the knee is brought to full extension and the wound and skin closed in layers in routine fashion When associated pathology such as anterior cruciate ligament deficiency, tibiofemoral and patellofemoral malalignment or subtotal meniscal loss is present then concomitant treatment needs to be planned either with the ACI or as a staged separate procedure. The best approach for each individual patient is dependent upon the degree or severity of the symptomatic problem, the actual co-existing pathology(s), surgeon experience, and patient factors such as work or sport functional demands disability or recovery time issues and the ability to comply with the necessary rehabilitation protocols. In general, carrying out only one additional procedure at the same time as the ACI is preferred. (such as an ACL reconstruction or osteotomy or meniscal transplantation or anteromedialization of the tibial tubercle in addition to the ACI). However, when several co-existing knee pathologies exist and/or where three or more definitive reconstructive procedures may be indicated, staging seems more prudent.

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Bone grafting for bone deficiency routinely requires staging. In cases where the bony depth of the defect exceeds 7 to 8 mm, a separate staged bone grafting procedure is performed. Open bone grafting techniques have been traditionally used, however, arthroscopic techniques using autologous iliac crest cancellous bone or allograft paste with interspersed cancellous bone can be inserted into the debrided bony defect through an 8 mm cannula, impacted, and sealed with fibrin glue. The ACI procedure is then performed at least 4 to 6 months later after the bone graft has incorporated. Postoperative Rehabilitation The rehabilitation protocol for ACI is based on the natural maturation process of the chondrocytes.75-77 There are three phases associated with this healing process. First is a proliferative phase that occurs early after the cells are implanted. A matrix production phase follows, where the tissue becomes incorporated and integrated into the host. The key principles during this healing process are early motion, to help with cellular orientation and the prevention of adhesions, protection of the graft from mechanical overload, and strengthening exercises to allow for a functional gait. Continuous passive motion and touch weight bearing are used during these early phases. Progression to full weight-bearing is generally started between 4 to 6 weeks post-operatively. Addition of further exercises should be based upon the size, location and amount of containment of the lesion by normal surrounding cartilage. The final phase is the maturation phase, which can take an extended period of time as the repair fully matures with its stiffness closely resembling the surrounding articular cartilage. The knee is gradually loaded with increased strengthening exercises and various impact loading activities during this final phase. Following these principles during the repair maturation continuum will provide an optimum environment for the tissue to grow and mature. Overloading the graft too early either repetitively or with a traumatic event can lead to graft failure. The addition of concomitant procedures does not change the rehabilitation protocol for the specific site of the ACI. Clinical Results Since initiating the procedure of ACI in Sweden, Peterson and colleagues have performed over 1000 ACI procedures.74,78 Additionally, experience has grown rapidly in the US and Europe, further documenting and defining the clinical applicability of this

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technique.76,81-83 Peterson et al.78 reported on the results of the first 101 patients that were treated with ACI. Ninety-three of the 94 patients (98%) were available for follow-up between 2 to 9 years. The average size lesion treated was 4.5 cm2 and 62% of the patients had failed at least one prior procedure. Multiple rating scales, including the Modified Cincinnati, Tegner, Lysholm scores were used to assess the clinical and functional outcomes. The clinical outcomes showed that 24 out of the 25 isolated femoral condyle lesions were graded as having good to excellent results, a 92% success rate. In the OCD group, 16 of 18 patients were rated good to excellent, representing an 89% success rate. In this initial OCD group, no bone grafting was performed and only the cells were implanted into the defects where the depth ranged between 3 to 10 mm of bony involvement. In the multiple lesion group, there was an average of 2.5 lesions per knee; 15 of 20 patients, or 67% were rated good to excellent. In the ACL reconstruction group, 16 patients had concomitant ACL reconstruction at the same time, 12 were rated good or excellent, equaling a 75% success rate. Three patients had revision ACL reconstruction. In the patella group, 11 of 19 patients were graded as having good to excellent results. Sixty-five patients underwent second-look arthroscopies. Of those, 53 of the patients showed good repair fill, with good adherence to both the underlying bone and had a seamless integration into the adjacent cartilage. The remaining 12 patients had either tissue hypertrophy, incomplete fill or were not fully integrated. The firmness of the repair tissue was tested using an arthroscopic resistance probe. The stiffness measurements correlated closely to the histology findings. Biopsies that were assessed as hyaline-like had similar stiffness measurements to the adjacent cartilage; whereas those with a fibrous repair had much lower scores. Histologically, 33 biopsies were obtained, 70% of those biopsies obtained were identified as a hyaline-like repair tissue by independent observers. The remaining 30% were either a combination hyaline/fibrous or a fibrocartilage tissue. Autologous chondrocyte implantation can result in a durable repair tissue that can resurface large chondral lesions and relieve symptoms, allowing patients to return to functional activities (Figs 7 and 8). The outcomes of multiple studies have demonstrated that 84 to 91% of the patients were able to achieve good to excellent outcomes and return to active lifestyles. ACI is a safe, effective, and reproducible treatment that should be considered a viable option for patients with

large cartilage lesions greater than 2 cm2 that want to resume an active lifestyle. OSTEOCHONDRAL ALLOGRAFTS In cases in which larger lesions are noted (⬎2.5 cm2) or where significant concerns exist regarding the morbidity associated with donor site issues or staged surgical procedures, osteochondral allografts transfer provides a valuable treatment option. Osteochondral allografts have the advantage of providing fully formed articular cartilage without specific limitations with respect to size of the defect. The initial clinical experience with osteochondral allografts came from the use of massive grafts during tumor resections and other limb sparing procedures.67 Indications Clinical studies have indicated that younger patients with an isolated lesion secondary to trauma or OCD, and without other joint pathology, tend to have more optimal outcomes after after osteochondral allografting.84-98 Contraindications to allograft resurfacing include lesions due to diffuse disease processes, such as osteoarthritis and inflammatory arthropathies, although avascular necrosis, if limited and focal, is a relative contraindication. Defects limited to one joint surface (unipolar) tend to have a more favorable outcome than in those cases in which lesions are present on opposing joint surfaces (bipolar or kissing lesions). The presence of an intact meniscus has been found to improve results when treating a femoral or tibial lesion. Conversely, ligamentous instability and/or angulatory deformities have a negative effect on results and need to be corrected before or at the time of allograft placement. Patient age remains an area of controversy. The majority of investigators recommend the age limit be 40-45 years, while others have extended this to 60 years of age.84-88,92-96 While there is no specific limitation as to the largest size of defect that can be treated with an allograft, the minimum size to use one is of some debate. Although surgeons have used allografts to treat lesions as small as 1 cm2, most reports recommend the lesion be at least greater than 2 to 3 cm2.91-98 Surgical Technique The procedure begins with templating the lesion in order to obtain an allograft that matches the size and contour of the defect to be treated. While multiple

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FIGURE 8. (A) A 41-year-old man with lateral femoral condyle defect s/p 5 previous failed procedures to include chondroplasty, drilling, and osteochondral allograft. LFC defect at time of staged bone grafting for cystic cavity. (B) Defect 5 months after ACI. Note complete fill with soft undulating surface during matrix production phase, patient still with symptoms. (C) Defect at 1 year. Note smooth contour with firmness consistent with surrounding articular cartilage, more mature repair with loss of patient symptoms. (D) Defect at 3 years with return to full activity, symptom free, with repair indistinguishable from surrounding tissue.

methods have been described, the most commonly used is via plain x-rays of the recipient. By using a magnification marker to correct for any error in size, the bone can be measured from the radiographs and match the size of the allograft, which is measured during procurement.98 Allograft tissue processing has been significantly evolving over the last decade with many advances noted since tissue substitution was first reported.67,99-105 Regarding the choice of allograft tissue, to ensure graft quality and minimize the risk of disease transmission, the allografts should be retrieved, handled, and processed in strict accordance with the standard guidelines of the American Association of Tissue Banks.102 Even prior to graft harvest,

a detailed social and medical history of the donor is taken as well as serology testing. The grafts are then procured within 24 hours of the donor’s death in an effort to maintain cell viability and then processed in a clean room environment. The grafts are thoroughly lavaged to remove blood components, which are the main source of disease transmission and immunologic sensitization. They are transferred to an antibiotic solution for a day at 37°C to kill microorganisms and subsequently stored at 4°C until used. Initially, the osteochondral allografts were implanted within a day or two after the processing in an effort to maintain chondrocyte survival. Because of the logistic difficulties this presented, the time frame

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for use was expanded to 5 to 7 days without affecting results. More recent studies have found that even at 4 weeks, the cell appearance and biomechanic properties are without significant change.103,104 While the minimum percent of chondrocyte survival for clinical success is still unknown, it is clear they play a vital role. The preservation methods of fresh freezing, freeze drying, and cryopreservation have each been studied extensively in efforts to prolong tissue storage, but all have inferior results compared to fresh grafts.100,103,104 Although the risk of disease transmission is minimal, sterilization methods have been tried as a means to eliminate the risk. Unfortunately, the dose of irradiation needed to be virucidal not only destroys the chondrocytes, but also alters the graft’s material properties and is not clinically applicable.105 The immunologic response to the allograft is another area of concern and studies have shown that musculoskeletal allografts are capable of inducing both cellmediated and humoral immune responses in the host. The most common reaction is a cell-mediated response to the allograft’s surface antigens. With the primary source of allografts cells being the bone marrow elements, lavage during procurement significantly reduces the immune load. Matching of the chondrocyte surface antigens of the major histocompatibility complex (MHC) has been found to be one method to decrease the immune load. Several animal studies have found improved graft incorporation with MHC antigen matching. Human studies have shown the HLA sensitization can occur, but there is varied opinion as to the clinical significance.106-113 Friedlaender et al. evaluated the immunologic response to the clinical outcome in 29 patients that received massive osteochondral allografts at least ten years previous.112 They found 8 patients (28%) had anti-class II HLA responses with 5 (63%) good to excellent results. Of the 21 without response, 18 (86%) had satisfactory outcomes. They concluded the presence of sensitization was a factor in success, but summarized that even with massive grafts it did not preclude a satisfactory result as 79% of the patients as a whole had good to excellent results. Other series reported tissue matching had little effect on clinical success. Langer and Gross have found that while free chondrocytes are immunogenic, theorized if the cartilage matrix remains intact, sensitization does not occur.111 If the cartilage deteriorates and allows the chondrocytes to be exposed, sensitization is similar to free cells. They concluded the dense matrix in which the chondrocytes are embedded acts as a barrier that limits antigen exposure and can prevent the rejection process. The use of

immunosuppressants is another way to decrease the host response to the allograft however, their use is not recommended for it is generally felt the morbidity of this treatment greatly outweighs the potential benefit.113 Once the allograft is obtained and inspected for size and quality, the surgical exposure is routinely through a mid-line anterior incision. A medial or lateral arthrotomy is then made, depending on the involved size. If the lesion is on the anterior femur, a mini-arthrotomy is sufficient. The allograft can be fashioned in many ways, but the most common graft types are shell and dowel grafts configurations (Figs 9 and 10).93-96,98 Both are comprised of the articular cartilage with a thin wafer of bone present to enable healing. The basic principle is to remove any sclerotic bone or fibrous tissue in the defect to leave a vascular base to allow the allograft to heal. The difference being shell grafts are hand fashioned, while dowel grafts are cylindrical plugs prepared with commercially available instruments. Dowel grafts are most commonly used when treating central patella lesions or well-delineated femoral defects. Shell grafts are the method of choice when treating larger lesions and those located on the tibia and posterior femur, as well as patella defects that are not well circumscribed. In both cases the allograft is typically 8 to 10 mm in thickness, which allows just enough bone to have the graft heal to the host. Thicker grafts are not recommended since the greater the allograft bone, the greater the possible immune load and longer healing time. If the depth of the host defect to reach healthy cancellous bone is greater than a centimeter, autograft bone should be used to fill to the desired depth. The allograft should be in direct apposition with the host at its base, and flush with the adjacent articular cartilage. If the allograft is countersunk, it will not serve adequate func-

FIGURE 9.

Shell donor graft with host site prepared.

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such as swimming and bicycling are permitted when weight bearing is begun, although stationary cycling can be started in some cases during the limited weightbearing phase. Full return to activities is usually 6 months with femoral grafts, and 12 months with tibial grafts. While moderate levels of activities are frequently allowed, contact and high impact activities such as football and basketball are discouraged. Clinical Results

FIGURE 10.

Dowel allograft for femoral condyle lesion.

tion. If left proud, recent evidence has shown shear forces can result in damage to the articular cartilage.72 The dowel technique uses circular cutters in diameters of 5 mm increments up to 35 mm to prepare the host and donor plug to match the defect. The advantages of dowel grafts are relatively easy to prepare, readily reproduced, and often inserted in press-fit fashion.95 Shell grafts, although normally square or rectangular in shape, have the advantage of not being limited by shape or size and thus are able to be used for any defect although the technique for fixing them can be more difficult and commonly requires supplemental fixation.96 Postoperative Rehabilitation Postoperative treatment is dependent on many variables including stability of fixation, location and size of the graft, and additional procedures performed.95-99,114-117 While continuous passive motion (CPM) is routinely used during the initial few weeks after surgery, weight bearing protocols vary according to different investigators. Dowel grafts that are well secured in press-fit fashion are typically healed enough by six weeks to permit weight bearing. Nonweight bearing for shell grafts of the femur has been recommended to be as short as six weeks for small grafts to as long as 12 weeks for grafts that are large in size. Tibial grafts which replace half of the plateau require non-weight bearing for at least 12 weeks. Patella grafts are allowed immediate weight bearing, but squatting, kneeling, and strenuous activities are not permitted for two months to prevent shear forces dislodging the graft. In all cases, radiographic evidence of healing is the final determinate as to when full weight bearing is permitted. Functional activities

The University of Toronto was the first of the three to begin use of osteochondral allografts when in 1972 it was included as part of their orthopaedic transplant program. In 1985 they reported the results of their initial 100 cases with shell grafts used in treating lesions of the femur or tibia in 95, patella in 3, and talus in 2.115 The average follow-up time was 3.8 years. Using a modified Hospital for Special Surgery knee scoring system the success rate for the group was only 56%, but the etiology of the defect was a significant determinate of outcome. Traumatic defects were treated in 48 patients with 36 (75%) successful, but only 10 of 24 (42%) osteoarthritic lesions and 3 of 11 (27%) avascular necrosis defects fared well. Reoperation was performed in 29 patients with 13 arthroplasties, 7 arthrodesis, 5 repeat allografts, 3 debridements, and 1 autograft. In a subsequent report of 126 knees in 123 patients treated specifically for defects secondary to trauma or OCD, 108 knees (86%) were successful.96 The average follow-up for the group was 7.5 years (2-22 years) with a survivorship analysis of 95% at 5 years, 71% at 10 years, and 66% at 20 years. Factors related to failure included patient age over 50 years, bipolar lesions, knee malalignment, and workers compensation cases. The University of California at San Diego began their osteochondral program in 1983, and in 2000 presented their results of treating lesions due to trauma, OCD, or AVN in 211 knees.96 Evaluation was performed using a modified 18 point D’Aubigne scale which equally weighed pain, range of motion, and function. The mean follow-up was 52 months with a range of 12 to 186 months. The reported good to excellent results in 116 of 125 (93%) femoral grafts, 26 of 40 (65%) tibiofemoral grafts, and 35 of 46 (76%) patellofemoral grafts for an overall success rate of 84%. Analysis of their failures confirmed the importance of careful patient selection as shown by uncorrected ligamentous instability and limb malalignment being

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associated with a higher failure rate. In addition, unipolar grafts faired substantially better than bipolar with 92% versus 69% successful for patellofemoral lesions and 86% versus 50% successful for tibiofemoral defects, respectively. Of the failures who had further surgery, 13 had joint replacements, 9 had repeat allografts, and one arthrodesis. Garrett’s use of osteochondral allografts also began in 1983 with the results of his initial 17 patients treated for OCD of the femur reported in 1994.117 Dowel grafts were used in 10 cases and shell in 7 with a follow-up of 2-9 years (mean 3.5 years). Sixteen were asymptomatic with the only failure being a nonunion of a shell graft at 15 months. All patients had repeat arthroscopies with most being at 6 weeks to 6 months, but three were performed at 15 months, 24 months and 6 years. The articular cartilage was found to be intact with flush margins in all except the one failure. A radiographic study of 103 patients who had pre- and postoperative plain films found that 18 of 88 (20%) subjectively successful patients had poor radiographic results, as shown joint-space narrowing or graft collapse.94 However, several of these patients had traits that have since been found to contribute to failure including the grafts being at least 10 mm thick. A comparative study with more stringent patient selection and current surgical techniques is warranted to see how this may effect radiographic results. The overall clinical experience with allograft transplantation indicates that with strict patient selection and meticulous attention to concomitant knee pathology, the success rates on the order of 70-80% at five to ten years follow-up can be expected (Fig 11). Conclusions The resurfacing of focal articular cartilage lesions using osteochondral allografts has been associated with a successful outcome at even long-term follow-up and compares favorably to other available treatment means. A disadvantage of osteochondral allografts is the concern for disease transmission and immunologic rejection. While immune response can occur, the clinical effects appear to be limited. Even if tissue type matching is of some benefit, it would be difficult to implement due to the already limited allograft supply. At the present time, osteochondral allografts should be considered as a viable option when treating articular defects 2 cm2 or greater, and in cases of extensive bone loss, fracture fragmentation or expanded OCD lesions.

FIGURE 11. (A) A 2 cm2 medial femoral condyle OCD lesion. (B) Condyle 8 months after osteochondral allograft transfer.

HOW CAN WE ACCURATELY AND VALIDLY ANALYZE RESULTS? Outcomes analysis is essential to document the efficacy of various articular cartilage procedures. Prospective, randomized, controlled data analysis is what is needed but is most difficult to obtain when studying the variable presentation of articular cartilage pathology, extended injury to surgery interval and evolving treatment techniques. In addition, the long term natural history associated with the articular cartilage pathophysiology requires extended follow-ups perhaps over the course of a lifetime. At the very least, matched cohort comparison studies validating the advantages of one technique over another are essential. Various categories of bias can be easily introduced when analyzing the numerous types, sizes and sites of lesions as well as commonly associated pathologies

TRAUMATIC FOCAL ARTICULAR CARTILAGE LESIONS such as meniscal tearing, ACL deficiency and malalignment which can all be confounders. Many rating scales and scores have been used as clinical assessment tools. The multitude of different methodologies make accurate comparisons between study data difficult, confusing and potentially invalid. Also, it is important to recognize that clinical success as usually measured as improvement in pain and function does not necessarily correlate with histomorphologic, biochemical and biomechanical success. We know this from our patients who have documented osteoarthritic lesions yet are not clinically symptomatic. The ICRS has introduced a rating scale based upon the International Knee Documentation Score and is working towards validating this tool for assessment of patients with chondral pathology pre- and postoperatively.25 Furthermore, cartilage-specific MR scanning has the potential to be a useful tool for postoperative assessment of “repair” tissue viability, quality, quantity, thickness and perimeter integration which could then provide correlation with clinical rating and symptom assessment.18-20 Arthroscopic second look documentation remains the gold standard for visual evaluation of chondral lesion surface restoration and various scales for grading the appearance of the lesion have been reported. Arthroscopic treatment of patellofemoral pain has taught us that viewing or probing the repair tissue surface does not always correlate with the patient’s problem and also may not be a reliable indicator of “optimal” tissue or healing. Histologic study through tissue biopsy can provide more detailed information about the type of repair, tissue profile, perimeter and subchondral bone integration and status of the adjacent host tissue. It is essential to point out that hyaline tissue is but one component of a highly organized and structured system that constitutes articular cartilage and contributes to joint function.13 Another limitation in the interpretation of treatment results after chondral surgery is in the area of biomechanical function of the repair tissue under loaded conditions. In order to establish whether the restored tissue will function in a mechanically efficient manner, some measure of the mechanical properties of the repair tissue is useful. Microindentation analysis has been performed using nondestructive mechanical stiffness probes. Reports on the use of these probes indicate that they may provide valuable data on the response of chondral repair tissue to compressive loading which can be compared with “normal” articular surfaces.78

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FUTURE DIRECTIONS: WHERE ARE WE HEADING? Where are we currently headed at least as far as the treatment of focal chondral lesions? Certainly, restoration of hyaline cartilage seems feasible and it is established that chondrogenesis as well as chondrocyte viability after transfer can be realized and carried out. Unfortunately, the complex and variable presentation of articular cartilage pathology including the multiple significant confounders make comparisons of treatments difficult. Younger patients with pure traumatic lesions benefit greater from chondral surgery, however we all recognize from our clinical experiences that there is a significant cohort of patients with symptomatic lesions that are middle-aged and do not have a distinct trauma history. The future will most certainly need to address all patients and cost-benefit analyses have supported the approach to treatment of these lesions.118 What Is Required? In general, when treating an articular cartilage defect, there are several methods that can be considered to achieve a congruent, biomechanically efficient and durable resurfacing. Repair, by definition would include an injury response mechanism while regeneration defines a developmental process that may recapitulate the embryonic tissue cascade. Replacement would depend on a biological prosthesis or polymer. Repair and regeneration may both be realized through the incorporation of the essential components of type II hyaline articular cartilage including a cell source for replication, biologic turnover and matrix production. The cell source could either be the differentiated chondrocyte or some other chondroprogenitor cell line including mesenchymal stem cells. Also, autogenous versus allogeneic cell sources can be considered depending upon availability, cost effectiveness and compatibility. The cell line would be required to effectively produce a matrix that would proliferate and remodel and would be responsible for the biomechanical function of the new tissue. The matrix would include a fibrillar meshwork of type II collagen fibers imbedded in a proteoglycan aggregate containing glycoaminoglycans. The ultrastructure of this composite would require a unique interaction of all components as well as water. In addition, as a tissue the composite would require an organizational architecture and temporary scaffold in order to provide a three-dimensional structure for all components to be arranged during the proliferative and maturation phases. This

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tissue would also need to be attached to the underlying bone via a tidemark and transitional zone and be able to effectively integrate with the surrounding perimeter native hyaline tissue. A significant challenge remains in this area of fixation and bioadhesives and how the new maturing construct would be anchored to the surrounding tissue.119-121 Functionally, restored articular cartilage would require the superior loading characteristics including optimal function in compression and optimal viscoelastic qualities. These characteristics would need to be durable over time. The other essential requirement would be a validated method in order to precisely document efficacy using a prospective, randomized, controlled, comparison study. Currently, we are heading in the direction of regenerating tissue but remain far off the mark as far as several issues are concerned. Gene-modified tissue engineering holds great promise both in terms of controlling and manipulating repair and regeneration sequences, however a number of deficiencies remain and need to be worked out. Site and zonal specific articular architecture replication remains a significant challenge in terms of restoring the precise surface of the trochlea or the patella versus say the lateral or the medial femoral condyles. These areas of the knee all have distinct surface topographic and underlying zonal architectural differences which need to be appreciated and reproduced. There are still significant issues and difficulties associated with obtained native-new tissue integration as well as tidemark and underlying bone restoration.121 The concept of whole tissue regeneration needs to be kept in mind particularly when considering bone defects or irregularities associated with fracture or OCD. In cases where immature repair or regenerated tissue is remodeling, it remains a challenge to calculate what is the proper load to apply to this tissue in order to avoid counterproductive effects yet maintain “normal” patterns. More recently, medical research, particularly in the area of stem cell biology and genetic engineering, has grown more politically charged with enormous media and public attention and frequent debate. As the controversies are clarified, government funding and grants for advanced work may be affected. Progress in the areas of stem cell biology, gene-modified tissue engineering and tissue regeneration will most certainly be tied to the media and public’s awareness, perception and approval of this work.119,122

Where Are We Going? The future holds much promise especially in the area of gene-modified tissue engineering. Newer command and knowledge of the mapped genome will permit better understanding of the mechanisms of cartilage physiology and degradation. Regulation of catabolic and anabolic bioactive protein factors will most certainly allow manipulation and amplification of cellular mechanisms contributing to a more ordered repair process. Development of biomechanical tissue loading bioreactors may allow ex vivo whole tissue processing and expansion that may through dynamic compression result in a biomechanically mature and proven replacement construct. Work in the area of biologic and biomaterial related tissue scaffolds and matrices as well as bioadhesives continues to improve and will provide an effective method of introducing and fixating ex vivo prepared osteochondral grafts or repair tissue. Although many rapid advances and progress has been realized particularly in these areas of engineering and biology, much work still needs to be done. Many questions remain. Which cells to use: mesenchymal stem cells (muscle, periosteum or marrow derived) versus chondral cells including chondroprogenitor or differentiated chondrocytes? Which source of cells: autogenous versus allogeneic? What type of scaffold or carrier should be used to fill the defect: biological matrices versus polymer or copolymer prosthetic matrices which may or may not be bioresorbable. What are the most effective soluble regulators and bioactive factors: what extent should the effects be catabolic versus anabolic and in what dose, delivery method, timing and combination? Which cells should be “treated”: chondrocytes, host cells or pluripotential cells? These questions and others will ultimately need to be answered before an effective and reproducible treatment is realized. Ultimately moving toward a comprehensive approach incorporating basic science, genetic engineering, biochemistry and clinical orthopaedics, tremendous goals may be reached.119-122 CONCLUSIONS Much attention has been focused on the subject of the surgical treatment of focal chondral injuries and associated lesions in the knees of active individuals. Numerous procedures have been reported and continue to be introduced as evolving technology and understanding regarding osteochondral joint pathophysiology expand. A considerable drawback remains

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FIGURE 12.

29

Clinical algorithm for articular cartilage lesion treatment.

in that there is a significant limitation of published, peer-reviewed treatment result data. Although the relatively recent introduction of a multitude of various surgical techniques limits the ability to accurately compare and conclusively document long term outcome results, most authors and clinicians would agree that restoration of hyaline cartilage defects in active individuals remains a worthwhile goal. Treatment guidelines are useful in order to more precisely approach this problem and a clinical algorithm is included to serve as a guideline model for decision making (Fig 12). Adherence to stringent indications, precise techniques and valid prospective or at least controlled comparison data analysis is essential when considering chondral surgery in symptomatic patients. Attention to correcting concomitant pathology is equally important. The choice of which procedure should be selected is dependent upon patient understanding of expectations and goals as well as lesion characteristics and surgeon experience. The treatment of focal articular cartilage lesions in active individuals remains a significant challenge with many controversies remaining and although most would agree that we are certainly heading in the right direction, we are not yet there. Expanding surgical options and exciting and potentially valuable advances ensures that this disci-

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