Cartilage repair remains one of the fastest evolving areas within the field of orthopaedic surgery. Indications continue to be refined and new techniques emerge yearly, with more than 10 new implant technologies in mid- to late-stage clinical trials at this time.
In this chapter we provide a concise overview of current techniques for cartilage repair, present new developments in this evolving area, and subsequently discuss our preferred techniques in more detail.
Damage to the articular cartilage comprises a spectrum of disease ranging from single, focal chondral defects to diffuse osteoarthritis, the latter of which is not discussed in this review. Left untreated, articular cartilage defects have no spontaneous repair potential, and therefore various techniques have evolved to stimulate defect repair or overtly replace damaged cartilage and bone.
Conventional marrow-stimulation techniques, such as abrasion arthroplasty, drilling, or microfracture, attempt to fill the defect with a fibrocartilaginous scar produced by marrow-derived pluripotent stem cells. This tissue, however, is of lesser biologic and mechanical quality than hyaline cartilage and is therefore inadequate to treat larger defects. Tissue engineering technologies, such as autologous chondrocyte implantation (ACI) or matrix autologous chondrocyte implantation (MACI), achieve a tissue that more closely approximates the original hyaline cartilage, but they are expensive and more invasive, at least in their present form.
Relevant Anatomy and Biomechanics
Partial-thickness chondral lesions do not penetrate the subchondral bone and are therefore avascular, do not heal, and may enlarge over time. Full-thickness defects, especially with injury to the underlying vascular bone, have the potential to fill with a fibrocartilaginous scar formed by cells invading from the marrow cavity. The resulting tissue, however, is predominantly composed of type I collagen, resulting in inferior mechanical properties compared with type II collagen-rich hyaline cartilage.
Long implicated in the subsequent development of osteoarthritis, focal chondral defects result from various etiologies. Patients are approximately evenly divided in reporting a traumatic versus an insidious onset of symptoms; athletic activities are the most common inciting event associated with the diagnosis of chondral lesions. Traumatic events and developmental etiologies such as osteochondritis dissecans (OCD) predominate in younger age groups. For example, traumatic hemarthroses in young athletes with knee injuries are associated with chondral defects in up to 10% of cases. Patellar dislocation is strongly associated with damage to the articular surface, with chondral defects of the patella seen in up to 95% of patients ; the incidence of OCD is estimated at 30 to 60 cases per 100,000 people. Several large studies have found high-grade chondral lesions (Outerbridge grade III and IV) in 5% to 11% of younger patients (i.e., younger than 40 years), and up to 60% in older age groups. The most common locations for these defects are the medial femoral condyle (up to 32%) and the patella, and most are detected incidentally during meniscectomy or anterior cruciate ligament (ACL) reconstruction. Notably, despite this relatively high incidence, many of these defects are incidental in nature and asymptomatic.
Upon careful evaluation, a large percentage of chondral defects are found to be associated with structural abnormalities, such as malalignment, patellar instability, and insufficiency of the ligamentous and meniscal structures. The disappointing early results of cartilage repair have been explained by the failure to diagnose and correct these associated bony and ligamentous abnormalities. For example, in early studies of patellar defects treated with ACI alone, good and excellent results were found in only one third of patients. Later studies, however, identified patellar maltracking as an important associated abnormality, and performance of a corrective osteotomy concurrently with cartilage repair led to good or excellent results in 70% to 80% of patients. These reports emphasize the importance of a thorough patient evaluation to correctly identify and treat all associated abnormalities to ensure the long-term success of chondral repair.
Varus or valgus malalignment of the lower extremity results in compartment overload and is associated with degeneration of the articular surface. Coventry’s early work with osteotomies popularized this technique for the treatment of osteoarthritis with comparatively large correction angles. The population treated for chondral defects today, however, is predominantly athletic and does not tolerate large degrees of overcorrection. When performed concurrently with cartilage repair, osteotomy around the knee should restore the mechanical axis to neutral alignment, with the goal of decreasing abnormal pressures to normal rather than unloading the respective compartment through overcorrection. Even in patients with early joint space narrowing, overcorrection of the mechanical axis should be limited to 2 degrees or less.
Ligamentous insufficiency, most commonly of the ACL, increases shear forces in the knee joint and predisposes the joint to further injury and thus contributes to chondral damage. Any patient undergoing cartilage repair should therefore be carefully evaluated for instability, which can be corrected in a staged or concomitant fashion.
Meniscal insufficiency, such as after a subtotal meniscectomy, increases contact stresses by up to 300% in the respective compartment and is associated with the development of osteoarthritis. In carefully selected patients with meniscal insufficiency, meniscal allograft transplantation can provide pain relief and improved function. The ideal candidate for allograft transplantation has a history of prior total or subtotal meniscectomy with refractory, activity-related pain localized to the involved compartment. After meniscal allograft transplantation, good to excellent results are achieved in nearly 85% of cases, and patients demonstrate a measurable decrease in pain and increase in activity level.
Classification
Earlier classification schemes were mainly descriptive in nature and have largely been abandoned. Newer systems have evolved to classify chondral defects based on size and depth to establish a universal language among clinicians and researchers and to ideally provide a correlation of lesion grade with clinical outcome. Currently, the most commonly used arthroscopic classifications are the Outerbridge and International Cartilage Repair Society systems ( Table 97-1 , Fig. 97-1 ). The International Cartilage Repair Society has also published a grading system for arthroscopic evaluation after prior cartilage repair procedures (see Table 97-1 ).
| Lesion Grade | DESCRIPTION | |
|---|---|---|
| Outerbridge Classification | ICRS Classification (with Subclassifications) | |
| 0 | Normal cartilage | Normal cartilage |
| 1 | Cartilage with softening and swelling |
|
| 2 | Partial-thickness defect with fissures on the surface that do not reach subchondral bone or exceed 1.5 cm in diameter | Less than one-half cartilage depth |
| 3 | Fissuring to the level of subchondral bone in an area with a diameter >1.5 cm | More than one-half cartilage depth, and
|
| 4 | Exposed subchondral bone | Osteochondral lesion violating the subchondral plate |
History
Patients often present with a history of knee injury or prior surgical procedures such as meniscectomy or ACL reconstruction. They report activity-related knee pain and swelling, especially with impact activities such as running. The pain often localizes to the affected compartment and occasionally synovitis develops, resulting in diffuse pain. Larger defects can be associated with mechanical symptoms, profound crepitus, popping, and giving-way.
Physical Examination
Depending on the acuity of symptoms, typical physical examination findings include an antalgic gait, soft tissue swelling, joint effusion, quadriceps atrophy, tenderness with palpation of the joint line and femoral condyle, and occasionally mild varus/valgus laxity due to loss of cartilage and/or meniscal substance. With the exception of very advanced cases, or in large lesions with loose bodies, motion is generally preserved. It is important to evaluate limb alignment and ligamentous stability, because any deficiencies should be treated in either staged or concomitant procedures.
Imaging
Radiographic evaluation should include a standard weight-bearing anteroposterior view in extension, a posteroanterior view in 45 degrees of flexion (Rosenberg view), a flexion lateral view, and an axial view of the patellofemoral joint (Merchant or skyline view). Double-stance, weight-bearing, long-leg radiographs are obtained to quantify lower extremity alignment to determine if a corrective osteotomy is required.
Computed tomography (CT) scans are used infrequently unless the lesion also affects the subchondral bone, such as in persons with OCD, traumatic osteochondral defects, or failed prior marrow stimulation techniques. Here, CT, especially when combined with arthrography, can be very helpful to more precisely delineate the exact dimensions of the defect and assess bone healing ( Fig. 97-2 ).
Magnetic resonance imaging (MRI) assessment of the articular surface has received increased attention because of newly developed protocols for cartilage-specific high-resolution imaging and contrast enhancement with intravenous and intraarticular gadolinium. Delayed gadolinium-enhanced MRI of cartilage is an imaging protocol that provides an assessment of the glycosaminoglycan content of cartilage ( Fig. 97-3 ). It represents a useful tool for noninvasive follow-up evaluation after cartilage repair techniques such as ACI. The recent discovery of gadolinium-associated nephrogenic systemic fibrosis has raised concerns about the use of contrast MRI; however, this disease predominately appears to affect patients with renal insufficiency. Additional noncontrast techniques are being developed, including T2-weighted mapping and T1-rho that allow indirect evaluation of the biochemical composition of cartilage, such as the glycosaminoglycan and collagen content. Although arthroscopy remains the gold standard for assessing articular injury, sensitivities and specificities approaching 90% have been reported with MRI protocols using a 1.5-Tesla magnet. However, the choice of correct sequences is more important than magnet strength ( Fig. 97-4 ). Furthermore, MRI provides additional information on the ligamentous and meniscal structures, which, if compromised, would require staged or concomitant treatment. Several scoring systems have been developed to characterize the structural outcomes after cartilage repair, such as the MOCART system. At this time, however, no clinical correlation has been demonstrated between MRI and clinical outcomes.
Another application for both CT and MRI is in the evaluation of patellofemoral cartilage lesions because these lesions allow calculation of the tibial tubercle-to-trochlear groove distance, a measure of the lateral translation of the tibial tubercle in relation to the trochlear groove. This parameter is considered more objective than the clinical evaluation of the quadriceps (Q) angle and is important when considering a tibial tubercle osteotomy or anteromedialization. A normal range is less than 15 mm, whereas patients with patellar instability typically demonstrate a tibial tubercle to trochlear groove distance greater than 20 mm.
Decision-Making Principles
Indications for Cartilage Repair
Many cartilage defects seen on imaging or arthroscopy are asymptomatic, and thus careful assessment of alternative sources of pain is necessary. Conservative treatment with physical therapy should be continued for at least 3 to 6 months in conjunction with activity modification and weight normalization unless a young patient has a large defect that can be expected to deteriorate over time. Injection therapy, although not indicated in these young patients, might be considered in older patients who are within a few years of age eligibility for joint replacement surgery.
Surgical intervention is indicated for a full-thickness (grade 3 or 4) cartilage defect and after adequate nonoperative management has failed to provide acceptable pain relief. A thorough discussion of the details of this complex surgery and recovery is a necessary part of the informed consent process.
Contraindications
Smoking, obesity (body mass index >35), inflammatory conditions, or uncorrected articular comorbidities such as malalignment, meniscal deficiency, and ligamentous laxity are contraindications to cartilage repair. Advanced degenerative changes (>50% joint space narrowing) are considered a contraindication to cartilage repair in all but very young patients who have intolerable symptoms and no other options.
Treatment Algorithm
Treatment strategies for cartilage repair are based primarily on defect location and size. The two most common locations for cartilage defects are on the (medial) femoral condyle and the patellofemoral joint. The tibiofemoral and patellofemoral compartments behave quite differently and require different treatment approaches.
Treatment Choice Based on Defect Location
Treatment decisions in the tibiofemoral compartment are based on defect size. Knutsen et al. conducted a randomized controlled trial (RCT) of microfracture versus ACI and reported similar overall clinical results. However, larger defects (>4 cm 2 ) treated with microfracture did significantly worse, whereas ACI outcomes were not correlated with size. The authors therefore recommended that larger defects should be considered for ACI. Basad et al. investigated this issue further with an RCT of ACI and microfracture, specifically for defects larger than the threshold found in Knutsen’s trial (4 cm 2 ), and reported significantly better results with ACI. Another recent RCT demonstrated significantly better histologic and functional outcomes after ACI when compared with microfracture for defects that were not yet chronic (<3 years).
Other studies have reported that the microfracture technique should be limited to smaller lesions, for which this technique, as well as osteochondral autograft transfer (OAT), produce good and excellent results in 60% to 80% of patients.
The decision to use microfracture versus OAT is based on several factors, including the surgeon’s familiarity with the techniques, patient demand, and associated bone loss. The incidence and magnitude of OAT harvest site morbidity are controversial but are generally considered to be approximately 5%. An athletic population has shown better return to play with OAT when compared with microfracture (93% vs. 52%, respectively). Therefore OAT is recommended for smaller lesions, lesions in athletes who place a high demand on their knees, and for patients with associated bone loss, whereas microfracture is suited for medium-size defects with little or no bone loss in patients who place a lower demand on their knees.
Both ACI and osteochondral allograft transplantation have produced good and excellent results in more than 70% of patients presenting with larger defects, but no randomized trials have been conducted to compare the two procedures. Surgeon and patient preference, as well as graft availability, are key factors guiding the treatment decision. Furthermore, associated bone loss or bone abnormalities (e.g., cysts, sclerosis, and edema) influence the decision; bone loss of 8 to 10 mm or more severe bony abnormalities can be treated with ACI but would require bone grafting in a staged or concurrent fashion (sandwich ACI), whereas osteochondral allografting presents a single-stage treatment option.
The patellofemoral (PF) compartment is a challenging location, and all interventions, including partial replacements, do worse here when compared with the femoral condyles. The aggressive correction of patellar maltracking is crucial for success.
Although microfracture, OAT, and osteochondral allograft procedures have generally good outcomes in the femoral condyles, on the basis of limited studies and expert opinion, consensus is growing that they should be used cautiously in the PF compartment. Kreuz et al. found only transient improvement for 18 to 36 months after microfracture in the PF compartment. The use of OAT in the PF compartment has shown varying results. Hangody and Fules reported results only slightly worse than in the femoral condyle, whereas Bentley and colleagues reported universal failure of OAT in the patella. Jamali et al. investigated the use of osteochondral allografts in the PF compartment and reported 60% good and excellent results. Recent studies of ACI report successful outcomes in more than 80% of patients. Therefore even though use of ACI in the patella is an off-label indication, it has emerged as the cartilage repair option of choice in the PF compartment.
Osteochondritis Dissecans Lesions
Symptomatic osteochondral defects, such as OCD or fresh osteochondral fractures after patellar dislocation, should be repaired whenever possible. One exception is the adolescent with open growth plates, for whom nonoperative treatment of stable OCD lesions can be successful.
Debridement alone without subsequent repair can provide good short-term pain relief but should only be considered in specific circumstances, such as when athletes are in the midst of their playing season, when defects are very small, and when patients are unable or unwilling to follow the rehabilitation associated with repair. In long-term follow-up studies, high rates of osteoarthritis were found as early as 9 years after fragment removal, especially in lesions larger than 2 cm 2 . Repair for OCD defects with OAT revealed better outcomes than did repair with microfracture at 4 years in a randomized trial (83% vs. 63%, respectively). ACI is associated with greater than 80% success in younger patients, and osteochondral allograft transplantation is successful in approximately 70%.
Patient Age and Defect Chronicity
The most age-dependent procedure appears to be microfracture, with patients older than 35 years demonstrating worse outcomes. Although older patients generally do less well than younger patients, this age dependency is less pronounced for other procedures, such as OAT, ACI, and osteochondral allograft transplantation.
Chronic defects demonstrate worse outcomes, whereas repairs of acute injuries tend to demonstrate better results.
Treatment Options
Prior to the development of modern bioengineering technology, orthopaedists were restricted to procedures that aim to palliate the effects of chondral lesions or attempt to stimulate a healing response initiated from the subchondral bone, resulting in the formation of a fibrocartilaginous repair tissue. Simple arthroscopic lavage and debridement of arthritic joints has been used since the 1940s in an effort to reduce symptoms resulting from loose bodies and cartilage flaps. Although lavage alone has not been found to be effective, in combination with debridement, it can result in adequate pain reduction in slightly more than half of patients. The goal of debridement of chondral defects is to remove any loose flaps of articular cartilage and create a defect shouldered by a stable rim of intact cartilage leading to reduced mechanical stresses in the defect bed. Currently, its use is limited to the treatment of small, incidental lesions found during arthroscopy or for larger and usually more diffuse arthritic lesions associated with mechanical symptoms in an attempt to delay the need for more invasive procedures such as total joint replacement.
Marrow stimulation techniques (MSTs), such as drilling, abrasion arthroplasty, and microfracture, attempt to induce a reparative response. This response is achieved by perforation of the subchondral bone after radical debridement of damaged cartilage and removal of the tide mark “calcified” zone, which has been found to enhance the volume and integration of repair tissue. The currently favored technique is microfracture, in which an awl is used to perform multiple perforations in the subchondral plate. However, recent studies have demonstrated that subchondral drilling with a drill bit (rather than smooth Kirschner wire) results in the formation of better repair tissue and better reconstitution of the subchondral bone. Perforation of the subchondral bone results in the extravasation of blood and marrow elements with formation of a blood clot in the defect. Over time, this blood clot, and the primitive mesenchymal cells contained within, differentiate into fibrocartilaginous repair tissue that fills the defect. Unlike hyaline cartilage, fibrocartilage largely consists of type I collagen and exhibits inferior wear characteristics. Postoperatively, MSTs require extended periods of relative non–weight bearing for 6 or more weeks, as well as the use of continuous passive motion (CPM) for up to 6 hours per day to enhance maturation of the repair tissue. Even though MSTs result in reparative tissue with inferior wear characteristics, treatment of smaller defects (<4 cm 2 ) results in good outcomes in 60% to 70% of patients. However, especially with larger defects or those located in the PF compartment, symptoms tend to worsen again after 18 to 24 months.
Osteochondral Autograft Transfer
OAT brings mature autologous cartilage from a lesser weight-bearing area of the knee into the defect, using instrumentation such as OATS (Arthrex, Naples, FL), COR (Mitek, Raynham, MA), or mosaicplasty (Smith & Nephew, Andover, MA) to address medium-size defects (1 to 4 cm 2 ). In this technique, multiple small osteochondral cylinders are harvested from lesser weight-bearing areas of the same knee joint, mostly from the lateral or medial aspects of the trochlea, the sulcus terminalis, or the intercondylar notch. Traditionally the lateral trochlea was the preferred harvest site, but studies have demonstrated lesser PF loading in the medial trochlea, which might therefore be a more advantageous harvest site. The chondral defect is prepared with a punch to create a recipient hole that matches the graft cylinders, which are then press-fitted into the defect. Commonly, multiple cylinders must be transferred to fill larger defects. Osteochondral autografting is limited by the amount of cartilage that can be harvested without substantially violating the weight-bearing articular surface. The main advantage lies in its autogeneity, thus avoiding the risk of disease transmission, providing immediate graft availability through harvesting of the patient’s own tissue, and resulting in a decreased cost of this single-stage procedure. Furthermore, because of the transfer of mature cartilage with primary bone-to-bone healing, return to play is generally faster than for procedures that require graft maturation, such as marrow stimulation and ACI.
Autologous Chondrocyte Implantation
ACI introduces chondrogenic cells into the defect area, resulting in the formation of a repair tissue that more closely resembles the collagen type-II rich hyaline cartilage. The original technique of ACI was developed more than 15 years ago and has been used in the United States to treat more than 10,000 patients since its approval by the Food and Drug Administration (FDA) in 1997. Second- and third-generation techniques that involve the use of collagen matrices to replace the periosteal patch cover or as a preseeded carrier are available in Europe, with more than 5-year follow-up results. These techniques offer the benefit of a less-invasive surgical approach through arthroscopic application and have demonstrated excellent results without the periosteum-related problems seen in conventional ACI, but they have not yet been approved by the FDA.
ACI is indicated for the treatment of medium- to large-size chondral defects with either no osseous deficits or shallow associated osseous deficits. ACI has been approved by the FDA for application in the femoral condyle (medial, lateral, and trochlea) after failure of an MST, but it has also been used to treat patellar defects in an off-label fashion. Originally reported in 1994 for the treatment of chondral defects in the knee, it has more recently been applied to other joints such as the shoulder and ankle, although such use is off-label.
ACI in its current form is a two-stage procedure in which a cartilage biopsy of approximately 200 to 300 mg is harvested during an initial arthroscopic procedure, most commonly from the intercondylar notch or the trochlear margin. The tissue contains approximately 200,000 to 300,000 chondrocytes, which are released by enzymatic digestion of the surrounding matrix and expanded in a monolayer culture for several weeks followed by staged reimplantation through an arthrotomy. Although the ideal cell density for reimplantation is controversial, in current practice, reimplantation of approximately 12 million cells is recommended for an average size lesion of 4 to 6 cm 2 . The postoperative rehabilitation is similar to that of marrow-stimulating techniques, utilizing protected weight bearing for 6 to 8 weeks and CPM for up to 6 weeks. Return to impact and pivoting activities is considered after 9 to 12 months.
Particulated Juvenile Cartilage Allograft
Rather than transplanting osteochondral cylinders, the particulated juvenile cartilage allograft technique (DeNovo NT; Zimmer, Warsaw, IN) uses only articular cartilage allografts. The cartilage is retrieved from juvenile donors, because the density and metabolic activity of chondrocytes is substantially higher in this age group. The tissue is minced into cubes with a side length of 1 mm, promoting chondrocyte migration out of the extracellular matrix. The chondrocytes then attach to the subchondral plate of the defect and produce new matrix, slowly filling the defect with repair tissue in a process comparable with other cell-based therapies. At this point, few clinical outcomes data have been published, because the graft is regulated as minimally manipulated allograft tissue, and therefore it did not require the same extensive FDA-mandated studies necessary for other products in the United States.
Preserved Osteochondral Allograft
The preserved osteochondral allograft (Chondrofix; Zimmer) was recently developed to address major logistical issues in the use of fresh osteochondral grafts, namely limited availability and a short window to schedule surgery once a suitable graft has been found. Although frozen grafts offer similar benefits, the freezing process causes substantial damage not only to the chondrocytes but also to the extracellular matrix itself, causing decreased survival of frozen grafts. The proprietary processing protocol used to treat the preserved osteochondral allograft cylinders removes cells, lipids, and potential pathogens, allowing off-the-shelf storage at room temperature. Given that grafts are provided preshaped in various diameters (7, 9, 11, and 15 mm) and a length of 10 mm, there is no need for size, side, or compartment-specific matching, which has greatly improved graft availability. Depending on diameter, the grafts can be implanted either arthroscopically or through a mini arthrotomy. The technique is closely related to OAT but avoids the need for graft harvest with its associated issues of donor site morbidity, mismatch in donor/recipient site cartilage thickness, and the technical difficulty of harvesting a perpendicular graft.
The implant is regulated as minimally manipulated human allograft tissue and therefore no clinical outcome data were generated during the approval process. Therefore, until the clinical outcomes have been established, the procedure should be viewed as an investigational second-line treatment option.
Osteochondral Allograft Transplantation
More than 750,000 musculoskeletal allografts were transplanted in 1999, mainly for the treatment of bone defects and reconstruction of the ACL. More recently, the treatment of chondral defects with fresh osteochondral allografts has garnered significant attention because of its potential to restore and resurface even extensive areas of damaged cartilage and bone. Unfortunately, the supply of osteochondral allograft tissue remains limited because of issues related to the donor pool and aseptic processing. However, improved preservation techniques have been developed that allow storage times of up to 4 weeks with acceptable compromise in chondrocyte viability with grafts stored at 4°C.
Osteochondral allograft transplantation is used predominantly in the treatment of large and deep osteochondral lesions resulting from osteochondritis dissecans, osteonecrosis, and traumatic osteochondral fractures, but it can also be used to treat peripherally uncontained cartilage and bone defects. Furthermore, osteochondral allografting presents a viable salvage option after failure of other cartilage resurfacing procedures. When it is used for the treatment of cartilage or shallow osteochondral lesions, a thin subchondral bone graft (5 to 7 mm) results in the most rapid integration and best chance of success, because the mechanism of bulk allograft failure historically has been through creeping substitution and collapse of the transplanted osseous bed rather than failure of the articular cartilage itself.
The main advantages compared with OAT are the ability to closely match the curvature and thickness of the recipient cartilage by harvesting the graft from a corresponding location in the donor condyle, the ability to transplant large grafts, and the avoidance of donor site morbidity. These techniques require relatively atraumatic seating of the osteochondral plugs; multiple studies have demonstrated deleterious effects of excessive forces during the insertion, such as using a mallet to seat the plug all the way flush with the surrounding articular surface.
The main concern with fresh allograft transplantation is the small risk of disease transmission, which is estimated at 1 in 1.6 million for the transmission of human immunodeficiency virus. Since the advent of strict donor screening criteria in combination with polymerase chain reaction testing for human immunodeficiency virus and hepatitis, no cases of viral disease transmission have been identified.
We have developed a comprehensive treatment algorithm based on defect size and location that takes into consideration the patient’s activity and demand level ( Fig. 97-5 ). In the following sections, we discuss four commonly used techniques and their application in our clinical practice.
Marrow Stimulation
Marrow stimulation is most commonly performed as an all-arthroscopic procedure, and the setup and patient positioning is the same as that for routine knee arthroscopy. In very posterior defects, the patient should be positioned so that knee hyperflexion can be achieved.
Approach and Defect Preparation
After routine diagnostic arthroscopy to evaluate the cartilage defect ( Fig. 97-6, A ), loose chondral flaps are first debrided with the shaver; a curette is then used to achieve stable vertical shoulders and remove the layer of calcified cartilage ( Fig. 97-6, B ).
Marrow Stimulation
After thorough debridement, multiple holes are created in the subchondral bone with a microfracture awl or small drill bit ( Fig. 97-6, C ). In an effort to remain perpendicular to the chondral surface, it may be necessary to rotate the articular surface in line with the awl or create accessory portals. It is important to preserve the integrity of the subchondral bone, which can be violated if holes are not spaced wide enough and thus connect or become confluent. Ideally, the holes should be spaced approximately 3 to 4 mm apart, resulting in 3 to 4 holes per cm 2 . Stability of the transition zone between surrounding cartilage and regenerate fibrocartilage can be improved by placing holes directly adjacent to the defect shoulders. After completion of the microfracture, pump pressure is lowered and bleeding should be observed from all holes.
Closure
Arthroscopy portals are closed with interrupted sutures. The patient should be counseled that occasionally joint aspiration may become necessary because of persistent bleeding from the treated defect.
Osteochondral Autograft Transplantation
Osteochondral autograft transplantation can be performed through either an arthroscopic or open approach ( Fig. 97-7, A ), based on the exact defect size and location and the surgeon’s preference.
