Cartilage repair: generations of autologous chondrocyte transplantation

Articular cartilage in adults has a limited capacity for self-repair after a substantial injury. Surgical therapeutic efforts to treat cartilage defects have focused on delivering new cells capable of chondrogenesis into the lesions. Autologous chondrocyte transplantation (ACT) is an advanced cell-based orthobiologic technology used for the treatment of chondral defects of the knee that has been in clinical use since 1987 and has been performed on 12,000 patients internationally. With ACT, good to excellent clinical results are seen in isolated post-traumatic lesions of the knee joint in the younger patient, with the formation of hyaline or hyaline-like repair tissue. In the classic ACT technique, chondrocytes are isolated from small slices of cartilage harvested arthroscopically from a minor weight-bearing area of the injured knee. The extracellular matrix is removed by enzymatic digestion, and the cells are then expanded in monolayer culture. Once a sufficient number of cells has been obtained, the chondrocytes are implanted into the cartilage defect, using a periosteal patch over the defect as a method of cell containment. The major complications are periosteal hypertrophy, delamination of the transplant, arthrofibrosis and transplant failure. Further improvements in tissue engineering have contributed to the next generation of ACT techniques, where cells are combined with resorbable biomaterials, as in matrix-associated autologous chondrocyte transplantation (MACT). These biomaterials secure the cells in the defect area and enhance their proliferation and differentiation.     

Autologous chondrocyte transplantation

Since its introduction in 1987, autologous chondrocyte transplantation (ACT) for the management of full-thickness chondral defects of the knee has gained considerable attention and has renewed interest in cartilage repair. At this time there are patients with 10 to 13 years of follow-up who have continued to benefit from ACT. ACT is indicated for the management of full-thickness femoral articular Outerbridge grade III and IV lesions. Treatment of other surfaces such as the patella and tibia have also been successful. A thorough knowledge of patient selection and indications, good laboratory practices (GLP), standards of cell culturing, meticulous surgical technique, understanding of the normal time course of healing, the appropriate functional postoperative rehabilitation, and the management of specific ACT-related complications are all essential to good clinical outcomes. The success of this procedure with its excellent clinical outcomes and durability of the articular repair have made it a cost-effective procedure comparable to other technologies.     

Arthroscopic second generation autologous chondrocyte implantation

A biodegradable, hyaluronian-based biocompatible scaffold was used for autologous chondrocyte transplantation. This prospective study analyzes a clinical outcome of 70 consecutive patients treated by arthroscopic autologous chondrocyte transplantation at minimum 24 months follow up (47 of these patients achieved minimum 36 months follow-up and 21 patients minimum 48 months follow-up) in order to establish clear indication criteria for this type of treatment. 31 of these patients presented isolated chondral lesions, while 39 patients with associated lesions (23 ACL lesions, 28 meniscal lesions, 1 varus knee) were treated during the same surgical procedure with cartilage harvesting. A statistically significant clinical improvement was shown just at 24 months and the second-look arthroscopy demonstrated a complete coverage of the grafted area with a hyaline cartilage-like tissue in 12 of 15 analyzed patients. A better clinical outcome was observed in young, well-trained patients and in traumatic lesions. Other factors, such as defect size, localization, previous and associated surgery did not influence significantly the results. This matrix autologous chondrocyte transplantation procedure simplifies the surgical procedure and can be performed arthroscopically, thus reducing surgical morbidity and recovery time. Level of evidence: Level IV (Prospective case series study)     

Three-year clinical outcome after chondrocyte transplantation using a hyaluronan matrix for cartilage repair

Repair of articular cartilage represents a significant clinical problem and although various new techniques - including the use of autologous chondrocytes - have been developed within the last century the clinical efficacy of these procedures is still discussed controversially. Although autologous chondrocyte transplantation (ACT) has been widely used with success, it has several inherent limitations, including its invasive nature and problems related to the use of the periosteal flap. To overcome these problems autologous chondrocytes transplantation combined with the use of biodegradable scaffolds has received wide attention. Among these, a hyaluronan-based scaffold has been found useful for inducing hyaline cartilage regeneration. In the present study, we have investigated the mid-term efficacy and safety of Hyalograft C grafts in a group of 36 patients undergoing surgery for chronic cartilage lesions of the knee. Clinical Outcome was assessed prospectively before and at 12, 24, and 36 months after surgery. No major adverse events have been reported during the 3-year follow-up. Significant improvements of the evaluated scores were observed (P < 0.02) at 1 year and a continued increase of clinical performance was evident at 2 and 3 years follow-up. Patients under 30 years of age with single lesions showed statistically significant improvements at all follow-up visits compared to those over 30 with multiple defects (P < 0.01). Hyalograft C compares favorably with classic ACT and is particularly indicated in younger patients with single lesions. The graft can be implanted through a miniarthrotomy and needs no additional fixation with sutures except optional fibrin gluing at the defect borders. These results suggest that Hyalograft C is a valid alternative to ACT.     

Functional outcome of knee articular cartilage repair in adolescent athletes

BACKGROUND: Limited information exists about the treatment of full-thickness articular cartilage lesions of the knee in adolescent athletes. PURPOSE: To evaluate the functional outcome and athletic activity after articular cartilage repair in the knees of adolescent athletes. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Twenty adolescent athletes with full-thickness articular cartilage lesions of the knee were treated with autologous chondrocyte transplantation. Functional outcome was evaluated by subjective patient outcome rating, knee activity scores, and level of athletic participation. RESULTS: At a mean of 47 months after autologous chondrocyte transplantation, 96% of adolescents reported good or excellent results with significant increases in postoperative Tegner activity scores and Lysholm scores. Ninety-six percent returned to high-impact sports and 60% to an athletic level equal or higher than that before knee injury. Return to preinjury sports correlated with shorter preoperative symptoms and a lower number of prior operations. All adolescents with preoperative symptoms < or =12 months returned to preinjury-level athletics, compared to 33% with preoperative intervals longer than 12 months. CONCLUSION: Treatment of full-thickness articular injuries of the knee in adolescent athletes with autologous chondrocyte transplantation yields a high rate of functional success at a mean follow-up of 47 months. The rate of return to demanding athletic activities is higher in cases in which the preoperative duration of symptoms is 12 months or less.     

MR imaging of cartilage repair surgery of the knee

Articular cartilage is a complex tissue with unique properties that are essential for normal joint function. Many processes can result in cartilage injury, ranging from acute trauma to degenerative processes. Articular cartilage lacks vascularity, and therefore most chondral defects do not heal spontaneously and may require surgical repair. A variety of cartilage repair techniques have been developed and include bone marrow stimulation (microfracture), osteochondral autograft transfer system (OATS) or osteochondral allograft transplantation, autologous chondrocyte implantation (ACI), matrix-assisted chondrocyte implantation (MACI), and other newer processed allograft cartilage techniques. Although arthroscopy has long been considered as the gold standard for evaluation of cartilage after cartilage repair, magnetic resonance (MR) imaging is a non-invasive method to assess the repair site and can be scored using Magnetic resonance Observation of Cartilage Repair Tissue (MOCART). MR also provides additional evaluation of the subchondral bone and for other potential causes of knee pain or internal derangement. Conventional MR can be used to evaluate the status of cartilage repair and potential complications. Compositional MR sequences can provide supplementary information about the biochemical contents of the reparative tissue. This article reviews the various types of cartilage repair surgeries and their postoperative MR imaging appearances.     

MR imaging of cartilage repair surgery of the knee

Articular cartilage is a complex tissue with unique properties that are essential for normal joint function. Many processes can result in cartilage injury, ranging from acute trauma to degenerative processes. Articular cartilage lacks vascularity, and therefore most chondral defects do not heal spontaneously and may require surgical repair. A variety of cartilage repair techniques have been developed and include bone marrow stimulation (microfracture), osteochondral autograft transfer system (OATS) or osteochondral allograft transplantation, autologous chondrocyte implantation (ACI), matrix-assisted chondrocyte implantation (MACI), and other newer processed allograft cartilage techniques. Although arthroscopy has long been considered as the gold standard for evaluation of cartilage after cartilage repair, magnetic resonance (MR) imaging is a non-invasive method to assess the repair site and can be scored using Magnetic resonance Observation of Cartilage Repair Tissue (MOCART). MR also provides additional evaluation of the subchondral bone and for other potential causes of knee pain or internal derangement. Conventional MR can be used to evaluate the status of cartilage repair and potential complications. Compositional MR sequences can provide supplementary information about the biochemical contents of the reparative tissue. This article reviews the various types of cartilage repair surgeries and their postoperative MR imaging appearances.     

Disease-specific clinical problems associated with the subchondral bone

The subchondral bone is involved in a variety of diseases affecting both the articular cartilage and bone. Osteochondral defects in distinct locations and of variable sizes are the final results of different etiologies. These include traumatic osteochondral defects, osteochondritis dissecans, osteonecrosis, and osteoarthritis. Traumatic osteochondral defects are caused by osteochondral fractures, separating an osteochondral fragment that includes articular cartilage and both subchondral and trabecular bone from the joint surface. In osteochondritis dissecans, the disease originates in the subchondral bone and secondarily affects the articular cartilage. Location, stage, size, and depth of osteochondral lesions play a role in the treatment of traumatic osteochondral defects and osteochondritis dissecans. Surgical options include fragment refixation, transplantation of osteochondral autografts, or bone restoration by impacted cancellous bone grafts combined with autologous chondrocyte transplantation. An insufficiency fracture of the subchondral bone may be the initiating factor of what was formerly believed to be a spontaneous osteonecrosis of the knee (SPONK). Recent histopathological studies suggest that each stage of SPONK reflects different types of bone repair reactions following a fracture of the subchondral bone plate. Osteoarthritis is a disease that does affect not only the articular cartilage, but also the subchondral bone. Reconstructive surgical techniques aim at preserving joint function, inducing fibrocartilaginous repair, and at correcting malalignment. This review summarizes the current status of the clinical treatment of traumatic osteochondral defects, osteochondritis dissecans, osteonecrosis, and osteoarthritis as they affect the subchondral bone region and its adjacent structures.     

Articular cartilage repair in soccer players with autologous chondrocyte transplantation: functional outcome and return to competition

BACKGROUND: The ability of autologous chondrocyte transplantation to produce and maintain an effective articular cartilage repair under high mechanical demands has not been investigated. HYPOTHESIS: Autologous chondrocyte transplantation provides a reliable and durable repair of full-thickness knee articular cartilage lesions in high-demand athletes. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A total of 45 soccer players were evaluated 41 +/- 4 months after autologous chondrocyte transplantation for their ability to return to soccer, the timing of their return, skill level, and functional outcome rating by the Tegner activity rating scale score and Brittberg score. The factors influencing the return to sport were analyzed. RESULTS: Of these players, 72% reported good to excellent results, with significant overall improvement of Tegner activity rating scale scores; 33% returned to soccer, including 83% of competitive-level players and 16% of recreational players. Of the returning players, 80% returned to the same skill level and 87% maintained their ability to play soccer at 52 +/- 8 months postoperatively. Players who successfully returned to soccer were significantly younger and had a shorter preoperative duration of symptoms than did patients who did not return to the sport. Concomitant adjuvant procedures did not adversely affect the ability to return to soccer. CONCLUSION: Repair of knee articular cartilage lesions by autologous chondrocyte transplantation in high-performance athletes is particularly successful in younger, competitive athletes with limited preoperative intervals.     

Treatment of tear of the anterior cruciate ligament combined with localised deep cartilage defects in the knee with ligament reconstruction and autologous periosteum transplantation

An acute tear of the anterior cruciate ligament (ACL) is frequently associated with injuries to the joint cartilage and subchondral bone. These injuries may progress to deep cartilage defects, causing disabling pain, and represent a therapeutic challenge in patients with the combination instability and pain. At our clinic we treat patients with the combined injury with simultaneous ACL reconstruction and autologous periosteum transplantation of the cartilage defect. This report describes the technique for periosteum transplantation of full-thickness cartilage defects in the medial femoral condyle. Our clinical report includes the first 7 patients (6 men and 1 woman, mean age 29.1 years at operation) who have been followed for 2 years or longer of 14 consecutive patients (12 men and 2 women). All patients had suffered a total tear of the ACL and a full-thickness defect of the cartilage at the medial femoral condyle. The cartilage defects had a mean area of 7.3 cm² (range 1.0–13.5 cm²). All patients had disabling instability and medial knee pain when walking. The anterior cruciate ligament was reconstructed with a bone-tendon-bone graft of the central third of the patellar ligament. After preparation of the cartilage lesion, the periosteum transplant was anchored to the underlying bone with suture anchors and fibrin glue. Postoperatively, these patients (n = 7) were initially treated with continuous passive motion, followed by active flexibility training and slowly progressing strength training and weight-bearing activities. At follow-up a mean of 31.3 months (range 24–38 months) later, 6 patients evidenced subjectively stable knees, no pain during rest or when walking, and had returned to not too heavy knee-loading work. One patient had a subjectively stable knee, but felt medial knee pain. Meticulous surgical technique and rigorous postoperative rehabilitation are probably of the greatest importance in this procedure. With the use of suture anchors and fibrin glue, the periosteum transplant can be well adapted to the condylar subchondral bone bed. Received: 14 April 1998 Accepted: 4 September 1998     

MR imaging of autologous chondrocyte implantation of the knee

Autologous chondrocyte implantation (ACI) is a surgical technique that is increasingly being used in the treatment of full-thickness defects of articular cartilage in the knee. It involves the arthroscopic harvesting and in vitro culture of chondrocytes that are subsequently implanted into a previously identified chondral defect. The aim is to produce a repair tissue that closely resembles hyaline articular cartilage that gradually becomes incorporated, restoring joint congruity. Over the long term, it is hoped that this will prevent the progression of full-thickness articular cartilage defects to osteoarthritis. This article reviews the indications and operative procedure performed in ACI. Magnetic resonance imaging (MRI) sequences that provide optimal visualization of articular cartilage in the post-operative period are discussed. Normal appearances of ACI on MRI are presented along with common complications that are encountered with this technique.     

Autologous chondrocyte implantation versus debridement for treatment of full-thickness chondral defects of the knee: an observational cohort study with 3-year follow-up

BACKGROUND: Studies that compare the effectiveness of different cartilage repair treatments are needed to update treatment algorithms. HYPOTHESIS: Autologous chondrocyte implantation provides greater improvement in overall condition score than does debridement at a minimum of 3 years' follow-up. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: Cohorts for debridement and autologous chondrocyte implantation each included 58 Cartilage Repair Registry patients who met study criteria. A retrospective analysis was performed on prospectively collected baseline and follow-up data. RESULTS: Patients in the autologous chondrocyte implantation and debridement groups had similar demographics and chondral lesions at baseline. However, more autologous chondrocyte implantation patients failed a previous debridement or marrow stimulation procedure than did debridement patients. Follow-up outcome assessments were completed by 54 autologous chondrocyte implantation patients and 42 debridement patients. Eighty-one percent of the autologous chondrocyte implantation patients and 60% of the debridement patients reported median improvements of 5 points and 2 points, respectively, in the overall condition score. Autologous chondrocyte implantation patients also reported greater improvements in the median pain and swelling scores than did debridement patients. The treatment failure rate was the same for both autologous chondrocyte implantation and debridement patients. Eighteen autologous chondrocyte implantation patients and 1 debridement patient had at least 1 subsequent operation. CONCLUSION: Although patients treated with debridement for symptomatic, large, focal, chondral defects of the distal femur had some functional improvement at follow-up, patients who received autologous chondrocyte implantations obtained higher levels of knee function and had greater relief from pain and swelling at 3 years.     

Treatment of patellofemoralarticular cartilage injuries with autologous chondrocyte implantation

Autologous chondrocyte implantation (ACI) has successfully been used to repair chondral injuries of the knee. Articular cartilage defects of the patella and trochlea represent a class of cartilage lesions of the knee that have recently been considered an increasing indication for treatment with ACI. These lesions often differ from condyae lesions, having a different etiology and coexisting pathologic conditions in the knee associated with them. Patellar and trochlear cartilage lesions are often associated with patellofemoral maltracking. To obtain good results with these cartilage injuries with ACI, it is essential to address the underlying maltracking issues. Additionally, the contours of the patellar and trochlear cartilage differ from that of the condyles, requiring a modification in the standard technique of periosteal attachment used with condylar lesions. Although results of treating trochlear lesions with ACI have shown good results, the initial reports of treating patellar lesions with ACI were diminished compared to condylar lesions. Recognizing and treating the coexisting pathologic conditions and carefully modifying the standard technique of periosteal attachment has resulted in improved results.     

Articular cartilage repair in the adolescent athlete: is autologous chondrocyte implantation the answer?

OBJECTIVE: To determine the evidence base for recommendations regarding autologous chondryocyte implantation in adolescent athletes. MATERIALS AND METHODS: All literature on articular cartilage repair from MEDLINE search dated 1990 to 2006 was reviewed. The majority of articles describe surgical technique and indications. Three techniques for secondary articular cartilage repair have been identified: autologous chondrocyte implantation, autologous osteochondral implants, and marrow stimulation techniques. The initial literature search identified 4 studies that reported the effectiveness and durability of autologous chondrocyte implantation in adults and 2 studies that reported the outcomes of autologous chondrocyte implantation in adolescent athletes. No results of osteochondral implantation or marrow stimulation techniques in adolescent athletes have been published. RESULTS: Acceptable repair rates with all 3 techniques have been reported in adult athletes. Two studies reported high success using autolgous chondrocyte implantation (ACI) in children. CONCLUSIONS: Articular cartilage injury in young athletes remains a difficult problem. The ideal situation is early diagnosis and primary repair, particularly with lesions of the knee, elbow, and ankle. In cases where primary repair is not possible or has been unsuccessful and the lesion is large or symptomatic, secondary repair with either marrow stimulation, microfracture, autologous chondrocyte implantation, or autologous osteochondral grafting may be used. However, at present only the results of ACI repair have been reported for adolescent athletes.     

Technical note: the “double eye” technique as a modification of autologous chondrocyte implantation for the treatment of retropatellar cartilage defects

Retropatellar cartilage defects treated with autologous chondrocyte implantation (ACI) are still associated with inferior clinical outcome compared to defects being located on the femoral condyles. This is partly because of the biomechanical characteristics of the patellofemoral section of the joint, in which, in contrast to the medial or lateral compartments of the knee joint, prejudicial shearing forces are dominant. The patellar ridge has a particularly important role in the reduction of these shearing forces. The double eye technique was developed as a modification of ACI with preserving the important patellar ridge for the treatment of retropatellar cartilage defects extending beyond the patellar ridge and involving the medial and lateral retropatellar facets. This technique provides for a separate reconstruction of the medial and the lateral facets by means of ACI, but the ridge region is preserved to maintain the original thickness of cartilage at this point. The present paper describes the “double eye” technique as a modification of autologous chondrocyte transplantation (ACI) for treatment of cartilage defects of the patella, that involve both lateral and medial facets, and gives first clinical results of 11 patients. The average follow-up was 41.6 (±15.0) months, and the average age at diagnosis was 40.4 (±10.1) years. The Lysholm score, the subjective IKDC score, and the ICRS score were the instruments used to measure the outcome. This paper focuses on the introduction of the double eye technique with preservation of the patella ridge in the treatment of retropatellar cartilage lesion. Nevertheless, first clinical results of 11 patients are given, with an average Lysholm score of 75 (±14) points and an average subjective IKDC score of 60 (±14). Objective evaluation according to the criteria of the IKDC score showed very good or good treatment results in 9 of the 11 cases, with only 2 poor results. In conclusion, with the double eye modification presented in this paper, the potential for successful results in the treatment of combined cartilage defects of the medial and lateral facets of the patella is high; it takes into account the specific biomechanical properties of the patella ridge. The procedure needs further evaluation in clinical studies involving larger numbers of patients so that the indications can be determined more precisely.     

Osteochondral allograft transplantation

Experience with fresh osteochondral allografting for cartilage defects in the knee now extends two decades. Clinical outcomes and basic scientific investigations have supported the theoretic basis for this procedure. At the University of California, San Diego, our experience has encouraged us to continue to offer this procedure as a primary treatment for both large and small articular cartilage defects in the young knee. The success rate of fresh osteochondral allografting, particularly in isolated femoral condylar defects, compares favorably with other presently available cartilage repair and resurfacing techniques. In our second hundred cases, which we are currently evaluating, failure of monopolar allografts has been exceedingly rare in short-term follow-up. Fresh osteochondral allografting also appears to be effective in treating larger osteochondral lesions, where there are few other attractive alternatives. Fresh osteochondral allografts can thus be used to treat a wide spectrum of articular pathology. Technical refinements, and improvement in our understanding of graft-host interaction, as well as chondrocyte biology, should continue to improve clinical results. Disadvantages of fresh osteochondral allografting include the relative paucity of donor tissue, complexities in procurement and handling, and the possibility of disease transmission through the transplantation of fresh tissue. At present, only institutions that have overcome these obstacles seem capable of routinely performing this type of articular cartilage transplantation. In the future, as tissue banking and cartilage storage technology advance, fresh allograft tissue may become more available, allowing more widespread use of fresh osteochondral allografting in the treatment of articular cartilage lesions.     

MR imaging of osteochondral grafts and autologous chondrocyte implantation

Surgical articular cartilage repair therapies for cartilage defects such as osteochondral autograft transfer, autologous chondrocyte implantation (ACI) or matrix associated autologous chondrocyte transplantation (MACT) are becoming more common. MRI has become the method of choice for non-invasive follow-up of patients after cartilage repair surgery. It should be performed with cartilage sensitive sequences, including fat-suppressed proton density-weighted T2 fast spin-echo (PD/T2-FSE) and three-dimensional gradient-echo (3D GRE) sequences, which provide good signal-to-noise and contrast-to-noise ratios. A thorough magnetic resonance (MR)-based assessment of cartilage repair tissue includes evaluations of defect filling, the surface and structure of repair tissue, the signal intensity of repair tissue and the subchondral bone status. Furthermore, in osteochondral autografts surface congruity, osseous incorporation and the donor site should be assessed. High spatial resolution is mandatory and can be achieved either by using a surface coil with a 1.5-T scanner or with a knee coil at 3 T; it is particularly important for assessing graft morphology and integration. Moreover, MR imaging facilitates assessment of complications including periosteal hypertrophy, delamination, adhesions, surface incongruence and reactive changes such as effusions and synovitis. Ongoing developments include isotropic 3D sequences, for improved morphological analysis, and in vivo biochemical imaging such as dGEMRIC, T2 mapping and diffusion-weighted imaging, which make functional analysis of cartilage possible.     

Rehabilitation after autologous chondrocyte implantation for isolated cartilage defects of the knee

Autologous chondrocyte implantation for treatment of isolated cartilage defects of the knee has become well established. Although various publications report technical modifications, clinical results, and cell-related issues, little is known about appropriate and optimal rehabilitation after autologous chondrocyte implantation. This article reviews the literature on rehabilitation after autologous chondrocyte implantation and presents a rehabilitation protocol that has been developed considering the best available evidence and has been successfully used for several years in a large number of patients who underwent autologous chondrocyte implantation for cartilage defects of the knee.     

Treatment algorithm for osteochondral injuries of the knee

The treatment of osteochondral fractures and OCD lesions in the knee is controversial. Many new procedures and techniques have been developed recently to address osteochondral lesions, indicating that no single procedure is accepted universally. Our treatment algorithm is based on the age of the patient, skeletal maturity, and the presence of adequate subchondral bone attached to the chondral lesion. Most nondisplaced lesions in the patient with open physes will heal with conservative treatment. The onset of skeletal maturity indicates a need for a more aggressive treatment approach. If adequate cortical bone is attached to the fragment, drilling of stable lesions, or drilling with fixation of unstable or loose fragments is appropriate. Autologous bone graft can be necessary to stimulate healing and properly reconstruct the subchondral bony contour. For failed fixation attempts or lesions not amenable to fixation, each treating surgeon must be proficient and comfortable with an articular surface reconstruction technique. The goal for the reconstructive procedure, to produce a smooth gliding articular surface of hyaline or hyaline-like cartilage, is possible using current techniques including mosaicplasty, osteochondral allograft transplantation, and autologous chondrocyte transplantation. Débridement, drilling, microfracture, and abrasion chondroplasty have been shown to result in fibrocartilage with inferior mechanical properties when compared with hyaline cartilage. No long-term studies have been published, however, to confirm the benefits of replacing osteochondral defects with hyaline cartilage rather than fibrocartilage. Although the results of many reconstructive procedures are quite encouraging with early follow up, the ultimate goal is to prevent long-term degenerative arthritis. Only well-designed prospective studies with long-term follow up will determine the adequacy of these procedures in reaching the ultimate goal. This treatment algorithm is based on the senior author's (WGC) experience with the complex dilemma of osteochondral lesions of the knee.