July 24, 2024

Dr. Richard Katz Discusses ACI Superiority to Microfracture and provides NBME style Questions related to Orthopedics

Dr. Richard Katz Discusses Third-Generation Autologous Chondrocyte Implantation (ACI) Superiority to Microfracture and provides NBME style Questions related to Orthopedics for the self-evaluation of future biomedical – minded practitioners  

Danbury, Connecticut, 22nd June 2023, ZEX PR WIRE, Dr. Richard Katz has in-depth knowledge of regenerative-biological cell-based therapies. He has contributed to the development and management of assessments of healthcare professionals in the life sciences ensuring that the future practitioner can apply essential concepts as tested by NBME.  Dr. Katz’s vast experience in the pharmaceutical and life science industries has focused on delivering more effective and affordable treatments to improve patient health outcomes through the education of patients, practitioners and other stakeholders.

Dr. Katz’s mission is to make a global impact on healthcare than what is possible by treating one patient at a time. In this interview, Dr. Katz discusses why third-generation autologous chondrocyte implantation (ACI) is superior to microfracture for focal chondral defects of the knee joint – a topic applied to the generation of thought provoking NBME style questions for self-evaluation.

Can you first tell us a little about focal chondral defects of the knee joint?

Focal chondral defects of the knee joint refers to localized areas of damage or loss of articular cartilage in the knee. Articular cartilage is the smooth, protective covering that lines the ends of bones within the joint. It allows for smooth movement and acts as a cushion, reducing friction and absorbing shock during joint motion.

Chondral defects can occur due to various factors, including traumatic injuries, repetitive stress, degenerative conditions, or genetic predisposition. These defects can range in size and depth, from small lesions to larger areas of cartilage damage. The severity of the defect determines the impact on joint function and the potential for symptoms such as pain, swelling, stiffness, and limited range of motion.

Focal chondral defects can be challenging to manage as articular cartilage has limited regenerative capacity. It is a relatively avascular structure, and the dense extracellular matrix located between chondrocytes prevents movement of these cells and nutrients to the defect site. This makes cartilage repair difficult.   If left untreated, these defects can progress, leading to further cartilage degeneration, joint instability, and the development of osteoarthritis (OA).

The treatment of focal chondral defects aims to promote cartilage repair and restoration of joint function. Various surgical techniques and interventions are utilized to achieve this goal, including autologous chondrocyte implantation (ACI), microfracture, osteochondral grafting, and other emerging technologies. It is important to address focal chondral defects promptly and effectively to prevent further joint deterioration and to improve the patient’s quality of life. Treatment options continue to evolve with advancements in regenerative medicine, providing hope for enhanced outcomes in the management of these knee joint conditions.

NBME style question pertaining to the above subject matter: 

Q1. Tissue-regeneration engineering has become an important method for articular cartilage repair. This intervention may prevent chronic degeneration of cartilage tissue, an irreversible degenerative process that eventually develops into osteoarthritis (OA). A Researcher reasons that a main component of cartilage may contribute to this degenerative process.

Identify the likely component.

  1. Glycoproteins
  2. Proteoglycans
  3. Hyaluronan
  4. Collagen


ANS. b. Proteoglycans

Articular cartilage plays a vital role in joint health and its function, providing a smooth surface for frictionless movement and cushioning the joint during weight-bearing activities. The key components of articular cartilage are proteoglycans, which are large molecules composed of a core protein and attached glycosaminoglycan (GAGs) chains. Chondroitin sulfate is the most predominant glycosaminoglycan found in articular cartilage, and it binds to the core protein to form proteoglycan aggregates. These aggregates are what give articular cartilage its unique properties, allowing it to absorb and distribute mechanical loads and offer resistance to compression. However, when articular cartilage degeneration sets in, the structure and composition of proteoglycans break down, leading to a range of issues. Age, trauma, genetics, and inflammatory conditions can all contribute to this degeneration, which highlights the essential role proteoglycans play in maintaining articular cartilage health and function.

Proteoglycan degradation in articular cartilage is a significant contributor to the development of conditions such asOA. Enzymes such as matrix metalloproteinases (MMPs) and aggrecanases are responsible for breaking down the core protein and GAG chains of proteoglycans, leading to a decrease in their concentration and altering the mechanical properties of the cartilage. This loss of proteoglycans has a detrimental effect on the cartilage’s ability to cushion and retain water, resulting in increased friction, joint stiffness, and pain for the individual. Not only does the breakdown of proteoglycans trigger an inflammatory response, but it also exacerbates the degeneration process. For this reason, it is essential to understand the role of proteoglycans in articular cartilage degeneration. Various therapeutic approaches, including the use of chondroitin sulfate supplements, intra-articular injections, and tissue engineering, are being explored as potential strategies to prevent or treat this common and often debilitating condition.

You mentioned some different treatment options. Can you first explain what ACI is?

Autologous chondrocyte implantation, or ACI, is a surgical procedure that involves the transplantation of autologous chondrocytes into the damaged area of the knee joint. The process typically includes three stages: (1) arthroscopy to assess the extent of the chondral defect, (2) harvesting of healthy cartilage cells, and (3) re-implantation of the chondrocytes into the lesion. 

There are three generations of ACI:

  • 1st generation ACI with a chondrocyte suspension injected under a periosteal flap
  • 2nd generation ACI with a chondrocyte suspension injected under a collagen membrane
  • 3rd generation ACI with chondrocytes seeded on or in a scaffold

As stated in the National Library of Medicine, Autologous Chondrocyte Implantation (ACI) is a two-step procedure that has been used clinically in humans since the 1980’s.  In the original ACI technique (first-generation), the first step consisted of surgically removing small biopsies of normal cartilage from non-weight-bearing areas of the knee. Chondrocytes were then enzymatically isolated from the biopsies, expanded ex vivo in monolayer culture and harvested as a cell suspension several weeks later. In the second step, surgeons injected the cell suspension under a periosteal flap harvested from the proximal medial tibia and previously sutured over the cartilage.

ACI that uses suspended cultured chondrocytes with a covering of collagen type I/III membrane is called a second-generation. The first and second generations of ACI required a longer and more invasive procedure. The earlier ACIs required a surgeon to use a separate membrane to secure new cartilage cells in place over a patient’s cartilage using sutures. This was time consuming and cumbersome for surgeons and caused trauma and scar tissue formation to surrounding tissue.

Third-generation ACI comprises those procedures that deliver autologous cultured chondrocytes using cell carriers or cell-seeded scaffolds. The second and third generation are also known as autologous chondrocyte implantation using collagen membrane-associated autologous chondrocyte implantation, and scaffold-based ACI. These procedures addressed most of the concerns related to the earlier generation ACI. The use of scaffolds to create a cartilage-like tissue in a three-dimensional culture system allows for the optimization of the procedure from both a biological and surgical standpoint.

ACI offers several advantages over other techniques, including the ability to address larger lesions and provide more durable and long-lasting repair.  

What are some of the limitations of the microfracture technique?

Microfracture is a procedure that has its limitations when it comes to its effectiveness. Even though it is minimally invasive, it generates tissue that is primarily fibrocartilage instead of hyaline cartilage. This fibrocartilage is also prone to degenerating over time, which potentially leads to weakened long-term outcomes. Moreover, microfracture is typically less suitable for large lesions, as it is less effective at generating enough repair tissue to fill the site successfully. Despite these limitations, microfracture remains an option for certain cases where the defects are small enough for it to be effective. It has shown some success in stimulating the release of marrow elements into the defect site and repairing cartilage.

NBME style question  pertaining to this subject matter: 

Q2 Microfracture is a surgical procedure used to treat articular cartilage defects in joints. During the procedure, small holes or microfractures are made in the damaged cartilage surface creating a pathway for the migration of cells from the underlying bone marrow into the defect. How may the component in question be involved in this process?

  1. The component is not involved in this process
  2. The component is essential for the formation and organization of the new cartilage tissue
  3. The migrated component cells from the bone marrow arrive at the defect as chondrocytes
  4. The component will promote crystal deposition Explanation: 

ANS. b. The component is essential for the formation and organization of the new cartilage tissue

During a microfracture surgical procedure, small holes are made in damaged cartilage to create a pathway for the migration of cells from the underlying bone marrow to the affected area. This process is crucial in the healing of articular cartilage defects in joints. The migrated cells differentiate into chondrocyte-like cells, responsible for the production of new cartilage tissue. However, the role of proteoglycans cannot be overlooked in the process of producing new cartilage tissue. Proteoglycans contribute to the compressive strength, load distribution, and hydration properties of the cartilage. In the context of microfracture surgery, they play a crucial role in the formation and organization of the newly produced cartilage tissue. Therefore, proteoglycans are an integral component of the extracellular matrix in articular cartilage and an essential factor in the healing process following microfracture surgeries.

The presence of proteoglycans during the healing process is necessary for the functional and mechanical properties of regenerated cartilage. Once chondrocyte-like cells have migrated into the defective area and synthesized proteoglycans, these synthesized components help rebuild the cartilage matrix and provide structural support to the newly formed tissue. Proteoglycans contribute to the tissue’s resistance against compressive forces, allowing it to withstand mechanical stress. They also aid in retaining water within the tissue and maintain its hydration and lubrication properties. However  the benefits of proteoglycans don’t stop there. These molecules are also crucial in regulating cellular behavior during the healing process. Proteoglycans interact with growth factors and signaling molecules, influencing cell migration, proliferation, and differentiation, key factors in proper tissue regeneration following microfracture surgery.

Proteoglycans are a key player in the healing process following microfracture surgery. Their contribution in forming and organizing new cartilage tissue cannot be overstated. These molecules play an essential role in the functional and mechanical properties of the regenerated cartilage, ensuring proper hydration, load distribution, and cellular regulation. Without proteoglycans, the healing process would be incomplete, and the outcome of microfracture surgeries would be less successful. Therefore, the presence of these molecules is crucial for a speedy and effective recovery.

What are some of the benefits of ACI as opposed to microfracture for treating focal chondral defects of the knee joint?

Multiple studies and clinical evidence support the superiority of Autologous Chondrocyte Implantation (ACI) over microfracture for the treatment of focal chondral defects of the knee joint. Some of the key points include–

  1. Enhanced Cartilage Regeneration: ACI has been shown to promote the formation of hyaline-like cartilage, which closely resembles the native articular surface. In contrast, microfracture primarily yields fibrocartilage, which as already discussed, lacks the biomechanical properties and durability of hyaline cartilage. Several studies have demonstrated the superior quality of cartilage repair achieved with ACI compared to microfracture.
  1. Improved Clinical Outcomes: Numerous clinical studies have reported better clinical outcomes and patient satisfaction with ACI compared to microfracture. For example, one study compared ACI and microfracture outcomes and found significantly higher clinical scores, improved pain relief, and better patient-reported outcomes in the ACI group. Patients who underwent ACI also had a lower need for subsequent surgical interventions, indicating the durability of the repair achieved by this technique over time.
  1. Long-term Durability: Long-term follow-up studies have shown the sustained efficacy of ACI in maintaining cartilage repair. One review evaluated the long-term outcomes of ACI and microfracture and concluded that ACI provided superior repair quality and durability for at least 6 years post-surgery. This suggests that ACI offers a more viable long-term solution for patients with focal chondral defects.
  1. Lesion Size: ACI is generally considered more suitable for treating larger chondral defects, while microfracture may be limited in its effectiveness for larger lesions. Microfracture relies on the migration and differentiation of marrow elements into the defect, which may be less efficient for larger lesions. ACI, on the other hand, allows for the transplantation of a greater number of chondrocytes, facilitating the regeneration of larger areas of damaged cartilage.
  1. Advancements in ACI Techniques: The introduction of third-generation ACI techniques, such as matrix-assisted ACI or scaffold-based ACI, has further improved the outcomes of ACI procedures. These techniques enhance chondrocyte delivery, cell viability, and integration with the surrounding native cartilage, leading to more successful cartilage repair compared to microfracture.

Additional NBME style questions pertaining to this subject matter: 

Q3 The researcher wants to test the degradation of this component as a potential pathological marker of early OA lesions. What method would the researcher likely use 

  1. Quantified degradation products present in synovial fluid using enzyme-linked immunosorbent assays (ELISAs)
  2. Blood Creatinine
  3. Dual-energy computerized tomography (DECT)
  4. The component deposits hydroxyapatite crystals


ANS. a. Quantified degradation products present in synovial fluid using enzyme-linked immunosorbent assays (ELISAs)

Biomarker analysis in synovial fluid or blood samples is an informative approach to assessing proteoglycan degradation in osteoarthritis. By measuring specific proteoglycan fragments or degradation products in these samples, potential biomarkers of the condition can be identified. This allows for a better understanding of the ongoing breakdown of proteoglycans in the articular cartilage, which is an essential component of osteoarthritis. Synovial fluid is particularly useful for this process because it is present in the joints and in direct contact with the articular cartilage. Proteoglycan degradation products can be quantified in synovial fluid through the use of enzyme-linked immunosorbent assays (ELISAs).. Overall, biomarker analysis provides valuable insights into the molecular changes that occur in osteoarthritis, which could lead to new treatments and therapies for managing this condition.

Researchers and clinicians have discovered that specific biomarkers may be released into the bloodstream due to cartilage breakdown. By measuring proteoglycan fragments or degradation products in synovial fluid or blood, professionals can gain insight into the extent of proteoglycan degradation and the progression of OA. In turn, this information can aid in the diagnosis of OA, monitoring disease progression, evaluating treatment responses, and potentially predicting the risk of future joint damage. However, it is crucial to keep in mind that the development and validation of these biomarkers are still ongoing. While promising biomarkers have been identified, further research is required to establish their clinical utility, reliability, and accuracy.

Q4 Name the  amino acid responsible for the structure and function of the component in question?

  1. Valine
  2. Leucine
  3. Serine
  4. proline 

ANS. c. Serine

Serine is a crucial component of the glycosaminoglycan chains that make up proteoglycans. These chains, including chondroitin sulfate and keratan sulfate, are long and linear polymers composed of repeating disaccharide units. The biosynthesis of GAG chains involves the attachment of amino sugars to serine residues on the core protein of the proteoglycan. This molecular interaction plays a vital role in forming the proteoglycan structure. Through a covalent linkage known as O-glycosylation, the serine residues serve as attachment points for the GAG chains. The GAG chains, in conjunction with the core protein, generate the proteoglycan aggregates. These aggregates are needed for the unique properties of articular cartilage, including its ability to absorb shock and withstand mechanical stress. In short, the amino acid serine is an important building block for the structure and function of proteoglycans.

Q5 Would supplementation of this amino acid likely halt OA progression?

  1. Yes, supplementation of this essential amino acid will address underlying causes of OA and halt the progression of the disease
  2. No, OA is a complex degenerative joint disease that involves multiple factors
  3. Yes, deficiency of this nonessential amino acid is common even in healthy individuals
  4. No, most people, obtain a surplus of this amino acid with a balanced diet

ANS. b. No, OA is a complex degenerative joint disease that involves multiple factors

OA is a degenerative joint disease, it is a multifaceted condition resulting from various factors. While serine is an essential amino acid involved in the structure of proteoglycans, there is no evidence to suggest that supplementing with serine can prevent or treat OA. The breakdown of proteoglycans is a key feature of OA, but it is influenced by multiple factors beyond serine availability. Therefore, supplementing with serine alone is unlikely to address the underlying causes of OA or halt the progression of the disease. Instead, treatment and management of OA typically involve a comprehensive approach that may include lifestyle modifications, pain management, physical therapy, exercise, weight management, and surgical interventions if needed. It’s important to note that the body naturally synthesizes serine from various dietary sources, and a deficiency of serine is rare in healthy individuals. 

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