Microfracture, osteochondral transplants, and implantation of cultured autologous chondrocytes help repair, replace, and regenerate tissue

The goals of treating articular cartilage lesions haven’t changed, but the treatment techniques themselves have evolved in recent decades, according to a master lecture presented by Nicholas A. Sgaglione, MD, at the Arthroscopy Association of North America meeting in San Francisco last month. Orthopaedic surgeons now have an armamentarium of techniques that range from marrow stimulation to arthroscopic harvesting, culturing, and implantation of autologous chondrocytes.

Basic débridement techniques, designed to preserve native hyaline, should be used for small lesions (0.5 cm2 to < 1 cm2) due to the superiority of native tissue, the healing potential, the reduced risk for progression, and the less traumatic arthroscopic technique. However, as the size of the lesion increases, other techniques may be more effective.

Microfracture treatment
Patients younger than 50 years old with Grade IV focal traumatic lesions of approximately 2 cm2 and minimal bone loss may be candidates for arthroscopic microfracture treatment. According to Dr. Sgaglione, microfracture has the following advantages:

• It is a surgeon-friendly, arthroscopic, single-stage procedure.
• It is cost-effective.
• It is safe, with minimal morbidity.
• It is especially appealing for young patients with acute, smaller, aligned, and contained lesions.

However, the procedure—which involves arthroscopic débridement and perforation of subchondral bone to stimulate a fibrous healing response—has some limitations. The durability of the repair tissue over time is still unknown, and for distal femoral lesions, patients have an extended recovery, with limited weight bearing for several months.

“Two key considerations are alignment and patient education,” reported Dr. Sgaglione. “Bad mechanics will ruin good biology, so although this is an ‘easy’ procedure, technique is important. Microfracture—as well as all articular cartilage biosurgical resurfacing procedures—is optimally indicated only in knee compartments that are not mechanically malaligned. In addition, it is essential to prepare patients for the postoperative recovery and rehabilitation protocols.”

Osteochondral transplantation
For defects of less than 3 cm2, osteochondral autograft transplantation may be an excellent option. Dr. Sgaglione offered the following “pearls and pitfalls” associated with this technique:

• Larger diameter grafts are generally more robust, with improved pullout strength and more hyaline; their usage also requires fewer technical steps. An optimal size is 6 mm to 8 mm in diameter, and 13 mm to 20 mm in length.
• Harvest site selection varies, although at least two studies have identified the superomedial trochlea as optimal; backfilling the harvest site with a recipient site bone plug or bone graft substitute may reduce potential morbidity.
• Inserting the graft flush to the surface is key to reducing shear stress and subsequent graft toggling that can result in clefting and fibrillation. If the graft cannot be inserted flush, a slight (1 mm) countersinking of the graft (rather than leaving it protrude) may provide optimal biomechanical results.
• After surgery, the patient should have immediate, full range of motion, with use of a continuous passive motion device. Weight bearing is allowed at 4 weeks; a return to sports at 4 to 6 months.

“Although this is a cost-effective, single-stage procedure, osteochondral autograft transplantation does present some technical challenges,” said Dr. Sgaglione. “Precise technique is important, and results for defects on the trochlea and patella have been less than optimal. Surface mismatches can lead to abnormal stresses, edge loading, fibrous overgrowth, perimeter fissuring, clefts, and cysts.”

Osteochondral allograft transplantation
Osteochondral allograft transplantation is indicated for symptomatic larger (3 cm2 or greater) and deeper (greater than 1 cm) lesions. This technique represents an excellent method of restoring both larger bony and chondral defects and is especially useful for revision of failed primary treatments and salvage cases. Recent studies, however, have raised concerns about the effects of fresh cold-stored grafts and chondrocyte cellular viability when grafts are stored beyond 21 days. Precise clinical evaluation and selection of proper tissue bank procurement, processing, and practices are essential.

Autologous chondrocyte implantation
Autologous chondrocyte implantation (ACI) is defined as “implantation of in vitro cultured autologous chondrocytes using a periosteal tissue cover after expansion of isolated dedifferentiated and then redifferentiated chondrocytes;” essentially, it is “cartilage transplantation.”

This technique is most effective in younger, high-demand patients (15 to 55 years old) with larger chondral lesions in whom prior primary treatment methods have failed. ACI does require an arthroscopic autologous cartilage biopsy/harvest and staged implantation through an arthrotomy.

Several longer term studies have been published to support this cell-based therapy. In one long-term study, more than 80 percent of patients reported good to excellent short-term (2 years) and long-term (5 to 11 years) results. Problems remain in a subset of patients who experience subsequent symptomatic periosteal patch hypertrophy that requires débridement and another procedure. A recently published European study has found that using collagen membranes rather than a periosteal patch may prevent this problem.

Next steps
Improved treatments for articular cartilage lesions depend on several advances, including identification of the best source for chondrocytes, development of a matrix/scaffold, and increased research into bioactive proteins to regulate cell and tissue behavior.

According to Dr. Sgaglione, the following key developments are on the horizon:

• the potential to precisely assay autologous (or allogeneic) cells for chondrocyte phenotypic potency
• the use of volume stable and easily delivered off-the-shelf biodegradable scaffolds and cost-effective, platelet-rich, fibrin matrix-loaded bioactive factors

Tissue engineering and gene therapy remain promising avenues that could be tools to deliver proteins to specific targets to promote new tissue growth. Regulatory issues, cost-effective concerns, and clinical practicality, however, remain as obstacles.

“One rapidly evolving advance is the development of cartilage-specific magnetic resonance sequencing,” he concluded. “Noninvasive imaging will most likely continue to improve and facilitate precise diagnostic definition as well as structural tissue repair and regeneration outcomes validation.”