Orthobiologics: Can They Be Effective For Osteochondral Lesions?
Given the prevalence of hallux abducto valgus deformity, these authors offer a prmer on micro-and macrobiological fundamentals involving the first metatarsophalangeal joint (MPJ) and the impact of joint surface deterioration. They also examine an emergine implant for repair of first MPJ osteochondral lesions.
It has been estimated that 209,000 patients undergo surgery for hallux abducto valgus correction each year in the United States.1 The National Center for Health Statistics states that hallux abducto valgus affects 1 percent of the adult population in the U.S.2
Hallux abducto valgus (HAV) deformities have traditionally been classified as ranging from mild to severe. A recent study by Engel correlated the relationship of subchondral bone cyst formation of the first metatarsophalangeal joint (MPJ) and the severity of HAV deformity.3 The intraoperative repair of subchondral defects is imperative during the surgical correction of HAV for articular force distribution during propulsion and to circumvent progression of the osteolytic lesion.
Current orthobiological options offer an alternative to the traditional microfracture or marrow stimulating technique (MST). New orthobiological implantable materials have demonstrated evidence of resurfacing the articular surface with hyaline-like soft tissue that adheres to the osteoconductive, bioabsorbable substrate.
Key Insights On Micro- And Macrobiological Concepts
Having a strong understanding of “normal” histology allows for the differentiation of pathological processes. Osteophyte production, lipping of the joint and osteochondral lesions are all indications of a pathological process.
The diarthrotic joint is grossly comprised of the soft tissue structures adjacent to and including the bone that provides the foundation of the two (or more) adjacent articular surfaces. The articular surfaces are composed of hyaline cartilage devoid of perichondrum. The hyaline cartilage is comprised of calcified and uncalcified layers. The uncalcified layer is closest to the articular surface and has three distinct zones. The uncalcified layer is anchored to the subchondral bone by the calcified layer of hyaline cartilage.
Surrounding the articular surface are plicated folds of synovial membrane that smooth out as their distance from the articular surface increases. Ligaments, tendons (rare) and a dense fibrous capsule support the synovial membrane.
The synovial cells filter the adjacent capsular blood supply for water and ions to be delivered into the joint. The synovial cells, which are classified into type A and type B cells, also have other functions based on their respective type. Type A cells are phagocytic and produce hyaluronic acid while the type B cells produce various proteins.
Hyaline cartilage is comprised of chondrocytes and surrounding matrix. It does not have a blood supply, lymphatics or enervation. The matrix provided by and surrounding chondrocytes is composed of type II collagen, water and chondroitin sulfate. The combination of water and chondroitin sulfate provides excellent compression strength. Some of the synovial fluid from the joint can diffuse into the outermost layer of the hyaline cartilage. The synovial fluid can then exude upon compression, allowing for instant articular surface lubrication.