Knee orthopedics as a template for the temporomandibular joint

Abstract

Although the knee joint and temporomandibular joint (TMJ) experience similar incidence of cartilage ailments, the knee orthopedics field has greater funding and more effective end-stage treatment options. Translational research has resulted in the development of tissue-engineered products for knee cartilage repair, but the same is not true for TMJ cartilages. Here, we examine the anatomy and pathology of the joints, compare current treatments and products for cartilage afflictions, and explore ways to accelerate the TMJ field. We examine disparities, such as a 6-fold higher article count and 2,000-fold higher total joint replacement frequency in the knee compared to the TMJ, despite similarities in osteoarthritis incidence. Using knee orthopedics as a template, basic and translational research will drive the development and implementation of clinical products for the TMJ. With more funding opportunities, training programs, and federal guidance, millions of people afflicted with TMJ disorders could benefit from novel, life-changing therapeutics.

Keywords: TMJ disc; cartilage; knee joint; oral and maxillofacial surgery; orthopedic surgery; osteoarthritis; temporomandibular disorder; temporomandibular joint; tissue engineering; translational medicine.

Graphical abstract

Figure 1

Knee and TMJ anatomy and proximity to crucial sensory structures (Top) Both the knee and TMJ are diarthrodial joints with two articular surfaces and an interpositional fibrocartilage. Specifically, the meniscus is situated between the tibia and the femur in the knee, and the TMJ disc is situated between the zygomatic arch and the mandible. (Bottom) Within a 3-cm sphere (red circle representation in 2D space) centered around the meniscus and the TMJ disc, the knee has no crucial sensory structures, although the TMJ has numerous structures present, including components of the inner ear, the brain, the trigeminal ganglion, and the mandibular and auriculotemporal nerves.

Figure 2

Clinical practices for the knee and TMJ (A) The cartilages of knee and TMJ share similar treatment pathways. Progressing from noninvasive to surgical approaches, conservative treatment is often indicated prior to end-stage surgeries, such as grafting (e.g., fat and rib) for the TMJ and osteochondral allografts for the knee. (B) Orthopedic surgery leads oral and maxillofacial surgery in residency program quantity. Oral and maxillofacial surgery residents are exposed to a lower quantity and percentage of total cases in open joint and arthroscopic procedures compared to orthopedic residents. (C) Males are overrepresented in both senior resident numbers and professional society memberships in AAOMS and AAOS.

Figure 3

The vicious cycle of TMJ translational research Primary research is lacking in the TMJ field, leading to little translation and resulting human clinical trials. Without clinical trials, approved, marketed products do not exist, resulting in little to no commercial market for TMJ products. This disincentivizes regulatory and funding agencies from publishing guidance and providing funding for the TMJ field, feeding back into the loop and resulting in a lack of precedent for researchers.