An athlete, after years of pitching, requires surgery to repair his glenohumeral ligaments. Which joint has been injured?

The marked structure is the sagittal suture, a fibrous immovable joint (synarthrosis) located between the two parietal bones along the midline of the superior skull. It runs anteroposteriorly from the coronal suture anteriorly to the lambdoid suture posteriorly. The sagittal suture plays a key role in skull growth during childhood by allowing expansion of the cranial vault to accommodate brain development. It later ossifies progressively in adulthood, becoming more rigid.

A. Coronal suture: The coronal suture is located between the frontal bone and the paired parietal bones. It runs transversely across the skull from side to side, separating the anterior cranial vault from the superior region. It allows growth of the skull in the anterior-posterior direction during early development. Unlike the sagittal suture, it is not located along the midline but rather forms a horizontal junction.

B. Lambdoid suture: The lambdoid suture is found at the posterior aspect of the skull, where the parietal bones meet the occipital bone. It has a characteristic inverted “V” or lambda shape. It plays a role in posterior cranial expansion during development. Compared to the sagittal suture, it is posterior and not located along the midline of the skull.

C. Squamous suture: The squamous suture is located laterally between the temporal bone and the parietal bone. It is curved and relatively flat, forming part of the lateral skull wall. It allows articulation between these bones and contributes to cranial stability. It is not midline like the sagittal suture and is instead positioned on the sides of the skull.

D. Sagittal suture: The sagittal suture is a fibrous joint located along the midline between the two parietal bones. It extends from the coronal suture anteriorly to the lambdoid suture posteriorly. It is a key growth site during infancy and childhood, allowing expansion of the skull to accommodate brain growth. Since the circled structure lies centrally between the parietal bones, it corresponds to the sagittal suture.

The skin is composed of three main layers: the epidermis, dermis, and hypodermis. The dermis is the middle layer and provides the skin with strength, elasticity, and structural support. It contains blood vessels, nerves, hair follicles, and glands embedded within a supportive extracellular matrix. The dominant tissue type in the dermis is a specialized connective tissue that allows the skin to resist mechanical stress from multiple directions.

A. Adipose tissue: Adipose tissue is primarily found in the hypodermis (subcutaneous layer) rather than the dermis. Its main functions include energy storage, insulation, and cushioning of underlying structures. While small amounts of fat may extend into deeper dermal regions, it does not form the structural framework of the dermis. Therefore, adipose tissue is not the primary dermal component.

B. Dense irregular connective tissue: the dermis is mainly composed of dense irregular connective tissue. This tissue contains thick bundles of collagen fibers arranged in multiple directions, allowing the skin to withstand tension and mechanical stress from various angles. It also contains elastin fibers that provide elasticity and fibroblasts that maintain the extracellular matrix. This structural composition gives the dermis its strength and flexibility.

C. Simple squamous epithelium: Simple squamous epithelium is a thin, single layer of flat cells found in structures such as alveoli of the lungs, blood vessel linings (endothelium), and serous membranes. It is specialized for diffusion and filtration rather than structural support. It is not found in the dermis, which is composed primarily of connective tissue rather than epithelial tissue.

D. Hyaline cartilage: Hyaline cartilage is a flexible connective tissue found in structures such as the trachea, nose, larynx, and articular surfaces of joints. It provides support and smooth surfaces for movement but is not a component of skin structure. The dermis does not contain cartilage tissue, making this option anatomically and histologically incorrect.