Morphological classification and dimensions of the human patella
Authors: Borges Carlos Augusto Servato , de Carvalho Arthur Teixeira , Júnior Valdir Mazzucato , Savoldi Marcelo , Bim Waldeci Roberto , Fazan Valéria Paula Sassoli 
Published: November 2023

The patella (kneecap) is commonly described as a flat, triangular bone, situated on the front of the knee‐joint. It is usually regarded as a sesamoid bone, developed in the tendon of the Quadriceps femoris (QF), serving to protect the front of the joint, and increase the leverage of the QF by making it act at a greater angle. Patellofemoral syndrome (PFS) is characterized by a group of symptoms that are easily diagnosed and often respond to simple management. The common presentation is knee pain in association with positions of the knee that result in increased or misdirected mechanical forces between the kneecap and femur. Ironically, as simple as its presentation is, lack of consensus on the fundamental factors associated with PFS remains. Accordingly, synonyms for the PFS go in and out of fashion. No agreement exists on the exact pathophysiology, but significant work is being completed on the extent and direction of the associated forces on the patella, as well as on the tracking and alignment of the patella. The morphology of the patella has been identified as an important factor in the appearance of PFS. Thus, we investigated the morphology of the adult human skeletons kneecaps, providing classification and measurements of normal patellas aiming to contribute with information useful for clinical application. Based on the visual analysis, 37 kneecaps of the Anatomy Laboratory of the School of Medicine of Ribeirão Preto‐USP could be divided in three groups according to the morphology: the triangular patellas, classified as type I (25 of the 37, 67.6%); the oblong ones, classified as type II (8 of the 37, 21.6%); and irregular patellas classified as type III (4 of the 37, 10.8%). With the aid of a stainless steel caliper (range of 0–300 mm, resolution 0.01 mm) measurements of the kneecaps were taken as follows: longitudinal diameter (longest diameter form the base to the top), the base width (larger lateral‐lateral diameter), the medial and lateral articular surfaces diameter and the length of the non articular surface. The statistical analysis showed that: the right kneecap's longitudinal diameter and base width are larger compared to left ones in type I patellas; the lateral articular surface is larger than the medial, for right and left patellas; and the right kneecap's medial articular surface is larger than the left ones. Comparing the results between type I and type II patellas, we found that the longitudinal diameter is larger in type I compared to type II patellas, with no difference between the base widths. The statistical analysis of type III patella couldn't be done because the sample was unrepresentative (2 on each side). Probably, the predominance of type I patella results from the fact that this is a sesamoid bone; therefore, it receives longitudinal tendon forces. Furthermore, the bigger dimensions of right kneecap, compared with left ones, could be explained by the predominance of the right‐handed population over the left‐handed (about 10% only). Finally, comparing the types I and II patellas, the information that the type I longitudinal diameter is bigger, but the width of the base is equal on both types, shows that the difference between the types is just the most prominent apex on type I.Support or Funding InformationFAEPA, CNPq, FAPESP