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  • General
    • Largest sesamoid bone in the body
    • Embedded in quadriceps tendon
  • Osseous features
    • Medial and lateral facets, lateral is large
    • Separated by vertical ridge
  • Extensor Mechanism
  • Patellar Retinaculum
  • Cartilage
    • Posterior surface covered with thick articular cartilage (up to 1 cm)
  • Ligaments
    • Medial Patellofemoral Ligament
    • Lateral Patellofemoral Ligament
  • Embriology
    • Ossifies between ages 4 and 7
    • Although most individuals have a single ossification center, up to 23% of folks have 2 or 3 ossification centers
    • 2% of individuals do not ossify at these centers resulting in bipartite or tripartite patella
    • In 50% of cases this is seen bilaterally
  • Wiberg subtypes[1]
    • Type I: medial and lateral facets are approximately equal
    • Type II & Type III: medial facet becomes steadily smaller


  • Functions as a lever arm during extension[2]
    • Augments quadriceps and extensor mechanism
    • Augments the lever arm by up to 30% at full extension[3]
  • Knee Flexion
    • Located in the groove of the femoral trochlea acting primarily as a link between the quadriceps muscle and the proximal tibia
    • Most pressure occurs at 45°-60° flexion[4]
  • Resistance to flexion[5]
    • Converts tensile forces into compression forces
    • Decelerates knee flexion in particular during walking down stairs or downhill
    • Sometimes termed “patella femoral joint reaction (PFJR)”

Vascular Supply

  • Branches of the following arteries form anastomotic ring
    • Descending genicular
    • Superior medial and lateral genicular
    • Inferior medial and lateral genicular
    • Anterior genicular


  • Medial and lateral patellar nerves

Clinical Significance

See Also


  1. Wiberg G. Roentgenographs and anatomic studies on the femoropatellar joint: with special reference to chondromalacia patellae. Acta Orthop Scand. 1941;12:319–410.
  2. colaro J, Bernstein J, Ahn J. Patellar fractures. Clin Orthop Relat Res. 2011 Apr;469(4):1213–1215.
  3. Kaufer H. Mechanical function of the patella. J Bone Joint Surg Am. 1971 Dec;53(8):1551–1560.
  4. Goldstein SA, Coale E, Weiss AP, Grossnickle M, Meller B, Matthews LS. Patellar surface strain. J Orthop Res. 1986;4(3):372–377.
  5. Hungerford DS, Barry M. Biomechanics of the patellofemoral joint. Clin Orthop Relat Res. 1979 Oct;(144):9–15.
Created by:
John Kiel on 18 October 2020 01:23:05
Last edited:
23 March 2021 17:15:06