The Common Vein Copyright 2011
Definition
Fractures of the patella are usually caused by either direct or indirect trauma. Direct mechanisms of injury include trauma to the patella that lead to the fracture. Indirect mechanisms are the most common cause of injury to the patella resulting in fracture. These occur when there is a contraction of the quadriceps muscle. The musculotendinous pull on the patella causes the fracture which is usually transverse. A patellar fracture can also arise as a result of a combined direct and indirect mechanism as a result of a fall from a height.
The level of displacement of the fracture fragments is variable.
The OTA classification consists of undisplaced, transverse, lower or upper pole, stellate (multifragmented undisplaced), multifragmented displaced, vertical, and osteochondral. Transverse fractures occur as a transverse line running medial to lateral typically over the center of the patella. Either the lower pole or upper pole of the patella can be fractured. Some fractures can contain many fragments and be either displaced or non-displaced.
The fracture may be complicated in the acute phase by neurovascular injury, or in the subacute or chronic phases by nonunion, malunion, infection, osteonecrosis, and osteoarthritis. Complications specific to the patella include loss of knee motion, osteonecrosis of the proximal fragment, painful retained hardware, patellar instability, loss of extensor muscle strength or an associated extensor lag.
The diagnosis of this injury is usually made by a combination of physical examination and x-ray imaging.
Imaging includes the use of plain x-rays, and if indicated CT-scan, or MRI.
Nonoperative treatment is indicated for patients who have nondisplaced or minimally displaced (2 to 3 mm) fragments. The articular disruption must be minimal and the extensor mechanism must be intact. These patients can be treated with an immobilization for 4 to 6 weeks. Physical therapy and weight bearing activities can be performed early on.
Operative indications include there being greater than 2 mm of articular incongruity and/or displacement of fragments greater than 3 mm. Patients can be treated with tension banding, circumferential cerclage wiring, and interfragmentary screw compression with cerclage wiring. Some patients require a partial or total patellectomy when there is comminution. Any retinacular damage from the initial injury needs to be repaired. Patients post-operatively are splinted for anywhere from a few days to a few weeks depending on the initial injury.
The Normal Patella on the Sunrise View |
| Courtesy Ashley Davidoff MD 71223c02 71223.800 |
 
The Normal Patella on the A-P and Lateral Projection |
| Courtesy Ashley Davidoff MD 45215 |
References
Davis MF, Davis PF, Ross DS. Expert Guide to Sports Medicine. ACP Series, 2005.
Elstrom J, Virkus W, Pankovich (eds), Handbook of Fractures (3rd edition), McGraw Hill, New York, NY, 2006.
Koval K, Zuckerman J (eds), Handbook of Fractures (3rd edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.
Lieberman J (ed), AAOS Comprehensive Orthopaedic Review, American Academy of Orthopaedic Surgeons, 2008.
Moore K, Dalley A (eds), Clinically Oriented Anatomy (5th edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.
Wheeless’s Textbook of Orthopaedics: Fractures of the Patella (http://www.wheelessonline.com/ortho/fractures_of_the_patella)