Transverse Patella Fracture: A Unique Case Study
Clinical Vignette
A) Intact extensor mechanism
B) Negative anterior drawer test
C) Absent joint effusion
D) Increased knee ROM
Introduction
A transverse patellar fracture occurs when the patella fractures into two parts in the transverse plane, dividing the bone into an upper and lower portion. Patellar fractures constitute about 1% of all skeletal fractures. Roughly 50-80% are the transverse type that are likely to disrupt the extensor mechanism of the knee[1]Heusinkveld MH, den Hamer A, Traa WA, Oomen PJ, Maffulli N. Treatment of transverse patellar fractures: A comparison between metallic and non-metallic implants. British Medical Bulletin. … Continue reading. It is commonly caused by direct trauma to the patella or a fall. 80% of patella fractures occur in the middle to lower third of the patella with up to two-thirds of them displace[2]Jarraya M, Diaz LE, Arndt WF, Roemer FW, Guermazi A. Imaging of patellar fractures. Insights Imaging. 2017 Feb;8(1):49-57. doi: 10.1007/s13244-016-0535-0. Epub 2016 Nov 30. PMID: 27905071; PMCID: … Continue reading.
Anatomy
The patella is variable in its shape, however it is typically ovoid. It assists with the extensor mechanism along with the quadriceps tendon, medial and lateral retinacula, and patellar tendon. The extensor mechanism is responsible for extending the knee and maintaining an erect, extended position. The patella serves three main functions: provides protection of the knee joint, lengthens the lever arm of the quadriceps femoris to allow for better knee extension, increases the area of contact between the patellar tendon and the femur[4]White TD, Black MT, Folkens PA. Chapter 12 – Leg: Femur, Patella, Tibia, and Fibula. In: Human Osteology. San Diego, CA: Academic Press; 2011..
Diagnosis
X-ray imaging is most often used in the diagnosis of a transverse patellar fracture with a sensitivity and specificity approaching 100%[5]Avci M, Kozaci N. Comparison of X-Ray Imaging and Computed Tomography Scan in the Evaluation of Knee Trauma. Medicina (Kaunas). 2019 Sep 23;55(10):623. doi: 10.3390/medicina55100623. PMID: 31547588; … Continue reading; however it has been shown that CT imaging provides more accurate evaluation to assess if there is comminution in other areas of the patella. Ultrasound has also been used as a first line imaging modality to diagnose patellar fractures with a sensitivity and specificity of 93.3%% and 94.8% respectively[6]Kilic TY, Yesilaras M, Atilla OD, Turgut A. The accuracy of point-of-care ultrasound as a diagnostic tool for patella fractures. The American Journal of Emergency Medicine. 2016;34(8):1576-1578. … Continue reading. MRI may be used if there is concern for underlying occult fracture.
Physical Exam
Physical exam may reveal tenderness, redness, and swelling overlying the patella. The edges of the fracture may also be felt through the skin, especially if the fracture is displaced. It is important to identify any defects in the quad tendon, patella or patella tendon. Note if the patella is high or low riding. Hemarthrosis is typically present. Range of motion should be assessed, and the extensor mechanism should be evaluated to see if it is intact. The examiner should consider a structural exam depending on the mechanism and patients tolerance.
Management
Case Conclusion
Author: Dr Kareem Shahin
Vignette Answer
As discussed in the case presentation, the most important physical exam component in the setting of patella fractures is evaluation of the extensor mechanism. A negative drawer test is reassuring if you are able to evaluate this. Hemarthrosis is common following a patella fracture and range of motion is often decreased due to pain and swelling.
References[+]
↑1 | Heusinkveld MH, den Hamer A, Traa WA, Oomen PJ, Maffulli N. Treatment of transverse patellar fractures: A comparison between metallic and non-metallic implants. British Medical Bulletin. 2013;107(1):69-85. doi:10.1093/bmb/ldt013 |
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↑2 | Jarraya M, Diaz LE, Arndt WF, Roemer FW, Guermazi A. Imaging of patellar fractures. Insights Imaging. 2017 Feb;8(1):49-57. doi: 10.1007/s13244-016-0535-0. Epub 2016 Nov 30. PMID: 27905071; PMCID: PMC5265199. |
↑3 | Image courtesy of intechopen.com, “Surgical Approaches for Total Knee Arthroplasty” |
↑4 | White TD, Black MT, Folkens PA. Chapter 12 – Leg: Femur, Patella, Tibia, and Fibula. In: Human Osteology. San Diego, CA: Academic Press; 2011. |
↑5 | Avci M, Kozaci N. Comparison of X-Ray Imaging and Computed Tomography Scan in the Evaluation of Knee Trauma. Medicina (Kaunas). 2019 Sep 23;55(10):623. doi: 10.3390/medicina55100623. PMID: 31547588; PMCID: PMC6843286. |
↑6 | Kilic TY, Yesilaras M, Atilla OD, Turgut A. The accuracy of point-of-care ultrasound as a diagnostic tool for patella fractures. The American Journal of Emergency Medicine. 2016;34(8):1576-1578. doi:10.1016/j.ajem.2016.05.073 |
↑7 | Rich J, Powers RH, Dean DE. Forensic Medicine of the Lower Extremity: Human Identification and Trauma Analysis of the Thigh, Leg, and Foot. Scholars Portal |
↑8 | Melvin SJ, Mehta S. Patellar fractures in adults. American Academy of Orthopaedic Surgeon. 2011;19(4):198-207. doi:10.5435/00124635-201104000-00004 |