Purpose
Knee radiographs are widely utilised after trauma to detect knee joint effusions as a marker of significant intraarticular injury.
Classically, knee joint effusions are detected by a suprapatellar fat pad separation measuring >10mm in anteroposterior dimensions on an overhead lateral knee radiograph[1].
An accurate assessment of joint fluid can be obtained with magnetic resonance imaging (MRI), which has been proven to be able to detect even small volumes of fluid[2].
The aim of this study is to :
Compare the accuracy of both overhead and...
Methods and materials
A retrospective study was conducted on all knee MRI performed from the 1 January 2015 to 31 May 2019 inclusive, from the Western Australian PACS/RIS database.
Only examinations performed on the same day as a plain radiograph of the ipsilateral knee were included.
The suprapatellar fat pads were measured on the lateral knee radiographs (Figure 1).[Fig 1]
Secondary signs of an effusion on lateral radiographs were also assessed.
On MRI the suprapatellar knee joint recess on sagittal, the deep part of the central recess (Figure...
Results
A total of 212 cases were included in this study.
The majority of lateral radiographs were performed with an overhead beam (73.5%).
Only 28 measured above the 10mm threshold suggested by Hall1(Table 1).[Fig 4]
Only a small proportion of cases demonstrated secondary signs of knee joint effusion on plain radiographs (Table 2).[Fig 5]
On MRI, a total of 46 cases had a Bakers cyst present.
The presence of internal derangement within the knee, including osteoarthritis and meniscal tears, was seen in 77.4% (164) cases.
A...
Conclusion
Our study confirmed that both lateral knee x-ray techniques demonstrated moderate correlation with the midline sagittal measurement of the knee effusion on MRI.
Similar results were demonstrated on previous studies performed by Schweitzer and Tai[2,3].
The overhead lateral projection proved to have a better sensitivity and specificity compared to a horizontal beam projection in the detection of a knee joint effusion.
This is possibly related to the redistribution of fluid.
The optimal threshold for effusion detection on a radiograph that corresponds to internal derangement is...
References
1.F Hall. Radiographic diagnosis and accuracy in knee joint effusions. 1975. Radiology 115: 49 – 54.
2.ME Schweitzer, A Falk, D Berthoty, M Mitchell, D Resnick. Knee effusion: Normal distribution of fluid. 1992. American Journal of Radiology. 159: 361 – 363.
3.AW Tai, et al. Accuracy of cross-table lateral knee radiography for evaluation of joint effusions. 2009. AJR; 193: W339-W344