Why indicators of intra-articular pathology seen on ultrasound may require further investigation.
In the two-part post “fractures can be seen on ultrasound” (part 1 here and part 2 here) we talked about the utility of ultrasound in detecting fractures, suggesting that fractures in cortical bone may be seen both when X-ray does and does not detect them,1 in locations where the fracture involves the superficial surface of the cortex.2 Ultrasound cannot detect pathology in areas where direct access is not possible, i.e., intra-articular fractures. In such locations, which are effectively invisible to ultrasound, only modalities that can ‘see through’ the bone (X-ray, MRI or CT) can be used to diagnose pathology. Ultrasound-detected fractures still require X-ray:
- to determine the extent of bone involvement; ultrasound sees the surface break but not into the bone, and
- to ascertain whether the fracture is related to other bone pathologies.
Following ultrasound, it is possible a fracture may not be seen on the X-ray. This does not change the diagnosis to “no fracture”. Conversely a normal ultrasound does not mean no X-ray is required.
In addition, ultrasound gets a better view of periosteal changes seen with fracture, has spatial resolution capable of enabling visualisation of very fine detail3 such as bone fragments. Probe pressure may enable matching symptoms to subtle findings. This makes ultrasound particularly sensitive to detecting minimally/non-displaced fractures and avulsion fractures as cortical bone disruption is often superimposed over normal bone on X-ray.
Within these clear caveats, this case demonstrates that there may be indirect signs of intra-articular fracture on ultrasound.
The images in part 1 of this case suggest haemarthrosis. The fine particulate appearance in the joint fluid, in the clinical context of recent trauma, is consistent with blood, which suggests intra-articular injury.4 Indeed, detection of intra-articular injury by ultrasound is not new, with well-known sonologist Stefano Bianchi and his research group establishing the appearance of joint fluids characteristic of intra-articular fracture in 1994.5 In some cases, it may be possible to see layering within the fluid, a brighter increased echogenic layer of fat lying above a reduced echogenic blood layer.4 When fracture occurs fat is released into the joint capsule along with blood. Detection of this fat layer allows tentative differentiation between joint injuries involving fracture or severe capsuloligamentous injury, and those without such injuries.4,5
The case presented here is an example of using ultrasound early after injury to better match findings with acute injury appearances to enable differentiating patients requiring early referral for specialist review and those to be managed conservatively.
Coming in the next post (or maybe even two):
Scott Allen will share his opinions about when and how he thinks ultrasound imaging matters. He will talk about the increasing power of ultrasound imaging in the diagnostic picture, as well as what his extensive experience allows him to conclude about MSK findings, including those indicating fracture.
It will be a good read.
- Wang CL, Shieh JY, Wang TG, Hsieh FJ. Sonographic detection of occult fractures in the foot and ankle. J Clin Ultrasound [Internet]. 1999 Oct [cited 2020 Oct 21];27(8):421–5. Available from: https://pubmed.ncbi.nlm.nih.gov/10477883/
- Shung KK. High Frequency Ultrasonic Imaging [Internet]. Vol. 17, Journal of Medical Ultrasound. Elsevier (Singapore) Pte Ltd; 2009 [cited 2020 Nov 2]. p. 25–30. Available from: /pmc/articles/PMC2863319/
- Nicholson JA, Tsang STJ, MacGillivray TJ, Perks F, Simpson AHRW. What is the role of ultrasound in fracture management? Bone Jt Res [Internet]. 2019 [cited 2020 Oct 21];8(7):304–12. Available from: /pmc/articles/PMC6691369/
- Rippey J. Ultrasound for knee effusion: lipohaemarthrosis and tibial plateau fracture. Australas J Ultrasound Med [Internet]. 2014 Nov [cited 2020 Oct 21];17(4):159–66. Available from: /pmc/articles/PMC5024930/
- Bianchi S, Zwass A, Abdelwahab IF, Ricci G, Rettagliata F, Olivieri M. Sonographic evaluation of lipohemarthrosis: clinical and in vitro study. J Ultrasound Med [Internet]. 1995 Apr 1 [cited 2020 Oct 21];14(4):279–82. Available from: http://doi.wiley.com/10.7863/jum.1918.104.22.1689