A 77 y.o. woman with a hx of stage III squamous cell cancer of the lung complains of R knee pain after a fall.
What do you notice on her film?
What do you notice on her CT?
how about now?
Our patient had a lipohemarthrosis, blood and fat laying within the joint capsule. This results from an intra-articular fracture with marrow escaping into the joint space. Since fat floats on water layering of the fluid in the joint occurs if the patient has been lying down for 3-5 minutes. If it is seen, most commonly a tibial plateau fracture is present. Plain xrays identify a tibial plateau fracture only 79% of the time. it is a useful sign. Especially In the elderly osteoporotic patients, where plain films are often normal for two weeks until there is a collapse of the cancellous bone in the tibial plateau.
the lipohemarthrosis with layering in the suprapatellar bursa
Up to 64% of tibial plateau fractures do not have a lipohemarthrosis but rather a simple hemarthrosis so its absence does not exclude an intraarticular fracture. A simple hemarthrosis can separate into serum and red cells causing two layers to form. If fat is also present three layers are visible. This is called the parfait sign.
The parfait sign on US: the asterix is a layer of serum between the fat and RBCs
Another easily missed injury on plain films of the knee is the quadriceps tendon injury. The xrays are either normal or show a high riding patella. Quadriceps tendon injuries occur most often among middle-aged people who play running or jumping sports. Patients with a complete tear are unable to extend at the knee since the tendon attaches to the patella. It is important to diagnose this condition early since the tendon contracts and scars over time making the surgical repair difficult. Ciprofloxacin, rheumatoid arthritis, lupus, renal failure, diabetes and peripheral vascular disease predispose individuals to quadriceps tendon rupture.
the high riding patella and inability to extend at the knee are hallmarks of the quadraceps tendon rupture
Our patient had a Ct confiming the diagnosis and elected for non operative management and was treated with a brace.
the fracture in our patient was much easier to see on CT
Maheshwari J, Pandey V, Mhaskar V. Anterior tibial plateau fracture:an often missed injury. Indian J Orthop. 2014;48(5):507-10. .
Prasad N, Murray J, Kumar D,et al. Insufficiency fracture of the tibial plateau; an often missed diagnosis. Acta Orthop Belg 2006;72(5):587-01.
Non S. Quadriceps tendon rupture. J Family Med Prim Care 2018 Jan-Feb. 7 (1 ):257-260. Doi:10.4103/jfmpc.jfmpc_341_16.
Khiabani A, Khiabani D, Priddy W, Derr C. University of South Florida Emergency Medicine Program veroincarodriguez@usf.edu jan 7,2022https://www.tampaemergencymedicine.org/blog/a-holiday-ultrasound-parfait-recipe-thats-sure-to-be-a-hit A good review of how to find the quadriceps tenson on US.
Karistinos A, Paulos LE. “Ciprofloxacin-induced” bilateral rectus femoris tendon rupture. Clin J Sport Med. 2007;17:406–7.