Joint Fluid and the Time of Death

14 Apr

One of the most important things that the medical examiner must determine in any death investigation is the time of death. This can spotlight or exonerate a suspect and support or refute a witness statement. An alibi can be upheld or shattered.

But it’s not that easy. The medical examiner uses things such as body temperature, degree of rigor mortis, lividity, stomach contents, degree of decomposition, insect activity, and a few other parameters to make a best guess as to time of death. Another determination that often proves helpful is the potassium level within the vitreous humor, the liquid inside the eyeball. The potassium level tends to increase in a linear fashion and at a known rate after death and this can help the medical examiner with his estimation.

Now it seems that assessing the level of potassium in the victim’s synovial fluid might be just as accurate. Synovial fluid is the liquid that lubricates our joints. This could prove useful in cases where the victim has been decapitated or the head is so damaged that the eyes have been destroyed.


Posted by on April 14, 2011 in General Forensics, Time of Death


7 responses to “Joint Fluid and the Time of Death

  1. Tanya

    April 14, 2011 at 4:17 pm

    Interesting, especially if there’s no “useable” head.


  2. Laura Mitchell

    April 14, 2011 at 5:43 pm

    How much synovial fluid is in a joint, for example, the knee? How much decomposition has to take place eliminate the presence of synovial fluid?


    • D.P. Lyle, MD

      April 15, 2011 at 10:52 am

      Only a very tiny amount. Just enough to lubricate the joint. Joints are protected by fibrous tissues and cartilage so they are much slower to decay than are other body tissues. But the potassium level might only be a useful tool for a couple of days–its usefulness gone long before any significant decay could occur.


      • Laura Mitchell

        April 15, 2011 at 6:33 pm

        So if decomp has started, we’re probably better off checking the levels of volatile fatty acids?


      • D.P. Lyle, MD

        April 16, 2011 at 7:48 am

        Testing for fatty acids has been explored and in some cases will help, but it depends on the rate and degree of decay and this in turn depends upon many factors the most important being the temperature and humidity level. So interpreting this data isn’t very straightforward either. Still a best guess most often. And this would come later, after the time the vitreous or joint potassium levels would be useful—after the first two days in most cases.


  3. J.D.

    April 15, 2011 at 5:03 am

    At what hour does the vitreous become useless? Does synovial fluid provide a longer lasting alternative?


    • D.P. Lyle, MD

      April 15, 2011 at 10:49 am

      The vitreous potassium level is usually useful only in the first 48 hours. One advantage is that it doesn’t seem to be effected by temperature and humidity as body temp, lividity, and rigor can be. I’m not sure what the timeline for synovial fluid is since this is a newer technique but I suspect it will be useful for at least 48 hours and perhaps longer.



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