Page 84 - Journal of Special Operations Medicine - Summer 2014

Intra-articular Morphine
versus Lidocaine for Acute Knee Pain

Ross F. Graham, MD; John Hughes, MD;
Anthony Johnson, MD; Peter Cuenca, MD; Trey Mosely, MD

ABSTRACT
Objective: The authors conducted an unfunded ran- knee injuries seen in the United States between 1999 and
domized controlled trial approved by the Brooke Army 2008 (rate of 2.29 knee injuries per 1000 population).
1
Medical Center (BAMC) Institutional Review Board The most common cause of knee injuries presenting to
(IRB) to determine the possible efficacy of intra-articular EDs during this time period was sports and recreation. 1
morphine for pain in acute knee injuries. Methods: Pa-
tients presenting to the emergency department at San Mu pain receptors are located in the central nervous sys-
Antonio Military Medical Center (SAMMC) from May tem and in peripheral tissues. The mu receptors are also
2012 to August 2013 with knee pain due to an acute in- positioned inside of joints and can be upregulated within
jury were consented and then enrolled based on a conve- minutes to hours when the tissue is subjected to trauma.
2
nience sample. Patients were randomized to one of three The morphine effect is reversible with naloxone, which
intervention arms (morphine, lidocaine, or morphine confirms that mu receptors are indeed being used. 2
and lidocaine) and were blinded to the intervention. The
respective solution was injected into the knee joint using There is ample orthopedic literature regarding intra-
standard techniques. The patients self-reported their lev- articular injections of morphine after elective arthros-
els of knee pain via a standard 100mm visual analogue copies that describes significant pain reduction and a
scale (VAS) at the time of injection and 30 minutes, 60 decreased requirement for oral pain medications.
3–5
minutes, 90 minutes, 2 hours, 6 hours, and 24 hours In 1999, a trial of intra-articular morphine after knee
postinjection. At 24 hours, the patients also reported surgery found that increasing doses of morphine were
the estimated amount of time they applied ice to the associated with increased pain relief and less use of sup-
knee and the amount of oral analgesia consumed in the plementary analgesia. Similarly, a 1997 German study
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previous 24 hours. Results: The primary outcome was detailed the use of intra-articular morphine in chronic
relative pain reduction as measured by the VAS. Second- pain patients with osteoarthritis with good effect, and a
ary outcomes were the total cumulative use of ice and double-blind randomized trial comparing normal saline
analgesics during the first 24 hours. Although this was a to morphine showed a significant decrease in pain for
small study, the results showed a possible trend toward 48 hours with two injections given 7 days apart in pa-
better pain control at all time intervals with injections tients with osteoarthritis. 7
containing morphine compared with lidocaine-only in-
jections. Ice and oral analgesia usage was equivalent be- In the majority of trials described here, morphine doses
tween the three intervention arms. Conclusion: Further between 0.5mg and 6mg were used with relief of pain
investigation with a larger sample is required to explore similar to that of local anesthetics, and with effects
whether these results are statistically significant and the lasting up to 48 hours. The exact reason for the long
possible superiority of intra-articular morphine to lido- duration is unknown, but several theories include opi-
caine for acute knee pain. oid anti-inflammatory effects and the relatively avas-
cular region of the knee joint, which slows removal
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Keywords: knee pain, acute; intra-articular morphine; intra- of the morphine. While minimal systemic absorption
articular lidocaine of the morphine may occur, it is thought that the pri-
mary analgesic action of morphine is its action on pe-
ripheral mu receptors in the joint itself. Advantages
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of targeting intra-articular peripheral mu receptors for
Introduction
providing analgesia include avoiding troublesome side
Patients with a knee injury are commonly seen in emer- effects of centrally acting morphine such as respiratory
gency departments (EDs), with approximately 6.6 million depression, sedation, and nausea and providing pain

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