Working Diagnosis:
Left medial knee pain secondary to trigger points along hip adductors referring to the medial knee.

Treatment:
7-10 Trigger point injections (TPIs) performed with a 25 gauge 1.5 inch needle.[ Photo 1] Multiple passes made to medial adductors in area of maximal tenderness. Multiple local twitch responses identified with 80% reduction in pain immediately following the procedure.

Outcome:
Patient continues to run marathons pain free with NO RECURRENCE OF SYMPTOMS.

Author's Comments:
As a result of ANCHORING on the MRI result of a meniscal tear, the physical exam, which revealed an extra-articular source of pain, was initially discounted. Premature closure halted the cognitive process of the diagnosis.
The presence of discrete focal tenderness in a palpable taught band of skeletal muscle which produces both referred regional pain and a local twitch response defines a trigger point.
Trigger points mimic a wide variety of MSK pathologies. Lower limb trigger points can produce intense knee, quadricep, calf, and low back pain.
To 'err is human'; however, use of a diagnostic time out to reflect on the working diagnosis and evidence supporting may prevent propagation of diagnostic error and premature closure.

Editor's Comments:
This case emphasizes the importance of starting with a broad differential diagnosis and correlating the history, physical and imaging findings. Despite the MRI findings of a meniscal tear, which can be asymptomatic in this age group, the history and exam suggested an extra- articular source of pain. Revisiting the broad differential diagnosis was appropriate and led to the discovery of the source of his symptoms.

Myofascial pain can refer pain, often from a more proximal site, and needs to be included in the differential diagnosis in situations where the history and physical exam do not strongly suggest a more common cause.

References:
1) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3465092/pdf/prm17321.pdf

2) http://www.aafp.org/afp/2002/0215/p653.html

3) http://www.namtpt.shuttlepod.org/MTPT_What_is_it

4) http://emedicine.medscape.com/article/89095-overview

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