Neurobiological Mechanisms of Pain and Shoulder Dislocation: A Report

This report analyzes the neurobiological mechanisms of pain associated with a shoulder dislocation, using the case of a football athlete, Katie, who experienced a recurrent shoulder dislocation. The report explores the factors contributing to pain, including the biomechanics of the injury, the somatosensory nervous system, and the resulting neuropathic pain. It details the involvement of the spinothalamic tract, central sensitization, and the role of afferent neuron loss. The report synthesizes the understanding of pain by examining the impact of injury on the nervous system, the role of descending antinociceptive systems, and the potential for deafferentation hypersensitivity. It concludes by highlighting the instability of the shoulder joint and the mechanisms leading to pain following dislocation, supported by references in JAMA style.

Running head: REPORT
Neurobiological mechanism of pain
Name of the Student
Name of the University
Author Note

1REPORT
Introduction
Damage caused to the shoulder are a direct consequence of manual labour, repetitive
movements, aging or sports. An individual might also injure the shoulder owing to an
accident or a fall1. The case scenario involves a football athlete Katie who dislocated her right
shoulder for the second time during this season, and is currently subjected to a physiotherapy
assessment. This report will elaborate on the factors that contribute to pain and the underlying
neurobiological mechanisms.
Factors that lead to pain
The shoulder joint is one of the most common joint located in the human body that
gets dislocated. The shoulder can either dislocate backward, forward, downward, and
partially, or completely, though under most circumstances, dislocation occurs anteriorly2.
Dislocation also gets complicated when fibrous tissue that form connection between the
bones get torn or stretched, thereby worsening the situation. Furthermore, dislocation
generally takes a stronger force, such as a strong blow to the shoulder that eventually pulls
out the bones from the place. In addition, extreme rotation of the joint leads to popping of the
shoulder from the socket3. Dislocated shoulder that was reported by Katie in this case study
can be accredited to contact sports injuries.
Neurobiological mechanisms
The shoulder dislocation in the patient can be accredited to anterior dislocation caused
due to positioning of the right arm in an extreme amount of external rotation and abduction.
At this position, the inferior glenohumeral complex acted in the form of a primary restraint,
in relation to anterior glenohumeral translation4. Owing to absence of adequate dynamic
stabilization and ligamentous support, the glenohumeral joint became most vulnerable to
dislocation. In addition, stretching of the anteroinferiorly moved humeral head and the tearing

2REPORT
causes loss of integrity of the associated anterior ligamentous capsule, thus detaching the
anterior inferior labrum. Mechanism involving injury typically encompasses blow to the
externally rotated, abducted or extended extremity. The condition involved damage to the
somatosensory nervous system, thus causing neuropathic pain. The dorsal horn of the spinal
cord leads to origin of spinothalamic tract (STT) that are a major component of nociceptive
pathway.
Afferent neuron loss due to shoulder dislocation might have induced a range of
functional alterations in dorsal horn neurons, thus decreasing the large fiber input5. This
directly reduced interneuron activity, thereby inhibiting the nociceptive neurons or causing
loss of afferent inhibition6. Furthermore, hypoactivity demonstrated by the descending
antinociceptive systems or absence of descending inhibition can be cited as a major
contributing factor to the shoulder pain, With the gradual loss of neuronal input, spontaneous
firing is initiated by the STT, also referred to as "deafferentation hypersensitivity”7. In
addition, central sensitization is also mediated by the neuroglia and any kind of peripheral
nerve injury to the glial cells trigger the release of glutamate and proinflammatory cytokines
that eventually influence the neurons.
Conclusion
Thus, it can be concluded that shoulder dislocations are one of the most widespread
joint dislocation, and anterior dislocation are the most common. The shoulder can be cited as
an unstable joint owing to the presence of a shallow glenoid that attaches to a small region of
the humeral head. Thus, Katie suffered from pain due to shoulder dislocation owing to
damage to the somatosensory nervous system.

3REPORT
References
1. Gokkus, K., Sagtas, E., Kara, H., & Aydin, A. T. Posterior shoulder dislocation
associated with the head (splitting) and humeral neck fracture: impact of
understanding radiologic signs and experience with an extended deltopectoral
approach. Techniques in hand & upper extremity surgery. 2018; 22(2): 57-64.
2. Atef, A., El-Tantawy, A., Gad, H., & Hefeda, M. Prevalence of associated injuries
after anterior shoulder dislocation: a prospective study. International orthopaedics.
2016; 40(3): 519-524.
3. Itoi, E., Kitamura, T., Hitachi, S., Hatta, T., Yamamoto, N., & Sano, H. External
Rotation and Abduction Bracing in the Management of First-Time Anterior Shoulder
Dislocation: Response. The American journal of sports medicine. 2015; 43(8): NP24-
NP25.
4. Itoigawa, Y., Hooke, A. W., Sperling, J. W., Steinmann, S. P., Zhao, K. D., Itoi, E., &
An, K. N. The effect of subscapularis muscle contraction on coaptation of
anteroinferior glenohumeral ligament–labrum complex after Bankart repair. Journal
of biomechanics. 2019; 85: 134-140.
5. Gutkowska, O., Martynkiewicz, J., Urban, M., & Gosk, J. Brachial plexus injury after
shoulder dislocation: a literature review. Neurosurgical review. 2018; 1-17.
6. Small, K. M., Adler, R. S., Shah, S. H., Roberts, C. C., Bencardino, J. T., Appel,
M., ... & Subhas, N. ACR Appropriateness Criteria® Shoulder Pain-
Atraumatic. Journal of the American College of Radiology. 2018; 15(11): S388-S402.
7. Park, H. R., Lee, G. S., Kim, I. S., & Chang, J. C. Brachial plexus injury in
adults. The Nerve. 2017; 3(1): 1-11.