Peripheral sensitization is demonstrated in subacromial pain syndrome, with central sensitization found only in females.

The objective of this study was to explore whether hypersensitivity in patients with subacromial pain syndrome (SPS) manifests purely as localized peripheral sensitization or central sensitization, is influenced by the presence of subacromial pain, and presents similarly in male and female patients. Pressure pain threshold was assessed in both a patient cohort with unilateral SPS and an uninjured matched control group. Control subjects were assessed twice, with a 15 minute rest period between testing, while patients were assessed at baseline and after an almost instantaneous reduction in pain arising from an anesthetic injection in patients. Patients received a subacromial injection consisting of both anesthetics (3 cc of 2% lidocaine and 6 cc 0.5% Marcaine with Epinephrine) and a corticosteroid agent (1 cc DepoMedrol). Patients demonstrated hypersensitivity across the involved shoulder only, providing evidence for peripheral sensitization. There were trends for hypersensitivity across remote joints, however when separated by sex, only female patients demonstrated both peripheral and central sensitization. Immediate pain reduction had no influence on hypersensitivity in the short-term. Clinical Significance: Neuropathic components are likely present in some patients with subacromial pain syndrome, and female patients may be particularly at risk for presenting with neuropathic pain. These findings are applicable towards understanding the heterogeneous etiology underlying subacromial pain syndrome and informing clinical management.

Weakness in patients with subacromial pain syndrome is local and more pronounced in females.

BACKGROUND: Subacromial pain syndrome is the predominant cause of shoulder pain, accounting for approximately half of all shoulder complaints. This population presents with weakness of the involved shoulder. However, there is a gap in our understanding of how pain contributes to this weakness, and whether there are sex related differences. METHODS: Regional and global isometric strength was tested at the involved shoulder joint and remote joints (uninvolved shoulder and both knees) in patients with subacromial pain syndrome. Data were collected before and after acute pain reduction with a subacromial injection. FINDINGS: Patients demonstrated weakness at the involved shoulder while remote joints demonstrated normal strength. When compared to healthy controls, male patients were shown to exhibit greater levels of weakness than female patients at the involved shoulder, based on comparisons with sex-matched controls using z-scores. Pain reduction (through an anesthetic injection) had no influence on strength in the short-term. INTERPRETATION: Weakness in patients appears to be sex dependent and is not resolved with reduction of pain. This calls into question the assumptions of the physiological causes of this weakness.

Joint position sense - There׳s an app for that.

Traditionally, proprioception has been assessed with a passive model, in which an external apparatus moves a body segment. Recently, protocols have been developed based on active movements, which are more representative of functional activities. However, even these approaches require expensive testing equipment and the necessity of a visit to a research lab, as there are no commercially available mobile instruments that allow for the assessment of proprioception outside of a laboratory setting. The objective of this study was to demonstrate the validity and feasibility of using a mobile device (iPod Touch) to assess joint position. We conducted a concurrent validity study in the lab (n=9) and a field based study (n=79). The field based study was conducted at the 2012 American Society of Biomechanics meeting in Gainesville, Florida. The results of both studies demonstrate good agreement with our established protocol using a magnetic tracking device, with angular errors decreasing with increasing shoulder flexion angles. The studies demonstrate the validity and feasibility of using mobile devices for assessing motion-based parameters, both inside and outside of a laboratory setting.

Joint position sense during a reaching task improves at targets located closer to the head but is unaffected by instruction.

The purpose of the present study was twofold. Our first purpose was to test whether joint position sense is similar under instructions to memorize hand position and instructions to memorize shoulder and elbow angles. We hypothesized that instructions to memorize hand position would produce smaller errors due to evidence suggesting that the CNS directly determines hand position but indirectly determines joint angles from proprioceptive information. Our second purpose was to assess biases in joint position sense at various joint angles in a sagittal workspace. We hypothesized that akin to previous single-joint investigations, the shoulder and elbow would demonstrate better joint position sense as joint angles approached 90° during our multi-joint task. Sixteen healthy and right-hand-dominant subjects participated in the present investigation. Subjects were required to actively position their right upper extremity to one of three targets for a memorization period. After returning to the rest position, subjects then actively repositioned back into the target. We did not find evidence of a substantial difference in joint position sense between instructions to memorize the hand position or joint angle. This finding, when considered in conjunction with other evidence, suggests that studies employing either a joint angle protocol or a hand estimation protocol likely produce results that are similar enough to be compared. Proprioception has been shown to be non-uniform across a two-dimensional horizontal workspace. The present investigation provides evidence that proprioception is also non-uniform across a two-dimensional sagittal workspace. Specifically, angular errors decrease as upper extremity joint angles approach 90° of flexion and endpoint errors decrease as targets are located increasingly closer to the head.

The shoulder and elbow joints and right and left sides demonstrate similar joint position sense.

Proper orientation of the shoulder and elbow is necessary for accurate and precise positioning of the hand. The authors' goal was to compare these joints with an active joint position sense task, while also taking into account the effects of joint flexion angle and arm dominance. Fifteen healthy subjects were asked to replicate presented joint angles with a single degree of freedom active positioning protocol. There were no significant differences in angular joint position sense errors with respect to joint (shoulder vs. elbow) and side (left vs. right). However, when considering linear positioning, errors were lower for the elbow, due to a shorter lever arm. Also, as flexion angles increased toward 90°, there was a consistent pattern of lower errors for both joints.