Chronic Pseudoparalysis Needs to Be Distinguished From Pseudoparesis: A Structural and Biomechanical Analysis

Abstract

Background: Chronic pseudoparalysis is generally defined as the inability to actively elevate the arm above 90° with free passive range of motion and no neurological deficits. It has been suggested that this arbitrary cutoff needs to be refined. Purpose: To analyze whether there are structural and biomechanical differences in patients with chronic pseudoparalysis and those with chronic pseudoparesis. Study Design: Case-control study; Level of evidence, 3. Methods: In this retrospective study, 50 patients with chronic massive rotator cuff tears (mRCTs; ≥2 tendons) and free passive and active scapular plane abduction <90° were divided into 2 groups: pseudoparalysis group (n = 24; active scapular plane abduction, <45°) and pseudoparesis group (n = 26; active scapular plane abduction, >45° and <90°). Radiographic measurements included the critical shoulder angle, acromiohumeral distance, posterior acromial tilt, anterior and posterior acromial coverages, and posterior acromial height on outlet views. Measurements on magnetic resonance imaging (MRI) included fatty infiltration of the rotator cuff muscles, anterior (subscapularis) and posterior (infraspinatus/teres minor) tear extensions, and global (anterior + posterior) tear extension in the parasagittal plane. A published musculoskeletal model was used to simulate the effect of different mRCTs on the muscle force required for scapular plane abduction. Results: Plain radiographs revealed no differences between patients with chronic pseudoparalysis and those with pseudoparesis. MRI assessment showed significant differences between patients with chronic pseudoparalysis and those with pseudoparesis with respect to fatty infiltration of the subscapularis (2.9 vs 1.6; P < .001) and infraspinatus (3.6 vs 3.0; P < .001) muscles, and anterior (−23° vs 4°; P < .001), posterior (−23° vs −14°; P = .034), and global rotator cuff (225° vs 190°; P < .001) tear extensions. The anterior tear extension in patients with chronic pseudoparalysis always involved more than 50% of the subscapularis, which was associated with an odds ratio of 5 for inability to actively abduct more than 45°. The biomechanical model was unable to find a combination of muscles that could balance the arm in space when the tear extended beyond the supraspinatus and the cranial subscapularis. Conclusion: This study confirms that chronic pseudoparalysis and pseudoparesis are associated with different structural lesions. In the setting of a chronic mRCT, involvement of more than 50% of the subscapularis tendon with fatty infiltration of stage 3 is associated with pseudoparalysis of active scapular plane abduction <45°. The key function of the subscapularis was confirmed in the biomechanical model.

Pseudoparalysis and pseudoparesis of the shoulder

“…Wieser et al [47] performed a fluoroscopic, magnetic resonance imaging, and electrophysiologic assessment of shoulders with massive posterosuperior RCT and showed that involvement of the inferior SSC tendon appeared to be the most predictive factor to lift the humerus above 90°. This finding was confirmed by a recent study [16] that showed that involvement of more than 50% of the SSC tendon with fatty infiltration of stage 3 is associated with active scapular plane abduction of less than 45°. Furthermore, this study showed a difference in structural lesions between pseudoparalysis and pseudoparesis.…”

“…2 and 3). These values are based on a recent structural and biomechanical analysis performed by Ernstbrunner et al [16], who showed that patients with chronic pseudoparalysis and pseudoparesis have different structural lesions. Patients with chronic pseudoparalysis have a significantly higher grade of fatty infiltration of the subscapularis (SSC) and infraspinatus muscles and a greater extension of RCT.…”

“…More recently, Lädermann et al [31] introduced a classification of mRCT considering the group of tendons involved. The pattern of the tear influences the biomechanics of the shoulder, particularly regarding the balance between anterior and posterior forces on the humeral head, resulting in a modification ACHD acromiohumeral distance, CSA critical shoulder angle, ISP infraspinatus, LoE level of evidence, MRI magnetic resonance imaging, RCT rotator cuff tear, SSC subscapularis of the active centralization of the humeral head [16]. If a mRCT leads to loss of active range of motion, the definition of "pseudoparalysis" or "pseudoparesis" is inconsistent.…”

“…Unfortunately, this systematic review does not specify exact values for active motion to differentiate between the two conditions. Therefore, the definition of pseudoparalysis and pseudoparesis of Tokish et al was combined with recent structural and biomechanical findings [16]: pseudoparalysis is defined as mRCT with maintained passive range of motion and limited active scapular plane abduction <45°without neurologic deficits; pseudoparesis is defined as mRCT withmaintained passive range of motion and limited active scapular plane abduction >45°and <90°w ithout neurologic deficits (. Table 1).…”

SCR 2021

“…21 A study in this month’s AJSM differentiated between pseudoparalysis, defined as active elevation less than 45°, and pseudoparesis, defined as active elevation greater than 45° but less than 90°. 11 Analysis of the results showed that the more severe degree of involvement was associated with stage 3 fatty infiltration of more than 50% of the subscapularis.…”