Pseudoparalysis and pseudoparesis of the shoulder

Background: Clinical presentation of massive rotator cuff tears range from pain to loss of active range of motion. Pseudoparalysis and pseudoparesis are defined inconsistently in the literature, but both include limited active with maintained passive range of motion. Objective: This article aims to provide a consistent definition of pseudoparalysis and pseudoparesis of the shoulder and show structural and biomechanical differences between these two types of rotator cuff tear with their implications for treatment. Methods: A literature review including key and basic papers discussing clinical symptoms, biomechanical differences, and their impact on therapeutic options for pseudoparalysis and pseudoparesis was performed. Results: Biomechanically, structural differences between pseudoparalysis (active scapular plane abduction <45°) and pseudoparesis (active scapular plane abduction 45–90°) exist. For massive posterosuperior rotator cuff tears, the integrity of the inferior subscapularis tendon is themost predictive factor for active humeral elevation. Patients with pseudoparalysis have a higher grade of subscapularis tendon involvement (>50%) and fatty infiltration of the subscapularis muscle. Treatment options depend on the acuteness and repairability of the tear. Rotator cuff repair can reliably reverse the active loss of active range of motion in acute and reparable rotator cuff tears. In chronic and irreparable cases reverse total shoulder arthroplasty is the most reliable treatment option in elderly patients. Conclusion: The most concise definition of pseudoparalysis is a massive rotator cuff tear that leads to limited active (<45° shoulder elevation) with free passive range of motion in the absence of neurologic deficits as the reason for loss of active elevation. The integrity of the subscapularis tendon is the most important difference between a pseudoparalytic and pseudoparetic (active shoulder elevation 45–90°) shoulder. Decision-making for surgical options depends more on reparability of the tendon tear and patient age than on differentiation between pseudoparalysis and pseudoparesis.

Massive rotator cuff tears (mRCT) comprise approximately 10 to 40% of all treated rotator cuff tears (RCT) [1,13]. In 1985, Cofield [6] introduced a definition of mRCTas a tear greater than 5 cm in diameter. A more reliable and generally accepted definition was reported by Gerber et al. [22], as complete disinsertion of two or more ten-dons of the rotator cuff (RC). 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 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. Werner et al. [46] originally defined pseudoparesis as active shoulder anterior elevation of less than 90°in the presence of free passive anterior elevation caused by an mRCT. Despite paresis being defined as weakness with some motion and paralysis as no motion, most authors use the term pseudoparalysis inconsistently to describe a lack of active anterior shoulder elevation greater than 90°with free passive elevation after an mRCT. Tokish et al. [44] suggested clarifying the terms and recommended reserving pseudoparalysis for patients with 0°active range of motion, while pseudoparesis should be referred to in patients who are able to actively elevate their arm up to 90°. 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). This article focuses on clinical presentation, biomechanical behavior, and implications for therapy of pseudoparalysis and pseudoparesis of the shoulder based on current literature and the authors' opinions and experience.

Clinical presentation
Clinical presentation of patients suffering from mRCT differs substantially and can range from free active range of motion without pain to painful or pain-free inability to actively elevate the affected arm. The diagnosis of an mRCT is based on clinical and imaging findings. Patients with pseudoparalysis or pseudoparesis suffer from loss of active range of motion with almost free passive range of motion. Differentiation of pseudoparalysis and pseudoparesis can be assessed clinically by active scapu-lar plane abduction. Patients with pseudoparalysis cannot forward elevate their arm higher than 45°(. Fig. 1), while patients with pseudoparesis can forward elevate their arm higher than 45°but not higher than 90°(. Figs. 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. Furthermore, these patients showed an anterior extension of the posterosuperior RC tear involving more than 50% of the SSC tendon, which correlated to an inability to actively abduct more than 45°.

Biomechanics
Stability of the glenohumeral joint in all possible positions of the humerus is achieved by the interaction of all scapulohumeral muscles, thus equilibrating

Loss of forward elevation
Pseudoparalysis of the shoulder is associated with a complete tear of the SSC and supraspinatus tendon or the involvement of at least three tendons of the RC [7]. 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. In a biomechanical computer model, the key function of the SSC in developing pseudoparalysis with inability of active abduction >45°was confirmed [16].
The SSC acts against the posterior deltoid and cuff to initiate the movement of forward flexion when starting with the arm at the side of the body. When SSC is completely torn, the humeral head subluxates anteriorly and superiorly (anterosuperior escape), making any forward flexion impossible (. Fig. 1). In pseudoparesis, the remaining SSC (more than 50%) may be active enough to maintain active centralization of the humeral head during the initial phase of the forward flexion move-ment, to enable the anterior deltoid to take over (. Figs. 2 and 3).

Bony anatomy
The etiology of non-traumatic mRCT is not yet fully understood. Some authors suggest including the bony anatomy and the vector forces of the RC and the deltoid muscle to explain tear pattern and their functional consequences. Clinical observation and biomechanical observation of the pseudoparalytic shoulder by Bouaicha et al. [3] led to introduction of the Shoulder Abduction Moment (SAM) index. The SAM index is the ratio of the radii of two concentric spheres based on the center of rotation (COR) of the glenohumeral joint. One sphere captures the humeral head (so-called "numerator" to capture the stabilizing forces of the rotator cuff), while the other sphere includes the origin of the deltoid muscle around the acromion ("denominator" to capture the destabilizing forces of the deltoid muscles). Intheclinical analysis, atotal of 36 patients with pseudoparalysis were compared to an age-and gender-matched cohort of 36 patients without pseudoparalysis. All patients showed MRI-confirmed mRCT. A SAM <0.77 corresponded to 11-fold-elevated risk of pseudoparalysis. These findings suggest a strong correlation of anatomical features (small humeral head and lateral acromion and subsequent high critical shoulder angle [CSA] [39]). The initial hypothesis that acromial morphologic characteristics influence the development of pseudoparalysis was confirmed by showing that patients with pseudoparalysis have a larger CSA, smaller acromiohumeral distance (ACHD), and a higherpositioned acromion in the sagittal plane [17].

Implications for treatment
Deciding on the treatment for pseudoparetic or pseudoparalytic shoulders remains challenging. The most important differentiation is between acute and chronic mRCT, since this significantly influences the possible surgical treatment. In acute cases, the loss of active range might be influenced by pain and can in general be reliably reversed with early arthroscopic repair of the mRCT [9,43]. In chronic cases with a decentered humeral head and advanced myotendinous degeneration, RC repair is, however, prone to failure. Therefore, treatment options for chronic pseudoparalysis or pseudoparesis of the shoulder vary from nonoperative partial RC repair, superior capsular reconstruction, tendon transfers, or reverse total shoulder arthroplasty (RTSA) without or with muscle transfer. The most challenging aspect in the management of pseudoparalysis and pseudoparesis remains the repair or compensation of SSC tears. As detailed above, the manifestation of pseudoparalysis or pseudoparesis increases with the involvement of the SSC tear. Many chronic tears are well compensated until an acute SSC tear occurs ("acute on chronic RC tear"). This event often leads to emergence of a pseudoparalytic shoulder which can be efficiently treated by addressing the acute component of the tear even if some of the tears remain irreparable. The challenge becomes greater in cases of a pseudoparalytic shoulder with chronic anterior and superior cuff tears and a non-repairable SSC tear in young patients.

Conservative treatment
Nonoperative management in chronic pseudoparalysis or pseudoparesis involves corticosteroid injections and exercises for strengthening the deltoid and periscapular muscles. In addition, rehabilitation focuses on the work of scapulohumeral and thoracohumeral muscles, e.g., the latissimus dorsi, and on their ability to actively center the humeral head and counterbalance the deltoid forces to maintain a moment arm responsible for the scapular abduction. This treatment is an excellent first option in most patients with painful limitation of shoulder movement [44]. Some other authors add a specific anterior deltoid training to steroid injection and nonsteroidal drugs [32].

Surgical treatment
When conservative treatment fails, surgical options have to be evaluated. Therefore, the reparability of the RCT has to be assessed. Different instruments exist to decide whether an RCT is still reparable. Most important is to evaluate the fatty infiltration of the musculature according to the Goutallier classification initially described in CT scans [26] and adapted by Fuchs et al.
[19] to MRI. Fatty infiltration of a muscle higher than Goutallier grade II (>50% fatty muscle atrophy) is considered to be irreparable. Retraction of the supraspinatus tendonis another important risk factor. Tendon retraction is classified according to Patte [41] in stage 1 (stump near bony insertion), stage 2 (stump at the level of humeral head), and stage 3 (stump at the level of the glenoid). A combination of Goutallier grading and tendon retraction and tendon length appears to be a powerful tool to predict RC reparability [35]; however, evaluation of the quality of the tendon is also an important aspect that cannot always be achieved by the preoperative analysis. So far, no study exists that consequently distinguishes between pseudoparalysis and pseudoparesis and the impact on treatment depending on the consistent definition. Therefore, all cited studies are summarized in . Table 2 to give an overview of diagnostic criteria and treatment options.

Debridement, biceps tenotomy, and balloon
In elderly patients with irreparable RCT where the main goal is pain relief and a more prolonged surgical time is not applicable, arthroscopic debridement with biceps tenotomy is a valuable option [20]. However, it may fail; therefore, patients must be aware that a second surgery may be required with the implantation of an RTSA. Even though decreased pain level and improved functional outcome scores are reported for patients with massive irreparable RCT with debridement only, reversal of pseudoparalysis or pseudoparesis has, however, not been reported in the literature and cannot be expected. Satisfactory clinical mid-term outcome is also achieved with arthroscopic subacromial balloon spacer implantation, but only in patients without preexisting pseudoparalysis [33].

Arthroscopic rotator cuff repair
If ever an RCT is reparable, arthroscopic reconstruction is preferred by the authors (. Figs. 1 and 2). In patients with absence of preoperative glenohumeral osteoarthritis, no fatty infiltration of the RC muscle grade 3 or higher, and acromiohumeral distance higher than 7 mm, arthroscopic RC repair can be successful and might lead to a reversal of preoperative pseudoparalysis [9,40]. In revision cases, the outcome was much worse [9]. Where a complete repair cannot be achieved, even a partial repair is a considerable alternative. In patients with irreparable posterosuperior RCT, arthroscopic partial repair was an effective treatment, with an improvement of pain values and clinical scores despite a high failure rate of the repair (41.6%) [5]. So far, no evidence exists that a partial repair can successfully reverse chronic pseudoparesis or even pseudoparalysis. Therefore, the authors do not see an indication for arthroscopic partial repair alone without any additional procedure, e.g., tendon transfer, in chronic pseudoparetic or pseudoparalytic shoulders.

Tendon transfer
In younger patients in whom RTSA is not yet an option, tendon transfer should be considered. Tendon transfer not only offers the potential for pain relief but also improves the function of the affected shoulder. For irreparable posterosuperior RCT, Gerber et al. [21] introduced the latissimus dorsi transfer (LDT) in 1988, with benefits for the patients concerning pain and function [23]. Birmingham and Neviaser [2] reported on patients with failed RC repair and limited active elevation (mean 56°, range 20-80) but free passive motion (mean 126°, range 110-150) preoperatively treated with LDT and 100% pseudoparesis reversal. Unfortunately, the term pseudoparalysis was not defined nor mentioned. Nowadays, different techniques from initially reported open to arthroscopically assisted or full arthroscopic LDT exist, eliciting marked improvement in shoulder pain, strength, and function, with a low risk of complications as reported in a recent systematic review [34]. Preoperative assessment of the remaining RC is crucial, since fatty infiltration of the teres minor, as well as insufficiency of the subscapularis muscle, are negative predictors for a good outcome of LDT [24].
There is increasing interest in using lower trapezius transfer for posterosupe-rior irreparable RCT, since a biomechanical study showed effectiveness in restoring external rotation [27]. Recently, Elhassan et al. [11] reported good short-term clinical outcomes of an arthroscopically assisted lower trapezius transfer, even in patients with pseudoparalysis. Of note, true shoulder pseudoparalysis (defined as active shoulder flexion and abduction <60°) was a factor that significantly predicted a negative result.
In the authors' experience, a tendon transfer cannot by itself restore the function of a chronic pseudoparalytic shoulder, even though it may in a pseudoparetic shoulder, unless anteroposterior stabilization of the humeral head is achieved. Indeed, the misbalance of the anterior and posterior forces must be restored to prevent anterior and superior migration of the humeral head induced by contraction of the posterior and middle deltoid and cuff during the attempt of a forward flexion movement.
The aim of this article was not to provide a description of the tendon transfers, as this has been done previously; however, alongside the historical gold standard for irreparable SSC tears-pectoralis major transfer [28, 42]-anterior LDT has gained popularity and is a reasonable option, providing a better force vector with a line of pull which is very similar to that of the SSC [12]. So far, no subgroup analysis of patients with a pseudoparalysis or pseudoparesis exists for irreparable SSC tendon tear.
[38] introduced superior capsular reconstruction (SCR) in a biomechanical cadaveric study where the superior humeral head translation was restored by SCR after cutting the supraspinatus tendon. Early follow-up (mean 34 months) showed promising radiological and clinical results in patients with irreparable RCT [37]. Reversal of pseudoparalysis was achieved in 90-96% of the patients treated with an arthroscopic SCR, even after a mean follow-up of 60 months [4,36]. Surgeons who are familiar with this procedure propagate using a 6-8 mm thick and stiff autologous fascia lata graft to achieve good functional outcome. At the authors' institution, this procedure is rarely performed and profound expertise is therefore lacking.

Reverse total shoulder arthroplasty
The most valuable option for older patients with chronic irreparable mRCT and pseudoparalysis or pseudoparesis, showing improved outcomes for up to even 20 years after surgery, is RTSA [15]. This is also the authors' preferred option in elderly patients in whom conservative treatment has failed (. Fig. 3). A systematic review showed an increased average active elevation of 56°and reversal of pseudoparalysis in 96% of patients treated with RTSA [10]. It should be mentioned that the term "pseudoparalysis" was inconsistently or incorrectly defined as "ROM less than 90°." Nevertheless, implantation of RSTA remains the best option for older patients with pseudoparalysis and pseudoparesis and is even a justifiable treatment for patients under the age of 60 years [14]. Despite the improvement of functional outcome scores at a mean followup of 12 years after RTSA, the complication rate was 39%, revision rate 17%, and failure rate 9%, so that the indication in patients younger than 60 years has to be considered carefully.

Conclusion
Massive rotator cuff tear is a disabling condition for patients and can lead to pseudoparalytic or pseudoparetic shoulders with loss of active range of motion. Structural differences exist between pseudoparalysis and pseudoparesis: patients with pseudoparalysis have a higher grade of involvement of subscapularis tendon tears and a higher grade of fatty infiltration of the subscapularis muscle compared to patients with pseudoparesis. Decisionmaking regarding therapeutic options is mainly based on acuteness, repairability of the RCT, and patient age. RC repair can reliably reverse the loss of active range of motion in acute and reparable RCT. In chronic and irreparable cases, options vary from nonoperative, partial RC repair, tendon transfer, and SCR, to RTSA. Skillful preoperative patient selection is the key to success. RTSA shows good re-sults in predominantly older patients with painful pseudoparalysis or pseudoparesis. In young and active patients with an intact or repairable SSC lesion for whom shoulder arthroplasty is not yet an option, SCR and tendon transfer can lead to reliable clinical outcomes with improvement regarding the range of motion and function.