Shoulder posterior cuff assessment

1. High-Yield Summary

• Target Anatomical Structures: The posterior rotator cuff comprises the infraspinatus (inserting on the middle facet of the greater tuberosity, innervated by the suprascapular nerve C5-C6) and the teres minor (inserting on the inferior facet, innervated by the axillary nerve C5-C6). Together, they anchor the posterior rotator cable and form the posterior component of the transverse glenohumeral force couple opposing the subscapularis.
• Pathognomonic Physical Lag Signs: Clinical detection relies on provocative lag signs that unmask the loss of active external rotation holding torque against anterior capsular elastic recoil: the External Rotation Lag Sign (ERLS) of Hertel (tested at 20° abduction in the scapular plane) isolates the infraspinatus; the Dropping Sign of Walch (tested at 0° or 45° abduction) identifies severe infraspinatus deficiency; and Hornblower’s Sign (Patte test / Signe du clairon at 90° abduction) is pathognomonic for teres minor failure or advanced fatty degeneration.
• Validated Statistical Accuracy: The ERLS demonstrates a pooled sensitivity of 70% to 82% and a specificity of 95% to 100% (LR+ 4.4 to 14.2) for full-thickness infraspinatus tears. The Dropping Sign yields 73% sensitivity and 98% specificity (LR+ 36.5). Hornblower’s Sign demonstrates 88% to 100% sensitivity and 93% to 96% specificity (LR+ 12.6 to 22.0) for complete teres minor disruption or Goutallier stage 2 to 4 fatty infiltration.
• Critical Diagnostic Pitfalls: Passive glenohumeral stiffness (adhesive capsulitis or osteoarthritis) precludes valid lag testing and generates false-positive interpretations. Subacromial pain induces reflex muscular inhibition that mimics true structural tear, which must be distinguished via the diagnostic subacromial lidocaine injection test. Conversely, teres minor compensatory hypertrophy or an intact anterior rotator cable can preserve resisted external rotation strength at 0° of abduction, masking extensive infraspinatus detachment.

2. Clinical Indications & Target Pathology

Assessment of the posterior rotator cuff is indicated in patients presenting with posterolateral shoulder pain, progressive weakness in active external rotation, inability to control hand trajectory in space, or compensatory posturing during overhead reaching and eating. Clinical evaluation is mandatory before planning reconstructive shoulder surgery, including arthroscopic rotator cuff repair, superior capsular reconstruction, tendon transfer, or reverse total shoulder arthroplasty.

The posterior cuff examination systematically interrogates a specific spectrum of pathological entities:

• Full-Thickness Infraspinatus Tears: Traumatic avulsions or chronic degenerative tears propagating posteriorly from the supraspinatus across the rotator cable into the middle facet of the greater tuberosity.
• Teres Minor Disruption & Fatty Degeneration: Structural rupture or myosteatotic atrophy of the teres minor, representing the critical tipping point into posterior pseudoparalysis and irreversible loss of spatial arm control.
• Suprascapular Neuropathy at the Spinoglenoid Notch: Selective entrapment of the inferior branch of the suprascapular nerve beneath the inferior transverse scapular ligament, typically secondary to a spinoglenoid paralabral ganglion cyst arising from a posterior labral tear, resulting in isolated infraspinatus denervation without tendon detachment.
• Axillary Neuropathy & Quadrilateral Space Syndrome: Compression or traction injury to the posterior division of the axillary nerve, producing selective teres minor denervation and posterolateral deltoid sensory disturbance.
• Posterior Rotator Cuff Pseudoparalysis: Complete inability to actively externally rotate the arm with preserved passive range of motion, caused by combined, massive infraspinatus and teres minor deficiency.
• Subacromial-Subdeltoid Bursitis with Pain Inhibition: Reactive inflammatory bursitis causing secondary weakness without tendon continuity loss, differentiated by diagnostic anesthetic infiltration.

3. Functional Anatomy & Biomechanical Mechanism

The posterior rotator cuff consists of two discrete musculotendinous units with distinct architectural footprints, vascular zones, and peripheral innervations.

Anatomical Footprint and Innervation Patterns

The infraspinatus originates from the medial two-thirds of the infraspinatus fossa on the dorsal scapular blade. Its unipennate muscle belly transitions into a wide, trapezoidal tendon that traverses the posterior glenohumeral capsule to insert onto the middle facet of the greater tuberosity. The tendon spans approximately 1.5 to 2.0 cm anteroposteriorly, interdigitating anteriorly with the supraspinatus to form the posterior suspension bridge of the rotator cable. Innervation is derived from the suprascapular nerve (C5-C6 roots, upper trunk), which travels through the suprascapular notch, supplies motor branches to the supraspinatus, and then navigates the fibro-osseous spinoglenoid notch around the lateral margin of the scapular spine to reach the infraspinatus fossa.

The teres minor arises from the superior two-thirds of the lateral (axillary) scapular border. It courses obliquely upward and outward to insert onto the inferior facet of the greater tuberosity and the adjacent proximal humeral shaft. It receives motor supply exclusively from the posterior branch of the axillary nerve (C5-C6 roots, posterior cord). Because the teres minor possesses a separate innervation from the infraspinatus, compression of the suprascapular nerve at either notch spares teres minor contractility.

Transverse Force Couple and Concavity-Compression

In the transverse plane, dynamic glenohumeral stability requires equilibrium between the subscapularis anteriorly and the infraspinatus and teres minor posteriorly. Co-activation of this transverse force couple drives the convex humeral head into the shallow glenoid socket, generating stabilizing concavity-compression. Disruption of the posterior anchor eliminates posterior compressive vectors. The unopposed anterior pull of the subscapularis and superior shear of the deltoid cause anterosuperior humeral head subluxation, coracoacromial contact wear, and severe mechanical inefficiency.

Vector Mechanics of Lag Signs: Elastic Recoil vs. Active Holding Torque

Lag signs operate on a precise biomechanical equilibrium between passive tissue elasticity and active muscular torque:

• Passive Elastic Recoil: When the arm is passively externally rotated toward terminal range, the anterior joint capsule, coracohumeral ligament, and subscapularis tendon are placed on passive mechanical tension, generating an internal rotation recoil vector.
• Active Holding Torque: In a structurally intact posterior cuff, the isometric holding torque of the infraspinatus and teres minor neutralizes this passive recoil the moment examiner support is withdrawn.
• The Lag Manifestation: When the posterior tendon is detached or the muscle fascicles have undergone advanced fatty degeneration (Goutallier stage 2 or greater), active holding torque is abolished. Upon release, passive internal rotation recoil pulls the forearm forward into a visible lag or rapid drop.

4. Step-by-Step Examination Technique

Patient Positioning

The patient is seated upright on a backless examination stool with an erect spine and feet placed flat on the floor. Seating without back support is critical because it permits unrestricted visualization of scapular winging, allows symmetric palpation of the infraspinatus and teres minor bellies, and prevents the patient from leaning against a chair back to substitute with torso extension.

Examiner Hand Placement & Setup

The examiner stands slightly behind and to the side of the affected shoulder. The examiner uses a two-handed stabilization and mobilization technique:

• Stabilizing Hand: Cups the patient’s elbow, supporting the upper arm in the desired abduction plane while blocking involuntary shoulder abduction, adduction, or humeral elevation.
• Manipulating Hand: Grasps the patient’s distal forearm or wrist to passively guide the extremity through rotation, deliver controlled resistance, and release the limb smoothly during lag assessment.

Provocative Maneuver Execution

A comprehensive posterior cuff evaluation requires executing five distinct maneuvers to differentiate infraspinatus from teres minor involvement and assess both resting tone and maximal contractile strength:

• External Rotation Lag Sign (ERLS) of Hertel (at 20° Abduction): The patient’s elbow is flexed to 90°, and the arm is positioned in 20° of abduction in the scapular plane with 20° of forward flexion to prevent anterior capsular over-stretching. The examiner supports the elbow with one hand and uses the other hand to passively rotate the shoulder into near-maximal external rotation. Crucially, the examiner backs off by approximately 5° from maximal passive rotation to disengage pure capsular end-range elastic rebound. The patient is explicitly instructed: “Hold your hand right here; do not let it drift forward.” The examiner releases the patient’s wrist while continuing to support the elbow. The examiner observes for forward drift (lag).
• Dropping Sign of Walch (at 0° or 45° Abduction): With the patient seated and the elbow flexed to 90°, the arm is held at the side (0° abduction) or in 45° of abduction in the scapular plane. The examiner passively brings the shoulder into maximal external rotation (approximately 45°). The examiner asks the patient to actively maintain this externally rotated posture and releases the wrist. If the infraspinatus is incompetent, the forearm immediately drops back into neutral or internal rotation.
• Hornblower’s Sign (Patte Test / Signe du Clairon at 90° Abduction): The examiner passively elevates the patient’s arm to 90° of abduction in the scapular plane with the elbow flexed to 90°. The examiner supports the elbow from below and passively rotates the arm into maximal external rotation. The patient is instructed to maintain this vertical forearm position, and the examiner releases the wrist. To assess functional performance (Signe du clairon / Bugler’s sign), the examiner asks the patient to bring the hand directly to the mouth. In severe teres minor failure, the patient cannot externally rotate the humerus and must abduct the elbow above 90° to deliver the hand to the face, mimicking a horn blower.
• Resisted External Rotation at 0° Abduction (Infraspinatus Strength Test): The patient’s elbows are tucked firmly against the torso at 90° of flexion with the forearms pointing straight forward in neutral rotation. The examiner places palms against the dorsal aspects of both distal forearms simultaneously. The patient is instructed to push outward against symmetric, progressive examiner resistance. Strength is graded on the 0 to 5 Medical Research Council (MRC) scale, noting pain reproduction versus painless weakness.
• Resisted External Rotation at 90° Abduction in Scapular Plane (Teres Minor Test): The arm is placed in 90° of abduction and 30° of horizontal adduction (scapular plane) with the elbow flexed to 90°. The examiner stabilizes the distal humerus with one hand to maintain the elevation plane. The examiner places the other hand on the posterior aspect of the distal forearm and instructs the patient to externally rotate against resistance. Isolated weakness at 90° abduction strongly indicates teres minor dysfunction.

5. Positive Test Criteria & Interpretation

Each maneuver possesses specific quantitative and qualitative thresholds denoting structural pathology, functional failure, and muscle degeneration:

• External Rotation Lag Sign (ERLS): Positive when there is an angular difference (lag) greater than 5° between passive external rotation and active holding capacity. A lag of 5° to 10° correlates with partial-thickness or isolated anterior infraspinatus tears, whereas a lag greater than 15° to 20° indicates complete full-thickness disruption of both supraspinatus and infraspinatus tendons. A negative finding is present when the patient holds the arm motionless within 5° of passive positioning.
• Dropping Sign: Positive when the forearm immediately drops back into neutral (0°) or internal rotation upon release despite maximum voluntary holding effort. This sign is pathognomonic for extensive full-thickness infraspinatus tendon disruption or advanced infraspinatus fatty infiltration (Goutallier stage 3 or 4).
• Hornblower’s Sign (Patte Test / Bugler’s Sign): Positive when the patient is unable to maintain external rotation in 90° of abduction (forearm swings forward into the horizontal plane), or exhibits mandatory compensatory elbow hyper-abduction (>90°) when bringing the hand to the mouth. This sign is pathognomonic for teres minor failure (complete rupture or Goutallier stage 2 to 4 fatty degeneration), establishing posterior pseudoparalysis in massive tears.
• Resisted External Rotation at 0° (Infraspinatus Strength): Painless weakness (MRC Grade ≤3/5) is highly specific for complete tendon avulsion or suprascapular denervation. Painful normal strength (MRC Grade 5/5) indicates subacromial bursitis or non-retracted tendinopathy. Painful weakness (MRC Grade 4/5) represents partial-thickness tearing, tendinosis, or reflex pain inhibition requiring diagnostic anesthetic blockade.
• Resisted External Rotation at 90° (Teres Minor Strength): Isolated weakness in 90° abduction in the scapular plane with preserved strength at 0° isolates teres minor dysfunction and differentiates it from isolated infraspinatus pathology.

6. Diagnostic Accuracy & Statistical Benchmarks

The diagnostic utility of posterior rotator cuff physical examination maneuvers has been rigorously quantified across prospective diagnostic cohorts and meta-analyses. Likelihood ratios demonstrate exceptional confirmatory power for lag signs compared to resisted strength tests.

7. Confounders, Diagnostic Traps & False Results

Physical examination of the posterior rotator cuff is susceptible to biomechanical and neurovascular confounders that produce false-positive and false-negative interpretations if not systematically controlled.

Causes of False-Positive Results

• Passive Glenohumeral Stiffness (Adhesive Capsulitis or Osteoarthritis): If a patient has lost passive external rotation, forcing the arm into relative terminal range generates tremendous capsular and ligamentous tension. Upon release, this capsular stiffness produces an immediate elastic rebound that mimics a positive lag sign in a patient with a completely intact tendon.
• Acute Subacromial Bursitis & Pain Inhibition: Severe subacromial inflammation triggers reflex arthrogenic motor inhibition. The patient drops the arm not due to structural disruption, but because active contraction evokes sharp subacromial pain.
• Spinoglenoid Notch Ganglion Cyst Entrapment: Paralabral cysts arising from posterior labral tears compress the inferior branch of the suprascapular nerve. This produces marked weakness, infraspinatus muscle wasting, and a positive ERLS in the presence of an anatomically intact rotator cuff tendon insertion.
• Axillary Nerve Palsy or Quadrilateral Space Syndrome: Posterior cord or axillary nerve injury denervates the teres minor, generating a positive Hornblower’s sign despite intact tendon morphology.
• Scapular and Trunk Substitution: Inexperienced examiners may misinterpret torso twisting or scapular retraction as preserved active holding torque, or conversely misidentify trunk relaxation as an abnormal lag.

Causes of False-Negative Results

• Partial-Thickness Infraspinatus Tears: Articular-sided or bursal-sided partial tears frequently retain enough intact cable fibers to generate sufficient isometric torque to resist passive recoil, resulting in a normal (negative) lag sign.
• Preserved Rotator Cable Suspension Bridge: If the anterior and posterior anchors of the rotator cable remain intact, tension is transmitted across the glenohumeral joint despite a crescent-shaped tendon tear, masking weakness and lag signs.
• Compensatory Teres Minor Hypertrophy: In chronic, isolated infraspinatus tears, the teres minor often undergoes compensatory hypertrophy, generating sufficient external rotation torque at 0° of abduction to mask weakness during resisted manual testing.

Clinical Strategies to Eliminate Diagnostic Traps

• Contralateral Range-of-Motion Screening: Always document passive external rotation on the unaffected side before performing lag tests. If passive external rotation is restricted on the affected side, lag tests cannot be validated.
• The Diagnostic Subacromial Injection Test (Neer Block): Infiltrate 8 to 10 mL of 1% lidocaine into the subacromial space. Re-test external rotation strength after 10 minutes: resolution of weakness confirms pain inhibition (bursitis/tendinopathy), whereas persistent lag confirms true mechanical disruption or denervation.
• The 5° End-Range Offset Maneuver: When executing the ERLS, always back off 5° from maximal passive external rotation before releasing the wrist to disengage non-physiological capsular spring-back.
• Sagittal Oblique MRI Correlation: Correlate clinical exam findings with T1-weighted sagittal oblique sequences to evaluate Goutallier fatty infiltration, muscle atrophy (tangent sign of Habermeyer), and spinoglenoid paralabral cysts.

8. Comparative Utility & Clinical Decision Algorithm

Physical examination maneuvers for the posterior rotator cuff must be executed in a structured diagnostic sequence, combining high-sensitivity screening maneuvers with high-specificity confirmatory lag tests to dictate downstream imaging and reconstructive surgery.

Systematic Physical Examination Sequence

• Step 1: Visual Inspection & Palpation: Inspect the dorsal scapula for infraspinatus fossa hollowing (indicating chronic atrophy or suprascapular denervation) and inspect the axillary border for teres minor wasting.
• Step 2: Passive Range-of-Motion Assessment: Document passive external rotation at 0° and 90° of abduction compared to the normal contralateral shoulder to rule out capsular restriction.
• Step 3: High-Sensitivity Screening (Resisted Testing): Test resisted external rotation at 0° of abduction. Normal strength (5/5) rules out full-thickness infraspinatus tears with high negative predictive value.
• Step 4: High-Specificity Confirmation (Lag Signs): If weakness or pain is encountered, systematically perform the ERLS at 20° abduction, the Dropping Sign at 0°/45°, and Hornblower’s Sign at 90° abduction.
• Step 5: Diagnostic Stratification: In pain-inhibited patients, administer a subacromial lidocaine block and repeat strength and lag maneuvers.

Diagnostic Clustering

Diagnostic clustering dramatically enhances post-test probability. When Resisted External Rotation Weakness, a Positive ERLS, and a Positive Dropping Sign are all present, the post-test probability of a full-thickness posterosuperior rotator cuff tear exceeds 98%. Adding a Positive Hornblower’s Sign confirms extension into the teres minor, establishing posterior pseudoparalysis.

Reconstructive Decision Tree

• Cluster A (ERLS Negative, Resisted ER Weak, Resolves Post-Injection): Indicates subacromial bursitis, partial-thickness cuff tear, or non-retracted tendinopathy. Initiate non-operative management (physical therapy, periscapular retraining, subacromial corticosteroid injection). Obtain non-contrast shoulder MRI if symptoms are refractory after 6 weeks.
• Cluster B (ERLS Positive, Hornblower’s Sign Negative): Indicates full-thickness infraspinatus tear with an intact, functional teres minor. Obtain shoulder MRI to evaluate tear retraction (Patte stage) and fatty infiltration (Goutallier stage). For Goutallier stage 0 to 2 (reparable), perform arthroscopic rotator cuff repair with margin convergence and anatomical footprint restoration. For Goutallier stage 3 to 4 in younger active patients (<65 years) with preserved joint space, perform lower trapezius tendon transfer with Achilles allograft or latissimus dorsi transfer.
• Cluster C (ERLS Positive AND Hornblower’s Sign Positive): Indicates massive posterosuperior rotator cuff tear with combined infraspinatus and teres minor deficiency (Posterior Pseudoparalysis). Obtain shoulder MRI and radiographs to evaluate Hamada stage of cuff tear arthropathy. In younger active patients (<65 years) without arthritis (Hamada 1-2), perform arthroscopically assisted lower trapezius or latissimus dorsi tendon transfer. In elderly patients (>65-70 years), low-demand patients, or those with advanced cuff tear arthropathy (Hamada ≥3), perform Reverse Total Shoulder Arthroplasty (rTSA) combined with latissimus dorsi and teres major transfer to restore active external rotation and feeding function.
• Cluster D (Isolated Infraspinatus Wasting, ERLS Positive, MRI Showing Intact Tendon): Indicates suprascapular neuropathy secondary to a spinoglenoid paralabral cyst. Obtain electromyography and nerve conduction studies (EMG/NCS) for electrodiagnostic confirmation, followed by arthroscopic labral repair and spinoglenoid notch cyst decompression.

9. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

10. References

• Hertel R, Ballmer FT, Lambert SM et al. Lag signs in the diagnosis of rotator cuff rupture. J Shoulder Elbow Surg. 1996. doi:10.1016/S1058-2746(96)80058-9 [Level II: Prospective Diagnostic Cohort Study]
• Walch G, Boulahia A, Calderone S et al. The ‘dropping’ and ‘hornblower’s’ signs in evaluation of rotator-cuff tears. J Bone Joint Surg Br. 1998. doi:10.1302/0301-620x.80b4.8651 [Level II: Prospective Diagnostic Validation Study]
• Collin P, Treseder T, Denard PJ et al. What is the Best Clinical Test for Assessment of the Teres Minor in Massive Rotator Cuff Tears?. Clin Orthop Relat Res. 2015. doi:10.1007/s11999-015-4392-9 [Level II: Prospective Diagnostic Cohort Study]
• Gismervik SØ, Drogset JO, Granviken F et al. Physical examination tests of the shoulder: a systematic review and meta-analysis of diagnostic test performance. BMC Musculoskelet Disord. 2017. doi:10.1186/s12891-017-1400-0 [Level I: Systematic Review & Meta-Analysis]
• Hegedus EJ, Goode AP, Cook CE et al. Which physical examination tests provide clinicians with the most value when examining the shoulder? Update of a systematic review with meta-analysis of individual tests. Br J Sports Med. 2012. doi:10.1136/bjsports-2012-091066 [Level I: Systematic Review & Meta-Analysis]

11. Master Class Pro-Tip

When executing the External Rotation Lag Sign (ERLS), never release the arm at the extreme physiological end-range of passive external rotation. At true end-range, passive tension in the anterior capsuloligamentous complex and subscapularis creates an elastic rebound vector that causes the limb to spring back forward 5° to 10° even in a completely intact rotator cuff, generating a false-positive result. Instead, passively rotate the arm to maximal external rotation, then back off by approximately 5° into the ‘unloaded zone’ before instructing the patient to actively maintain the position and releasing the wrist. If the hand drifts forward even 5° from this backed-off position, the sign is truly positive, specifically isolating infraspinatus failure. Furthermore, always test resisted external rotation at 90° of abduction (Hornblower’s / Patte position) whenever planning a reverse total shoulder arthroplasty: a positive Hornblower’s sign indicates irreversible teres minor insufficiency, signifying that rTSA alone will not restore active external rotation, mandating a concomitant latissimus dorsi or lower trapezius tendon transfer to avoid persistent ‘bugler’ dysfunction and loss of hand-to-mouth control.

Master Class Clinical Pearl: Precision Diagnostics in Shoulder Posterior Cuff Assessment