Normal Shoulder & Glenoid Pathoanatomy

1. Bony Framework of the Normal Shoulder

Clavicle

• The only bony bridge between the trunk and upper limb; palpable throughout its S-shaped length.
• The acromial (lateral) end is flat and articulates with the acromion at the AC joint.
• The sternal (medial) end is quadrangular and articulates with the manubrium and first costal cartilage.
• The inferior surface of the lateral third bears the conoid tubercle and trapezoid line - attachment points for the coracoclavicular ligament.

Scapula

• Large, flat triangular bone with three angles (lateral, superior, inferior), three borders (superior, lateral, medial), and three processes (acromion, spine, coracoid).
• The lateral angle bears the shallow, comma-shaped glenoid cavity, which articulates with the humeral head to form the glenohumeral joint.
• The infraglenoid tubercle (inferior to the glenoid) anchors the long head of triceps brachii.
• The supraglenoid tubercle (superior to the glenoid) anchors the long head of biceps brachii.
• Gray's Anatomy for Students

2. Normal Glenoid Anatomy

Shape and Orientation

• (a) Concave - most common
• (b) Flat
• (c) Convex - associated with instability

Normal Variants (Beware - Don't Mistake for Pathology)

• Tubercle of Assaki: A focal ridge/elevation of subchondral bone at the center of the glenoid with overlying cartilage thinning. Should NOT be mistaken for a cartilage defect.
• Bare area: An oval area denuded of cartilage in the mid-third of the glenoid; developmental, should be differentiated from true cartilage injury.
• Glenoid dysplasia: Osseous hypoplasia of the posteroinferior glenoid edge with flattening and sloping, marked retroversion on axial images, and hypertrophy of adjacent cartilage/labrum. Can lead to instability, accelerated OA, or posterior labral tears.
• Imaging Anatomy: Bones, Joints, Vessels and Nerves (Thieme)

3. Glenoid Labrum - Normal Anatomy

Key Biomechanical Functions:

Regional Variation:

• Superiorly (above equator): Loosely attached; significant anatomic variability is normal
• Anteroinferior labrum: Intimately attached to glenoid rim - any detachment here is abnormal

Labral Shape Variants (normal):

Morphologic variants: (a) triangular - 50%, (b) rounded - 20%, (c) comma-shaped/flattened - 7%, (d) absent - 3%, (e) cleaved, (f) notched, (g/h) signal variants

Important Labral Normal Variants (must distinguish from tears):

• Physiologic recess at the 11-1 o'clock position
• Smooth margins, < 2 mm width
• Extends medially along glenoid rim, does not extend posterior to biceps anchor
• Must be distinguished from a Type II SLAP lesion (which extends laterally/posteriorly)

• Normal detachment of the anterosuperior labrum (1-3 o'clock)
• Communicates between glenohumeral joint and subscapular recess

• Cord-like MGHL with an absent anterosuperior labrum
• Can mimic a labral tear - the key is the normal posterior labrum and the cord-like MGHL

Schematic: (a) normal anatomy; (b) sublabral recess; (c) sublabral foramen; (d) Buford complex. LHBT = long head biceps tendon; SGHL, MGHL = superior/middle glenohumeral ligaments; ant/post IGHL = inferior glenohumeral ligament

• Imaging Anatomy: Bones, Joints, Vessels and Nerves (Thieme)

4. Glenohumeral Ligaments (GHLs)

Superior GHL (SGHL)

• Origin: supraglenoid tubercle (anteroinferior to biceps origin)
• Insertion: proximal tip of the lesser tuberosity
• Function: limits inferior translation and external rotation in the adducted arm; limits posterior translation with arm in FAIR position (flexion, adduction, internal rotation)

Middle GHL (MGHL)

• Most variable - absent in up to 30%, poorly defined in another 10%
• Origin: superior glenoid (1-3 o'clock), inferior to SGHL
• Insertion: blends with subscapularis tendon (~2 cm medial to lesser tuberosity)
• Function: limits anterior translation at 45° abduction + ER; limits external rotation and inferior translation when adducted
• Buford complex: cord-like MGHL with absent anterosuperior labrum (normal variant)

Inferior GHL Complex (IGHL)

• A hammock-like structure - the primary static stabilizer against anterior dislocation
• Three components: anterior band (AIGHL), posterior band (PIGHL), and the axillary pouch between them
• Origin: anteroinferior glenoid rim and labrum
• Insertion: inferior humeral articular surface and anatomic neck
• The anterior band is the primary restraint to anterior translation in 90° abduction + ER (the position of dislocation)
• Also reinforced on the glenoid side by the spiral GHL (fasciculus obliquus)

Rotator Interval

• The triangular zone between the superior border of subscapularis and anterior border of supraspinatus
• Contains: SGHL and coracohumeral ligament (CHL)
• CHL: extends from the lateral coracoid to greater and lesser tuberosities (adjacent to bicipital groove)
• Rotator interval deficiency → multidirectional instability (MDI)
• Rotator interval contracture → restricted ER and FF (adhesive capsulitis, post-traumatic stiffness)
• Rockwood and Green's Fractures in Adults 10e

5. Glenoid Pathoanatomy

A. Anterior Instability - Bankart Lesion & Bone Loss

• Avulsion of the anteroinferior glenoid rim with the attached labrum and IGHL complex
• Prevalence of glenoid rim lesions in recurrent instability: up to 90% (50% bony Bankart + 40% glenoid erosion)
• The "inverted pear" glenoid morphology (loss of the normal pear shape) is associated with 25-27% loss of anteroinferior glenoid width - a critical finding indicating need for bony augmentation

• Measurement: Glenoid bone loss is calculated by comparing the surface area of the defect to the surface area of the inferior 2/3 of the glenoid (best-fit circle method) - A/B × 100 where A = missing anterior glenoid width and B = diameter of the inferior glenoid circle.

B. Degenerative Glenoid Wear - Walch Classification (Modified by Bercik)

Bercik modification of Walch glenoid wear classification (A1, A2, B1, B2, B3, C, D)

• Central (Type A) wear is most common in rheumatoid arthritis; < 1 cm depth generally precludes glenoid component fixation without bone grafting
• Posterior (Type B) wear is most common in osteoarthritis (posterior humeral subluxation tendency); can progress to severe B2/B3 patterns
• Sperling classification grades severity: None → Mild (erosion to subchondral bone) → Moderate (hemispheric deformation + medialization) → Severe (bone loss to coracoid base)
• Campbell's Operative Orthopaedics 15e 2026

C. Glenoid Dysplasia

• Developmental osseous hypoplasia of the posteroinferior glenoid
• Features: flattening and sloping of the posterior glenoid edge, marked retroversion on axial MRI, hypertrophy of adjacent cartilage and labrum
• Consequences: posterior shoulder instability, accelerated OA, posterior labral tears

Summary Table: Normal vs. Pathological Glenoid

• Gray's Anatomy for Students (glenohumeral bony anatomy)
• Imaging Anatomy: Bones, Joints, Vessels and Nerves, Vol. 3 (glenoid variants, labral anatomy, GHLs)
• Rockwood and Green's Fractures in Adults, 10e 2025 (labral biomechanics, GHLs, critical bone loss)
• Campbell's Operative Orthopaedics, 15e 2026 (Walch/Bercik glenoid wear classification)

Recurrent Patellar Dislocation

1. Overview & Epidemiology

• Recurrence rate after a first-time dislocation: 15% to 60%
• Associated with ongoing anterior knee pain even between episodes
• Risk factors for recurrence: younger age, female sex, patella alta, and trochlear dysplasia
• In patients with joint hypermobility, instability is attributed to ligamentous laxity combined with muscular imbalance - joint hypermobility is a poor prognostic factor for operative outcomes
• Miller's Review of Orthopaedics 9e; Rheumatology 2e (Elsevier)

2. Pathoanatomy & Risk Factors

A. Trochlear Dysplasia (Most Important Bony Risk Factor)

• Crossing sign: The trochlear groove floor line crosses the anterior femoral condyle on a true lateral radiograph (normally intersects the anterior femoral cortex, not the condyle)
• Supratrochlear spur: a bony prominence at the proximal trochlea
• Types C and D are the most severe forms

Dejour Type A: crossing sign on lateral radiograph; shallow trochlea on axial view (sulcus >145°)

Dejour Type C: double contour on lateral radiograph; lateral convexity with medial hypoplasia

B. TT-TG Distance (Tibial Tubercle - Trochlear Groove Offset)

TT-TG distance = lateral offset of the tibial tubercle (TT) from the trochlear groove (TG) on superimposed axial CT cuts

C. Patella Alta

• Measured by the Caton-Deschamps or Insall-Salvati ratio
• A component of the "Dejour triad" of pathoanatomy (trochlear dysplasia + patella alta + increased TT-TG)

D. MPFL Disruption (Soft Tissue)

• In an acute dislocation: MPFL is disrupted in virtually all cases, most frequently at its patellar insertion
• MRI finding after dislocation: bone bruise pattern on the lateral femoral condyle and medial patellar facet (pathognomonic kissing contusions)
• Chronic MPFL insufficiency → recurrent lateral dislocation

E. Q Angle / Lower Limb Alignment

• Femoral anteversion
• Genu valgum
• External tibial torsion (planted-foot mechanism)
• Pronated feet
• When all present together: "Miserable Malalignment Syndrome" - especially symptomatic in adolescents

F. VMO Insufficiency

3. Clinical Features

4. Investigations

Radiographs

• AP, lateral, and Merchant (axial/skyline) views
• Identify: fractures, loose bodies, patella alta, malalignment, trochlear morphology
• Crossing sign and supratrochlear spur for trochlear dysplasia on the lateral view
• Congruence angle and sulcus angle on the axial view
  • Normal sulcus angle: ~138° (>150° = abnormally shallow groove)
  • Normal congruence angle: ~-6° (lateral displacement of ridge = positive)

CT

• Gold standard for TT-TG measurement (MRI underestimates)
• Evaluates trochlear morphology (Dejour classification)
• Assesses patellar tilt and subluxation

MRI

• Bone bruise pattern: lateral femoral condyle + medial patella = pathognomonic of lateral dislocation
• MPFL disruption - most often at patellar attachment
• Articular cartilage damage assessment
• TT-TG measurable but less accurate than CT
• Soft tissue anatomy (retinaculum, tendons)

5. Management

A. Acute First-Time Dislocation

• Traditionally managed non-operatively: patellar stabilizing brace + physiotherapy focused on VMO strengthening
• Surgery considered if: loose body present, significant chondral damage, or associated fracture
• Some advocate early arthroscopic MPFL repair at the medial epicondyle (controversial)

B. Recurrent Patellar Dislocation - Surgical Options

Proximal Realignment - MPFL Reconstruction

• Primary surgical treatment for recurrent patellar instability
• Graft: usually gracilis or semitendinosus autograft (or allograft)
• Femoral attachment at the Schottle point (anatomic origin):
  • 1 mm anterior to the posterior cortex extension line
  • 2.5 mm distal to the posterior origin of the medial femoral condyle
  • Proximal to the posterior point of the Blumensaat line on lateral radiograph

FIG: Schottle point on (A) diagram, (B) lateral radiograph, (C) intraoperative fluoroscopy for anatomic MPFL femoral tunnel placement

• Critical tunnel placement principle:
  • Too proximal → graft tight in flexion (over-constrains)
  • Too distal → graft loose in flexion (fails to stabilize)
• Complication: Medial patellar instability or medial patellar OA from overtightening

Techniques Now Largely Abandoned:

• VMO advancement (Green procedure)
• Isolated medial retinacular plication
• Isolated lateral release should NOT be performed for patellar instability (does not address the problem and can worsen medial instability)

Distal Realignment - Tibial Tubercle Osteotomy (TTO)

• Anterior medialization of the tibial tubercle (Fulkerson-type osteotomy)
• Indicated when Q angle is increased OR TT-TG distance >20 mm
• Contraindication: proximal arthrosis of the medial patellar facet (medialization will load the already damaged medial facet)
• Combined with MPFL reconstruction in many cases

Trochleoplasty

• Indicated for severe trochlear dysplasia (Dejour C or D) that cannot be adequately addressed by soft-tissue procedures alone
• Reshapes/deepens the trochlear groove
• Generally reserved for cases where other procedures have failed or severe dysplasia is the primary driver

6. Summary Algorithm

Recurrent Patellar Dislocation
        ↓
  Evaluate anatomy:
  - TT-TG (CT)
  - Trochlear dysplasia (Dejour)
  - Patella alta
  - MPFL integrity (MRI)
        ↓
  TT-TG <20 mm         TT-TG >20 mm
  No bony dysplasia     OR increased Q angle
       ↓                        ↓
  MPFL reconstruction    MPFL + distal TTO
                         (Fulkerson-type)
        ↓
  Severe trochlear dysplasia (C/D)?
       ↓
  Add trochleoplasty

• Miller's Review of Orthopaedics, 9e (epidemiology, Dejour classification, TT-TG, MPFL reconstruction, Schottle point)
• Rheumatology 2e - Elsevier (hypermobility-related instability, prognosis)
• Roberts and Hedges' Clinical Procedures in Emergency Medicine (acute management)

Recurrent Patellar Dislocation - Quick Reference

Pathoanatomy (The "Dejour Triad")

Recurrence Risk Factors

Dejour Trochlear Dysplasia Classification

Key Imaging Findings

• MRI: Kissing bone bruise (lateral femoral condyle + medial patellar facet) - pathognomonic of lateral dislocation; MPFL tear most often at patellar insertion
• CT: Gold standard for TT-TG measurement; trochlear morphology
• Lateral XR: Crossing sign, supratrochlear spur, sulcus angle
• Axial XR: Sulcus angle (normal ~138°; >150° = shallow groove); congruence angle (normal ~-6°)

TT-TG Distance

Surgical Decision Framework

Recurrent instability confirmed
           ↓
     TT-TG ≤20 mm?          TT-TG >20 mm / increased Q angle?
           ↓                           ↓
  MPFL reconstruction         MPFL + Tibial Tubercle Osteotomy
  (gracilis/ST graft at         (Fulkerson anteromedialization)
   Schottle point)
           ↓
  Severe dysplasia (C/D) driving instability?
           ↓
     Add trochleoplasty

MPFL Reconstruction - Key Technical Points

• Graft: gracilis or semitendinosus (auto or allograft)
• Femoral tunnel at Schottle point (1 mm anterior to posterior cortex line; 2.5 mm distal to posterior MFC origin; proximal to Blumensaat line)
• Too proximal = tight in flexion; Too distal = loose in flexion
• Patellar attachment: dual-tunnel or transosseous technique
• Complication: Medial patellar instability / OA from overtightening

Tibial Tubercle Osteotomy (TTO)

• Anteromedialization (Fulkerson) for increased TT-TG or Q angle
• Contraindication: proximal/medial patellar arthrosis (medialization loads damaged cartilage)

Abandoned / Deprecated Procedures

• Isolated lateral release - should NOT be performed for instability
• VMO advancement (Green procedure)
• Isolated medial retinacular plication

Non-Operative Treatment