Vertical Shear (VS) Pelvic Injuries

Introduction

Vertical shear (VS) pelvic injuries represent the most severe form of pelvic ring disruption. Unlike lateral compression (LC) and anteroposterior compression (APC) injuries, which have components of rotational instability, VS injuries have complete disruption of all stabilizing structures allowing the hemipelvis to migrate vertically (cephalad) relative to the sacrum.

These injuries result from high-energy axial loading mechanisms and are characterized by the complete loss of the weight-bearing function of the pelvic ring. The term "vertical shear" refers to the direction of the displacing force and resultant displacement pattern.

Epidemiology

Incidence:

• 5-10% of all pelvic ring injuries
• Least common of the major injury patterns
• Most severe subtype

Mechanism:

• Fall from height landing on extended leg (most common)
• Motor vehicle collision with axial load
• Motorcycle ejection
• Pedestrian struck

Demographics:

• Young adults predominate
• Often high ISS scores
• Polytrauma almost universal
• Occupational (falls from scaffolding, construction)

Clinical Significance

Why VS Injuries Are Most Severe:

1. Complete instability: No residual ligamentous support
2. High energy: Greater associated injuries
3. Weight-bearing lost: Cannot transmit load
4. Neurological injury: Traction on lumbosacral plexus
5. Hemorrhage: Significant (though less than APC typically)

Pelvic Ring Stability

The pelvis functions as a ring structure. When disrupted, the injury cannot occur at a single location - there must be a second break in the ring (or a combination of bone and ligament injuries).

Stabilizing Structures

Posterior Tension Band (Primary Stability):

• Posterior SI ligaments (strongest)
• Interosseous SI ligaments
• Sacrotuberous ligament
• Sacrospinous ligament
• Iliolumbar ligaments

Anterior Structures:

• Pubic symphysis
• Pubic rami
• Anterior SI ligaments

VS Injury Pathoanatomy

In vertical shear injuries, BOTH anterior and posterior structures fail completely:

Anterior Disruption:

• Symphysis diastasis, OR
• Pubic rami fractures (ipsilateral), OR
• Combined symphysis and rami injury

Posterior Disruption:

• Sacral fracture (Denis zone I-III), OR
• SI joint diastasis (complete), OR
• Iliac wing fracture (crescent pattern)

Force Vectors

Classic Mechanism:

• Axial load through extended lower extremity
• Force transmitted through femur to acetabulum
• Hemipelvis driven cephalad
• Sequential failure: anterior then posterior, or vice versa

Resultant Displacement:

• Vertical (cephalad) translation
• May have rotational component (combined injury)
• Shortening of affected lower limb

Associated Soft Tissue Injuries

Vascular:

• Superior gluteal artery
• Internal iliac branches
• Presacral venous plexus
• Less severe bleeding than APC (closed ring effect)

Neurological:

• L5 nerve root (exits under ala)
• Lumbosacral trunk
• S1-S4 roots (sacral fractures)
• Overall neurological injury rate: 30-50%

Classification

Primary Survey

VS injuries occur in major trauma context. Assessment follows ATLS principles.

Mechanism History

High-Risk Mechanisms:

• Fall from height greater than 3 meters
• Motorcycle ejection
• Pedestrian vs vehicle
• Industrial crush injury
• Landing on extended leg

Physical Examination

Inspection:

• Limb length discrepancy (SHORT LEG on affected side)
• Asymmetric iliac crest heights
• Destot sign: Scrotal/labial hematoma
• Perineal ecchymosis
• External rotation or internal rotation component

Palpation:

• Iliac crest height asymmetry
• SI joint tenderness
• Symphysis gap or step-off
• Single pelvic spring test (ONCE only)

Measurement:

• Measure ASIS to medial malleolus bilaterally
• True shortening indicates vertical displacement
• Document amount of leg length discrepancy

Neurological Examination (CRITICAL)

Motor Assessment:

• Hip flexion (L1-2)
• Knee extension (L3-4)
• Ankle dorsiflexion (L4-5) - L5 most vulnerable
• Great toe extension (L5)
• Ankle plantarflexion (S1-2)

Sensory Assessment:

• L5 dermatome: Dorsum of foot
• S1 dermatome: Lateral foot
• Perineal sensation: S2-S4

Reflexes and Special Tests:

• Ankle jerk (S1)
• Bulbocavernosus reflex (sacral roots)
• Rectal tone

Documentation:

• ASIA score if complete injury
• Detailed motor/sensory documentation
• Serial examinations (may evolve)

Associated Injuries

Common Associations:

• Acetabular fractures
• Proximal femur fractures
• Lumbar spine fractures
• Intra-abdominal injuries
• Head injuries

Differential Diagnosis of a Shortened Limb with Pelvic Trauma

True limb shortening with a pelvic injury is highly suggestive of vertical shear, but several conditions can mimic the presentation and must be distinguished.

Imaging Approach

Plain Radiography

AP Pelvis:

• First-line in trauma bay
• Assess for vertical displacement
• Compare iliac crest heights
• Compare obturator foramen size (smaller on elevated side)

Radiographic Signs of Vertical Displacement:

• Cephalad migration of hemipelvis
• Asymmetric iliac crest heights
• Different sized obturator foramina
• Superior displacement of ischial tuberosity

Inlet View:

• Posterior displacement
• SI joint widening
• Rotational component

Outlet View:

• Vertical displacement best seen
• Sacral fracture visualization
• Foraminal involvement

CT Imaging

Essential for All VS Injuries:

• Defines posterior injury precisely
• Sacral fracture pattern (Denis zone)
• SI joint injury morphology
• Associated acetabular injury
• Soft tissue hematoma

Key Findings:

• Sacral fracture location and comminution
• SI joint widening and displacement
• Anterior injury pattern
• Vertical displacement measurement

3D Reconstruction:

• Surgical planning
• Demonstrates displacement clearly
• Communication with patient/team

MRI (Selective Use)

Indications:

• Neurological deficit
• Suspected cauda equina injury
• Soft tissue planning for complex reconstruction

Findings:

• Nerve root compression
• Disc herniation (traumatic)
• Ligament integrity

Algorithm

View larger

Treatment Decision-Making

Percutaneous Iliosacral Screw Fixation

Early Complications

Hemorrhage:

• Significant but typically less than APC
• Retroperitoneal hemorrhage
• Presacral venous plexus

Neurological Injury:

• Most common complication (30-50%)
• L5 root most vulnerable
• Sacral root injuries with sacral fractures
• Cauda equina syndrome with Zone III

Thromboembolic:

• Very high DVT risk
• Early prophylaxis essential
• May need IVC filter if anticoagulation contraindicated

Infection:

• Open fractures: High risk
• Surgical site infection
• Higher with extensive approaches

Late Complications

Malunion:

• Residual vertical displacement
• Limb length discrepancy
• Gait abnormality
• Painful weight bearing

Nonunion:

• Sacral nonunion (more common with vertical pattern)
• SI joint nonunion
• May need revision fixation or fusion

Neurological Deficit (Permanent):

• Footdrop (L5)
• Bladder/bowel dysfunction (sacral roots)
• Sexual dysfunction
• May require long-term management

Hardware Complications:

• SI screw loosening
• Screw migration
• Symptomatic hardware

Chronic Pain:

• SI joint arthritis
• Sacral pain
• Low back pain

Immediate Postoperative Management

Weight Bearing:

• Non-weight bearing for 8-12 weeks minimum
• Bilateral VS injuries: May need 12-16 weeks
• Gradual progression based on healing

Mobilization:

• Bed to chair with walker assistance
• Upper extremity strengthening
• Core stability exercises (non-weight bearing)

DVT Prophylaxis:

• Essential given immobility
• LMWH or direct oral anticoagulants
• Sequential compression devices
• Continue until mobile

Pain Management:

• Multimodal analgesia
• Regional techniques if available
• Minimize opioids when possible

Monitoring

Serial Neurological Exams:

• Daily for first week
• Document any changes
• May see delayed deficits

Radiographic Follow-up:

• AP pelvis at 2, 6, 12 weeks
• Inlet/outlet views as needed
• CT if concern for loss of reduction

Wound Care:

• Monitor for infection
• Percutaneous wounds typically heal quickly
• Open approaches need standard care

Rehabilitation Protocol

Phase 1 (0-6 weeks):

• Non-weight bearing
• Upper body conditioning
• Hip isometrics
• Core strengthening

Phase 2 (6-12 weeks):

• Progressive weight bearing if healing confirmed
• Gait training with assistive devices
• Hip strengthening
• Balance exercises

Phase 3 (12+ weeks):

• Full weight bearing
• Advanced strengthening
• Proprioceptive training
• Return to activities

Long-term Follow-up

Clinical Assessment:

• Gait pattern
• Leg length discrepancy (persistent)
• Neurological status
• Pain levels

Functional Goals:

• Independent ambulation
• Return to work (variable timeline)
• Activities of daily living

Complications Monitoring:

• SI joint arthritis symptoms
• Hardware symptoms
• Chronic pain

Global Epidemiology

VS injuries arise from high-energy axial loading - falls from height onto an extended limb, motorcycle ejection, pedestrian-versus-vehicle and crush mechanisms - and so cluster in young men in polytrauma worldwide. The mechanism is universal and not region-specific.

Major Guidance, Side by Side

Evidence level: the operative principles above rest largely on Level III-IV evidence (retrospective series such as Matta 1989, Routt 1997, Schildhauer 1998); there is no randomised trial defining VS fixation strategy, which is a genuine area of uncertainty.

Registry and Cohort Evidence

• Population trauma registries (e.g. Ontario Trauma Registry) show stable incidence and stable approx 11% 30-day mortality despite rising injury severity, indicating improving systems of care (Mann et al., Injury 2018).
• Long-term patient-reported outcomes after pelvic ring injury (SMFA, EQ-5D) remain significantly worse than the general population regardless of operative versus non-operative treatment, reflecting the burden of associated and neurological injury (Banierink et al., 2019).
• There is no dedicated implant/joint registry for pelvic fixation comparable to arthroplasty registries; evidence is from trauma registries and surgical series.

Global Practice Variation

Across all settings the non-negotiable principle is the same: a vertically unstable injury needs both anterior and posterior stabilisation, and the posterior lesion is the primary problem.

Thromboprophylaxis and Rehabilitation (global principles)

• Pelvic ring trauma carries high venous thromboembolism risk from immobility and vascular injury; mechanical prophylaxis plus pharmacological prophylaxis (low-molecular-weight heparin, or a direct oral anticoagulant where appropriate) once haemostasis is secured is standard, continued until mobile.
• Rehabilitation follows protected weight-bearing with graduated progression; persistent L5 foot-drop may require an ankle-foot orthosis, and neurological recovery determines long-term function.

High-Yield Concepts

Quick Differentiation

VS vs LC-III:

• VS: Vertical displacement, axial mechanism, high neuro risk
• LC-III: Internal rotation, lateral mechanism, windswept pelvis

VS vs APC-III:

• VS: Vertical displacement, limb shortened
• APC-III: External rotation, open book, highest hemorrhage

Surgical Principles

Non-Negotiables:

1. BOTH anterior AND posterior fixation
2. Reduce vertical displacement first (traction)
3. Posterior fixation is primary stabilization
4. SI screws into S1 BODY (not ala)
5. Document neurology before and after surgery

Denis Zone Significance

• Zone I: L5 at risk, 5-10% neuro injury
• Zone II: S1 at risk, 25-30% neuro injury
• Zone III: Cauda equina, up to 60%, often permanent