Vertical Shear (VS) Pelvic Injuries

A vertical shear (VS) injury is the most severe form of pelvic ring disruption. Lateral compression (LC) and anteroposterior compression (APC) injuries have components of rotational instability; in a VS injury every stabilising structure is disrupted, and the hemipelvis migrates vertically (cephalad) relative to the sacrum. The name describes both the direction of the displacing force and the displacement it produces.

The load is a high-energy axial one, and the result is complete loss of the weight-bearing function of the pelvic ring.

Incidence. VS accounts for 5-10% of all pelvic ring injuries, the least common of the major patterns and the most severe subtype.

Mechanism. A fall from height landing on an extended leg is the most common. The others:

• Motor vehicle collision with axial load
• Motorcycle ejection
• Pedestrian struck

Who. Young adults predominate, and occupational falls from scaffolding and construction work are among the mechanisms. Polytrauma is almost universal and the ISS is often high.

Why it is the most severe pattern. No ligamentous support remains, so the ring can no longer transmit load. The energy that produced it brings greater associated injuries, and traction on the lumbosacral plexus brings neurological injury. Haemorrhage is significant but typically less than in APC injuries, so severity here is a matter of instability and nerve injury rather than lethality (see Mortality, under Outcomes).

The ring. The pelvis functions as a ring, so it cannot be disrupted at a single location. There must be a second break in the ring, or a combination of bone and ligament injuries.

What holds it together. The posterior tension band provides the primary stability and the anterior structures complete the ring.

• Posterior tension band - posterior SI ligaments (the strongest), interosseous SI ligaments, sacrotuberous, sacrospinous and iliolumbar ligaments
• Anterior structures - pubic symphysis, pubic rami, anterior SI ligaments

What fails in VS. Both the anterior and the posterior structures fail completely. Anteriorly the break is a symphysis diastasis, ipsilateral pubic rami fractures, or both. Posteriorly it is a sacral fracture (Denis zone I-III), a complete SI joint diastasis, or an iliac wing fracture in the crescent pattern, and of these sacral fractures are the most common.

The force. An axial load through the extended lower limb is transmitted through the femur to the acetabulum and drives the hemipelvis cephalad. The ring fails in sequence, anterior then posterior or the reverse. The result is vertical (cephalad) translation and shortening of the affected limb; a rotational component may be present as well, which makes it a combined injury.

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The vessels. The superior gluteal artery, the internal iliac branches and the presacral venous plexus are at risk. Bleeding is less severe than in APC injuries (the closed-ring effect).

The nerves. The L5 root, which exits under the ala, the lumbosacral trunk, and the S1-S4 roots in sacral fractures. The overall neurological injury rate is usually given as 30-50%; that is a conventional teaching range for VS patterns, and the Denis zone figures in the classification are the sourced anchor.

The crescent fracture. When the posterior injury runs through the ilium rather than the sacrum or a pure SI joint, the pattern is the crescent fracture, a posterior iliac wing fracture-dislocation of the SI joint. The posterior SI ligaments stay attached to a crescent-shaped postero-superior iliac fragment while the anteroinferior SI joint dislocates. Because the strong posterior tension band remains with the crescent fragment, reducing and fixing the iliac fracture restores stability.

The Day classification grades the crescent fracture by how much of the SI joint the intact crescent fragment still covers, and the fragment size chooses between iliac fixation and an SI screw:

• Type I - a large crescent with only the anteroinferior third of the SI joint dislocated; fix the iliac fracture, e.g. with anterior-column/iliac screws or a plate
• Type II - an intermediate fragment with one-third to two-thirds of the joint involved; combined iliosacral screw plus iliac fixation
• Type III - a small crescent with most of the SI joint dislocated; behaves like a pure SI dislocation and is fixed with an iliosacral screw

Context. VS injuries occur in the setting of major trauma, and the primary survey follows ATLS principles.

The history. The high-risk mechanisms:

• Fall from height greater than 3 metres
• Motorcycle ejection
• Pedestrian versus vehicle
• Industrial crush injury
• Landing on an extended leg

Inspection. The leg on the affected side is short and the iliac crests sit at different heights. Look for Destot's sign, a scrotal or labial haematoma, for perineal ecchymosis, and for an external or internal rotation component.

Palpation and measurement. Palpate the iliac crests for height asymmetry, the SI joints for tenderness and the symphysis for a gap or step-off, and perform the pelvic spring test once only. Measure from the ASIS to the medial malleolus on both sides: true shortening indicates vertical displacement, and the amount of discrepancy is documented.

The neurological examination. This is the critical part of the assessment, and L5 is the most vulnerable root.

• Motor - hip flexion (L1-2), knee extension (L3-4), ankle dorsiflexion (L4-5), great toe extension (L5), ankle plantarflexion (S1-2)
• Sensory - L5 on the dorsum of the foot, S1 on the lateral foot, S2-S4 in the perineum
• Reflexes and special tests - ankle jerk (S1), bulbocavernosus reflex (sacral roots), rectal tone

Record motor and sensory findings in detail, with an ASIA score if the injury is complete. Repeat the examination serially, because the deficit may evolve.

Associated injuries. Acetabular fractures, proximal femoral fractures, lumbar spine fractures, intra-abdominal injuries and head injuries are the common associations.

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

The AP pelvis. The first-line film in the trauma bay, read for vertical displacement. The hemipelvis has migrated cephalad, and the signs are:

• Asymmetric iliac crest heights
• Obturator foramina of different sizes, the smaller on the elevated side
• Superior displacement of the ischial tuberosity

Inlet and outlet views. The inlet view shows posterior displacement, SI joint widening and any rotational component. The outlet view shows vertical displacement best, along with the sacral fracture and any foraminal involvement.

Two avulsions that mean the tension band has failed. Both are small findings on the AP film, and both are easy to scroll past.

• The L5 transverse process. The iliolumbar ligament runs from the L5 transverse process to the posterior iliac crest and is one of the restraints holding the hemipelvis to the axial skeleton. A vertically displacing hemipelvis pulls it off, taking a fragment of transverse process with it. The fracture is trivial; it marks lost vertical restraint, and it should stop you calling a subtle pelvis "stable".
• The ischial spine or the sacral margin, where the sacrotuberous and sacrospinous ligaments attach. An avulsed fleck where a posterior ligament inserts is a failed ligament, and these ligaments are the vertical and rotational restraints of the ring.

Look for both deliberately, and treat either as an instruction to obtain CT rather than as an incidental finding.

CT. Essential in every VS injury, because it defines the posterior injury precisely: the location and comminution of a sacral fracture and its Denis zone, and the morphology, widening and displacement of an SI joint injury. It also shows the anterior injury pattern, any associated acetabular injury and the soft-tissue haematoma, and it measures the vertical displacement. 3D reconstruction demonstrates the displacement clearly and serves surgical planning and communication with the patient and the team.

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MRI is selective. It is indicated for a neurological deficit, a suspected cauda equina injury, or soft-tissue planning before complex reconstruction, and it shows nerve root compression, traumatic disc herniation and ligament integrity.

Percutaneous iliosacral screw fixation is the most common posterior fixation method, for the indications under Management.

Positioning. Supine on a radiolucent table, which allows anterior access if needed; prone or lateral decubitus are the alternatives. The C-arm is positioned for inlet, outlet and lateral sacral views.

The safe corridor. The target is the S1 body, the widest safe corridor, with the screw parallel to the S1 superior endplate. Knowing this corridor is essential to placing the screw safely. Around it lie:

• Anterior - iliac vessels, L5 nerve root
• Lateral - L5 nerve in the ala
• Superior - L5-S1 disc
• Inferior - S1 foramen

The steps.

1. Reduce - longitudinal traction through the skeletal pin, confirmed on inlet and outlet views, with clamps if more control is needed
2. Entry point - the posterior iliac cortex, between the PSIS and PIIS, lateral to the SI joint
3. Guidewire - aimed at the centre of the S1 body, parallel to the superior endplate, checking all three views continuously
4. Confirm - on the inlet view the wire is within the S1 body and not anterior to the sacrum; on the outlet view it is parallel to the endplate and not in the foramen; on the lateral sacral view it is in the centre of the S1 body
5. Screw - drill over the wire, measure the depth, and insert a 7.3 mm cannulated partially threaded screw; a washer is optional
6. Final check - position on all views and reduction maintained; VS injuries may need a second screw for added stability

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Pitfalls. The most serious complication is L5 nerve injury from a screw placed through the sacral ala: stay within the S1 body, avoid an alar trajectory, and use all three views. Vessel injury follows a breach of the anterior sacral cortex, and the inlet view is the critical guard against it. Malreduction follows using the screw as a reduction tool, so reduce before the screw goes in.

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Early complications.

• Haemorrhage - significant but typically less than APC; retroperitoneal haemorrhage, presacral venous plexus
• Neurological injury - the most common complication; sacral root injuries with sacral fractures, and cauda equina syndrome with zone III
• Thromboembolism - very high DVT risk; early prophylaxis is essential, and an IVC filter may be needed if anticoagulation is contraindicated
• Infection - high risk in open fractures; surgical site infection is higher with extensive approaches

The open pelvic fracture. A pelvic ring injury communicating with a perineal, rectal, vaginal, groin or buttock wound, or with a degloving/Morel-Lavallée injury, is a distinct and far more lethal entity. Historically quoted mortality is up to 30-50%, driven by uncontrolled haemorrhage and later pelvic sepsis. Recognising the wound is the whole point: a "closed" vertical shear injury and an open one are managed very differently.

Finding the wound. In any high-energy pelvic injury, always perform a rectal and (in females) vaginal examination and inspect the perineum and the gluteal and sacral skin. An occult rectal or vaginal laceration makes the fracture open.

Managing it. The standard ring algorithm is supplemented by:

• Early broad-spectrum antibiotics and tetanus cover
• Aggressive haemorrhage control (binder, packing, angioembolisation)
• Repeated wound debridement
• For a rectal or perineal wound contaminating the fracture, a diverting (defunctioning) colostomy with distal rectal washout to prevent faecal soiling and pelvic sepsis

The Faringer anatomical zones (anterior perineum, posterior perineum/buttock, iliac wing) help predict which wounds mandate diversion.

Late complications.

• Malunion - residual vertical displacement, limb length discrepancy, gait abnormality, painful weight-bearing
• Nonunion - sacral (more common with the vertical pattern) or of the SI joint; may need revision fixation or fusion
• Permanent neurological deficit - foot drop (L5), bladder and bowel dysfunction (sacral roots), sexual dysfunction; may require long-term management
• Hardware - SI screw loosening, screw migration, symptomatic hardware
• Chronic pain - SI joint arthritis, sacral pain, low back pain

Weight-bearing. Non-weight-bearing for 8-12 weeks at minimum, and bilateral VS injuries may need 12-16 weeks. Progression is gradual and based on healing.

Mobilisation. Bed to chair with a walker, upper limb strengthening, and core stability exercises done non-weight-bearing.

Thromboprophylaxis. Essential given the immobility: LMWH or a direct oral anticoagulant, with sequential compression devices, continued until the patient is mobile.

Analgesia. Multimodal, with regional techniques if available, minimising opioids when possible.

Monitoring. Examine the nerves daily for the first week and document any change, because deficits may appear late. Radiographs are an AP pelvis at 2, 6 and 12 weeks, with inlet and outlet views as needed and CT if there is concern for loss of reduction. Percutaneous wounds typically heal quickly; open approaches need standard wound care, and every wound is watched for infection.

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Rehabilitation.

• 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 is 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. Review gait, any persistent leg length discrepancy, neurological status and pain, and watch for SI joint arthritis, hardware symptoms and chronic pain. The functional goals are independent walking, return to work on a variable timeline, and independence in activities of daily living.

The percentages in this section (good-to-excellent outcome rates, nerve-recovery rates, union rates, hardware-removal rates) are conventional teaching ranges drawn from retrospective pelvic-trauma series, not measurements from a single cited cohort. The sourced population figures on this page are the Mann 2018 and Whitbeck 1997 numbers in the Evidence section.

Function. With appropriate treatment 60-70% have good to excellent outcomes. The result depends heavily on neurological injury, associated injuries, the quality of reduction and the stability of fixation. The poor prognostic factors:

• Neurological injury
• Bilateral injuries
• Zone III sacral fractures
• Delayed fixation
• Malunion or nonunion

Neurological recovery. Complete recovery occurs in 50-60% of L5 injuries and 60-70% of S1 injuries; sacral root recovery is variable and often partial. Improvement may continue for 12-24 months, with peak recovery typically at 6-12 months. Permanent deficits include foot drop requiring an AFO in 15-20%, bladder dysfunction in 5-10% (zone III injuries), and sexual dysfunction to a variable degree.

Return to activities.

• Walking - independent at 3-6 months, a normal gait at 6-12 months; a limp may be permanent
• Work - sedentary at 3-6 months, physical labour at 6-12 months; modifications may be needed
• Sport - low-impact at 6-9 months, high-impact at 9-12+ months; some activities may be permanently limited

Mortality. Around 11% at 30 days for high-energy pelvic ring fractures in population data, with reported ranges of 6-35% depending on injury severity (Mann et al., Injury 2018). Mortality is driven by associated injuries and total injury burden (ISS), not by the ring fracture pattern alone. In complete ring disruption the APC (open-book) mechanism carries a higher haemorrhage and mortality risk than VS (Whitbeck/Burgess, JOT 1997), so the long-held view that VS is the most lethal pattern is not supported.

Long-term. Most survivors achieve independent function and chronic pain is common. Quality of life depends on neurological recovery and is measurably reduced versus the general population after pelvic ring injury (Banierink et al., Arch Orthop Trauma Surg 2019).

Radiographic outcome. Union rates are 85-90% for the SI joint, 80-85% for sacral fractures and greater than 95% for the symphysis. Residual displacement is common, affects long-term outcomes and may need corrective surgery. SI screws are typically well tolerated, and removal is rarely needed (10-15%).

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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

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