Lateral Compression Pelvic Injuries

Lateral compression (LC) injuries are the most common pelvic ring injury pattern, accounting for 50-60% of all pelvic fractures. A laterally directed force rotates the hemipelvis inwards, and the damage ranges from stable rami fractures with a sacral impaction (LC-I) to a rotationally and vertically unstable pelvis (LC-III). LC-I is by far the most common subtype, 70% of all LC injuries.

Who. All age groups are affected and there is no significant gender predilection. The distribution is bimodal: the young in high-energy motor vehicle accidents and the elderly in low-energy falls. Incidence is higher where traffic volume is higher.

How. Motor vehicle accidents, classically the T-bone collision, and pedestrian strikes account for most of these injuries:

• Motor vehicle accidents: 60-70%
• Pedestrian versus vehicle: 15-20%
• Falls from height: 10-15%
• Other mechanisms: 5%

What comes with it. Associated injuries are common:

• Head injuries: 40-50%
• Long bone fractures: 30-40%
• Acetabular fractures: 20-30%
• Thoracic injuries: 20-30%
• Neurological injuries: 10-20%, with sacral fractures

The ring. The anterior ring is the pubic symphysis with the superior and inferior pubic rami; the posterior ring is the sacrum, the sacroiliac joints and the posterior ilium. A ring cannot break in one place: an anterior injury means there is a posterior injury, and vice versa, so always search for the second break.

What holds it together. About 60% of pelvic stability comes from the posterior structures: the sacroiliac ligament complex (anterior, posterior and interosseous) and the posterior tension band of the iliolumbar, lumbosacral, sacrospinous and sacrotuberous ligaments. That is why the posterior lesion, not the visible rami fractures, decides stability in an LC injury:

• LC-I: posterior ligaments intact, sacral impaction only - stable
• LC-II: partial posterior disruption through a crescent fracture - variable stability
• LC-III: both sacroiliac joints disrupted, ipsilateral LC and contralateral APC - unstable

Mechanism. The force arrives from the side: a T-bone collision, a pedestrian struck, a fall from height landing on the side. It drives the hemipelvis into internal rotation, so the pelvis narrows, the opposite of the APC injury which widens it, and there is compression both anteriorly and posteriorly.

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Why LC bleeds less. Internal rotation closes the pelvic volume, leaving less space for haemorrhage and tamponading bleeding to some extent, so LC injuries are generally less haemodynamically unstable than APC injuries. Do not be complacent: severe LC can still bleed significantly, LC-III can have substantial bleeding, associated injuries may contribute, and haemodynamic status needs assessing and reassessing.

Head injury. Very common with the LC mechanism, because the same lateral force that hits the pelvis also hits the head. Assess neurological status in every patient.

The Morel-Lavallée lesion. A closed internal degloving injury: the same lateral force shears the skin and subcutaneous fat off the underlying fascia, typically over the greater trochanter, and the cavity can fill to form a large fluid collection that may become infected. There need be no external wound, and presentation may be delayed. Identify it before any surgical incision; MRI is diagnostic, showing the fluid collection between fat and fascia.

Young-Burgess classifies by the direction of the injuring force, and grades the LC injury by its posterior lesion and by whether the opposite hemipelvis is involved. The type tells you where to look on the CT and how stable the ring is likely to be.

Tile correlation. Tile grades by the posterior lesion and stability rather than by force vector, so the mapping between the two systems is a convenience rather than an equivalence:

History. The mechanism is a lateral impact, and the answers that shape the assessment are few:

• Level of consciousness, because an associated head injury is common
• Ability to walk
• Where the pain is

Primary survey. ABC, haemodynamic status, a single gentle test of pelvic stability and a search for associated injuries.

Examination. Look for leg length discrepancy, rotational deformity, ecchymosis over the pelvis and perineum, open wounds (including the perineum, vagina and rectum) and the bruising or fluctuance over the trochanter of a Morel-Lavallée lesion. Palpate the symphysis, the sacroiliac joints and the iliac crests for tenderness; crepitus may indicate unstable fragments.

Associated injuries. The lateral mechanism injures more than the ring, and each system needs a deliberate check:

• Urogenital: blood at the urethral meatus means urethral injury (do not catheterise), haematuria, a high-riding prostate on rectal examination, vaginal or scrotal haematoma
• Neurological: the lumbosacral plexus and the L4-S1 nerve roots with sacral fractures; assess motor and sensory function
• Head injury, abdominal injuries, long bone fractures and acetabular fractures from the same mechanism

Differential diagnosis. When an AP pelvis shows rami fractures or there is pelvic pain after a fall or collision, distinguish lateral compression from its main mimics. The discriminating features are the direction of the deforming force, the posterior ring lesion on CT, and the patient's bone quality.

Radiographs. The AP pelvis is standard in all trauma patients; the inlet and outlet views complete the series:

• AP pelvis: pelvic ring continuity, rami fractures, symphysis width, sacroiliac joint symmetry
• Inlet view: anteroposterior and internal rotation displacement, posterior displacement, sacral impaction
• Outlet view: superior and inferior displacement, sacral fractures, the neural foramina

CT. Mandatory for all pelvic ring injuries. The sacral impaction of an LC-I is often occult on radiographs, and CT is what identifies the sacral fracture and its Denis zone, the integrity of the sacroiliac joint, a crescent fracture, the posterior ligamentous structures, neural canal involvement and any associated acetabular or lumbar spine injury. With that it classifies the injury accurately, assesses posterior ring stability and plans the surgical approach if one is needed.

MRI is reserved for selected cases:

• Suspected ligamentous injury without fracture
• Evaluation of a neurological deficit
• Assessment of sacroiliac joint instability
• Evaluation of a Morel-Lavallée lesion

Sacral fracture zones (Denis). The zone of the sacral fracture tells you which nerves are at risk:

Algorithm

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The first decision is haemodynamic. The unstable patient is resuscitated on ATLS principles, with the massive transfusion protocol if needed and a pelvic binder, and the bleeding is controlled by damage-control means: angiography and embolisation first-line for arterial bleeding, preperitoneal packing if angiography is unavailable or the bleeding is venous, and external fixation for temporary stabilisation. Once the patient is stabilised, definitive internal fixation follows at 24-72 hours. The stable patient is imaged completely with CT and the injury classified.

The binder. Apply it in the emergency department if instability is suspected, centred at the level of the greater trochanters, not the iliac crests; a sheet will do if there is no commercial binder, and the skin under it needs monitoring. A binder is a reduction device that closes an open, externally rotated ring, restoring the tamponading pelvic volume by internally rotating the hemipelvis. That is exactly the APC deformity, which is why a binder is dramatically effective there. In a pure LC injury the pelvis is already internally rotated and closed, so the binder has little volume to reduce and adds little haemorrhage benefit; pushed hard it can over-compress the ring, theoretically worsening the deformity, overlapping the rami and even compromising pelvic viscera. In practice:

• Still apply it if the pelvis is unstable, and monitor for worsening internal rotation
• In a bleeding LC patient do not rely on it for haemorrhage control; escalate early to angioembolisation or preperitoneal packing plus resuscitation, because the closed ring will not be tamponaded further by squeezing it
• The one LC pattern where a binder genuinely helps is LC-III, because the contralateral side is an open APC injury that the binder closes
• Remove or convert it promptly to avoid skin necrosis

LC-I. Usually conservative: multimodal analgesia, DVT prophylaxis, early mobilisation as tolerated, weight-bearing as tolerated and guided by symptoms, a physiotherapy assessment and follow-up imaging at 6 weeks. The indications are a stable LC-I with minimal displacement in a patient who can tolerate limited mobilisation, and most such injuries do well non-operatively.

Is this LC-I really stable? "LC-I" is not by itself an answer. Two features call for a stress examination: a complete sacral fracture, and an oblique rather than transverse superior pubic ramus fracture, which allows significantly more deflection under load (Marenghi 2022). The test does not need theatre. Done awake in the emergency department, 10 mm or more of rami overlap on a stress inlet view is positive and indicates fixation; a negative test reliably predicts successful nonoperative treatment (DeKeyser 2022: 81% negative, and all of those followed to three months united without significant displacement, although two patients with a negative test still could not mobilise and were converted to surgery). Under anaesthesia the corresponding threshold is more than 2 cm of translation, which in Tosounidis's series occurred only in pelvises with a complete sacral fracture.

LC-II. Test stability clinically. A stable LC-II may be treated conservatively; if it is unstable, consider fixation, posterior fixation if needed.

LC-III. Surgical fixation is required, of both sides, posteriorly with anterior fixation as indicated, timed for when the patient is optimised.

Indications for surgery. Instability, rotational or vertical, and displacement are the recurring themes:

• LC-II with instability
• All LC-III injuries
• Significant displacement
• Failed conservative management
• An associated acetabular fracture requiring fixation
• Polytrauma requiring mobilisation

Options and timing. Posteriorly, percutaneous sacroiliac screws are the most common fixation, with posterior plating and, for severe instability, spinopelvic fixation as the alternatives. Anteriorly, the symphysis is plated if it is disrupted in an LC-III, rami plating is rarely needed for LC, and external fixation is the damage-control tool. External fixation goes on acutely in damage control and definitive fixation is done when the patient is optimised; an LC-I may never need surgery.

Early. Haemorrhage is less than in APC but still significant, arterial from the superior gluteal or pudendal vessels or venous, and may need angioembolisation or packing. Urethral injury is less common in LC than in APC; bladder injury and neurological injury with sacral fractures also occur. A Morel-Lavallée lesion may need drainage or debridement, can delay wound healing, and risks infection if it is not addressed.

Late. Malunion produces leg length discrepancy, pelvic obliquity, gait abnormality and difficulty sitting. Sacroiliac joint arthritis develops in 20-40% of LC injuries, the risk higher with residual displacement though it may develop despite a good reduction; chronic sacroiliac pain is common and may need delayed fusion. Persistent nerve injury (L5, S1-S4) is more common with sacral fractures through the foramina.

The first 24-48 hours. Monitor neurovascular status, control pain with multimodal analgesia, start DVT prophylaxis, which is critical in this high-risk group, use incentive spirometry and mobilise early to the chair.

Weight-bearing and rehabilitation. After conservative treatment of an LC-I the patient bears weight as tolerated, with walking aids at first and progression guided by pain. After fixation of an LC-II or LC-III weight-bearing is staged, and rehabilitation follows the same phases:

Bilateral injuries may need a wheelchair initially, posterior ring instability delays full weight-bearing, and serial radiographs track healing.

DVT prophylaxis. Pelvic fractures carry a high VTE risk, so prophylaxis is mechanical and pharmacological combined: LMWH or fondaparinux started when safe, compression stockings or intermittent pneumatic compression, and early mobilisation. Continue for a minimum of 6 weeks, and consider 3 months in high-risk patients.

Follow-up. Review at set intervals:

• 2 weeks: wound check, neurovascular assessment
• 6 weeks: radiographs, assess healing, advance weight-bearing
• 12 weeks: radiographs, consider full weight-bearing
• 6 months: final radiographs, functional assessment
• 12 months: long-term outcome evaluation

The red flags at any visit are increasing pain (hardware failure or nonunion), loss of reduction, neurological change, wound complications, and signs of DVT or PE.

By type. LC-I has an excellent prognosis: conservative treatment is highly successful and long-term disability is minimal. LC-II does well, though some patients keep residual sacroiliac pain and need long-term analgesia, and outcomes are better with appropriate fixation when the ring is unstable. LC-III is fair to good, often limited by the associated injuries; patients may require workplace modifications, and the psychological impact is significant.

What predicts the outcome. Better outcomes follow a stable LC-I pattern, age under 50, no associated injuries, early mobilisation and appropriate treatment selection. Worse outcomes follow an unstable LC-III pattern, age over 65, multiple associated injuries, delayed or inadequate treatment, and comorbidities such as diabetes and osteoporosis.

Union. Most LC injuries unite, with conservative or surgical treatment, in 8-12 weeks. Nonunion is rare, under 5%, and malunion is more common than nonunion. Healing depends on the degree of displacement, the stability of fixation and compliance with weight-bearing restrictions; smoking delays it, and NSAIDs may impair it and are used cautiously.

Life afterwards. Sexual function may be affected, especially after LC-III; discuss it openly and refer to the appropriate specialist if needed. Most women can deliver vaginally after a healed LC injury, though caesarean section may be needed if there is significant pelvic deformity, so involve obstetrics early in pregnancy.

OrthoVellum is a worldwide resource: this section gives the global standard of care for lateral compression injuries plus the regional differences a candidate may be examined on. Lateral compression is the most common pelvic ring pattern internationally, and the principles below apply across all major trauma systems.

Global Epidemiology

A second, growing population is the elderly low-energy fragility fracture of the pelvis, which is rising with ageing populations worldwide and behaves differently from the high-energy LC injury above.

Major Guidelines Side by Side

Key area of genuine convergence: stable LC-I is treated nonoperatively with early weight-bearing; key area of evolving practice: how aggressively to detect occult instability in LC-1 with a complete sacral fracture (stress examination vs early fixation).

Registry and Trauma-System Evidence

• Trauma registries (e.g. the UK TARN and the Victorian State Trauma Registry) define the small, resource-intensive subgroup of haemodynamically unstable pelvic ring injuries and have shown that survival is driven by haemodynamic control rather than which centre delivers definitive care (Gabbe 2011, PMID 21733513).
• Joint-replacement registries (NJR, AJRR, AOANJRR) are not applicable to acute LC fixation; registry evidence here comes from trauma rather than arthroplasty registries.

Global Practice Variation

Thromboprophylaxis (Global Principle)

Pelvic fractures carry a high venous thromboembolism risk, so combined mechanical and pharmacological prophylaxis is standard worldwide. Low-molecular-weight heparin is the usual agent, started once haemorrhage is controlled, with renal dose adjustment, plus intermittent pneumatic compression and early mobilisation. Extended prophylaxis (commonly up to 6 weeks, longer in high-risk patients) is recommended for major pelvic injury, in line with international guidance.