Biomechanics and stability of the pelvic ring
The pelvic ring is formed by two hip bones and the sacrum. Functionally, in relation to the acetabulum, it is divided into two parts:
- Posterior ring (weight-bearing). Includes the sacrum, sacroiliac joints, and the posterior parts of the iliac bones. It is through this ring that body weight is transmitted to the lower limbs.
- Anterior ring. Consists of the pubic rami and the pubic symphysis.
The main rule for assessing stability: pelvic integrity depends on the state of the posterior ligamentous complex (sacrotuberous, sacrospinous, and dorsal sacroiliac ligaments). These are what prevent the pelvis from "falling apart" under the influence of rotational and vertical shear forces.
Classification of pelvic fractures (AO/ASIF)
There are three main groups of pelvic ring injuries:
- Type A (Stable). These are marginal fractures where the integrity of the ring is preserved (e.g., isolated pubic bone fractures — "straddle" fractures, iliac wing fractures, sacral fractures below the articulation, or coccyx fractures).
- Type B (Rotationally unstable). The ring is disrupted anteriorly, but the posterior ligaments remain intact. The pelvis may "open book" around the vertical axis without vertical displacement. A classic example is the "open book" fracture (B1), where the symphysis ruptures due to anteroposterior compression of the pelvis.
- Type C (Absolutely unstable). The integrity of both the anterior and posterior segments is disrupted. One half of the pelvis shifts freely both laterally and vertically.
Acetabular fractures are a separate category, resulting from indirect trauma (axial impact to the femur or lateral impact to the greater trochanter). The most severe variant is a fracture of the acetabular floor with central hip dislocation.
Clinical presentation and diagnostics
Patients often present in severe shock. The cause of shock is twofold: irritation of powerful reflexogenic zones and massive hemorrhage into the intrapelvic tissue.
Specific symptoms of pelvic trauma:
- Bruising in the perineum, scrotum, or groin (pathognomonic for the anterior ring).
- "Frog-leg" posture (Volkovich's sign): legs are flexed and abducted.
- Gabay's sign: the patient turns in bed, supporting the injured leg with the healthy foot.
- Sharp pain upon attempting to gently compress or spread the iliac wings.
- In complete ruptures (Type C), one half of the pelvis is displaced upward by 2–3 cm (measured from the xiphoid process to the anterior superior iliac spine).
Pseudo-abdominal syndrome Extensive retroperitoneal hematoma can irritate the peritoneum, causing abdominal muscle rigidity, as in peritonitis. To rule out internal organ rupture, Joyce's sign is checked: during abdominal percussion, dullness in dependent areas does not shift when the patient is turned to the side, as the blood is trapped retroperitoneally.
Treatment tactics: from first aid to surgery
At the pre-hospital stage, the patient should not be unnecessarily repositioned. Transportation must be performed strictly on a rigid board.
Hospital stage: Shock management is the primary priority. Shkolnikov-Selivanov intrapelvic blockade (injection of 300 ml of 0.25% procaine into the iliac fossa) is extremely effective. It not only relieves pain but also acts as a hydraulic tamponade, compressing bleeding vessels.
Principles of further treatment:
- Conservative: Used for stable fractures (bed rest, bolsters, Böhler splint). "Open book" fractures can be treated using a special hammock: the patient's pelvis is suspended, and under the weight of their own body, the separated pubic bones approximate. Traction duration is 6–7 weeks.
- Surgical: Indicated if the diastasis of the pubic bones exceeds 2.5 cm, or if closed reduction fails within the first 10–14 days. It is important to reduce the fragments as early as possible, because after 2 weeks even surgical reduction becomes extremely difficult, leading to disability.
Briefly: answers to topical questions
How is the Shkolnikov-Selivanov intrapelvic blockade technically performed?
The Shkolnikov-Selivanov intrapelvic blockade is performed by inserting a needle into the iliac fossa through the area of the anterior superior iliac spine.
Technique:
- Injection point — 1 cm medial to the anterior superior iliac spine (spina iliaca anterior superior).
- Instrument — 14–15 cm long needle.
- Direction — from anterior to posterior toward the inner surface of the iliac wing.
- Drug administration — as the needle advances using the "walking-finger" infiltration method, 400–500 ml of 0.25% procaine solution is injected.
The anesthetic is injected into the fascial sheath of the iliac fossa, from where it spreads into the pelvic tissue. To prolong the effect, procaine is mixed with a gelatin solution.
Which internal pelvic organs are most frequently injured in anterior ring fractures?
In injuries of the anterior pelvic ring, the bladder and urethra may be damaged.
The risk of urethral injury is particularly high in bilateral fractures of the pubic and ischial bones. Urethral injuries occur in approximately 10% of major pelvic fractures and typically affect the proximal (posterior) urethra, predominantly in men. With a displaced pelvic fracture, the bladder can become incarcerated; such an injury requires open reduction and plasty. Bladder ruptures can be extraperitoneal, intraperitoneal, or combined.
What are the absolute indications for surgical treatment of pelvic fractures?
The absolute indication for surgical treatment of pelvic fractures is the failure of closed manual reduction and skeletal traction.
Which special radiographic projections are used for accurate diagnosis of pelvic ring fractures?
For accurate diagnosis of pelvic ring fractures, anteroposterior, lateral, and oblique radiographic projections are used.
The following positioning techniques are used:
- Anteroposterior (AP) projection — overview radiograph performed strictly in the supine position with extended legs.
- Lateral projection — used to diagnose displaced sacral fractures or coccyx injuries.
- Oblique projections — iliac and obturator, performed at a 45° angle.
- Oblique views of the sacroiliac joints — performed with the pelvis tilted 15–25° away from the side being imaged (two symmetrical views are taken for comparison).
The letters of the AO/ASIF classification are easy to associate with severity: A — Absolutely stable, B — Bouncing (rotational instability), C — Completely detached (vertical and rotational instability).
Class and exam questions
What is the «stuck-heel sign» and is it characteristic of pelvic trauma?
The patient cannot independently lift the straightened leg off the couch. This is a classic sign of an anterior pelvic ring fracture (pubic or ischial bones).
How to determine the extent of injury based on the width of symphyseal diastasis?
If the pubic bones have separated by less than 2.5 cm, it means the posterior ligaments are intact. If the separation exceeds 2.5 cm, the sacrospinous and anterior sacroiliac ligaments are ruptured.
What else to study on this topic
- Technique and injection points for the Shkolnikov-Selivanov blockade
- Specific radiographic positioning for evaluating the sacroiliac joints
- Mechanisms of central hip dislocation in acetabular fractures
- Functional blockade of the sacroiliac joint and its consequences
- Limb positioning rules for isolated marginal fractures (Type A)
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