Anatomical and biomechanical features and pathogenesis
The hip joint is a ball-and-socket (spheroidal) joint. The congruence of its articular surfaces is complemented by the cartilaginous labrum, which also acts as a shock absorber during axial loads. The most crucial structure of the joint is the ligament of head of femur, extending from the floor of the acetabulum to the femoral head. Nurturing blood vessels run inside it.
Any hip dislocation is always accompanied by a rupture of the round ligament and the artery within it. Additionally, the blood vessels of the femoral neck are compressed by the ruptured capsule and spastic muscles. Acute ischemia of the femoral head develops. Golden rule: the longer the joint remains unreduced, the more severe the vascular disorders and the higher the risk of developing avascular necrosis.
Mechanisms of injury
Hip dislocations occur predominantly due to indirect impact of immense force (e.g., in motor vehicle accidents).
- Posterior dislocations: occur with sharp adduction and internal rotation of a flexed thigh. A classic example is a blow to the knee along the axis of the thigh with a flexed hip joint. The head ruptures the posterior part of the capsule and displaces posteriorly.
- Anterior dislocations: occur with fixed abduction of the leg in a state of external rotation. According to the first-class lever rule, the head abuts against the edge of the acetabulum and dislocates anteriorly.
- Central dislocation: the result of axial loading with the leg in a neutral position. The head fractures the bottom of the acetabulum and penetrates into the pelvic cavity.
Classification of hip dislocations
Depending on the direction of displacement of the femoral head, there are two major groups (anterior and posterior), which are subdivided into four main types:
- Posterosuperior (iliac) — occurs most frequently.
- Posteroinferior (sciatic).
- Anterosuperior (pubic) — the rarest.
- Anteroinferior (obturator).
Clinical presentation and diagnostics
Patients complain of excruciating pain, cannot stand on the leg, and active movements are absent. An attempt at passive movements reveals the specific «springing resistance» sign.
The main diagnostic marker is the forced position of the limb:
- Posterior dislocations: the leg is adducted to the midline and internally rotated. In an iliac dislocation, the thigh is slightly flexed (the head is palpated in the gluteal region above the Nélaton-Roser line, limb shortening is present). In a sciatic dislocation, the thigh is sharply flexed (the head is identified posteriorly and inferiorly to the acetabulum, easily palpable upon passive rotation).
- Anterior dislocations: the leg is abducted and externally rotated. In a pubic dislocation, the leg is extended, the head is palpated under the inguinal crease as a bulge. In an obturator dislocation, severe flexion (according to other data, extension) and maximal external rotation are pronounced, the head bulges in the obturator foramen area.
In posterior and obturator dislocations, an «empty» acetabulum can be palpated. Also, on the affected side, the finger sinks deeper into the tissues lateral to the femoral artery.
Complications and treatment
Dislocations are often accompanied by fractures of the acetabular rim, femoral neck, or head. In posterior dislocations, the sciatic nerve is damaged in 12% of cases, so a neurological examination is mandatory. Anterior dislocations are dangerous due to compression of the main femoral vessels.
Management Strategy:
- Prehospital stage: analgesia and transportation on a stretcher in the supine position (immobilization with rolls, since applying a standard splint is difficult due to deformation).
- Reduction: performed urgently under general anesthesia with muscle relaxants (or spinal anesthesia). The most popular method is Janelidze's method (the patient lies prone, the injured leg hangs off the table). Important: Janelidze's method is contraindicated in pubic dislocation due to the risk of femoral neck fracture.
- Post-traumatic period: skeletal traction, followed by walking on crutches without weight-bearing on the injured leg, functional therapy.
Briefly: answers to topical questions
Which specific major vessels can be compressed during anterior hip dislocations?
During anterior hip dislocations, the femoral vessels can be compressed. The specific names of the major vessels are not specified in the sources, but it is indicated that this complication is characteristic of both anterosuperior (pubic) and anteroinferior (obturator) dislocations. Compression leads to vascular disorders and impaired distal blood circulation, which clinically manifests as cyanosis and weakened pulse on the arteries of the foot.
What methods of hip dislocation reduction exist, other than Janelidze's method?
In addition to Janelidze's method, Kocher's method (Kocher) and its modifications are used for hip dislocation reduction. This method is performed with the patient strictly in the supine position with rigid fixation of the pelvis by an assistant. Reduction of posterior dislocations according to Kocher includes the following stages:
- First stage — flexion of the leg at the hip and knee joints with powerful traction along the axis of the thigh vertically upwards.
- Second stage — external rotation of the thigh with inward deviation of the lower leg.
- Third stage — performed against the background of continuous traction along the axis of the thigh.
Through which anatomical landmarks does the Roser–Nelaton line pass?
The Nélaton-Roser line passes through two main anatomical landmarks: the anterior superior iliac spine (of the iliac wing) and the ischial tuberosity. Normally, when the thigh is flexed at an angle of 135°, the apex of the greater trochanter of the femur is projected onto this projection line. In pathologies such as an iliac (posterosuperior) hip dislocation or fracture-dislocation, the apex of the greater trochanter is displaced and lies above this line.
What clinical symptoms are characteristic of a central hip dislocation?
A central hip dislocation is characterized by depression of the greater trochanter. This injury is always accompanied by a fracture of the acetabular floor, through which the femoral head is displaced into the pelvic cavity. As with other acetabular injuries, patients predominantly experience hip joint pain, which increases with axial loading on the thigh and percussion on the greater trochanter, as well as impaired joint function.
How to remember the position of the leg: Posterior dislocations — the leg is «closed» (adducted and internally rotated). Anterior dislocations — the leg is «open» (abducted and externally rotated).
Class and exam questions
Why is hip dislocation reduction an emergency procedure?
Due to the rupture of the round ligament and compression of the femoral neck vessels, acute ischemia of the head develops. Delay sharply increases the risk of developing irreversible avascular necrosis.
What is the essence of Janelidze's method?
This is a low-trauma reduction method in which the patient is placed prone so that the injured leg hangs off the edge of the table. Gravity and muscle relaxation facilitate the procedure.
When is Janelidze's method contraindicated?
It is strictly contraindicated in anterosuperior (pubic) dislocation, as traction in this position can lead to an iatrogenic femoral neck fracture.
What else to study on this topic
- Technique of Janelidze's method and Kocher's methods
- Techniques for palpating the empty acetabulum
- Radiological landmarks (Nélaton-Roser line, Shenton's line)
- Central hip dislocation and acetabular fractures
- Algorithm for patient management on skeletal traction after reduction
Master the entire topic in the "Traumatology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on «Hip dislocations» and another 812 pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 35 video lessons on the subject
Other topics in the "Specialized Adult Traumatology" section
The entire "Specialized Adult Traumatology" sectionPrepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.