Total hip arthroplasty, dislocation
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18-Oct-2014 -
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total hip arthoplasty dislocation
Transcript of Total hip arthroplasty, dislocation
HIP JOINT
• Synovial ball-and-socket joint
• Capsule
• Acetabular labrum medially
• Intertrochanteric line, posterior aspect of the neck laterally
• Ligaments
MOVEMENTS
• Flexion
• iliopsoas, rectus femoris, and sartorius and also by the adductor muscles.
• Extension
• gluteus maximus and the hamstring muscles.
• Abduction
• gluteus medius and minimus, assisted by the sartorius, tensor fasciae latae, and piriformis.
• Adduction
• adductor longus and brevis and the adductor fibers of the adductor magnus. These muscles are assisted by the pectineus and the gracilis.
• Lateral rotation
• piriformis, obturator internus and externus, superior and inferior gemelli, and quadratusfemoris, assisted by the gluteus maximus
• Medial rotation
• anterior fibers of the gluteus medius and gluteus minimus and the tensor fasciae latae.
• Circumduction
MOVEMENTS
FEATURES OF AN IDEAL JOINT REPLACEMENT
• Biocompatible
• Well fixed to the host tissue, stable and allowing a good range of movement
• Bearing surfaces should be designed to minimise friction
• Material released from the bearings should be non-toxic
• Remove the minimum amount of bone
• Produce mechanical stability
• Should ideally outlive the patient
• The ratio of the length of the lever arm of the body weight to that of the
abductor musculature is about 2.5 : 1
• The force of the abductor muscles must approximate 2.5 times the body
weight to maintain the pelvis level when standing on one leg
• The estimated load on the femoral head in the stance phase of gait is equal to
three times the body weight
CHARNLEY CONCEPT OF TOTAL HIP ARTHROPLASTY
• Shorten the lever arm of the body weight by deepening the acetabulum and to lengthen the lever arm of the abductor mechanism by reattaching the osteotomized greater trochanter laterally
• The lengths of the two lever arms can be surgically changed to make their ratio approach 1 : 1
• Theoretically, this reduces the total load on the hip by 30%
PEAK CONTACT FORCES
Body position X body weight
Gait 3.5 to 5.0
Single-limb stance 6
Running, jumping 10
• The forces on the joint act not only in the coronal plane but also in the sagittal plane to bend the stem posteriorly
• The forces acting in this direction are increased when the loaded hip is flexed
• These so-called out-of-plane forces have been measured at 0.6 to 0.9 times body weight.
• These are directed against the prosthetic femoral head from a polar angle between 15 and 25 degrees anterior to the sagittal plane of the prosthesis
• The location of the center of rotation of the hip from superior to inferior also affects the forces generated around the implant
• Isolated superior displacement without lateralization produces relatively small increases in stresses in the periacetabular bone
• Placement of the acetabular component in a slightly cephalad position allows improved coverage or contact with viable bone
COMPLICATIONS OF THR
• Mortality
• Hematoma formation
• Heterotopic ossification
• Thromboembolism
• Nerve injuries
• Vascular injuries
• Limb-length discrepancy
• Dislocation and subluxation
• Fractures
• Trochanteric nonunion and migration
• Infection
• Loosening
• Osteolysis
DISLOCATION
• The average incidence of dislocation after total hip arthroplasty is approximately 3%
EPIDEMIOLOGICAL
• Previous hip surgery
• Female sex
• Advanced age
• Prior hip fracture
• Preoperative diagnosis of osteonecrosis or inflammatory arthritis
SURGICAL
• Posterior approach
• Component malposition
• Uncorrected bony and/or component impingement
• Inadequate soft tissue tension
• Smaller head size
ANATOMICAL
• Trochanteric nonunion
• Abductor muscle weakness
• Increased preoperative range of motion
ALARMING SIGNS OF DISLOCATION
• Excessive pain on motion of the hip
• Abnormal internal or external attitude of the hip with limited active and passive motion
• Shortening of the limb
• Reduction usually is not difficult if dislocation occurs in the early postoperative period and
a timely diagnosis is made
• Reduction techniques should always be gentle to minimize damage to the articulating
surfaces
• Open reduction with replacement of the liner or revision of the acetabular component may
be required
• If the components are in satisfactory position, closed reduction is followed by a period of
bed rest
• Mobilization is accomplished in a prefabricated abduction orthosis that maintains the hip
in 20 degrees of abduction and prevents flexion past 60 degrees
• Immobilization for 6 weeks to 3 months is recommended
• If one or both components are malaligned, and dislocation becomes recurrent, revision surgery
usually is required
• If instability is compounded by neurological deficit or abductor insufficiency, revision to a
bipolar prosthesis may be considered
• Constrained socket design can be used in which the femoral head is locked into the socket
• These devices should be used only as a last resort because of their complexity and multiple methods of
mechanical failure
• Noncompliant individuals, elderly debilitated patients, and patients with several previous failed attempts to stop recurrent dislocation are best treated by removal of the components without further reconstruction
