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Total hip arthroplasty, dislocation
- 2. HIP JOINT • Synovial ball-and-socket joint • Capsule • Acetabular labrum medially • Intertrochanteric line, posterior aspect of the neck laterally • Ligaments dr.basit@live.com
- 4. 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. dr.basit@live.com
- 5. • Lateral rotation • piriformis, obturator internus and externus, superior and inferior gemelli, and quadratus femoris, assisted by the gluteus maximus • Medial rotation • anterior fibers of the gluteus medius and gluteus minimus and the tensor fasciae latae. • Circumduction MOVEMENTS dr.basit@live.com
- 6. 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 dr.basit@live.com
- 9. • 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 dr.basit@live.com
- 10. 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% dr.basit@live.com
- 13. PEAK CONTACT FORCES Body position X body weight Gait 3.5 to 5.0 Single-limb stance 6 Running, jumping 10 dr.basit@live.com
- 14. • 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 dr.basit@live.com
- 15. • 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 dr.basit@live.com
- 17. 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 dr.basit@live.com
- 18. DISLOCATION • The average incidence of dislocation after total hip arthroplasty is approximately 3% dr.basit@live.com
- 19. CONTRIBUTORY FACTORS • Epidemiological • Surgical • Anatomical dr.basit@live.com
- 20. EPIDEMIOLOGICAL • Previous hip surgery • Female sex • Advanced age • Prior hip fracture • Preoperative diagnosis of osteonecrosis or inflammatory arthritis dr.basit@live.com
- 21. SURGICAL • Posterior approach • Component malposition • Uncorrected bony and/or component impingement • Inadequate soft tissue tension • Smaller head size dr.basit@live.com
- 22. ANATOMICAL • Trochanteric nonunion • Abductor muscle weakness • Increased preoperative range of motion dr.basit@live.com
- 23. 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 dr.basit@live.com
- 24. • 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 dr.basit@live.com
- 25. • 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 dr.basit@live.com
- 26. • 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 dr.basit@live.com
- 27. • 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 dr.basit@live.com