Instability following thr
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Most hip dislocations occur within the first 3 months after surgery. Risk factors for dislocation include surgical approach, soft tissue tension, component malposition, and femoral head size. Treatment depends on the cause but may include closed reduction, bracing, modular components, larger heads, constrained liners, or soft tissue reinforcement. Surgeon experience also impacts dislocation rates.
![FEMORAL HEAD SIZE
The larger the femoral head,
the further it must sublux
before it can dislocate, a
distance referred to as the
Jump distance.
Berry et al[29] in a study of
21047 THAs, found a
significantly decreased rate of
dislocation with the use of
larger femoral heads in all
surgical approaches.](https://image.slidesharecdn.com/instabilityfollowingthr-170704134637/85/Instability-following-thr-15-320.jpg)
Instability following thr
- 1. INSTABILITY AFTER TOTAL HIP ARTHROPLASTY Dr. Giridhar Boyapati M.S (Ortho), FIJR MAXCURE HOSPITALS HITECH CITY, HYDERABAD
- 2. Instability is one of the most common complications of THA Dislocation rate of : Primary THR : 3.2% Revision THR : 7.4%
- 3. Most of dislocations occur within the first 3 months following surgery 50%-70% of dislocations occur within the first 5 week to 3 months postoperatively, and more than 3/4 th of dislocations occur within the first year following surgery. The cumulative risk of dislocation does not remain constant following THA, increasing with time due to trauma, polyethylene wear, increased pseudocapsule laxity and deteriorating muscle strength The cumulative risk of dislocation within the first postoperative month is 1% and within the first year approximately 2% . Thereafter, the cumulative risk continuously increases by approximately 1% per 5-year period and amounts to approximately 7% after 25 years
- 4. Late dislocations are caused by progressive improvement in motion after surgery Late dislocations are more likely to be come recurrent and require surgical intervention
- 5. ● Cranial dislocation – Excessive inclination of the cup, abductor insufficiency, polyethylene wear – Dislocation along with adduction of the extended hip joint ● Dorsal dislocation – Insufficient anteversion or retroversion of the cup, joint hyperlaxity, primary or secondary impingement – Dislocation with internal rotation and adduction of the flexed hip joint or with deep flexion ● Anterior dislocation – Excessive combined antetorsion of stem and cup, joint hyperlaxity, primary or secondary impingement – External rotation and adduction of the extended hip joint.
- 7. Positional dislocations had a reoperative rate of 17% Soft tissue imbalance had a reoperative rate of 46%, and 15% of these hips ultimately underwent resection arthroplasty. Component malposition had a reoperative rate of 77%, and in 33% of those hips the final result was a resection arthroplasty.
- 8. RISK FACTORS ANATOMICAL FACTORS EPIDEMILOGICAL FACTORS SURGICAL FACTORS
- 9. ANATOMICAL FACTORS TROCHANTERIC NONUNION ABDUCTOR MUSCLE WEAKNESS INCRESED PREOPERATIVE ROM
- 10. EPIDEMILOGICAL FACTORS FEMALE GENDER AGE > 80 NEUROMUSCULAR DISORDERS COGNITIVE DISORDERS ALCOHOLISM PREVIOUS HIP SURGERY PRIOR HIP FRACTURE PREOPERATIVE DIAGNOSIS OF OSTEONECROSIS INFLAMMATORY ARTHRITIS
- 11. SURGICAL FACTORS Surgical approach Capsular repair Soft tissue tension Component malpositioning Femoral head size Impingement Surgeon experience
- 12. SURGICAL APPROACH Dislocation rates of : 1.27% for Trans-Trochanteric, 3.23% for posterior (2.03% with capsular repair), 2.18% for anterolateral 0.55% for the direct lateral approach
- 13. 75% to 90% of dislocations are in the posterior direction, thus surgical approaches that compromise posterior soft tissues theoretically could contribute to posterior instability Therefore, when risk of dislocation is of particular concern, the posterior approach historically has been the least favoured. With adequate soft tissue repair there is ten fold reduction in dislocation rates ( 4.46% to 0.4%)
- 14. SOFT TISSUE TENSION Soft tissue tension, influenced by the Joint capsule Short external rotators and gluteal muscles Femoral offset Reconstruction of the posterior capsule and short external rotators and restoration of femoral offset has been shown to significantly reduce dislocation rate
- 15. FEMORAL HEAD SIZE The larger the femoral head, the further it must sublux before it can dislocate, a distance referred to as the Jump distance. Berry et al[29] in a study of 21047 THAs, found a significantly decreased rate of dislocation with the use of larger femoral heads in all surgical approaches.
- 17. Modular femoral head components that have extension or SKIRT to provide additional neck length : Reduce head to neck diameter Reduce ROM Reduce Stability
- 18. COMPONENT MALPOSITION Component malposition is the most common cause of instability following THA. Excessive anteversion of the acetabulum may result in anterior dislocation Excessive retroversion may result in posterior dislocation Excessive inclination of the cup can lead to superior dislocation with abduction If cup is inclined almost horizontally, impingement can occur in flexion and hip dislocates posteriorly.
- 19. Ali Khan et al found that the most common surgical error was placement of the acetabular component in excessive anteversion and abduction Forward rotation of the pelvis must be taken into account, or excessive retroversion of the cup can result In lateral position : Women with broad hips and narrow shoulders there is a tendency to implant the cup more horizontally Men with narrow pelvis and broad shoulders there is tendency to implant the cup more vertically Placement of acetabular component in orientation relative to the operating table produces inadvertent retroversion relative to pelvis
- 20. SAFE RANGE ANTEVERSION OF 15° ± 10° INCLINATION OF 40° ± 10° Dislocation rate with cup in safe range is 1.5%, whereas 6.1% of those outside this safe range Lowest risk values for dislocation were 15deg anteversion and 45 deg of inclination
- 21. COMBINED ANTEVERSION Sum of ante version of cup and stem Total of 35 deg Acceptable range 25 to 50 Dorr proposed the so-called “stem-first” procedure for the CA technique in which the stem is set first, and cup alignment is determined to consider the target CA value.
- 22. RANAWAT TEST FOR CA CA can be easily checked intraoperatively by internally rotating the femur until the neck of the prosthesis is perpendicular to the opening plane of the cup.
- 23. INTERNAL ROTATION TEST To assess the capsular integrity and risk of hip dislocation after the posterior approach
- 24. A positive internal rotation test is indicative of proper healing of the posterior soft tissue, which includes the capsule and short external rotators, with a specificity of 100%. The high sensitivity and specificity of the internal rotation test for the healed capsule/tendon unit makes it a clinically useful test during the physical examination to demonstrate an appropriate repair and thus safely discontinue hip precautions, thereby allowing patients to return to full activities of daily living.
- 25. IMPINGEMENT Bone or cement protruding beyond the flat surface of the cup; it serves as a fulcrum to dislocate the hip in the direction opposite to its location. Residual osteophytes Capsular scar tissue Heterotopic ossification Impingement of femoral neck on liner elevation
- 27. Surgeon experience The rate of dislocation has an inverse relationship to the experience of the surgeon. For every ten primary arthroplasties performed yearly, there is a 50% reduction in the postoperative dislocation rate
- 28. MANAGEMENT CLOSED REDUCTION BRACING MODULAR COMPONENT EXCHANGE BIPOLAR AND TRIPOLAR ARTHROPLASTY LARGE FEMORAL HEAD CONSTRAINED LINER SOFT TISSUE REINFORCEMENT GREATER TROCHANTER ADVANCEMENT
- 29. CLOSED REDUCTION If the components are in satisfactory position, closed reduction is followed by a period of bed rest. Abduction Orthosis : maintain hip in 20 deg abduction and prevent flexion more than 60 deg immobilisation for 6 weeks to 3 months is recommended
- 30. MODULAR COMPONENT EXCHANGE Increasing femoral head size Increasing neck length Various liner options. Minor malposition of a acetabular component can be managed with changing the position of the liner or adding an elevated rim liner Inadequate femoral neck length require exchange of modular head or revision of femoral component. MALPOSITION OF MORE THAN 10 DEGREES REQUIRE REVISION OF THE COMPONENTS
- 31. Bipolar and tripolar arthroplasty The bipolar arthroplasty component consists of a small femoral head located inside a polyethylene shell that is then covered by a larger femoral head. This theoretically allows motion between the small femoral head and the liner as well as the larger femoral head and the acetabulum. Placement of a bipolar prosthesis inside an acetabular component with a liner is known as a tripolar arthroplasty
- 33. LARGE FEMORAL HEADS Larger femoral heads (e.g. 36 mm) allow a wider mechanical range of motion compared with smaller head diameters (e.g. 28 mm) before the neck of the prosthesis strikes the rim of the acetabular component . In addition, the distance a larger femoral head has to move away from the center of the acetabular component (“jumping distance“) before it can dislocate over the rim of the cup is longer. Thus, a larger head diameter offers better protection against dislocation
- 34. Kung et al evaluated 230 patients for the effect of femoral head size (28 mm vs 36 mm) on postoperative stability. At a mean follow up of 27 mo, they found that the use of the larger femoral head brought the dislocation rate from 12.7% down to 0%. However, if the abductor mechanism was absent, there was no statistically significant reduction in dislocation rate.
- 35. Disadvantages: Inlay thickness has to decrease with increasing head diameters Increased abrasion along the head-neck plug connection The stabilizing effect is lost in case of abductor insufficiency Increased range of motion promotes secondary impingement with resulting contact between proximal femur and pelvic bone. For these reasons, femoral heads with diameters of more than 36 mm are not normally used.
- 36. Constrained liners Constrained liners are designed to physically resist dislocation of the femoral head by locking the head into the acetabular cup Surgical management of recurrent dislocation in the setting of abductor deficiency, recurrent dislocation of undetermined etiology and in patients with multiple dislocations due to neurological impairment liners offer the ability provide enhanced stability to a hip without the need to revise well-fixed, well-positioned acetabular components
- 38. Soft tissue reinforcement Additional static restraint to augment the deficient posterior capsule or enhance a deficient abductor mechanism Lavigne et al were the first to report the use of an Achilles tendon allograft placed between the greater trochanter and the ischium to reduce the range of internal rotation and enhance stability. Barbosa et al described the successful use of a synthetic ligament prosthesis to treat patients with recurrent posterior dislocation of THA Soft-tissue procedures provide an additional approach to achieving THA stability in patients who are poor candidates for other options such as constrained liners.
- 39. Greater trochanter advancementIncrease abductor tension and stability Improve the resting length and functioning of the abductor mechanism, which consequently affords increased hip stability in 81%-90% of cases. The advent of modular implants allows the surgeon to increase femoral neck length to accomplish the same goals without the potential morbidity of greater trochanteric nonunion. Used only as an option when there is proximal migration of an ununited trochanter after a trochanteric osteotomy
- 40. Resection arthroplasty Patients who fail to respond to any measures may be candidates for end stage revision to a resection arthroplasty.