6-THR PDF

THA Prof. Mazen Samir Abulsaad, MD, PhD Consultant of Orthopaedic Surgery Mansoura University  Objectives  Indication & contraindication of THA  Technique of THA  Stability after THA  Complications  Rehabilitation following THA  Total hip arth...

THA Prof. Mazen Samir Abulsaad, MD, PhD Consultant of Orthopaedic Surgery Mansoura University  Objectives  Indication & contraindication of THA  Technique of THA  Stability after THA  Complications  Rehabilitation following THA  Total hip arthroplasty (THA) - Is also known as total hip replacement (THR) - Consists of resection of the diseased articular surfaces of the hip, followed by replacement with prosthetic hip components. - Outcomes  Excellent clinical & functional outcomes for properly selected patient  Mortality rate : < 1% (30 – 90 days) & is primarily related to preexisting medical comorbidities Indications of THA: 1) Advanced Hip Osteoarthritis (most common indication) 2) Inflammatory arthritides (eg, rheumatoid arthritis, psoriatic arthritis,…. etc) 3) Trauma. 4) Neoplasms. 5) Osteonecrosis. Contraindications of THA 1) Active infection (is perhaps the most significant). 2) Significant medical problems (eg, recent MI, unstable angina, HF,…etc), 3) Skeletal immaturity, 4) Quadriplegia, or permanent muscle weakness in the absence of pain.  Arthroplasty technique  THA is carried out in a stepwise fashion 1- Surgical incision 2- Exposure of the hip & femoral neck cut. 3- Exposure & preparation of the acetabulum. 4- Preparation of the femur & insertion of femoral stem. 5- Femoral head is placed over the stem & hip is reduced. 6- Check proper functioning of completed hip replacement 7- The incision is then closed and is dressed. 1- Surgical incision A. Posterolateral B. Direct lateral (Hardinge) This approach is more commonly associated with gluteus medius lurch. C. Anterior (Smith-Peterson) Only approach with inter-nervous plan between Sartorius (femoral nerve) & Tensor fascia (superior gluteal nerve) 2- Exposure of the hip & femoral neck cut : Hip joint is exposed & the femoral neck is cut (with or without dislocation of the femoral head) and the femoral head is removed 3- Exposure & preparation of the acetabulum.  Reaming of the acetabulum & inserting a cementless or cemented acetabular component.  Size of the implant is determined by diameter of last reamer used.  A component that is oversized by 1 - 2 mm can be press-fit into position to provide a greater degree of initial stability.  Optimal ranges for acetabular component position is : Acetabular Abduction : 40 - 45° & Anteversion : 10-20° Acetabular reaming A -Implantation of cementless acetabular component - Fixation can be augmented with screws (Acetabular screw fixation)  Draw quadrants: divide acetabulum into 4 quadrants with 2 bisecting lines - First line drawn from ASIS to center of acetabulum - Second line drawn perpendicular to first line  Quadrants 1- Posterior-superior quadrant (target zone) Ideal place for supplemental component screws. 2- Posterior-inferior quadrant (caution zone) 3- Anterior-inferior quadrant (danger zone) 4- Anterior-superior quadrant (death zone)  Insert the polyethylene liner Insertion of liner. B- Implantation of cemented acetabular component  Drill holes in subchondral bone plate of ilium & ischium for cement intrusion  Mix one or two packages of cement , Reduce the porosity of the cement by vacuum mixing or centrifugation. Inject the cement in an early dough phase.  Insert acetabular component using appropriate positioning device.  Hold the positioner motionless as the cement begins to polymerize. 4- Preparation of the femur & insertion of femoral stem The femur is prepared :  Removal of remaining lateral edge of femoral neck and medial portion of greater trochanter with box osteotome.  Reaming of femoral canal Occlusion of medullary canal  Insert femoral stem when the cement has entered a medium dough phase, typically at about 6 minutes after the start of mixing for Simplex cement.  Femoral stem is placed in proper anteversion of 10°- 15° injection of cement Cement cement is inserted cement is pressed with gun pressurization manually with thumb, 5- Femoral head is placed over the stem & hip is reduced. 6- Check proper functioning of completed hip replacement 7- The incision is then closed and is dressed.  Stability of THA Four important variables determine the stability of THA 1) Component design 2) Component position 3) Soft-tissue tensioning 4) Soft-tissue function  Stability of THA 1) Component design a- Femoral component design: Ι - Large femoral heads ΙΙ- Femoral offset (see "soft tissue tensioning" later) b- Acetabular component design 2) Component position a- Acetabular position. b-Femoral stem position. 3) Soft-tissue tensioning a-Abductor Integrity b-Restoration of offset 4) Soft-tissue function Three main factors controlling proper soft tissue function : CNS,PNS & local Soft-tissue integrity.  1- Component design a- Femoral component design Large femoral heads increase stability of THA & decrease dislocation rates due to 1- Head-neck ratio increased (diameter of femoral head/diameter of femoral neck) - Larger head-neck ratios allow greater arc ROM prior to impingement 2- Jump-distance is increased (amount of translation prior to dislocation) - large femoral heads are seated deeper within acetabulum increasing jump distance 3- Skirts can be avoided - Skirts are attachments used to extend the length of femoral neck. - Skirts decrease the head-neck ratio b- Acetabular component design  Two acetabular liner designs can increase hip stability 1- Elevated rim liner  A posteriorly placed elevated rim liner may increase joint stability 2- Lateralized liner  increases soft-tissue tension by increasing offset  2) Component position a- Acetabularposition: Abduction : 40 - 45° & Anteversion : 10-20° - medialization of the cup increases moment arm of the abductors (gluteus medius & minimus) * increased moment arm leads to decreased joint reactive forces. - Complications 1-excessive retroversion : posterior dislocation 2- excessive anteversion: anterior dislocation 3- excessive abduction (vertical cup): posterior superior dislocation with eccentric polyethylene wear and late instability 4- excessive adduction (horizontal cup): impingement in flexion & inferior dislocation  2) Component position b- Femoral stem position: 10°- 15° of anteversion - Component malposition (acetabualr &/or femoral) generally requires revision & cannot be compensated for by abductor strengthening or orthoses 10- 15° anteversion Excessive anteversion  3) Soft-tissue tensioning  Abductor Integrity : gluteus medius serves as the major hip abductor muscle; insufficiency/tear leads to Trendelenburg gait  Restoration of offset Femoral horizontal offset : is perpendicular distance from femoral head center of rotation to the axis of the femur - increasing offset improves hip stability Benefits of increasing offset Decreased offset disadvantages Increases soft tissue tension without increasing leg length Instability Decrease impingement Abductor weakness Decrease joint reaction force Gluteus medius lurch Techniques to increase horizontal offset 1) Increasing length of femoral neck 2) Decreasing neck-shaft angle 3) Medializing the femoral neck while increasing femoral neck length 4) Trochanteric advancement 5) Alteration of the acetabular liner (see "component design" before)  Hip biomechanics  Can be simplified by the equation Force Abductors (Ab) x Distance to center of head(A) = Force from body weight (W) x Distance to center of head (B).  This relationship can be altered by changing 1- Offset (affects distance of abductor to center of head) or 2- Cup position (medial or lateral position of cup affects distance of body weight to center of head).  If the force of the abductor can't be improved by changing the distance to the head (offset) patients get a trendelenburg gait. The reason they therefore lurch to the affected side is so that they shift the force of body weight laterally thus decreasing the W to center of head distance.  Clinical implication of hip biomechanics Actions that decrease joint reaction force (JRF) include - Increase in ratio of A/B (shift center of rotation medially) a- Acetabular side: moving acetabular component medial, inferior, & anterior b- Femoral side: 1- increasing offset of femoral component 2- long stem prosthesis 3- lateralization of greater trochanter 4- Varus neck-shaft angulation c-Patient's gait  Shifting body weight over affected hip results in Trendelenburg gait  Cane in contralateral hand: reduces abductor muscle pull & decreases the moment arm between the center of gravity & the femoral head. N.B.: Valgus neck-shaft angulation increase JRF. Complications of THA : 1) Dislocation 2) Nerve injury 3) LLD 4) Periprosthetic Fractures 5) Heterotopic ossification (HO) 6) Aseptic loosening 7) Infection  1- Dislocation after THA  Incidence after primary THA : 1–2%.  Risk factors : 1) Decreased femoral head to neck ratio 2) Mal-positioning of acetabular components 3) Decreased femoral offset (decreases tissue tension & stability) 4) Prior spinal fusion or fixed spinopelvic alignment 5) Polyethylene wear - common cause of late instability occurring >5 years after procedure - X ray : eccentric position of femoral head as an indication of polyethylene wear and risk for impending dislocation 6) Patient position that provokes dislocation (hip flexion, adduction, internal rotation) as shoe tying, sitting in low seat or toilet.  Dislocation after THA Treatment  Closed reduction under conscious sedation.  If a closed reduction is failed, open reduction.  If component positioning or compromise is the cause of instability, the components may be revised at the time of reduction or may be revised at a later date. 2- Nerve injury during THA  May involve: 1- Sciatic nerve (80%) or 2- Femoral nerve (20%). Sciatic nerve injury  Causes of sciatic nerve injury are: 1) Errant retractor placement (most common cause). 2) Hematoma 3) Excessive leg lengthening.  Post-operative complaints of numbness and paresthesias along the sciatic nerve distribution & weakness of foot dorsiflexors. Treatment is - Place the hip in extension & knee in flexion post-operatively. - In presence of foot drop: Observation, AFO & monitor recovery of the nerve 3- Leg Length Discrepancy  2nd most common reason for litigation following THA (following nerve injury)  Mechanism A- Contracture leads to pelvic obliquity - ABDuction contracture causes involved hemipelvis to be lower, creating apparent long leg - ADDuction contracture causes involved hemipelvis to be higher, creating apparent short leg B- Weak abductors - May provide sensation of a long leg in the absence of true LLD - Usually resolve within 3-6 months post-operatively  Shoe-lift is adequate in most cases (wait 6 months to allow muscle relaxation) 4- Periprosthetic Fractures  Can be intraoperative fractures or postoperative fractures (most common at femoral stem tip)  Can be acetabular or femoral fractures.  Treatment may be nonoperative or operative based on location of fracture, implant stability and bone stock available  5- Heterotopic ossification (HO)  is the process by which bone tissue forms outside of the skeleton.  Is seen more often in males and with the direct lateral approach to the hip (Hardinge approach).  Predisposing risk factors : hypertrophic osteoarthritis, ankylosing spondylitis, prolonged surgical time, excessive soft tissue handling during procedure & prior hip arthrodesis.  Prophylactic treatment of high-risk patients with 1- a single dose of radiation (600 cGy ) within 72 hrs of surgery. 2- Oral indomethacin for 6 weeks.  Surgical excision -For those with sever limitation of movement -must wait 6 months after initial procedure to allow for maturation. -Followed by irradiation & indomethicin  6- Aseptic loosening  is a macrophage-induced inflammatory response that results in bone loss and implant loosening in the absence of an infection  X-ray : 1) migration or subsidence of the component. 2) fracture of the cement 3) 2 mm lucent line completely surrounding prosthesis.  Serum labs: ESR & CRP will be normal  Aseptic loosening is frequently associated with osteolysis, which is resorption of bone around the prosthesis mediated by collagenases, prostaglandins & proteases.  6- Aseptic loosening.  Osteolysis is thought to be the result of the body’s reaction to polyethylene particulate debris that forms from polyethylene wear.  Factors that can minimize polyethylene debris include: 1) proper head size. 2) maximal polyethylene thickness (at least 6 mm) 3) alternative bearing surfaces, such as ceramics or metal. 4) highly cross-linked polyethylene.  Indications of revision THA 1) pain due to aseptic loosening 2) pain with evidence of osteolysis 3) extensive osteolysis that would compromise revision surgery in the future.  7- Postoperative infection  Early Infection: within 3 weeks of the joint replacement surgery.  Late chronic infection: Infection present for > 3 weeks. - Persistent infection enters the bone–prosthesis interface & a bacterial biofilm has developed over the implant (biofilm formation may be organism dependent).  Treatment : 1) Surgical irrigation and debridement, 2) In early infection: Exchange of modular/polyethylene component ( metallic component is retained). In late chronic infection: removal of the prosthetic components usually with placement of a temporary antibiotic impregnated spacer. 3) Postoperative intravenous antibiotics for 4–6 weeks. Rehabilitation Goals in hospital 1) sitting upright --> 2) gait training, ambulation with walker, out of bed to chair --> 3) transfers, gait normalization --> 4) independence Discharge home criteria 1) independent ambulation with assistive device 2) independent transfers & ADLs 3) stairs with supervision 4) appropriate home assistance (spouse, family, visiting nurses) Rehabilitation Posterolateral approach (Dislocate posterior)  Limit flexion (past 90) , extreme internal rotation & adduction (past body's midline) Direct lateral (Hardinge) approach (Dislocate anterior)  Limit extension, extreme external rotation & adduction (past the body's midline) Direct anterior (Smith-Peterson) (Dislocate anterior)  Avoid bridging  Limit extension, extreme external rotation & adduction past (body's midline) Rehabilitation Outpatient care  Return to sport - low-impact exercises are preferred - high-impact exercises increase revision rates in pts < 55 years.  Driving recommendations: - 3-4 weeks after right THA, less than 3-4 weeks after a left THA - reaction time returns to preoperative levels at 4-6 weeks  Return to work: within a month if no manual labor What is an advantage of utilizing a 36-mm instead of a 28-mm femoral head in the setting of a revision total hip arthroplasty? 1Compensating for abductor deficiency 2Decreasing volumetric wear 3Decreasing trunion stress 4Delaying neck-socket impingement 5Compensating for vertical cup placement A patient with a Trendelenburg sign as evident by the pelvis tilting down on the right during a single-leg stance on the left lower extremity secondary to weak abductors of the left hip. Which of the following modifications during a left-sided total hip arthroplasty would exacerbate this condition? 1Decreasing femoral offset 2Changing from a standard offset neck to an extended offset neck 3Increasing femoral head size 4Increasing femoral neck length 5Moving acetabular cup inferiorly In total hip arthroplasty, which of the following techniques will lead to improved stability by increasing the abductor tension? 1Use of a high offset femoral component 2Decreasing neck length 3Use of a low offset femoral component 4Increasing the head size 5Medializing the acetabular component During total hip arthroplasty, which of the following techniques increases range of motion prior to impingement? 1Using implants with a smaller femoral head 2Using implants with a larger femoral head to neck ratio 3Using a ultra high molecular weight polyethylene liner on the acetabulum 4Decreasing femoral offset 5Cementing the femoral stem Which of the following factors is most likely to increase the risk of hip dislocation after a total hip arthroplasty (THA)? 1Large head-to-neck ratio 2Use of a skirted femoral head 3Femoral component in 15 degrees of anteversion 4Acetabular cup in 15 degrees of anteversion 5Acetabular cup in 50 degrees of abduction Patient had foot drop following THR. CT scan of the hip is obtained and reveals screw penetration into the sciatic notch. Where was this screw most likely inserted in the acetabulum? 1Anterior superior quadrant 2Through the medial wall 3Anterior inferior quadrant 4Posterior superior quadrant 5Through the femoral nerve