Summary THA Postoperative Abductor Deficiency is a serious complication of primary and revision THA caused by repair failure, muscular atrophy, traumatic rupture, implant loosening or malposition, nerve injury, or greater trochanteric disruption that leads to instability of the hip. The condition typically presents with early or late instability and dislocations, gait abnormalities, and pain. Diagnosis can be made with an appropriate clinical history and exam findings including a Trendelenburg gait, and a review of plain radiographs. MRI can be used to evaluate integrity of the abductor mechanism. Treatment is dependent on the etiology of the deficiency but options include nonoperative management, repair of abductors or trochanter fracture, or reconstruction of abductor muscle complex. Epidemiology Incidence 0.08-22% in first 12 months Demographics female > male increased incidence with age Etiology Pathophysiology failure of abductor repair more common in anterolateral or direct lateral approach to hip iatrogenic superior gluteal nerve injury more common in anterolateral or direct lateral approach to hip recommended to avoid splitting gluteus medius too proximal (>5cm proximal to greater trochanter) SGN injury can occur from vigorous acetabular retraction or extreme leg positioning decreased femoral offset decrease in offset >5mm decreases myofascial tension and abductor strength shortened neck low neck cut or short prosthetic neck length (or both) shortens abductor muscle length, resulting in functional abductor weakness will also decrease offset, weakening abductor complex periprosthetic greater trochanter fracture intraoperatively or postoperatively greater trochanteric escape often a result of failed trochanteric fixation after revision THA or a result of trauma adverse local tissue reaction metal-on-metal hips may cause abductor deficiency secondary to metal debris with destruction of abductors prior spine surgery causing compression of the superior gluteal nerve Anatomy Abductor muscle group gluteus medius originates on the ilium between anterior and posterior gluteal lines inserts on posterior aspect of greater trochanter of proximal femur innervated by superior gluteal nerve abducts and internally rotates the thigh gluteus minimus originates on the ilium between anterior and inferior gluteal lines inserts on anterior aspect of greater trochanter innervated by superior gluteal nerve abducts and internally rotates the thigh tensor fascia lata (TFL) originates on the iliac crest and anterior superior iliac spine (ASIS) inserts on the iliotibial band and proximal tibia innervated by superior gluteal nerve abducts, flexes, and internally rotates the thigh Nervous System the superior gluteal nerve innervates the abductor muscle complex L4-S1 contribution exits the pelvis superior to piriformis in greater sciatic notch runs in gluteus medius fascia approximately 5 cm proximal to greater trochanter Classification Basic Classification System for the Unstable THA Type I acetabular component malposition Type II femoral component malposition Type III abductor deficiency Type IV impingement Type V late wear Type VI unresolved Advanced Classification System for the Unstable THA Type Acetabular Component Orientation Femoral Component Orientation Abductor-Trochanteric Complex Impingement Late Wear Type I Incorrect Correct Intact Absent Absent Type II Correct Incorrect Intact Absent Absent Type III Correct Correct Absent Absent Absent Type IV Correct Correct Intact Present Absent Type V Present Correct Intact Absent Present Type VI Correct Correct Intact Absent Absent Goutallier Classification of Fatty Degeneration of Gluteal Muscles Grade 0 Normal muscle Grade 1 Muscle contains some fatty streaks Grade 2 Fatty infiltration, but still more muscle than fat Grade 3 Equal amounts of fat and muscle Grade 4 More fat than muscle is present Presentation History onset, location, and duration of hip pain and limp episodes of trauma, subluxation, dislocation history of anterolateral or lateral approach to hip Symptoms pain over greater trochanter area trendelenburg gait instability dislocation Physical exam inspection deformity swelling leg length discrepancy palpation of a defect in abductors may be present in traumatic cases abductor strength testing patient in lateral position examination with knee bent and extended bending knee will remove tension from IT band, excluding it as a cause of pain Trendelenburg gait defective abductors will cause the contralateral side to droop during stance phase on the affected leg abductor lurch as patient places center of gravity over affected hip Trendelenburg test examiner stands behind patients, observing iliac-crest height between left and right site, patient raises nonstance leg off the ground with the hip in 30° of flexion positive when patient is unable to maintain pelvic elevation for 30 seconds, or the pelvis droops Imaging Radiographs recommended views AP, lateral hip standard hip radiographs to evaluate component status, osteolysis, offset findings evaluating implant positioning, offset, osteolysis presence of greater trochanter fracture CT indications evaluating alignment of components findings safe zone for THA implants acetabular anteversion: 15°-25° acetabular lateral inclination: 35°-45° femoral stem anteversion: 15°-20° MRI indications gold standard for visualizing abductor tears views axial T1 sequence coronal T2 sequence metal artifact reduction sequences may be helpful findings advanced fatty atrophy and signal changes of gluteus medius and minimus tendons fatty atrophy of the anterior two-thirds of the gluteus minimus is common in unaffected hips hyperintensity superior to greater trochanter on T2 images sensitivity and specificity 73% sensitive, 95% specific Studies Labs must rule out infection in setting of dislocation or pain white blood-cell count, C-reactive protein, Erythrocyte sedimentation rate (ESR) arthrocentesis, cultures Electrophysiologic studies EMG studies may be helpful to confirm and quantify a superior gluteal nerve injury Treatment Nonoperative physical therapy with serial radiographs or EMG indications greater trochanteric fracture with less than 2 cm displacement superior gluteal nerve palsy secondary to surgical approach or technique partial tears or avulsions Operative component revision indications decreased femoral offset or neck length causing abductor insufficiency intact abductor musculature and superior gluteal nerve technique goal of component revision is to restore proper abductor hip tension by restoring head offset or neck length conversion to a constrained liner indicated in patient with inadequate abductor complex function but appropriate component alignment abductor muscle repair indications adequate gluteus medius muscle belly is seen on MRI abductor avulsion techniques direct abductor repair with or without TFL augmentation outcomes early repair (<15 months) associated with better outcomes obesity associated with worse outcomes gluteus maximus transfer indications abductor complex is irreparably separated or missing patient must have normal donor musculature technique advancement of gluteus maximus or vastus lateralis can be performed with or without tensor fascia lata transfer some authors will transfer the posterior portion of the TFL to the greater trochanter with the gluteus maximus for increased repair strength flaps are attached and tensioned in abduction greater trochanter advancement (Charnley tensioning) indications appropriate component alignment adequate distal bone surface for bony fixation and healing intact superior gluteal nerve technique perform trochanteric osteotomy, distalize the greater trochanter on lateral femur and fix with cables, wires, or claw-plate complications nonunion of greater trochanter increased risk on nonunion if trochanter shifted > 2 cm distal augmented repair indications appropriate component alignment inadequate excursion of abductor muscle complex for direct repair salvage procedures require viable trochanteric bone for anchorage technique achilles tendon with calcaneal bone block allograft acellular human dermal allograft latissimus dorsi tendon transfer synthetic mesh Techniques Nonoperative management indications partial abductor tendon tear or avulsion with intact abduction greater trochanteric fracture with less than 2 cm displacement superior gluteal nerve palsy secondary to surgical approach or technique technique physical therapy greater trochanteric fracture no active abduction exercises until fracture healed partial weight bearing platelet-rich plasma injections for partial tears or avulsions efficacy has not been proven SGN palsy serial EMG used for diagnosis and assessment of recovery spontaneous recovery seen in 95% of patients up to 2 years after THA component revision indications inappropriate component positioning causing abductor insufficiency intact abductor musculature with intact superior gluteal nerve technique ideal implant position ideal acetabular inclination = 35°to 45° ideal acetabular anteversion = 15° to 25° ideal femoral anteversion = 15° to 20° increase head offset offset is distance form center of femoral head to center of stem higher offset lateralizes the femoral stem, increasing tension on abductor mechanism for higher stability offset can be adjusted by using higher offset stem moderns systems feature high offset stems that allow increasing offset without increasing vertical height disadvantage includes over tensioning abductors and trochanteric bursitis increase femoral neck length short neck length causes decreased abductor muscle length and effective abductor deficiency adjusted by modular heads with variable internal bores for increasing neck length addition of neck skirt may be necessary to fully engage morse taper in smaller heads (<32 mm) increase femoral head size larger femoral head size will increase jump distance, increasing hip stability jump distance is the distance the head must travel to dislocate out of acetabulum (radius of femoral head) larger femoral head will increase head-neck ration, leading to a larger arc of motion before impingement larger heads have an increased volumetric wear with theoretical increased risk of debris formation complications trochanteric bursitis theoretical increased wear with increased femoral head size conversion to constrained liner indications multiple dislocations with inadequate abductor complex function but appropriate component alignment recurrently dislocating appropriately positioned dual mobility constructs neuromuscular disorders or poor compliance best indicated in elderly, low-demand patients who are not amenable to soft tissue repair design prevent dislocation by holding the femoral head in the acetabular component, compensating for deficient abductors locking ring past the equator of femoral head keeps femoral head in socket constrained liners result in a reduced primary arc of motion increasing risk of impingement can be used without the need to revise well-fixed and well-positioned acetabular components technique ensure appropriate placement of acetabular shell polyethylene liner is placed into acetabular shell inner liner or femoral head component is secured with a locking ring postoperative protocol some authors elect for hip abduction bracing for 6 weeks to prevent increased range of motion and prosthetic impingement weight bearing as tolerated complications impingement (secondary to decreased arc of motion) is primary mechanism of failure constraining the cup puts higher forces across the construct, leading to increased polyethylene wear or mechanical cup loosening dislocation, although rare, often requires open reduction failure of locking ring mechanism abductor muscle repair indications abductor avulsion or complete tear visualized on MRI adequate gluteus medius muscle belly visualized on MRI recent (<15 months) primary THA intact superior gluteal nerve technique approach repeat lateral approach abductor release gentle elevation of abductors from lateral pelvic wall elevation limited to 3-4 cm superior to joint line to avoid damage to SGN abductor tensioning and fixation suture abductor tendon ends with nonabsorbable suture in Bunnel-type technique transosseous tunnels made in greater trochanter abductors sutured into greater trochanter in slight (20-30°) abduction post-operative protocol hip is maintained in 20-30° of abduction and 15° of external rotation for up to 3 months weight-bearing as tolerated active abduction exercises delayed until 6 weeks postoperatively outcomes early repair (<15 months after primary) associated with better outcomes obesity (BMI > 30 kg/m2) associated with worse outcomes complications repair failure SGN iatrogenic injury over or undertightening repair gluteus maximus transfer indications abductor complex is irreparably separated or missing patient must have normal gluteus maximus technique approach standard posterior approach parallel to gluteus maximus with 10 cm distal extend to greater trochanter gluteus maximus release split gluteus maximus in line with fibers in middle third for half the length of the muscle release gluteus maximus fascia from fascia lata up to iliac crest release glutues maximus flap off underlying gluteus medius and minimus gluteus maximus tensioning and fixation the anterior half of the gluteus maximus is transferred to greater trochanter by suturing the muscle into greater trochanter under the vastus lateralis osteotome used to make 4-cm long trough in lateral cortex of greater trochanter drill holes in lateral trochanteric trough suture gluteus maximus flap into greater trochanter with nonabsorbable suture flap is attached and tensioned in slight abduction post-operative protocol 6 weeks of touch-down weight bearing with two-handed support full weight bearing and standing abduction exercises can begin at 6 weeks post-operative cane use encouraged for 1 year post-operatively complications failure of repair over or under tightening of repair greater trochanter advancement (Charnley tensioning) indications appropriate component alignment adequate distal bone surface for bony fixation and healing intact superior gluteal nerve, intact abductors greater trochanteric fracture with > 2 cm of displacement technique osteotomy while protecting insertion of abductors, osteotomy made of lateral aspect of greater trochanter advancement and reaatachment greater trochanter is advanced distally to tension abductors, 1-2 cm greater trochanter is reattached and fixed with figure of 8 tension-band wires or a claw palte post-operative protocol nonweight bearing for 6 weeks in hip abduction brace to limit tension on repair serial radiographs to evaluate union average time of healing of 5 months complications nonunion of greater trochanter (trochanteric escape syndrome) increased risk on nonunion if advanced > 2 cm achilles allograft indications appropriate component alignment inadequate excursion of abductor muscle complex for direct repair technique allograft tendon is woven into abductor muscle complex tendinous portion of achilles graft is sutured into remaining gluteus medius musculature calcaneal bone block graft is inserted into greater trochanter inserted in a dovetail fashion, secured with heavy wire or cable complications graft failure Complications Greater trochanteric escape greater trochanter pulls away from proximal femur as a result of failed trochanteric fixation or trauma Heterotopic Ossification more common in direct lateral approach Superior gluteal nerve injury more common in anterolateral or direct lateral approach to hip recommended to avoid splitting gluteus medius too proximal (>5cm proximal to greater trochanter) Recurrent instability Abductor repair or hardware failure Persistent Pain may occur with effective abductor insufficiency after inadequate repair