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Protrusio acetabuli and inflammatory hip disease

Protrusio on plain film and inflammatory arthropathies affecting the hip

29 questions 2 source pages 1 images 1 fact-check flags

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29 questions
Q1Describe the X-ray findings in ankylosing spondylitis with hip arthropathy.📷▸
G g spondylitis
G g spondylitis
  • Decreased joint space over bilateral hip joints, R > L, with OA changes
  • Pelvis extended, like an outlet view
  • SIJ fused
  • Diagnosis: AS with hip arthropathy
Q2How do you diagnose ankylosing spondylitis?▸
  • Modified New York criteria 1984: 1 clinical + 1 radiological criterion
  • Back pain > 3 months improving with exercise, not relieved by rest
  • Limited chest expansion; limited lumbar spine ROM in coronal and sagittal planes
  • SIJ involvement: bilateral grade 2-4 or unilateral grade 3-4
  • SIJ XR grades: 0 normal, 1 suspicious, 2 erosion/sclerosis, 3 narrowed joint space, 4 fused
Q3How common is hip involvement in AS and why is the pelvis tilted?▸
  • 30% of AS have ankylosis of both hips; 90% have bilateral involvement
  • Loss of lumbar lordosis and fixed thoracic kyphosis -> pelvis hyperextended (outlet view)
  • Fixed hip contracture -> pelvis flexed (inlet view)
Q4Describe the distraction provocation test for the SIJ.▸
  • Patient supine
  • Examiner applies posterolateral directed pressure to bilateral ASIS
  • Positive = reproduction of pain
Q5Describe the compression provocation test for the SIJ.▸
  • Patient side-lying
  • Examiner compresses the pelvis, pressure over the iliac crest directed at the opposite iliac crest
  • Positive = reproduction of symptoms
Q6Describe the thigh thrust test for the SIJ.▸
  • Patient supine, hip placed in 90 deg flexion and adduction
  • Examiner applies posteriorly directed force through the femur at varying abduction/adduction angles
  • Positive = reproduction of buttock pain
Q7Describe the sacral thrust test for the SIJ.▸
  • Patient prone
  • Examiner delivers an anteriorly directed thrust over the sacrum
  • Positive = reproduction of pain
Q8Describe Gaenslen's test.▸
  • Patient supine with the symptom leg hyperextended below the bed, asymptomatic leg flexed
  • Press on the hyperextended leg
  • Positive = reproduction of pain
Q9What are the surgical difficulties in THR for AS and how can you tackle them?▸
  • Pre-op: stop biological agent, assess lung and heart function, ulcer prophylaxis; C-spine XR r/o C1/2 instability, may need fibre-optic intubation
  • Ortho: decide hip or spine first - usually hip first; expect more bleeding, inform anaesthetist +/- cell saver
  • Intra-op: careful positioning (trunk vertical axis parallel to table), posterior approach, sliding trochanteric osteotomy, protect sciatic nerve
  • Acetabulum: identify true floor using TAL (Beverland); graft protrusio; set version for tilted pelvis - if PT<20, decrease cup 5 deg for every 10 degrees beyond 20 deg PT; aim combined anteversion 35 deg
  • Post-op: HO risk 10%, anterior dislocation, pneumonia, DVT prophylaxis
Q10What is the sequence and rationale for surgery in an RA patient?▸
  • 1. Life saving (C1/2 instability)
  • 2. Function (ruptured tendon, acute carpal tunnel, most painful joints)
  • 3. Sure win procedure
  • 4. Lower limb: foot > hip > knee - Foot – eliminate ulcers as source of infection; THR improves flexion range for TKR (typically delay TKR for 6 month due to risk of dislocation)
  • 5. Upper limb: proximal to distal
Q11What do you assess in a patient with AS?▸
  • Treatment and control of AS
  • Associated conditions - Ortho: spine; Others: chest expansion, eye, heart
  • Function: walking, sitting, gaze
Q12What are the ASAS classification criteria for spondyloarthritis?▸
  • > 3 months back pain + age < 45
  • SI joint on imaging (MRI+ or definite XR by modified NY criteria) + >= 1 SpA feature, OR HLA-B27 + >= 2 SpA features
  • Sensitivity 82.9%, specificity 84.4%
  • SpA features: inflammatory back pain, arthritis, enthesitis, uveitis, psoriasis, dactylitis, IBD, good NSAID response, family history, HLA-B27, elevated CRP
Q13What are the medical and anaesthetic pre-operative considerations in THR for AS?▸
  • Medical: stop biological agent; assess chest (lung function test) and heart (echocardiogram); ulcer prophylaxis
  • Anaesthetist: C-spine X-ray to rule out C1/2 instability
  • Limited C-spine range may need fibre-optic assisted intubation; assess TMJ condition
  • Expect more bleeding - inform anaesthetist +/- cell saver
Q14What positioning and draping issues arise in THR for AS?▸
  • Cautious during positioning, especially over the neck
  • Trunk vertical axis (ear to greater trochanter) parallel to the OT table with eye level perpendicular -> functional axis used as reference for anteversion
  • Good padding of all pressure points
  • Draping difficult in an adducted position with immobility of the other side (may need to break table)
Q15How do you manage exposure and soft tissues in THR for AS?▸
  • Consider posterior approach (better exposure, lower risk of anterior dislocation)
  • Difficult exposure: sliding trochanteric osteotomy to increase exposure (needs extensive soft tissue release; hip dislocation + soft bone = fracture risk; consider double cut osteotomy)
  • Sequential soft tissue release for scarring; protect the sciatic nerve
Q16How do you identify the true acetabulum in a fused AS hip?▸
  • Use TAL (Beverland) as landmark
  • Drill through the acetabulum and measure
  • Intra-op image intensifier
  • Protrusio may need bone graft/cage
Q17What femoral and post-operative problems occur in THR for AS?▸
  • Femoral preparation: risk of iatrogenic fracture; osteopenic bone may need a cemented implant
  • Post-op: high risk of heterotrophic ossification (heterotopic ossification) - previous hip surgery, complete ankylosis - 10%
  • Risk of anterior dislocation - hip precautions; contralateral fused hip causes compensatory flexed position -> stiffness and dislocation
  • Pneumonia with limited chest expansion; DVT prophylaxis
Q18Hip or spine first in AS? What is the rationale?▸
  • Controversial; lecturer usually does hip first - regains hip mobility to compensate for a stiff spine, may regain horizontal gaze, avoids high-risk spine surgery
  • Downsides of hip first: THR dislocation; kyphotic spine + fall -> spine fracture; catastrophic neurological complications during THR rehab
  • If spinal imbalance is severe such that THR will not restore horizontal gaze, restore spinopelvic harmony first
  • Individualized decision involving multidisciplinary input
Q19How do spinal flexibility and balance guide hip vs spine surgery and cup position (Phan, JBJS 2015)?▸
  • Depends on spinal flexibility and overall spinal balance
  • Stiff spine, normal balance: increase acetabular anteversion (avoid anterior impingement/posterior dislocation when sitting - the pelvis will not retrovert)
  • Stiff spine, unbalanced (retroverted pelvis): decrease anteversion (avoid posterior impingement/anterior dislocation when standing) OR do spine osteotomy first
  • Flexible, unbalanced spine: same as stiff unbalanced, but lean more towards hip first (more likely to regain horizontal gaze after THR)
  • Flexible, normal balance: unlikely in AS
Q20What are the risk factors for heterotopic ossification?▸
  • Patient: age > 60, male, previous HO, diseases (AS, DISH, hypertrophic OA, Paget's disease)
  • Injury: head injury, burns
  • Surgery: SP > Hardinge, extensive dissection, revision; posterior approach = lowest risk
  • Post-op: prolonged immobilisation
Q21What are the radiographic features of protrusio acetabuli?▸
  • Femoral head medial to the ilioischial line
  • Violation of the ilioischial line (> 3mm in men, > 6mm in women)
  • Decreased CEA (centre-edge angle)
  • LLD (leg length discrepancy)
Q22How is protrusio acetabuli classified and how does it differ from coxa profunda?▸
  • Hirst classification by degree of medial migration (distance between acetabulum and ilioischial line)
  • Lecture ranges: 5-10, 10-15, > 15mm
  • Not equal to coxa profunda: lateral border of the acetabular teardrop in line with or medial to the ilioischial line
Q23What are the causes of protrusio acetabuli?▸
  • Uncommon; rule out other pathologies
  • Primary: Otto's disease (arthrokatadysis)
  • Congenital: Marfan, OI
  • Metabolic: osteomalacia, rickets, osteoporosis
  • Inflammatory: RA, psoriasis, AS; Infection: TB
  • Others: migration of hemiarthroplasty, Paget's disease
Q24What are the aims and operative plan for THR in protrusio acetabuli?▸
  • Aims: stable, painless, mobile joint; restore vertical and horizontal offset and restore LLD
  • Choose hybrid THR with ceramic-on-PE articulation
  • Posterior approach, protect sciatic nerve; difficult dislocation - extensive capsular incision, may need in-situ osteotomy
  • Acetabulum: bone graft the floor and lateralise the hip centre; use TAL as reference; cementless cup with line-to-line fit; cemented standby
  • Femur: low level neck cut with enhanced offset to restore abductor tension; Dorr cc ratio > 75% -> cemented
Q25How do you manage the acetabular bone defect in protrusio acetabuli?▸
  • Essentially a IIc defect
  • Contained: morselized autograft from the femoral head
  • Uncontained: mesh + impaction bone graft technique, aim for peripheral fit
  • Large reamer first (hourglass deformity), do not deepen the acetabulum further
Q26What history and examination findings are relevant in protrusio acetabuli?▸
  • Hx: age, occupation, premorbid walking, PMHx
  • Hx: pain and functional limitations
  • Local PE: soft tissue, scar, sinus, ROM, FFC
  • Systemic PE: LLD, gait, nerve exam, scoliosis, pelvic obliquity, knee FFC, ankle equinus
Q27What investigations are needed in protrusio acetabuli?▸
  • Bloods
  • CT
  • Scannogram
  • Mx: conservative or operative
Q28What general technical principles apply to THR in protrusio acetabuli?▸
  • Soft bone - careful reaming and broaching
  • Bone graft the floor and lateralise the hip centre; use TAL as reference
  • Cementless cup line-to-line; cemented standby
  • Restore abductor tension: low level neck cut with enhanced offset femoral component
Q29How is reduction and rehabilitation managed after THR for protrusio acetabuli?▸
  • Release soft tissue (gluteus maximus, anterior capsule, iliopsoas) before reduction
  • Rehab: hip precautions
  • Rehab: FWB (full weight bearing)

Fact check

HIRST classification grades protrusio acetabuli by medial migration of 5-10, 10-15 and >15mm — incorrect ranges — Hirst grading is gender-specific by acetabulum-ilioischial line distance: men 3-8/8-13/>13mm (grade III with fragmentation); women 6-11/12-17/>17mm. The 5-10/10-15/>15 grouping resembles other classifications — source
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