Protrusio

 

Bilateral Hip Protrusio

 

Definition

 

Abnormal protrusion of the femoral head into the acetabulum

- centre edge angle > 40o

- protrusion of the acetabulum beyond ilioischial line / Kohlers line

 

Etiology

 

Primary 

 

Otto's Disease

- middle aged females

- ? related to osteomalacia / coxa vara

 

Secondary

 

PROFSHAMN

- Paget's

- Rheumatoid arthritis

- Osteomalacia / Osteogenesis imperfect

- Fracture / central dislocation

- Septic arthritis especially TB

- Hemiarthroplasty

- Ankylosing Spondylitis 

- Marfan's syndrome, malignancy

- Neurofibromatosis

 

Ansari et al Hip Pelvis 2024

- systematic review

- 783 cases

- most common cause inflammatory arthritis

- RA / psoriatic / SLE / ankylosing spondylitis

 

Sotelo-Garza / Charnley classification

 

Medial wall of acetabulum as ilioischial line

Grade I:   Mild protrusion  1-5mm                               

Grade II:  Moderate protrusion  6-15 mm                           

Grade III: Severe protrusion  >15 mm

 

Hip Protrusio Grade 1Hip Protrusio Grade 3Grade III Protrusio                          Grade I                                                  Grade II                                                          Grade III

 

Natural history

 

Can be progressive, especially with inflammatory causes

- chronic steroids

- osteomalacia

 

Management

 

A.  Skeletally immature 

 

Triradiate fusion +/- valgising osteotomy

 

Sponseller et al JBJS Am 2006

- 173 patients with Marfan's syndrome

- incidence protrusio 16%

- all protrusio developed in firths 2 decades of life

 

Steel et al J Pediatr Orthop 1996 

- triradiate fusion in 22 hips with Marfan's syndrome

- 12 of 19 restored to normal

 

B.  Young adult 

 

Valgising intertrochanteric femoral osteotomy (VITO)

- aim for 20-30° valgus correction

- if neck shaft angle is 130° aim for 155°

- trapezoid shortening to minimize LLD

 

Require soft tissue release especially psoas

 

C.  Middle aged / elderly

 

THA

 

THA Protrusio

 

Principle

 

1. Place hip center anatomically 

- reduces revision rates

 

Baghdadi et al CORR 2013

- THA in 162 hips with protrusio

- 89% survival at 15 years with uncemented cups

- increased revision risk with non anatomical hip center

 

2. Manage bone defects

- contained defect - morcellized bone graft

- uncontained defect / deficient medial wall - mesh / cage / reinforcement rings

 

Assess medial wall integrity with CT

 

Hip Protrusio CT Medial Wall IntactHip Protrusio CT Medial Wall Intact 2

 

 

Determine Hip Centre 

 

Hip Protrusio Teardrop Method Centre RotationHip Protrusio Ranawat Method Centre Rotation

 

1.  Teardrop

- average 2 cm vertical & 4 cm horizontal from teardrop

 

2.  Ranawat Method 

- draw parallel horizontal lines at the levels of the iliac crests and ischial tuberosity and mark 3 points

- Point 1: 5mm lateral to intersection of Shenton's and Kohler's lines

- Point 2: located superior to point 1 by a distance 1/5 of the pelvic height

- Point 3: similar distance horizontally from vertical line

- Isosceles triangle between 1/2/3 locates the acetabulum: line 2/3 through subchondral bone

 

Management Bone Defects

 

Algorithm

A.  < 5mm - no graft required

B.  > 5mm but medial wall intact - morcellised bone graft

C.  No medial wall - mesh / reinforcment ring / cage + morcellised bone graft

 

Hip Protrusio Grade 1THR Protrusio Type 1

No bone graft required

 

Hip Protrusio Type 3THR Protrusio Medial Morcellised Bone Graft

Medial wall intact, morcellized bone graft

 

Technique

 

Approach

- sciatic nerve is nearer the joint than normal - identify and protect early

- dislocation of the hip can be difficult -  in situ neck cut

 

Reaming

- enlarge rim only

- avoid creating peripheral defect

 

Contained acetabular defect

- morcellised bone graft

- rim fit uncemented cup

- cemented cup

 

Uncontained acetabular defect

- wire mesh / bone graft / cemented cup

- cage

 

Restore anatomical center

- intra-operative landmarks - acetabular rim

- fluoroscopy

- image less navigation

- CT guided navigation

- Robotic assistance