adult hip dysplasia Flashcards
define adult hip dysplasia
A disorder of abnormal development of the hip that can affect the acetabulum, the proximal femur and the surrounding soft tissues
Describe the relevant radiological measurements?
lateral centre edge angle
* assess superolateral femoral head coverage
* angle bwn vertical line from femoral head and femoral head to lat border of acetabulum
* <20 deg = dysplasia
* >40 deg = pincer type FAI
Tonnis angle
* Inclination of the WB portion of the acetabulum
* angle bwn horiztonal and WB surface of acetabulum
* >10 deg dysplastic
anterior centre edge angle
* assesses anterior coverage/ subluxation
* false profile view
* angle bwn line drawn vertically and from most anterior point of acetabulum
* <20deg = dysplasia
acetabular angle of sharp
* horizontal line through tear drop
* angle bwn tear drop line and line drawn to lateral margin of acetabulum
* normal is 33-38 deg
* dysplasia >38 deg
How do you classify adult hip dysplasia?
Hartofilakidis - classified according to whether hip enlocated in true or false acetabulum
* type 1 - dysplasia - femoral head contained in socked
* type 2 - low hip dislocation
* type 3 high hip dislocation
what deformities can arise with hip dysplasia
Femur
* small femoral head
* short anteverted valgus neck
* narrow canal
* small posteriorly displaced GT
Acetabulum
* shallow
* poor bone stock
* anteverted
**Soft tissues **
* elongated capsule
* hypertrophied psoas tendon
* transversely orientated abductors
* hamstring, adductors and rectus femoris muscles usually shortened
* Sciatic nerve shortened and femoral nerve/artery forced laterally, both vulnerable to injury
what is the role of CT in adult DDH surgery planning
Allows assessment of:
* bone stock
* morphology
* dimensions and orientation of the femur and acetabulum
* design of a custom femoral stem
* degeneration
Planning based on xray may lead to:
* overanteverted cup - if the abnormal acetabulum anatomy is followed too closely - leads to anterior instability
* Prox fem fracture during implantation of an uncemented stem in anteverted femur - not shown on xray
what are the management options for a young adult with DDH?
**non-op - no pain **
* symptom control
* shoe raise
**operative - pain - no arthritis **
Acetabular osteotomies
* Reconstruction - congruent, reduced hip with concentric femoral head
1.PAO - periarticular osteotomy - redirectional
* Salvage - for unreduced, incongruent hips with inadequate coverage
1. shelf
2. chiari
Operative - pain - arthritis
* THR
what does a periarticular osteotomy do?
Aims of surgery
* to achieve a congruent, stable hip joint, medialising the hip joint centre and reducing contact pressures
* to reduce pain, improve function and reduce uneven load through the hip
How:
* reorientates the acetabulum to enhance coverage of the femoral head
* multiple osteotomies around the acetabulum to cause a 3D change in shape
what are the advantages and disadvantages of a PAO?
advantages
* 3D correction
* increases acetabulum depth
* makes THR easier
* posterior column and pelvic ring left intact
disadvantages
* technically difficult
* adults only - triradiate closed
* needs a congruent, reduced hip with a concentric femoral head
what are the indications for performing a PAO?
- symptomatic acetabular dysplasia and persistent pain
- centre edge angle <25 deg
- congruent hip
- maintain hip flexion >110 deg
- no or minimal oa changes - tonnis 0-1
tonnis 1 - slight narrowing/ sclerosis
what are the considerations when performing a THR for DDH?
- approach
- low or high hip centre
- bone defect
- leg length discrepancy
- narrow femur
what are the considerations for the approach?
Approach
* need to be able to see both the true and false acetabulums
* risk of sciatic nerve injury
* extensile option
* posterior fine for mild dysplasia
* may need a trochanteric osteotomy
true or false acetabulum?
high or low hip centre
Position of the acetabulum, degree of anteversion, mode of fixation, component size and LLD needs determining preoperatively
low acetabulum:
Advantages
* restores length
* reduced JRF - reduced revision rate compared to false
* better function
* lower revision rates
* better bone stock
Disadvantages
* Bone graft for superior coverage of cup - risk of graft resorption
* need screws if uncemented cup
* Shortening subtrochanteric osteotomy of the femur - if >4cm lengthening
* technically difficult
**high acetabulum **
Hip centre located 35mm prox to the interteardrop line
Advantages
* avoid traction injury to sciatic nerve and need for osteotomy
* technically easier
* less need for graft
* component completed covered by native bone
*Disadvantages *
* small socket and thin poly only - wear risk & no ceramic insert as needs bigger socket
* small head - instability
* femoral-pelvic impingement in flexion/ extension
* increased sheer forces and risk of early loosening
* difficult revision surgery as bone stock not restored
what are the considerations for the femur?
- custom stem
- combined subtroch osteotomy - need long uncemented stem with fixation of fracture - cement interferes with fracture healing
- restoration of offset
what are tantalum augments?
Hemispherical augments used for acetabular defects - 2-3x more porous than cobalt chrome to allow bony ingrowth
why is cemented cup
