Austin Moore’s ProsthesisTechnique

Vinod NaneriaGirish Yeotikar

Arjun WadhwaniChoithram Hospital & Research Centre,

Indore, India

The philosophy

• Proximal fixation of the implant is crucial in the success of the surgery.

• A tight fixation gives mechanical stability, and allow the grafts in the fenestration to consolidate, making it a self-locking device.

• This prevents over-loading of calcar – no subsidence, no loosening, no failure.

Painful AMP

• An AMP fails on the table.• Almost always the success of the surgery can

be predicted on the table.• Be prepared for change to plan “B” or “C”.• Be prepared for peri-operative calcar split.

Painful AMP- two primary reasons

• Inadequate Proximal Fixation– Loose Prosthesis– Calcar absorption– Subsidence of the prosthesis– Loss of varus alignment in the canal

• Acetabular cartilage erosion

Inadequate Proximal Fixation

• Not under our control– Elderly– Osteoporotic– Wide canal

• Under our control– Faulty operative technique– Over reaming by improper Rasp– Improper selection of Implant

Proximal FixationTips & Tricks

• Pre-operative assessment of the Canal.• Proper neck cut.• Avoid comminuting Calcar Femoris.• Save at least 1cm of neck at Calcar• Insert canal finder from Piriformis Fossa• In wider canal, avoid use of rasp.

Proximal FixationTips & Tricks

• Select proper Implant which will fill the proximal femur without increasing comminution.

• Use a artery forcep in the prosthesis proximal hole ( originally for extraction), for rotation control during insertion.

Proximal FixationTips & Tricks

• Impaction grafting:– The most important area is the medial side near calcar.

Graft should be inserted when nearly half of the prosthesis has gone inside.

– Fill the fenestrations of the prosthesis with bone grafts, as the prosthesis advances in to the canal.

– The color of the implant should not over-hang on the calcar.

– If done properly, it should rest on the neck and will compress the grafts.

Posterio-lateral incision in lateral decubitous position

Quadratus

Gemeli PiriformisSciatic NerveGluteus Maximus

Cut the rotators close to the bone

Incise the capsule in “T” shape

Measure the size of the head

Superior lateral neck attched to Gr. Troch must be removed

Neck Cut

Piriformis fossa as entry point

Bone grafts harvesting

Selection of Implant

• Pre operative planning• Intra-operative planning• Correct head diameter• Correct stem width• Correct length of collar• Cement• Tension band wiring

Variables - Implant

• Head size• Stem size• Collar width• Offset• Neck – shaft angle• Stem width • Number & size of stem holes

Prosthesis design:Proper OffsetStem DiameterNeck over hangFitness at proximal part

Half inserted prosthesis

Packing of graft in the medial wall

Graft in the distal hole

Grafts in the proximal hole

Final setting

Trochanteric index

Reduction by gentle pressure

Capsular repair

Post Op X-ray

Bone growth on medial side and in the fenestrations

AMP - summary• Pre operative planning• key to ensuring success is careful planning• It’s all in the mind• If you work on the surgery before hands on

mind in brief you can have both hand free and brain free surgery

AMP - Summary

• Femoral head size• Neck preparation according to AMP• Entry point • Reaming• Pack the bone grafts in fenestrations.• Impaction bone grafting

AMP - Summary

Post operative Regimen antibiotic – 24 hrs Abduction pillow Bed side sitting – 24 – 48 hrs Walking with support – 3rd – 5th day Weight bearing as tolerated

Failure & Success - Amp?

• Most AMP fails on the table • Subsidence and Loosening depends on

proximal fixation achieved on table• Once the proximal locking holes filled with

bone – the prosthesis is stable & long lasting.• Hypertrophy of medial side, lateral wall

hypertrophy, & new bone at the tip ensures long term success.