Hip Arthroplasty

Pre-Admission clinic pre-op (for patients admitted prior to ‘day of surgery’)

  • Skin preparation: Night prior to and morning of operation, patient to wash leg, hip and pubic area to midline with sponge provided in the pre-admission clinic. Betadine Skin test occasionally is used if suspicion of allergy to iodine.
  • Bowel Prep: Glycerin suppositories will be provided at the pre-admission clinic. Patient to administer evening prior to surgery (instruction leaflet given at the pre-admission clinic).
  • Investigative procedures: FBC, MSU, MBA Group & Hold, Hep B, Hep C, HIV If patient donating to Bone Bank, add CMV, EBV and Syphilis. ECG, CXR, when requested and Results to be faxed to Doctors Rooms.
  • Patient education: Physiotherapy assessment will include: instruction of gait training, use of crutches and pre and postoperative exercises. Patient will be fitted for crutches to take home and practice preoperatively.

DAY OF SURGERY

Skin preparation:

  • Clipping will be performed on ward.
  • Area to be prepared extends from the iliac crest, laterally down the hip and thigh to the knee (i.e. side of leg only). Do not clip pubic/genital region.
  • Betadine skin prep to above area and wrap.
  • All x-rays to be sent with patient to theatre.

Prophylactic therapy:

  • Fragmin, 1st dose to be given on induction.
  • IV Flucloxcillin1g, 1st dose to be given in theatre (check for allergies).
  • Gentamicin 240mg prior to insertion of IDC in OT (check for allergies) (IDC for obese women only).
  • Venous thrombo-embolism prophylaxis.
  • Sequential Compression Device (SCD) to commence in theatre.
  • Anti-Embolic stockings (to be worn to theatre).

POST OPERATIVE

Medications:

NB: post operative medications listed on this protocol must not be administered unless they are written on appropriate medication chart and signed by the doctor.

  • Analgesia: Endone (as per doctors orders), then digesic / panadeine forte (as per Doctors orders).
  • Prophylactic therapy: IV antibiotics as ordered, Fragmin daily until discharge as ordered by the doctor, Patient to wear anti-embolic stockings for 6 weeks, SCD to continue for 48 hours, Calf Exercises.
  • Investigate procedures: FBC, MBA 1st Post-operative day and Check X-ray 1st post –operative day.

Activity:

Follow clinical pathway unless otherwise staged by Dr Al Muderis. Elevate foot of bed.

Day 1

Exercises in bed, up with physiotherapist (drains in) late am or pm at physiotherapist discretion using FASF, WBAT, Sit out of bed as tolerated.

Day 2 on

 Progress mobility with physiotherapist.

Day 3

Commence hydrotherapy at physiotherapist discretion & commence crutches as able.

Day 4-6

 Education handouts given ‘Care of hip’ + ‘Home Exercise program’. Stair practice and discharge information should be given.

***Patient should have raised bed, chair and toilet***

Day 4

*Special* - Patient to be dressed in ‘day clothes’.

Drains: Doctor will order removal at 24hrs and IDC 36hrs at 12 MN ABT drains not be on ‘free drainage’.

Wound Management: Change dressings when drain removed and then review twice daily and re-new PRN. Waterproof dressing for showering, and hydrotherapy, Re-apply steri-strips as necessary. Re-dress with Island Tegaderm, Sutures end clipped Day 7.

Day 5-7

Discharge: Directly home if patient is independent with ADL’s, Dopplers before discharge, Patient may be discharged earlier if being transferred to a rehabilitation facility. Follow up appointment to be made with Dr Al Muderis (6 weeks following discharge) and outpatient physiotherapy/hydrotherapy.

THR Technique Incision

Centred on tip of GT.

Superficial dissection

Cut down to fascia.
Use a sponge to spread fat from fascia.
Make a small split in fascia with knife and extend with scissors.
Distally in fascia – make sure it extends enough distally.
Proximally in line of fibres of Gluteus maximus.
Insert Charnely hip retractor.
NB – we use it with D at knee, Charnley actually had it other way.

Deep dissection

+/- excision of bursa.
Place the foot on the Mayo table, IR of the femur.
Use a sponge to wipe fat etc off the short ER’s.
Put a Langenbeck under the Gluteus medius, pulling proximally.
Use a Bristow to identify the plane between Superior Gemellus and Gluteus medius.
May need to use diathermy to make a small incision in the region of this plane to identify it clearly.
Pass a sharp Homans in to this plane, under gluteus minimus over the superior joint capsule.
Put a 1-Vicryl stay suture into Piriformis, and pulling on this suture use diathermy to detach the short ER’s from the Piriform fossa.
Stay as close to bone as possible.
Assistant should be IR’ing the femur.
May need to take upper portion of Quadratus femoris and some of Gluteus maximus insertion.
Use a Bristow to complete sweeping the ER’s from the capsule.
Incise the capsule.
Various techniques:
Simple longitudinally – make sure you extend proximally and distally enough.
T-incision – needed if hip is tighter.
Dislocate the hip.
If unable to dislocate may need to release more soft tissue, cut the femur in situ.
Use template to give rough idea of direction.
Get height of the cut correct – can always correct the version of the cut later.
To get head out use corkscrew or cut the head in half and remove piecemeal.

Femur initial preparation

Dr Morris uses ‘Christmas tree’ reamer to open femur BEFORE cutting the neck.
Get as lateral as possible.
It often comminutes the proximal, posterior femur.
Then use T-handle reamer to fully enter shaft, and use a bone spike to feel all 4 walls to confirm intramedullary position.
Cut the neck.
Measure height from the LT using templating to give correct height.
Use the guide to give direction of the cut.
Place a Homan’s under the proximal neck.

Acetabulum

Get leg off the Mayo, and let it rest on other leg.
Complete capsulotomy.
Often need to incise the inferior capsule which is usually tight.
May need to make other radial cuts in capsule as needed.
Place the retractors:
- Spiked Homan’s anteriorly – this will lift femur up and away.
- ‘Fag retractor’ or Homans inferiorly (region of acetabular notch).
Charnley spikes:
- Superior.
- +/- Posterior – hammer into ischium. Be very careful of Sciatic nerve – stay on bone and be careful of the pin sliding posteriorly as it is hammered in.
View of the acetabulum.
Must have a complete view of the bony rim.
This requires removal of the labrum circumferentially.
Use Charnley curette to get soft tissue out of base so that the true floor can be viewed.
Ream.
Orientation is crucial.
15-20 degrees anteverted.
40-50 degrees open.
Most common error is to not be anteverted enough.
Usually try to recreate the position of the native acetabulum.
Initial ream is medial until the true floor is reached.
Successive reaming is to expand the cup.
Finish when bleeding bone is reached circumferentially.
Size to ream is determined by the prosthesis: 

  • Smith and Nephew “Reflection” cups. (Standard reflection cup) is circumferential.Under-ream by 1-2mm.Trial with a cup 1mm under the final size.
  • Interfit cup – is 1.8mm wider at the circumference than in the base, thus need to ream line-to-line. Is used when you have a deficient medial bone, and you are depending on rim fit.

Insert the cup. Take care with orientation. Ensure it is down. Listen to tone. Check depth in screw hole. If using screw hole have them orientation in the ‘Safe quadrant’.

safe quadrent

Divide into 4 quadrants by a line drawn from the ASIS to the middle of the acetabulum, and another line perpendicular to this.
The safe quadrant is the posterosuperior one.

Femur

Place a Raytec in the cup to protect it.
The assistant puts the leg vertically, and holds 2 Homan retractors, under the neck of the femur.
Another is placed over the tip of the GT holding the abductors out of the way.
Prepare the femur.
Box osteotome.
T-handle reamer.
Sequential reaming – STAY LATERAL.
Broaching.
Stay lateral.
Control version (15 degrees of anteversion) on the way in AND out.
Increase size until cortical bone is reached – often a little cancellous bone in the region of calcar – this is positive.

Trial

Assess for:

  • Length – this can be difficult.
  • Impingement – remove any osteophytes which impinge through ROM, as they will lever the hip outwards.
  • Stability - Put in extreme positions. Check for degree of ‘Pistoning’. Positioning of components. Put leg in 30° flexion, 30° IR, neutral abduction – the head should be sitting circumferentially in the liner.


THR design 

History

1st – Wiles, 1938, stainless steel.
Mckee-Farrar – CoCr (Austin-Moore with a CoCr cup fixed with PMMA), then metal on poly.
Charnley 1962.
Muller – Curved stem, avoiding the need for a trochanteric osteotomy.
Exeter – 1972.
Original theory.
Polished stem because of industry standard production at the time.
No collar – as it was observed that in collared stems where the collar did NOT touch the calcar the results benefitted.
Double taper – thought to be optimal shape for forcing cement extrusion into bone.
Metal centralizer.
1976 – Changed to Matt finish, failure.
Wear at interface changed from fretting at the implant side, to abrasion at the cement side.
1986 – Converted back to polished.
Plastic centraliser with air in the tip introduced with the importance of subsidence into the cement for longevity recognised.
1988 – Modularity introduced.

Biomechanics

3X Body Weight (BW) when walking.
Abductors generate force of 2.5X BW during single stance.
Charnelys theories:

  • Medialise the Centre Of Rotation (COR) to joint reaction forces.  This is no longer done.
  • Lateralise the GT osteotomy to abductor lever arm.  This is no longer done.
  • Minimise frictional torque via small head.  This is no longer used.

Femoral load.
Peak stresses are either proximally, or at the tip.
Flexible stem, more proximal loading.
Flexibility also interface stresses with stem flexibility.
Stiff stem, more distal loading.
Any unloading of the proximal femur compared with the native hip will result in proximal stress shielding.  The less proximal load, the more stress shielding.

Polyethylene

Each stem generates 500,000 particles.
Particle size of 0.5-10m are needed to induce osteolysis, via stimulating macrophages to produce IL-6.

Sterilisation
Gamma irradiation chain scission followed by one of 2 possible reactions depending on the environment.
1) In air – Oxidation - poor physical characteristics.
2) In inert gas – Cross-linking improved characteristics (tougher/less abrasion, however more brittle).

Cement

Components of PMMA.
Liquid.
Methylmethacrylate monomer.
Hydroquinone – a polymerisation inhibitor (to prevent premature polymerisation due to heat or light).
N,N-dimethyl-p-toluidine – accelerates polymerisation and offsets the effects of the hydroquinone once polymerisation has begun.
Powder.
PMMA or blend of PMMA + PMMA-polystyrene or PMMA-methacrylic acid.
The copolymers provide more toughness to the cement.
Dibenzoyl peroxide.
An initiator which starts the liquid polymerising.
Overcomes the hydroquinone inhibitor.
BaSO4 or ZrO2.
Radio-opaque.
There is high polydispersity (Mw/Mn) indicating a broad range of molecular weights.

Reaction on mixing
The methylmethacrylate monomers are linked during polymerisation.
The original C=C double bonds in methylmethacrylate are broken.
New C-C single bonds are formed in the polymer chain.


Titanium  

Advantages

  • Less corrosion – due to TiO coat.
  • High biocompatibility – bone ingrowth occurs without formation of a fibrous layer.
  • Lower modulus – 50% of SS.

Disadvantages

  • High notch sensitivity - crack propagation and implant fracture.
  • Soft – not good as an articulation.
  • Suitability for porous coatings.

Metal-on-metal

Advantages

  • Low wear rates.
  • Linear wear rates of 25m in first year, and continues with 5m/year thereafter – 20 less than metal on poly.
  • Volumetric wear of 0.3mm 2/year – 60 less than poly.
  • Less biological response to the wear particles.
  • Smaller particles - less foreign body reaction.

Disadvantages

  • Risk of effect of metal ions in local and systemic tissues.

Ceramic on ceramic

Zirconia – This can articulate with ploy, but NOT with itself.
Alumina – This can articulate with itself.

Advantages

  • Hardness
  • Wettability

Disadvantages

  • Fracture 
  • squeaking 

Wear

Mechanism of wear
Adhesion – bonding occurs between surface particles when they are pressed together, and then as they move some particles are taken off
Abrasion – asperites on the harder surface cut through the softer surface
Fatigue – cumulative stress which exceeds the fatigue strength of the material

Hip - adhesive and abrasive wear
Knee - fatigue wear (pitting and delamination)

Wear modes
Mode 1 – From motion at the intended articulation.
Mode 2 – Primary surface articulating with something is not intended to articulate with; such as when the neck impinges on the acetabulum rim.
Mode 3 – 3rd body wear.
Mode 4 – From motion at secondary joint surface; such as at the taper, or backside wear in knee polyethylene.

Average wear rates
Head size, linear wear, with volumetric wear.
Bearing surface.
Metal on poly – 0.1mm/year (linear, 22mm head).
Metal on metal – 0.025-0.005mm/year.
Ceramic on ceramic.