Technique Considerations
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- It is the ratio of canal and calcar width measured at 3cm and 10cm from the middle of the lesser trochanter
- Dorr A = CC ratio < 0.5
- Dorr B = CC ratio 0.5-0.75
- Dorr C = CC ratio > 0.75 (canal width almost equals calcar width)
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- Orthopaedic Data Evaluation Panel with 3 key factors:
- Years of follow-up, strength of evidence (registry data being stronger), and presence of a star denoting benchmark replacement rate of less than 5% at 10 years
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- Linear wear rates (mm/year):
- MOP (conventional) - 0.1
- MOP (XLPE) - 0.05
- CoP - 0.05
- MoM - 0.005
- CoC - 0.0005
- Metal on original PE - 0.037 mm/year
- Metal on XLPE - 0.005 mm/year (however, particles are more submicron and thus more biologically active)
- Thomas et al. 7-year wear of XLPE. RCT with radiosterometric analysis
- Ceramic on Poly - 0.1 mm/year
- MOM - 0.01 mm/year
- COC - 0.002 mm/year
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- "I will use the posterior approach for 2 reasons:
- 1. I am familiar and trained in it.
- 2. It is extensile to deal with complications.
- I will be mindful to repair the posterior joint capsule and short external rotators attachment to reduce risk of dislocation."
- Kwon et al. 2006 systematic review – found comparable dislocation rates with AL, direct lateral and posterior approaches with soft tissue repair
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- Posterior advantages: No violation of abductor mechanism, better acetabulum exposure, similar dislocation rates if soft tissue is repaired.
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- There is no consensus on which is the better approach and literature is conflicted
- I am aware that AOJNRR found OVERALL no difference in revision rates for all approaches.
- But additionally:
- Data from Australian registry (Wayne Hoskins et al. JBJS 2020) suggests higher rate of early major revision for periprosthetic fracture/loosening
- 2019 Frank Stinchfield Award paper suggests higher rates of infection in anterior approach (2.2x) BUT AOJNRR shows lower revision rates for infection for Anterior approach
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- Swedish and Norwegian registry shows no difference in dislocation rates in posterior vs lateral approaches
- Norwegian registry
- Swedish Registry
- AOJNRR - overall no difference in revision rates for all approaches
- When I use the posterior approach, I will repair the posterior soft tissue to reduce the risk of dislocation. This is based on Kwon et al. 2006 systematic review – which found comparable dislocation rates with AL, direct lateral and posterior approaches with soft tissue repair
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- Ideal is to place the implant primary arc range within patient's functional range
- Lewinnek proposed Safe zones in 1978
- Cup inclination 40 ± 10°; anteversion 15 ± 10°
- Stem anteversion ~ 15°
- However, studies show that dislocations still occur even when implants are placed within these safe zones
- Recent publications suggest alternative methods such as the concept of Combined anteversion proposed by Dorr et al. in 2009. Target is 35° ±10°
- Without navigation, this can be assessed with the Ranawat Sign intraoperatively, though less accurately. Patient must be in lateral position with hip stabilized
- This is done by placing the operated leg in extension and internally rotating from neutral foot position until the base of femoral head is parallel to the acetabulum component
- This angle will be the combined anteversion angle. Target is 35° ±10°
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- Draw a line from the ASIS to the center of the acetabulum, then draw a perpendicular line to it
- Aim for the posterior-superior quadrant
- Dangers in the other quadrants:
- Anterior inferior – Obturator neurovascular bundle
- Anterior superior – External iliac neurovascular bundle
- Posterior inferior – Sciatic nerve (acceptable but use screws < 20mm)
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- Gruen Zones – 14 zones! Tip is in zones 7 and 11
- Cup - DeLee and Charnley Zones (3 zones)
- CEMENTED - Barrack and Harris Grading – radiolucency at the cement-bone interface
- A = Complete filling
- B = Radiolucent line <50%
- C = Radiolucent line >50%
- D = Complete radiolucent line (100%)
- UNCEMENTED - features of fixation
- "Spot-welding" - endosteal bone that contacts the porous surface of the implant
- No subsidence on serial radiographs (no migration)
Joint Registry and Implant Choice
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- It is a longitudinal collection of data on implants and outcomes from all surgeons in one region (i.e., all comers)
- The oldest is the Swedish Hip Registry, established in 1975
- The UK National Joint Registry was established in 2002 and is the largest registry
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- Hospital - identify trends in implant use and outcomes
- Individual Surgeon - track revision rates, compare to peers to identify outliers, and refine techniques
- Implant company - conduct post-market surveillance and recall faulty implants early
- Research - perform survival analysis
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- Large sample sizes - helps overcome bias
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- Outcome studied
- Outcome studied is revision - failures that don't result in revision aren't captured
- No patient reported outcome measures (only recently added to NJR)
- No radiological or clinical outcomes
- Quality depends on data entry - potential flaws include missing entries, unlinked entries, and case mix issues
- Fails to account for standards achievable by experts (since it includes all-comer data)
- Costly to maintain registry data
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- 3M Capital Hip
- It was marketed from 1991 to 1997, but performance concerns were only raised in 1995
- A surgeon survey found a 5% revision rate, which the implant company dismissed as "industry standard" before further monitoring led to the device's withdrawal
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- Hip Replacements
- < 70 years: no difference between hybrid vs. cementless
- > 70 years, NOF #: Cementless has higher revision rates than hybrid; no difference between hybrid vs. cemented
- All age groups: hybrid has lower revision rates than cementless; no difference between cemented vs. hybrid
- Age < 55: No difference between cementless vs. hybrid
- Age 55-64: No difference between cement vs. hybrid
- Age > 65: Cementless has higher revision rates than hybrid
- Age > 75: Cementless has higher revision rates than both cemented and hybrid
- The Australian Registry found no difference until after 10 years, but at 14 years, the revision rate was 8.5% (66,973 primary THA) with 36 mm heads and 4.6% (84,157 primary THA) with 32 mm heads. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6259905/)
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- Ankle replacement - 10-year survival 77%
- Total elbow Arthroplasty - 88%
- Reverse shoulder arthroplasty 94%
- Anatomical Total Shoulder Arthroplasty 93% (Young et al.)
- High Tibial Osteotomy and Unicompartmental Knee Arthroplasty 80% (Dettoni)
- Total knee replacement 95%
- Total hip replacements 95%
Implant/Approach Choice
What is your implant choice?
Answer opening: "My Implant choice based on basic science principles, my training, and registry data - categorized by fixation type"
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- Hybrid fixation, as this is what I am trained and comfortable with
- Cup -
- Cemented cups are theoretically vulnerable to shear forces, which is cement's weakness.
- However, I recognize that systematic reviews show no significant difference in survival rates
- Nevertheless, I prefer cementless cups to avoid shear stresses and allow for biological integration
- Stem
- My choice is the Exeter taper slip stem, a cemented stem with force-closed design for controlled subsidence
- I selected Exeter because it has an ODEP 15A* rating with at least 15 years of registry data and a benchmark replacement rate below 5% at 10 years
- My decision is supported by the Australian registry, which finds no difference in revision rates between hybrid and cementless fixation for patients under age 64
- For patients over 65, cementless fixation has a higher revision rate than hybrid fixation, especially in those over 75 years old, with 15-year revision rates of 7.9% vs 4.9%
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- [For all age groups]
- I will use Metal on XLPE (cross-linked polyethylene) for this patient
- This offers superior wear properties compared to non-XLPE on Metal
- I am aware of alternatives like Ceramic on poly or Ceramic on Ceramic, but they come at a higher cost. CoC also has unique failure mechanisms including squeaking, edge loading, patch wear, and risk of catastrophic failure
- My decision is supported by the Australian registry showing similar revision rates at 15 years
- 6.2% (MoP) vs 5.0% (CoP) vs 7.1% (CoC)
- Regarding XLPE vs non-XLPE
- 15-year revision rates were 6% vs 11%
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- Head size selection requires balancing wear and stability
- Larger heads improve stability but increase wear rates. According to the Australian registry, revision rates are lowest with 32mm head size
- I'm aiming for a 32mm head size, which has the lowest revision rates compared to smaller (<32mm) and larger sizes – per Australian registry data
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Whoever brings blessing will be enriched, and one who waters will himself be watered. Proverbs 11:25