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- Creep is normal loading of the polyethylene cup and occurs superomedially.
- It is normal to see slight thinning in the weight-bearing area as the plastic molds itself. Abnormal loading creates pressure more laterally, resulting in polyethylene wear on the superolateral side.
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- According to UKNJR, aseptic loosening is the most common reason for revision.
- All primary THR – Aseptic loosening > Pain > Instability
- < 1 year THR – Instability > Fracture > Infection > Aseptic loosening
- > 1 year – Aseptic loosening > Pain > Infection > Instability
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- TRO INFECTION!
- TRO Extrinsic causes of pain!
- Features of loosening - start-up pain
- Classic features
- Pain on IR/ER - femoral component loosening
- Groin pain with resisted SLR - Acetabular loosening
- Hx =
- Features of sepsis - fever, pain
- Duration of symptoms? Pain-free interval since operation?
- Pain characteristics - start-up? groin/buttock? (acetabulum), thigh (stem)?
- Function
- Co-morbidities
- Initial operation - op notes, wound issues? antibiotic suppression?
- OTHER CAUSES OF THIGH PAIN - spine
- PE
- Inspection of wound, sinus/redness
- Gait - Trendelenburg
- LLD?
- Check ROM, neurovascular status
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- Bloods - TRO infection: FBC, CRP, ESR
- XR - AP/Lateral
- Long leg films
- CT scan - assess extent of loosening, bone stock
- Aspiration if any concerns of infection
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- Regarding the acetabular component
- Acetabular tear drop - integrity of medial wall
- Kohler line (ilioischial) - integrity of medial wall
- Ischial lysis - integrity of posterior column
- Vertical migration - integrity of superior dome
- Extent of migration - < 2 or > 2cm
- Regarding the femoral component
- Extent of metaphyseal/diaphyseal lysis
COMPLICATIONS
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- Approximately 50% have unknown etiology
- Compression from hematoma or intraoperative retraction
- Direct trauma from misplaced screws
- Limb lengthening exceeding 5cm
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- Peroneal division in 80% of cases [same pattern observed in hip dislocation]
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- MRI to evaluate for hematoma
- Early nerve conduction studies (NCS) and EMG
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- Acute phase - immediately flex knee with pillows to reduce tension
- Surgical evacuation if hematoma is present
- If MRI is normal → proceed with serial NCS
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- One-third of patients achieve full recovery, one-third partial recovery, and the remaining third show no improvement
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- No clear consensus exists on the optimal approach
- Meta-analysis comparing single-stage vs. two-stage procedures shows no significant differences in mortality, pulmonary embolism, cardiovascular complications, or infection rates
- Single-stage procedures demonstrate lower risk of deep vein thrombosis, shorter operative time, and reduced hospital stay
- Benefits: single anesthesia event, one hospital stay, and reduced overall costs
- Drawbacks: increased blood transfusion requirements, higher overall risk, and longer single operation
- Each approach offers distinct advantages and disadvantages that should be weighed according to individual patient factors and preferences
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Robotics/ Navigation
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- Image-dependent vs. imageless
- Image-dependent systems require CT scan/MRI to generate a 3D model, while imageless systems use intraoperative calibration of landmarks
- Passive vs. Semi-active vs. Active
- Passive systems have no haptic feedback; Semi-active systems provide surgeon guidance within constraints with haptic feedback; Active systems are fully automatic
- Closed vs. open platforms
- Closed platforms are paired with specific implants, while open platforms can be used with multiple brands
CEMENTED HIP Failure
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- Gruen's Mode of failure
- 1 = Pistoning A and B
- 1A = pistoning in cement
- 1B = cement pistoning
- 2 = Medial midstem pivot = distal + calcar toggling (Both proximal and distal loosening)
- 3 = Calcar pivot = distal toggling, but proximal stable (ONLY distal loosening)
- 4 = Bending cantilever = implant break at neck due to fatigue failure
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- This is an issue of fatigue failure due to cyclic stresses at the cement mantle
- This can be described with an S-n curve
- Stresses at the cement mantle that exceed the fatigue endurance limit of both the stem–cement interface and the cement material itself
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- Good alignment - avoid varus. Varus positioning leads to thin cement mantle in the proximal medial (Gruen zone 7) and distal lateral (Gruen zone 3) zones
- No cement voids - mix in vacuum and use pressurization (3rd gen)
- 3. Good cement mantle >2mm - use centralizers (3rd gen)
- However, be aware of the french paradox regarding cement mantle width. What is the french paradox?
CEMENTLESS HIP Failure
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- Assess according to Glassman and Engh 1992
- Divides fixation modes into 3 categories; these classifications determine ease of extraction
- If stable fibrous fixation = cannot be removed by simple disimpaction → requires ETO and burr
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- Uncemented - subsidence, pedestaling, progressive radiolucent lines, fracture
- Cemented - cement mantle fracture, change in implant position, radiolucent lines
REVISION PRINCIPLES
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- Looking at 4 lines - Kohler (ilioischial line), Roof, Tear drop and ischial lysis
- Acetabulum = Paprosky
- 1 = Minimal "undistorted hemispherical acetabulum"
- A - Superomedial
- B - Superolateral
- C – Medial - Protrusio but does not go past Kohler line
- 3A = "Up and Out"
- Moderate ischial lysis
- Medial tear drop intact
- Intact ilioischial and iliopubic lines
- 3B = "Up and In" - pelvic discontinuity
- Broken Kohler's line
- Extensive ischial osteolysis
- Loss of tear drop
- High risk of occult pelvic discontinuity
- Pelvic discontinuity
- Fracture line through both columns
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- Paprosky Classification
- 1 = minimal
- 2 = extensive metaphyseal loss, diaphysis intact
- 3A = diaphyseal loss > 4cm left
- 3B = diaphyseal loss < 4cm left
- 4 = no support in diaphysis
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- This is a complex revision case that can be divided into 3 phases
- Key goals: implant stability and hip stability
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- Anesthetic review - assess comorbidities and fitness for anesthesia
- Templating
- CT scan - to evaluate bone stock
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- "Moreland Extraction" set - comes with tools for removal
- "Trephination set" - core reamers to allow reaming into broken distal stem for removal
- Cemented - remove stems, then remove cement mantle with OSCAR US Cement removal system (if not removing cement, consider cement-on-cement revision)
- CEMENTLESS - Microsagittal saw blade, flexible thin osteotomes
- Acetabular Explant tool
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- Acetabular - structural grafts to augment lateral acetabulum, augments for 3B, triflange cage-cup constructs
- Femur - bypass the most distal defect by 2 × cortical diameter
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- Exposure – extensile posterior approach, release gluteus maximus, psoas tendon. Prepare for ETO (extended trochanteric osteotomy) - typically not needed for unstable fixation per Engh paper
- Longitudinal cut 12-15cm from greater trochanter
- Transverse cut leaving 2/3 of diameter
- Prophylactic cerclage 1cm below to prevent propagation
- Extraction WHILE PREVENTING PROXIMAL FEMUR FRACTURE –
- If cemented → can consider cement-on-cement revision
- Based on Glassman and Engh's Experience in 1992
- If XR shows unstable → likely no need for ETO
- If XR shows stable fixation → ETO likely needed
- First, remove all granulation tissue around neck
- Test stability by attaching extraction device to implant; give 4-5 firm blows. If not moving = STABLE → proceed to divide the bone-implant interface
- Use pencil burr or microsagittal saw to cut as far distally as possible
- Use thin flexible osteotome to create a plane between bone and implant
- Remove implant with a vice grip holder or a device around the collar
- Examine – assess bone loss
- Reconstruct – consider bone grafts from iliac crest
- Replace – based on Paprosky classification
- Rehabilitation – allow gentle toe-touch weight bearing with follow-up X-rays
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- Rehab - TTWB with follow-up X-rays
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- 1 = Hemispherical cup (Miller's textbook suggests 85% of cases can be revised with a standard larger hemispherical cup)
- 2A = Metal augments or structural graft e.g., bulk femoral head + hemispherical cup
- 2B = Restore superolateral loss with metal augments or structural graft e.g., bulk femoral head + hemispherical cup (like DDH)
- 2C = Restore medial bone stock with metal augments or structural graft e.g., bulk femoral head + hemispherical cup OR cup-on-cup revision with smaller cup as medial augment
- 3A =
- Replace defect with metal augments (Trabecular metal cup/oblong cups/jumbo cups (> 60mm)), column augment with screw fixation
- OR bone graft (ICBG + mesh + cemented cup)
- 3B = pelvic discontinuity = Tri-flange cage-cup construct with flanges to ilium, ischium, pubis
- Place cup, then cage on the cup, then PE cemented into the cup
- Acts as a scaffold for structural and morsellized bone graft
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- Key principle = bypass the most distal defect by 2 × cortical diameter
- 1 = Extensively coated stem
- 2 = Extensively coated calcar replacement stem
- 3A = Long modular tapered stem (distal fixation)
- 3B = Impaction Bone grafting (IBG) with cemented polished stem +/- cortical strut allograft
- 4 = IBG with cemented stem, megaprosthesis, Allograft-Prosthetic Composite (APC)
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- Optimize component positioning
- Restore anatomy - offset
- Increase head/neck ratio
- Constrained liner (aka captive cup)
- Convert to bipolar hemiarthroplasty
- Dual mobility bearing
Ceramic Catastrophic Failure
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- Ceramic is a brittle material, and fails by Crack initiation and propagation
- Microscopic cracks can occur from stress
- Cracks may become critical size and then
- Propagate through the structure in a fast manner, leading to sudden failure
- Failure occurs suddenly, soon after the yield point.
- This differs from ductile materials, where cracks gradually enlarge until the remaining area cannot support the load.
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- CT scan
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- This is a "Complex Revision" - requiring Pre op preparation and EEERRR Mnemonic
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- Prepare explant equipment
- Have another full implant set available in case all components need changing
- Revise as soon as possible to prevent ceramic fragments from further damaging metal tapers
- In the interim, patient must not bear weight to prevent taper damage
- Exposure - extensile posterior approach
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- Profuse joint lavage to remove damaged ceramic liner without scratching the metal shell of acetabular component
- Perform extensive synovectomy to remove as many ceramic fragments as possible
- Replace both components even if only one component failed
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- If stem morse taper damaged ➔ need to revise stem
- If cup damaged but stable ➔ revise cup; if too hazardous to revise whole cup, then use XLPE (plan for ceramic on PE)
- If any mal-alignment, replace components as poor orientation can lead to impingement and failure
- Reconstruct bone defect if present
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- Bearing choice is controversial
- Some authors suggest replacing with ceramic head again ➔ same hardness prevents 3rd body wear and not metal head because ceramic particles will ALWAYS remain and can lead to 3rd body wear of a metal head
- Other option is XPLE on Ceramic
- XLPE on metal is not recommended
- Rehab
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