Uh/ Tamc Millers Adult Reconstruction

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Best bearings for hard-soft couple

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Co-Cr-PE

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Best bearings for ceramic components

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Alumina best. Zirconia bad- undergoes phase transformation -->changes surface roughness

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Hip lubrication type in hard-soft bearings

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Boundary (synovial fluid can't separate asperites)

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Indication for Ti alloy THA components

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Nickel allergy

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Best technique for polyethylene manufacturing

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direct compression molding

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Effects of calcium stearate on polyethylene

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Creates areas w/ unfused PE particles--> dec mechanical properties

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Advantages of PE cross-linking

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improves resistance to adhesive and abrasive wear

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Disadvantages of PE cross-linking

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Decreased: tensile strength/fatigue strength/fracture toughness/ ductility

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Effects of PE oxidation

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molecular chain scission. Accelerated PE wear/failure.

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Effects of crystallinity on cross-linking

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Only amorphous areas cross-link. If crystallinity over 70% then higher failure rates

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Particles generated hard-hard bearings

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more particles. Much smaller (0.015-0.12 micron). Run in period during first million cycles. Cleared locally via lymph.

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Lubrication type hard-hard bearings

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Mixed (boundary/hydrodynamic-completely separated). Hydrodynamic phase d.o. head size >38mm/velocity/roughness.

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Smoothness of bearings

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Ceramic>metal>>>PE

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Radial clearance

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Difference in radius of head and cup. Bigger head--> equatorial contact. Smaller head-->polar contact. Optimal <150 micron clearance- w/ polar contact with high bearing conformity.

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Stripe wear

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Seen w/ hard on hard bearings. Assoc w/ edge loading. Represents surface wear.

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Positions associated with hip edge loading

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heel strike/ stair climbing/rising from chair

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Third generation cement preparation

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Vacuum-->dec porosity. Pressurized cement. Precoated stem. Rough surface finish. Stem centralizer.

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Cement mantle

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2mm suggested. 2/3 rule: 2/3 canal filled w/ stem- 1/3 filled w/ cement. NO contact bet femoral stem and cortex

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Femoral component design cemented THA

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Stiffer preferred (elastic-->transfers stress to cement). Precoating--> no difference. Medial flange--> no difference.

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Porous coated components

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Bony ingrowth. Pore size 50-350 microns. Porosity 40-50%. Gaps < 50 microns

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XR findings of stem fixation

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Spot weld: inc bone density surrounding distal extent of porous coating (well fixed). Intramedullary pedestal: e/o loose components.

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Prime factor contributing to stress shielding

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Stem stiffness

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Factors affecting stem stiffness

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1. 4th power of stem radius. 2. metal (Co-Cr stiffer than Ti). 3. Geometry

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Incidence of dislocation

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1-2% primary. 26% revision. Highest in elderly with THA post failed femoral neck fx fixation

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Main determinant of primary arc

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head-neck ratio

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Excursion distance

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Distance head must travel to dislocate (1/2 diameter of femoral head)

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Ideal acetabular alignment

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15-30deg anteversion. 35-45deg coronal tilt

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Need for revision post dislocation

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2/3 treated succesfully nonop. 1. if dislocates within functional range post-reduction. 2. after >2 dislocations

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Treatment total hip w/ loss of greater troch attachment

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Reattachment not succesfull. Tx: larger head +/- constrained liner

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Most common cause of THA revision

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Cemented: failure of acetabular component. Non-cemented: failure of femoral component (osteolysis)

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Most common complication hip resurfacing

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Femoral head fracture- risk: notching/osteoporosis/osteonecrosis/misplaced acetabular cup--> impingement

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Acetabular revision

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Porous coated hemisphere cup w/ screws best. Can use hemisphere cup if 2/3 rim remains. Cavitary defects filled w/ graft. Structural allograft- high failure rate (secondary to graft resorption/component migration). Recon cage: for segemental defects. Fail 2/2 abduction pullout.

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Acetabular component screw placement

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Posterosuperior: safe- risk: sciatic n/superior gluteal a/v. Anterosuperior: risk: external iliacs. Posteroinferior: safe if <20mm. Risk: sciatic/inferior gluteals/internal pudendals. Anteroinferior: risk: anterior inferior obturator n/a/v.

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Femoral stem revision

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noncemented/extensively coated porous coated/long-stem. Pass 2-3cm below original or 2 shaft diameters below defect.

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Timing of periprosthetic fractures

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non-cemented: <6 months- stress risers . Cemented: 5yrs ave @ stem tip/distally- cortical defects

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Tx periprosthetic greater troch fracture

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nonoperative

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HO after THA

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higher risk: contralateral HO/ direct lateral approach/prior fusion. Reop only if severe dec ROM/pain. Nonop tx not effective. Prevention: 600-750cGy w/in 48hrs (shield noncemented parts). Indomethacin 75mg x6wks

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Nerve injury post THA

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peroneal div sciatic most common- closest to acetabulum at ischium. Usually 2/2 retractors. Risk: lengthening over 3.5cm

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Balancing varus deformity

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1. osteophytes. 2. deep MCL. 3. posteromedial corner. 4. sup MCL. 5. PCL- rare

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Balancing valgus deformity

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1. osteophytes. 2. lateral capsule. 3. IT if tight in extension/ popliteus if tight in flexion. 4. LCL

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Balancing sagittal plane deformities

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Symmetric: adjust tibia. Asymmetric: adjust femur

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Indications for cruciate substituting design

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previous patellectomy/ inflammatory arthritis/ PCL deficiency

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TKA component alignment- patellofemoral balancing

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Femur: ER/medialize. Tibia: ER/center over medial 1/3 tubercle. Patella: medialize/central.

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Femoral condyle size

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Medial larger than lateral

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Addressing pateall baja during TKA

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Lower joint line. Patella: small dome placed superiorly. Cut but don't resurface or patellectomy if severe

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PE thickness TKA

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Thinnest portion larger than 8mm.

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Effects of PE machining

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shearing forces--> stretch subsurface 1-2mm-->sensitize to oxidation (white band of subsurface oxidation)

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Flexion closure

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assoc w/ quicker flexion recovery. Avoids need for CPM

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Manipulation arthrofibrosis post TKA

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4-6wks postop ideal. Inc risk supracondylar fx if wait longer or femoral notching.

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Patellar clunk syndrome

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PS knees only. Tissue on posterior quad above sup pole of patella- catches in box at 35-40deg- pops back out--> clunk

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Rectus snip

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oblique transverse cut medial--> lateral quad tendon- risk diastasis of repair--> extensor lag

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Indications for constrained non-hinged TKA

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MCL attenuation/ LCL deficiency/ flexion gap laxity. Controversial for MCL deficiency- high stress

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Indications for constrained hinged knee

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global ligament deficiency/hyperextension instability/ s/p joint resection. Must have medullary stems and rotating platform.

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Location of knee joint line

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1.5-2cm above fibular head

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Tx nondisplaced supracondylar periprosthestic fx

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cast/brace

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Tx supracondylar periprosthetic fx extends distal to flange/ comminuted

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revision TKR w/ medullary stem

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Flap coverage TKA

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medial gastroc flap (off medial sural artery)--> medial/lateral. Lateral gastroc flap only useful for lateral wounds.-- risk common peroneal palsy from flap traction

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UKA vs TKA

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faster early recovery/rehab. Fewer short term complications. Smaller incision. Worse long term complications.

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Contraindications UKA

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1. ACL deficiency. 2. fixed varus. 3. knee flexion less than 90deg. 4. inflammatory arthritis. 5. highly active patient/laborer.

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Correction varus deformity w/ UKA

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correct to 1-5deg valgus

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Failure UKA

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fixed bearing: mechanical loosening. Mobile bearing: disease progression

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Most common complication TSA approach

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axillary nerve injury

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Most common reason for failure of TSA

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glenoid loosening

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Glenoid bone stock and TSA

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Can't proceed of glenoid wear to coracoid. Relative retroversion common 2/2 OA

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Humerus positioning TSA

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20-30 deg retroversion.

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Instability s/p TSA

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anterior- 2/2 subscap pull-off

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TSA s/p 4 part humeral fx

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Anatomic positioning tuberosities key to function. Nonunion--> instability

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Rotator cuff arthropathy tx

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1. reverse TSA. 2. hemi w/ large head--> 40-70 deg elevation. 3. RTC reconstruction- combine w/ resurfacing. Must retain CA ligament- avoid superoanterior escape.

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Wiberg angle

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lateral center edge angle (>20deg nml)

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Lequesne angle

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anterior center edge angle (>20deg nml)

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Acetabular index

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>5deg nml (Tonnis angle)

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Crossover sign

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e/o acetabular retroversion

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THA s/p DDH

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Place head into native acetabulum. May need subtroch osteotomy for shortening to realign. Lengthening over 3.5cm--> risk sciatic nerve injury.

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Advantages of ganz periacetabular osteotomy

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1. multiplanar. 2. allows large corrections. 3. medializes joint. 4. inherent stability (post column intact). 5. avoids hip abductors

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Subtrochanteric osteotomy for DDH

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Correction of coxa valga and excessive femoral anteversion. Do not use closing wedge for flexion (compromises future THA)

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Contraindications HTO for knee OA

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1. lateral tibial subluxation >1cm. 2. bone loss medial compartment. 3. flexion contracture >10deg. 4. Knee flexion less than 90deg. 5. Varus >10 deg.

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Poor prognostic indicators HTO

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Unable to obtain 8-10 deg valgus/ overweight patient-- if both then 60% failure @ 3yrs

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Proximal tibia lateral closing wedge osteotomy- complication

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Main complication: recurrence, loss of posterior tibial slope, patella baja

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Proximal tibia opening wedge osteotomy- complication

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nonunion, collapse of opening wedge. Better at maintaining posterior slope than closing wedge

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Distal femoral varus-producing osteotomy

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Goal: produce horizontal joint line w/ tibiofemoral angle of 0 deg. Most common complication after converting to TKA is inability to restore anatomic valgus

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Hip arthrodesis

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Indication: <35yo w/ severe post-traumatic arthritis. Requires 30% more energy. DJD 15-25yrs postop in lumbar spine (55-100%)>ipsilateral and contralateral knee>contralateral hip. Position: 0 add/0-15 ER/20-25 flexion.

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Conversion hip arthrodesis to THA concern

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abductor function: consider EMG/NCS of gluteus medius preop. If absent then conversion contraindicated.

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Knee arthrodesis

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Indication: most common- failed TKR. Position: 5 valgus/ 0-10 ER/ 0-15 flexion. IM fixation preferred if bone loss.

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Shoulder arthrodesis

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Contraindicated if ipsilateral elbow arthodesis. Position: 30/30/30. Rotation most critical in optimal function.

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Mechanism osteolysis

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Particles ingested by macrophages--> activated macrophages release TNF-alpha/IL-1/IL-6/PG/hydrogen peroxide/acid phosphatase-->activate osteoclasts

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Tx osteolysis around acetabular screw

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if cup well fixed: poly exchange, debride and bone graft osteolytic lesion. Revise cup if not well fixed

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Early postoperative infection- total joint

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within 3wks of implantation. Tx: poly exchange/ I&D/ abx x 4-6wks

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Hematogenous infection- total joint

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Seeding well established implant. Tx: poly exchange/I&D/ abx x 4-6wks. Implant exchange if recurrent.

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Chronic infection- total joint

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infection present >3wks. Usually coag - staph aureus. Tx: implant exchange

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Dental prophylaxis s/p arthroplasty

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First 2yrs. Lifetime if immunocompromised/immunosuppressed (RA/SLE/DM/previous total joint infection)

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Core decompression osteonecrosis

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Indications: early ON before collapse. Effects: pain relief. Poorer results if steroid induced

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Rotational osteotomy for osteonecrosis

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Indications: small lesion in weight-bearing area (<50%). Goals: rotate affected area out of weight-bearing area. CI if over 50% involvement.

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Vascularized bone graft for osteonecrosis

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Indication: early stage ON. CI if whole head involvement. Goal: prevent subchondral collapse.