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Calcar replacing prosthesis Indications - salvage of failure of fixation - severe comminution - RA Problems - high cost - higher morbidity / mortality - high risk of dislocation Causes - poor screw position - 150° screw - high tip apex distance Options - 95o DCS - THR / calcar replacing prosthesis THR Issues A. Cemented femoral component - cement will come out screw holes - Option 1: leave screws in laterally, and strip medially to insert small screws - Option 2: use uncemented stem B. Length of femoral stem - should bypass distal screw hole by 2 cortical diameters C. Calcar - normal stem usually sufficient if LT healed back on Cause 1. Long screw 2. Collapse with insufficent lateral buttress 3. Reverse obliquity fracture Management 1. Fracture united - remove screw 2. Fracture non union - revise fixation in young patient - THR Femoral medialisation Due to - insufficient lateral cortex - reverse obliquity fracture Use 95° plate Uncommon / 1% - exclude infection Presentation - continued pain (case 1) - hardware failure (case 2) Case 1 Case 2 Options A.

75-84 - unipolar monoblock 8.5% 9 years - unipolar modular 5.5% 7 years - bipolar 3.5% 7 years 3. - unipolar monoblock 17.5% 7 year - unipolar modular 13.4% 7 year - bipolar 6% 7 year revision rate Types Unipolar - non modular - Austin Moore / Thompsons / - modular Bipolar Fixation Cement - minimises fracture risk - reduced risk thigh pain - slightly increased cardiac risk with cement Australian Joint Registry - revision rates lower for cemented than uncemented - for all types of hemiarthroplasty for NOF fractures Approach Posterior approach - increased short term morbidity - may increase dislocation risk Hardinge - take off anterior 1/3 abductor tendons Austin Moore - press fit non modular unipolar - only 2 sizes of stem - small patients can fracture femur - larger patients the stem can be loose - AJR: 7.8% 9 year revision rate Thompson's - cemented non modular prosthesis - no offset options - AJR: 5.1% 7 year revision rate Modular Unipolar - based on standard THR concepts - trial and insert femoral component / cemented or uncemented - can use standard or high offset - opportunity to adjust neck length - attach head Bipolar Concept - metal femoral head articulates with polyethylene socket - reduces motion at acetabular / metal interface - in theory reduces acetabular cartilage wear / degeneration / pain Advantages - less dislocation compared with THR - less acetabular wear / protrusio compared with unipolar - less pain compared with unipolar - more motion - lower revision rates compared with unipolar (AJR) Disadvantage - high cost (close to some THR) - may need open reduction in dislocation if femoral head disassociates from socket - loss of motion interface / becomes unipolar) Infection Dislocation - similar to THR in long term GT Fracture LLD Loosening Groin pain from acetabular cartilage erosion - most common complication Severe acetabular wear Acetabular disease (RA, Paget's, OA) Young, active, mobile patient 1. Dislocation Increased early dislocation rate Long term dislocation rate similar to hemiarthroplasty Keating et al Health Technol Assess 2005 - randomised study of bipolar v THR - 2.7% dislocation rate v 4.3% 2.

Fitmore ® Hip Stem - Zimmer Biomet

Austin Moore Hip Prosthesis – Excel Stainless Steel (Standard Stem)

Hip Prosthesis are indicated for degenerated femoral head replacement

Medialise cup A. Recreate centre of rotation Place in true acetabulum - transverse ligament is anatomical landmark Template hip centre - inter-tear drop line is inferior margin - ilio-ischial line is medial margin - superior edge acetabulum lateral margin B. Need for augmentation Superior defect must be Options - bulk femoral head autograft - mesh + impaction bone graft - reinforcement rings / cages - augmented cups Bulk Femoral Head Autograft Advantage - restore hip centre - improve bone stock for revisions Technique - fashion femoral head into 7 graft - screw into place with 2 x 6.5 mm cancellous screws - ream into inferior aspect of graft Spangehl et al JBJS Am 2001 - 44 hips followed up for 7.5 years - femoral autograft with uncemented cup - 4 revisions / 10% - acceptable early results Harris JBJS 1997 - 55 autogenous bulk autograft + cemented acetabulum - average follow up 16.5 years - average age of patient at time of surgery 42 years - average size of acetabulum 40mm - average coverage of cup by graft 49% - 29% (16/55) revised and further 31% (17/55) radiographically loose - those grafts 30% or less of cup coverage were well fixed at 16 years - the greater the coverage of bone graft initially, the greater the rate of late revision - most hips did well for initial 5 - 10 years Mesh + Impaction Bone Grafting Reinforcement ring / cage + bone graft Technique - morcellised bone graft - support with acetabular reinforcement ring - usually screwed into ilium and ischium - cement acetabular component into ring Muller JBJS 1998 - 87 hips, majority Crowe 3 - Muller acetabular roof reinforcement ring - autograft and cemented polyethylene cup - 10% revision at 9.4 years Ganz J Arthroplasty 2005 - 33 cases at 10.8 years - 3 revisions (9%) - 2 of the revisions had structural allograft DDH augmented cups Advantage - allows coverage by native bone - decreases need for femoral shortening Disadvantages - very small acetabular component - very thin poly - abnormal hip biomechanics - risk of bony impingement - may lateralise hip centre Results Kaneuji et al J Arthroplasty 2009 - 30 hips followed up for 15 years - mild superior hip centre compared to contralateral normal hip (13 mm average) - 1/30 revised Technique - controlled medialisation with deliberated over-reaming - can deliberately fracture medial wall Advantage - improves lateral coverage - decreases JRF through medialisation Disadvantage - loss of medial bone stock compromising future revision - risk of early catastrophic component migration medially into pelvis Results Small and narrow Excess anteversion Small components Uncemented Need to be modular A. Abnormal shape of proximal femur - difficult to obtain press fit / risk fracture - diaphyseal press fit - small modular metaphyseal component B. Need modularity to adjust anteversion - SROM prosthesis - dial in version Cemented DDH prothesis Design - smaller with minimal metaphyseal flare - this allows stem to be orientated independently of patients anteversion Only lengthen sciatic nerve 4cm Abductors very tight and prevent lengthening Difficulty reducing hip 1. Psoas release 2. Subtrochanteric osteotomy 3. GT osteotomy Trochanteric slide allows - acetabular exposure - retensioning abductors - reposition abductor insertion to correct anteversion Subtrochanteric osteotomy Advantage - acetabular exposure (lift up) - correction anteversion - shortening femur Technique - mark rotation with 2 x small drill holes - make osteotomy - transverse osteotomy allows rotational adjustment - step cut more difficult but gives rotational stability - insert trial femur proximally - reduce hip joint - calculate resection based on overlap of proximal and distal femoral segments - uncemented or cemented stem - use bone resected as onlay Crowe I Mildly dysplastic - minimal deformity, good bone stock - small standard cup medialised for coverage - - small femoral stem Crowe II / III Usually very deficient laterally - due to femoral head eroding acetabulum - restore hip centre by reaming medially - then need to provide superolateral coverage - autograft + mesh / allograft / DDH cup / tantalum Crowe IV Usually good bone stock in true acetabulum - femoral head has not eroded bone - recreate acetabulum and place small component - use teardrop and fovea as landmarks Crowe I/II Minimal LLD - sess femoral shortening required - avoid excessive anteversion based on abnormal femoral neck - otherwise get anterior instability and loss ER Crowe III/IV If greater than 4cm LLD - need to shorten femur

& other muscles - ground reaction force is under calculated - GRF recorded in prosthetic femur is much higher than FBD would suggest Forces Body weight during one-legged stance - 5/6 BW (1/6 BW is weight of leg patient standing on) - effective body weight will act in a vertical direction Single leg stance 3x BW Walk ~4x BW Jog~ 6x BW Stumble ~9x BW Shifting the body weight over the centre of the hip joint - eliminating the need for the abductors to balance body weight - reduce joint reaction force Impact of walking aids Walking with cane in contralateral hand - analytical and in vivo studies - clearly shown reduces the joint force Mechanism - moment arm of the cane is much larger than that of the abductor muscles - lower muscle forces are now required to balance the effective BW moment Longitudinally and posteriorly directed loads - most critical in generating stem fractures - most fractures start at the anterolateral corner. Posteriorly directed forces - occur when the hip is flexed - result in retroversion of the stem - may play a significant part in loosening femoral stems Mechanical ability of the abductors are affected by - head-neck angle - neck length - joint centre position Aims - recreate centre of rotation - decrease JRF - increase offset - Increase abductor strength Joint centre Joint forces are minimized when the joint centre is moved medially, inferiorly, and anteriorly - maximizes the moment-generating capacity of the abductors OA displaces femoral head laterally, superiorly, and posteriorly - largest joint forces and moments are generated in this position Lateral and distal joint centre - decreases the abductor's moment arm - therefore preventing contralateral pelvic drop now requires an increased muscle force - increases the joint's compressive force Superior joint centre - inferior functional outcome - decreased abductor strength - loss of passive hip flexion - can compensate with increased neck length Higher contact force / increased wear and loosening - superior and lateral joint centre - decreased femoral offset - decreased abductor moment arms Head Neck Angle Varus hip - decreased head-neck angle - increases the mechanical advantage of the abductors - therefore should minimise joint contact forces - also improves stability with increased congruence Valgus Stem - decreased bending moment or shear on stem - increased axial stem loading If excessive - increases knee valgus strain - lengthens limb - superior dislocation Varus Stem - increases shear on neck - decreases axial loading If excessive - shortens femur - increases dislocation Neck length Decreasing the neck length - similar to increasing the head-neck angle (valgus) - compromise the abductor function and increase the joint reaction force

Surgical Techniques - Zimmer Biomet

& other muscles - ground reaction force is under calculated - GRF recorded in prosthetic femur is much higher than FBD would suggest Forces Body weight during one-legged stance - 5/6 BW (1/6 BW is weight of leg patient standing on) - effective body weight will act in a vertical direction Single leg stance 3x BW Walk ~4x BW Jog~ 6x BW Stumble ~9x BW Shifting the body weight over the centre of the hip joint - eliminating the need for the abductors to balance body weight - reduce joint reaction force Impact of walking aids Walking with cane in contralateral hand - analytical and in vivo studies - clearly shown reduces the joint force Mechanism - moment arm of the cane is much larger than that of the abductor muscles - lower muscle forces are now required to balance the effective BW moment Longitudinally and posteriorly directed loads - most critical in generating stem fractures - most fractures start at the anterolateral corner. Posteriorly directed forces - occur when the hip is flexed - result in retroversion of the stem - may play a significant part in loosening femoral stems Mechanical ability of the abductors are affected by - head-neck angle - neck length - joint centre position Aims - recreate centre of rotation - decrease JRF - increase offset - Increase abductor strength Joint centre Joint forces are minimized when the joint centre is moved medially, inferiorly, and anteriorly - maximizes the moment-generating capacity of the abductors OA displaces femoral head laterally, superiorly, and posteriorly - largest joint forces and moments are generated in this position Lateral and distal joint centre - decreases the abductor's moment arm - therefore preventing contralateral pelvic drop now requires an increased muscle force - increases the joint's compressive force Superior joint centre - inferior functional outcome - decreased abductor strength - loss of passive hip flexion - can compensate with increased neck length Higher contact force / increased wear and loosening - superior and lateral joint centre - decreased femoral offset - decreased abductor moment arms Head Neck Angle Varus hip - decreased head-neck angle - increases the mechanical advantage of the abductors - therefore should minimise joint contact forces - also improves stability with increased congruence Valgus Stem - decreased bending moment or shear on stem - increased axial stem loading If excessive - increases knee valgus strain - lengthens limb - superior dislocation Varus Stem - increases shear on neck - decreases axial loading If excessive - shortens femur - increases dislocation Neck length Decreasing the neck length - similar to increasing the head-neck angle (valgus) - compromise the abductor function and increase the joint reaction force

|prosthesis donation| - abetterworld111

Calcar replacing prosthesis Indications - salvage of failure of fixation - severe comminution - RA Problems - high cost - higher morbidity / mortality - high risk of dislocation Causes - poor screw position - 150° screw - high tip apex distance Options - 95o DCS - THR / calcar replacing prosthesis THR Issues A. Cemented femoral component - cement will come out screw holes - Option 1: leave screws in laterally, and strip medially to insert small screws - Option 2: use uncemented stem B. Length of femoral stem - should bypass distal screw hole by 2 cortical diameters C. Calcar - normal stem usually sufficient if LT healed back on Cause 1. Long screw 2. Collapse with insufficent lateral buttress 3. Reverse obliquity fracture Management 1. Fracture united - remove screw 2. Fracture non union - revise fixation in young patient - THR Femoral medialisation Due to - insufficient lateral cortex - reverse obliquity fracture Use 95° plate Uncommon / 1% - exclude infection Presentation - continued pain (case 1) - hardware failure (case 2) Case 1 Case 2 Options A.

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How Are Joint Replacement Implants Held in the Bone?


A longer stem might be needed and they may use metal augment pieces.

When reconstruction of proximal bone stock important
- young patient in whom biological solution more desirable
Technique
Templating
- choose stem 2 cortical diameters longer than most distal lytic area
Exposure
- full exposure of proximal femur
- removal stem & cement Can leave distal plug
- not infected
- > 2 cm past planned tip location
Create contained defect
- reconstitute femoral tube
- create contained defect
- wire mesh & cerclage wire
- prophylactically cerclage wire shaft if diaphysis flimsy
Distal Occlusion
- threaded intramedullary plug inserted on guide rod
- impacters tested to see max depth of insertion before abutment on canal
- morsellised allograft inserted
- impactor & slap hammer slid over guide wire
- graft impacted to predetermined depth
- continued by introducing more chips with larger impacters
- stopped when level is 10 cm from tip of GT
Proximal Impaction
- appropriate proximal impactor equivalent to selected stem used
- used to force chips against walls of canal
- then larger distal impactor used
- alternated till canal filled
- should be firm neo-canal
Trial Reduction
- trial stem inserted
- depth of insertion marked
- proximal impactor driven in another 5 mm
- creates room for cement
Prosthesis
- cemented polished collarless double tapered stem
Post-op
- NWB for ?

Prosthetic implants with bioabsorbable coating

75-84 - unipolar monoblock 8.5% 9 years - unipolar modular 5.5% 7 years - bipolar 3.5% 7 years 3. - unipolar monoblock 17.5% 7 year - unipolar modular 13.4% 7 year - bipolar 6% 7 year revision rate Types Unipolar - non modular - Austin Moore / Thompsons / - modular Bipolar Fixation Cement - minimises fracture risk - reduced risk thigh pain - slightly increased cardiac risk with cement Australian Joint Registry - revision rates lower for cemented than uncemented - for all types of hemiarthroplasty for NOF fractures Approach Posterior approach - increased short term morbidity - may increase dislocation risk Hardinge - take off anterior 1/3 abductor tendons Austin Moore - press fit non modular unipolar - only 2 sizes of stem - small patients can fracture femur - larger patients the stem can be loose - AJR: 7.8% 9 year revision rate Thompson's - cemented non modular prosthesis - no offset options - AJR: 5.1% 7 year revision rate Modular Unipolar - based on standard THR concepts - trial and insert femoral component / cemented or uncemented - can use standard or high offset - opportunity to adjust neck length - attach head Bipolar Concept - metal femoral head articulates with polyethylene socket - reduces motion at acetabular / metal interface - in theory reduces acetabular cartilage wear / degeneration / pain Advantages - less dislocation compared with THR - less acetabular wear / protrusio compared with unipolar - less pain compared with unipolar - more motion - lower revision rates compared with unipolar (AJR) Disadvantage - high cost (close to some THR) - may need open reduction in dislocation if femoral head disassociates from socket - loss of motion interface / becomes unipolar) Infection Dislocation - similar to THR in long term GT Fracture LLD Loosening Groin pain from acetabular cartilage erosion - most common complication Severe acetabular wear Acetabular disease (RA, Paget's, OA) Young, active, mobile patient 1. Dislocation Increased early dislocation rate Long term dislocation rate similar to hemiarthroplasty Keating et al Health Technol Assess 2005 - randomised study of bipolar v THR - 2.7% dislocation rate v 4.3% 2.

fixation of a presfit (cementless) femoral hip implant can occur ..

Triple taper concept - femoral component tapers to a point in both the AP and lateral planes - in addition, the stem is more narrow medially and widens laterally - Cement fails in fatigue - Centrifugation decreases pore size in cement - approximately 200 to 400 nm in diameter - results in an increase in cross-sectional area - 25% increase in ultimate tensile strain - 125% increase in tension-compression fatigue strength - Similar benefits demonstrated with vacuum mixing Cement viscosity - in vitro and in vivo tests - structural superiority of high viscosity over low viscosity cement - i.e.

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