Primary Total Hip Arthroplasty Majdi S Qutob MD, FRCSC, MSc, MBA

History 1891 Themistocles Glück (1853-1942) carried out the first reported Femoral Hemiarthroplasty in Germany, using ivory to replace the femoral head 1940 Dr. Austin T. Moore (1899–1963), first metallic (Vitallium) Femoral Hemiarthroplasty 1960 Dr. San Baw (1922 –1984) ivory Femoral Hemiarthroplasty for neck fractures 1970 Dr Sir John Charnley (1911 –1982) Low Friction Arthroplasty

Demographics By 2030, the demand for primary total hip arthroplasties is estimated to grow by 174% to 572,000 The Journal of Bone & Joint Surgery.  2007; 89:780-785

Arthritis Arthritis is the second most common chronic condition in the US (sinusitis is first) Most common among elderly 20-30% of people over age 70 suffer from osteoarthritis (OA) of the hip Arthritis affects over 32 million people in the US Total costs associated with arthritis are over $82B/year, including hospital and drug costs, nursing home costs, and lost productivity and work

Normal ROM IR- 35° ER - 45° Flexion - 135° Extension - 15° Abduction - 45° Adduction - 25°

Non-Surgical Intervention Activity Modification Weight Loss Cane/walker Physical Therapy Medications: NSAIDs COX-2 Inhibitors Nutritional supplements Injections: Corticosteroid Viscosupplementation

Joint Anatomy Femoral Head Diameter 46mm Neck Shaft Angle Average 130 degrees > 135 deg coxa valga < 120 deg, coxa vara Femoral Anteversion Angle 12-15 degrees Femoral Offset variable Acetabular Anteversion Average 15 (0-20) degrees Acetabular Abduction Angle 45 degrees (30-50) AP Curve of Femur is about 4 degrees

Biomechanical Considerations 1-2million steps/year 3-6x body weight due to abductors- 7-8x sporting activities Descending stairs causes highest JRF Abductors provide two thirds of the hip joint force parallel to the long axis of femur Increasing the offset and cup medialization reducing the joint reaction force by increasing the abductor lever arm

Biomechanical Considerations Increasing the offset and cup medialization reducing the joint reaction force by increasing the abductor lever arm 10mm increase femoral offset decreases 10% abductors force requirement

Bone Biomechanics Young’s Modulus (flexibility) =stress/strain Stress =force/area Strain= change in length Bone is anisotropic (compression>shear) Exhibits creep: constant pressure will deform at a decreasing rate Strain rate low with rapid application of modest force leads to fracture

Singh et. al. JBJS. 1970 (52-A) 457-467

Singh Classification for Femoral Neck Osteoprosis Singh et. al. JBJS. 1970 (52-A) 457-467

Dorr suggested that there are three types of proximal femur, A is the normal taper top and thick cortex, C is a clear loss of taper and thin cortex, and B is in between.

Types of Total Hip Arthroplasty Cemented vs Uncemented

GOALS of THA “Position the primary arc range of the prosthetic hip in the centre of the functional range of motion required by the patient, in order to optimize the range of motion and reduce the chances of dislocation”

Patient’s Goals “Patients’ satisfaction with hip replacement depends on the surgeon’s ability to relieve pain, equalize leg length and produce a stable hip which will not dislocate” Dr. Charles Engh (2007)

Cemented Components Polymethylmetacrylate (PMMA) interdigitates within bone (grout) Endosteal heat necrosis 500 micrometers Cement mantle of minimum 2mm circumferentially Cement in Gruen Zone 7 allows load in proximal third femur Third Generation Techniques

Cemented Femoral Implants Two Schools of Thought Surface Properties Implant-to-cement adhesion Increase roughness, precoating, macroscopic grooves Debonding and increased wear debris Implant Shape Smooth stem with straight taper to allow subsidence and create hoop stress Broad laterally than medially diffuse compressive stresses and increase torisional and bending rigidity Less debris

Cemented Femoral Implants Indications Dorr Type C Femurs Singh Grades 1-3 Poor Bone Quality Failure Rates Revision rates 0-5% in 10yrs Poor Operative Technique Revision outcomes worse (26% failure rate)

Cemented Acetabular Component “Not Suitable for younger active patients” Lower demand with soft bone (rheumatoids, acetabular protrusio) High failure rates (10-23% at 10yrs) Causes of failure Poor operative techniques Failure to remove peripheral cartilage Poor pressurization Poor design of implant (flanged sockets)

Uncemented Components “Potential life long dynamic bond between host bone and implant” Decreased failure rates in young patients Surgical trauma causes mesenchymal stem cells to become osteoblasts and intramembranous bony ingrowth or on-growth into the prosthesis

Press Fit Femoral Implants Types Tapered- metaphysis wedge fixation Cylindrical- diaphyseal and metaphyseal fixation Anatomic-metaphyseal fill in coronal and sagittal plains Porous Coating Grit Blasting HA Coating

Press Fit Femoral Implants Metallurgy Cobalt-Chrome High Modulus of Elasticity (Stress Shielding) Stainless Steel Lower fatigue strength Corrosion Lower cost, easy workability Titanium-alloy Lower elastic modulus (reducing stress shielding) Titanium-oxide corrosion resistance Osseointergration Easily scratched and notch sensitivity decrease fatigue life

Cortical Defects Perils Stress patterns of tubular bone return to normal 2 cortical diameters past Stem must bypass 2-3 internal bone diameters 4-5cm of distal femoral isthum and implant Stem greater than 90% canal fill Stem stiffness fourth power of diameter (higher causes more stress shielding)

Rules of 50’s Implant-to-host distance minimum 50um Excessive Interface motion >50um (30-150um)leads to fibrous non-union Pore Density of implant 50% Pore Size < 500um (100-400um) Gaps Less than 0.5mm Under Reaming 3-4mm significantly increases risk of fracture

Bearing Surfaces Hard-on-Soft Acetabular Liner polyethylene(PE) and fermoral heads of Cobalt-Chrome, Ceramic, Titanium UHMWPE with vitamin E CC-PE 0.28mm/yr volumetric wear C-PE 150um/yr volumetric wear

Bearing Surfaces Hard-on-Hard Ceramic-on-Ceramic, Metal on Metal, Ceramic-on-Metal Initial wear in period self-polishing (2.5-5 um/yr) Aseptic lymphocytic Vasculitis Associated Lesions (ALVAL) Delayed Type Hypersensitivity COC 0.5-2.5um/yr COC volumetic wear 0.004mm/year Failure rates of 0.004% (Catastrophically!!!)

Mechanisms of Wear in THA Abrasive Wear- two surfaces of differing hardness Adhesive Wear-PE sheared off and deposit in joint space Fatigue Delamination Third Body Wear- particles trapped between joint space causing wear of softer surface

Aseptic Loosening & Osteolysis Four Mechanisms of Cemented Component Failure Pistoning of stem/cement causing subsidence Medial Stem Pivot- varus position stem causes failure in proximo-medial and distolateral areas Calcar Pivoting- distal aspect of stem shifts within distal mantle Cantilever Bending (Fatigue) "Modes of failure" of cemented stem-type femoral components: a radiographic analysis of loosening. Gruen TA, McNeice GM, Amstutz HC 1979

Gruen Zone Classification for Femoral Prosthesis Loosening

Aseptic Loosening & Osteolysis 0.1-10 micrometres in size (most potent 0.1-0.5)

Head and Head-Neck Ratios Head Size Less volumetric wear secondary to small arc of motion Greater Linear wear because JRF distributed over smaller area 28mm Head trade-off between volumetric and linear wear (new PE allows 32mm head) Optimal ratio HN is 2:1 Hard on Hard Articulations Hydrodynamic lubrication and low volumetric wear (with suction effect)

Abductor Tensioning Increasing lateral offset and neck length increases abductor lever arm and tension, stability and reduces JRF Increases torsional stresses on implant Increases trochanteric bursitis Increases leg length discrepancy Average femoral offset 45mm Sex differences

Abductor Tensioning

Abductor Tensioning Women Shorter femoral necks Thinner femoral shafts Lower cervio-diaphyseal angles Lower femoral offsets Greater femoral neck anteversion

Leg Length Discrepancy Lateral Decubitus highest risk Pre-op templating critical Intra-op assessment of patients feet and knees in symmetrical knee flexion Measuring height of femoral cut from top of LT Assess relationship of GT to femoral centre before and after osteotomy

Clinical Assessment of a Difficult THA GOLDEN STEPS! Choosing the right patients Is it the right operation What is the operative plan What are the x-ray land marks Check the template Identify Surgical Landmarks Getting the Leg Length Right

Step 1: Choosing the Right Patient Groin Pain or Thigh Pain or Knee Pain!!! Back Pathology Bilateral Hip Pain No Groin Pain Unable to Localize pain Negative leg roll test Back movement reproduces the pain If in doubt interventional radiology assisted intraarticular injection

Step 1: Choosing the Right Patient Assess Gait and Hip ROM Evaulation knee, lumbosacral spine Actual Limb-Length Discrepancy- ASIS to medial malleolus Functional Limb-Length Discrepancy- Using blocks until patient feels equal

Step 1: Choosing the Right Patient Difference actual and functional lengths evaluate for Suprapelvic Obliquity (scoliosis, DD spine) persists with sitting Intrapelvic Obliquity (necrosis, arthritis, infection, malunions, congenital hemihypertrophy, etc…) corrects with sitting Equalization of functional limb length improves gait and increased comfort

Step 2: The Right Operation Altering the THA to suit the patient High dislocation risk patient Young active patient Small CDH or Juvenile Rheumatoid Patients The Deformity Patient Short Varus Neck Patients Surgical Approach Components Constrained Cups, Modular Implants, etc

Step 2: The Right Operation High Risk Dislocation Patients after THA Initial Leg Length >2cm Fixed Pelvic Tilt Elderly, Cachectic female patient Hypermobility Neuromuscular Problems Fusion Takedown/no Abductors Multiple Previous Surgeries Demented/Substance Abuse Patients Post Fracture neck of femur Patient with a previous spinal fusion

Step 3: Planning the Operation Plan A-D Plan A: Usual default for THA used in 95% of cases Plan B: If “Plan A” Fails (e.g. sterility of instruments breached or implants not available) Plan C: Hand over complex case to senior colleague Plan D: At time of surgery things are going wrong and not able to obtain satisfactory outcome. Call a senior surgeon Close without an implant with skin or skeletal traction

Step 4: Xray Landmarks Hips in 10-15 degrees internal rotation (true AP of femoral neck) Marker of known diameter between legs (coin)

X-ray minus 15° rotation X-ray plus 30° rotation True femoral offset will be underestimated if hips are externally rotated Magnification is proportional to the distance between pelvis and film (20%+/-6%)

Step 4: AP Xray Landmarks Tear Drops Superolateral edge of Acetabulum Centre of rotation of Head New Centre of rotation of hip joint Lesser Trochanters

Step 4: Lateral Xray Landmarks

Step 5: Check the Template Should follow steps of surgery acetabular side first then femoral Horizontal reference line base of teardrops (most accurate landmark) (can use SI or ischial tuberosities)

Step 5: Check the Template Key Radiographic Landmarks Tear Drop Ilioischial line Superolateral margin of the acetabulum

Step 5: Check the Template Acetabular Templating Cup sized when placed at 40degrees (+/- 10) of abduction medial boarder approximates ilioischial line Must have adequate lateral coverage Inferior boarder cup level with inferior tear drop If cemented uniform cement mantle of 2-3mm Lateral coverage lacking metal augments or bone (number 7 graft) Center of rotation is marked and compared to opposite side

Step 5: Check the Template Protrusio Acetabuli Template to anatomic position lateral to tear drop and Kohler’s line with peripheral rim contact Measure medial defect for graft filling

THA for Acetabular Protrusio Causes: Osteogensis imperfecta Osteomalacia Paget’s Disease Bone Tumors Rheumatoid Arthritis Ankylosing Spondylitis Trauma

Step 5: Check the Template Lateralized Acetabulum Acetabulum reamed until pulvinar, ligamentum teres, cotyloid notch and transverse acetabuluar ligament (beware medial osteophytes!!!)

Step 5: Check the Template Dysplastic Acetabulum Insufficient acetabular coverage and superolateral migration of femoral head Mild/Moderate dysplasia well developed posteriosuperior wall (70%coverage) Additional coverage more proximal (high hip center) or medial non-anatomic position

Step 5: Check the Template Femoral Templating & Restoration of Leg Length GOAL “Achieve adequate alignment and fixation to restore femoral offset and optimize leg length”

Step 5: Check the Template Femoral Templating & Restoration of Leg Length Center of Rotation Line perpendicular to femoral shaft at the level of the tip of the GT inaccurate Coxa Valga- center of rotation is above the GT Coxa Vara or Coxa Brevis- COR below the GT Normal 130 Coxa Vara <120 Coxa Valga >140

Step 5: Check the Template Femoral Offset Restoration of original offset Beware xray rotation!!!! Template off normal contralateral side Measure distance center of rotation to tip GT before neck cut Measure distance proximal LT to COR Measure distance proximal LT to proposed neck cut Cemented stem Optimal diameter distal centralizer, plug size, and depth insertion

X-ray minus 15° rotation X-ray plus 30° rotation True femoral offset will be underestimated if hips are externally rotated Magnification is proportional to the distance between pelvis and film (20%+/-6%)

Step 5: Check the Template Utility of Preoperative Templating Eggli et al 1998 (JBJS) 90% agreement cup size 92% agreement stem size Actual difference COR hip 2.5 +/- 1.1mm vertical 4.4 +/- 2.1mm horizontal Mean LLD 3 +/- 1mm clinically, 2 +/- 1 mm radiographically 80% difficulties were anticipated (trochanteric osteotomy, acetabular autografts, reinforcement rings and resection osteophytes)

Adapting the Preoperative Planning to Intraoperative Findings Feedback during acetabular reaming and femoral broaching Reduction of trial prosthesis ROM (removal osteophytes) Soft tissue tension with correct LLD then increase stem with increased offset Elderly tolerate LLD

Adult Congenital Hip Disease

THA for Congenital Hip Disease Classifications Crowe Classification <50% 50-75% 75-100% >100%

New Classification Dysplastic Contained in true acetabulum High Dislocation Femur superior posterior Segmental defect rim Increased bone posterosuperior Excessive anteversion Iliac wing hypoplastic and anterverted FN Shorter and anterverted Diaphysis is hypoplastic narrow and thin cortices Dysplastic Contained in true acetabulum Superior defect Fossa osteophytes Low Dislocation Femoral Head articulates false acetabulum Anterio-superior defect Increased anteversion Lack posterior bone FN short

Preoperative Planning Low and High Dislocations obtain CT Estimates bone stock, accurate sizes and anteversion acetabulum and femoral neck Plain films for templating

Technical Difficulties Narrow diaphysis and angular deformities of femur Trochanter osteotomy Restoration true vs high hip center Acetabulum osseous coverage 80% Small 40-42mm cup with thin poly Augmentation superior defects Cotyloplasty

Technical Difficulties

Technical Difficulties High Hip Center Lever arm body weight longer than abductors causing excessive shearing and loading forces of the hip Does not correct leg length limp and low back pain Shortening of femur if >4cm lengthening (subtrochanteric osteotomy) Stem short cementless conical distal bearing

THA for Arthrodesed Hips

THA for Arthodesed Hips Indications for Conversion: painful pseudarthrosis pseudorthrosis rates are 0-10% using modern techniques for fusion mechanical low back pain -#1 complaint multi-level arthritic changes seen in LS spine malposition (especially increased abduction) is a major cause excessive leg length inequality knee pain/instability Adduction causes ipsilateral pain Abduction causes contralateral pain

THA for Arthodesed Hips Preoperative Evaluation: Physical exam and EMG (abductors) AP pelvis, cross table lateral and Judet Views to identify bone stock CT scan heterotopic bone to neurovascular structures an abductor muscle mass

Surgical Considerations Anterior approach, posterior approach or a direct lateral or a trans-trochanteric (Gaunz) Osteotomy Indications for an trochanteric osteotomy Exposure decrease injury to atrophied/weakened abductors during the case advancement (improve stability) Existing hardware and HO should be removed Neck cut in situ; proximal cuts results in fractures of the pubis and the ischium if in doubt, place guide pins and obtain a radiograph soft tissue releases (ilio psoas, adductors, etc.) PRN

Acetabular component: structural grafting (metal augments) one should be prepared to cement the socket if the shell has <50 % contact with native bone a constrained liner is frequently required because of insufficient soft tissue tension post-op (esp. abductors)

Femoral component: modular femoral components if the trochanter is bald and there are no abductors, the proximal femur can be sewn to the tensor fascia lata anteriorly and the gluteus maximus and ITB posteriorly    

Results: relief of low back pain occurs 70-95% of the time leg lengths can usually be improved ipsilateral knee pain typically improves but it persists in at least 1/3 (especiailly if instability was a problem pre-op) a trendelenberg gait typically persists though abductor function improves for 2-5 years results from conversion of spontaneous fusions are typically better than results of conversion of surgical fusions

Complications: deep infection 1.9-15.3% (higher in conversion of surgical fusion) dislocation 1.7 - 6.25% sciatic nerve palsy 1.8-13.4% femoral nerve palsy 3.6%

CASES

SH 58yo female High Speed MVA (t-boned) 1yr ago ORIF Rt Acetabulum Referred to office for increasing right hip pain

Post Op

Today

Next Step?

Options?

SR 63 yr male, previous Lt femoral osteotomy for OA – uncomplicated index surgery plus subsequent hardware removal. Incapacitating pain Lt hip Otherwise well Severely restricted RoM, well healed scars, T/berg/antalgic gait

BP 51 yr female, brain damage, LTC resident, recurrent seizures Previous Rt bipolar for subcap.# Previous Lt DHS for Intertroch # Remote Lt femoral shaft # Pain Lt Hip, unable to weightbear Afebrile

BP Family and caregivers request solution for pain and inability to mobilize… 1. No surgery 2. Remove hardware only 3. Stage hardware removal and bipolar 4. Remove hardware and Bipolar 5. Stage hardware removal and THA 6. Remove hardware and THA

BP What about the femoral deformity distal to plate? 1. Try to bypass (+/- osteotomy) 2. Ignore

KK 34 yr male, OA Lt hip secondary to LCPD Previous periacetabular osteotomy 6ys prior Severe pain and functional limitation 30° external rotation deformity 2.5cm short

KK Direct lateral approach Entire acetabulum retroverted 30° Tight external rotators – released Ant column “shaved” and Ant column screw advanced to reduce femoral impingement in flexion Iliac screws removed via separate incisions “External landmarks” for cup orientation Posterior aspect shell 20-30% uncovered

DS 58yr male, previous acetabular fracture (MVA) – ORIF 12 yrs prior 8hr procedure, transtrochanteric approach, no reported postop complications Severe pain etc No systemic symptoms Fit and good health

DS Approach? 1.Transtrochanteric 2. Iliofemoral 3. Direct lateral 4. Posterior 5. Invent a new one

DS Hardware removal… 1. Plan to stage 2. Remove all – at time of THA 3. Try to ignore at time of THA

Managed to ignore most of the hardware Lateral approach with unintentional transtrochanteric component