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 ROMIR- 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 ImplantsTwo Schools of Thought1. Surface Properties– Implant-to-cement adhesion – Increase roughness, precoating, macroscopic

grooves– Debonding and increased wear debris

2. 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 QualityFailure 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

Types1. Tapered- metaphysis wedge fixation 2. Cylindrical- diaphyseal and metaphyseal fixation3. Anatomic-metaphyseal fill in coronal and sagittal

plains 4. Porous Coating5. Grit Blasting6. HA Coating

Press Fit Femoral ImplantsMetallurgy1. Cobalt-Chrome– High Modulus of Elasticity (Stress Shielding)

2. Stainless Steel– Lower fatigue strength– Corrosion– Lower cost, easy workability

3. 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 Failure1. Pistoning of stem/cement causing subsidence2. Medial Stem Pivot- varus position stem causes

failure in proximo-medial and distolateral areas3. Calcar Pivoting- distal aspect of stem shifts

within distal mantle4. 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!1. Choosing the right patients2. Is it the right operation3. What is the operative plan4. What are the x-ray land marks5. Check the template6. Identify Surgical Landmarks7. 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 patient1. High dislocation risk patient2. Young active patient3. Small CDH or Juvenile Rheumatoid Patients4. The Deformity Patient5. Short Varus Neck Patients

• Surgical Approach• Components – Constrained Cups, Modular Implants, etc

• High Risk Dislocation Patients after THA1. Initial Leg Length >2cm2. Fixed Pelvic Tilt3. Elderly, Cachectic female patient4. Hypermobility5. Neuromuscular Problems6. Fusion Takedown/no Abductors7. Multiple Previous Surgeries8. Demented/Substance Abuse Patients9. Post Fracture neck of femur10. Patient with a previous spinal fusion

Step 2: The Right Operation

Step 3: Planning the OperationPlan 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)

• True femoral offset will be underestimated if hips are externally rotated

• Magnification is proportional to the distance between pelvis and film (20%+/-6%)

X-ray minus 15° rotation X-ray plus 30° rotation

Step 4: AP Xray Landmarks1. Tear Drops2. Superolateral edge of Acetabulum3. Centre of rotation of Head4. New Centre of rotation of hip joint5. 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 TemplateKey Radiographic Landmarks 1. Tear Drop2. Ilioischial line3. Superolateral margin of the acetabulum

Step 5: Check the Template

Acetabular Templating1. Cup sized when placed at 40degrees (+/- 10) of abduction

medial boarder approximates ilioischial line2. Must have adequate lateral coverage3. Inferior boarder cup level with inferior tear drop4. If cemented uniform cement mantle of 2-3mm5. Lateral coverage lacking metal augments or bone

(number 7 graft)6. Center of rotation is marked and compared to opposite

side

Step 5: Check the TemplateProtrusio Acetabuli1. Template to anatomic position lateral to tear drop

and Kohler’s line with peripheral rim contact2. 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 TemplateLateralized Acetabulum1. Acetabulum reamed until pulvinar, ligamentum

teres, cotyloid notch and transverse acetabuluar ligament (beware medial osteophytes!!!)

Step 5: Check the TemplateDysplastic Acetabulum1. Insufficient acetabular coverage and superolateral migration of femoral

head2. Mild/Moderate dysplasia well developed posteriosuperior wall

(70%coverage)3. Additional coverage more proximal (high hip center) or medial non-

anatomic position

Step 5: Check the TemplateFemoral Templating & Restoration of

Leg LengthGOAL

“Achieve adequate alignment and fixation to restore femoral offset and optimize leg length”

Step 5: Check the TemplateFemoral Templating & Restoration of Leg LengthCenter 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 TemplateFemoral 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

• True femoral offset will be underestimated if hips are externally rotated

• Magnification is proportional to the distance between pelvis and film (20%+/-6%)

X-ray minus 15° rotation X-ray plus 30° rotation

Step 5: Check the TemplateUtility 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• Superior defect• Fossa osteophytes

Low Dislocation• Femoral Head

articulates false acetabulum

• Anterio-superior defect

• Increased anteversion• Lack posterior bone• FN short

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

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