1. Principles of THR
Moderator: Dr Geletaw Tessema (Trauma & Arthroplasty
Surgeon)
Presenter: Yasin Awil (OSR)

2. Outline
• History
• Anatomy of hip
• Biomechanics
• Design and selection of components
• Preoperative Templating
• Procedure
• complications

3. History
 1891
• Dr. Gluck performs first reported attempt at a hip
replacement with ivory.
 1940
• Austin Moore performs first metallic hip replacement
surgery (hemiarthroplasty)
 1952
• Austin Moore prosthesis developed

4.  1960s
• Sir John Charnley introduces concept of low friction arthroplasty
• Concept
• termed "low friction" as a small femoral head was used to reduce wear
• Components
• metal femoral stem
• polyethylene acetabular component
• acrylic bone cement

5. Hip anatomy
 Acetabulum
• Anteverted 15 degrees
• Abducted 45 degrees
• Divided into four quadrants
• Proximal femur
• Femur head
• Femur neck
• anteverted 15 degrees
• neck shaft angle of 125 degrees

7. Applied Hip Biomechanics
 Forces acting on the hip:

8. Forces producing torsion of stem.
• Forces acting on hip in coronal plane:
• Tend to deflect stem medially
• Forces acting in sagittal plane especially with hip
flexed or when lifting:
• Tend to deflect stem posteriorly.
• . Combined, they produce torsion of stem.

9. Clinical implications
 Actions that decrease joint reaction force include:
• increase in ratio of A/B (shift center of rotation medially)
• acetabular side
• moving acetabular component medial, inferior, and anterior
• Femoral side
• Increasing offset of femoral component
• Long stem prosthesis
• Lateralization of greater trochanter

10. CONT…
• Patient's gait:
• Shifting body weight over affected hip
• This results in Trendelenburg gait
• Cane in contralateral hand
• Reduces abductor muscle pull and decreases the moment arm
between the center of gravity and the femoral head
• Carrying load in ipsilateral hand
• Produces additional downward moment on same side of
rotational point

11. STRESS TRANSFER
TO BONE
 Bone Morphology
• Dorr classification:
• Type A – funnel
shape/champagne flute
appearance
• Type B – medial and posterior
cortex are minimally lost
• Type C – stovepipe appearance

12. Cont…..
 Stress shielding:
• Proximal femoral bone loss in the setting of
a well-fixed stem
• Risk factors:
• Stiff femoral stem
• Large diameter stem
• Extensively porous coated stem
• Greater preoperative osteopenia

13. DESIGN AND SELECTION OF
TOTAL HIP COMPONENTS
• No implant design or system is appropriate for every patient
• Selection is based on:
• Patient’s needs,
• Patient’s anticipated longevity
• Level of activity,
• Bone quality and dimensions,
• Ready availability of implants and proper instrumentation,
• Experience of the surgeon

14. FEMORAL COMPONENTS
• The primary function of the femoral component is:
• Replacement of the femoral head and neck after resection of the
arthritic or necrotic segment
• The ultimate goal of a biomechanically sound, stable hip joint
is to restoration of the normal center of rotation of the
femoral head.
• This location is determined by three factors:
• Vertical height (vertical offset),
• Medial offset(Horizontal offset)
• Version of the femoral neck

15. Cont….
• Vertical height and offset increase as the neck is
lengthened.
• In most modern systems, neck length is adjusted by
using modular heads with variable internal bores.
• Vertical height (vertical offset) is determined primarily
by the:
• base length of the prosthetic neck plus the length gained
by the modular head used.

16. Cont….
• Offset ( horizontal offset):
• distance from the center of the femoral head to a
line through the axis of the distal part of the stem
• Inadequate restoration of offset shortens the
moment arm of the abductor musculature
• Offset can be increased by simply:
• using a longer modular neck.
• reducing the neck-stem angle
• attaching the neck more medial position

17. CONT..
• Head-to-neck ratio of implants,
• Large-diameter head with trapezoidal neck
has greater ROM and less impingement than
smaller diameter head..
• ROM with different head sizes,
• Jump distance
• distance the head must travel to escape the rim
of the socket
• approximated to be half the diameter of the
head

18. CEMENTED FEMORAL COMPONENTS
• Rely on cement fixation
• The stem should be fabricated of high-strength superalloy,
• Cobalt-chrome or stainless steel
• Most common
• Reduce cement stresses
• Titanium
• Prone to micromotion and debonding
• less stiff than cobalt-chrome or stainless steel stems

19. Cont..
• The cross section of the stem should have:
• Broad medial border
• Broader lateral border
• To load the proximal cement mantle in compression
• Sharp edges produce local stress risers
• Collar aids in determining the depth of insertion
• Stem shape:
• Noncircular shapes ( rounded rectangle, ellipse)
• surface irregularities (grooves or a longitudinal slot)

20. CONT…
• Stems should be available in a variety of sizes,
• Allow the stem to occupy 80% of the cross section of the
medullary canal
• with an optimal cement mantle of approximately 4 mm
proximally and 2 mm distally
• the optimal length of the stem depends on:
• Geometry and size of the femoral canal
• The lengths of current stem designs range from 120
to 150 mm.

21. Cont…..
• Cement fixation is optimized by:
• limited porosity of cement
• cement mantle > 2mm
• stiff femoral stem
• stem centralization
• smooth femoral stem
• absence of mantle defects
• proper component positioning within femoral cana

22. Radiographic analysis
 Barrack and Harris grading system:
• grade A
• complete filling of medullary canal
• "white-out" of cement-bone interface
• grade B
• slight radiolucency of cement-bone interface
• grade C
• radiolucencies > 50% of bone-cement interface or incomplete cement mantles
• grade D-gross radiolucencies and/or failure of cement to surround tip of
stem

23. CEMENTLESS FEMORAL COMPONENTS
• Rely on biologic fixation:
• Immediate mechanical stability at the time of surgery
• Intimate contact between the implant surface and viable host bone
• Two materials most commonly used:
• Titanium alloy with one of a variety of surface enhancements
• Cobalt-chromium alloy with a sintered beaded surface
• A variety of surface modifications
• Porous coatings, grit blasting, plasma spraying, and hydroxyapatite coating

24. CONT…
 Biologic fixation
• Mechanism:
• Ingrowth:
• bone grows into porous structure of implant
• Optimum pore size for ingrowth – b/n 100 and 400 µm
• Ongrowth:
• bone grows onto the microdivots in the grit blasted surface.

25. Cont…
• Biologic fixation is optimized with:
• pore size 50-300um
• porosity of 40-50%
• gaps < 50um
• micromotion < 150um
• maximal contact with cortical bone

26. CONT…
 Classification system for cementless stems based
on shape:
• Types 1 -5 are straight stems,
• Type 6 is an anatomic shape
• Type 1 stems (single-wedge stems)
• Flat in the AP plane
• Tapered in the mediolateral plane
• Fixation is by cortical engagement only in the mediolateral
plane and by three-point fixation along the length of the
stem.

27. • Type 2 stems( double-wedge)
• engage the proximal femoral cortex in both ML and AP planes
• used safely in Dorr type A femurs
• Type 3 (Tapered)
• Tapered in two planes,
• Fixation is achieved more at the metaphyseal-diaphyseal
junction
• Has 3 subgroups

28. • Type 4
• Extensively coated implants
• With fixation along the entire length of the stem
• . Canal preparation requires distal cylindrical
reaming and proximal broaching
• Excellent long-term results
• Femoral stress shielding and thigh pain

29. • Type 5 (modular stems)
• Separate metaphyseal sleeves and diaphyseal
segments
• Separate preparation
• Recommended for patients with altered
femoral anatomy,
• Used for all Dorr bone types,

30.  Type 6(anatomic femoral Stem)
• incorporate a posterior bow in the metaphyseal
portion
• anterior bow in the diaphyseal portion
• Corresponding to the geometry of the femoral
canal
• Right and left stems are required,

31. Radiographic analysis
• signs of a well-fixed cementless femoral component
• Spot-welds
• new endosteal bone that contacts porous surface of implant
• absence of radiolucent lines around porous portion of
femoral stem
• proximal stress shielding in extensively-coated stems
• absence of stem subsidence on serial radiographs

32. SPECIALIZED AND CUSTOM-MADE FEMORAL
COMPONENTS
• used most commonly in
minimally invasive anterior
approaches
• Used salvage procedures
• some malignant or aggressive
benign bone

33. CEMENTED ACETABULAR
COMPONENTS
• Thick-walled polyethylene cups
• Addition of Vertical and horizontal grooves to external
surface
• increase stability within the cement mantle
• wire markers were embedded
• better assessment of position on postoperative radiographs
• PMMA spacers (3mm height)
• To avoid buttoming out
• A flange at the rim
• aids in pressurization of the cement

34. CEMENTLESS ACETABULAR
COMPONENTS
• Circumferentially Porous coated for bone ingrowth
• oversizing of the implant 1 to 2 mm larger than the reamed
• Fixation of the porous shell with transacetabular screws
• Most systems use
• Metal shell with an outside diameter (40 to 75 mm)
• Typically accommodates head sizes 22-40mm
• Secure liner to the cup
• Failure- back wear

35. Cont…..

36. CONT…
 Constrained acetabular component includes:
• Mechanism to lock head to the liner
• Tripolar mechanism
• A locking ring applied to the rim
• Indications:
• Insufficient soft tissues,
• Weak abductors,
• Neuromuscular disease
• Recurrent hip dislocation despite well-
positioned prosthesis

37.  Dual mobility acetabular component:
• Unconstrained Tripolar design
• Porous coated shell
• Polished interior
• Large polyethylene ball
• Smaller metal or ceramic head
• 2 sites of motion
• External bearing – b/n polyethylene and metal Moves at extremes of
motion
• Internal bearing – b/n head and polyethylene

38.  Custom components (reconstruction):
• Rarely indicated
• Most deficient acetabula can be restored to a hemispherical
shape
• A cementless acetabular component
• With modular porous metal augments
• used instead of a large structural graft
• Augments of various sizes are screwed into bony defects
• The augments are joined to the implant with the use of bone
cement
• Antiprotrusio rings and cages.

39. Bearing surfaces
 Metal-on-polyethylene:
• Metal (cobalt-chrome) femoral head on polyethylene acetabular line
• Benefits:
• longest track record of bearing surfaces
• lowest cost
• most modularity
• Disadvantages:
• higher wear and osteolysis rates
• smaller head leads to higher risk of impingement

40.  Metal-on-metal
• Benefits:
• Better wear properties than metal-on-polyethylene
• Lower linear wear rate
• Debris particles much smaller
• larger head allows for increased ROM before impingement
• Disadvantages:
• more expensive than metal-on-polyethylene
• increased metal ions in serum and urine
• May form pseudotumors

41.  Ceramic on Ceramic
• Benefit:
• best wear properties of all bearing surfaces
• lowest coefficient of friction of all bearing surfaces
• inert particle
• Disadvantages
• more expensive than metal-on-polyethylene
• worst mechanical properties
• Squeaking
• stripe wear

42.  Ceramic on polyethylene
• Benefits:
• Standard of care
• Alumina ceramic heads
• Results in less polyethylene wear than metal-on-polyethylene
• Disadvantages:
• zirconia undergoes tetragonal to monoclinic phase
transformation with time

43. Indications for THR
• Original primary indication:
• alleviation of incapacitating arthritic pain in patients>65 yrs
• whose pain could not be relieved by non surgical means
• For whom the only surgical alternative was resection arthroplasty (Girdlestone resection
arthroplasty) or arthrodesis.
• Secondary importance was:
• the improved function of the hip.

45. Contraindications to THR
• Absolute:
• Active infection of the hip or any other region
• Medical unfit for surgery
• Relative:
• Morbid obesity
• Severe dementia
• Tobacco use
• Severe osteoporosis
• Untreated skin infection
• Absent or insufficient abductor musculature

46. Preoperative Patient Evaluation And
Optimization
 Hx:
• Pain: groin, lateral hip, anterior thigh and knee,
• Worse during activity, relieved by rest and limited weight bearing
• Through medical evaluation
• Cardiopulmonary disease, Renal insufficiency, infection, Malignancy and DM
• Anticoagulant medication:
• D/C Aspirin, clopidogrel 7-10 days before surgery
• D/C warfarin 5 days prior surgery

47. Cont….
• Pyogenic skin lesions should be eradicated
• Preoperative skin preparation with chlorhexidine
• Dental problems, and urinary retention should be addressed
• Preop counselling:
• Expectations
• Social support
• VTE prophylaxis
• Anesthesia
• Pain management plan

48. CONT…
 Physical exam- includes:
• Spine
• upper and lower extremities.
• Inspection
• Skin-Discoloration, wounds, or gross deformity
• Bony-Length, Position
• Gait-Antalgic, Trendelenburg

49. Cont…
 Palpation
• Greater Trochanter / Bursae
• Anterior Superior Iliac Spine
• Ischial tuberosity
• Iliac crest
• Iliotibial band / TFL
• NV-motor/sensory, pulses, reflexes

50. Cont…..
 ROM
• Flexion-120-135 deg
• Thomas test
• Evaluates hip flexion contractures
• Extension-20-30 deg
• Abduction-40-50 deg
• Adduction-20-30 deg
• Internal rotation 30 deg
• External 50 deg

51.  Special test:
• FADIR test
• hip Flexed to 90 deg, Adducted and Internally Rotated
• Positive test if patient has hip or groin pain
• Can suggest possible labral tear or FAI
• FABER test (aka Patrick's test)
• hip Flexed to 90 deg, ABducted and Externally Rotated
• positive test if patient has hip or back pain or ROM is limited
• suggest intra-articular hip lesions, iliopsoas pain, or sacroiliac
disease

52. Harris hip score

53. PREOPERATIVE RADIOGRAPHS
• Minimum requirement –AP pelvis showing proximal femur
and lateral view
• Review the integrity of the acetabulum
• Review width of femoral canal
• Look for femoral bowing, malrotation or occult fracture
• Templating
• Spine and knee x-rays maybe needed
• Obturator oblique and iliac oblique
• For patients with previous acetabulum fracture
• CT with 3D rendering is also recommended

54. Preoperative Templating
 Importance
• allows surgeon to anticipate potential difficulties
• reproduce hip biomechanics
• minimizes leg length inequality
• Accuracy
• 52-98% accurate +/- one size
• related to experience and practice

55. Cont…..
 Steps
• obtain appropriate radiographs
• record vital patient information on template (age, height, weight, etc)
• establish radiographic landmarks
• establish limb length discrepancy
• template acetabular component
• template femoral component

56. Appropriate radiograph
LLD

57. Template acetabular component

58. Template femoral component

59. Cont….

60. THA Stability Technique
• Four important variables that help determine the stability of THA:
• Component design
• Position component
• Soft-tissue tensioning
• Soft tissue function component

61. PREPARATION AND DRAPING
• Appropriate operating table
• Positioning devices
• Preop tranexamic acid
• hip and entire limb are prepared with a
suitable bactericidal solution
• a U-shaped plastic drape are applied
• Protect bony prominences

62. SURGICAL APPROACHES AND
TECHNIQUES
• The choice of specific surgical approach is:
• Matter of personal preference
• Training
• prior incisions
• obesity
• risk for dislocation
• implant selection and degree of deformity
• Anterior
• Supine
• medial border of TFL muscle;

63. Cont….
 Anterolateral
• Charnley- supine with GT osteotomy
• Amstutz-lateral with GT osteotomy
 Direct lateral-supine or lateral with split of abductors
• Dall- removed the abductor with a flake of bone
• Head-reflect vastus lateralis & G. medius together
 Posterolateral- lateral with hip delivery
 Extensile

66. THA Through Posterolateral Approach

67. EXPOSURE AND PREPARATION OF
THE ACETABULUM

68. Reaming of acetabulum

69. Acetabular cup placement (cementless)

70. Cont….

71. IMPLANTATION OF CEMENTED
ACETABULAR COMPONENT

72. EXPOSURE AND PREPARATION OF
THE FEMUR

73. Reaming of Femoral Canal

74. Femoral stem placement (cementless)

75. Femoral stem placement (cemented)

76. THA THROUGH THE
DIRECT ANTERIOR APPROACH

77. THA Postoperative Inpatient Management
• Care can be broken down into different
phases including:
• Preoperative teaching
• Inpatient acute care (hospital)
• Inpatient extended care (rehab)
• outpatient home care

79. Acute complications
• Periprosthetic Fracture
• Dislocation
• Sciatic Nerve Palsy
• Leg Length Discrepancy
• Vascular Injury & Bleeding

81. Chronic complications
• Aseptic Loosening
• Iliopsoas Impingement
• Trunnionosis
• Pseudotumors

82. References
• Campbell's OPERATIVE ORTHOPAEDICS 14TH EDITION
• Orthobullets
• CLINICAL ORTHOPAEDICS AND RELATED RESEARCH
• BMC musculoskeletal disorder