Role of templating in total hip replacement

1. By Dr Bushu
Post graduate 3rd year
LNJP

2.  Concept of Templating
 Methodology of Templating
 Templating in Difficult Hips

3.  Total hip replacement (THR) is a process in which
the hip joints are replaced with artificial joints or
prosthesis.
THR is a surgical procedure that replaces the
diseased cartilage and joint with artificial
materials made of metal and plastic. The use of
these implants is intended to help the patients
lead a normal life without any interference or pain
in the joints when walking and performing daily
activities.
 The three main components involved in THR are
the stem & neck, acetabular cup and head.

5.  What does template mean?
A pre formed pattern made of metal, plastic, or
paper, used for making many copies of a shape
or to help cut material accurately

6.  Templating in THR is a radiographic exercise using
preformed templates in the preoperative planning
process.
 Main Goals of templating :
i. To estimate the position and insertion depth of acetabular
and femoral components
ii. To anticipate potential difficulties to reproduce hip
biomechanics with the available implants
iii. Helps recognising “difficult hips” where restoration of
the original hip anatomy is difficult.
iv. To predict implant size.
 By combining clinical data with careful templating, the surgeon has the
best chance of achieving successful, reproducible results while
efficiently utilizing resources and minimizing perioperative
complications.

7.  Anticipated peroperative problems :
 At the acetabular side : mainly to recognize protrusion and
the need for bone grafting.
 At the femoral side : mainly to recognize coxa vara & Coxa
valga.
 Hip templating allowed to restore stem offset in 58-86% of
cases and to restore the position of the hip rotation centre
within 5 mm, and leg length within 3 mm in 87-91% and 89%
respectively
 According to Maurice Müller hip templating
“forces the surgeon to think in three dimensions, greatly
improves the precision of surgery, shortens the length of the
procedure, and greatly reduces the incidence of
complications”.

8. A four-step approach for hip templating on a
standardised standing pelvic radiograph :
 1. Assess the quality of the radiograph
 2. Identify anatomical landmarks
 3. Identify mechanical references
 4. Optimise implant positioning to restore hip
biomechanics.

9.  The first step : Appropriate radiographs.
 A minimum of two views required, one in the
anteroposterior (AP) projection and one lateral view.
 A low AP pelvic radiograph with the x-ray beam centred
on the pubis is preferred for hip templating.
 The proximal third of the femur in 15o internal rotation.

11.  An AP view of the pelvis
 The standard distance from the x-ray tube to the table
top is 40 inches.
 Template X-rays are 120% magnified.
If a grid cassette is placed directly beneath the hip,
magnification of the bones of approximately 10% is seen in
an average-size patient, but in most radiology departments a
x-ray tray is placed in a compartment approximately 2
inches below the table top, resulting in magnification of 15%
to 20%.
The degree of magnification is directly related to the
distance from the bone to the cassette.
The marker used in our department consists of 5 paper pins
kept at 1cm distance.

13.  In case of flexion contracture the radiographic
technique should be modified.
 In presence of a flexion contracture, typically the
femur will be off of the table top with the patient
supine, or there will be increased lumbar lordosis.
 These inaccuracies can be minimized by obtaining
the AP radiographs in a semisitting position.

14.  To estimate the length of the femoral neck, both femora should
be positioned in 15 to 20° of internal rotation,
corresponding to the natural femoral anteversion .
 When the femoral neck is parallel to the film, the lesser
trochanter is on average 2.3 ± 3.1 mm broad and in most
cases less than 5 mm of lesser trochanter should be visible
medially from the proximal femur.

16.  Patients with degenerative disease tend to develop
external rotation contractures.
 If the pathologic hip cannot be internally rotated 15°,
templating can be done on the contralateral normal or less
involved side.
 In many cases, however, both hips have external rotation
contractures. In such cases, a PA radiograph can be
obtained with the patient placed prone, with the affected
limb in 15° to 20° of external rotation and the hip directly
against the table top

18.  If there has been a previous fracture or osteotomy, long
films of the entire femur are advisable.
 A standing film that includes the hip, knee, and ankle
will give a more accurate assessment of the effect of the
angular deformity on the overall limb alignment.
 In patients with posttraumatic arthritis subsequent to
acetabular fractures, further radiographic evaluation is
advisable like Judet views and CT scans.
 Radiographs should be examined for bone quality.

19.  Dorr classification

20.  Dossick et al. described a method of classifying
proximal femoral geometry based on the calcar-to-
canal ratio. It corresponds to Dorr classification of
femoral medullary canal.
1. Type A bone : ratio <0.5, champagne type. Favours the
use of uncemented stem
2. Type B bone : ratio 0.5- 0.75.
Thinning of the posterior cortex on the
lateral view.
3. Type C bone : ratio >0.75
Thinning of cortices on both views,
typical of a stovepipe•femur. Favours
the use of cemented stem.

22.  Anatomical landmarks should be easy to identify, both
on an anteroposterior (AP) pelvic radiograph and during
surgery, even in cases where the anatomy has been
distorted by pathology.
 At the femoral side, the medullary canal, the lesser and
the greater trochanter & “the saddle”, i.e. the most distal
part of the junction between the superior aspect of the
femoral neck and the greater trochanter. It can be used to
transpose the position of the planned femoral neck cut.
 At the acetabular side, the acetabular roof and the
“teardrop” are adequate landmarks.

23.  The “teardrop” is a radiographic landmark created by
the superposition of the most distal part of the medial
wall of the acetabulum.
 The most distal aspect of the teardrop corresponds to
the most distal and medial part of the acetabulum,
behind the transverse ligament and at the superior
border of the foramen obturatum.
 The ilioischial line (Kohler's line) has been used to
estimate the degree of protrusio acetabuli
radiographically. This line extends from the sciatic
notch to the lateral edge of the obturator foramen.

24. Standing anteroposterior pelvic radiograph suitable for hip templating. Anatomical
landmarks : 1. Femoral shaft ; 2. Greater trochanter ; 3. “Saddle” ; 4. Lesser trochanter ;
5. Acetabular roof ; 6. Teardrop. Landmarks for radiographic quality assessment : I.
Foramen obturatum ; II. Symphysis ; III. Sacrum ; IV. Distance between symphysis and
sacro coccygeal joint

25. Femoral and Acetabular rotation centre
 The acetabular rotation centre can be defined as the point
around which all hip movements occur.
 If the acetabulum and the femoral head are preserved, the
acetabulum and the femoral head are concentric and both, the
acetabular and the femoral rotation centre project on the hip
rotation centre.
.

26. Identifying the Center of Rotation
 The ideal position for the acetabular template (and
component) is achieved by placing the inferomedial edge
adjacent to the lateral margin of the teardrop.
 In most patients, this will restore the center of rotation
very close to an anatomic and desirable location.
 This can be checked by measuring the horizontal and
vertical distances from the teardrop to the templated
center of rotation, and comparing them to the coordinates
from the teardrop to the center of the normal or
unaffected contralateral hip.

27.  If the distances are equal and there is no difference in
limb length, then this point can be utilized as the point
about which the reconstruction can be planned.
 If a limb-length discrepancy is present with the affected
side short, which is most often the case, the femoral
center of rotation planning point is moved superiorly
above the acetabular rotation center. Templating is done
to plan correction of shortening.

29.  Femoral, Acetabular and Combined offset
 The femoral offset is defined as the perpendicular distance
from the neutral long axis of the femur and the center of
rotation of the hip. Restoring the normal degree of offset is
a primary goal of hip replacement, thus making this
measurement valuable.
 If pathology has deformed the femoral head, the original
femoral offset can be estimated as the distance between the
original femoral rotation centre and the longitudinal axis
of the proximal femur.

31.  The femoral offset is important because it controls the
tension and moment arm of the abductor muscles, the
tension of the soft tissues , the wear of the acetabular
component and the load imposed on both, the acetabular
and femoral implants .
 Failure to restore the femoral offset may lead to excessive
wear, limping and/or hip instability .
 Excessive femoral offset has the potential to overload
the femoral implant, to generate micromotion at the
implant-bone interface and to cause pain in the abductor
muscles and the region of the greater trochanter.

32.  The acetabular offset can be defined as the shortest
distance between the acetabular rotation centre and a
perpendicular to the interteardrop line, drawn along the
projection of the most distal part of the teardrop .
 The acetabular offset is important because it controls the
tension of the abductor muscles and the soft tissues as
well as the lever arm of the body weight and thus the
load transmitted to the acetabulum.

33.  Decreasing the acetabular offset by excessive
medialisation of the acetabular component may lead
to limping and/or hip instability.
 Increasing the acetabular offset may overload the
cup.
 The combined offset can be defined as the sum of the
femoral and acetabular offset.
 Vertical offset

34.  The neck shaft angle, defined as the angle between the
central axis of the femur and the axis of the femoral
neck.
 There is wide variation of this angle, with a reported
mean of 124.7± 7.4o.
 The abductor moment arm is estimated by drawing a
line between the anterior superior and posterior
superior iliac spines. A line is drawn from a point one
third of the way from the posterior to the anterior
superior spine, to the tip of the trochanter. This
approximates the line of the pull of the gluteus medius.
A perpendicular is then constructed from the center of
rotation of the head to this line, and its length represents
the abductor moment arm.

36. Limb Length.
 This is commonly estimated by drawing a horizontal
line along the inferior margin of both ischial
tuberosities (interischial line).
 The vertical distance from this line to either the top
or the middle of the lesser trochanter of each hip is
measured. The distance between the two is recorded
as the limb length discrepancy. This should be
correlated with clinical measurements.
 The amount of desired lengthening should be well
established preoperatively and incorporated into the
plan.

38. POSITIONING OF THE PROSTHESIS
(Templates used are from Stryker for uncemented THR with
proximal coated stem)
 The main goal is to restore as nearly as possible the
anatomic or premorbid centre of rotation and femoral
offset, while equalizing limb length.
 If the anatomy of the hip to be replaced is well preserved,
templating can easily be performed on the pathological
side. However, when the pathological hip is deformed or
radiographed in an inappropriate position, it can be easier
to template the healthy contralateral hip and to mirror the
result to the pathological side.

39. Acetabular Side
 Templating appropriately begins with the acetabular
side, because this is the sequence that is followed in
surgery.
 The acetabular template is placed just lateral to the
lateral edge of the teardrop at a 45° angle.
 Ideally, the cup should be completely covered by bone
and should span the distance between the teardrop and
the superolateral margin of the acetabulum. The
component size that best accomplishes this with minimal
removal of subchondral bone is selected.

40.  For cemented sockets, a uniform 2- to 3-mm space must
be left for cement. This is often indicated on templates
by a dashed line.
 The center of rotation is marked through the template. If
the component's medial edge is just lateral to the
teardrop.

41. Protrusio Acetabuli
 Protrusio acetabuli is present in a number of primary hip
replacements, particularly in cases of rheumatoid
arthritis, ankylosing spondylitis, Paget's disease, and any
metabolic bone disease that weakens the subchondral
bone.
 Leaving the hip center in the medialized location is not
advisable, because there is often not optimal structural
support for the component in that position, and the
opportunity to restore medial bone should be utilized.

42.  The femoral head can be morselized and used as a
medial graft to lateralize the component to a more
normal anatomic position. It should be noted that a
large volume of morselized bone may be necessary
to achieve component lateralization, and it may be
necessary to utilize additional allograft material in
addition to the autograft from the femoral head

44.  Lateralizing the component in cases of protrusio acetabuli
has the additional advantage of increasing combined
offset.
 Because the cup is contacting bone graft medially rather
than structurally supportive subchondral bone, a large
acetabular component is needed to achieve peripheral rim
contact.
 Failure to achieve initial stability through a tight rim fit
risks fracture of the medial wall during insertion or
medial migration and recurrence of protrusio acetabuli
over time.
 Significant lengthening occurs through the acetabulum in
protrusio acetabuli cases. This is often desirable, since the
limb is often short in these cases.

45.  When lengthening occurs through lateralizing the socket,
the amount of further lengthening that can reasonably be
obtained may be limited, a lower neck cut and shorter
prosthetic neck segment may be utilized in these cases.
 In cases where protrusio acetabuli is associated with
severe osteoporosis, as in rheumatoid arthritis, it is
occasionally prudent to consider a protrusio ring or cage.

46. Lateralized Acetabulum
 In many cases of degenerative osteoarthritis, the presence
of hypertrophic osteophytes in the acetabulum causes
lateralization of the hip's center of rotation.
 This becomes apparent during templating when 1 or 2 cm
of reaming is noted to be necessary to place the
component in the vicinity of the teardrop.
 Failure to recognize this will result in placement of the
acetabular component in a lateralized position with
incomplete bony coverage and suboptimal stability.

47.  Identifying the anatomic location of the hip joint in such
cases can be difficult.
 The most reliable structural landmark is the transverse
acetabular ligament that marks the inferior border of the
true acetabulum.
 If reaming is initiated above the transverse acetabular
ligament in a straight medial direction for several
millimeters, the location of the cotyloid notch becomes
apparent and it can be curetted of bone, cartilage, and soft
tissue.
 Straight medial reaming to within a few millimeters of the
planned depth of reaming is advisable to avoid superior
placement of the component.

49.  If the cup remains more than 10% to 20% uncovered in
spite of all of these maneuvers, a structural graft fixed to
the pelvis can be considered.
This possibility should be recognized during templating,
because a significant amount of additional equipment
may be required.

50. When the template is placed adjacent to the teardrop and
the lateral margin is uncovered, a number of options
exist:-
 Medial reaming to the subchondral plate.
10% to 20% uncoverage can be accepted, and screws can
be used to augment fixation of cementless components
because there will not be circumferential peripheral
contact.
In cemented components, cement augmentation of the
superolateral deficiency has been described without
deleterious effects on component fixation.
 The acetabular component can be positioned somewhat
vertically.

51. Femoral Templating
 After the planned center of rotation of the reconstruction
is marked on the radiograph, the femur is templated.
 Femoral implant is chosen to fit the medullary canal.
 The longitudinal axis of the implant is positioned parallel
to the longitudinal axis of the femur and the
approximate insertion depth is chosen in order to
correctly restore the leg or hip length.
 Fine tuning to restore the offset and the original femoral
rotation centre, can be done in three different ways :
(i) medialising or lateralising the femur by using a
standard or offset stem,
(ii)choosing a stem with a different neck-shaft angle
(iii) modifying the length of the femoral neck

52.  The goals and emphasis of femoral templating vary
depending on whether a cementless proximally coated,
cementless extensively coated, or cemented stem is
planned.
 It is prudent to template for both a cemented and
cementless stem, particularly in cases where any
anatomic abnormality is identified.

53.  Component size is judged from the AP radiograph of the
hip.
 For proximally coated components, proximal fit and fill
are generally emphasized.
 For cemented stems, it is important to leave adequate
room for a cement mantle. A 2- to 3-mm circumferential
cement mantle is optimal.

54.  A repeated “trial and error technique” allows selecting the
correct stem size and type as well as the right neck-shaft
angle and neck length.
 The femoral template is moved vertically until there is
proximal fitting of stem in femur.
 Regardless of the stem type utilized, the templates should be
kept centered along the neutral axis of the femur, rather than
in any varus or valgus inclination
 With the appropriate template in place, the insertion depth
and the level and orientation of the femoral neck cut are
noted in relation to the greater and lesser trochanter.
 Traditionally, the distance between the lesser trochanter and
the medial border of the femoral neck cut is used as a
landmark to evaluate the height of the neck cut and the stem
insertion depth, which is ideally around 1-2cm.

55.  If the center of the femoral head template lies medial to
the planned center of hip rotation when the template is
at the appropriate height, stem insertion to this level
will increase femoral offset, which is generally an
advantage, particularly if it is a matter of a few
millimeters.
 Excessive increase in offset may cause prominence of
the trochanter with a tendency toward bursitis and
should be avoided.
 If the center of the femoral head template lies lateral to
the planned center of hip rotation, then the
reconstruction will decrease femoral offset, and this is
particularly to be avoided.

56.  Limb Length Discrapency
 Shortening, which is present in most of the cases.
2.7- 4 cm of limb lengthening can be done safely.
The shortening can be compensated by :
i) Using longer neck length
ii) Prosthesis with higher neck- shaft angle
iii) High neck cut +/- with proud stem.
Lengthening can be compensated by:
i) Using shorter neck lengths.
ii) Prosthesis with lower neck-shaft angle
iii) Low neck cut

58. Neck Shaft Angle
 If the neck shaft angle is measured preoperatively, it can
be compared to the neck shaft angle of the implant to be
utilized. If there is a difference of more than a few
degrees, a predictable pattern of intraoperative
adjustments can be made.
 The average neck shaft angle is approximately 125°,
whereas most implant systems have a neck shaft angle of
130° to 135°.
 Values significantly lower than this represent coxa vara,
and values above this represent coxa valga.

60. Coxa Vara
 Patients with coxa vara have higher than usual
femoral offset. This can be compensated for by
utilizing a component with a lower neck shaft angle,
or by making a lower neck cut and utilizing a longer
neck.
 Making a standard-length neck cut can significantly
lengthen the leg without restoring offset.
 To avoid limb lengthening a distal neck cut and a
low stem insertion position are often required.

62. Coxa Valga
 The opposite situation exists when the patient's neck
shaft angle significantly exceeds that of the prosthesis.
 There is a relatively low offset and more length.
 To compensate for this with a component with less
valgus, it is necessary to make a higher neck cut and use
a shorter neck to maintain length and offset.

68. THANK YOU