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Nicholas Wei and Paul Banaszkiewicz
and lateral approaches to hip arthroplasty have
been shown to increase the risk of HO formation
in retrospective studies.
HO formation is a common complication
following operative repair of acetabular fractures,
particularly those treated with posterior, combined and extensile approaches.
Rheumatoid arthritis is said to be protective
against HO, which may be partly due to the
NSAIDs these patients take for pain relief.
Pavlou G et al. Risk factors for heterotopic
ossification in primary total hip arthroplasty. Hip
Int. 2012;22:50–55.
Zhu Y et al. Incidence and risk factors for
heterotopic ossification after total hip arthroplasty: a meta-analysis. Arch Orthop Trauma
Surg. 2015;135:1307–1314.
23. Answer A. An initial mode Ia failure may pro-
gress into mode II failure
Gruen’s (1979) original paper reported that three
cases of Mode 1a failure progressed into mode II
failure. The cemented femoral component initially loosened into mode la failure and the subsequent distal punch-out fracture rendered
inadequate distal acrylic support. Together with
poor proximal medial cement support, these
cases progressed into mode I1 failure.
The modes of failure were based on a Charnley
prosthesis.
Gruen’sseminal paper isregarded asa classicin
orthopaedics. It introduced the concept of Gruen
femoralzones dividingthe femur into 7 regions for
detailed review of anteroposterior (AP) radiographs of cemented femoral components for signs
of loosening. In addition, it presents a detailed
analysis of the modes of failure of cemented femoral stems (Banaszkiewicz 2014).
Gruen TA, McNeice GM, Amstutz HC.
“Modes of failure” of cemented stem-type femoral
components: a radiographic analysis of loosening.
Clin Orthop Relat Res. 1979;141:17–27.
Banaszkiewicz PA. “Modes of failure” of
cemented stem-type femoral components: a radiographic analysis of loosening. In Classic Papers
in Orthopaedics,35–38. London: Springer; 2014.
24. Answer A. Component malalignment
Early dislocation following THA is usually either
due to component malalignment or failure to
comply with post-operative instructions. The
giveaway in the stem is the relative inexperience
of the surgeon and the fact it is day 1 postoperatively with the patient not yet having been
mobilised. The dislocation rate is double for surgeons who have performed less than 30 hip
replacements when compared with surgeons
who have performed more than 30. Whilst close
trainee supervision by a consultant will likely
lessen the chance of dislocation this does not
prevent it occurring. Sources of impingement
such as cement or osteophytes may cause dislocation in the early post-operative period but are
very rare causes.
The occurrence of dislocation after THA is
variable. Surgeons usually advise patients of a
1–3% dislocation risk (Meek et al. 2006).
However, data from an arthroplasty registry in
the UK suggest a higher rate of 5% at 5 years
post-operatively (Fender et al. 1999). Several
studies have suggested THA dislocation is related
to the experience of the surgeon including
the volume of surgery performed. Hedlundh et
al. (1996) reported that surgeons who perform
less than 10 THAs a year have three times the
risk of dislocation in the THA recipient.
However, the rate did not decrease once the
surgeon reached a volume of more than 30
THAs per year.
Meek RM, Allan DB, McPhillips G, Kerr L,
Howie CR. Epidemiology of dislocation after
total hip arthroplasty. Clin Orthop Rel Res.
2006;447:9–18.
Fender D, Harper WM, Gregg PJ. Outcome
of Charnley total hip replacement across a single
health region in England: the results at five years
from a regional hip register. J Bone Joint Surg Br.
1999;81:577
Hedlundh U, Ahnfelt L, Hybbinette CH,
Weckstrom J, Fredin H. Surgical experience
related to dislocation s after total hip arthroplasty.
J Bone Joint Surg Br. 1996;78:206–209.
25. Answer E. Spinal fusion
Both patient-related factors and surgeoncontrolled factors influence the likelihood of dislocation after THA. A number of technical modifications were developed in the 2000s to address
THA instability, including increasing the femoral
head diameter, use of posterior lip acetabular
–581.
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Hip III Structured SBA
liners and the introduction of the dual mobility
bearing. These adaptions have been as sociated
with a dec lining rate of dislocation.
A recent study by Gausden et al. (2018)
reviewed a Nationwide Readmission Database.
A total of 207,285 THAs were identified between
2012 and 2014. Of the total, 2842 dislocationassociated readmissions (1.4%) were identified,
at a median of 40 days post-THA. A history
of spinal fusion was the strongest independent
predictor of dislocation. Parkinson’s disease was
also significantly associated with dislocation,
as well as dementia, depression and chronic lung
disease.
Gausden EB, Parhar HS, Popper JE, Sculco
PK, Rush BN. Risk factors for early dislocation
following primary elective total hip arthroplasty.
J Arthroplasty 2018;33:1567–1571.
26. Answer B. Cup inclination angle
This SBA is fairly small point as it deals with the
contact patch area of a MoM hip. We think it is
useful to include as it introduces biomechanical
concepts worth knowing about if you are going
for the gold medal.
The contact patch is the area of the femoral
head articular surface that makes contact with
the acetabular component during any and all
functions (Yoon et al. 2013).
The ‘contact patch to rim’ (CPCR) distance
describes the distance from the edge of the contact
area to the acetabular rim (Underwood et al. 2012).
Edge loading occurs when the contact area
between the head and cup intersects the rim of
the cup. It is thought that CPCR can determine
the susceptibility of a MOM to edge loading and
is likely to correlate with component wear and
blood metal ion levels.
In order of decreasing effect on CPCR the
variables were: cup inclination angle, cup version
angle, arc of cover, femoral diameter and clearance (Matthies et al. 2014).
The Articular Surface Replacement (ASR;
DePuy Orthopaedics) was more susceptible to
suboptimal cup position. In addition, its reduced
arc of cover was also associated with increased
wear rates and higher ion levels.
An understanding of the design features of
the ASR implant that led to its failure and recall
from market is useful.
Design features such as the reduced ‘arc of
cover’ (the angle subtended by the articular surface of the cup) and head-cup clearance are
thought to have increased the likelihood of edge
loading and high wear.
Suboptimal component position and design
are thought to lead to edge wear and raised blood
metal ion levels in metal-on-metal hips.
It is thought that edge loading leads to
increased contact pressures and disruption of
the lubrication regime.
Matthies AK et al. Predicting wear and blood
metal ion levels in metal-on-metal hip resurfacing. J Orthop Res. 2014 ;32:167–174.
Underwood RJ, Zografos A, Sayles RS, Hart
A, Cann P. Edge loading in metal-on-metal hips:
low clearance is a new risk factor. Proc Inst Mech
Eng H. 2012;226:217–226.
Yoon JP et al. Contact patch to rim distance
predicts metal ion levels in hip resurfacing. Clin
Orthop Relat Res. 2013;471:1615–1621.
27. Answer A. Decreased femoral head offset
In general terms when the femoral neck impinges
on the acetabular cup, it begins to lever out of the
socket. The range of motion allowed be fore the
hip dislocates is termed the lever range. The
excursion distance is the distance the head must
travel to dislocate. In effect this excursion distance is equal to half the diameter of the femoral
head. Most textbooks regard excursion distance
and jump distance (JD) as similar equivalent
terms but this is an approximation and not
strictly true.
The JD is the degree of lateral translation of
the femoral head centre required before dislocation occurs.
Sariali et al. (2009) evaluated jump distance
and its variation according to implant characteristics. They found that JD varies according to (1)
cup abduction angle, (2) cup anteversion angle,
(3) fem oral head diameter and (4) cup centre
offset.
It is only partly true that JD increases with
femoral head diameter. JD depe nds not only on
femoral head size, but also on orientation of the
implanted cup and on cup offset. The position of
the implanted cup has two variables that affect
JD: (1) abduction angle and (2) anteversion
angle.
95
Nicholas Wei and Paul Banaszkiewicz
Force
vector
CPER
distance
Racial clearance + R
cup
-R
head
CPCR
distance
Contact
patch
Joint Reaction
force vector
CPCR
distance
-ve CPER
distance
CAAA - Cup
articular arc angle
Low clearance
CPCR Distance
Contact Patch
Figure 5.24 Contact patch centre to rim (CPCR) distance describes the distance from the centre of the contact area to the acetabular rim.
Contact patch edge to rim (CPER) distance. When the contact patch between head and cup extends over the cup rim this leads to a large
increase in local contact pressure, disruption to the lubrication mechanism and increases wear rate at the cup rim occurs.
JD decreases as the abduction angle increases.
JD increases as the acetabular anteversion
increases but this variation is much lower
than the variation according to abduction
angle.
CPER Distance
Contact Patch
ofthecup,whichisthecasewhenthecupis
not a full hemisphere or when the acetabular
liner is offset to increase the amount of
material medially in the polyethylene liner.
The offset is negative (and is called an inset)
when the head centre lies inside the opening
With regard to the femoral head
JD was found to decrease as the femoral head
offset increases.
JD increases as the femoral head diameter
increases.
plane of the cup. Increasing the offset causes
thecentreofrotationtolayoutsidethe
opening plane of the cup, thereby making
the cup shallower and increasing susceptibility to dislocation.
The net gain obtained by increasing the fem-
Femoral head offset is the shortest distance
from the centr e of the head to the opening
planeofthecup.Theoffsetispositivewhen
theheadcentreliesoutsidetheopeningplane
oral head diameter is counterbalanced by the
increase in femoral head offset.
A final point to consider is that dislocation
after THA is nevertheless a multifactorial
96
Hip III Structured SBA
phenomenon and cannot be analysed with only
the jump distance as a predictive parameter.
Sariali E, Lazennec JY, Khiami F, Catonné
Y. Mathematical evaluation of jumping distance
in total hip arthroplasty: influence of abduction
angle, femoral head offset, and head diameter.
Acta Orthopaedica 2009;80:277–282.
Table 5.1 Factors affecting the jump distance
Factors that decrease jump distance
Increase in femoral head offset
Smaller acetabular hemisphere
Polyethylene liners with an offset
Increased abduction angle
Factors that increase jump distance
Decreased femoral head offset
Increased anteversion
Larger acetabular hemisphere
Figure 5.25 Jump
distance is the
femoral head centre
translation distance
required for a head
to dislocate from
a socket
28. Answer D. Intraosseous extravascular factors
This SBA neatly summarises possible vascular
causes for ON otherwise aetiological factors can
end up becoming a random list of causes that
candidates may find difficult to structure to aid
1
recall.
Extraosseous arterial factors.
The femoral head is at increased risk because
blood supply is an end-organ system with poor
collateral developme nt. Blood supply can be
interrupted by trauma, vasculitis (Raynaud’s disease) or vasospasm.
Intraosseous arterial factors.
May block the microcirculation of the femoral head through circulating microemboli.
Possible causes include sickle cell disease (SCD),
fat embolisation or air embolisation from dysbaric phenomena.
Intraosseous venous factors
Reduce venous blood flow causing stasis.
Causes include Caisson disease, SCD or enlargement of intramedullary fat cells.
Intraosseous extravascular factors
Increased pressure in the femoral head that
results in a femoral head compartment syndrome.
Causes include fat cells hypertrophy after steroid
administration or lipid deposit in the marrow.
Cytotoxic factors (alcoholism, steroid use) have a
direct toxic metabolic effect on osteogenic cells.
Extraosseus extravascular (capsular) factors
This involves tamponade of the lateral epiphyseal vessels resulting in ON.
OFF SET
165°
A
29. Answer D. Total hip arthroplasty
The patient’s radiographs demonstrate Ficat
grade III ON. There is ill-defined mixed sclerotic
and lytic lesion of the left femoral head.
Additional cortical collapse of the superior aspect
of the femoral head is noted with a linear area of
Figure 5.26 The femoral head offset is
the distance from the centre of the head
(O) to the opening plane of the cup (red
line). (a) If the head centre is outside the
IN SET
B
cup, the offset is positive (A); (b)
otherwise, it is negative and is called inset
(B). The use of large heads above 38 mm
in diameter generally imposes the use of
an offset because the cup is usually a
truncated hemisphere of 165° for the
large heads
97
Nicholas Wei and Paul Banaszkiewicz
lucency below it (crescent sign). Evidence of secondary degenerative change.
Surgical management can be broadly divided
into joint preserving or joint replacing procedures.
The ON is too far advanced for a joint preserving
procedure and the best choice would be for total
hip arthroplasty. Although hip resurfacing has
been used in the past it has fallen out of favour in
recent years because of the risks of ARMD.
30. Answer D. Second-generation HXLPE involves
sequential irradiation and annealing
First generation HXLPE involves either
annealing or remelting PE. The annealing
method involved a single thermal treatment
below the crystalline melt transition in polyethylene to preserve crystallinity and mechanical
properties, but also results in a material containing residual free radicals with the potential to
oxidise in vivo.
The remelting method involved thermal
treatment above the melt transition. This
resulted in a material with undetectable free radicals but at the expense of reduced crystallinity
and lower material properties.
Second-generation annealed HXLPE was
developed to further improve on first-generation
annealed HXLPE to achieve oxidative resistance,
and to maintain low wear and mechanical
strength. Cross-linking is achieved using a
sequential irradiating and annealing process,
which increases the amount of cross-linking.
Sequential annealing mops up most free radicals.
Second-generation methods were aimed at
quenching free radicals effectively without
remelting HXLPE and the related loss of crystallinity/mechanical properties.
Vitamin E-infused HXLPE is a secondgeneration HXLPE thatstabilises freeradicals without the need for sequential annealing or melting.
Vitamin-E stabilised HXLPE was introduced
to provide enhanced oxidation resistance without
compromising the fatigue strength. Vitamin E
improves oxidation resistance by stabilising free
radicals induced by irradiation, and avoids the
need for post-irradiation melting.
In summary
▪ Crystalline phase – provides mechanical
properties to PE.
▪ Amorphous phase – only amorphous area
can cross-link.
▪ Post irradiation melting eliminates all free
radicals but reduces mechanical properties.
▪ Cross-linking of free radicals occurs
during melting which prevents
recrystallisation.
▪ This results in lower crystallinity with
lowered mechanical properties.
▪ Annealing eliminates some but not all free
radicals.
▪ During annealing, crystalline areas do not
unravel and eliminate free radicals.
▪ Crystalline areas do not cross-link, so free
radicals remain leading to oxidation risk.
▪ Increased crystallinity – chain scissor
oxidation and wear. Mechanical properties
good but wear properties poor.
▪ Decreased crystallinity – decreased mechanical
properties but wear characteristics good.
Figure 5.27 Structure of HXLPE
98
Hip III Structured SBA
For the gold medallist
Loose loop – polymer chains will often
decide they want to come back into the lamella
after wandering around outside for a while.
Cilia – somet imes a polymer chain is indeci-
sive with part of it in the crystalline lamella and
part of it staying outside the lamella in the
amorphous region.
Tie molecule – some chains start in one
lamella, cross the amorphous r egion, and then
join another lamella. These chains are called
tie molecules. They provide a unique property
of tying the lamellae to each other. In a sense,
they act like cross-links and strengthen the
solid polymer, giving it better mechanical
properties.
31. Answer D. Radiographs hip
Most likely the surgeon would go in and reexplore the hip looking for any bruising, haematoma or discontinuity of the sciatic nerve. The
key words are dense and painful which alerts
for a major concern with the state of the nerve.
Most surgeons routinely check the sciatic
nerve to see if it is free from any suture entrapment or compression after repairing the short
external muscles and before moving on to close
the fascia lata but this is not mentioned in the
stem.
MRI could potentially locate a large haem-
atoma around the sciatic nerve pushing a surgeon towards re-exploration but a radiograph
would be the most useful all-round management
to see if the leg has been inappropriately
lengthened, if there is posteriorly protruded
cement, bony fragments or proud screws or any
other possible cause for the foot drop. This
should be done before you take the patient to
theatre.
If the footdrop is partial and/or painless the
situation is more debatable as to what to do next
and you may wish to consider ordering an MRI
scan before surgery.
32. Answer A. Bone marrow oedema syndrome
Bone marrow oedema syndrome (BMES) is a
diagnosis of exclusion that is characterised
by pain and increased interstitial fluid within
bone marrow without an obvious cause. It is a
distinct, benign disorder with a distinctive
self-limiting course.
With BMES radiographs are normal but an
MRI has characteristic findings. An MRI scan
will demonstrate diffuse marro w oedema, that
can extend to the intertrochanteric area, with
no focal or subchondral findings.
It generally affects middle-aged men (30–50
years) or women in the third trimester of pregnancy. In most cases no triggering events can be
found. The clinical course of the disease is often
self-limiting, with a spontaneous resolution in
4–24 months.
The first month is characterised by initial
pain and dysfunction. The next 1–2 months are
characterised by maximum pain levels. Finally,
symptoms regress over the next few months
following the period of maximal pain, but it
should be noted that the presentation and resolution of symptoms are highly variable.
Many theories have been proposed about the
pathogenesis of BMES. These include microvascular injuries, venous obstructions, abnormal
mechanical stress, metabolic and endocrine
factors.
There are other conditions that can cause
bone marrow oedema. They can be classified
according to their mechanism. The first group,
which is associated with an ischaemic mechanism, includes osteonecrosis and osteochondritis
dissecans. The second group have a mechanical
aetiology and includes stress fractures, microfractures and bone bruise. In the third group
the bone marrow oedema is reactive and includes
arthritis, tumour and post-operative oedema.
Balfousias T, Karadimas EJ, Kakagia DD,
Apostolopoulos A, Papanikolaou A. Lower limb
pain attributed to bone marrow edema syndrome: a commonly ignored pathology. Cureus
2020;12:e7679.
33. Answer A. Decreased ductility
Compared with standard UHMWPE HXLPE
has:
Better wear resistance.
The PE particles tend to be smaller in size and
produce less osteolytic reaction. There is
generally a decreased number of particles
generated.
99
Nicholas Wei and Paul Banaszkiewicz
Disadvantages include:
Decreases tensile strength which is the
pulling force to break.
Decreased fatigue strength which is the
maximum cyclic stress the material can
withstand.
Decreased fracture toughness which is the
force to propagate a crack.
Decreased ductility which is elongation
without fracture.
Although compared with standard
UHMWPE HXLPE has much better wear characteristics its mechanical properties are reduced.
34. Answer D. There are equivalent clinical results
with a ceramic and HCPLE bearing surface
combination
The incidence of squeaking varies in the literature with a figure around 7% being acceptable. It
is extremely rare to have to revise a hip due to
squeaking. It is more of an annoyance to patients
than anything else. The use of a CoC bearing
surface combination has halved in recent years
due to the risk of catastrophic failure, cost
and squeaking. More importantly for most
surgeons is that long-term results of ceramic
and new-generation HCPLE bearing surface
are now equivalent to that of CoC without
all the drawbacks of using a CoC bearing
combination.
Ceramic-on-ceramic bearings require
meticulous surgical technique both to avoid
chipping of the liner during insertion and to
place both the acetabular and femoral components in the appropriate anatomic position.
Failure to place the implants in the correct position has led to early failure of the acetabular
liner due to impingement.
Many surgeons have abandoned the use of a
ceramic articulation due to the concerns of
squeaking, limited intraoperative options, failure
of randomised clinical trials to demonstrate significantly improv ed survival rates, and the necessity for ‘perfect’ compo nent placement to reduce
the risk of catastrophic failure. Emerging longterm results of ceramic on HCPLE are showing
compatible survival rates when compared with
CoC bearing surfaces.
35. Answer B. Arrange for urgent clinic follow up
Radiographs demonstrate an anteverted and open
cup. These radiographs have not been reviewed
whilst the patient was in hospital. An anteverted
cup increases the risk of impingement, edge
loading, instability, dislocation, increased wear
and reduced longevity of the implant. This SBA is
about how to deal and prioritise two problems.
What (if anything) needs to be done about
the anteverted cup?
Is there a need for a duty of candour and on
what basis?
Bringing the patient back to the next available arthroplasty clinic to discuss the radiographs
is the best option. You can tell the patient that
you are not entirely happy with the postoperative radiographs and mention your concerns with the anteverted cup. The options are a
wait and see policy or revision of the cup.
On balance there is a duty of candour issue
due to (1) excessive anteversion of the cup and
(2) no post-operative review of radiographs.
Protocols in place to ensure patients have
their radiographs reviewed by a medical team
before they are discharged are important.
However, they are not an immediate issue, and
can be dealt with at a later date with drafting of
new department rules.
Asking the patient to attend the ED so that
the orthopaedic team on call can r eview them is
likely to significantly and unnecessarily worry
the patient. It is also futile as you are not going
to admit the patient acutely to a ward.
A duty of candour should be arranged and
preferably added at the end of the urgent outpatient review.
Ideally a senior nurse should be present when
you see the patient. Avoid a duty of candour letter
being sent out to the patient before you see them.
Whilst it is vital to discuss the case at an
MDT a patient-centred approach means that
the surgeon should meet with the patient as soon
as possible and not wait for an MDT meeting
before making contact.
In summary your main priority is to arrange
an urgent outpatient appointment to discuss the
anteverted cup and make a shared care decision
about what next if anything to do about it.
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Hip III Structured SBA
Reikerås O, Gunderson RB. Acetabular
component anteversion in primary and revision
total hip arthroplasty: an observational study.
Open Orthop J. 2013 Oct 4;7:600–4.
36. Answer A. Adopting a watch and wait policy for
the hip
This SBA is forcing you to rationalise your own
decision-making choices rather than default to
an MDT. The debate is whether the cup needs
to be immediately revised or whether to adopt a
watch and wait policy. This would need to be
fully discussed and documented with the patient.
In real life the case would have been discussed at
an MDT and the MDT’s recommendations
explained to the patient.
With a CoP bearing surface a position of watch
andwaitmaybethebestpolicyIfthepatient
develops pain or instability then these symptoms
would be strong indications for a revision
If the bearing surface was CoC and because
he is young, fit and active the cup should ideally
be revised as there is a significant risk of catastrophic failure.
Be guided by what the patient wants to do
and what the MDT recomme nds.
Physiotherapy whilst helpful is peripheral to
the two main choices of either to revise or
adopting a wait and see.
Most surgeons are highly unlikely to revise
the cup to a dual liner as prophylaxis to reduce
the dislocation risk.
Ultrasound scan would be to check for iliopsoas tendinitis but this is a feature of a retroverted cup.
Prophylactic hip bracing can be very useful in
certain situations but is a poor choice in this
particular patient.
37. Answer D. To recommend that THA should be
performed before TKA
The patient has end-stage rheumatoid disease
and is struggling with pain control and mobility.
In this situation there is not a huge amount of
benefit delaying surgery to perform steroid injections. In most situations most surgeons would
choose to perform a THA before a TKA. It is
therefore not critical to resolve the source of any
knee pain (including referred pain) with a steroid
injection into the hip unless there were major
worries from the patient about the decision to
proceed with the hip first.
38. Answer B. In patients with brittle rheumatoid
arthritis hip surgery is likely to be more
straightforward than knee surgery and a
patient’s confidence will be gained with performing relatively easy surgery
THA in a rheumatoid patient can be just as
equally difficult to perform as TKA so this statement is not as correct or valid a reason as the
other four options.
There is some controversy regarding the priority of joint surgery in patients with both joints
affected in the same limb; however, in most
cases, it is accepted that THA should be undertaken before TKA, when both are indicated. The
symptoms of these two conditions may overlap
and pain relief obtained from hip replacement
may delay knee replacement. The rehabilitation
may be more tolerable after hip replacement even
with significant ipsilateral knee involvement,
whereas the converse is not always true.
Additionally, adequate arc of hip motion is
required for deep knee flexion, which is often
required for successful TKA procedures.
If the knee is operated first the pain and
difficult rehabilitation may put the patient off
going ahead with THA.
39. Answer A. Decreasing the neck shaft angle
It is important for a hip arthroplasty surgeon to
have some idea about how to be able to alter the
offset of a THA. Five methods are available to
increase femoral offset (Charles et al. 2005). Four
of these are based on altering the geometry of the
femoral component or the proximal femoral
anatomy. The fifth one involves alteration of
the geometry of the acetabular liner.
1. Increasing the leng th of the femoral neck or
head
Increasing the length of the femoral neck or
head increases the resting length of the hip
abductors and, depending on the angle of the
femoral neck, increases their contractile
efficiency while concomitantly lengthening
the abductor lever arm. Unfortunately, an
increase in the neck length also increases the
limb length, resulting in a limb-length
101
Nicholas Wei and Paul Banaszkiewicz
discrepancy. This is an undesirable clinical
outcome in most cases.
2. Decreasing the neck shaft angle
Decreasing the neck shaft angle reduces the
height of the femoral head, and thus the limb
length, while increasing offset. This construct
directly increases the magnitude of the
abductor lever arm. It also has the positive effect
of increasing abductor tension, making the
muscles more efficient. However, this change
in implant dimension has the negative effect
of increasing the rotational torque imparted
to the implant from out-of-plane forces.
3. Medialising the femoral neck while
concomitantly lengthening the femoral neck
(high-offset femoral components)
High-offset femoral components either vary
the neck shaft angle of the implant or medialise
the neck to vary offset. This geometry
maintains the neck-shaft angle relationship
while concomitantly restoring offset. A major
advantage of this technique is that it can be
used to enhance abductor tensioning without
substantially affecting limb length. Therefore,
medialisation and concomitant lengthening of
the femoral neck represents the basis for the
high-offset femoral design.
4. Trochanteric osteotomy
Trochanteric osteotomy provides a
biomechanical advantage by laterally and
distally advancing the point of insertion of
the abductors. It has a positive effect in that it
increases the strength of the abductors and
hence decreases the likelihood of a
Trendelenburg gait.
5. Use of lateralised acetabular liners
Modular ‘offset’ or ‘lateralised’ liners have
been shown to increase offset while
preserving limb length. The of fset may be
altered by modifying the relationship of the
articulation at the socket so that the centre of
rotation at the hip is translated both laterally
and inferiorly. A laterally displaced socket
increases the abductor tension, which is a
desirable outcome. However, it also increases
the body weight lever arm which is
considered an adverse outcome.
Use of a dual motion implant is a distractor.
Charles MN et al. Soft-tissue balancing of
the hip: the role of femoral offset restoration.
Instr Course Lect. 2005;54:131–141. PMID:
15948440.
40. Answer C. With the patient supine, the hip is
brought from a position of flexion, abduction
and external rotation into extension, adduction
and internal rotation
This SBA topic is about snapping but it is focusing on its clinical diagnosis. With the reduced
amount of patient exposure in the clinical exams
there has been an evolving process of including
more clinically based SBAs into the Part 1 exam.
This is a classic example of this process.
This is the test for internal snapping of the
hip. This is a well-recognised pathological hip condition particularly seen in young athletes such as
ballet dancers. On occasion, the iliopsoas tendon
can snap over the anterior capsule or iliopectineal
ridge during hip movements. This is because the
iliopsoas tendon moves from lateral to the iliopectineal ridge in flexion to medial in extension. The
clue to separate the iliopsoas tendon from the ITB
is ballet dancer and groin pain.
Coxa saltans refers to snapping hip and
encompasses three main causes, extra-articular
(either external or internal) or intra-articular.
Extra-articular external (Coxa saltans externa)
involvesthe posterior iliotibial band asit travels
over the greater trochanter during hip flexion
and extension orinternal and external rotation.
It is one of the causes of greater trochanteric
pain syndrome, which also includes greater
trochanteric bursitis and strains or
tendinopathy of the hip abductor mechanism.
However, many patients can present with a
snapping hip that does not cause pain.
Extra-articular internal (Coxa saltans interna)
most commonly involves snapping of the
iliopsoas tendon over the iliopectinal eminence
or the anterior capsule during hip movements.
Intra-articular causes can be variable and can
result in different clinical manifestations,
which can be intermittent. Causes include
labral tears, ligamentum teres tears, loose
bodies (osteochondral, chondral fragments,
synovial chondromatosis) and even subtle
instability of the joint. The sensation of
snapping may be described as a clicking or
catching and may reflect movement of the
labral tear or loose body.
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Hip III Structured SBA
In the supine position, dynamic testing, starting
in a position of FAbER (flexion, abduction and
external rotation) to EAdIR (extension, adduction and internal rotation), will often elicit the
snapping of the iliopsoas tendon.
A is the piriformis test. This piriformis test
evaluates pathology within the piriformis
muscle itself or irritation of the sciatic nerve.
The test stretches the piriformis muscle.
B is the test for an external snapping hip. The
ITB snaps over the greater trochanter. A snap
is felt over the greater trochanter during
movement.
D is FAdIR for anterior impingement. The
FAdIR (flexion, adduction and internal
rotation or impingement) test can be used to
assess for labral or intra-articular pathology.
E is the posterior impingement test (hip
extension, adduction, external rotation). A
positive test elicits pain deep within the groin
and/or medial aspect of the buttock. This
tests for posterior rim impingement.
Posterior hip impingement results from the
abnormal contact of the lesser trochanter/
intertrochanteric ridge or posterior femoral
neck with the ischium (including the
posterior acetabulum).
41. Answer E: Tissue culture of intraoperative
biopsies
There is no single test that can reliably and reproducibly predict infection. Therefore, a combination
of clinical assessment,biochemicaltesting and diagnostic imaging should be utilised. ESR and CRP are
key tests that should always be analysed in assessment for PJI. However, these markers can be
affected by age and medical co-morbidities. An
ESR >30mm/h and a CRP >10mg/L have been
shown to represent elevated levels. If both the ESR
and CRP are normal, the probability of infection
has been shown to be around 3%.
Joint aspiration is an invasive diagnostic
method often used as the first step in suspected
PJI cases. Antibiotics should be withheld for a
minimum of 2 weeks before aspiration. The
analysis of the synovial fluid typically includes
synovial WBC and synovial PMN%. In acute
infections, a synovial WBC of 20,000 cells/ml
and synovial PMN% of 89% are considered
threshold values (Fink et al. 2008). These figures
differ in the context of chronic infection. The
aspirate should be sent for enriched cultures
and antimicrobial sensitivity.
Sampling of joint fluid through aspiration
has variable results with a wide range of reported
sensitivities (50–93%) and specificities (82–97%).
The diagnostic accuracy of synovial fluid culture
is lower than intraoperative sampling of periprosthetic tissue and sonication fluid culture
from biofilms. Furthermore, joint fluid collection is limited in the case of dry tap.
The MSIS consensus meeting stressed sev eral
points regarding intraoperative biopsies. Each
tissue sample is taken with separate, sterile
instruments. They also stated that at least three,
but no more than five samples should be taken
and incubated in both aerobic and anaerobic
environments. The use of sterile broth containing Ballotini beads can increase the pick-up of
Figure 5.28 External snapping hip. Iliotibial band snapping. (a) The patient lies on their side with the affected side uppermost. Patient actively
flexes their hip and then adducts. (b) From this position it is passively brought by the candidate into extension and abduction. A snap is felt
over the greater trochanter
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