Pathoanatomy and Associated Injuries of Posterior Malleolus Fracture of the Ankle

Abstract

Background:
We present a classification system that progresses in severity, indicates the pathomechanics that cause the fracture and therefore guides the surgeon to what fixation will be necessary by which approach.

Methods:
The primary posterior malleolar fracture fragments were characterized into 3 groups. A type 1 fracture was described as a small extra-articular posterior malleolar primary fragment. Type 2 fractures consisted of a primary fragment of the posterolateral triangle of the tibia (Volkmann area). A type 3 primary fragment was characterized by a coronal plane fracture line involving the whole posterior plafond.

Results:
In type 1 fractures, the syndesmosis was disrupted in 100% of cases, although a proportion only involved the posterior syndesmosis. In type 2 posterior malleolar fractures, there was a variable medial injury with mixed avulsion/impaction etiology. In type 3 posterior malleolar fractures, most fibular fractures were either a high fracture or a long oblique fracture in the same fracture alignment as the posterior shear tibia fragment. Most medial injuries were Y-type or posterior oblique fractures. This fracture pattern had a low incidence of syndesmotic injury.

Conclusion:
The value of this approach was that by following the pathomechanism through the ankle, it demonstrated which other structures were likely to be damaged by the path of the kinetic energy. With an understanding of the pattern of associated injuries for each category, a surgeon may be able to avoid some pitfalls in treatment of these injuries.

Level of evidence:
Level III, retrospective comparative series.

Full text

https://doi.org/10.1177/1071100717719533
Foot & Ankle International®
2017, Vol. 38(11) 1229 –1235
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Article
Introduction
Posterior malleolar fractures of the ankle have been reported
to occur in more than 40% of ankle fractures.18 This inci-
dence has been increasing especially in women over the age
of 65.3 A number of studies have reported clinically poorer
outcomes in ankle fractures that have sustained a posterior
malleolar fracture.18,29 However, many published studies of
these fractures have been limited by considering them to be
one homogenous group.*
Several papers have considered the effect of size of the
fragment as a proportion of the tibial plafond. Biomechanically,
the tibiotalar contact area significantly decreases as the size
of the fragment surpasses 33%,15,20 posterior subluxation sig-
nificantly increases between 25% and 40%,25,26 and the
stress on the remaining joint increases.9 The size of the
fragment has not been demonstrated to correlate with the
functional outcome.6,11,23,31 It has been suggested that the
unevenness in reduction and increased fragment size may be
related to posttraumatic arthritis6,32; however, fixation may
not consistently improve the evenness, and radiographic
arthritis may not correlate to a clinically significant differ-
ence in function.6
Attempts have been made to categorize these fractures by
the pathoanatomy of their primary fracture fragment.2,13,21
The clinical relevance of these systems is limited, however,
by their failure to understand the posterior malleolar fracture
719533FAIXXX10.1177/1071100717719533Foot & Ankle InternationalMason et al
research-article2017
1University Hospital Aintree, Lower Lane, Liverpool, United Kingdom
Corresponding Author:
Lyndon W. Mason, MBBCh, MRCS(Eng), FRCS(Tr&Orth), Trauma and
Orthopaedic Department, University Hospital Aintree, Lower Lane,
Liverpool, L9 7AL, United Kingdom.
Email: lyndon.mason@aintree.nhs.uk
Pathoanatomy and Associated
Injuries of Posterior Malleolus
Fracture of the Ankle
Lyndon W. Mason, MBBCh, MRCS(Eng), FRCS(Tr&Orth)1,
William J. Marlow, MBChB, MRCS(Eng)1,
James Widnall, MBChB, MRCS(Eng)1, and
Andrew P. Molloy, MBChB, MRCS(Ed), FRCS(Tr&Orth)1
Abstract
Background: We present a classification system that progresses in severity, indicates the pathomechanics that cause the
fracture and therefore guides the surgeon to what fixation will be necessary by which approach.
Methods: The primary posterior malleolar fracture fragments were characterized into 3 groups. A type 1 fracture was
described as a small extra-articular posterior malleolar primary fragment. Type 2 fractures consisted of a primary fragment
of the posterolateral triangle of the tibia (Volkmann area). A type 3 primary fragment was characterized by a coronal plane
fracture line involving the whole posterior plafond.
Results: In type 1 fractures, the syndesmosis was disrupted in 100% of cases, although a proportion only involved the
posterior syndesmosis. In type 2 posterior malleolar fractures, there was a variable medial injury with mixed avulsion/
impaction etiology. In type 3 posterior malleolar fractures, most fibular fractures were either a high fracture or a long
oblique fracture in the same fracture alignment as the posterior shear tibia fragment. Most medial injuries were Y-type or
posterior oblique fractures. This fracture pattern had a low incidence of syndesmotic injury.
Conclusion: The value of this approach was that by following the pathomechanism through the ankle, it demonstrated
which other structures were likely to be damaged by the path of the kinetic energy. With an understanding of the pattern
of associated injuries for each category, a surgeon may be able to avoid some pitfalls in treatment of these injuries.
Level of Evidence: Level III, retrospective comparative series.
Keywords: ankle fracture, posterior malleolar, classification
*References 1, 4, 5, 10, 14, 27-30, 32, 34, 35.

1230 Foot & Ankle International 38(11)
fragment in relation to the pathomechanism and how it inte-
grates into the pattern of the ankle injury as a whole.
Our aim in this study was to identify the injury patterns
sustained in combination with posterior malleolar ankle
fractures and to integrate this with pathomechanisms to fur-
ther understand the injury. We have hypothesized 3 distinct
pathomechanics groups, related to the anatomy of the ankle
complex to explain the 3 primary fracture lines that were
observed.
Methods
Between June 2014 and March 2017, we prospectively col-
lected data on 121 consecutively treated patients that
attended our unit having sustained a posterior malleolar
fracture. It is well recognized that plain radiographs under-
estimate posterior malleolar fractures,8 and CT scans are
routine for these fractures in our institution as the posterior
malleolus is commonly underestimated on radiographs.22
All radiographs and CT imaging were analyzed using digi-
tal imaging software (Vue PACS, Carestream, Version
11.4.1.0324). There were 121 patients included in this
study. Within this patient group, there were marginally
more women than men (72 females [60%] and 49 males
[40%]). The left ankle was more commonly injured than the
right (66 left [55%], 55 left [45%]). The average age of this
cohort of patients was 48 (range 17-90).
The primary fracture fragments were characterized into
3 groups dependent on a theorized mechanism of injury
(Figure 1). A type 1 fracture was described as an extra-
articular posterior malleolar primary fragment, sustained
by avulsion from the distal posterior tibial cortex by the
pull of the posterior inferior tibiofibular ligament (PITFL).7
The mechanism of this injury was theorized to occur with
the ankle in plantarflexion with an unloaded talus and a
rotational force applied to the foot. A type 2A fracture con-
sisted of a primary fragment of the posterolateral triangle
of the tibia (Volkmann area) extending into the incisura,
sustained by the impact of a rotating talus on the tibial pla-
fond (Figure 2). The mechanism of this injury was theo-
rized to occur with the ankle in neutral to plantarflexion,
with a loaded talus and a rotational force applied to the
foot. If the talus continues to rotate in the mortise, a sec-
ondary fragment on the posteromedial aspect of the tibia is
produced, usually at a 45° angle to the primary fragment
(type 2B). A type 3 primary fragment was characterized by
a coronal plane fracture line involving the whole posterior
plafond. The mechanism was of the typical posterior pilon
fracture with axial loading of a plantarflexed talus.
The cases were anonymized, blinded, and radiographi-
cally categorized by 2 blinded foot and ankle consultants.
Inter-observer reliability was assessed using Cohen’s kappa
coefficient. Associated patterns of fracture in the tibial pla-
fond, the medial malleolus, the fibula and diastasis of the
Figure 1. Schematic representation of the different types of posterior malleolar fractures. Axial CT view 5 mm proximal to tibial
plafond, and sagittal CT view 1 cm medial to the incisura.

Mason et al 1231
syndesmosis were noted for each fracture. The medial mal-
leolar fracture configuration was quite variable. Despite the
attempt by Herscovici Jr et al16 at classifying medial mal-
leolar fractures, only the small avulsion fracture (which we
term an anterior collicular fracture) was persistently compa-
rable with our series. We categorized the larger fracture
fragments into anterior oblique and posterior oblique frac-
tures, which were comparable with the Herscovici Jr type B
and C fractures. A separate fracture configuration was a Y
shape fracture theoretically caused by a push off posterior
fragment and a separate avulsion anteromedially. This vari-
ability is illustrated in Figure 3. Medial ligamentous injuries
were identified by medial clear space widening of 4 mm
without medial malleolar fracture.
The fibular fracture was categorized to low (at or below
the syndesmosis), high (above syndesmosis), or long
oblique (spans from syndesmosis to above in a long oblique
configuration). Syndesmotic diastasis was defined as >5
mm gap between fibula and incisura on CT, as previously
described by Yeung et al.33
Results
When categorized by primary fracture fragment, of the 121
cases, 41 (34%) were type 1, 55 (45%) were type 2, and 25
(21%) were type 3. Of the type 2 fractures, 25 (45%) were the
2B variant, with the presence of a secondary posteromedial
fragment. The Cohen’s kappa coefficient for interobserver
reliability was 0.919. Tables 1 to 3 illustrate the associated
injuries with each type of posterior malleolar fracture. Table
4 compares our proposed classification system with the
Haraguchi et al classification.13
Figure 2. An illustration of the pathomechanics of a type 2 posterior malleolar fracture, where the loaded talus pushes off the
posterolateral corner of the tibia when rotated in the conforming tibial plafond. With continued rotation, the posteromedial corner is
also fractured as a separate fragment.
Figure 3. Medial malleolar variability showing the differing
fracture patterns.
Table 1. Fibular Fracture Anatomy Associated With Posterior
Malleolar Fracture Type.a
Fracture
Type
Fibular Fracture
None,
n (%)
Low,
n (%)
Long Oblique,
n (%)
High,
n (%)
I 2 (5) 29 (71) 4 (10) 6 (14)
II 4 (7) 31 (56) 8 (15) 12 (22)
III 1 (4) 10 (40) 7 (28) 7 (28)
aPercentage given of fibular fracture type per posterior malleolar
fracture type.
Table 2. Syndesmotic Injury Associated With Posterior
Malleolar Fracture Type.a
Fracture
Type
Syndesmosis Injury
None,
n (%)
Full Syndesmotic Injury,
n (%)
Posterior,
n (%)
I 0 31 (76) 10 (24)
II 28 (51) 16 (29) 11 (20)
III 20 (80) 5 (20) 0
aPercentage given of syndesmotic injury type per posterior malleolar
fracture type.

1232 Foot & Ankle International 38(11)
In type 1 fractures, most cases demonstrated a low fibu-
lar fracture (71%). There was a medial-sided injury in 78%
of cases, and most injuries were either ligamentous or ante-
rior collicular avulsions. This illustrates the avulsion injury
pattern in this fracture type. The syndesmosis was disrupted
in 100% of these cases, although approximately a quarter
involved the posterior syndesmosis only.
In type 2 posterior malleolar fractures, the fibula fracture
was again predominantly low (56%). There was a medial
injury in 96% of cases, although these injuries were vari-
able, in keeping with mixed avulsion/impaction etiology.
There was syndesmotic diastasis in 49% of cases, with a
large proportion being posterior syndesmosis.
In type 3 posterior malleolar fractures, most fibular frac-
tures were either a high fracture or a long oblique fracture in
the same fracture alignment as the posterior shear tibia frag-
ment. Almost a third (28%) had no fibular fracture. There
was a medial injury in 92% of cases, with only 1 (4%) being
ligamentous. The majority, 16 (64%), were Y-type fractures
or posterior oblique. This fracture pattern had a low level of
syndesmotic injury (20%) with no solitary posterior syndes-
motic diastasis, as the distal fibula went posteriorly with
the posterior malleolar fracture. Figure 4 demonstrates
3-dimensional CT reconstructions of the 3 different types of
posterior malleolar fractures.
Discussion
Our results clearly indicate that posterior malleolar frac-
tures are variable in their nature, and as such should not be
grouped together for analysis. Each fracture type had its
own injury associations, which in themselves can determine
the management and final outcomes of these fractures. On
initial analysis, we attempted to use the Haraguchi et al
classification13 to assess the associated injuries; however,
this did not address the injury mechanism and as such we
have modified the classification as illustrated in Table 4.
Our type 1 fracture is comparable to their type 3 small
shell–type fractures. Our type 2A fractures are comparable
to their type 1 fracture (a posterolateral-oblique type), and
our type 2B fractures to their type 2 medial-extension type.
We believe we have illustrated in this research that the
Haraguchi type 1 (our proposed type 2A) is a “push-off”
fracture and not an avulsion fracture as thought in the
Haraguchi classification.13 Our modification of the
Haraguchi classification allowed better understanding of
this injury as a rotational pilon fracture. The Haraguchi type
3 (our proposed type 1) is a PITFL avulsion fracture, which
we believe has been significantly underestimated in the cur-
rent literature. We have included true posterior pilon frac-
tures in our classification as type 3 fractures, which were
not included in the Haraguchi classification. Our fracture
classification system progresses in severity, with type 3
fractures being worse than type 1, although this system’s
prognostic accuracy has not been addressed in this paper.
The value of this classification system is in its guidance
of treatment. The knowledge of the mechanism and its asso-
ciated injury patterns allows thorough treatment planning.
With a type 1 injury, the fragment is extra-articular and
often too small to fix with a screw. There is, however, in
every case a syndesmotic diastasis, be it a full diastasis or a
solitary posterior diastasis. The posterior syndesmosis does
not open on conventional intraoperative screening tech-
niques,24 and thus it is prudent to also screen with internal
rotation under arthroscopic or live radiologic screening.
Intraoperatively, all patients who had posterior syndesmotic
displacement on CT had instability on stress testing. We
believe a low threshold should be maintained for fixation of
the syndesmosis in these cases.
With type 2 cases, where the fracture line ran into the
incisura, the posterior malleolar fragment displaced, and
thus changed, the shape of the incisura. Only approxi-
mately half the injuries had syndesmotic instability, as a
Table 3. Medial Malleolar Fracture Anatomy Associated With Posterior Malleolar Fracture Type.a
Fracture Type
Medial Malleolar Fracture
Nil,
n (%)
Deltoid Injury,
n (%)
Anterior Collicular,
n (%)
Anterior Oblique,
n (%)
Posterior Oblique,
n (%)
Y Fracture,
n (%)
I 9 (22) 11 (27) 16 (39) 2 (5) 0 3 (7)
II 2 (4) 10 (18) 19 (34) 11 (20) 5 (9) 8 (15)
III 2 (8) 1 (4) 6 (24) 0 8 (32) 8 (32)
aPercentage given of medial malleolar fracture type per posterior malleolar fracture type.
Table 4. Comparison of Previous Haraguchi Classification
System With Current Proposed Classification System.
Proposed
Classification
Haraguchi
Classification Number
1 3 41
2A 1 30
2B 2 25
3 – 25

Mason et al 1233
proportion of the posterior inferior tibiofibular ligament
(PITFL) footprint remained intact in these push-off frac-
tures without syndesmotic instability, strengthening the
hypothesis that this was not an avulsion injury. In the inju-
ries with syndesmotic diastasis, the PITFL footprint was
involved. In these injuries, if the syndesmosis was first
reduced into the deformed incisura, the fibular could
become posteriorly malreduced in the syndesmosis, and
consequently block subsequent anatomical reduction of the
posterior malleolar fragment. This complication was also
described by Irwin et al,17 who felt it was prudent to fix the
posterior malleolus under direct vision in these cases, as
syndesmotic clamping can result in the malreduction. Since
the PITFL is attached to the primary fracture fragment,
once the posterior fragment is reduced, a proportion of
these fractures will require no further syndesmotic stabili-
zation. This finding is in keeping with Gardner et al12
where in a cadaveric study they found that posterior mal-
leolar fixation conferred 70% syndesmotic stability in
comparison to 40% with screw fixation.
In the type 2B variant, the posteromedial fragment
occurred in general at 45° to the posterolateral fragment, and
propagated below the posterolateral fragment in an antero-
medial direction. As such, the posteromedial fragment
needed to be reduced and fixed before the posterolateral
fragment, as the posterolateral fragment would otherwise
prevent the posteromedial fragment anatomical reduction.
We believe the preoperative identification of fracture type is
important for identifying the surgical approach that will
need to be used. A type 2A primary fragment plus fibula
fracture should be approached via a single lateral (deep dis-
section anterior and posterior to peroneal tendons to expose
both fractures) or via separate lateral and posterolateral inci-
sions, depending upon size of fragments and patient habitus.
A type 2B primary fragment will require an additional pos-
teromedial incision to fully expose, reduce, and fix the
medial part of the fracture. This is because of the consistent
45° obliquity of the fracture line splitting the posterior mal-
leolar fragment. If just approached from the lateral side,
fixation can only be placed in the same plane as this fracture
line. The posteromedial incision is performed either just
medial to the Achilles tendon (moving the flexor hallucis
longus medially) or between the tibia and tibialis posterior,
depending on comminution and fracture pattern.
In type 3 cases, only 20% had a syndesmotic diastasis,
with no instances of isolated posterior syndesmotic dis-
placement. This was commonly a consequence of a long
oblique fracture of the fibula remaining attached posteriorly
to the displacing posterior malleolar pilon fragment and
anteriorly, attached to the remaining tibia. The clinical test-
ing of the syndesmosis is therefore in these cases, more
likely to be reliable, and a higher threshold for syndesmotic
fixation can be maintained. Specific elements to this frac-
ture pattern are the high preponderance of associated pos-
teromedial malleolar injuries. A Y-type fracture was
demonstrated in 32% of cases, and in these cases the larger
Figure 4. Three-dimensional computed tomographic reconstructions of the different posterior malleolar fractures. The type 1
fracture shows the typical avulsion appearance of the medial malleolus. The type 2B fracture demonstrates the 2 separate posterior
malleolar fractures (posterolateral and posteromedial) and an associated anterior oblique medial malleolar fracture. The type 3
fracture exemplifies the long oblique fibular fracture in the same orientation as the posterior pilon fragment.

1234 Foot & Ankle International 38(11)
fragment was in the posterior oblique direction with a sepa-
rate anterior collicular avulsion. This fracture pattern was
also described by Klammer et al.19 In fixation of this frac-
ture, we find it is more successful in reduction and fixation
of the larger fragment first, followed by attachment of the
smaller anterior fracture fragment to this stable construct.
As for the type 2 fractures, the approach will be determined
by the fracture pattern. If a Y-type fracture is present, it is
usually necessary to carry out a posteromedial incision.
Conclusion
We present a classification system of posterior malleolar
fractures based on a large series. The system progresses in
severity as well as indicating the pathomechanics that cause
the fracture. We have demonstrated predictable associated
injuries for each fracture type and how both these factors
determine which surgical approaches will be necessary.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect
to the research, authorship, and/or publication of this article.
ICMJE forms for all authors are available online.
Funding
The author(s) received no financial support for the research,
authorship, and/or publication of this article.
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