Historical overview and biomechanical principles of intramedullary ...

P OSTGRADUATE SCHOOL OF SURGICAL TECHNIQUES
Historical overview and
biomechanical principles of
intramedullary nailing
Iztok A. Pilih, Andrej Čretnik
Abstract
Intramedullary nailing is a brainchild of Gerhardt Küntscher and his co-workers in the first half of
20 th century. They developed technical and clinical basis for a broad use of the method. After great
enthusiasm at the beginning disappointment followed which considerably limited its use. Emerging of
new designs of intramedullary nails and locking in the second half of 20 th century brought method new
popularity and considerably increased its use. Contemporary intramedullary nailing represents quick,
secure, biologic and minimally invasive way for the treatment of long bones fractures.
Introduction
“Elastic nailing” – the concept of long metal intramedullary nails attached to the endostal surface
of the bone was a brainchild of Gerhardt Küntscher and his co-workers, professor Fischer
and engineer Ernst Pohl, at University in Kiel in Germany in the 1930’s. The original nails
were in the shape of the letter V, but he later introduced the four-leaved clover form for additional
strength and easier use. Dr. Küntscher published his first book on intramedullary nailing
in 1945 (1). Küntscher was a technically exquisite surgeon. The results of his intramedullary
treatment were so impressive that his technique spread all over Europe after the Second World
War. Soon disappointments came and narrowed the use of the intramedullary method solely
to treatment of femoral fractures. As Professor Lorenz Böhler wrote in the preface of his book
published in 1945: “... Latter experiences proved the risks of intramedullary nailing to be a lot
higher than expected. Therefore it is only used as a rule in cases of femoral fractures... Medullary
nailing of other long bone fractures that I myself had recommended turned out to be more
dangerous than efficient…”
Historical overview
The “beginnings” of intramedullary fixation go back into the 16 th century. The conquistadors
in America described how the Indians used wooden wedges to treat bone fractures. By the end
of the 19 th century, first experimental intramedullary fixations were performed in Europe. The
pioneers were Bircher, König, von Langenbeck, Cheyne and Lane. Several methods of fixation
of proximal femoral fractures were introduced that included the use of bony, ivory or metal
(silver) screws and wedges. In the beginning of the 20 th century, Ernest Hey Groves (England)
already used specially designed three- or four-edged intramedullary nails for the fixation of
diaphyseal long bone fractures. But due to the common infections which associated the operation,
Groves was eventually nick-named “septic Ernie” and his method did not spread. Smi-
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th-Petersen made a huge step forward regarding fracture treatment when he introduced a nail
to fixate subcapital femoral fractures in the 1920’s. In 1940, Lambrinudi suggested the placement
of strong wires and thin metal sticks through the medullary canal. This method was later
upgraded by the Rush brothers (1). After the previously mentioned greatest work of Gerhard
Küntscher in the 1940’s the use of intramedullary fixation of long bone fractures spread again
in the second half of the 20 th century, with the works of Madny, Kemm, Schelman, Grosse,
Kempf, and of the AO group (Arbeitsgemeinschaft für Osteosynthesefragen). The introduction
of locking screws spread the indications widely (1-5). The evolution of intramedullary nails
is presented in Picture 1.
The principles of intramedullary fixation
The basic principle of intramedullary nailing is “dynamic osteosynthesis”. If we nail an object
(nail, stick) along-side a structure, certain pressure is applied to the structure, which provokes
reverse pressure, and that brings to elastic ‘’binding’’ between the object and the structure.
Küntscher used this basic idea when he placed nails into the medullary canal. The nail’s
cross section was wider than the canal, which allowed tight match to the wall and therefore
stable fixation. Despite the additional four-leaved clover shape, which allowed additional fitting
Picture 1. Development of intramedullary nails. Upper row – first generation, lower row – second
generation.

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and easier placement (Picture 2), trouble occurred either with the application of the nails (there
happened additional fractures or so-called “explosion”) as well as with ensuring longitudinal
and rotational stability. These all brought to the development of locking intramedullary nails.
They are narrower than the medullary canal (easier placement), but their structure (a thicker
wall) and the locking screws provide stable fixation. When deciding on intramedullary nailing,
it is important to know different types and characteristics of nails (their features), to take into
consideration the basic characteristics of the bone and soft tissue along with other factors that
are relevant for the procedure.
Types and characteristics of intramedullary nails
When we are deciding for intramedullary fixation, we must know the nail’s geometrical features
(curvature, diameter, its shape in the longitudinal section, etc.) and the characteristics of the
material it is made of.
Most contemporary nails are made of stainless steel (mark 316L stainless steel) or of titanium
alloys. The material must be firm and stiff. Titanium nails are approximately 1.6 times firmer
than steel nails. Their elastic module is almost 50% lower than that of steel nails. This means
they are much stiffer (they keep the fragments in the proper position), but they are also easier
to break, although the use of modern titanium alloys practically eliminated these problems (1,
5).
Once the intramedullary nail is inserted, longitudinal, transverse and rotational forces
start acting. The magnitude of forces and thus
the stability of the fixation depend strongly on
the position of the entry point and the proper
position of the nail in the medullary canal.
The purpose of the variety of nails cross section
was to achieve the optimal grip and by that
stability along with best possible preservation
of blood supply. By splitting the nail we can
place a nail that is wider than the medullary
canal to provide better elastic grip and more
stability. But, on the other hand, a split nail is
not very stiff and this type of fixation is not
very stable (1, 3, 5).
The grip and stability of the fixation depend
strongly on the size of the contact surface
between the nail and the bone. It can
be enlarged if we curve the nail with regard
to the anatomic curvature of the bone. This
explains why the curvature radius of femoral
nail measure 109 cm (picture 3). We can
also enlarge the contact surface by reaming,
which allows us to insert nails of larger dia-
Picture 2. Basic principles of intramedullary
fixation.
meter that are naturally stronger. When the
diameter increases, so does the stiffness of the
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nail, meaning that the wall of the nail can be thinner, which facilitates the placement (1, 3, 5).
But reaming causes the cortex to become thinner. This increases the risk of additional bone
fractures during the placement of the nail. This risk also remains when we remove the nail after
complete bone reparation.
Another important characteristic of a nail is its working length (WL), the length of the
unsupported part of the nail between the proximal and the distal firm grip of the nail and the
bone (Picture 4) (1, 5). In comminuted fractures, this length can be very large, which means
the along-side support is small. As stability of fixation against the forces of bending is inversely
proportional with working length square (1/WL 2 ), stability is very small if we use regular intramedullary
nails in long comminuted fractures (1, 5). This fact together with the invention
of X-ray image intensifier (C-arm), led to development of nails with locking screws. This nails,
upgraded with locking screws through the bone and through the hole in the nail, provide increased
rotational and longitudinal stability of the fixation. We can lock the nail statically (screws
prevent movement and therefore compression of fragments) or dynamically (the openings
are oval, which allows compression of fragments and accelerates the formation of callus; or the
nail is only locked at the proximal side or the screws at the distal side are removed early - dynamization).
We must be aware but that with locking at one side only or when the nail is locked dynamically,
stability decreases, which causes up to 10% of mal-unions (fractures healed in malposition).
The closed nailing method (preserving the fracture haematoma) results in successful
bone healing in up to 98% of cases, despite static locking and therefore dynamic locking and
early dynamization (removal of locking screws) is less and less used. Thanks to the stability of
locking screws, there is less and less need to ream the canal to enlarge the contact surface and
we can use thinner nails but with thicker wall which are still stronger. The nails are cannulated
and placed over the guiding wire, which enables us to place a thin and appropriately shaped nail
with minimal or no reaming of the medullary canal to the precise position. Lately even thinner
nails (7 mm in diameter) have been developed to eliminate the risk of infection and to preserve
the blood supply to the bone, but there is still a lack of proven studies about effectiveness of this
a
c
b
Picture 3. Curvature of the nail. a, b, c, d,
e - see text
e
d
a
Locking mechanism
in the proximal part
Gap between the bone and
the nail
(reamed/non-reamed)
Quality of the bone
The quality of material
and form of nail
Unsupported,
working length
Locking mechanism
in the distal part
Picture 4. Important factors in intramedullary
fracture fixation.

P OSTGRADUATE SCHOOL OF SURGICAL TECHNIQUES
concept. Stable fixation allows early bearing weight on the fractured bone. As we can avoid
(excessive) reaming, the risk of additional fractures on thinned cortex is eliminated. Thinner
nails also call for thinner locking screws holes. Thinner and thus weaker locking screws (and
nails) break easier at early burdening (in 12-30%), so we don’t recommend early (full) weight
bearing in the early post-operative period in cases of comminuted fractures.
Characteristics of bones and soft tissue
Sufficient blood supply plays an important role in the process of healing. In the diaphyseal
area, bones are mostly supplied with blood through nutrient artery and its endostal branches,
partially also through periosteal vessels, which spring from adjoining structures (muscles), and
metaphyseal vessels. Both types form an anastomosis with endostal vessels. The more we approach
the epiphysis (distally or proximally), the bigger is the relevance of blood supply from the
extramedullary vessels, which only supply 10-30% of the cortex in the diaphysis, otherwise two
thirds of blood are carried through the endostal circulation. Reaming the medullary canal and
placement of the intramedullary nail into the medullary canal has considerable effect on the
circulation. Studies show that minimal reaming to the extent smaller than the diameter of the
medullary canal has relatively little effect on the cortical and diaphyseal circulation. Reaming
to the extent that equals the diameter of the medullary canal already decreases the diaphyseal
blood supply by half and cortical circulation by one third, whereas reaming wider than that of
the medullary canal causes the diaphyseal blood supply to decrease to only a third of the normal
amount of blood (excessive reaming can diminish total blood flow for up to 83%). Doing
that reaming triggers a strong hyperemic reaction in the preserved vessels and reaches its peak
two to four weeks after the injury. Vessels start to ingrowth and the circulation in cortex changes
from centrifugal to centripetal (from outside inwards instead of vice-versa). The re-establishment
of normal circulation depends mainly on the extramedullary vessels (1). The circulation
through other tissues (skin, nerves, muscles ...) increases along with increased circulation
through the bone. Therefore it is important to preserve the soft tissue undamaged (the closed
nailing technique without opening the haematoma above the fracture, where the circulation
has already been disrupted because of the fracture) or to close the open fracture (or the soft
tissue damage above the fracture) as quickly and as efficiently as possible. Another factor that
affects the re-establishment of blood circulation is the intramedullary nail itself, as its presence
prevents endostal ingrowth of vessels. Thinner nails that do not fill the intramedullary area
(specially shaped nails in the lateral section) have an important advantage as they allow good
or even complete recuperation of blood circulation. That (along with stability) makes fracture
treatment with elastic fixation (wires, sticks, Ender or Prevot nails) so successful.
Other factors
Reaming also causes parts of bone marrow and spongy bone to be embolized out through the
fractured bone into the haematoma (and through (torn) vessels in the circulation – see below).
This way, beside the increase of blood supply, the osteoinductive process is triggered through
pluripotent and osteoprogenitory cells and bone morphogenetic proteins that arrive to the area
of haematoma. Comparison between the reamed and non-reamed technique of intramedullary
nailing shows the decrease of blood supply through the bone immediately after reaming is
followed by a large increase of circulation through the muscles within a few weeks and later
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by formation of a large ossificated callus (approximately 6 weeks after the injury). If we do not
ream, callus is formed sooner (within 4 weeks), but it lasts longer for the fracture to repair completely
in terms of X-ray and clinical criteria. In practice, completely non-reamed technique is
performed very rarely, and nails are normally divided into those inserted with minimal reaming
and those inserted with extensive reaming or into thinner (7-12 mm in diameter) and thicker
(more than 12 mm in diameter) nails. Placement of the nail with minimal reaming is considered
a compromise between the pros and the cons of reaming.
Reaming causes forces and pressure between the drill, the bone and in the medullary canal;
this naturally increases if the drill is not sharp enough (from 45 N to over 100 N and from 300
mmHg to over 1000 mmHg). If the pressure is increased by 1.8 times in average, the temperature
at the point of the drill can increase for up to 2.8 times during reaming. Appropriate instrumentary
(pointy drill ...) and appropriate reaming technique (soft pressure, distal opening
to reduce pressure if possible, precise entering into the canal, etc.) can therefore often prevent
unnecessary complications.
Because of the pressure reaming can also lead to embolization of the content of the medullary
canal into the blood vessels. Consequently, the content of the medullary canal (bone fragments,
fat and blood cells, mediators, etc.) are spilled through the vessels into other organs,
which can lead to severe complications (ARDS, fat and pulmonary embolism). That is why
(despite not completely uniform results of studies) many authors dissuade from immediate use
of reamed intramedullary nails in poly-traumatized patients, in patients with pulmonary damage
or in those threatened by ARDS. It seems reasonable to treat these patients in several
stages. Definitive fracture fixation is thus performed only in stabilized patients when we can
perform it safely.
Conclusion
Intramedullary fixation has progressed importantly with the introduction of new nails and various
locking techniques. According to modern principles of its application it is shifted to the less
invasive method of treatment. Biomechanical characteristics of the contemporary nails allow
quick and sufficient bone healing even in complicated long bone fractures.
References
1. Browner BD, Jupiter JB, Levine AM, et al. Skeletal trauma. Second edition. Philadelphia: WB Saunders, 1998.
2. Müller ME, Allgöwer M, Schneider R, et al. Manual of internal fixation. Berlin: Springer, 1991.
3. Rüedi TP, Murphy WM. AO Principles of fracture management. Stuttgart, New York: Thieme, 2001.
4. Sabiston DC, ed. Textbook of surgery. Philadelphia: Saunders, 1997.
5.
Schatzker J, Tile M. The Rationale of Operative Fracture Care. Berlin: Springer, 1996.