J. Biomedical Science and Engineering, 2010, 3, 638-643
doi:10.4236/jbise.2010.36087 Published Online June 2010 (http://www.SciRP.org/journal/jbise/
JBiSE
).
Published Online June 2010 in SciRes. http://www.scirp.org/journal/jbise
Classification of femoral neck fractures according to pauwels:
interpretation and confusion
——Reinterpretation: a simplified classification based on mechanical considerations
Andrej Maria Nowakowski1, Peter Emil Ochsner2, Martin Majewski1
1Orthopedic Department, University of Basel, Basel, Switzerland;
2Clinic for Orthopedics Lucerne, Klinik St. Anna, Luzern, Switzerland.
Received 29 March 2010; revised 3 May 2010; accepted 9 May 2010.
ABSTRACT
The Pauwels Classification of femoral neck fractures,
initially published in 1935, is used world-wide. Un-
fortunately, modern textbooks give varying angle and
anatomic specifications between the classified frac-
ture grades. This inconsistency is perpetuated in the
literature, so that it is difficult to compare conclu-
sions made by different authors. Pauwels himself left
room for interpretation. He published two studies,
one in 1935 and one in 1973, each including 3 dia-
grams. The 1935 version cited an angle of 8° repre-
senting the vector of static forces acting on the femo-
ral head. The 1973 diagrams, however, cited an angle
of 16° to represent dynamic forces, without changing
the angle from horizontal. This already complex sche-
me is complicated by the fact that it depends on other
factors such as femoral neck shaft (CCD) angle,
femoral neck and head diameter, and/or distance of
the fracture from the center of the femoral head. The
multitude of factors argues against a rigid classifica-
tion based on fixed angles from horizontal. Pauwels
himself did not establish fixed critical angles between
the fracture grades. In his own explanation of the
system, he placed more value on mechanical consid-
erations such as compression stress, shear stress, ten-
sile force, shearing force, and torque. We propose
therefore a simplified version of the Pauwels Classi-
fication: Grade I for fractures impacted in valgus,
Grade II for fractures without free torque, and Grade
III for fractures with free torque.
Keywords: Pauwels; Garden; Classification; Femoral
Neck Fracture
1. INTRODUCTION
There is a pervasive wish for a simple classification
system corresponding to the treatment of femoral neck
fractures. One frequently used classification is that of
Pauwels, originally published in 1935 [1]. Unfortunately,
modern textbooks give varying angles and anatomic
specifications to differentiate the three fracture grades.
These inconsistencies are perpetuated in the scientific
literature, so that it is difficult to make a clear correla-
tion between fracture type, treatment modality and
course of healing (Table 1).
The ambiguity of this system has doubtless contrib-
uted to the lack of consensus regarding its use. How-
ever, the classification per se is not at fault, instead, its
interpretation. For example, some authors ignore entire
segments (50° to 70°) of injury in their interpretations.
In addition, there are numerous publications that make
comparison impossible, since they do not indicate wh-
ich interpretation of the classification they are using
[2-7].
Bartoniček [8] remarked on this problem in 2001 in
his study, “Pauwels’ Classification of Femoral Neck
Fractures: Correct Interpretation of the Original,” and
stipulated the following categories:
Grade I < 30°, Grade II 30-50°, and Grade III > 50°.
However, Pauwels considers the fracture in his Fig-
ure 40 (page 39), to be a Grade I injury despite an an-
gle of 35°. This, he explains, is because impaction ne-
gates the shearing forces [1]. (Figure 1).
Redefining the distinction between Grade I and II
fractures as 35° instead of 30° is counterproductive.
Instead, the original intent of Pauwels should be re-
spected. This was to classify these fractures based on
mechanical considerations.
2. MATERIAL AND METHODS
We examined the classification of femoral neck fractures
based on pre-determined angles, using the two original
publications from Pauwels [1,9]. In addition, theoretic
considerations and modifiable variables were compiled

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639
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Table 1. Diverse interpretations of the pauwels classification.
Grade Ⅰ Grade Ⅱ Grade Ⅲ Literature
< 30º 30-50º > 50º [80,10,14,19,21,22]
< 30º 30-60º > 60º [23]
< 30º 30-70º > 70º [13,20,24,25]
30º 50º 70º [12,26,27]
< 50º 50-65º > 65º [28]
< 30º 30-50º > 70º [29]
Figure 1. Original illustration by Pauwels 1935 [1] showing a
fracture impacted in valgus without free shearing force (Grade
I). Reprinted by courtesy of Georg Thieme Verlag KG, Stuttgart,
after transfer of Ferdinand Enke Verlag, Stuttgart, from 1971.
and incorporated into a simplified version of the Pau-
wels’ Classification.
3. RESULTS
The most important criteria for the Pauwels Classifica-
tion are found in the legend describing his Figure 2 [1].
Grade I: The partial compressive force component P
acts only as its magnitude approaches the value of R.
The partial force of pure displacement S is countered by
friction at the fracture site. P generates compression
forces distributed evenly over the entire fracture surface,
because R intersects the fracture surface adjacent to the
mid-line.
Grade II: Here the free shearing force Ks will act on
the zone of fracture healing. The compression compo-
nent P will not act on this area, instead will generate latent
compressive forces in only one portion of the fracture
surface.
Grade III: The free shearing force Ks and tensile
force Z are generated by free torque (R, OA).
Only the lowest corner of the trochanter fragment (O),
the fulcrum for the head fragment, will be acted upon by
latent compressive forces.
Differentiation between Grade I and Grade II fractures,
then, is made based on the presence or absence of the
free shearing force Ks. When shearing force is present,
the fracture is a Grade II. This explains why some frac-
tures impacted in valgus, despite steep fracture angles,
are considered Grade I fractures. Impaction neutralizes
Ks. (Figure 1) According to Pauwels [1]: “Under certain
circumstances, impaction may have a decided influence
on the course of healing, because it neutralizes a certain
measure of the displacement force S and therefore re-
duces the extent to which the free shearing force Ks acts
on the zone of fracture healing.” In cases of more verti-
cal fractures, however, the compression achieved from
impaction can no longer neutralize the dynamic shearing
forces [1].
The differentiation between Grade II and III fractures
is made based on the free torque (R, OA). When free
torque is present, the fracture is Grade III.
Interestingly, almost 40 years after the initial paper,
Pauwels published modified diagrams [9]. These stipu-
late a dynamic force vector R with an angle of 16° in-
stead of the static vector of 8° found in the original ver-
sion. (Figure 3)
It is possible that improved operative techniques and
implant devices allowing partial weight bearing and early
mobilization of the patient led to this alteration.
Pauwels wrote even in 1935 [1] that Grade II fractures
are those with a fracture inclination up to 50°. His own
diagram shows a fracture with a distinctly steeper frac-
ture angle than 50°, however, without free torque. (Fig-
ure 3(c)) Manipulation of the vector angles alone, de-
pendent on other factors, can blur the distinction be-
tween categories, i.e., the values of the angles of inclina-
tion.
Figure 4 demonstrates this for the border between
Grade II and III fractures. (Figure 4)
The location of the fracture along the femoral neck
medially or laterally has a definite influence on the pres-
ence or absence of free torque. (Figure 5)
Other factors influencing the critical angles are: the
femoral neck shaft (CCD) angle, the femoral neck and
head diameters, and/or distance from the fracture to the

640 A. M. Nowakowski et al. / J. Biomedical Science and Engineering 3 (2010) 638-643
Figure 2. Original illustration by Pauwels 1935 [1]: Classification of femoral neck fractures.
Reprinted by courtesy of Georg Thieme Verlag KG, Stuttgart, after transfer of Ferdinand Enke
Verlag, Stuttgart, from 1971.
Figure 3. Original illustration by Pauwels 1973 [9]: Classification of femoral neck fractures.
Reprinted by courtesy of Springer-Verlag Berlin/Heidelberg.
center of the femoral head. For example, then, fractures
in varus hips will reach a higher fracture grade when the
angles are smaller than those of fractures in valgus hips.
(Figure 6)
These issues clearly demonstrate that a rigid classifi-
cation system using defined angle measurements is not
practical. The Pauwels study [1] assigns fractures in valgus
an exceptional position. We propose, therefore, a simpli-
fied version of Pauwels’ Classification, based on mechan-
ical considerations:
Grade I: fractures impacted in valgus,
Grade II: fractures without free torque,
Grade III: fractures with free torque.
4. DISCUSSION
Figure 4. Impact of different vectors on the classifica-
tion of femoral neck fractures. Relationship demon-
strated for the border between Grade II and III fractures.
Parker and Dynan [10] declared the Pauwels Classifica-
tion clinically irrelevant due to the multitude of studies
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Figure 5. Demonstration of boundary zone for femoral neck fractures Grades II and III at a
theoretical fracture starting point X0 and a fracture angle of 50° to horizontal; (a) More lateral
fractures (XL) lead to the presence of free torque, more medial fractures (XM) do not. (b)
Magnification of (a) and (c): more lateral fractures or more vertical fracture angles at critical
point P lead to the presence of free torque (R, OA). (c) More vertical angles (red zone) lead to
the presence of free torque, more horizontal fractures (green zone) do not.
Figure 6. Influence of the CCD-angle on boundary zones for the Pauwels Classification 1973
[9], demonstration of Grades II and III, starting at a theoretical fracture point X0: (a) More
varus CCD-angles lead to the presence of free torque (R, OA) at critical point P in many cases.
(b) More valgus CCD-angles seldom lead to the presence of free torque (R, OA).

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showing no correlation between Pauwels’ angles and
non-union. This statement is based most notably on two
large studies, from Otremski, et al. [3] and Raaymakers
and Marti [11], which showed no correlation between
fracture angle and secondary displacement and/or non-
union in impacted femoral neck fractures. Verheyen et al.
[12] determined that the critical angle between Grade I
and Grade II injuries is impractical, since almost all
cases of impacted femoral neck fractures lie in the gray
area and it is too difficult to differentiate them.
However, in his original 1935 work, Pauwels [1] em-
phasized the exceptional nature of impacted femoral neck
fractures (Figure 1).
The conclusions from individual studies are difficult
to compare, but this is due to varying interpretations of
the critical angles. The problem does not lie with the
Classification itself. For instance, Krastman, et al. [13]
established a Pauwels Grade II as 30° to 70°, and allo-
cated 71% of 112 cases as Grade II injuries. In contrast,
Prinčič, et al. [5] identified only 7.1% of 351 cases as
Pauwels Grade II injuries. They did not indicate which
critical angles they used.
The Pauwels Classification has also been criticized
regarding the difficulty to determine angles preopera-
tively because of rotational error [3,11]. Projection errors
are a generalized problem for fracture evaluation, how-
ever, and are ubiquitous in all two-dimensionally imaged
fractures that are not taken orthograde. Graphic tech-
niques, i.e., comparison of the contralateral side, can be
of assistance. As well, intraoperative radiographs post-
reposition, as suggested by Raaymakers [14,15] can be
used to combat this problem.
Another criticism of femoral neck fracture classifica-
tions is that they don’t consider the second plane. This is
true of the Pauwels Classification [1], which doesn’t use
the lateral plane, as well as the Garden Classification
[16], for which in clinical practice it is often neglected.
Because of this, and because of variability in interpreta-
tions, Frandsen, et al. [17] and Zlowodszki, et al. [18]
suggested that the Garden Classification [16] is no longer
useful in clinical practice.
Individual studies have identified correlations between
fracture angle and the occurrence of secondary display-
cement and/or non-union [4-6]. Many authors use the
Pauwels [1] as well as the Garden [16] Classifications to
evaluate the respective risks of non-union or femoral
head necrosis and to determine the best mode of treat-
ment [2,7,13,19,20].
On the one hand, there is the need to predict post-op-
erative course based on measurable pre-operative para-
meters, and to thereby choose the best method of treat-
ment. On the other hand, these parameters should not be
too complicated for regular clinical use, since that can
lead to confusion and sub-optimal therapeutic choices.
Therefore, the newer classification developed by Ca-
viglia, et al. [21], with its six grades of fracture and ten
subdivisions, appears too complex for routine clinical
use in evaluating femoral neck fractures. The inclination
of the fracture continues to be an important considera-
tion to estimate the course of healing and determine the
best method of treatment. Fractures impacted in valgus
remain a special category. Although in these cases more
vertical fractures can be more mechanically favorable, it
is important to pay close attention for the presence of
dorsal tilting.
At the time of Pauwels’ writing, it was important to
distinguish non-impacted femoral neck fractures having
a moderate fracture angle but no free torque, since this
influenced the choice of therapy. However, simple nail-
ing procedures are no longer performed. Instead, more
reliable techniques such as minimally-invasive fixation
with two to three gliding or pressure screws or larger
implants such as a dynamic hip screw (DHS) are used.
We believe that the indications for internal fixation ver-
sus hemi-arthroplasty should be based not only on the
risk of femoral head necrosis (i.e., using the Garden Clas-
sification), but also on the mechanical constellation of
injury. This is generally accepted for the treatment of
femoral neck non-unions. In the area of femoral neck frac-
tures, however, no classifications using pure mechanical
analysis can be implemented, either because they are too
complex, or because they have not been comparably
interpreted by the literature.
For all of these reasons, we propose the following
simplified version of the Pauwels Classification system
for femoral neck fractures based on mechanical consid-
erations. Grade I fractures are those impacted in valgus,
Grade II are fractures without free torque, and Grade III
are fractures with free torque. To differentiate between
Grade II and III fractures, the dynamic resulting vector R
(16°) should be projected from the center of the femoral
head onto the level of fracture. If the vector intersects
the fracture surface, the injury is a more mechanically
favorable Grade II injury without free torque. If, how-
ever, the vector projection intersects medial to the frac-
ture plane, free torque is present and the injury is an un-
favorable Grade III type, with increased risks of secon-
dary displacement, femoral head necrosis, and/or non-
union.
This extrapolation, strictly interpreted, is a simplifica-
tion of a complex mechanical relationship. The angle of
incidence of the resulting vector R is dependent on the
leverage variables (CCD angle, femoral neck length, etc.)
and multidimensional. However, overall it is better de-
fined and more reproducible as a measure of the presence
of free torque than the fracture angle from horizontal.

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643
This classification can be used for borderline cases,
definitively, in the operating room. Moreover, an enhan-
cement of the mechanical constellation can be obtained
using valgisation of the fracture.
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Whether this modified classification is sufficient to
predict the development of mal/non-union and/or femoral
head necrosis, and therefore the need for fixation versus
hemi-arthroplasty, remains to be seen. Further studies will
be necessary to evaluate its use in the clinical setting.
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