Gross Anatomy Dissections
Twenty femora from the bone box specimens of the Department of Anatomy at
the University of Minnesota were qualitatively analyzed to examine the osseous
prominences of the medial side of the knee. The locations of these osseous
prominences were then used to help to identify and analyze the osseous
prominences seen during the fresh-frozen knee dissections.
Dissections were performed on eight nonpaired fresh-frozen cadaveric knees
that had no sign of previous injury, knee abnormality, or disease. The mean
age of the donors had been fifty-nine years (range, forty-four to seventy-two
years) at the time of death. Each cadaveric knee was stored frozen at
—20°C and was allowed to thaw overnight prior to dissection.
Anatomic Measurements
The Polhemus FASTRAK electromagnetic three-dimensional tracking sensor
system (Polhemus, Colchester, Vermont) was used to quantitatively identify the
insertion sites of the measured structures and related osseous
landmarks22,23.
This device is a six-degrees-of-freedom measuring device that tracks the
position and orientation of a receiver relative to a transmitter with use of
low-frequency magnetic fields. The transmitter device produces a pulsed
magnetic field. In turn, the receiver device contains a small solenoid that
senses the magnetic field. The magnetic field produced by the transmitter
device has different effects depending on the receiver position in the
magnetic field, and the position and orientation with respect to the axes of
the transmitter can then be calculated instantaneously (MotionMonitor;
Innovative Sports Training, Chicago, Illinois). The transmitter-to-receiver
separation range in the present study was 300 to 480 mm, which was within the
previously reported optimal range of 100 to 700 mm for these testing
conditions to minimize positional
error22. The knee
was placed into a device that fixed the specimen relative to the transmitter
device. A probe was connected to the electromagnetic tracking system and acted
as the receiver device to measure the three-dimensional coordinate location of
the structure or structures of interest. Distances of interest were calculated
with use of three-dimensional data points. The accuracy of this measurement
system has been reported to be within 0.3° and 0.3
mm23.
After placement of the knee into the holding device, meticulous sharp
dissection of the structures of the medial and posteromedial aspects of the
knee was performed with use of either a knife blade or a fine-pointed
hemostat. After the initial measurements of each specific structure were made
by placing the Polhemus measuring probe against the edge of the structure and
recording its three-dimensional coordinate location, the attachment sites were
dissected down to bone and outlined and the perimeters of the attachment sites
were identified with the measuring probe.
The perimeters of the tibial attachment sites of the medial structures were
identified first. All measurements were made by the same individual (R.F.L.)
to avoid interobserver error. Each attachment site was recorded by tracing its
outline with the measuring probe immediately after it was sharply dissected
off bone. Measurements were made along the periphery of each attachment site.
Joint line measurements were made to the edge of the articular cartilage
surfaces of the medial femoral condyle for structures attached to the femur
and to the medial tibial plateau for structures attached to the tibia.
Once all of the desired structures and osseous landmarks were identified,
the outlines of both the distal part of the femur and the proximal part of the
tibia were collected to establish a three-dimensional axis on which to map the
locations of the structures. The coordinates of each identified point were
used to calculate the areas of the insertion sites, the centroid of each
insertion, and the distances between the centroids. The distances between
structures were then broken down into anterior-posterior, medial-lateral, and
proximaldistal components. The distances measured with this system were
straight-line distances and did not take into account osseous prominences or
depressions. For this reason, small variations in measured distances occurred
between the osseous landmarks and the separate anatomic structures.
Measurements are reported to the midpoint of a structure's attachment site
and osseous landmarks. All distances and areas are reported as averages for
each structure (see Appendix). Attachment areas for identified structures are
listed in a table the Appendix. Straight-line distances between the centers of
structures are reported in tables in the Appendix, whereas proximal-distal and
anterior-posterior attachment relationships are described in this section.
Medial Femoral Osseous Landmarks
Qualitative analysis of the femora from the bone box specimens revealed
that the medial epicondyle was the most anterior and distal osseous prominence
over the medial aspect of the medial femoral condyle. The adductor tubercle
was located at the distal edge of a thin ridge of bone, called the medial
supracondylar line, along the medial aspect of the distal part of the femur.
The adductor tubercle was located proximal and posterior to the medial
epicondyle. A third osseous prominence, which we have called the gastrocnemius
tubercle, was identified; this structure was slightly distal and posterior to
the adductor tubercle and was close to a small depression, which corresponded
to the location of the attachment of the medial gastrocnemius tendon (Figs.
1 and
2).
Quantitative analysis of these osseous landmarks in the dissected knees
revealed that the adductor tubercle was 12.6 mm (range, 9.0 to 15.2 mm)
proximal and 8.3 mm (range, 5.9 to 11.6 mm) posterior to the medial
epicondyle. The gastrocnemius tubercle was 9.4 mm (range, 7.1 to 11.8 mm)
distal and 8.7 mm (range, 6.8 to 12.5 mm) posterior to the adductor tubercle
and 6.0 mm (range, 4.4 to 8.9 mm) proximal and 13.7 mm (range, 10.8 to 15.8
mm) posterior to the medial epicondyle.
Superficial Medial Collateral Ligament (Tibial Collateral
Ligament)
The superficial medial collateral ligament was the largest structure over
the medial aspect of the knee. It had one femoral and two tibial attachments.
The quantitative relationships and attachment areas of the superficial medial
collateral ligament are listed in tables in the Appendix.
The femoral attachment of the superficial medial collateral ligament was
round to slightly oval in shape and was located in a depression that was an
average of 3.2 mm (range, 1.6 to 5.2 mm) proximal and 4.8 mm (range, 2.5 to
6.3 mm) posterior to the medial epicondyle (Figs.
2 and
3). There was no firm
attachment between the superficial medial collateral ligament and the
underlying deep medial collateral ligament, and no definable bursae were
identified between these two structures.
As the superficial medial collateral ligament coursed distally, it had two
separate tibial attachments (Figs.
2 and
4). Between these two distinct
tibial attachments, the superficial medial collateral ligament was separated
from the tibia by the inferior medial genicular artery and vein, along with
its corresponding nerve branch from the tibial nerve, and some fine fascial
and adipose tissues. The proximal attachment of the superficial medial
collateral ligament was primarily to soft tissues rather than directly to
bone. The majority of the soft tissue deep to the proximal tibial attachment
of the superficial medial collateral ligament was the anterior arm of the
semimembranosus tendon, which itself attached directly to bone. The distal
tibial attachment was broad-based and was located just anterior to the
posteromedial crest of the tibia. The majority of the distal attachment was
located within the pes anserine bursa and formed a large portion of the
posterior floor of this bursa. The posterior aspect of the tibial portion of
the superficial medial collateral ligament blended with the distal tibial
expansion off the semimembranosus
tendon24 along its
distal aspect.
Deep Medial Collateral Ligament (Mid-Third Medial Capsular
Ligament)
The deep medial collateral ligament was a thickening of the medial joint
capsule that was most distinct along its anterior border, where it roughly
paralleled the anterior aspect of the superficial medial collateral ligament.
It was most easily identified along its anterior femoral course, where the
joint capsule that coursed toward the medial part of the patella was visibly
thinner and had a different fiber orientation. The posterior border of the
deep medial collateral ligament blended with and became inseparable from the
central arm of the posterior oblique ligament, just posterior to the posterior
edge of the superficial medial collateral ligament.
The deep medial collateral ligament consisted of distinct meniscofemoral
and meniscotibial ligament components (Fig.
5). The meniscofemoral ligament was consistently longer in the
proximal-to-distal direction than the meniscotibial portion (see Appendix).
The meniscotibial ligament portion of the deep medial collateral ligament was
a consistently shorter and thicker structure and attached just distal to the
edge of the articular cartilage of the medial tibial plateau (see
Appendix).
Posterior Oblique Ligament
The posterior oblique ligament consisted of three fascial attachments that
coursed off the distal aspect of the semimembranosus tendon at the knee and
have been previously termed the superficial, central (tibial), and the
capsular
arms2,17
(Fig. 6). The distances from
the femoral attachment of the posterior oblique ligament to other specific
osseous landmarks are listed in a table in the Appendix. On the average, the
posterior oblique ligament attached on the femur 7.7 mm (range, 6.1 to 9.8 mm)
distal and 6.4 mm (range, 4.5 to 10.6 mm) posterior to the adductor tubercle
and 1.4 mm (range, 0.8 to 2.1 mm) distal and 2.9 mm (range, 2.1 to 4.1 mm)
anterior to the third osseous prominence over the medial part of the knee, the
gastrocnemius tubercle.
The superficial arm of the posterior oblique ligament consisted of a thin
fascial expansion. Proximally it coursed medial to the anterior arm of the
semimembranosus, and distally it followed the posterior border of the
superficial medial collateral ligament
(Fig. 6). Proximally it blended
into the central arm of the posterior oblique ligament, whereas distally it
was parallel to the posterior border of the superficial medial collateral
ligament until it blended into the distal tibial expansion of the
semimembranosus and its tibial
attachment24.
The central arm was the largest and thickest portion of the posterior
oblique ligament (Figs. 7-A and
7-B). It coursed from the distal aspect of the main
semimembranosus tendon and was a thick fascial reinforcement of both the
meniscofemoral and meniscotibial portions of the posteromedial capsule, and it
also had a stout attachment to the medial meniscus. Anteriorly, it merged with
the posterior fibers of the superficial medial collateral ligament. The
central arm of the posterior oblique ligament could be differentiated from the
superficial medial collateral ligament by the proximal course of its fanlike
fibers, which ran more posteriorly toward its femoral attachment than did the
fibers of the superficial medial collateral ligament, which coursed more
anteriorly toward its femoral attachment
(Fig. 6). Its distal attachment
was primarily to the posteromedial aspect of the medial meniscus, the
meniscotibial portion of the posteromedial capsule, and the posteromedial part
of the tibia.
The capsular arm of the posterior oblique ligament consisted of a thin
proximal fascial expansion off the anterior aspect of the distal part of the
semimembranosus tendon (Fig.
6). It was located posterior and lateral to the meniscofemoral
capsular attachments of the central arm and had no fibers that coursed toward
the tibia. The capsular arm primarily blended with the meniscofemoral portion
of the posteromedial joint capsule and the medial aspect of the oblique
popliteal ligament, and it also attached to the soft tissues over the medial
gastrocnemius tendon, the adductor magnus tendon expansion to the medial
gastrocnemius, and the adductor magnus tendon femoral attachment.
Qualitatively, it was less stout overall than the central arm, and it did not
have any osseous attachment.
Medial Patellofemoral Ligament
The medial patellofemoral ligament was located anterior to, and in a
distinct extra-articular layer from, the medial joint capsule. The distal
border of the vastus medialis obliquus muscle attached along the majority of
the proximal edge of the medial patellofemoral ligament
(Fig. 8). It was from this
proximal margin that the medial patellofemoral ligament was consistently
identified. Distally, it could be distinguished as a distinct thickening
within the fascial layer, which coursed between the proximal-medial edge of
the patella and its femoral attachment. The medial patellofemoral ligament had
a broad-based attachment to the superomedial aspect of the medial border of
the patella. On the average, the midpoint of the medial patellofemoral
ligament patellar attachment was located 41.4% of the length from the proximal
tip of the patella along the total patellar length (proximal to distal). The
average overall length of the patella in these knees was 48.4 mm (range, 38.1
to 55.8 mm). The ligament then coursed medially toward the femoral attachments
of the adductor magnus tendon and superficial medial collateral ligament and
attached primarily to soft tissues between these two structures
(Fig. 2). The medial
patellofemoral ligament attachment on the femur was an average of 10.6 mm
(range, 8.0 to 13.4 mm) proximal and 8.8 mm (range, 6.7 to 10.3 mm) posterior
to the medial epicondyle and 1.9 mm (range, 1.3 to 3.2 mm) anterior and 3.8 mm
(range, 2.1 to 6.3 mm) distal to the adductor tubercle. The average length of
the medial patellofemoral ligament was 65.2 mm (range, 56.8 to 77.8 mm)
between its patellar and femoral attachment sites.
Adductor Magnus Tendon
The adductor magnus tendon attached in an osseous depression an average of
3.0 mm (range, 1.8 to 4.6 mm) posterior and 2.7 mm (range, 1.6 to 4.3 mm)
proximal to the adductor tubercle and did not attach directly to the adductor
tubercle (Fig. 2). The
distal-medial aspect of the adductor magnus tendon had a thick fascial
expansion, which fanned out posteromedially and attached to the medial
gastrocnemius tendon, the capsular arm of the posterior oblique ligament, and
the posteromedial capsule (Fig.
9). At its attachment site to the medial gastrocnemius tendon, the
fascial expansion averaged 15.7 mm (range, 11.2 to 21.3 mm) in width.
The distal-lateral aspect of the adductor magnus tendon had a very thick
tendinous sheath that attached to the medial supracondylar line. The vastus
medialis obliquus muscle had its medial attachment both along this thick
tendinous sheath and also along the lateral aspect of the adductor magnus
tendon.
Medial Gastrocnemius Tendon
The medial gastrocnemius tendon was formed at the medial edge of the medial
gastrocnemius muscle belly (Fig.
10). It attached an average of 2.6 mm (range, 1.4 to 4.4 mm)
proximal and 3.1 mm (range, 2.6 to 3.6 mm) posterior in a depression adjacent
to a third osseous prominence over the medial aspect of the medial femoral
condyle, the gastrocnemius tubercle, and the tendon attachment was an average
of 5.3 mm (range, 4.0 to 7.2 mm) distal and 8.1 mm (range, 6.1 to 10.3 mm)
posterior to the adductor tubercle (Figs.
2 and
10) (see Appendix). As noted
previously, the medial gastrocnemius tendon had a thick fascial attachment
along its lateral aspect to the adductor magnus tendon and a thin fascial
attachment along its medial and posterior aspect to the capsular arm of the
posterior oblique ligament.
Pes Anserine Tendon Attachments
The pes anserine tibial attachment consisted of the sartorius, gracilis,
and the semitendinosus tendinous attachments on the anteromedial aspect of the
proximal part of the tibia. The sartorius tendon fascia was intimately
attached to the superficial fascial layer, whereas the gracilis and
semitendinosus tendons were located on the posterior (deep) surface of the
superficial fascial layer over the medial aspect of the knee. Once the pes
anserine tendons were reflected laterally, their distinct individual
attachment sites were easily identified as each individual tendon attached in
an almost linear fashion at the lateral edge of the pes anserine bursa, which
was present in all knees (Fig.
11). The sartorius tendon attached more proximally, followed by
the gracilis tendon and the semitendinosus tendon. The average tendon widths
were 8.0 mm (range, 5.7 to 9.3 mm) for the sartorius, 8.4 mm (range, 6.2 to
11.4 mm) for the gracilis, and 11.3 mm (range, 7.5 to 15.8 mm) for the
semitendinosus at their tibial attachment sites. The midpoint of the lateral
attachment of the gracilis on the tibia averaged 8.2 mm (range, 2.8 to 11.3
mm) proximal and 13.4 mm (range, 10.3 to 15.5 mm) anterior to the distal
osseous attachment of the superficial medial collateral ligament.
Semimembranosus Tendon Tibial Attachments
The semimembranosus tendinous attachments on the medial and posteromedial
parts of the tibia consisted of the anterior and direct arms (see Appendix).
The anterior arm attached deep to the proximal tibial attachment of the
superficial medial collateral ligament in an oval-shaped pattern, and its
attachment was distal to the tibial joint line. The direct arm attached to the
proximal aspect of the posteromedial part of the tibia in a small groove just
proximal to the tuberculum tendinis
prominence25. The
attachment was posterior to the medial tibial crest and distal to the
posteromedial aspect of the joint line. The semimembranosus bursa had its
distal border along the proximal edge of the tibial attachment of the direct
arm. The semimembranosus bursa continued medial to the anterior arm, until the
anterior arm attached to bone along the posteromedial part of the tibia.
While the qualitative anatomy of the medial side of the knee has been
described
previously2,10,11,13-15,17,20,26,
no comprehensive detailed quantitative anatomy descriptions have been
published, to our knowledge. We found that many previous descriptions of the
qualitative attachment sites of the medial part of the knee were inaccurate
once the individual structures were isolated and measured, especially for the
femoral attachment sites of the superficial medial collateral ligament, the
posterior oblique ligament, and the medial patellofemoral ligament.
We believe that it is important to report on and understand the course of
the individual structures and the attachment sites rather than to attempt to
describe them in
layers10. The
layered description is not useful for surgical approaches because the area
where the medial sided structures are actually separated into three layers is
quite small10. In
fact, the authors who introduced this layered description reported that the
only distinct location where there were three tissue planes was directly over
the superficial medial collateral ligament and occasionally over the medial
patellofemoral
ligament10. In the
majority of locations, there are only individual structures deep to the
superficial crural fascial layer and there is not an intervening middle layer.
Thus, we recommend that consideration be made to minimizing the use of the
three-layered anatomy description of medial-sided knee structures and that
clinical and magnetic resonance imaging descriptions of medial knee anatomy
refer to individual structures.
Femoral Osseous Prominences
In all femora that were analyzed for the present study, there were always
three separate osseous prominences over the medial aspect of the knee. Until
this study, we were unaware of the presence of a third femoral osseous
prominence. In some knees, this prominence was the largest of the three. It
was located slightly distal and posterior to the adductor tubercle. As the
medial gastrocnemius tendon attached close to this third osseous prominence,
we propose that it be named the gastrocnemius tubercle. We also found
that the posterior oblique ligament attachment was adjacent to the
gastrocnemius tubercle, which means that its attachment was closer to the
gastrocnemius tubercle than to the adductor tubercle. We believe that a great
deal of the confusion in the previously published literature with regard to
the location of the femoral attachments of the medial patellofemoral ligament
and the posterior oblique ligament has been due to the lack of recognition of
the gastrocnemius tubercle. In addition, we believe that it is important for
clinicians to recognize the presence of this gastrocnemius tubercle as it
could be incorrectly identified as the adductor tubercle by palpation,
resulting in non-anatomic repairs or reconstructions of medial knee
injuries.
Superficial Medial Collateral Ligament (Tibial Collateral
Ligament)
The superficial medial collateral ligament is the largest structure of the
medial part of the knee and has been qualitatively well described in the
literature10,13-15,20.
Our measurements agree with those of previous investigators, who have
described it to be between 10 and 12 cm in overall
length10,20,26.
We found the superficial medial collateral ligament to have one proximal
femoral attachment, which was not directly to the medial epicondyle but was
centered in a small depression slightly proximal and posterior to the center
of the medial epicondyle. Palmer's
description27 of
the femoral attachment of the superficial medial collateral ligament, although
vague, seems to be the closest one to our findings; he noted that it attached
in an approximately 2-cm oval pattern "in the neighborhood of the area
over which the condylar axis shifts". While other authors have reported
that the superficial medial collateral ligament attached directly to the
medial
epicondyle10,13-15,17,18,20,25,26,28,29,
we did not find any instances in which it attached directly there.
We found the superficial medial collateral ligament had two distinct tibial
attachments. The proximal tibial attachment was primarily to soft tissues
directly over the anterior arm of the semimembranosus, whereas the distal
tibial attachment was directly to bone. Brantigan and
Voshell14,15
also previously reported that the superficial medial collateral ligament
attached inferiorly to two points on the tibia, and other
investigators14,27
have reported that the distal aspect of the superficial medial collateral
ligament attached approximately 6 cm distal to the joint line, which is in
agreement with our findings.
Deep Medial Collateral Ligament (Mid-Third Medial Capsular
Ligament)
We found the deep medial collateral ligament to consist of a thickening of
the medial joint capsule, deep and firmly adherent to, but separable from, the
superficial medial collateral ligament, with distinct meniscofemoral and
meniscotibial components. The meniscofemoral ligament portion attached distal
and deep to the femoral attachment of the superficial medial collateral
ligament. The meniscotibial portion, which was much shorter and thicker than
the meniscofemoral ligament portion, attached just distal to the edge of the
articular cartilage of the medial tibial plateau. Others have also reported
that the deep medial collateral ligament was composed of meniscofemoral and
meniscotibial
portions26,30.
Posterior Oblique Ligament
The attachment sites and course of the posterior oblique ligament have been
a source of confusion in the
literature17,18,20,25.
We found the three components of the posterior oblique ligament, previously
described by Hughston and
Eilers17 as the
superficial, central, and capsular arms, to be readily identified. While we
found that all three structures were continuous with each other, defined
attachment patterns were consistently identified and outlined. The two
primarily anterior arms, the central and superficial arms, blended into each
other to form a common femoral attachment, which was proximal and posterior to
the femoral attachment of the superficial medial collateral ligament. The
femoral attachment of the posterior oblique ligament was not to the adductor
tubercle17,18
or medial
epicondyle25, as
described previously; rather, the ligament attached 7.7 mm distal and 6.4 mm
posterior to the adductor tubercle and 1.4 mm distal and 2.9 mm anterior to
the gastrocnemius tubercle. Thus, in effect, the femoral attachment of the
posterior oblique ligament is closer to the gastrocnemius tubercle than to the
adductor tubercle.
We also found that the central arm of the posterior oblique ligament forms
the main portion of this structure. While the central arm has been also
referred to as the tibial arm in the
literature2,4,16,17,
we have chosen to call this portion of the posterior oblique ligament the
central arm according to the original description by Hughston and
Eilers17. This is
because this structure is centrally located, with its main structure and
static
function5,9
being more intertwined with its proximal femoral course rather than its more
distally based tibial course. The other two components are thin structures.
The superficial layer is a thin structure that runs parallel to the posterior
aspect of the superficial medial collateral ligament, which blends distally
with the distal tibial expansion of the
semimembranosus24,
while the capsular arm is also thin and attaches primarily to the
posteromedial joint capsule. Thus, it appears that the main structure that
would need to be repaired or reconstructed in this anatomic area following a
posteromedial knee injury would be the central arm of the posterior oblique
ligament. In fact, we found that the central arm was the portion of the
posterior oblique ligament that merged with and reinforced the posteromedial
capsule, was adherent to the medial meniscus, and formed the main portion of
the femoral attachment of the posterior oblique ligament.
In some of the earlier literature on medial knee
anatomy10,13-15,
the superficial medial collateral ligament was reported to have an oblique
posterior portion, which is now recognized as the posterior oblique ligament.
All of those previous
descriptions10,13,14,15
fit with our description of the main portion of the central arm of the
posterior oblique ligament.
Medial Patellofemoral Ligament
We found that the medial patellofemoral ligament was a distinct structure
that was located anterior to the deeper medial joint capsule and was
distinctly extracapsular from the underlying medial joint capsule in all
cases. We found that its attachment width along the superomedial border of the
patella was similar to the attachment width described by Steensen et
al.31. It then
coursed distal-medial to the adductor tubercle to its femoral attachment. The
location of its femoral attachment has been variably described to be at either
the medial
epicondyle25,32,
at the anterior aspect of the medial
epicondyle31,33,
or just distal to the adductor
tubercle34. As
noted previously, we found its femoral attachment to be located closer to the
adductor tubercle than to the medial epicondyle, which agrees with the
description provided by Tuxoe et
al.34.
Adductor Magnus Tendon
In the present study, we found that the adductor magnus tendon attached in
a small depression slightly posterior and proximal to the adductor tubercle
and not directly to the tip of the tubercle as described
previously13,25,29.
It also had a thick fascial attachment, which extended posteriorly from the
distal aspect of the tendon to attach to the proximal aspect of the medial
gastrocnemius tendon and posteromedial joint capsule. To our knowledge, this
fascial attachment between the adductor magnus and medial gastrocnemius
tendons has not been specifically described previously.
Medial Gastrocnemius Tendon
We found that the medial gastrocnemius tendon attached in a small
depression that was proximal and adjacent to a third osseous prominence, which
we have called the gastrocnemius tubercle, located over the posteromedial edge
of the medial femoral condyle. Our findings differed somewhat from those
reported by
Standring25, who
did not note the presence of the gastrocnemius tubercle and who reported that
the medial gastrocnemius tendon attached in a depression at the upper and
posterior aspect of the medial femoral condyle, just behind the adductor
tubercle. While we did find that the medial gastrocnemius tendon attached in a
small osseous depression in this region, it was actually posterior to the
gastrocnemius tubercle and not the adductor tubercle.
In the present study, we quantitatively determined the anatomic attachment
sites of the medial knee structures and their relationships to pertinent
osseous landmarks. In addition, a third osseous prominence over the medial
part of the knee, the gastrocnemius tubercle, was identified. With the
improved knowledge of the attachment anatomy and courses of structures of the
medial part of the knee, knee surgeons and radiologists should be able to
improve their interpretation of injuries to the soft-tissue structures of this
area. In addition, this detailed knowledge of the quantitative attachment
sites of these medial knee structures will prove to be useful in the
evaluation of techniques and outcomes studies of anatomic repairs and
reconstructions of posttraumatic ligamentous injuries that involve the medial
and posteromedial knee structures.