Floating bones - Knee joint compressive forces

The page is aimed at those who have swallowed Steven Levin's silly theory that bones float in a sea of tension.

Use of a load transducer in the knee joint has been reported in the literature on many occasions - e.g. here:

[Biomechanical study on contact pressure in the femoro-tibial joint]
[Article in Japanese]
Inaba H.

Department of Orthopedic Surgery, Akita University School
of Medicine, Japan.

To clarify the function of the menisci, dynamic contact
pressure in femoro-tibial joints obtained from postmortem or
surgical specimens with intact menisci, following partial
and total meniscectomy was measured using transistor
pressure transducers and Buldon tube pressure gauges. After
meniscectomy, the peak contact pressure increased strikingly
and contact area decreased markedly. The lower contact
pressure after partial meniscectomy than after total
meniscectomy is probably one reason why the results of
partial meniscectomy are clinically much better than those
of total meniscectomy. With flexion of the knee, the region
of peak contact pressure shifted posteriorly and high
contact pressure was detected below the posterior segment of
the medial meniscus. Stress release in articular cartilage
varies from region to region, and occurs remarkably after
meniscectomy. These findings suggest that the main function
of the menisci is load bearing and protection of the
cartilage from overload applied to the knee joint.

http://calorierestriction.org/pmid/?n=3437173



Impact load transmission of the knee joint-influence of
leg alignment and the role of meniscus and articular
cartilage.

Fukuda Y, Takai S, Yoshino N, Murase K, Tsutsumi S, Ikeuchi K, Hirasawa Y.

Department of Orthopaedic Surgery, Kyoto Prefectural
University of Medicine, Kawaramachi Hirokoji, Kamigyo-ku,
Kyoto, Japan. f.yuki@mb.newsb.ne.jp

OBJECTIVE. The objective of this study was to evaluate load
transmission in the cancellous bone of the tibia under
static and impact load.BACKGROUND. Abnormal transmission of
loads may result in osteoarthritis and fractures. However,
the role of the cancellous bone in these processes is not
well understood.METHODS. The compressive stresses in the
subchondral bone, epiphysis and diaphysis of the tibia of
porcine knees were measured under static and impact load
using mini-pressure transducers. The tests were performed
using a drop-tower type testing machine in neutral, varus
and valgus alignments. Tests were repeated after
meniscectomy and again after removing the articular
cartilage.RESULTS. In the intact knee in all alignments, the
highest stress on the medial side was found in the
epiphysis, and in the subchondral bone on the lateral side.
After meniscectomy, a significant increase was observed in
the stress in the subchondral bone on both sides. After the
articular cartilage was also removed, the stress in the
subchondral bone increased again, but slightly.CONCLUSION.
The importance of the meniscus in load transmission is
supported by this study. The contribution of the articular
cartilage to load transmission is less than that of the
meniscus.Relevance. The patterns of static and dynamic load
transmission observed in this study correlate with the sites
of insufficiency fractures of the medial tibial plateau and
traumatic lateral tibial plateau fractures observed
clinically. Examination of the load transmission is key to a
more complete understanding of the causes of osteoarthritis
and tibial plateau fractures.

http://calorierestriction.org/pmid/?n=10831811




[Impact absorbing properties of the human knee joint]
[Article in Japanese]
Hoshino A, Wallace WA.

Department of Orthopaedic Surgery, Tokyo Medical and Dental
University School of Medicine, Japan.

A biomechanical study has been carried out on 20 cadaveric
knee joints to investigate the load absorbing mechanism of
the knee. The impact load was applied using a falling weight
onto the transected proximal femur and the force transmitted
through the knee joint was measured at the transected distal
tibia using a load transducer. The transmitted peak force
applied through the joint was first measured through the
intact knee (100%). After the lateral and medial menisci
were cut radially the transmitted peak force increased to
113% and it reached 121% after the meniscus and all the soft
tissues had been removed. Next the articular cartilage and
subchondral bone were removed and this resulted in the
transmitted peak force increasing to 135%. When a knee joint
replacement was then carried out, the peak transmission
force was found to increase to 180%. These results show that
the knee joint has an impact absorbing property in each
segment and comparison of the results reveals that
osteoarthritic joint is capable of less shock absorption
than the normal knee. The high impact force in an implanted
knee suggests micro-fractures of the cancellous bone might
be expected and may produce long term loosening.

http://calorierestriction.org/pmid/?n=2723499



Impact-absorbing properties of the human knee.
Hoshino A, Wallace WA.

Queen's Medical Centre, Nottingham, England.

A biomechanical study has been carried out on 20 cadaveric
knees to investigate their load-absorbing mechanism. The
impact load was applied using a weight falling onto the
transected proximal femur and the force transmitted through
the knee was measured at the transected distal tibia using a
load transducer. The peak force transmitted increased as,
sequentially, meniscus, articular cartilage and subchondral
bone were damaged or removed. The most striking result was
found in an implanted knee replacement where the transmitted
force reached 180% of that in the intact knee. The results
show that the joint has an impact-absorbing property in each
segment and that in the osteoarthritic knee there is less
absorption of shock than in the normal knee. The high impact
force in an implanted knee suggests that microfractures of
the cancellous bone might be expected and may produce
loosening.

http://calorierestriction.org/pmid/?n=3680348


The role of the menisci in force transmission across the knee.
Walker PS, Erkman MJ.

Fourteen knees were studied by a method called spatial
location, to determine the contact and load-bearing areas
between the femur and the upper tibia in non-loaded and
loaded conditions, at various angles of flexion. Under no
load, contact occurred primarily on the menisci; the lateral
aspects contacted at 0 degrees flexion, moving to the
posterolateral aspects at 90 degrees flexion. An area of
cartilage which frequently contacted was the medial tibial
spine. Under loads of up to 150 kg, the lateral meniscus
appeared to carry most of the load on that side of the
joint, while on the medial side, the load was shared
approximately equally by the meniscus and the exposed
cartilage. These findings were verified on two knees by
measuring contact pressure with a miniature transducer. Two
implications of these findings are that the area of load-
bearing is greatly increased and that the stability of the
knee joint is enhanced by the menisci.

http://calorierestriction.org/pmid/?n=1173360


The contact area and pressure distribution pattern of the
knee. A study of normal and osteoarthrotic knee joints.

Fukubayashi T, Kurosawa H.

Seven knees were studied to determine the contact area and
pressure distribution of the tibiofemoral joint, under
various loads and at 0 degrees flexion, using the casting
method and special sensor sheets. At a load of 1000N
(Newton) the contact area of the knee was 11.5 x 10(2) mm2
with menisci and 5.2 x 10(2) mm2 without menisci, and the
menisci occupied 70% of the total contact area. Peak
pressure at 1000N was 3MPa (Mega Pascal) with the menisci
and 6MPa without them. The high pressure areas were located
on the lateral meniscus as well as on the uncovered part of
the articular cartilage of the lateral compartment, and on
the uncovered cartilage in the medial compartment. After
removal of the menisci the contact area decreased to below
one half that of the intact knee and the contact pressure
considerably increased. These facts imply that the menisci
have load bearing and load spreading functions. The contact
areas were also measured in two osteoarthrotic knees and
they were significantly larger than those in normal knees.
In these arthrotic knees the menisci seemed to play a less
significant role in transmission of weight than in the
normal knees.

http://calorierestriction.org/pmid/?n=6894212


In vitro study of contact area and pressure distribution in
the human knee after partial and total meniscectomy.

Ihn JC, Kim SJ, Park IH.

Department of Orthopaedic Surgery, Kyungpook National
University Hospital, Taegu, Korea.

Many investigators have attempted to find the cause of the
osteoarthritic changes after meniscectomy. Alteration of the
mechanical factors resulting in stress concentration, is now
thought to be one of the most important causes but few
experimental studies have reported the differences in
contact area and pressure distribution after partial or
total meniscectomy. By using pressure sensitive film, we
have calculated the contact area and the pattern of weight
distribution in three different situations; intact meniscus,
partial and total meniscectomy. The experimental materials
were obtained from 5 above knee amputation specimens. The
knee joint was fixed in full extension to an Instron machine
using an aluminium box and mounting resin. Load was
transmitted to the tibiofemoral joint containing the special
film, within a physiological range. Analysis of the contact
area for each situation (intact meniscus, partial and total
meniscectomy) was made by reviewing the film. By measuring
the contact area after meniscectomy, we showed that the
meniscus performs a load transmitting function in the knee
joint. The medial contact area of the tibiofemoral joint
with an intact meniscus is always larger than the lateral
compartment (1.36:1), but in partial and total meniscectomy
the difference between them gradually decreased. There was a
minor decrease in contact area after partial meniscectomy
and a much greater decrease after total meniscectomy. The
degree of stress concentration in the contact area was
increased when part or all the meniscus was excised. There
was little change of contact area in the opposite, intact
side of the joint after partial meniscectomy, but marked
change after total meniscectomy.

http://calorierestriction.org/pmid/?n=8407035


The contact area and pressure distribution pattern of the
knee. A study of normal and osteoarthrotic knee joints.

Fukubayashi T, Kurosawa H.

Seven knees were studied to determine the contact area and
pressure distribution of the tibiofemoral joint, under
various loads and at 0 degrees flexion, using the casting
method and special sensor sheets. At a load of 1000N
(Newton) the contact area of the knee was 11.5 x 10(2) mm2
with menisci and 5.2 x 10(2) mm2 without menisci, and the
menisci occupied 70% of the total contact area. Peak
pressure at 1000N was 3MPa (Mega Pascal) with the menisci
and 6MPa without them. The high pressure areas were located
on the lateral meniscus as well as on the uncovered part of
the articular cartilage of the lateral compartment, and on
the uncovered cartilage in the medial compartment. After
removal of the menisci the contact area decreased to below
one half that of the intact knee and the contact pressure
considerably increased. These facts imply that the menisci
have load bearing and load spreading functions. The contact
areas were also measured in two osteoarthrotic knees and
they were significantly larger than those in normal knees.
In these arthrotic knees the menisci seemed to play a less
significant role in transmission of weight than in the
normal knees.

http://calorierestriction.org/pmid/?n=6894212

Biomechanical considerations of the menisci of the knee.

McBride ID, Reid JG.

School of Physical and Health Education, Queen's University
Kingston, Ontario.

The menisci of the knee are important structures for
maintaining a healthy joint since they absorb shock and
prevent rotatory instability. The shapes of the menisci and
the orientations of their collagen fibres are naturally
suited for bearing weight of the joint. Their shape also
allows the tibial plateau contact area to be three times
greater, thereby decreasing the stress by up to seven times.
The medial and lateral menisci are able to move to different
extents as a result of the variable laxities of the
adjoining ligaments. Often a meniscus becomes injured and
must be surgically removed by either a partial or total
meniscectomy. Many meniscal injuries occur during sports
activities and are caused predominantly by a twisting
motion. A meniscectomy has been shown to have detrimental
effects including increased joint laxity, osteoarthritis,
and other structural changes. Approximately 25% of those who
have had a total meniscectomy must stop or restrict their
sports activities.

http://calorierestriction.org/pmid/?n=3064900



Anatomy and biomechanics of the menisci.

Renstrom P, Johnson RJ.

Department of Orthopaedics and Rehabilitation, University of
Vermont, College of Medicine, Burlington.

The shape of the menisci and the orientation of the collagen
fibers are optimal for weight bearing and shock absorption.
The menisci are of clinical importance to knee biomechanics
as they function to maintain knee joint stability and
congruity, resist capsular and synovial impingement during
knee motion, support the screw home mechanism, and
distribute load over a large area of the articular surface.
Because of these vital roles, an attempt should be made to
save viable meniscus when performing knee surgery.

http://calorierestriction.org/pmid/?n=2199066



Menisci and knee stability]

[Article in German]

Muller W.

Orthopadische Klinik, Kantonsspital Bruderholz, Basel.

The menisci are of primary importance for the knee and its
stability. They assure functional congruence guided by the
crucial ligaments. They break up the greatest amount of
contact-impact force and limit "elastically" rotation and
translation movements. They are polyfunctional. That is the
reason why it is so difficult to measure their physiologic
behavior and mechanical effects. The medial and lateral
compartments, and therefore the medial and lateral meniscus
function and anatomy, are not symmetric but are quite
different. The menisci are important for "fine tuning" in
the control of normal motion and its limits. By achieving
functional congruity they create stability ex vacuo, as in
the shoulder joint.

http://calorierestriction.org/pmid/?n=8190513



Approximately 80% of patients with a whole meniscus removed
develop significant arthritis in that compartment of the
knee within 20 years.

http://www.sportsdoc.umn.edu/Patients_Folder/Knee/meniscal%20allograft/meniscalallograft.htm


Unfortunately, most patients who have significant portions
of their meniscus removed develop arthritis over the ensuing
decades.

http://www.orthop.washington.edu/uw/allograftmeniscus/tabID__3368/ItemID__287/PageID__3/Articles/Default.aspx