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Medial Knee Compartment Osteoarthritis and Pedorthic Treatment

Lateral Knee Wedging as an Aid in the Reduction of Knee Osteoarthritis

The Prevalence of Osteoarthritis

Osteoarthritis (OA) is one of the most common musculoskeletal disorders affecting
an aged population. OA involves the degeneration of joints causing symptoms of chronic pain
and stiffness in the affected joints of the body. OA of the medial compartment of the knee
affects approximately 20% to 40% of individual’s over the age of sixty five years (Rubin &
Menz, 2005). The medial knee compartment is particularly susceptible to OA during everyday
walking, as a repetitive varus torque at the knee is reported to cause a compressive force within
this compartment. As this varus torque increases in the knee, the medial compartment gradually
decreases in joint space, and consequently, increases its risks towards the development of knee
OA. A logic rehabilitative approach has been geared towards conservative treatment in reducing
this varus torque (Kerrigan et al, 2002). A lateral wedged insole has been the topic of current
research, as a conservative treatment aimed at reducing the varus torque of the knee during
walking (Kerrigan et al, 2002). The goal of research is to find a conservative means of reducing
the torque applied in the medial knee compartment, and consequently decreasing pain and the
progression of knee OA. Research in this area is still currently undergoing exploration.

Current Research

Kerrigan and associates studied the effects of lateral wedged insoles on knee varus torque
in patients with knee OA. The fifteen participants in the study required a minimum radiographic
osteoarthritic severity of a grade three according to the Kellgren and Lawrence scale. Based on
this grading scale, ten subjects were of grade three severity, while the remaining five subjects
were of grade four severity. Each participant walked their normal walking speed across a 10m
laboratory walkway. Five conditions were testing in each participant: walking in their own shoes,
walking with a control insole of 3.175mm thick, walking with a 5? lateral wedge, walking with a
control insole of 6.35mm thick and lastly, walking with a 10? lateral wedge. The conditions where
wedges were incorporates into the insole, the wedge was only placed on the patients affected side.
Both control insole were not wedged. Gait velocity, stride length and kinematic information were
recorded with three-dimensional retroreflective markers placed on specific bony landmarks on
patients. Results indicated a decrease in varus knee torque and reported pain with the 5? lateral
wedge compared to either no insole or the 3.175mm thick control insole. The reduction in varus
knee torque was significantly greater with the 10? lateral wedge. There are two major knee varus
torques throughout participant’s gait cycle (see figure…). With the 10? lateral wedge, the first
peak was reduced by 8.3%, and the second peak was reduced by 8% respectively (Kerrigan,
2002).

In the Kerrigan et al. study, discomfort was noted by all participants when walking with
the 10? lateral wedge. One importance to note is the wedged insoles were placed directly into
the participants shoes, and not incorporated into an orthotic device. Russel Rubin and Hylton B.
Menz took the lateral wedging principle a step further, and did in fact incorporated the wedge
into an orthotic device. The principle of their study was to incorporate lateral wedges into
custom made orthoses in patients with medial compartment knee pain. Participants included
thirty subjects aged 29 to 77 years of age. The exclusion criterion was similar between both
the Kerrigan et al. study and the Rubin and Menz study. A radiographically confirmed medial
compartment OA of the knee needed to be evident in each participants. Furthermore, patients
needed to be currently experiencing some degree of pain, not receiving physiotherapy, not taking
anti-inflammatory medications, or currently using any form of orthotic device. Each participant
in the Rubin and Menz study was casted in a non-weight bearing prone position and pain was

assessed based on a subjective pain scaling system. Results indicated zero relationship between
the effects of orthoses on pain levels, and zero relationship between age of participants and
percentage of pain improvement. The interesting finding of this study is the relationship found
between pain reduction and the severity of knee OA. A negative association was found between
the severity of OA and the degree of pain reduction. In other words, patients with less severe OA
experiences the largest reductions in pain with the use of orthoses (Rubin & Menz, 2005).

Shimada et al.’s study looked at both the effects of lateral wedges on knee kinetics and
kinematics, as well as the effects of lateral wedging on differing diseases severity of patients
with medial knee compartment OA. Participants included 23 patients suffering from bilateral
medial knee compartment OA, and 19 healthy volunteers constituting the control group. A
similar exclusion criterion was implied as the two previously described studies. The results
of this study support the findings of Rubin and Menz, where the use of orthoses has different
effects with different severity grades of OA. Stride length, stride width and walking velocity
were significantly lower in the experimental group than the control group. Patients with OA
experienced an increase in stride width with the use of lateral wedges, however there were
no changes in the other two gait parameters. With the use of lateral wedges, OA participants
with grades I and II experienced significant reductions in peak adduction moment values and
decreased first acceleration peak after heel strike. The importance of this study lies in the
insignificant results found in these parameters of OA participants with severity grades of III and
IV., regardless of the use of a lateral wedge.

In 2008, Tuda & Tsukimura did a comprehensive study examining the influences on
heeled footwear when wearing a lateral wedged insole, in everyday walking shoes and socks to
flat footwear without heels. 207 participants completed the study, each placed in one of five
groups of prepared orthotic devices: a neutrally wedged insole, a traditional shoe inserted insole, a
sock-type ankle supporter with the lateral rubber heel wedge insert sewn in, a urethane 12mm
wedge or simply flat footwear. Participant’s knee OA and pain was recorded at both baseline and
at a 12 week follow-up, based on the Lequesne index of algo-functional disability and the ‘Visual
Analogue Scale’ (VAS). Results between baseline and the 12 week follow-up reported improved
Lequesne index scores in all groups except placebo with shoes, and inserted insole with shoes.
The subjective VAS pain scores showed improvements between baseline and the 12 week follow-
up in groups of strapped insoles with and without shoes. Groups with the placebo with shoes,
inserted insole with shoes and without shoes showed no VAS subjective pain score
improvements. A final aspect of Tsukimura et al’s study looked at the days in which participants
needed the use of a non-steroidal anti-inflammatory drug (NSAID). There was a decrease in the
usage of NSAID between baseline and the 12 week follow-up in most groups (Tuda &
Tsukimura, 2008).

A knee varus torque is present throughout the entire gait cycle, therefore, Kerrigan et al. justified
using a full length laterally wedged insole as being the most effective. In both the 5? and 10?
lateral wedge, the material choice of the insole was identical. This controlled condition in the
study lead Kerrigan et al. to conclude that the lateral wedge was directly altering participant’s
knee joint biomechanics, as oppose to a result of the insole cushioning. Tuda & Tsukimura’s
study “considered the differences in the varus moments between wearing the strapping insole
added to a bare foot and wearing moderate high-heeled shoes alone might be greater than the
differences shown between wearing moderate high-heeled shoes alone and when inserting
wedges into the shoes” (Tuda & Tsukimura, 2008). Tsukimura found great subjective pain
improvement in shoes with a strapped insole. A main disadvantaged to this type of footwear,

is the large amount of discomfort experienced by every participant in the study. In the
patient’s everyday walking shoes, all patients experienced cramping in their shoes in order
to accommodate the thickness of the insole. Weeks following the study’s 12 week follow-up,
compliance with this type of foot wear would most likely decrease. The study’s result showed
promise in suggesting that “the beneficial effect of the inserted insole was due to the reduction in
the medial knee joint surface loading with a concurrent reduction in lateral tensile forces” (Tuda
& Tsukimura, 2008).

Based on the findings of Rubin and Menz, their study suggests positive results when
incorporating a lateral wedge into a custom made orthoses for the treatment of patients
with medial compartment OA. Secondly, there were no participants in their study who
reported an increased amount of pain in both the knee and foot at the 6 week follow-up.
Furthermore, “subjects with less severe osteoarthritis exhibited relatively greater reductions in
pain. Subjects with more pronounced osteoarthritis and sever loss of joint space seem to obtain
only limited benefit from laterally wedged orthoses” (Rubin & Menz, 2005). Shimada and
colleagues study support these findings. An increased stride length found in participant’s who
were laterally wedge proves to be of importance to these researchers. This result is attributed
to a change in the moment at the knee as a result of a laterally shifted location of the center of
pressure, and consequently, decreased pain (Shimada et al, 2006). One major consideration when
lateral wedging a patient, is the aftermath of such actions. There is an increased susceptibility
to placing an excessive magnitude of eversion through the foot and lower leg when laterally
wedging (Rubin & Menz, 2005). In these cases, the alignment of the lower limb is compromised
and the long term effects on dynamic function still remain uncertain.

Limitations, Future Research, and the Pedorthics School of Thought

These studies have a few important limitations that require serious consideration. The
assessment of pain in each study is based on subjective assessment. Each patient’s pain levels
are extremely individualized. Tsukimura et al. note that their study had “no provision for arch
support in the midfoot of the inserted lateral wedge with shoes, and therefore it was possible that
a flexible low arched foot type would pronate in the midfoot as a result of the lateral wedging
as opposed to translating the effect of the wedge to the knee” (Tuda & Tsukimura, 2008). An
important consideration of all the presented studies is that “it cannot be inferred that lateral
wedging alters the natural progression of gross arthritic changes in the knee” (Rubin & Menz,
2005). An understanding needs to be ascertained that these studies are implying a link between
lateral wedging and reducing medial knee compartment joint space; these results are not applying
a direct causation. Furthermore, the highlighted studies were only six and twelve weeks in
duration. Whether pain reduction would continue on past the length of these studies remains
unknown. Current conservative treatment needs to be geared towards the OA patients with more
advanced cases of the disease, and other biomechanical changes need to be further investigated.
For example, Maley and colleagues studied the gait biomechanics with patient’s wearing laterally
wedged orthoses. These researchers attributed an out-toed gait pattern as the foot positioning
which reduced the knee medial joint load. Additional studies need to support these findings.
From a pedorthics standpoint, “reducing both pain and knee varus torque is particularly appealing
because treatment modalities that may reduce pain do not necessarily reduce varus torque”
(Kerrigan et al, 2002). There is early success here is reducing patients pain when lateral wedging
is incorporated into full length orthoses. The continuation of support towards lateral wedging may
be dictated by its effects on dynamic function in the long term.