ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

High tibial osteotomy (HTO) surgery (Fig 1.) is a treatment
option for medial compartment knee osteoarthritis (OA). The
joint is realigned to correct varus malalignment and relieve pain.
This is achieved through the lateral removal or medial addition
of a wedge of bone in the proximal tibia, followed by rigid
fixation. The ‘opening wedge’ procedure is becoming more
commonly employed [9] and is used for subjects in this study.
This involves a cut across the proximal tibia, which is opened
up, filled with calcium phosphate or bone graft and rigidly fixed
with a plate [10]. The gap subsequently fills with bone. The
change in joint alignment intends to shift the location of force
transmission and the mechanical stresses from the diseased
medial to the healthy lateral knee compartment. It delays the need for a joint
replacement, making it a favorable treatment option for younger and active patients.
Studies investigating the relationship between dynamic gait measurements and longterm
clinical outcome have identified peak external knee adduction moment (EKAM) as
an important clinical marker [8, 11-13] of medial compartment loading and OA severity
[14], where an increase in EKAM indicates an increase in medial compartment loads. It
has been identified as a predictor of the ratio of medial-to-lateral proximal tibial bone
mineral content and load distribution on the tibial plateau. Studies using two and threedimensional
models have found correlations between KAM and internal kinetic changes
[15,16]. Therefore it can be used to quantify the benefits of HTO. Increased external
EKAMs is indicative of increased loads in the medial compartment relative to the lateral
compartment. Peak adduction moment for subjects with no pathology ranges between
2.5 to 4.75 (% Body weight (BW) x height (h)). Patients with OA have been reported to
have a higher 1 st peak EKAM than subjects with no pathology. Those with severe OA
with a KL score greater than 3 also have a higher 2 nd peak EKAM [17]. Patients with
below-average KAMs post-surgery (less than about 2.5 %BW x h) were found to have
better long-term clinical outcome [11], regardless of their pre-surgery moment.
Birmingham [18] have shown that the largest change in EKAM moment occurs at 6
months post op, with only a small increase (13%) observed from 6 to 24months. Thus
patient assessments between 6-9 months post-op were selected for investigation in this
study.
3. METHODS
Bi-lateral knee function during gait was evaluated for 10 subject’s pre-HTO surgery
(height: 1.71±0.11m, mass: 85.9±15.9Kg). 6 subjects were re-assessed between 6 to 9
months following unilateral HTO using the opening wedge approach. Ethical approval
was granted by the Research Ethics Committee for Wales and Cardiff and Vale
University Health Board. 49 light retro-reflective markers were positioned in a
modified Cleveland clinic marker set [19] and 3D motion capture (Qualisys, Sweden
and Bertec Corporation) used to record 6 trials of level gait at self-selected speeds.
Biomechanical models of each subject were created in Visual3D (C-motion, Inc) to
compute temporal, kinematic and kinetic data. Each subject completed the Knee
Outcome Survey (KOS) [20] and Oxford Knee Score (OKS) [21] at the start of each
data collection. One way ANOVA was performed to identify changes in EKAM and
KAAI (for the operative and non-operative leg), OKS and KOS following HTO surgery.