Knee gait mechanics and cartilage stress in those with/without medial compartment knee osteoarthritis five years after anterior cruciate ligament reconstruction
Date
2016
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Premature knee osteoarthritis (OA) after anterior cruciate ligament
reconstruction (ACLR) surgery is a growing concern. Aberrant knee gait mechanics
and joint loads are thought to affect cartilage stress distribution and the incidence of
knee OA after ACLR. Knee OA occurs more frequently in the medial compartment,
compared to the lateral compartment. All subjects with medial compartment knee OA
demonstrate a radiographic osteophyte near the medial joint margin. However, not all
subjects get knee OA five years after ACLR. Comparing knee gait mechanics and
joint loads in subjects with and without knee OA may be key in establishing
rehabilitation and treatment strategies to delay the progression of the disease.
The first question this proposal evaluates is “what are the differences in knee
gait mechanics and joint loads in those with/without medial compartment knee OA
after ACLR, and when are these differences present?” To that end, knee OA was
evaluated five years after ACLR, while knee gait mechanics and joint loads were
evaluated at multiple time points, i.e. before ACLR, six months, one year and five
years after ACLR. All parameters were evaluated at the first peak of vertical ground
reaction force during the stance phase of gait. Gait analysis and electromyography
(EMG)-informed neuromusculoskeletal (NMS) modeling methods were used for this
aim. Six months after ACLR, subjects with knee OA demonstrated inter-limb
differences in flexion angle/moment, adduction moment and joint loads, with lower
values for the involved knee, compared to the uninvolved knee. These inter-limb
differences ceased to exist at later time points. These results indicate that an initial
period of under-loading of the involved knee is followed by an extended period of
symmetrical loading, in subjects who get medial compartment knee OA five years
after ACLR. For the involved knee, five years after ACLR, subjects with knee OA
demonstrated lower values for flexion angle/moment, higher value for adduction
moment (not statistically significant, but with large effect size) and similar joint loads,
compared to subjects without knee OA. These results indicate that while both groups
show inter-limb symmetry five years after ACLR, knee gait mechanics are different
between these groups. Hence, the uninvolved knee (of subjects with knee OA in the
involved knee) may also be at risk of developing knee OA at future time points.
The second question this proposal evaluates is “how is cartilage stress
distribution near the medial joint margin (region of radiographic osteophyte, under the
medial meniscus) affected due to knee gait mechanics and joint loading, in those
with/without medial compartment knee OA after ACLR?” Utilizing a combination of
knee gait mechanics, joint load and load distribution between deformable knee joint
structures is necessary to estimate cartilage stress distribution. Hence, finite element
(FE) modeling was used for this aim. Medial tibial cartilage stresses were evaluated at
multiple time points, i.e. six months, one year and five years after ACLR, using knee
gait mechanics and joint loads from the first aim as inputs. For the involved knee, five
years after surgery, subjects with knee OA demonstrated higher values for peak
effective stress in the region near the medial joint margin. These results show that
stresses are indeed higher in the region where radiographic osteophytes are observed
five years after ACLR in subjects with knee OA, compared to subjects without knee
OA. These results help to reinforce the link between altered gait and knee OA.
The third question this proposal explores is “how soon can changes in cartilage
tissue be detected, and is there a relation between joint loading and cartilage tissue
level changes?” For inter-limb differences in subjects who get medial compartment
knee OA five years after ACLR, evidence of under-loading was present at early time
points (six months) after ACLR. Also, cartilage tissue level changes, which may be
present at early time points after ACLR, would precede the appearance of radiographic
osteophytes. To explore the changes in cartilage at early time points, T2 maps (using
quantitative magnetic resonance imaging, or qMRI) were established for two
additional subjects, one with evidence of under-loading in the involved knee, and one
with symmetric loading. Both subjects had completed gait analysis one year after
ACLR. The subject with under-loading of the involved knee did demonstrate higher
T2 values (indicative of potential collagen matrix degradation) in the involved knee,
compared to the uninvolved knee, and also greater inter-limb differences, compared to
the subject with symmetric loading. These results, while from a very small number of
subjects, warrant further investigation to establish or reject a potential correlation
between early inter-limb loading differences and early cartilage tissue level changes.
The sooner that the presence of OA related changes is detected, either directly or
indirectly, the greater the potential for intervention to delay the progression of OA.
Future studies that implement a combination of the above methodologies
(NMS + FE + qMRI) can aid in early detection, prediction and treatment of knee OA.