Knee joint stiffness and function following total knee arthroplasty
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Date
2010Author
Lane, Judith
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Abstract
Introduction: Studies show that Total Knee Arthroplasty (TKA) is successful for
the majority of patients however some continue to experience some functional
limitations and anecdotal evidence indicates that stiffness is a common complaint.
Some studies have suggested an association between stiffness and functional
limitations however there has been no previous work which has attempted to
objectively quantify knee joint stiffness following TKA. The purpose of this study
was to pilot and evaluate a method for the quantitative evaluation in joint stiffness in
replaced knees, OA knees and healthy controls and to explore whether there is an
association between stiffness and functional limitations post-TKA surgery.
Methods: The first part of the study created a biomechanical model of knee
stiffness and built a system from which stiffness could be calculated. A torque
transducer was used to measure the resistance as the knee was flexed and extended
passively and an electrogoniometer concurrently measured the angular displacement.
Stiffness was calculated from the slope of the line relating the passive resistive
torque and displacement. The torque and joint angle at which stiffness was seen to
increase greatly was also noted. The system was bench tested and found to be
reliable and valid. Further tests on 6 volunteers found stiffness calculations to have
acceptable intra-day reliability.
The second part was conducted on three groups: those with end-stage knee OA (n =
8); those who were 1 year post-TKA (n = 15) and age matched healthy controls (n =
12). Knee range of motion was recorded and participants then completed the
WOMAC, the SF-12 and a Visual Analogue Score for stiffness as well as indicating
words to describe their stiffness. Four performance based tests – the Timed Up and Go (TUG), the stair ascent/descent, the 13m walk and a quadriceps strength test were
also undertaken. Finally, passive stiffness at the affected knee was measured.
Results: 100% of OA, 80% of TKA and 58% of controls reported some stiffness at
the knee. The OA group reported significantly higher stiffness than the OA or TKA
groups. There was no difference in self-reported stiffness between the TKA and
control groups. Of the total number of words used to describe stiffness, 52% related
to difficulty with movement, 35% were pain related and 13% related to sensations.
No significantly differences were found between groups in the objective stiffness
measures. Significant differences were found however in threshold flexion stiffness
angles between groups. When this angle was normalised, differences between groups
were not significant. No significant differences were found between groups in the
threshold stiffness torque. Greater self-reported stiffness was found to be associated
with worse self-reported function. A higher flexion stiffness threshold angle was
associated with slower timed tests of function but also with better quadriceps muscle
strength.
Conclusions: The results support anecdotal reports that perceived stiffness is a
common complaint following TKA but there was no evidence to show that patients
with TKA have greater stiffness than a control group. There was however evidence
to show that patients’ were unable to distinguish between sensations of stiffness and
other factors such as pain. Self-perceived increased stiffness was associated with
worse functional performance. Greater stiffness however was not necessarily
negative. Stiffness increases earlier in flexion range were associated with better
functional performance. These results suggest that an ideal threshold range for
stiffness may exist; above which negative perceptions of the knee result in worse
function but below which, knee laxity and instability may also result in worse
function.