The aim of the thesis was to investigate deficits and compensatory strategies after total knee arthroplasty (TKA) in different conditions during gait and quiet standing. Although TKA is considered the gold standard treatment for end-stage knee osteoarthritis, it is associated with a number of implications. Reduced physical function after osteoarthritis is partly, but apparently not fully, remedied by surgery. The two most common deficits are reduced knee muscle strength and limited range of knee joint motion (ROM), partly due to prosthesis mechanics. Reduced postural control has also been shown shortly after surgery. In spite of sufficient passive knee joint ROM for normal ambulation, gait patterns are characterized by reduced knee flexion. Several factors such as reduced knee muscle strength, reduced proprioception, habitual strategies or fear of movement may be suggested as explanations for difficulties in gait and posture. As an effect, compensatory strategies may result. In order to focus on the implications of TKA, participants had to be less than 65 years of age and healthy, TKA being the only factor different form controls. The same 23 individuals with unilateral TKA ~ 19 months post-operative and 23 controls participated in all studies.
3D whole body kinematics was used to assess gait and posture and electromyography was used to record muscle activity. Isokinetic measurements were used to determine dynamic knee muscle strength. Gait in the frontal and sagittal planes were assessed. The tasks included in the test protocol were negotiation up and down stairs, gait on hard and soft surface, quiet standing with sensory modulation (with and without vision and on soft surface), and single limb stance. Primary outcome variables addressed were: knee and hip joint kinematics in frontal and sagittal planes, upper body inclination, postural sway and relative knee muscle activity as an indicator of relative effort. Background factors used to explain group differences in the primary outcomes were derived from demographics, clinical examination, and questionnaires. Demographic factors were age, body mass index (BMI), and time since surgery. Clinical examinations were conducted for passive knee joint ROM, joint position sense, knee muscle strength, anterior knee joint laxity, and leg length. Questionnaires assessed fear of movement, pain, and knee related function and quality of life. The results showed that knee flexion was reduced during stair descent in both the prosthetic and the contralateral knee in the TKA group compared to controls. Although reduced passive knee joint flexion in the TKA group was sufficient for normal stair descent, it was the only factor identified that explained reduced knee flexion in stair descent. As knee muscle strength was significantly reduced in the TKA group, it is reasonable to suggest that as a contributing factor. Furthermore, the TKA group also displayed increased hip adduction during stair descent, which may indicate both a compensatory strategy as well as reduced hip muscle strength. In stair ascent, no significant group differences were found in relative knee muscle activity as expected due to knee muscle weakness. Nor were there any indications of compensatory forward inclination of the trunk to reduce knee joint moments. Instead, probably compensating for muscle weakness, the TKA group ascended stairs at a significantly slower speed. Surface modulation during level gait showed that reduced knee flexion in the prosthetic knee during the stance phase when walking on a hard surface was further decreased during gait on a soft surface. Knee and hip adduction at the stance phase were not affected by surface conditions. Nevertheless, the TKA group displayed increased knee adduction and hip adduction compared to controls, particularly in the prosthetic side. In addition, the TKA group displayed increased step width on the soft compared to hard surface. Single-limb stance for 20 seconds failed in 30 % of the TKA group and in 4 % of the control group. Those in the TKA group who were able to perform single-limb stance performed equally well as controls. During bilateral quiet standing, postural sway was similar in both groups, and inability to stand on one leg did not affect bilateral stance. Older age, higher BMI and reduced quadriceps strength determined the failure to maintain single-limb stance in the TKA group.
In conclusion, this thesis indicates that reduced knee muscle strength is a common denominator as part of the explanatory factors for reduced performance and compensatory strategies in individuals with TKA. Reduced speed during stair ascent as well as reduced knee flexion during stair descent may be compensations for reduced lower extremity strength. Increased hip adduction may compensate for reduced knee flexion in stair descent, but may also represent hip muscle weakness or reduced motor control as increased hip adduction is found also in level gait. The failure to maintain single-limb stance in the TKA group is also partly explained by reduced knee muscle strength. Muscle weakness may be and indicator for reduced physical capacity in general.
Umeå: Umeå universitetet , 2014. , p. 84