Appendix 1. Description of testing procedures
Outpatient study assessments were performed at the University of Colorado Anschutz Medical
Campus preoperatively and at 3 weeks and 3 months after the bilateral TKAs. Study assessments
were also performed during the hospital stay on the second postoperative day.
For all outpatient testing, isometric quadriceps muscle torque (primary outcome) was measured
during a maximum voluntary isometric contraction (MVIC) using a HUMAC NORM (CSMi,
Stoughton, MA, USA) electromechanical dynamometer. Data were collected with a Biopac Data
Acquisition System at a sampling frequency of 2000 Hz (Biodex Medical Systems, Inc, Shirley,
NY, USA) and analyzed using AcqKnowledge software, Version 3.8.2 (Biodex Medical
Systems, Inc). Quadriceps activation testing was performed using the doublet interpolation test,
as previously described [7, 8, 34, 52, 53]. Briefly, a Grass S48 stimulator with a Grass Model
SIU8T stimulus isolation unit (Grass Instruments, West Warwick, RI, USA) was used to deliver
an electrical stimulus to the muscle through self-adherent, flexible electrodes (7.6 × 12.7 cm;
Supertrodes; SME, Inc, Wilmington, NC). Patients were positioned seated in the
electromechanical dynamometer with the knee stabilized at 60º of flexion. The intensity of the
stimulation was set while the muscle was relaxed using a two-pulse, 600-μs duration, 100-Hz
electrical train and increasing the output in 10-V increments until the electrically induced torque
reached a plateau (ie, supramaximal stimulus). Voluntary activation of the quadriceps muscle
was then assessed by comparison of torque amplitude during a resting supramaximal stimulus
with the increase in amplitude observed after stimulus during an MVIC. A value of 100%
represents full voluntary muscle activation and anything less than 100% represents a deficit in
muscle activation (incomplete motor unit recruitment or decreased motor unit discharge rates).
The hamstrings were not tested for voluntary activation, but isometric hamstrings torque was
measured using the same positioning described previously. Quadricep and hamstring strength
assessments were performed twice and the maximum voluntary torque value was recorded. If
maximal torque differed by more than 5%, a third trial was performed.
Measures of knee function included an assessment of active ROM (AROM) and single-limb
balance ability. AROM of the knee was measured in the supine position using a long-arm
goniometer as previously described [37]. When measuring active knee extension, the heel was
placed on a 4-inch block and the participant was instructed to actively extend the knee. Negative
values of extension represented hyperextension. For active knee flexion, the participant was
instructed to actively flex the knee as far as possible keeping the heel on the supporting surface.
The unilateral balance test (UBT), a common test of static balance [5], was chosen as a surrogate
measure of unilateral knee function. Calf girth (20 cm proximal to the medial malleolus), knee
girth (suprapatellar), and thigh girth (10 cm proximal to the superior border of the patella) were
recorded to assess lower extremity edema. Finally, pain was measured using an 11-point verbal
numeric pain rating scale. Patients were asked to rate the pain in each knee on a scale of 0 to 10
with 0 representing no pain and 10 representing the worst pain imaginable.
In the inpatient setting, assessments were performed on the second postoperative day to allow for
attenuation of femoral nerve block effects. To measure strength, a force transducer device
(Lebow Products, Troy, MI, USA), which had been validated in pilot testing against an
electromechanical dynamometer, was used to measure the force of MVIC of the hamstring and
quadriceps muscles. This device was chosen to maximize the accuracy of strength assessments in
the early postoperative period, when electromechanical dynamometry was not accessible. Other
strength testing methodologies such as handheld dynamometry and manual muscle testing have
demonstrated relatively poor validity and sensitivity to change for the quadriceps [11, 16, 27, 32,
48]. Patient positioning was similar to the electromechanical dynamometer. Patients were again
positioned in a seated position at approximately 60º of knee flexion (Fig. 1), and the peak torque
of MVIC was captured through the stabilized force transducer using software (LabVIEW;
National Instruments, Austin, TX, USA) developed by a research assistant (JW). The stronger of
two MVIC trials was recorded for both hamstring and quadriceps muscles. Assessments of
AROM and lower extremity edema were also performed on the second postoperative day.
Quadriceps activation testing and UBT were not performed in the inpatient setting.
Fig. 1 Strength testing setup for (A) outpatient and (B) inpatient (postoperative Day 2) assessments.
A
B