The Effects of Task Complexity on Brake Response Time Before and After Primary Right Total Knee Arthroplasty

Study Design 

To study the effects of task complexity on BRT, a prospective study with repeated-measures design was used. On each measurement day, patients performed a series of 10 trials in a simple and a further series of 10 trials in a complex BRT task. Task complexity was increased by adding a second task to the first task performed. The measurements took place 1 day before and 10 and 30 days after TKA.

Participant Selection 

Subject selection took place at the ENDO-Klinik in Hamburg, Germany. To be eligible, all subjects had to meet 3 criteria: (1) was admitted for primary total arthroplasty of the right knee, (2) drove frequently (at least once a week), and (3) would be available for the third measurement. Patients who could not fulfill one of these requirements or who had a neurologic disease were excluded. Before participating all patients were required to read and sign an informed consent form. The research proposal was approved by the Medical Ethics Commission of the Federal State of Hamburg.

Study Sample 

Twenty-seven patients (13 men, 14 women) admitted for primary total arthroplasty of the right knee agreed to participate in the study and were assessed before and 10 days after surgery. Twenty-one of them returned to the clinic 30 days after surgery to be assessed for the third time. Six patients did not return for the third test for unknown reasons.

The data of 21 patients (9 men, 12 women) were pooled for analysis. The patients' ages ranged from 57 to 85 years; the mean age for the sample was 69.1±7.8 years (table 1). Before surgery, there was no significant difference (P=.85) between the mean ages of the men and women. The total driving load during the previous year did not differ significantly (P=.19) when comparing both sexes. All patients were admitted for primary right TKA as a result of osteoarthritis of the knee joint. A rotational knee system prosthesis was used in 7 (33.3%) patients, and a bicondylar sled prosthesis was used in 14 (66.7%) patients. Gait training commenced on the second postoperative day with weight bearing as tolerated.

Table 1. Demographic Data

	Variables	Right TKA
		All	Men	Women
	n	21	9	12
	Age (y)	69.1±7.8	69.5±7.4	68.9±8.4
	Kkm/y	8.2±4.4	9.6±3.2	7.1±4.9
	Height (cm)	167.8±9.5	176.1±7.9	161.6±4.7
	Weight (kg)	78.9±11.5	86.2±11.6	73.4±8.1

NOTE. Values are mean ± standard deviation (SD). Abbreviation: Kkm/y, thousand kilometers driven in the past year.

Equipment 

The components of the BRT (RT and movement time) were assessed in a car simulator. The car simulator (fig 1) and the pedal layout (fig 2) were built by the technical department of the clinic. The ergonomic distances between the components of the simulator (seat to steering wheel, seat to pedals, steering wheel to simulator floor) were based on European standards. The seat was adjustable in the frontal plane (closer to or farther away from the pedals) and in the transversal plane (higher from or lower to the floor).

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Fig 1. Car simulator with the Biopac measurement system.

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Fig 2. Pedal layout: front view (I) with (A) the accelerator and (B) the brake pedal sizes and lateral separation. Side view (II) with the inclination of the pedals and the positive perpendicular separation of the brake pedal.

The data acquisition system consisted of a Biopac MP100A-CE system with the universal interface module UIM100C,a 1 laptop with the Acqknowledge software, version 3.8.1,a 1 red light-emitting diode (LED) lamp located at patients' eye levels, and 1 trigger and switches on the accelerator and brake pedals. Four analog channels were used, and the channel sample rate was set at 1000Hz.

Procedures and Tasks 

After sitting down in the car simulator, patients were required to adjust the seat to a comfortable position. On each measurement day, patients performed 5 practice and 10 test trials for 2 tasks, a simple and a complex BRT task. In the simple task, patients were instructed to press the accelerator pedal as if they were driving (fig 3A). When the red LED lamp switched on, patients had to brake as quickly as possible (fig 3B). After pressing the brake pedal, patients were instructed to move the foot back to the accelerator and to wait for the next stimulus. Stimulus triggering varied randomly from 1 to 5 seconds. In the complex task, patients were instructed to perform the same way as in the first task. In addition, they were instructed to turn the steering wheel 90° to the left simultaneously with the foot brake action (fig 4). The complexity of the task was increased by adding a second movement. Both movements had to be performed simultaneously.

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Fig 3. Overview of the pedal with (A) the right foot pressing the accelerator and (B) the foot pressing the brake pedal.

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Fig 4. Steering wheel positions in the complex task: (A) start position and (B) end position.

RT was defined as the time interval between the lighting of the LED lamp and initiation of foot movement. Movement time was defined as the time between initiation of foot movement and first contact with the brake pedal. BRT was defined has the sum of the RT and movement time.

Data Analysis 

The 10 test BRT trials of each task were filtered using a 95% confidence interval of the mean. The trials outside the interval were eliminated, and the mean BRT, RT, and movement time were calculated for each patient at each time interval for analysis.

Descriptive statistics of the sample were performed. Differences between the values in both tasks at each moment in time were analyzed with paired-sample t tests. Differences in mean BRT, RT, and movement time values at the 3 points in time were analyzed with a univariate approach to repeated-measures analysis of variance for each task separately. Multiple comparisons were made with paired t tests using the Bonferroni adjustment of α.

All statistical tests were carried out using the SPSS software.b For all statistical tests, the .05 level of probability was accepted as the criterion for statistical significance.

Study Limitations 

Use of an age-matched control group would have been interesting to (1) find out whether movement time would increase with an increase of task complexity in subjects without impairment and (2) situate the performance of patients in the sample in the context of a normative population.

Patients participating in our study did not resume driving during the measurement period, because they were advised not to drive during the first 3 months after TKA (standard advice for all patients in the hospital). It would have been interesting to have data on the exact time when these patients did, in fact, resume driving.

The data and results of this study must be seen in the context of the population studied. Patients not represented in the sample—for example, those after revision arthroplasty—may have other values. The results of the present study can be used as a reference when advising patients on this issue; they should not be used as deadlines for resumption of driving after primary TKA.