Patients with knee osteoarthritis (OA) who undergo total knee arthroplasty (TKA) show a significant reduction in pain and an improvement in walking. However, some patients report a feeling of instability during stair stepping after TKA.

There are several studies on performance during daily life after TKA [1-5]. Benedetti et al. reported that knee kinematic and kinetic abnormalities during load acceptance after TKA were associated with co-contractions in the muscular activation pattern [6]. Beswick et al. reported patient dissatisfaction regarding pain, function, and restoration of quality of life improvement in their gait relative to their preoperative state, despite the overall effectiveness of TKA [7].

It has also been suggested that kinematic studies and gait analyses are necessary for proper assessment following TKA.

We previously reported that joint stability during stair-stepping was affected by the design of the femorotibial joint rather than the post/cam engagement or ball and socket joint in the Bi-Surface PS (Kyocera Medical Corporation, Japan) arthroplasty [8]. Based on gait analysis, we considered it necessary to assess trunk and gait function. Therefore, we reported on gait oscillations during gait and stair- stepping in patients after TKA with Bi-Surface PS, and in those with two total knee replacement designs [9, 10]. However, the change in gait oscillation appeared chronologically after TKA, rather than immediately. This study aimed to assess the chronological change in gait oscillation during gait, in patients after TKA.

Twenty patients (14 female and 6 male patients) who underwent TKA with the Bi-Surface PS knee prosthesis and who were followed up for 1 year were assessed. All patients had been diagnosed with varus knee OA. Their average age was 73.6 (range: 64-86) years (Table 1). A single surgeon performed all TKA procedures, using the parapatellar approach. The patella was resurfaced, and all implants were fixed with cement.

The mean postoperative Hospital for Special Surgery score was 94.1 for the Bi-Surface KU5 knee prosthesis, respectively.

Gait oscillation analyses in this study were performed by examining gait acceleration (anterior-posterior, vertical, and lateral-contralateral directions). We performed a preoperative analysis and postoperative analyses at 3,6,9, and 12 months.

The root mean square (RMS) of acceleration, which shows the magnitude of acceleration, is frequently used in gait analysis studies [11, 12]. Using a two-point gait oscillometer MVP-WS2-S (Microstone Corp., Japan), we assessed gait oscillation during gait (10 m). Two compact wireless sensors were attached to the dorsal vertebral and sacral regions using a harness and belt [9, 10]. Three successful measurements were recorded, and used for the final analysis. The sacral-dorsal vertebra ratio was defined as the RMS value of the sacral region / the RMS value of the dorsal vertebral region. Statistical analysis was performed using R version 2.8.1software. The Shaffer method was used for the multiple comparison procedure [13].

The mean and standard deviation values of the observed variables are shown in Table 2.

Some patients report restrictions in daily living activities after TKA. Dickstein et al. reported that one of the factors that lead to dissatisfaction after TKA is the limitation in the use of stairs [14]. Additionally, Benedetti et al. and Hilding et al. reported that gait impairment remains after TKA [15, 16]. Banks et al. reported that superior performance was associated with devices that provided the greatest intrinsic control of knee motion. Intrinsically stable knees may be significantly beneficial for patient function and reduction of wear [17]. Prieto-Alhambra et al. reported that the risk of hip fractures increased significantly in the year after TKA. These rates then declined to correspond with those seen in controls 3 years postoperatively and continued to decrease until the end of the follow-up period [18]. These reports suggest that improvements in knee function and gait oscillation are essential and can influence daily living activities after TKA. We previously assessed the influence of the knee joint on gait oscillation during gait and stair-stepping in patients with knee OA. Knee OA influenced acceleration in the anterior and lateral directions in the dorsal vertebral; it also influenced the ratio of the center of gravity maximum values during gait oscillation [10].

In this study, the gait oscillation change during gait in patients after TKA was assessed chronologically. RMS of acceleration provided a better understanding of gait oscillation than our previously reported values. Acceleration in the anterior direction in the sacral region tended to increase until 6 months after TKA, but remained almost unchanged thereafter. In the dorsal vertebral region, acceleration in the anterior direction tended to decrease over time. These findings suggested that gait oscillation to the anterior direction in the trunk might have improved chronologically during the postoperative course after TKA. Regarding acceleration to the lateral side, the ratio of sacral-dorsal vertebra in the lateral direction (TKA side) tended to have increased over time after TKA, and the values in the contralateral side direction tended to have increased up to 6 months; however, there was no significant change thereafter. These findings suggest chronological improvement in gait oscillation to the lateral direction (TKA side) after TKA, and gait performance mainly on the sacral region or pelvic girdle during the postoperative course of TKA. Therefore, adjustment in gait oscillation may occur chronologically during the postoperative course after TKA.

This study has some limitations. The small number of patients weakens the statistical power of the results. Further investigations with larger sample sizes are required to obtain more clinical data. In addition, no control group was included in the analysis, and the standard error of the measurements may have decreased the generalization power of this study. Despite these limitations, this study contributes significantly to the understanding of the improvement in gait oscillation after TKA.

Acceleration to the anterior and lateral direction (TKA side) may improve chronologically after TKA, and gait may be performed mainly on the pelvic girdle during the postoperative course after TKA. Acceleration to the lateral direction (contralateral side) may increase for up to 6 months after TKA; thereafter, an adjustment in gait oscillation may occur, although the changes may not be significant.