Abstract
Introduction
According to previous reports, unilateral total knee arthroplasty (TKA) would produce the asymmetric changes of lower extremity in the coronal plane in patients with bilateral knee osteoarthritis (OA). To our knowledge, little attention has been paid to the alignment changes of trunk and contralateral limb. It was hypothesized that the unilateral correction of knee deformity would affect trunk bending in the coronal plane after unilateral total knee arthroplasty. The purpose of the current study was to investigate trunk bending in the coronal plane before and after the surgery.
Methods
Twenty patients (17 Females and 3 Males; mean 76 years old) with bilateral symptomatic knee osteoarthritis participated. They had radiographic bilateral OA of at least grade 3 severities according to the Kellgren-Lawrence scale. All the subjects underwent unilateral TKA using Balanced Knee System®, posterior stabilized design (Ortho Development, Draper, UT). All the subjects provided informed consent. All methods and procedures were approved by our institution's ethics committee. They were asked to step on the two scales and perform relaxed standing for five seconds, placing each foot on each scale independentlys. Thereafter, anteroposterior radiographs of the whole spine and bilateral long legs were taken with use of a vertical 35.4 × 101.7-cm film.
The shoulder tilting angle was defined by the height difference between the centers of the right and left acromioclavicular joints, and the pelvic tilting angle was defined by the height difference between the centers of the right and left femoral heads. To evaluate trunk bending, the shoulder-pelvis bending angle was defined as the angle between the shoulder girdle line (Fig. 1, Line a) and the pelvic line (Fig. 1, Line b). Femorotibial angle (FTA) was also evaluated. These radiographs were taken before the surgery and on postoperative day 21.
Simultaneously, knee flexion angles on TKA side, subjective pain level on TKA side and vertical knee forces (% body weight; BW) on TKA side during relaxed standing were also examined. Data evaluations were done both before and on postoperative day 21. Statistical difference between the data was evaluated using two-tailed Wilcoxon t-test. P-values of < 0.05 were considered as significant.
Results (Table 1)
After unilateral TKA, the shoulder tilted more to the TKA side and the pelvis inclined more to the contralateral OA side. Thus, asymmetrical trunk bending in the coronal plane occurred after the surgery. In terms of contralateral limb alignment, FTA significantly decreased on non-operated knees.
After TKA, significantly smaller flexion angle (11.1) was observed on postoperative day 21. In terms of pain level, on postoperative day 21, pain score (29.2) was significantly smaller than preoperative score. Concerning the vertical knee force on TKA side, knee force (50.4) on postoperative day 21 was significantly larger than preoperative force.
Discussion
These results support our hypothesis that unilateral TKA would affect trunk bending in the coronal plane after. The postural changes in the trunk during relaxed standing suggested that the trunk would bend away from the contralateral OA side.
