Summary

Posterior tibial slope was measured before and after surgery in patients who underwent Unicompartment knee arthroplasty to investigate the relationship between PTS and knee symptoms.

Abstract

【Object】
The posterior tibial slope (PTS) is one of the important parameters of knee sagittal alignment, which is considered an important factor related to postoperative outcomes. However, the effect of changing amount of PTS on clinical outcomes in unicompartmental knee arthroplasty (UKA) is unknown. The purpose of this study was to investigate the relationship between changing amount of PTS and postoperative outcomes of UKA.

【Method】
A total of 86 knees (26 males and 60 females) in 72 patients, who underwent UKA, and could be followed for at least 1 year after surgery were included in the study. Their mean age was 75.2 ± 5.9 (62 - 91) years. Pre- and postoperative PTS on lateral X-ray images were measured according to Dean’s method, and changing amount of PTS were calculated. Changing amount of PTS of less than -2.5° was defined as a decreasing group, -2.5° to 2.4° as an unchanging group, and more than 2.5° as an increasing group. Pre- and postoperative knee range of motion was assessed. Knee symptoms were assessed using the knee injury and osteoarthritis outcome scales (KOOS). Pre- and postoperative PTS, changing amount of PTS, and pre- and postoperative range of motion among the three groups were compared using analysis of variance.

【Result】
Mean preoperative PTS was 8.5 ± 2.8° (ranged: 2.9 - 14.4°), postoperative PTS was 9.4 ± 2.7° (ranged: 0.6 - 17.5°), and changing amount of PTS was -0.9 ± 3.6° (ranged: -8.7 - 11.6°). Based on the changing amount of PTS, 14 knees were classified into the decreased group, 43 knees into the unchanged group, and 29 knees into the increased group. There was no significant correlation between overall preoperative PTS and postoperative PTS. There was a negative correlation between preoperative PTS and PTS change (p<0.001, r=-0.65). There was no significant correlation between changing amount of PTS and KOOS. Preoperative PTS was highest in the decreased group (11.5 ± 2.9°, p<0.001) and postoperative PTS was highest in the increased group (11.3 ± 2.1°, p<0.001). There were no significant differences between the pre- and postoperative range of motion (preoperative extension p=0.491, preoperative flexion p=0.909, postoperative extension p=0.968, postoperative flexion p=0.214) and KOOS subscales (symptom: p=0.871, pain: p=0.744, ADL: p=0.532, Sports: p=0.217, and QOL: p=0.243) among the three groups.

【Discussion】
A negative correlation was found between preoperative PTS and changing amount of PTS. Previous reports have suggested that postoperative PTS in UKA should be less than 8 degrees, indicating that there may be an awareness of convergence of PTS to around 8 degrees during osteotomy. In addition, postoperative PTS had no effect on knee symptoms or range of motion. Changing amount of PTS also had no effect on knee symptoms. Similar reports have been made in the past, and our results were consistent with those.

【Conclusion】
Greater preoperative PTS was correlated with less changing amount of PTS. Pre- and postoperative PTS change did not affect range of motion and postoperative patient reported outcome measures.