Description
Objectives
It has been reported that bone mineral density (BMD) affects postoperative outcomes after total knee arthroplasty. However, little is known about the influence of BMD on postoperative outcomes after unicompartmental knee arthroplasty (UKA). The purpose of this study was to clarify the effect of low BMD on short-term postoperative clinical outcomes after UKA.
Methods
One hundred and fifty-six patients who underwent Oxford mobile bearing (OMB) UKA between 2012 and 2020 in our institute were included in this study. The young adult mean (YAM) values of BMDs were calculated using our artificial intelligence (AI) osteoporosis diagnosis assistance system, which can estimate BMD and YAM values of the proximal femur from preoperative postero-anterior chest X-ray images with high accuracy with AUC of 0.89 in discrimination of YAM <80%. Based on the estimated YAM, those with low BMDs were identified from the studied patients (Group O; YAM <80%; 35 patients; 34 females and 1 male, average age 75.1 years). Then, from the remaining 121 patients, an age- and sex-matched group with normal BMDs was extracted (Group N; YAM ≥80%; 35 patients; 34 females and 1 male, mean age 75.0 years). Pre- and postoperative knee joint range of motion, hip-knee-ankle angle (HKA), coronal and sagittal angles of implant placement, and patient-reported outcome measure (Knee injury and Osteoarthritis Outcome Score [KOOS]) preoperatively, 3- and 6-month (M), and 1-, 2-, and 3-year (Y) postoperatively were compared between the two groups. T tests for independent samples were performed to compare group differences. Comparisons of categorical data were performed using the Fisher's exact test. Significance was set at p <0.05.
Results
There were no significant differences in pre- and postoperative range of motion, HKA, implant placement, or preoperative KOOS between the two groups. The KOOS Pain score was significantly lower in the O group at 3 and 6 M (3 M: 69.8 vs 77.5; P=0.045, 6 M: 76.9 vs 83.5; P=0.043), but there were no significant differences after 1Y postoperatively. On the other hand, KOOS QOL scores were not significantly different until 1 Y postoperatively, but were significantly lower in group O at 2 and 3 Y (2 Y: 63.2 vs 73.1; p=0.049, 3 Y: 66.3 vs 76.7; p=0.038). The other KOOS subscales were not significantly different at all time points, and there was no implant migration or subsidence in both groups.
Conclusions
The result of this study revealed that low BMD estimated from preoperative chest X-ray using AI was associated with worse pain in the very early period and poorer quality of life in the short-term period after OMB UKA surgery. These facts suggest that preoperative interventions to increase BMD are beneficial to improve postoperative clinical outcomes after OMB UKA for patients with low BMDs.
