Implant Alignment and Patient Factors Affecting the Short-Term Patient-Reported Clinical Outcomes after Oxford Unicompartmental Knee Arthroplasty

Abstract

This study aims at clarifying implant alignment and other patient factors' influence on clinical outcomes, particularly on patient-reported outcomes (PRO), following Oxford unicompartmental knee arthroplasty (OUKA). A total of 142 patients after OUKA were divided into two groups according to the validated Japanese version of the knee injury and osteoarthritis outcome score (KOOS) for each subscale of pain, symptoms, and activities of daily living (ADL) at postoperative year 1 and 2: group 1 had ≥80 scores and group 2 had <80 scores. Postoperative clinical and radiographical findings were then compared among groups in each subscale. Using postoperative year 1 and 2 data, a multivariable logistic regression analysis was conducted to clarify factors for clinical outcomes' improvement. In the analysis of KOOS subscale of symptoms at postoperative year 1, gender distribution, preoperative body mass index, and postoperative maximum knee flexion angles differed significantly among groups. In the analysis for KOOS subscale of ADL, significant differences were observed in postoperative tibial component varus angles. Multivariable logistic regression analysis revealed that all of these parameters significantly related to ≥80 KOOS scores of each subscale at postoperative year 1. Additionally, at postoperative year 2, larger postoperative knee flexion angles and tibial component varus angles related to ≥80 KOOS subscale of symptoms and ADL were observed. In conclusion, tibial component's larger varus alignment was associated with the better PRO at both 1 and 2 years after OUKA. Importantly, larger postoperative knee flexion angle helped achieve good short-term PRO after OUKA.

The varus/valgus angle of the femoral component relative to the tibial component can lead to a deviation of the bearing position in mobile bearing unicompartmental knee arthroplasty which can increase the risk of bearing dislocation

“…Previous studies have reported postoperative radiographic measurements for the alignment of the femoral component relative to the femur and the alignment of the tibial component relative to the tibia [15,[17][18][19][20][21]. We believe that bearing movement is related to changes in the relative position and angle between the femoral and tibial components.…”

Superior component position during robotic-assisted Oxford unicompartmental knee arthroplasty (UKA) compared with conventional technique: A 5-year follow-up study

“…Nonetheless, it has also been brought up that the degenerative disorders in lateral compartments can be promoted by overcorrecting the varus deformity [22,23]. According to some reports of Oxford UKA, all the alignment of the knees via balancing the ligaments passed through the central line of the knees, which was usually similar to the contralateral part [8,[24][25]. Additionally, it was demonstrated that the operations with robotic assistance remarkably improved the alignment of the limbs following medial UKA in comparison with the conventional technique [26,27].…”

Effects of a 1-mm difference in bearing thickness on intraoperative bearing movement and kinematics in Oxford unicompartmental knee arthroplasty

“…Femoral drilling was performed with an Oxford Microplasty device (MP: Biomet Ltd., Swindon, UK) to facilitate reproducible implant alignment [ 15 ]. After these procedures, we performed the same gap-balancing procedure between knee flexion and extension and a modified keel cutting method as that previously reported [ 16 , 17 ]. With the trial components in place, we used two candidate trial MBs with a 1-mm thickness difference with the trial components to prospectively investigate the effects of a 1-mm difference in MB thickness.…”