The dynamic nature of alignment and variations in normal knees

Abstract

The restoration of knee alignment is an important goal during total knee arthroplasty (TKA). In the past surgeons aimed to restore neutral limb alignment during surgery. However, previous studies have demonstrated alignment to be dynamic, varying depending on the position of the limb and the degree of weight-bearing, and between patients. We used a validated computer navigation system to measure the femorotibial mechanical angle (FTMA) in 264 knees in 77 male and 55 female healthy volunteers aged 18 to 35 years (mean 26.2). We found the mean supine alignment to be a varus angle of 1.2° (standard deviation (sd) 4), with few patients having neutral alignment. FTMA differs significantly between males and females (with a mean varus of 1.7° (sd 4) and 0.4° (sd 3.9), respectively; p = 0.008). It changes significantly with posture, the knee hyperextending by a mean of 5.6°, and coronal plane alignment becoming more varus by 2.2° (sd 3.6) on standing compared with supine. Knee alignment is different in different individuals and is dynamic in nature, changing with different postures. This may have implications for the assessment of alignment in TKA, which is achieved in non-weight-bearing conditions and which may not represent the situation observed during weight-bearing.

Effect of lengthening along the anatomical axis of the femur and its clinical impact

“…The situation is further complicated by differences in the alignment of the limb when measured in a lying position (which is non-weight bearing) and in a weight-bearing standing position[16]. In a study by Deep et al[17], they found the limb alignment to be dynamic process that differs according to different postures, and also varies between males and females in normal knees. Deep et al[17] found also a greater tendency into varus malalignment in the study group with normal non-arthritic knees, that go into more varus when changing the position from supine to standing.…”

“…In a study by Deep et al[17], they found the limb alignment to be dynamic process that differs according to different postures, and also varies between males and females in normal knees. Deep et al[17] found also a greater tendency into varus malalignment in the study group with normal non-arthritic knees, that go into more varus when changing the position from supine to standing. Walcox et al[16] found similar changes in arthritic knees.…”

Dynamic Alignment Analysis in the Osteoarthritic Knee Using Computer Navigation

“…The IR technology used in this study provided a real-time kinematic dynamic measurement of the FTMA, resulting in a powerful tool for intraoperatively supporting and guiding the surgeon in a very demanding challenge, such as the adequate postoperative balance of the knee. 6,[32][33][34][35] A change in coronal alignment between standing and supine positions has been previously demonstrated in normal, osteoarthritic, and postoperative knees. 6,7 Patients who are in varus or up to 2.5 degrees valgus while supine, tend to become more varus on standing.…”

“…6,[32][33][34][35] A change in coronal alignment between standing and supine positions has been previously demonstrated in normal, osteoarthritic, and postoperative knees. 6,7 Patients who are in varus or up to 2.5 degrees valgus while supine, tend to become more varus on standing. 6 This trend is also observed in a flexed position when compared with hyperextending.…”

“…6,7 Patients who are in varus or up to 2.5 degrees valgus while supine, tend to become more varus on standing. 6 This trend is also observed in a flexed position when compared with hyperextending. This kinematic pattern for the three groups suggests that the soft tissue constraints, rather than the underlying deformity, are more influential in the control of the alignment from lying to standing.…”