Lower limb alignment becomes more varus and hyperextended from supine to bipedal stance in asymptomatic, osteoarthritic and prosthetic neutral or varus knees

Abstract

Purpose Knee alignment is a fundamental measurement in the assessment, monitoring and surgical management of patients with osteoarthritis. There is a lack of data regarding how static tibiofemoral alignment varies between supine and standing conditions. This study aimed to quantify the relationship between supine and standing lower limb alignment in asymptomatic, osteoarthritic (OA) and prosthetic (TKA) knees. Methods A non-invasive position capture system was used to assess knee alignment for 30 asymptomatic controls and 31 patients with OA both before and after TKA. Coronal and sagittal mechanical femorotibial angles were measured supine with the lower limb in extension and in bipedal stance. Changes between conditions were analysed using paired t tests. Vector plots of ankle centre displacement relative to the knee centre from supine to standing were produced to allow three-dimensional visualisation. Results All groups showed a trend towards varus and extension when going from supine to standing. Mean change for asymptomatic knees was 1.2° more varus ( p = 0.001) and 3.8° more extended ( p < 0.001). For OA knees this was 1.1° more varus ( p = 0.009) and 5.9° more extended (p < 0.001) and TKA knees 1.9° more varus ( p < 0.001) and 5.6° more extended ( p < 0.001). Conclusion The observed consistent changes in lower limb alignment between supine and standing positions across knee types suggests the soft tissue envelope restraining the knee may have a greater influence on dynamic alignment changes than the underlying bony deformity. This highlights the importance of quantifying soft tissue behaviour when planning, performing and evaluating alignment dependent surgical interventions of the knee. When routinely assessing any type of knee, clinicians should be aware that subtle consistent alignment changes occur under weightbearing conditions and tailor their treatments accordingly. Level of evidence II.

Factor affecting the discrepancy in the coronal alignment of the lower limb between the standing and supine radiographs

“…As in previous studies [10,[13][14][15][16][17][18], this study showed signi cant differences in pairwise comparisons of radiographic parameters regarding the coronal alignment of the lower limb measured in the standing and supine radiographs. The difference was not limited to the HKA angle but also observed in most radiographic parameters, which are considered to have been in uenced by the change in joint space according to weight-bearing conditions [14]. The load applied to the knee joint affects the soft tissue surrounding the knee joint, leading to a change in the joint space and may have caused a difference in the overall measurement results of pairwise comparisons.…”

“…Consequently, this study revealed that in the cases of increased body mass index and advanced osteoarthritis, the discrepancy in the coronal alignment of the lower limb between the standing and supine radiographs increased. Since it is well known that weight-bearing condition itself can affect lower limb alignment [10,[13][14][15][16][17][18], this is a conceivable range of results. An increased body mass index would increase the load applied to the knee joint [33], and advanced osteoarthritis would change the properties of the soft tissue surrounding the joint [34], which in turn affect the lower limb alignment.…”

“…Furthermore, lower limb alignment is used as a parameter in evaluating the clinical outcomes and prognosis after treatment [3,[6][7][8][9].Most assessments of the coronal alignment of the lower limb are performed with full-length radiographs taken at standing in weight-bearing status [10][11][12][13]. The knee joint consists not only of bony structures but also of soft tissue such as ligaments, meniscus, and capsular structures, which could be affected by physiologic loading conditions [14]. Therefore, it is desirable to evaluate the lower limb alignment in a standing status so that the actual physiologic load applied to the joint can be adequately re ected.…”

“…Although the measurements using the radiographs taken in a supine position can be used, the measured values of coronal alignment of the lower limb may differ depending on the weight-bearing conditions [10,[13][14][15][16][17][18]. Therefore, information on factors that can predict the discrepancy in the coronal alignment of the lower limb between radiographs taken in the standing and supine status is required, which has been seldom investigated.…”

Three-dimensional Alignment of the Upper Extremity in the Standing Neutral Position in Healthy Subjects

“…It is clinically useful to understand the alignment of the standing neutral position and numerous studies have investigated the neutral position of loaded joints, such as the spine and the lower extremities [8][9][10].…”