Can anatomic alignment measured from a knee radiograph substitute for mechanical alignment from full limb films?

Abstract

Objectives To examine whether categories of anatomic alignment (varus, neutral,valgus) measured from knee x-rays agree with similar categories of mechanical alignment from the full limb film and whether varus anatomic malalignment predicts medial joint space loss on knee x-rays as well as varus mechanical alignment. Methods We used data from the OAI (full limb and flexed knee x-rays) to examine agreement of anatomic and mechanical alignment and data from BOKS to evaluate the association of full limb mechanical alignment vs. knee x-ray anatomic alignment with joint space loss. A four degree offset was used to correct for the more valgus angulation of the anatomic alignment. Results Of 143 subjects whose knee x-rays and full limb films were publicly released from the OAI, the agreement of varus, neutral and valgus alignment was only moderate (κ= 0.43, p<.001). In BOKS, varus mechanical and anatomic alignments measured from full limb and knee x-rays respectively both predicted a high risk of medial joint space loss vs. neutral alignment (for mechanical alignment, OR = 4.82 (95% CI 1.93, 12.00) and for anatomic alignment OR = 4.25 (95% CI 2.08,8.72). Conclusions While agreement of alignment from knee x-ray to full limb film was only moderate, varus malalignment measured from a flexed knee predicted the likelihood of progression well. Flexed knee alignment may be more relevant to knee OA risk than that of a fully extended knee, but a measurement of alignment from a short limb is an imperfect surrogate for full limb alignment.

Sensitivity of different measures of frontal plane alignment to medial and lateral joint space narrowing: From the osteoarthritis initiative

“…Concurrent validity between measurement methods was modest and consistent with previous studies [5][6][7][8][9][10][11]15,26], and correlations were similar when stratifying for sex and JSN. IranpourBoroujeni et al [12] reported correlations with HKA using the traditional FTA method (r ¼ 0.68) and the new FTA method (r ¼ 0.75), which were larger than those reported in the present study.…”

“…The position of fixed knee flexion required for the acquisition of short knee films has previously been suggested to represent a better functional position of loading compared to full limb radiographs acquired in knee extension [11]. Therefore, these findings are reasonable to suggest that the new FTA measure differentiates best between a measure of compartmental disease and structural progression during activity.…”

“…Consequently, an offset between these measurement methods [6,10,11] has previously been reported, with FTA being skewed in the valgus direction (i.e., FTA: 31-51) compared to knees with neutral HKA (i.e., HKA ¼ 01). Despite this systematic difference, correlations between HKA and FTA have been reported to be moderate to high (r: 0.46-0.93) but vastly inconsistent between studies [5][6][7][9][10][11][12]. The method proposed by Kraus et al [6] originally defined FTA as the angle between the distal femur and proximal tibia, (i.e., the traditional method).…”

Ist die postoperative Ganzbeinaufnahme nach Knie-TEP-Implantation notwendig?

“…Sie stellten fest, dass das koronare Alignement nach Knie-TEP anhand einer a.-p.-Zielaufnahme des Kniegelenkes nicht zu bestimmen ist und folgerten, dass eine Ganzbeinaufnahme nach Knie-TEP unabdingbar sei, um die mechanische Achse zu bestimmen. Zu der gleichen Schlussfolgerung kamen weitere Autoren, welche die Übertrag-barkeit des anatomischen femorotibialen Winkels auf den mechanischen femorotibialen Winkel untersuchten [2,6,8,21]. Eine Messung der anatomischen Kniegelenkswinkel und deren Reproduzierbarkeit erfolgten jedoch in keiner der Arbeiten.…”

The relationship between external knee moments and muscle co-activation in subjects with medial knee osteoarthritis

“…Although we did not monitor the walking speed, we believe that this limitation did not affect our findings as the included trials showed small variability (less than 5% of the average) within trials. Sixth, we measured the lower limb alignment using the antero posterior knee radiograph, which is not the gold standard method (Felson et al , 2009), however it presents good reproducibility and demonstrated high correlation with the gold standard method (r= 0.87 -0.92). Finally, our sample was not matched for BMI, which is also a limitation.…”