For many years, achieving a neutral coronal Hip-Knee-Ankle angle (HKA) measured on radiographs has been considered a factor of success for total knee arthroplasty (TKA). Lower limb HKA is influenced by the acquisition conditions, and static HKA (sHKA) may not be representative of the dynamic loading that occurs during gait. The primary aim of the study was to see if the sHKA is predictive of the dynamic HKA (dHKA). A secondary aim was to document to what degree the dHKA changes throughout gait.

We analysed the 3-D knee kinematics during gait of a cohort of 90 healthy individuals (165 knees) with the KneeKG™ system. dHKA was calculated and compared with sHKA values. Knees were considered “Stable” if the dHKA remained positive or negative – i.e. in valgus or varus – for greater than 95% of the corresponding phase and “Changer” otherwise. Patient characteristics of the Stable and Changer knees were compared to find contributing factors.

The dHKA absolute variation during gait was 10.9±5.3° [2 .4° – 28.3°] for the whole cohort. The variation was greater for the varus knees (10.3±4.8° [2.4° – 26.3°]), than for the valgus knees (12.8±6.1° [2.9° – 28.3°], p=0.008). We found a low to moderate correlation (r = 0.266 to 0.553, p < 0 .001) between sHKA and the dHKA values for varus knees and no correlation valgus knees. Twenty two percent (36/165) of the knees demonstrated a switch in the dHKA (Changer). Proportion of Changer knees was 15% for varus sHKA versus 39% for valgus sHKA (p < 0.001).

Lower limb radiographic measures of coronal alignment have limited value for predicting dynamic measures of alignment during gait.

Purpose of the study: The long-term results after surgical treatment of idiopathic scoliosis depends not only on the correction in the coronal plane but also the restoration of good sagittal balance and thus satisfactory sagittal curvatures. Recent publications have shown moderate correction of the thoracic hypokyphosis of idiopathic scoliosis with instrumentations using hooks and pedicular screws. We report results in the coronal and sagittal play with a reduction technique by simultaneous translation on two rods (ST2R).

Material and method: The radiographic parameters were measured preoperatively, at 6 weeks, at 1 year, and at last follow-up (range 2 – 7.4 years) in a consecutive series of 72 patients treated with posterior instrumentation and reduction using the ST2R system. The same operator performed all procedures using stable anchors (pedicle screws or self-stabilizing clamps). Screws and clamps had a threaded polyaxial extension which was linked to the rod by a connector. The deformity was reduced by progressively tightening the two rods alternatively using the nuts on the threaded extensions. This manoeuvre enabled the vertebrae to migrate progressively toward the rods, producing an anteroposterior translation.

Results: In the coronal plane, the mean main curvature was reduced from 54 to 17 and was maintained (70%) without loss of angle at last follow-up. There was not difference between the 56 patients with thoracic scoliosis (Lenke 1–4) and the 16 patients with thoracolumbar or lumbar scoliosis (Lenke 5 and 6). In the sagittal plane, for the patients with preoperative hypokyphosis (32 patients < 20), the mean kyphosis was significantly improved from 9 to 30 and remained stable at last follow-up (31) with a mean gain of 21 (p< 0.001). One patient still had hypokyphosis (18) at last follow-up. For patients with normal kyphosis preoperatively (> 20), the mean gain was 7.

Conclusion: In this consecutive series of 72 adolescents with idiopathic scoliosis, reduction by simultaneous translation on two rods was a simple and effect method which restored normal thoracic kyphosis.