Characterization of Gait Function in Patients with Post-Surgical Sagittal (Flatback) Deformity: A Prospective Study of 21 Patients

*Hospital for Special Surgery, New York, NY, USA
~Tokyo Medical University, Tokyo, Japan

PURPOSE:
To analyze the functional implications of sagittal imbalance with respect to gait deviations, compensatory mechanisms and adverse effects of these on hip and knee joints.

MATERIALS AND METHODS:
21 patients with postoperative flatback were evaluated at a minimum of 2 years after index surgery. Data were collected using 3D video based motion analysis six-camera system with two force platforms. X-rays of these patients were evaluated for lumbar lordosis and sagittal imbalance.

RESULTS:
The average lumbar lordosis was 16.9º (0 - 44º) and average sagittal imbalance was 14.6 cm (4 - 30 cm). The step length was 43 cm (vs. normal 70) (p<0 .001), stride length 90 cm (vs. 142) (p.001), velocity 85 cm/s 139) (p<0.001), cadence 111 steps/min 117) (p =0.35) stance phase duration 65% 60%) swing 34% 39) initial double support time 15% 10) (p<0.001) and step width 13 10 cm) Kinetics kinematics data showed increased hip flexion (10º vs. - 15º normally in midstance) throughout external rotation -5º) gait cycle. Knee hyperflexion (18ºvs.5º) valgus was present (5ºvs-3º) during stance. The normal loading response biphasic pattern absent the knee rotated internally cycle (-10ºvs.-25º). Forward tilt of trunk (10ºvs.-5º) with decreased movements. This dampening effect also seen pelvis. Hip Flexor-extension moments were despite while adduction moment midstance. flexion-extension varus-valgus reduced.

DISCUSSION:
Standing with the trunk bent forward is inefficient and unstable. This hips and knees flex to compensate, producing crouched posture and gait. This decreases the length of the stride in swing and, thus, patient's velocity. The instability created by an anterior center of gravity is partly overcome by a broad based gait and by externally rotating the femur. Despite these compensatory mechanisms that worsened with the degree of imbalance and patient's efforts to keep moments low, a prolonged stance phase and decreased rate of rise indicated that the gait was still unstable. The decrease in trunk and pelvic motion in all 3 planes sows that they act as one rigid lever arm. The joint power evaluation showed the same amount of power generation, as in normal, accomplishes a shorter distance travel at a slower velocity; making gait inefficient and labored. The effect of abnormally increased hip and knee joint movements on joint cartilage and ligaments is unclear is the result of constant loading of the knee and hip. The patients with flatback develop several compensatory mechanisms to make their gaits as efficient as body mechanics will allow. Back pain and thoracic hypokyphosis are known problems associated with flatback syndrome. This study shows that flatback syndrome also affects the hip and knee joints adversely, producing an inefficient gait.