The alignment of the trunk and pelvis during walking in achondroplasia and factors increasing anterior pelvic tilt

Achondroplasia (ACH) is the most common skeletal dysplasia and characterized by shorter long bones relative to the torso. Concerning the upper body, frequent features are cranio-cervical compression, thoracolumbar kyphosis, lumbar lordosis and stenosis [1,2]. Secondary symptoms can be lower back pain, claudication, weakness and paresthesias. What is the sagittal spinopelvic alignment during gait in ACH and which characteristics affect the pelvic tilt? 34 paediatric and juvenile patients with ACH (age:10.5±4.2 years, height: 108±15 cm) were statistically compared to 27 age-matched typically developing controls (age: 10.8±4.4 years, height: 145±23 cm). All underwent a 3D gait analysis [Vicon Nexus, mod. PiG-Model] to capture upper and lower body kinematics. Thorax, pelvic and lumbar spine rotations were extracted. All subjects were clinically examined for anthropometrics, passive RoM and manual strength. The presence of symptoms was documented. Correlations between clinical parameters, anthropometrics and pelvic tilt were analyzed. 17 of 34 patients reported back pain, sensory deficits or sudden leg weakness. During gait, patients with ACH showed +11.1° more anterior pelvic tilt (P<0.001), -4.0° less anterior thorax tilt (P= 0.005) and - 15.9° more lumbar extension (P<0.001). In both cohorts, subjects who took longer steps, had more pelvic tilt (Fig. 1), yet the tilt was still significantly larger in ACH, irrespective of longer relative steps (P<0.01). In ACH, negative correlations with anterior pelvic tilt were found for popliteal angles (r= -0.40, P=0.018) and for limb length to body height ratio (r=-0.65, P<0.001). Passive hip flexion contracture (Thomas-Test) in ACH was not related to anterior pelvic tilt (r=-0.14, P=0.43). ACH patients with symptoms walked with similarly severe spinopelvic malignment than asymptomatic patients, yet at 11.2% reduced speed (P=0.025). Upon clinical exam, patients with more tilt showed less knee extensor and plantarflexor strength (r=-0.45 and -0.40, both P< 0.027). No such correlations were found in controls.Download : Download high-res image (123KB)Download : Download full-size image Pelvic tilt and hyperlordosis in ACH was pronounced and the rate of symptoms hinting to neurological deficits and spinal compression was 50%. The link of pelvic tilt and reduced knee and ankle extensor strength fits within this considerations. Although anterior pelvic tilt was not a sole compensation to increase step length, it seems to some degree be a consequence of disproportionally short leg length. Notably, after surgical femoral lengthening, sagittal lumbar lordosis has been reported to decrease [3]. Next to leg growth promoting therapeutics and drugs, interventions that increase hamstrings tone in ACH may potentially also be beneficial for the upper body.