Three-dimensional mechanical evaluation of joint contact pressure in 12 periacetabular osteotomy patients with 10-year follow-up

Background and purpose Because of the varying structure of dysplastic hips, the optimal realignment of the joint during periacetabular osteotomy (PAO) may differ between patients. Three-dimensional (3D) mechanical and radiological analysis possibly accounts better for patient-specific morphology, and may improve and automate optimal joint realignment

Biomechanical Optimization-Based Planning of Periacetabular Osteotomy.

Modern computerized planning tools for periacetabular osteotomy (PAO) use either morphology-based or biomechanics-based methods. The latter rely on estimation of peak contact pressures and contact areas using either patient-specific or constant thickness cartilage models. We performed a finite element analysis investigating the optimal reorientation of the acetabulum in PAO surgery based on simulated joint contact pressures and contact areas using patient-specific cartilage model. Furthermore we investigated the influences of using patient-specific cartilage model or constant thickness cartilage model on the biomechanical simulation results. Ten specimens with hip dysplasia were used in this study. Image data were available from CT arthrography studies. Bone models were reconstructed. Mesh models for the patient-specific cartilage were defined and subsequently loaded under previously reported boundary and loading conditions. Peak contact pressures and contact areas were estimated in the original position. Afterward we used validated preoperative planning software to change the acetabular inclination by an increment of 5° and measured the lateral center-edge angle (LCE) at each reorientation position. The position with the largest contact area and the lowest peak contact pressure was defined as the optimal position. In order to investigate the influence of using patient-specific cartilage model or constant thickness cartilage model on the biomechanical simulation results, the same procedure was repeated with the same bone models but with a cartilage mesh of constant thickness. Comparison of the peak contact pressures and the contact areas between these two different cartilage models showed that good correlation between these two cartilage models for peak contact pressures (r = 0.634 ∈[0.6, 0.8], p 0.8, p < 0.001). For both cartilage models, the largest contact areas and the lowest peak pressures were found at the same position. Our study is the first study comparing peak contact pressures and contact areas between patient-specific and constant thickness cartilage models during PAO planning. Good correlation for these two models was detected. Computer-assisted planning with FE modeling using constant thickness cartilage models might be a promising PAO planning tool when a conventional CT is available

Impact of triple pelvic osteotomy on contact stress pressure distribution in the hip joint

PURPOSE: We studied changes of contact stress distribution in the hip joint after Tonnis triple pelvic osteotomy applied in the treatment of dysplasia and hip joint incongruence in adolescents. METHODS: In a group of 75 patients, 54 (72 %) female, who underwent surgery by triple pelvic osteotomy in adolescence for developmental disorder of the hip and avascular necrosis of the femoral head, a three-dimensional hip joint model was used based on the radiography of the pelvis with hips. The following biomechanical parameters were calculated: resultant hip force normalised to body weight (R/Wb), inclination of the resultant hip force (θ−R), the position of the stress pole (θ), peak contact hip stress (Pmax), and peak contact hip stress normalised to body weight (Pmax/Wb). Gait quality was also assessed. RESULTS: After surgery the Wiberg CE angle was increased by 17.85° (114 %), resultant hip force normalised to body weight (R/Wb) was decreased by 0.107 (3.3 %), the position of the stress pole was shifted medially by 27.59° (63.5 %), and peak contact hip stress normalised to body weight (Pmax/Wb) was decreased by 2249.74 (55.9 %). Waddling gait was reduced from 17 (23.9 %) to four cases (5.6 %). All changes were statistically highly significant (p<0.01). CONCLUSIONS: The effect of Tonnis triple pelvic osteotomy lies in the improvement of stress distribution across the acetabular cartilage of the hip joint, thus slowing down the degenerative damage of the hip joint