Biomechanical validation of computer assisted planning of periacetabular osteotomy: A preliminary study based on finite element analysis

Periacetabular Osteotomy (PAO) is a joint preserving surgical intervention intended to increase femoral head coverage and thereby to improve stability in young patients with hip dysplasia. Previously, we developed a CT-based, computer-assisted program for PAO diagnosis and planning, which allows for quantifying the 3D acetabular morphology with parameters such as acetabular version, inclination, lateral center edge (LCE) angle and femoral head coverage ratio (CO). In order to verify the hypothesis that our morphology-based planning strategy can improve biomechanical characteristics of dysplastic hips, we developed a 3D finite element model based on patient-specific geometry to predict cartilage contact stress change before and after morphology-based planning. Our experimental results demonstrated that the morphology-based planning strategy could reduce cartilage contact pressures and at the same time increase contact areas. In conclusion, our computer-assisted system is an efficient tool for PAO planning.

Three-dimensional measurement of cemented femoral stem stability: an in vitro cadaver study

OBJECTIVE

To compare the in vitro stability of two cemented hip stem designs: Stem I was a collarless, double-tapered, highly polished implant; Stem II had a collar and matt finish.

BACKGROUND

Stability of the femoral component of a hip implant is important for its long-term clinical success. Excessive migration or cyclic motion can increase the risk of early implant failure.

METHODS

The stems were implanted in paired human cadaver femurs, and custom-designed micromotion sensors were used to measure three-dimensional motions of the stems at proximal, middle and distal locations during simulated in vivo loading cycles.

RESULTS

This study found that despite 'rigid' fixation, cemented stems exhibit detectable motions under a limited number of cycles of simulated physiologic loads. At four times the donor body weight, Stem I showed a subsidence of 90 microm, compared to 25 microm of Stem II (P<0.05). In contrast, the proximal end of Stem II exhibited greater cyclic motions in the medial-lateral direction (P<0.05).

CONCLUSIONS

The different motion patterns could be due to the design differences, such as surface finish and geometry. RelevanceImplant design is an important factor related to the behavior of the cement/bone interface and the overall success of the implant. This study compares in vitro micromotion of two cemented femoral prostheses with differing proximal designs.

Ipsilateral fractures of the pelvis and the femur--floating hip? A retrospective analysis of 42 cases

A consecutive series of 40 patients, who sustained 42 ipsilateral pelvic and femoral fractures, is reported. There were eight (26.6%) traumatic neurological deficits and three open femoral fractures. Two multiply injured patients died in the postraumatic period because of the severity of their injuries. No associated vascular injuries could be identified. All but two fractures of the femur, 8 of the 15 fractures of the pelvic ring and 17 of the 30 fractures of the acetabulum were treated by internal fixation. In 26 patients internal fixation was performed on both fracture components (in 17 patients this was done under the same period of anaesthesia). Postoperatively, a deep venous thrombosis in three patients, one deep wound infection and five (18.5%) iatrogenic neurological deficits had to be notified. In this series we could not identify any specific associated injuries and complications as known for the floating knee or the floating elbow. The term floating hip is inprecise and misleading, and its use is not recommended. The treatment of this fracture-combination follows the guidelines established for the individual lesions.

Periacetabular osteotomy through the Smith-Petersen approach

Sixty-six hips in 58 patients that had undergone periacetabular osteotomy for residual acetabular dysplasia were available for clinical and radiographic followup at a minimum of 2 years (average, 4 years) after surgery. The final clinical results were graded as 17% excellent, 59% good, 12% fair, and 12% poor. No patient who met the ideal indications for surgery had a poor result during the study period. After reviewing the results, the authors remain positive regarding the periacetabular osteotomy and recommend it for individuals with hip pain and radiographic evidence of acetabular dysplasia.

Acetabular reconstruction in developmental dysplasia of the hip: results of the acetabular reinforcement ring with hook

This study examined the clinical results and technical challenges associated with acetabular reconstruction in developmental dysplasia of the hip using the acetabular reinforcement ring with hook. We reviewed 33 consecutive reconstructions performed by a single surgeon. At an average follow-up of 6.7 years, the mean Merle-d'Aubigne score had increased from 7 to 16. Two revisions were performed for aseptic loosening. Of the unrevised hips, 1 was classified as definitely loose and 1 as possibly loose. These results compare favorably with others in the literature. The acetabular reinforcement ring may prevent graft resorption and cup migration, major causes of socket failure in reconstruction of the deficient acetabulum.