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1.  Three-dimensional mechanical evaluation of joint contact pressure in 12 periacetabular osteotomy patients with 10-year follow-up 
Acta orthopaedica  2009;80(2):155-161.
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.
Patients and methods
We evaluated the 10-year outcomes of 12 patients following PAO. We compared 3D mechanical analysis results to both radiological and clinical measurements. A 3D discrete-element analysis algorithm was used to calculate the pre- and postoperative contact pressure profile within the hip. Radiological angles describing the coverage of the joint were measured using a computerized approach at actual and theoretical orientations of the acetabular cup. Quantitative results were compared using postoperative clinical evaluation scores (Harris score), and patient-completed outcome surveys (q-score) done at 2 and 10 years.
The 3D mechanical analysis indicated that peak joint contact pressure was reduced by an average factor of 1.7 subsequent to PAO. Lateral coverage of the femoral head increased in all patients; however, it did not proportionally reduce the maximum contact pressure and, in 1 case, the pressure increased. This patient had the lowest 10-year q-score (70 out of 100) of the cohort. Another hip was converted to hip arthroplasty after 3 years because of increasing osteoarthritis.
The 3D analysis showed that a reduction in contact pressure was theoretically possible for all patients in this cohort, but this could not be achieved in every case during surgery. While intraoperative factors may affect the actual surgical outcome, the results show that 3D contact pressure analysis is consistent with traditional PAO planning techniques (more so than 2D analysis) and may be a valuable addition to preoperative planning and intraoperative assessment of joint realignment.
PMCID: PMC2689368  PMID: 19404795
2.  Cellular, matrix, and growth factor components of the joint capsule are modified early in the process of posttraumatic contracture formation in a rabbit model 
Acta orthopaedica  2008;79(1):116-125.
Background and purpose
A recently developed animal model of posttraumatic contractures reflects the chronic stages of the human condition. To understand the initiation of the process, we evaluated the cellular, matrix, and growth factor changes in the joint capsule in the early stages of the animal model, which would not be possible in humans.
18 skeletally mature rabbits had intraarticular cortical windows removed from the medial and lateral femoral condyles, and the knee joint was immobilized. The contralateral unoperated limb served as a control. Equal numbers of rabbits were killed 2, 4, and 6 weeks after surgery. Myofibroblast, mRNA, and protein determinations were done with immunohistochemistry, RT-PCR, and western blot, respectively.
Myofibroblast numbers were statistically significantly elevated in the joint capsules of the experimental knees as compared to control knees. The mRNA and protein levels for collagen types I and III, matrix metalloproteinases 1 and 13, and transforming growth factor β1 were statistically significantly greater, and for tissue inhibitor of matrix metalloproteinases 1 significantly less, in the experimental capsules than in the control capsules.
The experimental joint capsule changes in the acute stages of posttraumatic contractures are similar to those in the chronic stages of the process in this model. Thus, it appears that the mechanisms that attenuate the acute stages of the response to injury are circumvented, contributing to a prolonged modulation of myofibroblast numbers, matrix molecules and growth factors, and leading to joint contractures. Thus, in clinical practice, new approaches to prevention of posttraumatic contractures should be implemented as soon as possible.
PMCID: PMC2950862  PMID: 18283583 CAMSID: cams854
3.  Outcome of periacetabular osteotomy 
Acta orthopaedica  2005;76(3):303-313.
Due to wide variations in acetabular structure of individuals with hip dysplasia, the measurement of the acetabular orientation may not be sufficient to predict the joint loading and pressure distribution across the joint. Addition of mechanical analysis to preoperative planning, therefore, has the potential to improve the clinical outcome.
We analyzed the effect of periacetabular osteotomy on hip dysplasia using computer-aided simulation of joint contact pressure on regular AP radiographs. The results were compared with the results of surgery based on realignment of acetabular angles to the normal hip.
Patients and methods
We studied 12 consecutive periacetabular osteotomies with no femoral head deformity. The median age of patients, all females, was 35 (20−50) years. The median follow-up was 2 years (1.3−2.2). Patient outcome was measured with the total score of a self-administered questionnaire (q-score) and with the Harris hip score. The pre- and postoperative orientation of the acetabulum was defined using reconstructed 3D CT-slices to measure angles in the three anatomical planes. Peak contact pressure, weight-bearing area, and the centroid of the contact pressure distribution (CP-ratio) were calculated.
While 9 of 12 cases showed decreased peak pressure after surgery, the mean changes in weight-bearing area and peak contact pressure were not statistically significant. However, CP-ratio changed (p < 0.001, paired t-test) with surgery. For the optimal range of CP-ratio (within its mid-range 40−60%), the mechanical outcome improved significantly.
Verifying the correlation between the optimal CP-ratio and the outcome of the surgery requires additional studies on more patients. Moreover, the anatomically measured angles were not correlated with the ranges of CP-ratio, suggesting that they do not always associate with objective mechanical goals of realignment osteotomy. Mechanical analysis, therefore, can be a valuable tool in assessing two-dimensional radiographs in hip dysplasia.
PMCID: PMC2745131  PMID: 16156455
4.  Polymethylmethacrylate Particles Stimulate Bone Resorption of Mature Osteoclasts In Vitro 
Acta orthopaedica  2008;79(2):281-288.
The interaction between wear particle debris and the cells at the implant-bone interface is an important contributing factor to periprosthetic bone loss seen in total joint arthroplasties.
To investigate this particle-induced response on different stages of osteoclast maturation, polymethylmethacrylate (PMMA) particles were added to a murine osteoclastogenic bone marrow cell culture system at either day 0, day 4, or day 8 culture time, which represented PMMA particle stimulation of precursor osteoclasts, mature osteoclasts, or end stage osteoclasts respectively. The number of TRAP-positive multinucleated cells (MNCs) and percentage of bone resorption in culture was measured.
Particles added to precursor osteoclasts resulted in a significant increase in TRAP-positive MNCs that persisted for four days, but no significant increase in bone resorption. Particles added to mature osteoclasts resulted in a significant increase in TRAP-positive MNCs that persisted for eight days, and a significant increase in bone resorption. Particles added to end stage osteoclasts did not increase the number of TRAP-positive MNCs or bone resorption.
PMMA particles added to mature osteoclasts resulted in an increase in TRAP-positive cells which persisted over a longer time period, and a larger increase in bone resorption compared to the other stages of osteoclast development.
PMCID: PMC2662348  PMID: 18484256
5.  Cement/implant interface gaps explain the poor results of CMW3 for femoral stem fixation: a cadaver study of migration, fatigue and mantle morphology. 
Acta orthopaedica  2005;76(5):679-687.
Background: Norwegian Arthroplasty Register (NAR) reported that CMW3 cement performed poorly for femoral stem fixation.
Methods: Collared, satin-finished stems (Ra = 0.35μm) were implanted into cadaver femora using CMW3 and Simplex as control. Cement mantle function was quantified by stem migration after 300,000 cycles of “stair-climbing”. Cement cracks and interface gaps were quantified in transverse sections.
Results: The variances of the CMW3 migrations were substantially and significantly higher (p < 0.0001): subsidence (CMW3 = -32(SD42)μm, Simplex = -7(SD9)μm, p = 0.16); retroversion (CMW3 = 0.60(SD0.25)°, Simplex = 0.37(SD0.04)°, p = 0.08). Crack length-densities were similar (CMW3 = 50(SD15)μm/mm2, Simplex = 45(SD12)μm/mm2, p = 0.30). CMW3 had significantly more non-apposed stem/cement interface: 52(SD17)% versus 33(SD8)% (p = 0.040).
Migrations were predicted by fraction of non-apposed stem/cement interface (retroversion: R2 = 0.80, p < 0.0001, subsidence: R2 = 0.46, p = 0.016) but not by cement cracks or non-apposed cement/bone interface (R2 < 0.05, p = 0.49—0.77)
Interpretation: This study showed that increased stem/cement non-apposition resulted in increased stem migration. Early migration is known to correlate with revision risk. Therefore, the higher stem-revision risk for CMW3 cement reported by the NAR may have been due to inferior and variable stem/cement apposition.
PMCID: PMC1383657  PMID: 16263615

Results 1-5 (5)