No abstract

Extraction of bone contours from radiographs plays an important role in disease diagnosis, preoperative planning, and treatment analysis. We present a fully automatic method to accurately segment the proximal femur in anteroposterior pelvic radiographs. A number of candidate positions are produced by a global search with a detector. Each is then refined using a statistical shape model together with local detectors for each model point. Both global and local models use Random Forest regression to vote for the optimal positions, leading to robust and accurate results. The performance of the system is evaluated using a set of 839 images of mixed quality. We show that the local search significantly outperforms a range of alternative matching techniques, and that the fully automated system is able to achieve a mean point-to-curve error of less than 0.9 mm for 99% of all 839 images. To the best of our knowledge, this is the most accurate automatic method for segmenting the proximal femur in radiographs yet reported.

Rarely, patients exposed to high circulating concentrations of cobalt from failed hip replacements develop neurological damage, hypothyroidism and/or cardiomyopathy, which may not resolve completely even after removal of the prosthesis. The greatest risk of systemic cobalt toxicity seems to result from accelerated wear of a cobalt-containing revision of a failed ceramic prosthesis, rather than from primary failure of a metal-on-metal prosthesis.

No abstract

Metal-on-metal hip replacement (MOMHR) using large diameter bearings has become a popular alternative to conventional total hip arthroplasty, but is associated with elevated local tissue and circulating levels of chromium (Cr) and cobalt (Co) ions that may affect bone health. We examined the effects of acute and chronic exposure to these metals on human osteoblast and osteoclast formation and function over a clinically relevant concentration range previously reported in serum and within hip synovial fluid in patients after MOMHR. SaOS-2 cells were cultured with Co(2+), Cr(3+) and Cr(6+) for 3 days after which an MTS assay was used to assess cell viability, for 13 days after which alkaline phosphatase and cell viability were assessed and for 21 days after which nodule formation was assessed. Monocytes were isolated from human peripheral blood and settled onto dentine disks then cultured with M-CSF and RANKL plus either Co(2+), Cr(3+) or Cr(6+) ions for 21 days from day 0 or between days 14 and 21. Cells were fixed and stained for TRAP and osteoclast number and amount of resorption per dentine disk determined. Co(2+) and Cr(3+) did not affect osteoblast survival or function over the clinically equivalent concentration range, whilst Cr(6+) reduced osteoblast survival and function at concentrations within the clinically equivalent serum range after MOMHR (IC(50) =2.2 μM). In contrast, osteoclasts were more sensitive to metal ions exposure. At serum levels a mild stimulatory effect on resorption in forming osteoclasts was found for Co(2+) and Cr(3+), whilst at higher serum and synovial equivalent concentrations, and with Cr(6+), a reduction in cell number and resorption was observed. Co(2+) and Cr(6+) within the clinical range reduced cell number and resorption in mature osteoclasts. Our data suggest that metal ions at equivalent concentrations to those found in MOMHR affect bone cell health and may contribute to the observed bone-related complications of these prostheses.

No abstract

We studied the relationship between polyethylene wear and osteolysis in 230 subjects after cemented Charnley total hip arthroplasty in order to examine the validity of the wear rate threshold concept. Polyethylene wear measured using image analysis (EBRA) software was compared in 1 1 5 subjects with osteolysis versus 115 control subjects that were individually matched for age, sex, and follow up period. Subjects with osteolysis had almost twice the mean annual wear rate versus the controls. The incidence of osteolysis increased in a linear manner with each quintile increase in wear rate throughout the range 0.01-0.54 mm/year. The odds-ratio for osteolysis approximately doubled with each quintile increase in wear rate above the middle quintile (wear rate 0.08-0.1 1 m d year), and decreased at a similar rate with each quintile decrease in wear rate below the middle quintile. Our data suggests that the association of osteolysis with polyethylene wear rate represents a continuous dose-response relationship and does not support the concept of a discrete critical wear rate threshold above which the risk of osteolysis is disproportionately increased.

The outcomes of this technique are satisfactory in adulthood; reoperation rates are high but are most commonly related to the patient outgrowing the rods. Concerns regarding insertion of this fixed device at the knee and ankle were unfounded, although proximal femoral fixation remains a problem.