Arild Aamodt

Determination of the Hounsfield value for CT-based design of custom femoral stems

Ct and advanced computer-aided design techniques offer the means for designing customised femoral stems. Our aim was to determine the Hounsfield (HU) value of the bone at the corticocancellous interface, as part of the criteria for the design algorithm. We obtained transverse CT images from eight human cadaver femora. The proximal femoral canal was rasped until contact with dense cortical bone was achieved. The femora were cut into several sections corresponding to the slice positions of the CT images. After obtaining a computerised image of the anatomical sections using a scanner, the inner cortical contour was outlined and transferred to the corresponding CT image. The pixels beneath this contour represent the CT density of the bone remaining after surgical rasping. Contours were generated automatically at nine HU levels from 300 to 1100 and the mean distance between the transferred contour and each of the HU-generated contours was computed. The contour generated along the 600-HU pixels was closest to the inner cortical contour of the rasped femur and therefore 600 HU seem to be the CT density of the corticocancellous interface in the proximal part of cadaver femora. Generally, femoral bone with a CT density beyond 600 HU is not removable by conventional reamers. Thus, we recommend the 600 HU threshold as one of several criteria for the design of custom femoral implants from CT data.

Changes in proximal femoral strain after insertion of uncemented standard and customised femoral stems: AN EXPERIMENTAL STUDY IN HUMAN FEMORA

We have compared the changes in the pattern of the principal strains in the proximal femur after insertion of eight uncemented anatomical stems and eight customised stems in human cadaver femora. During testing we aimed to reproduce the physiological loads on the proximal femur and to simulate single-leg stance and stair-climbing. The strains in the intact femora were measured and there were no significant differences in principal tensile and compressive strains in the left and right femora of each pair. The two types of femoral stem were then inserted randomly into the left or right femora and the cortical strains were again measured. Both induced significant stress shielding in the proximal part of the metaphysis, but the deviation from the physiological strains was most pronounced after insertion of the anatomical stems. The principal compressive strain at the calcar was reduced by 90% for the anatomical stems and 67% for the customised stems. Medially, at the level of the lesser trochanter, the corresponding figures were 59% and 21%. The anatomical stems induced more stress concentration on the anterior aspect of the femur than did the customised stems. They also increased the hoop strains in the proximomedial femur. Our study shows a consistently more physiological pattern of strain in the proximal femur after insertion of customised stems compared with standard, anatomical stems.

Wear and Migration of Highly Cross-Linked and Conventional Cemented Polyethylene Cups with Cobalt Chrome or Oxinium Femoral Heads: A Randomized Radiostereometric Study of 150 Patients

This randomized study was performed to compare wear and migration of five different cemented total hip joint articulations in 150 patients. The patients received either a Charnley femoral stem with a 22.2 mm head or a Spectron EF femoral stem with a 28 mm head. The Charnley articulated with a γ‐sterilized Charnley Ogee acetabular cup. The Spectron EF was used with either EtO‐sterilized non‐cross‐linked polyethylene (Reflection All‐Poly) or highly cross‐linked (Reflection All‐Poly XLPE) cups, combined with either cobalt chrome (CoCr) or Oxinium femoral heads. The patients were followed with repeated RSA measurements for 2 years. After 2 years, the EtO‐sterilized non‐cross‐linked Reflection All‐Poly cups had more than four times higher proximal penetration than its highly cross‐linked counterpart. Use of Oxinium femoral heads did not affect penetration at 2 years compared to heads made of CoCr. Further follow‐up is needed to evaluate the benefits, if any, of Oxinium femoral heads in the clinical setting. The Charnley Ogee was not outperformed by the more recently introduced implants in our study. We conclude that this prostheses still represents a standard against which new implants can be measured.

Documentation of hip prostheses used in Norway: a critical review of the literature from 1996--2000.

We have conducted a systematic review of the scientific literature concerning outcome and clinical effectiveness of prostheses used for primary total hip replacement (THR) in Norway. The study is based on two Health Technology Assessment reports from the UK (Faulkner et al. 1998, Fitzpatrick et al. 1998), reviewing the literature from 1980 to 1995. Using a similar search strategy, we have evaluated the literature from 1996 through 2000. We included 129 scientific and medical publications which were assessed according to a specific appraisal protocol. The majority (72%) were observational studies, whereas only 9% were randomized studies. We could not retrieve any peer-reviewed documentation for one third of the implants. The Charnley prosthesis had by far the best and most comprehensive evidence base with better than 90% implant survival after about 10 years. Survival of the Charnley prosthesis declines by about 10% during each of the two following decades. Except for the Charnley and Lubinus IP, no other prosthesis on the market in Norway has given long-term results (> 15 years). 5 other cemented implants have given comparable results at about 10 years of follow-up. Some uncemented stems have shown promising medium-term outcome, but no combination of uncemented cup and stem fulfilled the benchmark criterion of ≥ 90% implant survival at 10 years, which we propose as a minimum requirement for unrestricted clinical use for prostheses used in primary THR. New or undocumented implants should be introduced through a four-step model including preclinical testing, small series evaluated by radiosterometry, randomized clinical trial involving comparison with a well-documented prosthesis, and finally, surveillance of clinical use through registers.

Effect of in-hospital comprehensive geriatric assessment (CGA) in older people with hip fracture. The protocol of the Trondheim Hip Fracture Trial

BackgroundHip fractures in older people are associated with high morbidity, mortality, disability and reduction in quality of life. Traditionally people with hip fracture are cared for in orthopaedic departments without additional geriatric assessment. However, studies of postoperative rehabilitation indicate improved efficiency of multidisciplinary geriatric rehabilitation as compared to traditional care. This randomized controlled trial (RCT) aims to investigate whether an additional comprehensive geriatric assessment of hip fracture patients in a special orthogeriatric unit during the acute in-hospital phase may improve outcomes as compared to treatment as usual in an orthopaedic unit.Methods/designThe intervention of interest, a comprehensive geriatric assessment is compared with traditional care in an orthopaedic ward. The study includes 401 home-dwelling older persons >70 years of age, previously able to walk 10 meters and now treated for hip fracture at St. Olav Hospital, Trondheim, Norway. The participants are enrolled and randomised during the stay in the Emergency Department. Primary outcome measure is mobility measured by the Short Physical Performance Battery (SPPB) at 4 months after surgery. Secondary outcomes measured at 1, 4 and 12 months postoperatively are place of residence, activities of daily living, balance and gait, falls and fear of falling, quality of life and depressive symptoms, as well as use of health care resources and survival.DiscussionWe believe that the design of the study, the randomisation procedure and outcome measurements will be of sufficient strength and quality to evaluate the impact of comprehensive geriatric assessment on mobility and other relevant outcomes in hip fracture patients.Trials registrationClinicalTrials.gov, NCT00667914

An in vitro study of the strain distribution in human femora with anatomical and customised femoral stems

Hydroxyapatite-coated standard anatomical and customised femoral stems are designed to transmit load to the metaphyseal part of the proximal femur in order to avoid stress shielding and to reduce resorption of bone. In a randomised in vitro study, we compared the changes in the pattern of cortical strain after the insertion of hydroxyapatite-coated standard anatomical and customised stems in 12 pairs of human cadaver femora. A hip simulator reproduced the physiological loads on the proximal femur in single-leg stance and stair-climbing. The cortical strains were measured before and after the insertion of the stems. Significantly higher strain shielding was seen in Gruen zones 7, 6, 5, 3 and 2 after the insertion of the anatomical stem compared with the customised stem. For the anatomical stem, the hoop strains on the femur also indicated that the load was transferred to the cortical bone at the lower metaphyseal or upper diaphyseal part of the proximal femur. The customised stem induced a strain pattern more similar to that of the intact femur than the standard, anatomical stem.

Primary stability of custom and anatomical uncemented femoral stems A method for three-dimensional in vitro measurement of implant stability

BACKGROUND Lack of primary stability of cementless hip stems prevents bone ingrowth and may lead to loosening of the stem. Direct measures of the implant stability require drilled holes in the bone at the measuring site. These holes weaken the cortical bone, limit the number of possible measuring points and inhibit other biomechanical measurements. This in vitro study aimed to develop a method for indirect measurement of primary stability of femoral stems, leaving the specimen intact. The method was used to compare the primary stability of two uncemented femoral stems with different proximal fit and fill and different stem length. METHODS An in vitro method for indirect full three-dimensional measurement of implant-bone interface motion was developed. Uncemented customized (n=10) and anatomical stems (n=10) were inserted in human cadaver femora and the primary stability during one leg stance and stair climbing was measured. FINDINGS The method had high precision, and the errors due to necessary assumption of rigid body components were minimal. The customized stem with optimal proximal fit and fill provided the best initial stability for rotation in retroversion. The anatomical stem with longer stem length was more resistant to permanent rotation in varus. INTERPRETATION During stem design development the primary stability can be measured at all wanted measuring sites with the presented method, leaving the specimen intact for further analyses.

Periprosthetic bone loss after insertion of an uncemented, customized femoral stem and an uncemented anatomical stem: A randomized DXA study with 5-year follow-up

Background and purpose Customized femoral stems are designed to have a perfect fit and fill in the femur in order to achieve physiological load transfer and minimize stress shielding. Dual-energy X-ray absorptiometry (DXA) is regarded as an accurate method for detection of small alterations in bone mineral density (BMD) around hip prostheses. We present medium-term DXA results from a randomized study comparing a customized and an anatomical femoral stem. Methods 100 hips were randomized to receive either the anatomical ABG-I stem or the Unique customized femoral stem, both uncemented. DXA measurements were conducted postoperatively and after 3, 6, 12, 24, 36, and 60 months, and BMD was computed for each of the 7 Gruen zones in the proximal femur. Results Results from 87 patients were available for analysis. 78 completed the 5-year follow-up: 35 patients in the ABG group and 43 patients in the Unique group. In both groups, we found the greatest degree of bone loss in the proximal Gruen zones. In zone 1, there was 15% reduction in BMD in the ABG-I group and 14% reduction in the Unique group. In zone 7, the reduction was 28% in the ABG-I group and 27% in the Unique group. The only statistically significant difference between the groups was found in Gruen zone 4, which is distal to the tip of the stem, with 1.6% reduction in BMD in the ABG-I group and 9.7% reduction in the Unique group (p = 0.003). Interpretation 5-year DXA results showed that because of stress-shielding, proximal bone loss could not be avoided—either for the anatomical ABG-I stem or for the customized Unique stem.

High local concentrations without systemic adverse effects after impaction of netilmicin-impregnated bone

Background When cancellous bone is impregnated with antibiotics the subsequent release of antibiotics from the bone shows a high early release. Hence, impaction of large amounts of netilmicin-impregnated bone may cause toxic netilmicin values in serum.Patients and methods We studied kidney and otovestibular function after impacting 50 g of netilmicin-impregnated cancellous bone during revision hip or knee arthroplasty in 20 patients. The bone was impacted in the acetabulum (n = 8), proximal femur (n = 9) and distal femur/proximal tibia (n = 3). Serum creatinine concentration was measured and audiometry was performed before and after the operation. Netilmicin concentrations in serum, joint fluid, and in urine were recorded postoperatively at regular intervals. We analyzed pharmacokinetics in two study groups receiving bone impregnated with netilmicin (50 mL), at either 50 mg netilmicin/mL (group I) or 100 mg netilmicin/mL (group II).Results Neither netilmicin-induced renal toxicity, nor otovestibular toxicity was registered. Peak serum netilmicin values in group I and group II were 0.9 (0.5–1.3) mg/L and 1.8 (0.6–4.0) mg/L, respectively (p = 0.04). Peak netilmicin concentrations in wound drainage fluid in group I and group II were 237 (9–647) mg/L and 561 (196–1132) mg/L, respectively (p = 0.01). In both groups, netilmicin was recovered in urine samples for approximately 4 weeks.Interpretation 50 grams of cancellous bone impregnated with 100 mg/mL netilmicin solution was impacted in the hip or knee joint with no adverse effects. Extremely high local concentrations of netilmicin in joint fluid were recorded postoperatively. The use of antibioitic-impregnated cancellous could be an option when performing revision of hip and knee prostheses.

Changes in proximal femoral strain after insertion of uncemented standard and customised femoral stems

We have compared the changes in the pattern of the principal strains in the proximal femur after insertion of eight uncemented anatomical stems and eight customised stems in human cadaver femora. During testing we aimed to reproduce the physiological loads on the proximal femur and to simulate single-leg stance and stair-climbing. The strains in the intact femora were measured and there were no significant differences in principal tensile and compressive strains in the left and right femora of each pair. The two types of femoral stem were then inserted randomly into the left or right femora and the cortical strains were again measured. Both induced significant stress shielding in the proximal part of the metaphysis, but the deviation from the physiological strains was most pronounced after insertion of the anatomical stems. The principal compressive strain at the calcar was reduced by 90% for the anatomical stems and 67% for the customised stems. Medially, at the level of the lesser trochanter, the corresponding figures were 59% and 21%. The anatomical stems induced more stress concentration on the anterior aspect of the femur than did the customised stems. They also increased the hoop strains in the proximomedial femur. Our study shows a consistently more physiological pattern of strain in the proximal femur after insertion of customised stems compared with standard, anatomical stems.