Michael Mørk Petersen

Effect of external hip protectors on hip fractures

Most hip fractures seem to be related to trauma near the hip, so a controlled trial was conducted to investigate the effect of external hip protectors on the prevention of such fractures in residents of a nursing home. 10 of the 28 wards in the nursing home were randomised to receive external hip protectors; thus 167 women and 80 men were given protectors and 277 and 141 men no protectors. A fall register was set up for 2 treatment wards (45 residents) and 2 control wards (76 residents). There were 8 hip and 15 non-hip fractures in the hip-protector group and 31 hip and 27 non-hip fractures in the control group. The relative risk of hip fractures among women and men in the intervention group was 0.44 (95% CI 0.21-0.94). None of the 8 residents in the intervention group who had a hip fracture was wearing the device at the time of the fracture. 154 falls were registered and 20% of these falls produced a direct impact to the hip. In 25 falls direct impact to the hip was sustained at a time when hip protectors were not being worn, and 6 fractures were produced. The study indicates that external hip protectors can prevent hip fractures in nursing-home residents.

Changes in bone mineral density of the distal femur following uncemented total knee arthroplasty

The aim of the study was to quantitate changes in bone mineral density (BMD) in the distal femur following uncemented porous-coated total knee arthroplasty. Eight patients with total knee arthroplasties (PCA Primary, Howmedica, Rutherford, NJ) (female:male ratio, 6:2; mean age, 70 years; range, 51-77 years) were scanned by dual-photon absorptiometry within 3 months after surgery and at 2 years. An average decrease of 36% (P = .01) was found in BMD behind the anterior flange of the femoral prosthesis. Proximal to the fixation pegs, BMD increased by 22% (P = .12), but behind the posterior flange of the femoral component, BMD remained unchanged (P = .53). Stress shielding anteriorly in the distal femur occurred in all patients examined 2 years after surgery, and the increase in BMD proximal to the fixation pegs was probably a result of increased and altered mechanical loading.

Changes in bone mineral density of the proximal tibia after uncemented total knee arthroplasty A 3-year follow-up of 25 knees

We measured bone remodeling of the proximal tibia prospectively for 3 years after uncemented total knee arthroplasty (TKA) in 25 knees with primary arthrosis. In the trabecular bone below the tibial component, bone mineral density (BMD) was measured in 6 different regions of interest (ROI), using dual photon absorptiometry (DPA). In the tibial condyles, where the change in knee alignment indicated that the load was reduced postoperatively, a fast bone loss of 7-20% was seen during the first 6 months after surgery. A small, but significant increase in BMD of 2-7% was seen in the tibial condyles, where the load was increased. On average, the density for all ROI below the tibial component showed a significant and progressive decrease in BMD, reaching 22% at 3 years follow-up.

Preoperative Bone Mineral Density of the Proximal Tibia and Migration of the Tibial Component After Uncemented Total Knee Arthroplasty

Twenty-two patients with primary osteoarthrosis of the knee all operated on with insertion of an uncemented total knee arthroplasty had a preoperative measurement of bone mineral density (BMD) in the coronal plane of the proximal tibia performed by dual-photon absorptiometry. Postoperatively and with follow-up after 6 weeks (n = 21), 1 year (n = 22), and 3 years (n = 19), radiographs suitable for radiostereometric analysis of the tibial component migration were obtained. One year postoperatively, stress examinations were performed with the aim of measuring inducible displacement of the tibial component. Most of the migration, expressed as maximal total point motion (MTPM), occurred during the first year with an average migration of approximately 1 mm. Regression analysis showed a positive relation between BMD and MTPM after 6 weeks (P = .03, r = .47), 1 year (P = .0005, r = .68), and 3 years (P = .02, r = .54). Inducible displacement did not reveal any significant relation to BMD. MTPM between 1 and 3 years, which is the clinically most important parameter with respect to later loosening of the tibial component, showed a negative relation to BMD (P = .04, r = -.47). Thus, tibial components of knees with preoperative high tibial BMD showed less continuous migration.

Decreased bone density of the distal femur after uncemented knee arthroplasty: A1 -year follow-up of 29 knees

We measured the early adaptive bone remodeling of the distal femur prospectively for 1 year after uncemented total knee arthroplasty (TKA) in 29 knees with primary arthrosis. 18 patients were randomized to receive a PCA Modular femoral component (n 9) or a modified version of the same prosthesis (n 9) with an altered location of the porous coating. The other 11 patients (n 11) formed a consecutive series with the Duracon femoral component. In the trabecular bone above the femoral component, bone mineral density (BMD) was measured in 2 regions of interest (ROI) anteriorly to the fixation pegs (ROI 1) and above the pegs (ROI 2), using dual photon absorptiometry (DPA). There were no differences between the Modular component and the modified version regarding the postoperative decrease in BMD. There was a decrease in BMD in both ROI 1 and ROI 2 with all 3 different femoral components, and in both ROIs the highest bone loss rate was observed during the first 3 months after surgery. On average (n 29), a significant bone loss of 44% and 19% in ROI 1 and ROI 2, respectively, was reached at the 1-year follow-up, compared to the initial values. A decrease of this magnitude in BMD in the anterior distal femur 1 year after TKA may be an important determinant of periprosthetic fracture and later failure of the femoral component. In this experimental set-up, a modified femoral component with an altered location of the porous coating did not influence the development of bone loss.

The Relation Between Trabecular Bone Strength and Bone Mineral Density Assessed by Dual Photon and Dual Energy X-Ray Absorptiometry in the Proximal Tibia

Abstract. The feasibility of two noninvasive methods [dual photon absorptiometry (DPA) and dual energy X-ray absorptiometry (DXA)] for prediction in vivo of local variations of trabecular bone strength within the proximal tibia was evaluated in 14 cadaveric knees. Trabecular bone strength was measured using an osteopenetrometer and from destructive compression tests performed on bone cylinders, thus measuring the penetration strength and ultimate strength in the medial, lateral, and central part of the tibial bone specimens. Linear regression analysis showed significant relations between BMD measured by DPA (r2= 72%) or DXA (r2= 73%) and ultimate strength. Even closer relations between BMD (DPA: r2= 80%, DXA r2= 81%) and penetration strength of trabecular bone were found. We conclude that DPA and DXA are suitable methods for evaluation in vivo of local variations in trabecular bone strength within the proximal tibia, and could easily be performed preoperatively before insertion of total knee arthroplasty.

Loss of bone mineral of the hip assessed by DEXA following tibial shaft fractures

We measured prospectively early changes (0-6 months) in bone mineral of the hip, the lumbar spine, and the tibia following tibial shaft fractures (n = 12), and in a cross-sectional study we evaluated the maximal amount of bone loss possible at the hip and tibia following long-term (average 3 years) impaired limb function as a consequence of complicated tibial shaft fractures [delayed union or nonunion (n = 7), chronic osteomyelitis (n = 5), decreased limb length (n = 1), or bone defect (n = 1)]. Bone mineral measurements were performed by dual energy X-ray absorptiometry. Following tibial shaft fractures, a significant decrease in bone mineral density (BMD) was seen at the hip reaching 7% [confidence limits (CL): -10.2%; -3.5%] and 14% (CL: -19.6; -7.8%) after 6 months for the femoral neck and greater trochanter, respectively. In the proximal tibia, bone mineral content (BMC) decreased and was 19% (CL: -27.4%; -9.9%) below the initial value after 6 months. BMD of the lumbar spine remained unchanged. In the cross-sectional study, BMC in the tibia of the injured legs was 43% (CL: -53.2%; -31.9%) below the value in the healthy contralateral legs, and BMD in the femoral neck and greater trochanter, respectively, was 22% (CL: -27.4%; -17.6%) and 24% (CL: -36.3%; -12.1%) below the values in the healthy contralateral legs. With respect to the expected age-related decay of bone mineral after peak bone mass, the loss of bone mineral of the hip and tibia associated with tibial shaft fractures may be considered of clinical importance with increased risk of sustaining a fragility fracture of the lower extremity later in life; and the complicated fractures may even represent a present risk of fracture.

Radiocarbon dating reveals minimal collagen turnover in both healthy and osteoarthritic human cartilage

The turnover of cartilage collagen matrix is minimal in human adults and is not influenced by disease. Cartilage claims a permament home It has long been debated for many tissues in our bodies whether they are permanent or constantly refreshed as we go through life. Nuclear bomb testing in the 1950s and 1960s released a large amount of the carbon-14 isotope into the atmosphere, giving researchers the ability to determine the age and turnover of human tissues, ranging from the heart to the brain to, now, the cartilage. Heinemeier and colleagues used this so-called “14C bomb pulse” method to date cartilage from 23 individuals ranging from 18 to 76 years of age. They examined cartilage from knee joints, taking samples from both highly and moderately loaded areas, in both healthy individuals and those with osteoarthritis. The authors discovered that the collagen matrix of human cartilage is essentially permanent, with no major replacement even with disease. This finding has important implications for the tissue engineering and regenerative medicine fields, where the structural permanence of collagen will need to be contemplated when designing new cartilage repair strategies. The poor regenerative capacity of articular cartilage presents a major clinical challenge and may relate to a limited turnover of the cartilage collagen matrix. However, the collagen turnover rate during life is not clear, and it is debated whether osteoarthritis (OA) can influence it. Using the carbon-14 (14C) bomb-pulse method, life-long replacement rates of collagen were measured in tibial plateau cartilage from 23 persons born between 1935 and1997 (15 and 8 persons with OA and healthy cartilage, respectively). The 14C levels observed in cartilage collagen showed that, virtually, no replacement of the collagen matrix happened after skeletal maturity and that neither OA nor tissue damage, per se, influenced collagen turnover. Regional differences in 14C content across the joint surface showed that cartilage collagen located centrally on the joint surface is formed several years earlier than collagen located peripherally. The collagen matrix of human articular cartilage is an essentially permanent structure that has no significant turnover in adults, even with the occurrence of disease.

Local control and survival in patients with soft tissue sarcomas treated with limb sparing surgery in combination with interstitial brachytherapy and external radiation

PURPOSE The purpose of this study was to evaluate local control, survival and complication rate after treatment of soft tissue sarcoma (STS) with limb-sparing surgery combined with pulsed-dose rate (PDR) interstitial brachytherapy (BRT) and external beam radiotherapy (EBRT). PATIENTS AND METHODS A retrospective review of 39 adult patients (female/male=25/14, mean age 51(range 21-78) years) with STS who underwent primary limb-sparing surgery combined with PDR BRT (20Gy) and additional post-operative EBRT (50Gy) during the years 1995-2004. RESULTS Five patients developed local recurrence after a mean follow-up of 3.4 (1.5-5.9) years. The probability of local recurrence free 5 years survival was 83%. At the time of follow-up 10 patients had died (mean follow-up 2.3 (0.8-7.1) years) and 29 patients were still alive (mean follow-up 5.9 (2.1-11.2) years). The overall 5-year survival rate was 76%. Nineteen (49%) patients suffered from some degree of decreased force or function of the affected extremity, 16 (41%) suffered from oedema, 12 (31%) had persistent pain, 8 (21%) suffered from wound complications, and in 4 (10%) of these patients plastic surgery were required. CONCLUSION Limb sparing surgery, combined with PDR BRT and EBRT can result in good local control in patients with soft tissue sarcomas. BRT is an effective modality with good cosmetic results and acceptable toxicity.

Influence of pre-operative bone mineral content of the proximal tibia on revision rate after uncemented knee arthroplasty

Between 1986 and 1991, 106 patients (127 knees) underwent uncemented knee arthroplasty for osteoarthritis. There were 106 total knee arthroplasties and 21 medial unicompartmental knee arthroplasties. The arthroplasties were evaluated for aseptic loosening during the year 2000. For total arthroplasty we used 77 porous-coated anatomic prostheses and 29 press-fit condylar prostheses. The mean bone mineral content of the proximal tibia, measured the day before surgery using dual-photon absorptiometry was 5.48 g/cm for the porous-coated anatomic prostheses which were revised for aseptic loosening (n = 9). This was significantly higher (p = 0.02) than the mean of 4.33 g/cm for those which were not revised. Values for the two revised press-fit condylar knees (4.78 and 4.93 g/cm) were above the mean value (4.23 g/cm) for those which were not revised. We found no statistically significant (p = 0.38) difference between the bone mineral content of the 12 revised and nine unrevised unicompartmental arthroplasties. Low trabecular bone quality, measured as the pre-operative bone mineral content of the proximal tibia, was not a predictor for later revision surgery following uncemented total knee or unicompartmental knee arthroplasty.