Per Aspenberg

Fluid flow is important in many biomechanical models, but there is a lack of experimental data that quantifies soft tissue permeability. We measured the tissue permeability in fibrous soft tissue, using a novel technique to obtain specimens by allowing soft tissue to grow into coralline hydroxyapatite scaffoldings implanted between the abdominal muscle layers of rats.

Animal experiments show a dramatic improvement in skeletal repair by teriparatide. We tested the hypothesis that recombinant teriparatide, at the 20 µg dose normally used for osteoporosis treatment or higher, would accelerate fracture repair in humans. Postmenopausal women (45 to 85 years of age) who had sustained a dorsally angulated distal radial fracture in need of closed reduction but no surgery were randomly assigned to 8 weeks of once‐daily injections of placebo (n = 34) or teriparatide 20 µg (n = 34) or teriparatide 40 µg (n = 34) within 10 days of fracture. Hypotheses were tested sequentially, beginning with the teriparatide 40 µg versus placebo comparison, using a gatekeeping strategy. The estimated median time from fracture to first radiographic evidence of complete cortical bridging in three of four cortices was 9.1, 7.4, and 8.8 weeks for placebo and teriparatide 20 µg and 40 µg, respectively (overall p = .015). There was no significant difference between the teriparatide 40 µg versus placebo groups (p = .523). In post hoc analyses, there was no significant difference between teriparatide 40 µg versus 20 µg (p = .053); however, the time to healing was shorter in teriparatide 20 µg than placebo (p = .006). The primary hypothesis that teriparatide 40 µg would shorten the time to cortical bridging was not supported. The shortened time to healing for teriparatide 20 µg compared with placebo still may suggest that fracture repair can be accelerated by teriparatide, but this result should be interpreted with caution and warrants further study. © 2010 American Society for Bone and Mineral Research

(2009). Black holes in bone – irresistible attractors of foreign materials? Acta Orthopaedica: Vol. 80, No. 1, pp. 2-3.

(2008). Bisphosphonate-induced fractures: Nature strikes back? Acta Orthopaedica: Vol. 79, No. 4, pp. 459-460.

Roentgen stereometric analysis (RSA) cannot discern whether a single prosthesis is fixed or migrating below the detection level. Samples of patients usually show migration values that appear to be continuously distributed. Is there such continuity, or is there a dichotomy between stable and migrating prostheses? The hypothesis of a dichotomy has, to our knowledge, not been tested. We present an exploratory evaluation of such a dichotomy using a mixture distribution algorithm. We analyzed the migration (as determined by RSA) of 147 cemented acetabular cups of 7 different designs by using a new set of algorithms for frequency distribution analysis called Rmix. We first analyzed a migration vector, regardless of direction. After 2 years there was a significant dichotomy between 2 lognormal subgroups within the sample. Although some types of cups were over-represented in one of the subgroups, neither cup design, sex, nor operating department could explain the dichotomy into two groups, which appears to reflect the existence of two basically different types of behavior of the cups. We next analyzed the migration along the 3 axes in space, and found a similar dichotomy. During the second year, around 80% of the patients belonged to a distinct, normally distributed subgroup with a mean not different from 0 mm and a small variation. The remainder differed significantly from this subgroup and showed migration. There is a dichotomy in migration pattern. During the second postoperative year, most cups belonged to a subpopulation that appeared stable. The remainder is probably at risk of loosening. For a single type of prosthesis, the relative size of the stable subgroup may be a good index of the expected performance. The possibility of detecting subgroups within a seemingly continuous sample might be useful in many fields of medicine.

After resection and repair of the intestines, tissue degradation leads to weakening of the repair site and risk of postoperative leakage. Matrix metalloproteinases (MMPs) are thought to be responsible for collagenolysis in the direct vicinity of surgical sutures in many tissues. Several experimental studies show that MMP inhibitors administered systemically alleviate postoperative weakening of intestinal anastomoses. We hypothesised that local delivery of MMP inhibitors would achieve a similar effect. Implementing a novel method for the coating of biomaterials, we coated sutures with a cross-linked fibrinogen film and bound the MMP inhibitor doxycycline into this film. The sutures were then used in a standard rat model for evaluating mechanical properties of colonic anastomoses 3 days after surgery. The breaking strength of the anastomoses on the critical third day after operation was 17% higher with doxycycline-coated sutures compared to controls (P = 0.026). Energy uptake at failure was enhanced by 20% (P = 0.047). Drug delivery by means of MMP-inhibitor-coated sutures appears to improve tissue integrity during anastomotic repair and may reduce postoperative complications.

There are presently few methods described for in vivo monitoring of the mechanics of healing human tendon ruptures, and no methods for prediction of clinical outcome. We tested if Roentgen stereophotogrammetric analysis (RSA) can be used to follow the restoration of mechanical properties during healing of ruptured Achilles tendons, and if early measurements can predict clinical results.