Mark Walton

Fat embolism and acute hypotension during vertebroplasty: an experimental study in sheep.

Study Design. An experimental study of cardiovascular complications that arise during vertebroplasty was conducted. Objective. To investigate the sequential occurrence of fat embolism and hypotension during vertebroplasty. Summary of Background Data. Vertebroplasty, the augmentation of vertebrae with polymethylmethacrylate, is a technique for treating osteoporotic compression fractures and achieving prophylactic stabilization of osteoporotic vertebral bodies at risk of fracture. However, there is concern that fat embolism and acute hypotension could occur as in a variety of other orthopedic procedures. Methods. In six sheep, 6 mL of polymethylmethacrylate was injected unilaterally into L1. Transesophageal echocardiography monitored the pulmonary artery for echodense particles. Heart rate, arterial and venous pressures, and blood gas values were recorded before and for 25 minutes after injection. The lungs were subjected to postmortem histologic evaluation and compared with lung specimens from two sheep that had not undergone vertebroplasty. Results. Injection of cement elicited a very rapid decrease in heart rate (within 2 ± 1 seconds) and a rapid increase in venous pressure (within 3 ± 1 seconds), which was followed by a fall in arterial pressure (within 5 ± 2 seconds) (phase 1). Thereafter, showers of echogenic material appeared (within 6 ± 1 seconds) and lasted for 138 ± 36 seconds. A second more severe fall in arterial pressure was observed beginning at 18 ± 2 seconds (phase 2). The injection resulted in an increase in partial pressure of carbon dioxide and a decrease in pH. The histology showed intravascular fat globules and bone marrow cells in lung tissue. Conclusions. The results suggest that immediately after cement injection, there was a reflex fall in heart rate and arterial pressure. The second fall in arterial pressure was a consequence of fat emboli passing through the heart and getting trapped in the lungs.

Long-term in vivo Degradation of Poly-L-lactide (PLLA) in Bone

The use of absorbable orthopedic implants has increased substantially during the last decade. Currently, most of them are fabricated from poly-L-lactide (PLLA), its co-polymers, or mixtures with other constituents. In vivo, PLLA persists for years after its surgical role has ended, which is confirmed by a long-term histological study of PLLA implanted in sheep either as functional interference screws or nonfunctional rods. The first tissue reaction is the sequestration of the implant within new bone during the initial 3 months. After a nonreactive period, a second tissue reaction is associated with the early signs of structural disintegration of the PLLA at 1 year. Subsequently, as the polymer mass reduces, it is replaced by a relatively avascular fibrous tissue containing macrophages and having an occasional multinucleated giant cell on the implant surface. After 3 years much of the polymer is still present, although as isolated fragments. The tissue reactions can be explained in terms of the physical chemistry of PLLA degradation. Though biocompatible, the excessive longevity of PLLA and the absence of its replacement by bone, indicates that despite being satisfactory clinically, it is not an ideal implant material, and that improved absorbable materials need to be developed.

Bone thickening in osteoarthrosis. Observations of an osteoarthrosis-prone strain of mouse.

Estimations were made of the amount of bone (histologically) and the rate of bone formation (85Sr incorporation) in the epiphyses of the knees of osteoarthrosis-prone (STR/ORT) and normal (CBA/ORT) mice. Though the bone was significantly thicker in the STR/ORT mice, this was not the cause of the articular degeneration. Bone sclerosis and cartilage breakdown were chronologically very closely related with perhaps the cartilage changes occurring initially. In male STR/ORT mice bone formation was depressed in the cancellous bone of the epiphyses as, unlike the normal mice, it was at the same level as the compact bone of the femoral shaft. As there was no elevation of the osteoblastic activity in knee joints with developing osteoarthrosis, it would appear that bone sclerosis associated with the disease was due to decreased osteoclasis.

Cell Structure and Biology of Bone and Cartilage

Bone and cartilage are highly specialized connective tissues that are engineered by nature to perform a variety of specialized tasks. As a result, these tissues have unique cellular constituents and ultrastructural organization that help optimize the biochemical demands and biomechanical loads in vivo. Our understanding of these connective tissues has increased over the past few centuries, and progress continues as techniques are defined and improved or new ones are developed. The understanding of the ultrastructural and mechanical properties of bone and cartilage is a dynamic area that is constantly evolving with new understanding. This chapter departs from traditional overviews of bone and cartilage, and presents an examination of cellular constituents and ultrastructural organization of these tissues in the context of recent experimental and theoretical studies. It is the hope of the authors to bring to light many new and exciting findings.

Interleukin-6 as an early marker for fat embolism

BackgroundFat Embolism is a complication of long bone fractures, intramedullary fixation and joint arthroplasty. It may progress to fat embolism syndrome, which is rare but involves significant morbidity and can occasionally be fatal. Fat Embolism can be detected at the time of embolization by transoesophageal echocardiography or atrial blood sampling. Later, a combination of clinical signs and symptoms will point towards fat embolism but there is no specific test to confirm the diagnosis. We investigated serum Interleukin-6 (IL-6) as a possible early marker for fat embolism.MethodsAn animal study was conducted to simulate a hip replacement in 31 adult male Sprague Dawley rats. The procedure was performed under general anesthesia and the animals divided into 3 groups: control, uncemented and cemented. Following surgery and recovery from anaesthesia, the rats allowed to freely mobilize in their cages. Blood was taken before surgery and at 6 hours, 12 hours and 24 hours to measure serum IL-6 levels. The rats were euthanized at 24 hours and lungs removed and stained for fat. The amount of fat seen was then correlated with serum IL-6 levels.ResultsNo rats in the control group had fat emboli. Numerous fat emboli were seen in both the uncemented and cemented implant groups. The interleukin levels were raised in all groups reaching a peak at 12 hours after surgery reaching 100 pg/ml in the control group and around 250 pg/ml in the uncemented and cemented implant groups. The IL-6 levels in the control group were significantly lower than any of the implant groups at 12 and 24 hours. At these time points, the serum IL-6 correlated with the amount of fat seen on lung histology.ConclusionSerum IL-6 is a possible early marker of fat embolism.

Sildenafil Attenuates Pulmonary Hypertension Following Fat Embolism in an Anaesthetised Rat Model

Release of fat and bone marrow during medullary pressurisation leads to fat embolism and pulmonary hypertension resulting in serious cardiorespiratory complications. This study aimed to determine whether pre-treatment with the phosphodiesterase type 5-inhibitor, Sildenafil, prevents pulmonary artery hypertension in an animal model. The animals either received Sildenafil (5 mg kg-1) or saline intra peritoneally 15 minutes prior to medullary pressurisation with bone cement. Cardiovascular parameters were recorded throughout the procedure. At the end radiopaque contrast was injected into the pulmonary circulation; the lungs were then harvested and imaged using micro CT. Medullary pressurisation in the control animals caused pulmonary hypertension and systemic hypotension. This was associated with a decrease in the area of perfusion of the lungs. These changes were attenuated by pretreatment with Sildenafil. We conclude that in this animal model fat embolism causes similar cardiovascular changes as observed in clinical practice and pretreat- ment with Sildenafil attenuates these effects.

FlaCeramic-loaded mineralizing bioresorbable polymers for orthopaedic applications

Bioresorbable polymers are widely used in biomedical applications, for example in surgical sutures and orthopaedic screws. One class of these materials is broadly based on poly(lactide)-poly(glycolide) copolymers, whose proportions govern the rate of physiological resorption. One difficulty encountered in implantation of resorbable polymers into bone is local acidification as the polymer breaks down and the body mounts an inflammatory response. Another is that resorbable polymers are usually neither bioactive nor osteoconductive. This presentation explores a novel bioresorbable polymer-inorganic particulate composite implant that both buffers local acidity and promotes osteoconductive replacement of the implant by bone over a one-year time span.