Rapid and reliable healing of critical size bone defects with genetically modified sheep muscle.

Large segmental defects in bone fail to heal and remain a clinical problem. Muscle is highly osteogenic, and preliminary data suggest that autologous muscle tissue expressing bone morphogenetic protein-2 (BMP-2) efficiently heals critical size defects in rats. Translation into possible human clinical trials requires, inter alia, demonstration of efficacy in a large animal, such as the sheep. Scale-up is fraught with numerous biological, anatomical, mechanical and structural variables, which cannot be addressed systematically because of cost and other practical issues. For this reason, we developed a translational model enabling us to isolate the biological question of whether sheep muscle, transduced with adenovirus expressing BMP-2, could heal critical size defects in vivo. Initial experiments in athymic rats noted strong healing in only about one-third of animals because of unexpected immune responses to sheep antigens. For this reason, subsequent experiments were performed with Fischer rats under transient immunosuppression. Such experiments confirmed remarkably rapid and reliable healing of the defects in all rats, with bridging by 2 weeks and remodelling as early as 3-4 weeks, despite BMP-2 production only in nanogram quantities and persisting for only 1-3 weeks. By 8 weeks the healed defects contained well-organised new bone with advanced neo-cortication and abundant marrow. Bone mineral content and mechanical strength were close to normal values. These data demonstrate the utility of this model when adapting this technology for bone healing in sheep, as a prelude to human clinical trials.

Use of genetically modified muscle and fat grafts to repair defects in bone and cartilage.

We report a novel technology for the rapid healing of large osseous and chondral defects, based upon the genetic modification of autologous skeletal muscle and fat grafts. These tissues were selected because they not only possess mesenchymal progenitor cells and scaffolding properties, but also can be biopsied, genetically modified and returned to the patient in a single operative session. First generation adenovirus vector carrying cDNA encoding human bone morphogenetic protein-2 (Ad.BMP-2) was used for gene transfer to biopsies of muscle and fat. To assess bone healing, the genetically modified ("gene activated") tissues were implanted into 5mm-long critical size, mid-diaphyseal, stabilized defects in the femora of Fischer rats. Unlike control defects, those receiving gene-activated muscle underwent rapid healing, with evidence of radiologic bridging as early as 10 days after implantation and restoration of full mechanical strength by 8 weeks. Histologic analysis suggests that the grafts rapidly differentiated into cartilage, followed by efficient endochondral ossification. Fluorescence in situ hybridization detection of Y-chromosomes following the transfer of male donor muscle into female rats demonstrated that at least some of the osteoblasts of the healed bone were derived from donor muscle. Gene activated fat also healed critical sized defects, but less quickly than muscle and with more variability. Anti-adenovirus antibodies were not detected. Pilot studies in a rabbit osteochondral defect model demonstrated the promise of this technology for healing cartilage defects. Further development of these methods should provide ways to heal bone and cartilage more expeditiously, and at lower cost, than is presently possible.

The apparent elastic modulus of the juxtarticular subchondral bone of the femoral head.

An experiment was undertaken to obtain approximate values for the intrinsic elastic modulus of subchondral bone. Shallow spherical caps, with uniform and incrementally controlled thickness, were machined from subchondral bone in the weight-bearing regions of 11 fresh-frozen normal femoral head autopsy specimens. Under application of polar point loads, the measured deflections were compared with a corresponding analytical shell solution, thus allowing back-calculation of the apparent modulus. Analogous tests were performed on similarly shaped specimens of stock Plexiglas of known modulus in order to estimate the precision of the testing method. The aggregate results for subchondral bone showed that its intrinsic stiffness correlated inversely with nominal shell thickness, but even the thinnest (1.0 mm thick) of these shells had an apparent modulus (mean = 1.372 GN/m2, SD = 414 MN/m2) well below that generally accepted for "pure" cortical bone (about 14 GN/m2). This stiffness deficit was very likely due to the presence of histologically evident marrow spaces. However, the low apparent modulus values measured in this study may not be fully representative of complex in vivo behavior, because in the testing of excised shells there is no radial compressive stress transfer to underlying cancellous bone.

Method to impact in vivo rabbit femoral cartilage with blows of quantifiable stress.

The purpose of this study was to develop a technique by which a known stress could be applied uniformly across the femoral cartilage of a rabbit as a model for the development of post-traumatic arthritis. A system to impact the cartilage was designed that consisted of an apparatus to deliver a blow of quantifiable force, a method to apply the stress uniformly over the impact area, and a way to accurately measure the impact area. The knee joints of cadaveric New Zealand White rabbits were surgically exposed with the knee flexed so that the distal femoral articular surface was perpendicular to an impactor. With the knee fixed in position, a cup containing polymethylmethacrylate bone cement was applied to create an exact contour of the femoral surface, and the cement was allowed to cure. The form was then rested on the rabbit knee, and a drop tower released a weight of known mass from a known height onto an impactor (instrumented with strain gauges to measure the compressive force) that was attached to the cup. The area of the impacted surface was determined and, with the measured force, was used to calculate an accurate estimate of the impact stress. This method can be performed under sterile conditions, and therefore it is well suited for survival experiments in which the long-term effects of impact to cartilage will be studied.

The effects of simulated transverse, anterior column, and posterior column fractures of the acetabulum on the stability of the hip joint.

BACKGROUND: Knowledge of the location of the weight-bearing portion of the acetabulum would assist orthopaedic surgeons in the treatment of acetabular fractures. With use of controlled experimental transverse, anterior column, and posterior column osteotomies, we investigated the weight-bearing region of the acetabulum. METHODS: Twenty-four fresh-frozen cadaveric hip joints were tested. Simulated transverse fractures were evaluated in twelve specimens, and simulated anterior column and posterior column fractures were tested in six specimens each. Each femur and acetabulum was potted and mounted in an aluminum fixture, with the acetabulum positioned in 25 degrees of flexion and 20 degrees of abduction. Each specimen was tested intact and after successive osteotomies. The transverse osteotomies had roof-arc angles of 60, 50, 40, and 30 degrees. The anterior column and posterior column osteotomies were classified as very low, low, intermediate, or high. Compressive loading to 800, 1200, and 1600 newtons was performed four times for each intact specimen and after each osteotomy. A specimen was considered to be stable if no gross dislocation occurred during any of the four loading cycles. Translation of the femur within the acetabulum also was measured during each trial. RESULTS: The number of stable specimens decreased both with higher applied loads and with more superior osteotomies. The stability of the hip was significantly affected by both the location of the fracture and the magnitude of the applied load (p < 0.00005). Translation of the femur within the acetabulum increased with higher applied loads and with more superior osteotomies. CONCLUSIONS: Fractures that have a medial roof-arc angle of 45 degrees or less, an anterior roof-arc angle of 25 degrees or less, or a posterior roof-arc angle of 70 degrees or less cross the weight-bearing portion of the acetabulum and necessitate operative treatment.

Contribution of passive tissues to the intersegmental moments at the hip.

Many anatomic structures around the hip contribute either actively (i.e., muscle contractile elements) or passively (i.e., capsule, ligaments, non-contractile portions of muscles) to the intersegmental resultant forces and moments. Investigators have often assumed that the passive elements contribute negligibly to those moments, but without substantial supporting data. We explored this assumption by measuring the 'passive moments' in 15 normal subjects from near full extension to 60 degrees of hip flexion at speeds used in slow and normal walking. The data suggest that throughout most of the gait cycle and normal stair climbing, the passive structures contribute a small portion of the total moment, usually well less than 10%. Thus, for this limited range of activities, the assumption of negligible contribution of passive structures is reasonable.

Perioperative lower urinary tract infections and deep sepsis in patients undergoing total joint arthroplasty.

Deep sepsis in the involved joint after hip or knee arthroplasty may be the result of hematogenous seeding from a remote infectious source. This mechanism has been used to explain the well-documented association between postoperative urinary tract infections and subsequent joint infection after hip or knee arthroplasty. However, it is unclear whether there is an association between preoperative bacteriuria and deep prosthetic infection. The purpose of this review is to identify perioperative risk factors associated with bacteriuria that have a positive correlation with deep joint sepsis following total hip or knee arthroplasty. The classic symptoms of dysuria, urgency, and frequency seen with urinary tract infections are often absent in the elderly despite the presence of urine coliforms; in these patients, pyuria (as indicated by the presence of more than 1x10(3) white blood cells per milliliter of noncentrifuged urine) may be used as a preliminary screening criterion. If there are irritative symptoms, the presence of more than 1x10(3) bacteria per milliliter of urine should be regarded as indicative of a urinary tract infection. If there is bacteriuria without symptoms of urinary irritation or obstruction, the current literature supports proceeding with total joint arthroplasty and treating those patients with urine colony counts greater than 1x10(3)/mL with an 8- to 10-day postoperative course of an appropriate oral antibiotic. Postponement of total joint surgery should be considered if preoperative evaluation reveals symptoms related to obstruction of the urinary pathway. Irritative symptoms in combination with a bacterial count greater than 1x10(3)/mL should also serve as an indication to postpone surgery. To diminish postoperative urinary tract infection, a bladder catheter should be inserted immediately preoperatively and removed within 24 hours of surgery to diminish the risk of urinary retention, which has been shown to increase the likelihood of a postoperative urinary tract infection.

Surgical approaches to the acetabulum.

This article presents a concise outline of the indications, surgical techniques, and approaches to the acetabulum: Kocher-Langenbeck approach, ilioinguinal approach, iliofemoral approach, combined approaches, extended iliofemoral approach, and the triradiate approach. No one surgical appproach is ideal for all fractures of the acetabulum. The type of approach used is determined by the fracture pattern and condition of the soft tissues in the area under consideration.

Effect of intraarticular stainless steel implants on the health of the rabbit knee joint: an experimental study.

OBJECTIVE: This study was designed to investigate the histologic changes to the knee joints of rabbits after insertion of a metal implant in retrograde fashion. DESIGN: Eighteen rabbits had a modified stainless steel screw implanted in one knee, with the other knee serving as a sham-operated control. The animals were killed after two, six, or twelve months. OUTCOME MEASURES: The histologic status of the cartilage and synovium were graded by the Modified Mankin and Mirra criteria, respectively. RESULTS: At the time of killing, every insertion site was covered by fibrous tissue. Statistical analysis showed no significant differences in histologic scores between implanted and control knees. CONCLUSIONS: Insertion of a stable, well-fixed implant results in no deleterious effect to the knee joint.

Damage to rabbit femoral articular cartilage following direct impacts of uniform stresses: an in vitro study.

OBJECTIVE: To determine the acute gross and histologic damage resulting to femoral cartilage from an in vitro direct impact of uniform stress. DESIGN: Gross and histologic evaluations were performed on rabbit femoral condyles impacted by a drop-tower device. BACKGROUND: It is thought that impacts above a given threshold stress may initiate post-traumatic arthritis. The extent of damage following impacts of specific stress has not been previously studied. METHODS: 12 New Zealand White rabbit medial femoral condyles were divided into three groups by impact type and magnitude. A drop tower was used to strike the femoral condyle with a flat impactor, or with a custom contoured impactor. Gross and histological grades were given depending on the depth and number of fissures and cracks in the impacted condyle. RESULTS: The degree of damage correlated best with the type of impactor used and with the impact force; correlation between damage and impact stress was less significant. Contoured impactors tended to produce superficial fibrillation, while flat impactors tended to produce deep cracks. Impact forces above 500 N tended to create more severe damage than impact forces below 500 N. Subchondral bone remained intact in all cases and deep cartilage damage did not occur without disruption of more superficial layers. Poor correlation was found between damage as graded by gross examination versus damage graded histologically. CONCLUSIONS: Acute damage corresponds best with type of impactor and impact force, and not as well with impact stress. Micro structural injuries may be present in the absence of gross findings. RELEVANCE: Post-traumatic arthritis is a disabling disease thought to occur when a blow of stress above a given threshold is delivered to articular cartilage. Current animal models of post-traumatic arthritis are unable to characterize the impact stress applied to an articular surface. This study examines grossly and histologically the structural damage occurring as a result of impacts of given stress and force.

The Thomas splint. Questionable boast of an indispensable tool.

The Thomas splint has been used since the late 1800s. During World War I, physicians began using it for the acute management of femoral fractures and attributed its use to reduced mortality associated with these injuries. However, articles differ as to the actual percentage of mortality reduction. Even though these discrepancies exist, the Thomas splint has been useful and is still used today, especially for patient transport while awaiting definitive management.

The effect of knee immobilization on degree of hip flexion: a clinical correlation with posterior wall acetabular fractures.

The purpose of this investigation was to determine whether maintaining the knee in extension substantially limits hip flexion. The dominant lower extremity in 22 male subjects was goniometrically evaluated to determine hip flexion both when the knee was allowed to flex and when the knee was held in extension. Pelvic rotation values were subtracted from thigh rotation values to show true flexion of the femur in relation to the pelvis. Hip flexion averaged 49.25 degrees +/- 9.08 degrees in the straight-leg raise test and 94.14 degrees +/- 4.94 degrees in the flexed-knee raise test. This study shows that using a knee immobilizer in the postoperative treatment of posterior wall acetabular fractures should serve to protect the fracture site while still affording early ambulation.

Arthroscopic management of tibial plateau fractures: an unselected series.

The present series reports the results of arthroscopically assisted fixation of tibial plateau fractures. No effort was made to include or exclude any specific fracture type from the all-arthroscopic reduction technique. Fourteen of 17 tibial plateau fractures treated arthroscopically, with an average follow-up of 14.6 months (range, 5-30 months), were retrospectively evaluated. The average patient age was 43 years (range, 25-65 months). The average knee range of motion obtained was 5 degrees-126 degrees, with 9 of 14 patients regaining full symmetric motion. The Lysholm scale was administered to this group with 5 (36%) receiving an excellent rating, 6 (43%) receiving a good rating, and 3 (21%) receiving a poor rating. Two patients experienced complications: one had painful hardware requiring removal, and the other had an infection that resolved after appropriate treatment. The present report advances the treatment of tibial plateau fractures by documenting the feasibility of the arthroscopic management of many fracture types.

Prophylaxis of deep vein thrombosis in trauma patients.

Orthopedists who use prophylaxis for deep vein thrombosis (DVT) in total joint arthroplasty are often called on to care for trauma patients. Much less is known or published about the effects of such prophylaxis in the trauma patient than in the arthroplasty patient. The questions to ask are: what is the incidence of DVT in trauma patients; what are the benefits of DVT prophylaxis; and what are the risks of DVT prophylaxis, and do the risks outweigh the benefits?

A simple method to measure compartment pressures using an intravenous catheter.

A simple method was investigated to measure compartment pressures using 16-ga intravenous catheters with or without side ports attached by arterial line tubing to a pressure transducer. Pressure measurements from the experimental catheters were within 4 mm Hg of the slit catheter for 99% of all readings, and pressure measurements from the Stryker device were within 5 mm Hg of the slit catheter for 95% of all readings. The addition of one or two side ports to the experimental catheters did not alter the pressure readings. This method is comparable in accuracy to the slit catheter and in simplicity to the Stryker device.

Comparison of fixation methods for preventing pelvic ring expansion.

Several methods of external and internal fixation are used in urgent situations to lessen intrapelvic bleeding associated with unstable pelvic fractures. Pelvic stabilization limits pelvic expansion and thereby restricts the space for potential blood loss. This study compared several fixation methods using cadaveric pelves to determine which method best prevents pelvic expansion. Three methods of internal fixation and three methods of external fixation were compared. Anteroposterior fixation provided the greatest control against pelvic expansion; however, it is clinically impractical for emergency use. Therefore, external fixation provided the most reliable control of pelvic expansion in the emergency setting.

Delayed administration of adenoviral BMP-2 vector improves the formation of bone in osseous defects.

The direct, local, administration of adenovirus carrying human BMP-2 cDNA (Ad.BMP-2) heals critical-sized femoral bone defects in rabbit and rat models. However, the outcome is suboptimal and the technology needs to provide a more reliable and uniform outcome. To this end, we investigated whether the timing of Ad.BMP-2 administration influenced the formation of mineralized tissue within the defect. Critical-sized defects were created in the femora of 28 Sprague-Dawley rats. Animals were injected intralesionally with a single, percutaneous injection of Ad.BMP-2 (4 x 10(8) plaque-forming units) either intraoperatively (day 0) or 24 h (day 1), 5 days or 10 days after surgery. The femora were evaluated 8 weeks after surgery by X-ray, microcomputed tomography, dual-energy X-ray absorptiometry and biomechanical testing. The incidence of radiological union was markedly increased when administration of Ad.BMP-2 was delayed until days 5 and 10, at which point 86% of the defects healed. These time points also provided greater bone mineral content within the defect site and improved the average mechanical strength of the healed bone. Thus, delaying the injection of Ad.BMP-2 until 5 or 10 days after surgery enables a greater percentage of critical-sized, segmental defects to achieve radiological union, producing a repair tissue with enhanced mineralization and greater mechanical strength.

Pressure-volume characteristics of the intact and disrupted pelvic retroperitoneum.

Hemorrhage is a major cause of mortality in pelvic fractures. Bleeding can be controlled in hypotensive patients by direct ligation, angiographic embolization, pelvic packing, and acute external fixation. Acute application of an external fixator can reduce pelvic volume and reduce bleeding fractures to effect tamponade. This therapy assumes that the pelvis represents a closed space, which clearly is not true anatomically. However, the premise may hold functionally. This study explored the relationship between pressure and volume in the intact and disrupted pelvic retroperitoneum. In cadaveric specimens, the external iliac vein was dissected, ruptured, and cannulated. This method allowed controlled flow of fluid, with simultaneous measurement of pressure, into the intact retroperitoneum. Open book pelvic fractures were created by applying external rotation to the pelvis through the femoral heads. The pressure-volume measurements, without and with external fixation applied, were repeated after the fracture, as well as after a laparotomy. In the intact retroperitoneum, pressures rapidly rose to an average of 30 mm Hg after infusion of 5 liters of fluid. After fracture, up to 20 liters of fluid could be infused at pressures not exceeding 35 mm Hg. External fixation increased pressures approximately 3 mm Hg at low fluid volumes, and approximately 11 mm Hg at the highest fluid volumes. Laparotomy decreased retroperitoneal pressure from approximately 35 mm Hg to approximately 15 mm Hg. The results of the study suggest that low-pressure venous hemorrhage may be tamponaded by an external fixator, given that enough fluid volume is present in the pelvic retroperitoneum. However, external fixation may not generate sufficient pressure to stop arterial bleeding. In any case, it seems that a large volume of fluid must be lost into the pelvis before an external fixator can have much effect on retroperitoneal pressures.

Dysplasia epiphysealis hemimelica of the sacroiliac joint: a case report.

Dysplasia epiphysealis hemimelica is a rare developmental abnormality involving aberrant epiphyseal cartilage growth. This is the first known case report describing dysplasia epiphysealis hemimelica arising from the sacroiliac joint. The operative technique described through an indirect computed tomography guided approach limited the exposure and potential morbidity involving the sacroiliac joint.