Which patients need critical care intervention after total joint arthroplasty? : a prospective study of factors associated with the need for intensive care following surgery.

Older patients with multiple medical co-morbidities are increasingly being offered and undergoing total joint arthroplasty (TJA). These patients are more likely to require intensive care support, following surgery. We prospectively evaluated the need for intensive care admission and intervention in a consecutive series of 738 patients undergoing elective hip and knee arthroplasty procedures. The mean age was 60.6 years (18 to 91; 440 women, 298 men. Risk factors, correlating with the need for critical care intervention, according to published guidelines, were analysed to identify high-risk patients who would benefit from post-operative critical care monitoring. A total of 50 patients (6.7%) in our series required critical care level interventions during their hospital stay. Six independent multivariate clinical predictors were identified (p < 0.001) including a history of congestive heart failure (odds ratio (OR) 24.26, 95% confidence interval (CI) 9.51 to 61.91), estimated blood loss > 1000 mL (OR 17.36, 95% CI 5.36 to 56.19), chronic obstructive pulmonary disease (13.90, 95% CI 4.78 to 40.36), intra-operative use of vasopressors (OR 8.10, 95% CI 3.23 to 20.27), revision hip arthroplasty (OR 2.71, 95% CI 1.04 to 7.04) and body mass index > 35 kg/m(2) (OR 2.70, 95% CI 123 to 5.94). The model was then validated against an independent, previously published data set of 1594 consecutive patients. The use of this risk stratification model can be helpful in predicting which high-risk patients would benefit from a higher level of monitoring and care after elective TJA and aid hospitals in allocating precious critical care resources.

Intensive care monitoring after total joint replacement.

Patient safety is a critical issue in elective total joint replacement surgery. Identifying risk factors that might predict complications and intensive care unit (ICU) admission proves instrumental in reducing morbidity and mortality. The institution's experience with risk stratification and pre-operative ICU triage has resulted in a reduction in unplanned ICU admissions and post-operative complications after total hip replacement. The application of the prediction tools to total knee replacement has proven less robust so far. This work also reviews areas for future research in patient safety and cost containment.

Biological and mechanical characteristics of the interface between a new swelling anchor and bone.

We recently evaluated the peak pullout loads for anchors made from our new copolymeric swelling-type material compared with anchors made of a nonswelling material. In vitro and in vivo peak pullout loads of these anchors were evaluated after different intervals of implantation in the lateral femoral condyles of New Zealand White rabbits. Scanning electron microscopy and energy dispersive x-ray analyses were additionally performed on selected retrieved samples after pullout to examine the characteristics of bone attachment to the implant. The mean peak pullout load was greater for the swelling anchors than for the nonswelling anchors after 48 hours in vitro (46.0 +/- 15.8 compared with 10.8 +/- 9.1 N, p = 0.0541). After 2 weeks in vivo, it was significantly greater for the swelling anchors than for the nonswelling controls (177.7 +/- 41.3 compared with 53.7 +/- 17.5 N, p = 0.0024). The peak pullout load was also greater for the swelling anchors after 8 weeks in vivo; however, this difference was less pronounced than at 2 weeks (101.8 +/- 35.0 compared with 58.9 +/- 9.7 N, p = 0.0508). Furthermore, the swelling implants tended to induce bone deposition at the bone-implant interface. Results from this investigation reveal that the new family of dynamic implants has potential for applications requiring fixation to cancellous or osteoporotic bone.

Reconstruction of the scapholunate ligament in a cadaver model using a bone-ligament-bone autograft from the foot.

This study is an investigation of a new procedure in which the scapholunate interosseous ligament (SLIL) is reconstructed using a bone-ligament-bone autograft from the foot. After investigation, the dorsal medial portion of the navicular-first cuneiform ligament (NFCL) was chosen for testing as a potential donor since it is similar in length and thickness to the SLIL and it is easily harvested with minimal potential donor site morbidity. Eight SLILs and NFCLs were harvested from fresh-frozen cadavers. Biomechanical extensometry testing was performed using an Instron 1000 machine. A 5-mm-wide central portion of the NFCL was tested since this width was compatible with the technical aspects of reconstructing the SLIL. Both ligaments were tested for elastic properties, including stiffness, load to failure, and deformation to failure. Mean length of the NFCL was 7.6 mm (range, 5.5-8.5 mm). Stiffness of the NFCL was 10.6 x 10(5) Nm (range, 8.0-13.0 Nm) compared with 14.4 x 10(5) Nm for the SLIL (range, 10.0-19.5 Nm). Peak load to failure for the NFCL was 1,980 N (range, 1,530-2,940 N) compared with 2,940 N for the SLIL (range, 1,780-4,050 N). Total elongation to failure for the NFCL was 2.50 mm (range, 1.7-3.2 mm) compared with 3.2 mm for the SLIL (range, 2.1-5.2 mm). Thus, the biomechanical characteristics of the NFCL were found to be very similar to those of the SLIL. Having established the biomechanical similarities of the 2 ligaments, we are currently using the NFCL to reconstruct the sectioned SLIL in a fresh-frozen cadaver model. Early results suggest that this procedure is feasible for restoration of normal kinematics of the wrist.

Biomechanical analysis of the effectiveness of in-line skating wrist guards for preventing wrist fractures.

The purpose of this investigation was to determine the effectiveness of commercially available wrist guards in preventing wrist fractures. Forty arms were harvested from 20 cadaveric specimens. The forearms from each cadaver, one with a wrist guard and one without a wrist guard, were then fractured using an instron Servohydraulic Material Testing System. The group of forearms tested to failure without wrist guards failed at an average force of 2245 N, while the group tested with wrist guards fractured at an average force of 2285 N, revealing no statistical difference. Similarly, observed fracture patterns were not noted to be different in the two groups. The in-line skating wrist guards tested were not effective in preventing wrist fractures under the experimental conditions of our study.

Bone fragility in transgenic mice expressing a mutated gene for type I procollagen (COL1A1) parallels the age-dependent phenotype of human osteogenesis imperfecta.

An inbred strain of transgenic mice that expressed a mutated gene for type I procollagen and that developed spontaneous fractures was used to study the effects of age on the phenotype of fragile bones. The mutated gene has been shown to cause depletion of type I collagen in the transgenic mice because it generated shortened pro alpha 1(I) chains that bound to and produced degradation of normal pro alpha 1(I) chains synthesized from the endogenous mouse COL1A1 gene. For this study, femurs from transgenic mice ranging in age from 0.5-24 months were examined. The results demonstrated that the level of expression of the transgene was independent of age. Femurs from the transgenic mice were more fragile than controls at 0.5 and 1.5 months, they were biomechanically normal at 6 months, and then they were more fragile at 24 months. The normal biomechanical properties of the bones from the transgenic mice at 6 months were accompanied by periosteal thickening of the bones together with an increase in the collagen content that was not associated with a proportional increase in mineral content. The results indicated that the effects of age, mechanical stress, and hormonal action produced a biological compensation for the mutated gene by either increasing collagen synthesis of bone, decreasing collagen degradation, or both. The biological compensation was apparently lost by 24 months when the outer diameters of the femurs were again less than in controls, the cortical thickness was about the same as in controls, and both the collagen and mineral contents were less than controls. The results demonstrated that bone fragility in the transgenic mice paralleled the age-dependent phenotype of human osteogenesis imperfecta. Therefore the transgenic mice appeared to be useful models for osteogenesis imperfecta. They also may be useful models for some forms of osteoporosis.

Splicing patterns of fibronectin mRNA from normal and osteoarthritic human articular cartilage.

Fibronectin, a large extracellular glycoprotein, mediates the interaction of cells with the extracellular matrix. Heterogeneity in the structure of fibronectin is largely due to the alternative splicing of three exons (IIIB, IIIA and V) during processing of the fibronectin primary transcript. Osteoarthritis, a degenerative disease of synovial joints, is characterized by a progressive loss of the articular cartilage eventually resulting in pain and loss of joint function. In contrast to the loss of most cartilage matrix proteins accompanying this process, osteoarthritic cartilage contains more fibronectin than disease-free cartilage. We examined the splicing patterns of fibronectin mRNA from adult human articular cartilage of normal and osteoarthritic joints by RNase protection (exon IIIA and exon IIIB) and reversed transcription-polymerase chain reaction (exon V) assays to determine whether or not the increased fibronectin content in osteoarthritic cartilage is also associated with differences in the splicing patterns of these three alternatively spliced exons. The results revealed no gross differences in splicing of these exons between the fibronectin mRNA isolated from adult human articular normal and osteoarthritic cartilage. Thus alterations in the structure of cartilage fibronectin do not appear to correlate with the increased level of fibronectin protein associated with osteoarthritis.

Medial collateral ligament injuries: evaluation of multiple signs, prevalence and location of associated bone bruises, and assessment with MR imaging.

PURPOSE: To investigate the multiple signs of medial collateral ligament (MCL) sprains, including the location and prevalence of associated bone bruises, and evaluate the accuracy of the criteria proposed for magnetic resonance (MR) imaging in grading these sprains. MATERIALS AND METHODS: MR images were evaluated for signs of MCL injury in 76 patients with MCL sprains and 25 asymptomatic volunteers. These signs were then correlated with standards used to determine MCL injury at clinical evaluation. The grade of MCL injury as determined with MR imaging criteria was compared with clinical findings. RESULTS: All signs demonstrated little interobserver variability and were specific. The most sensitive signs were fascial edema and loss of demarcation from adjacent fat. This MR imaging grading system was inaccurate for classification of grade 3 MCL tears and was only questionably accurate for grades 1 and 2. CONCLUSION: Multiple signs of MCL sprains on MR images have varying sensitivities. MR grading systems may not be accurate for classification of MCL injuries.

The effect of torque pressure on halo pin complication rates. A randomized prospective study.

At Thomas Jefferson University Hospital, 102 consecutive patients treated in a halo vest orthosis were randomized into one of two torque protocol groups based on their date of birth. The pins of patients who were born in even-numbered months were inserted with 8 inch-lbs of torque and those born in odd-numbered months were inserted with 6 inch-lbs. All patients were placed in an identical model halo using a standardized technique of application. The patients were followed prospectively, and all potential complications were evaluated by a member of the orthopedic attending staff, using protocols established at the onset of the study. Statistical analysis indicated no significant differences in halo pin loosening, infection, pain, or scarring between the torque protocols, but there was a trend toward a higher complication rate in the 8-inch-lbs group. There was no direct evidence of skull penetration in either group, and no patients developed a deep infection. Based on the results of this study, we conclude that insertion torque has no significant effect on halo pin complications within the ranges tested by this study. Our current protocol calls for routine insertion of halo pins with 6 inch-lbs of torque.

Diagnosis of osteomyelitis: utility of fat-suppressed contrast-enhanced MR imaging.

PURPOSE: To assess the value of fat-suppressed contrast material-enhanced magnetic resonance (MR) imaging in the diagnosis of osteomyelitis. MATERIALS AND METHODS: T1- and T2-weighted MR imaging was performed in 51 cases of suspected osteomyelitis. Nonenhanced and contrast-enhanced T1-weighted fat-suppressed MR images were also obtained. Three-phase bone scan results were available for 30 cases. Complicating clinical factors, including chronic osteomyelitis (n = 26), postoperative state (n = 17), and neuropathic disease of the foot (n = 5), were identified in 73% of cases. RESULTS: In the diagnosis of osteomyelitis, scintigraphy demonstrated a sensitivity of 61% and specificity of 33%. For nonenhanced MR imaging, sensitivity was 79% and specificity was 53%. For fat-suppressed contrast-enhanced imaging, sensitivity was 88% and specificity was 93%. CONCLUSION: In diagnosing osteomyelitis in patients with complicating clinical factors, fat-suppressed contrast-enhanced MR imaging was significantly more sensitive than scintigraphy (P = .04) and significantly more specific than nonenhanced MR imaging (P = .02) or scintigraphy (P = .008).

An inbred line of transgenic mice expressing an internally deleted gene for type II procollagen (COL2A1). Young mice have a variable phenotype of a chondrodysplasia and older mice have osteoarthritic changes in joints.

Studies were carried out on a line of transgenic mice that expressed an internally deleted COL2A1 gene and developed a phenotype resembling human chondrodysplasias (Vandenberg et al. 1991. Proc. Natl. Acad. Sci. USA. 88:7640-7644. Marked differences in phenotype were observed with propagation of the mutated gene in an inbred strain of mice in that approximately 15% of the transgenic mice had a cleft palate and a lethal phenotype, whereas the remaining mice were difficult to distinguish from normal littermates. 1-d- and 3-mo-old transgenic mice that were viable showed microscopic signs of chondrodysplasia with reduced amounts of collagen fibrils in the cartilage matrix, dilatation of the rough surfaced endoplasmic reticulum in the chondrocytes, and decrease of optical path difference in polarized light microscopy. The transgenic mice also showed signs of disturbed growth as evidenced by lower body weight, lower length and weight of the femur, decreased bone collagen, decreased bone mineral, and decreased resistance of bone to breakage. Comparisons of mice ranging in age from 1 d to 15 mo demonstrated that there was decreasing evidence of a chondrodysplasia as the mice grew older. Instead, the most striking feature in the 15-mo-old mice were degenerative changes of articular cartilage similar to osteoarthritis.

The results of chemonucleolysis as a function of three dimensional volumetric analysis of disc herniation.

Spinal canal and dural sac morphometry as demonstrated by CT scan analysis in patients undergoing chemonucleolysis for the treatment of herniated lumbar discs was analyzed in an attempt to develop a method of predicting positive or negative follow-up clinical results. The morphometry of the canal and dural sac at the intervertebral disc level was defined by reviewing normal levels of CT scans. Levels with herniated discs were then analyzed for comparison of treatment results between successful and unsuccessful procedures. The concept of spinal reserve capacity was evaluated. Significant differences between canal morphometric parameters of patients with treatment success or failure were then identified. The concept of spinal reserve capacity may be applicable in spinal stenosis, but we were unable to delineate any predictive value in the evaluation of patients with herniated lumbar discs undergoing chemonucleolysis.

Transgenic mice expressing a partially deleted gene for type I procollagen (COL1A1). A breeding line with a phenotype of spontaneous fractures and decreased bone collagen and mineral.

A line of transgenic mice was prepared that expressed moderate levels of an internally deleted human gene for the pro alpha 1(I) chain of type I procollagen. The gene construct was modeled after a sporadic in-frame deletion of the human gene that produced a lethal variant of osteogenesis imperfecta by causing biosynthesis of shortened pro alpha 1(I) chains. 89 transgenic mice from the line were examined. About 6% had a lethal phenotype with extensive fractures at birth, and 33% had fractures but were viable. The remaining 61% of the transgenic mice had no apparent fractures as assessed by x ray examination on the day of birth. Brother-sister matings produced eight litters in which approximately 40% of the mice had the lethal phenotype, an observation indicating that expression of the exogenous gene was more lethal in putative homozygous mice from the line. Examination of femurs from the transgenic mice indicated that the bones were significantly shorter in length and had a decrease in wet weight, mineral content, and collagen content. However, there was no statistically significant change in the mineral to collagen ratio. Biomechanical measurements on femurs from the mice at 6 wk indicated a decrease in force and energy to failure. There was also a decrease in strain to failure and an increase in Young's modulus of elasticity, observations indicating increased brittleness of bone matrix. The results suggested that the transgenic mice may be an appropriate model for testing potential therapies for osteogenesis imperfecta. They may also be a useful model for studying osteoporosis.

Biomechanics of pulley reconstruction.

The biomechanics of the reconstructed flexor retinacular pulley system are poorly defined. We used a mathematical theoretical model, confirmed by a cadaver model, and a clinical radiographic model to evaluate a variety of different joint and pulley combinations. We examined twenty-four sets of radiographs of 12 fingers in 9 patients for whom excursion was measured and predicted by the mathematical model. The 30 pulley combinations evaluated in the in vitro cadaver model showed statistical correlation with the biomechanical mathematical model. Recommendations of clinical application on the basis of this information include the following: (1) Two pulleys should be placed, one proximal and one distal to each joint. (2) These two pulleys should be balanced about the joint axis both in distance from the axis and in pulley height. (3) They should be positioned at the edge of the flare of the metaphysis. (4) The three individual joints can be balanced, one to another, by maintaining minimal bowstringing at all three joints. In this way, the relative excursion at the joint and torque at the joint will be maintained in a physiological ratio as close to normal as possible.

Rotation affects apparent radiographic positioning of femoral components in total hip arthroplasty.

The authors have noted a change in the varus/valgus positioning of femoral components on anteroposterior (AP) radiographs that is dependent on limb rotation after total hip arthroplasty (THA). This effect, called pseudoposition, was demonstrated in six cadaver femurs implanted with an uncemented prosthesis that is noncanal-filling in the AP dimension. The distal tip of the prosthesis was positioned posteriorly in all specimens due to the bow of the femur. External rotation causes pseudovalgus positioning, and internal rotation causes pseudovarus positioning. Awareness of this phenomenon is important in the longitudinal analysis of femoral components after THA and emphasizes the need for standardized radiographic technique.

Initial stability of a collarless wedge-shaped prosthesis in the femoral canal.

A collarless wedge-shaped implant was inserted with cementless technique in seven fresh-frozen adult femora. Micromotion of the implant in the proximal femur was evaluated by applying an axial load of 3,000 N or a rotational force of 12 Nm. Six femurs were prepared using a cemented implant, and their stability was similarly determined for comparative purposes. In all tests, the amount of plastic deformation after load relief was quantitated. The cementless prosthesis had excellent initial stability with axial and rotational loading; also the micromotion was similar to that of the cemented implant. Deformation under these experimental conditions was predominantly elastic. The stability demonstrated with this cementless prosthesis satisfies the conditions necessary for bone ingrowth in vivo.

Insertional femoral fracture: a biomechanical study of femoral component stability.

A Taperloc femoral component (Biomet Inc, Warsaw, IN) was implanted in seven fresh-frozen cadaver femora. In loads simulating single-leg stance and stair climbing, axial and rotational stability were tested before fracture, after fracture, and after fracture but with the addition of A-O cerclage wire fixation. All fractures were incomplete, began proximally at the anteromedial neck, and extended distally. More than 90% of the components showed decreased axial and rotational stability after fracture. The addition of cerclage wire fixation after femoral fracture provided acceptable axial stability in only three of seven femora and rotational stability in five of seven femora. In order to provide satisfactory initial implant stability after femoral fracture, improved methods of fixation and longer stemmed implants may be necessary.

Biomechanical analysis of cervical distraction.

A biomechanical analysis of cervical distraction is presented, and a model comparing closed reduction of cervical spine dislocations to spring mechanics is developed. Behavior of a spring may be described as F = k delta x where F = distraction force; delta x = elongation of the spring; and k = spring constant. The records and roentgenograms of 24 cervical spine dislocations were reviewed retrospectively. Evaluation of cervical distraction vs traction weight indicates that Ftraction = kneck delta x; where F = traction weight and x = distraction at the injured level. The constant, kneck, is different for bilateral and unilateral dislocations (P less than .001) and is a function of magnitude of injury and neck morphology. As determined in this study, traction weight needed for reduction of facet dislocations may be estimated using the formulae: Ftx = 107.1 lbs/cm (x) unilateral, and Ftx = 76.4 lbs/cm (x) bilateral.