Association between sagittal alignment and loads at the adjacent segment in the fused spine: a combined clinical and musculoskeletal modeling study of 205 patients with adult spinal deformity

PURPOSE

Sagittal malalignment is a risk factor for mechanical complications after surgery for adult spinal deformity (ASD). Spinal loads, modulated by sagittal alignment, may explain this relationship. The aims of this study were to investigate the relationships between: (1) postoperative changes in loads at the proximal segment and realignment, and (2) absolute postoperative loads and postoperative alignment measures.

METHODS

A previously validated musculoskeletal model of the whole spine was applied to study a clinical sample of 205 patients with ASD. Based on clinical and radiographic data, pre-and postoperative patient-specific alignments were simulated to predict loads at the proximal segment adjacent to the spinal fusion.

RESULTS

Weak-to-moderate associations were found between pre-to-postop changes in lumbar lordosis, LL (r =  - 0.23, r =  - 0.43; p < 0.001), global tilt, GT (r = 0.26, r = 0.38; p < 0.001) and the Global Alignment and Proportion score, GAP (r = 0.26, r = 0.37; p < 0.001), and changes in compressive and shear forces at the proximal segment. GAP score parameters, thoracic kyphosis measurements and the slope of upper instrumented vertebra were associated with changes in shear. In patients with T10-pelvis fusion, moderate-to-strong associations were found between postoperative sagittal alignment measures and compressive and shear loads, with GT showing the strongest correlations (r = 0.75, r = 0.73, p < 0.001).

CONCLUSIONS

Spinal loads were estimated for patient-specific full spinal alignment profiles in a large cohort of patients with ASD pre-and postoperatively. Loads on the proximal segments were greater in association with sagittal malalignment and malorientation of proximal vertebra. Future work should explore whether they provide a causative mechanism explaining the associated risk of proximal junction complications.

Intraoperative Load Tolerance of the Thumb Carpometacarpal Joint After Resection-Suspension-Interposition Arthroplasty

Purpose

The objective was to measure the intraoperative load tolerance of the thumb carpometacarpal (CMC) joint after trapeziectomy, tendon suspension, and interposition.

Methods

In this single-center prospective study, preoperative pinch grip, thumb mobility, and hypermobility of the thumb CMC joint were determined by 2 hand surgeons. Patients completed the brief Michigan Hand Outcomes Questionnaire. During surgery and upon removal of the trapezium, the surgeon subjectively rated the degree of thumb CMC load tolerance as “stable,” “medium stable,” or “unstable.” A measurement system with an integrated force sensor was used to measure intraoperative thumb CMC load tolerance. The thumb ray was displaced manually by 10 mm toward the scaphoid, and the counteracting force was measured over the entire displacement. The objective load tolerance was determined as the maximal measured force after trapezium resection, tendon suspension, and interposition. Analysis of variance was used to test for the differences in load tolerance between the surgical steps. Spearman’s coefficient was used to find correlations between load tolerance and clinical or patient-reported variables.

Results

Twenty-nine patients with a mean age of 70 years (SD, 8.1 years) were available for analysis. The measured intraoperative load tolerance after trapeziectomy was 15.5 N (SD, 5.4 N) and significantly increased to 18.7 N (SD, 5.5 N) after suspension. Load tolerance only slightly increased after tendon interposition, increasing the force to 20.3 N (SD, 6.7 N). Neither the surgeon’s subjective stability rating nor the clinical or patient-reported variables correlated with the measured load tolerance after trapeziectomy.

Conclusions

Our results show that tendon suspension leads to the highest increase in thumb CMC load tolerance during resection-suspension-interposition arthroplasty.

Clinical relevance

Tendon suspension appears to be the most important step in stabilizing the metacarpal base after trapeziectomy, whereas tendon interposition does not seem to have a relevant additional effect regarding load tolerance, at least immediately after surgery.

Variable fixation promotes callus formation: an experimental study on transverse tibial osteotomies stabilized with locking plates

Background

A new locking screw technology, named variable fixation, has been developed aiming at promoting bone callus formation providing initial rigid fixation followed by progressive fracture gap dynamisation. In this study, we compared bone callus formation in osteotomies stabilized with standard locking fixation against that of osteotomies stabilized with variable fixation in an established tibia ovine model.

Methods

A 3 mm tibial transverse osteotomy gap was stabilized in three groups of six female sheep each with a locking plate and either 1) standard fixation in both segments (group LS) or 2) variable fixation in the proximal and standard fixation in the distal bone segment (group VFLS₃) or 3) variable fixation in both segments (group VFLS₆). The implantation site and fracture healing were compared between groups by means of radiologic, micro tomographic, biomechanical, and histological investigations.

Results

Compared to LS callus, VFLS₃ callus was 40% larger and about 3% denser, while VFLS₆ callus was 93% larger and its density about 7.2% lower. VFLS₃ showed 65% and VFLS₆ 163% larger amount of callus at the cis-cortex. There wasn’t a significant difference in the amount of callus at the cis and trans-cortex in groups featuring variable fixation only. Investigated biomechanical variables were not significantly different among groups and histology showed comparable good healing in all groups. Tissues adjacent to the implants did not show any alteration of the normal structure in all groups.

Conclusions

Variable fixation promoted the formation of a larger amount of bone callus, equally distributed at the cis and trans cortices. The histological and biomechanical properties of the variable fixation callus were equivalent to those of the standard fixation callus. The magnitude of variable fixation had a biological effect on the formation of bone callus. At the implantation site, the usage of variable fixation did not raise additional concerns with respect to standard fixation. The formation of a larger amount of mature callus suggests that fractures treated with variable fixation might have a higher probability to bridge the fracture gap. The conditions where its usage can be most beneficial for patients needs to be clinically defined.

Intramedullary screw fixation for metacarpal shaft fractures: a biomechanical human cadaver study

Intramedullary cannulated compression screws have been introduced for the fixation of unstable metacarpal fractures. In the present study, this technique was compared with dorsal compression plating to evaluate its biomechanical performance in stabilizing metacarpal shaft fractures. In a first set of experiments, the biomechanical characteristics of the screws were analysed in an artificial bone model. In subsequent experiments, midshaft osteotomies were performed in human cadaver metacarpals, followed by plating or intramedullary screw osteosynthesis. The metacarpals were tested to failure in cantilever bending, following a stepwise increasing cyclic loading protocol. We found a significantly lower load at failure and a significantly lower number of cycles to failure in the intramedullary screw group, but both methods offered sufficient stability under these loads. With reference to published loads on the metacarpals during use of the hand, we conclude that intramedullary osteosynthesis yields sufficient strength and stiffness for early active motion. A difference in its fixation stability is noted compared with plate fixation, which may not be clinically relevant.

P5257Prediction of 12-month cardiovascular event-free survival with regadenoson perfusion cardiovascular magnetic resonance

Background

To identify and stratify coronary artery disease (CAD) non-invasively, cardiovascular magnetic resonance (CMR) derived perfusion imaging holds a class Ia recommendation.

As Gold standard, hyperemia is induced by an intravenous application of adenosine in a body weight adapted dosage over a constant time. However, adenosin has two disadvantages: 1.) efficacy of adenosine to induce maximal hyperemia via peripheral line is imperfect and 2.) additional adenosine specific effects exclude patients having comorbidities (e.g. AV-blocks and obstructive lung disease). Fortunately, regadenoson as aselective A2A-receptor agonist has the main advantages of being easier to handle (bolus application) and to be not restricted to patients without specific comorbidities. However, there is a lack of comprehensive data on the prognostic value of regadenoson perfusion CMR to predict clinical endpoints. To assess the predictive value of regadenoson perfusion CMR, our hypothesis was, that a “negative” ischemia test result by regadenoson-CMR predicted freedom from MACE at 12 month.

Methods

676 patients, with known or suspected CAD with intermediate risk were retrospectively analyzed from May 2015 till December 2016. Cardiovascular risk factors (CVRF) like age, sex, arterial hypertension, dis-/hyperlipidemia, cigarette smoking status and diabetes were documented. All included patients received perfusion CMR (Philips 1.5 Tesla) with regadenoson (0.4 mg) and a positive ischemia test was defined as perfusion defects in ≥1,5 cardiac segments (using the 17-segment model). Major cardiovascular events (MACE) were defined as cardiovascular death, rehospitalisation due to myocardial infarction and rehospitalisation due to revascularization. The follow-up time was 12 month.

Results

80,3% (n=543) of all analyzed patients showed negative ischemia testing in CMR and were thus followed up for 12 month. From these patients, 284 (52,3%) had a pre-existing coronary artery disease. The mean age regarding only the patients with negative ischemia was 66 years (65% male and 35% female) with 1,35±1,03 CVRF. The primary endpoint (MACE) occurred in 6 patients (1,1%): 3 (0,6%) died due to cardiovascular events, 1 (0,2%) suffered from a myocardial infarction and 2 (0,4%) received coronary revascularization. Consequently, an event-free survival was correctly predicted in 98,9% of all patients. No undesirable adverse reactions have appeared.

Conclusion

Regadenoson-CMR predicts a very low MACE-rate and an event-free survival in 98,9% in over 500 patients. In our study, Regadenoson was well tolerated and no side effects were reported.

[The clinical spectrum of urea cycle defects in adult patients]

Urea cycle defects belong to the most common metabolic disorders with a cumulative incidence of 1:8000. A common trait of urea cycle defects is a disturbed detoxification of ammonia leading to hyperammonemia in the event of a high nitrogen load. Most patients develop symptoms in the neonatal period or in infancy, e. g. vomiting, seizures and disturbed consciousness. Depending on the affected enzyme and its residual activity, patients differ in the age at first presentation, the character and severity of symptoms and in the susceptibility to metabolic derangement. The presence of hyperammonemia and an altered plasma amino acid profile give the essential diagnostic clues. Since modern therapeutic measures have prolonged the life expectancy of these patients and provided the possibility of a first presentation in adulthood, patients with urea cycle defects have become an increasing challenge in internal medicine. The reported case series illustrates the heterogeneous clinical course of these disorders from childhood to adulthood.

[Development and current possibilities of cerebrospinal fluid diagnosis in the routine laboratory. 2. Studies on protein composition]

In the 1st part of this paper (Schulz et al. 1979) a survey was given of the cytological and the chemical procedures at present available for cerebrospinal fluid diagnostics. The 2nd part describes different laboratory methods to separate the protein mixture of cerebrospinal fluid into protein fractions or single proteins. These surveys intend both an improvement of the quality and a unification of laboratory methods regarding diagnostic examinations of cerebrospinal fluid.