Lars P. Mueller

Influence of formalin fixation on the biomechanical properties of human diaphyseal bone

Abstract Owing to the lack of fresh human bones, formalin-fixed specimens are frequently used in biomechanical testing. However, formalin fixation is assumed to affect the biomechanical properties of bone. The aim of this study was to compare axial and torsional stiffness and bone mineral density in fresh and embalmed human bones. The subtrochanteric regions of 12 pairs of fresh human femora were randomised into two groups for paired comparison. After bone mineral density measurement, one group was preserved in 4% formalin. After 6 weeks, bone mineral density was remeasured and each specimen underwent axial and torsional loading. The formalin group showed significant higher stiffness values for torsional and axial loads than the fresh group. Axial stiffness increased by 14.1%, whereas torsional stiffness increased by 14.3%. These differences were not reflected in bone mineral density values. Formalin fixation significantly influences the stiffness of human cadaveric bones. Fresh bones represent the in vivo conditions better than formalin fixed bones.

New intramedullary locking nail for olecranon fracture fixation--an in vitro biomechanical comparison with tension band wiring.

BACKGROUND The aim of this study was to determine the difference in displacement of a newly designed intramedullary olecranon fracture fixation device compared with multifilament tension band wiring after 4 cycles and 300 cycles of dynamic continuous loading. METHODS In eight pairs of fresh-frozen cadaver ulnae, oblique olecranon fractures were created and stabilized using either newly designed intramedullary olecranon nail or multifilament tension band wiring. The specimens were then subjected to continuous dynamic loading (from 25 N to 200 N) using matched pairs of cadaveric upper extremities. The Wilcoxon test was used to determine statistical differences of the displacement in the fracture gap. RESULTS After 4 cycles and 300 cycles, the displacement in the fracture model was significantly higher in the tension band wiring group than in the intramedullary nailing group. CONCLUSIONS The newly designed interlocking nailing system showed higher stability in comparison with multifilament tension band wiring after continuous dynamic loading.

Intramedullary nailing vs. palmar locked plating for unstable dorsally comminuted distal radius fractures: A biomechanical study

BACKGROUND The purpose of this study was to compare the stability of a 2.4mm palmar locking compression plate and a new intramedullary nail-plate-hybrid Targon DR for dorsally comminuted distal radius fractures. METHODS An extraarticular 10mm dorsally open wedge osteotomy was created in 8 pairs of fresh frozen human radii to simulate an AO-A3-fracture. The fractures were stabilized using one of the fixation methods. The specimens were loaded axially with 200 N and dorsal-excentrically with 80 N. 2000cycles of dynamic loading and axial loading-to-failure were performed. FINDINGS Axial loading revealed that intramedullary osteosynthesis (Targon DR: 369 N/mm) was significantly (p=0.017) stiffer than plate osteosynthesis (Locking compression plate: 131 N/mm). With 214 N/mm the intramedullary nail also showed higher stability during dorsal excentric loading than the Locking compression plate with 51 N/mm (p=0.012). After 2000 cycles of axial loading with 80 N the Targon DR-group was significantly stiffer than the Locking compression plate-group under both loading patterns. Neither group showed significant changes in stiffness after 2000 cycles. Under dorsal excentric loading the Targon DR-group was still significantly stiffer with 212 N/mm than the Locking compression plate-group with 45 N/mm (p=0.012). The load to failure tests demonstrated higher stability of intramedullary nailing (625 N) when compared to plate osteosynthesis (403 N) (p<0.025). INTERPRETATION The study shows that intramedullary fixation of a distal AO-A3 radial fracture is biomechanically more stable than volar fixed-angle plating under axial and dorsal-excentric loading in an experimental setup.

Screw fixation of radial head fractures: Compression screw versus lag screw—A biomechanical comparison

INTRODUCTION Secondary loss of reduction and pseudarthrosis due to unstable fixation methods remain challenging problems of surgical stabilisation of radial head fractures. The purpose of our study was to determine whether the 3.0mm Headless Compression Screw (HCS) provides superior stability to the standard 2.0 mm cortical screw (COS). MATERIALS AND METHODS Eight pairs of fresh frozen human cadaveric proximal radii were used for this paired comparison. A standardised Mason II-Fracture was created with a fragment size of 1/3 of the radial heads articular surface that was then stabilised either with two 3.0 mm HCS (Synthes) or two 2.0 mm COS (Synthes) according to a randomisation protocol. The specimens were then loaded axially and transversely with 100 N each for 4 cycles. Cyclic loading with 1000 cycles as well as failure load tests were performed. The Wilcoxon test was used to assess statistically significant differences between the two groups. RESULTS No statistical differences could be detected between the two fixation methods. Under axial loads the COS showed a displacement of 0.32 mm vs. 0.49 mm for the HCS. Under transverse loads the displacement was 0.25 mm for the COS vs. 0.58 mm for the HCS group. After 1000 cycles of axial loading there were still no significant differences. The failure load for the COS group was 291 N and 282 N for the HCS group. CONCLUSION No significant differences concerning the stability achieved by 3.0 mm HCS and the 2.0 mm COS could be detected in the experimental setup presented.

Progressive femoral cortical and cancellous bone density loss after uncemented tapered-design stem fixation

Background Aseptic implant loosening and periprosthetic bone loss are major problems after total hip arthroplasty (THA). We present an in vivo method of computed tomography (CT) assisted osteodensitometry after THA that differentiates between cortical and cancellous bone density (BD) and area around the femoral component. Method Cortical and cancellous periprosthetic femoral BD (mg CaHA/mL), area (mm2) and contact area between the prothesis and cortical bone were determined prospectively in 31 patients 10 days, 1 year, and 6 years after uncemented THA (mean age at implantation: 55 years) using CT-osteodensitometry. Results 6 years postoperatively, cancellous BD had decreased by as much as 41% and cortical BD by up to 27% at the metaphyseal portion of the femur; this decrease was progressive between the 1-year and 6-year examinations. Mild cortical hypertrophy was observed along the entire length of the diaphysis. No statistically significant changes in cortical BD were observed along the diaphysis of the stem. Interpretation Periprosthetic CT-assisted osteodensitometry has the technical ability to discriminate between cortical and cancellous bone structures with respect to strain-adapted remodeling. Continuous loss of cortical and cancellous BD at the femoral metaphysis, a homeostatic cortical strain configuration, and mild cortical hypertrophy along the diaphysis suggest a diaphyseal fixation of the implanted stem. CT-assisted osteodensitometry has the potential to become an effective instrument for quality control in THA by means of in vivo determination of periprosthetic BD, which may be a causal factor in implant loosening after THA.

Ultrasound-guided spinal fracture repositioning, ligamentotaxis, and remodeling after thoracolumbar burst fractures.

Study Design. Computed tomography aided evaluation of spinal decompression by ultrasound-guided spinal fracture repositioning, ligamentotaxis, and remodeling after thoracolumbar burst fractures. Objectives. To determine the necessity of spinal canal widening by ultrasound-guided fracture repositioning for fractures with and without neurologic deficit. Summary of Background Data. Ultrasound-guided spinal fracture repositioning is an alternative new approach. Reports have varied concerning ligamentotaxis and remodeling. Methods. Computed tomography aided planimetry of the spinal canal (64 consecutive burst fractures) and neurologic evaluation by Frankel grades. Results. Ultrasound-guided spinal fracture repositioning (n = 37) reduced the stenosis of the spinal canal area from 45% before surgery to 20% after surgery of the estimated original area. Fifteen patients had a primary neurologic deficit, which improved markedly in 11 cases after treatment. Patients with neurologic symptoms had a greater preoperative spinal stenosis than those without. No correlation was seen between the degree of pretreatment spinal stenosis, fracture type, and severity of the neurologic deficit. Ligamentotaxis (n = 27) reduced the stenosis from 30% before surgery to 18% after surgery and remodeling (n = 11) from 25% after surgery to 13% after metal removal. Conclusion. Ultrasound-guided fracture repositioning is an efficient method for spinal canal decompression of burst fractures with neurologic symptoms. The marked degree of widening of the spinal canal due to the effects of ligamentotaxis and remodeling may render the reposition of retropulsed fragments unnecessary in cases of fractures without a neurologic deficit.

Acute Compartment Syndrome of the Upper Extremity.

Compartment syndrome of the upper extremity is rare, but happens frequently. It most often affects the forearm, compartment syndromes of the upper arm and hand are seen much more seldom. Early diagnosis and efficient fasciotomy is of highest importance to achieve good outcome and prevent development of Volkmanns ischemic contracture.

Dynamische Analyse von Osteosynthesen am Olecranon: ein in-vitro Vergleich zweier Osteosynthesesysteme / Dynamic analysis of olecranon osteosyntheses – an in vitro comparison of two osteosynthesis systems

Zusammenfassung Hintergrund: Ziel dieser Studie war die Entwicklung eines Test-Setups mit kontinuierlicher Winkeländerung für die Imitation der Gelenkbewegung des Ellenbogens zum mechanischen Vergleich von Zuggurtungosteosynthese und einem neu entwickelten intramedullären Nagelsystem. Material und Methode: Der Rotationsmotor des servopneumatischen Testapparates arbeitet winkelgesteuert für die Ellenbogenbewegung, der Linearmotor kraftgesteuert für den M. triceps brachii. Das Frakturmodell wurde dynamisch unter zyklischer Belastung getestet. An 14 frischen Leichenulnae wurde eine schräge Osteotomie des Olecranon durchgeführt und zwei verschiedene Osteosynthesesysteme angelegt. Eine Gruppe erhielt die Zuggurtungsosteosynthese, die andere Gruppe den intramedullären Nagel implantiert. Das Bewegungsausmaß des Ellenbogengelenkes änderte sich zwischen 0° Extension und 100° Flexion unter einer dynamischen Zugkraftvariation zwischen 25 und 150 N. Anhand zweier Paare von Markerpins, die jeweils am proximalen und am distalen Fragment frakturnah angebracht waren, wurde die Relativbewegung zwischen den Pins gemessen. Die Bewegungsanalyse wurde nach 4 und nach 300 Zyklen kontinuierlicher Belastung durchgeführt. Ergebnisse: Nach 300 Zyklen war die Lockerung der Zuggurtungsosteosynthese signifikant höher als die der intramedullären Nagelosteosynthese. Diskussion: Andere Untersuchungen von Osteosynthesen mit Gelenkbeteiligung veränderten die Krafteinwirkung nicht dynamisch. Das Test-Setup der vorliegenden Studie imitiert die Gelenkbewegung mit einer kontinuierlichen Änderung des Gelenkwinkels. Das ist eine wichtige Voraussetzung für eine akkurate biomechanische Untersuchung von unterschiedlichen Osteosyntheseverfahren zur Fixierung von Olecranonfrakturen. Das getestete intramedulläre Nagelsystem zeigte im Vergleich zur Zuggurtungsosteosynthese eine signifikant geringere Lockerung unter Belastung. Abstract Introduction: The aim of the present study was to develop a test setup with continuous angle alteration to imitate elbow joint motion for the mechanical evaluation of tension band wiring and a newly designed intramedullary nail. Materials and methods: The servo-pneumatical test stand worked with a rotational angle-adjusted and a linear force-adjusted engine. The fracture model was dynamically tested under cyclic loading imitating elbow joint motion. In total, 14 fresh cadaver upper extremities underwent olecranon fracture by means of transverse osteotomy and were assigned to two groups: tension band wiring and intramedullary nailing. There was a continuous angle alteration between 0 and 100° of flexion, with continuous changing pull force between 25 N and 150 N. Two steel pins were placed in the proximal, two in the distal olecranon fragment for video analysis of the motion between the two pairs of pins. Displacement in the fracture gap was determined after 4 and 300 cycles. Results: After 300 cycles, the displacement in the fracture fixation model was significantly higher in the tension band wiring group than in the intramedullary nailing group. Discussion: Other studies evaluating biomechanical properties of olecranon osteosyntheses with joint involvement did not change the force direction dynamically. We introduced a test setup with continuous angle alteration to imitate joint motion. This is an important step for accurate biomechanical evaluation of the treatment of different fixation methods in olecranon fractures. The tested nailing system showed significant advantages in loosening under cyclic loading compared to tension band wiring.

Hypothenar Hammer Syndrome in a Golf Player

The hypothenar hammer syndrome was first described by von Rosen in 1934 in a factory worker who struck the edge of a metal bar with the palm of his right hand in an attempt to loosen a tightly fixed screw. The factory worker experienced repetitive ischemia and pain attacks in all his digits. At surgery, von Rosen found a 2.5-cm thrombosed segment of the distal ulnar artery overlying the hamate bone. Since this first description, repetitive blunt or single severe trauma leading to thrombus formation of the ulnar artery and hand ischemia related to occupational exposure in patients who use vibrating hand tools or who hammer objects with the hypothenar aspect is well known. Such injury may also be seen in sports where the athlete’s hand is subjected to repeated or single severe impact. A review of the literature revealed 12 different sports that have been associated with hypothenar hammer syndrome (Table 1). This is the first report of a golf player who sustained traumatic ulnar artery thrombosis in a setting of repetitive swinging of a golf club.