Brake response time returns to the pre-surgical level 6 weeks after unicompartmental knee arthroplasty.

PURPOSE: The objective of the study was to clarify whether driving abstinence should be recommended when patients are discharged from hospital after unicompartmental knee arthroplasty (UKA). We tested the hypotheses that there are differences in the peri-operative course of brake response time in patients undergoing right-sided (1) or left-sided (2) UKA. Additionally, we tested whether brake response time is significantly influenced by pain (3), driving experience (4) or age (5). METHODS: In 43 patients undergoing UKA, brake response time was measured with a custom-made driving simulator pre-operatively and 1 and 6 weeks after UKA. Patients' visual analogue scales for knee pain and their self-reported driving experience were also assessed. RESULTS: In patients with right-sided UKA, brake response time changed from 786 (261) ms pre-operatively to 900 (430) ms 1 week post-operatively (p = 0.029). At 6 weeks post-operatively, brake response time had returned to 712 (139) ms, which was deemed to be an insignificant change from the pre-operative reference benchmark. When surgery was performed on the contralateral left side, no effect was found onto the right side's brake response time. Knee pain and driving experience were significantly correlated with brake response time. No such correlations were found between brake response time and age. CONCLUSIONS: On the basis of the current findings, it is concluded that brake response time returns to pre-operative levels 6 weeks after UKA surgery. Therefore, it is proposed that driving be abstained from for that period.

Impaction bone grafting: a laboratory comparison of two methods.

In revision total hip replacement, bone loss can be managed by impacting porous bone chips. In order to guarantee sufficient mechanical strength, the bone chips have to be compacted. The aim of this study was to determine in an in vitro simulation whether the use of a pneumatic hammer leads to higher primary stability than manual impaction. Bone mass characteristics were measured by force and distance variation of a penetrating punch, which was lowered into a plastic cup filled with bone chips. From these measurements bulk density, contact stiffness, impaction hardness and penetration resistance were calculated for different durations of impaction. We found that the pneumatic method reached higher values of impaction hardness, contact stiffness and bulk density suggesting an increase in stability of the implant. No significant differences were found between the two different methods concerning the penetration resistance. The pneumatic method might reduce the risk of fracture in vivo, as force peaks are smaller and applied for a shorter period. Results from manual impaction showed higher variability and depend much on the experience of the surgeon. The pneumatic hammer is a suitable tool to standardise the impaction process.

Proximal humeral fractures: what is semi-rigid? Biomechanical properties of semi-rigid implants, a biomechanical cadaver based evaluation.

INTRODUCTION: Proximal humerus fractures remain challenging especially in the elderly. Biomechanical data put semi-rigid implants in favour of osteopenic or osteoporotic situation. Little surgical side damage is associated with a minimal invasive approach of these implants. The aim of this study was to evaluate the mechanical properties of three such implants. MATERIAL AND METHODS: Fresh frozen cadaver specimens were mounted as proposed by the distributors. Three different implants were used: LCP-PH (locking compression plate proximal humerus, Synthes, Austria), HB (humerus block, Synthes, Austria), and IMC (intramedullary claw, ITS, Austria). Subcapital fracture was simulated by resecting a 5 mm gap. All specimens were comparable in "B" (one), "M" (ineral) and "D" (ensity). Four load cases were tested: varus bending, medial shearing and axial torque. A cyclic test (1,000 cycles) was performed in the first load case (varus stress) for all three implants. RESULTS: The LCP-PH was the most rigid in all three load cases, always followed by the HB. The IMC was the most elastic device with almost immeasurable values in axial torque. In the cyclic setting, the load reduction of the HB followed by the LCP-PH was significantly better than that for the IMC. CONCLUSION: The differences in stiffness are varying tremendously. The IMC is the implant with the lowest stiffness in all load cases and the highest load reduction. New "semi-rigids" claim good clinical performance, yet prospective clinical studies have to prove this. It is unlikely that the IMC can maintain fracture reduction in fracture situations of complex nature (no ligamentotaxis).

Decrease in eccentric hamstring strength in runners in the Tirol Speed Marathon.

BACKGROUND: The local muscular endurance of knee flexors, during eccentric work in particular, is important in preventing or delaying kinematic changes associated with fatigue during treadmill running. This result, however, may not be transferable to overground running. OBJECTIVE: To test the hypothesis that overground running is associated with eccentric hamstring fatigue. METHODS: Thirteen runners (12 male and one female) performed an isokinetic muscle test three to four days before and 18 hours after a marathon. Both legs were tested. The testing protocol consisted of concentric and eccentric quadriceps and hamstring contractions. RESULTS: There were no significant differences between peak torque before and after the race, except that eccentric peak hamstring torque (both thighs) was reduced. CONCLUSION: Overground running (running a marathon) is associated with eccentric hamstring fatigue. Eccentric hamstring fatigue may be a potential risk factor for knee and soft tissue injuries during running. Eccentric hamstring training should therefore be introduced as an integral part of the training programme of runners.

[Therapy for static scapholunate instability -- reconstruction of the dorsal part of the scapholunate ligament with a periosteal flap of the iliac crest]. / Therapie der statischen skapholunären Instabilität -- Bandrekonstruktion des dorsalen skapholunären Bandes mit einem Perioststreifen vom vorderen Darmbeinkamm.

Recurrent instability is frequent following capsulodesis, tenodesis, or ligament reconstruction in static scapholunate instability. Therefore a periosteal flap of the iliac crest was designed to reconstruct the dorsal part of the SL ligament, which is known to be the biomechanically strongest portion and also the axis of rotation between the scaphoid and lunate. Biomechanical testing of ten fresh frozen dorsal SL ligaments and ten periosteal flaps of the iliac crest showed similar properties concerning failure force, failure displacement, failure stress, energy to failure and stiffness. Results of eight specimens in each group were available following successful testing. Failure force of the dorsal SL ligament was 171.8 N (SD 44.2), energy to failure amounted 269.1 N-mm (SD 98.9), failure stress was 10.3 N/mm (2) (SD 1.3), failure displacement 2.9 mm (SD 0.4), and stiffness 77.2 N/mm (SD 21.4). Testing of the periosteal flap gave the following values: failure force 144.3 N (SD 38.7), energy to failure 217.9 N-mm (SD 85.0), failure stress 9.9 N/mm (2) (SD 1.7), failure displacement 3.0 mm (SD 0.4) and stiffness 60.5 N/mm (SD 14.7). In addition to these test values, clinical and radiological data of eleven patients were available following reconstruction of the dorsal SL ligament with a periosteal flap of the iliac crest. The interval between trauma and surgery was 15 months, mean follow-up was 29 months. One patient was free of pain, whereas ten mentioned pain during or following strenuous work. Two patients were completely satisfied, nine complained about some restriction during special activities. Active range of motion amounted to 56 degrees extension, 46 degrees flexion, 17 degrees radial abduction, 30 degrees ulnar abduction. Grip strength was 38.5 kg, which was 79 % of the contralateral side. Radiological evaluation demonstrated a correction of the static instability in nine cases. In two patients recurrence of static instability was obvious. The prerequisite for success of the procedure is the easy reduction of the carpals. In cases of a fixed rotatory subluxation of the scaphoid, the technique cannot maintain the reduction.

P-Match: transcription factor binding site search by combining patterns and weight matrices.

P-Match is a new tool for identifying transcription factor (TF) binding sites in DNA sequences. It combines pattern matching and weight matrix approaches thus providing higher accuracy of recognition than each of the methods alone. P-Match is closely interconnected with the TRANSFAC database. In particular, P-Match uses the matrix library as well as sets of aligned known TF-binding sites collected in TRANSFAC and therefore provides the possibility to search for a large variety of different TF binding sites. Using results of extensive tests of recognition accuracy, we selected three sets of optimized cut-off values that minimize either false negatives or false positives, or the sum of both errors. Comparison with the weight matrix approaches such as Matchtrade mark tool shows that P-Match generally provides superior recognition accuracy in the area of low false negative errors (high sensitivity). As familiar to the user of Matchtrade mark, P-Match also allows to save user-specific profiles that include selected subsets of matrices with corresponding TF-binding sites or user-defined cut-off values. Furthermore, a number of tissue-specific profiles are provided that were compiled by the TRANSFAC team. A public version of the P-Match tool is available at http://www.gene-regulation.com/cgi-bin/pub/programs/pmatch/bin/p-match.cgi.

Scapholunate ligament reconstruction using a periosteal flap of the iliac crest: a biomechanical study.

INTRODUCTION: Advances continue to improve direct reconstruction of the dorsal scapholunate (SL) ligament, which is the strongest part of the entire SL ligament and is known as the turning point between the scaphoid and lunate. This study was designed to compare the biomechanical properties of the dorsal SL ligament with those of a periosteal flap of the iliac crest, which is a new graft candidate for dorsal SL reconstruction. MATERIALS AND METHODS: A bone-ligament-bone complex was harvested for biomechanical testing from the iliac crest and the dorsal SL complex. Ten specimens could be prepared in each group. After potting the bone blocks in methylmethacrylate for stable fixation, the specimens were tested, using a servohydraulic testing system, at a rate of 10 mm/min. RESULTS: Failure displacement, failure force, failure stress, energy to failure, and stiffness were assessed for both groups. Eight specimens in each group were tested successfully. In the ligament group, six specimens failed at the ligament level, whereas two failed at the insertion of the scaphoid. In the periosteum group, all eight specimens failed at the ligament level. The failure force of the dorsal SL ligament averaged 171.8 N, failure stress was 10.3 N/mm2, and failure displacement amounted to 2.9 mm. Energy to failure was 269.1 N-mm, and stiffness averaged 77.2 N/mm. Failure force of the periosteal flap amounted to 144.3 N, failure stress was 9.9 N/mm2, failure displacement was 3.0 mm, and energy to failure was 217.9 N-mm. Stiffness of the periosteal flap measured 60.5 N/mm. Comparison of the dorsal SL ligament and the periosteal flap of the iliac crest revealed no significant biomechanical differences. CONCLUSION: Therefore, the biomechanical properties of the periosteal flap recommend its use for reconstruction of the dorsal SL ligament.

Effect of a prosthetic disc nucleus on the mobility and disc height of the L4-5 intervertebral disc postnucleotomy.

OBJECT: Current procedures for treatment of degenerative disc disease may not restore flexibility or disc height to the intervertebral disc. Recently, a prosthetic device, intended to replace the degenerated nucleus pulposus, was developed. In this biomechanical in vitro test the authors study the effect of implanting a prosthetic nucleus in cadaveric lumbar intervertebral discs postnucleotomy and determine if the flexibility and disc height of the L4-5 motion segment is restored. METHODS: The prosthetic disc nucleus device consists of two hydrogel pellets, each enclosed in a woven polyethylene jacket. Six human cadaveric lumbar motion segments (obtained in individuals who, at the time of death, were a mean age of 56.7 years) were loaded with moments of +/- 7.5 Nm in flexion-extension, lateral bending, and axial rotation. The following states were investigated: intact, postnucleotomy, and after device implantation. Range of motion (ROM) and neutral zone (NZ) measurements were determined. Change in disc height from the intact state was measured after nucleotomy and device implantation, with and without a 200-N preload. CONCLUSIONS: Compared with the intact state (100%), the nucleotomy increased the ROM in flexion-extension to 118%, lateral bending to 112%, and axial rotation to 121%; once the device was implanted the ROM was reduced to 102%, 88%, and 90%, respectively. The NZ increased the ROM to 210%, lateral bending to 173%, and axial rotation to 107% after nucleotomy, and 146%, 149%, 44%, respectively, after device implantation. A 200-N preload reduced the intact and postnucleotomy disc heights by approximately 1 mm and 2 mm, respectively. The original intact disc height was restored after implantation of the device. The results of the cadaveric L4-5 flexibility testing indicate that the device can potentially restore ROM, NZ, and disc height to the denucleated segment.

Creatine kinase, myosin heavy chains and magnetic resonance imaging after eccentric exercise.

The aim of this study was to examine the relationship between myosin heavy chain (MHC) release as a specific marker of slow-twitch muscle fibre breakdown and magnetic resonance imaging (MRI) of skeletal muscle injury after eccentric exercise. The effects of a single series of 70 high-intensity eccentric contractions of the quadriceps femoris muscle group (single leg) on plasma concentrations of creatine kinase and MHC fragments were assessed in 10 young male sport education trainees before and 1 and 4 days after exercise. To visualize muscle injury, MRI of the loaded thigh was performed before and 4 days after the eccentric exercise. All participants recorded an increase (P < 0.05) in creatine kinase after exercise. In five participants, T2 signal intensity was unchanged post-exercise compared with pre-exercise and MHC plasma concentration was normal; however, they showed an increase (P < 0.05) in creatine kinase after exercise. For the remaining five participants, there was an increase in T2 signal intensity of the loaded vastus intermedius and vastus lateralis. These changes in MRI were accompanied by an increase in MHC plasma concentration (P< 0.01) as well as an increase in creatine kinase (P < 0.01). We suggest that changes in MRI T, signal intensity after muscle damage induced by eccentric exercise are closely related to damage to structurally bound contractile filaments of some muscle fibres. Additionally, MHC plasma release indicates that this damage affects not only fast-twitch fibres but also some slow-twitch fibres.

Excessive heat generation during cutting of cement in the Robodoc hip-revision procedure.

The ROBODOC system is a promising new method for removing cement with high-speed milling. Heat is generated during the milling process. This study was designed to measure temperatures in the cutting area, and to assess the risk of heat injury and the effectiveness of irrigation. We measured temperatures at the bone-cement cutting area in three experimental settings, two involving the proximal area comprising a cement mantle, and one the distal cement plug beneath the prosthesis. Without cooling facilities, a mean temperature of 94 degrees C was measured in proximal areas. However, this could effectively be reduced below 70 degrees C with irrigation. In the area of the distal cement plug, we measured a mean temperature of 172 degrees C without irrigation. In this area, the integrated irrigation system with an additional high-flow irrigation system could not guarantee cooling to an acceptable temperature of below 70 degrees C since the irrigation stream was impeded by the cutter in the narrow cavity. We need an integrated irrigation device that guarantees continuous cooling at the cutting interface in front of the cutter.

Motion in lumbar functional spine units during side bending and axial rotation moments depending on the degree of degeneration.

STUDY DESIGN: Human lumbar spine specimens were tested in axial rotation and side bending. Motion was related to the grade of degeneration. OBJECTIVES: To determine the degree to which degeneration with fissure formation in the disc affects axial rotation of the lumbar functional spine unit. SUMMARY OF BACKGROUND DATA: There is controversy in the literature regarding the influence of severe degeneration and fissures of the disc on the range of axial rotation. METHODS: Thirty-six lumbar spine specimens were tested in axial rotation and side bending, by applying pure moments in an unconstrained setting. The motion in 6 df was recorded by dial gauges. The grade of degeneration was established by the grading schemes of Nachemson, Thompson, Adams, and Mimura. RESULTS: A significant increase of axial rotation and lateral translation under torque was found. This increase mainly took place between Grade 3 according to the schemes of Nachemson, Thompson, and Adams (no fissure formation) and the higher grades of degeneration (defined by fissure formation). Reduced disc height was always associated with fissures. CONCLUSIONS: A reduced lumbar disc height in radiographs seems to be associated with fissure formation in the disc. In this case, the range axial rotation after torque is increased in comparison with cases with less degeneration.

Effects of specimen length on the monosegmental motion behavior of the lumbar spine.

STUDY DESIGN: An in vitro biomechanical analysis of the segmental motion behavior of the same segments in polysegmental (five segments), bisegmental, and monosegmental specimens using sheep lumbosacral spines. OBJECTIVES: To investigate the effect of specimen length on monosegmental motion behavior. These data may be helpful in planning in vitro tests and in comparing results of studies using specimens of different lengths. SUMMARY OF BACKGROUND DATA: The length of spinal specimens used for in vitro stability tests varies greatly, depending on the purpose of the study. Some investigators prefer testing specimens with one adjacent segment on either end of the region of interest. Others favor specimens as short as possible. METHODS: In a first step, seven sheep spine specimens, L3-S1 (note that sheep spines normally have seven lumbar vertebrae), each were tested without preload in a spine-loading apparatus. Alternating sequences of pure lateral bending, flexion/extension, and axial rotation moments (+/-3.75 Nm) were applied continuously. The motion in each single segment was measured simultaneously. Then, these polysegmental specimens were cut into two bisegmental specimens, L3-L5 and L6-S1, and tested in the same way. Finally, another vertebra was removed to obtain two monosegmental specimens, L3-L4 and L7-S1, and to test them as described. RESULTS: In general, the range of motion at L3-L4 and L7-S1 was smaller when tested in polysegmental than in monosegmental specimens. In polysegmental specimens (five segments), the range of motion at L3-L4 and L7-S1 was approximately 80% (range, 70.6-92.5%) and in bisegmental specimens approximately 95% (range, 66.7-100%) of their range of motion measured in monosegmental specimens. Neutral zone and coupled motions showed the inverse behavior. Significant differences were found. However, they were not consistent with either the loading direction or with the specimen length. CONCLUSIONS: For comparison of results, the specimen length should be kept constant within one experiment. Segmental motion behavior of specimens with different lengths should be compared only qualitatively.

Different treatment modalities of tinnitus at the EuromedClinic.

A retrospective study at the ear, nose, and throat department of the EuromedClinic showed considerable improvements immediately after the end of the treatments for acute and for chronic tinnitus. Eighty percent of our patients suffering from acute tinnitus showed an improvement with intravenous medication without hyperbaric oxygen treatment, and 65.7% showed improvement with infusion therapy and hyperbaric oxygen. However, at 3 months and then later (long-term results), the figures decreased to 67% and 46%, respectively. In the chronic tinnitus group, the therapeutic effect dropped from 66.7% to 34% (with only intravenous medication) and from 60% to 28% (with combined therapy). These facts can explain the importance of beginning the treatment of patients suffering from tinnitus as early as possible (i.e., acute stage).

Measurement of vertebral rotation: a comparison of two methods based on CT scans.

This study compared Ho's and Aaro's method to measure vertebral axial rotation in order to find the more accurate one. Two hundred fifty-nine CT scans were taken from 11 cadaver vertebrae. The scans were performed with vertebrae in neutral position and angulated up to 20 degrees in the sagittal and frontal plane to simulate kyphosis/lordosis and side bending. Axial rotation was measured according to both methods. The mean difference between true and measured values was 3.7 +/- 6.7 (95% confidence limit) (Ho's method) and 2.3 +/- 3.7 (Aaro's method), respectively. Correlation with true axial rotation was r2 = 0.66 (Ho's method) and r2 = 0.77 (Aaro's method). We recommend using Aaro's method as the more accurate measure of axial rotation in scoliotic vertebrae.

The prediction of failure of the stem in THR by measurement of early migration using EBRA-FCA. Einzel-Bild-Roentgen-Analyse-femoral component analysis.

We report the ten-year results for three designs of stem in 240 total hip replacements, for which subsidence had been measured on plain radiographs at regular intervals. Accurate migration patterns could be determined by the method of Einzel-Bild-Roentgen-Analyse-femoral component analysis (EBRA-FCA) for 158 hips (66%). Of these, 108 stems (68%) remained stable throughout, and five (3%) started to migrate after a median of 54 months. Initial migration of at least 1 mm was seen in 45 stems (29%) during the first two years, but these then became stable. We revised 17 stems for aseptic loosening, and 12 for other reasons. Revision for aseptic loosening could be predicted by EBRA-FCA with a sensitivity of 69%, a specificity of 80%, and an accuracy of 79% by the use of a threshold of subsidence of 1.5 mm during the first two years. Similar observations over a five-year period allowed the long-term outcome to be predicted with an accuracy of 91%. We discuss the importance of four different patterns of subsidence and confirm that the early measurement of migration by a reasonably accurate method can help to predict long-term outcome. Such methods should be used to evaluate new and modified designs of prosthesis.

Measuring forces and frequency during active compression decompression cardiopulmonary resuscitation: a device for training, research and real CPR.

Active compression decompression (ACD) cardiopulmonary resuscitation (CPR) is possibly a superior alternative to standard (STD) CPR, but an optimal compression and decompression pattern has to be ensured. ACD-CPR can be evaluated during CPR training sessions using commercially available manikins; however devices for recording compression and decompression forces or frequency during real CPR are lacking. Using the Ambu CardioPump without changing its mechanical characteristics, two force transducers were integrated into the ACD device. Using specially designed electronics and a portable computer, compression and decompression forces were measured and displayed continuously and compression frequency and the compression decompression phase are calculated on-line during real CPR action. All measured parameters were stored on a hard disk for later retrieval and analysis. Linearity of force measurement was better than 6% within a -250- +500 N range. The error in repeatability was below 5% thus outperforming the original mechanical force measurement system of the Ambu CardioPump. Compression frequency was calculated very accurately (error < 1%). The system has been successfully used during CPR training, during ACD-CPR in 37 corpses under research conditions and in five out-of-hospital CPR casualties. Simple and safe in use, our modified CardioPump with integrated electronics provides an important, technically advanced solution for monitoring ACD-CPR on-line. It warrants quality assurance during ACD-CPR training and in real CPR scenarios and guarantees accurate recording of compression and decompression forces and compression frequency.

Effects of prolonged strenuous endurance exercise on plasma myosin heavy chain fragments and other muscular proteins. Cycling vs running.

BACKGROUND: This study evaluates creatine kinase, myosin heavy chain, and cardiac troponin blood levels following three types of exercise: 1) short-distance uphill or downhill running; 2) alpine ultramarathon; and 3) alpine long-distance cycling. EXPERIMENTAL DESIGN: Comparative field study; follow-up up to 10 days. SETTING: Department of Sports Medicine. All biochemical markers were analysed at the Department of Medical Chemistry and Biochemistry. PATIENTS OR PARTICIPANTS: Subjects included healthy, trained males (N = 53). All subjects were nonsmokers and free from medication prior to and during the study. Each volunteer was an experienced runner or cyclist, who had at least once successfully finished the Swiss Alpine Marathon of Davos or the Otztal-Radmarathon before. INTERVENTIONS: Running or cycling. MEASURES: Plasma concentrations of creatine kinase, myosin heavy chain fragments and cardiac troponins were measured to diagnose skeletal and cardiac muscle damage, respectively. RESULTS: Skeletal muscle protein release is markedly different between uphill and downhill running, with very little evidence for muscle damage in the uphill runners. There is considerable muscle protein leakage in the ultramarathoners (67 km distance; 30 km downhill running). In contrast, only modest amounts of skeletal muscle damage are found after alpine long-distance cycling (230 km distance). CONCLUSIONS: This study proves that there is slow-twitch skeletal muscle fiber damage after prolonged strenuous endurance exercise and short-distance downhill running. Exhaustive endurance exercise involving downhill running and short-distance downhill running lead to more pronounced injury than strenuous endurance exercise involving concentric actions. From our results there is no reason for suggesting that prolonged intense exercise may induce myocardial injury in symptom-less athletes without cardiac deseases.

Acoustic Tumor Surgery and Tinnitus.

A total of 311 patients with a unilateral acoustic neurinoma were operated on via the enlarged middle cranial fossa approach. A total tumor removal was achieved in 98% of cases. The mortality was 0.6%. Overall in acoustic neurinoma surgery, the percentage rates of meningitis (1.6%), cerebrospinal fluid fistula (1.6% requiring surgery), and neurological deficits were fairly low. The facial nerve could be preserved anatomically in 99%. A House I or House II classification was demonstrated in 91% of all tumors and in 98% of small- and medium-sized tumors. Preservation of the hearing function was possible in 49% of all patients (71% in small tumors). A positive effect on tinnitus usually occurred in 45% of cases. The enlarged middle cranial fossa approach allows function-preserving surgery of the cranial nerves (e.g., the facial and cochlear nerves) and cerebral structures, even including total removal of large acoustic neurinomas of up to 3-4 cm.

Review of active compression-decompression cardiopulmonary resuscitation (ACD-CPR). Analysis of iatrogenic complications and their biomechanical explanation.

Our review takes a critical look at the active compression-decompression technique (ACD) for cardiopulmonary resuscitation (CPR). ACD-CPR was developed following a report of successful resuscitation performed by a medical amateur using a household plunger. The efficacy of the principle of active decompression has been demonstrated by animal and human studies. Potential iatrogenic complications from the CardioPump were evaluated only when large clinical trials were already underway. Our prospective analysis of autopsy patients and systematic randomised studies in corpses prove that ACD-CPR using the CardioPump considerably increases the rate of iatrogenic complications and especially of sternum fractures. The experimental use of the CardioPump in corpses and the analysis of a variety of different parameters, especially of the rubber cushion pads mounted in the silicone cup to prevent skin abrasions, revealed a statistically significant correlation between sternum fractures and female sex (P < 0.01) and usage of the rubber cushion pad (P = 0.045). Biomechanical studies showed that the transmission of forces from the CardioPump is greatly dependent on chest shape. The lower the sternum is sunken compared with the surrounding structures, the higher the force which is transmitted via the central area of the device onto the sternum. The rubber cushion pad shortens the distance between CardioPump and sternum by 5 mm and therefore increases the sternal loading. Sex differences in the shape of the sternum and especially the thickness may account for the significant correlation between sternum fractures and female sex.

Active compression-decompression resuscitation: the influence of different chest geometries on the force transmission.

Active compression-decompression cardiopulmonary resuscitation (ACD-CPR) is performed using a plunger-like suction device applied onto the chest. Forces are partly transferred through the center of this device as well as through the peripheral ring of the plunger's lip seal. We analysed the load transmission distribution of the Ambu CardioPump; therefore a homemade mechanical model was used for simulating different chest geometries. We applied compression forces up to 750N on the device using a 'material testing machine', and we determined the load transferred through the central part of the device and the peripheral ring respectively. The results show that the deeper the sternum is inbeded in the chest the more force is distributed onto the peripheral ring of the plunger's vacuum cup. For a simulated flat chest, 70 N was transferred through the peripheral ring; at a simulated sternal depression of 20 mm, more than 300 N were transferred peripherally. This study points out that different chest geometries have to be considered when using CardioPump.