Antonius Rohlmann

Publications (169) View all

• Article: In vivo measurement of shoulder joint loads during walking with crutches.

  P Westerhoff, F Graichen, A Bender, A Halder, A Beier, A Rohlmann, G Bergmann
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  ABSTRACT: Following surgery or injury of the lower limbs, the use of walking aids like crutches can cause high loads on the shoulder joint. These loads have been calculated so far with computer models but with strongly varying results. Shoulder joint forces and moments were measured during crutch-assisted walking with complete and partial unloading of the lower limbs. Using telemeterized implants in 6 subjects axillary crutches and forearm crutches were compared. A force direction was more in the direction of the long humeral axis, and slightly lower forces were assumed using axillary crutches. Similar force magnitudes as those experienced during previously measured wheelchair weight relief tasks were expected for complete unloading. The friction-induced moment was hypothesized to act mainly around the medio-lateral axis during the swing phase of the body. Maximum loads of up 170% of the bodyweight and 0.8% of the bodyweight times meter were measured with large variations among the patients. Higher forces were found in most of the patients using forearm crutches. The hypothesized predominant moment around the medio-lateral axis was only found in some patients. More often, the other two moments had larger magnitudes with the highest values in female patients. The assumed different load direction could only be found during partial unloading. In general the force magnitudes were in the range of activities of daily living. However, the number of repetitions during long-lasting crutch use could lead to shoulder problems as a long-term consequence. The slightly lower forces with axillary crutches could be caused by loads acting directly from the crutch on the scapula, thus bypassing the glenohumeral joint. The higher bending moments in the female patients could be a sign of lacking muscle strength for centring the humeral head on the glenoid.
  Clinical biomechanics (Bristol, Avon) 05/2012; 27(7):711-8. · 1.76 Impact Factor
• Article: Spinal loads during position changes.

  A Rohlmann, R Petersen, V Schwachmeyer, F Graichen, G Bergmann
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  ABSTRACT: Recommendations exist how patients should change from one body position to another in order to keep the spinal loads low. However, until now it is not clear whether the loads are in fact lower if the patients follow these recommendations. The aim was to measure the loads while changing the body position. Telemeterized vertebral body replacements have been inserted into 5 patients who had a severe compression fracture of a lumbar vertebral body. The acting loads were measured during a changing of the body position while lying and when moving from lying to sitting, from sitting to standing and vice versa. When the lying patients changed their position according to the physiotherapist's recommendations, the resultant force was nearly as high as it was during relaxed standing. Otherwise, the force was nearly twice as high. Changing from a lateral lying position to sitting and vice versa caused forces of about 180% of those seen for standing when the recommendations were heeded. Without instructions, the loads were about 70% higher. Use of a trapeze bar mounted to the bed did not increase the loads. Rising from a chair with the arms hanging down laterally led to average resultant forces of 380% related to standing. Placing the hands on armrests reduced this value to 180%. High forces may act on the spine when changing from one body position to another. These loads can be minimized when following the physiotherapist's instructions and when supporting the upper body by the arms.
  Clinical biomechanics (Bristol, Avon) 05/2012; 27(8):754-8. · 1.76 Impact Factor
• Article: Einfluss von Implantaten zum Ersatz eines Wirbelkörpers auf das mechanische Verhalten der Lendenwirbelsäule

  A. Rohlmann, T. Zander, M. Fehrmann, C. Klöckner, G. Bergmann
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  ABSTRACT: Es wurde ein detailliertes Computermodell der Lendenwirbelsäule erstellt. In das Rechenmodell wurden ein bisegmentales Wirbel-Fixateur-interne-System sowie nacheinander 2 unterschiedliche Implantate zum Ersatz eines Wirbelkörpers eingebaut. Belastet wurde das Modell mit Momenten in den 3 anatomischen Hauptebenen, sowie mit Kräften wie beim Stehen. Durch einen Wirbelkörperersatz wird die Beweglichkeit im betreffenden Bereich drastisch reduziert. In den benachbarten Segmenten hat ein Implantat bei den gewählten Belastungen nur einen minimalen Einfluss auf die Beweglichkeit und Spannungen. Eine Vorlast, wie sie beispielsweise durch die zusätzliche Distraktion eines passgenau eingebrachten ventralen Implantats aufgebracht wird, hat einen starken Einfluss auf die Spannungen in den implantatnahen Endplatten. Unterschiedliche Größen der Kontaktflächen zwischen Implantat und Wirbelkörper haben nur einen lokalen Effekt auf die Spannungsverteilung. A three-dimensional, nonlinear finite element model of the lumbar spine was created. A bisegmental internal spinal fixation device and successively two kinds of vertebral body replacements were integrated into the computer model. The model was loaded with pure moments in the three anatomical main planes as well as with forces that are expected during standing. A vertebral body replacement drastically reduces the mobility in the implant region. An implant has only a minor influence on the mobility and stresses in the adjacent regions for the loading cases chosen. A preload, for example, caused by additional distraction from the precisely fitted ventral implant, exerts a very strong effect on the stresses in the end plates that are in contact with the implant. Different sizes of the contact area between implant and vertebral body have only a local effect on stress distribution.
  Der Orthopäde 04/2012; 31(5):503-507. · 0.51 Impact Factor
• Article: Stabilisierung der osteoporotischen Wirbelsäule unter biomechanischen Gesichtspunkten

  C.-E. Heyde, A. Rohlmann, U. Weber, R. Kayser
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  ABSTRACT: Die Osteoporose der Wirbelsäule führt zu Veränderungen der knöchernen Struktur und damit der biomechanischen Eigenschaften der Wirbelkörper mit einer erhöhten Vulnerabilität und einer Reduktion der Belastbarkeit der gesamten Wirbelsäule. Operative Maßnahmen müssen diese Veränderungen berücksichtigen. Die Stabilität zementaugmentierter Wirbel und damit die resultierende Belastung angrenzender Strukturen werden durch eine Reihe von Faktoren beeinflusst. Hinsichtlich des Volumens, der Eigenschaften, der Art der günstigsten Einbringung und der Verteilung des Knochenzements im Wirbel liegen unterschiedliche Untersuchungsergebnisse vor. Damit verbleibt die optimale Vorgehensweise bezüglich der zementaugmentierenden Verfahren bei nachgewiesen guten klinischen Ergebnissen in der Diskussion. Beim Einsatz von Implantaten liegen heute Daten vor, die einen an die veränderten biomechanischen Eigenschaften des Knochens angepassten Implantateinsatz ermöglichen. Mit längerstreckigen Instrumentationen, additiven stabilisierenden Maßnahmen, einer Zementaugmentation der Schrauben und einer Anpassung des Implantatdesigns lässt sich die Sicherheit für die Patienten erhöhen. Unabhängig von der gewählten Vorgehensweise scheint der Wiederherstellung des regelrechten Profils der Wirbelsäule eine überragende Bedeutung zuzukommen. The altered trabecular structure of the osteoporotic spine leads to an increased vulnerability of its biomechanical characteristics and reduction of load resistance. Therefore, any surgical procedure must account for these circumstances. In cement-augmented vertebrae, both the overall stability and load transfer to the adjacent structures are influenced by a variety of factors. This has been demonstrated by different findings regarding volume, special characteristics, choice of approach and application, as well as distribution of the cement within the vertebral body. Independent of the well-known good clinical results, these features leave the discussion regarding the most appropriate form of cement-augmenting technique open. In cases where implants are required, there are increasing data to allow for an appropriate choice of stabilizing devices to fit the biomechanical demands in poor bone quality. Thereby, multilevel instrumentation, additive stabilization techniques, cement-augmented pedicle screws and adapted implant designs ensure and increase patient safety. However, regardless of the procedure chosen to stabilize the osteoporotic spine, reconstruction of the column profile appears to be of pre-eminent importance. SchlüsselwörterWirbelsäule-Osteoporose-Biomechanische Veränderungen-Implantate-Zementaugmentation KeywordsSpine-Osteoporosis-Biomechanical alteration-Implants-Cement augmentation
  Der Orthopäde 04/2012; 39(4):407-416. · 0.51 Impact Factor
• Article: Measurement of shoulder joint loads during wheelchair propulsion measured in vivo.

  P Westerhoff, F Graichen, A Bender, A Halder, A Beier, A Rohlmann, G Bergmann
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  ABSTRACT: Recent in vivo measurements show that the loads acting in the glenohumeral joint are high even during activities of daily living. Wheelchair users are frequently affected by shoulder problems. With previous musculoskeletal shoulder models, shoulder joint loading was mostly calculated during well-defined activities like forward flexion or abduction. For complex movements of everyday living or wheelchair propulsion, the reported loads vary considerably. Shoulder joint forces and moments were measured with telemeterized implants in 6 subjects. Data were captured on a treadmill at defined speeds and inclinations. Additional measurements were taken in 1 subject when lifting the body from the wheelchair, using his arms only, and in 2 subjects when rapidly accelerating and stopping the wheelchair. The influence of the floor material on shoulder joint loading was accessed in 2 subjects. In general, the maximum shoulder loads did not exceed those during daily living but the time courses and magnitudes of the loads intra-individually varied much. The highest forces acted during maximum acceleration and lifting from the wheelchair (128% and 188% of body weight). Grass was the only surface which led to a general load increase, compared to a smooth floor. The increased incidence of overuse injuries in wheelchair users are probably not caused by excessive load magnitudes during regular propulsion. The high number of repetitions is assumed to be more decisive.
  Clinical biomechanics (Bristol, Avon) 06/2011; 26(10):982-9. · 1.76 Impact Factor