- Email: [email protected]
Forces in the forefoot during locomotion
Abstracts
490
Assessment of the patellofemoral articulation by vibration arthrometry D.A. Barr, A. Hamllton, P. Maginn, P. Watson, W.G. Kemohan, R.A.B. Mollan Department of Otthopcledic Surgery, Muegmve Park Hospbl,
Belfaet, Northern Ireland, BTS 7JB
Movement of the knee joint at low speed Induces vibration of the patella which has been detected by means of accelerometers.
Amplitude ar$ frequency of this vibration is extremely sensitive to the speed of joint movement.
In
order, therefore, to constrain the joint to move at constant angular speed, a machine has been constructed to control joint movement. The machine consists of a raised reclining seat, with a moving cradle to support the lowerlimb.The vibrations Induced In the patella when the joint is moved at constant angular speed, under the control of the machine, have been detected and analysed. The vibrational signal was continuous, comprising a series of similar vibration “beats” and has been termed Physiological Patellofemoral Crepltus.
This signal has been found to vary in frequency and
amplitude depending on the frictional and compliance mechanical properties of patellofemoral articular cartilage, which are believed to contribute to anterior knee pain. This technique may therefore be used as a non-invasive means of assessing In-viva the properties of patellofemoral articular cartilage and of diagnosing the cause of anterior knee pain.
PATELLAR STRESS PREDICTION BY MATHEMATICAL SIMULATION M. LENGSFELD, P. DbRNER, G. RAZICH, P. GRISS Department ofOrthopedic Surgrry, Phlllpps - University Marburg, Germany The presented model is a sagittal 2-D approximation of the joint, which is similiar to previously published mathematical models (VAN EIJDEN et al. 1986, PLlTZ and REITHMEIER 1987) and validated by morphological data. Calculation of stress distribution is based on the model of the patella to be a beam, which is supported by a fulcrum (MAQUET 1987). Geometry and mineral distribution is evaluated on x-rays of 5 mm thick cross-sections from 22 patellae by morphometry and densitogmphy. ‘Ihe horizontal plane of the patella, where the contact point is located. represents always the part of maximal patellar stress in that particular position of the knee joint. investigations close to the proximal and distal patellar pole reveal small stress exposure up to 150 % only (Quadriceps force * 100 I). At a flexion angle of SO degree stress reaches its maximum within the central part of the patella. The plane more distal reaches maximal stress at about 80 degree flexion of the knee joint. Superficial contents reach its maximum at the planes of cross sections corresponding to the planes maximum stress is predicted. In agreement to the asymmetry of the stres distribution diagram, mineral concentration is higher at the ventral margin of the patella. Besides other clinical and biological aspects, our results give basic biomechanical data to perform postoperative exercises, which are individually adapted to the heigth of a transversal patellar fracture.
FOOT FORCES IN THE FOREFOOT DURING LOCOMOTION. H.A.C.JACOB Biomechanics Lab., Dept. of Orthopaedic Surgery, Balgrist, University of Zurich, Switzerland. The object of this study was to estimate the forces acting along tendons and across joint surfaces of the forefoot during locomotion, especially within the first two rays of the foot. After obtaining anthropometric information on the foot that included the topography of joint surfaces and the spatial position of tendons relative to the joints, external ground reaction forces acting under the toe pads and metatarsal heads during normal level walking at a speed of 80 m/min were measured, thus enabling the internal forces within the structure of the forefoot to be calculated. The results obtained from eleven test subjects with 'normal' feet showed that the pad of the great toe is subjected to a mean peak load of about 30% body weight (BW) whereas that of the 2nd toe is loaded only to about 6% BW. This necessitates corresponding forces in the flexor tendons which in turn leads to the important observation that the tension in the flexor hallucis tendons (short and long) actually support the 1st ray like a compression member of a truss (longitudinal arch support!), whereas the 2nd metatarsal is exposed mainly to bending.stresses, being held firmly at its base in a cantilever fashion. Simultaneously, average peak forces under the metatarsal heads of 15 % BW and 30 % BW for the 1st and 2nd rays, respectively, were observed. Literature: Jacob, H.A.C.: Biomechanics of the Forefoot. Ph.D.Thesis, University of Strathclyde, Glasgow, 1989.
490
Assessment of the patellofemoral articulation by vibration arthrometry D.A. Barr, A. Hamllton, P. Maginn, P. Watson, W.G. Kemohan, R.A.B. Mollan Department of Otthopcledic Surgery, Muegmve Park Hospbl,
Belfaet, Northern Ireland, BTS 7JB
Movement of the knee joint at low speed Induces vibration of the patella which has been detected by means of accelerometers.
Amplitude ar$ frequency of this vibration is extremely sensitive to the speed of joint movement.
In
order, therefore, to constrain the joint to move at constant angular speed, a machine has been constructed to control joint movement. The machine consists of a raised reclining seat, with a moving cradle to support the lowerlimb.The vibrations Induced In the patella when the joint is moved at constant angular speed, under the control of the machine, have been detected and analysed. The vibrational signal was continuous, comprising a series of similar vibration “beats” and has been termed Physiological Patellofemoral Crepltus.
This signal has been found to vary in frequency and
amplitude depending on the frictional and compliance mechanical properties of patellofemoral articular cartilage, which are believed to contribute to anterior knee pain. This technique may therefore be used as a non-invasive means of assessing In-viva the properties of patellofemoral articular cartilage and of diagnosing the cause of anterior knee pain.
PATELLAR STRESS PREDICTION BY MATHEMATICAL SIMULATION M. LENGSFELD, P. DbRNER, G. RAZICH, P. GRISS Department ofOrthopedic Surgrry, Phlllpps - University Marburg, Germany The presented model is a sagittal 2-D approximation of the joint, which is similiar to previously published mathematical models (VAN EIJDEN et al. 1986, PLlTZ and REITHMEIER 1987) and validated by morphological data. Calculation of stress distribution is based on the model of the patella to be a beam, which is supported by a fulcrum (MAQUET 1987). Geometry and mineral distribution is evaluated on x-rays of 5 mm thick cross-sections from 22 patellae by morphometry and densitogmphy. ‘Ihe horizontal plane of the patella, where the contact point is located. represents always the part of maximal patellar stress in that particular position of the knee joint. investigations close to the proximal and distal patellar pole reveal small stress exposure up to 150 % only (Quadriceps force * 100 I). At a flexion angle of SO degree stress reaches its maximum within the central part of the patella. The plane more distal reaches maximal stress at about 80 degree flexion of the knee joint. Superficial contents reach its maximum at the planes of cross sections corresponding to the planes maximum stress is predicted. In agreement to the asymmetry of the stres distribution diagram, mineral concentration is higher at the ventral margin of the patella. Besides other clinical and biological aspects, our results give basic biomechanical data to perform postoperative exercises, which are individually adapted to the heigth of a transversal patellar fracture.
FOOT FORCES IN THE FOREFOOT DURING LOCOMOTION. H.A.C.JACOB Biomechanics Lab., Dept. of Orthopaedic Surgery, Balgrist, University of Zurich, Switzerland. The object of this study was to estimate the forces acting along tendons and across joint surfaces of the forefoot during locomotion, especially within the first two rays of the foot. After obtaining anthropometric information on the foot that included the topography of joint surfaces and the spatial position of tendons relative to the joints, external ground reaction forces acting under the toe pads and metatarsal heads during normal level walking at a speed of 80 m/min were measured, thus enabling the internal forces within the structure of the forefoot to be calculated. The results obtained from eleven test subjects with 'normal' feet showed that the pad of the great toe is subjected to a mean peak load of about 30% body weight (BW) whereas that of the 2nd toe is loaded only to about 6% BW. This necessitates corresponding forces in the flexor tendons which in turn leads to the important observation that the tension in the flexor hallucis tendons (short and long) actually support the 1st ray like a compression member of a truss (longitudinal arch support!), whereas the 2nd metatarsal is exposed mainly to bending.stresses, being held firmly at its base in a cantilever fashion. Simultaneously, average peak forces under the metatarsal heads of 15 % BW and 30 % BW for the 1st and 2nd rays, respectively, were observed. Literature: Jacob, H.A.C.: Biomechanics of the Forefoot. Ph.D.Thesis, University of Strathclyde, Glasgow, 1989.