Biomedical subjects

Michael M Morlock

Publications and source records attributed to Michael M Morlock.

8 recordsLinked to original sources

PubMed2007

Intra-articular pressure measurement in the radioulnocarpal joint using a novel sensor: in vitro and in vivo results.

PURPOSE: To determine the amount and distribution of forces transmitted across the human radioulnocarpal joint under physiologic conditions in vivo. We performed an in vitro validation of a specifically developed capacitive pressure-sensor device and an in vivo measurement of force transmission and pressure distribution at the radioulnocarpal joint in a healthy volunteer. METHODS: A new capacitive pressure-sensor device was adapted for intra-articular pressure measurement in the human radioulnocarpal joint. The technical characteristics of the device were determined and the sensor was validated in fresh-frozen cadaver tests. Force transmission across the radioulnocarpal joint then was measured in healthy volunteers under local anesthesia. RESULTS: The sensor delivered reproducible measurements of forces across the radioulnocarpal joint and their distribution in the cadaver experiment. In vivo, 2 centers of force transmission were identified. None of these centers correlated with previous findings in the literature. More force is transmitted across the ulnar side of the radioulnocarpal joint than previously thought. The results are consistent with clinical findings. CONCLUSIONS: The novel sensor device is suitable for intra-articular pressure measurement in the human radioulnocarpal joint in vitro and in vivo.

Biomechanical Phenomena↗

PubMed2006

Consistent hydration of intervertebral discs during in vitro testing.

Spinal specimens are commonly sprayed with saline solution during mechanical testing to ensure adequate hydration. However, potting of vertebrae inhibits physiological fluid exchange through the porous endplates during loading. This un-physiological flow regime may influence mechanical properties of intervertebral discs and therefore of the whole spinal unit. The objective of this study was to evaluate a new method of spinal specimen hydration through the vertebral body during in vitro testing in order to improve consistency of mechanical behaviour. Ovine lumbar anterior column units were prepared for testing. Half of the specimens were sprayed with Ringer's solution and wrapped in plastic foil. The remainder received an additional saline infusion into the centre of each vertebral body. Three consecutive compression steps were applied by a hydraulic testing machine. Average forces within four sectors of the relaxation curves were compared. Applying saline infusion improves the consistency of consecutive relaxation curves. Differences between consecutive relaxation curves were less than those for standard hydration. The forces at the beginning of the relaxation curve were also lower for the infusion method. The standard deviation between specimens of each group was lower for saline infusion of vertebrae. Hence, the new method leads to more consistent in vitro testing conditions.

Animals↗

PubMed2005

Relationship between physical, biochemical and biomechanical properties of tissue-engineered cartilage-carrier-constructs.

Three-dimensional cartilage-carrier-constructs were produced according to a standard protocol from chondrocytes of an adult mini-pig. Physical parameters (height and weight) correlated very well with total DNA content (r2 = 0.86, re. 0.94). The relation between DNA content and glycosaminoglycan content was less but still significant. No significant relationship was found between the elasticity module and the DNA content, even if the elasticity module increased slightly at higher DNA content. With respect to later implantation, selection of a construct for implantation based on the weight, which can be determined non-invasive and under sterile conditions, seems to be justifiable.

Animals↗

PubMed2005

Load-shift--numerical evaluation of a new design philosophy for uncemented hip prostheses.

All hip replacement prostheses alter the load transfer from the hip joint into the femur by changing the mechanical loading of the proximal femur from an externally to an internally loaded system. This alteration of the load transfer causes stress shielding and might lead to severe bone loss, especially with uncemented prostheses. To minimize these effects, load transfer to the femur should occur as proximal as possible. In order to support sufficient primary stability, however, directly post operative (PO) distal stabilization is reasonable. Consequently, the prostheses have to alter its mechanical characteristics after implantation. This concept is referred to as load-shift concept. Primary stability during the early PO state is provided by a prosthesis shaft, which is widened at the tip by a biodegradable pin. After resorption of the pin load transfer occurs no longer distally. The objective of this study was the numerical evaluation of the load-shift concept. The analysis was performed with a finite element model. Three-dimensional non-linear dynamic gait analyses data were used to evaluate whether the load transfer during walking can be altered effectively by insertion and resorption of a distal pin. Directly PO 38% of the transverse load is transferred through the prosthesis shaft and micromotion of the proximal prostheses tip is below 55 microm. After resorption of the pin, no transverse loads are transferred through the prosthesis shaft. Therefore, the loading of the proximal bone tissue is far more pronounced than in the case of a standard prosthesis, demonstrating the feasibility of the load-shift concept. A balanced degradation of the pin simultaneously with the ingrowth of the prosthesis is expected to reduce hip replacement complications.

Absorbable Implants↗

PubMed2004

Adaptation of mechanical, morphological, and biochemical properties of the rat growth plate to dose-dependent voluntary exercise.

Mechanical loading has been shown to modulate longitudinal bone growth and cellular activity of the growth plate. Nevertheless, limited and controversial results exist regarding the effect of exercise on a physiological level on the growth plate. The present study investigated whether dose-dependent voluntary exercise has an influence on morphological, biochemical, and mechanical factors of the distal femoral growth plate of immature rats. Female growing Sprague-Dawley rats were randomly assigned to a unlimited exercise group (UE, n = 10), a limited exercise group (LE, n = 10), and a sedentary control group (CON, n = 10). The exercise groups were trained voluntarily in a running wheel for 8 weeks. The UE group could use the running wheel every time, whereas the LE group had timely restricted (50%) access. After sacrifice, the right femur was prepared for histomorphometric analysis and immunohistochemical staining of the distal growth plate. Mechanical testing was carried out on the distal growth plate of the left femur in shear direction. At the end of the study, the UE group had a significantly lower body mass than the CON group. There was no significant difference in overall femoral length between the groups. The height of the growth plate and the proliferation zone was significantly greater in the CON group than in both exercise groups. Only the LE group had a significantly lower hypertrophic zone and matrilin-3 staining pattern than the CON group. Osteonectin was located in the matrix of the upper hypertrophic zone in the UE group, whereas the LE and CON group showed more chondrocytes in the hypertrophic and lower proliferation zones stained for osteonectin, suggesting a higher level of mineralization in the growth plate of the UE group. No variations of mechanical properties of the distal femoral growth plate were detected. These results clearly demonstrate adaptations of morphology and biochemical parameters to the dose of running exercise, which do not result in significant differences in mechanical properties or bone length between the UE, LE, and CON groups.

Adaptation, Physiological↗

PubMed2003

The influence of resting periods on friction in the artificial hip.

Insufficient tribologic performance of total joint components is a major cause of prostheses failure. Wear has been studied intensively using testing machines that apply continuous motions. Human locomotion, however, is not well represented by continuous motions alone. Singular events and resting periods are a substantial part of daily activities. Resting does influence adhesion in the artificial joint with possible effects on friction, wear, and loosening. The current study evaluated the effects of resting on the frictional properties of hip prosthesis components. The activity measurements of 32 patients with artificial hip replacements were analyzed for resting durations of the hip. A pin-on-ball screening device was used to determine friction after characteristic resting periods and during continuous oscillating motion. All common articulation pairings were investigated. Prolonged and frequent resting periods of the hip were found for the patients. Initial friction increased with increasing resting duration for all tested materials (between 41% and 191%). The metal-on-metal articulations showed the highest friction level (0.098 for sliding) and the highest increase (191%) in friction with resting duration (0.285 after resting periods of 60 seconds). A high static frictional moment after resting periods might present a risk for aseptic implant loosening. Therefore, large head diameters of metal-on-metal joints should be used with caution, especially when additional unfavorable risk factors such as obesity, weak bone-implant interface, or high activity level are present.

Aged↗

PubMed2003

Comparison of robotic-assisted and manual implantation of a primary total hip replacement. A prospective study.

BACKGROUND: Robotic-assisted total hip replacement has become a common method of implantation, especially in Europe. It frequently has been postulated that robotic reaming would result in an improved clinical outcome due to the better fit of the prosthesis, but that has never been demonstrated in a prospective study, to our knowledge. The purpose of this study was to compare robotic-assisted implantation of a total hip replacement with conventional manual implantation. METHODS: One hundred and fifty-four patients scheduled for total hip replacement were randomly assigned to undergo either conventional manual implantation of an S-ROM prosthesis (eighty patients) or robotic-assisted implantation of such a prosthesis (seventy-four patients). The five-axis ROBODOC was used for the robotic-assisted procedures. Preoperatively as well as at three, six, twelve, and twenty-four months after surgery, the scores according to the Harris and Merle d'Aubigné systems and the Mayo clinical score were determined. Radiographs made at these intervals were analyzed for evidence of loosening, prosthetic alignment, and heterotopic ossification. RESULTS: Thirteen (18%) of the seventy-four attempted robotic implantations had to be converted to manual implantations as a result of failure of the system. The duration of the robotic procedures was longer than that of the manual procedures (mean and standard deviation,107.1 +/- 29.1 compared with 82.4 +/- 23.4 minutes, p < 0.001). Limb-length equality (mean discrepancy, 0.18 +/- 0.30 compared with 0.96 +/- 0.93 cm, p < 0.001) and varus-valgus orientation of the stem (mean angle between the femur and the shaft of the prosthesis, 0.34 degrees +/- 0.67 degrees compared with 0.84 degrees +/- 1.23 degrees, p < 0.001) were better after the robotic procedures. At six months, slightly more heterotopic ossification was seen in the group treated with robotic implantation. The group treated with robotic implantation had a better Mayo clinical score at six and twelve months and a better Harris score at twelve months; however, by twenty-four months, no difference was found between the groups with regard to any of the three scores. Dislocation was more frequent in the group treated with robotic implantation: it occurred in eleven of the sixty-one patients in that group compared with three of eighty in the other group (p < 0.001). Recurrent dislocation and pronounced limping were indications for revision surgery in eight of the sixty-one patients treated with robotic implantation compared with none of the seventy-eight (excluding two with revision for infection) treated with manual insertion (p < 0.001). Rupture of the gluteus medius tendon was observed during all of the revision operations. CONCLUSIONS: The robotic-assisted technology had advantages in terms of preoperative planning and the accuracy of the intraoperative procedure. Disadvantages were the high revision rate; the amount of muscle damage, which we believe was responsible for the higher dislocation rate; and the longer duration of surgery. This technology must be further developed before its widespread usage can be justified.

Aged↗

PubMedDate not supplied

Bone-patellar tendon-bone grafts for anterior cruciate ligament reconstruction: an in vitro comparison of mechanical behavior under failure tensile loading and cyclic submaximal tensile loading.

BACKGROUND: Secure fixation is an important factor in the success of anterior cruciate ligament reconstruction. HYPOTHESIS: There is no difference in the mechanical behavior of reconstructions from method of fixation or method of testing. STUDY DESIGN: Controlled laboratory study. METHODS: Anterior cruciate ligament reconstructions were performed with bone-patellar tendon-bone grafts in 48 human cadaveric knees. Three different fixation methods (Endobutton, interference screw, suture-post fixation) were compared under failure tensile loading and cyclic submaximal tensile loading. RESULTS: No difference was observed in ultimate load among the three techniques. Stiffness of the grafts was significantly lower for the suture technique than for the interference screw technique. Cyclic loading revealed significantly different failure rates: 0% of the Endobutton, 38% of the interference screw, and 100% of the suture-post groups. The relative movement of the femoral bone plug and the migration of the bone plug out of the femoral canal were lowest in the interference screw group. CONCLUSIONS: The suture-post fixation is not recommended. The interference screw technique showed the best results, but results were age-dependent, suggesting its best use is in younger patients. The Endobutton technique is recommended for older patients. CLINICAL RELEVANCE: Results of testing are useful to the surgeon in making a choice of reconstruction technique.

Adult↗