Biomedical subjects

Christof Hurschler

Publications and source records attributed to Christof Hurschler.

At least 19 recordsLinked to original sources

PubMed2007

Dynamic measurement of patellofemoral kinematics and contact pressure after lateral retinacular release: an in vitro study.

The purpose of this study was to investigate the influence of lateral retinacular release and medial and lateral retinacular deficiency on patellofemoral position and retropatellar contact pressure. Human knee specimens (n = 8, mean age = 65 SD 7 years, all male) were tested in a kinematic knee-simulating machine. During simulation of an isokinetic knee extension cycle from 120 degrees to full extension, a hydraulic cylinder applied sufficient force to the quadriceps tendon to produce an extension moment of 31 Nm. The position of the patella was measured using an ultrasound based motion analysis system (CMS 100, Zebris). The amount of patellofemoral contact pressure and its pressure distribution was measured using a pressure sensitive film (Tekscan, Boston). Patellar position and contact pressure were first investigated in intact knee conditions, after a lateral retinacular release and a release of the medial and lateral retinaculum. After lateral retinacular release the patella continuously moved from a significant medialised position at flexion (P = 0.01) to a lateralised position (P = 0.02) at full knee extension compared to intact conditions, the centre of patellofemoral contact pressure was significantly medialised (0.04) between 120 degrees and 60 degrees knee flexion. Patellofemoral contact pressure did not change significantly. In the deficient knee conditions the patella moved on a significant lateralised track (P = 0.04) through the entire extension cycle with a lateralised centre of patellofemoral pressure (P = 0.04) with a trend (P = 0.08) towards increased patellofemoral pressure. The results suggest that lateral retinacular release did not inevitably stabilise or medialise patellar tracking through the entire knee extension cycle, but could decrease pressure on the lateral patellar facet in knee flexion. Therefore lateral retinacular release should be considered carefully in cases of patellar instability.

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PubMed2006

Dynamic measurement of patellofemoral contact pressure following reconstruction of the medial patellofemoral ligament: an in vitro study.

BACKGROUND: Surgical reconstruction of the medial patellofemoral ligament used to stabilize the patella against lateral dislocation may concomitantly produce alteration of the patellofemoral contact pressure distribution. Two different tendon transfer techniques of reconstructing the medial patellofemoral ligament, one dynamic and one static, as well as a proximal soft tissue realignment of the patella were investigated. METHODS: Eight human knee specimens were mounted in a kinematic knee simulator and isokinetic extension motion was simulated. Patellofemoral pressure was measured using a pressure sensitive film while a 100 N laterally directed dislocation load was applied to the patella. The specimens were evaluated in a physiologic state, as well as after dynamic reconstruction of the medial patellofemoral ligament using a distal transfer of the semitendinosus tendon, following static reconstruction using a semitendinosus autograft, and following proximal soft tissue realignment of the patella. FINDINGS: Following both reconstruction techniques of the medial patellofemoral ligament patellofemoral contact pressure was not significantly (P=0.49) altered. In contrast, after proximal realignment a trend (P=0.07) towards higher contact pressure near knee extension was observed. In the absence of a lateral dislocation load dynamic and static reconstruction resulted in a medialization (P=0.04) of the center of pressure, whereas under the application of a 100 N dislocation load the center of pressure showed no significant alteration. Following proximal realignment the center of pressure was significantly medialized without (P<0.01) and with a dislocation load (P=0.01) throughout the entire range of knee motion. INTERPRETATION: Static and dynamic ligament reconstruction of the medial patellofemoral ligament did not alter patellofemoral pressure. Proximal realignment, on the other hand, resulted in a constant medialization of the patellofemoral pressure. The data suggest that the reconstruction techniques would be associated with a low risk of causing premature cartilage degeneration due to excessive patellofemoral contact pressure, whereas proximal realignment could cause medial overload of the patellofemoral joint.

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PubMed2006

Influence of an infrapatellar fat pad edema on patellofemoral biomechanics and knee kinematics: a possible relation to the anterior knee pain syndrome.

INTRODUCTION: An edema of the infrapatellar fat pad following knee arthroscopy or in case of chronic anterior knee pain syndrome is suspected to increase the patellofemoral pressure by a modification of the patellofemoral glide mechanism. The study was performed to evaluate this hypothesis. MATERIALS AND METHODS: Isokinetic knee extension from 120 degrees of flexion to full extension was simulated on 10 human knee cadaver specimens (six males, four females, average age at death 42 years) using a knee kinemator. Joint kinematics was evaluated by ultrasound sensors (CMS 100, Zebris, Isny, Germany), and retro-patellar contact pressure was measured using a thin-film resistive ink pressure system (K-Scan 4000, Tekscan, Boston). Infrapatellar tissue pressure was analyzed using a closed sensor cell which was implanted inside the fat pad (GISMA, Buggingen, Germany). An inflatable fluid cell was implanted by ultrasound control in the center of the infrapatellar fat pad and filled subsequently with water to simulate a fat pad edema. All parameters were recorded and analyzed from 0 to 5 ml volume of the fluid cell. RESULTS: Simulating a fat pad edema resulted in a significant (P < 0.01) increase of the infrapatellar fat pad pressure (247 mbar at 0 ml to 615 mbar at 5 ml volume). In knee extension and flexion the patella flexion (sagittal plane) was decreased while we did not find any other significant influence of the edema on knee kinematics. During the analysis of the patellofemoral biomechanics, a simulated fat pad edema resulted in a significant (P < 0.05) decrease of the patellofemoral force between 120 degrees of knee flexion and full extension. The contact area was reduced significantly near extension (0 degree-30 degrees) by an average of 10% while the contact pressure was reduced at the entire range of motion up to 20%. CONCLUSION: An edema of the infrapatellar fat pad does not cause an increase of the patellofemoral pressure or a significant alteration of the patellofemoral glide mechanism. Anterior knee pain in case of a fat pad edema may be related to a significant increase of the tissue pressure and possible histochemical reactions.

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PubMed2006

In vitro measurement of patellar kinematics following reconstruction of the medial patellofemoral ligament.

This study compares the effects of two different techniques of medial patellofemoral ligament (MPFL) reconstruction, and proximal soft tissue realignment on patellar stabilization against lateral dislocation. Eight human cadaver knee specimens with no radiological pathomorpholgy on a straight lateral view, contributing to patellofemoral instability, were mounted in a kinematic knee simulator and isokinetic extension was simulated. Patellar kinematics were measured with an ultrasound positioning system (zebris) while a 100 N laterally directed force was applied to the patella. The kinematics were compared with intact knee conditions under MPFL deficient conditions, as well as following dynamic reconstruction of the MPFL using a distal transfer of the semitendinosus tendon, following static reconstruction by a semitendinosus autograft, and following proximal soft tissue realignment of the patella (Insall procedure). Dynamic reconstruction of the MPFL resulted in no significant alteration (P = 0.16) of patellar kinematics. Static reconstruction of the MPFL significantly medialized (P < 0.01) the patellar movement without, but restored intact knee kinematics under the laterally directed force. In contrast, following proximal soft tissue realignment, the patellar movement was constantly medialized and internally tilted (P = 0.04). Dynamic and static reconstruction of the MPFL create sufficient stabilization of the patella. Following proximal soft tissue realignment, the patellar position was over-medialized relative to intact knee conditions, which could lead to an overuse of the medial retropatellar cartilage.

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PubMed2006

Quantitative assessment of glenohumeral translation after anterior shoulder dislocation and subsequent arthroscopic bankart repair.

BACKGROUND: During the past decade, developments in arthroscopic technology have made arthroscopic repair of labral lesions feasible. However, results with the use of the transglenoid suture technique, or with the use of bioabsorbable tacks, have remained variable in the literature, and the recurrence rates are still inferior to those of open Bankart repair. HYPOTHESIS: Arthroscopic Bankart repair with suture anchors can re-create translational and rotational range of motion of the intact glenohumeral joint, and the number of preoperative dislocations has an influence on the result. STUDY DESIGN: Controlled laboratory study. MATERIALS: Twelve cadaveric shoulders were tested in a robot-assisted shoulder simulator. Anterior and posterior translation and external rotation were measured for intact, dislocated (shoulders were randomly selected to 1 of 3 groups, which were dislocated 1, 3, or 7 times), and repaired conditions at 0 degrees and 90 degrees of glenohumeral elevation. RESULTS: After shoulder dislocation, a significant increase was found in translation and rotation, confirming the creation of a traumatic shoulder instability model. Further testing of the specimen revealed that translational and rotational ranges of motion were reduced by arthroscopic Bankart repair at both testing positions. External rotation was decreased significantly at 0 degrees and 90 degrees of abduction. No significant differences were found between the 3 dislocation groups. CONCLUSION: The results demonstrate a sufficient biomechanical performance of arthroscopic Bankart repair using suture anchors in a traumatic anterior shoulder instability model. With the numbers available, no relationship was found between the number of dislocations and the postoperative result concerning translational or rotational motion. CLINICAL RELEVANCE: Glenohumeral translation and rotation after arthroscopic Bankart repair with use of suture anchors approached near normal values, confirming the clinical success of this technique.

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PubMed2006

In vitro investigation of the influence of tibial slope on quadriceps extension force after total knee arthroplasty.

The purpose of this study was to investigate the influence of tibial base plate angulation on knee kinematics and kinetics during knee arthroplasty. The amount of quadriceps force required to extend the knee and the anteroposterior displacement of a mobile bearing insert as well as tibiofemoral position were measured during an in vitro simulation of an isokinetic knee extension cycle. Human knee specimens (n = 7, mean age 62, range 52-75 years, all male) were tested in a kinematic knee simulating machine after total knee arthroplasty (TKA) with a mobile bearing insert prosthesis (Interax), Stryker/Howmedica). During simulation, a hydraulic cylinder applied sufficient force to the quadriceps tendon to produce an extension moment of 31 N m about the knee. The quadriceps load was measured using a load cell attached to the quadriceps tendon, the anteroposterior displacement of the mobile bearing insert as well as the relative tibiofemoral position was measured using an ultrasound base motion analysis system (CMS 100, Zebris). Quadriceps load, insert and tibial displacement were first investigated with the tibial base plate implanted with a neutral tibial base plate orientation, and subsequently after 10 degrees posterior angulation. The quadriceps forces needed to produce a 31 N m knee extension moment after TKA with neutral slope reached levels as high as 1,391 N (SD 82 N). After applying a posterior slope of 10 degrees , maximum quadriceps force was measured to be up to 1,303 N (SD 34 N, P = 0.04). The mobile bearing insert was observed to move up to 0.1 mm (SD 4.2 mm) anteriorly relative to the tibial base plate with neutral tibial slope, and up to 1.0 mm (SD 4.5 mm, P = 0.47) with tibial slope. Femoral position relative to the tibia moved from a posterior position of 13.1 mm (SD 4.0 mm) anteriorly up to 0.5 mm (SD 6.3 mm), and from 16.0 mm (SD 6.4 mm, P = 0.67) to 9.5 mm (SD 9.9 mm, P = 0.33) with a 10 degrees tibial slope. Posterior slope of the tibial base plate resulted in a more physiologic insert movement with a more posterior position of the femur and reduced quadriceps force especially in knee flexion angles above 60 degrees compared to TKA with a neutral slope of the tibial base plate. Thus, the data suggest that the quadriceps lever arm was improved, which might have positive effect in mobilization of patients after TKA.

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PubMed2006

Dynamic in vitro measurement of posterior cruciate ligament load and tibiofemoral stress after TKA in dependence on tibiofemoral slope.

BACKGROUND: To prevent excessive tension on the posterior cruciate ligament, some knee prosthesis-systems offer the option of creating a posterior tibiofemoral slope of the tibial component. The objective of this study was to investigate the effect of the amount of tibiofemoral slope on the posterior cruciate ligament load and tibiofemoral contact stress after total knee arthroplasty under isokinetic in vitro conditions. METHODS: Twelve fresh frozen knee specimens were tested in a knee simulator. After implantation of the Interax I.S.A. knee prosthesis-system with a mobile bearing inlay, a bow shaped load transducer was fixed in the medial fibres of the posterior cruciate ligament. A pressure sensitive film was fixed on the femoral inlay surface. The test cycle simulated an isokinetic extension cycle from 120 degrees of flexion to full extension. First, posterior cruciate ligament load and tibiofemoral peak contact stress were measured with the tibial component implanted with a neutral tibial slope and then with 10 degrees posterior slope. FINDINGS: After implantation of the tibial component without tibial slope, posterior cruciate ligament load reached a maximum load of 29.5 N (SD 17.1 N) at 97.8 degrees knee flexion. Tibiofemoral contact stress on the medial compartment reached a maximum of 11.9 MPa (SD 2.4 MPa) on the medial compartment and 15.0 MPa (SD 6.1 MPa) on the lateral compartment. With a tibial slope of 10 degrees , posterior cruciate ligament load reached a maximum of 14.5N (SD 4.9N, P = 0.04) at 100.5 degrees knee flexion and tibiofemoral stress increased to a maximum of 13.3 MPa (SD 4.7 MPa, P = 0.38) medial and 17.4 MPa (SD 8.2 MPa, P = 0.22) lateral in knee extension. INTERPRETATION: Maximum posterior cruciate ligament load was observed at high knee flexion angles, decreasing to full extension. The implantation of the tibial base plate with 10 degrees dorsal slope reduced posterior cruciate ligament load significantly in knee flexion above 50 degrees and slightly increased tibiofemoral contact stress in knee extension. Therefore a posterior tibial slope prevents an excessive load on the posterior cruciate ligament while having little effect on tibiofemoral stress at high knee flexion angles.

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PubMed2006

In vitro investigation of the effect of medial patellofemoral ligament reconstruction and medial tibial tuberosity transfer on lateral patellar stability.

PURPOSE: Two different operative techniques for stabilizing the patella against lateral displacement movement were investigated. TYPE OF STUDY: In vitro experimental study. METHODS: Five human cadaver knee specimens with a normal Q-angle were mounted in a kinematic knee simulator and investigated under simulated isokinetic extension motions. Patellar movement was measured while a 100-N laterally directed subluxation load was applied to the patella. Ligament loading of the medial patellofemoral ligament was measured using a strain gauge based buckle transducer inserted in the fibers of the ligament. The knee was evaluated in an intact physiologic state, as well as after medial transfer of the tibial tuberosity, and after the medial patellofemoral ligament was transected and reconstructed using a hamstring autograft. RESULTS: A significant reduction in lateral displacement and ligament load was observed with the use of the hamstring autograft reconstruction compared with the medial transfer of the tibial tuberosity. CONCLUSIONS: Medial transfer of the tibial tuberosity showed no significant relief of ligament loading and stabilizing effect on patellar movement, whereas reconstruction of the medial patellofemoral ligament showed a significant stabilizing effect on patellar movement. CLINICAL RELEVANCE: In cadaver specimens, we evaluated the effect of tibial tubercle transfer and the patellofemoral ligament and found that reconstruction of the patellofemoral ligament alone was sufficient to restore stability in a cadaveric model. Additionally, we found that the flexion angle had little effect on the loading of the medial patellofemoral ligament autograft, which would support early mobilization of patients after surgery. We found that the graft was not unduly loaded.

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PubMed2005

The influence of intraoperative pretensioning on the chondroprotective effect of meniscal transplants.

BACKGROUND: Meniscal replacement has become more common in recent years. The meniscal transplant's ability to transfer load effectively depends on its ability to bear circumferential loading. HYPOTHESIS: Intraoperative pretensioning on the meniscal transplant sutures has a positive influence on meniscal transplants' chondroprotective effect. STUDY DESIGN: Controlled laboratory study. METHODS: Thirty-six sheep were divided into 6 groups (n = 6), subjected to a sham operation (group A), a meniscectomy (group B), or a meniscal autograft using tag sutures with different levels of pretensioning (group C, 0 N; group D, 20 N; group E, 40 N; group F, 60 N). Macroscopic (International Cartilage Repair Society score) and histologic evaluations (Mankin score) of the articular cartilage were performed after 6 months. RESULTS: Higher suture pretension (40 N, 60 N) resulted in less cartilage degeneration than in meniscectomized (P =.047; P =.036) and nonpretensioned (P =.028; P =.015) knees, with International Cartilage Repair Society scores of 1.63 +/- 0.57 and 1.66 +/- 0.51 in groups E and F, respectively, and scores of 2.40 +/- 0.27 and 2.68 +/- 0.46 observed after meniscectomy and meniscal transplantation with no pretensioning, respectively. Group F had a significantly better Mankin score of 6.66 +/- 2.15 (P =.05) compared with group D. Regarding criterion cells, trends toward less degeneration compared with meniscectomized and nonpretensioned knees (P = .054 and P =.055) were found. The coefficient of variation of the Mankin scores was greater than that of the International Cartilage Repair Society score. Group A had significantly better cartilage than all other groups. CONCLUSION: Adequate intraoperative pretensioning has a significant influence on the chondroprotective effect of meniscal transplants but did not prevent the development of articular cartilage degeneration. CLINICAL RELEVANCE: The results suggest that intraoperative pretensioning could improve the chondroprotective effect of meniscal transplantation.

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PubMed2005

Primary stability of anterior lumbar stabilization: interdependence of implant type and endplate retention or removal.

This is a comparative in vitro biomechanical study of the primary stability of an anterior lumbar interbody stabilization. The objective was to compare the stability of a interbody stabilizing titanium cage with and without the retention of the bordering vertebral endplates, as well as to compare the titanium cage with a tricalcium phosphate block when the endplates are removed. An adequate blood supply is critical for interbody fusion, which suggests surgical treatment of the bordering endplates. On the other hand, primary stability is improved by the retention of the endplates. Furthermore, bone substitute materials are finding more frequent use due to complications associated with autologous bone grafts. Ten bovine lumbar spine motion segments (average age 6 months) were investigated. Pure bending loadings as well as eccentric axial compression loadings were applied. A titanium cage and tricalcium phosphate block, were tested in conjunction with an anterior augmentation (MACS). Range of motion, neutral zone (NZ) and bending stiffness were measured under pure bending to 10 Nm, and bending stiffness under axial loads of up to 1,500 N. Range of motion of both implants in flexion-extension was significantly smaller than physiologic (cage without endplates 4.3 degrees , cage with 2.8 degrees , block without 3.4 degrees , and physiologic 6.6 degrees , all p<0.001). The cage with endplates and the block without endplates were both significantly stiffer than physiologic in all directions except left lateral bending. The block without endplates and the cage with endplates were both stiffer than the cage without endplates. The results suggest that the use of the bone substitute block provides better stability than the cage when the endplates are removed.

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PubMed2005

Comparative biomechanical testing of anterior and posterior stabilization procedures.

STUDY DESIGN: This is a comparative in vitro biomechanical study in a calf lumbar spine model. OBJECTIVES: The objective was to compare the primary stability of an anterior instrumentation, an intercorporal cage in combination with an anterior instrumentation, and a posterior instrumentation for monosegmental spondylodesis. SUMMARY OF BACKGROUND DATA: Spondylodesis can be achieved through a posterior lumbar fusion, posterior lumbar intercorporal fusion, or an anterior lumbar intercorporal fusion. The posterior lumbar fusion is the gold standard, although the anterior approach offers some potential advantages to the transpedicular posterior techniques. METHODS: Stability testing was performed on 30 calf lumbar spine motion segments in a physiologic state (n = 30), with either an isolated anterior (MACS) or posterior instrumentation (SOCON), and with an anterior instrumentation augmented with an intercorporal cage (MACS-Cage, n = 10, respectively). Range of motion, neutral zone, and bending stiffness were measured under pure bending to 10 Nm, and bending stiffness under axial loads of up to 1500 N. RESULTS: The isolated posterior instrumentation was found to be more stable than the isolated or augmented anterior instrumentation in flexion/extension, although no significant differences were observed in lateral bending or axial rotation. The results of this biomechanical study suggest that an augmented anterior instrumentation provides similar stability for bony fusion as does the golden standard posterior instrumentation, with the exception of flexion/extension. CONCLUSION: An augmented anterior instrumentation may provide similar stability for bony fusion as does the posterior instrumentation.

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PubMed2005

Dynamic in vitro measurement of patellar movement after total knee arthroplasty: an in vitro study.

BACKGROUND: Changing the kinematic behaviour of patellar movement could be one of the reasons for anterior knee pain after implantation of a total knee arthroplasty (TKA). The aim of the current study was to measure the potential influence on patellar kinematics of patellar resurfacing during TKA. METHODS: Patellar movement before and after TKA with and without patellar resurfacing was measured under dynamic conditions in an in vitro cadaver simulation. Physiologic Musculus quadriceps forces were applied to five physiologic human knee specimens undergoing simulated isokinetic extension motions, patellar movement was measured using an ultrasonic measurement system. Thereafter, the Interax I.S.A.-prosthesis system was implanted without and with resurfacing the patella, and patellar movement was again measured. RESULTS: The physiologic patella center moved on a semilunar path up to 6.4 mm (SD 6.4 mm) medially during extension. After TKA, the unresurfaced patella showed significantly less medial translation (p = 0.04) than the resurfaced patella. Subsequent resurfacing of the patella then resulted in a return to mediolateral positioning of the patella similar to the physiological case, whereas the resurfaced patella tilted up to twice as much as physiologic. CONCLUSION: The results of this study suggest that resurfacing of the patella during TKA can result in a restoration of the physiologic mediolateral shift of the patellofemoral joint while angulation of the patella remains unphysiologic.

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PubMed2005

Distribution of substance-P nerves inside the infrapatellar fat pad and the adjacent synovial tissue: a neurohistological approach to anterior knee pain syndrome.

INTRODUCTION: The purpose of the study was to determine the distribution and number of nerves inside the infrapatellar fat pad and the adjacent synovium, in particular with regards to nociceptive substance-P nerves. MATERIALS AND METHODS: The infrapatellar fat pad of the knee was resected from 21 patients (4 male, 17 female, mean age 69 years) during the course of standard total knee arthroplasty operations performed in our clinic. The fat pad was dissected into five standardized segments, fixed in formalin and embedded in paraffin. Immunohistochemical techniques using antibodies against S-100 protein and substance-P (SP) were employed to determine and specify the nerves. RESULTS: Studying all the detectable nerves present in 50 observation fields (200-fold magnification), we found an average of 106 S-100 versus 25 SP nerves (24%) in the synovium and 27 S-100- versus 7 SP nerves (26%) in the interior of the fat pad. The total nerve count was significantly (P < 0.001) higher in the synovium than in the fat pad for both marker types. The number of S-100 nerves was significantly (P < 0.05) higher in the central and lateral segments of the fat pad, while SP nerves were equally distributed throughout all segments of the fat-pad. SP nerves were significantly more frequently associated with blood vessels inside the fat pad (43%, P < 0.05) than in the synovial tissue (28%). CONCLUSION: The occurrence and distribution of SP nerves inside the infrapatellar fat pad suggest a nociceptive function and a neurohistological role in anterior knee pain syndrome. The data support the hypothesis that a neurogenous infection of the infrapatellar fat pad could contribute to anterior knee pain syndrome.

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PubMed2004

Infrapatellar fat pad pressure and volume changes of the anterior compartment during knee motion: possible clinical consequences to the anterior knee pain syndrome.

This biomechanical study was performed to measure tissue pressure in the infrapatellar fat pad and the volume changes of the anterior knee compartment during knee flexion-extension motion. Knee motion from 120 degrees of flexion to full extension was simulated on ten fresh frozen human knee specimens (six from males, four from females, average age 44 years) using a hydraulic kinematic simulator (30, 40, and 50 Nm extension moment). Infrapatellar tissue pressure was measured using a closed cell sensor. Infrapatellar volume change in the anterior knee compartment was evaluated subsequent to removal of the fat pad using a water-filled bladder. We found a significant increase of the infrapatellar tissue pressure during knee flexion, at flexion angles of <20 degrees and >100 degrees . The average tissue pressure ranged from 343 (+/-223) mbar at 0 degrees to 60 (+/-64) mbar at 60 degrees of flexion. The smallest volume in the anterior knee compartment was measured at full extension and 120 degrees of flexion, whereas the maximum volume was observed at 50 degrees of flexion. In conclusion, the data suggest a biomechanical function of the infrapatellar fat pad at flexion angles of <20 degrees and >100 degrees , which suggests a role of the infrapatellar fat pad in stabilizing the patella in the extremes of knee motion.

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PubMed2004

Biomechanical and kinematic influences of a total infrapatellar fat pad resection on the knee.

BACKGROUND: This biomechanical study was performed to evaluate the consequences of total infrapatellar fat pad resection on knee kinematics and patellar contact pressure. HYPOTHESIS: Resection of the infrapatellar fat pad produces significant changes in knee kinematics and patellar contact pressure. STUDY DESIGN: Biomechanical cadaveric study. METHODS: Isokinetic knee extension was simulated on 10 human knee cadaveric specimens (6 men, 4 women; mean age at death, 44 years). Joint kinematics were evaluated by an ultrasound-based 3D motion analysis system, and retro-patellar contact pressure was measured using an electronic pressure-sensitive film. All data were taken before and after resection of the infrapatellar fat pad and statistically analyzed. RESULTS: A total resection of the infrapatellar fat pad resulted in a significant decrease of the tibial external rotation relative to the femur between 63 degrees of flexion and full knee extension (maximum: 3 degrees rotation difference at 0 degrees knee flexion, P = .011), combined with a significant medial translation of the patella between 29 degrees and 69 degrees of knee flexion (range, 0.9-1.3 mm, P = .017-.028). Retro-patellar contact pressure was significantly reduced (from 20% to 25%, P = .008-.021) at all flexion angles. CONCLUSION: A resection of the infrapatellar fat influences patellar biomechanics and knee kinematics. CLINICAL RELEVANCE: The infrapatellar fat pad may have a biomechanical function and may play a role in anterior knee pain syndrome.

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PubMed2003

Application of a probabilistic microstructural model to determine reference length and toe-to-linear region transition in fibrous connective tissue.

This study shows how a probabilistic microstructural model for fibrous connective tissue behavior can be used to objectively describe soft tissue low-load behavior. More specifically, methods to determine tissue reference length and the transition from the strain-stiffening "toe-region" to the more linear region of the stress-strain curve of fibrous connective tissues are presented. According to a microstructural model for uniaxially loaded collagenous tissues, increasingly more fibers are recruited and bear load with increased tissue elongation. Fiber recruitment is represented statistically according to a Weibull probability density function (PDF). The Weibull PDF location parameter in this formulation corresponds to the stretch at which the first fibers begin to bear load and provides a convenient method of determining reference length. The toe-to-linear region transition is defined by utilizing the Weibull cumulative distribution function (CDF) which relates the fraction of loaded fibers to the tissue elongation. These techniques are illustrated using representative tendon and ligament data from the literature, and are shown to be applicable retrospectively to data from specimens that are not heavily preloaded. The reference length resulting from this technique provides an objective datum from which to calculate stretch, strain, and tangent modulus, while the Weibull CDF provides an objective parameter with which to characterize the limits of low-load behavior.

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PubMed2003

In vitro simulation of stance phase gait part I: Model verification.

An in vitro simulator was developed to reproduce the kinematics and kinetics of stance phase gait on cadaver foot specimens. Ground reaction force was applied by a tilting angle- and force-controlled translation stage upon which a pressure measuring platform was mounted; tibial rotation was reproduced by a servomotor. Force was applied to nine tendons of the foot flexor and extensor muscle groups, and three-dimensional hind- and forefoot motion was measured. The model was verified based on in vivo kinematic and kinetic measurements. It was found to be in good general agreement with some exceptions which include a slightly more lateral gait line.

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PubMed2003

In vitro simulation of stance phase gait part II: Simulated anterior tibial tendon dysfunction and potential compensation.

The diagnosis of anterior tibial tendon tear is often missed. The ability of the remaining ankle extensor muscles to compensate for lost anterior tibial force was thus investigated. The effect of tibialis anterior deficiency on tarsal bone motion and plantar pressure was measured during in vitro simulated stance phase gait on eight cadaver specimens. Increased internal rotation, plantarflexion, and inversion of the talus and calcaneus (p < or = .001), as well as significant reductions of plantar pressure on the heel (p < or = .04) were observed during the first half of the stance phase. The observed drop foot was partly compensated by increased extensor muscle force.

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