Postural control learning dynamics in Parkinson's disease: early improvement with plateau in stability, and continuous progression in flexibility and mobility.

BACKGROUND: Balance training improves postural control in Parkinson's disease (PD). However, a systematic approach for the development of individualized, optimal training programs is still lacking, as the learning dynamics of the postural control in PD, over a training program, are poorly understood. OBJECTIVES: We investigated the learning dynamics of the postural control in PD, during a balance-training program, in terms of the clinical, posturographic, and novel model-based measures. METHODS: Twenty patients with PD participated in a balance-training program, 3 days a week, for 6 weeks. Clinical tests assessed functional balance and mobility pre-training, mid-training, and post-training. Center-of-pressure (COP) was recorded at four time-points during the training (pre-, week 2, week 4, and post-training). COP was used to calculate the sway measures and to identify the parameters of a patient-specific postural control model, at each time-point. The posturographic and model-based measures constituted the two sets of stability- and flexibility-related measures. RESULTS: Mobility- and flexibility-related measures showed a continuous improvement during the balance-training program. In particular, mobility improved at mid-training and continued to improve to the end of the training, whereas flexibility-related measures reached significance only at the end. The progression in the balance- and stability-related measures was characterized by early improvements over the first 3 to 4 weeks of training, and reached a plateau for the rest of the training. CONCLUSIONS: The progression in balance and postural stability is achieved earlier and susceptible to plateau out, while mobility and flexibility continue to improve during the balance training.

On the mechanical characteristics of graphene nanosheets: a fully nonlinear modified Morse model.

In this paper, the mechanical properties of graphene nanosheets are evaluated based on the nonlinear modified Morse model. The interatomic interactions including stretching and bending of the covalent bonds between carbon atoms, are replaced by nonlinear extensional and torsional spring-like elements. The finite element method is implemented to analyze the model under different loading conditions and linear characteristics of the graphene structure including the Young's modulus, surface modulus, shear modulus and Poisson's ratio are evaluated for various geometries and chirality where these properties are shown to be size and aspect ratio dependent. It is also found that when the dimensions of the sheets are greater than a certain threshold, the structure behaves quasi-isotropically and the directional elastic moduli become close to each other by a relative difference no more than 1%. Using the nonlinear stress-strain curve, the yielding point and ultimate stress and strains of the graphene sheet are also evaluated. The results of this study are compared with available experimental data and previous numerical simulations, where good agreement is achieved.

Numerical Investigations of Hepatic Spheroids Metabolic Reactions in a Perfusion Bioreactor.

Miniaturized culture systems of hepatic cells are emerging as a strong tool facilitating studies related to liver diseases and drug discovery. However, the experimental optimization of various parameters involved in the operation of these systems is time-consuming and expensive. Hence, developing numerical tools predicting the function of such systems can significantly reduce the associated cost. In this paper, a perfusion-based three dimensional (3D) bioreactor comprising encapsulated human liver hepatocellular carcinoma (HepG2) spheroids are analyzed. The flow and mass transfer equations for oxygen as well as different metabolites such as albumin, glucose, glutamine, ammonia, and urea were solved in three different domains, i.e., free flow, hydrogel, and spheroid porous media sections. Since the spheroids were encapsulated inside the hydrogel, shear stress imposed on them were found to be less than tolerable thresholds. The predicted cumulative albumin concentration over the 7 days of culture period showed a good agreement with the experimental data. Based on the critical role of oxygen supply to the hepatocytes, a parametric study was performed and the effect of various parameters was investigated. Results illustrated that convection mechanism was the dominant transport mechanism in the main-stream section contrary to the intra spheroids parts where the diffusion was the prevailing transport mechanism. In the hydrogel parts, the rate of diffusion and convection mechanisms were almost identical. As expected, higher perfusion rate would provide high oxygen level for the cells and, smaller spheroids with a diameter of 100 µm were at the low risk of hypoxic conditions due to short diffusive oxygen penetration depth. Numerical results evidenced that spheroids with diameter size >200 µm at low porosities (ε = 0.2-0.3) were at risk of oxygen depletion, especially at locations near the core center. Therefore, these results could be beneficial in preventing hypoxic conditions during in vitro experiments. The presented numerical model provides a numerical platform which can help researchers to design and optimize complex bioreactors and obtain numerical indexes of the main metabolites in a very short time prior to any fabrications. Such numerical indexes can be helpful in certifying the outcomes of forensic investigations.

Disentangling stability and flexibility degrees in Parkinson's disease using a computational postural control model.

BACKGROUND: Impaired postural control in Parkinson's disease (PD) seriously compromises life quality. Although balance training improves mobility and postural stability, lack of quantitative studies on the neurophysiological mechanisms of balance training in PD impedes the development of patient-specific therapies. We evaluated the effects of a balance-training program using functional balance and mobility tests, posturography, and a postural control model. METHODS: Center-of-pressure (COP) data of 40 PD patients before and after a 12-session balance-training program, and 20 healthy control subjects were recorded in four conditions with two tasks on a rigid surface (R-tasks) and two on foam. A postural control model was fitted to describe the posturography data. The model comprises a neuromuscular controller, a time delay, and a gain scaling the internal disturbance torque. RESULTS: Patients' axial rigidity before training resulted in slower COP velocity in R-tasks; which was reflected as lower internal torque gain. Furthermore, patients exhibited poor stability on foam, remarked by abnormal higher sway amplitude. Lower control parameters as well as higher time delay were responsible for patients' abnormal high sway amplitude. Balance training improved all clinical scores on functional balance and mobility. Consistently, improved 'flexibility' appeared as enhanced sway velocity (increased internal torque gain). Balance training also helped patients to develop the 'stability degree' (increase control parameters), and to respond more quickly in unstable condition of stance on foam. CONCLUSIONS: Projection of the common posturography measures on a postural control model provided a quantitative framework for unraveling the neurophysiological factors and different recovery mechanisms in impaired postural control in PD.

Assessing the role of Ca2+ in skeletal muscle fatigue using a multi-scale continuum model.

The Calcium ion Ca2+ plays a critical role as an initiator and preserving agent of the cross-bridge cycle in the force generation of skeletal muscle. A new multi-scale chemo-mechanical model is presented in order to analyze the role of Ca2+ in muscle fatigue and to predict fatigue behavior. To this end, a cross-bridge kinematic model was incorporated in a continuum based mechanical model, considering a thermodynamic compatible framework. The contractile velocity and the generated active force were directly related to the force-bearing states that were considered for the cross-bridge cycle. In order to determine the values of the model parameters, the output results of an isometric simulation were initially fitted with experimental data obtained for rabbit Extensor Digitorum Longus muscle. Furthermore, a simulated force-velocity curve under concentric contractions was compared with reported experimental results. Finally, by varying the Ca2+ concentration level and its kinetics in the tissue, the model was able to predict the evolution of the active force of an experimental fatigue protocol. The good agreement observed between the simulated results and the experimental outcomes proves the ability of the model to reproduce the fatigue behavior and its applicability for more detailed multidisciplinary investigations related to chemical conditions in muscle performance.

An in silico parametric model of vertebrae trabecular bone based on density and microstructural parameters to assess risk of fracture in osteoporosis.

Osteoporosis is a progressive bone disease characterized by deterioration in the quantity and quality of bone, leading to inferior mechanical properties and an increased risk of fracture. Current assessment of osteoporosis is typically based on bone densitometry tools such as Quantitative Computed Tomography (QCT) and Dual Energy X-ray absorptiometry (DEXA). These assessment modalities mainly rely on estimating the bone mineral density (BMD). Hence present densitometry tools describe only the deterioration of the quantity of bone associated with the disease and not the affected morphology or microstructural changes, resulting in potential incomplete assessment, many undetected patients, and unexplained fractures. In this study, an in-silico parametric model of vertebral trabecular bone incorporating both material and microstructural parameters was developed towards the accurate assessment of osteoporosis and the consequent risk of bone fracture. The model confirms that the mechanical properties such as strength and stiffness of vertebral trabecular tissue are highly influenced by material properties as well as morphology characteristics such as connectivity, which reflects the quality of connected inter-trabecular parts. The FE cellular solid model presented here provides a holistic approach that incorporates both material and microstructural elements associated with the degenerative process, and hence has the potential to provide clinical practitioners and researchers with more accurate assessment method for the degenerative changes leading to inferior mechanical properties and increased fracture risk associated with age and/or disease such as Osteoporosis.

Real time simulation of grasping procedure of large internal organs during laparoscopic surgery.

Surgical simulation systems facilitate safe and efficient training processes of surgical trainees by providing a virtual environment in which the surgical procedure can be repeated unlimitedly in a wide variety of situations. The present study attempted to develop a real time simulation system for the grasping procedure of large internal organs during laparoscopic surgery. A mass-spring-damper model was developed to simulate the nonlinear viscoelastic large deformations of the spleen tissue while interacting with a triple-jaw grasper. A novel collision detection algorithm was designed and implemented to determine the contact points between the tissue and the grasper jaws. Force or geometrical based boundary conditions were imposed at the contact nodes, depending upon the relative magnitudes of the external pull force and the tangential component of the contact force. The efficacy of the model to calculate and render the grasper-spleen interactions in real time was examined in a number of simulations. The results of the model were qualitatively acceptable. The deformation of the tissue was realistic and its stress relaxation behavior could be reproduced. Also, the tool-tissue interactions in slippage-free and slippage-accompanied grasping conditions could be replicated when appropriate coefficients of friction were employed.

Stiffness of knee-spanning external fixation systems for traumatic knee dislocations: a biomechanical study.

OBJECTIVE: The purpose of this study was to compare the relative stiffness of four common external fixation (XF) configurations used to span and stabilize the knee after knee dislocation. METHODS: Synthetic composite femora and tibiae connected with cords were used to simulate a knee. Four configurations of external fixation were tested: anterior femoral pins with monotube (XF1), anterolateral femoral pins with monotube (XF2), anterolateral femoral pins with two connecting rods (XF3), and hinged ring fixator (XF4). Six specimens of each configuration were loaded nondestructively in varus/valgus, anterior-to-posterior shear, flexion/extension, axial compression, internal/external torsion, and failure in varus. RESULTS: XF2 was stiffer than XF1 in varus, valgus, and axial loading (P < 0.01) demonstrating that anterolateral pins provided greater stiffness than anterior femoral pins. XF3 was stiffer than XF2 in varus, valgus, and anterior-to-posterior shear (P < 0.002), indicating that two connecting rods provided greater stiffness than the monotube. XF4 was similar to the other configurations in anterior-to-posterior shear and torsion, indicating the hinged frame provided adequate stability. The average load to failure in varus mode was 250 N-m, which was far beyond the nondestructive loading of all specimens. There was no statistical difference between the different constructs in load to failure. CONCLUSIONS: The stiffest construct for external fixation of a knee dislocation was achieved when pins were placed anterior lateral on the femur and two connecting rods were used. A stiffer construct may provide a better clinical outcome and we therefore recommend this frame configuration.

Extensor tendon repair with and without central slip reattachment to bone: a biomechanical study.

PURPOSE: Swanson's technique for repair of the extensor tendon of the proximal interphalangeal (PIP) joint, entailing bony reattachment of the extensor tendon to the base of the middle phalanx, is a common procedure. We introduce a repair technique that is less complicated and that may be equally appropriate for approach to the PIP joint. The extensor tendon is incised longitudinally directly over the PIP joint. The insertion of the central slip and capsule are elevated off of the base of the middle phalanx. This allows excellent visualization of the PIP joint. The extensor tendon is then repaired by side-to-side approximation using Ethibond suture. The purpose of this study was to test and compare the strength of this proposed technique with that of Swanson in a cadaver model. METHODS: The index, long, and ring fingers from 4 pairs of fresh-frozen cadaver hands were harvested (24 digits total). One technique was performed and tested in all digits of the 3-digit contralateral pairings from 2 pairs of hands (3 digits x 4 hands; 12 digits total per technique). Twelve control digits were used to measure the fixation strength and stiffness of the Swanson approach, and the other 12 digits were used to measure the fixation strength and stiffness of the new procedure. RESULTS: All tendon repairs tolerated physiologic loading of 25 N. There was no statistically significant difference in stiffness between the control and experimental groups (mean +/- SD, 4.74 N/mm +/- 0.46 and 4.62 N/mm +/- 0.30, respectively; p >.05). CONCLUSIONS: Simple repair of the central slip without reattachment to bone preserves the function of the extensor mechanism at the PIP joint and provides excellent exposure to the joint.

Assessment of rotational instability with disruption of the accessory collateral ligament of the thumb MCP joint: a biomechanical study.

OBJECTIVES: The objective of this paper was to biomechanically investigate rotational stability of the thumb after ulnar collateral ligament (UCL) and accessory collateral ligament (ACL) disruption and repair at the metacarpal joint of the thumb. METHODS: Twelve fresh frozen adult cadaveric thumbs were used. The torsion test was performed under constant rotation of 1/s through 30 arc of metacarpal phalangeal (MCP) joint. The torsional resistance was determined for four categories: first no intervention of the UCL structures (control), next with the proper UCL cut at the distal insertion, then with the additional ACL ligament cut, and lastly with the repair of only the proper UCL. The decrease on the amount of torsional rigidity for each of the last three categories was determined and compared. Each thumb was used as its own control. Significance of the differences in each test categories was statistically determined. RESULTS: After the proper UCL was cut, the torsional rigidity of the MCP joint was reduced 35.18 +/- 17.56% (p < 0.001). When, additionally, the ACL was cut, the torsional rigidity of the MCP joint was further reduced to 49.34 +/- 16.82% (P < 0.001). After repair of only the proper UCL, the torsional rigidity of the MCP joint improved, but still showed a considerable reduction from controls. The amount of reduction was not consistent among specimens and was 13.52 +/- 16.40%. CONCLUSIONS: The ACL ligament is a contributor of rotary stability as well as a provider of lateral stability. Leaving the ruptured ACL unrepaired causes some residual rotating instability and that may lead to future rotational instability of the MCP joint.

Bicortical screw fixation of distal fibula fractures with a lateral plate: an anatomic and biomechanical study of a new technique.

One of the potential drawbacks of lateral plating of distal fibula fractures is less than satisfactory fixation of unicortical screws commonly placed in the distal fragment to avoid implant penetration of the ankle joint. This study examines the anatomy of the distal fibula, proposes new techniques for bicortical screw fixation and radiographic evaluation of screw placement, and compares pullout strength of unicortical versus bicortical screws in this area. Sixteen pairs of human cadaver feet were used in this study. It was found that a large percentage of the surface area of the distal fibula is nonarticular and that the distal fibula could be divided into 3 zones with distinct anatomic features. Zone I is defined as the distal most 1.5 cm of the fibula, zone II is the next 1 cm of fibula proximal to zone I, and zone III is defined as the fibula above the ankle joint, starting at just over 2.5 cm proximal to the tip of the fibula. We determined a safe corridor for bicortical screw placement by means of a lateral plate in each zone. An improved radiographic view is described for confirmation of extraarticular screw placement. Screw pullout testing was performed on 8 pairs of fresh-frozen human cadaver fibulas. In both zone I and zone II, the bicortical screw fixation was significantly stronger than the unicortical screw fixation. In zone I, the average pullout strength for the bicortical screw fixation was 2.3 times higher than the unicortical screw fixation. In zone II, the average pullout strength for the bicortical screw fixation was 3.3 times higher than the unicortical screw fixation. This study shows that not only is bicortical screw placement in the distal fibula technically feasible, but it is also biomechanically stronger than unicortical placement in this area.

Biomechanic comparison of 3 tendon transfers for supination of the forearm.

PURPOSE: Flexion-pronation of the hand and the forearm is a common deformity when the upper extremity is affected by cerebral palsy. Solutions used to improve the pronation deformity and increase supination include transfer of the flexor carpi ulnaris to the extensor carpi radialis brevis, pronator teres rerouting, and brachioradialis rerouting. The purpose of this study was to compare the biomechanic efficacy of these 3 tendon transfers in simulated supination in cadaveric forearms. METHODS: Ten fresh-frozen adult cadaveric above-elbow upper extremities were used. In each specimen the 3 tendon transfers were performed sequentially in random order and were loaded in increments of 4 N (1 lb) to a maximum of 36 N (8 lb). Measurements were recorded from the starting point of 90 degrees of pronation. Statistical analysis of the data included the Student t test with the Bonferoni correction. RESULTS: For all transfers, supination increased in a nonlinear manner as the load was increased in a nonlinear manner. For the flexor carpi ulnaris transfer, the forearm reached its neutral position at a load of 9 N (2 lb). The forearm continued to rotate to up to 84 degrees of supination with 36 N (8 lb) of load. With the brachioradialis transfer, the forearm reached its neutral position at 13 N (3 lb) of load and continued to rotate to up to 33 degrees of supination with 36 N of load. With the pronator teres transfer, the forearm never reached the neutral position. Under a maximum load of 36 N, only 55 degrees of rotation from full pronation was obtained. CONCLUSIONS: Transfer of the flexor carpi ulnaris to the extensor carpi radialis brevis proved to be the most effective transfer for producing supination in cadavers. The brachioradialis transfer was second best. The pronator teres rerouting was the least effective transfer in effecting simulated supination in this experiment.

Biomechanical analysis of pinning techniques for pediatric supracondylar humerus fractures.

BACKGROUND: Closed reduction and percutaneous pin fixation is the recommended treatment of displaced (Gartland types 2 and 3) supracondylar humerus fractures. The need for a medial pin for maximal stability remains controversial. The purpose of this study was to develop a model of supracondylar humerus fractures simulating medial column comminution and to evaluate the torsional stability of various pin configurations recommended in the current literature. METHODS: Transverse cuts were made in synthetic humeri with a wedge taken from the medial aspect of the proximal fracture fragment in one half of the specimens to simulate medial column comminution. Each fracture was then reduced and fixed with 1 of 4 pin configurations using 0.062 in K-wires. The fixed specimens were then subjected to a torsional load producing internal rotation of the distal fragment. Rotation in degrees and the corresponding torque was recorded for statistical analysis. RESULTS: Specimens with the medial wedge removed demonstrated less torsional stability than their identically fixed counterparts with the intact medial column. In specimens with the intact medial column, the greatest torsional stability was achieved with the 2 lateral divergent and medial cross pin configuration followed by 3 lateral pins, then standard crossed pins with 2 lateral divergent pins demonstrating the least torsional stability. For the medial comminution group the 2 lateral, 1 medial pin construct again had the greatest torsional stability and 2 lateral pins the least. The standard crossed pin and 3 lateral pin constructs were not significantly different in the presence of medial comminution. CONCLUSIONS: In a synthetic humerus model of supracondylar humerus fractures, medial comminution was shown to reduce torsional stability significantly in all pin configurations. There was no statistical difference in torsional stability between 3 lateral pins and standard crossed pins in specimens with medial comminution.

Extensor hallucis capsularis: frequency and identification on MRI.

BACKGROUND: The extensor hallucis capsularis (EHC) is the most common name given to the accessory tendon sporadically seen medial to the extensor hallucis longus (EHL). We performed cadaver dissections and MRI evaluation to determine the frequency of its occurrence, the pattern of its origin and insertion, and its potential suitability as tendon graft. METHODS: The EHC was examined by dissection in 81 cadaver feet. Physical parameters pertaining to EHC size and location were recorded. MRI was performed on six cadaver legs to determine if the EHC can be identified radiographically. MRI images were evaluated independently by a foot and ankle specialist and a radiologist. RESULTS: The EHC was present in 71 (88%) of the specimens. It originated from the EHL tendon or muscle in 93% and inserted into the first metatarsophalangeal joint capsule in 99% of cases. All EHC tendons were less than or equal to 4 mm in width; only 16% were more than 2 mm wide. Correct prediction of the presence or absence of EHC by MRI varied according to EHC width: two of two in tendons more than 2 mm, five of eight in tendons 1 to 2 mm, and zero of two in tendons 1 mm or less. CONCLUSION: Up to 14% of the population may have an EHC tendon suitable for grafting in reconstructive surgeries, particularly surgeries related to hallux dysfunction. MRI may have a role in the preoperative identification of the EHC.

Measurement of rotation of the first metacarpal during opposition using computed tomography.

PURPOSE: Opposition is an important movement of the hand and rotation of the first metacarpal is the essential component. There is no agreement on the exact magnitude of rotation of the first metacarpal during opposition. This study used computed tomography to describe rotation measurement of the first metacarpal in the hands of a group of healthy individuals. METHODS: The rotation of the first metacarpal was measured with reference to the fixed unit of the hand. Computed tomographic images were taken of the hands of 10 healthy individuals with the thumb in retroposition, resting position, and opposition to the index, middle, ring, and small fingers. On each image a tangential line was drawn along the dorsal margin of the second and third metacarpals. A second line was drawn through the head of the first metacarpal at the level of the sesamoids. The angle between the 2 lines was measured as the angle of rotation of the first metacarpal in different thumb positions. RESULTS: The mean angle of rotation of the first metacarpal in retroposition was 54 degrees+/-10 degrees with reference to the fixed unit of the hand. In the resting position the angle of rotation of the first metacarpal changed to 74 degrees+/-10 degrees. In the position of opposition to the index, middle, ring, and small fingers the angle of rotation of the first metacarpal increased to 100 degrees+/-7 degrees , 103 degrees+/-6 degrees, 105 degrees+/-6 degrees, and 110 degrees+/-7 degrees, respectively. CONCLUSIONS: The first metacarpal rotates 56 degrees when it moves from retroposition to the position of opposition to the small finger.

Dynamic effects of joint-leveling procedure on pressure at the distal radioulnar joint.

PURPOSE: Wrist joint-leveling procedures for decompression of the radiocarpal and ulnocarpal joints are accompanied by the risk for subsequent disorders of the adjacent distal radioulnar joint (DRUJ). This study evaluated the dynamic change of the pressure pattern at the DRUJ after joint-leveling procedures. METHODS: Thirteen fresh-frozen adult cadaveric upper extremities were used. A segment of the radius was excised at its midshaft to allow lengthening and shortening via a mini external fixator attachment. Dynamic pressure sensors were inserted into the DRUJ and the ulnocarpal joint. Axial loads were applied to the extensor carpi radialis brevis, extensor carpi radialis longus, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris for a total of 89 N with or without 30 N of radioulnar loading. The dynamic pressure distribution for full range of forearm rotation was recorded from 6 mm of radial shortening to 6 mm of radial lengthening in increments of 1 mm. RESULTS: The peak pressures at the DRUJ before the joint-leveling procedures averaged 3.3 MPa without radioulnar loading and 5.0 MPa with radioulnar loading. The peak pressures with axial and radioulnar loading increased 85% at 6 mm of lengthening and only 8% at 6 mm of shortening. The peak pressures at the DRUJ for radial lengthening of 4 mm or more were significantly greater than that of the original length. Pressure at the ulnocarpal joint increased in proportion to the amount of radial shortening and decreased with radial lengthening. CONCLUSIONS: Radial lengthening but not radial shortening significantly increases the peak pressure at the DRUJ.

Smart intramedullary rod for correction of pediatric bone deformity: a preliminary study.

We were interested in determining if a smart intramedullary rod made of nitinol shape-memory alloy is capable of correcting deformed immature long bones. Because of limitations in our study design the process was reversed in that we examined the smart rod's ability to create a deformity rather than to correct one. Smart rods of different lengths and diameters were heat-treated to resume a radius of curvature of 30 to 110 mm. The low and high temperature phases of the smart rods were set, respectively, at 0 degrees C to 4 degrees C and 36 degrees C to 38 degrees C. The preshaped smart intramedullary rods were implanted in the cooled martensite phase in the medullary canal of the tibia in eight rabbits, where they restored their austenite form, causing a continuous bending force. On a weekly basis anteroposterior and lateral radiographs of the surgically treated tibia and the contralateral tibia were obtained for comparison. Rabbits were euthanized 6 weeks after surgery and computed tomography scans of both tibias were used for image analysis. Smart rods with a larger radius of curvature showed only minimal signs of remodeling; however, rods with a radius of curvature of 50 and 70 mm generated enough force history to create bone remodeling and deformation. The amount of bone deformation was highly magnified when unicortical corticotomy on the tension side was done. Based on this preliminary study the technology of the smart intramedullary rod may provide a valuable alternative method to correct pediatric skeletal deformities.

Thumb amputations from team roping.

BACKGROUND: Thumb injuries during team roping have elements of both avulsion and crush, resulting in a poor prognosis for replantation success. PURPOSE: To review 19 cases of thumb amputation from team roping at our institution since 1983. STUDY DESIGN: Retrospective cohort study. METHODS: Cases were included in the study only if a microvascular repair of artery and vein was needed for the thumb to survive. Vein grafts were used to span the damaged vessel segment. Of the 19 thumb amputation cases, 15 attempts were made to replant the thumb. In the remaining four cases, patients had bone shortening and primary closure. The force of injury was calculated based on mechanism. RESULTS: Of the 15 attempts at replantation, only 5 (33%) were successful, despite meticulous technique. One patient subsequently had an emergency toe-to-thumb transfer after an unsuccessful replant, and the remaining nine underwent amputation. Nine of the 10 patients with failed replants had poor flow intraoperatively. In the group of patients younger than 15, the success was 3 of 5 (60%) and in the group 15 years or older the success was 2 of 10 attempts (20%.) Follow-up was available in 13 of the 15 cases of replanted thumbs. CONCLUSIONS: All patients were subjectively satisfied with their results, and all patients with successful replants and seven patients with no thumb returned to rodeo. Biomechanical analysis showed a huge amount of force and pressure, several times larger than that of ring avulsion injury, results when a steer pulls on the thumb.

A study of ulnar collateral ligament of the thumb metacarpophalangeal joint.

The current study examined the biomechanical properties of intact and repaired ulnar collateral ligaments of the metacarpophalangeal joint of the thumb to determine a safe rehabilitation protocol after repair. In the first part of the study mechanical properties of the ligament were examined and the induced stress and strain were determined during simulated pinch and grip. In the second part of the study the strength and limitations of ulnar collateral ligament repair using a mini-Mitek bone suture anchor was determined. The biomechanical study was done on 16 fresh-frozen thumbs from male cadavers. Failure load, maximum stress, and Young's modulus of intact ulnar collateral ligament were 294.3 +/- 28.2 N, 11.4 +/- 1.2 MPa, and 37.3 +/- 5.1 MPa, respectively. There was no significant correlation between the low grip force and the ligament strain. There was, however, a significant correlation between the pinch force and the ligament strain. The failure load and joint rigidity of intact ulnar collateral ligaments were significantly higher (3.1 and 2.3 times, respectively) than the mini-Mitek repaired ligaments. The current study suggests that pinch activity during the rehabilitative process after repair or reattachment of the ulnar collateral ligament should be eliminated. Repaired ligaments with mini-Mitek bone suture anchors may be able to do a moderate range of motion during postoperative rehabilitation; however, additional in vivo studies are necessary before any clinical recommendation is made.