Effects of sitting postures on risks for deep tissue injury in the residuum of a transtibial prosthetic-user: a biomechanical case study.

Transtibial amputation prosthetic-users are at risk of developing deep tissue injury (DTI) while donning their prosthesis for prolonged periods; however, no study addresses the mechanical loading of the residuum during sitting with a prosthesis. We combined MRI-based 3D finite element modelling of a residuum with an injury threshold and a muscle damage law to study risks for DTI in one sitting subject in two postures: 30°-knee-flexion vs. 90°-knee-flexion. We recorded skin-socket pressures, used as model boundary conditions. During the 90°-knee-flexion simulations, major internal muscle injuries were predicted (>1000 mm(3)). In contrast, the 30°-knee-flexion simulations only produced minor injury ( < 14 mm(3)). Predicted injury rates at 90°-knee-flexion were over one order of magnitude higher than those at 30°-knee-flexion. We concluded that in this particular subject, prolonged 90°-knee-flexion sitting theoretically endangers muscle viability in the residuum. By expanding the studies to large subject groups, this research approach can support development of guidelines for DTI prevention in prosthetic-users.

Surgical and morphological factors that affect internal mechanical loads in soft tissues of the transtibial residuum.

The residual limb of transtibial amputation (TTA) prosthetic users is threatened daily by pressure ulcers (PU) and deep tissue injury (DTI) caused mainly by sustained mechanical strains and stresses. Several risk factors dominate the extent of internal tissue loads in the residuum. In this study, we developed a set of three-dimensional finite element (FE) models that were variants of a patient-specific FE model, built from magnetic resonance imaging scans. The set of FE modes was utilized to assess the impact of the following risk factors on the strain/stress distribution in the muscle flap: (i) the tibial length, (ii) the tibial bevelment, (iii) a fibular osteophyte, (iv) the mechanical properties of the muscle, and (v) scarring in different locations and depths. A total of 12 nonlinear FE model configurations, representing variations in these factors, were built and solved. We present herein calculations of compression, tension and shear strains and stresses, von Mises stresses, and strain energy density averaged in critical locations in the muscle flap as well as volumes of concentration of elevated stresses in these areas. Our results overall show higher stresses accumulating in the bone proximity rather than in outlying soft tissues. The longer bone configurations spread the loads toward the external surfaces of the muscle flap. When shortening the truncated bones from 11.2 to 9.2 cm, the von Mises stresses at the distal edges of the bones were relieved considerably (by up to 80%), which indicates a predicted decreased risk for DTI. Decreasing the tibial bevelment mildly, from 52.3 degrees to 37.7 degrees caused propagation of internal stresses from the bone proximity toward the more superficial soft tissues of the residuum, thereby also theoretically reducing the risk for DTI. An osteophyte at the distal fibular end increased the strain and stress distributions directly under the fibula but had little effect (<1%) on stresses at other sites, e.g., under the tibia. Elevation of muscle stiffness (instantaneous shear modulus increase from 8.5 to 16.2 kPa), simulating variation between patients, and muscle flap contraction or spasm, showed the most substantial effect by an acute rise of the von Mises stresses at the bone proximity. The mean von Mises stresses at the bone proximity were approximately twofold higher in the contracted/spastic muscle when compared to the flaccid muscle. Locating a surgical scar in different sites and depths of the residuum had the least influence on the overall loading of the muscle flap (where stresses changed by <7%). Pending further validation by epidemiological PU and DTI risk factor studies, the conclusions of this study can be incorporated as guidelines for TTA surgeons, physical therapists, prosthetists, and the TTA patients themselves to minimize the onset of PU and DTI in this population. Additionally, the present analyses can be used to guide or focus epidemiological research of PU and DTI risk factors in the TTA population.

Patient-specific analyses of deep tissue loads post transtibial amputation in residual limbs of multiple prosthetic users.

Active transtibial amputation (TTA) patients are at risk for developing pressure ulcers (PU) and deep tissue injury (DTI) while using their prosthesis. It is therefore important to obtain knowledge of the mechanical state in the internal soft tissues of the residuum, as well as knowledge of the mechanical state upon its surface. Our aim was to apply patient-specific MRI-based non-linear finite element (FE) models to quantify internal strains in TTA prosthetic users (n=5) during load-bearing. By further employing a strain injury threshold for skeletal muscle, we identified patients susceptible to DTI. The geometrical characteristics of the residuum of the TTA participants varied substantially between patients, e.g. the residuum lengths were 7.6, 8.1, 9.2, 11.5 and 13.3cm. We generally found that internal strains were higher in the bone proximity than in the muscle flap periphery. The highest strains, which in some patients exceeded 50% (engineering strain) for compressive, tensile and shear strains, were found in the shortest residual limbs, i.e. the 7.6 and 8.1cm-long limbs. Correspondingly, the lowest strains were found in the 13.3cm-long residuum, which had the bulkiest muscle flap. Yet, even in the case of a long residuum, about a third of the soft tissue volume at the distal tibial proximity area was occupied by large (>5%) internal compressive, tensile and shear strains. For both patients with shorter residual limbs, the internal principal compressive strains above 5% occupied almost the entire distal tibial proximity area. For a patient whose distal tibial end was flat (non-beveled), internal strains were more uniformly distributed, compared to the strain distributions in the other models, where focal elevated strains accumulated in the bone proximity. We found no muscle strains above the immediate injury threshold, indicating that all patients were not at immediate risk for DTI. Two patients whose residuum fat padding was minimal to none, were the only ones identified as theoretically prone to DTI at long (>3h) continuous weight-bearing periods. We conclude that there is a wide variability in internal mechanical conditions between residual limbs across subjects, which necessitates patient-specific quantitative analyses of internal mechanical states in TTA patients, to assess the mechanical performance of the reconstructed limb and in particular, the individual risk for deep PU or DTI.

Internal mechanical conditions in the soft tissues of a residual limb of a trans-tibial amputee.

Most trans-tibial amputation (TTA) patients use a prosthesis to retain upright mobility capabilities. Unfortunately, interaction between the residual limb and the prosthetic socket causes elevated internal strains and stresses in the muscle and fat tissues in the residual limb, which may lead to deep tissue injury (DTI) and other complications. Presently, there is paucity of information on the mechanical conditions in the TTA residual limb during load-bearing. Accordingly, our aim was to characterize the mechanical conditions in the muscle flap of the residual limb of a TTA patient after donning the prosthetic socket and during load-bearing. Knowledge of internal mechanical conditions in the muscle flap can be used to identify the risk for DTI and improve the fitting of the prosthesis. We used a patient-specific modelling approach which involved an MRI scan, interface pressure measurements between the residual limb and the socket of the prosthesis and three-dimensional non-linear large-deformation finite-element (FE) modelling to quantify internal soft tissue strains and stresses in a female TTA patient during static load-bearing. Movement of the truncated tibia and fibula during load-bearing was measured by means of MRI and used as displacement boundary conditions for the FE model. Subsequently, we calculated the internal strains, strain energy density (SED) and stresses in the muscle flap under the truncated bones. Internal strains under the tibia peaked at 85%, 129% and 106% for compression, tension and shear strains, respectively. Internal strains under the fibula peaked at substantially lower values, that is, 19%, 22% and 19% for compression, tension and shear strains, respectively. Strain energy density peaked at the tibial end (104kJ/m(3)). The von Mises stresses peaked at 215kPa around the distal end of the tibia. Stresses under the fibula were at least one order of magnitude lower than the stresses under the tibia. We surmise that our present patient-specific modelling method is an important tool in understanding the etiology of DTI in the residual limbs of TTA patients.

MR-guided focused ultrasound surgery (MRgFUS) for the palliation of pain in patients with bone metastases--preliminary clinical experience.

BACKGROUND: Magnetic resonance-guided focused ultrasound surgery (MRgFUS) is a noninvasive thermal ablation technique, shown to be clinically effective in the treatment of uterine fibroids and is being evaluated as a method of thermal ablation of benign and malignant breast tumors. To evaluate the safety and initial efficacy of MRgFUS for the palliation of pain caused by bone metastases, in patients for whom other treatments are either not effective or not feasible. MATERIALS AND METHODS: Thirteen patients suffering from symptomatic bone metastases underwent MRgFUS procedure. Treatment safety was evaluated by assessing the incidence and severity of device-related complications up to 6 months after treatment. Effectiveness of pain palliation was evaluated by visual analog scale, pain questionnaires and changes in the patients' medication. RESULTS: Fifteen procedures were carried out. Mean follow-up was 59 days. Twelve patients received adequate treatment and were available for follow-up. Two patients died due to disease progression during the first month after treatment. No severe adverse events were recorded. The remaining 10 patients reported prolonged improvement in pain score and/or reduced analgesic dosage. CONCLUSION: MRgFUS may provide a safe and effective noninvasive alternative for the palliation of pain, caused by bone metastases.

Partial interosseous ligament tears of the wrist: difficulty in utilizing either primary or secondary MRI signs.

PURPOSE: Prior reports on scapholunate ligament (SLL) and lunotriquetral ligament (LTL) tears have evaluated complete tears. As these complete tears have markedly different biomechanical manifestations and surgical considerations than do partial tears, we evaluated the accuracy of MR and the usefulness of secondary MR signs to diagnose partial interosseous ligament tears. METHOD: Fifty wrists in 50 patients underwent arthroscopy following 1.5 T MR. Images were evaluated by two independent blinded observers for normal or partially torn SLL and LTL and for three secondary signs potentially seen as mechanical sequelae of tears: osseous offset, arc disruption, or focal osteoarthritis. RESULTS: Arthroscopically, there were 16 SLL and 14 LTL partial tears. Accuracy of primary MR signs of partial tears was lower than that described in the literature for complete tears [sensitivity/specificity (kappa) = 0.56/0.56 (0.12)-SLL, 0.31/0.76 (0.13)-LTL]. Secondary signs showed low sensitivity but high specificity, particularly for LTL tears: arc disruption [0.17/0.83 (0.43)-SLL, 0.0/1.00 (1.0)- LTL], focal osteoarthritis [0.32/0.78 (0.18)-SLL, 0.11/0.91 (0.12)-LTL], and focal osseous offset [0.39/0.75 (0.10)-SLL, 0.26/0.93 (0.39)-LTL]. Additionally, there was poor interobserver consistency for both primary and secondary signs. CONCLUSION: The sensitivity of morphologic evaluation for diagnosing partial intercarpal ligament tears, particularly those of the LTL, is limited. Secondary signs increase specificity but have low sensitivity, and with the exception of arc disruption, all signs had poor interobserver agreement.

Are L5 fractures an indicator of metastasis?

OBJECTIVE: To determine whether L5 vertebral body fractures are an indicator of malignancy. DESIGN AND PATIENTS: A retrospective study of L5 vertebral body fractures was carried out using plain radiographs, CT, and/or MRI. Over a 5-year period, 51 patients with L5 vertebral body fractures were seen at our institution. Since L1 vertebral body fractures are common, 51 age- and gender-matched (20 men, 31 women; mean age 60 years) patients with L fractures were utilized as the control group. The frequency of neoplastic infiltration of the vertebrae was compared between these two populations to determine whether pathologic fracture was more frequent at L5. RESULTS: Twelve (24%) of the L5 fractures were pathologic compared with four (8%) of the L1 fractures (chi-square test, P<0.05). Neoplasm types included multiple myeloma (n=4), prostate (n=3), breast (n=2), lung (n=2), melanoma (n=2), bladder, colon, and leukemia (each n=1). CONCLUSION: Although most L5 fractures are not pathologic, there is an increased incidence of pathologic fractures in this location compared with L1. Therefore, a fracture of L5 should raise the suspicion of metastasis.

Hallux valgus and hallux rigidus: MRI findings.

The purpose of this article is to describe the MR findings of Hallux Valgus (HV) and Hallux Rigidus (HR). Twenty-four patients (11 with HV, 4 with HR, and 9 with both HV and HR) were studied at 1.5 Tesla MRI. Two separate observers evaluated the first ray blindly for the following signs: sesamoid position, sesamoid proliferation, hypertrophy of the median eminence, presence of a lateral facet, presence of an adventitial bursa, shape of the first metatarsal head, relative length of the first metatarsal, joint space loss, osteophytes (dorsalor lateral), marrow edema, geodes, subchondral sclerosis, intra-articular ossicle, and pes planus. The most common findings observed in HV were a hypertrophic medial eminence (95%), sesamoid proliferation (90%) and adventitial bursitis (70%). The most common findings observed in HR were osteophytes (77% and 69%), geodes, and marrow edema. We conclude that traditional routine radiograph signs of HV and HR may be applied to MR images.