Ronald W. Hendrix

Use of helical computed tomography for the assessment of acetabular osteolysis after total hip arthroplasty.

Background: Acetabular osteolysis is a major problem affecting long-term survival of total hip prostheses. Since lytic lesions may be asymptomatic until extensive bone loss has occurred, early detection of lytic lesions is important. The purposes of this study were to determine the efficacy and potential role of high-resolution helical (or spiral) computed tomography with metal-artifact minimization in the early detection of osteolysis of the pelvis and to use the method to determine if there was a relationship between the extent of osteolysis and the amount of polyethylene wear. Methods: Forty patients (fifty hips) who had undergone primary cementless total hip arthroplasty between 1988 and 1994 were evaluated as part of an ongoing prospective study. These patients had a history of high-level activity that was believed to place them at increased risk for accelerated polyethylene wear. The most recent follow-up radiographs were compared with the three-month postoperative radiographs. Helical computed tomography scans with metal-artifact minimization were made, and evidence of osteolytic lesions on these scans was compared with that on the radiographs. Two-dimensional wear analysis was performed with use of digitized radiographs, and the results were compared with loss of bone volume as calculated from the computed tomography scans. Results: Acetabular lysis was identified on the radiographs of sixteen hips and on the computed tomography scans of twenty-six hips. Radiographs underestimated the extent of the lysis in thirteen of the sixteen hips. There was no correlation (r = 0.036) between linear wear and the measured volume of bone loss, with the numbers available. On the basis of the amount of lysis seen on the computed tomography scans, one patient underwent a revision procedure. Conclusions: Helical computed tomography with metal-artifact minimization is more sensitive for identifying and quantifying osteolysis after total hip arthroplasty than is plain radiography. Since computed tomography scans show both the extent and the location of lytic lesions, they are useful to guide treatment decisions as well as to assist in planning for surgical intervention, when needed, in patients with suspected osteolysis.

Sitting with adjustable ischial and back supports: biomechanical changes.

Study Design. The seat and back contact force, pressure distribution, lumbar lordosis, and low back muscle activities associated with a new seat design with adjustable ischial support and backrest were investigated using kinematic, kinetic, electromyographic, and radiographic measurements. Objectives. To investigate the biomechanical effects of adjusting ischial and backrest supports during sitting. Summary of the Background Data. Sitting may induce posterior rotation of the pelvis, reduction of lumbar lordosis, and increases in muscle tension, disc pressure, and pressure on the ischium and coccyx, which may be associated with low back pain. A device that reduces the ischial load and maintains lumbar lordosis may help increase seating comfort and reduce low back pain. Methods. Fifteen office workers with no known low back pain history were tested. Contact pressure distributions, reaction forces between the buttock-thighs and seat and between the back and backrest, load carried by the seat pan and backrest, sacral inclination, lumbar lordosis, intervertebral space of lumbar spine, and muscular activity in stabilizing the trunk were measured for sitting with and without ischial support and with adjustable back support. Results. When the ischial support was relieved, the center of the force on the seat and on the legs of the chair, and the peak center of pressure on the seat, were significantly (P < 0.002) shifted forward toward the thighs. The total contact area on the seat pan and on the backrest was significantly decreased and increased, respectively (P < 0.001). The sacral inclination, total and segmental lumbar lordosis, and lumbar spine disc height were significantly increased for sitting upright with backrest, with the lumbar curve close to that during standing. Conclusions. Sitting with reduced ischial support and fitted backrest to the lower spine altered the contact area, reduced peak pressure under the ischia, reduced muscular activity, maintained total and segmental lumbar lordosis, rotated the sacrum forward, and increased lumbar intervertebral disc heights, which could potentially reduce low back pain.

In vivo noninvasive evaluation of abnormal patellar tracking during squatting in patients with patellofemoral pain

BACKGROUND Patellofemoral pain syndrome is one of the most common knee problems and may be related to abnormal patellar tracking. Our purpose was to compare, in vivo and noninvasively, the patellar tracking patterns in symptomatic patients with patellofemoral pain and those in healthy subjects during squatting. We tested the hypothesis that patients with patellofemoral pain exhibit characteristic patterns of patellar tracking that are different from those of healthy subjects. METHODS Three-dimensional patellar kinematics were recorded in vivo with use of a custom-molded patellar clamp and an optoelectronic motion capture system in ten healthy subjects and nine subjects with patellofemoral pain. The position of osseous knee landmarks was digitized while subjects stood upright, and then patellofemoral kinematics were recorded during squatting. The tracking technique was validated with use of both in vitro and in vivo methodologies, and the average absolute error was <1.2 degrees and <1.1 mm. RESULTS At 90 degrees of knee flexion, the patella showed lateral spin (the distal pole of the patella rotated laterally) in subjects with patellofemoral pain (mean and standard deviation, -10.13 degrees +/- 2.24 degrees) and medial spin in healthy subjects (mean, 4.71 degrees +/- 1.17 degrees) (p < 0.001). At 90 degrees of knee flexion, the patella demonstrated significantly more lateral translation in subjects with patellofemoral pain (mean, 5.05 +/- 3.73 mm) than in healthy subjects (mean, -4.93 +/- 3.93 mm) (p < 0.001). CONCLUSIONS Kinematic differences between healthy subjects and subjects with patellofemoral pain were demonstrated through a large, dynamic range of knee flexion angles. Increased lateral patellar translation and lateral patellar spin in subjects with patellofemoral pain suggest that the patella is not adequately balanced during functional activities in this group. Prospective studies are needed to identify when patellofemoral pain-related changes begin to occur and to determine the risk for the development of patellofemoral pain in individuals with abnormal kinematics.

The diagnosis of osteomyelitis in patients with pressure sores

A prospective blind trial was undertaken to assess the usefulness of commonly used tests to diagnose osteomyelitis underlying pressure sores. Sixty-one pressure sores were studied, with a histopathologic diagnosis from the ostectomy specimen being available in 52. White cell count, erythrocyte sedimentation rate, plain pelvic x-ray, technetium-99m bone scan, computerized tomography, and Jamshidi needle bone biopsy were studied. The most useful individual test was a needle bone biopsy, with a sensitivity of 73 percent and a specificity of 96 percent. Technetium-99m bone scans and computerized tomography are not indicated in the diagnosis of osteomyelitis associated with pressure sores. Plain pelvic x-ray, white cell count, and erythrocyte sedimentation rate, with a diagnosis of osteomyelitis if any test is positive, is the most sensitive (89 percent), specific (88 percent), noninvasive workup. Jamshidi needle biopsy may be useful where these tests are negative and a clinical suspicion of osteomyelitis remains. Extent of surgical debridement and antibiotic therapy can then be rationally decided on the basis of this information.

In vivo and Noninvasive Three-Dimensional Patellar Tracking Induced by Individual Heads of Quadriceps

PURPOSE Unbalanced actions of the quadriceps components are closely linked to patellar mal-tracking and patellofemoral pain syndrome. However, it is not clear how individual quadriceps components pull and rotate the patella three dimensionally. The purpose of this study was to investigate in vivo and noninvasively patellar tracking induced by individual quadriceps components. METHODS Individual quadriceps component was activated selectively through electrical stimulation at the muscle motor point, and the resulting patellar tracking was measured in vivo and noninvasively in 18 knees of 12 subjects. The in vivo and noninvasively patellar tracking was corroborated with in vivo fluoroscopy and in vitro cadaver measurements. RESULTS Vastus medialis (VM) mainly pulled the patella first in the medial and second in the proximal directions and vastus lateralis (VL) pulled first in the proximal and second in the lateral directions. The oblique portion (VMO) of the VM pulled the patella mainly medially and the longus portion (VML) more proximally. Medial tilt was the major patellar rotation induced by VMO contraction at full knee extension. With the knee at the more flexed positions, the amplitude of patellar movement induced by comparable quadriceps contractions was reduced significantly compared to that at full knee extension, and VMO changed its main action from extending to flexing the patella. CONCLUSIONS The medial and lateral quadriceps components moved the patella in rather different directions, and rotated the patella differently about the mediolateral tilt and mediolateral rotation axes but similarly in extension. The approach can be used to investigate patellar tracking in vivo and noninvasively in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.

Finite Element Analysis for Evaluation of Pressure Ulcer on the Buttock: Development and Validation

The interface pressure is currently the only clinical tool to estimate the risk of sitting-related pressure ulcers. However, it provides little information on the loading condition in deep tissues. We present a comprehensive 3-D finite element (FE) model for human buttocks with the consideration of the joint configuration and realistic boundary conditions in a sitting posture. Sitting induced soft tissue deformation, internal pressure, and von-Mises stress were computed. The FE model was well validated qualitatively using actual displacement obtained from magnetic resonance imaging (MRI) images. FE analysis demonstrated that the deformation induced by sitting pressure was substantially different among muscle, fat, and skin. The deformation of the muscle varied with location and the maximum was seen in the regions underneath the bony prominence of ischial tuberosity. In these regions, the range of compressive pressure was 65-80 kPa, 50-60 kPa, and 55-65 kPa, for skin, fat, and muscle, respectively. The von-Mises stress distribution had a similar pattern. In conclusion, this study suggests a new methodology for the development and validation of FE models for investigating the risk of sitting-related soft tissue injury. The proposed model may provide researchers and therapists with a powerful technique for evaluating the effectiveness of various postural modulations in preventing deep tissue ulcers.

Biomechanical effects of sitting with adjustable ischial and lumbar support on occupational low back pain: evaluation of sitting load and back muscle activity.

BackgroundCompared to standing posture, sitting decreases lumbar lordosis, increases low back muscle activity, disc pressure, and pressure on the ischium, which are associated with occupational LBP. A sitting device that reduces spinal load and low back muscle activities may help increase sitting comfort and reduce LBP risk. The objective of this study is to investigate the biomechanical effect of sitting with a reduced ischial support and an enhanced lumbar support (Off-Loading) on load, interface pressure and muscle activities.MethodsA laboratory test in low back pain (LBP) and asymptomatic subjects was designed to test the biomechanical effect of using the Off-Loading sitting posture. The load and interface pressure on seat and the backrest, and back muscle activities associated with usual and this Off-Loading posture were recorded and compared between the two postures.ResultsCompared with Normal (sitting upright with full support of the seat and flat backrest) posture, sitting in Off-Loading posture significantly shifted the center of the force and the peak pressure on the seat anteriorly towards the thighs. It also significantly decreased the contact area on the seat and increased that on the backrest. It decreased the lumbar muscle activities significantly. These effects are similar in individuals with and without LBP.ConclusionSitting with reduced ischial support and enhanced lumbar support resulted in reduced sitting load on the lumbar spine and reduced the lumbar muscular activity, which may potentially reduce sitting-related LBP.

ACL impingement prediction based on MRI scans of individual knees.

Although tibial external rotation and abduction do not load the ACL strongly in cadaver-based biomechanical studies, such knee positions are associated with ACL injuries in clinical practice. We hypothesized the ACL could be injured in such knee positions because of its impingement against the intercondylar notch. We developed a three-dimensional geometric ACL impingement model through segmentation of MR images of individual knees. We investigated impingement by determining the deformed geometry and elongation of the ligament as it wrapped around the notch surface during impingement. When impingement did not occur, the gap width separating the ligament and the notch surface was computed. Tibial external rotation/abduction could cause the ACL to impinge against the lateral notch wall and elongate as it wraps around the surface of the notch wall. The impingement occurred between the middle portion of the ligament (at 45% ± 8% [mean ± standard deviation] of the ligament length) and the convex surface of the lateral notch wall. Considering the multiband fiber architecture of the ligament, the anteromedial band of the ACL sustained greater elongation during impingement and showed a smaller gap width from the notch surface than the intermediate band or the posterolateral band.

Computed tomography of posterior fracture-dislocations of the shoulder : case reports

Computed tomographic (CT) evaluation of seven posterior shoulder dislocations in five patients is reported. Computed tomography provided better visualization of the trough fracture in the humeral head than did conventional x-ray films or tomography. It also demonstrated fracture fragments not seen on conventional roentgenograms. The two cases of bilateral dislocation and one case of unilateral dislocation were caused by seizures. The two other cases of unilateral dislocation were caused by trauma.

Preiser's disease: Identification of two patterns

PURPOSE A large series of patients with Preisers disease was reviewed to compare 2 potentially different categories of this disorder: complete versus partial vascular impairment of the scaphoid bone as determined by magnetic resonance imaging (MRI). METHODS Nineteen patients with Preisers disease were identified retrospectively from 2 institutions. Using MRI criteria, 2 disease patterns were identified: diffuse necrosis and/or ischemia of the scaphoid (type 1 disease, 11 cases) and segmental vascular impairment of the scaphoid (type 2 disease, 8 cases). Risk factors for osteonecrosis, treatment methods, and serial radiographs were reviewed in all cases. Sixteen patients were examined for the purpose of this study at an average follow-up of 25 months. RESULTS MRI signal changes of necrosis and/or ischemia involved 100% of the scaphoid in type 1 cases and on average approximately 42% in type 2 cases (range, 33% to 66%). In type 1 cases, regardless of the treatment used, the scaphoid typically fragmented and collapsed. In type 2 cases, scaphoid architecture was altered minimally after similar treatment methods. A history of wrist trauma was significantly more common in type 2 cases, and the results of treatment were generally better in this group of patients (mean Mayo modified wrist scores, 86 vs 58 points). CONCLUSIONS This study supports the concept of 2 patterns of scaphoid involvement in Preisers disease. Type 1 cases are characterized by MRI signal changes of necrosis and/or ischemia involving the entire scaphoid bone. Patients in this group have a propensity for scaphoid deterioration. Type 2 cases have MRI signal changes involving only part of the scaphoid. These patients commonly report a history of wrist trauma, show fewer tendencies toward scaphoid fragmentation, and may have a more favorable clinical outcome.