Joseph J. Schreiber

Hounsfield Units for Assessing Bone Mineral Density and Strength: A Tool for Osteoporosis Management

BACKGROUND Measurements obtained from clinical computed tomography examinations may yield information leading to the diagnosis of decreased bone mineral density, without added expense to the patient. The purpose of the present study was to determine if Hounsfield units, a standardized computed tomography attenuation coefficient, correlate with bone mineral density and compressive strength. METHODS Twenty-five patients (including eighteen female and seven male patients with a mean age of 71.3 years) undergoing both lumbar spine dual x-ray absorptiometry scans and computed tomography imaging were evaluated to determine if Hounsfield units correlated with bone mineral density and T-scores. Normative data were generated from lumbar spine computed tomography examinations for eighty consecutive trauma patients and were stratified by age and sex. Separately, polyurethane foam blocks of varying densities were imaged with computed tomography and were subjected to mechanical testing to determine compressive strength. Compressive strength values and Hounsfield units were analyzed for correlation. RESULTS Significant correlations were found between Hounsfield units and bone mineral density, age, and T-scores and between Hounsfield units and compressive strength (p < 0.001). CONCLUSIONS Hounsfield units obtained from clinical computed tomography scans that are made for other purposes correlate with dual x-ray absorptiometry scores as well as compressive strengths based on osseous models and potentially provide an alternative method for determining regional bone mineral density at no additional cost to the patient. The information could conceivably be applied toward fracture risk assessment, diagnosis of osteoporosis, and early initiation of needed treatment.

Circulating precursors of human CD1c+ and CD141+ dendritic cells

The Liu and Nussenzweig groups identify the immediate precursor of CD1c+ and CD141+ dendritic cells in the circulation of healthy donors. These precursor cells (hpre-cDC) were detectable in cord blood, bone marrow, blood, and peripheral lymphoid organs.

Use of computed tomography for assessing bone mineral density

Assessing local bone quality on CT scans with Hounsfield unit (HU) quantification is being used with increasing frequency. Correlations between HU and bone mineral density have been established, and normative data have been defined throughout the spine. Recent investigations have explored the utility of HU values in assessing fracture risk, implant stability, and spinal fusion success. The information provided by a simple HU measurement can alert the treating physician to decreased bone quality, which can be useful in both medically and surgically managing these patients.

An Online Video Investigation Into the Mechanism of Elbow Dislocation

PURPOSE Acute elbow instability leading to dislocation is thought to be a spectrum initiated by an injury to the lateral stabilizing structures of the elbow. Previous cadaveric studies have shown elbow dislocations to occur in flexion. The purpose of this study was to analyze videographic evidence of the deforming forces and upper extremity position during elbow dislocations. We sought to corroborate previous biomechanics studies with in vivo observations. METHODS We included 62 YouTube.com videos with a clear videographic view of an elbow dislocation. Three senior elbow surgeons independently evaluated arm position at the time of dislocation, along with the suspected deforming forces at the elbow based on these positions. RESULTS Of the 62 visualized elbow dislocation events, the vast majority (92%) dislocated at or near full extension. The most common arm positions were forearm pronation (68%) with shoulder abduction (97%) and forward flexion (63%). The typical elbow deforming forces were a valgus moment (89%), an axial load (90%), and progressive supination (94%). We identified 4 discrete patterns of arm position and deforming forces. CONCLUSIONS Acute elbow dislocations in vivo occur in relative extension irrespective of forearm position, a finding distinct from previous cadaveric studies. The most common mechanism appears to involve a valgus moment to an extended elbow, which suggests a requisite disruption of the medial collateral ligament, the known primary constraint to valgus force. These videographic findings suggest that some acute elbow dislocations may result from acute valgus instability and therefore are distinct in nature and mechanism from posterolateral rotatory instability. This information could lead to improved understanding of the sequence of structural failure, modification of rehabilitation protocols, and overall treatment.

Volar Plate Position and Flexor Tendon Rupture Following Distal Radius Fracture Fixation

PURPOSE To determine whether there were differences between plate position in patients who had postoperative flexor tendon ruptures following volar plate fixation of distal radius fractures and those who did not. METHODS Three blinded reviewers measured the volar plate prominence and position on the lateral radiographs of 8 patients treated for flexor tendon ruptures and 17 matched control patients without ruptures following distal radius fracture fixation. We graded plate prominence using the Soong grading system, and we measured the distances between the plate and both the volar critical line and the volar rim of the distal radius. RESULTS A higher Soong grade was associated with flexor tendon rupture. Patients with ruptures had plates that were more prominent volarly and more distal than matched controls without ruptures. Plate prominence projecting greater than 2.0 mm volar to the critical line had a sensitivity of 0.88, a specificity of 0.82, and positive and negative predictive values of 0.70 and 0.93, respectively, for tendon ruptures. Plate position distal to 3.0 mm from the volar rim had a sensitivity of 0.88, a specificity of 0.94, and positive and negative predictive values of 0.88 and 0.94, respectively, for tendon ruptures. CONCLUSIONS We identified plate positions associated with attritional flexor tendon rupture following distal radius fracture fixation with volar plates. To decrease rupture risk, we recommend considering elective hardware removal after union in symptomatic patients with plate prominence greater than 2.0 mm volar to the critical line or plate position within 3.0 mm of the volar rim. TYPE OF STUDY/LEVEL OF EVIDENCE Therapeutic III.

Magnetic Resonance Imaging Findings in Acute Elbow Dislocation: Insight Into Mechanism

PURPOSE To identify with magnetic resonance imaging the location and severity of ligamentous injury after acute elbow dislocations. Based on observations that many elbow dislocations arise from an initial acute valgus load, we hypothesized that all patients would have a high-grade medial injury but not all would demonstrate injury of the lateral ligaments. METHODS The medial collateral ligament was subdivided into anterior bands of the anterior bundle of the medial collateral ligament (MCL) and posterior bands of the anterior bundle of the MCL, whereas the lateral collateral ligament was divided into the lateral ulnar collateral ligament and the radial collateral ligament. Distinction on magnetic resonance imaging was made between normal morphology and low-grade partial tear (< 50% of the ligament fibers), high-grade partial tear (≥ 50%), and full-thickness disruption. The site of disruption was also characterized. RESULTS Acute magnetic resonance imaging studies for 16 patients were included. No low-grade tears or intact evaluations of either the anterior or posterior bands of the anterior bundle of the MCL were observed; most demonstrated complete tears. The lateral ulnar collateral ligament most frequently showed complete disruption but was occasionally intact. The radial collateral ligament infrequently showed full disruption. Complete tears involving either the anterior or posterior portions of the anterior band of the MCL were significantly more common than complete tears involving the ligaments on the lateral side. CONCLUSIONS After elbow dislocation, complete ligamentous tears were more common on the medial versus the lateral side. Whereas the lateral ligaments were occasionally preserved, this was never observed on the medial side. These data suggest a sequence of failure starting on the medial side with subsequent variable energy dissipation laterally. TYPE OF STUDY/LEVEL OF EVIDENCE Diagnostic IV.

Optimal axon counts for brachial plexus nerve transfers to restore elbow flexion.

Background: Nerve transfer surgery has revolutionized the management of traumatic brachial plexus injures. However, the optimal size ratio of donor to recipient nerve has yet to be elucidated. The authors investigated the axon count ratios of ulnar and median fascicular transfers to restore elbow flexion. The authors hypothesized that donor nerve axon counts would be correlated with historical success of various nerve transfers used to restore elbow flexion. Methods: Ten cadaveric specimens were used for a histomorphologic analysis of fascicular nerve transfers. Review of previously published axon counts and clinical results following transfer to the musculocutaneous nerve to restore elbow flexion was performed for the following donor nerves: medial pectoral, spinal accessory, intercostal, thoracodorsal, ulnar, and median fascicular. Results: The average number of fascicles identified was 7.9 in the ulnar nerve and 8.0 in the median nerve. The mean fascicular axon count was 1318 for the ulnar nerve and 1860 for the median nerve. Mean recipient nerve axon count was 1826 for the musculocutaneous biceps branch and 1840 for the brachialis branch. A significant correlation between axon count and clinical results of transfers to restore elbow flexion was observed. Donor-to-recipient nerve axon count ratios below 0.7:1 were associated with a decreased likelihood of a successful outcome. Conclusions: In nerve transfers to restore elbow flexion, an appropriate size match between donor and recipient nerves appears to be a factor affecting clinical success. These data support a donor-to-recipient axon count ratio greater than 0.7:1 as the goal for brachial plexus nerve transfers to restore elbow flexion.

Opportunistic Osteoporosis Screening— Gleaning Additional Information from Diagnostic Wrist CT Scans

BACKGROUND Although screening for and treating osteoporosis can prevent subsequent fractures, the rates of such interventions are low following a distal radial fracture. One potential method for identifying metabolic bone disease is via Hounsfield unit (HU) measurements from diagnostic computed tomography (CT) scans. We hypothesized that HU values of the distal aspect of the radius could be used to assess local bone quality and would be predictive of distal radial fracture risk, thereby allowing the identification of patients in need of further management. METHODS Measurements of bone mineral density (BMD) were made for 100 patients on the basis of HU values of cancellous portions of the distal aspect of the radius, the ulnar head, and the capitate. The HU values in twenty-five male and twenty-five female patients with an acute distal radial fracture documented on CT were compared with those of age and sex-matched control patients who had a CT scan obtained for other indications. RESULTS Among the control patients, HU values decreased as age increased. When assessed on the basis of sex, both male and female patients with a distal radial fracture had significantly lower regional BMD compared with nonfracture control patients. A distal radial HU value of 218 for females and 246 for males optimized sensitivity and specificity; values below this threshold were associated with an increased risk of distal radial fracture. CONCLUSIONS HU measurements can be obtained from any diagnostic CT scan using modern software programs and can be obtained by physicians in the office setting with minimal effort and at no additional cost or radiation exposure to the patient. Regardless of imaging indications, we suggest that patients with HU values below the identified thresholds be considered for further metabolic bone disease work-up, such as additional imaging, laboratory assessments, the initiation of osteoporosis treatment, or appropriate referral.

Conservative Management of Elbow Dislocations With an Overhead Motion Protocol

PURPOSE To report the results of using an overhead motion protocol in 27 patients and to assess final range of motion and incidence of persistent instability in this cohort. METHODS A total of 27 patients were included who sustained a simple elbow dislocation and were treated nonsurgically with an overhead motion protocol designed to convert gravity from a distracting to a stabilizing force. Motion was initiated within 1 week of injury and average follow-up was 29 months. Final arc of motion and prevalence of instability were the primary outcomes measures. RESULTS Final mean arc of extension to flexion was from 6° to 137°, and of pronation to supination was from 87° to 86°. No recurrent instability was observed in this cohort and all patients were fully functional and without limitations at latest follow-up. CONCLUSIONS The overhead motion protocol was a reliable rehabilitation program after elbow dislocation that allowed for controlled early motion by placing the elbow in an inherently stable position. Prompt initiation of motion in a protected position can optimize final motion and satisfaction outcomes, and when done in a mechanically advantageous position it can potentially limit the risk of recurrent instability. TYPE OF STUDY/LEVEL OF EVIDENCE Therapeutic IV.

Using Hounsfield Units to Assess Osteoporotic Status on Wrist Computed Tomography Scans: Comparison With Dual Energy X-Ray Absorptiometry.

PURPOSE Rates of evaluation and treatment for osteoporosis following distal radius fragility fractures remain low. As a subset of patients with these fractures undergo diagnostic computed tomography (CT) scan of the wrist, utilizing bone mineral density (BMD) measurements available with this imaging can be used to detect osteopenia or osteoporosis. This information may consequently prompt intervention to prevent a subsequent fracture. The purpose of this study was to determine if Hounsfield unit (HU) measurements at the wrist correlate with BMD measurements of the hip, femoral neck, and lumbar spine and to assess the ability of these HU measurements to detect osteoporosis of the hip. METHODS Forty-five female patients with distal radius fractures who underwent CT scan and dual energy x-ray absorptiometry scan as part of the management of their wrist fracture were identified. Bone mineral density measurements were made using the regional cancellous bone HU value at the capitate and compared with values obtained by a dual energy x-ray absorptiometry scan. RESULTS Hounsfield unit values at the capitate were significantly correlated with BMD and t scores at the femoral neck, hip, and lumbar spine. An HU threshold of 307 in the capitate optimized sensitivity (86%) and specificity (94%) for detecting osteoporotic patients. CONCLUSIONS By demonstrating that capitate HU measurements from clinical CT scans are correlated with BMD and t scores at the hip, femoral neck, and lumbar spine, our data suggest that clinical CT scans should have a role in detecting osteopenia and osteoporosis. TYPE OF STUDY/LEVEL OF EVIDENCE Diagnostic III.