Changes in disc height and posteroanterior displacement after fusion in patients with idiopathic scoliosis: a 9-year follow-up study.

INTRODUCTION: In scoliosis patients treated with long segment spinal fusion, degenerative changes like retrolisthesis and disc space narrowing below fusion have been observed. However, there is disagreement concerning their incidence and dependency on the location of the lowest instrumented vertebra. MATERIALS AND METHODS: To evaluate temporal changes in disc height and posteroanterior displacement (indicating listhesis) below fusion, 40 patients with adolescent idiopathic scoliosis, mainly treated with Cotrel-Dubousset instrumentation, were retrospectively investigated in this longitudinal study with a follow-up of on average 9.2 years (median 9.4 y) after surgery. Disc height and displacement were measured from lateral radiographs by means of distortion-compensated roentgen analysis (DCRA). Additionally, a mathematical model was developed to determine the influence of vertebral tilt in scoliosis on disc height and displacement. RESULTS: Overall, no significant decrease in disc height was observed during follow-up. Concerning listhesis a small but significant retrolisthesis was found in segments L2/L3 and L3/L4. Compared with normative data, there was no significant listhesis for the L5/S1 segment. Nevertheless, separating the study group into subsamples of identical distal fusion level revealed a significant correlation between the amount of posteroanterior displacement at L5/S1 and the location of the lowest instrumented vertebra. With a reduction of free motion segments, listhesis increased into posterior direction. Taking the tilt correction into account led to considerably increased values of disc height whereas displacement was affected only to a minor degree. CONCLUSIONS: Long segment spinal fusion in young patients with idiopathic scoliosis did not lead to disc space narrowing during 9.2 years follow-up. However, the observed increase in retrolisthesis potentially indicates the initiation of a degenerative process. These only minimal changes might be referred to the preservation of a physiologic lumbar lordosis. Without correction for vertebral tilt disc space narrowing is overestimated.

Locating the axis of rotation when fitting an elbow orthosis: a comparison of measurement and palpation.

No other previously published studies consider the relative motion of orthotic components positioned on the upper arm and the forearm. This study therefore measured the location and direction of the axis of rotation of an orthotic component fixed to the forearm in relation to an orthotic component fixed to the upper arm, and compared the results with those obtained by palpation. A plane flexion or extension motion of the forearm component in relation to the component on the upper arm can be described as a pure rotation about a fixed centre. However, activation of the biceps or triceps shifts that centre by around 2 cm, due to a displacement of the humerus within the orthotic component on the upper arm. Within a range of approximately 1 cm, the location of the axis of rotation was similar to that obtained by palpation. Neither custom-made plastic/foam orthoses with their hinges aligned to the measured axis, nor orthoses with their hinges aligned to the palpated axis, exhibited any difference in the wearer's comfort. It is concluded that the best choice for the location of the axis of a hinge-type orthosis for the elbow constitutes a compromise between the axes for active flexion and active extension. In view of the large influence that muscle activation has on axis location, errors in the order of 1 cm seem to be negligible when adjusting the hinge of an orthosis in individual cases.

Mobility of lumbar segments instrumented with a ProDisc II prosthesis: a two-year follow-up study.

STUDY DESIGN: Longitudinal prospective study on a sample of 41 consecutive disc prosthesis patients, covering a postoperative time period of at least 2 years. OBJECTIVES: To document the rotational and translational range of segmental motion of patients instrumented with ProDisc II prostheses in the lumbar spine and to compare motion between instrumented and untreated adjacent segments with respect to a normative database. To discuss potential causes of the low range of rotational motion observed after instrumentation with a Prodisc II prosthesis. SUMMARY OF BACKGROUND DATA: Disc replacement is intended to restore physiologic motion and height of the affected levels. Published reports show, however, that the goal of restoring motion at the operated segment is missed in the majority of cases. The cause of this failure is unresolved. METHODS: Rotational and translational segmental motion in the sagittal plane, disc height, and posteroanterior displacement were measured from lateral radiographic views taken standing (before surgery) and in flexion and extension (1 year and 2 years after surgery) by Distortion Compensated Roentgen Analysis (DCRA). The protocol permits to take measurements from all segments imaged on the radiographic views and compensates for variations in stature, magnification, and posture. Data from instrumented and untreated segments can be compared and related to a previously determined normative database. RESULTS: The rotational range of motion of segments instrumented with a ProDisc II prosthesis was low, especially at L4-L5 and L5-S1. In the majority of cases, it amounted to less than 45% of the normal range. Virtually no improvement occurred between 1 and 2 years after surgery. Malalignment of the axis of rotation of the prosthesis with respect to the anatomic axis, persisting clinical symptoms, or the significant increase of intervertebral space documented after instrumentation are unlikely to cause the low range of motion. As the range of rotational motion of the untreated segments was low with respect to normal as well, it is conjectured that tissue adaptation during the preoperative symptomatic time period might have caused the postoperative motion deficit. This conjecture complies with fragmentary previous observations of a low postoperative segmental range of motion from untreated segments of fusion patients. CONCLUSIONS: Disc replacement in the lumbar spine by a ProDisc II implant fails to restore normal segmental rotational motion in the sagittal plane, specifically at levels L4-L5 and L5-S1. As segmental motion of the untreated segments was lower than normal as well, though not quite as conspicuous as that of instrumented segments, adaptation of soft tissue taken place during the preoperative symptomatic time period is conjectured to cause the observed motion deficit. Postoperative physical therapy might be considered if restoration of a normal range of rotational motion is desired.

Congenital cervical block vertebrae are associated with caudally adjacent discs.

BACKGROUND: Knowledge on the time course of changes in cervical disc height and cervical kinematics at motion segments adjacent to congenital block vertebrae is fragmentary. Compared with this, after surgical fusion of cervical spine segments some find increased degenerative processes in combination with hypermobility or instability while others were unable to confirm these changes. This cross sectional study was undertaken to investigate whether congenital block vertebrae are associated with an increased risk of disc degeneration and hypermobility at adjacent motion segments. METHODS: In 25 subjects (mean age 40 years) disc height, vertebral height and segmental mobility at motion segments adjacent to a congenital block vertebra were assessed quantitatively by distortion-compensated Roentgen analysis. The findings were compared to a normal database. FINDINGS: Height of the disc cranially adjacent to the block vertebra did not deviate from the norm while height of the caudally adjacent disc was significantly reduced. The height of the vertebrae adjacent to the block did not deviate from normal. The motion segments formed by the block vertebra and the adjacent discs and vertebrae exhibited no deviation from normal with respect to sagittal plane rotational or translational motion. INTERPRETATION: Congenital block vertebrae do not result in rotational or translational hyper- or hypomobility at motion segments adjacent to the block. Whether the observed, significant height reduction of the caudally adjacent disc is caused by degeneration following the block formation cannot undoubtedly be concluded as the initial state is not known. Further longitudinal studies are needed to investigate this issue.

Increased sagittal plane segmental motion in the lower cervical spine in women with chronic whiplash-associated disorders, grades I-II: a case-control study using a new measurement protocol.

STUDY DESIGN: Case-control study comparing sagittal plane segmental motion in women (n = 34) with chronic whiplash-associated disorders, Grades I-II, with women (n = 35) with chronic insidious onset neck pain and with a normal database of sagittal plane rotational and translational motion. OBJECTIVE: To reveal whether women with chronic whiplash-associated disorders, Grades I-II, demonstrate evidence of abnormal segmental motions in the cervical spine. SUMMARY OF BACKGROUND DATA: It is hypothesized that unphysiological spinal motion experienced during an automobile accident may result in a persistent disturbance of segmental motion. It is not known whether patients with chronic whiplash-associated disorders differ from patients with chronic insidious onset neck pain with respect to segmental mobility. METHODS: Lateral radiographic views were taken in assisted maximal flexion and extension. A new measurement protocol determined rotational and translational motions of segments C3-C4 and C5-C6 with high precision. Segmental motion was compared with normal data as well as among groups. RESULTS: In the whiplash-associated disorders group, the C3-C4 and C4-C5 segments showed significantly increased rotational motions. Translational motions within each segment revealed a significant deviation from normal at the C3-C4 segment in the whiplash-associated disorders and insidious onset neck pain groups and at the C5-C6 segment in the whiplash-associated disorders group. Significantly more women in the whiplash-associated disorders group (35.3%) had abnormal increased segmental motions compared to the insidious onset neck pain group (8.6%) when both the rotational and the translational parameters were analyzed. When the translational parameter was analyzed separately, no significant difference was found between groups, or 17.6% (whiplash-associated disorders group) and 8.6% (insidious onset neck pain group), respectively. CONCLUSION: Hypermobility in the lower cervical spine segments in 12 out of 34 patients with chronic whiplash-associated disorders in this study point to injury caused by the accident. This subgroup, identified by the new radiographic protocol, might need a specific therapeutic intervention.

Detection of subtle undisplaced rib fractures in a porcine model: radiation dose requirement--digital flat-panel versus screen-film and storage-phosphor systems.

PURPOSE: To compare a large-area direct read-out flat-panel detector radiography system with screen-film and storage-phosphor systems with regard to detection of subtle undisplaced rib fractures and to assess the diagnostic performance of the flat-panel system with decreasing exposure level. MATERIALS AND METHODS: Subtle fractures were created artificially in 100 of 200 porcine rib specimens. Specimens were enclosed in containers of water to generate absorption and scatter radiation conditions similar to those of a human chest wall. Imaging was performed with flat-panel, screen-film, and storage-phosphor systems with conditions that were exactly matched. Different exposure levels equivalent to speed classes (S) of 400, 800, 1,600, and 6,400 were used. All images were independently assessed for the presence of fracture by three radiologists with a five-level confidence scale. Receiver operating characteristic (ROC) analysis was performed for a total of 4,200 observations (600 for each imaging system and exposure level). Diagnostic performance was estimated with area under the ROC curve (Az). Significance of differences in diagnostic performance was tested with analysis of variance. RESULTS: ROC analysis yielded mean Az values for the flat-panel system of 0.879 (S = 400), 0.833 (S = 800), 0.765 (S = 1,600), and 0.576 (S = 6,400). Az values were 0.834 (S = 400) for the screen-film system and 0.789 (S = 400) and 0.729 (S = 800) for the storage-phosphor system. Analysis of variance revealed significant differences in diagnostic performance between various combinations of imaging system and exposure levels (P <.05). CONCLUSION: The flat-panel system is superior to the screen-film and storage-phosphor systems for detection of subtle undisplaced rib fractures at clinical exposure settings (eg, S = 400). With the flat-panel system, radiation dose can be reduced by 50% to achieve diagnostic performance comparable to that of a speed class 400 screen-film system.