Background

Chronic nerve compression neuropathies result in decreased blood flow at the site of compression. Surgical decompression of the nerve often has variable postoperative results. The current study examines whether the timing of surgical intervention is an important variable in reversing the compression-induced ischemia and associated changes in biochemical markers.

Methods

An established model of chronic nerve compression injury was created in 100 C57BL/6 mice, and serial electrophysiological examinations were used to confirm the creation of a chronic nerve compression injury. Laser speckle imaging was used to measure neural blood flow. Nerves in the animals that did not undergo decompression were harvested at two, four, and six weeks after injury and analyzed for hypoxia-inducible factor 1α (HIF1α), catalase, superoxide dismutase (SOD), and matrix metalloproteinases (MMPs) 2 and 9. Surgical decompression in other animals was performed at either an early (two-week) or late (six-week) time point after injury, with specimens harvested at multiple time points after decompression. One-way analysis of variance with Bonferroni correction was performed.

Results

Chronic nerve compression injury initially induced hyperemia (1.37 ± 0.50 times that in the contralateral, uninjured nerve) followed by a decline in neural blood flow by four weeks (0.66 ± 0.14, p = 0.0313). In parallel, HIF1α, catalase, and SOD were elevated early after compression, whereas extracellular matrix-altering proteins were elevated later in the disease. Although early decompression yielded a return of blood flow to a hyperemic state (1.35 ± 0.16, p = 0.0057), late decompression did not result in reversal of the abnormal neurovascular flow. With late decompression, an MMP9-mediated structural alteration of the extracellular matrix was seen, producing irreversible changes in blood flow parameters. Although nerve conduction velocity measurements returned to normal two weeks after decompression irrespective of the timing of the surgical intervention, distal latency returned to normal only after early decompression (0.97 ± 0.06 msec compared with 1.22 ± 0.06 msec for late decompression, p = 0.009).

Conclusions

Chronic nerve compression injuries decreased neurovascular flow and induced ischemia by upregulating HIF1α, catalase, and MMP9. Early surgical intervention offered better return to normal electrophysiological parameters compared with late intervention.

Clinical relevance

These data present a clinical correlate to the variable functional outcomes seen following surgical release of chronic nerve compression injuries and provide early support for using distal latency as a predictor of outcomes following surgical release.

BACKGROUND: Chronic nerve compression neuropathies result in decreased blood flow at the site of compression. Surgical decompression of the nerve often has variable postoperative results. The current study examines whether the timing of surgical intervention is an important variable in reversing the compression-induced ischemia and associated changes in biochemical markers. METHODS: An established model of chronic nerve compression injury was created in 100 C57BL/6 mice, and serial electrophysiological examinations were used to confirm the creation of a chronic nerve compression injury. Laser speckle imaging was used to measure neural blood flow. Nerves in the animals that did not undergo decompression were harvested at two, four, and six weeks after injury and analyzed for hypoxia-inducible factor 1α (HIF1α), catalase, superoxide dismutase (SOD), and matrix metalloproteinases (MMPs) 2 and 9. Surgical decompression in other animals was performed at either an early (two-week) or late (six-week) time point after injury, with specimens harvested at multiple time points after decompression. One-way analysis of variance with Bonferroni correction was performed. RESULTS: Chronic nerve compression injury initially induced hyperemia (1.37 ± 0.50 times that in the contralateral, uninjured nerve) followed by a decline in neural blood flow by four weeks (0.66 ± 0.14, p = 0.0313). In parallel, HIF1α, catalase, and SOD were elevated early after compression, whereas extracellular matrix-altering proteins were elevated later in the disease. Although early decompression yielded a return of blood flow to a hyperemic state (1.35 ± 0.16, p = 0.0057), late decompression did not result in reversal of the abnormal neurovascular flow. With late decompression, an MMP9-mediated structural alteration of the extracellular matrix was seen, producing irreversible changes in blood flow parameters. Although nerve conduction velocity measurements returned to normal two weeks after decompression irrespective of the timing of the surgical intervention, distal latency returned to normal only after early decompression (0.97 ± 0.06 msec compared with 1.22 ± 0.06 msec for late decompression, p = 0.009). CONCLUSIONS: Chronic nerve compression injuries decreased neurovascular flow and induced ischemia by upregulating HIF1α, catalase, and MMP9. Early surgical intervention offered better return to normal electrophysiological parameters compared with late intervention. CLINICAL RELEVANCE: These data present a clinical correlate to the variable functional outcomes seen following surgical release of chronic nerve compression injuries and provide early support for using distal latency as a predictor of outcomes following surgical release.

Purpose

The purpose of this study was to define the incidence of trochlear dysplasia in an infant cohort being screened for developmental dysplasia of the hip (DDH).

Methods

Newborns screened for DDH that were evaluated with ultrasound for the presence of trochlear dysplasia were retrospectively reviewed. The sulcus angle and trochlear depth were measured. Based on previous work, trochlear dysplasia was defined as a sulcus angle of > 159°. Our newborn cohort was then analyzed to identify potential risk factors for trochlear dysplasia.

Results

A total of 383 knees in 196 infants were studied. In total, 52% were referred for breech intrauterine positioning and 21% were ultimately diagnosed with DDH and had treatment initiated with a Pavlik harness. Of the entire cohort, 8% of knees were deemed to have trochlear dysplasia. Breech patients were found to have a flatter sulcus angle than those that were not breech (149.5° (sd 7.2°) versus 147.9° (sd 7.5°); p = 0.028). Similarly, a shallower trochlear depth was identified in breech patients versus non-breech patients (1.6 mm (sd 0.4) versus 1.8 mm (sd 0.4); p = 0.019). Those with trochlear dysplasia (as defined by sulcus angle > 159°) did show a smaller alpha angle (i.e. more dysplastic hip) as compared with those without trochlear dysplasia (59.2° (sd 10.2°) versus 65.9° (sd 7.5°); p < 0.001). Hips with DDH were 2.4-times more likely to have knees with trochlear dysplasia (95% confidence interval 1.1 to 5.3).

Conclusion

Ultrasound screening of newborn knees reveals that trochlear dysplasia is relatively common in breech babies with DDH.

Level of evidence

III.

Background

We analyzed preoperative CT scans of hips with slipped capital femoral epiphysis (SCFE) for characteristics that could be predictive of intraoperative epiphyseal stability and developed a set of imaging criteria for stable and unstable SCFE. We then compared this grading system with the Loder classification.

Methods

We reviewed preoperative CT imaging to develop a SCFE stability classification system. Three orthopaedic surgeons used the classification system to grade stability on a series of SCFE hips. Kappa was used to evaluate intra- and interobserver reliability among the observers. A series of SCFE hips treated with open procedures in which intraoperative stability was determined under direct visualization was evaluated. Intraoperative stability was compared with stability ratings as determined by the CT classification system and the Loder classification system.

Results

Interobserver reliability among our three observers was κ = 0.823 (95% confidence interval (CI) 0.414 to 1.0; p < 0.001). Intraobserver reliability was κ = 0.901 (95% CI 0.492 to 1.31; p < 0.001). In all, 27 hips were used in the comparison of intraoperative stability with the Loder and CT classification systems. CT-predicted stability exhibited 78% concordance with intraoperative stability. The sensitivity and specificity of CT-predicted stability was 75% and 82%, respectively, versus Loder sensitivity of 69% and specificity of 91%.

Conclusion

The CT evaluation method provided is easy to use and can help to improve the accuracy in determining preoperative epiphyseal stability, which may lead to improved treatment outcomes for this population.

Level of evidence

III.

Study design

Retrospective chart review.

Objectives

To evaluate the efficacy of tobramycin and vancomycin powder in reducing surgical site infections in posterior lumbar instrumented fusion.

Methods

A multicenter, electronic database search was conducted for all patients who underwent posterior instrumented lumbar fusions.

Results

The addition of vancomycin powder decreased postoperative infections from an incidence of 5.7% down to a rate of 2.0%. This difference was statistically significant (P = .018). The addition of tobramycin powder to the wound in addition to vancomycin further decreased the infection rate down to 1.8%. The postoperative infection rate was statistically significant (P = .041) when compared with the no-powder group. However, the difference was not statistically significant (P = 1.00) when compared with vancomycin alone. There was also a trend toward gram-negative organisms with the addition of more antibiotic powder. In the control group, for example, the organisms cultured were 66% methicillin-sensitive Staphylococcus aureus and 33% gram-negative organisms. In the vancomycin group, 30% of the organisms cultured were Staphylococcus aureus and 60% gram-negative organisms. In the vancomycin and tobramycin powder group, 100% of the organisms cultured were gram-negative.

Conclusions

There is a reduction in surgical site infections with addition of antibiotic powder to the wound prior to closure. However, the reduction in the infection rate was not as great with the addition of tobramycin powder to vancomycin alone and there was a noticeable change in the spectrum of organism cultured with this addition. Clinicians should consider the risk-to-benefit ratio in each case when deciding to use antibiotic powder.