Determination of Availability of Safety Margin for Placement of C3-C6 Pedicle Screw on CT Angiography

BACKGROUND

Cervical pedicle screws (CPS) in the subaxial cervical spine (C3-C6) are faced with high incidence of perforating the lateral pedicular cortex endangering the vertebral artery (VA). The present study analyzes the pedicle width (PW) from C3 to C6 and defines the relation of VA with regard to pedicle and transverse foramen (TF) to determine the safety margin in cases of lateral pedicular breach.

METHODS

Computed tomography angiograms of 500 patients were retrospectively studied to identify the pedicle width (PW), VA area, TF area, and the lateral pedicle to vertebral artery distance (LPVA). Occupancy ratio (OR; the percentage area of transverse foramen occupied by VA) and safety margin (SM; permissible displacement of VA in TF), along with LPVA were considered to be protective parameters against VA injury if lateral pedicle breach happens.

RESULTS

PW was 4.7 mm at C3, 4.83 mm at C4, 5.26 mm at C5 and 5.41 mm at C6. Mean LPVA at different levels was between 0.97 mm and 1.15 mm, OR was around 20% at all levels, and mean SM was between 2.34 mm and 2.92 at various levels. Sex differences were statistically significant for PW but not for LPVA, SM, or OR.

CONCLUSIONS

This study gives us an idea about the various parameters in placement of cervical pedicle screw in subaxial cervical spine and the probable reasons there are few vertebral artery injuries despite high incidence of cervical pedicle breach. LPVA, safety margin, and OR may explain why even very significant CPS misplacement does not lead to vascular injury or neurologic deficit.

Does change in occupancy ratio and fatty infiltration of the supraspinatus influence functional outcome after single-row rotator cuff repair? A magnetic resonance imaging-based study

INTRODUCTION

The purpose of this study was to analyze the correlation of occupancy ratio (OR) and fatty infiltration (FI) to functional outcome and retear rate following rotator cuff repair by single-row technique.

MATERIAL AND METHODS

Retrospectively, all the patients (n = 100) with rotator cuff tear were evaluated preoperatively and postoperatively with functional scores (American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form [ASES], University of California-Los Angeles [UCLA] shoulder score, Constant score) and magnetic resonance imaging (MRI) for OR and FI. Two observers studied the MRI data separately. Statistical analysis was done using SPSS (version 16), paired t test, Pearson correlation, and intraclass correlation coefficients.

RESULTS

The mean (± standard deviation) follow-up was 16.24 ± 6.39 months, and the mean age was 56.18 ± 7.5 years. There was a significant increase in muscle atrophy (decreased OR) and FI (P < .01). The mean preoperative and postoperative ORs were 0.57 and 0.51, respectively. However, the mean functional scores improved significantly for ASES (55.78 to 82.09), UCLA (19.44 to 28.47), and Constant score (49.73 to 75.07) (P < .001). There was no significant difference in functional outcome among the different stages of FI (ASES P = .341, UCLA P = .839, Constant P = .376). Seven patients had asymptomatic retear during follow-up, of which 2 patients had grade 3, 4 patients had grade 2, and 1 patient had grade 1 FI, preoperatively.

CONCLUSION

Muscle atrophy and FI are irreversible phenomena and continue even after successful repair; however, they do not have a significant influence on the functional outcome at short-term follow-up after cuff repair. Repairing cuff with higher grades of FI can be performed as they achieve significantly improved functional outcomes.