Deviations in positioning variable pitch screws- scaphoid waist fractures

Treatment of scaphoid nonunion by arthroscopic cancellous bone grafting

INTRODUCTION

In order to avoid Scaphoid Nonunion Advanced Collapse (SNAC) type osteoarthritis, which progressively affects the radial and midcarpal joints, several vascularized and non-vascularized grafting techniques have been described. Over the past decade, there has been growing interest in arthroscopic cancellous bone grafts for scaphoid nonunion. The aim of this novel prospective study was to assess the healing rate of scaphoid grafts under arthroscopy, and the prognostic factors for healing.

MATERIAL AND METHODS

This prospective study was carried out across 10 centers between September 2019 and April 2021, in patients aged 16 to 65. Scaphoid nonunion grafting was performed arthroscopically. Union was assessed on CT scans and displacement correction angles were measured preoperatively and then at 3 and 6months. We assessed mobility, Jamar wrist strength, functional results as per the Patient Related Wrist Score (PRWE) and the Quick Disabilities of the Arm, Shoulder and Hand (Quick DASH) score. Risk factors for nonunion were assessed.

RESULTS

We included 77 patients with a mean age of 24years (18 to 55years) with a mean time between trauma and treatment of nonunion of 34.8months (6 to 180months). The population was represented by 46 manual workers and 20 were smokers. In 42 cases, the nonunion was proximal, in Schernberg zone I or II. At the last follow-up of 12.9months on average (Standard Deviation: 8.7months), union was achieved in 72 patients (93.5%). The average duration of union was 3.4months (Standard Deviation 1.6). Among the 5 patients who did not heal, grafting was performed in addition to the fixation. We did not identify any contributory factors for nonunion.

CONCLUSION

This study demonstrated the effectiveness of arthroscopic treatment of scaphoid nonunion with a union rate at least equivalent to pedicled vascularized grafts. Smoking and delayed treatment were no longer considered unfavorable prognostic factors in the context of arthroscopic treatment.

LEVEL OF EVIDENCE

III.

Fixation Methods for Replacement Screws in Scaphoid Fractures: A Biomechanical Study

Purpose

To investigate the changes in biomechanical fixation of an initial and replacement headless compression screw by quantifying interfragmentary compression and shear displacement.

Methods

A bone model was created with 2 blocks of rigid polyurethane foam to simulate a fracture site. A 24-mm headless compression screw was inserted into the model at a perpendicular or oblique angle, removed, and replaced with the 22-mm screw. The 22-mm screw replaced the 24-mm screw in either the same or reverse direction of initial insertion. All 4 methods of initial and replacement screw fixation were trialed 15 times for a total of 60 trials. Two button load cells measured compression. A digital microscope recorded shear displacement. Statistical analysis was performed to determine the differences in compression and sheer between the initial and replacement screw for each angle and screw insertion group with a 2-sided paired Student t test.

Results

In comparison with the average compression force achieved by placement of the primary screw, there was a significant loss of average compression force when the secondary screw was placed in the same direction and perpendicular to the fracture plane (50 N, P < .001), in the reverse direction and perpendicular to the fracture plane (9 N, P = .049), and in the same direction and 60º to the fracture plane (11 N, P < .001). A significantly greater average shear displacement was noted for initial screw insertion at oblique compared with perpendicular orientations (0.03 mm, P < .001).

Conclusions

This study demonstrates loss of compression when replacing screws despite varying orientations. Additionally, shear displacement in obliquely placed screws increased compared with perpendicularly placed screws.

Clinical relevance

This study provided quantitative evidence to support the importance of establishing the correct screw length initially to avoid compression loss caused by replacing a primary screw.

[Comparison between navigated and conventional percutaneous screw fixation of non-displaced scaphoid fractures]

BACKGROUND

Incorrect screw placement and penetration in screw fixation of scaphoid fractures are found in 5 to 30 %. Therefore, optimizing of screw placement is desirable, especially because an exact central position of the screw in the proximal fragment leads to a significant higher stability as a more peripheral position.

PATIENTS UND METHODS

36 patients with an acute non-displaced scaphoid fracture were included in this randomized prospective study. 18 patients underwent navigated, the other 18 conventional percutaneous screw fixation of an acute non-displaced scaphoid fracture through a dorsal approach. Operation time and x-ray dose were measured. In both groups the position of the screw in the scaphoid was calculated on CT scans and compared with each other. Clinically, 17 patients with navigated and 11 with conventional percutaneous screw fixation with an average age of 52 resp. 43.2 years were available for follow-up examination including Krimmer- and DASH-score.

RESULTS

All scaphoids healed within an adequate time. Two cases of navigated screw fixation have been converted to conventional percutaneous screw fixation. The average operation time in the navigated group was 83.2 minutes, in the conventional group 42.1 minutes. X-ray dose measured 106,5 ± 19,9cGy/cm² in the navigated group and 45,6 ± 8,0cGy/cm² in the conventional group. Screw penetration using an intraosseous compression screw (HSC) was observed in 5 conventionally fixed scaphoids, 4 distally (2,27 ± 1,47 mm), 1 proximally. In the navigated group there were 11 screw penetrations, 4 proximally (2,01 ± 0,81 mm) and distally (1,21 ± 0,64 mm), 3 distally (1,18 ± 0,44 mm), and 4 proximally (1,61 ± 0,57 mm). Axial screw position was more accurate in the conventional group. The 17 navigated patients averaged a Krimmer-Score of 83.6 and a DASH-score of 5,6 points at follow-up. The 11 conventional treated patients averaged a Krimmer-Score of 95 and a DASH-score of 8.0 points at follow-up.

CONCLUSION

In this study navigated screw fixation of acute non-displaced scaphoid fractures was not superior to conventional percutaneous screw fixation, neither for screw position, screw penetration nor with respect to the clinical outcome.