Comparison of bone reamer and trephine for foraminoplasty in ...

Foraminoplasty is an important step in PELD, especially the TESSYS technique [11]. The amount of bone resection and X-ray exposure during the procedure is closely related to the selection of the foraminoplasty tool [12]. The bone reamer and the trephine, as commonly used foraminoplasty instruments in current clinical practice [13], have their own advantages and disadvantages. The bone reamer restored more bone mass [14], but were low-efficiency and led to more X-ray exposure. The trephine was efficient [15], while the degree of bone resection was higher and might lead to lumbar instability [16]. Therefore, this study intended to find an equilibrium between the amount of X-ray exposure and bone resection, aiming to provide a theoretical basis for the selection of foraminoplasty tools in clinical practice.

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As to the bone resection volume, the Group-R (173.22&#;±&#;88.19 mm3) was significantly less than the Group-T (549.31&#;±&#;231.43 mm3). There may be two reasons for this discrepancy: (i) the bone reamer grinded away the bone through the frictional force generated by rotating the front outer drill teeth, so the amount of bone excised was limited [17]. (ii) The trephine removed bone through the shearing force generated by rotating the frontannular teeth, and it was capable of resecting all the bone mass within the range of the annular teeth. In addition, the Group-R (13.56&#;±&#;6.57%) destrcted less of SAP than the Group-T (40.83&#;±&#;14.20%) according to the percentage of resection The SAP is an important component of the lumbar stabilization system, and more than 30% [8] of the SAP resected increases the risk of instability [18], [19]. Therefore, in accordance with the comparative results of the amount of bone destruction, the bone reamer had less negative impact on lumbar spine stability than the trephine and was more suitable to be selected as a foraminoplasty instrument.

Foraminoplasty in both groups was all successfully achieved. Regarding the enlarged FPZ, the Group-R (12.96&#;±&#;11.41 mm2) was slightly less than the Group-T (27.30&#;±&#;21.48 mm2), consistent with the results of the amount of bone resection. The results revealed that the bone reamer destroyed less bone in the SAP, and the enlarged FPZ would be relatively limited.

As to the comparison of X-ray exposure, the Group-R (20.52&#;±&#;5.38 times) was significantly more than the Group-T (13.25&#;±&#;3.06 times). The bone reamer used for foraminoplasty in this study was graded, which would naturally be less efficient than a single-shape trephine. Currently most of bone reamers the clinical used for foraminoplastywas step-by-step in clinical practice, because surgeons needed to insert the head end of bone reamer deep into the foramen in order to effectively perform the foraminoplasty [20]. If the 7.5 mm bone reamer was used directly for foraminoplasty, the head end of the bone reamer was often unable to enter the foramen directly. Rotation happened immediately and cause the bone reamer to slip, which would change the direction of foraminoplasty. In contrast, the head end of the trephine can anchor on the SAP due to the presence of annular serrations [21], which avoided slippage during rotation. In addition, the amount of X-ray exposure was almost proportional to the foraminoplasty time, and an increase in the number of fluoroscopic views predicted a longer foraminoplast time, which added physiological and psychological stress on the patient. Therefore, the results from the amount of X-ray exposure indicated that bone reamer molding was less efficient than trephine.

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To further investigate the relevant factors affecting the foraminoplasty efficiency, we performed correlation analysis with linear fitting on all data. In the Group-R, there was a significant correlation between the number of fluoroscopic views and the preoperative area of FPZ and there was a significant inflection point in the curve when the number of fluoroscopic views were 20. The regression equation yielded that number of fluoroscopic views&#;=&#;40.566&#;0.377*area of preoperative FPZ, and the area of preoperative FPZ was 54.55 mm2 when the number of fluoroscopic views was 20. Therefore, we believed that when the area of preoperative FPZ was no less than 54.55 mm2, the head end of the bone reamer with a diameter of 7.5 mm can enter the foramen, and the head end of the bone reamer was not prone to rotate. In contrast, when the preoperative molding area was less than 54.55 mm2, the head end of the bone reamer with a diameter of 7.5 mm may be unable to enter the foramen smoothly. There was also the possibility of relative slippage, which made it necessary to increase the number of fluoroscopic views during the process to make sure that the direction of the head end of the bone reamer was correct before continuing the foraminoplasty, thus increasing the number of fluoroscopic views and prolonging the molding time. In addition, after reviewing the case of bone fragment falling into the lateral recess in the Group-R, we concluded that the patient was an elderly woman and the preoperative molding area was 43.22 mm2, which was less than 54.55 mm2, so the head end of the 7.5 mm bone reamer did not enter the foramen during foraminoplasty. When the bone reamer rotated, the head end slided subsequently. Moreover, the patient had risk factors of osteoporosis, and the bone mass of the SAP was loose. As a result, the fragmented bone fell into the lateral recess under the push force of the head end of the bone reamer and compressed the exiting nerve root.

However, this study also has the following limitations: first, the sample size was small with 63 cases included in this study; Second, the boundary and boundaries of the molding zone were determinated on the sagittal plane, and there was usually a certain dorsal offset in the puncture angle of the foraminoplasty tool [22], thus the cross-section of the intervertebral foramen in contact with the foraminoplasty tool may tend to be more elliptical. Additionally, not always 3D slicer and Digimizer might be available for adequate measurement of the foraminal area in all medical centers, this can be a problem when trying to measure FPZ area. The above deficiencies are also the next direction we will consider.

Trephines features a quick-lock structure for attachment to a handle, allowing for the use of various gauges of ring saws. These trephines are employed during surgery to perform laminotomy or to expand the intervertebral foramen. This process is essential for establishing an endoscopic channel, enabling surgeons to access and treat the affected spinal disc with precision and efficiency.

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