Transpedicular Screw Fixation for Microinstability in Recurrent Lumbar Disc

INTRODUCTION

Microinstability represents the initial stage of the degenerative cascade defined by Kirkaldy-Willis. From the clinical and pathoanatomical point of views, it had a specific criteria (e.g., low back pain) corresponding to interested segment of vertebrae, and absent spondylolysthesis on the radiography carried in flexion-extension. It considered grade-1instability and equals to grade zero spondiololythesis.¹

It is more apparent in recurrent lumbar disc herniation, ipsi- or contra-lateral, in a patient  who is pain free at least for 6 months after primary discectomy.²

Recurrent lumbar disc herniation (RLDH) is a major etiology of surgical failure, with an incidence of 5 to 23%, that increased with extended follow up period.^3,4,5

The surgical choices for recurrent herniation are usually limited. This limitation ascribed to many factors, for example the duration of operative time (it usually needs a longer time). The second factor of limitation of surgical options is the high rate of comorbidities.^6,7,8

The current study aimed to assess (evaluate) the surgical outcome of Transpedicle screw fixation for microinstability in recurrent herniation of lumbar disc with ipsilateral or bilateral transpedicle fixation by screws, with highlights on the classification of lumbosacral instability.

 PATIENTS AND METHODS

The current work was designed as a prospective, randomized, comparative research work. It included patients who presented with herniation of the lumbar disc for the first time. It conducted from January 2014 to January 2018 at Al-Azhar university hospitals. It included 200 subjects with recurrent herniation of the lumbar disc. They were defined into: Group A (100) patients, managed by discectomy, curettage induced fusion with single side [unilateral] Transpedicle screw fixation, and Group B (100) patients, managed by discectomy with endplate curettage induced fusion and bilateral Transpedicle screw fixation. 

The preoperative criteria were: dynamic pain of the lower back, which associated or not associated with radicular pain developed after primary lumbar discectomy for a duration equal of longer than 6 months; existence of radicular, unilateral recurrent pain with no response to medical therapy for a duration of 6 weeks or longer; and MRI revealed herniated disc at the identical level of the first discectomy, dynamic x-ray of lumbosacral spine showing no sliding.

Patients experienced one or more of the following were excluded: stenosis of spinal canal at multiple segments, disc herniation at adjacent levels; lumbosacral sliding in dynamic x-ray or with nay deformities of the spine. The preoperative manifestations were dynamic pain of the lower back, single side radicular or claudication pain of the lower limb.

Radiological evaluation was achieved by lumbosacral X-ray (lateral, A-P, oblique and dynamic views in different positions (neutral, flexion, and extension) and magnetic resonance with gadolinium augmentation.

Surgical technique: All patients were operated under general anesthesia. The surgery was done through previous mark of the scar. Laminectomy and disc resection were performed done with extreme caution [at scare removal from lamina] to create a perfect recognition of laminectomy edges of the previous surgery. Then, curettes were inserted to completely dissect the scar from bone margins and to meticulously define the bone attached to the scar to prevent violation of the dura. Facet recognition followed by pedicles permits the scar tissue to be completely separated from bone and also permits an accurate recognition of the lumbar disc space. Exposure had been advanced laterally, to permit good visualization and prevent damage of the nerve root (especially lateral edge of the nerve). The disc fragment was then exposed by gentle mobilizations with nerve root medially retracted. Occasionally, nerve root was adherent to herniated fragment of the disc or other ligamentous parts and sharp dissection to separate adherent parts was implemented. In first group [A], total facetectomy had been completed prior to nerve root dissection, until clear visualization of the pedicle. This led to recognition of disc structure and the nerve root, to achieve a decompression completely without the need to extensively dissect and retract neural tissues then unilateral fixation by transpedicle screw was done. In the second group [B], the same was done with bilateral fixation by transpedicle screw. For all patients, curettage of the end plates of the herniated disc was performed. A lateral view image obtained by fluoroscopic projection had been obtained during the whole surgery for confirmation of accurate placing of the screw in the desired level. All subjects had been instructed to start ambulation 6 hours after surgery. Japanese Orthopedic Association scoring system (JOA; maximum score, 29 points)⁹ had been used to assess the neurological state and clinical results. All subjects were examined in the pre- and post-operative times to assess their neurological status and clinical improvement.

The rate of complete recovery had been calculated by the following equation:  “recovery rate = [postoperative- preoperative JOA score] /[normal- preoperative JOA score].

Ethical considerations: the research plan (protocol) was revised and accepted by the local board for research ethics (Al-Azhar faculty of Medicine), and all patients signed an informed consent for participations. They were assured that, the collected data were for research purposes, and their confidentiality was guaranteed

Data analysis: The collected data were coded and fed to a statistical software package (The SPSS package), version 18 (SPSS Inc., USA). 1Qualitative variables were expressed in their number and percentage, while quantitative data presented in their mean and standard deviations (SD). Groups were compared by independent samples (t) test and Chi square for quantitative and qualitative data respectively. P value 2< 0.05 was set as the margin of significance.

RESULTS

Patients of group A were 62 males and 48 females; the mean age was 45 years (ranged between 35 and 60 years). The level was L5-S1 (30), L4-5 (60), L3-4 (6), L2-3 (2) and L2-1 (2). In group B, there were 60 males and 40 females; the mean age was 40 years (ranged between 30 and 65 years). The affected levels were L5-S1 (40), L4-5 (55), L3-4 (3), L2-3 (1) and L2-1 (1) (Table 1).

The side was the left in 120 (60 %) and the right side in 80 (40%) of studied subjects. The mean follow up period was 36±785 [range 24-48 months]. The mean recurrent time after the primary discectomy was 18±6.01 months [range 10-30 months].

The clinical outcome at the last follow up visit revealed that, recurrence and dural tears were confined to group A (each was reported in 1 patient), while root injury and spinal instability were confined to group B (one patient for each (Table 2).

Regarding recovery rate, it was 0.888 for group A and 0.807 for group B, with statistically significant difference (Table 3).

GA: group A; GB: group B; PO: preoperative; JOA: Japanese Orthopedic Association

Table 1: Presenting the preoperative data.

Table 2: The clinical outcome among studied groups

Table 3: The rate of recovery (percentage) among studied groups.

DISCUSSION

The word ‘instability’ is still poorly defined in-spite of being an important etiology of pain affecting the lower back and can be associated with substantial disability. There are two main categories: the first is macroinstability and the second is microinstability.¹⁰

Macroinstability (radiological instability) is apparent in dynamic x-rays and staged on the basis of the sliding degree into 4 degrees and a fifth grade was added by Hu et al.¹¹ at 2008, and there are medicolegal implications due to its radiological presence. The second is microinstability which is manifested clinically but without apparent radiological sliding, and called first degree instability or zero-degree spondiololythesis. So, the grouping of spondylolysthesis may be modified.¹ The next table showed proposed classification

Table (4): showing modification of grading of spondiololythesis¹