This prospective observational cadaveric study was carried out at the Department of Anatomy at Smt BK Shah Medical Institute and Research Centre, Sumandeep Vidyapeeth, Gujarat, India from August 2018-2020. Ethical approval to undertake the present study was obtained from the Institution Ethical Committee (SVIEC No: Medical/PhD/18005).

The specimens without any obvious externally visible deformity or signs of injury, pathology, or surgical procedures were included. The SP of lumbar vertebrae was examined in 30 formalin-fixed adult human cadavers (15 females and 15 males). The cadavers were placed in a prone position on a flat table with hips extended. With midline incision around the lumbar region, the superficial and deep muscles of the back were identified and removed until the lumbar vertebral column was exposed. The SP of all the lumbar vertebrae was cleaned in each specimen and was observed to find out the occurrence of fusion amongst adjacent SP.

The data was recorded and analysed using Statistical Package for the Social Sciences (SPSS) version 23. Data was presented as absolute numbers and percentages.

The present study has examined the lumbar spine in 30 adult cadavers (range of 60-95 years, mean of 77.5 years). The fusion between adjacent SP was noted in 11 cadavers (36.67%). The fusion of the SP of L4 to S1 was most common and was found in three specimens [Table/Fig-1]. The fusion of the adjacent LSP was more common in males (53.3%) compared to females (20%) [Table/Fig-2].

[Table/Fig-1]:

Showing fusion of spinous process of lumbar vertebra: a) Fusion of L1 to L5 spinous process; b) Fusion of L1 to S1 spinous process; c) Fusion of L2 to L5 spinous process; d) Fusion of L2 to S1 spinous process; e) Fusion of L3 to S1 spinous process; f) Fusion of L4 to L5 spinous process; g) Fusion of L4 to S1 spinous process; h) Fusion of L5 to S1 spinous process.

The fusion of the SP was so complete that no trace of the line of fusion was evident in any specimen. The transverse processes of none of the adjacent lumbar vertebrae were found to be fused.

The problem of Wrong Level Spinal Surgery (WLSS) is a unique surgical problem with detrimental consequences for both the patient and the surgeon. WLSS occurs when a surgeon performs decompression, resection, or reconstructive procedure on an unintended anatomic location along the spinal axis [7]. The knowledge of anatomical variations of spine may help in reducing the incidence of WLSS. The present study has attempted to determine the prevalence of fusion of LSP in cadavers at the Department of Anatomy at the study institute.

Although the exact incidence of WLSS remains unknown, most researchers agree that the lumbar level is more prone to WLSS. Mody M et al., had done a questionnaire-based survey among members of the American Academy of Neurosurgeons [8]. They reported that the prevalence of wrong level spinal operations to be 1 in 3110 procedures. Also, out of these wrong level operations, majority were performed on the lumbar region (71%), followed by the cervical (21%), and the thoracic (8%) regions. Jhawar BS et al., have also reported that the WLSS are more common in the lumbar region (12.8/10 000) than that of the cervical region (7.6/10 000) [2]. Ammerman JM et al., [9] have reported the incidence of wrong level lumbar spinal surgeries to be as high as 15% while Barrios C et al., have reported it to be around 3.3% [10].

Abnormal anatomy is one of the risk factors for WLSS [4]. The SP of vertebrae, because of its readily accessible location, is commonly used for counting vertebral level. However, their fusion can very easily misguide the surgeon. The aetiology of fusion may be congenital, acquired, or surgical.

There is a wide variation in the prevalence of lumbar vertebral fusion reported by various researchers [Table/Fig-3] [11-14]. This is partly due to the methods used for calculation of prevalence rate. The denominator used for calculation of prevalence rate by Sar M et al., and Vikani S and Javia MD, was the number of vertebrae [11,12]; while the studies of Deepa M and Rajasekar SS, and Sharma M et al., have used number of vertebral columns as the denominator [13,14]. The present study has observed fusion between adjacent LSP in 36.67% of the specimen, which is quite higher than other studies. This may be illusory as the findings are not confirmed by the X-rays.

The present study has also found that there are wide variations in the number of adjacent LSP involved in fusion. Both these factors viz., high prevalence and the variable pattern of fusion of LSP may make the counting of the lumbar level extremely difficult for clinicians. This can very easily lead to WLSS having profound medical and legal consequences [10,15].

Considering the wide variations amongst study reports about prevalence of lumbar vertebral fusion in the Indian population, the authors recommend preoperative and intraoperative imaging in each patient to reduce the incidence of WLSS.

The findings were not confirmed with the X-ray of the concerned region. So, the higher prevalence may be illusory.

The fusion between the LSP is common among the Indian adult population. The number of lumbar vertebrae involved in fusion also varies amongst individuals. Preoperative and intraoperative imaging in patients is recommended to reduce the incidence of wrong level lumbar spinal surgeries.

The authors also suggest that a large sample sized multicentric, prospective study among Indian adult population, with use of X-ray of lumbar spine, will help to determine the exact prevalence of the fusion of adjacent LSP in the population.