Objective: To find out the long term outcome of deformity correction by hemivertebra resection in congenital thoracolumbar spinal deformities by a single posterior approach.
Methods: This is a retrospective study carried out at the Department of Spine Surgery, Combined Military Hospital, Rawalpindi, Pakistan from April 2006 to April 2013. All operated patients having single level hemivertebrae of thoracolumbar spine with at least two years follow up were included. Data was analyzed using SPSS ver. 17.
Results: There were 24 patients with mean age of 17 years (SD=8.41). Male to female ratio was 9(37.5%): 15(62.5%). Mean operation time was 4.23 hours (SD=1.2). Mean blood loss was 787 ml (SD=479). Mean follow up was for 5 years and 7 months (SD=30 months). Mean pre-op scoliosis was 51 degrees (SD=22), which improved to 20 degrees (SD=15) on last follow up (61% improvement). Mean pre-op kyphosis was 42 degrees (SD=35), which improved to 13 degrees (SD=15) on last follow up (69% improvement). Mean pre-op sagittal shift was 22mm (SD=24.9), which improved to 6mm (SD=9.37) on last follow up (73% improvement). Mean pre-op coronal shift was 34mm (SD=27.1), which improved to 8mm (SD=8.58) on last follow up (76% improvement). Five patients had complications. One proximal junctional kyphosis, one implant failure, one transient deficit and two wound infections.
Conclusion: Posterior resection of hemivertebrae for congenital thoracolumbar deformities gives excellent correction of deformity in experienced hands and has acceptable complication rate.
Keywords: Hemivertebra resection, Congenital, Kyphosis, Scoliosis, Posterior approach. (JPMA 65: S-142 (Suppl. 3); 2015).
Hemivertebrae develop at 4-6 weeks of gestation due to failure of formation.1 They may be associated with contra lateral bars which are due to failure of segmentation at same time of gestation. Both these deformities if left untreated in childhood lead to severe kyphoscoliosis in later life. There are four main methods of treatment of hemivertebra described in literature; insitu fusion, convex hemiepiphysiodesis, fusion less surgery and resection of hemivertebra. Out of all these, resection of hemivertebra gives the best immediate measureable outcome.2
Techniques of hemivertebra resection include; anterior, posterior and combined techniques. Anterior and combined techniques carry more morbidity and complication rates, however almost similar amount of curve correction can be achieved by all techniques. Posterior technique requires more surgical experience however it can be completed in less time and gives better fixation options. Initially only anterior or combined techniques were described but now more literature is coming up in support of posterior technique.3,4
We have studied hemivertebra resections done in our department for single level disease at thoracolumbar level by a single posterior approach in all patients with at least two years follow up which is presented here.
Patients and Methods
This retrospective review study was carried out at the department of spine surgery, CMH Rawalpindi, Pakistan. Data was retrieved from spine database of the department by querying on hemivertebra resection by posterior approach at thoracolumbar spine level with complete follow up for at least two years. Patients with multi-level hemivertebrae and incomplete follow up were excluded. 24 matching primary operations were found between April 2006 and April 2013 (7 years). Operation notes were reviewed for surgery details, operation time and blood loss. Pre-op and last follow up x-rays were reviewed for calculation of Cobb\'s angles for scoliosis and kyphosis. Sagittal balance was calculated by dropping a plumb line from middle of 7th cervical vertebra (C7) body and noting its distance in mms from posterosuperior corner of 1st sacral vertebral body. Coronal balance was calculated in mms between C7 plumb line and central sacral vertical line.
Operation technique: All operations were performed in prone position under general anaesthesia. Midline incision was made from two levels above to two levels below the hemivertebra. In lumbar spine pedicle screws were placed one level above and one level below the hemivertebra. In thoracic spine and at thoracolumbar junction pedicle screws were placed 1-3 levels above and 1-2 levels below the hemivertebra depending upon local fixation circumstances. Hemivertebra was fully exposed. Laminectomy and partial facetectomies was performed at level of hemivertebra to identify dural sleeve and to trace nerve roots above and below the hemivertebra. Temporary contra lateral rod was fixed to stabilize the spine. Discs above and below the hemivertebra were removed. Complete resection of hemivertebra was performed. Ipsilateral rod was applied and gap was closed by compression on ipsilateral side and loosening rod on contra lateral side (Figure-1 and 2).
Implants used: Pedicle screw fixation was used in all patients. 3.5mm AO screws and stainless steel wire was used in two patients. 4.5mm AO screws and stainless steel wire was used in two patients. M7 pedicle screw system by Medtronics was used in one patient. M8 pedicle screw system by Medtronics, USA, was used in 10 patients. Polynices pedicle screw system by Kanghui, China, was used in nine patients. Follow up was done after surgery at two weeks, six weeks, three months, six months and yearly. Pre-op and last follow up data was used for all calculations.
Statistical analysis was done using SPSS version 17. Frequencies were calculated for all numerical data. Paired sample T-test was applied for finding out significant difference between pre-op and last follow up angles and translations. P value of < 0.001 was taken as significant.
There were 24 patients with mean age of 17 years (SD=8.41). Male to female ratio was 9(37.5%):15(62.5%). 15 patients had thoracic hemivertebrae (T2-T11). Six patients had thoracolumbar-junction level hemivertebrae (T12-L1). Three patients had lumbar hemivertebrae (L2-L4). One patient had grade 4/5 power in lower limbs before surgery. Rest of the patients had complete power in lower limbs before surgery. Mean operation time was 4.23 hours (SD=1.2). Mean blood loss was 787 ml (SD=479). Mean follow up was for 5years and 7months (SD=30 months).
Mean pre-op scoliosis was 51 degrees (SD=22), which improved to 20 degrees (SD=15) on last follow up (61% improvement, p value <0.001). Mean pre-op kyphosis was 42 degrees (SD=35), which improved to 13 degrees (SD=15) on last follow up (69% improvement, p value <0.001). Mean pre-op sagittal shift was 22mm (SD=24.9), which improved to 6mm (SD=9.37) on last follow up (73% improvement, p value = 0.001). Mean pre-op coronal shift was 34mm (SD=27.1), which improved to 8mm (SD=8.58) on last follow up (76% improvement, p value < 0.001) (Table).
Five patients had complications. One patient developed proximal junctional kyphosis, she was eight years old when resection of hemivertebra was done at T8 level. Five years after surgery she presented with deformity above level of fixation with back pain. She underwent osteotomy at level of kyphosis (T6) and extension of instrumentation up to T4. She had complete correction of deformity and resolution of back pain.
One patient presented with sudden onset of back pain and swelling at level of surgery, one year after operation. X-rays revealed breakage of one of the rods. There was solid fusion so only implants were taken out and patient had resolution of pain. One patient woke up with grade 3/5 power in lower limbs. Urgent MRI did not show any compressive pathology. He completely improved in three months. Two patients developed wound infections necessitating antibiotics for six weeks, wound debridement and washout. Both healed without need for removal of implants.
Fully segmented hemivertebra has growth potential at both of the end plates. Continuous asymmetric growth with age leads to development of gross spinal deformity depending upon the location of the hemivertebra.5 With continued growth compensatory curves develop above and below the primary curve. If the primary curve is not addressed early in life secondary curves also become structural. There are many ways of addressing this problem but the most sure one is to take out the hemivertebra, balance the spine and fix it in position such that there is no chance left for asymmetric growth.3,6
Initially a combined approach was described for hemivertebra resection. This approach needs more operation time, has higher risk of complications and keeps patient in hospital for longer period of time. A single posterior approach is more demanding but saves time and has lesser rate of complications.7 Initially it was thought that posterior approach is safe only in lumbar spine below the level of the conus but recently many authors describe this approach in thoracic spine as well with equal safety.8-10 We are also doing it at all levels of thoracolumbar spine as shown by our study.
Our study has shown that hemivertebra resection by a single posterior approach could correct scoliosis by 61%, kyphosis by 69%, sagittal balance by 73% and coronal balance by 76%. All these values were highly significant. There were few complications and all were rectified easily. Mean operation time was 4.23 hours (SD=1.2) and blood loss was 787 milliliters (SD=479). Other authors have shown similar results. There are some papers which show better correction of deformity but they have a younger patient group as compared to our patients. It is well known that with increasing age deformity becomes more rigid and lesser degree of correction can be achieved after resection of hemivertebra.11
Studies have shown that normal sized spinal canal diameter develops by the age of one year, hence pedicle screw fixation in young children should not cause spinal stenosis. Furthermore younger pedicles are more flexible and can accommodate pedicle screws which are relatively bigger in size as compared to the pedicles. Short segment fixation is recommended in younger patients such that growth is not affected. Three rod technique has been described to decrease load on the pedicle screws by using laminar hooks and rod for compression after hemivertebra resection.12,13
Hemivertebra resection is a better option than long segment fusions in adults as well, provided secondary curves have not become structural and are still flexible on bending films.14,15 This has been proven by our study and some other studies as well. However degree of deformity correction after hemivertebra resection is less in adults as compared to the children. Complication rate, operation time and blood loss is more in adults. Rate of pedicle screw cut out is more in children as compared to adults due to small pedicle size and weak bones. Maximum cut outs occur on the convex side during compression.12 These cut outs can be prevented by complete removal of the discs with annulus, release of all the tethers on concave side, osteotomy of the contra lateral bar and fused ribs in the concavity of the curve.
Major neurological complications are rarely reported in literature after this procedure, however minor root palsies may occur and mostly recover.15,16 Other complications include, wound infection, pseudoarthrosis and junctional deformity in growing children. One limitation of our study is large gap in age groups from 6 to 44 years and it needs further study to find out the outcome in young vs old patients after hemivertebra resection by posterior approach.
Our study has shown that excellent correction of deformity can be achieved by a single posterior approach for hemivertebra resection in congenital scoliosis at all levels in thoracolumbar spine with minimal risk of complications provided surgeon is experienced and all the facilities for spinal surgery are available.
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