TRUNK MOBILITY AFTER MINIMALLY INVASIVE ONE-LEVEL LUMBAR

Objective: To evaluate the impact of a minimally invasive lumbar one-level fixation on trunk mobility and quality of life compared with the preoperative condition in 26 consecutive patients. Methods: The following data were collected preoperatively and postoperatively for the statistical analysis: maximal trunk extension and flexion angles, Visual Analog Scale of pain and Oswestry Disability Index scores. Results: There was improvement in all variables. Statistical significance was observed in trunk extension, pain, and Oswestry Disability Index. Although mobility in trunk flexion was higher in average values after surgery, this difference was not statistically demonstrated. Conclusion: Minimally invasive one-level lumbar fixation does not cause reduction of trunk flexibility in comparison to the mobility before surgery.


INTRODUCTION
A frequent question for the spine surgeon when indicating a lumbar fusion is the amount of movement restriction that will be imposed by the fixation, and how much this will impact on the patient's quality of life.Although most of the doctors' attention is focused on neurological status and pain control, the patient's concerns include the degree of limitation that the treatment could cause.There are several papers on spine mobility after fixation, the effects on adjacent levels, lesion of the back muscles, and the impacts on quality of life.In vitro and virtual experiments can measure the impact of some isolated factors on spine mobility, but this information does not necessarily reflect the clinical significance and the impact on activities of daily living.Although the biomechanical manifestation of disc degeneration is segmental hypermobility with widening of the neutral zone, 1,2 the clinical complaint is usually limitation of movement, with consequent pain or neuromuscular stabilization mechanisms.In this context, a study was conducted to evaluate trunk mobility before and after one-segment minimally invasive lumbar fixation, and its relationship with pain and functional performance, using physical evaluation instruments and validated clinical outcome scales.

METHODS
A prospective longitudinal observational study was conducted on a series of 26 consecutive patients who underwent one-segment minimally invasive lumbar spine fixation.
The sample was composed of patients who sought the services of a private practice specialized in spinal surgery, between February 2011 and January 2013.The surgical technique in all cases was Transforaminal Lumbar Interbody Fusion (TLIF) associated with bilateral pedicle screw fixation, through a minimally invasive transmuscular approach, as described in a previous paper. 3,4Treatment was indicated and conducted by the two main authors.Inclusion criteria were degenerative disease in a single lumbosacral segment, associated with low back pain, with or without associated radicular symptoms, not responsive to at least tree months of conservative treatment, and availability of the patient to attend the follow-up visits.Subjects with a history of previous spine surgery, any major anatomical anomaly, hip problems, or other pathology that could interfere with the data collection were excluded from the study.There were no comparisons between different interventions or groups.The ethical principles highlighted by the Helsinki declaration were strictly observed, and all the participants were asked to sign an informed consent form.
Patients were evaluated for pain, disability and trunk mobility, preoperatively and 4 months after surgery.In the interval between surgery and reevaluation, patients were referred for physical therapy with back strengthening and muscle stretching of the lower limbs, avoiding trunk mobility exercises.The physical therapy was not standardized, and was performed in different clinics, according to availability and the preferences of the individual patients.Pain evaluation was performed with the Visual Analog Scale (VAS), and the degree of disability was determined using the Oswestry Disability Index Questionnaire (ODI) -validated version in Portuguese.Trunk mobility in flexion and extension was measured in degrees, with a Sanny™ fleximeter (American Medical do Brasil Ltda.São Bernardo do Campo, São Paulo/Brazil).The measurements were taken according to the technique described by the manufacturer, by only one physical therapist not involved with the patient's care.
The data were analyzed using the software IBM SPSS Statistics 21.0™.The preoperative and postoperative mean values of VAS, ODI and trunk flexibility were compared by the Student's t test.The null hypothesis is that trunk mobility is the same before and after surgery, and the alternative hypothesis is that they are different.A confidence interval of 95% was adopted.

RESULTS
A total of 26 patients were evaluated: 20 (77%) males and 6 (23%) females.The mean age was 41.6 years (range 18 to 58 years).The fused segment was L4-L5 in 13 patients (50%) and L5-S1 in the other 13 (50%).The mean time interval between the initial evaluation and surgery was 18 days (minimum of 0 and maximum of 84 days).The mean interval between surgery and postoperative evaluation was 123 days (minimum of 71 and maximum of 223 days).The mean values for pre-and postoperative VAS were 4.2 and 1.3, respectively.The mean values for ODI were 43.5 on pre and 26.1 in the postoperative evaluations.The differences were statistically significant (p<0.05).The mean value for trunk extension before surgery was 20.1 degrees, increasing to 23.8 degrees after surgery.Although small, the difference of 3.7 degrees was statistically significant (p=0.01).The mean value for trunk flexion before surgery was 52.5 degrees, increasing to 58.6 degrees after surgery.The difference of 6.1 degrees was not statistically significant (p=0.138).The data are summarized in Table 1.

DISCUSSION
Questions about the consequences of spine fixation have been present since the popularization of the technique in recent decades.The impact of loss of a mobile segment on the patient's functional capabilities, and the biomechanical repercussions on the adjacent spinal segments is a field of extensive discussion, and alternative techniques to avoid fusion have been proposed, aimed at reducing the damage imposed by this surgery.In cases of hip and knee surgery, there is no doubt as to importance of retaining or restoring the mobility of the joint, and no question as to the huge progress represented by the advent of reliable arthroplasty techniques.It is tempting to apply the same principles to the spine; however, the behavior of the functional spinal unit is fundamentally different from that of the other joints, and the question of functional impairment due to the loss of a single mobile segment has not yet been scientifically resolved. 5Moreover, in cases of low back pain, the association between loss of trunk mobility and quality of life do not seem to hold true.The patient's degree of disability seems to be more closely related to pain and neurological deficit than to trunk mobility. 6The results show that with good indication criteria and appropriate surgical techniques, one-level minimally invasive lumbar fixation can bring statistically significant benefits in terms of reducing the pain and disability, within a few months after surgery, as evaluated by VAS and ODI.Concerning trunk mobility, fixation of a single segment increased the global range of movement in flexion and extension, with a statistically significant value for extension.Segmental instability, loss of disc height, facet overload, ligament folding, foramina stenosis and other painful degenerative conditions can impose a greater limitation on mobility than that resulting from fusion of a segment, such that fixation of the diseased segment can enable better performance of the other segments.Obviously, the preoperative limitation of mobility has some subjective components, as the patient learns to avoid movements that can cause pain.When the painful condition is resolved, the movement limitation is more objective, related mainly to the mechanical restriction of the fixation.In this context, the minimally invasive approach is very important because it causes less muscular damage and preserves more motor and proprioceptive neuromuscular units.
Trunk flexibility was measured with the pelvis fixed by the physical therapist and a single fleximeter placed over L1.The use of 2 fleximeters, one placed over L1 and one over the sacrum, can better isolate the pelvis and give a more precise indication of trunk mobility.The option for the single fleximeter technique was based on papers demonstrating that mobility restriction in cases of low back pain can be related to functional restriction of hip movement, therefore a the single fleximeter technique can better estimate the overall trunk flexibility in patients' routine activities Another issue in the methodology is the inclusion of two different segments in the sample, L4-L5 and L5-S1, each of which makes different contributions to the range of motion.For extension movements of the spine, L5S1 fusion limits movement more than L4L5.On the other hand, fusion of L4L5 involves lesser mobility in spinal flexion. 7,8lthough the gain in extension represented a very small portion of the overall mobility, it was statistically significant.The mean post-operative gain in flexion had a higher value, but was not statistically significant, probably due to the effect of sample size.Nevertheless, even though the gain in flexion was not statistically significant, it was possible to demonstrate that minimally invasive fixation of L4-5 or L5-S1 does not cause loss of mobility, compared with the preoperative state, and can bring significant benefits in terms of pain and functionality.

CONCLUSION
Based on the results, it can be concluded that one-level

Table 1 .
Collected data before and after single level lumbar spinal arthrodesis