Keywords
extreme lateral interbody fusion - hip flexion - spine - weakness - psoas
Palavras-chave
fusão intersomática por via extremo-lateral - flexão de quadril - coluna - fraqueza
- psoas
Introduction
Degenerative diseases of the lumbar spine can cause back pain irradiating to the legs
that may compromise the health and the well-being of the patient. These diseases range
from intervertebral disc degeneration to vertebral canal stenosis.[1] Treatments vary on a case-by-case basis, from conservative therapy in milder conditions
to interbody fusion in patients with more severe radiological and clinical features.[2]
Interbody fusion is a surgical treatment for various degenerative diseases of the
lumbar spine. Vertebral bodies can be fused through some surgical techniques, including
interbody fusion by extreme lateral access via transpsoas or extreme lateral lumbar
interbody fusion (XLIF),[3] which has been widely used and is highly applicable for several pathologies.[3]
[4] However, like any other surgical approach, this access has disadvantages, such as
the risk of injury to the lumbar plexus, which can lead to postoperative motor and
sensory deficits in the lower limbs.[3] Considering the inherent risks of this surgical technique, the present study aimed
to evaluate the flexion strength of the hip before and after surgical intervention
in cases of lumbar spine degeneration.
Materials and Methods
This was a prospective, single-center, non-randomized study. The present study was
approved by the Research Ethics Committee of the Hospital Nove de Julho, São Paulo,
SP (66616317.0.0000.5455). A total of 60 patients (39 females), with a mean age of
61.8 years old, were submitted to the XLIF technique by the same spinal team. The
inclusion criteria were: patients with degenerative lumbar spine submitted to interbody
fusion by the XLIF surgical technique after conservative treatment failure for at
least 6 months. One to 3 lumbar levels were instrumented (mean level, 1.37; 63% cases
in only 1 level; 68% cases involving L4-L5). Surgeries were performed with retroperitoneal
lateral access via the transpsoas approach by senior spinal surgeons.[4]
The hip flexion strength was evaluated in the sitting position with a handheld dynamometer
(Lafayette Instrument, Lafayette, IN, USA).[5] Three measurements of peak force (N) were performed, and the means were calculated.
These measurements were assessed in pre- and postoperative evaluations at 10 days,
6 weeks, 3 and 6 months postsurgery, both ipsilateral and contralateral to the surgical
access. The strength in both sides was compared. Pain on both sides was also assessed
using the visual analogue scale (VAS) questionnaire.[6] Descriptive and comparative statistical analyses were performed with the SPSS software
(IBM SPSS, Armonk, NY, USA). The comparative statistical analyses between groups were
performed using the student t-test and an α value of 0.05.
Results
Lateral interbody fusions were performed in 60 patients. The mean age was 61.8 years
old (ranging from 22 to 85 years old), and 39 patients were female. Among the 60 cases
included in the present study, 38 were single-level arthrodesis, and 41 involved the
L4-L5 level ([Table 1]).
Table 1
Demographics and surgical data
|
Cases
|
60
|
|
Male/female ratio (%)
|
35/65
|
|
Mean age
|
61.8 (22–85)
|
|
Surgical time (minutes)
|
114.3 (30–400)
|
|
Blood loss (mL)
|
166 (50–1,700)
|
|
Operated levels (mean)
|
1.37
|
|
1 level
|
42 (70%)
|
|
2 levels
|
15 (25%)
|
|
3 levels
|
3 (5%)
|
|
Postoperative walking (hours)
|
20 (0.5–120)
|
A significant 25.4% reduction in the strength of the psoas at the instrumented side
was observed between the preoperative measures and those obtained at the 10th day visit (13 N and 9.7 N, respectively) ([Fig. 1]). Despite this decrease at the 1st postoperative follow-up, the force level returned to baseline 6 weeks after the surgery,
and it was sustained until the 3rd month. At the end of the study, the hip flexion strength was higher than before the
surgery (16 N).
Fig. 1 Ipsilateral and contralateral mean hip flexion forces before and after extreme lateral
interbody fusion (XLIF).
The reduction of the ipsilateral psoas strength at the 1st postoperative follow-up was not observed on the contralateral side (13.3 N and 13.4 N,
respectively). The strength remained constant until the 10th day visit, followed by a 20% increase in subsequent visits, reaching 16.1 N 6 months
postsurgery.
No differences were observed between the strength of the ipsilateral and of the contralateral
sides before the surgery (p = 0.71). However, a 38% increase in the hip flexion strength was observed on the
contralateral side (13.4 N) compared with the ipsilateral side (9.7 N) 10 days postsurgery,
a difference that ceased to exist after the 6-week evaluation until the end of the
study, at the 6-month visit (p > 0.05).
Regarding the pain in the ipsilateral and contralateral sides, it was observed that,
even before the surgery, there was already 27.4% more pain on the instrumented side
(6.05 and 4.75, respectively). This difference remained until the 3-month evaluation,
leaving no distinction between both sides at the 6-month visit (2.77 and 2.57, respectively).
Some adverse effects were observed during the present study. In addition to the reduction
in the strength of the psoas, five patients also presented with quadriceps deficit.
However, all of the patients regained both psoas and quadriceps strength, with no
permanent deficit. No case has progressed to reoperation due to plexopathy. In addition
to lumbar XLIF, 1 patient underwent a lateral arthrodesis at the thoracic level, and,
in this procedure, the intraoperative bleeding was more pronounced (1,700 mL). However,
this blood loss did not cause additional harm to the patient.
Discussion
Interbody fusion is a widely used surgical approach for the treatment of lumbar spine
degenerative diseases.[3] To achieve this goal, extreme transpsoas lateral access has great applicability
and biomechanical advantages over other options, mainly for maintaining the integrity
of the posterior and anterior longitudinal ligaments, the latter the most important
stabilizing ligament of the spine.[7]
[8] To reach the disc space, XLIF uses the transpsoas approach, crossing between the
muscular fibers. This is one of the main spinal stabilizing muscles, and it is transected
by a nerve network called the lumbar plexus. To minimize the risks of nerve damage,
this technique uses a directional monitoring system that evaluates the conduction
of nerve impulses to the extremities, preserving neural integrity. However, even with
the navigation tool, this technique still has postoperative side effects. Reduction
of hip flexion strength is the main postoperative effect of XLIF. This strength is
mainly performed by the psoas muscle, which is transected by dilators for disc space
access. Literature studies commonly assess the frequency of this weakness in XLIF
patients.[8]
[9]
[10]
[11]
[12] This phenomenon is usually reported by the patient, and it can often go unnoticed
or be overlooked. In addition, only a few papers report strength degree reductions.
In a different way, the present work evaluates this parameter in a force scale in
N, using measurements obtained with a dynamometer in an objective and systematic form.
In the present study, clinical parameters were evaluated in five different visits.
Results showed a significant decrease of ∼ 24% in the hip flexion strength on the
ipsilateral side shortly after the surgery, returning to preoperative values 6 weeks
after the procedure. Although not assessing psoas strength in the same way as the
present study, Sharma et al observed a similar phenomenon of postsurgical hip flexion
strength reduction, with all of the patients returning to preoperative strength values
at 6 weeks.[8] Similarly, other studies in the literature have also shown that hip flexion weakness
is a transient phenomenon.[9]
[11] This effect is transient since it is not a plexopathy, but a relaxation of the intrinsic
innervation of the psoas itself, causing weakness, which is transitory, provided that
the muscle is stimulated with regular daily activity.[13] In addition to this side effect, it was observed that 8.3% of the patients presented
with quadriceps weakness after the surgery as an adverse effect, a number similar
to those observed in other studies in the literature.[8]
[9]
[11]
[12]
The present study has some limitations. First, since it was conducted at a single
research center, the small number of patients diminishes the power and the strength
of the study. Second, the lack of data about psoas muscle retraction time from all
of the patients is also a limitation, since it is not possible to directly relate
this parameter with the presence of postoperative symptoms.
Conclusion
In summary, the present study brings a quantitative measure in a direct force scale.
Thus, it does not depend on the report of the patients regarding the possible side
effect of decreased hip flexion strength. This is a common side effect on the ipsilateral
side due to the retraction of the psoas muscle, which is, however, transient. The
patient should be instructed before surgery about the possibility of this phenomenon,
to avoid possible falls—resulting from this loss of strength in the first days postsurgery—that
could compromise a better postoperative result. Studies with greater casuistry are
necessary to better understand these side effects and the complications resulting
from lateral access.
