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July2013 Vol.50 Issue:      3 (Supp.) Table of Contents
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Determinants of Recovery of Pre-operative Acute and Chronic Foot Drop after Microdiscectomy for Lumbar Disc Herniation

Ahmed Galal

Department of Neurosurgery, Ain Shams University; Egypt

 



ABSTRACT

Background: There are a few studies reporting the prognosis of pre-operative foot drop due to lumbar disc herniation after microdiscectomy especially as it relates to weakness onset and chronicity. Objective: To determine clinical outcome and identify prognostic factors for recovery. Methods: This is a retrospective study of 31 patients. Foot drop was defined as scoring less than 3 on manual muscle testing for the tibialis anterior muscle. The postoperative outcome was analyzed in relation to patient factors, clinical presentation, pre-operative radiographic parameters and operative findings. Results: All patients had a unilateral foot drop. There were 2 clinical categories of patients: those presenting with an acute foot drop (10 patients (32.3%)) and a second group of patients with a gradual onset of dorsiflexion weakness that progressed to foot drop (21 patients (67.7%)). A complete/ near complete recovery was observed in 15 (48.2%) patients. A partial recovery was observed in 12 (38.7%) patients. No improvement was observed in 4 (12.9%) patients. The mean follow-up duration was 9.8 months. Conclusion: There was significant recovery of foot drop regardless of age, gender, history of smoking, duration of weakness or weakness grade. Prognostic factors related to worse outcome were history of diabetes and diminution of preoperative radicular pain with progression of foot weakness. Foot drop recovery was superior in the group of patients presenting with acute foot drop and operated upon within 24-48 hours of weakness onset, as opposed to recovery in the group of patients with chronic progressive weakness. [Egypt J Neurol Psychiat Neurosurg.  2013; 50(3): 257-264]

Key Words: Foot drop, lumbar discectomy, outcome, prolapsed lumbar disc

Correspondence to Ahmed Galal, Department of Neurosurgery, Ain Shams University, Egypt. Email: ahmedoc2004@yahoo.com




 INTRODUCTION

              

The term "foot drop" refers to paralysis or weakness of the ankle dorsiflexors. Degenerative lumbar spinal disorders (disc herniation or spinal stenosis) are known causes of nerve root dysfunction resulting in ankle dorsiflexor muscle weakness (tibialis anterior, extensor digitorum, peroneus tertius, extensor hallucis longus) which are innervated by the L4 and L5 roots.1

               There are only a few reports discussing the postoperative recovery of foot drop. There is little and sometimes conflicting information on the factors determining postoperative recovery. Furthermore, there is little data in the literature addressing foot drop recovery after root decompression as it relates to its onset and chronicity.1-7

 

Aim of Work

The purpose of this study was to determine recovery rates of foot drop after microdiscectomy and to evaluate possible factors that may affect recovery. This study will also evaluate differences in recovery in two patient subgroups: patients presenting with an acute foot

drop versus patients with a chronic progressive ankle dorsiflexion weakness that progressed to foot drop.

 

SUBJECTS AND METHODS

 

Thirty-one consecutive patients presenting with foot drop that were treated by a standard lumbar discectomy between September 2007 and July 2012 at Ain Shams University Hospitals (Cairo, Egypt) were retrospectively reviewed. Foot drop was defined as scoring between zero and 2 on manual muscle testing for the tibialis anterior muscle. The patients presenting symptoms and signs were identified with particular attention given to the onset, course, duration and grade of foot drop. The patient's associated symptoms as sciatic pain and history of non-operative pain management (pharmacological and epidural steroid injections) were analyzed. The patients' demographics and medical co-morbidities were also noted. Patients presenting with foot drop as a part of cauda equina syndrome and patients with a recurrent disc prolapse were excluded from this study.

Plain X-rays and MRI of the lumbosacral spine done pre-operatively for all patients were reviewed to establish the location and morphology of the disc herniation, the compressed root level and any additional compressing factors as ligamentum flavum hypertrophy. The grading system reported by Pfirmann and colleagues8 was used for grading disc herniation and nerve root compromise: grade 0 (normal): No compromise of the nerve root is seen; grade 1 (contact): There is visible contact of disk material with the nerve root and the normal epidural fat layer between the two is not evident; grade 2 (deviation): the nerve root is displaced dorsally by the disk material; grade 3 (compression): the nerve root is compressed between disk material and the wall of the spinal canal; it may appear flattened or indistinguishable from disk material.

Standard microsurgical discectomy was performed in all patients. Operative findings were correlated with the radiological findings as regards to the morphological characteristics of the herniated disc, the relation of the nerve root to the disc space and disc herniation. The type of disc herniation was classified according to Jonsson and colleagues9 into contained or non-contained types (extruded, sequestrated).

The patients were evaluated in the early postoperative period and at 2 weeks, 1 month, 3 months, 6 months and 1 year. A patient was defined as recovered when the tibialis anterior muscle strength improved to a grade 4 or 5; partial recovery for an improvement in muscle strength to a grade 3; and not recovered if motor strength was < 3.

The data was analyzed to determine factors associated with prognosis including: medical co-morbidities (as diabetes), patients' demographics, history of smoking, pre-operative muscle weakness (onset, course, duration and grade), presence or absence of radicular pain, type of disc herniation as determined operatively (contained/ non-contained), time to initial muscle grade improvement (if any) in the postoperative period.

 

Statistical Analysis

Statistical analysis was performed using SPSS software. Univariate analysis of clinical, surgical and radiographic parameters was performed using Fisher’s exact test and Mann-Whitney U test. Statistical significance was accepted at p values less the 0.05.

 

RESULTS

 

Thirty-one patients were included in this retrospective study. Clinical and radiographical results are summarized in Table (1).

All patients had unilateral foot drop prior to presentation. There were 2 clinical categories of patients. Those presenting with an acute foot drop (10 patients who underwent surgery within 24-48 hours of weakness onset) and a second group of patients (21 patients) with a gradual onset dorsiflexion weakness that progressed to foot drop (underwent surgery days-weeks after weakness onset (mean duration of weakness prior to surgery was 75 days). All 31 patients had a history of radicular symptoms (mean duration was 20.4 months). A clinical feature that was common to 11 (35.5%) patients presenting with gradual onset weakness that progressed to grade 0 or 1 was the diminution of the radicular pain. All patients have a history of conservative treatment (pharmacological treatment ± epidural steroids).

The affected level was L4-5 in 26 patients (83.9%) and L3-4 in 5 patients (16.1%). The Pfirmann and colleagues criteria8 was used for grading disc herniation and nerve root compromise. Analysis of the MR images showed a grade 3 disc herniation in all cases (the nerve root is compressed between disk material and the wall of the spinal canal). There were 6 (19.4%) cases with associated ligamentum hypertrophy (all 6 cases belonged to the group of patients with gradual progressive dorsiflexion weakness).

The type of disc herniation at surgery was either a subligamentous extrusion (20 cases (64.5%)) or disc sequestration (11cases (35.5%)).

None of patients suffered worsening of ankle dorsiflexion weakness after surgery. A complete/near complete recovery (improvement to grade IV/V) was observed in 15 (48.2%) patients. A partial recovery (to grade III) was observed in 12 (38.7%) patients. Thus 27 (87.1%) patients showed signs of improvement after surgery. No improvement was observed in 4 (12.9%) at the last follow-up visit. The mean follow-up duration was 9.8 months. The mean time to initial weakness grade improvement was 45 days.

There were 10 patients presenting with an acute foot drop and were operated upon within 24-48 hours, all of which showed variable degrees of improvement. Differences in outcome are summarized in Table (2).

Table (3) shows a univariate analysis of clinical, surgical and radiographic parameters thought related to foot drop recovery. The patients were classified by age, sex, medical co-morbidities (as diabetes), history of smoking, pre-operative muscle weakness (onset, duration and grade), presence or absence of radicular pain, type of disc herniation as determined operatively (contained/ non-contained), time to initial muscle grade improvement (if any) in the postoperative period.

 

 


 


 

Table 2. Postoperative patient recovery as it relates to the onset of the foot drop.

 

 

 

Acute foot drop

Chronic foot drop

Number of patients

10 (32.3%)

21 (67.7%)

Mean duration of weakness prior to surgery

24-48 hours

76 days

Recovered (grade IV/V)

8 (80%)

7 (33.3%)

Partially recovered (grade III)

2 (20%)

10 (47.6%)

Not recovered (grade 0/I/II)

-

4 (19%)

 

 

Table 3. Outcome in 31 patients with foot drop.

 

Variables

No. of patients

Partial/Complete Recovery

Unrecovered

P-value

Age (years)                                                      

<50                         

≥ 50

 

22

9

 

21

6

 

1

3

 

0.0627*

Gender                                                           

Male

Female

 

14

17

 

14

13

 

0

4

 

0.1075*

Diabetic                                                           

Yes

No

 

8

23

 

4

23

 

4

0

 

0.002*

Smoker                                                          

Yes

No

 

7

24

 

7

20

 

0

4

 

0.5497*

Preoperative muscle weakness

- Onset                                               

Acute

Chronic

 

- Mean duration in chronic foot drop patients (days)

 

- Weakness grade (T.A)                       

0/I

II

 

 

10

21

 

21

 

 

21

10

 

 

10

17

 

51.2

 

 

17

10

 

 

0

4

 

132.3

 

 

4

0

 

 

0.277*

 

 

0.283†

 

 

0.277*

Preoperative radicular symptoms

Present

Diminished

 

20

11

 

20

7

 

0

4

 

0.0105*

Type of disc herniation

Extruded

Sequestrated

 

20

11

 

18

9

 

2

2

 

0.6015*

† Mann-Whitney test *Fisher exact test, TA Tibialis anterior

 

 

Table 4. Recent studies of pre-operative foot drop recovery after discectomy for lumbar disc herniation.

 

Study Reference

Number of patients

Outcome

Prognostic factors

Guigui et al.,

19984

50

30% complete recovery

50% partial recovery

- < 65 years

-Disc herniation, stenosis at one level

-Preoperative duration of motor weakness <6 weeks

-Monoradicular deficit

(severity of  initial motor weakness was not a variable)

Girardi et al,

20023

55

71% complete recovery

 

                       

-No statistically significant relationship was found between the extent of recovery and age, diagnosis (prolapsed lumbar disc versus lumbar spinal stenosis), duration of symptoms or the severity of pre-operative weakness

Postacchini et al., 20029

116

(lumbar disc herniation at different levels causing a motor deficit (not limited to foot drop))

76% complete recovery

-The peronei, tibialis anterior and EHL had the least capacity to recover normal strength.

-Other factors were not found to relate significantly to the recovery of muscle function.

Aono et al.,

20072

46 patients

61% complete recovery

-Preoperative motor strength

-Weakness duration               

Suzuki et al.,

200913

43

93% complete recovery

-Preoperative severity of motor deficit

-Symptom duration before surgery was not a significant risk factor for delayed recovery

Iizuka et al.,

20095

28

-16 with a PLD

-12 with lumbar spinal stenosis

 

75% complete recovery

25% complete recovery

-No statistically significant factor identified

-Muscle recovery was significantly superior to that in patients with surgically treated lumbar stenosis

-Preoperative tibialis anterior and EHL strength showed an association with recovery but not statistically significant

EHL extensor hallucis longus, PLD prolapsed lumbar disc.

 

 


DISCUSSION

 

A small number of authors have published the prognosis of foot drop due to lumbar disc herniation with complete recovery rates ranging from 25%-93%.2-6,10 Furthermore previous studies reported varying conclusions as to which factors are associated with recovery specifically as regards to the preoperative duration of weakness. This raises the question of whether foot drop due to prolapsed lumbar disc herniation  should be treated as a surgical emergency in the same manner as that reported for cauda equina syndrome11,12 for optimum outcome or not? The discrepancy in conclusions may be explained by noting that there are 2 clinical categories of patients presenting with foot drop: a group of patients with a known diagnosis of prolapsed lumbar disc presenting with an acute foot drop that usually present emergently within 24-48 hours of weakness onset and receive urgent surgical management versus a second group of patients with a gradual onset and progressive weakness, eventually opting for surgery weeks or months after onset of weakness.

In this series there were 31 patients presenting with foot drop due to lumbar disc herniation treated by lumbar discectomy, with 6 (19.4%) patients having associated ligamentum flavum hypertrophy. The commonest herniated disc level was L4-5 (83.9%) and less commonly was the L3-4 level (16.1%). All disc herniation were a Pfirmann8 grade III herniation. Operatively there were 64.5% subligamentous extrusion and 35.5% disc sequestration. It should be noted that intra-operatively there were varying origins of the L5 root as it relates to the disc (above, below and at the disc level) as previously reported by Suh and colleagues13 in a cadaveric study that describes the origin of the lumbar spinal roots and their relationship to intervertebral discs. Although this operative finding was not documented in this study, it is an anatomical variation worth noting and helps to explain why in practice one can see similar radiographic findings of perhaps a sequestrated L4-5 disc herniation and a similar degree of compression, yet absence of a neurological deficit. One possible explanation is that the root origin is below the disc level and hence further away from disc compression.

 

This study focused on foot drop recovery rates and attempted to analyze prognostic factors thought related to recovery. In no patient did ankle dorsiflexion weakness become worse after surgery. There were 87.1% of patients showing improvement to at least a grade III; 48.2% had a complete/near complete recovery, while 38.7% improved only to a grade III. The mean follow-up duration was 9.8 months, with a mean time to initial weakness improvement of 45 days. The clinical outcome in this patient series as well as prognostic factors compared with the results of recently reported series are summarized in Table (4).

In the current study foot drop recovery was statistically significant better in non-diabetic patients and in those patients with ongoing radicular pain with the onset and progression of foot drop. Foot drop recovery was superior (but not statistically significant) in the group of patients presenting with acute foot drop and operated upon within 24-48 hours of weakness onset, as opposed to weakness recovery in the group of patients with chronic progressive weakness. 

A continuing area of controversy is whether the duration of weakness influences the chances of recovery of function. Some studies support this contention2,10 whereas others do not3,5,6. In the current study preoperative weakness duration was not a statistically significant factor, though foot drop recovery was superior in the group of patients presenting with an acute foot drop who were operated upon within 24-48 hours of weakness onset, as opposed to weakness recovery in the group of patients with a chronic progressive weakness (with a mean weakness duration of 76 days). However, both groups still showed a favorable recovery after surgery with 100% of patients with an acute foot drop achieving at least a grade III recovery versus 80.9% in patients with a chronic foot drop.

Another variable that is unclear in the literature is whether to offer surgery for patients with a painless foot drop and what recovery rates are expected in such a clinical scenario. Aono and colleagues2 reported 8 patients out of a series of 41 patients with this clinical entity, 5 of which (63%) made a full recovery but there was no statistical difference in neurologic recovery between these patients and those suffering from leg pain. In the current study there were 11 patients with diminished radicular pain with progression of weakness to grade 0/1; 7 (63.6%) showed a partial or a complete recovery and 4 (36.7%) showed no evidence of recovery. This was of statistical significance when correlated with recovery in patients who maintain radicular symptoms with weakness onset and progression. Thus it may be noted that painless foot drop does carry a worse prognosis but recovery of function does occur in some patients. This data may be of help when counseling patients about the significance of resolution of the radicular pain and how it may affect outcome and recovery of the foot drop.

Multiple studies2,5 have shown improved surgical outcome in patients with a better preoperative grade  while others 3,4,6,10 have not. In the current study the severity of the initial motor weakness was not a statistically influential variable, though it was noted that patients with chronic foot drop with clinical evidence of movement (grade I/ II) showed a shorter time to show signs of improvement as compared to patients with a grade 0 motor strength. This may be explained by the fact that having any ankle dorsiflexion movement is  better starting point for recovery.

In the current study age, gender and history of smoking were not found to be of statistical significance to outcome. However, preoperative diabetes was of statistical significance, with diabetic patients having a less favorable recovery. This factor could have been further analyzed to note control of diabetes including preoperative HbA1C and postoperative blood glucose control in the recovery period, but this data was not available for all the diabetic patients.

The recovery process was notably of a faster pace in the patients presenting with an acute foot drop, with 6 out of the 10 patients showing signs of improvement in the first postoperative day versus a mean  duration of 97 days before signs of motor improvement was evident in patients with chronic foot drop  (17 (54.8%) patients). There were also a notably higher percentage of acute foot drop patients achieving a full recovery (80%) versus 33.3% in the chronic foot drop group of patients. Experimental studies have shown that severe and rapid compression of spinal nerve roots produces more pronounced damage to the neural tissue than mild or slow compression14,15, so perhaps an acute compression does imply a surgical emergency and the favorable outcome seen in this study was due to the early presentation and surgery that was done in 24-48 hours. However, such a conclusion is merely observational as there was no other group of patients with acute foot drop treated in a delayed fashion for statistical comparison.

There are several limitations of this study. This study is subject to all the limitations of any retrospective study as well as the relatively small sample size. Then again seeing this category of patients who opt for conservative treatment until progression of weakness to a foot drop is relatively infrequent. The results are comparable to the few studies that have been published in the literature and re-enforcing conclusions can be drawn. This may prove valuable for patient counseling as regards to  prognosis for recovery.

 

Conclusion

The recovery of foot drop due to prolapsed lumbar disc after lumbar discectomy is generally favorable, with significant improvement occurring regardless of age, gender, history of smoking, duration of weakness or weakness grade. Prognostic factors related to worse outcome were history of diabetes and diminution of preoperative radicular pain with progression of foot weakness. Foot drop recovery was superior in the group of patients presenting with acute foot drop and operated upon within 24-48 hours of weakness onset, as opposed to foot drop recovery in the group of patients with a chronic progressive weakness. 

 

[Disclosure: Author reports no conflict of interest]

 

REFERENCES

 

1.      Andersson H, Carlsson CA. Prognosis of operatively treated lumbar disc herniation causing extensor paralysis. Acta Chir Scand. 1966; 132:501-6.

2.      Aono H, Iwasaki M, Ohwada T, Okuda S, Hosono N, Fuji T, et al. Surgical outcome of drop foot caused by degenerative lumbar diseases. Spine. 2007; 32(8): 262-6.

3.      Girardi FP, Cammisa FP, Huang RC, Parvataneni HK, Tsairis P. Improvement of preoperative foot drop after lumbar surgery. J  Spinal Disord Tech. 2002; 15(6): 490-4.

4.      Lizuka Y, Iizuka H, Tsutsumi S, Nakagawa Y, Nakajima T, Somrimachi Y, et al. Foot drop due to lumbar degenerative conditions: mechanism and prognostic factors in herniated nucleus pulposus and lumbar spinal stenosis. J Neurosurg Spine. 2009; 10:260-4.

5.      Postacchini F, Giannicola G, Cinotti G. Recovery of motor deficits after microdiscectomy for lumbar disc herniation. J Bone Joint Surg. 2002; 84-B:1040-5.

6.      Suzuki A, Matsumura A, Konishi S, Terai H, Tsujio T, Dozono S, et al. Risk factor analysis for motor deficit and delayed recovery associated with L4/5 lumbar disc herniation. J Spinal Disorder Tech. 2011; 24(1):1-5.

7.      Weber H. The effect of delayed disc surgery on muscular process. Acta Orthop Scan. 1975; 46:631-42.

8.      Pfirrmann CW, Dora C, Schmid MR, Zanetti M, Hodler J, Boos N. MR image-based grading of lumbar nerve root compromise due to disk herniation: reliability study with surgical correlation. Radiology. 2004; 230(2): 583-8.

9.      Jonsson B, Stromqvist B. Clinical appearance of contained and noncontained lumbar disc herniation. J Spinal Disord. 1996; 9:32-8.

10.    Guigui P, Benoist M, Delecourt C, Delhoume J, Deburge A. Motor deficit in lumbar spinal stenosis: a retrospective study of a series of 50 patients. J Spinal Disord. 1998; 11:283-8.

11.    Shapiro S. Cauda equina syndrome secondary to lumbar disc herniation. Neurosurgery. 1993; 32 (5):743-7.

12.    Shapiro S. Medical realities of cauda equina syndrome secondary to lumbar disc herniation. Spine. 2000; 25: 348-52.

13.    Suh SW, Shingade VU, Lee SH, Bae JH, Park CE, Song JY. Origin of lumbar spinal roots and their relationship to intervertebral discs: a cadaver and radiological study. J Bone Joint Surg Br. 2005; 87(4):518-22.

14.    Olmaker K, Rydevik B, Holm S. Edema formation in spinal roots induced by experimental graded compression: an experimental study on the pig cauda equina with special reference to differences in effects between rapid and slow onset compression. Spine. 1989; 14:569-73.

15.    Yoshizawa H, Kobayashi S, Morita T. Chronic nerve root compression: pathophysiologic mechanism of nerve root dysfunction. Spine. 1995; 20: 397-407.


 

 

 


الملخص العربى

 

محددات  شفاء سقوط القدم الحادة والمزمنة بعد استئصال الانزلاق الغضروف القطنى

 

خلفية: هناك عدد قليل من الدراسات المنشورة عن مدى شفاء سقوط القدم الناتج عن الانزلاق الغضروفى القطنى وذلك بعد عملية استئصال الغضروف المنزلق، وبخاصة ما يتعلق بسرعة ظهور الضعف أو إذا كان هذا الضعف مزمنا قبل إجراء الجراحة، لذا فالهدف من هذه الدراسة هو تحديد النتائج السريرية لمدى تحسن سقوط القدم بعد استئصال الغضروف المنزلق وتحديد العوامل التى تحدد النتيجة.

الطريقة: هذه دراسة بأثر رجعي تشمل 31 مريضا يعانون من سقوط للقدم، وقد تم تعريف سقوط القدم على أن القوة أقل من 3 فى اختبار العضلات، المعلومات التى تم ملاحظتها تشمل ديموغرافية المرضى، التاريخ المرضى، الفحص الأكلينيكى قبل الجراحة، مدة الأعراض، الأمراض المزمنة، وكذلك أشعات المرضى، والتقارير الجراحية والتحسن الإكلينيكي الملاحظ من متابعة المرضى، كما تم تحليل نتائج ما بعد الجراحة لتحديد علاقة النتائج  بعدة عوامل: عوامل المريض، الفحوص الإكلينيكية، أشعات ما قبل إجراء الجراحة وكذلك العوامل الملاحظة أثناء الجراحة.

النتائج: كان جميع المرضى يعانون من سقوط لإحدى القدمين، كما كان هناك صنفين من المرضى: مجموعة تعانى من سقوط فجائى للقدم (10 مرضى (32.3٪) ومجموعة ثانية من المرضى الذين يعانون من ضعف تدريجي تقدم إلى سقوط للقدم (21 مريضا (67.7٪)، وكان أحد عشر (35.5٪) مريضا لاحظوا تحسن لألام جذر العصب عند تقدم سقوط القدم لدرجة 0 أو1 لمقياس قوة العضلات. وكان الشفاء الكامل/شبه الكامل قد حدث في 15 (48.2٪) من المرضى. أما الشفاء الجزئي فلوحظ في 12 (38.7٪) من المرضى، ولم يلاحظ أي تحسن في 4 (12.9٪) من المرضى. هذا وكان متوسط ​​مدة المتابعة 9،8 أشهر، وكانت متوسط المدة التى لوحظ فيها تحسن لسقوط القدم 45 يوما. بعد الحسابات الإحصائية للعوامل المتصلة بالنتائج أظهرت أن مرض السكر وتقلص الألم الجذرى مع سقوط القدم كان لها تأثير سلبى على تحسن سقوط القدم.

الاستنتاج: أظهرت النتائج أن تحسن ملحوظا لسقوط القدم حدث بغض النظر عن العمر والجنس وتاريخ التدخين ومدة أو درجة الضعف، وكانت النتائج سلبية لمرض السكر وكذلك للمرضى الذين حدث لهم تقلص لحدة آلام جذع العصب مع تطور ضعف القدم، كما كان التحسن للمرضى فى المجموعة التى كانت تعانى من سقوط فجائى للقدم أفضل من مجموعة المرضى الذين كانوا يعانون من ضعف تدريجي ومزمن للقدم.

 

 



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