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Spine

The management of weakness caused by lumbar and lumbosacral nerve root compression



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Abstract

Spinal stenosis and disc herniation are the two most frequent causes of lumbosacral nerve root compression. This can result in muscle weakness and present with or without pain. The difficulty when managing patients with these conditions is knowing when surgery is better than non-operative treatment: the evidence is controversial. Younger patients with a lesser degree of weakness for a shorter period of time have been shown to respond better to surgical treatment than older patients with greater weakness for longer. However, they also constitute a group that fares better without surgery. The main indication for surgical treatment in the management of patients with lumbosacral nerve root compression should be pain rather than weakness.

Two of the most common causes of lumbosacral radicular symptoms are disc herniation and spinal stenosis.1-5 The peak incidences of lumbar disc herniation are in the third and fifth decades.1-4 Fortunately, only 3% to 6% of lumbosacral disc herniations become symptomatic.1-4 Spinal stenosis tends to occur in the fifth and sixth decades.5 There are many ways of treating patients who present with radicular weakness, but few randomised controlled trials that have compared the efficacy of one treatment over another.

Radiculopathy is defined as ‘significant alteration in the function of a nerve root’.6 Symptoms include pain, numbness, paraesthesia and weakness. Additional clinical findings may include a limited straight leg raise with positive tension signs, muscle atrophy and absent reflexes. As spinal nerves are mixed nerves, the clinical picture often has mixed sensory and motor components, either of which may predominate.

The incidence of radicular weakness varies widely and largely depends on how it is assessed. The prospective evaluation of weakness and the documentation of its mild, non-disabling forms increase the prevalence, which has been reported to be as high as 30% to 50% in patients with disc herniation.7,8 There are many other causes for acute muscle weakness, including central nervous system disorders; lower motor neurone conditions; tumours; systemic disturbances such as hypothyroidism and polymyalgia rheumatica, and localised or systemic infections.9-11 This review will only consider radicular weakness due to lumbosacral spinal stenosis and disc herniation, and will describe its natural history, non-operative and surgical management, and the factors that predict outcome after surgery.

Literature search

We conducted a literature review with the aim of answering the following questions: what is the management of radicular weakness in relation to its natural history?; when should lumbosacral radicular weakness be managed operatively and when non-operatively?; and what are the factors that predict the outcome after surgery? We searched Medline, Embase and The Cochrane Library databases up to May 2011. Only the relevant references were included.

Natural history

Hakelius12 reported that patients’ weakness improve with time if managed non-operatively, reporting that 80% of disc-herniated patients showed a major improvement after six weeks; 90% had improved after 12 weeks and 93% had improved after 24 weeks. There was no advantage to be gained by operating on patients with a stable motor deficit: in the conservatively-treated group 45% improved compared with 53% in the operated group.12 Other studies have supported these conclusions and suggest that 56% to 75% of patients recover to Medical Research Council (MRC)13 grade 4 or 5 by six months.14-17

There is uncertainty about the indications for surgery and the long-term outcome of treatment in patients with radicular weakness due to spinal stenosis.18-20 Johnsson et al20 studied 32 untreated patients with spinal stenosis: in 70% of their patients, their symptoms failed to improve, 15% improved and 15% worsened over a mean period of 49 months.

Can non-operative measures improve radicular weakness?

The currently accepted indication for non-operative management of patients with lumbosacral disc herniation is the absence of progressive neurological signs or cauda equina syndrome21; most patients who present with radicular weakness will initially be treated non-operatively. There is a wide variety of non-operative treatments: bed rest, lumbar support, oral analgesics, muscle relaxants, spinal manipulation, physiotherapy, behavioural therapy and epidural steroid injections.3,4

Bed rest is thought to reduce the pressure of the intervertebral disc on the nerve root,21 though there is no evidence that this affects the natural history of radicular weakness. Other studies have reported that early mobilisation is better than bed rest in the treatment of acute low back pain.22 We are unsure whether the same principles apply to radicular weakness.

The effects of non-steroidal anti-inflammatory drugs (NSAIDs) on radicular weakness are not known. They have only been shown to be helpful in the management of acute low back pain.21 A meta-analysis found no benefit from NSAIDs in the treatment of patients with radicular weakness compared with a control group (odds ratio = 0.99).23 Often radicular pain can affect the patient’s description of weakness and the findings on clinical examination and thus mimic muscle weakness. Other drugs such as oral steroids, muscle relaxants and anti-depressants have been used to treat acute low back pain with radicular weakness but their effect on weakness is unknown.

Spinal manipulation seems to be more effective than sham manipulation at relieving local or radiating pain in patients with acute back pain and sciatica due to disc herniation.3,24,25 However, there is concern about the possibility of further herniation from spinal manipulation in those who are candidates for surgery.3,24,25 Traction remains of unproven benefit in the treatment of radicular weakness due to lumbosacral disc herniation. A meta-analysis of pooled data from four randomised controlled trials showed some benefit of traction compared with a placebo (odds ratio = 1.2),23 however, it is also associated with adverse effects such as pain, anxiety, lower limb weakness and fainting.26

Epidural steroid injection is often used in patients with a radiculopathy and is better than control treatments in the short term (odds ratio = 2.2).23 Buttermann27 reported no significant difference in the number of patients with persisting muscle weakness (MRC grade < 3) between those treated operatively and those treated by epidural steroid injection at three years follow-up.

Fluoroscopically-guided transforaminal injection techniques have the theoretical advantage of delivering steroid and local anaesthetic accurately to the site of nerve root compression. They are better than trigger-point injections in the short-term but there is no evidence of a beneficial effect on radicular weakness.21

In summary, there is a lack of evidence to support the effectiveness of non-operative treatment and no evidence to suggest any positive effect on the natural history of radicular weakness.3,4 Conservative treatment should consist of adequate analgesia, reassurance and advice to mobilise as early as possible and maintain a normal lifestyle.

Is early operative management best for radicular weakness?

The Swedish National Spine Registry reported that 2182 lumbar decompressions/discectomies were performed in 2003 for lumbar radicular symptoms, usually persistent pain or pain and weakness.28

Dubourg et al29 studied 67 patients with weakness due to lumbosacral disc herniation. Patients who underwent surgery had a higher rate of extruded disc, a greater number of paretic muscles and a longer course of sciatica than those treated non-operatively. The mean number of paretic muscles, initially and at six months, was 6.3 and 2.1 in the operated group and 5 and 1.4 in the operated group, respectively. In the operated group of 39 patients, 25% (ten patients) recovered (MRC Grade 5) and 53% (21 patients) had improved (MRC Grade 4) after six months. In the non-operated group of 28 patients, 40% (11 patients) recovered and 56% (16 patients) improved at six months.29

In 1983, Weber14 conducted a retrospective study of 63 patients and reported a 70% rate of recovery independent of operative or non-operative treatment. Other studies have reported similar findings.12,16,17,30 He reported that surgical treatment produced better results than conservative management at one year, but no significant difference after four years.14 Long-term (> ten years) results from Atlas et al31 showed that patients treated operatively had worse baseline symptoms than those treated non-operatively but after ten years the mean and standard deviation of the sciatic index frequency (pain score, pain frequency, weakness score, weakness frequency)31 was not significantly different between the two groups. Patients treated operatively reported better early outcomes.31

Peul et al32 randomly assigned 141 patients with sciatica to early surgery (at a mean of 2.2 weeks) and 142 patients to conservative management. Of those managed conservatively, 55 (38.7%) came to surgery after a mean of 18.7 weeks. They found that those patients who had an early operation perceived that they had been relieved of their leg pain more quickly than those treated later. There was, however, no significant overall difference between the two groups after one year.

The long term Spine Patient Outcomes Research Trial (SPORT) compared the outcome of operatively and non-operatively treated patients in a randomised controlled study over two and four years. The report concluded that patients treated operatively had a better outcome; however, weakness was not evaluated separately.30,33

In 1975, Weber34 studied 128 patients in groups treated non-operatively and operatively. Two weeks after admission and at one-year follow-up the muscle strength of the lower limbs was measured in each patient during maximal isometric voluntary contractions using strain gauges. There was no significant difference in motor function after one year in the two groups.34

There are no studies in the literature that have specifically compared the outcome of operative and non-operative treatment for radicular weakness in patients with spinal stenosis. Those studies that have evaluated weakness have used a frequency index,19,31 which includes pain, numbness and weakness as an outcome measure. Chang et al19 showed that patients who had been managed operatively were better after ten years than those treated non-operatively, but weakness was not evaluated separately. This study also had a large crossover of patients from the non-operated to the operated group.

In 2005, Atlas et al31 concluded that at ten years, decompression for stenosis gives a slightly better outcome in terms of leg pain and weakness than non-operative treatment. Some studies showed improvement with operative treatment, but their absolute benefit has been very variable.35,36 Other studies have assessed trends over time and have reported a decline in the initial surgical benefit.37-39

There is no evidence to suggest that early surgical treatment improves the recovery of radicular weakness in patients with lumbosacral disc herniation or spinal stenosis.

Outcomes of surgery

The main indication for the surgical treatment of nerve compression is pain. In patients with non-progressive radicular weakness, conservative treatment gives a reasonable outcome and there is no evidence to suggest that early surgical treatment gives better results at long-term follow-up. Postacchini, Giannicola and Cinotti40 showed that patients with severe weakness (MRC grade ≤ 2) have a worse functional outcome, independent of pain. It is therefore important to establish when, and in whom, surgical treatment should be considered where there is functional disability due to weakness without radicular pain.

Effectiveness

Mariconda et al41 reported that 135 patients, 75% of their total 180 patients with pre-operative muscle weakness who underwent lumbar discectomy, had normal muscle strength at 20 years and, even if mild to moderate weakness failed to improve, it was with little detriment to late function and quality of life.8,41 Aono et al42 found that 28 (61%) of their total 46 patients who had been treated operatively for foot drop (MRC grade < 3) had improved (MRC grade ≥ 3) at a mean follow-up of 3.7 years and Postacchini et al40 reported that 88 (76%) of their total 116 patients had recovered normal power (MRC grade 5) at a mean follow-up of 6.4 years. Girardi et al43 reported an improvement of 98% in the mean strength of dorsiflexion from MRC 3.3 to MRC 4.7 at a mean follow-up of 36 months. Matsui et al44 found that 51 (80%) of 64 patients showed some improvement without actually reporting the extent of recovery. However, Andersson and Carlsson45 only reported a 50% improvement in ankle dorsiflexion in the patients on whom they had operated.

The literature shows that radicular weakness improves markedly in 50% to 80% of patients. However, as we have already established, the natural history is also good without operative intervention. The discrepancies between these studies are likely to be due to differences in their inclusion criteria.

Severity of pre-operative weakness

There is consistent evidence that the outcome after surgery is related to the degree of pre-operative weakness.40,42,43,46,47 Ghahreman et al46 reported complete recovery (MRC grade 5) in 38 (68%) of their total 56 patients in whom the power of dorsiflexion against gravity was preserved (MRC grade 3 and 4). There was complete recovery in only ten patients (27%) who had more severe weakness pre-operatively (MRC grade < 3).46 Other studies40,42,43,46,47 have also shown an inverse relationship between the severity of muscle weakness pre-operatively and recovery post-operatively. Pearson et al47 reported that worsening symptoms are associated with a greater treatment effect of discectomy (difference between the operative and non-operative mean change from baseline). However, Girardi et al43 found no statistically significant relationship between the severity of pre-operative weakness and the extent of recovery but their patients only had weakness of between MRC grades 2 and 4. Iizuka et al48 also found that the pre-operative strength of tibialis anterior and extensor hallucis longus did not affect post-operative recovery.

Overall, the evidence suggests that improvement after surgery is better and occurs more consistently in patients with milder weakness.

Duration of pre-operative weakness

The duration of pre-operative weakness seems to have an inconsistent effect on recovery.46 Girardi et al43 and Iizuka et al48 agree that the duration of symptoms has no effect on the outcome of surgery.

Other studies have suggested that the duration of weakness before surgery does influence the outcome after surgery.40,42,44,49-51 Aono et al42 reported that all of their patients who recovered were weak for a maximum of three months. Postacchini et al40 reported that patients who recovered completely had a significantly shorter mean duration of weakness (84 days) than patients who had residual weakness (120 days). Similarly, in the group with severe weakness, there was a significant difference in the mean duration of the pre-operative deficit between those who recovered their muscle strength completely (35 days) and those with residual weakness (69 days).40

It should be appreciated that the duration of weakness before surgery is determined from the patient’s history and is subject to error. Also, it can be difficult to distinguish pain from weakness. The evidence suggests that the longer the duration of weakness, the less likely recovery is after surgery: this may be more important for those patients with weakness severe enough to cause disability. More research is needed to answer this question but surgery should be considered at two to three months for those patients in whom the only indication for surgery is disabling weakness. However, surgery should not be discounted in those whose symptoms are more long-standing. The decision to operate should probably be delayed in patients with milder weakness until approximately six months have elapsed.

Associated factors

There seems to be no association between gender and the outcome of surgery,40,41,46 and the association between age and recovery of radicular weakness after surgery is unclear. Some studies report that age has an adverse effect on the recovery of radicular weakness.41,42,45,50 Aono et al42 reported that increasing age at surgery adversely affected post-operative tibialis anterior strength (1.45 times with each ten year rise in age). However, multiple linear regression analysis eliminated age as a significant factor in favour of duration of symptoms as older patients were weaker for longer.42 Ghahreman et al46 reported that younger patients made a better recovery in the first six weeks after surgery. Stratification of patients based on age revealed that patients between the ages of 25 and 40 years make a better recovery than those between the ages of 41 and 60 years, who also make a better recovery than patients over the age of 60. Mariconda et al41 reported that older age and longer pre-operative duration of symptoms are negative predictors for the recovery of radicular weakness after surgery.

Other studies have reported no significant correlation between age and the recovery of motor weakness after surgery.20,40,43,45 Girardi et al43 reported that age was not a predictor of full motor recovery.

Diabetes and smoking have been reported to have no influence on motor recovery.40 No other study has evaluated these factors.

Type and location of affected site

The level most frequently affected by degenerative disease of the lumbar spine is L4/5.42 Compression of two nerve roots by a disc herniation is seen more commonly in patients with radicular weakness. Similarly, multiple levels including L4-5 are commonly decompressed in patients with weakness due to spinal stenosis.48 Aono et al42 reported no significant difference in motor recovery between patients with single-level and multi-level compression.

Extruded and sequestrated herniations are weakly associated with a severe or very severe pre-operative deficit and only partial recovery after surgery.40 The peronei, extensor hallucis longus (EHL)and tibialis anterior have the least capacity to recover to their normal strength. Both Matsui et al44 and Girardi et al43 reported that the recovery of extensor hallucis longus is slower than that of tibialis anterior. Girardi et al43 also noted that persistent weakness of extensor hallucis longus is the most common deficit, remaining present in 36% of those who were weak pre-operatively.

The quadriceps femoris is rarely severely weakened, and all patients so affected will make a complete or almost complete recovery.40 This is of clinical relevance as isolated EHL weakness rarely causes disability while even moderate quadriceps weakness will cause some disability.

Postacchini et al40 reported that severe muscle weakness due to L2 to L4 nerve root involvement almost always recovers if a microdiscectomy is performed within two months of presentation. However, in patients with severe weakness due to L5 or S1 root compression, early surgery gives mixed results and patients are often left with marked residual disability.24

Lumbosacral disc herniation or stenosis

The evidence is mixed: two studies have shown no difference in the degree of post-operative weakness caused by a herniated disc and spinal stenosis.42,43 Both of these retrospective studies had < 20 patients in the stenosis group. Iizuka et al48 found that patients with spinal stenosis had a poorer outcome after surgery. In 12 of 16 patients with lumbosacral disc herniation, the recovery reached MRC grade > 3 in contrast to only 3 of 12 patients with spinal stenosis.48 These findings may reflect the patient’s age; the older patients being stenotic and the younger having disc herniation.

Painful or painless weakness

The difference in outcome between the patient with a painless foot drop and one with a painful foot drop is unclear. Aono et al42 reported no significant difference in neurological recovery between patients with painless and painful motor weakness in surgically treated patients. Anderson and Carlsson45 and Naylor51 reported poor recovery in weakness of the foot extensors, especially when painless in surgically treated patients. These two conflicting reports allow us to draw no specific conclusion about the effect of radicular pain on the recovery of strength after surgery. Clinically, if a patient still has radicular pain two or three months after the onset of symptoms, then the main indication for surgery is the relief of pain and improvement in motor function is less likely to occur. Following decompression surgery, there is no evidence at the current moment, that the absence of pain predicts a worse outcome in terms of radicular weakness.

Rate of recovery

The rate of recovery has been well documented and most studies agree that recovery happens soon after surgery. Ghahreman et al46 reported that most clinically significant improvement in weakness occurs within six weeks of surgery for disc herniation. In their study, none of the patients improved by more than one MRC grade after this. In 37 patients (66%) there was no improvement after six weeks.46 Aono et al42 reported that the earliest recovery to full strength was at six weeks and the latest at two years. Jönsson and Strömqvist52 reported that 17 patients (50%) recovered motor power within two years of surgery, but most occurred within the first four months. Postacchini et al40 found that 96 patients (83%) recovered most of their strength between two and four months after surgery, while five (4%) showed no further improvement after six months. Patients with a severe pre-operative motor deficit were slower to recover: six patients (16%) were still showing further signs of improvement at six months.

Millisdotter et al53 reported that sciatica resolves quickly after surgery for disc herniation, and disability improves significantly six weeks after surgery with further improvement at four months but no further change at 12 months. Muscular strength improves throughout the first year.53 Interestingly, they also found that proximal muscle function six weeks post-operatively was related to low back pain and disability after one year and also to leg pain at both four months and one year.53

In summary, most of the recovery happens within the first six months of surgery but motor recovery can continue, for up to two years after surgery. After discectomy, pain relief occurs first, followed by motor function and finally by improvement in sensation.8 Persistence of a minor dermatomal sensory deficit is common and usually trivial.8

Vocational outcome

Jensen et al54 identified patients with an unfavourable vocational prognosis (< 40 weeks employment within the second year of hospital contact (receiving treatment from a hospital setting)) in patients with lumbar disc herniation.54 They found no significant difference in risk related to discectomy compared with conservative treatment.54 This is in line with other randomised controlled studies.17,33 However, an unfavourable vocational prognosis is associated with unskilled work (hazard ratio = 2.1), skilled work (hazard ratio = 1.9), and semi-academic work (hazard ratio = 1.5) compared with academic work and < 40 weeks employment within year two before hospital contact (receiving treatment from a hospital setting) (hazard ratio = 2.1).54 Further negative predictors of vocational prognosis are lumbar fusion alone or fusion combined with discectomy.54 The outcome after lumbar fusion may simply reflect a more serious underlying disorder.

Use of anti-adhesion (Oxiplex) gel

There is some evidence that Oxiplex gel/SP Gel (FzioMed, Inc., San Luis Obispo, California) may improve motor recovery after surgery. A randomised controlled trial looking at its effectiveness also evaluated its effect on motor weakness in patients having surgery for disc herniation.55 The authors, who were funded by the manufacturers, found a greater improvement in motor weakness in those patients treated with Oxiplex than in those who were not.55 However, this was a secondary outcome measure and further studies are needed.

Conclusions

The natural history of non-progressive lumbosacral radicular weakness is of resolution: early surgery offers no benefit in any patient group. If the condition of the patient deteriorates, urgent surgery is indicated although the precise timing for this has not been established.

Significant radicular weakness affects the long-term functional outcome. If a patient has had significant pain and weakness for two or three months, the risks and potential benefits of surgery for both problems should be discussed. If radicular weakness persists but is not causing disability, surgery is not indicated. If radicular weakness is causing significant disability after two to three months and there is no significant radicular pain, surgery should be considered. The chances of recovery are better with less severe weakness, younger age, L2-L4 nerve involvement and disc herniation rather than stenosis.

Many of these factors are controversial and require further research. This should include a careful clinical evaluation of weakness and agreement for inclusion and exclusion criteria based on the degree of weakness and its resulting disability. Other factors, although not all significantly related to outcome, should be carefully documented: these include duration and severity of weakness, age, gender, smoking habits, diabetes, nerve root level(s), cause and number of nerve roots compressed and pain.


Correspondence should be sent to Mr H. Sharma; e-mail:

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Supplementary material. Two tables, detailing a) the results of the literature search in terms of the evidence for and against prognostic factors predicting surgical outcome in radicular weakness and b) treatment options, are available alongside the electronic version of this article on our website www.bjj.boneandjoint.org.uk