Keywords

Introduction

Carpal tunnel syndrome (CTS) is a collection of symptoms and signs arising from compression and/or traction on the median nerve at the level of the carpal tunnel. It is a common condition, with a prevalence of 3.8 % in a healthy population and is probably on the increase, related to an increasing mean Body Mass Index (BMI) [1, 2]. It is the commonest nerve compression syndrome and is therefore of great interest to health purchasers and providers alike. The response to the financial burden of treating carpal tunnel syndrome has been varied throughout the UK. In some areas carpal tunnel release (CTR) has been designated as an operation that requires exceptional funding, whilst in other areas it is available on a one stop clinic basis. The 2013 tariff for CTR is between £900 and £1,250 and it is likely to be one of the conditions that is very appealing to healthcare providers, in that it is usually simple to diagnose and straightforward to treat [3]. CTS is a clinical diagnosis, requiring assessment by a clinician with sufficient experience to filter out those patients that need investigation of an alternative cause of their symptoms. There is concern that the oversimplification of the treatment pathway, if there is no assessment by a hand surgeon, may lead to problems such that some patients may undergo unnecessary or unsuccessful CTR surgery before it is established that CTS is an incorrect diagnosis. Also the operation, though usually straightforward, is not without complications which can, on rare occasions, be catastrophic.

Aetiology

Normal nerve function is dependent on the nerve being free to glide without constriction or localised pressure. Nerve compression symptoms of tingling and numbness occur when there is a mismatch between the space available for the nerve and the space needed by that nerve and/or tethering of the nerve.

Gelberman measured pressures within the carpal tunnel and showed that patients with CTS have a mean pressure of 32 mmHg, compared to a mean of 2.5 mmHg in controls [4]. In chronic compression there is a physical deformation effect, as well as an ischaemic effect. The deformation leads to detachment and retraction of myelin seen as a slowing of conduction. The ischaemic effect reduces the efficiency of the Na+ and K+ pumps and alters the fibroblast to schwann cell balance, which in time leads to fibrosis within the nerve. This is seen as loss of conduction and failure to transmit an impulse.

Ultrasound studies have shown that nerve gliding is reduced in patients with CTS, when compared to the normal population [5].

A mismatch in available space may be due to a narrow tunnel, a reduction of the space available within the tunnel, or an increase in the volume of the nerve itself. Obviously a combination of these factors is possible and may give rise to symptoms with very small changes in one of them. There are also a number of conditions in which the nerve shows an increased susceptibility to the effects of compression.

Narrow Tunnel

A case-control study of patients with carpal tunnel syndrome has shown that the mean wrist depth to wrist width ratio is lower in symptomatic patients, although this difference is small and may in fact be due to the difference in BMI [6]. Flexion and extension of the wrist further reduces the space available, accounting for the onset of symptoms in these positions, for example when driving.

Reduction in Space Available Within the Tunnel

This may be due to an inflammatory process, tumour or anomalous structures such as a persistent median artery or the muscle belly of a long flexor extending into the carpal tunnel. Space occupying lesions were found to be the cause of CTS in 3 % of cases, in a series of 779 cases, of which almost half were tophaceous gout, tenosynovitis, ganglia, lipomata and fibromata [7].

An Increase in the Volume of the Nerve

A common example of this is in diabetes, where changes in the phospholipid content within the nerve increases its volume.

Nerve Susceptibility to Compression

Diabetes

Diabetes also impairs axonal transport mechanisms within nerves, rendering them more susceptible to the adverse effects of compression. This may account for the incomplete recovery of the nerve seen in diabetics after decompression.

Acromegaly

Acromegaly gives rise to an increase in the endonuerial tissue, in which carpal tunnel syndrome may be superimposed on a peripheral neuropathy. CTS may be the first presenting symptom in acromegaly, so this diagnosis should be considered and those patients known to have acromegaly need to be aware of the possibility that they may develop CTS, so that they seek medical advice at the appropriate time.

Hypothyroidism

Hypothyroidism leads to axonal degeneration and altered conductivity and CTS may again be the first presentation. Administration of thyroxine usually reverses the changes relieving the symptoms.

Hereditary Liability to Pressure Paralysis (HLPP)

Hereditary liability to pressure paralysis (HLPP) These are rare disorders, occurring in a small number of families, in which there is a reduced axonal diameter and poor development of the myelin layers. Patients may get recurrent lesions involving peripheral nerves that usually resolve spontaneously but may leave them with persistent paralysis. Some of these patients have been found to have electrophysiological changes at expected entrapment sites without the expected symptoms. These disorders are due to dysfunctional voltage gated ion channels which may also be referred to as channelopathies.

The Double Crush Phenomena

The double crush phenomena is a clinically observed situation in which a nerve that is compressed at one site appears to have an increased susceptibility to symptoms from compression at another site. This is probably explained by an effect on axonal transport.

Acute CTS can occur in association with wrist trauma, or secondary to sudden severe swelling in the carpal tunnel, such as after a bleed from a vascular malformation. This will present as rapidly evolving paraesthesia in the median nerve distribution, progressing to numbness if untreated. The threshold for this to occur will also be lower in any patient who already has any of the predisposing factors above.

The aetiology in this case is rapid onset of ischeamia, secondary to the sudden increase in pressure and is in effect a compartment syndrome of the carpal tunnel. As such, it needs to be released as a matter of urgency to prevent permanent nerve damage. An urgent carpal tunnel release should be performed, if necessary, using an extended approach to also address the underlying cause.

Presentation, Investigation and Treatment Options

If the patient’s history and clinical findings are typical for CTS, the diagnosis can usually be made on assessment by an experienced clinician. However, the addition of nerve conduction studies (NCS) may be helpful when there are atypical findings and other confounding factors, such that the diagnosis is not as clear cut.

Patients with CTS typically present with a history of intermittent tingling in the hand, especially at night when the hand has assumed a flexed posture. The patient may be able to localise the tingling to the palm and radial digits of the hand on questioning. This often wakes the patient, who will demonstrate how they shake their hands until the tingling stops. Symptoms may also be associated with activities in which the hand is held in flexion, such as reading a book, driving, knitting and typing. With time, tingling will become more frequent and persistent, progressing to intermittent numbness and then to permanent numbness of the area innervated by the median nerve. The tendency to drop things may be noticed at quite an early stage as the sensory and proprioceptive fibres are affected. Weakness presents later, but becomes progressively worse in untreated CTS.

Hand pain is often a feature and may also be referred proximally into the forearm.

Symptoms that come and go without obvious provocation and are intermittent may indicate cervical involvement.

Examination (Table 12.1) follows the same routine as with any nerve compression syndrome;

Table 12.1 Examination of typical findings in carpal tunnel syndrome
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Inspection, together with an examination of sensation to the digit. Motor power, particularly of the intrinsic, following by provocation tests of all potential compression sites along the nerve.

Provocation Tests

Tinel’s Sign

The term ‘Tinel’s sign’ in this context is actually a misnomer, as Tinel described paraesthesia occurring in the distribution of a nerve when the nerve has been injured and percussion is used distal to the point of injury. This is specifically a sign indicating progression of recovery following a nerve injury, by eliciting symptoms from the immature advancing nerve ends. However, it is very commonly used in the context of carpal tunnel syndrome and other compression syndromes where it is taken to mean paraesthesia provoked by percussion at the site of the compression.

Percussive tapping is used to provoke the symptoms and should be started from the index or middle finger distally to proximal to the elbow following the line of the median nerve. The patient should be asked before the percussion is started to indicate if at any point it causes unpleasant tingling. Symptoms elicited at the CT indicate likely compression, although percussion should continue proximally to check whether they are also elicited at the pronator teres (PT) site.

Phalen’s Test

In 1966 Phalen described his wrist-flexion test in which ‘the patient is asked to hold the forearms vertically and to allow both hands to drop into complete flexion at the wrist for approximately 1 min’ [8]. Figure 12.2 shows the posture the hands should be placed in to perform Phalen’s test. The test is positive if it produces CTS symptoms in less than 1 min.

Fig. 12.1
figure 1

(a) The O sign for testing FPL Shows a competent O and the strength of FPL can be tested by the examiner linking a finger through the O and attempting to break it against resistance from the patient. (b) When FPL is very weak the patient is unable to make an O as seen here

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Fig. 12.2
figure 2

The position of the hands for eliciting Phalen’s sign

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Many variations on this test have been described, some of which are thought to be more sensitive, although this may be at the expense of a higher false positive rate. Also, most of them involve an amount of pressure applied either by the examining doctor or by the patient pressing their hands together. Both of which introduce an element of variability that may make the sign less reliable and comparison between case series’ more difficult.

Pronator Provocation

The space available for the nerve deep to PT is reduced by resisted contraction of the muscle with the elbow extended. If the gap between the two heads of pronator is palpated and light pressure applied, the patient will experience discomfort if compression is present. Rarely, however, actual paraesthesia is elicited.

It can be seen from the table that in the early stages there is little to find on examination, other than possible positive provocation signs. However, if there is a clear history of typical symptoms and one or more positive provocation signs, this is usually enough to make a diagnosis of CTS. In later stages, provocation tests may become negative, but other signs become apparent. If the history or findings are NOT typical then nerve conduction studies (NCS) should be considered in order to confirm or exclude the diagnosis.

Clinical Pearl

  • If there are any findings indicating possible compression by pronator teres (PT) then nerve conduction studies (NCS) should be used to assess involvement of the nerve at this level.

  • However, when a referral for NCS is made to confirm the diagnosis of CTS many centres would only carry out a focused examination at the carpal tunnel level. Therefore, if there is suspicion about possible compression at PT level, then these clinical findings must be included in the NCS referral to help guide the appropriate tests – i.e. for the NCS to assess the median nerve at the CT and more proximally in the forearm. Similarly, if symptoms extend into the ulnar nerve territory this should be highlighted.

Treatment Options

Treatment options that have been found to be of benefit include splinting, steroid injection and surgery.

Ultrasound treatment may be beneficial, but the quality of the evidence is poor and the benefit is probably no greater than that seen with other conservative treatments [9]. Lastly, there is no evidence of any benefit from the use of diuretics [10].

Splinting

A recent Cochrane review concluded that many of the trials for splinting were poorly conducted and provided only weak evidence of beneficial effect. However, where patient’s symptoms are mainly nocturnal, a night splint can be very effective at relieving their symptoms in the short term, with benefit being experienced up to 1 year from the initiation of treatment [10].

Clinical Pearl

  • The splint needs to be positioned, such that it holds the wrist in neutral, which maximises the cross sectional area within the carpal tunnel. However, many commercially available wrist splints are designed to support a painful wrist in a functional position and they therefore hold the wrist in 20–30° of extension. This is not appropriate for carpal tunnel syndrome, as it increases the traction on the nerve and reduces the space within the tunnel. As a consequence, patients who are using off the shelf splints may experience little benefit, or even be made worse.

Steroids

Treatment of carpal tunnel syndrome with injection of steroids into the carpal tunnel has also been the subject of a recent Cochrane review.

The conclusion was that:

  • Steroid injection provided clinical improvement 1 month after injection, compared with a placebo,

  • Compared with oral steroid, an injection of steroids at the carpal tunnel provided greater benefit for up to 3 months,

  • The improvement seen with steroid injection is not significantly greater than that seen with anti-inflammatory medication and splintage,

  • Improvement is no greater with 2 injections than 1

  • Long term benefit has not been demonstrated [11].

Relief of symptoms with steroid injection is both diagnostic and predictive of a beneficial outcome from surgical release. It may, therefore, be useful in those cases where there is doubt over the diagnosis and symptoms are severe enough to warrant an invasive diagnostic procedure that may also give temporary relief. However, the injection requires expertise, so injection into the carpal tunnel by an untrained practitioner should not be used as a substitute for expert clinical review. Long term effects of steroid injection into the carpal tunnel are not known and, in the author’s experience of referrals following injection in the primary care setting, complications of injection can include complex regional pain syndrome and tendon rupture. In conclusion, steroid injection has a limited place, but can be offered to patients with mild symptoms of recent onset, in whom splintage has not sufficiently relieved their symptoms. Follow up, or clear instructions to return if symptoms are not relieved within 4 weeks, should be given so that there is no undue delay to further investigation or treatment. Also, the likelihood of the temporary nature of the relief should be explained to the patient, along with the advice that if symptoms return surgical treatment should be considered.

Surgery

Surgery has been shown to be more effective than steroids or splinting and many patients who are managed with these non-operative measures will at some stage require surgical release [12].

Surgical Techniques and Rehabilitation

Surgical Techniques

Surgical decompression should be considered where symptoms are of greater than 6 months duration and progressive, or severe. Surgical approaches can be divided into

  • Open

  • Endoscopic

    •  Single portal

    •  Dual portal

Open Carpal Tunnel Release (CTR)

Open CTR can usually be carried out under local anaesthetic. A tourniquet is not necessary if bupivacaine with adrenaline is used and infiltrated with sufficient time to allow maximal effect from the adrenaline [13].

The incision needs to be within the safe zone to avoid injury to the palmar cutaneous branch of the median nerve and to approach the median nerve from its ulnar side to minimise risk of injury to the recurrent motor branch. Common approaches involve a longitudinal incision from a point midway between the pisiform and the scaphoid tubercle, either along the midline of the 4th ray or towards the 3rd web space. The distal extent of this incision is usually limited to Kaplan’s cardinal line. This was originally described by Kaplan in 1953 as a line from the apex of the first web space parallel to the middle palmar crease [14]. This marks the distal extent of the transverse carpal ligament (TCL) and the superficial palmar arch is always distal to this. The space between these limits can therefore be considered as the safe zone (Fig. 12.3). However, if a good view of the distal part of the dissection cannot be obtained the skin incision can be extended judicially in order to provide safe exposure, as long as the surgeon is aware that they are approaching the area where critical deep structures are likely to be present. Proximally, the incision can be extended if exposure is needed proximal to the distal palmar crease, with either a short transverse limb along the distal palmar crease in an ulnar direction, or a zig zag across it.

Fig. 12.3
figure 3

The safe zone for incisions in carpal tunnel release

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After incising the skin, the incision continues down through the subcutaneous fat and the palmar fascia before dividing the TCL. It is essential that the surgeon is cognisant, not only of the normal anatomy, but also of the anatomical variations as have been described, in order to minimise the risk of nerve damage [15]. The recurrent motor branch is particularly at risk when it traverses the TCL, or emerges from the ulnar side of the median nerve. Incision of the TCL should be carried out with great care and ideally loupe magnification, proceeding both proximally and distally until there is a complete release. Distally this is indicated by the exposure of the palmar fat pad, with appropriate care being taken to protect the superficial palmar arch. Proximally, the release should include any thickened or tight distal forearm fascia. The completeness of the release can be tested by carefully inserting a Macdonald’s dissector along the line of the nerve – there should be plenty of room for it to move freely.

The result of a review of randomised control studies of internal neurolysis concludes that there is no evidence of any benefit, indeed the increased scarring on a nerve would seem to indicate that it may actually be harmful [16].

In cases with severe muscle weakness and loss of opposition a Camitz procedure (Fig. 12.4) can be performed at the same time. This provides mainly abduction rather than opposition and is weaker than the alternative opposition transfers. However, it places the thumb such that the action of flexor pollicis longus can be used to provide some opposition.

Fig. 12.4
figure 4

The Camitz Procedure; Transfer of Palmaris Longus to the base of the thumb to provide abduction. (a) The tendon to palmaris longs is released distally with an extension from the palmar fascia (b) this is attached to the Abductor Pollicis Brevis tendon to abduct the thumb. This transfer therefore provides abduction but also places the thumb in a position from which FPL can provide some opposition

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Skin closure should be with interrupted sutures, with either a rapidly absorbed suture such as Vicryl Rapide ©, or a nonabsorbable monofilament.

Post-operative Regime for Open CTR

Traditionally patients were splinted post-operatively and told to refrain from heavy use of the hand for up to 6 weeks. However, a well designed randomised control trial showed that patients who are splinted post-operatively have more scar pain and take longer to return to work than those who have a padded dressing removed on the first day after the operation and were then allowed full active motion of the fingers [17]. In this trial, the mean number of days for unsplinted patients to return to activities of daily living was 6, light duty work 15 and full work 17 days. These findings are confirmed by a review of subsequent randomised control trials, showing that there is no benefit in splinting CTR patients post-operatively and that patients instructed to return to all normal activities at 2 weeks showed no adverse effects from doing so [18].

Authors preferred regime:

  • Small dressing to incision, followed by padded wool and crepe

  • Instructions to rest and elevate the hand for 24–48 h

  • Reduce the dressing and start to use the hand after this and carry out a home physiotherapy regime

  • Wound check at 7 days

  • Return to full normal use at 2 weeks

  • Expect to have some discomfort on weight bearing to the base of the hand for 3–6 months, but not to be concerned by this as it will usually settle

Endoscopic Carpal Tunnel Release

Indications for endoscopic release include pressure to return to work, particularly in bilateral cases and avoidance of a palmar scar where patients need to do a significant amount of weight bearing – for example in paraplegic patients who self propel in a wheelchair. Cost implications for the equipment prevent the universal usage of endoscopic techniques in the absence of a significant benefit for most patients as the return to full function is little different than that following an open technique and pillar pain can still be a problem [19]. What is relevant, however, is that surgeons who do offer endoscopic release do need to ensure that they undertake a sufficient number of cases to maintain their skills.

Dual Portal Technique

A 1 cm transverse incision is made midway between the proximal and distal wrist creases ulnar to palmaris longus. A Macdonald’s blunt dissector is introduced through this incision into the carpal tunnel and used to clean the dorsal surface of the TCL – this action provides tactile feedback on the texture of this surface confirming that the correct space has been entered. The trocar and slotted sheath is then introduced into this same space and the second portal site is defined by palpating the trocar tip and incising over it as close to the distal edge of the transverse carpal ligament as possible. The trocar and slotted sheath are then advanced out through this second portal to exit the skin and the central trochar can be withdrawn. In this way the slotted sheath is present within the carpal tunnel, with the slot facing volarly. The camera is introduced into the slotted sheath from distal to proximal and a hook knife is inserted through the proximal portal, so that the TCL can be divided under direct vision. The metal casing is visible outside of the hand, meaning the correct alignment of the slot can be maintained and confirmed at all times.

Single Portal Technique

In this technique only a proximal portal is required and a camera and blade are inserted from proximal to distal. The CTR is then divided in a single distal to proximal movement, taking care not to alter the alignment of the blade, as confirmation of the correct alignment is more difficult once division of the TCL has been started.

Post-op Regime for Endoscopic CTR

Minimal dressings are applied and the patient is allowed to return to normal use of the hand as soon as it is comfortable to do so, elevating the hand when at rest.

Outcomes

There is very little known about the natural history of carpal tunnel syndrome. The functional impairment in severe cases can be extreme and therefore treatment is indicated in order to relieve symptoms and to prevent permanent nerve damage and functional impairment. However, there is some evidence that this expected progression may not always occur, as shown in a review of the outcome at 6 years of those patients who were listed for CTR but cancelled their surgery. In this paper, improvement was seen in both those who cancelled their surgery and their matched controls who did have surgery, although the improvement was greater in the latter. Also, the rate of recovery is not known in the untreated group [20].

CTR is considered to be a very effective, satisfying and reliable operation, as 87 % of patients rate their outcome as good to excellent. However, in one study a return of symptoms in 57 % was observed at around 2 years later, although these were rarely of sufficient severity to cause the patient to seek further medical assistance [21]. In this same report it was noted that the number of patients involved in heavy occupational use of their hands dropped from 27 % of patients pre-operatively to 6 % post-operatively.

Outcomes are similar between open CTR and endoscopic CTR as shown by a randomised control trial of the two techniques, with the exception of return to work. This was on average 8 days earlier in the endoscopic CTR group, with the additional cost per patient totalling £98 [19] However, the patients undergoing open CTR were not instructed to return to full normal activity at 2 weeks, although this is now known to be an acceptable time frame for recovery (see above).

Complications of Treatment

Complications

Complications include haematoma, bleeding, infection, nerve damage, pillar pain and complex regional pain syndrome. A review of 186 patients who had undergone CTR by expert hand surgeons found 34 complications in 22 patients. These were incomplete division of the TCL in 12 cases (6 %), damage to the palmar cutaneous branch of the median nerve in 11 cases (6 %), complex regional pain syndrome in 4 cases (2 %), hypertrophic scarring, palmar haematoma and bowstringing of the tendons each in 2 cases (1 %) and adhesions of the flexor tendons in 1 case (0.5 %) [22]. These are acceptable figures, with no major transection of the median nerve. However, in a postal questionnaire of 708 hand surgeons in the USA, concerning complications they had treated (though not necessarily caused) from CTR in a 5 year period, there were 495 cases of laceration of the median or ulnar nerve or one of their branches and 88 tendon lacerations [23]. This finding shows that there are a significant number of severe complications from CTR in the wider setting, where not all the primary surgeons would have been specialist hand surgeons.

Recalcitrant and Recurrent Cases (Fig. 12.5)

Fig. 12.5
figure 5

Flow chart illustrating a suitable care pathway for failed CTR. *MRI may be helpful in differentiating these groups diagnostically [25]

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If a patient is found to still have symptoms at review, the history, examination and investigations must be revisited very carefully in order to determine the management pathway.

In a review of 200 cases requiring further surgical interventions the findings were of incomplete release in 54 %, tethering of the nerve in scar tissue in 23 %, circumferential fibrosis around and within the nerve in 8.5 %, nerve laceration in 6 %, tumour in 0.5 % and no specific cause found in the remainder [24].

Conclusions

Carpal tunnel syndrome is a common condition. In the vast majority of cases it is a straightforward clinical diagnosis, but expertise is required to exclude other pathologies in some cases.

A splint and/or steroid injection can be considered in mild cases of short duration.

Surgical release of the transverse carpal ligament is the only treatment with proven long term benefit. This can be done either endoscopically or open, depending on the patients requirements for return of function and the surgeon’s expertise.

Significant complications of carpal tunnel release are rare but can be severe.

Recurrent or recalcitrant cases need careful evaluation and treatment by a hand specialist.