ORIGINAL ARTICLE

 

Comparative study between endoscopic technique by a proximal port and mini palmary incision in the surgical treatment of carpal tunnel syndrome

 

 

Eduardo A.R. Pereira^I; Rames Mattar Jr.^II; Ronaldo J. Azze^III

^IMaster
^IIHead, Hand Group
^IIIChairman

Correspondence

 

 

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Summary

The authors present a prospective study comparing two surgical techniques for carpal tunnel release. A minimal - incision open decompression⁽³⁾ is compared with an endoscopic release⁽²⁾, that utilizes only a single proximal portal. There were operated on, 28 wrists in 28 patients, with clinical signs and EMG changes consistent on idiopathic carpal tunnel syndrome, that failed under previous conservative treatment. They were randomized into two groups , undertaken surgical treatment, either by endoscopic release or by open decompression. Grip strength (measured by dynamometric), sensitivity (measured by Semmes-Weinstein monofilaments), presence of pain and paresthesia, date of return to activities of daily living and complications were evaluated pre-operative and at 1, 2, 4, 6, 12 weeks after surgery. After 12 months average follow up, the results indicated that this proximal portal endoscopic technique can be safely performed, showing advantages over open conventional method, in terms of sooner return of grip strength, date of return to activities of daily living, and less incidence of pillar pain. No differences in paresthesia resolution, sensibility improvement or complications incidence were found.

Key Words: Comparative study; Surgical decompression; Carpal tunnel syndrome; Endoscopic.

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INTRODUCTION

Carpal tunnel decompression through division of carpal transverse ligament by an open technique is used as election technique for treatment of patients with CTS not responding to conservative treatment (use of splints, NSAIDs, local steroid infiltration).

However, according to Kuschner⁽¹¹⁾ this is not a totally harmless method, with several reports of post operative complications as symptoms persistence, hypertrophic painful scar, strength reduction for a long period; these factors avoid palmary pressure thus delaying the maximal functional use of the hand and a long period away of work.

These data prompted studies looking for less morbidity treatment methods. Several endoscopic techniques of decompression were so presented^(1,5,15) selectively dividing the carpal transverse ligament, leaving intact other anatomical structures (palmary skin, subcutaneous tissue, palmary aponeurosis, short palmary muscles). Several works confirm the advantages of this new technique in regard of less postoperative pain, strength recovery and early return to daily life activities, with a small number of associated complications⁽¹⁶⁾.

However, this fact is not accepted by all, and there is controversy mainly in regard of safety and efficacy of endoscopic methods⁽¹⁹⁾.

The aim of this study is to evaluate and to compare, in a prospective and randomized mode, the results found in the treatment of CPS by open mini-palmary-incision method⁽³⁾ and endoscopic technique using a proximal portal⁽¹⁾.

 

CASES AND METHODS

Twenty-eight wrists of 28 patients with clinical and ENMG diagnosis of idiopathic carpal tunnel syndrome underwent surgical treatment and postoperative evaluation. They were divided into two groups of 14 patients in a randomized way from March,1997 to January, 1999 at IOT HC-FMUSP.

Were excluded patients with diabetes or hypothyroidism, previous wrist surgery, psychiatric diseases, chronic renal impairment needing dialysis, presence of clinical signs of trapezius-metacarpal osteoarthrosis of the thumb, history of the evaluated wrist and other causes of CTS.

Average age in the endoscopic group was 53.6 years, ranging from 30 to 83 years, while in the open group was 52 years, ranging from 29 to 81 years. All 28 patients but one in the open group were female.

All patients were right handed but one single female patient in the open group who was left handed. In the endoscopic group the surgery was performed in the right wrist in eight patients and in the left wrist in six patients. In the open group, the right wrist was operated eight times while the left one, five.

Most of the patients, 64.28% in the endoscopic group, and 57.14% in the open group, respectively, only performed housekeeping activities.

The average time of symptoms duration before surgery was of 43.43 months in the endoscopic group and 38.93 months in the open group. The follow-up time was in average 12 months for both groups.

In 75.86% of the patients both sides were involved. In these cases, only the wrist the patient chose to be of more intensive symptoms was operated. All patients had nocturnal pain and fall of objects from the hand. Tinnel and Phalen tests were positive in 100% of the cases.

Six patients in the endoscopic group, and seven in the open one presented muscle hypotrophy.

Both groups underwent intravenous sedation and local anesthesia at distal forearm portion, proximal to the incision place (5.0 ml) and inside the carpal tunnel (3.0 ml), driving the needle in an oblique direction from the same point in proximal skin. Compression with esmarch band from distal to proximal was applied, and a pneumatic tourniquet insufflated with 250 mmHg pressure.

The endoscopic group underwent carpal tunnel decompression by the technique described by Agee et al.⁽¹⁾, whith an optical system with a blade activated by a trigger mechanism introduced through a proximal portal.

The transversal 2.0 cm incision is performed in one of the wrist flexion folds, between the ulnar carpal flexor and the palmaris longus. A little piece of antebrachiopalmar fascia is open in an "U" shape turned to distal, for introduction of the equipment. The transverse carpal ligament (TCL) is identified and a dilator is introduced. Following the ulnar limit of the carpal tunnel is found with a hamatum probe, always to the hamatum. Following the ulnar border of the carpal tunnel is delimited by means of a hamatum´s probe, always introduced against the hamatum. A synovial retractor is then applied from below to above inside the tunnel, removing any eventual synovitis that may interfere with viewing. The jacket of the mechanism with the optical system and the blade is introduced under the TLC and through the video monitor were identified the transversal fibers of the TLC. The distal border of the TLC can be delimited by combination of monitor view and external palpation, displacing the fat distal to the TLC. Then the trigger is released allowing the blade to raise. The material is then pulled towards proximal in the axis of the fourth finger, keeping against the TLC and the hamatum with the blade viewed at the monitor, this way dividing the TLC from distal to proximal (Figure 1a, 1b).

 

 

 

 

Open technique (Mini-palmary incision)

A 2.5 cm incision is performed in the skin (Figures 2a and 2b) over the TCL in the palmary region parallel to thenal fold, 5 mm ulnar to interthenal depression, not crossing the wrist proximal flexion fold and Kaplan's distal line. Aponeurosis layer is blunt dissected up to TLC is visible, characterized by its transversal fibers, parallel to the incision. Limits of the TLC are identified and after a small hole is open with a scalpel in ulnar portion of TLC and a small cannular probe is introduced under the TLC and parallel to median nerve, and TLC is divided with a #15 blade scalpel, the cutting edge upwards, proximal and distally, respecting distal boundary (Kaplan's line).

 

 

Patients who underwent endoscopic decompression remained with a plaster splint for one day, while those with open method used immobilization for 14 days. The patients were re-evaluated at one, two, four, six and twelve weeks follow-up in regard to need of analgesics, paraesthesia vanishing, palmary grip strength return to preoperative level (with Jamar dynamometer), sensitivity (using two-point discrimination and Semmes-Weinstein's monofilaments), time to retake daily life activities and presence of complications.

 

RESULTS

There was no statistically significant difference between the groups in regard of age, professional activity, time of symptoms, presence of thenal muscles hypotrophy, pain in postoperative period, postoperative grip strength, postoperative sensitivity, using Semmes-Weinstein's monofilaments.

All patients in this study reported symptom relief after the surgical treatment. In 100% of them paraesthesia symptoms and nocturnal pain vanished just after the surgery.

In a visual analogical zero to ten pain scale the endoscopic group rated in average 9.29 the preoperative pain and 1.71 by the 12^th postoperative week, while the open group rated in average 9.21 the preoperative pain and 3.50 by the 12th postoperative week. (Graphic 1).

 

 

Regarding time needed to get back the preoperative grip strength, endoscopic group took in average 4.93 weeks (around 35 days) while the open group took in average 11.14 weeks (around 78 days). (Graphic 2).

 

 

It was observed by means of Semmens-Weinstein's monofilaments in the preoperative period that both groups had an average reduction of protective sensitivity (Graphic 3a), presenting a postoperative recovery however keeping a light tactile restriction. (Graphic 3b).

 

 

 

 

Time to resume daily life activities averaged 2.93 weeks (about 21 days) in the endoscopic group and 8.42 weeks (about 59 days) in the open group (Graphic 4).

 

 

Presence of pain in ulnar edge of the palmary region after the surgery, called ulnar pillar pain, was found in four endoscopic (28.57%) and 10 open (71.43%) group patients (Graphic 5).

 

 

COMPLICATIONS

In our comparative study it was not found any intra-operative complication. No patient needed reoperation for incomplete TCL division. Transient neuropraxis of median nerve branch to the ring finger was found in two (14.28%) patients of endoscopic group and in two (14,28%) of the open group. One patient in the open group developed a superficial infection successfully treated with oral antibiotic.

 

DISCUSSION

Nevertheless there is a series of literature references commending the endoscopic techniques ^(2,5,16) there is not yet a consensus regarding the best surgical decompression technique ^(6,19).

According to Kurschner et al ⁽¹¹⁾ division of structures that are superficial to TCL (skin, subcutaneous tissue, palmary aponeurosis) is inherent to open decompression. Healing of these tissues located in the hand palm may result in sensitivity at the scar place that will rest for a while, what can prevent palmary grip. Thus, even when we completely succeed in open decompression, the time of functional impairment and the long lead time for recovery may be inconvenient for the patient. According to Kelsey et al ⁽¹⁰⁾ it is estimated that two thirds of hand surgery costs in USA are related to the time of impairment.

We agree with Phalen ⁽¹⁷⁾ who states that open decompression of the carpal tunnel, when well indicated has a high success rate.

However, even in absence of eventual complications, which are inherent of any surgical treatment, the morbidity related to strength loss, hand palm pain and functional incapacity cannot be ignored, and may, according to Gellman et al⁽⁷⁾ last for up to three months.

There are, even nowadays, many controversies on surgical approach to CTS.

We agree with Mackinnon et al⁽¹²⁾ who recommend not performing concomitant neurolysis for adding no additional benefit for the patient. In our opinion, TCL reconstruction, as proposed by Jakab et al⁽⁹⁾ in order to avoid flexor tendons sub dislocation during wrist flexion, should not be used as a routine since, according to Szabo ⁽¹⁹⁾ it involves a much larger dissection, when a short-term immobilization can avoid this complication. In endoscopic decompression, however, preservation of volar to TCL structures prevent the risk of flexor tendons sub dislocation, including making unnecessary postoperative immobilization.

We stand by Hanssen and Amadio's⁽⁸⁾ standpoint when stating that tendon synovectomy does not affect the final result of carpal tunnel decompression, and is linked to a higher incidence of infection.

Another point addressing our attention was the conclusion by Chow⁽⁵⁾ stating TCL is poorly innervated, while palmary skin has a rich nervous network, explaining the sensitivity of the palmary scar.

Surge of several endoscopic techniques for dividing TCL was carefully observed by several authors^(4,6) in regard to cost of the instruments and fear of complications.

In endoscopic release of carpal tunnel there are some differences in regard to other endoscopic methods: the place of the operation is a non-extensible synovial hole and not an elastic cavity as joints, abdomen and uterus. The view is through air and liquid.

We agree with North and Kaul ⁽¹⁴⁾ that this procedure should not be confused with arthroscopy through a skin hole, and that due to the complex local anatomy and disastrous possible complications, we should rigorously stick to the topographic landmarks for succeeding in the endoscopic technique, with an exact location of hamatum's hook, flexors retinaculum, superficial palmary arch and axis of the ring finger, that, at the moment of the TCL division avoid the instrument entering the Guyon's canal, potentially leading to vascular and nervous injuries.

It was not found any interference in intraoperative view as well as compliant of pain or intolerance to the pneumatic tourniquet, demonstrating local anesthesia to be safe for surgical decompression of CTS.

We elected as open technique the one recommended by Bromley ⁽³⁾ due to the good results with this technique in our service, and for agreeing that incisions crossing the proximal limit of the wrist flexion palmary flexion skin fold lead to longer postoperative recovery time. We should additionally avoid eventual injuries to palmary cutaneous branch of median nerve, for correct incision positioning.

As endoscopic technique we elected the one through a proximal port as recommended by Agee et al ⁽¹⁾, mainly because safety related issues. The blade only divides from distal to proximal and is protected by a dull plastic piece which serves as a retractor of neighbor anatomical structures.

It is possible for the surgeon, through a window in the plastic piece, to perfectly view the TCL (identified by its characteristic transversal fibers), precisely identify the distal limit of TCL in its transition into fatty tissue (through a combination of hand palpation and optic view), confirm blade raise, monitor TCL division and to assure its release.

Division of TCL is performed from distal to proximal, making the method very safe. In our opinion, any method recommending a proximal to distal division takes a considerable risk in regard of anatomical structures that are distal to TCL.

By introducing an instrument, it is important to be sure that this is actually under the TCL. The presence of flexor tendons under antebrachiopalmar fascia indicates the carpal canal topography. Absence of flexor tendons under the instrument may mean a wrong exploration of Guyon's canal.

The hamatum probe serves for finding the ulnar limit of carpal tunnel. It is convenient to keep the instrument always against the hamatum for avoiding any inadvertent pressure over common digital nerve to third and fourth fingers.

The presence of synovitis in three patient of the endoscopic group (21.43%) impaired the vision, however did not prevent that, after a synovial retractor was used, TCL fibers were recognized. We agree with Tsai ⁽²⁰⁾ that is mandatory to only divide CTL when accordingly seen, conversely we should be ready to migrate to an open decompression.

Postoperative pain measurement is always a challenge. We decided to use an analogical visual pain scale before the surgery and by the 12^th postoperative week. Nevertheless it is a subjective method, we found a significantly lower level of pain amongst patients in the endoscopic group, thus confirming a higher degree of satisfaction among these patients.

The resulting grip strength loss after carpal tunnel decompression is a common issue bringing great difficulties to the patient. Several theories try to find an explanation: Richman et al ⁽¹⁸⁾ supported by MRI, relate the paresis to carpal tunnel volume increase; TCL division leads to a widening of palmary arch, changing the strengths of thenal and hypothenal muscles that are inserted in TCL. Other theories, according to Menon ⁽¹³⁾ relate this weakness to a possible sub-dislocation of flexor tendons, or to pain in hypothenal region, called "ulnar pillar pain".

In general, our results are similar to the findings by Agee et al ⁽²⁾. The endoscopic group had a significantly faster return to preoperative grip strength levels (about five weeks), while the open group had a lead-time about 12 weeks, similarly to Gellman et al ⁽⁷⁾. This is an expressive average difference of 7 weeks (42 days), an important period of functional impairment endoscopic method allow to avoid. In our opinion this can be attributed to keeping structures above TCL intact.

The high incidence of bilateral involvement prevented the use of the contra lateral side as a control for palmary grip strength.

Protective sensitivity reduction, that was common for both groups before surgical treatment in according to the symptoms attributed to CTS, and, even though both methods lead to an important improvement, there wasn't, after 3 months, an statistically significant difference between the compared surgical techniques, what is according to the findings by Palmer et al. We should stress that recovery in both techniques in average was not complete and the patients remained with a slight reduction of tactile sensitivity. This is an important point, since return of sensitivity prognosis may be related to time of compression of the nerve and the patient's age. We should advise the patient that the surgery frequently aims to stop progression of the disease.

We elected to evaluate the time for returning to daily life activities as a morbidity index, once it is correlated to the functional status of the hand. We considered that returning to work, a parameter used in several studies is not trustful, because it is dependent on the kind of job and the moral integrity and desire of each individual.

Regarding complications, that is a fact concerning several authors making them skeptic in regard to endoscopic CTS decompression methods, endoscopic technique was shown to be as safe as open technique. The incidence of complications was also lower than in the open group, however the small number of complications prevented an statistical study.

We did not find in our series any case of symptoms persistence that could result from incomplete carpal tunnel decompression.

The presence of pain in the ulnar pillar region at hand palm was a constant finding in the open group (71.42%), clearly superior to the findings in the endoscopic group (28.57%). This is of extreme importance for it prejudices the use of palmary pressure in the local, delaying the functional use of the hand.

One of the most feared complications of the open technique is the injury of the cutaneous branch of the median nerve, which is responsible for innervation of interthenal region of the hand palm. This complication was not found in our study, most probably due to a faithful adherence to anatomical parameters for determination of the incision location.

Cadaver studies by Watchmaker et al ⁽²²⁾ found both thenal and hypothenal folds, as well as the ring finger axis, have a wide range of variations and fail to precisely locate the safest place for open technique incision. The author suggests that in open decompression it should be used the deepest point between the thenal and hypothenal muscles, that he called interthenal depression. The cutaneous branch of the median nerve is in average located 5 mm radial to this depression (ranging from zero to 2 mm), thus, it can be considered as safer to place an incision five millimeters ulnar to the interthenal depression, extending towards the third interdigital space.

The incidence of temporary hypoesthesia at radial aspect of ring finger (14.28%) in the endoscopic group may be explained by a neuropraxis resulting from inadvertent instrument pressure over the common digital nerve, stressing the need of keeping the instrument close to the radial aspect of the hamatum and directed towards the ring finger.

We should be careful with the risk factors related to decompression of the carpal tunnel: bad view due to bleeding of synovitis, presence of anatomical abnormalities, inexperience of the surgeon, badly planned incision, or deviation from the technique standards.

After this study was performed, that gave us opportunity to extensively experience and depth our knowledge on carpal tunnel syndrome, we agree with Urbaniak et al ⁽²¹⁾ that the biggest problem with treatment of this disease is related to misdiagnosis and surgical indication problems.

Endoscopic technique, nevertheless related to higher technology demands and being instrumental dependent, has shown to be very safe with significant short term advantages.

Maybe the future will bring decompression techniques of carpal tunnel even less invasive, that allow to view all structures inside carpal tunnel.

A better understanding of the pathophysiology will contribute for the emergence of treatments acting on biochemical and hormonal areas, avoiding the median nerve compression development, that leads to carpal tunnel syndrome.

 

CONCLUSIONS

The endoscopic decompression technique through the proximal portal allows a recovery of palmary grip strength and return to daily life activities earlier than the observed in the mini-palmary incision technique.

Regarding paraesthesia resolution, or sensitivity improvement, there were no differences between proximal portal endoscopic technique and mini-palmary incision technique.

Endoscopic decompression performed through the proximal portal has a lower incidence of pain in ulnar pillar in comparison to the mini-palmary incision technique.

 

REFERÊNCIAS BIBLIOGRÁFICAS

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Correspondence to
Eduardo A.R. Pereira
Av. Albert Einstein, 627, sala 1204, Morumbi
CEP 05651-901 São Paulo, SP
E-mail: edupera@attglobal.net

Work performed at Instituto de Ortopedia e Traumatologia of Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, IOT HC, FMUSP.
Trabalho recebido em 27/07/2002
Aprovado em 20/11/2002