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Eur J Cardiothorac Surg 2000;18:656-661
© 2000 Elsevier Science NL

Muscle sparing thoracotomy: a biomechanical analysis confirms preservation of muscle strength but no improvement in wound discomfort

Northern Ireland Regional Thoracic Surgical Unit, Royal Victoria Hospital, Grosvenor Road, Belfast BT12 6BA, UK

Received 18 May 2000; received in revised form 31 August 2000; accepted 25 September 2000.

Corresponding author. Tel.: +44-28-9089-4773; fax: +44-28-9031-4159
e-mail: kieran.mcmanus{at}royalhospitals.n-i.nhs.uk

	Abstract

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
Objectives: This study compares the posterior auscultatory triangle thoracotomy incision (muscle sparing) with full posterolateral thoracotomy (where latissimus dorsi muscle is always cut across its full width), with particular attention to the difference between latissimus dorsi muscle strength, post operative pain and chronic wound related symptoms. Methods: Ten patients who had undergone auscultatory triangle thoracotomy (ATT) at least 1 year previously were matched with ten patients who had undergone posterolateral thoracotomy (PLT). Each pair was matched for age, sex, dominant hand, side of the operation, time since operation and presence or absence of history of previous muscle training. Latissimus dorsi muscle strength was assessed by testing the shoulder adduction strength through an arc of 90–0° using isokinetic technique. Early post-operative pain was assessed indirectly by calculating the analgesic requirement in the first 5 post-operative days. A subjective assessment of chronic post-thoracotomy pain was made using a questionnaire presented to the patients at the time of muscle testing. Variability of the torque curves, recorded as coefficient of variance at the time of muscle strength testing, provided objective measurements of chronic pain. Data were analysed using two sample t-tests. Results: All patients reported at least one chronic post-thoracotomy symptom. There was no significant difference between the two groups in terms of acute or chronic wound pain and other long term wound related symptoms. Shoulder adduction strength was 24% greater in ATT than PLT (95% confidence limits=1–43%, P=0.04). Conclusions: All thoracotomy patients have long term wound related symptoms. This situation is not improved by performing a muscle sparing incision. However thoracotomy through the triangle of auscultation can preserve latissimus dorsi strength which is compromised in a posterolateral thoracotomy incision. We therefore recommend that a muscle sparing thoracotomy be considered for patients where preservation of muscle strength is deemed important, providing the operation is not compromised due to inadequate access.

Key Words: Thoracotomy • Muscle sparing incisions • Muscle strength testing • Post thoracotomy pain

	1. Introduction

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
Posterolateral thoracotomy (PLT) is a standard incision for non-cardiac, thoracic surgical procedures. It provides good access and can easily be extended if necessary. However, it involves cutting at least one (latissimus dorsi) and sometimes many (trapezius, rhomboids, serratus anterior) of the major chest wall muscles. Experience has shown it to be one of the most painful surgical incisions [1–3].

Various authors have described muscle sparing thoracotomy [4–10] and made claims for reduced post operative pain [3,8,10–13], decreased long term neuralgia [2], preservation of an accessory muscle of respiration [8,14], conservation of muscle strength and shoulder girdle movement (particularly in manual labourers) [4,6,10–12] and better cosmetic results [5,6,10]. Preservation of these major muscles also allows their subsequent use for transposition flaps if necessary [15]. It is generally conceded by most authors that muscle sparing incision provides somewhat inferior access to the chest when compared with a full posterolateral thoracotomy [3,7,10,11]. An increased incidence of seroma and wound haematoma has also been reported following muscle sparing incisions [3,4,10,12,14]. Of the described muscle sparing incisions, in only the thoracotomy through auscultatory triangle (ATT) is no muscle cut. In other described muscle sparing incisions, when a lateral incision is used, slips of serratus anterior usually need to be elevated from the ribs, and the anterolateral and vertical axillary incision both require splitting of the serratus muscle in line with its fibres.

This study was designed to compare the posterior ATT as described by Horowitz and colleagues [4] with full PLT where latissimus dorsi is always cut across its whole width, with particular attention to the difference between latissimus dorsi muscle strength, post operative pain and chronic wound problems.

The consistent difference between PLT and ATT is division or sparing of the latissimus dorsi respectively. It was postulated that patients undergoing PLT would suffer a loss of shoulder adduction strength as a result of division of the latissimus dorsi, this muscle being the major contributor (with contribution from pectoralis major and teres major) to shoulder adduction through an arc of 90–0°.

	2. Materials and methods

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
2.1. Patient selection
Ten patients who had undergone ATT at least 1 year previously (mean time since operation=37 months; range=12–60 months) were matched with ten patients who had undergone PLT over the same period. Each pair was matched for age (difference of <10 years), sex, dominant hand, side of the operation, time since operation (difference of 10 months) and presence or absence of history of previous muscle training (Table 1). In the ATT group, the operations performed were bullectomy and pleurectomy (6), decortication (2), segmentectomy (1) and metastasectomy of lung (1). In PLT patients, bullectomy and pleurectomy (3), decortication (2), lobectomy (2), excision of oesophageal diverticulum (1), repair of para oesophageal hernia (1) and excision of neurilemoma (1) were the operations performed.

2.2. Incisions
2.2.1. Auscultatory triangle thoracotomy
The skin incision traverses the auscultatory triangle in line with the fifth intercostal space. After exposing the trapezius and latissimus by subcutaneous dissection the triangle of fascia is reflected superiorly. The serratus fascia is divided along the posterior border of the muscle and the intercostal muscles are divided extensively along the superior border of the sixth rib. This rib was not divided though the posterior costovertebral ligament was divided. In addition to the standard rib retractor a second identical retractor is placed at a right angle to retract the paraspinal and latissimus dorsi muscles. (Fig. 1)

View larger version (56K): [in this window] [in a new window]   Fig. 1. Auscultatory triangle Thoracotomy

2.3. Chest drains
Apical and basal chest drains were placed through separate lower intercostal incisions except in the case of the segmentectomy in the ATT group where a single apical drain was used, and the excision of oesophageal diverticulum in the PLT group where a single basal drain was used.

2.4. Muscle strength testing
Shoulder adduction strength was tested using KIN-COM 125-E Plus (Chattanooga Group Inc., TN, USA; http://www.chattgroup.com) muscle strength testing machine. This machine tests muscle strength using isokinetic technique so that the maximum strength of a muscle is tested throughout the range of action of that muscle. This is the recommended method of muscle strength testing for clinical trials [16]. Before testing each patient was familiarised with the machine. The patients then underwent supervised pre-test stretching exercises followed by two warm up test cycles on the machine. After a 3 min rest period, three consecutive readings were taken during which the subject performed shoulder adduction through an arc 90–0° (concentric) and 0–90° (eccentric) using isokinetic technique. The best of the three efforts were taken as the final recording. High demand instructions were used in all cases to encourage the patient to perform with maximum effort. Muscle strength was tested bilaterally and strength of the operated side was compared with the non-operated side (shoulder adduction strength ratio, SASR).

2.5. Assessment of early post-operative pain
Early post operative pain was indirectly assessed by the analgesic requirement in the first 5 post-operative days. All patients received intravenous morphine (by patient controlled analgesia) in addition to dihydrocodeine and diclofenac sodium in varying combinations. It is known that 1 mg of parental morphine is equivalent to 20 mg of dihydrocodeine in its analgesic activity [17]. Nuutinen et al. [18] suggested that 75 mg of diclofenac and 10 mg morphine given parentally are equipotent doses for clinical purpose. While studying the morphine sparing effect of diclofenac sodium after abdominal surgery, Hodsman et al. [19] also demonstrated that intramuscular administration of 150 mg diclofenac sodium in first 24 h post operatively produced a morphine sparing of 21 mg. When used enterally, the analgesic efficacy of diclofenac is reduced to half due to first past metabolism [20]. We therefore assume that 75 mg of diclofenac given orally and 5 mg of parental morphine can be considered equivalent. Based on these data, a cumulative analgesic score (CAS) was calculated by awarding 1 point for every mg of morphine used, 3 points for each dose of oral dihydrocodeine (60 mg) and 5 points for each dose of oral diclofenac sodium (75 mg) administered in the first 5 post-operative days.

2.6. Assessment of long term wound discomfort
A subjective assessment was made according to the questionnaire in Table 2. Scores awarded for the five answers were aggregated to reach a wound-related symptom score (WSS), a higher score indicating more wound discomfort. At the time of muscle testing, the variability of the torque curves was recorded as coefficient of variance (CV). The CV provided objective measurements, which have been reported as a useful measure of chronic pain, especially low back pain [21]. We used the ratio of CV on the operated side versus the non-operated side as a surrogate measure of long term wound discomfort. An incision with more severe long-term scar discomfort will have a higher CV ratio.

Muscle strength ratio (SASR) and CV ratios (operated/non-operated side) were converted to their natural logs before the analysis to decrease the effect of skewing and thus obtain a more normal distribution of data. In the multivariate regression analysis the incision group, age, sex, time since operation and the relationship of the incision to the dominant side were tested as explanatory variables. The natural logs of muscle strength ratio (SASR), natural log of CV ratios, CAS and WSS were the dependent variables.

	3. Results

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
Infection or wound dehiscence occurred in none of the patients. One ATT was complicated by seroma. None of the ATTs required conversion to PLT. In this series no rib fractures were noted at the time of surgery or on postoperative chest radiograph.

All patients suffered to varying degrees from chronic post-thoracotomy pain (CPP). Though 25% of patients did not report this as ‘wound pain’, they each reported some other wound related symptom (Table 3). Therefore in all the 20 patients WSS was higher than the minimum possible of zero. It is also noteworthy that 50% of the patients had taken at least one dose of analgesics for wound discomfort within 2 weeks prior to the muscle testing.

Multivariate analysis showed that age, sex, and time since operation were not significant factors in determining either shoulder adduction strength or acute or chronic wound discomfort.

	4. Discussion

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
Reduced post operative wound pain [2,3,9,11–13] and preservation of major chest wall muscles [4–6,8,9,11,12,14] are the two main proposed benefits of muscle sparing thoracotomy, both of which may contribute to improved post operative pulmonary functions. Our findings do not support the thesis that muscle sparing thoracotomy results in reduced early and/or late post-operative pain. In our patients, the difference in both early post-operative and long-term wound pain in the two groups was minor, though the sample size is too small to say that no difference exists. However, ATT did have a significant advantage in preservation of latissimus dorsi strength.

The lack of difference in early and late post thoracotomy pain has also been reported in comparisons of PLT and the axillary muscle sparing thoracotomy [14,15]. Most of the post-thoracotomy pain is likely to originate from pressure, crush and stretch inflicted upon the intercostal nerves by the blades of the rib spreader [2] and nerve entrapment by pericostal sutures. Some pain may also come from trauma to paraspinal ligaments and muscles and small joints of the back. The incidence of these injuries is at least equal in both ATT and PLT or may actually be more severe in ATT as retraction may need to be increased to compensate for decreased exposure. Attention towards avoiding intercostal nerve damage, improvement in rib spreader design and avoiding excessive spreading of the ribs may be more effective in reducing post thoracotomy wound discomfort than choosing between muscle cutting or muscle sparing thoracotomy.

Only one patient reported drain site pain in our study. Paraesthesia affecting the area of skin incision and anterior chest wall above and medial to the incision was the commonest complaint. We found out that patients reported two distinct types of paraesthesia i.e. hypoaesthesia and hyperaesthesia, with little overlap between the two types. The distribution of paraesthesia was similar for both incisions. Two patients in the ATT group complained of diffuse unilateral chest pain, which they described as ‘sore lung’. One of these patients had a decortication for empyema while the other had two wedge resections of lung for pulmonary metastasis. Although we have no proof, we feel that this may be due to unusually extensive adhesion formation between the lung and the chest wall in these cases causing diffuse inwards traction on the chest wall. Whether occurrence of this symptom after an ATT in both cases is just a co-incidence is unknown.

The reported incidence of wound seroma varies from 11.8–23% with muscle sparing thoracotomy [12,14]. We encountered one such seroma (10%) in an ATT patient but as has been found by other authors [12], this resolved without any need for intervention.

Preservation of major chest wall muscles with the aim of preserving shoulder girdle movement and strength has repeatedly been described as an advantage of various types of muscle sparing thoracotomies [3–6,8–12,14]. There is however surprisingly little objective evidence for this as was also noted by Ginsberg [10]. Using a subjective grading system measured by their physical therapists, Hazelrigg et al. [12] concluded that there was no significant long term difference in muscle strength between PLT and muscle sparing thoracotomy. Landreneau [15] reported similar results when assessing shoulder dysfunction 1 year after operation. Using an isokinetic method of muscle testing, our study demonstrates better preservation of latissimus dorsi strength by ATT than PLT. This difference in latissimus dorsi strength is statistically significant despite the small numbers in the study. As the muscle strength testing was carried out at least 1 year after the operation, one can reasonably assume that this latissimus dorsi strength represents the final stable situation.

Preservation of muscle strength by ATT may be useful in young adults, manual workers, athletes (e.g. tennis players, golfers, and swimmers) particularly if the operation involves the dominant side. It is noteworthy that this is exactly the group of people in whom muscle sparing thoracotomy is technically difficult and exposure more limited due to bulky musculature as was also noted by Horowitz [4]. Age need not be a contradiction to ATT despite reports by other authors [6]. Not only is the incision easier to perform in the older patient due to decreased muscle bulk but preservation of chest wall muscles may improve post-operative respiration and mobility which is a frequent problem in this age group.

	5. Conclusions

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 
All thoracotomy patients have long term wound related symptoms. This situation is not improved by performing a muscle sparing incision. However thoracotomy through the triangle of auscultation can preserve latissimus dorsi strength which is compromised in a posterolateral thoracotomy incision. We therefore recommend that a muscle sparing thoracotomy be considered in patients where preservation of muscle strength is deemed important, providing the operation is not compromised due to inadequate access. Developments need to be made in the areas of rib retraction and intrathoracic visualisation during surgery to reduce long term post-thoracotomy wound pain.

	Acknowledgments

 
The authors thank Dr Michael Stevenson, Medical Statistican, Department of Epidemiology and Public Health and Epidemiology, Queen's University, Belfast, for his assistance with the detailed statistical analysis.

	References

Top Abstract 1. Introduction 2. Materials and methods 3. Results 4. Discussion 5. Conclusions References

 

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