The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 85, Issue 11

Scientific Articles | November 01, 2003

Accuracy and Reliability of Torque Wrenches Used for Halo Application in Children

Lawson A.B. Copley, MD¹; John P. Dormans, MD²; Matthew D. Pepe, MD³; Virak Tan, MD⁴; Richard H. Browne, P¹

¹ Texas Scottish Rite Hospital for Children, 2222 Welborn Street, Dallas, TX 75219. E-mail address for L.A.B. Copley: lawson.copley@tsrh.org
² Department of Orthopaedic Surgery, The Children's Hospital of Philadelphia, 34th and Civic Center Boulevard, Wood Building, 2nd Floor, Philadelphia, PA 19104
³ 2500 English Creek Avenue, Building D, Egg Harbor Township, NJ 08234
⁴ Overlook Hospital, Medical Arts Center, 99 Beauvoir Avenue, Suite L02, Summit, NJ 07901

View Disclosures and Other Information

In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from DePuy/Acromed/Bremer (L.A.B.C, J.P.D, and M.D.P.). None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Investigation performed at The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2003 Nov 01;85(11):2199-2204

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Abstract

Background: Halo ring and vest application in children requires torque wrenches capable of delivering a spectrum of torque values ranging from 0.11 to 0.68 N-m (1 to 6 in-lb). Published evaluations of torque wrenches commonly used in adults have shown that the measured torque values were within 10% of the target torque in only 64% of trials. The objective of the present study was to evaluate the accuracy, reliability, and interobserver variability of halo wrenches capable of applying the lower torque levels commonly used in children.

Methods: Torque wrenches from four distributors (Bremer, Jerome Medical, Mountz, and PMT) were tested with use of a calibrated torque-meter. Five wrenches of each type were tested by a single observer, with fifty trials performed at six different torque settings (0.11, 0.23, 0.34, 0.45, 0.57, and 0.68 N-m). One wrench of each type was then tested by two additional observers at a torque setting of 0.34 N-m, with each observer performing fifty trials per wrench.

Results: The measured torque value was within 10% of the target value in 69.2% of the 6400 trials, including 50.7% of the trials performed with the PMT wrench, 51.8% of those performed with the Bremer wrench, 84.5% of those performed with the Mountz wrench, and 90% of those performed with the Jerome wrench. Significant variability (p < 0.05) was found between at least two, and as many as five, wrenches of the same variety at each of three torque settings used for comparison (0.23, 0.45, and 0.68 N-m). Significant interobserver variability (p < 0.05) was found between at least two observers during testing of the Jerome and Mountz wrenches, but no significant differences were shown between observers during testing of the PMT and Bremer wrenches.

Conclusions: The Jerome and Mountz wrenches are more accurate and reliable at low torque settings than the PMT and Bremer wrenches are. Variability among different wrenches from the same manufacturer may be seen with any of the wrenches studied.

Clinical Relevance: An optimum technique of halo pin insertion in children should avoid the problems of overtightening, which may lead to skull penetration, and undertightening, which may lead to halo dislodgment. To reduce the rate of complications associated with halo use in children, the methods of halo application should be standardized. This may be accomplished, in part, by utilizing the most accurate and reliable torque wrenches available.

Figures in this Article

Halo application in children is influenced by skull thickness in the safe parietal and frontal locations where pins are placed^1-4. In small children eight to ten pins may be placed at low torque settings ranging from 0.11 to 0.56 N-m (1 to 5 in-lb), whereas in adolescents four pins may be applied at higher torque settings ranging from 0.68 to 0.90 N-m (6 to 8 in-lb) in the same manner in which they are applied in adults.

Although no definite standards have been established for insertion torque in pediatric patients, some authors have suggested clinical guidelines. Mandabach et al.⁵ suggested using 0.56 N-m (5 in-lb) of torque per pin for children older than four years and a torque (in inch-pounds) that approximates the age of the patient (in years) for younger children. Mubarak et al.⁶ described the application of a halo device in a seven-month-old patient, with each pin being applied to finger tightness. With such a spectrum of proposed insertion torque values for the application of halo fixation in pediatric patients, there is a need for wrenches that are capable of delivering a broad range of torque values ranging from 0.11 to 0.68 N-m (1 to 6 in-lb).

Torque wrenches that are used for halo application in adults have been investigated with respect to accuracy and reliability. Garfin et al.⁷ demonstrated that five commercially available devices withstood 1600 cycles of testing at torques of 0.68 and 1.14 N-m (6 and 10 in-lb) and performed within 8% of the original calibration after cyclic testing as compared with 4% prior to cyclic testing. Smith et al.⁸ demonstrated the inaccurate nature of torque wrenches used in adults at settings ranging from 0.68 to 0.90 N-m (6 to 8 in-lb). Those authors reported that the measured torque value was within 10% of the desired torque value in only 64% of trials and that there was significant variability in torque values delivered by any given wrench when different observers used the same wrench (p < 0.05)⁸.

In an effort to evaluate the accuracy and reliability of halo wrenches used for pediatric patients, we tested four commercially available torque wrenches that have torque settings in the spectrum that is used for halo application in children. We performed comparisons between different wrenches of the same design as well as between different observers using the same wrench.

Materials and Methods

Materials and Methods | Results | Discussion | References

Four models of commercially available torque wrenches, with manufacturer-specified settings capable of delivering torque values ranging from 0.11 to 0.68 N-m (1 to 6 in-lb), were identified for testing. Five wrenches of each model were obtained from the halo distributor or wrench manufacturer. There were two varieties of wrenches. Adjustable wrenches were available from PMT (Chanhassen, Minnesota), DePuy/Acromed/Bremer (Raynham, Massachusetts), and Mountz (San Jose, California). A spring-loaded wrench was available from Jerome Medical (Moorestown, New Jersey) (Fig. 1). Specific details on each type of wrench are listed in Table I. In our product search, we found no commercially available singleuse, shear-off devices for use at the lower values of torque that were evaluated in this study.

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The torque wrenches that were used in the present study included, from left to right, the PMT, Bremer (Tohnichi), Jerome (Seekonk), and Mountz wrenches.

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TABLE I Torque Wrench Descriptions and Specifications

Halo Distributor	Wrench Manufacturer	Model	Type	Certification	Cost Estimate
Bremer	Tohnichi (Northbrook, Illinois)	12 RTD-A	Adjustable	±3%	$142
Jerome	Seekonk (Seekonk, Massachusetts)	SL-12	Spring	±3%	$83
PMT	PMT (Chanhassen, Minnesota)	1201-8	Adjustable	±6% of 20% of the full scale	$175
N/A*	Mountz (San Jose, California)	EMT 20-160	Adjustable	±6%	$260

N/A = not applicable.

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TABLE I Torque Wrench Descriptions and Specifications

Halo Distributor	Wrench Manufacturer	Model	Type	Certification	Cost Estimate
Bremer	Tohnichi (Northbrook, Illinois)	12 RTD-A	Adjustable	±3%	$142
Jerome	Seekonk (Seekonk, Massachusetts)	SL-12	Spring	±3%	$83
PMT	PMT (Chanhassen, Minnesota)	1201-8	Adjustable	±6% of 20% of the full scale	$175
N/A*	Mountz (San Jose, California)	EMT 20-160	Adjustable	±6%	$260

N/A = not applicable.

Torque Accuracy and Reliability of Each Wrench Variety

Each of the twenty wrenches was tested by a single investigator (L.A.B.C.) with use of a commercially available digital torque-meter (Electronic Torque Tester, model 4001-0-ETT; Consolidated Devices, City of Industry, California). The manufacturer's written certification verified that this device has a calibrated accuracy to ±0.5% of the observed value. The torque-meter was rigidly mounted to a base platform and was fitted with adapters to accommodate the various bit pieces of each wrench to be tested (Fig. 2).

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The Electronic Torque Tester (Consolidated Devices, City of Industry, California).

The wrenches were separately hand-tested with fifty trials performed at each of six torque settings (0.11, 0.23, 0.34, 0.45, 0.57, and 0.68 N-m), for a total of 6000 trials. The values were recorded from the torque-meter to the nearest tenth in N-cm and subsequently were converted to N-m.

Accuracy was evaluated with use of the definition suggested by Smith et al.⁸ in their study of adult torque wrenches, in which an accurate reading was considered to be one within ±10% of the target torque value. Reliability was evaluated with use of the standard deviation.

An analysis of variance using the Tukey multiple-comparison test was performed to compare each variety of wrench with the other three in order to detect significant differences in measured torque. Each variety of wrench also was evaluated for accuracy by comparing the measurements at each torque setting with the target torque with use of the one-sample t test.

Comparison of Wrenches Within Each Wrench Variety

The five wrenches from each distributor were then compared with each other on the basis of the results of trials performed at three separate torque settings (0.23, 0.45, and 0.68 N-m). These values were selected to provide a range of values from the low, middle, and high regions of the torque spectrum. An analysis of variance was performed with use of the Tukey multiple-comparison method to compare all pairs of each specific type of wrench.

Interobserver Reliability

One wrench of each type was then tested by two additional investigators at a chosen torque value of 0.34 N-m (3 in-lb); each investigator performed fifty trials per wrench, for a total of 400 trials. The setting of 3 in-lb was determined by selecting the torque value at which the five wrenches demonstrated the highest collective number of trials that fell within ±10% of the target torque during the single-observer portion of the study. An analysis of variance using the Tukey multiple-comparison test was performed to determine significant differences between the three observers using the same wrench.

Results

Materials and Methods | Results | Discussion | References

Torque Accuracy and Reliability of Each Wrench Variety

The measured torque value was within 10% of the target value in 69.2% of the 6400 trials. Individual types of wrenches demonstrated a spectrum of performance in this regard, with the measured value being within 10% of the target value in 50.7% of the trials performed with the PMT wrench, 51.8% of those performed with the Bremer wrench, 84.5% of those performed with the Mountz wrench, and 90% of those performed with the Jerome wrench. The standard deviation also varied between the different types of wrenches as follows: 0.38 N-m for the PMT wrench, 0.35 N-m for the Bremer wrench, 0.013 N-m for the Jerome wrench, and 0.012 N-m for the Mountz wrench.

Comparison of the mean measured torque of each type of wrench against the target torque resulted in highly significant differences (p < 0.0001) in all but three instances: testing of the Jerome wrench at 0.11 N-m (p = 0.0015), testing of the Mountz wrench at 0.23 N-m (p = 0.486), and testing of the PMT wrench at 0.57 N-m (p = 0.1588). Figure 3 illustrates the relationship of the mean measured torque for each of the wrenches to the target torque value.

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Graph showing the mean measured torque (N-m) plotted against the target torque wrench settings. The data points represent composite data from 250 trials of five different wrenches of each type.

Comparison of Wrenches Within Each Wrench Variety

Significant differences (p < 0.05) were noted between individual wrenches of the same design for at least two of five, and as many as five of five, wrenches at each of the three torque settings tested. On the average, there were significant differences (p < 0.05) between three of five wrenches within each group at each torque setting tested.

Interobserver Variability

Significant differences (p < 0.05) were identified between two of three observers for the Jerome wrench and three of three observers for the Mountz wrench at the torque setting of 0.34 N-m. No significant differences were noted between observers during testing of the PMT and Bremer wrenches. Table II illustrates the analysis of the agreement between observers with regard to the percentage of trials in which the measured torque fell within 10% of the target torque (0.34 N-m).

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TABLE II Percentage of Trials in Which Measured Torque Value was Within 10% of Target Torque Value*

Wrench Type	Observer 1	Observer 2	Observer 3
Bremer	18%	4%	8%
Jerome	98%	90%	100%
PMT	68%	22%	94%
Mountz	94%	98%	92%

The target torque value was 0.34 N-m.

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TABLE II Percentage of Trials in Which Measured Torque Value was Within 10% of Target Torque Value*

Wrench Type	Observer 1	Observer 2	Observer 3
Bremer	18%	4%	8%
Jerome	98%	90%	100%
PMT	68%	22%	94%
Mountz	94%	98%	92%

The target torque value was 0.34 N-m.

Discussion

Materials and Methods | Results | Discussion | References

Following the introduction of the halo ring and vest in 1959 as an immobilization device for postpolio paralytic deformities of the cervical spine in adults, the indications for halo use gradually expanded to include immobilization of the cervical spine in children affected by trauma, instability, or deformity^9,10. Dormans et al. reported a 68% prevalence of problems with the halo ring and vest in children¹¹, whereas Garfin et al. reported a rate of only 36% in adults¹². While most problems associated with halo use in children are minor, such as pin loosening, superficial infection at the pin sites, or pain at the pin sites, more serious problems such as cerebral abscess formation, halo dislodgement, and failure to properly immobilize the cervical spine have been reported^11,13-17. The rate of complications along with the nature of the pediatric skull, with its variable thickness and the presence of fontanelles and open sutures in very young children, raises concerns about the methods of application of invasive devices for immobilization of the pediatric cervical spine.

The present study demonstrates that the halo wrenches presently available for pediatric application have a spectrum of reliability and accuracy. Compared with the research previously reported by Smith et al.⁸, our data suggest a similar degree of inaccuracy for the entire group of wrenches tested. However, the Mountz and Jerome wrenches performed better than did the PMT and Bremer wrenches as indicated by a higher percentage of trials in which the measured torque was within 10% of the target torque and a lower magnitude of standard deviation. Our results differ from those reported by Smith et al.⁸ in that the PMT wrench, which had shown the best performance when tested at 0.68 and 0.9 N-m, demonstrated inferior performance at the low torque settings that we studied.

Although a highly significant difference was shown between the measured torque and the target torque for almost all wrenches at each torque setting tested, the differences most likely reflect the large number of trials performed. Such differences are not necessarily an indication that these wrenches cannot be effective for the clinical application of halo pins in children. We believe that the percentage of trials in which the measured torque was within 10% of the target torque is likely to be a more realistic assessment of the clinical usefulness of a torque wrench.

As illustrated in Figure 3, the plotted values of the Jerome and Mountz wrenches most closely approximated the target torque line, whereas the Bremer and PMT wrenches showed greater divergence from the target torque. For the PMT wrench, the divergence was above the target torque value at the three lowest torque settings (0.11, 0.23, and 0.34 N-m), whereas for the Bremer wrench the values remained above the target torque at all settings. This may represent a safety concern in the use of those wrenches when the intention is to avoid skull penetration. The purposeful choice of wrenches with superior accuracy and reliability at low torque settings may be a feasible means of reducing error during halo application in children.

The present study suggests that the spring wrench may have a design advantage compared with the adjustable wrenches. The adjustable wrenches, however, might have certain advantages despite their inferior performance in the present study. Because direct visual observation of the wrench face (a requirement with the spring wrench) is not necessary during the application of torque with adjustable wrenches, the latter may be more readily utilized in situations in which direct vision is limited. Adjustable wrenches also provide a palpable sense when the desired torque has been reached, thus giving the clinician a clear sense that the end point has been achieved. Occasionally, adjustable wrenches might be the only type available in a clinical setting because of the fact that they are supplied with the specific halo system that is being used at a given hospital. Under such circumstances, it would be beneficial to have specific product knowledge of the nature that we have demonstrated in this study. Otherwise, clinicians might be misled by the assumption that all of these devices perform in an equivalent fashion with respect to accuracy and reliability.

All of the wrenches tested in the present study demonstrated performance below the reported certifications of accuracy provided by the manufacturers (Table I). The percentage of trials in which the measured torque was within the accuracy limits proposed by each company was 35.8% for the Bremer wrench, 36.3% for the PMT wrench, 39.6% for the Jerome wrench, and 57.1% for the Mountz wrench. The apparent improvement in performance of the Mountz and PMT wrenches compared with that of the Bremer and Jerome wrenches was largely a factor of the increased accuracy limits reported by the manufacturers of the Mountz and PMT wrenches versus those of the Bremer and Jerome wrenches (±6% compared with ±3%).

Surprisingly, significant differences were noted between observers during testing of the Mountz and Jerome wrenches but not during testing of the PMT and Bremer wrenches. The information in Table II suggests that significant differences between observers would have been more likely to occur during testing of the PMT and Bremer wrenches because a greater spectrum of wrench accuracy was demonstrated between observers during testing of those wrenches than was demonstrated during testing of the Mountz and Jerome wrenches. However, when the means were compared, the statistical differences yielded results that were counterintuitive. This finding may be explained, in part, by the large number of trials performed per wrench, which tended to normalize the means of the relatively inaccurate wrenches.

Further halo modifications specific for children are likely to be arbitrary unless specific standards and uniformity are used^8,18-24. The present study showed that the uncertainty introduced by a single pediatric halo wrench used by a single observer may be important. Extrapolating this finding to multiple observers using a variety of wrenches and methods of application might increase the prevalence of complications in children. Furthermore, such circumstances make it less easy to prove that simple interventions such as adjusting the torque during halo pin insertion will have as beneficial an outcome in children as has been suggested in adults²⁵.

The results of the present study support the use of the Jerome (Seekonk) wrench when halo application in children involves torque settings ranging from 0.11 to 0.68 N-m (1 to 6 in-lb). Use of the Mountz wrench is also supported if an adjustable wrench is to be used.

Our previous research involving a fetal calf skull model established that an improved halo pin design and perpendicular pin insertion may result in increased stability of the pin-bone interface^18,19. The purpose of establishing standardized methods of halo application is to improve invasive cervical spine immobilization in children. More information is needed, specifically with respect to the relationship between skull thickness and the optimum torque needed in order to safely achieve a maximum load at the pin-skull interface without causing pin penetration. In order to conduct this testing, it will be necessary to utilize the most accurate and reliable wrench along with a halo pin specifically designed for pediatric application¹⁹.

References

Materials and Methods | Results | Discussion | References

Garfin SR, Botte MJ, Centeno RS, Nickel VL. Osteology of the skull as it affects halo pin placement. Spine.1985;10: 696-8.10696 1985 [PubMed][CrossRef]

Garfin SR, Roux RD, Botte MJ, Centeno R, Woo SL. Skull osteology as it affects halo pin placement in children. J Pediatr Orthop.1986;6: 434-6.6434 1986 [PubMed][CrossRef]

Loder RT. Skull thickness and halo-pin placement in children: the effects of race, gender, and laterality. J Pediatr Orthop.1996;16: 340-3.16340 1996 [PubMed][CrossRef]

Wong WB, Haynes RJ. Osteology of the pediatric skull. Considerations of halo pin placement. Spine.1994;19: 1451-4.191451 1994 [PubMed][CrossRef]

Mandabach M, Ruge JR, Hahn YS, McLone DG. Pediatric axis fractures: early halo immobilization, management and outcome. Pediatr Neurosurg.1993; 19: 225-32.19225 1993 [PubMed][CrossRef]

Mubarak SJ, Camp JF, Vuletich W, Wenger DR, Garfin SR. Halo application in the infant. J Pediatr Orthop.1989;9: 612-4.9612 1989 [CrossRef]

Garfin SR, Botte MJ, Woo SL, Nickel VL. Reliability after repeated use of a torque screwdriver employed for halo pin fixation. J Orthop Res.1985;3: 121-3.3121 1985 [PubMed][CrossRef]

Smith MD, Johnson LJ, Perra JH, Rawlins BA. A biomechanical study of torque and accuracy of halo pin insertional devices. J Bone Joint Surg Am.1996;78: 231-8.78231 1996 [PubMed]

Kostuik JP. Indications for the use of the halo immobilization. Clin Orthop.1981;154: 46-50.15446 1981 [PubMed]

Perry J, Nickel VL. Total cervical-spine fusion for neck paralysis. J Bone Joint Surg Am.1959;41: 37-60.4137 1959

Dormans JP, Criscitiello AA, Drummond DS, Davidson RS. Complications in children managed with immobilization in a halo vest. J Bone Joint Surg Am.1995;77: 1370-3.771370 1995 [PubMed]

Garfin SR, Botte MJ, Waters RL, Nickel VL. Complications in the use of the halo fixation device. J Bone Joint Surg Am.1986;68: 320-5.68320 1986 [PubMed]

Baum JA, Hanley EN Jr, Pullekines J. Comparison of halo complications in adults and children. Spine.1989;14: 251-2.14251 1989 [PubMed][CrossRef]

Cooper PR, Maravilla DR, Sklar FH, Moody SF, Clark WK. Halo immobilization of cervical spine fractures. Indications and results. J Neurosurg.1979; 50: 603-10.50603 1979 [PubMed][CrossRef]

Glaser JA, Whitehill R, Stamp WG, Jane JA. Complications associated with the halo-vest. A review of 245 cases. J Neurosurg.1986;65: 762-9.65762 1986 [PubMed][CrossRef]

Murphy MJ, Wu JC, Southwick WO. Complications of halo fixation. Orthop Trans.1979;3: 126.3126 1979

Rockswold GL, Bergman TA, Ford SE. Halo immobilization and surgical fusion: relative indications and effectiveness in the treatment of 140 cervical spine injuries. J Trauma.1990;30: 893-8.30893 1990 [CrossRef]

Copley LA, Pepe MD, Tan V, Sheth N, Dormans JP. A comparison of various angles of halo pin insertion in an immature skull model. Spine.1999;24: 1777-80.241777 1999 [PubMed][CrossRef]

Copley LA, Pepe MD, Tan V, Dormans JP, Gabriel JP, Sheth NP, Asada N. A comparative evaluation of halo pin designs in an immature skull model. Clin Orthop.1998;357: 212-8.357212 1998 [PubMed][CrossRef]

Garfin SR, Lee TQ, Roux RD, Silva FW, Ballock RT, Botte MJ, Katz MM, Woo SL. Structural behavior of the halo orthosis pin-bone interface: biomechanical evaluation of standard and newly designed stainless steel halo fixation pins. Spine.1986;11: 977-81.11977 1986 [PubMed][CrossRef]

Letts M, Girouard L, Yeadon A. Mechanical evaluation of fourversus eightpin halo fixation. J Pediatr Orthop.1997;17: 121-4.17121 1997 [CrossRef]

Letts M, Kaylor D, Gouw G. A biomechanical analysis of halo fixation in children. J Bone Joint Surg Br.1988;70: 277-9.70277 1988

Perry J. The halo in spinal abnormalities: practical factors and avoidance of complications. Orthop Clin North Am.1972;3: 69-80.369 1972 [PubMed]

Triggs KJ, Ballock RT, Lee TQ, Woo SL, Garfin SR. The effect of angled insertion on halo pin fixation. Spine.1989;14: 781-3.14781 1989 [PubMed][CrossRef]

Botte MJ, Byrne TP, Garfin SR. Application of the halo device for immobilization of the cervical spine utilizing an increased torque pressure. J Bone Joint Surg Am.1987;69: 750-2.69750 1987

Topics

torque ; halo-vest immobilization

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Lawson A.B. Copley, John P. Dormans, Matthew D. Pepe, Virak Tan, Richard H. Browne; Accuracy and Reliability of Torque Wrenches Used for Halo Application in Children. The Journal of Bone & Joint Surgery. 2003 Nov;85(11):2199-2204.

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