P. R. Thomas, R. J. Saunders and K. R. Means Abstract Our purpose was to determine whether there was a significant difference in sensory recovery after digital nerve repair using loupe magnification or an operating microscope. We identified patients aged 21–75 who had primary proper digital nerve repairs at least 24 months before our study. A total of 12 patients with 13 digital nerve injuries repaired with loupe magnification and nine patients with 12 digital nerve injuries repaired using the operating microscope, agreed to return for assessment by a therapist blinded to treatment. We found no significant difference in sensory recovery between the two groups as measured by static two-point discrimination, moving two-point discrimination, and Semmes–Weinstein monofilament. There were also no significant differences in average Disabilities of the Arm Shoulder and Hand or visual analogue pain scores. Level of evidence: IV Keywords Digital nerve, loupe repair, operating microscope repair, sensory recovery Date received: 8 April 2014; revised: 18 September 2014; accepted: 25 September 2014
Primary minimal-tension repair using microsurgical techniques is currently the standard treatment for patients with proper digital nerve transection (Dvali and Mackinnon, 2007). Previous comparative studies have shown no difference in the results of repairs of the median and ulnar nerves done with the aid of loupes or the operating microscope (Marsh and Barton, 1987; McManamny, 1983). Bernstein et al. (2013) reported that 48% of members of the American Society for Surgery of the Hand in the southern states of the US used loupe magnification for digital nerve repairs. They also noted that although 78% of those who used loupes for repairs used 2.5–3.5× magnification, there were no comparative studies between the results achieved with this level of magnification and higher levels of loupe or operating microscope magnification. We examined our results using these two methods of magnification. Our null hypothesis was that there is no significant difference in recovery of sensibility between digital nerve repairs by surgeons using loupe magnification or the operating microscope.
We obtained institutional review board approval for the study from our research institute and the study was funded by an internal grant. We searched our computer database of Current Procedural Terminology (CPT) codes for patients with digital nerve repair codes 64831 and 64832, carried out between 2005 and a minimum of 24 months before our study, which started in January 2012. We limited our search to those patients who had surgery at our centre’s main hospital where operating microscopes are readily available. We also searched our database for CPT codes with a known association with proper digital nerve injury, such as Zone II flexor tendon repair. All surgeons who did the repairs were accredited hand The Curtis National Hand Center, MedStar Union Memorial Hospital, Baltimore, MD, USA Corresponding author: K. R. Means Jr, c/o Anne Mattson, The Curtis National Hand Center, MedStar Union Memorial Hospital, 3333 North Calvert Street, #200, Baltimore, MD 21218, USA. Email: [email protected]
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The Journal of Hand Surgery (Eur)
surgeons who had completed hand/microsurgery fellowships and used 2.5–3.5× magnification loupes when operating.
Power analysis A power analysis was done before patient recruitment. We assumed a two-tailed normal distribution with equal variances between means with a standard deviation of static and moving two-point discrimination of 2 mm, based on previous studies (Rinker and Liau, 2011;Weber et al., 2000). We determined that 12 nerve repairs per group would provide an 80% chance of detecting a 25% difference between groups at the 95% confidence level. This equates to a one-grade difference in objective sensory outcomes using the American Society for Surgery of the Hand and American Society of Hand Therapists guidelines, i.e. poor-to-fair, fair-to-good (Bushnell et al., 2008).
Inclusion criteria We reviewed the operative reports for all of the patients identified by our initial search to confirm that the surgeon carried out primary end-to-end repair of at least one complete proper digital nerve transection. We recorded whether the repair(s) were done with loupe or operating microscope magnification. Because this was a retrospective study, the choice of the repair method was at the discretion of the surgeon. All digital nerves in the same patient were repaired with the same technique. Patients with associated tendon or bone injuries were eligible for inclusion. Patients had to be able to provide informed consent and comply with an assessment by a certified hand therapist. We also had to be able to directly contact the patient for them to be eligible and we offered them $75 and free parking if they agreed to return for assessment. The patients had the choice of whether or not to participate in the study.
Exclusion criteria We excluded patients who had revascularization or replantation of the same digit as the digital nerve repair (Sanmartin et al., 2004). We also excluded patients whose nerve injury occurred by a crush or avulsion mechanism, those who had an end-to-side nerve repair, had any other nerve injuries proximal to the proper digital nerve repair, or had a history of peripheral neuropathy.
Patients A total of 22 patients who met the inclusion/exclusion criteria were contacted and 21 patients with 25 digital
nerve injuries agreed to return. The patient who did not agree to return lived several hundred miles away from our centre. Thirteen of the nerve injuries (12 patients), were repaired with loupe magnification, whereas in 12 nerve injuries (nine patients) operating microscope magnification was used.
Digital nerve designations We designated each injured and repaired proper digital nerve as the ‘cut’ nerve. We designated the corresponding digital nerve on the uninjured contralateral digit as the ‘contralateral’ nerve. We designated an uncut nerve on the injured finger, if present, as the ‘uncut’ nerve. We designated the matching nerve on the uninjured contralateral digit as the ‘uncut contralateral’ nerve. This allowed assessment for possible cross-over reinnervation. Two of the patients, one in each group, had complete transection and repair of both digital nerves in a single digit but did not require revascularization. We removed these patients from the comparison of uncut and uncut contralateral sensory testing, but they were kept for the comparison of cut versus contralateral nerves.
Outcomes measures Our primary outcome was the sensory testing results for the repaired proper digital nerves. An independent, certified hand therapist who was blinded to the method of digital nerve repair carried out the assessments. Sensation was assessed in the autonomous distribution of the repaired and uninjured digital nerve(s) in the injured digit(s) and in the digital nerves of the same digit(s) in the uninjured hand. Static and moving twopoint discrimination (S2PD and M2PD, respectively) were determined using the standard protocol of the American Society for Surgery of the Hand and the International Federation of Societies for Surgery of the Hand (Dellon, 1978). The Semmes–Weinstein monofilament (SWM) threshold for each of these digital nerve distributions was measured (Bell-Krotoski, 1999). The MacKinnon–Dellon Disk-criminator (North Coast Medical, Arcata, CA) was used to test the patients’ S2PD and M2PD and the results were recorded in mm. For the purposes of statistical analysis, if a patient was unable to discriminate two points at any distance tested, they were assigned an S2PD and M2PD value of 16 mm. We did this so that patients who had an ‘infinite’ 2PD would still be included in the statistical analysis so as to not falsely improve the results. SWM testing was done with the five-piece Touch-Test Sensory Evaluators (North Coast Medical, Arcata, CA) and the results converted to a point value based on the Rosén and Lundborg Physical Impairment Summary Scale for statistical analysis (MacDermid,
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Thomas et al. Table 1. Demographic, DASH, and VAS pain score results.
Average age of patient at time of repair (years) Male (%) Average months after surgery Smoker (%) DASH score VAS pain score
47 (SEM 5; range 21–75)
43 (SEM 4; range 24–66)
61 48 (SEM 6; range 24–86) 15 7.1 (SEM 2.6; range 1–27) 0.2 (SEM 0.2; range 0–2)
75 53 (SEM 4; range 37–75) 8 8.9 (SEM 2.0; range 1–22) 0.4 (SEM 0.3; range 0–2)
0.31 0.43 0.43 0.43 0.45
DASH: Disorders of Arm, Shoulder and Hand; VAS: visual analogue scale; SEM: standard error of the mean
2005; Rosén et al., 2000). The maximum point value of this scale is 5 and the minimum is 0. Each patient also completed a demographic questionnaire, a 10-point visual analogue score (VAS) for pain (Hicks et al., 2001), and a Disabilities of the Arm Shoulder and Hand (DASH) (Hudak et al., 1996) questionnaire.
Statistical methods We analysed demographic data by either the unpaired t-test or Chi-square test as appropriate. Statistical analysis for our primary outcomes was by a two-way analysis of variance and designated the two factors as: loupe versus microscope repair; cut versus contralateral nerves; or uncut versus uncut contralateral nerves as repeated measures.
Results Eight of the nine patients in the microscope group had associated tendon injuries, whereas seven of the 12 patients in the loupe group had associated tendon injuries, and one in the loupe group had an associated middle phalangeal fracture. The longest time from injury to surgery for the patients was about 1 week; most patients had surgery the same day as the injury or the following day. The operative records revealed that surgeons typically did the operating microscope repairs about 1 week after injury on an isolated injury, whereas loupe-assisted repairs were done as emergency procedures, along with multiple reconstructive procedures in acutely injured patients. Demographic data, DASH, and VAS pain score results for the loupe and microscope repair group are summarized in Table 1. There were no significant differences between the loupe and microscope groups for any of the demographic variables or patient-rated outcomes.
S2PD results S2PD values for the cut digital nerves in both the loupe and microscope groups were significantly
worse than those for the respective contralateral nerves (p
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