Introduction

Following surgical repair of a hand trauma injury, patients may describe an altered or heightened sensation to stimuli and are diagnosed with hypersensitivity. Hypersensitivity to touch is a sensory disorder affecting the perception of tactile stimuli. Hypersensitivity is synonymous with hyperalgesia, an increased sensitivity to stimuli, which encompasses allodynia and hyperesthesia. Allodynia is used to describe when pain is felt from a stimulus that normally does not provoke pain, i.e., light touch causing pain. In hyperesthesia, the quality of tactile sensation is not altered [1]. In our practice, it was noted that hand trauma patients were more likely to complain post operatively of hypersensitivity symptoms when their wounds had been closed with a particular suture material. The aim of this study was to investigate the prevalence and risk factors of hypersensitivity in the post-operative patient that has undergone an emergency surgery for trauma involving the hand or forearm, and to see if there was a correlation to suture material types.

Methods

This single-centre retrospective observational study identified patients who received an emergency hand operation under the care of the plastic surgery department over a period of 5-month consecutive period. Ethical approval for this trial was obtained from Peninsula Health’s research office (Reference No. QA/65319/PH-2020–221,629(v2)). Patient data was collected from the hospital’s electronic medical records. Operation reports were used to record suture material used for closure, indication for the operation, structures found to be injured, and the surgical repair performed. Hypersensitivity was identified from the post-operative outpatient clinic notes in both the plastic surgical clinic and the concurrent hand therapy clinic. In this observational study, the diagnosis was made by either the clinic doctor or hand therapist based on the patients’ description of their symptoms. Hypersensitivity was recorded when it was reported in post-operative dressings clinics or hand therapy clinics post-operatively. Patients who did not have their wounds closed were excluded from the study. Patients who did not attend a follow-up appointment were excluded from the study.

Data analysis was performed with GraphPad Prism statistical software. Mann–Whitney U tests and Fisher exact tests were performed to compare patient and surgical factors. Odds ratios were used to determine any significant risks of hypersensivity. A p value of 0.05 or less was considered to be statistically significant.

Results

Over a 5-month period, two hundred and seventy-three emergency hand or forearm operations were performed by the plastic surgery department at Frankston Hospital. Forty-two patients did not have closure of their wounds resulting in those patients being excluded from the study. A further thirty-one patients were excluded due to inadequate follow-up. 184 patients were included in the study. The wounds were all as a result of trauma and therefore varying in dimensions and anatomical locations on the hand and/or forearm. The wounds were all repaired by the plastic surgery team in the hospital, either by a consultant plastic surgeon, or under their supervision. The location of the hypersensitivity varied but was either directly related to the wound or distal to the site of injury.

Chromic gut (CG) (chromic catgut, Ethicon, Raritan) sutures were used for 53 (29%) patients. For the remaining 131 patients, Ethilon (nylon) (Polyamide, Ethicon, Raritan) was used for 67 (36%) patients, Vicryl-Rapide (VR) (Polyglactin 910, Ethicon, Raritan) was used for 51 (28%) patients, and the remainder received either monocryl (Poliglecaprone 25, Ethicon, Raritan), fast gut (fast absorbing plain gut, Ethicon, Raritan), or prolene (polypropylene, Ethicon, Raritan) sutures, a combination of sutures, or staples (Fig. 1). A variety of suture material was recorded in our study but using nylon, VR, monocryl, and CG would all be considered standard practice in Australia for closing wounds.

Fig. 1
figure 1

Breakdown of materials used for wound closure

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Mean age (± SD) for all patients was 41.3 (± 20.9) and 134 (72.8%) patients were male. 30 (16.3%) patients reported hypersensitivity post-operatively. CG sutures were used in 53.3% of the patients who experienced hypersensitivity compared to 24.0% of patients who did not develop hypersensitivity (Fig. 2). Relative to the number of cases using each suture type, 30.8% of patients with CG sutures developed hypersensitivity, compared to 6.5% with nylon and 11% with VR (Fig. 3). Overall, patients who had CG used in their surgery were 2.82 (95% CI 1.49–5.37), p = 0.0015) times more likely to develop hypersensitivity post-operatively than patients who did not have CG used. There were no statistical differences in age or gender between the CG and non-CG groups.

Fig. 2
figure 2

Number of hypersensitivity patients using the varying suture materials

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Fig. 3
figure 3

Percentage of patients developing hypersensitivity relative to suture usage

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10 patients required a repair of at least one nerve. Those 10 patients that had a nerve repaired were 3.48 (95% CI 1.70–7.14, p = 0.0007) times more likely to develop hypersensitivity independent of the sutures used. If a patient had a nerve repaired and CG suture used, they were 6.50 (95% CI 4.62–9.13, p < 0.0001) times more likely to develop hypersensitivity. Age, gender, flexor tendon repair, extensor tendon repair, and fractured bone were not identified as risk factors for developing hypersensitivity post-operatively.

Discussion

Hypersensitivity is an unfortunate potential outcome in patients undergoing surgery following traumatic injuries to their hands. In our population of hand and forearm emergency plastic surgery patients, 1 in 6 experienced hypersensitivity post-operatively. More notable is that the use of CG sutures statistically significantly increased the risk of hypersensitivity by a factor 2.82 on its own, or 6.5 when combined with nerve repair surgery. This apparent issue with CG has not been described before in the current literature regarding hand trauma surgery; however, in a randomised trial of episitomy repairs, VR compared with CG was shown to cause less discomfort and have less wound healing problems [2]. CG sutures have been shown to induce a greater inflammatory response compared to plain gut sutures and monofilament non-absorbable synthetic sutures, such as nylon. This inflammatory reaction may be responsible for the increased risk of hypersensitivity; however, no obvious signs of inflammation were recorded in our study to support this hypothesis. Reports of allergic reaction to CG have been published previously [3].

In our practice, CG is a widely used suture material for its strength, absorbable properties, and secure knot tying. Some countries no longer use the material due to concerns with the transfer of prion diseases. CG suture is a variant of plain catgut sutures, whereby the suture is treated with chromic acid salts, typically 0.5% chromium dioxide (CrO2). This process effectively doubles the time the suture can maintain its tensile strength. Proteolytic enzymes are responsible for the process of absorbing chromic catgut sutures and are naturally found in higher concentrations in locations such as the stomach and cervix. CG maintains its tensile strength for 21 days in comparison to 14 days for VR. Suture absorption absorption however is reportably much longer in CG (90 days) in comparison to VR (42 days) (Ethicon website — ethicon.com). In an animal model, VR and CG both produced a similar inflammatory response; however, VR was undetectable in the tissues after 60 days, whereas CG was still present at 120 days [4]. In our practice nylon sutures would routinely be removed 10-14 days post operatively. Therefore, one potential mechanism we propose for the increased hypersensitivity is that the delayed dissolving of CG suture material interferes with patient participation in hand therapy exercises. Patients are reluctant to touch wounds and scars when sutures are still in place and so do less of the important tactile stimulation and massage exercises early on in their recovery.

Cold hypersensitivity has been recognised as a long-term consequence of nerve injury or digital replant surgery [5]; however, there are no accurate incidence rates for hypersensitivity recorded in the literature. Additionally, hypersensitivity is a subjective symptom which can lead to difficulties in identification and diagnosis. Hypersensitivity warrants prompt attention especially for hand surgery patients as it can impair functional activity and recovery. Moreover, awareness of the risk factors can aid clinicians to prevent and promptly identify hypersensitivity. Hand therapists managing patients with hypersensitivity may utilise a variety of treatment modalities such as cold therapy, heat therapy, ultrasound, laser, transcutaneous electrical nerve stimulation (TENS), systematic desensitisation, vibration, and compression/distraction. Wrapping the effected digits in a thin adherent polyurethane film may improve patient symptoms [6]. Hypersensitivity is treated in our unit with hand therapy to de-sensitise the area, along with simple analgesia. The addition of a neuromodulating drug like pregabalin or gabapentin would often be considered.

As a retrospective cohort study, the true incidence of post-operative hypersensitivity in our patient group may be higher due to inadequate screening and incomplete follow-up. A further limitation of this study is that the severity of hypersensitivity was not recorded; however, on review of the literature, the authors have been unsuccessful in identifying a previous validated scale or grading system for hypersensivity in the hand or forearm. Future research investigating suture materials and the severity of hypersensivity, along with the functional impact on the patient in the form of a randomised prospective trial, is planned to give more clarity on this common complication.

Conclusions

Our findings of increased hypersensitivity may prompt hand surgeons to reconsider using CG sutures, especially in digital nerve repair cases where hypersensitivity will significantly worsen patient outcomes.