SJS. Original Research Article. M. Manninen 1, T. Karjalainen 2, J. Määttä 1, T. Flinkkilä 1

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1 665544SJS / Epidemiology of flexor tendon injuriesm. Manninen, et al. research-article2016 Original Research Article SJS SCANDINAVIAN JOURNAL OF SURGERY Epidemiology of Flexor Tendon Injuries of the Hand in a Northern Finnish Population M. Manninen 1, T. Karjalainen 2, J. Määttä 1, T. Flinkkilä 1 1 Department of Surgery, Oulu University Hospital, Oulu, Finland 2 Department of Surgery, Central Hospital of Central Finland, Jyväskylä, Finland Abstract Background: Flexor tendon injuries cause significant morbidity in working-age population. The epidemiology of these injuries in adult population is not well known. The aim of this study was to describe the epidemiology of flexor tendon injuries in a Northern Finnish population. Material and Methods: Data on flexor tendon injuries, from 2004 to 2010, were retrieved from patient records from four hospitals, which offer surgical repair of the flexor tendon injuries in a well-defined area in Northern Finland. The incidence of flexor tendon injury as well as the gender-specific incidence rates was calculated. Mechanism of injury, concomitant nerve injuries, and re-operations were also recorded. Results: The incidence rate of flexor tendon injury was 7.0/100,000 person-years. The incidence was higher in men and inversely related to age. The most common finger to be affected was the fifth digit. In 37% of injuries also digital nerve was affected. The most common finger to have simultaneous digital nerve injury was the thumb. Conclusion: Flexor tendon laceration is a relatively rare injury. It predominantly affects working-aged young males and frequently includes a nerve injury, which requires microsurgical skills from the surgeon performing the repair. This study describes epidemiology of flexor tendon injuries and therefore helps planning the surgical and rehabilitation services needed to address this entity. Key words: Epidemiology; hand; incidence; tendon injuries; trauma Introduction The epidemiology of flexor tendon injuries of the hand is poorly studied in adult patients. The primary treatment is surgery in the majority of cases and obtaining good results remains a challenge to hand Correspondence: Teemu Karjalainen Department of Surgery Central Hospital of Central Finland Keskussairaalantie Jyväskylä Finland teemu.karjalainen@ksshp.fi Scandinavian Journal of Surgery 2017, Vol. 106(3) The Finnish Surgical Society 2016 Reprints and permissions: sagepub.co.uk/journalspermissions.nav DOI: journals.sagepub.com/home/sjs

2 Epidemiology of flexor tendon injuries 279 surgeons despite developments in repair materials and techniques (1). In addition, the post-operative rehabilitation requires both resources and expertise, and secondary expenses are substantial due to the long convalescence of working-aged patients Therefore, the economic burden of these injuries is significant to the society (2 3). Previously, an incidence of 4.8/100,000 has been reported in a study on musculoskeletal tendinous and ligamentous injuries of a well-defined adult population of Edinburgh Orthopaedic Trauma Unit (4). In the United Kingdom, a review of 4867 emergency patients with upper extremity traumas included only five flexor tendon injuries (5). In Finnish population, an epidemiological study revealed an annual incidence of 3.6/100,000 in pediatric patients (6). In the United States, an incidence of 33/100,000 personyears was found in all hand tendon injuries between 2001 and 2010 (7). The purpose of this descriptive population-based cohort study was to investigate the epidemiology of flexor tendon injuries in a welldefined adult population in Northern Finland. We also recorded the incidence of concomitant nerve injuries, which required microsurgical repair as well as complications, which necessitated specialized hand surgical care. Material and Methods Data Collection This is a descriptive retrospective population-based cohort study. Oulu is a city of 145,000 inhabitants in the region of Northern Ostrobothnia and the largest city in the northern part of Finland. The population is employed mostly in services, commerce, and industry. Construction and transport provide moderate employment while farming, forestry, and mining employ a clear minority. Oulu University Hospital is the primary public referral hospital for flexor tendon injuries for the city population as well as 20 municipalities surrounding it. Only the municipalities that refer patients solely to Oulu University Hospital, as opposed to other regional hospitals, were included in the study. Patients living outside the defined population but operated in the hospital were excluded from the study. The population at risk during the study period was 1,517,228 according to the Statistics Finland website. The same source was used to determine the age and sex distributions of the population at risk. Data on flexor tendon injuries, which occurred between 2004 and 2010, were retrieved from hospital s computerized patient records using both the International Classification of Diseases, 10th Revision (ICD-10) diagnosis codes and the registered procedure codes from the hospital s computerized patient administration system. In pilot data extraction, we noticed that some of the tendon injuries were coded as nerve injuries or hand wounds in the system. Therefore, to be able to catch all the potential cases for tendon injuries, the ICD-10 diagnosis codes included for the search were: S51.x and S61.x, (wounds of the hand and forearm), S56.x and S66.x (any sort of tendon injury in hand or forearm), S54 and S64.x (any sort of nerve injury in hand or forearm). X notes any possible number referring to different subcategories of injuries. The operation codes were NDLxx (xx noting any possible number combination for different tendon repair subcategories), ACC19, and ACC29 (peripheral nerve repairs). The search by operative codes was subtracted from the search by diagnosis codes to remove duplicates. During the time period, there were also three private clinics providing consulting and operative services in hand surgery. To obtain reliable and accurate epidemiological data on flexor tendon injuries, the patient records from these three private hospitals were recorded by similar patient administration system searches. The case files were then reviewed to identify flexor tendon injuries. Demographic data, mechanism of injury, the repair method, rehabilitation, and complications were recorded from patient files. Inclusion criteria for admittance for the study were age of 15 years or older with a simple flexor tendon injury of one or several flexor tendons with or without injury to digital nerves. Patients with partial lacerations, fractures, and critical arterial injuries requiring microsurgical repair were excluded. In the post-operative rehabilitation of flexor tendon injuries, the modified Kleinert s early controlled motion protocol was used. The wrist was supported with a dorsal blocking splint in 30 of volar flexion, the metacarpophalangeal joints in flexion, and the interphalangeal joints straight. Rubber band traction was used for passive flexion. Four weeks post-operatively, a dorsal blocking splint was modified to hold the wrist in neutral position and was used only at night as a protective splint. The wrist was mobilized during the day and rubber band traction was used with a wrist band. Normal activities were allowed weeks after the repair. In the case of simultaneous digital nerve injury, the affected finger was immobilized for 3 weeks. A major complication was defined as either a rupture of a repaired tendon or if the patient was offered secondary surgery because of adhesions. These complications in most cases lead to re-operation, but there were also exceptions when patients declined further surgery. Infections and other miscellaneous complications including skin scar contracture and post-operative pain syndromes were recorded as well. The crude and gender-specific incidences were calculated per 100,000 person-years for the study period. The age-specific incidence was calculated using 10-year intervals. The 95% confidence intervals were calculated with CIA (Confidence Interval Analysis for Windows). Permission to use patient records for the study was received from the hospital administration of the Oulu University Hospital. For private hospitals, permission to use patient administration data was received from the National Institute for Health and Welfare. Results There were 106 patients, 88 males (83%) and 18 females (17%), with flexor tendon injuries between the years 2004 and The population at risk was 1,517,228;

3 280 M. Manninen, et al. Fig. 1. The annual incidence rates and 95% confidence intervals of flexor tendon injuries per 100,000 person-years. thus, the incidence of flexor tendon injury was 7.0/100,000 person-years (95% confidence interval (CI), ). The gender-specific incidence rates for flexor tendon injuries were 11.6/100,000 person-years (95% CI, ) for men and 2.4/100,000 person-years (95% CI, ) for women. The mean age of the patients was 39 (standard deviation (SD), 16; range 15 72) years. The mean age for women was 44 (SD, 14; range 19 72) years and for men was 32 (SD, 6; range, 15 67) years. The annual incidence was decreasing during the study period (Fig. 1). The incidence rate was higher in men in all age groups for every year of the study period. The peak incidence rate was observed in the 15- to 19-year-old age group and was 16.1/100,000 person-years (95% CI, ). The incidence was inversely related to age (Fig. 2). There were 22 (20%) complications in this study. The most common complication was the development of adhesions in 12 cases (11%), followed by a re-rupture of a repaired flexor tendon in six cases (5.6%). There were two infections (1.9%). The two other complications were limited motion due to scar contracture. Five patients with no useful flexion after rehabilitation declined secondary surgery for adhesions. Thus, the rate of re-operation was 16%. Majority of the injuries were inflicted by a knife (41/106, 39%), broken glass (15/106, 14%), or other sharp object (26/106, 25%). Injury by blunt trauma was relatively rare (9/106, 8.5%). In all, 11 patients (10%) were reported to be under the influence of alcohol during the injury and the injury was work-related in 14 patients (13%). There were 59 (56%) injuries of the right hand and 47 (44%) of the left. The most common finger to be affected was the fifth digit (Table 1). In nine cases (8%), there was a simultaneous flexor tendon injury of two Fig. 2. The annual incidence rate of a flexor tendon injury per 100,000 person-years, according to age group. digits, and in two cases (2%), there was a simultaneous injury of three digits. In 39 patients (37%), there was simultaneous injury to either or both of the digital nerves (Table 1). In all, 35 (33%) of the tendons were lacerated in zone I, 59 (56%) in zone II, 1 (0.9%) in zone III, 3 (2.8%) in zone IV, and 7 (6.6%) in zone V. In one patient, the zone could not be defined reliably from the case notes. The repair technique could be defined in 102/106 cases. During the whole study period, there were 42 (40%) two-strand repairs, 32 (30%) four-strand repairs, 11 (10%) bone anchors or pull-out sutures, and 17 (16%) reconstructions. The frequency of two-strand repairs decreased and four-strand repairs increased

4 Epidemiology of flexor tendon injuries 281 Table 1 Flexor tendon injuries of the hand according to digit. Ray I II III IV V Tendons affected FPL 19 FDS 2 FDS 2 FDS 2 FDS 4 FDP 13 FDP 14 FDP 6 FDP 18 FDS + FDP 7 FDS + FDP 0 FDS + FDP 7 FDS + FDP 25 Digital nerve injuries NDR 3 NDU 4 Both 1 NDR 5 NDU 4 NDR 2 NDU 0 NDR 2 NDU 2 Digital nerve injuries (%) NDR 7 NDU 8 Both 1 FPL: flexor pollicis longus; FDS: flexor digitorum superficialis; FDP: flexor digitorum profundus; NDR: nervus digitalis radialis; NDU: nervus digitalis ulnaris. during the study period. In all, 68 (64%) of the injuries were repaired by a hand surgeon and 35 (33%) by hand surgery residents. Three injuries (2.8%) were repaired by consultant surgeons or surgical residents with no previous formal training in hand surgery. Discussion Our data show that the incidence of flexor tendon injury was 7.0/100,000 person-years (95% CI, ). The incidence of flexor tendon injury was highest among young men, and in all, a flexor tendon injury was rare among females. We also found that injuries decreased with increasing age. Based on the cumulative incidence calculated in this study, the estimation for annual number of flexor tendon injuries in the Finnish population over 15 years of age is 314 using the population data from the year The incidence had a decreasing trend during the study period. Our data do not explain the reasons for this. The mechanisms of injuries remained similar during the study period. We postulate that the decreasing trend might reflect improvement in occupational safety and automatization of industrial processes as well as shift toward more urban lifestyle and leisure time activities. There has been one previous population-based study, which reported all the tendon injuries in hand or wrist in a defined population in the United States (7). The authors found an incidence of 33/100,000 person-years, of which 43% were flexor tendon and 57% extensor tendon injuries. Our data collection period completely overlapped theirs. The incidence of flexor tendon injuries in our study was lower. This suggests that there are cultural differences in the incidence of flexor tendon injuries. A ratio of 1:5 between female and male patients was similar in both studies as was the proportion of alcohol-related injuries (10% vs 7%). Similar to us, they also found slightly decreasing trend in the overall incidence during the study period. The difference between genders in the incidence of flexor tendon injury is probably connected to the cause of injury. The most common injury mechanism was a knife cut or other sharp injury. The use of sharp tools is more common in predominately male professions and leisure activities. Our data doesn t explain why injuries are more common in younger population, but we assume that the reason could be higher exposure time and less cautious attitude toward sharp objects or both. According to the case notes, the patient was reported to be under the influence of alcohol during the injury in 11 cases out of 106 (10%). It is common practice that use of alcohol is not always reported in medical records unless its role affects the treatment. Therefore, the observed rate could slightly underestimate the involvement of alcohol in flexor tendon injuries. The distribution of injuries reflects the vulnerability of the outermost fingers of the hand. The most common fingers to be affected were the fifth digit and the second digit. Only 10% of the cases were multifinger injuries. Flexor tendon injuries are commonly seen in crush injuries as well, but crush injuries are a different entity and were excluded from this study. Digital nerve was affected in 39% of the injuries. Adequate repair of the digital nerve requires microsurgical skills and equipment. Therefore, we feel that the repairs should be performed only by those care providers who can offer microsurgical service. Our re-operation rate was higher than in previous studies (8 9) as well as the recent meta-analysis by Dy et al. (10). However, also similar rates of re-operation have been reported (11 12). When it comes to the rerupture rate of repaired flexor tendon, which was 5.6% of the tendons repaired, our results were similar to those from a recent review concerning flexor tendon repair and its complications (10). The higher reoperation rate compared with previous results (10) can be attributed to the development of adhesions, as tenolysis was more common than could be anticipated from previous studies (10). A passive rehabilitation protocol with a Kleinert-type splint was used throughout the study period. A passive flexion protocol causes very little tension in the tendon juncture and the ruptures typically occur only when the hand is used without the splint, against instructions (13). We suspect that the amount of adhesions in this study reflects an overly cautious post-operative protocol. The theoretical mechanical advantage of multi-strand repairs nowadays commonly used might be lost in passive protocols and result in adhesions. In addition, indications to perform tenolysis are not as easily defined compared to a re-rupture of a repaired tendon. The indication for tenolysis depends greatly on the demands and expectations of the patient as well as the surgeon. Furthermore, cultural and socio-economic factors probably play an important role too.

5 282 M. Manninen, et al. We acknowledge that the retrospective data collection is a limitation of this study. Injury mechanisms were mostly reported in sufficient detail, and the repair techniques were reported uniformly when hand surgeons repaired the tendon. The specific details of the rehabilitation are impossible to verify retrospectively from patient records. We are aware that not all patients who suffer a flexor tendon injury seek medical advice. However, the cost of the operation is covered by public health insurance in Finland, and therefore, we expect very low rate of completely neglected injuries. Furthermore, some of the population at risk might have injured themselves while traveling abroad. However, a simple flexor tendon injury without fracture or vascular injury is seldom considered a medical emergency, and often the definitive treatment apart from closing the wound is delayed until the patient returns home. Patients who injure themselves in another city in Finland are consistently referred to their own healthcare district to receive treatment. Our data, collected from a Northern Finnish population, are probably also valid for the rest of the Finnish population. We surveyed the National Hospital Discharge Register and found our estimate of 314 injuries annually in the Finnish population aged 15 years or older to correspond to the 345 flexor tendon repairs reported for all age groups in the registry. Therefore, we feel the incidence rates of this study reflect the current incidence of these injuries in the Finnish population. Our study had the strength of collecting also the cases, which were incorrectly recorded under nerve repairs, which national registry based data collection would fail to do. However, as the numbers in the national register corresponds acceptably well with our results, the registrybased data collection can be justified in future studies. In the last decade, the increase in costs has drawn more attention to economic considerations of healthcare, and in a recent study by de Putter et al. (3), hand and wrist injuries were ranked the most expensive types of injuries. Increased knowledge of the epidemiology of this injury type provided by our study helps to estimate the resources needed for the repair and rehabilitation of flexor tendon injuries. Our study provides much needed knowledge of persons at risk and the causes of injury. The treatment, especially of complications, is expensive (2). Consequently, in addition to optimizing the surgical repair, a future aim should be to identify ways to prevent these injuries. This study provides information for optimizing the national surgical and rehabilitation services for caring of flexor tendon injuries of the hand. Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Funding The author(s) received no financial support for the research, authorship, and/or publication of this article. References 1. Strickland JW: Development of flexor tendon surgery: Twentyfive years of progress. J Hand Surg Am 2000;25A: Rosberg HE, Carlsson KS, Höjgård S et al: What determines the costs of repair and rehabilitation of flexor tendon injuries in zone II? A multiple regression analysis of data from southern Sweden. J Hand Surg Br 2003;28(2): De Putter CE, Selles RW, Polinder S et al: Economic impact of hand and wrist injuries: Health-care costs and productivity costs in a population-based study. J Bone Joint Surg Am 2012;94(9):e Clayton RA, Court-Brown CM: The epidemiology of musculoskeletal tendinous and ligamentous injuries. Injury 2008;39(12): Hill C, Riaz M, Mozzam A et al: A regional audit of hand and wrist injuries. A study of 4873 injuries. J Hand Surg Br 1998;23(2): Nietosvaara Y, Lindfors NC, Palmu S et al: Flexor tendon injuries in pediatric patients. J Hand Surg Am 2007;32(10): De Jong JP, Nguyen JT, Sonnema AJ et al: The incidence of acute traumatic tendon injuries in the hand and wrist: A 10-year population-based study. Clin Orthop Surg 2014;6(2): Elliot D, Moiemen NS, Flemming AF et al: The rupture rate of acute flexor tendon repairs mobilized by the controlled active motion regimen. J Hand Surg 1994;19B: Hung LK, Pang KW, Yeung PL et al: Active mobilisation after flexor tendon repair: Comparison of results following injuries in zone 2 and other zones. J Orthop Surg (HongKong) 2005;13: Dy CJ, Hernandez-Soria A, Ma Y et al: Complications after flexor tendon repair: A systematic review and meta-analysis. J Hand Surg Am 2012;37(3): Tang JB: Clinical outcomes associated with flexor tendon repair. Hand Clin 2005;21: Hatanaka H, Kojima T, Mizoguchi T et al: Aggressive active mobilization following zone II flexor tendon repair using a two-strand heavy-gauge locking loop technique. J Orthop Sci 2002;(7) Harris SB, Harris D, Foster AJ et al: The aetiology of acute rupture of flexor tendon repairs in zones 1 and 2 of the fingers during early mobilization. J Hand Surg 1999;24B: Received: March 13, 2016 Accepted: July 15, 2016