Results from the external validation study have been published in Shah et al.17 This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: http://creativecommons.org/licenses/by/4.0/.
Introduction
The second phase of this study was to produce, for the first time, the age- and sex-specific incidence rates for shoulder dislocations in the UK. These would then allow the comparison of numbers and incidence rates of shoulder dislocations in the UK with those published from the USA and Canada. The comparison will facilitate an external validation of the data contained within the CPRD on shoulder dislocations.
Objectives of Chapter 3
The objectives of this chapter are to produce age- and sex-specific incidence rates for shoulder dislocation for the UK population and to validate UK data by comparing age- and sex-specific incidence rates of first-time TASD with those of similar studies from the USA and Canada.15,16
Methods
Data source
The CPRD of population-based primary care data was used to identify a cohort of patients diagnosed with a traumatic shoulder dislocation aged 16–70 years during 1995–2015 in the UK. A description of the CPRD and the potential risk factors available within it was presented in Chapter 2.
Participants
The cohort of 16,763 CPRD patients aged 16–70 years with a TASD during 1995–2015 in the UK was used. The patients were identified using predefined Read codes as described in Chapter 2 (see also Appendix 1).
Statistical analysis
Descriptive statistics were used to summarise the epidemiology of primary shoulder dislocations by demographic factors. The incidence rates by age and sex per 100,000 person-years and incidence rate ratios with 95% CIs and p-values were calculated for all age and sex groups using Stata® software version 14.1 (StataCorp LP, College Station, TX, USA).
Incidence rate denominators were constructed using the patient-level data from the CPRD. Observation time per patient was calculated between 1995 and 2015 as the sum of total year-time contributed by all subjects, wherein person-years start as the latest of first registration date, practice up-to-standard date and 1 January 1995, and end as the earliest from patient transfer out date, practice last collection date, death date and 31 December 2015.
Results
An initial cohort of 63,324 patients with codes for shoulder dislocation was identified. A predefined set of exclusion criteria was applied (Table 5). During this process, many patients were excluded either because they had a shoulder dislocation diagnosis outside the study time period (55%) or because they were outside the study age limits (16–70 years) (8%).
| Exclusion | n (%) |
|---|---|
| Total number of CPRD shoulder dislocation patients received | 63,324 (100) |
| Unacceptable patients (i.e. CPRD flags that data quality for a patient is insufficient for medical research) | 806 (1) |
| Unacceptable dates (i.e. impossible to find a shoulder dislocation code between the CPRD minimum and maximum acceptable dates, as defined by data management standard operating procedures for clinical research) | 34,710 (55) |
| Shoulder dislocation date prior to 1 January 1995 | 1446 (2) |
| Shoulder dislocation date after 31 December 2015 | 75 (< 1) |
| < 2-year minimum washout period (i.e. washout period defined using the date the GP was classified as ‘up to standard’ and the date the patient first registered at the general practice) | 4008 (6) |
| Aged < 16 years | 878 (1) |
| Aged > 70 years | 4638 (7) |
| Patients remaining in cohort | 16,763 (26) |
The final cohort produced included 16,763 patients aged 16–70 years who were diagnosed with a shoulder dislocation between 1995 and 2015 in the UK. The numbers of patients identified by CPRD Read codes are given in Table 6. Table 7 highlights the baseline characteristics of the cohort. Most (72%) of the shoulder dislocations occurred in men and the median age for the whole cohort was 36 years [interquartile range (IQR) 24–52 years]. Most patients had a ‘normal’ BMI (18.5–24.9 kg/m2) and 88% of patients had no comorbidities.
| Description | Read code | Number of patients |
|---|---|---|
| Dislocation or subluxation of shoulder | S41..00 | 9600 |
| Dislocation of shoulder NOSa | S41z.00 | 2066 |
| H/O: dislocated shouldera | 14G5.00 | 2331 |
| Closed reduction of dislocation of shoulder | 7K6G300 | 739 |
| Closed traumatic dislocation of shoulder | S410.00 | 410 |
| Recurrent dislocation of shoulder, anterior | N083A00 | 646 |
| Anterior dislocation of shoulder | S410111 | 424 |
| Recurrent joint dislocation, of shoulder region | N083100 | 176 |
| Recurrent subluxation of shoulder, anterior | N083C00 | 168 |
| Closed traumatic dislocation shoulder joint, anterior (subcoracoid) | S410100 | 64 |
| Closed traumatic dislocation shoulder joint, unspecified | S410000 | 78 |
| Closed traumatic subluxation, shoulder | S412.00 | 61 |
| Total | 16,763 | |
| Characteristic | n (%) |
|---|---|
| Total | 16,763 (100) |
| Sex | |
| Male | 12,148 (72) |
| Female | 4615 (28) |
| Age at shoulder dislocation (years) | |
| 16–20 | 2561 (15) |
| 21–30 | 4266 (25) |
| 31–40 | 3021 (18) |
| 41–70 | 6915 (41) |
| BMI (kg/m2) | |
| < 18.5 | 180 (1) |
| 18.5–24.9 | 3392 (20) |
| 25.0–29.9 | 3020 (18) |
| 30.0–34.9 | 1292 (8) |
| ≥ 35.0 | 768 (5) |
| Missing | 8111 (48) |
| Smoking | |
| Non-smoker | 6674 (40) |
| Current smoker | 3388 (20) |
| Ex-smoker | 2014 (12) |
| Missing | 4687 (28) |
| Drinking | |
| Current drinker | 6854 (41) |
| Non-drinker | 1113 (7) |
| Ex-drinker | 188 (1) |
| Missing | 8608 (51) |
| CCI score | |
| 0 | 14,834 (88) |
| 1 | 950 (6) |
| 2 | 523 (3) |
| ≥ 3 | 456 (3) |
| Region | |
| East Midlands | 600 (4) |
| East of England | 1444 (9) |
| London | 1484 (9) |
| North East | 279 (2) |
| North West | 2071 (12) |
| Northern Ireland | 602 (4) |
| Scotland | 1626 (10) |
| South Central | 2005 (12) |
| South East Coast | 1572 (9) |
| South West | 1462 (9) |
| Wales | 1591 (9) |
| West Midlands | 1470 (9) |
| Yorkshire and the Humber | 557 (3) |
| IMD 2004 (quintile of deprivation) | |
| 1 (affluent) | 2790 (17) |
| 2 | 2345 (14) |
| 3 | 2001 (12) |
| 4 | 1793 (11) |
| 5 (deprived) | 1309 (8) |
| Missing | 6525 (39) |
The age distribution of primary shoulder dislocation patients during 1995–2015 in the UK within the CPRD is given in Figure 1. A peak of > 500 patients per year of age occurs in patients aged 17–21 years, which then decreases until the age of 53 years. Between 55 years and 70 years, there is a gradual increase in the number of patients with a primary shoulder dislocation.
FIGURE 1 Distribution of primary shoulder dislocation patients by age (years), demonstrating the overall distribution within CPRD during 1995–2015 in the UK. (Figure not reproduced here; see the original article.)
UK incidence rates
The incidence rates and incidence rate ratios by age and sex for primary shoulder dislocation patients in the UK are presented in Table 8. The overall incidence rate in males was seen to be 40.39 per 100,000 person-years (95% CI 40.38 to 40.41 per 100,000 person-years) and in females was 15.52 per 100,000 person-years (95% CI 15.51 to 15.52 per 100,000 person-years). The highest incidence observed was in 16- to 20-year-old males (80.55 per 100,000 person-years, 95% CI 80.45 to 80.65 per 100,000 person-years). The incidence in men decreased with an increase in age. A U-shaped pattern of incidence was observed in women. The incidence was 16.36 per 100,000 person-years in those aged 16–20 years. This decreased in women aged 21–50 years and then increased to 28.64 per 100,000 person-years in women aged 61–70 years. Overall, the incidence was significantly higher in men than in women in almost all age groups, with an overall incidence rate ratio of 2.60 (95% CI 2.52 to 2.69). The exception was found in men and women aged 61–70 years, in whom no significant difference in incidence was observed (p = 0.334).
| Demographic category | Number of patients | Person-yearsa | Incidence rateb | 95% CI | Demographic comparison | Incidence rate ratio | 95% CI | p-value |
|---|---|---|---|---|---|---|---|---|
| Sex | ||||||||
| Male | 12,148 | 30,074,078 | 40.39 | 40.38 to 40.1 | Male vs. female | 2.60 | 2.52 to 2.69 | < 0.001 |
| Female | 4615 | 29,741,559 | 15.52 | 15.51 to 15.52 | ||||
| Age (years) | ||||||||
| 16–20 | 2561 | 5,245,428 | 48.82 | 48.78 to 48.87 | ||||
| 21–30 | 4266 | 11,006,586 | 38.76 | 38.74 to 38.78 | 16–20 vs. 21–30 | 1.26 | 1.20 to 1.32 | < 0.001 |
| 31–40 | 3021 | 12,362,061 | 24.44 | 24.42 to 24.45 | 16–20 vs. 31–40 | 2.00 | 1.90 to 2.11 | < 0.001 |
| 41–50 | 2472 | 12,244,890 | 20.19 | 20.18 to 20.20 | 16–20 vs. 41–50 | 2.42 | 2.29 to 2.56 | < 0.001 |
| 51–60 | 2091 | 10,583,309 | 19.76 | 19.75 to 19.77 | 16–20 vs. 51–60 | 2.47 | 2.33 to 2.62 | < 0.001 |
| 61–70 | 2352 | 8,373,363 | 28.09 | 28.07 to 28.11 | 16–20 vs. 61–70 | 1.74 | 1.64 to 1.84 | < 0.001 |
| Age (years), sex (male) | ||||||||
| 16–20 | 2137 | 2,653,062 | 80.55 | 80.45 to 80.65 | ||||
| 21–30 | 3588 | 5,463,830 | 65.67 | 65.61 to 65.72 | 16–20 vs. 21–30 | 1.23 | 1.16 to 1.29 | < 0.001 |
| 31–40 | 2316 | 6,265,348 | 36.97 | 36.94 to 36.99 | 16–20 vs. 31–40 | 2.18 | 2.05 to 2.31 | < 0.001 |
| 41–50 | 1733 | 6,243,377 | 27.76 | 27.74 to 27.78 | 16–20 vs. 41–50 | 2.90 | 2.72 to 3.094 | < 0.001 |
| 51–60 | 1244 | 5,342,095 | 23.29 | 23.27 to 23.31 | 16–20 vs. 51–60 | 3.46 | 3.22 to 3.71 | < 0.001 |
| 61–70 | 1130 | 4,106,366 | 27.52 | 27.49 to 27.54 | 16–20 vs. 61–70 | 2.93 | 2.72 to 3.15 | < 0.001 |
| Age (years), sex (female) | ||||||||
| 16–20 | 424 | 2,592,366 | 16.36 | 16.34 to 16.38 | ||||
| 21–30 | 678 | 5,542,756 | 12.23 | 12.22 to 12.24 | 16–20 vs. 21–30 | 1.34 | 1.18 to 1.51 | < 0.001 |
| 31–40 | 705 | 6,069,714 | 11.56 | 11.55 to 11.57 | 16–20 vs. 31–40 | 1.41 | 1.25 to 1.60 | < 0.001 |
| 41–50 | 739 | 6,001,514 | 12.31 | 12.30 to 12.32 | 16–20 vs. 41–50 | 1.33 | 1.18 to 1.50 | < 0.001 |
| 51–60 | 847 | 5,241,214 | 16.16 | 16.15 to 16.17 | 16–20 vs. 51–60 | 1.01 | 0.90 to 1.14 | 0.840 |
| 61–70 | 1222 | 4,266,996 | 28.64 | 28.61 to 28.67 | 16–20 vs. 61–70 | 0.57 | 0.51 to 0.64 | < 0.001 |
| Age (years), sex (male vs. female) | ||||||||
| 16–20 | 16–20 vs. 16–20 | 4.92 | 4.44 to 5.47 | < 0.001 | ||||
| 21–30 | 21–30 vs. 21–30 | 5.37 | 4.95 to 5.83 | < 0.001 | ||||
| 31–40 | 31–40 vs. 31–40 | 3.20 | 2.94 to 3.48 | < 0.001 | ||||
| 41–50 | 41–50 vs. 41–50 | 2.25 | 2.07 to 2.46 | < 0.001 | ||||
| 51–60 | 51–60 vs. 51–60 | 1.44 | 1.32 to 1.57 | < 0.001 | ||||
| 61–70 | 61–70 vs. 61–70 | 0.96 | 0.89 to 1.04 | 0.334 | ||||
Comparison of UK incidence data with Canadian incidence data
Incidence rates for TASD in the UK were also compared by age and sex with those reported in Canada.16 A comparative summary of the characteristics of the UK and Canadian cohorts is shown in Table 9. The UK cohort included in the analysis consisted of 15,666 patients aged 16–70 years with a primary shoulder dislocation in the UK as recorded in the CPRD between 1 April 1997 and 31 March 2015. Denominators for incidence analyses were obtained from the CPRD by individual year, age and sex. Data on urban or rural residence were not available in the CPRD, and thus this comparison could not be made.
| Details | Canadian data (Leroux et al.16) | UK data |
|---|---|---|
| Setting | Hospital records of patients having closed reduction of the shoulder | Primary care records of coded shoulder dislocations |
| Geography | Ontario cohort | UK sample (CPRD) |
| Dates | April 2002–September 2012 | April 1997–March 2015 |
| Patient age (years) | 16–70 | 16–70 |
| Numbers of patients | 20,719 | 15,666 |
The demographic data for the UK cohort (Table 10) were similar in age and sex distribution to those observed in the Canadian cohort.16 The median age in both cohorts was 35 years, with a similar IQR. In the UK, 72% of primary shoulder dislocations occurred in men; in the Canadian cohort, this was slightly higher, at 74%.
| Demographic variable | UK cohort | Canadian cohort (Leroux et al.16) |
|---|---|---|
| Cohort size (n) | 15,666 | 20,719 |
| Age (years) | ||
| Mean (SD) | 38.29 (16.31) | 37.99 (16.62) |
| Median | 35 | 35 |
| IQR | 24–52 | 22–51 |
| Sex, n (%) | ||
| Male | 11,357 (72) | 15,399 (74) |
| Female | 4309 (28) | 5320 (26) |
| Deprivation quintile,a n (%) | ||
| 5 (most deprived) | 1224 (8) | 3698 (18) |
| 4 | 1686 (11) | 3862 (19) |
| 3 | 1889 (12) | 4071 (20) |
| 2 | 2188 (14) | 4356 (21) |
| 1 (most affluent) | 2625 (17) | 4732 (23) |
| Missing | 6054 (39) | 0 (0) |
The English IMD 200419 is a composite deprivation index at the small-area level, based on seven domains: income, employment, health and disability, education, barriers to housing and services, living environment, and crime. The Canadian measure of deprivation is solely based on income. These two measures are not directly comparable but a similar pattern of deprivation is observed, with increasing numbers of patients linked to increasing affluence. There was a large number of missing data for the UK cohort because the IMD results were available for English patients only, whereas complete data on deprivation were available for the Canadian patients.
Figures 2 and 3 present the percentage of primary shoulder dislocation patients by age and sex in the UK and Canada, respectively. In the UK, the peak in numbers for men is spread over those aged 17–22 years, whereas there is a distinct peak in men aged 17 years in Canada. The pattern in the number of women with shoulder dislocations is similar in both cohorts, with a high percentage in those aged 16 years, which decreases up to the early 30s and then increases until the age of 70 years.
FIGURE 2 The percentage of primary shoulder dislocation patients by age (16–70 years) and sex recorded within CPRD (UK) between 1 April 1997 and 31 March 2015. Reproduced from Shah et al.17 This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: http://creativecommons.org/licenses/by/4.0/. (Figure not reproduced here; see the original article.)
FIGURE 3 The percentage of primary shoulder dislocation patients by age and sex recorded in Canada. Leroux T, Wasserstein D, Veillette C, Khoshbin A, Henry P, Chahal J, et al., American Journal of Sports Medicine, vol. 42, issue 2, pp. 442–50, copyright © 2014 by American Orthopaedic Society for Sports Medicine, reprinted by Permission of SAGE Publications, Inc.16 (Figure not reproduced here; see the original article.)
The incidence rates by age and sex for primary shoulder dislocation patients in the UK and an extract of similar Canadian incidence data are presented in Table 11. The patterns of incidence by age and sex were similar and are also represented in Figures 4 and 5. Incidence rates were higher in the UK for all combinations of age groups and sex, except for men aged 16–20 years [UK men (81.6 per 100,000 person-years) vs. Canadian men (98.3 per 100,000 person-years)].
| Demographic category | UK cohort | Canadian cohort (Leroux et al.16) | |
|---|---|---|---|
| Incidence ratea | 95% CI | Incidence ratea | |
| Sex | |||
| Male | 40.4 | 40.4 to 40.4 | 34.3 |
| Female | 15.5 | 15.5 to 15.5 | 11.8 |
| Age (years) | |||
| 16–20 | 48.8 | 48.8 to 48.9 | 56.6 |
| 21–30 | 38.8 | 38.7 to 38.8 | 27.0 |
| 31–40 | 24.4 | 24.4 to 24.5 | 16.5 |
| 41–70 | 22.2 | 22.2 to 22.2 | 18.8 |
| Age (years), sex (male) | |||
| 16–20 | 80.5 | 80.5 to 80.6 | 98.3 |
| 21–30 | 65.7 | 65.6 to 65.7 | 46.9 |
| 31–40 | 37.0 | 36.9 to 37.0 | 25.9 |
| 41–70 | 26.2 | 26.2 to 26.2 | 22.3 |
| Age (years), sex (female) | |||
| 16–20 | 16.4 | 16.3 to 16.4 | 13.8 |
| 21–30 | 12.2 | 12.2 to 12.2 | 7.5 |
| 31–40 | 11.6 | 11.6 to 11.6 | 7.1 |
| 41–70 | 18.1 | 18.1 to 18.1 | 15.2 |
FIGURE 4 The incidence rate of primary shoulder dislocation by age and sex among patients aged 16–70 years with a primary shoulder dislocation recorded within CPRD (UK) between 1 April 1997 and 31 March 2015. (Figure not reproduced here; see the original article.)
FIGURE 5 The overall IDR of primary anterior shoulder dislocation in Canada requiring closed reduction in accordance with both age and sex. The y-axis depicts the IDR per 100,000 person-years and the x-axis depicts each age category. IDR, incidence density rate. Leroux T, Wasserstein D, Veillette C, Khoshbin A, Henry P, Chahal J, et al., American Journal of Sports Medicine, vol. 42, issue 2, pp. 442–50, copyright © 2014 by American Orthopaedic Society for Sports Medicine, reprinted by permission of SAGE Publications, Inc.16 (Figure not reproduced here; see the original article.)
Comparison of UK incidence data with US incidence data
The age and sex incidence rates for primary shoulder dislocation in the UK were also compared with published data from the USA.15 A comparison of the characteristics between the UK and US cohorts is shown in Table 12. The UK cohort included in the analysis comprised 20,784 patients of all ages with a primary shoulder dislocation between 1 April 1997 and 31 March 2015. Data on ethnicity were not available within the CPRD, thus this comparison could not be made. Denominators for incidence analyses were obtained from the CPRD by individual year, age and sex.
| Details | USA data (Zacchilli and Owens15) | UK data |
|---|---|---|
| Setting | Hospital records of patients presenting to 100 hospital emergency departments with a shoulder dislocation | Primary care records of coded shoulder dislocations |
| Geography | USA sample (NEISS) | UK sample (CPRD) |
| Dates | 2002–2006 | April 1997–March 2015 |
| Patient age (years) | All ages | All ages |
| Numbers of patients | 8940 | 20,784 |
The overall incidence rate in the UK was 26.6 per 100,000 person-years (95% CI 26.2 to 26.9 per 100,000 person-years), which was similar to the incidence rate reported in the USA (23.9 per 100,000 person-years, 95% CI 20.8 to 27.0 per 100,000 person-years). The peak incidence occurred in patients aged 20–29 years in the UK (41.8 per 100,000 person-years, 95% CI 40.6 to 43.1 per 100,000 person-years) (Table 13), which is similar to the peak in 20- to 29-year-olds observed in the USA (47.8 per 100,000 person-years, 95% CI 41.0 to 54.5 per 100,000 person-years).15 Significantly higher rates of incidence were observed in the UK among patients aged > 50 years in comparison with those in the USA (see Table 13).
| Demographic category | UK cohort data | USA cohort data (Zacchilli and Owens15) | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Incidence ratea | 95% CI | Incidence rate ratio | 95% CI | p-value | Incidence ratea | 95% CI | Incidence rate ratio | 95% CI | p-value | |
| Sex | ||||||||||
| Female | 19.02 | 18.59 to 19.45 | Referenceb | 13.26 | 11.56 to 14.96 | Referenceb | ||||
| Male | 34.29 | 33.71 to 34.88 | 1.80 | 1.75 to 1.86 | < 0.001 | 34.90 | 30.08 to 39.73 | 2.64 | 2.39 to 2.88 | < 0.05 |
| Age (years) | ||||||||||
| 0–9 | 1.23 | 1.01 to 1.49 | 0.06 | 0.05 to 0.08 | < 0.001 | 0.92 | 0.56 to 1.29 | 0.07 | 0.04 to 0.10 | < 0.05 |
| 10–19 | 27.34 | 26.32 to 28.41 | 1.38 | 1.30 to 1.46 | < 0.001 | 39.71 | 34.05 to 45.37 | 3.07 | 2.62 to 3.53 | < 0.05 |
| 20–29 | 41.80 | 40.55 to 43.08 | 2.11 | 2.00 to 2.23 | < 0.001 | 47.76 | 41.02 to 54.50 | 3.70 | 3.15 to 4.25 | < 0.05 |
| 30–39 | 25.05 | 24.14 to 25.99 | 1.26 | 1.19 to 1.34 | < 0.001 | 25.69 | 21.85 to 29.53 | 1.99 | 1.73 to 2.25 | < 0.05 |
| 40–49 | 20.66 | 19.84 to 21.51 | 1.04 | 0.98 to 1.11 | 0.169 | 17.59 | 14.22 to 20.96 | 1.36 | 0.91 to 1.82 | > 0.05 |
| 50–59 | 19.81 | 18.95 to 20.70 | Referenceb | 12.89 | 10.48 to 15.30 | Referenceb | ||||
| 60–69 | 26.71 | 25.60 to 27.87 | 1.35 | 1.27 to 1.43 | < 0.001 | 16.96 | 14.06 to 19.87 | 1.31 | 0.98 to 1.65 | > 0.05 |
| 70–79 | 41.12 | 39.48 to 42.82 | 2.08 | 1.95 to 2.20 | < 0.001 | 22.56 | 17.51 to 27.61 | 1.74 | 1.45 to 2.03 | < 0.05 |
| 80–89 | 58.03 | 55.40 to 60.79 | 2.93 | 2.75 to 3.12 | < 0.001 | 31.34 | 25.05 to 37.63 | 2.43 | 1.93–2.93 | < 0.05 |
| ≥ 90 | 65.55 | 59.65 to 72.03 | 3.31 | 2.98 to 3.67 | < 0.001 | 28.38 | 17.97 to 38.79 | 2.20 | 1.30–3.10 | < 0.05 |
In the UK, the incidence of primary shoulder dislocation was significantly higher in men (34.3 per 100,000 person-years, 95% CI 33.7 to 34.9 per 100,000 person-years) than in women (19.0 per 100,000 person-years, 95% CI 18.6 to 19.5 per 100,000 person-years) (p < 0.001), which is similar to the pattern observed in the USA (see Table 13). Incidence of shoulder dislocation in men was similar between the UK and US cohorts, but incidence in women in the UK was much higher than incidence in women in the USA. In the UK cohort, 36% of shoulder dislocations occurred in women, in contrast to 28% of shoulder dislocations in the US cohort.
Figure 6 shows the peak of incidence in men aged 20–29 years in the UK (71.5 per 100,000 person-years), which was similar to the peak in men in the same age group in the USA (79.2 per 100,000 person-years) (Figure 7). The peak in women in the UK was observed in those aged > 90 years (71.7 per 100,000 person-years), in contrast with the 38.8 per 100,000 person-years in women aged 80–89 years in the USA. A possible reason for the differences in incidence may be caused by the UK study being based on primary care records and the US study being based on emergency department records.
FIGURE 6 Shoulder dislocation incidence rates and 95% CIs by age and sex in CPRD (UK) between 1 April 1997 and 31 March 2015. (Figure not reproduced here; see the original article.)
FIGURE 7 Total weighted NEISS estimates of all US shoulder dislocations between 2002 and 2006 by age and sex, demonstrating a bimodal distribution with peaks among men (aged 20–29 years) and women (aged 80–89 years). The vertical bars denote the 95% CIs.15 Zacchilli MA, Owens BD. Epidemiology of shoulder dislocations presenting to emergency departments in the United States. J Bone Joint Surg 1992;3:542–9. https://insights.ovid.com/pubmed?pmid=20194311. Reprinted by permission of Wolters Kluwer. (Figure not reproduced here; see the original article.)
Conclusion
This chapter describes a large population-based cohort of 16,763 patients aged 16–70 years in the UK during 1995–2015 identified in the CPRD data set in relation to shoulder dislocations. Most shoulder dislocations occurred in males (72%), with an overall incidence rate of 40.4 per 100,000 person-years. In females, the overall incidence rate was 15.5 per 100,000 person-years. The highest incidence was observed in 16- to 20-year-old males (80.5 per 100,000 person-years). An unexpected finding was that incidence in women increased beyond the age of 50 years to 28.1 per 100,000 person-years among those aged 61–70 years; this pattern was not observed in men.
The results from the UK cohort were then compared with other cohorts in other countries. The UK cohort was similar in age, sex distribution and incidence patterns to those observed in the Canadian, US and Norwegian cohorts.15,16,20 Although the incidence patterns were similar between countries, in the UK the peak in numbers observed for men is spread over those aged 17–22 years, whereas there is a distinct peak in men aged 17–18 years in Canada and the USA. Possible reasons for this difference may be the high numbers of young men playing ice hockey and American football at school, aged 17–18 years, of whom not all continue to play at college. In a smaller study of the causes of shoulder dislocations in Sweden, incidence was high (8%) among ice-hockey players.13 Other explanations might be the under-reporting of shoulder dislocations among college students or a genuine decrease because of better skeletal maturity and shoulder muscle strength and control.
Incidence rates were higher in the UK than in Canada for all combinations of age groups and sex, except for men aged 16–20 years (UK men, 80.5 per 100,000 person-years; vs. Canadian men, 98.3 per 100,000 person-years). These higher incidence rates may be explained by UK data being based on primary care records in contrast to Canadian data, which are based on accident and emergency hospital records.16
A study conducted in Denmark identified the same bimodal age distribution of incidence, and also specifically noted that older people most frequently dislocated their shoulders at home by falling on their arm, whereas young people most frequently suffered a shoulder dislocation while playing sports.21 However, the increasing incidence of shoulder dislocations seen in UK women aged > 50 years is a new finding that is of both interest and concern because the reasons for it are not known. Such injuries in the elderly are usually associated with rotator cuff tears and fractures with subsequent loss of function, as well as instability. However, further work will be required to examine the reasons that may explain this increased risk of shoulder dislocations in ageing women. Possible reasons include biological differences between ageing men and women, including differences in joint proprioception, soft tissue tendon quality and protective muscle bulk. Other possibilities might be a difference in the incidence of falls between men and women. This is of particular importance, given that the population of the UK continues to change to include more elderly people. The increasing population priority needs to be given to increasing the safety of the elderly to reduce falls, dislocations and fractures, as advocated by the National Institute for Health and Care Excellence (NICE),22 which suggests that this is a finding that needs further investigation and research.
The main strength of this study is its large population-based cohort that uses real-world data from primary care. The CPRD is representative of the UK general population by age and sex and the age- and sex-specific incidence of primary shoulder dislocations observed are similar to those observed in Canada and the USA. Although some differences were observed, the incidence of traumatic shoulder dislocations in these other countries has only been calculated using regional data or hospital data. This is, therefore, the first time, to our knowledge, that the incidence of shoulder dislocations has been studied using population-based primary care data and the first time, to our knowledge, that results for the UK have been produced. The findings in this chapter and Chapter 2 support the use of CPRD for the subsequent study chapters and work package 2 studies.
In summary, in the UK most primary shoulder dislocations during the selected time period occurred in young men. An unexpected finding was that incidence increased in women aged > 50 years but not in men of the same age. The reasons for this are unknown. Priority and attention should be directed towards increasing preventative measures for young people playing contact sports, and to the research of the possible causes of the increase in primary shoulder dislocation incidence for women aged > 50 years.