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Incidence of Congenital Upper-Limb Deficiencies

Research planning and, more specifically, the allocation of priorities among alternative resource activities, require accurate estimates of the population affected. While the incidence of some common conditions is known quite accurately, the incidence of less common conditions, especially those which are not life-threatening, can only be determined approximately and with considerable difficulty. In our research (concerning myoelectric arm prostheses) we are interested in upper-limb amputees for whom a functional prosthesis should be considered. We are particularly interested in determining the incidence of congenital upper-limb deficient clients whom physicians could reasonably consider for a myoelectric fitting. The problems encountered in this condition undoubtedly plague other congenital disorders as well. The main difficulty arises because reporting is not mandatory in many jurisdictions and often all musculoskeletal disabilities are grouped. Thus, the incidence of a given condition is not easily determined.

We have estimated the incidence of congenital upper-limb deficiencies by comparing data from diverse sources. For the most part these data come from two types of sources, clinical reports and birth-census data. Somewhat informal reports are available from various clinics, but these have the disadvantage that usually they exclude persons not under active treatment. For example, only the most severe cases (or those most suited for treatment) may be referred to specialized clinics. On the other hand, clinic reports have the advantage that the conditions are often classified in some detail and often in terms of the treatment available.

The other sources of data are periodic surveys or censuses of congenital anomalies conducted by various government agencies. The disadvantage of these sources is that the classification systems tend to lump anomalies. Clearly, estimates determined from such data must be considered very tentative especially in view of the added risks involved in extrapolating from one country or region to another and in comparing data from different sources. Despite these dangers a reasonably consistent picture emerges.

Data Sources

In 1980, the 74 clinics throughout Canada and the United States comprising the Association of Children's Prosthetic-Orthotic Clinics (ACPOC) conducted a census of the child amputee populations comprising their caseloads.1 I Usable data were obtained from 45 clinics, with a total active treatment population of 4,105 cases. While these data do not enable us to determine the absolute incidence, it is instructive to note the relative frequency of different types of limb deficiencies reported among children from birth to 12 years. Of these 67 per cent (2,750) were congenital in origin and 33 per cent were acquired.

Of the congenital population, 49 per cent (1,347) were unilateral upper limb, 27 per cent (743) were unilateral lower limb, and 24 per cent (660) were multiple limb deficiencies. All together, upper limbs were involved in 62 per cent (1,705) of all cases. The situation for acquired amputations was quite different. The incidence of lower-limb amputations was highest, with 66 per cent (894) of all cases. The congenital, unilateral, upper-limb deficiency was by far the most common single category, while acquired upper-limb amputations were the least common. Congenital conditions accounted for 85 per cent of all upper-limb deficiencies.

In 1981 the United Kingdom (UK) Department of Health and Social Security reported a total population of 12,700 clinic patients with some form of limb deficiency, including both congenital and acquired deficiencies.2 In that year the UK population was 56,379,000; thus, the overall incidence would be approximately 1:4400 for upper and lower limbs. That report did not indicate the ratio of congenital to acquired. In the absence of a more reliable guide, the estimate of 67 per cent obtained from the ACPOC data could be used as a tentative guide. Particular caution is needed in view of the differences in referral systems in the UK, Canada, and the United States. Using this estimate, the incidence of congenital limb deficiency would be 1:6567.

The incidence decreases when we restrict the sample to amputees with upper-limb deficiencies. UK clinics reported about 80 to 90 new patients under 10 years of age each year with upper-limb deficiencies.3 Since the UK reported 73 1,000 live births in 1981, the incidence of upper-limb deficiencies in that year would have been approximately 1:8600. We have no way of knowing how many of these were congenital in origin but, in this age range, it is probable that a very high percentage of them were congenital. The ACPOC data reported above indicated that 85 per cent of all upper-limb deficiencies among children were congenital. If this estimate is used, the incidence of congenital upper-limb deficiency would decrease to 1:10118. These ratios are likely underestimates because it is almost certain that a number of patients, especially those with relatively minor deficiencies, would not have been seen by these specialized clinics.

Statistics Canada reports 375,727 live births in Canada for 1985.4 Informal discussions with the major clinics across Canada suggest that the total number of congenital upper-limb amputees referred to these clinics each year varies from 25 to 50. Such figures would suggest an incidence which varies from a minimum of 1:15000 to a maximum of 1:7500. On average, these ratios suggest an average incidence of 1:10000. As mentioned above, it is certain that some cases are missed by these clinics, so the actual value is likely to be closer to the maximum estimate.

Government Surveys

A more systematic study by Rogala, Wynne-Davies, and Littlejohn reported census data collected from the Edinburgh area over a six year period between 1962 and 1967.5 The incidence of "congenital amputation" of upper and lower limbs was 1:3000 over a sample of 52,000 consecutive live births. This is a somewhat higher incidence than obtained from clinic sources. It cannot be accounted for by the thalidomide tragedy (which took place between 1958 and 1961). It turns out, though, that it is not too discrepant with other census data concerning anomalies in live births. One problem with the above ratio is that it is not possible to determine the separate incidences for upper and lower limb anomalies.

The Ontario Ministry of Health conducted a survey over three years (1969-1971) of the incidence of congenital anomalies including "reduction deformities" of limbs.6 This survey is particularly useful as it enables us to compare the incidence for upper and lower limbs. During this period there were 93 reduction deformities of upper limbs in 395,517 live births which yields a rate of 1:4253. There were also 46 cases of lower-limb deformities, giving a ratio of 1:8598. The overall rate of limb deformities was 1:2845. The percentage of upper-limb deformities was 67 per cent which is similar to the ACPOC data.

In 1966 an agreement between several provinces and Health Protection Branch of Health and Welfare Canada resulted in the formation of the Canadian Congenital Anomalies Surveillance System (CCASS). CCASS is a "discretionary" program which exists without specific enabling legislation. CCASS does not publish data, but topics can be searched upon request. At present eight provinces participate in the program: British Columbia, Alberta, Manitoba, Ontario, New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland .7 The Surveillance System uses birth records obtained directly from hospitals. In many cases insufficient details are provided to enable an accurate classification of birth anomaly. These cases are included in an unspecifiable category. It should also be noted that births that occur outside of hospitals would not be counted. We know of several clinics in rural regions who appear to have been missed in the census.

At our request, CCASS recently conducted a search for cases of congenital upper-limb deficiency in participating provinces over a five year period (1980-1984). A total of 302 births were identified in which reduction deformities of upper limbs were reported. Over this period the total number of live births in participating provinces was 1,242,567; therefore, the incidence would be 1:4115. We examined the descriptions of each case in order to select those cases that would be most likely to be considered for fitting with a myoelectric prosthesis. On this basis, 132 were included in the final sample. Because of the variability of terminology used in descriptions of cases, some rather subjective decisions had to be made for a small number of cases. Participation of all the provinces was not uniform over this period so it was necessary to calculate incidence for each province separately and then average the data.

These data indicate that the incidence of congenital upper-limb deficient clients likely to be recommended for fitting has remained constant at about 1: 9400 over the period 1980 to 1984. It is premature to make a final judgement in view of the inconsistencies across the provinces.

In addition to these data, the United States Centers for Disease Control conducted a survey of congenital malformations during the calendar years 1979-1983.8 The project entitled the Birth Defects Monitoring Program obtained data on an average of 850,000 live births per year in a sample of 928 hospitals: a sample of approximately 21 per cent of US births. The average incidence for these data is 1:2736. If the incidence of upper-limb deformities is 67 per cent of the total, the ratio for upper limbs would be 1:4469. These data are consistent with the other census data.

Finally, Mastroiacovo9 and Camera and Mastroiacovo10 have reported on the Italian birth defects monitoring system which is a hospital-based system and, in 1982, covered 120,000 births, about 20 per cent of all Italian births. Incidence of fourteen malformations in Italy were compared with baseline rates in eleven European monitoring systems. Birth prevalence rates for limb reductions of all kinds vary from about 1: 1333 for Italy to 1:3330 for Denmark. Sweden's rate is reported to be about the same as Italy (1: 1429) while the others fall between 1:2000 and 1:3330. The average of these data is about 1:2200. These rates are slightly higher than those reported above. It is possible that differences are primarily due to differences in methods of reporting data; in addition, the data are presented only graphically necessitating interpolation of values.

The survey data from four diverse sources (Edinburgh, Canada, United States, and Italy) were obtained from independently published reports. Data recently obtained from CCASS resulted from a specific search aimed at finding the incidence of upper-limb congenital deficiencies which might benefit from a myoelectric prosthesis. Comparison of the published data with the CCASS data provides a reasonable validity check. The average ratio for the four surveys places the incidence of all congenital limb deficiencies at approximately 1:2760. If it is assumed that 67 per cent of congenital deficiencies involve upper limbs, then the ratio is 1:4121. The ratio for the CCASS data is 1:4115 and compares very favorably with these estimates.

Using current Canadian birth statistics, these estimates would predict approximately 86 to 92 new cases each year in a population of 375,727 live births. If we restrict the sample to those patients who are likely to be recommended for fitting with myoelectric prostheses, the incidence drops by about 44 per cent to 1:9413.

The data obtained from CCASS were sufficiently detailed that it was possible to select 114 cases which might be recommended for an upper-arm prosthesis. These cases were grouped according to the terms used to describe the condition. Table 1 shows the results of this grouping. It was also possible to classify these cases as left-sided, right-sided, bilateral or not indicated. These classifications are also included in Table 1 with similar data from the 1980 ACPOC survey of 74 clinics.

In almost two-thirds of the CCASS cases, the conditions were described in non-technical language. In some instances, the written descriptions were reasonably clear. In other cases, an interpretation was required. Results of the laterality classification of the CCASS data indicate that congenital anomalies were reported more frequently on the left side of the body. Chi square analysis of the three categories produced a X2 = 16.9 with 2 degrees of freedom. The differences among the three categories are significant with p less than .001. These results confirm the differences reported in the ACPOC survey. The chi square for the ACPOC data is' also significant, X2 = 303 with I degree of freedom and p less than .001. The CCASS data would be identical with the ACPOC data if the bilaterals (20%) and not-indicated cases (8%) were classified as left and right limb deficiencies. It is interesting to compare these data to a recent clinical source. Data from the Alberta Children's Hospital confirms this leftsided bias. Of 46 juvenile clients, 26 per cent of the anomalies occurred on the right side, 63 per cent on the left side, and I I per cent were bilateral or quadramembral. Clearly, this left-sided bias occurs consistently.

Discussion

From the birth census data the estimated incidence of congenital upper-limb deficiencies is approximately 1:4200 live births. For clients for whom prosthetic treatment may be considered, the estimate of upper-limb congenital defects based on CCASS reports was 1:9400. Considerable agreement exists among sources as diverse as CCASS and UK clinic reports. It is also noteworthy that the CCASS estimates of the incidence of all limb deficiencies agrees with the other four government sources. The clinic data may underestimate the census slightly. The reasons for this discrepancy include the fact that only those clients who are under active treatment are included in clinic data, whereas the census data include all degrees of congenital anomalies. Because CCASS estimates of the incidence of upper-limb deficiencies agree with other sources, it is possible that the data which were selected according to our search criteria provide an accurate estimate of the number of congenital clients which should be considered for fitting. It would be desirable to update our estimate yearly from CCASS sources.

If the incidence is consistently greater than clinic estimates it suggests that some persons may be missed who would be suitable for upper-limb prosthetic fittings. The consistency observed in both the clinic and the census data is very encouraging and suggests that we can rely on these sources for planning purposes so long as we appreciate their limitations and significance.

The multiplicity of terms employed to classify the upper-limb congenital anomalies is a problem. The percentage of unspecified cases reported across the country suggests that some simplification and standardization of terminology might increase consistency and accuracy of reports. From various medical textbooks and references we were able to select a list of 32 terms which referred to different kinds of congenital upper-limb deficiencies which could be considered for fitting with a prosthesis. Despite this extensive list, the terms used by hospital personnel were limited to familiar terms such as amelia, hemimelia, and phocomelia, or more commonly described in non-technical terms such as "no limb, no development". Clearly, hospital personnel or others responsible for providing birth census data should be encouraged to employ the most up-to-date classifications. The recommendations of the Dundee workshop10 would be appropriate for this application.

Estimates suggest an incidence of upper-limb deformity of 1:4200 in general and 1:9400 which might be suitable for prosthetic fittings. It is interesting to compare these incidences to other forms of congenital anomalies such as Down's syndrome. The United States data indicate that Down's has an incidence of 1: 1284. Cleft palate has a rate of 1: 1950 and spina bifida occurs with a rate of 1:2010. The overall incidence of reduction deformities is about 1:2760 which is about 72 per cent as frequent as Down's and about 42 per cent as frequent as spina bifida. The incidence of upper-limb deformity is about 31 per cent as frequent as Down's and 49 per cent as frequent as spina bifida. These comparisons are quite a bit higher than many of us had thought on the basis of clinical experience.

The consistent finding of a left-sided bias raises an interesting question concerning the success of prosthetic treatments on the left and right side. Is it possible that a prosthesis would be more successful when fitted on the side that would have been dominant? If so, one might expect greater success with prostheses fitted on the right side inasmuch as the right side is dominant in 85 per cent of the population. A retrospective study of the proportion of left- and right-side prosthesis rejections would be useful in determining if a difference exists. This phenomenon may be significant, also, for theories concerned with the origins of congenital deficiencies and also the origins of right and left handedness. For example, Corballis and Morgan postulated a left to right gradient in morphological development12 There are many possible ways to connect their theory to the left-sided bias of congenital limb deficiency but one interpretation is that the left limb is developing during an earlier and more vulnerable stage of cell differentiation.

Incidence of limb deficiencies and other congenital anomalies observed in North America and Europe may serve as an index to conditions such as the quality of prenatal care and the effects of environmental pollutants. The danger is, of course, that many teratogenic agents may not have the very specific effects of a drug like thalidomide and hence be far less easy to detect. If the incidence of congenital anomalies can be monitored accurately, it may be possible to detect slight changes in conditions. The Centers for Disease Control provide trend data that show a very constant incidence of reduction deformities from January, 1970 to December 1980. 13The CCASS data reported above also show a very constant incidence rate.

Conclusions

The United States, Canada, and the UK have no mandatory reporting of most birth anomalies. As a result it is often impossible for researchers and clinicians to determine the incidence of a particular condition. The data provided by clinics and from various birth defect monitoring programs are not sufficient to specify the incidence of a given category of birth defects. By combining information from several sources, it has been possible to arrive at a reasonable estimate of the incidence of congenital limb deficiencies. The validity of comparisons made across cultures, and between clinic and birth census data is established by the level of agreement found. The incidence of this class of congenital upper-limb deficiencies is estimated to be 1:9400 live births. The findings of this study suggest that improved and standardized reporting practices would facilitate identification and subsequent treatment of affected persons.

Dr. McDonnell is Professor, Department of Psychology, University of New Brunswick, Bag Service Number 45444, Fredericton, NB E3B 6E4; Professor Scott is Director of the University of New Brunswick Bio-Engineering Institute; Ms. McKay is in the Department of Psychology, University of New Brunswick.

References:

  1. Fishman S: Patient Census at Child Amputee Clinics-1980: Preliminary Report. Presented at Annual Meeting of the Association of Children's Prosthetic-Orthotic Clinics, 1982.
  2. Mendez MA: A Thai to Evaluate a Myoelectric Prosthesis for Young Children with a Single Below-Elbow Absence. Proceedings of the 8th International Congress of the World Federation of Occupational Therapists, 345-350, 1982.
  3. Department of Health and Social Security. Report on the Trial of the Swedish Myoelectric Hand for Young Children, 1981.
  4. Statistics Canada: Vital Statistics Vol. 1. Births and Deaths: Table 1. Vital Statistics Summary, 1984 and 1985 (Catalogue 84-204). Ottawa: Minister of Supply and Services, 1985.
  5. Rogala ET, Wynne-Davies R, and Littlejohn A: Congenital Limb Anomalies: Frequency and Aetiological Factors. J Med Genetics 11:221, 1974.
  6. Ontario Ministry of Health: Congenital Anomalies Reported by Physicians, Live Births and Stillbirths, 1973.
  7. Sherman CJ: The Canadian Congenital Anomalies Surveillance System CCASS Four Years Later. Ottawa: Health and Welfare, 1987.
  8. Centers for Disease Control: Congenital Malformations Surveillance Report, January 1981-December 1983, 1985.
  9. Mastroiacovo P: The Italian Birth Defects Monitoring System: Baseline Rates Based on 283,453 Births and Comparison with Other Registries. Prevention of Physical and Mental Congenital Defects, Part B: Epidemiology, Early Detection and Therapy, and Environmental Factors, pp. 17-21, 1985.
  10. Camera G, Mastroiacovo P: Birth Prevalence of Skeletal Dysplasias in the Italian Multicentric. Monitoring System for Birth Defects. Progress in Clinical and Biological Research 104:441-449, 1982.
  11. Kay H: A Proposed International Terminology for the Classification of Congenital Limb Deficiencies. Inter-Clinic Information Bulletin 13:1-16, 1974.
  12. Corballis MC, Morgan MJ: On the Biological Basis of Human Laterality: 1. Evidence for a Maturational Left-Right Gradient. The Behavioral and Brain Sciences 2:261-336, 1978.
  13. Centers for Disease Control: Congenital Malformations Surveillance Report, January-December 1980, 1982.