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Biomechanical evaluation of health visitor training in baby hip testing for developmental dysplasia of the hip
Biomechanical evaluation of health visitor training in
baby hip testing for
developmental dysplasia of the hip W. George Kernohan and lan Turner The aim of this study was to examine the performance of health visitors in the clinical testing for signs of hip dysplasia. A kinesiological method was devised to help analyse neonatal hip manoeuvres first described by Ortolani in 1937.The apparatus comprised miniature force, displacement and rotational transducers attached to a training doll. Nine health visitors were assessed before and after a 2-hour teaching session. Improvements were evident in the measures with a concurrent improvement in diagnostic accuracy. Editor's c o m m e n t
W. George Kernohan PhD, Professor of Health Research, School of Health Sciences, University of Ulster, Newtownabbey BT37 OQB, UK lanTurner PhD, Research Fellow, Experimental Electrophysiology Unit, Papworth Hospital, Cambridge CB3 8RE, UK Correspondence to: Professor W G Kernoharl~
Tel.: +44 1232 366532; Fax:+44 1232 368202; Email: wg.l
The United Kingdom Central Council for Nurses, Midwives & Health Visitors, through the 'Scope of Practice' initiative, has been given the opportunity to develop and create roles for the benefit of client care. There is no doubt that nurses, midwives and health visitors are very competent at detecting hip abnormalities in infants (Hough, Trainor & Kernohan 1997 Journal of Orthopaedic Nursing I (I): I I-16). This article describes how the competency of health visitors in baby hip testing can be established, improved and demonstrated to all. In this way standards of practice will be of the highest. Most importantly, hip abnormalities will be more accurately and effectively detected and treated at an early stage when intervention is easier, less radical and minimally stressful for all concerned. PD
INTRODUCTION Developmental dysplasia of the hip (DDH) has long been recognized as an important orthopaedic condition, and affects the stability of hip joints in approximately three per 1000 children within the UK (Dunn et al 1985, Macnicol 1992). Because DDH treatment is far simpler and more successful if the condition is detected at an early stage, screening programmes have been introduced and widely implemented, with mixed degrees of success (DHSS 1986, Hadlow 1988, Krikler & Dwyer 1992). A central part of the screening process for DDH is the physical examination of the child, often by staff such as health visitors, where a number of physical signs, such as leg length or skin crease asymmetry are assessed. The most important aspects of the examination in young children, how-
Journal of Orthopaedic Nursing (I 998) 2, 141-1479 1998Harcourt Brace& Co. L~d
ever, are the Ortolani (1937) and Barlow (1962) tests, where the hip joints are manipulated to assess their stability. Although specialist centres, which use dedicated staff, have reported very good results with this approach, other centres have reported poorer levels of performance and there has been some discussion as to the ability of less experienced staff to perform the tests (Krikler & Dwyer 1992, Haugh et al 1994). Video recording of staff has shown that many were not able to perform these physical tests correctly (E1-Shazly et al 1994). However, accurate assessment of video recordings and the definition of why a person was unable to correctly identify a hip abnormality proved difficult, even when viewing static images of the tests. Therefore, a method was developed for measuring the applied forces and exact movements of the hands during the Ortolani or Barlow tests using a force and displacement
142
Journdlof" Orthopaedic Nursing ,~,,~. . . . . . . . .
Dysplastic
. ~
Abduction
Dislocated
Fig. I A mildform of hip disease 'dysplasia'(left) is formed where the socket is shallow, denyingadequate coverage to the femoral head. A more shallow socket or general laxity (right) leads to a dislocatable or unstable hip.
transducer system (Chow et al 1994). This was able to identify the biomechanical events leading to the movement of the femoral head required to detect an abnormality. This system was used to assess the examination technique of a group of health visitors who were attending a refresher course on the screening for DDH in order to identify any weaknesses in their examination practice and to evaluate the success of the training course in overcoming these problems. Although broadly similar techniques have been used to measure hand forces during manual (Armstrong et al 1979) or medical (Sorsab et al 1988) applications, this is the first known application of such a technique to study force and motion during a physical examination process.
ORTOLANI AND BARLOWTESTS DDH is a range of abnormalities affecting the hip joints in young children. The normal hip joint is formed by a deep acetabulum into which fits the femoral head. The joint is given extra stability by the presence of ligaments within the joint and joint capsule, and also by a fibrous ring around the edge of the socket, the labrum. The mildest form of DDH is when the acetabulure is shallow (Fig. 1); a situation known as a dysplastic hip. If the joint is shallow enough, or if the supporting ligaments are lax, then the femoral head can be dislocated from the socket relatively easily; a dislocatable or unstable joint. Some cases exist where the femoral head is completely dislocated from the socket and force is required to reduce it back to a normal position; a reducibly dislocated joint. In severe cases, the femoral head cannot return to the socket due to the presence of some soft tissue defect such as an infolded labrum; an irreducibly dislocated hip. The Ortolani and Barlow tests involve the manipulation of the joint in order to dislocate and relocate the femoral head from the acetabulum. This movement of the femoral head can be felt as a palpable 'clunk' by the examiner, similar to the sensation of putting a car into gear. These 'clunks' have to
Fig. 2 Duringthe Ortolanitest (above) a dislocated hip is reduced in a combinationof abductionand gentleforce, causinga palpablevibrationthat can be felt or even heard by the examiner.Barlowamended the test (below) to obtain a test for a dislocatablehip usingstress applied posteriorly.
be differentiated from the more innocuous 'clicks', which are higher frequency vibrations produced by ligament movements and synovial fluid cavitation within the joint. Central to the whole test procedure is the correct manipulation of the hips to produce the conditions likely to dislocate or reduce the femoral head without causing discomfort or harm. The Ortolani test was developed to detect the dislocated femoral head. The hips and knees of the infant are flexed to 90 ~ and the legs then smoothly abducted whilst pressure is applied upwards and inwards by the examiners' fingers over the greater trochanter (Fig. 2). This pressure should be sufficient to reduce the femoral head when the force components are directed in the appropriate direction to lift the femoral head over any obstruction outside the acetabulum. The Barlow test is identical to the Ortolani test but with the addition of an extra manoeuvre at the start of the test to stress the joint in an attempt to dislocate the femoral head from the socket (Fig. 2). The reduction of the head back into the acetabulum can then be detected by the Ortolani abduction manoeuvre. Both of these tests are used on children up to 3 months or so of age, when most children are becoming too large to have the Barlow test performed accurately on them. The Ortolan] test can often be performed on children up to 9 months or so of age. Previous work by the group on the measurement of the biomechanical features of the two tests had highlighted a number of points. One of the most important was the need to move the leg being manipulated through the correct range of angles in order to
Health visitor training for developmental dysplasia of hip dislocate or relocate the femoral head. This appeared to be due to the geometrical properties of the joint, with a certain magnitude of force being required in the appropriate direction in order to lift the femoral head over any obstruction to movement. The correct manipulation of the leg, along with appropriate magnitudes of force, is essential for the safe execution of a test that can dislocate or relocate the femoral head, and therefore detect an abnormality. The force-displacement transducer system proved to be highly suited to the measurement of the applied forces during an examination, whilst also providing an accurate record of the motion of the femur. This allowed an insight into biomechanical processes during an examination, along with an objective record of the dislocation and relocation events produced by the manoeuvres. None of these could be accurately obtained from video recordings. This study therefore used a force-displacement transducer system to measure the manoeuvres performed by health visitors before and after training to evaluate both their performance and the ability of the system to identify faults in the examiners' techniques.
METHODS The aim of the project was to assess the examination skills of student health visitors before and after an update session on the correct examination techniques. During the study period, nine students attended the refresher course. All were in the final phase of their training and had already attended a 2-hour teaching session on DDH at the start of their course. They had also spent at least 6-months working within the community and all had experience of examining children regularly under clinical conditions. They attended classes in order to update their skills in the examination and history taking required in order to screen correctly for the condition. Only one student had received any further training in DDH between the initial lesson and the update session. All of the health visitors were asked to examine two 'baby hippy' models and to report their findings on the type of abnormalities detected. These models were developed in order to train medical staff in the examination techniques by closely simulating the dislocated and unstable hip abnormalities (Cole 1983). One of the models used in this study (model 1) was an unmodified example and exhibited a dislocated left hip and an unstable right hip. The second (model 2) had been modified using plastic inserts to deepen the acetabuhim to give a normal fight hip and using a foam insert into the acetabulum to simulate an irreducibly dislocated left hip. The health visitors were blinded as to which model they were examining in order to exclude the likelihood of them remembering which hip had which abnormality.
14:}
Splint
LVDT
i
R2
~
I Force P l a t e
Fig. 3 The apparatus consisted of a clamp (not shown) which secured a mannequinto a force plate, and a small displacement(linear VariableDifferentialTransformerand rotational transducer system (RI, R2) was attached to the model via a plastic splint.The examiner'sforefingerslay over this splintas shownto ensure a firm contact between the splintand the leg. Movementsof the splinttherefore reflected movements of the mannequin.
The students were first asked to examine a 'baby hippy' model mounted in the test apparatus. The apparatus consisted of. a clamp that attached the 'hippy' securely to the force transducer, and a small displacement and rotation transducer system that was attached to the model's leg via a plastic splint (Fig. 3). The examiner's forefingers lay over this splint to ensure a firm contact between the splint and the leg, so that movements of the splint accurately reflected movements of the leg. Each student was allowed to examine the hip as often as they liked in order to familiarize themselves with the procedure. This was carded out to ensure that the splint, although small, had as little effect as possible on the outcome. The first phase of the study involved the students examining model 1 whilst using the apparatus. After an initial familiarization period with the equipment, they were requested to perform whatever tests they would normally use during clinical practice. A separate recording was made for each test and each leg. Recordings from a pilot study on staff within the department had shown insignificant differences between the results obtained from both models. The decision was therefore made to concentrate on recordings from model 1 since this model exhibited abnormalities that were detectable by the Ortolani and Barlow tests, and time limitations precluded recordings from both models using the transducer system. Immediately after the first phase, the students were asked to repeat their examinations on both models without using the transducer system, i.e. as they would in clinical practice. In this phase they were simply asked to identify any abnormalities with each of the hip joints. The models were presented in a random order so that the students were unaware of the types of abnormality to expect. The first and second phases were repeated once the students had completed the training course. As before, they examined model 1 using the transducer system, followed by a blinded examination of both models to identify any hip abnormalities.
144
Journalof OrthopaedicNursing
Force, N Maximum,posterior dislocated hip Maximum,anterior dislocated hip Maximum,posterior unstablehip Maximum,anterior unstablehip Maximum,posterior both hips Maximum,anterior both hips To reduce dislocated hip joint
Force, N Maximum,posterior, dislocated hip Maximum,anterior, dislocated hip Maximum,posterior, unstablehip Maximum,anterior, unstablehip Maximum,posterior, both hips Maximum,anterior,both hips To reduce dislocated hip To dislocate unstablehip To reduce unstablehip
RESULTS The first feature that was apparent from the precourse analysis was that although all of the students knew some variations on the Ortolani and Barlow tests, they were unable to perform identifiable versions in some cases. For example, before training only six of the students were able to perform an Ortolani test. The remainder performed only a single test that, because it appeared to contain some stress element, was included under the Barlow test section during analysis (Table 1). Before training, the biomechanical features of the Ortolani test were available for the six students that attempted this manoeuvre for both the dislocated and unstable hips (Table 2). A wide range of peak posterior force (0-30 N) and peak anterior force (-20-0 N) were observed before training, with mean values of 9 N and - 8 N respectively. In all cases the magnitudes of these forces were relatively small. The force and displacement traces were also examined after filtering with a digital differentiator in order to identify transients where the femoral head moved rapidly into, or out of, the acetabulum. These signals of force and displacement allowed successful tests to be objectively identified and the pattern of applied force to be recorded.
Before trainin~ 7 (5) I I (7) I I (I I) -5 (5) 9 (8) -8 (7) 0 (9)
Before training 32 (16) -7 (8) 32 (26) 15 (9) 32 (21) -II (9) 20 (17) 14 (2) 3 (3)
After training I0 (9) -7 (8) 9 (8) -7 (5) 9 (8) -7 (6) 6 (9)
After training 30 (6) -7 (S) 22 (13) -9 (8) 26 (I I) -8 (6) 12 (I I) 13 (7) 5 (8)
The peak forces and force at relocation were also recorded after training and are shown in the second column of Table 2. The ranges of these values were similar to those before training, with the peak posterior force varying between 1 and 24 N, and the peak anterior force between -27 and 2 N. All nine students attempted some form of the Barlow test before training on both the dislocated and unstable hips (Table 3). All nine managed to reduce the dislocated hip during this manoeuvre, but only two were able to dislocate and relocate the unstable hip joint. The peak posterior forces ranged from 3 to 91 N and the anterior force ranged from -31 to 6 N before training. After training these ranges became 4-49 N and -23-1 N, respectively. The ranges of abduction and adduction of the femur were also recorded during the tests. The minimum and maximum abduction angles were recorded, along with the angles for any identified dislocation or relocation events (Table 4). Finally, the diagnostic accuracy of the students both before and after training was recorded for each of the hips when they were examined without using the transducer system (Table 5). An improvement in diagnosis was noted in the majority of hips after training, particularly in the ability to recognize the unstable hip.
Health visitor training for developmental dysplasia of hip
Angle (de~rees) Minimum,abduction,both hips-Ortolanitest Maximumabductionangle, both hips-OrtolaNtest Of relocation,dislocatedhip-OrtolaN test Maximum,adduction,both hips-Barlowtest Maximumabduction,both hips-Barlowtest Of dislocation,unstablehip-Barlowtest Of relocation,unstablehip-Barlowtest Of maximumexertion-Barlowtest
DISCUSSION Only six of the students were able to perform a recognizable Ortolani test before the course. A wide range of peak forces was noted although the mean peak posterior force (9 N) and mean peak anterior force (-8 N) over both hip types were relatively small. The wide range of forces appeared to reflect both different manipulation techniques and different amounts of stress applied by the examiners. This was particularly apparent with examiner 4 for example, who appeared to use significantly more force than the others (a mean of 30 N), and who also varied the amount of force used between the five successive tests (range 20-37 N). Despite these differences, all of the students that performed this test were able to relocate the femoral head into the acetabulum, as detected by force transients during the reduction manoeuvre. The posterior force applied to the two different types of hip did not appear to be significantly different (7 N vs 11 N; P=non-significant; Wilcox signrank test), whilst there was a small but significant difference in the peak anterior force (-11 N vs - 5 N; P<0.05; Wilcox sign-rank test). The examiners use different hands when testing the two hip types, the left hand for the unstable hip and the right hand for the dislocated hip. All of the examiners were righthanded, and these findings suggest the dominant hand applied some slight additional force when abducting the leg. These differences disappeared after training. The results for the Ortolani test after training were broadly similar to those before, except for the fact that all of the students performed a recognizable version of the test. All of the students could successfully relocate the hip joint, as detected by transients
Before training I (4) 58 (8) 23 (4) -6 (6) 45 (9) -3 (3) 23 (5) 15 (18)
145
After training 3 (6) 45 (I 2) 24 (S) -8 (7) 39 (I O) -2 (4) 25 (8) 92 (6)
in the force and displacement traces and were able to accurately describe the relocation events as 'clunks'. There was no significant difference in any of the force variables after training when compared with those before. One difference that was noted after training was that the students appeared to abduct the hips over a smaller range of angles after training. Maximum abduction was 58 ~ before training versus 45 ~ after (P<0.05; Wilcox rank sum test). There was no significant change in the minimum abduction angle. Before training, all of the students appeared to attempt some form of the Barlow test. This is similar to the Ortolani test, but involves an extra manoeuvre where the posterior stress is applied to the hip in order to dislocate an unstable hip from the socket so that it can be detected by palpating the 'clunk' as it is subsequently reduced during the abduction phase of the test. As a result of this extra stress phase of the test, the peak posterior force was significantly larger than that for the Ortolani test (Barlow = 32 N; Ortolani = 9 N; P<0.05) and forces up to 106 N were recorded. Forces this high are substantial and it has been suggested that excessive force could pose a possible risk to the integrity of the joint itself (Moore 1989, Jones 1991). Although the peak anterior forces were generally similar to those from the Ortolani test (Barlow mean = -11 N; Ortolani mean = - 8 N; P = NS) a few examiners used significantly larger forces, up to -31 N. This was unexpected since the abduction stage of the manoeuvre is the same as for the Ortolani test. Observation of the students and discussion with them about their techniques would suggest that this feature may well be due to the fact that the students tended to grip the legs harder when applying stress at the start of the test, and continued to apply more force during the abduction stage instead of relaxing their grip. Before training, all of the students were able to relocate the dislocated femoral head during the Barlow test, although one was unable to palpate the reduction events and recognize these as abnormal. The results from the unstable hip were more disappointing, however. Only two students were able to dislocate and relocate the femoral head successfully, and both of these students correctly identified the hip as abnormal. Two of the students failed to dislocate the head at all because they did not abduct the
146
Journalof Orthopaedic Nursing
leg to a large enough angle for the posterior force to be in the correct direction to lift the femoral head out of the socket. Four of the students applied the posterior force at the wrong stage of the test, i.e. during the abduction rather the adduction phase so that the force was in the wrong direction to dislocate the head. One released the stress too early so that the femoral head slid back into the socket before the abduction phase. The application of stress at the wrong stage was the most common reason for failure and is reflected in the difference in angle at which peak force was applied before and after training (Table 4). The early release of stress, before the abduction phase of the test, tends to produce a slow and smooth movement of the femoral head. This is very subtle and it appears that the slow movement is difficult for inexperienced staff to palpate compared to the much larger 'clunk' as the head jumps back into the socket during the abduction phase. After training there was a significant improvement in the ability of the students to perform a B arlow test. An important component in the training was the emphasis on the importance of gentle testing of the hips. This was reflected by the general reduction in the peak posterior force (32 N before vs 26 N after; P=non-significant) and peak anterior force (-12N before vs - 8 N after; P=non-significant) after training, although neither of these reached statistical significance. The ability to dislocate the unstable hip increased from 2/9 to 8/9 (P<0.05; McNemar test). The single failure was due to insufficient adduction of the hip during the initial stress phase of the test. A second student failed to detect an abnormality due to her inability to palpate the 'clunks' as the femoral head was dislocated or reduced. This student had similar problems in both the Ortolani and Barlow tests due to her small hand size. She was unable to place her fingers over the greater trochanters during abduction and was therefore unable to palpate the rapid movement of the femoral head. This was corrected in subsequent training courses by using a modified hand position for staff with smaller hands. All of the students who dislocated the hip were able to reduce the joint successfully. In the pilot study it had been noted that insufficient abduction of the legs meant that some examiners were unable to reduce the hips. The recognition of this factor had led to changes in the training practice before this particular course to ensure that all students abducted the hips through an appropriate range of angles. The figures quoted above show that there was a significant improvement in the examination technique of the students after training. This was reflected by the increase in detection rates for the dislocated hip (8/9-9/9; P = non-significant) and the unstable hip (2/9-7/9; P<0.05). There was little change in ability to recognize the irreducibly dislocated hip (3/9) or the normal hip (5/9-6/9; P = NS).
The irreducibly dislocated hip only exhibits very subtle signs of movement. Because this hip cannot be reduced no obvious 'clunk' can be felt, making diagnosis very difficult. Other physical signs of this hip abnormality, such as restriction of abduction, were not simulated in this case but may be included in further work. The normal hip model deteriorated during the course of this study, particularly after some of the students applied a large amount of force to the joints during the examination. When examined by experienced staff at the end of the study this hip was found to exhibit a small degree of movement in the hip which, although not diagnostic of a dislocation, was not completely normal. Only the last three students reported an abnormality with this hip and it may be that this movement was present throughout their examinations. In general the students reported a much greater confidence in their ability to detect the differences between normal and abnormal hips at the end of their training.
CONCLUSION The study identified and highlighted: 9 There were some small but significant changes in the main features of the Ortolani and Barlow tests after training. 9 The main use of the force and displacement transducer system was in the recognition of the reasons for the failure of the tests. For example, many students applied the correct force but at too small an adduction angle to dislocate the hip joint in the Barlow test, whilst some were found to be producing dislocation or relocation transients but were unable to recognize these as abnormal events. 9 Excessive force during examination could pose a risk to the integrity of the hip joint. 9 There is a need to use 'gentle' testing of the hips. 9 The application of stress at the wrong stage was the most common reason for failure. Although not part of this study, the ability of the system to identify faults suggests that further development of this approach may be worthwhile in order to provide feedback during training sessions for students who have difficulty in learning the tests.
REFERENCES ArmstrongT J, ChaffinD B, FoulkeJ A 1979A methodology for documentinghand positionsand force during manualwork. Journalof Biomechanics12: 131-133 Barlow T G 1962 Early diagnosisand treatmentof congenitaldislocationof the hip. Journal of Bone and Joint Surgery44B: 292-301
Health visitor training for developmental dysplasia of hip Chow Y W, Turner I, Kernohan W G, Mollan R A B 1994 Measurement of the forces and movements involved in neonatal hip testing. Medical Engineering and Physics 16:181-187 Cole W G 1983 Evaluation of a teaching model for the early diagnosis of congenital dislocation of the hip. Journal of Pediatric Orthopedics 3:223-226 DHSS 1986 Screening for the detection of congenital dislocation of the hip. Department of Health and Social Security, London Dunn P M, Evans R E, Thearle M J, Griffiths H E D, Witherow P J 1985 Congenital dislocation of the hip: early and late management compared. Archives of Disease in Childhood 6 0 : 4 0 7 4 1 4 El-Shazly M, Trainor B, Kernohan W G e t al 1994 Reliability of the Barlow and Ortolani tests for neonatal hip instability. Journal Medical of Screening 1:165-168 Hadlow V 1988 Neonatal screening for congenital dislocation of the hip: a prospective 21-year survey. Journal of Bone and Joint Surgery 70B: 740-743
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Haugh P E, Mason C, Trainor B P, Kernohan W G, Mollan R A B 1994 An evaluation of the adequacy of health visitor education for neonatal hip screening. Journal of Advanced Nursing 20:815-821 Jones D A 1991 Neonatal hip instability and the Barlow test. Journal of Bone and Joint Surgery 73B: 216-218 Krikler S J, Dwyer N St J P 1992 Comparison of results of two approaches to hip screening in infants. Journal of Bone and Joint Surgery 74B: 701-703 Macnicol M F 1992 The early management of congenital dislocation of the hip. Current Orthopaedics 6:245-251 Moore F H 1989 Examining infant hips - can it do harm? Journal of Bone and Joint Surgery 71B: 4-5 Ortolani M 1937 Un segno poco noto e sua importanza per la diagnosi percoce di prelussazione congenita dell'anca. Pediatria 45:129-136 Sorsab J, Allen R, Gonk B 1988 Tactile sensory monitoring of clinician-applied forces during delivery of newborns. IEEE Transactions Biomedical Engineering 35: 1090-1093
baby hip testing for
developmental dysplasia of the hip W. George Kernohan and lan Turner The aim of this study was to examine the performance of health visitors in the clinical testing for signs of hip dysplasia. A kinesiological method was devised to help analyse neonatal hip manoeuvres first described by Ortolani in 1937.The apparatus comprised miniature force, displacement and rotational transducers attached to a training doll. Nine health visitors were assessed before and after a 2-hour teaching session. Improvements were evident in the measures with a concurrent improvement in diagnostic accuracy. Editor's c o m m e n t
W. George Kernohan PhD, Professor of Health Research, School of Health Sciences, University of Ulster, Newtownabbey BT37 OQB, UK lanTurner PhD, Research Fellow, Experimental Electrophysiology Unit, Papworth Hospital, Cambridge CB3 8RE, UK Correspondence to: Professor W G Kernoharl~
Tel.: +44 1232 366532; Fax:+44 1232 368202; Email: wg.l
The United Kingdom Central Council for Nurses, Midwives & Health Visitors, through the 'Scope of Practice' initiative, has been given the opportunity to develop and create roles for the benefit of client care. There is no doubt that nurses, midwives and health visitors are very competent at detecting hip abnormalities in infants (Hough, Trainor & Kernohan 1997 Journal of Orthopaedic Nursing I (I): I I-16). This article describes how the competency of health visitors in baby hip testing can be established, improved and demonstrated to all. In this way standards of practice will be of the highest. Most importantly, hip abnormalities will be more accurately and effectively detected and treated at an early stage when intervention is easier, less radical and minimally stressful for all concerned. PD
INTRODUCTION Developmental dysplasia of the hip (DDH) has long been recognized as an important orthopaedic condition, and affects the stability of hip joints in approximately three per 1000 children within the UK (Dunn et al 1985, Macnicol 1992). Because DDH treatment is far simpler and more successful if the condition is detected at an early stage, screening programmes have been introduced and widely implemented, with mixed degrees of success (DHSS 1986, Hadlow 1988, Krikler & Dwyer 1992). A central part of the screening process for DDH is the physical examination of the child, often by staff such as health visitors, where a number of physical signs, such as leg length or skin crease asymmetry are assessed. The most important aspects of the examination in young children, how-
Journal of Orthopaedic Nursing (I 998) 2, 141-1479 1998Harcourt Brace& Co. L~d
ever, are the Ortolani (1937) and Barlow (1962) tests, where the hip joints are manipulated to assess their stability. Although specialist centres, which use dedicated staff, have reported very good results with this approach, other centres have reported poorer levels of performance and there has been some discussion as to the ability of less experienced staff to perform the tests (Krikler & Dwyer 1992, Haugh et al 1994). Video recording of staff has shown that many were not able to perform these physical tests correctly (E1-Shazly et al 1994). However, accurate assessment of video recordings and the definition of why a person was unable to correctly identify a hip abnormality proved difficult, even when viewing static images of the tests. Therefore, a method was developed for measuring the applied forces and exact movements of the hands during the Ortolani or Barlow tests using a force and displacement
142
Journdlof" Orthopaedic Nursing ,~,,~. . . . . . . . .
Dysplastic
. ~
Abduction
Dislocated
Fig. I A mildform of hip disease 'dysplasia'(left) is formed where the socket is shallow, denyingadequate coverage to the femoral head. A more shallow socket or general laxity (right) leads to a dislocatable or unstable hip.
transducer system (Chow et al 1994). This was able to identify the biomechanical events leading to the movement of the femoral head required to detect an abnormality. This system was used to assess the examination technique of a group of health visitors who were attending a refresher course on the screening for DDH in order to identify any weaknesses in their examination practice and to evaluate the success of the training course in overcoming these problems. Although broadly similar techniques have been used to measure hand forces during manual (Armstrong et al 1979) or medical (Sorsab et al 1988) applications, this is the first known application of such a technique to study force and motion during a physical examination process.
ORTOLANI AND BARLOWTESTS DDH is a range of abnormalities affecting the hip joints in young children. The normal hip joint is formed by a deep acetabulum into which fits the femoral head. The joint is given extra stability by the presence of ligaments within the joint and joint capsule, and also by a fibrous ring around the edge of the socket, the labrum. The mildest form of DDH is when the acetabulure is shallow (Fig. 1); a situation known as a dysplastic hip. If the joint is shallow enough, or if the supporting ligaments are lax, then the femoral head can be dislocated from the socket relatively easily; a dislocatable or unstable joint. Some cases exist where the femoral head is completely dislocated from the socket and force is required to reduce it back to a normal position; a reducibly dislocated joint. In severe cases, the femoral head cannot return to the socket due to the presence of some soft tissue defect such as an infolded labrum; an irreducibly dislocated hip. The Ortolani and Barlow tests involve the manipulation of the joint in order to dislocate and relocate the femoral head from the acetabulum. This movement of the femoral head can be felt as a palpable 'clunk' by the examiner, similar to the sensation of putting a car into gear. These 'clunks' have to
Fig. 2 Duringthe Ortolanitest (above) a dislocated hip is reduced in a combinationof abductionand gentleforce, causinga palpablevibrationthat can be felt or even heard by the examiner.Barlowamended the test (below) to obtain a test for a dislocatablehip usingstress applied posteriorly.
be differentiated from the more innocuous 'clicks', which are higher frequency vibrations produced by ligament movements and synovial fluid cavitation within the joint. Central to the whole test procedure is the correct manipulation of the hips to produce the conditions likely to dislocate or reduce the femoral head without causing discomfort or harm. The Ortolani test was developed to detect the dislocated femoral head. The hips and knees of the infant are flexed to 90 ~ and the legs then smoothly abducted whilst pressure is applied upwards and inwards by the examiners' fingers over the greater trochanter (Fig. 2). This pressure should be sufficient to reduce the femoral head when the force components are directed in the appropriate direction to lift the femoral head over any obstruction outside the acetabulum. The Barlow test is identical to the Ortolani test but with the addition of an extra manoeuvre at the start of the test to stress the joint in an attempt to dislocate the femoral head from the socket (Fig. 2). The reduction of the head back into the acetabulum can then be detected by the Ortolani abduction manoeuvre. Both of these tests are used on children up to 3 months or so of age, when most children are becoming too large to have the Barlow test performed accurately on them. The Ortolan] test can often be performed on children up to 9 months or so of age. Previous work by the group on the measurement of the biomechanical features of the two tests had highlighted a number of points. One of the most important was the need to move the leg being manipulated through the correct range of angles in order to
Health visitor training for developmental dysplasia of hip dislocate or relocate the femoral head. This appeared to be due to the geometrical properties of the joint, with a certain magnitude of force being required in the appropriate direction in order to lift the femoral head over any obstruction to movement. The correct manipulation of the leg, along with appropriate magnitudes of force, is essential for the safe execution of a test that can dislocate or relocate the femoral head, and therefore detect an abnormality. The force-displacement transducer system proved to be highly suited to the measurement of the applied forces during an examination, whilst also providing an accurate record of the motion of the femur. This allowed an insight into biomechanical processes during an examination, along with an objective record of the dislocation and relocation events produced by the manoeuvres. None of these could be accurately obtained from video recordings. This study therefore used a force-displacement transducer system to measure the manoeuvres performed by health visitors before and after training to evaluate both their performance and the ability of the system to identify faults in the examiners' techniques.
METHODS The aim of the project was to assess the examination skills of student health visitors before and after an update session on the correct examination techniques. During the study period, nine students attended the refresher course. All were in the final phase of their training and had already attended a 2-hour teaching session on DDH at the start of their course. They had also spent at least 6-months working within the community and all had experience of examining children regularly under clinical conditions. They attended classes in order to update their skills in the examination and history taking required in order to screen correctly for the condition. Only one student had received any further training in DDH between the initial lesson and the update session. All of the health visitors were asked to examine two 'baby hippy' models and to report their findings on the type of abnormalities detected. These models were developed in order to train medical staff in the examination techniques by closely simulating the dislocated and unstable hip abnormalities (Cole 1983). One of the models used in this study (model 1) was an unmodified example and exhibited a dislocated left hip and an unstable right hip. The second (model 2) had been modified using plastic inserts to deepen the acetabuhim to give a normal fight hip and using a foam insert into the acetabulum to simulate an irreducibly dislocated left hip. The health visitors were blinded as to which model they were examining in order to exclude the likelihood of them remembering which hip had which abnormality.
14:}
Splint
LVDT
i
R2
~
I Force P l a t e
Fig. 3 The apparatus consisted of a clamp (not shown) which secured a mannequinto a force plate, and a small displacement(linear VariableDifferentialTransformerand rotational transducer system (RI, R2) was attached to the model via a plastic splint.The examiner'sforefingerslay over this splintas shownto ensure a firm contact between the splintand the leg. Movementsof the splinttherefore reflected movements of the mannequin.
The students were first asked to examine a 'baby hippy' model mounted in the test apparatus. The apparatus consisted of. a clamp that attached the 'hippy' securely to the force transducer, and a small displacement and rotation transducer system that was attached to the model's leg via a plastic splint (Fig. 3). The examiner's forefingers lay over this splint to ensure a firm contact between the splint and the leg, so that movements of the splint accurately reflected movements of the leg. Each student was allowed to examine the hip as often as they liked in order to familiarize themselves with the procedure. This was carded out to ensure that the splint, although small, had as little effect as possible on the outcome. The first phase of the study involved the students examining model 1 whilst using the apparatus. After an initial familiarization period with the equipment, they were requested to perform whatever tests they would normally use during clinical practice. A separate recording was made for each test and each leg. Recordings from a pilot study on staff within the department had shown insignificant differences between the results obtained from both models. The decision was therefore made to concentrate on recordings from model 1 since this model exhibited abnormalities that were detectable by the Ortolani and Barlow tests, and time limitations precluded recordings from both models using the transducer system. Immediately after the first phase, the students were asked to repeat their examinations on both models without using the transducer system, i.e. as they would in clinical practice. In this phase they were simply asked to identify any abnormalities with each of the hip joints. The models were presented in a random order so that the students were unaware of the types of abnormality to expect. The first and second phases were repeated once the students had completed the training course. As before, they examined model 1 using the transducer system, followed by a blinded examination of both models to identify any hip abnormalities.
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Journalof OrthopaedicNursing
Force, N Maximum,posterior dislocated hip Maximum,anterior dislocated hip Maximum,posterior unstablehip Maximum,anterior unstablehip Maximum,posterior both hips Maximum,anterior both hips To reduce dislocated hip joint
Force, N Maximum,posterior, dislocated hip Maximum,anterior, dislocated hip Maximum,posterior, unstablehip Maximum,anterior, unstablehip Maximum,posterior, both hips Maximum,anterior,both hips To reduce dislocated hip To dislocate unstablehip To reduce unstablehip
RESULTS The first feature that was apparent from the precourse analysis was that although all of the students knew some variations on the Ortolani and Barlow tests, they were unable to perform identifiable versions in some cases. For example, before training only six of the students were able to perform an Ortolani test. The remainder performed only a single test that, because it appeared to contain some stress element, was included under the Barlow test section during analysis (Table 1). Before training, the biomechanical features of the Ortolani test were available for the six students that attempted this manoeuvre for both the dislocated and unstable hips (Table 2). A wide range of peak posterior force (0-30 N) and peak anterior force (-20-0 N) were observed before training, with mean values of 9 N and - 8 N respectively. In all cases the magnitudes of these forces were relatively small. The force and displacement traces were also examined after filtering with a digital differentiator in order to identify transients where the femoral head moved rapidly into, or out of, the acetabulum. These signals of force and displacement allowed successful tests to be objectively identified and the pattern of applied force to be recorded.
Before trainin~ 7 (5) I I (7) I I (I I) -5 (5) 9 (8) -8 (7) 0 (9)
Before training 32 (16) -7 (8) 32 (26) 15 (9) 32 (21) -II (9) 20 (17) 14 (2) 3 (3)
After training I0 (9) -7 (8) 9 (8) -7 (5) 9 (8) -7 (6) 6 (9)
After training 30 (6) -7 (S) 22 (13) -9 (8) 26 (I I) -8 (6) 12 (I I) 13 (7) 5 (8)
The peak forces and force at relocation were also recorded after training and are shown in the second column of Table 2. The ranges of these values were similar to those before training, with the peak posterior force varying between 1 and 24 N, and the peak anterior force between -27 and 2 N. All nine students attempted some form of the Barlow test before training on both the dislocated and unstable hips (Table 3). All nine managed to reduce the dislocated hip during this manoeuvre, but only two were able to dislocate and relocate the unstable hip joint. The peak posterior forces ranged from 3 to 91 N and the anterior force ranged from -31 to 6 N before training. After training these ranges became 4-49 N and -23-1 N, respectively. The ranges of abduction and adduction of the femur were also recorded during the tests. The minimum and maximum abduction angles were recorded, along with the angles for any identified dislocation or relocation events (Table 4). Finally, the diagnostic accuracy of the students both before and after training was recorded for each of the hips when they were examined without using the transducer system (Table 5). An improvement in diagnosis was noted in the majority of hips after training, particularly in the ability to recognize the unstable hip.
Health visitor training for developmental dysplasia of hip
Angle (de~rees) Minimum,abduction,both hips-Ortolanitest Maximumabductionangle, both hips-OrtolaNtest Of relocation,dislocatedhip-OrtolaN test Maximum,adduction,both hips-Barlowtest Maximumabduction,both hips-Barlowtest Of dislocation,unstablehip-Barlowtest Of relocation,unstablehip-Barlowtest Of maximumexertion-Barlowtest
DISCUSSION Only six of the students were able to perform a recognizable Ortolani test before the course. A wide range of peak forces was noted although the mean peak posterior force (9 N) and mean peak anterior force (-8 N) over both hip types were relatively small. The wide range of forces appeared to reflect both different manipulation techniques and different amounts of stress applied by the examiners. This was particularly apparent with examiner 4 for example, who appeared to use significantly more force than the others (a mean of 30 N), and who also varied the amount of force used between the five successive tests (range 20-37 N). Despite these differences, all of the students that performed this test were able to relocate the femoral head into the acetabulum, as detected by force transients during the reduction manoeuvre. The posterior force applied to the two different types of hip did not appear to be significantly different (7 N vs 11 N; P=non-significant; Wilcox signrank test), whilst there was a small but significant difference in the peak anterior force (-11 N vs - 5 N; P<0.05; Wilcox sign-rank test). The examiners use different hands when testing the two hip types, the left hand for the unstable hip and the right hand for the dislocated hip. All of the examiners were righthanded, and these findings suggest the dominant hand applied some slight additional force when abducting the leg. These differences disappeared after training. The results for the Ortolani test after training were broadly similar to those before, except for the fact that all of the students performed a recognizable version of the test. All of the students could successfully relocate the hip joint, as detected by transients
Before training I (4) 58 (8) 23 (4) -6 (6) 45 (9) -3 (3) 23 (5) 15 (18)
145
After training 3 (6) 45 (I 2) 24 (S) -8 (7) 39 (I O) -2 (4) 25 (8) 92 (6)
in the force and displacement traces and were able to accurately describe the relocation events as 'clunks'. There was no significant difference in any of the force variables after training when compared with those before. One difference that was noted after training was that the students appeared to abduct the hips over a smaller range of angles after training. Maximum abduction was 58 ~ before training versus 45 ~ after (P<0.05; Wilcox rank sum test). There was no significant change in the minimum abduction angle. Before training, all of the students appeared to attempt some form of the Barlow test. This is similar to the Ortolani test, but involves an extra manoeuvre where the posterior stress is applied to the hip in order to dislocate an unstable hip from the socket so that it can be detected by palpating the 'clunk' as it is subsequently reduced during the abduction phase of the test. As a result of this extra stress phase of the test, the peak posterior force was significantly larger than that for the Ortolani test (Barlow = 32 N; Ortolani = 9 N; P<0.05) and forces up to 106 N were recorded. Forces this high are substantial and it has been suggested that excessive force could pose a possible risk to the integrity of the joint itself (Moore 1989, Jones 1991). Although the peak anterior forces were generally similar to those from the Ortolani test (Barlow mean = -11 N; Ortolani mean = - 8 N; P = NS) a few examiners used significantly larger forces, up to -31 N. This was unexpected since the abduction stage of the manoeuvre is the same as for the Ortolani test. Observation of the students and discussion with them about their techniques would suggest that this feature may well be due to the fact that the students tended to grip the legs harder when applying stress at the start of the test, and continued to apply more force during the abduction stage instead of relaxing their grip. Before training, all of the students were able to relocate the dislocated femoral head during the Barlow test, although one was unable to palpate the reduction events and recognize these as abnormal. The results from the unstable hip were more disappointing, however. Only two students were able to dislocate and relocate the femoral head successfully, and both of these students correctly identified the hip as abnormal. Two of the students failed to dislocate the head at all because they did not abduct the
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Journalof Orthopaedic Nursing
leg to a large enough angle for the posterior force to be in the correct direction to lift the femoral head out of the socket. Four of the students applied the posterior force at the wrong stage of the test, i.e. during the abduction rather the adduction phase so that the force was in the wrong direction to dislocate the head. One released the stress too early so that the femoral head slid back into the socket before the abduction phase. The application of stress at the wrong stage was the most common reason for failure and is reflected in the difference in angle at which peak force was applied before and after training (Table 4). The early release of stress, before the abduction phase of the test, tends to produce a slow and smooth movement of the femoral head. This is very subtle and it appears that the slow movement is difficult for inexperienced staff to palpate compared to the much larger 'clunk' as the head jumps back into the socket during the abduction phase. After training there was a significant improvement in the ability of the students to perform a B arlow test. An important component in the training was the emphasis on the importance of gentle testing of the hips. This was reflected by the general reduction in the peak posterior force (32 N before vs 26 N after; P=non-significant) and peak anterior force (-12N before vs - 8 N after; P=non-significant) after training, although neither of these reached statistical significance. The ability to dislocate the unstable hip increased from 2/9 to 8/9 (P<0.05; McNemar test). The single failure was due to insufficient adduction of the hip during the initial stress phase of the test. A second student failed to detect an abnormality due to her inability to palpate the 'clunks' as the femoral head was dislocated or reduced. This student had similar problems in both the Ortolani and Barlow tests due to her small hand size. She was unable to place her fingers over the greater trochanters during abduction and was therefore unable to palpate the rapid movement of the femoral head. This was corrected in subsequent training courses by using a modified hand position for staff with smaller hands. All of the students who dislocated the hip were able to reduce the joint successfully. In the pilot study it had been noted that insufficient abduction of the legs meant that some examiners were unable to reduce the hips. The recognition of this factor had led to changes in the training practice before this particular course to ensure that all students abducted the hips through an appropriate range of angles. The figures quoted above show that there was a significant improvement in the examination technique of the students after training. This was reflected by the increase in detection rates for the dislocated hip (8/9-9/9; P = non-significant) and the unstable hip (2/9-7/9; P<0.05). There was little change in ability to recognize the irreducibly dislocated hip (3/9) or the normal hip (5/9-6/9; P = NS).
The irreducibly dislocated hip only exhibits very subtle signs of movement. Because this hip cannot be reduced no obvious 'clunk' can be felt, making diagnosis very difficult. Other physical signs of this hip abnormality, such as restriction of abduction, were not simulated in this case but may be included in further work. The normal hip model deteriorated during the course of this study, particularly after some of the students applied a large amount of force to the joints during the examination. When examined by experienced staff at the end of the study this hip was found to exhibit a small degree of movement in the hip which, although not diagnostic of a dislocation, was not completely normal. Only the last three students reported an abnormality with this hip and it may be that this movement was present throughout their examinations. In general the students reported a much greater confidence in their ability to detect the differences between normal and abnormal hips at the end of their training.
CONCLUSION The study identified and highlighted: 9 There were some small but significant changes in the main features of the Ortolani and Barlow tests after training. 9 The main use of the force and displacement transducer system was in the recognition of the reasons for the failure of the tests. For example, many students applied the correct force but at too small an adduction angle to dislocate the hip joint in the Barlow test, whilst some were found to be producing dislocation or relocation transients but were unable to recognize these as abnormal events. 9 Excessive force during examination could pose a risk to the integrity of the hip joint. 9 There is a need to use 'gentle' testing of the hips. 9 The application of stress at the wrong stage was the most common reason for failure. Although not part of this study, the ability of the system to identify faults suggests that further development of this approach may be worthwhile in order to provide feedback during training sessions for students who have difficulty in learning the tests.
REFERENCES ArmstrongT J, ChaffinD B, FoulkeJ A 1979A methodology for documentinghand positionsand force during manualwork. Journalof Biomechanics12: 131-133 Barlow T G 1962 Early diagnosisand treatmentof congenitaldislocationof the hip. Journal of Bone and Joint Surgery44B: 292-301
Health visitor training for developmental dysplasia of hip Chow Y W, Turner I, Kernohan W G, Mollan R A B 1994 Measurement of the forces and movements involved in neonatal hip testing. Medical Engineering and Physics 16:181-187 Cole W G 1983 Evaluation of a teaching model for the early diagnosis of congenital dislocation of the hip. Journal of Pediatric Orthopedics 3:223-226 DHSS 1986 Screening for the detection of congenital dislocation of the hip. Department of Health and Social Security, London Dunn P M, Evans R E, Thearle M J, Griffiths H E D, Witherow P J 1985 Congenital dislocation of the hip: early and late management compared. Archives of Disease in Childhood 6 0 : 4 0 7 4 1 4 El-Shazly M, Trainor B, Kernohan W G e t al 1994 Reliability of the Barlow and Ortolani tests for neonatal hip instability. Journal Medical of Screening 1:165-168 Hadlow V 1988 Neonatal screening for congenital dislocation of the hip: a prospective 21-year survey. Journal of Bone and Joint Surgery 70B: 740-743
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Haugh P E, Mason C, Trainor B P, Kernohan W G, Mollan R A B 1994 An evaluation of the adequacy of health visitor education for neonatal hip screening. Journal of Advanced Nursing 20:815-821 Jones D A 1991 Neonatal hip instability and the Barlow test. Journal of Bone and Joint Surgery 73B: 216-218 Krikler S J, Dwyer N St J P 1992 Comparison of results of two approaches to hip screening in infants. Journal of Bone and Joint Surgery 74B: 701-703 Macnicol M F 1992 The early management of congenital dislocation of the hip. Current Orthopaedics 6:245-251 Moore F H 1989 Examining infant hips - can it do harm? Journal of Bone and Joint Surgery 71B: 4-5 Ortolani M 1937 Un segno poco noto e sua importanza per la diagnosi percoce di prelussazione congenita dell'anca. Pediatria 45:129-136 Sorsab J, Allen R, Gonk B 1988 Tactile sensory monitoring of clinician-applied forces during delivery of newborns. IEEE Transactions Biomedical Engineering 35: 1090-1093