Leg length inequality is still the beloved of examiners in the FRCS Orth exam. If you cannot define a simple deformity such as leg length inequality then, so the examiners reasons go, you are not safe when it comes to the assessment of more complex deformities, hence the request “to try again” Furthermore nothing irritates an examiner so much as to come across a candidate whose ability to display physical signs at this level of examination is extremely poor. If you cannot work out the following you are in trouble! • Whether shortening is present or not • If yes is the shortening real or apparent? • If real is it above or below the knee. • If above the knee is it above or below the trochanter
Shortening in one limb is usually compensated by • Tiling the pelvis down (ASIS dips at a lower level) • Equinus position of the foot • Flexing the opposite lower limb at the hip and knee
True shortening The affected limb is physically shorter than the other leg. The cause may be above or below the trochanters. It is the measurement taken from the ASIS to the medial malleolar tip while both lower limbs are in identical positions and the pelvis is square
Apparent shortening The amount of apparent shortening is the sum of the true shortening plus the shortening due to fixed deformity. It is the apparent shortening that matters to the patient. This measurement helps in assessing the extent of natural compensation developed for concealing the actual disparity at the hip joint especially by tilting the pelvis sidewards (fixed abduction and fixed adduction deformity) On many occasions this natural compensation improves cosmetic appearance.
Be on guard if the examiners ask you about the difference between “true” and “apparent shortening”.You need a “tight, sharp and definitive” answer. If you seem uncertain you will very quickly get dragged down by the examiners. The examiners view would be that it is a good topic to potentially catch a candidate out on. Remember part of the skill of being an examiner is to somewhere along the way differentiate between good and bad candidates.The trouble is that examiners can easily end up confusing matters even for the best of candidate . “The candidate got confused on the difference between real and apparent shortening”
• If the true shortening is equal to apparent shortening it indicates there is no compensation. • If the true shortening is more than the apparent one it indicates that part of the shortening has been compensated for. • If the true shortening is less than the apparent shortening it would suggest a fixed adduction deformity besides shortening without any compensation
The difference in leg lengths can be at a number or combination of different sites. At FRCS Orth level you will have to demonstrate an understanding of the different segments and how you can clinically differentiate between the main areas. Keep it simply but be precise as the examiners can also get confused and will invariably turn it back on you.3
Possible sites of LLD (Proximal to distal) • Spine • Pelvis • Femoral head/neck • Femoral segment • Tibial segment • Hindfoot
Examination of shortening standing
Use the block adjustment method in the standing weight-bearing position Usually the patient compensates for shortening by abducting the leg thereby making the pelvis on that side tilt downwards This is represented by a lower level of the ASIS on that side. Ask the patient to bring the abducted lower limb to as far as the zero position while the trunk is erect. He/she is able to do so by gradually lifting the heel in the process of which the ASIS starts moving upwards As soon as both ASIS are level insert wooden blocks beneath the affected foot so as to keep up that level. The height of the wooden block required is the limb length disparity A more accurate method that may be brought up in a discussion is either a scanogram or spiral CT scout film
Examination of shortening supine
Make a point to the examiners of demonstrating that the pelvis is square to the table. Attempt to make the legs square with the pelvis and straight The legs should be put in equivalent positions if possible. If there is pelvic tilting due to an adduction contraction of the hip (as is the case with apparent shortening) it will not be possible to do this. Square up the pelvis and the hip deformity will show up The limb length from ASIS to the tip of the medial malleolus is measured in the deformed position of the limb. When the normal limb is being measured for comparison it is necessary that it be placed in the position as that of the affected limb If there is pelvic tilting due to a postural scoliosis, which is compensating for true shortening this should be able to be overcome by adjusting the position of the patient.
To measure for true shortening it is important that clear anatomical landmarks are established. Place the measuring tape over the centre of the ASIS and then press it backwards until it slides distally, hooking under its inferior edge. For the lower mark choose either the middle or inferior border of the medial malleolus The medial malleolus should present no problem as it is easily palpated subcutaneously but the ASIS can sometimes be difficult to palpate in obese patients. It is easy to introduce an error of a cm or so in leg length measurements if you do not measure from equivalent positions bilaterally. Do not appear awkward fumbling about for the ASIS
Apparent shortening may be roughly estimated by measuring the distance between any fixed central point on the trunk (usually xiphisternum)and distally to the sharp bony point of the medial malleolus. The lower limbs should be in a parallel position
Comment to the examiners on the presence of an adduction contracture. “I am unable to place the legs perpendicular to the pelvis because of an adduction contracture and therefore I must place the other leg in the same position.” This is difficult and cannot be done simultaneously
Advanced examination of leg shortening
If you have an intermediate case of leg shortening you would be expected to go on and perform more advanced examination procedures.These include Galleazzi’s test,Bryants triangle,Nelatons line and perhaps Schoemakers or Chienes line.
If there is shortening in a limb a candidate should go on and perform Galleazzi’s test. This test demonstrates whether the shortening is in the femur or tibia The patient is supine with the hips flexed to 45º and the knees flexed up to 90º. Place the malleoli together(the test is inaccurate if you are unable to do so). The examiner assesses the position of both knees from the end of the bed and from the side Comment on whether the knees are level or at a different level and on the parallelism of the femora and tibia. Normally both knees are at the same level When one knee projects farther forwards than the other,either that femur is longer or the contra-lateral femur is shorter When one knee is higher than the other,either the tibia of that side is longer or the contra-lateral tibia is shorter
This test measures supratrochanteric shortening Again candidates should know this test and be prepared to demonstrate it to the examiners. The patient can lie supine with the pelvis square and limbs in identical positions. We don’t think you will be asked to draw it out but you may need to be able to demonstate it with a tape measure An alternative position to demonstrate landmarks is lateral,some candidates find it easier
Identify the ASIS with your thumb and the tip of the greater trochanter with your main finger and the base of the triangle with your index finger.
This is not strictly Bryants triangle test- it is a test for proximal migration of the greater trochanter. Bryants triangle test involves officially drawing out with pen various lines on the pelvis
A perpendicular line is dropped from the anterior superior iliac spine (ASIS) onto the bed. From the tip of the greater trochanter another perpendicular line is dropped onto the first line (Base of the triangle). The tip of the greater trochanter is joined to the ASIS’s on the respective sides. This forms a triangle ABC.Each side of the triangle is compared with its counterpart on the opposite side The length of BC line is compared between the two sides. Relative shortening on one side indicates that the femur is displaced upwards as a result of a problem in or near the hip joint. If the problem is bilateral, Bryant’s triangle is unhelpful.
Shortening above the trochanter may be caused by destruction of the femoral head or acetabulum or both, a dislocated hip, coxa-vara deformity of a mal-united inter-trochanteric fracture.
“I would like now to perform Bryants triangle test to see whether there is any shortening above the trochanter (supra-trochanteric)”. “When Bryants triangle is constructed the perpendicular distance is shorter by 2 finger widths between the ASIS and greater trochanter on the right side.”
The patient lies with the affected side uppermost. With the hip flexed up 900 the tip of the greater trochanter should lie on or below a line connecting the anterior superior iliac spine and ischial tuberosity. In cases of supra-trochanteric shortening the trochanter will be proximal to this line
With the patient lying supine a line joining the ASIS and tip of the greater trochanter is extended on the side of the abdomen on both sides. Normally, these lines meet in the midline above the umbilicus. In the case of one of the greater trochanters migrating proximally, the lines will meet on the opposite side of the abdomen and below the umbilicus. If the problem is bilateral the lines will meet at or near the midline but below the umbilicus.
With the patient lying supine lines are drawn joining the two ASIS and the two greater trochanters. Normally, these make two parallel lines. In the case of one trochanter moving proximally, the lines will converge on that side
Testing for Adduction/Abduction contracture
In the presence of either an adduction or abduction deformity the patient will tilt their pelvis in order to conceal it.
An abduction contracture of the hip causes a functional leg length difference.The pelvis dips towards the affected side,the normal leg appears shortened and the affected leg lengthened.
The opposite occurs with an adduction deformity.The affected leg appears shortened and the patient attempts to compensate with elevating the ASIS on the affected side to bring his or her legs into parallel alignment.
• If both ASIS are at the same level and the pelvis is square there is no adduction or abduction deformity. • If the ASIS on the affected side is higher an adduction deformity is present.Squaring the pelvis will unmask the deformity • Similarly if the ASIS on the affected side is lower than the normal side an abduction deformity is being compensated for by the pelvic tilt.
Comment on the contracture to the examiners “I am unable to place the legs perpendicular to the pelvis because of an adduction/abduction contracture”
Fixed adduction at the hip on one side With a fixed adduction of the hip on one side you must place the other hip in a matching position by crossing the legs and then proceed with measurement of leg lengths This cannot be done simultaneously without assistance. Therefore the most practical way to measure leg lengths is to cross legs sequentially Cross one leg and measure and then cross the other leg and measure
Fixed abduction at the hip on one side Comment on the fixed abduction to the examiners “I am unable to place the legs perpendicular to the pelvis because of the abduction contraction and must place the normal leg in the same position.” Abduct the unaffected hip to the same degree Measure leg lengths
Flexion contracture of the knee Comment on this to the examiners “I am unable to place the legs straight because of the fixed flexion of the knee” You must place the other leg in the same position.One could flex the unaffected knee over a bolster to the same degree and then measure leg lengths
Valgus knee Comment on this deformity to the examiners “I am unable to place the leg straight because of the valgus knee. I am unable to place the opposite leg in the same position” Note the difficulty and therefore you must measure component parts of the leg.This approximates to a true leg length You measure from the ASIS to the tibial tuberosity and then from the tibial tuberosity to the medial malleolus
Long Case The long case had been a relatively straightforward osteoarthritis of the right hip complicated by a significant fixed adduction contraction. This had thrown the candidate badly. He had measured leg lengths in front of the examiners stating that the right leg was 4 cm shorter than the left. The examiners asked him if he was sure this was correct. They suggested he levelled the pelvis and position the left leg in the equivalent position as the right one, crossing the legs sequentially when measuring leg lengths. The candidate was forced to concede he had measured the leg lengths wrongly. “I don’t know how I got it mixed up so badly, maybe the stress of the examination but I looked a fool and knew straight away that I had blown the long case.” “There was no way the examiners could pass me if I could not do a simple thing such as measure leg lengths correctly” The candidate performed reasonably well otherwise although he had to bluff his way through an answer when questioned about how he could measure acetabular wear in a total hip replacement. [The examiners simply wanted him to say he would compare radiograph of the hip replacement with previous ones to see how much the head had migrated medially.] Unfortunately the candidate did in fact fail his long case.