Limb
Length Inequality: A Much Discussed but Little Understood Medico-legal Quandary.
Dr K.S. Dhillon. MBBS, FRCS, LLM.
Introduction
In law, a person who is injured, due to the fault of another individual, is entitled to compensation for personal injury. In the assessment of damages resulting from the injury and the assessment of award for damages, the legal fraternity depends on a medical report prepared by doctors. The medical report is required to categorise and identify the severity of the injuries as well as to know the effects/ disabilities produced by the injuries. There is a significant difference between a medical examination for treatment and that for legal purposes. An examination for treatment is aimed at treatment and that for legal purposes is to ascertain damages and compensation. In the assessment for damages the asymmetry of the lower limbs and shortening of the limb is taken into consideration for award of damages. It is common belief that the human body is symmetrical and many doctors as well as many in the legal fraternity are unaware that the human body is inherently asymmetrical.
In a normal population 90% of individuals have a 5.2mm limb length inequality. In 32% of the population there is limb length inequality of between 0.5 to 1.5 cm and in 4% there is inequality of more than 1.5cm. Limb length discrepancy of less than 2 cm does not appear to affect function and there is no need to equalise the limb length discrepancy. For accurate assessment of limb length inequality radiological imaging is required. Clinical assessment of discrepancy is a good screening technique but it is not a good technique for accurate assessment of limb length. The medical examiner has to take these factors into consideration before reaching a conclusion that a fracture has produced anatomical shortening or asymmetry.
Definition of limb length Inequality
Limb length inequality (anisomelia) could be due to structural asymmetry or functional inequality. In patients with structural asymmetry there can be actual shortening or lengthening of the limb. The actual structural skeletal length discrepancy is between the head of the femur and the ankle mortise and it could be in the femur or the tibia (not fibula). The causes of this discrepancy are varied and can be congenital/inherited or acquired. Congenital/inherited disorders include growth inhibiting conditions such as hypoplastic femur, Perthes disease and fibrous dysplasia and growth stimulating conditions such as vascular malformations, neurofibromatosis and fibrous dysplasia besides other causes.
The acquired causes of limb length discrepancy include growth inhibiting factors such as childhood fractures, infections and neurological damage (Polio, Cerebral Palsy, Head injury) and growth stimulating factors such as childhood fractures, haemangiomas, A-V malformations and infections [1]. In skeletally mature patients a common cause of acquired limb length discrepancy is due to fractures involving the femur or the tibia. However in the majority of patients the cause of the limb length discrepancy is not known even when there is a discrepancy of greater than 1 cm and it could be due to normal asymmetrical bone growth [2]. Genetic and environmental factors appear to influence ontogenesis of a person leading to this asymmetry [3].
Functional adaptation occurs in individuals with structurally short lower limbs which include foot pronation on the longer side and pelvic tilt leading to lower anterior and posterior iliac spine on the shorter side [3].
Functional inequality results when limb length discrepancy occurs in the absence of actual bone shortening or lengthening. It could be due to flexion contractures of the hip or knee and varus or valgus deformity of the knee besides other causes such as pelvic torsion and scoliosis. In functional limb lower limb inequality the pelvis rotates. The foot on the apparently short limb rotates externally, the heel goes into valgus and the foot arch collapses. The posterior iliac spine is higher on the apparently short side and the anterior iliac spine is high on the apparently longer side [3].
Classification of limb length discrepancy
The magnitude of limb length discrepancy has been classified into mild, moderate and severe [4].
Mild – difference of less than 3 cm
Moderate – difference of between 3 and 6 cm
Severe – difference of more than 6 cm
The definition of biomechanically significant limb length discrepancy remains controversial among orthopaedic surgeons. While most are convinced that moderate and severe discrepancies are associated with some structural and functional disturbances, mild (less than 3 cm) discrepancies have not been convincingly linked to any structural or functional disturbances [3].
Prevalence and clinical significance of structural/anatomic limb length inequality
Limb length inequality (LLI) appears to be universal phenomena. Knutson in a review of published data on limb length inequality obtained by accurate and reliable x-ray methods found a prevalence of anatomic inequality in 90% of the subjects studied and the mean magnitude of anatomic inequality was 5.2 mm (SD 4.1). He concluded that anatomic leg-length inequality does not appear to be clinically significant until it reaches a magnitude of 20 mm (3/4 inch) [5]. The shortening is more common on the right side but the difference between the two sides is not statistically significant [5].
The most common effect of this limb length inequality is pelvic torsion on weight bearing with the pelvis rotating anteriorly on the short side and posteriorly on the long side. The clinical impact of these dynamic changes remains unclear [6]. Pelvic torsion is the commonest method of compensation with up to 22mm of inequality. With greater degree of inequality knee flexion on the longer side is used as a compensatory mechanism [7].
Hellsing AL did a prospective study of young men during their military service to assess back function and pain before and after basic military training. Around 600 men were examined three times over a period of four years. The study found LLI of 0.5-1.5 cm in 32% of the subjects and 4% had a difference of more than 1.5cm. However there was no correlation between LLI and back pain or pain provocative tests [8].
Gross RH in 1983 studied the incidence and the degree of limb length discrepancy in 35 marathon runners, 70% of whom were in the 30s and 40s. His hypothesis was that the occurrence of asymmetry would be lower in marathon runners than in general population because of attrition of runners with LLI. However he found that 34 of 35 runners participating in the study had LLI when measured by radiography. Eighteen runners (51%) had LLI of less than 5mm, 10 (28.5%) had a LLI of 5 to 9 mm and 7 (20%) had LLI of 1cm or more. He concluded that ‘runners can function handsomely without equalization’ of asymmetry and ‘that discrepancies of 5 to 25 mm are not necessarily a functional detriment to marathon runners, and no consistent benefits could be attributed to the use of a lift’ [9].
Gross RH in 1978 in a ‘survey of 74 skeletally mature patients with LLI of 1.5 cm or more found that patients with less than 2.0 cm did not consider their short limb to be a problem in any way’. As the magnitude of discrepancy increased there were problems but there was no critical ‘cutoff’ point. Some subjects functioned well athletically with discrepancies of over 2.5 cm. He concluded that there is little indication for equalisation of discrepancies of less than 2cm and for larger discrepancies clinical judgement has to be used on an individual basis [10].
Kaufman et al studied gait asymmetry in patients with LLI. They investigated 20 subjects (mean age, 9.0 +/- 3.9 years) who had documented limb-length inequalities, to determine what magnitude of discrepancies resulted in gait abnormalities. The study involved dynamic gait analysis which showed that generally, a limb-length inequality > 2.0 cm (3.7%) resulted in gait asymmetry which was greater than that observed in the normal population. This gait asymmetry however varied for each individual [11]. Less than 2cm inequality does not seem to affect the kinematics [12].
A discrepancy in length of 5.5 per cent or more is associated with an increased mechanical work by the longer extremity and a greater vertical displacement of the centre of body mass. Clinically, this degree of discrepancy can be compensated by the use of toe-walking strategy while lesser degree of discrepancy can be overcome by a combination of compensatory strategies which normalize the mechanical work performed by the lower extremities [13]. Equalizing limb length can improve the symmetry of gait [14].
Gait asymmetry can easily be studied in a laboratory but it is more difficult to analyse the effect of limb length inequality on the spine, hip and the knee. The correlation between LLI and back pain, scoliosis, as well as knee and hip arthrosis has not been well established. The most commonly cited paper according to Knutson [5] which claims that LLI contributes to low back pain is that by Friberg [15]. Friberg studied 1,157 subjects from a military hospital who were exposed to extreme and repetitive loading military activities. Of these 1,157 subjects, 798 had chronic low back pain and the control was 359 with no low back pain. In 75.4% percent of those with back pain and 43.5% of controls there was a 5 mm or more of LLI. Friberg’s findings were questioned by other investigators [5] and Friberg defended his results and clarified that ‘LLI of less than 5mm has no relationship to lumbar scoliosis or back pain’ and ‘that even marked LLI per se neither produces LBP or contributes to its development if a person is not continually exposed to prolonged standing or gait, e.g., doing daily work, military training and sporting activities’ [16]. Soukka et al in a survey of 257 statistically matched working aged male and females subjects found that there was no increased risk of back pain with a LLI of 10 to 20 mm and that there was no conclusive evidence of increased risk of back pain with LLI of more than 20mm [17].
Gibson et al studied patients who had acquired LLI after femoral fractures. The study included patients between the age of 15 and 21 years who had sustained a fracture of the femur. There were 40 patients who were examined 10 or more years after the fracture. There were 15 patients with LLI of 1.5 cm or more who were studied further. The average LLI was 3 cm and ranged between 1.5 to 5.5 cm. During the 10 years only one patient wore a shoe raise and that too for a short period. None of the patients complained of low back pain and none had significant back pain over the 10 years. The acquired LLI produced little permanent structural abnormality in the spine and there was no degenerative changes seen in the spine after 10 years of the acquired LLI in skeletally mature individuals [18].
White et al studied 200 patients who had LLI after total hip replacement. They studied the relationship of LLI and functional outcome using the Harris hip score and the SF-36 Health Survey and found that leg lengthening (up to 35 mm) or shortening (up to 21 mm) had no correlation with functional outcome or patient satisfaction at six months after the surgery [19].
The association of LLI and lower limb complaints remains speculative. Tjernstrom and Rehnberg in a survey of 85 patients who had limb lengthening for shortening of between 3 and 14 cm (average 6cm) found that lower limb symptoms were not common in these patients and the effect of limb lengthening on joint symptoms was minor [20].
There appears to be no good evidence that LLI leads to osteoarthritis of the hip or the knee. In 2007 Golightly et al studied the relationship of LLI and osteoarthritis (OA) of the hip and knee. They examined the relationship of LLI with radiographic hip and knee OA in a community based sample. There were 926 subjects with knee OA and 796 with hip OA, and 210 (6.6%) had LLI of 2 cm or more. They found that there was a significant association between LLI and OA of the knee but there was no significant association with hip OA. The weakness of the study was that limb length measurements were clinical with a tape rather than the more reliable radiological method. Furthermore the authors admitted that LLI in patients with OA could have been contributed by the loss of joint space, disfigurement of the joint and malalignment of the joint that occurs with OA. In additions to these drawbacks, the joints were not examined for contractures which can contribute to LLI. The authors proposed that future research should study the relationship of LLI to OA of the hip and the knee [21].
Harvey et al [22] in a recent large prospective study used radiographs for LLI measurements. Their cohort consisted of 2964 individuals with the age between 50-79, who were with or at high risk for knee osteoarthritis. They found leg length inequality ≥1 cm in 14.5% of the study subjects at baseline. In individuals with LLI of ≥1 cm there was significantly higher prevalence of radiographic and symptomatic osteoarthritis at baseline. The predicted incidence of symptomatic knee osteoarthritis 30-months later was also higher in those with LLI of ≥1 cm. The shorter limbs were also at higher risk of of x-ray progression.
The authors however admitted that there are several weaknesses in their study. The number of incident radiographic OA cases were too small to effectively evaluate the effects of LLI and the authors were, for the same reason, unable to clearly define the risk associated with longer limbs and whether shorter or longer limbs were at higher risk of OA.
The second limitation of the study was the short duration of exposure due to the design of the study. A 30 month follow up was too short to detect progression of the OA. Furthermore even radiographic measurement limb length can be imperfect due to variation of knee flexion on standing radiographs. Hence there remains the possibility of misclassification and bias.
Gofton and Trueman [23] however stated that the LLI produces a pelvic tilt which leads to greater heel impact and stress on joints of the longer limb as compared with the shorter limb.
Kaj Tallroth et al [24] found that hip or knee arthroplasty due to primary OA was done 3 times more often in the longer lower limb than in the shorter limb.
There were however some limitations in this study. No knee radiographs were taken at baseline examination and neither was information about comorbidities, height, sporting activities and possible hip and knee problems during follow up, available. The only information available was the number arthroplasties done for primary OA of the hip or knee. In this 29 year follow up there was a surprisingly low incidence of OA [24].
Despite several studies having been published in the literature, the association of LLI and lower limb complaints remains largely speculative in nature.
Reliability of limb length assessment
Assessment of LLI is essential for appropriate treatment to be instituted. The limb can be measured clinically or by radiographic imaging techniques. Before using a particular technique it would be necessary to know the reliability (inter and intra-observer variation) and the accuracy (variation from actual length) of the technique used.
Clinical technique
The most convenient and commonly used method in clinical practice is the tape measure technique (TMM). The length of the lower limb is measured with a tape from the anterior superior iliac spine (ASIS) at the hip to the distal tip of the medial malleolus (MM) at the ankle.
However this method of measurement has some potential for errors, some of which include:
Limb Girth- The size of the limb may vary between the two sides due to muscle wasting or due to swelling and this can produce an error.
Difficulty in identifying the bony landmarks- The ASIS is difficult to palpate in obese individuals and MM can be difficult to palpate when there is swelling of the ankle. These bony landmarks may be deformed due to previous trauma making identification of the landmarks difficult.
Angular deformities- Presences of angular deformities at the thigh, knee, leg and the ankle can introduce errors. A varus deformity will produce shorting while a valgus deformity will produce lengthening of the limb.
Shortening distal to the ankle- This method does not measure shortening distal to the ankle mortise and can introduce error when there is bone loss distal to the ankle.
Contractures- Contracture at the hip and the knee as well as pelvic obliquity can produce functional shortening when there is no actual structural length discrepancy[25].
The problem of shortening distal to the ankle can be overcome by using an indirect method of measuring LLI. Blocks of known height can be place on the short side to obtain a level pelvis. This method also allows the treatment of LLI in patients with functional shortening.
A Galeazzi test is a quick and simple test which can be used to know whether the shortening is in the femur or the tibia. It is done with the person lying supine with the hip and knee flexed and the asymmetry of the level of the knees will confirm there is shortening and also reveal whether it is in the femur or the tibia. This test also eliminates the error of measurements when flexion contractures of the hip or knee are present. The actual length of the femur can be measured from the ASIS to the medial joint line and that of the tibia from the medial joint line to the MM.
Beattie et al studied the validity of tape measure method (TMM) for determining LLI when compared with a scanogram. They found that TMM derived measurement is a valid indicator of LLI and that the validity of the measurement is improved by taking the mean of two separate tape measurements. However the tape measurements were less reliable in healthy subjects as compared to those with LLI [26]. Cleveland et al on the other hand showed that there is a statistically significant and weak correlation between radiographic measurements and physical examination measurements [27]. With tape measurements the accuracy in identifying the bony landmarks in obese patients, discomfort of the patient during the examination, and correct positioning of the patient by the examiner must be kept in mind.
Harris et al studied LLI in 35 patients with femoral fracture who were treated with nailing. Of these 35 patients, 15 patients (43%) had a measurable LLD. They found that ‘there was a positive correlation between direct leg length measurement and the block test (P = 0.003), and between the block test and patient perception of limp and LLD’ however ‘there was no correlation between CT scanogram and clinical measurement of leg length or between CT scanogram and patient perception of LLD or limp’ [28].
Imaging technique
Imaging techniques commonly used for assessment of LLI include plain radiography and computerised radiography.
Plain radiography
Techniques for measurement of LLI by plain radiography include:
Orthoroentgenogram- This old technique requires a long cassette (longer than the limb length) with three exposures, each centred on the hip, knee and the ankle [29].
Plain radiographic scanogram- This technique uses 3 ordinary cassettes lined up under the limb with the patient supine and a radio-opaque ruler tape to the table. The cassette is moved with each exposure centred on the hip, knee and the ankle [30].
Teleroentgenogram- This technique involves a full length standing AP of the lower limbs using a long cassette with the X-ray beam at about 6 feet. The technique is similar to an Orthoroentgenogram but here a single exposure is used instead of three exposures. This technique is however subjected to magnification error.
Computed radiography- A full length radiograph of the lower limbs can be obtained by obtaining 3 images on a vertical cassette holder containing 3 cassettes. The images are then transferred to a computer where a good quality full image can be downloaded and measurements done [25].
The inter and intra-observer reliability may vary from about 1.5mm to about 5mm. Up to about 10mm would be a threshold for a meaningful difference when assessing differences in measurements by these techniques [25].
CT scanogram
A CT scan is a very useful tool for assessment of limb length discrepancy. A scout view of both femurs and tibias can be obtained and the length of the femurs and tibias can be easily measured. The length of the femur can be measured from the tip of the femoral head to the distal end of the medial femoral condyle and the length of the tibia from the upper end of the medial tibial condyle to the tibial plafond. This technique appears to be more accurate than the plain radiography techniques [25].
The use of a tape is a cheap, simple and non-invasive screening technique for LLI. However it has potential for errors such as difficulty in palpation of bony landmark, difference in size of the limbs, angular deformities of the limb and contractures of the hips and knees. For more accurate assessment of LLI, radiographic techniques need to be used. The type of radiographic technique used will depend on the resources available. CT scans appear to be more accurate and reliable and will require less training and supervision of radiographers when compared with plain radiographic techniques [25].
Limb shortening/lengthening- Legal perspective
There is a significant difference between a medical examination for treatment and that for legal purposes. An examination for treatment is aimed at treatment and that for legal purposes is to ascertain damages and compensation.
Limb length inequality in the upper limbs usually does not produce any major functional impairment unless it is substantial and produces a cosmetic disfigurement. For example most fractures of the clavicle are treated conservatively and some degree of shortening is inevitable because the bone heals with overlap of bone fragments. However this shortening does not produce significant functional disability [31]. However lower limb length inequality can produce functional disability depending on the severity of the discrepancy between the two limbs.
Clinical measurements for treatment of the patient are commonly taken from the ASIS to the medial malleolus, irrespective of whether the shortening is in the femur or the tibia, because the goal of treatment is to compensate for the shortening when necessary. However the aim of measurements for medico-legal purposes is to determine whether the fracture of the femur or the tibia has resulted in shortening. Hence for medico-legal reporting it will be logical, persuasive and sensible to measure the length of the femur and the tibia individually. It cannot be assumed that when there is limb shortening it is due to the fracture of the tibia or the femur, because there can be inherent asymmetry between the two sides or there can be functional shortening due to angular deformity at the knee (valgus/varus) and/or flexion contracture at the hip or the knee. The length of the femur can be easily measured from the ASIS to the medial knee joint line and that of the tibia from the medial knee joint line to the medial malleolus.
Clinical limb length measurements are prone to errors due to differences in limb girth, difficulty in palpation of bony landmarks, angular deformities of the limb and contractures of joints. For medico-legal reporting, if initial clinical screening shows the presence of LLI, it would be logical, persuasive and sensible to provide accurate radiological measurements, to prevent conflict and make assessment of award for damages simpler.
Conclusion
Anecdotal evidence suggests that limb length inequality is a much discussed but little understood entity in personal injury litigation. It is commonly believed by both the medical as well as the legal fraternity that the human body is symmetrical but clinical evidence shows that the human body is inherently asymmetrical. Ninety percent of individuals in the normal population have a 5.2 mm of lower limb length inequality. In 32% of the population there is LLI of 0.5 to 1.5 cm and 4% have inequality of more than 1.5 cm. Limb length inequality of below 2cm does not appear to affect function and there is no need for compensatory correction of the discrepancy. Some individuals function well athletically even with discrepancies of over 2.5 cm.
It is commonly believed that limb length inequality leads to back pain, scoliosis, as well as osteoarthritis of the hip and knee but clinical evidence does not support such beliefs. The association between LLI and back pain as well as osteoarthritis of the lower limb joints remains largely speculative.
Clinical measurements of lower limb length are commonly included in medico-legal reporting by orthopaedic surgeons. However such measurements are prone to error. The presence of LLI on clinical screening should be followed with accurate radiological measurements so that conflict can be avoided and the award for damages justified.
References
Introduction
In law, a person who is injured, due to the fault of another individual, is entitled to compensation for personal injury. In the assessment of damages resulting from the injury and the assessment of award for damages, the legal fraternity depends on a medical report prepared by doctors. The medical report is required to categorise and identify the severity of the injuries as well as to know the effects/ disabilities produced by the injuries. There is a significant difference between a medical examination for treatment and that for legal purposes. An examination for treatment is aimed at treatment and that for legal purposes is to ascertain damages and compensation. In the assessment for damages the asymmetry of the lower limbs and shortening of the limb is taken into consideration for award of damages. It is common belief that the human body is symmetrical and many doctors as well as many in the legal fraternity are unaware that the human body is inherently asymmetrical.
In a normal population 90% of individuals have a 5.2mm limb length inequality. In 32% of the population there is limb length inequality of between 0.5 to 1.5 cm and in 4% there is inequality of more than 1.5cm. Limb length discrepancy of less than 2 cm does not appear to affect function and there is no need to equalise the limb length discrepancy. For accurate assessment of limb length inequality radiological imaging is required. Clinical assessment of discrepancy is a good screening technique but it is not a good technique for accurate assessment of limb length. The medical examiner has to take these factors into consideration before reaching a conclusion that a fracture has produced anatomical shortening or asymmetry.
Definition of limb length Inequality
Limb length inequality (anisomelia) could be due to structural asymmetry or functional inequality. In patients with structural asymmetry there can be actual shortening or lengthening of the limb. The actual structural skeletal length discrepancy is between the head of the femur and the ankle mortise and it could be in the femur or the tibia (not fibula). The causes of this discrepancy are varied and can be congenital/inherited or acquired. Congenital/inherited disorders include growth inhibiting conditions such as hypoplastic femur, Perthes disease and fibrous dysplasia and growth stimulating conditions such as vascular malformations, neurofibromatosis and fibrous dysplasia besides other causes.
The acquired causes of limb length discrepancy include growth inhibiting factors such as childhood fractures, infections and neurological damage (Polio, Cerebral Palsy, Head injury) and growth stimulating factors such as childhood fractures, haemangiomas, A-V malformations and infections [1]. In skeletally mature patients a common cause of acquired limb length discrepancy is due to fractures involving the femur or the tibia. However in the majority of patients the cause of the limb length discrepancy is not known even when there is a discrepancy of greater than 1 cm and it could be due to normal asymmetrical bone growth [2]. Genetic and environmental factors appear to influence ontogenesis of a person leading to this asymmetry [3].
Functional adaptation occurs in individuals with structurally short lower limbs which include foot pronation on the longer side and pelvic tilt leading to lower anterior and posterior iliac spine on the shorter side [3].
Functional inequality results when limb length discrepancy occurs in the absence of actual bone shortening or lengthening. It could be due to flexion contractures of the hip or knee and varus or valgus deformity of the knee besides other causes such as pelvic torsion and scoliosis. In functional limb lower limb inequality the pelvis rotates. The foot on the apparently short limb rotates externally, the heel goes into valgus and the foot arch collapses. The posterior iliac spine is higher on the apparently short side and the anterior iliac spine is high on the apparently longer side [3].
Classification of limb length discrepancy
The magnitude of limb length discrepancy has been classified into mild, moderate and severe [4].
Mild – difference of less than 3 cm
Moderate – difference of between 3 and 6 cm
Severe – difference of more than 6 cm
The definition of biomechanically significant limb length discrepancy remains controversial among orthopaedic surgeons. While most are convinced that moderate and severe discrepancies are associated with some structural and functional disturbances, mild (less than 3 cm) discrepancies have not been convincingly linked to any structural or functional disturbances [3].
Prevalence and clinical significance of structural/anatomic limb length inequality
Limb length inequality (LLI) appears to be universal phenomena. Knutson in a review of published data on limb length inequality obtained by accurate and reliable x-ray methods found a prevalence of anatomic inequality in 90% of the subjects studied and the mean magnitude of anatomic inequality was 5.2 mm (SD 4.1). He concluded that anatomic leg-length inequality does not appear to be clinically significant until it reaches a magnitude of 20 mm (3/4 inch) [5]. The shortening is more common on the right side but the difference between the two sides is not statistically significant [5].
The most common effect of this limb length inequality is pelvic torsion on weight bearing with the pelvis rotating anteriorly on the short side and posteriorly on the long side. The clinical impact of these dynamic changes remains unclear [6]. Pelvic torsion is the commonest method of compensation with up to 22mm of inequality. With greater degree of inequality knee flexion on the longer side is used as a compensatory mechanism [7].
Hellsing AL did a prospective study of young men during their military service to assess back function and pain before and after basic military training. Around 600 men were examined three times over a period of four years. The study found LLI of 0.5-1.5 cm in 32% of the subjects and 4% had a difference of more than 1.5cm. However there was no correlation between LLI and back pain or pain provocative tests [8].
Gross RH in 1983 studied the incidence and the degree of limb length discrepancy in 35 marathon runners, 70% of whom were in the 30s and 40s. His hypothesis was that the occurrence of asymmetry would be lower in marathon runners than in general population because of attrition of runners with LLI. However he found that 34 of 35 runners participating in the study had LLI when measured by radiography. Eighteen runners (51%) had LLI of less than 5mm, 10 (28.5%) had a LLI of 5 to 9 mm and 7 (20%) had LLI of 1cm or more. He concluded that ‘runners can function handsomely without equalization’ of asymmetry and ‘that discrepancies of 5 to 25 mm are not necessarily a functional detriment to marathon runners, and no consistent benefits could be attributed to the use of a lift’ [9].
Gross RH in 1978 in a ‘survey of 74 skeletally mature patients with LLI of 1.5 cm or more found that patients with less than 2.0 cm did not consider their short limb to be a problem in any way’. As the magnitude of discrepancy increased there were problems but there was no critical ‘cutoff’ point. Some subjects functioned well athletically with discrepancies of over 2.5 cm. He concluded that there is little indication for equalisation of discrepancies of less than 2cm and for larger discrepancies clinical judgement has to be used on an individual basis [10].
Kaufman et al studied gait asymmetry in patients with LLI. They investigated 20 subjects (mean age, 9.0 +/- 3.9 years) who had documented limb-length inequalities, to determine what magnitude of discrepancies resulted in gait abnormalities. The study involved dynamic gait analysis which showed that generally, a limb-length inequality > 2.0 cm (3.7%) resulted in gait asymmetry which was greater than that observed in the normal population. This gait asymmetry however varied for each individual [11]. Less than 2cm inequality does not seem to affect the kinematics [12].
A discrepancy in length of 5.5 per cent or more is associated with an increased mechanical work by the longer extremity and a greater vertical displacement of the centre of body mass. Clinically, this degree of discrepancy can be compensated by the use of toe-walking strategy while lesser degree of discrepancy can be overcome by a combination of compensatory strategies which normalize the mechanical work performed by the lower extremities [13]. Equalizing limb length can improve the symmetry of gait [14].
Gait asymmetry can easily be studied in a laboratory but it is more difficult to analyse the effect of limb length inequality on the spine, hip and the knee. The correlation between LLI and back pain, scoliosis, as well as knee and hip arthrosis has not been well established. The most commonly cited paper according to Knutson [5] which claims that LLI contributes to low back pain is that by Friberg [15]. Friberg studied 1,157 subjects from a military hospital who were exposed to extreme and repetitive loading military activities. Of these 1,157 subjects, 798 had chronic low back pain and the control was 359 with no low back pain. In 75.4% percent of those with back pain and 43.5% of controls there was a 5 mm or more of LLI. Friberg’s findings were questioned by other investigators [5] and Friberg defended his results and clarified that ‘LLI of less than 5mm has no relationship to lumbar scoliosis or back pain’ and ‘that even marked LLI per se neither produces LBP or contributes to its development if a person is not continually exposed to prolonged standing or gait, e.g., doing daily work, military training and sporting activities’ [16]. Soukka et al in a survey of 257 statistically matched working aged male and females subjects found that there was no increased risk of back pain with a LLI of 10 to 20 mm and that there was no conclusive evidence of increased risk of back pain with LLI of more than 20mm [17].
Gibson et al studied patients who had acquired LLI after femoral fractures. The study included patients between the age of 15 and 21 years who had sustained a fracture of the femur. There were 40 patients who were examined 10 or more years after the fracture. There were 15 patients with LLI of 1.5 cm or more who were studied further. The average LLI was 3 cm and ranged between 1.5 to 5.5 cm. During the 10 years only one patient wore a shoe raise and that too for a short period. None of the patients complained of low back pain and none had significant back pain over the 10 years. The acquired LLI produced little permanent structural abnormality in the spine and there was no degenerative changes seen in the spine after 10 years of the acquired LLI in skeletally mature individuals [18].
White et al studied 200 patients who had LLI after total hip replacement. They studied the relationship of LLI and functional outcome using the Harris hip score and the SF-36 Health Survey and found that leg lengthening (up to 35 mm) or shortening (up to 21 mm) had no correlation with functional outcome or patient satisfaction at six months after the surgery [19].
The association of LLI and lower limb complaints remains speculative. Tjernstrom and Rehnberg in a survey of 85 patients who had limb lengthening for shortening of between 3 and 14 cm (average 6cm) found that lower limb symptoms were not common in these patients and the effect of limb lengthening on joint symptoms was minor [20].
There appears to be no good evidence that LLI leads to osteoarthritis of the hip or the knee. In 2007 Golightly et al studied the relationship of LLI and osteoarthritis (OA) of the hip and knee. They examined the relationship of LLI with radiographic hip and knee OA in a community based sample. There were 926 subjects with knee OA and 796 with hip OA, and 210 (6.6%) had LLI of 2 cm or more. They found that there was a significant association between LLI and OA of the knee but there was no significant association with hip OA. The weakness of the study was that limb length measurements were clinical with a tape rather than the more reliable radiological method. Furthermore the authors admitted that LLI in patients with OA could have been contributed by the loss of joint space, disfigurement of the joint and malalignment of the joint that occurs with OA. In additions to these drawbacks, the joints were not examined for contractures which can contribute to LLI. The authors proposed that future research should study the relationship of LLI to OA of the hip and the knee [21].
Harvey et al [22] in a recent large prospective study used radiographs for LLI measurements. Their cohort consisted of 2964 individuals with the age between 50-79, who were with or at high risk for knee osteoarthritis. They found leg length inequality ≥1 cm in 14.5% of the study subjects at baseline. In individuals with LLI of ≥1 cm there was significantly higher prevalence of radiographic and symptomatic osteoarthritis at baseline. The predicted incidence of symptomatic knee osteoarthritis 30-months later was also higher in those with LLI of ≥1 cm. The shorter limbs were also at higher risk of of x-ray progression.
The authors however admitted that there are several weaknesses in their study. The number of incident radiographic OA cases were too small to effectively evaluate the effects of LLI and the authors were, for the same reason, unable to clearly define the risk associated with longer limbs and whether shorter or longer limbs were at higher risk of OA.
The second limitation of the study was the short duration of exposure due to the design of the study. A 30 month follow up was too short to detect progression of the OA. Furthermore even radiographic measurement limb length can be imperfect due to variation of knee flexion on standing radiographs. Hence there remains the possibility of misclassification and bias.
Gofton and Trueman [23] however stated that the LLI produces a pelvic tilt which leads to greater heel impact and stress on joints of the longer limb as compared with the shorter limb.
Kaj Tallroth et al [24] found that hip or knee arthroplasty due to primary OA was done 3 times more often in the longer lower limb than in the shorter limb.
There were however some limitations in this study. No knee radiographs were taken at baseline examination and neither was information about comorbidities, height, sporting activities and possible hip and knee problems during follow up, available. The only information available was the number arthroplasties done for primary OA of the hip or knee. In this 29 year follow up there was a surprisingly low incidence of OA [24].
Despite several studies having been published in the literature, the association of LLI and lower limb complaints remains largely speculative in nature.
Reliability of limb length assessment
Assessment of LLI is essential for appropriate treatment to be instituted. The limb can be measured clinically or by radiographic imaging techniques. Before using a particular technique it would be necessary to know the reliability (inter and intra-observer variation) and the accuracy (variation from actual length) of the technique used.
Clinical technique
The most convenient and commonly used method in clinical practice is the tape measure technique (TMM). The length of the lower limb is measured with a tape from the anterior superior iliac spine (ASIS) at the hip to the distal tip of the medial malleolus (MM) at the ankle.
However this method of measurement has some potential for errors, some of which include:
Limb Girth- The size of the limb may vary between the two sides due to muscle wasting or due to swelling and this can produce an error.
Difficulty in identifying the bony landmarks- The ASIS is difficult to palpate in obese individuals and MM can be difficult to palpate when there is swelling of the ankle. These bony landmarks may be deformed due to previous trauma making identification of the landmarks difficult.
Angular deformities- Presences of angular deformities at the thigh, knee, leg and the ankle can introduce errors. A varus deformity will produce shorting while a valgus deformity will produce lengthening of the limb.
Shortening distal to the ankle- This method does not measure shortening distal to the ankle mortise and can introduce error when there is bone loss distal to the ankle.
Contractures- Contracture at the hip and the knee as well as pelvic obliquity can produce functional shortening when there is no actual structural length discrepancy[25].
The problem of shortening distal to the ankle can be overcome by using an indirect method of measuring LLI. Blocks of known height can be place on the short side to obtain a level pelvis. This method also allows the treatment of LLI in patients with functional shortening.
A Galeazzi test is a quick and simple test which can be used to know whether the shortening is in the femur or the tibia. It is done with the person lying supine with the hip and knee flexed and the asymmetry of the level of the knees will confirm there is shortening and also reveal whether it is in the femur or the tibia. This test also eliminates the error of measurements when flexion contractures of the hip or knee are present. The actual length of the femur can be measured from the ASIS to the medial joint line and that of the tibia from the medial joint line to the MM.
Beattie et al studied the validity of tape measure method (TMM) for determining LLI when compared with a scanogram. They found that TMM derived measurement is a valid indicator of LLI and that the validity of the measurement is improved by taking the mean of two separate tape measurements. However the tape measurements were less reliable in healthy subjects as compared to those with LLI [26]. Cleveland et al on the other hand showed that there is a statistically significant and weak correlation between radiographic measurements and physical examination measurements [27]. With tape measurements the accuracy in identifying the bony landmarks in obese patients, discomfort of the patient during the examination, and correct positioning of the patient by the examiner must be kept in mind.
Harris et al studied LLI in 35 patients with femoral fracture who were treated with nailing. Of these 35 patients, 15 patients (43%) had a measurable LLD. They found that ‘there was a positive correlation between direct leg length measurement and the block test (P = 0.003), and between the block test and patient perception of limp and LLD’ however ‘there was no correlation between CT scanogram and clinical measurement of leg length or between CT scanogram and patient perception of LLD or limp’ [28].
Imaging technique
Imaging techniques commonly used for assessment of LLI include plain radiography and computerised radiography.
Plain radiography
Techniques for measurement of LLI by plain radiography include:
Orthoroentgenogram- This old technique requires a long cassette (longer than the limb length) with three exposures, each centred on the hip, knee and the ankle [29].
Plain radiographic scanogram- This technique uses 3 ordinary cassettes lined up under the limb with the patient supine and a radio-opaque ruler tape to the table. The cassette is moved with each exposure centred on the hip, knee and the ankle [30].
Teleroentgenogram- This technique involves a full length standing AP of the lower limbs using a long cassette with the X-ray beam at about 6 feet. The technique is similar to an Orthoroentgenogram but here a single exposure is used instead of three exposures. This technique is however subjected to magnification error.
Computed radiography- A full length radiograph of the lower limbs can be obtained by obtaining 3 images on a vertical cassette holder containing 3 cassettes. The images are then transferred to a computer where a good quality full image can be downloaded and measurements done [25].
The inter and intra-observer reliability may vary from about 1.5mm to about 5mm. Up to about 10mm would be a threshold for a meaningful difference when assessing differences in measurements by these techniques [25].
CT scanogram
A CT scan is a very useful tool for assessment of limb length discrepancy. A scout view of both femurs and tibias can be obtained and the length of the femurs and tibias can be easily measured. The length of the femur can be measured from the tip of the femoral head to the distal end of the medial femoral condyle and the length of the tibia from the upper end of the medial tibial condyle to the tibial plafond. This technique appears to be more accurate than the plain radiography techniques [25].
The use of a tape is a cheap, simple and non-invasive screening technique for LLI. However it has potential for errors such as difficulty in palpation of bony landmark, difference in size of the limbs, angular deformities of the limb and contractures of the hips and knees. For more accurate assessment of LLI, radiographic techniques need to be used. The type of radiographic technique used will depend on the resources available. CT scans appear to be more accurate and reliable and will require less training and supervision of radiographers when compared with plain radiographic techniques [25].
Limb shortening/lengthening- Legal perspective
There is a significant difference between a medical examination for treatment and that for legal purposes. An examination for treatment is aimed at treatment and that for legal purposes is to ascertain damages and compensation.
Limb length inequality in the upper limbs usually does not produce any major functional impairment unless it is substantial and produces a cosmetic disfigurement. For example most fractures of the clavicle are treated conservatively and some degree of shortening is inevitable because the bone heals with overlap of bone fragments. However this shortening does not produce significant functional disability [31]. However lower limb length inequality can produce functional disability depending on the severity of the discrepancy between the two limbs.
Clinical measurements for treatment of the patient are commonly taken from the ASIS to the medial malleolus, irrespective of whether the shortening is in the femur or the tibia, because the goal of treatment is to compensate for the shortening when necessary. However the aim of measurements for medico-legal purposes is to determine whether the fracture of the femur or the tibia has resulted in shortening. Hence for medico-legal reporting it will be logical, persuasive and sensible to measure the length of the femur and the tibia individually. It cannot be assumed that when there is limb shortening it is due to the fracture of the tibia or the femur, because there can be inherent asymmetry between the two sides or there can be functional shortening due to angular deformity at the knee (valgus/varus) and/or flexion contracture at the hip or the knee. The length of the femur can be easily measured from the ASIS to the medial knee joint line and that of the tibia from the medial knee joint line to the medial malleolus.
Clinical limb length measurements are prone to errors due to differences in limb girth, difficulty in palpation of bony landmarks, angular deformities of the limb and contractures of joints. For medico-legal reporting, if initial clinical screening shows the presence of LLI, it would be logical, persuasive and sensible to provide accurate radiological measurements, to prevent conflict and make assessment of award for damages simpler.
Conclusion
Anecdotal evidence suggests that limb length inequality is a much discussed but little understood entity in personal injury litigation. It is commonly believed by both the medical as well as the legal fraternity that the human body is symmetrical but clinical evidence shows that the human body is inherently asymmetrical. Ninety percent of individuals in the normal population have a 5.2 mm of lower limb length inequality. In 32% of the population there is LLI of 0.5 to 1.5 cm and 4% have inequality of more than 1.5 cm. Limb length inequality of below 2cm does not appear to affect function and there is no need for compensatory correction of the discrepancy. Some individuals function well athletically even with discrepancies of over 2.5 cm.
It is commonly believed that limb length inequality leads to back pain, scoliosis, as well as osteoarthritis of the hip and knee but clinical evidence does not support such beliefs. The association between LLI and back pain as well as osteoarthritis of the lower limb joints remains largely speculative.
Clinical measurements of lower limb length are commonly included in medico-legal reporting by orthopaedic surgeons. However such measurements are prone to error. The presence of LLI on clinical screening should be followed with accurate radiological measurements so that conflict can be avoided and the award for damages justified.
References
- Coleman NW and Sponseller PD. Limb-length discrepancy: Etiology, effects and evaluation. Orthopedic hyperguide at http://www.ortho.hyperguides.com/index.php?option=com_content&view=article&id=1375:limb-length-discrepancy-etiology-effects-and-evaluation&catid=308:operating_techniques.
- Veterans Affairs Canada. Discussion Paper- Leg length Inequality (LLI) – Entitlement Eligibility Guidelines. March 2014 at http://www.veterans.gc.ca/eng/services/after-injury/disability-benefits/benefits-determined/entitlement-eligibility-guidelines/legleng
- McCaw MC and Bates BJ. Biomechanical implications of mild leg length inequality. Br J Sp Med 1991; 25(1):10-13.
- Reid DC, Smith B. Leg length inequality: a review of etiology and management. Physio Can 1984; 36: 177-82.
- Knutson GA. Anatomic and functional leg-length inequality: A review and recommendation for clinical decision-making. Part I, anatomic leg-length inequality: prevalence, magnitude, effects and clinical significance. Chiropractic & Osteopathy 2005, 13:11 doi: 10.1186/1746-1340-13-11.
- Cummings G, Scholz JP and Barnes K. The effect of imposed leg length difference on pelvic bone symmetry. Spine 1993; 18(3):368-373.
- Walsh M, Connolly P, Jenkinson A, O'Brien T: Leg length discrepancy – an experimental study of compensatory changes in three dimensions using gait analysis. Gait Posture 2000, 12(2):156-61.
- Hellsing AL. Leg length inequality. A prospective study of young men during their military service. Ups J Med Sci. 1988; 93(3):245-53.
- Gross RH. Leg length discrepancy in marathon runners. Am J Sports Med. 1983 May-Jun;11(3):121-4.
- Gross RH. Leg length discrepancy: how much is too much? Orthopedics. 1978;1(4):307-10.
- Kaufman KR, Miller LS, Sutherland DH. Gait asymmetry in patients with limb-length inequality. J Pediatr Orthop. 1996 Mar-Apr; 16(2):144-50.
- Goel A, Loudon J, Nazare A, et al: Joint moments in minor limb length discrepancy: a pilot study. Am J Orthop 26:852-856, 1997.
- Song KM, Halliday SE, Little DG: The effect of limb-length discrepancy on gait. J Bone Joint Surg Am 79:1690-1698, 1997.
- Bhave A, Paley D, Herzenberg JE: Improvement in gait parameters after lengthening for the treatment of limb-length discrepancy. J Bone Joint Surg Am 81:529-534, 1999.
- Friberg O. Clinical symptoms and biomechanics of lumbar spine and hip joint in leg length inequality. Spine. 1983;8:643–651.
- Friberg O. Letter-to-the-editor. Spine. 1992;17:458–460.
- Soukka A, Alaranta H, Tallroth K, Heliovaara M. Leg-length inequality in people of working age. The association between mild inequality and low-back pain is questionable. Spine. 1991;16:429–431.
- Gibson PH, Papaioannou T, Kenwright J: The influence on the spine of leg-length discrepancy after femoral fracture. J Bone Joint Surg (Br) 1983, 65(5):584-7.
- White TO, Dougall TW: Arthroplasty of the hip. Leg length is not important. J Bone Joint Surg (Br) 2002, 84-B:335-8.
- Bjorn Tjernstrom and Lars Rehnberg. Back pain and arthralgia before and after leg Lengthening: 75 patients questioned after 6 (1-1 1) years. Acta Orthop Scand 1994; 65 (3): 328-332.
- Golightly YM, Allen KD, and Jordan JM. Relationship of Limb Length Inequality with Radiographic Knee and Hip Osteoarthritis. Osteoarthritis Cartilage. Jul 2007; 15(7): 824–829.
- Harvey W F, Yang M, Cooke T D, Segal N A, Lane N, Lewis C E, Felson D T. Association of leg-length inequality with knee osteoarthritis: A cohort study. Ann Intern Med 2010; 152 (5): 287–95.
- Gofton J P, Trueman G E. Studies in osteoarthritis of the hip, II: Osteoarthritis of the hip and leg-length disparity. Can Med Assoc J 1971; 104 (9): 791–9.
- Kaj Tallroth, Leena Ristolainen & Mikko Manninen. Is a long leg a risk for hip or knee osteoarthritis? Acta Orthopaedica. 2017;88: 512-515.
- Sabharwal S, and Kumar A, “Methods for Assessing Leg Length Discrepancy” Clin. Orthop. Relat. Res, vol. 466, no. 12, pp. 2910-2922, Dec. 2008.
- Beattie P, Isaacson K, Riddle DL, Rothstein JM. Validity of derived measurements of leg-length differences obtained by use of a tape measure. Phys Ther. 1990;70:150–157.
- Cleveland RH, Kushner DC, Ogden MC, Herman TE, Kermond W, Correia JA. Determination of leg length discrepancy. A comparison of weight-bearing and supine imaging. Invest Radiol. 1988;23:301–304.
- Harris I, Hatfield A, Walton J. Assessing leg length discrepancy after femoral fracture: clinical examination or computed tomography? ANZ J Surg. 2005;75:319–321.
- Green WT, Wyatt GM, Anderson M. Orthoroentgenography as a method of measuring the bones of the lower extremities. J Bone Joint Surg Am. 1946;28:60–65.
- Moseley CF. Leg length discrepancy. In: Morrissy RT, Weinstein SL, eds. Lovell and Winter’s Pediatric Orthopedics. Philadelphia, PA: Lippincott Williams & Wilkins; 2006;1213–1256.
- Nordqvist A, Redlund-Johnell I, von Scheele A, Petersson CJ. Shortening of clavicle after fracture. Incidence and clinical significance, a 5-year follow-up of 85 patients. Acta Orthop Scand. 1997 Aug;68(4):349-51.
No comments:
Post a Comment