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Daurka JS, Dacombe P, Chen A, Gibbons C, Radford W. Use of the tip - implant distance reduces variability in leg length discrepancy following hip replacement surgery. OA Orthopaedics 2013 Oct 25;1(3):21.
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Section: Surgical Procedures
Use of the tip - implant distance reduces variability in leg length discrepancy following hip
replacement surgery
Daurka JS, Dacombe P, Chen A, Gibbons C, Radford W
Jasvinder S Daurka St Mary's Hospital, London [email protected]
Peter Dacombe Faculty of Medical Leadership & Management [email protected]
Alvin Chen High Wycombe & Stoke Mandeville Hospital [email protected]
Charles Gibbons Chelsea & Westminster Hospital, London [email protected]
Warwick Radford Chelsea & Westminster Hospital, London [email protected]
Corresponding author(s)
Name Institute Email Jasvinder S Daurka St Mary's Hospital, London [email protected]
2
Abstract
A minority of patients does suffer from symptomatic leg length discrepancy (LLD) following hip
replacement surgery (THR). We report the success of a simple method of reducing variability in
LLD using a single measurement of length made from a templated preoperative plan. A
radiographic comparative study was conducted on consecutive patients undergoing THR surgery.
The patients were separated into two groups dependent on the use of preoperative templating. The
Tip-Implant distance was measured in the templated group, and this was reproduced
intraoperatively. This is a measurement of the distance from the shoulder of the femoral implant to
the tip of the greater trochanter. There were 27 templated and 20 non-templated hips that met the
study criteria. The mean LLD (inter-teardrop to lesser trochanter) in the hips was not significantly
different at +1.1mm(SD 3.9) and +2.9mm(SD 8.1) in the templated and non-templated hips
respectively. The range of leg length discrepancy observed in the templated hips was -6mm to
11mm and in the non-templated hips was -6mm to 21mm. The pre and post operative mean Tip -
Implant measurement was 16.1mm(SD 4.5mm) and 16.5mm(SD 5.2mm) respectively, which
correlated strongly with paired t testing 0.749(p=.0001).There was a significant difference in
variances with a Levene's test for equality F value of 12.0(p=0.01) suggesting a far narrower spread
of LLD in the templated group. The Tip-Implant measurement determined preoperatively is
reproducible intraoperatively and reduces the likelihood of LLD outliers in THR surgery
3
Introduction
Total hip replacement remains a successful procedure, survivorship analysis and
functional assessments continue to suggest that outcomes are very good(1). Despite
these reported high satisfaction rates there are a number of well recognised complications.
Technical error in the placement of the implants remains a significant concern. A minority
of patients do suffer from symptomatic leg length discrepancy that can lead to claims of
negligence(2), back pain(3), dislocation(4), poor patient satisfaction(5) and even revision
surgery(6). Surgeons have tried a number of techniques to try and reduce this risk.
Variable degrees of success have been been reported with strategies that employ
preoperative templating(7–9), the use of intraoperative anatomical cues(10), jigs(11), and
implant navigation systems(12).
The advent of Picture Archiving and Communication Systems(PACS) in general use and
associated digital templating systems has added a further tool to the armamentarium of
orthopaedic surgeons trying to achieve a successful outcome. We report the success of a
simple method of reducing variability in leg length discrepancy utilising a single
measurement of length made off a templated preoperative plan.
We hypothesised that use of the Tip–Implant distance would reduce the variance in leg
length discrepancy seen in a series of patients that undergo hip replacement surgery. This
narrower spread should reduce the likelihood of a leg length discrepancy ‘outlier’ as shown
in figure 1.
Materials and methods
A retrospective radiographic comparative study was conducted on consecutive patients
undergoing total hip replacement surgery at our institution. The procedures were carried
out by three surgeons (WR, CG, JD).
4
Inclusion criteria for the study included patients with a diagnosis of primary osteoarthritis of
the hip requiring arthroplasty surgery, in whom adequate pre- and postoperative AP
radiographs centred on both hips were available. We excluded patients that had a
significant radiographic preoperative leg length discrepancy(>10mm), acetabular bone
erosion or fixed contractures. The patients were stratified into two groups dependent on
the use of preoperative templating, into a Templated and a Contemporary group. Where
templating was not used the surgeons used contemporary measures of establishing
adequate leg length by using clinical assessments intraoperatively. These included an
assessment of the relationship of the flexed knees to one another whilst in the lateral
decubitus position, soft tissue cues of anterior capsular and abductor musculature tension.
Radiographic cues included an estimate of the position of the centre of femoral head in
relation to the tip of the greater trochanter.
The use of templating was variable in the patient group as this was only performed on an
AP radiograph of the hips if a calibration marker ball had been used on the preoperative
radiograph and was adequately located to minimise error(13). An acetabular and femoral
component were templated using Traumacad, (Brainlab AG, Felkirchen, Germany) to best
fit the patients anatomical morphology in a position that corrected any preoperative leg
length discrepancy. The Tip-Implant distance was measured. This is a measurement of
the distance from the shoulder of the implant to the tip of the greater trochanter measured
parallel to the anatomical axis of the femur. (Figure 2)
The operative technique of all the surgeons was identical. The hip is approached
posteriorly. The femoral neck is osteotomised. After adequate retraction and preparation,
the acetabular component is seated. The aim of preparation of the acetabulum is to
remove the remaining cartilaginous tissue and present cancellous bone to allow the use of
a pressfit component.
The femur is broached sequentially until an adequate interference fit is achieved. In the
5
Contemporary group once the surgeon felt that the broach was in an appropriate position it
was trialled and clinical leg length assessed. Alterations were made thereafter as
required. In the Templated group the surgeon had an additional cue in the pre measured
Tip-Implant distance to try and reproduce, prior to trial reduction (Figure 3). Thereafter the
technique was the same with clinical leg lengths being assessed and adjustments made
accordingly.
Over a 12 month period we reviewed radiographs for patients that conformed to our
inclusion and exclusion criteria.
The radiographs were assessed for adequacy and measurements were taken after
calibration, using a marker ball preoperatively or the femoral head component
postoperatively. The diameter of a best fit circle in the contralateral head of the femur
allowed all radiographs for each patient to be calibrated to allow comparable
measurements to be taken.
The measurements recorded on all the radiographs included the perpendicular distance
from the interteardrop line to the lesser trochanter as validated previously(14). The Tip-
Implant distance was measured pre- and postoperatively in the Templated group. An
assessment of the leg length discrepancy was performed in all hips and we compared this
value between both Contemporary and Templated groups.
We tested the hypotheses that the group in which the surgeon had a preoperatively
determined the greater trochanter Tip-Implant distance should have a reduced variance
and range of values of leg length discrepancy
Statistical analysis
A power analysis was performed on the basis of a pilot study on ten previously performed
6
total hip replacements. With an alpha value of 0.05 and power of 0.8, a sample size of 20
in each arm would be adequate to detect a difference of 50% in variance between the
groups.
Descriptive statistics were reported as a mean and range or standard deviation.
Comparison of the mean leg length discrepancy was assessed using the Student’s t test
and variance was assessed using Levene’s test for equality of variances. SPSS v 21.0
(IBM, Armonk, USA) was used for statistical analysis and PASS 12 (NCSS, Kaysville,
USA) for the power analysis required.
Results
We reviewed the radiographs of 50 consecutive total hip replacements performed at our
institution. An adequate preoperative templated plan was recorded in 27 cases. In 20
cases adequate radiographs were available for review and the there had not been any
attempt to template the hip replacements preoperatively. In 2 cases the radiographs were
inadequate and 2 further cases were excluded for the presence of significant preoperative
deformity. The hip replacements used in the study included the Accolade and the Exeter
stems and the Trident acetabular system (Stryker, Kalamazoo, USA). There were 24
Accolade/Trident and 23 Exeter/Trident hip replacements.
There was no significant difference in the Contemporary and Templated groups when
assessed for age, sex, surgeon or type of implant used.
The mean age of the patients was 67.3 (range 54 to 85). The mean preoperative leg
length discrepancy was – 2.0mm(SD 5.8) and -3.7mm(SD 6.6) in the Templated and
Contemporary groups respectively (p=0.395), the corresponding postoperative leg length
discrepancy in the hips was + 1.1mm(SD 3.9) and +2.9mm(SD 8.1). This was not
significantly different between groups (Students t test p=0.326). The postoperative range
of leg length discrepancy observed in the Templated group was -6mm to 11mm and in the
Contemporary group was -6mm to 21mm
7
The mean templated Tip - Implant measurement was 16.1mm(SD 4.5mm) and the
achieved mean was 16.5mm (SD 5.2mm). A paired t test suggested a strong correlation in
the templated and actual values achieved of 0.749(p=.0001). There was no significant
difference in the mean values (p=0.535, paired t test)
There were 3 hips that were ‘outliers’ in the Contemporary group, seen in figure 4a
There was a significant difference in variances with a Levene’s test for equality F value of
12.0 and p=0.01 when comparing the Contemporary and Templated groups
Figure 4b reveals the distribution of leg length discrepancy in the Templated group.
Discussion
The mean change in leg length in this study is comparable to previous studies that have
reported a range of results for similar measurements from +1mm to +8.2mm (11,14–17).
We could not find any study that showed that the spread, variance or range of values was
improved with an intervention.
Historically surgeon orientated scoring systems such as the original Harris hip score only
acknowledged a discrepancy of greater than 3.2 cm(18). More recent studies have begun
to report a discrepancy of greater than 1cm as significant and now quote the percentage of
patients that are outside this range as one of their outcome measures(5,12,17,19). There
is a recognition that a hip surgeons practice, whether using anatomical cues,
intraoperative jigs or computer guided surgery, will produce a normal distribution of leg
length discrepancy. The aim we feel should be to have as narrow a spread around the
mean value as possible and thereby reduce the likelihood of statistical outliers. The mean
change in leg length of a cohort of patients is the most frequently quoted descriptive
statistic. We feel the mean value in this situation is not as clinically relevant as a measure
of the spread which includes the range of values, the standard deviation or the variance.
8
Contemporary hip replacement surgical techniques give good results when assessing the
mean change in leg length postoperatively as seen in the studies previously published, we
feel an emphasis should be placed on reducing the likelihood of outliers that have been
reported to have been lengthened by up to 35mm (19)
There are a number of limitations of this type of retrospective study, and the confounding
factors such as the type of implant and the surgeon may have an influence on the
outcome that failed to reach statistical significance. The intention of the study was
however not to determine subtle differences in mean leg length discrepancy, which is not a
clinically relevant statistic but to assess the variance of this value, which was achieved.
Conclusion
This study is the first to demonstrate that a simple Tip-Implant measurement taken from a
templated radiograph is reproducible intraoperatively and patients that have had it
measured as a cohort have a reduced range of leg length difference, and a narrower
statistical spread. There is therefore a reduced likelihood of patients having an
unacceptably large leg length difference and suffering from the associated morbidity.
9
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14. Meermans G, Malik A, Witt J, Haddad F. Preoperative radiographic assessment of limb-length discrepancy in total hip arthroplasty. Clin Orthop Relat Res. 2011 Jun;469(6):1677–82.
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18. Harris W. Traumatic arthritis of the hip after dislocation and acetabular fractures: Treatment by mold arthroplasty. J Bone Joint Surg[Am]. 1969;51:737–55.
19. White TO, Dougall TW. Arthroplasty of the hip. Leg length is not important. J Bone Joint Surg[Br]. 2002 Apr;84(3):335–8.
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Figure legends
Figure 1 – The typical distribution of leg length discrepancy in a population of patients following hip replacement surgery, showing ‘outliers’ Figure 2 - An AP radiograph of the hip with digital templating, and blue marker arrow demonstrating the Tip – Implant distance. Figure 3 – Intraoperative photograph demonstrating measurement of the Tip – Implant distance with the use of a needle and ruler, a white line represents the bone outline Figure 4a – A graph representing the distribution of leg length discrepancy in the Contemporary group Figure 4b – A graph representing the distribution of leg length discrepancy in the Templated group
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Table 1 – A summary of the previously published studies regarding leg length discrepancy (Abbreviations BI=bi-ischial, LT=lesser trochanter,
IT=inter-teardrop
Number of hips Radiological
measurement
Mean leg
length
discrepancy
(mm)
Range/(SD) Further results
Austin et al(20) 2003 105 BI – LT n/a n/a 87.6% within +/- 1cm
Eggli et al(7) 1998 100 IT – LT 2 +/- 1mm(1SD)
Gonzalez Della Valle et
al(8) 2005 139 IT – LT 2.8 -6 to 20
Khanduja et al(21) 2006 102 IT - LT 1.1 -20 to 17 93% within +/- 1cm
Konyves and Bannister(16) 2005 90 IT - LT 3.5 -22 to 27 62% long by 9mm
Maloney and Keeney(15) 2004 50 BI - LT 5.6 -12 to 7 82% within +/-5mm
Matsuda et al(9) 2006 45 IT - LT 2 +/- 2mm(1SD) Study group
47 IT - LT 7 +/- 4 mm(1SD) Control group
Murphy and Ecker(22) 2007 112 IT - LT 1 +/-5.2(-20 to 15)
Ranawat and
Rodriguez(23) 1997 100 IT - LT 1.9 -7 to 8 87% </=6mm LLI
Rand and Listrup(24) 1983 40 BI - LT 0.95 +/- 11(1SD) T28 THR group
40 BI - LT 2 +/-7mm Charnley THR group
Sathappan et al(25) 2008 132 IT - LT 9.87 +/-5.05mm(1SD) Spinal anaesthesia group
IT - LT 2.75 +/-2.59(1SD) GA anaesthesia group
Suh et al(26) 2004 96 BI - LT 3.1 -3.9 to 10.2mm
Unnanuntana et al(27) 2009 109 IT - LT 0.9 +/- 6.8mm(1SD) 93.5% within 10mm
13
Wedemeyer et al(28) 2008 40 IT - LT 2.55 +/-2.37(SD) range -
16.67 to 24.03mm
White and Dougall(19) 2002 200 IT - LT n/a -20 mm to 35mm 143 within 10mm
Williamson and
Reckling(29) 1978 12 BI - LT 16.1 9.51 (1SD)
Woolsen et al(17) 1999 351 IT - LT 1 -20 to +22(SD 4.7mm) 3% over 1cm LLD
Meemans et al(14) 2011 52 HC - ankle 3.88 -8 to 9.1
Manzotti et al (12) 2011 48 BI - LT 5.06 0-12 Computer assisted group
48 BI - LT 7.64 0-20 Freehand group
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Figure 1: Figure1.tif
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Figure 2: Figure2.tif
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Figure 3: Figure3.tif
Figure 4: Figure4a.tif
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Figure 5: Figure4b.tif
