LLD and a intraobserver mean error of 1.1

LLD can be quantified clinically and radiologically.Though radiographic measurement is expected to be moreaccurate than clinical measurement in determining leg length discrepancy16. There are twopopular methods for clinical measurement of limb length : (a) an ‘indirect method’ done in standing using lift blocks under theshort leg and visually examining the level pelvis, and (b) a ‘direct method’done in supine measuring the distance of fixed bony landmarks with a measuringtape. Two commonly used tape measure methods (TMM) include measuring thedistance between (a) the anterior superior iliac spine (ASIS) and the lateralmalleolus and (b) the ASIS and the medial malleolus.

  The literature testing the TMM has shown thatthe malleolus measurement is an inaccurate and imprecise method; with a meandifference in LLD measure of 8.6 mm compared to radiographs, and aintraobserver mean error of 1.1 mm.12 Two radiological techniques predominate in theliterature and are widely used in clinical practice. In  the methods described by Williamson andReckling distance between most inferior point of Ischia and lesser trochanteris measured, whereas  in method describedby Woolson et al distance between inferior point of acetabular tear drop andlesser trochanter is measured.17 Neither Woolson’s nor Williamson’s method takes account of hip flexion orabduction deformity at the time of the x-ray (which tends to reduce themeasured LLD) or any causes of LLD which does not involves the hip.

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18 Heaver et al16 reported that inter ischialline was best pelvic landmark for measurement of LLD, whereas Meermans et al19 reported teardrop line tobe better. Meermans et al19 further reported thatcentre of femoral head should be taken as femoral reference point instead oflesser trochanter.Tiptonet al reported that LLD measured by taking distance between inter teardrop lineand centre of femoral head was closest to true LLD.

The measurements used topredict LLD from an AP radiograph of the pelvis underestimates LLD and are notcomparable to the evaluated LLD as measured from a full-length radiograph. Thustaking only pelvic radiograph to assess LLD would not be adequate.20 Kerši? et al21 in a series of 119 primary THA reportedthat preoperative clinical LLD was on an average 5-8 mm more than radiographicLLD whereas postoperative clinical and , radiological LLD  differed only by 1-2mm. Similarly, Plaas et al4 stated that clinical andradiological measurement correlates poorly (?=0.36 pre- and ?=0.

186 postoperatively). Sayed-noor et al22, in their series of THA involving 139 patients reportedthat clinical method of measurement of LLD was not a reliable method to findout preoperative LLD. However they further reported a better correlationbetween clinical and radiological measurement when taken postoperatively. Thiswas probably on account of correction of any preoperative deformity existing athip joint. Gogia et al23 performed clinical leg length measurement and scanogramin 30 healthy subjects and reported that clinical LLD measurement (ASIS-medialmalleolus) and a radiological measurement had excellent correlation (ICC=0.99).They also stated that flexion deformity of knee and hip could alter the resultsand palpation of ASIS can be difficult in obese patients. Beattie et al24 also supported these findings in their study.

Howevertheir observation of good correlation between clinical and radiologicalmeasurement was probably on account of the fact that, in their study there wasno deformity at the hip joint as all the subjects were healthy. Patientperception of LLD and presence of actual LLD do not correlate well. One large-scale postal audit survey found theprevalence of patient-perceived LLD after THR to be 30%. In this  study of THR outcomes of 1114 patients , at 5 to 8 yearspost-op follow-up, 329 patients (30%) perceived an LLD following total hip replacement, while radiographicanalysis of this sub group of patients indicated that only 36% of thesepatients  had actual  LLD of ?5mm.

25 Konyvesand Bannister In their study they reported that 56 of their patients (62%) hadlimb lengthening by a mean of 9mm and it was perceived by 24 patients after three months and by 18 after 12months. They observed that patients who had lengtheningwere significantly more likely to detect LLD than those with shortening. Multiplestudies have shown that satisfaction and dissatisfaction after THA ismulti-factorial. There is, however, disagreement about significance ofradiologically evident LLD in comfort, satisfaction and functional outcome ofTHA.

Konyves and Banister reported that Oxford Hip Scoreof patients who perceived lengthening was significantly worse than patients whoconsidered their operated leg to be of equal length or short but, there was no association between the centre of rotation, surgeon basedHarris hip score, patient based general health questionnaire and postoperativeLLD.26 White et al in astudy concluded  that radiological lengthening (35 mm) or shortening (21 mm) during THRdoes not correlate with function, comfort or satisfaction six months afteroperation.27  There is a lack of agreement in the literature aboutwhat constitutes a significant LLD either pre or post operatively. Asymptomaticleg length inequality of 2cm or more is relatively common even in the generalpopulation who have not undergone hip replacement arthroplasty3,12 and it is well recognised that bothlengthening and shortening of this magnitude can occur with hip replacementarthroplasty.  Due to absence of aglobally accepted LLD measurement protocol there are differences in bothdefinitions and reported normative values. After reviewing the literature itappears that postoperative LLD of about 10mm or less is likely to beacceptable, but there is little agreement about a limit of LLD that would beconsidered definitively unacceptable.Approach to Minimizing Symptomatic LLDAlthough LLD after THAaltogether cannot be eliminated, the problem can be minimized. To preventpostoperative limb length discrepancy and its attendant problems, its importantto understand the various components of leg length assessment related to THA,including identification of patients at risk, preoperative planning,intraoperative measurements and postoperative management.

Identification of PatientsMost at RiskThere are several identifiable factors that increase the riskof a patient suffering a symptomatic LLD (Table 1).  Atypical anatomy, such as excessive femoralbowing, narrow femoral canal or poor bone stock can cause difficulties inobtaining proper alignment or insertion of the components. This can be furthercomplicated when using an uncemented femoral stem or in the obese patients.

18The short varus neck of femur makesthe abductor muscles sensitive to stretching thus resulting in a tiltedhemi-pelvis with the operated side lower (functional LLD).2 Short stature patients tend to havea narrower pelvis, which produces a greater amount of pelvic tilt for any givenLLD.18In the patients with pre-existinggluteal shortening, there is apparent lengthening because leg tend to lie in anabducted and externally rotated position. Postoperative lengthening in thesepatients will further increase their pelvic tilt or, if the requiredcompensation is too great, will have to pivot on the shorter leg to place thelonger leg on the ground. Patients with pre-existing but asymptomatic LLD maybe less likely to tolerate any increase in their leg length inequality and canexperience worse morbidity than would be associated with a similar LLD in otherpatients.

18 Methods for minimisingLLD The methods for minimising LLD can be divided into four maincategories28: In literaturevarious types of techniques have been used to minimise postoperative LLD whichcan be broadly divided in four broad categories. 1) Based on the preoperativetemplating to define the correct neck cut, the correct neck length of thefemoral component and correct depth of femoral component insertion. 2) Based onthe usage of a standard pelvic reference point and of a femoral referencepoint, and measurement of the distance of these two points as the limb lengthchanges intraoperatively. 3) Based on intraoperative clinical tests such as theshuck test, the drop kick test, and the leg-to-leg comparison 4) Based onnavigation system’s measurements.21In addition, some othertechniques have been described, such as measuring the gap between the tenotomylimb edges of the abductor musculotendinous insertion on the greater trochanteror evaluating the level of the center of the head in relation to the tip of thegreater trochanter with the aid of a plate in a femoral head slot29. A technique which usesintraoperative ultrasound to measure LLD is also described in literature.30Postoperative limb lengthening is more common than shortening. Invarious studies postoperative lengthening After THA varied from 48 – 62%whereas shortening have been seen in 10-32% of cases.

4,26,28 If the operated limb is short patients may not complain because theyhave been physiologically and psychologically accustomed to this condition. Amore common problem after THA, however, is lengthening of operated limb 31. However extent of lengthening is of utmost importance for it to beclinically significant. Preoperative techniquesMost of the preoperative techniques are based on overlay templating anddetermining accurate position and size of implants.6,17,32–37 The use of templates is the first step inobtaining acceptable clinical results with regard to limb length.

However, suchuse should be combined with a reliable intraoperative method to obtain optimallength.13Hofmannet al evaluated the template technique and reported that in 50% of cases theyhad to change the plan during surgery.38 Magnification in radiographs and errors inmeasurement makes it extremely difficult to predict implant size accurately26,37 leading to incorrect prediction of  size of implants in around 40% of cases,making it unreliable method.

37 Halaiet al, were able to reduce mean postoperative to 1.3mm (range 0.2-9.3mm) byExeter technique and templating and concluded that Exeter technique was  reproducible and was helpful in reducingincidence of leg-length discrepancy after THA.

39 Woolson et al were able to achieve desiredlevel of neck osteotomy within 6mm in 86% of patients and within 10 mm in 97%of patients.17Preoperative planning with overlay templates does nottakes account of soft tissue tension across hip joint and hence may lead toinstability around hip. Woolson et al17 reported that ninety-seven percentof the patients had a postoperative leg-length discrepancy that was less than10 mm (with a range of -20 to +20 mm) but twenty-two of their 351 patients (5%)sustained a postoperative dislocation of one hip during follow up, possibly onaccount of poor soft tissue tension.17 Valle et al in a retrospective study evaluated the utility of apreoperative planning with template technique and reported that acetabularcomponent size was predicted exactly in 83%; the femoral component size waspredicted exactly in 78% and the average limb-length discrepancy was 1.

71 mm(range -6 to +20 mm).32Preoperative measurement of limb length inequality, preoperativeplanning with radiographic templates and intraoperative corrections withmeasurements of limb lengths before and after the insertion of trial componentsusing limb length callipers can reduce the incidence and magnitude of theproblem of limb length discrepancy.Intraoperative TechniquesTo date there are around 20 intraoperative techniques are described inliterature and all are based on intraoperative measurement of distancebetween  2 reference points.

Most of thetechniques use one pelvic and one femoral reference points. While femoralreference point is usually GT in all the techniques, pelvic reference point maybe pins inserted in Ilium, callipers, Judd pins, or a suture fixed in pelvisand varies in each technique. These techniques however have not been reliable because they aredependent upon accurate femur repositioning. Sarin et al reported that a 5 and10 degrees of adduction/abduction intra-operatively can cause as much as 8mmand 17mm error in leg length measurement respectively. However effect on LLD due to incorrect flexion/extension repositioning is muchless pronounced. Malrotation of the pelvis with respect to the femur (oroperating room table) can also occur and contribute to leg length inequalityand incorrect femoral offset restoration. Techniques using pins or jigs thatare fixed at some distance away from the bone surfaceexaggerate the effect of rotational error because the measurements are madeaway from the rotational centre of the joint hence distance between the femurreference point and the joint centre should be minimised so that thedeleterious effect of malrotation can be reduced.

40Ng et al in their review ofliterature on LLD after THA described about the importance of acetabular andfemoral positioning and their effects on LLD. They stated that though external and internalreference marks may be used to guide acetabular implant positioning, fixedinternal anatomical landmarks such as the transverse acetabular ligament,acetabular sulcus on the ischium, and the superior aspect of the acetabulumwere less dependent on patient positioning and better indicators of implantpositioning as compared to external reference points. They stated thateccentric inferior reaming of the acetabulum and placement of the cup below theplanned level of the teardrop can increase the leg length.

They also advised totake caution while deciding about the level of femoral osteotomy, as achievingthe correct angle and level of the femoral osteotomy is important for seatingthe femoral implant accurately and avoiding leg length inequality. A highfemoral neck cut may lead to more visible space in the medial calcar and thestem may appear undersized and changing to a larger stem to fill this void maylead to inadvertent lengthening of the limb. Similarly if the femoral osteotomyis too low, the femoral stem may not seat within the metaphysis and appear toolarge and changing to a smaller stem size to improve seating may lead toshortening of the limb. Lengthening the femoral neck alone will lead toincreased femoral offset and limb length.41 These findings were also supported by Kayani et al in theirreview of literature on LLD after THA.42Konyves and Bannister in a study of 90 patients undergoing primary total hip arthroplasty sought to identifywhether the acetabular or femoral component was principally responsible for LLDafter THA and appropriate placementof the femoral component could significantly reduce postoperative LLD.

26Combineduse of templating to predict the necessary length correction and plan femoralneck osteotomy level and the intraoperative use of a simple pelvic referencepin with accurate-positioning of the leg during measurements will provide thesurgeon with a practical method for measuring leg length during THA.6Although techniques which use largeSteinmann pin have been described in literature, they have been criticized asunreliable as they are recommended to be removed and replaced during thesurgery in between the measurements.11 Mcgee and Scott inserted a Steinmann pin into the pelvis 1.

5 to 2 cmsuperior to the acetabulum and bent it into a U and made a mark at the pointwhere the free end of the U contacts the greater trochanter and restoring themark to the tip of the pin restored the preoperative length.43 Although sample size was 200 but they failed to substantiate theirclaim with any radiological or clinical data regarding LLD in their patients.11 Naito et al used Steinman pin andadjustable calliper to achieve intraoperative limb length correction.

Bose andShiramizu et al described similar techniques with similar results.18,19,45Jasty et al10 ina series of 85 consecutive patients used sliding limb length calliper overpelvic reference wire to measure distance between pelvic reference point andfemoral reference point and reported that 14 of 85 patients (16%) had limblength inequality after surgery and out of these 6 patients needed a shoeraise. In this series of85 THAs, 80 cases were still longer postoperatively. The study has severallimitations as it is retrospective, measurements being made by the operatingsurgeon, who was not blinded, and scanograms were used only pre operatively.Ranawat et al inserted vertical Steinmanpin at the infracotyloid groove of the acetabulum and another mark over greatertrochanter was made with electrocautry. Leg was kept in 20 degree of flexionand internal rotation.

They said that the points of reference in this methodare close to centre of rotation of hip hence variations in measurementsresulting from limb positions are less likely to occur. In their report postoperative LLD ranged from -7 mm to+9 mm (mean 2.62 mm). Difficulty in accurate positioning ofthe pin due to large osteophytes at the posterior lip of acetabulum was citedas main Limitation of this technique.47

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