To analyse the value and accuracy of preoperative

Transcription

1 The value of preoperative planning for total hip arthroplasty S. Eggli, M. Pisan, M. E. Müller From the University of Bern, Switzerland To analyse the value and accuracy of preoperative planning for total hip replacement (THR) we digitised electronically and compared the hand-sketched preoperative plans with the pre- and postoperative radiographs of 100 consecutive primary THRs. The correct type of prosthesis was planned in 98%; the agreement between planned and actually used components was 92% on the femoral side and 90% on the acetabular side. The mean (± SD) absolute difference between the planned and actual position of the centre of rotation of the hip was 2.5 ± 1.1 mm vertically and 4.4 ± 2.1 mm horizontally. On average, the inclination of the acetabular component differed by 7 ± 2 and anteversion by 9 ± 3 from the preoperative plans. The mean postoperative leg-length difference was 0.3 ± 0.1 cm clinically and 0.2 ± 0.1 cm radiologically. More than 80% of intraoperative difficulties were anticipated. Preoperative planning is of significant value for the successful performance of THR. J Bone Joint Surg [Br] 1998;80-B: Received 13 March 1997; Accepted after revision 2 October 1997 Preoperative planning has always been an integral part of total hip replacement (THR). Both Charnley 1 and Müller 2,3 emphasised the importance of preoperative radiographs in deciding the type and size of prosthesis, in achieving the correct position and orientation of the components, in equalising leg length and in reducing intraoperative complications. 1-5 Since 1968 we have stored all the preoperative plans of THRs as well as the pre- and postoperative radiographs on S. Eggli, MD M. Pisan, MD M. E. Müller, MD Department of Orthopaedic Surgery, University of Bern, Inselspital, Murtenstrasse 35, 3010 Bern, Switzerland. Correspondence should be sent to Dr S. Eggli British Editorial Society of Bone and Joint Surgery X/98/37764 $2.00 miniature, high-resolution photographs. A method of preoperative planning for THR was introduced by the senior author (MEM) in and has remained remarkably unchanged since then. We now present the technique and analyse its accuracy and limitations. Patients and Methods We assessed the plans of 100 consecutive patients (100 hips) with idiopathic osteoarthritis who had had THR between 1985 and The operations were carried out through an anterolateral approach with the patient supine. The senior author (MEM) was responsible for both the plans and operations, records of which had been digitised and stored, along with the radiographs. There were 45 men and 55 women with a mean age at surgery of 66 ± 8 years. There was no significant difference between them (Student s t-test, p = 0.192). In the women the mean weight was 67 ± 5 kg and the mean height 166 ± 5 cm and in the men, 77 ± 7 kg and 175 ± 8 cm, respectively. Six patients had had previous intertrochanteric femoral osteotomies and one had internal fixation for a subcapital fracture. In 33 patients the contralateral hip was normal, in 31 there were severe radiological signs of arthritis and in 36 it had already been replaced. The standard radiographs included a preoperative anteroposterior (AP) view of the pelvis with a lateral view of the hip, and postoperative AP views of pelvis and acetabulum and lateral views of the hip. The AP view of the pelvis is taken with the patient supine and the centre of the X-ray beam placed 2 cm above the pubic symphysis. The lateral view is obtained with the patient in a 45 lateral position with a flexed contralateral hip, and the acetabular view with the patient supine and the centre of the X-ray beam placed on the centre of rotation of the hip. To minimise variability in magnification, the distance of the X-ray source to the film cassette is standardised to 150 cm. All radiographs use a high-resolution film (Agfa Ortho 25;Agfa AG, Leverkusen, Germany) and a computerised, self-adjusting light source (Scantron: Elmedag AG, Obfelden, Switzerland). Since 1989, radiographs have been digitised with a CCDarray scanner (Photometrics, Tucson, Arizona). For this study radiographs taken between 1985 and 1988 were digitised retrospectively. 382 THE JOURNAL OF BONE AND JOINT SURGERY

2 THE VALUE OF PREOPERATIVE PLANNING FOR TOTAL HIP ARTHROPLASTY 383 Planning technique. We used the AP view of the entire pelvis, which included the proximal third of the femora. For orientation of the pelvis in the frontal plane, the two teardrops are identified and a line is drawn through their distal end. A second line perpendicular to this is drawn through the midpoint of the pubic symphysis. There are three basic steps: choosing the right prosthesis for type and size; determination of the anatomical position and orientation of the acetabular component; and restoration of leg length. Choice of appropriate type and size of prosthesis. All sizes of one type of prosthesis are represented on one template (standard magnification 1.15) (Fig. 1). The size of the femoral component is determined by adjusting its medial side to the medial wall of the medullary canal; the T-line (trochanteric line) of the template is placed at the apex of the greater trochanter. The size of the prosthesis determines the amount of offset; the larger the prosthesis the larger the offset. Three neck lengths allow for an additional increase in the offset by a maximum of 6 mm, as may be required in the case of a valgus knee. The acetabular component is then chosen by measuring the radiological diameter of the bony acetabulum with the template. Both components as well as the T-line and R-line (resection line) are marked on a transparent sheet. These lines assist in the correct placement of the femoral component during the operation (Fig. 2a). Anatomical position and orientation of the acetabular component. The acetabular component drawn on the transparent sheet is placed to fit exactly into the bony acetabulum of the radiograph. The transparent sheet is placed parallel to the line of the pubic symphysis marked on the radiograph Fig. 1 Planning template of the Müller SLS-88 system. All stem and cup sizes are represented on the same template. The levels of T (trochanteric line) and R (resection line) are indicated. The larger the prosthesis the more offset is created in relation to the central axis of the prosthesis. VOL. 80-B, NO. 3, MAY 1998

3 384 S. EGGLI, M. PISAN, M. E. MÜLLER Fig. 2a Fig. 2b Fig. 2c Fig. 2d Stepwise planning procedure. The different steps on the radiograph are illustrated on the left; on the right is the resulting planning on the transparent sheet. Figure 2a Choice of the appropriate type and size of prosthetic component and tracing on a transparent sheet. The T and R lines are indicated. Figure 2b Determination of cup positioning by tracing the affected hemipelvis. Figure 2c Superimposition of the traced hemipelvis on the opposite side. Figure 2d Turning the transparent sheet around the centre of rotation of the femoral head until the medial side of the prosthesis and the medial wall of the medullary canal are parallel. THE JOURNAL OF BONE AND JOINT SURGERY

4 THE VALUE OF PREOPERATIVE PLANNING FOR TOTAL HIP ARTHROPLASTY 385 Fig. 2e Fig. 2f Figure 2e The transparent sheet is moved until the prosthetic stem is perfectly central in the medullary canal. The levels of the greater and lesser trochanters are traced on the transparent sheet. Figure 2f Superimposition of the traced trochanters on the diseased side. Tracing of the femur and indication of resection line. Distances between the R-line and the lesser trochanter and between the T-line and the greater trochanter are measured. to obtain 40 of inclination. The acetabular component and subchondral bone are in close contact in the roof of the acetabulum. After correct positioning of the acetabular component, the hemipelvis is traced on to the transparent sheet (Fig. 2b). Restoration of leg lengths. The transparent sheet is turned over and superimposed on the image of the contralateral hip to determine the best coincidence of the traced hemipelvis (Fig. 2c). This is then rotated around the centre of rotation until the medial side of the femoral component and the medial inner cortex of the femur are parallel (Fig. 2d). Next, the transparent sheet is shifted horizontally along the teardrop line until the femoral component is perfectly placed in the proximal femur. The tips of the greater and lesser trochanter from this reference side are then traced on VOL. 80-B, NO. 3, MAY 1998 the transparent sheet (Fig. 2e). Finally, the transparent sheet is turned back to the original side so that the traced trochanters coincide with the trochanters of the diseased side. The contour of the femur and the resection lines of the affected sides are then drawn (Fig. 2f). All details such as the size and type of prosthesis, the use of allografts, and additional osteotomies are listed in order on the planning sheet. Measurements. These were performed using software developed by the Maurice E. Müller Foundation (Bern, Switzerland) in collaboration with the Department of Bioengineering at Clemson University (South Carolina, USA). The radiographs were scanned with a resolution of dpl, which results in a point-to-point discrim-

5 386 S. EGGLI, M. PISAN, M. E. MÜLLER Figure 3 Vertical positioning of the acetabular component was measured as the distance between the teardrop line and the centre of rotation (y). Horizontal positioning was measured as distance between the centre of rotation and a line through the centre of the teardrop, perpendicular to the teardrop line (x). Figure 4 Inclination of the acetabular component was measured as the angle to the teardrop line ( ) and anteversion by measuring the largest distance of the cup opening on the AP radiograph centred on the acetabular cup (A). Fig. 3 Fig. 4 Figure 5 Positioning of the femoral component. The distances between the centre of rotation and the tip of the greater trochanter (x), the centre of rotation and the most prominent point of the lesser trochanter (y), and the medial level of resection of the femoral neck and the most prominent point of the lesser trochanter (z). Figure 6 The difference in leg length was calculated as the difference on the two sides between the distance from the centre of rotation to the most prominent point of the lesser trochanter (y) minus the distance between the centre of rotation and the teardrop line (x). Fig. 5 Fig. 6 ination of 0.01 mm. The postoperative radiographs were calibrated using the known diameter of the prosthetic femoral head. Calibration of the preoperative radiographs and the plan was performed by comparing the measured distance between the two teardrops to the same distance on the calibrated postoperative radiograph. The following variables were evaluated. Variance in the magnification of radiographs. The magnification was determined by comparing the measured diameters of the prosthetic femoral heads to the known diameters. The variance was determined across the immediate postoperative radiographs. Agreement of prosthesis type and size. The type and size of each implanted prosthesis were compared with those chosen on the preoperative plans. Position of the acetabular component. The vertical and horizontal positions of the centre of rotation of the joint as well as the inclination and anteversion of the acetabular component as measured on the immediate postoperative radiographs were compared with the same measurements made on the preoperative plans. The vertical position was measured as the distance between the teardrop line and the centre of rotation and the horizontal position as the distance between the centre of rotation and the teardrop (Fig. 3). Inclination was measured as the angle between the longitudinal axis of the cup opening and the teardrop line and anteversion as the largest distance across the opening of the acetabular component (Fig. 4). The differentiation between ante- and retroversion of the cup was made by comparison of the AP pelvis with the AP acetabular views. An increase in the opening diameter of the cup on the AP acetabular view compared with that on the AP pelvis view indicates anteversion, and a decrease retroversion. Femoral component position. The position of the femoral component was measured on the immediate postoperative radiographs and compared with the same measurements on the preoperative plans (Fig. 5). Distances were measured between the centre of rotation and the tip of the greater trochanter, the centre of rotation and the most prominent point of the lesser trochanter, and the medial level of resection of the femoral neck and the most prominent point THE JOURNAL OF BONE AND JOINT SURGERY

6 THE VALUE OF PREOPERATIVE PLANNING FOR TOTAL HIP ARTHROPLASTY 387 of the lesser trochanter. Leg lengths. The difference in leg length was measured before and after operation as described by Gofton and Trueman. 6 With the patient standing, the knees positioned straight and parallel and the feet 15 cm apart, blocks of known thickness were put under the foot of the shorter leg to equalise pelvic balance and alignment of the lower back. Radiologically, the difference in the leg length was calculated as the difference between the distance of the centre of rotation to the most prominent point of the lesser trochanter and the distance of the centre of rotation to the teardrop line (Fig. 6). Operative technique. Any additional steps indicated on the preoperative plan were compared with the actual operative procedure such as trochanteric osteotomy, resection of osteophytes, the use of bone graft and the use of acetabular or femoral reinforcement devices. To assess intraobserver error all distances were measured on 50 radiographs a second time by the same orthopaedic surgeon and for interobserver error they were measured on 50 radiographs by a second independent orthopaedic surgeon. The Student s t-test was used for statistical evaluation of the intra- and interobserver error with a significance level set at p < Results Table I gives the details. The mean magnification of the immediate postoperative radiographs was 1.18 ± 0.02 SD (1.16 to 1.21). Agreement of the type and size of the prostheses planned preoperatively with those actually used during surgery was Table I. Results of deviation between preoperative planning and postoperative radiological evaluation Parameter Postop evaluation Agreement Prosthesis stem (%) Type 98 Size 92 Acetabular component (%) Type 100 Size 90 Cup position Mean vertical deviation (mm) 2.5 ± 1.1 Mean horizontal deviation (mm) 4.4 ± 2.1 Mean deviation in inclination (degrees) 7.0 ± 2.0 Mean deviation in anteversion (degrees) 9.0 ± 3.0 Mean deviation of stem in distance (mm) dx 3.3 ± 3.1 dy 3.1 ± 2.6 dz 4.2 ± 2.8 Mean leg-length difference (cm) Clinical Preop 0.9 ± 0.5 Postop 0.3 ± 0.1 Radiological Preop 1.1 ± 0.3 Postop 0.2 ± 0.1 Table II. Comparison between the preoperatively planned type and size of the prosthesis and those used Prosthesis component Planned Used Müller straight-stem Standard 5mm mm mm mm mm 3 2 Lateral 7.5 mm mm mm mm 3 3 Uncemented 7.5 mm mm mm 0 1 Self-locking 7.5 mm mm mm 9 8 Polyethylene cup Acetabular reinforcement ring Titanium shell with flange Titanium shell without flange % for the type and 92% for the size of the femoral component. For the size of the acetabular component agreement was 90% (Tables I and II). The type of acetabular component used during the investigation was always the same. The mean difference between the planned and actual centre of rotation was 2.5 ± 1.1 mm vertically and 4.4 ± 2.1 mm horizontally. In 64 cases the centre of rotation was placed distally and in 84 medially to the position that had been planned. The difference in planned and actual inclination of the acetabular component was 7 ± 2 and in anteversion 9 ± 3. The mean difference between the planned and actual distance from the centre of rotation to the lesser trochanter was 3.3 ± 3.1 mm, from the centre of rotation to the greater trochanter 3.1 ± 2.6 mm, and from the resection line to the lesser trochanter 4.2 ± 2.8 mm. The mean preoperative leg-length difference was 0.9 ± 0.5 cm and after operation 0.3 ± 0.1 cm. Radiologically, the mean preoperative leg-length difference was 1.1 ± 0.3 cm and after operation 0.2 ± 0.1 cm. Four trochanteric osteotomies had been planned and four were performed. Resections of osteophytes had been planned for 32 cases and carried out in 39. Thirty acetabular VOL. 80-B, NO. 3, MAY 1998

7 388 S. EGGLI, M. PISAN, M. E. MÜLLER autografts had been planned and 33 were performed. Eight acetabular allografts had been planned and eight were performed. The use of 34 acetabular reinforcement devices had been planned and 36 were used. The use of one femoral reinforcement device had been planned and one was used. The interobserver error was between 2% and 7% and the intraobserver error between 1% and 6%. Neither was statistically significant. Discussion Fig. 7 According to the law of radiation, the magnification (b) of an object (a) is dependent on the distance between the object and the X-ray source (d) as well as the distance between the object and the X-ray film (c). Our planning technique was developed for accuracy with minimal commitment of time from the surgeon. The teardrop line, chosen by the senior author (MEM) to determine vertical and horizontal orientation, was later identified in several studies as being the most accurate anatomical landmark in relation to the bony acetabulum for rotational consistency in both sagittal and coronal planes The production of an overlay for the contralateral hemipelvis allows adjustment for differences in the anatomical positions of the centres of rotation of the two hips. Leg-length discrepancies are equalised by comparing the distances between the two centres of rotation and the trochanters because these measurements avoid errors due to rotation in the frontal plane (abduction/adduction). Unequal flexion contractures, which may influence the radiological distance between the centres of rotation and the trochanters must be considered and corrected. This can either be done by adjusting the angle of incidence of the X-ray beam or by elevation of the patient s body until the central X-ray beam is perpendicular to the femora. An important factor in evaluating a preoperative planning procedure is the variance of radiological magnification which is influenced by the distance between the patient and the film and the distance between the patient and the X-ray source (Fig. 7). Variations in the former can be offset by adjusting the distance from the X-ray source to each patient according to Table III. Since 1980 we have taken pre- and postoperative radiographs using a film-to-source distance of 150 cm. In this study we found an average magnification factor of 1.18 ± 0.02, which is somewhat higher than the 1.15 magnification factor of many planning templates. This result agrees with the findings of Linclau, Dokter and Peene 11 and Knight and Atwater 4 who showed that there is a significant tendency for surgeons to underestimate the magnification of radiographs. The magnification error is more significant with increasing distance measured on the radiograph. An error of 6% is sufficient to give a single step error in the size of the acetabular component, but an error of at least 30% is required to produce a one-size error for the femoral component. Knight and Atwater 4 stated that magnification was a significant factor in predicting the size of the femoral component. We found that only four of the 100 preoperative radiographs showed a deviation of more than 5% from the magnification of the template (1.15). By choosing a template with a magnification factor of 1.18, there would have been no case with a deviation of more than 5%. We do not consider that magnification is a major limiting factor, especially for the femoral component. We found an agreement of 98% for the type of the prosthesis between the preoperative plans and the postoperative results. For the femoral component the size was planned correctly in 92% of cases and for the acetabular component in 90%. These rates are somewhat better than those reported in other studies 4,11 possibly because we included only patients with idiopathic osteoarthritis. We also used a cemented femoral component in more than 90% of the cases; cemented devices have recently been shown to be easier to plan and to yield better agreement between the preoperative plan and the postoperative result. 11 For the position of the acetabular component, we try to achieve complete coverage of the component without damage to the subchondral bone, which acts as a force transmitter to the central trabecular bundle of the innominate bone. 12 The centre of rotation is placed in a nearly anatomical position. We try to avoid lateral and superior shifts of the centre which increase loads on both components. 13,14 We direct acetabular reaming more against the medial and posterior wall than towards the acetabular roof, and produce a somewhat higher horizontal variance between the planned and actual positioning of the centre Table III. Magnification table calculated with different film-object and object-x-ray source distances Distance camera to object (cm) Distance object to film (cm) THE JOURNAL OF BONE AND JOINT SURGERY

8 THE VALUE OF PREOPERATIVE PLANNING FOR TOTAL HIP ARTHROPLASTY 389 of rotation. Recent studies have shown that by avoiding medialisation and cranialisation of the centre of rotation, both acetabular 15,16 and femoral 17 loosening is diminished. The average deviation of 1.5 mm vertically and 3.4 mm horizontally between the planned and actual centre of rotation was produced in 64% of the cases by a distal shift and in 84% by a medial shift of the acetabular component. This corresponds well to the values reported by Knight and Atwater 4 who measured an average medial shift of 5mm and a distal shift of 1 mm during the insertion of the acetabular component. With regard to the position of the acetabular component, we aim for 40 of inclination and 15 of anteversion in order to minimise the risk of dislocation. 1 We found a somewhat higher deviation in cup anteversion than in cup inclination between the preoperatively planned and the postoperatively measured orientation. Measurement of anteversion is highly dependent on pelvic rotation, X-ray-source-to-patient-to-film distances, and the position of the centre of the X-ray beam. The influence of these factors can be minimised by taking an AP view of the proximal femur with a fixed film-source distance. Flexion contractures can also be recognised, and appropriate adjustments can be made. A remaining problem is, however, the intraoperative loss of control of pelvic flexion which can result in malposition of the acetabular component, mainly in the coronal plane (anteversion/retroversion). With regard to the position of the femoral component, we found the greatest deviation in the distance between the resection line and the lesser trochanter because intraoperatively deviations of the vertical cup position are corrected by adjusting the depth of stem insertion into the femoral canal. Varying distances between the centre of rotation and greater trochanter and between the centre of rotation and lesser trochanter are produced either by varus/valgus malpositioning of the femoral component or by varying the radiological appearance of the two trochanters, due to differences in the rotation of the femur. Inequality in leg length has been shown to produce low back pain 18,19 and an abnormal gait. 20 Excessive lengthening has also been shown to produce sciatic nerve palsy. 21 Methods have been described to adjust leg length by preoperative planning 4,22 and by other techniques. 5,23,24 We emphasise the importance of using anatomical landmarks in preoperative planning that allow for intraoperative verification of the planned leg lengthening. We use a T-line (trochanteric line) and an R-line (resection line) to measure intraoperatively the distance of each of these two lines to the centre of rotation. Leglength differences postoperatively averaged 0.3 ± 0.1 mm clinically and 0.2 ± 0.1 mm radiologically. Only 6% of the patients had more than 5 mm of leg-length discrepancy postoperatively. In 1978, Williamson and Reckling 21 reported an average leg-length discrepancy of 16 mm after a preoperative planning procedure that included measuring the distance between the ischium and the lesser trochanter, which is highly influenced by changes in pelvic rotation. Hoikka et al, 25 in 1991, however, found an average leg-length discrepancy of 4 mm after revision arthroplasty in 30 patients who had had preoperative planning. Knight and Atwater 4 showed that in 92% of the cases, surgeons were able to achieve the preoperatively planned leg length within 5 mm. These data support our findings that leg-length equality can be planned preoperatively and achieved intraoperatively within an accuracy of 5 mm. An added benefit of preoperative planning is that it forces the surgeon to scrutinise the radiographs, thus increasing the chance of anticipating intraoperative difficulties such as the resection of osteophytes, trochanteric osteotomy, bone grafting, and the use of acetabular reinforcement devices. In our series, more than 80% of these intraoperative difficulties were foreseen so that suitable measures were taken before surgery. In particular, all hips requiring trochanteric osteotomies and/or acetabular allografts were recognised before operation. We would like to thank John Harrast of the Brigham and Women s Hospital in Boston for reviewing and contributing to this article. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. References 1. Charnley J. Low friction arthroplasty of the hip. Berlin: Springer Verlag, 1979: Müller ME. Total hip replacement: planning, technique and complications. In: Surgical management of degenerative arthritis of the lower limb. Philadelphia: Lea and Faber, 1975: Muller ME. Lessons of 30 years of total hip arthroplasty. Clin Orthop 1992;274: Knight JL, Atwater RD. Preoperative planning for total hip arthroplasty: quantitating its utility and precision. J Arthroplasty 1992;7: Hoikka V, Paavilainen T, Lindholm TS, Turula KB, Ylikoski M. Measurement and restoration of equality in length of the lower limbs in total hip replacement. Skeletal Radiol 1987;16: Gofton JP, Trueman GE. Studies in osteoarthritis of the hip: II. Osteoarthritis of the hip and leg-length disparity. Can Med Assoc J 1971;104: Goodman SB, Adler SJ, Fyhrie DP, Schurman DJ. The acetabular teardrop and its relevance to acetabular migration. Clin Orthop 1988; 236: Ilchmann T, Franzen H, Mjöberg B, Wingstrand H. Measurement accuracy in acetabular cup migration: a comparison of four radiologic methods versus roentgen stereophotogrammetric analysis. J Arthroplasty 1992;7: Massin P, Schmidt L, Engh CA. Evaluation of cementless acetabular component migration: an experimental study. J Arthroplasty 1989;4: Sutherland CJ, Bresina SJ. Measurement of acetabular component migration using two-dimensional radiography. J Arthroplasty 1992;7: Linclau L, Dokter G, Peene P. Radiological aspects in preoperative planning and postoperative assessment of cementless total hip arthroplasty. Acta Orthop Belg 1993;59: Kapandji IA. Physiologie articulaire. Fascicule II: Membre inférieur: 4ème edition. Paris: Maloine, Bombelli R. Osteoarthritis of the hip: pathogenesis and consequent therapy. Berlin: Springer-Verlag, Pauwels F. Gesammelte Abhandlungen zur funktionellen Anatomie des Bewegungsapparates. Berlin, etc: Springer-Verlag, VOL. 80-B, NO. 3, MAY 1998

9 390 S. EGGLI, M. PISAN, M. E. MÜLLER 15. Lachiewicz PF, McCaskill B, Inglis AE, Ranawat CS, Rosenstein BD. Total hip arthroplasty in juvenile rheumatoid arthritis: two to eleven year results. J Bone Joint Surg [Am] 1986;68-A: Callaghan JJ, Salvati EA, Pellicci PM, Wilson PD Jr, Ranawat CS. Results of revision for mechanical failure after cemented total hip replacement, 1979 to 1982: a two- to five-year follow-up. J Bone Joint Surg [Am] 1985;67-A: Yoder SA, Brand RA, Pedersen DR, O Gorman TW. Total hip acetabular component position affects component loosening rates. Clin Orthop 1988;228: Friberg O. Clinical symptoms and biomechanics of lumbar spine and hip joint in leg length inequality. Spine 1983;8: Giles LG, Taylor JR. Low-back pain associated with leg length inequality. Spine 1981;6: Wykman A, Olsson E. Walking ability after total hip replacement: a comparison of gait analysis in unilateral and bilateral cases. J Bone Joint Surg [Br] 1992;74-B: Williamson JA, Reckling FW. Limb length discrepancy and related problems following total hip joint replacement. Clin Orthop 1978; 134: Capello WN. Preoperative planning of total hip arthroplasty. Instr Course Lect 1986;35: McGee HMJ, Scott JHS. A simple method of obtaining equal leg length in total hip arthroplasty. Clin Orthop 1985;194: Woolson ST, Harris WH. A method of intraoperative limb length measurement in total hip arthroplasty. Clin Orthop 1985;194: Hoikka V, Santavirta S, Eskola A, et al. Methodology for restoring functional leg length in revision total hip arthroplasty. J Arthroplasty 1991;6: THE JOURNAL OF BONE AND JOINT SURGERY