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Accurate Femur Repositioning is Critical During Intraoperative Total Hip Arthroplasty Length and Offset Assessment
The Journal of Arthroplasty Vol. 20 No. 7 2005
Accurate Femur Repositioning is Critical During Intraoperative Total Hip Arthroplasty Length and Offset Assessment Vineet K. Sarin, PhD,* William R. Pratt, BA,* and Gary W. Bradley, MDy
Abstract: Techniques for intraoperative leg length equalization are based on measurements between fixed points on the pelvis and femur. These techniques have not been reliable because they are based on accurate femur repositioning. We examined the error that results from inaccurate femur repositioning during total hip arthroplasty. Total hip arthroplasty was simulated on a calibrated test bench and changes in leg length and femoral offset were measured. Before dislocation, the femur was held in neutral alignment. Total hip arthroplasty was simulated without changing length or offset and the femur was returned to neutral. Length and offset changes were measured with the femur held in 58 and 108 of abduction/adduction and flexion/extension. Five degrees of abduction/adduction malpositioning caused 8 mm of apparent change in leg length. Errors in femoral offset followed a similar trend. When using common techniques for intraoperative leg length equalization and offset restoration, inaccurate abduction/adduction repositioning of the femur with respect to the pelvis can cause substantial errors in the measurement of length and offset change. Key words: leg length inequality, leg length discrepancy, femoral offset, total hip arthroplasty, navigation. n 2005 Elsevier Inc. All rights reserved.
and compromised cardiopulmonary function [5,12]. Leg length inequality is also a primary cause for malpractice liability lawsuits after THA in the United States [2,9,14]. Accurate restoration of femoral offset is critical for reproducing the biomechanics of the hip joint after hip arthroplasty. Inadequate femoral offset can lead to joint instability, high joint reaction forces, increased polyethylene wear, and decreased range of motion [15,16]. Although not supported by cadaveric and animal studies [17,18], increased femoral offset can theoretically lead to increased implant bending moments and increased strain at the femur-implant interface, leading to early loosening. Intraoperative determination of both leg length equality and femoral offset restoration are therefore of significant clinical interest. Several intraoperative techniques are commonly used to assess leg length inequality and femoral offset
Leg length equality and femoral offset restoration are important functional parameters that are related to success in total hip arthroplasty (THA). Leg length inequality is common after primary and revision THA [1-9]. Leg length inequality can contribute to hip instability, ipsilateral knee pain, low back pain, sciatic nerve palsy, and abnormal force transmission across the hip joint [2,4,10-13] and may contribute to aseptic prosthesis loosening
From *Kinamed Navigation Systems LLC, Camarillo, California and y Alta Orthopaedics, Santa Barbara, California. Submitted January 26, 2004; accepted May 28, 2004. Benefits or funds were received in partial or total support of the research materials described in this article from Kinamed Inc. Reprint requests: Vineet K. Sarin, PhD, Kinamed Navigation Systems LLC, 820 Flynn Road, Camarillo, CA 93012. n 2005 Elsevier Inc. All rights reserved. 0883-5403/04/1906-0004$30.00/0 doi:10.1016/j.arth.2004.07.001
887
888 The Journal of Arthroplasty Vol. 20 No. 7 October 2005 larger errors in the measurement of length and offset [8]. The objective of this study is to use a commercially available computer-aided navigation system to determine the error that results from inaccurate femur repositioning during intraoperative assessment of leg length inequality and femoral offset. Total hip arthroplasty surgery was simulated on a calibrated hip joint fixture and the navigation system was used to accurately measure changes in leg length and femoral offset and to measure errors that result from inaccurate femur repositioning.
Materials and Methods Total hip arthroplasty surgery was simulated on a calibrated test bench. The test bench consisted of calibrated pelvis and femur fixtures that allow changes in leg length and femoral offset to be fixed and measured to within F1 mm. The fixture also
Fig. 1. Navigational tracking devices, attached to sawbones models of the pelvis and femur, serve as fixed reference points. The tracking devices are attached to the bones in accordance with common techniques for intraoperative leg length equalization.
restoration. These techniques are based on either visual comparison of fixed points located on preoperative and intraoperative radiographs, or identification and comparison of fixed points on the pelvis and femur before hip dislocation and after implantation of trial prostheses. Fixed points in this context refer to anatomic landmarks (such as the iliac spine, lesser trochanter, patella, ankle malleoli, etc) or rigid pins or other fixation devices that are temporarily attached to the pelvis and femur. Current techniques for leg length equalization and femoral offset restoration during THA are fundamentally based on a measurement of the distance between a fixed point on the pelvis and a fixed point on the operative leg [2,19-23]. Such techniques, however, have not produced reliable results [7,8,24,25]. Techniques that compare 2 linear measurements are fundamentally based on accurate repositioning of the leg in abduction, flexion, and rotation [8]. Furthermore, because the fixed reference points used in these techniques are located away from the center of the hip joint, small errors in femur repositioning can lead to
Fig. 2. Navigational tracking devices, attached to a calibrated pelvis and femur test bench, serve as fixed reference points. The calibrated pelvis allows for accurate registration of the pelvic landmarks used in navigation (both anterior-superior iliac spines and the pubic symphysis). The calibrated hip joint allows for accurate determination of femur rotation (flexion/extension, abduction/adduction, internal/external rotation) as well as length and offset.
Femur Re-positioning for THA Length and Offset ! Sarin et al 889 Table 2. Apparent Change in Leg Length with 108 of Repositioning Error 108 08 +108 (extension, mm) (neutral, mm) (flexion, mm) 108 (adduction) 08 (neutral) +108 (abduction)
13.8 0.5 16.7
14.7 0.0 16.5
13.4 1.0 17.4
Results are averaged over 3 samples.
Fig. 3. Intraoperative depiction of the tracking devices in clinical use. Tracking devices are attached to the pelvis and femur during THA surgery for navigation of length and offset.
allows the femur to be fixed in flexion/extension, abduction/adduction, and internal/external rotation to within F18. An image-free navigation system (NaviPro, Kinamed Navigation Systems LLC, Camarillo, Calif) was used to accurately measure changes in leg length and femoral offset during simulated THA. To allow image-free navigation of the hip joint, optical tracking devices were fixed to the pelvis and femur (Figs. 1 and 2) in accordance with common surgical practice (Fig. 3). The femur tracking device was fixed at the level of the greater trochanter in accordance with common techniques for intraoperative leg length equalization [2,25]. Before dislocation of the hip joint, the femur was held in neutral abduction, flexion, and rotation to establish an bindex Q position. The joint arthroplasty procedure was simulated without changing leg length or femoral offset and the
Table 1. Apparent Change in Leg Length With 58 of Repositioning Error
58 (adduction) 08 (neutral) +58 (abduction)
58 (extension) (mm)
08 (neutral) (mm)
+58 (flexion) (mm)
7.4 0.1 8.2
7.6 0.1 8.1
7.3 0.2 8.4
Results are averaged over 3 samples.
femur was returned to the index position. The navigation system provided real-time changes in leg length and femoral offset as the femur was returned to the index position. To quantify the amount of error resulting from inaccurate repositioning of the femur, apparent changes in leg length and femoral offset were measured with the femur held in 58 and 108 of abduction/adduction and flexion/extension. The errors due to inaccurate internal/external rotation were not studied. Each measurement was repeated 3 times and the average results are reported.
Results Inaccurate femur repositioning caused errors in the apparent measurement of leg length change (Tables 1 and 2). Inaccurate repositioning in terms of femur abduction/adduction caused substantially greater error than inaccurate flexion/extension repositioning. As little as 58 of abduction/adduction error in repositioning the femur caused approximately 8 mm of apparent change in leg length. The error introduced by 108 of abduction/ adduction error was approximately 14 to 17 mm (Table 2). Inaccurate femur repositioning had a similar, but slightly less pronounced, effect on the accuracy of intraoperative femoral offset restoration (Table 3).
Table 3. Apparent Change in Femoral Offset with 108 of Repositioning Error 108 08 +108 (extension, mm) (neutral, mm) (flexion, mm) 108 (adduction) 08 (neutral) +108 (abduction)
11.7 0.1 8.8
Results are averaged over 3 samples.
11.5 0.0 9.1
11.4 0.0 9.0
890 The Journal of Arthroplasty Vol. 20 No. 7 October 2005
Discussion This study demonstrates the importance of accurate femur repositioning during intraoperative assessment of leg length inequality and femoral offset restoration. When using common techniques for intraoperative leg length equalization and femoral offset restoration, inaccurate abduction/ adduction repositioning of the femur with respect to the pelvis can cause substantial errors in the measurement of length and offset change. As little as 58 abduction/adduction malpositioning caused 8 mm error in the leg length measurement, whereas 108 abduction/adduction malpositioning caused 14 to 17 mm error. Errors due to incorrect flexion/extension repositioning were much less pronounced. Errors in femoral offset followed a similar trend. This study focuses on malrotation of the femur with respect to the pelvis. Malrotation of the pelvis with respect to the femur (or operating room table) can also occur and contribute to leg length inequality and incorrect femoral offset restoration. Ranawat and Rodriguez [26] described how fixed pelvic obliquity (or tilt) can lead to functional leg length inequality. DiGioia and colleagues [27] used an image-based navigation system to study the motion of the pelvis during primary THA in 10 patients held in the lateral decubitus position. Each patient’s trunk and pelvis were stabilized with a series of anterior and posterior supports in addition to a beanbag. In spite of careful attention to pelvic stabilization, DiGioia et al [27] reported the following amounts of pelvic rotation during discrete steps of a hip arthroplasty procedure: 238 rotation of the pelvis in abduction/adduction (range, 15.98 to 7.08), 168 rotation of the pelvis in flexion/extension (range, 8.18 to 7.58), and 408 rotation of the pelvis in version (range, 19.58 to 20.18). Pelvic abduction/adduction, which would contribute to the malrotation errors described in the current study, was greatest just after hip dislocation and during range-of-motion testing with the leg held in maximal extension and maximal external rotation [27]. Even when the leg was returned to bneutralQ alignment, the pelvis was rotated by 14.68 (in abduction/ adduction) with respect to its initial orientation. The results of the current study may further explain why common techniques for intraoperative leg length equalization have not produced reliable results. Because such techniques compare 2 linear measurements, they are fundamentally based on accurate rotational repositioning of the leg with respect to the pelvis [8]. Techniques using pins or jigs that are fixed at some distance away from the
bone surface exaggerate the effect of rotational error because the measurements are made away from the rotational center of the joint [8]. If these types of techniques are to be used reliably, it is important to minimize the distance between the femur reference point and the joint center so that the deleterious effect of malrotation will be reduced.
Acknowledgments Support for this research was provided by Kinamed, Inc. The authors thank Clyde Pratt, JD, and Chitranjan Ranawat, MD, for helpful discussion.
References 1. Abraham WD, Dimon III JH. Leg length discrepancy in total hip arthroplasty. Orthop Clin North Am 1992;23:201. 2. Bose WJ. Accurate limb-length equalization during total hip arthroplasty. Orthopedics 2000;23:433. 3. Bourne RB, Rorabeck CH. Soft tissue balancing: the hip. J Arthroplasty 2002;17:4(Suppl 1):17. 4. Edeen J, Sharkey PF, Alexander AH. Clinical significance of leg-length inequality after total hip arthroplasty. Am J Orthop 1995;24:347. 5. Gurney B, Mermier C, Robergs R, et al. Effects of limb-length discrepancy on gait economy and lowerextremity muscle activity in older adults. J Bone Joint Surg 2001;83-A:907. 6. Hoikka V, Santavirta S, Eskola A, et al. Methodology for restoring functional leg length in revision total hip arthroplasty. J Arthroplasty 1991;6:189. 7. Jasty M, Webster W, Harris W. Management of limb length inequality during total hip replacement. Clin Orthop 1996;333:165. 8. Ranawat CS, Rao RR, Rodriguez JA, et al. Correction of limb-length inequality during total hip arthroplasty. J Arthroplasty 2001;16:715. 9. Woolson ST, Hartford JM, Sawyer A. Results of a method of leg-length equalization for patients undergoing primary total hip replacement. J Arthroplasty 1999;14:159. 10. Friberg O. Clinical symptoms and biomechanics of lumbar spine and hip joint in leg length inequality. Spine 1983;8:643. 11. Giles LG, Taylor JR. Low-back pain associated with leg length inequality. Spine 1981;6:510. 12. Turula KB, Freiberg O, Lindholm TS, et al. Leg length inequality after total hip arthroplasty. Clin Orthop 1986;202:163. 13. Williamson JA, Reckling FW. Limb length discrepancy and related problems following total hip replacement. Clin Orthop 1978;134:135. 14. Hofmann AA, Skrzynski MC. Leg-length inequality and nerve palsy in total hip arthroplasty: a lawyer awaits! Orthopedics 2000;23:943.
Femur Re-positioning for THA Length and Offset ! Sarin et al 891 15. McGrory BJ, Morrey BF, Cahalan TD, et al. Effect of femoral offset on range of motion and abductor muscle strength after total hip arthroplasty. J Bone Joint Surg 1995;77-B:865. 16. Sakalkale DP, Sharkey PF, Eng K, et al. Effect of femoral component offset on polyethylene wear in total hip arthroplasty. Clin Orthop 2001;388:125. 17. Davey JR, O’Connor DO, Burke DW, et al. Femoral component offset. Its effect on strain in bonecement. J Arthroplasty 1993;8:23. 18. Wong PKC, Otsuka NY, Davey JR, et al. The effect of femoral component offset in uncemented total hip arthroplasty. Presented at Canadian Orthopaedic Society, 48th Annual Meeting, Montreal, Quebec; 1993. 19. Bal BS. A technique for comparison of leg lengths during total hip replacement. Am J Orthop 1996; 25:61. 20. Huddleston HD. An accurate method for measuring leg length and hip offset in hip arthroplasty. Orthopedics 1997;20:331. 21. Itokazu M, Masuda K, Ohno T, et al. A simple method of intraoperative limb length measurement
22.
23.
24.
25.
26.
27.
in total hip arthroplasty. Bull Hosp Jt Dis 1997; 56:204. McGee HM, Scott JH. A simple method of obtaining equal leg length in total hip arthroplasty. Clin Orthop 1985;194:269. Naito M, Ogata K, Asayama I. Intraoperative limb length measurement in total hip arthroplasty. Int Orthop 1999;23:31. Schutte DH, Conrad JM, Barfield WR, et al. The effect of rotation on the measurement of femoral offset radiographs. Presented at International Society for Technology in Arthroplasty, San Francisco, CA; 2003. Woolson ST, Harris WH. A method of intraoperative limb length measurement in total hip arthroplasty. Clin Orthop 1985;194:207. Ranawat CS, Rodriguez JA. Functional leg length inequality following total hip arthroplasty. J Arthroplasty 1997;12:359. DiGioia AM, Jaramaz B, Blackwell M, et al. The Otto Aufranc award. Image guided navigation system to measure intraoperatively acetabular implant alignment. Clin Orthop 1998;355:8.
Accurate Femur Repositioning is Critical During Intraoperative Total Hip Arthroplasty Length and Offset Assessment Vineet K. Sarin, PhD,* William R. Pratt, BA,* and Gary W. Bradley, MDy
Abstract: Techniques for intraoperative leg length equalization are based on measurements between fixed points on the pelvis and femur. These techniques have not been reliable because they are based on accurate femur repositioning. We examined the error that results from inaccurate femur repositioning during total hip arthroplasty. Total hip arthroplasty was simulated on a calibrated test bench and changes in leg length and femoral offset were measured. Before dislocation, the femur was held in neutral alignment. Total hip arthroplasty was simulated without changing length or offset and the femur was returned to neutral. Length and offset changes were measured with the femur held in 58 and 108 of abduction/adduction and flexion/extension. Five degrees of abduction/adduction malpositioning caused 8 mm of apparent change in leg length. Errors in femoral offset followed a similar trend. When using common techniques for intraoperative leg length equalization and offset restoration, inaccurate abduction/adduction repositioning of the femur with respect to the pelvis can cause substantial errors in the measurement of length and offset change. Key words: leg length inequality, leg length discrepancy, femoral offset, total hip arthroplasty, navigation. n 2005 Elsevier Inc. All rights reserved.
and compromised cardiopulmonary function [5,12]. Leg length inequality is also a primary cause for malpractice liability lawsuits after THA in the United States [2,9,14]. Accurate restoration of femoral offset is critical for reproducing the biomechanics of the hip joint after hip arthroplasty. Inadequate femoral offset can lead to joint instability, high joint reaction forces, increased polyethylene wear, and decreased range of motion [15,16]. Although not supported by cadaveric and animal studies [17,18], increased femoral offset can theoretically lead to increased implant bending moments and increased strain at the femur-implant interface, leading to early loosening. Intraoperative determination of both leg length equality and femoral offset restoration are therefore of significant clinical interest. Several intraoperative techniques are commonly used to assess leg length inequality and femoral offset
Leg length equality and femoral offset restoration are important functional parameters that are related to success in total hip arthroplasty (THA). Leg length inequality is common after primary and revision THA [1-9]. Leg length inequality can contribute to hip instability, ipsilateral knee pain, low back pain, sciatic nerve palsy, and abnormal force transmission across the hip joint [2,4,10-13] and may contribute to aseptic prosthesis loosening
From *Kinamed Navigation Systems LLC, Camarillo, California and y Alta Orthopaedics, Santa Barbara, California. Submitted January 26, 2004; accepted May 28, 2004. Benefits or funds were received in partial or total support of the research materials described in this article from Kinamed Inc. Reprint requests: Vineet K. Sarin, PhD, Kinamed Navigation Systems LLC, 820 Flynn Road, Camarillo, CA 93012. n 2005 Elsevier Inc. All rights reserved. 0883-5403/04/1906-0004$30.00/0 doi:10.1016/j.arth.2004.07.001
887
888 The Journal of Arthroplasty Vol. 20 No. 7 October 2005 larger errors in the measurement of length and offset [8]. The objective of this study is to use a commercially available computer-aided navigation system to determine the error that results from inaccurate femur repositioning during intraoperative assessment of leg length inequality and femoral offset. Total hip arthroplasty surgery was simulated on a calibrated hip joint fixture and the navigation system was used to accurately measure changes in leg length and femoral offset and to measure errors that result from inaccurate femur repositioning.
Materials and Methods Total hip arthroplasty surgery was simulated on a calibrated test bench. The test bench consisted of calibrated pelvis and femur fixtures that allow changes in leg length and femoral offset to be fixed and measured to within F1 mm. The fixture also
Fig. 1. Navigational tracking devices, attached to sawbones models of the pelvis and femur, serve as fixed reference points. The tracking devices are attached to the bones in accordance with common techniques for intraoperative leg length equalization.
restoration. These techniques are based on either visual comparison of fixed points located on preoperative and intraoperative radiographs, or identification and comparison of fixed points on the pelvis and femur before hip dislocation and after implantation of trial prostheses. Fixed points in this context refer to anatomic landmarks (such as the iliac spine, lesser trochanter, patella, ankle malleoli, etc) or rigid pins or other fixation devices that are temporarily attached to the pelvis and femur. Current techniques for leg length equalization and femoral offset restoration during THA are fundamentally based on a measurement of the distance between a fixed point on the pelvis and a fixed point on the operative leg [2,19-23]. Such techniques, however, have not produced reliable results [7,8,24,25]. Techniques that compare 2 linear measurements are fundamentally based on accurate repositioning of the leg in abduction, flexion, and rotation [8]. Furthermore, because the fixed reference points used in these techniques are located away from the center of the hip joint, small errors in femur repositioning can lead to
Fig. 2. Navigational tracking devices, attached to a calibrated pelvis and femur test bench, serve as fixed reference points. The calibrated pelvis allows for accurate registration of the pelvic landmarks used in navigation (both anterior-superior iliac spines and the pubic symphysis). The calibrated hip joint allows for accurate determination of femur rotation (flexion/extension, abduction/adduction, internal/external rotation) as well as length and offset.
Femur Re-positioning for THA Length and Offset ! Sarin et al 889 Table 2. Apparent Change in Leg Length with 108 of Repositioning Error 108 08 +108 (extension, mm) (neutral, mm) (flexion, mm) 108 (adduction) 08 (neutral) +108 (abduction)
13.8 0.5 16.7
14.7 0.0 16.5
13.4 1.0 17.4
Results are averaged over 3 samples.
Fig. 3. Intraoperative depiction of the tracking devices in clinical use. Tracking devices are attached to the pelvis and femur during THA surgery for navigation of length and offset.
allows the femur to be fixed in flexion/extension, abduction/adduction, and internal/external rotation to within F18. An image-free navigation system (NaviPro, Kinamed Navigation Systems LLC, Camarillo, Calif) was used to accurately measure changes in leg length and femoral offset during simulated THA. To allow image-free navigation of the hip joint, optical tracking devices were fixed to the pelvis and femur (Figs. 1 and 2) in accordance with common surgical practice (Fig. 3). The femur tracking device was fixed at the level of the greater trochanter in accordance with common techniques for intraoperative leg length equalization [2,25]. Before dislocation of the hip joint, the femur was held in neutral abduction, flexion, and rotation to establish an bindex Q position. The joint arthroplasty procedure was simulated without changing leg length or femoral offset and the
Table 1. Apparent Change in Leg Length With 58 of Repositioning Error
58 (adduction) 08 (neutral) +58 (abduction)
58 (extension) (mm)
08 (neutral) (mm)
+58 (flexion) (mm)
7.4 0.1 8.2
7.6 0.1 8.1
7.3 0.2 8.4
Results are averaged over 3 samples.
femur was returned to the index position. The navigation system provided real-time changes in leg length and femoral offset as the femur was returned to the index position. To quantify the amount of error resulting from inaccurate repositioning of the femur, apparent changes in leg length and femoral offset were measured with the femur held in 58 and 108 of abduction/adduction and flexion/extension. The errors due to inaccurate internal/external rotation were not studied. Each measurement was repeated 3 times and the average results are reported.
Results Inaccurate femur repositioning caused errors in the apparent measurement of leg length change (Tables 1 and 2). Inaccurate repositioning in terms of femur abduction/adduction caused substantially greater error than inaccurate flexion/extension repositioning. As little as 58 of abduction/adduction error in repositioning the femur caused approximately 8 mm of apparent change in leg length. The error introduced by 108 of abduction/ adduction error was approximately 14 to 17 mm (Table 2). Inaccurate femur repositioning had a similar, but slightly less pronounced, effect on the accuracy of intraoperative femoral offset restoration (Table 3).
Table 3. Apparent Change in Femoral Offset with 108 of Repositioning Error 108 08 +108 (extension, mm) (neutral, mm) (flexion, mm) 108 (adduction) 08 (neutral) +108 (abduction)
11.7 0.1 8.8
Results are averaged over 3 samples.
11.5 0.0 9.1
11.4 0.0 9.0
890 The Journal of Arthroplasty Vol. 20 No. 7 October 2005
Discussion This study demonstrates the importance of accurate femur repositioning during intraoperative assessment of leg length inequality and femoral offset restoration. When using common techniques for intraoperative leg length equalization and femoral offset restoration, inaccurate abduction/ adduction repositioning of the femur with respect to the pelvis can cause substantial errors in the measurement of length and offset change. As little as 58 abduction/adduction malpositioning caused 8 mm error in the leg length measurement, whereas 108 abduction/adduction malpositioning caused 14 to 17 mm error. Errors due to incorrect flexion/extension repositioning were much less pronounced. Errors in femoral offset followed a similar trend. This study focuses on malrotation of the femur with respect to the pelvis. Malrotation of the pelvis with respect to the femur (or operating room table) can also occur and contribute to leg length inequality and incorrect femoral offset restoration. Ranawat and Rodriguez [26] described how fixed pelvic obliquity (or tilt) can lead to functional leg length inequality. DiGioia and colleagues [27] used an image-based navigation system to study the motion of the pelvis during primary THA in 10 patients held in the lateral decubitus position. Each patient’s trunk and pelvis were stabilized with a series of anterior and posterior supports in addition to a beanbag. In spite of careful attention to pelvic stabilization, DiGioia et al [27] reported the following amounts of pelvic rotation during discrete steps of a hip arthroplasty procedure: 238 rotation of the pelvis in abduction/adduction (range, 15.98 to 7.08), 168 rotation of the pelvis in flexion/extension (range, 8.18 to 7.58), and 408 rotation of the pelvis in version (range, 19.58 to 20.18). Pelvic abduction/adduction, which would contribute to the malrotation errors described in the current study, was greatest just after hip dislocation and during range-of-motion testing with the leg held in maximal extension and maximal external rotation [27]. Even when the leg was returned to bneutralQ alignment, the pelvis was rotated by 14.68 (in abduction/ adduction) with respect to its initial orientation. The results of the current study may further explain why common techniques for intraoperative leg length equalization have not produced reliable results. Because such techniques compare 2 linear measurements, they are fundamentally based on accurate rotational repositioning of the leg with respect to the pelvis [8]. Techniques using pins or jigs that are fixed at some distance away from the
bone surface exaggerate the effect of rotational error because the measurements are made away from the rotational center of the joint [8]. If these types of techniques are to be used reliably, it is important to minimize the distance between the femur reference point and the joint center so that the deleterious effect of malrotation will be reduced.
Acknowledgments Support for this research was provided by Kinamed, Inc. The authors thank Clyde Pratt, JD, and Chitranjan Ranawat, MD, for helpful discussion.
References 1. Abraham WD, Dimon III JH. Leg length discrepancy in total hip arthroplasty. Orthop Clin North Am 1992;23:201. 2. Bose WJ. Accurate limb-length equalization during total hip arthroplasty. Orthopedics 2000;23:433. 3. Bourne RB, Rorabeck CH. Soft tissue balancing: the hip. J Arthroplasty 2002;17:4(Suppl 1):17. 4. Edeen J, Sharkey PF, Alexander AH. Clinical significance of leg-length inequality after total hip arthroplasty. Am J Orthop 1995;24:347. 5. Gurney B, Mermier C, Robergs R, et al. Effects of limb-length discrepancy on gait economy and lowerextremity muscle activity in older adults. J Bone Joint Surg 2001;83-A:907. 6. Hoikka V, Santavirta S, Eskola A, et al. Methodology for restoring functional leg length in revision total hip arthroplasty. J Arthroplasty 1991;6:189. 7. Jasty M, Webster W, Harris W. Management of limb length inequality during total hip replacement. Clin Orthop 1996;333:165. 8. Ranawat CS, Rao RR, Rodriguez JA, et al. Correction of limb-length inequality during total hip arthroplasty. J Arthroplasty 2001;16:715. 9. Woolson ST, Hartford JM, Sawyer A. Results of a method of leg-length equalization for patients undergoing primary total hip replacement. J Arthroplasty 1999;14:159. 10. Friberg O. Clinical symptoms and biomechanics of lumbar spine and hip joint in leg length inequality. Spine 1983;8:643. 11. Giles LG, Taylor JR. Low-back pain associated with leg length inequality. Spine 1981;6:510. 12. Turula KB, Freiberg O, Lindholm TS, et al. Leg length inequality after total hip arthroplasty. Clin Orthop 1986;202:163. 13. Williamson JA, Reckling FW. Limb length discrepancy and related problems following total hip replacement. Clin Orthop 1978;134:135. 14. Hofmann AA, Skrzynski MC. Leg-length inequality and nerve palsy in total hip arthroplasty: a lawyer awaits! Orthopedics 2000;23:943.
Femur Re-positioning for THA Length and Offset ! Sarin et al 891 15. McGrory BJ, Morrey BF, Cahalan TD, et al. Effect of femoral offset on range of motion and abductor muscle strength after total hip arthroplasty. J Bone Joint Surg 1995;77-B:865. 16. Sakalkale DP, Sharkey PF, Eng K, et al. Effect of femoral component offset on polyethylene wear in total hip arthroplasty. Clin Orthop 2001;388:125. 17. Davey JR, O’Connor DO, Burke DW, et al. Femoral component offset. Its effect on strain in bonecement. J Arthroplasty 1993;8:23. 18. Wong PKC, Otsuka NY, Davey JR, et al. The effect of femoral component offset in uncemented total hip arthroplasty. Presented at Canadian Orthopaedic Society, 48th Annual Meeting, Montreal, Quebec; 1993. 19. Bal BS. A technique for comparison of leg lengths during total hip replacement. Am J Orthop 1996; 25:61. 20. Huddleston HD. An accurate method for measuring leg length and hip offset in hip arthroplasty. Orthopedics 1997;20:331. 21. Itokazu M, Masuda K, Ohno T, et al. A simple method of intraoperative limb length measurement
22.
23.
24.
25.
26.
27.
in total hip arthroplasty. Bull Hosp Jt Dis 1997; 56:204. McGee HM, Scott JH. A simple method of obtaining equal leg length in total hip arthroplasty. Clin Orthop 1985;194:269. Naito M, Ogata K, Asayama I. Intraoperative limb length measurement in total hip arthroplasty. Int Orthop 1999;23:31. Schutte DH, Conrad JM, Barfield WR, et al. The effect of rotation on the measurement of femoral offset radiographs. Presented at International Society for Technology in Arthroplasty, San Francisco, CA; 2003. Woolson ST, Harris WH. A method of intraoperative limb length measurement in total hip arthroplasty. Clin Orthop 1985;194:207. Ranawat CS, Rodriguez JA. Functional leg length inequality following total hip arthroplasty. J Arthroplasty 1997;12:359. DiGioia AM, Jaramaz B, Blackwell M, et al. The Otto Aufranc award. Image guided navigation system to measure intraoperatively acetabular implant alignment. Clin Orthop 1998;355:8.