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Leg-Length Discrepancy After Revision Hip Arthroplasty: Are Modular Stems Superior?
The Journal of Arthroplasty 28 (2013) 676–679
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Leg-Length Discrepancy After Revision Hip Arthroplasty: Are Modular Stems Superior? Yong Dou MD, Yixin Zhou MD, PhD, Qiheng Tang MD, Dejin Yang MD, Jian Liu MD Department of Orthopaedic Surgery, Beijing Jishuitan Hospital, Fourth Clinical College of Peking University, Beijing, China
a r t i c l e
i n f o
Article history: Received 18 March 2012 Accepted 8 August 2012 Keywords: revision hip arthroplasty modular stem monoblock stem leg-length discrepancy
a b s t r a c t We retrospectively reviewed data for 79 consecutive patients who underwent revision hip arthroplasty using cementless femoral stems at our center between September 2008 and November 2010. Two cohorts were included, one using MP (modular) femoral stems and the other using Wagner (monoblock) femoral stems. We assessed leg-length discrepancy (LLD) before and after revision and compared the occurrence of leglength inequality between the 2 cohorts. We found that the incidence of LLD was high in revision hip arthroplasty and that leg shortening was more common than lengthening. Both acetabular and femoral sides contributed to postoperative LLD. Appropriate placement of the femoral components was most critical in adjusting LLD. We also found that compared with monoblock stems, modular stems made adjustment of postoperative leg length easier. © 2013 Elsevier Inc. All rights reserved.
Leg-length discrepancy (LLD) is a common complication after both primary and revision hip arthroplasty. Patients can sometimes perceive even minor changes in leg length and develop severe clinical consequences, including limping, chronic lumbar pain, neurologic damage, greater trochanteric pain, general dissatisfaction, and the necessity of using shoe lifts [1,2]. In some cases, even surgical revision is needed [3]. Members of the American Association of Hip and Knee Surgeons cited LLD as the second most frequent cause of medical malpractice litigation [4]. LLD after primary THA has frequently been studied, but studies about LLD after revision hip arthroplasty have been scarce. Modular stems have recently enjoyed wide use in revision hip arthroplasty [5,6]. By combining independent proximal and distal parts, modular stems theoretically can be adjusted to compensate for LLD more flexibly and accurately than monoblock stems. However, few researchers have investigated this theory, so there is insufficient evidence to validate it. Therefore, we conducted a study to address the following questions: (1) What is the incidence of LLD after revision hip arthroplasty using cementless stems? (2) What factors contribute to the occurrence of LLD, and which one is more important? (3) Does the use of a modular stem help to decrease the incidence and magnitude of LLD?
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2012.08.009. Reprint requests: Yixin Zhou, MD, PhD, Department of Orthopaedic Surgery, Beijing Jishuitan Hospital, Fourth Clinical College of Peking University, Beijing, 100035 China. 0883-5403/2804-0027$36.00/0 – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2012.08.009
Materials and Methods We retrospectively reviewed data for 79 consecutive patients who underwent revision in our department between September 2008 and November 2010. Patients included in our study satisfied the following criteria: (1) the patient had unilateral hip joint revised but the contralateral hip joint was healthy or nearly so; (2) the revision stem had solid fixation into the femoral isthmus, and there was no undersizing of the femoral stem; and (3) the patient had detailed medical records and standard anterior posterior (AP) radiographs of the pelvis available both before and after the revision operation. On the basis of findings on preoperative full-length standing AP radiographs of the legs, patients with anatomic inequality of bone structures outside the affected hip joint were excluded from the study. A total of 79 patients were included in the study, among whom 39 received MP stems (Waldemar Link, Hamburg, Germany) and 40 received Wagner SL stems (Zimmer, Warsaw, IN, USA). There were 34 men and 45 women, with an average age of 61.3 years (range, 26–84 years). The reasons for revisions were: 71(89.9%) patients for aseptic loosening, 3(8.9%) patients for two-stage revision for infection, and 1 (1.2%) patient for acetabular wear after hemiarthroplasty. Of the 79 patients, 76 had both acetabular and femoral components revised, 2 had only the femoral stem revised, and 1 had a primary acetabular cup replacement because of loosening of a bipolar prosthesis. All revision cups used were cementless. Both Wagner and MP stems were designed to allow solid cementless fixation within the diaphysis by the use of distal flutes. The Wagner SL Revision Stem was introduced in 1986. It is a straight titanium alloy stem, and any version of it can be implanted with a 2° tapered stem with a circular cross-section. The MP prosthesis was
Y. Dou et al. / The Journal of Arthroplasty 28 (2013) 676–679
first introduced in Germany in 1993 and is based on the Wagner stem [7]. This modular stem has a tapered, fluted geometry incorporating a 3° angular bow to accommodate the curvature of the femur. There are 2 kinds of proximal components for MP stems: 65mm and 35-mm head–neck segments. Spacers are available to ensure appropriate leg length. Because our study was retrospective in nature, it did have certain factors that influenced prosthesis selection. The main reason for prosthesis selection was the commercial aspect: Before September 2009, the Wagner stem was unavailable in the Chinese market, and thus all patients who underwent surgery before then received MP stems (22 cases, 56.4% of all MP stems). Thereafter, the Wagner stem was obtainable. Before revision, the surgeon did the templating routinely. In reviewing preoperative radiographs, we found that either type of stem would work well in all patients. However, because the MP stem is much more expensive than the Wagner stem in our country and some patients needing revision surgery could not afford higher medical costs, prosthesis selection was mainly influenced in those cases by cost considerations and stem availability. Before and after surgery, all patients had standard AP radiographs taken of the pelvis with the legs placed in a clinically neutral position. We recorded the following radiologic markers as references for measurement: • The line connecting the inferior margin of the bilateral teardrops, which was deemed the reference line; if the teardrops were destroyed and could not be discerned clearly on radiographs, we drew a line connecting the inferior margin of the bilateral ischial tubercles and the paralleling line passing through the bottom of the teardrop of the healthy side, using it as an alternative reference line • The tips of bilateral lesser trochanters • The rotation centers of the bilateral femoral heads, which were identified by using a concentric ruler The following distances were measured: • The vertical distances from the rotation centers of the bilateral femoral heads to the reference line were recorded as DA for the nonoperated side and DA1′ and DA2′ for the operated side before and after surgery, respectively. The distance change was recorded as DA′ (DA′ = DA1′ – DA2′), representing the position change of the acetabular cup. • For the operated side, the vertical distance from the rotation center to the line parallel to the reference line passing through the tip of the lesser trochanter was recorded as VF1 before surgery and VF2 after surgery. The distance change was recorded as VF′ (VF′ = VF2 – VF1), representing the position change of the femoral stem. • The vertical distances from the tips of the bilateral lesser trochanters to the reference line were recorded as DF for the nonoperated side, and DF1′ (before surgery) and DF2′ (after surgery) for the operated side. • Preoperative and postoperative LLD were recorded as LLD1 and LLD2, respectively (LLD1 = DF1′ – DF; LLD2 = DF2′ – DF). The change in LLD after revision was recorded as LLD′ (LLD′ = LLD2 – LLD1) (Figs. 1, 2). The diameters of the femoral heads, both those retrieved and those newly implanted, were used as references in magnification assessment. A positive value for distance change indicated limb elongation, whereas a negative value indicated limb shortening. This method of measuring LLD has been described and used by many authors [8–10]. It is commonly accepted and has been reported to be reliable within ± 1 mm [9]. All measurements were obtained by the same observer, and radiologic measurements were achieved with a 1mm precision scale. The neck lengths of the prostheses used in revision were also noted. The postoperative LLD (LLD2) was classified as follows: LLD2 ≤ –20 mm, –20 mm b LLD2 b –10 mm, –10 mm ≤ LLD2 b –5 mm, –5 mm ≤
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Fig. 1. For the acetabular side, DA and DA′ represent the preoperative vertical distance of the healthy side and the operated side, respectively, whereas DF and DF1′ reflect the preoperative leg length for the nonoperated and the operated side, respectively. VF1 represents preoperative position of the femoral stem.
LLD2 ≤ 5 mm, 5 mm b LLD2 ≤ 10 mm, 10 mm b LLD2 b 20 mm, and LLD2 ≥ 20 mm. Considering the possibility of error measurement, leg lengths were regarded as equal if the LLD was within the range of 5 mm (–5 mm ≤ LLD2 ≤ 5 mm). We used SPSS Statistics (version 11.5; IBM, Armonk, NY, USA) to analyze the statistical data. The independent t-test was used to compare continuous data, and the chi-square test was used for ordinal data. A P value of b.05 was considered significant. Results Of all the participating patients, 84.8% (67/79) had shortened legs before surgery and 87.3% (69/79) had decreased LLD after revision surgery. The mean preoperative LLD was –18.1 (12.4) mm, and 67 patients (84.8%) had shortening on the affected side (N5 mm), of whom 31 patients (39.2%) had N 20 mm of leg shortening. Before
Fig. 2. After revision hip arthroplasty, measurements were obtained that were similar to preoperative measurements. DA2′ and DF2′ represent the vertical distance from the rotation center and from the tip of the lesser trochanter, respectively, to the line connecting the bilateral teardrops on the operated femoral side.VF2 represents postoperative position of the femoral stem.
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Y. Dou et al. / The Journal of Arthroplasty 28 (2013) 676–679
revision, 12 patients (15.2%) had legs of equal length, and no leg was lengthened N 5 mm. After revision, the rate of LLD was high, and only 27 (34.2%) patients had a LLD of b5 mm. The mean shortening was 5.6 mm (range, –28 to 11 mm). Forty (50.6%) patients had shortening of N 5 mm, whereas only 12 (15.2%) patients had had lengthening of N5 mm. Both the acetabular side and the femoral side contributed to LLD after revision. There were significant associations between postoperative LLD changes (LLD′) and DA′ (P = .002), as well as VF′ (P = .000). The mean VF′ and DA′ were 9.6 mm and 3.1 mm, respectively. There was a significant difference between VF′ and DA′ (P b .05). Prosthesis selection played a role in balancing limb length in revision hip arthroplasty, in that modularity allowed for superior adjustment of LLD. The incidence of LLD was lower in the MP group than in the Wagner group (Pb0.05). LLD was corrected in 41.0% of the patients in the MP group and in 27.5% in the Wagner group. The patients' preoperative LLD, age, and reasons for revision were all comparable between the 2 groups. The neck-shaft angle for both the Wagner and MP stems was 135°. The length of the femoral neck used was ±3.5 mm in the MP group and ±3.5 mm or +7 mm in the Wagner group. There was no difference in the rate of LLD in terms of use of different femoral neck lengths between the 2 groups (P N .05). We found no significant difference in DA′, VF′, or LLD′ between the 2 groups. Data relevant to LLD after revisions are shown in Tables 1 and 2.
Discussion LLD is a common complication for both primary and revision hip arthroplasty. Most previous reports have focused on LLD after primary THA, with only a few dealing with detailed revision hip arthroplasty. Knowing the incidence and the magnitude of LLD after revision, as well as the origins of LLD, is critical for successful revision. As for cementless stems, we also wanted to find out if modular stems are superior to monoblock stems for adjusting LLD. Restrepo et al [11] reported outcomes for 118 patients (122 hips) who had hips revised using modular stems (Restoration Modular stem, Stryker Orthopaedics, Mahwah, NJ, USA). Of the 122 hips, 95 (78%) had LLD within the 5-mm range. Of the patients whose preoperative LLD was b20 mm, 93% had a LLD of b 5 mm. These results are comparable to those for primary THA. In our study, only 27 patients (34.2%) had a postoperative LLD within the 5mm range. The difference between our results and those of Restrepo et al (34.2% vs 78%) might have been caused by the use of different prostheses, the use of different surgical techniques, and differences in patients' demographics. Most of our patients underwent surgery at a very late stage, and they usually had poor soft-tissue condition
Table 1 Preoperative and Postoperative LLD and Relevant Distance Changes. Parameter
Value
Preoperative LLD Postoperative LLD DA′ V′F LLD′ Length of femoral neck⁎ Standard Short Long
–18.0 (12.4) mm –5.6 (9.5) mm 3.1 (7.8) mm 9.6 (10.0) mm 12.7 (9.4) mm 35/79 (44.3%) 18/79 (22.8%) 26/79 (32.9%)⁎
DA′, position change of the acetabular cup; LLD, leg-length discrepancy. V′,F position change of the femoral stem. ⁎ In the MP stem group, +3.5 mm femoral necks were used in 12 hips. In the Wagner stem group, +3.5 mm femoral necks were used in 12 hips and +7-mm femoral necks were used in 2 hips.
Table 2 Distributions of LLD After Revision in 2 Groups.
LLD ≤–20 mm –20 mm b LLD b –10 mm –10 mm ≤ LLD b –5 mm –5 mm ≤ LLD ≤ 5 mm 5 mm b LLD ≤ 10 mm 10 mm b LLD1 b 20 mm LLD ≥ 20 mm
No. in MP Stem Group (%)
No. in Wagner Stem Group (%)
2/39 9/39 6/39 16/39 5/39 1/39 0/39
4/40 8/40 11/40 11/40 6/40 0/40 0/40
(5.1) (23.1) (15.4) (41.0) (12.8) (2.6) (0)
(10) (20) (27.5)⁎ (27.5)⁎ (15) (0) (0)
LLD, leg-length discrepancy. ⁎ There was a significant difference between the 2 groups.
and severe deformities, which generally makes restoring leg length more difficult. The incidence of LLD was high in our study, and there were more cases of shortening than lengthening in revision hip arthroplasty. Possible reasons are as follows: First, patients undergoing revision hip arthroplasty had undergone 2 or more hip operations. Most patients had shortening of the affected legs before the revision, and more than one third had shortening of N 20 mm. The shortening was somewhat a reflection of the poor condition of soft tissue and the complexity of the revisions. Many of these patients had severe scarring and poor elasticity of the soft tissues, and a scarred soft-tissue envelope might have restricted the restoration of limb length. Besides, complete release of contractures was challenging in many cases. To avoid too much damage to the abduction muscles and to decrease the dislocation rate, we could do only limited soft-tissue release. Second, most patients also had hip deformities (such as flexion or adduction contractures) and compensatory rotation and tilting deformity of the pelvis. Severe bone loss was also common, and in some cases, traditional bony landmarks such as the tip of the greater trochanter and the lesser trochanter were not present. The posture changes and the lack of reliable reference points might have made accurate intraoperative assessment of limb length difficult. Third, bony deficiency can sometimes necessitate superior and/or medial migration of a cementless cup during revision surgery. In revision hip arthroplasty, acetabular reconstruction is usually quite complex. Large cups are usually needed, and grating of bone against the bottom of the acetabulum is common [12]. In some cases, acetabular reconstruction can cause large position changes. All of these factors tend to result in a lower acetabular cup position than before revision. In a recent study, Kim et al [13] reported on the distance of change in the center of hip rotation in 35 cases of revision for acetabular loosening. They found that on average, the rotation center was 11.9 mm lower than before revision, but the rotation center often was still higher than the anatomic position, which explained why and how the affected leg was shortened. To fully restore leg length, the shortening caused by the acetabular side must be compensated for by the femoral side. Finally, during revision, the surgeons tended to pay more attention to prosthesis retrieval and management of bone defects and thus might have unintentionally neglected LLD. All of those factors made it challenging to restore limb length, resulting in a tendency to shortening. Both rotation center and femoral position contributed to LLD. Compared with preoperative conditions, 51 hips (64.6%) had relatively low rotation centers, 7 hips (8.9%) had unchanged rotation centers, and 21 hips (26.5%) had high rotation centers after revision. But compared with the contralateral hips, the acetabular centers of rotation after revision were still higher in 69 patients (87.4%), anatomic in 5 (6.3%), and lower in 5 (6.3%). The postoperative rotation center on average was 8.2 mm higher than the anatomic position. The mean VF′ was 9.6 mm, reflecting the distance change caused by femoral parts, including changes in the femoral stems and the lengths
Y. Dou et al. / The Journal of Arthroplasty 28 (2013) 676–679
of the femoral necks. It was difficult to isolate the impact of femoral neck length alone. Nonetheless, our results showed that the origin of LLD was mainly the femoral side. Thus, it is important to correctly position revision femoral stems according to preoperative plans. We also found that MP stems (modular stems) made it easier than Wagner stems (nonmodular stems) to adjust limb length. Twentyeight patients (70%) in the Wagner group and 27 patients (69.2 %) in the MP group had a LLD within a range of 10 mm, but only 11 patients (27.5%) in the Wagner group and 16 patients (41.0%) in the MP group had a LLD within a range of 5 mm. These findings indicate that modular stems may be more suitable for young and for patients who require high levels of precision. Achieving solid fixation of the femoral shaft is critical for successful revision hip arthroplasty, and MP stems separate this step from all other aspects of the revision procedure, which makes revision easier. Independent management of the distal and proximal parts can also be regarded as a kind of “modularity in process.” With the MP hip stem, leg length, femoral version, and femoral offset can be changed independently. Because these changes can be made in vivo without removing the stem, it is plausible to place the femoral stem according to preoperative templating and to control limb length exactly, which makes the revision easier for surgeons, especially for those who do not have extensive experience. Modularity of both different parts and different processes make the operation more flexible and management of LLD easier. Our study had several limitations. First, we did not take into account LLD caused by soft-tissue contractures, and we used only a radiologic method to measure LLD. Functional leg-length inequality (FLLI) is caused by secondary contracture of soft tissue (abduction, adduction, or flexion contractures), although there is no anatomic length difference between the 2 legs. FLLI can also be caused by pelvic tilting and scoliosis of the lumbar spine. For THA, transient FLLI is more common than true LLD. However, long-lasting FLLI is rare [10]. Therefore, in most cases, THA should aim to restore true leg length. Second, our study was retrospective and focused on a relatively small sample, and the operations were performed by several senior doctors. Thus, our results might not be consistent, so further welldesigned studies are needed to confirm our findings. Third, because there are no globally accepted LLD criteria for revision hip arthro-
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plasty, we did not take into account patients' opinions but focused only on objective measurements. In summary, we found that the incidence of LLD was high in revision hip arthroplasty and that shortening was more common than lengthening. Also, our study showed that in revision hip arthroplasty, LLD originates mainly with the femoral side and that modular stems allow for more delicate adjustment than do monoblock stems for balancing LLD.
Acknowledgment The authors thank Katharine O'Moore-Klopf, ELS, of East Setauket, New York, for providing editorial assistance.
References 1. Clark CR, Huddleston HD, Schoch III EP, et al. Leg-length discrepancy after total hip arthroplasty. J Am Acad Orthop Surg 2006;14:38. 2. Maloney WJ, Keeney JA. Leg length discrepancy after total hip arthroplasty. J Arthroplasty 2004;4(Suppl 1):108. 3. Parvizi J, Sharkey PF, Bisset GA, et al. Surgical treatment of limb-length discrepancy following total hip arthroplasty. J Bone Joint Surg Am 2003;85:2310. 4. Upadhyay A, York S, Macaulay W, et al. Medical malpractice in hip and knee arthroplasty. J Arthroplasty 2007;22(Suppl 2):3. 5. Yates PJ, Burston BJ, Whitley E, et al. Collarless polished tapered stem: clinical and radiological results at a minimum of ten years' follow-up. J Bone Joint Surg Br 2008;90:16. 6. Patel PD, Klika AK, Murray TG, et al. Influence of technique with distally fixed modular stems in revision total hip arthroplasty. J Arthroplasty 2010;25:926. 7. Kwong LM, Miller AJ, Lubinus P. A modular distal fixation option for proximal bone loss in revision total hip arthroplasty: a 2- to 6-year follow-up study. J Arthroplasty 2003;18:94. 8. Matsuda K, Nakamura S, Matsushita T. A simple method to minimize limb-length discrepancy after hip arthroplasty. Acta Orthop 2006;77:375. 9. Ranawat CS, Rao RR, Rodriguez JA, et al. Correction of limb-length inequality during total hip arthroplasty. J Arthroplasty 2001;16:715. 10. White TO, Dougall TW. Arthroplasty of the hip. Leg length is not important. J Bone Joint Surg Br 2002;84:335. 11. Restrepo C, Mashadi M, Parvizi J, et al. Modular femoral stems for revision total hip arthroplasty. Clin Orthop Relat Res 2011;469:476. 12. Deirmengian GK, Zmistowski B, O'Neil JT, et al. Management of acetabular bone loss in revision total hip arthroplasty. J Bone Joint Surg Am 2011;93:1842. 13. Kim DH, Cho SH, Jeong ST, et al. Restoration of the center of rotation in revision total hip arthroplasty. J Arthroplasty 2010;25:1041.
Contents lists available at SciVerse ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Leg-Length Discrepancy After Revision Hip Arthroplasty: Are Modular Stems Superior? Yong Dou MD, Yixin Zhou MD, PhD, Qiheng Tang MD, Dejin Yang MD, Jian Liu MD Department of Orthopaedic Surgery, Beijing Jishuitan Hospital, Fourth Clinical College of Peking University, Beijing, China
a r t i c l e
i n f o
Article history: Received 18 March 2012 Accepted 8 August 2012 Keywords: revision hip arthroplasty modular stem monoblock stem leg-length discrepancy
a b s t r a c t We retrospectively reviewed data for 79 consecutive patients who underwent revision hip arthroplasty using cementless femoral stems at our center between September 2008 and November 2010. Two cohorts were included, one using MP (modular) femoral stems and the other using Wagner (monoblock) femoral stems. We assessed leg-length discrepancy (LLD) before and after revision and compared the occurrence of leglength inequality between the 2 cohorts. We found that the incidence of LLD was high in revision hip arthroplasty and that leg shortening was more common than lengthening. Both acetabular and femoral sides contributed to postoperative LLD. Appropriate placement of the femoral components was most critical in adjusting LLD. We also found that compared with monoblock stems, modular stems made adjustment of postoperative leg length easier. © 2013 Elsevier Inc. All rights reserved.
Leg-length discrepancy (LLD) is a common complication after both primary and revision hip arthroplasty. Patients can sometimes perceive even minor changes in leg length and develop severe clinical consequences, including limping, chronic lumbar pain, neurologic damage, greater trochanteric pain, general dissatisfaction, and the necessity of using shoe lifts [1,2]. In some cases, even surgical revision is needed [3]. Members of the American Association of Hip and Knee Surgeons cited LLD as the second most frequent cause of medical malpractice litigation [4]. LLD after primary THA has frequently been studied, but studies about LLD after revision hip arthroplasty have been scarce. Modular stems have recently enjoyed wide use in revision hip arthroplasty [5,6]. By combining independent proximal and distal parts, modular stems theoretically can be adjusted to compensate for LLD more flexibly and accurately than monoblock stems. However, few researchers have investigated this theory, so there is insufficient evidence to validate it. Therefore, we conducted a study to address the following questions: (1) What is the incidence of LLD after revision hip arthroplasty using cementless stems? (2) What factors contribute to the occurrence of LLD, and which one is more important? (3) Does the use of a modular stem help to decrease the incidence and magnitude of LLD?
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2012.08.009. Reprint requests: Yixin Zhou, MD, PhD, Department of Orthopaedic Surgery, Beijing Jishuitan Hospital, Fourth Clinical College of Peking University, Beijing, 100035 China. 0883-5403/2804-0027$36.00/0 – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2012.08.009
Materials and Methods We retrospectively reviewed data for 79 consecutive patients who underwent revision in our department between September 2008 and November 2010. Patients included in our study satisfied the following criteria: (1) the patient had unilateral hip joint revised but the contralateral hip joint was healthy or nearly so; (2) the revision stem had solid fixation into the femoral isthmus, and there was no undersizing of the femoral stem; and (3) the patient had detailed medical records and standard anterior posterior (AP) radiographs of the pelvis available both before and after the revision operation. On the basis of findings on preoperative full-length standing AP radiographs of the legs, patients with anatomic inequality of bone structures outside the affected hip joint were excluded from the study. A total of 79 patients were included in the study, among whom 39 received MP stems (Waldemar Link, Hamburg, Germany) and 40 received Wagner SL stems (Zimmer, Warsaw, IN, USA). There were 34 men and 45 women, with an average age of 61.3 years (range, 26–84 years). The reasons for revisions were: 71(89.9%) patients for aseptic loosening, 3(8.9%) patients for two-stage revision for infection, and 1 (1.2%) patient for acetabular wear after hemiarthroplasty. Of the 79 patients, 76 had both acetabular and femoral components revised, 2 had only the femoral stem revised, and 1 had a primary acetabular cup replacement because of loosening of a bipolar prosthesis. All revision cups used were cementless. Both Wagner and MP stems were designed to allow solid cementless fixation within the diaphysis by the use of distal flutes. The Wagner SL Revision Stem was introduced in 1986. It is a straight titanium alloy stem, and any version of it can be implanted with a 2° tapered stem with a circular cross-section. The MP prosthesis was
Y. Dou et al. / The Journal of Arthroplasty 28 (2013) 676–679
first introduced in Germany in 1993 and is based on the Wagner stem [7]. This modular stem has a tapered, fluted geometry incorporating a 3° angular bow to accommodate the curvature of the femur. There are 2 kinds of proximal components for MP stems: 65mm and 35-mm head–neck segments. Spacers are available to ensure appropriate leg length. Because our study was retrospective in nature, it did have certain factors that influenced prosthesis selection. The main reason for prosthesis selection was the commercial aspect: Before September 2009, the Wagner stem was unavailable in the Chinese market, and thus all patients who underwent surgery before then received MP stems (22 cases, 56.4% of all MP stems). Thereafter, the Wagner stem was obtainable. Before revision, the surgeon did the templating routinely. In reviewing preoperative radiographs, we found that either type of stem would work well in all patients. However, because the MP stem is much more expensive than the Wagner stem in our country and some patients needing revision surgery could not afford higher medical costs, prosthesis selection was mainly influenced in those cases by cost considerations and stem availability. Before and after surgery, all patients had standard AP radiographs taken of the pelvis with the legs placed in a clinically neutral position. We recorded the following radiologic markers as references for measurement: • The line connecting the inferior margin of the bilateral teardrops, which was deemed the reference line; if the teardrops were destroyed and could not be discerned clearly on radiographs, we drew a line connecting the inferior margin of the bilateral ischial tubercles and the paralleling line passing through the bottom of the teardrop of the healthy side, using it as an alternative reference line • The tips of bilateral lesser trochanters • The rotation centers of the bilateral femoral heads, which were identified by using a concentric ruler The following distances were measured: • The vertical distances from the rotation centers of the bilateral femoral heads to the reference line were recorded as DA for the nonoperated side and DA1′ and DA2′ for the operated side before and after surgery, respectively. The distance change was recorded as DA′ (DA′ = DA1′ – DA2′), representing the position change of the acetabular cup. • For the operated side, the vertical distance from the rotation center to the line parallel to the reference line passing through the tip of the lesser trochanter was recorded as VF1 before surgery and VF2 after surgery. The distance change was recorded as VF′ (VF′ = VF2 – VF1), representing the position change of the femoral stem. • The vertical distances from the tips of the bilateral lesser trochanters to the reference line were recorded as DF for the nonoperated side, and DF1′ (before surgery) and DF2′ (after surgery) for the operated side. • Preoperative and postoperative LLD were recorded as LLD1 and LLD2, respectively (LLD1 = DF1′ – DF; LLD2 = DF2′ – DF). The change in LLD after revision was recorded as LLD′ (LLD′ = LLD2 – LLD1) (Figs. 1, 2). The diameters of the femoral heads, both those retrieved and those newly implanted, were used as references in magnification assessment. A positive value for distance change indicated limb elongation, whereas a negative value indicated limb shortening. This method of measuring LLD has been described and used by many authors [8–10]. It is commonly accepted and has been reported to be reliable within ± 1 mm [9]. All measurements were obtained by the same observer, and radiologic measurements were achieved with a 1mm precision scale. The neck lengths of the prostheses used in revision were also noted. The postoperative LLD (LLD2) was classified as follows: LLD2 ≤ –20 mm, –20 mm b LLD2 b –10 mm, –10 mm ≤ LLD2 b –5 mm, –5 mm ≤
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Fig. 1. For the acetabular side, DA and DA′ represent the preoperative vertical distance of the healthy side and the operated side, respectively, whereas DF and DF1′ reflect the preoperative leg length for the nonoperated and the operated side, respectively. VF1 represents preoperative position of the femoral stem.
LLD2 ≤ 5 mm, 5 mm b LLD2 ≤ 10 mm, 10 mm b LLD2 b 20 mm, and LLD2 ≥ 20 mm. Considering the possibility of error measurement, leg lengths were regarded as equal if the LLD was within the range of 5 mm (–5 mm ≤ LLD2 ≤ 5 mm). We used SPSS Statistics (version 11.5; IBM, Armonk, NY, USA) to analyze the statistical data. The independent t-test was used to compare continuous data, and the chi-square test was used for ordinal data. A P value of b.05 was considered significant. Results Of all the participating patients, 84.8% (67/79) had shortened legs before surgery and 87.3% (69/79) had decreased LLD after revision surgery. The mean preoperative LLD was –18.1 (12.4) mm, and 67 patients (84.8%) had shortening on the affected side (N5 mm), of whom 31 patients (39.2%) had N 20 mm of leg shortening. Before
Fig. 2. After revision hip arthroplasty, measurements were obtained that were similar to preoperative measurements. DA2′ and DF2′ represent the vertical distance from the rotation center and from the tip of the lesser trochanter, respectively, to the line connecting the bilateral teardrops on the operated femoral side.VF2 represents postoperative position of the femoral stem.
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Y. Dou et al. / The Journal of Arthroplasty 28 (2013) 676–679
revision, 12 patients (15.2%) had legs of equal length, and no leg was lengthened N 5 mm. After revision, the rate of LLD was high, and only 27 (34.2%) patients had a LLD of b5 mm. The mean shortening was 5.6 mm (range, –28 to 11 mm). Forty (50.6%) patients had shortening of N 5 mm, whereas only 12 (15.2%) patients had had lengthening of N5 mm. Both the acetabular side and the femoral side contributed to LLD after revision. There were significant associations between postoperative LLD changes (LLD′) and DA′ (P = .002), as well as VF′ (P = .000). The mean VF′ and DA′ were 9.6 mm and 3.1 mm, respectively. There was a significant difference between VF′ and DA′ (P b .05). Prosthesis selection played a role in balancing limb length in revision hip arthroplasty, in that modularity allowed for superior adjustment of LLD. The incidence of LLD was lower in the MP group than in the Wagner group (Pb0.05). LLD was corrected in 41.0% of the patients in the MP group and in 27.5% in the Wagner group. The patients' preoperative LLD, age, and reasons for revision were all comparable between the 2 groups. The neck-shaft angle for both the Wagner and MP stems was 135°. The length of the femoral neck used was ±3.5 mm in the MP group and ±3.5 mm or +7 mm in the Wagner group. There was no difference in the rate of LLD in terms of use of different femoral neck lengths between the 2 groups (P N .05). We found no significant difference in DA′, VF′, or LLD′ between the 2 groups. Data relevant to LLD after revisions are shown in Tables 1 and 2.
Discussion LLD is a common complication for both primary and revision hip arthroplasty. Most previous reports have focused on LLD after primary THA, with only a few dealing with detailed revision hip arthroplasty. Knowing the incidence and the magnitude of LLD after revision, as well as the origins of LLD, is critical for successful revision. As for cementless stems, we also wanted to find out if modular stems are superior to monoblock stems for adjusting LLD. Restrepo et al [11] reported outcomes for 118 patients (122 hips) who had hips revised using modular stems (Restoration Modular stem, Stryker Orthopaedics, Mahwah, NJ, USA). Of the 122 hips, 95 (78%) had LLD within the 5-mm range. Of the patients whose preoperative LLD was b20 mm, 93% had a LLD of b 5 mm. These results are comparable to those for primary THA. In our study, only 27 patients (34.2%) had a postoperative LLD within the 5mm range. The difference between our results and those of Restrepo et al (34.2% vs 78%) might have been caused by the use of different prostheses, the use of different surgical techniques, and differences in patients' demographics. Most of our patients underwent surgery at a very late stage, and they usually had poor soft-tissue condition
Table 1 Preoperative and Postoperative LLD and Relevant Distance Changes. Parameter
Value
Preoperative LLD Postoperative LLD DA′ V′F LLD′ Length of femoral neck⁎ Standard Short Long
–18.0 (12.4) mm –5.6 (9.5) mm 3.1 (7.8) mm 9.6 (10.0) mm 12.7 (9.4) mm 35/79 (44.3%) 18/79 (22.8%) 26/79 (32.9%)⁎
DA′, position change of the acetabular cup; LLD, leg-length discrepancy. V′,F position change of the femoral stem. ⁎ In the MP stem group, +3.5 mm femoral necks were used in 12 hips. In the Wagner stem group, +3.5 mm femoral necks were used in 12 hips and +7-mm femoral necks were used in 2 hips.
Table 2 Distributions of LLD After Revision in 2 Groups.
LLD ≤–20 mm –20 mm b LLD b –10 mm –10 mm ≤ LLD b –5 mm –5 mm ≤ LLD ≤ 5 mm 5 mm b LLD ≤ 10 mm 10 mm b LLD1 b 20 mm LLD ≥ 20 mm
No. in MP Stem Group (%)
No. in Wagner Stem Group (%)
2/39 9/39 6/39 16/39 5/39 1/39 0/39
4/40 8/40 11/40 11/40 6/40 0/40 0/40
(5.1) (23.1) (15.4) (41.0) (12.8) (2.6) (0)
(10) (20) (27.5)⁎ (27.5)⁎ (15) (0) (0)
LLD, leg-length discrepancy. ⁎ There was a significant difference between the 2 groups.
and severe deformities, which generally makes restoring leg length more difficult. The incidence of LLD was high in our study, and there were more cases of shortening than lengthening in revision hip arthroplasty. Possible reasons are as follows: First, patients undergoing revision hip arthroplasty had undergone 2 or more hip operations. Most patients had shortening of the affected legs before the revision, and more than one third had shortening of N 20 mm. The shortening was somewhat a reflection of the poor condition of soft tissue and the complexity of the revisions. Many of these patients had severe scarring and poor elasticity of the soft tissues, and a scarred soft-tissue envelope might have restricted the restoration of limb length. Besides, complete release of contractures was challenging in many cases. To avoid too much damage to the abduction muscles and to decrease the dislocation rate, we could do only limited soft-tissue release. Second, most patients also had hip deformities (such as flexion or adduction contractures) and compensatory rotation and tilting deformity of the pelvis. Severe bone loss was also common, and in some cases, traditional bony landmarks such as the tip of the greater trochanter and the lesser trochanter were not present. The posture changes and the lack of reliable reference points might have made accurate intraoperative assessment of limb length difficult. Third, bony deficiency can sometimes necessitate superior and/or medial migration of a cementless cup during revision surgery. In revision hip arthroplasty, acetabular reconstruction is usually quite complex. Large cups are usually needed, and grating of bone against the bottom of the acetabulum is common [12]. In some cases, acetabular reconstruction can cause large position changes. All of these factors tend to result in a lower acetabular cup position than before revision. In a recent study, Kim et al [13] reported on the distance of change in the center of hip rotation in 35 cases of revision for acetabular loosening. They found that on average, the rotation center was 11.9 mm lower than before revision, but the rotation center often was still higher than the anatomic position, which explained why and how the affected leg was shortened. To fully restore leg length, the shortening caused by the acetabular side must be compensated for by the femoral side. Finally, during revision, the surgeons tended to pay more attention to prosthesis retrieval and management of bone defects and thus might have unintentionally neglected LLD. All of those factors made it challenging to restore limb length, resulting in a tendency to shortening. Both rotation center and femoral position contributed to LLD. Compared with preoperative conditions, 51 hips (64.6%) had relatively low rotation centers, 7 hips (8.9%) had unchanged rotation centers, and 21 hips (26.5%) had high rotation centers after revision. But compared with the contralateral hips, the acetabular centers of rotation after revision were still higher in 69 patients (87.4%), anatomic in 5 (6.3%), and lower in 5 (6.3%). The postoperative rotation center on average was 8.2 mm higher than the anatomic position. The mean VF′ was 9.6 mm, reflecting the distance change caused by femoral parts, including changes in the femoral stems and the lengths
Y. Dou et al. / The Journal of Arthroplasty 28 (2013) 676–679
of the femoral necks. It was difficult to isolate the impact of femoral neck length alone. Nonetheless, our results showed that the origin of LLD was mainly the femoral side. Thus, it is important to correctly position revision femoral stems according to preoperative plans. We also found that MP stems (modular stems) made it easier than Wagner stems (nonmodular stems) to adjust limb length. Twentyeight patients (70%) in the Wagner group and 27 patients (69.2 %) in the MP group had a LLD within a range of 10 mm, but only 11 patients (27.5%) in the Wagner group and 16 patients (41.0%) in the MP group had a LLD within a range of 5 mm. These findings indicate that modular stems may be more suitable for young and for patients who require high levels of precision. Achieving solid fixation of the femoral shaft is critical for successful revision hip arthroplasty, and MP stems separate this step from all other aspects of the revision procedure, which makes revision easier. Independent management of the distal and proximal parts can also be regarded as a kind of “modularity in process.” With the MP hip stem, leg length, femoral version, and femoral offset can be changed independently. Because these changes can be made in vivo without removing the stem, it is plausible to place the femoral stem according to preoperative templating and to control limb length exactly, which makes the revision easier for surgeons, especially for those who do not have extensive experience. Modularity of both different parts and different processes make the operation more flexible and management of LLD easier. Our study had several limitations. First, we did not take into account LLD caused by soft-tissue contractures, and we used only a radiologic method to measure LLD. Functional leg-length inequality (FLLI) is caused by secondary contracture of soft tissue (abduction, adduction, or flexion contractures), although there is no anatomic length difference between the 2 legs. FLLI can also be caused by pelvic tilting and scoliosis of the lumbar spine. For THA, transient FLLI is more common than true LLD. However, long-lasting FLLI is rare [10]. Therefore, in most cases, THA should aim to restore true leg length. Second, our study was retrospective and focused on a relatively small sample, and the operations were performed by several senior doctors. Thus, our results might not be consistent, so further welldesigned studies are needed to confirm our findings. Third, because there are no globally accepted LLD criteria for revision hip arthro-
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plasty, we did not take into account patients' opinions but focused only on objective measurements. In summary, we found that the incidence of LLD was high in revision hip arthroplasty and that shortening was more common than lengthening. Also, our study showed that in revision hip arthroplasty, LLD originates mainly with the femoral side and that modular stems allow for more delicate adjustment than do monoblock stems for balancing LLD.
Acknowledgment The authors thank Katharine O'Moore-Klopf, ELS, of East Setauket, New York, for providing editorial assistance.
References 1. Clark CR, Huddleston HD, Schoch III EP, et al. Leg-length discrepancy after total hip arthroplasty. J Am Acad Orthop Surg 2006;14:38. 2. Maloney WJ, Keeney JA. Leg length discrepancy after total hip arthroplasty. J Arthroplasty 2004;4(Suppl 1):108. 3. Parvizi J, Sharkey PF, Bisset GA, et al. Surgical treatment of limb-length discrepancy following total hip arthroplasty. J Bone Joint Surg Am 2003;85:2310. 4. Upadhyay A, York S, Macaulay W, et al. Medical malpractice in hip and knee arthroplasty. J Arthroplasty 2007;22(Suppl 2):3. 5. Yates PJ, Burston BJ, Whitley E, et al. Collarless polished tapered stem: clinical and radiological results at a minimum of ten years' follow-up. J Bone Joint Surg Br 2008;90:16. 6. Patel PD, Klika AK, Murray TG, et al. Influence of technique with distally fixed modular stems in revision total hip arthroplasty. J Arthroplasty 2010;25:926. 7. Kwong LM, Miller AJ, Lubinus P. A modular distal fixation option for proximal bone loss in revision total hip arthroplasty: a 2- to 6-year follow-up study. J Arthroplasty 2003;18:94. 8. Matsuda K, Nakamura S, Matsushita T. A simple method to minimize limb-length discrepancy after hip arthroplasty. Acta Orthop 2006;77:375. 9. Ranawat CS, Rao RR, Rodriguez JA, et al. Correction of limb-length inequality during total hip arthroplasty. J Arthroplasty 2001;16:715. 10. White TO, Dougall TW. Arthroplasty of the hip. Leg length is not important. J Bone Joint Surg Br 2002;84:335. 11. Restrepo C, Mashadi M, Parvizi J, et al. Modular femoral stems for revision total hip arthroplasty. Clin Orthop Relat Res 2011;469:476. 12. Deirmengian GK, Zmistowski B, O'Neil JT, et al. Management of acetabular bone loss in revision total hip arthroplasty. J Bone Joint Surg Am 2011;93:1842. 13. Kim DH, Cho SH, Jeong ST, et al. Restoration of the center of rotation in revision total hip arthroplasty. J Arthroplasty 2010;25:1041.