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Review article
Lower limb length and offset in total hip arthroplasty X. Flecher ∗ , M. Ollivier , J.N. Argenson Service d’Orthopédie-Traumatologie, CHU Sud, 270, boulevard Sainte-Marguerite, 13009 Marseille, France
a r t i c l e
i n f o
Article history: Received 4 February 2015 Accepted 6 November 2015 Keywords: Total hip arthroplasty Leg length discrepancy Femoral offset Preoperative templating
a b s t r a c t Restoration of normal hip biomechanics is a key goal of total hip arthroplasty (THA) and favorably affects functional recovery. Furthermore, a major concern for both the surgeon and the patient is preservation or restoration of limb length equality, which must be achieved without compromising the stability of the prosthesis. Here, definitions are given for anatomic and functional limb length discrepancies and for femoral and hip offset, determined taking anteversion into account. Data on the influence of operatedlimb length and offset on patient satisfaction, hip function, and prosthesis survival after THA are reviewed. Errors may adversely impact function, quality of life, and prosthetic survival and may also generate conflicts between the surgeon and patient. Surgeons rely on two- or three-dimensional preoperative templating and on intraoperative landmarks to manage offset and length. Accuracy can be improved by using computer-assisted planning or surgery and the more recently introduced EOS imaging system. The prosthetic’s armamentarium now includes varus-aligned and lateralized implants, as well as implants with modular or custom-made necks, which allow restoration of the normal hip geometry, most notably in patients with coxa vara or coxa valga. Femoral anteversion must also receive careful attention. The most common errors are limb lengthening and a decrease in hip offset. When symptoms are caused by an error in length and/or offset, revision arthroplasty may deserve consideration. © 2015 Elsevier Masson SAS. All rights reserved.
1. Introduction
2. Definitions
Restoring normal hip biomechanics is a key goal of total hip arthroplasty (THA) and benefits functional recovery [1]. Another major concern is preservation or restoration of limb length equality, which must be achieved without compromising the stability of the prosthesis [2]. Lower limb length discrepancy (LLLD) is a common source of patient dissatisfaction and litigation [3–10]. The discrepancy may be either anatomical (structural) or functional, and a clear understanding of all the factors that create a sensation of length discrepancy is essential. Offset became a focus of interest more recently, when cementless stems were introduced. We will discuss the measurement of offset, which is highly controversial, and the impact of offset on function. Anteversion influences offset and must be taken into account.
2.1. Length
∗ Corresponding author. Tel.: +33 491 745 012; fax: +33 491 745 625. E-mail address: xavier.fl[email protected] (X. Flecher).
2.1.1. Anatomical (structural) lower limb length discrepancy (LLLD) LLLD can be measured by determining the difference between the two sides in the distance from the antero-superior iliac spine and the medial malleolus. Another method consists in placing increasingly thick boards under the foot on the shorter side until the two iliac crests are on the same horizontal line. 2.1.1.1. Preoperative measurement. A full-length antero-posterior standing radiograph should be obtained, given the limited reliability of clinical measurement techniques [1]. The preoperative LLLD is measured as the difference in length of the line segments extending from the top of the femoral head to the center of the ankle on each side. This length is modified in patients with flexion contracture of the hip and/or knee. Another relevant parameter is the height of the center of rotation of the femoral heads, as a difference in this value can induce LLLD despite identical lower limb lengths.
http://dx.doi.org/10.1016/j.otsr.2015.11.001 1877-0568/© 2015 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: Flecher X, et al. Lower limb length and offset in total hip arthroplasty. Orthop Traumatol Surg Res (2016), http://dx.doi.org/10.1016/j.otsr.2015.11.001
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Fig. 1. Measurement of lower limb length on a full-length radiograph of both legs: length of the line segment connecting the top of the iliac crest (IC) to the middle of the tibio-tarsal joint line (TT) and running through the center of rotation of the femoral head (C).
Lower limb length should therefore be measured as the length of the line starting at the top of the iliac crest (or, if this structure is not visible on the radiographs, the sacro-iliac joint), running through the center of rotation of the femoral head, and ending at the middle of the tibio-tarsal joint space (Fig. 1). The two lower limbs must be aligned perpendicularly to the pelvis, with no flexion. 2.1.1.2. Postoperative measurement. The following landmarks are identified on a pelvic radiograph taken under the above-described conditions: the bi-ischial line [10] or radiological teardrops [11] at the pelvis and the centers of the lesser trochanters at the femurs (Fig. 2). Measuring the distance separating these two landmarks before and after THA reflects the lower limb length change induced by the procedure. The change in length may be due to the femur and/or acetabulum. 2.1.2. Functional lower limb length discrepancy (LLLD) About 1 in every 3 patients reports a sensation of LLLD after THA [5,12]. In a questionnaire survey, 329 (30%) of 1114 patients reported perceived LLLD after THA, but only 36% of these patients had anatomical LLLD [13]. The remaining 64% had functional LLLD. Functional LLLD can be related to pelvic obliquity, which may be due to an abnormality in the lower limbs, spine, or both. Pelvic obliquity is common in patients with hip dysplasia or dislocation, particularly when unilateral. In this situation, fixed spinal malalignment develops secondarily, contributing to the pelvic obliquity that was initially due only to a lower limb abnormality. Another contributor to perceived LLLD is postoperative tension of the gluteus medius and minimus muscles, which is due in some cases to a need for elongation; when the two lower limbs are aligned along the axis of the body, the operated limb seems longer. This distal pelvic obliquity is short-lived, as the muscle tension resolves within the first year. A postoperative limp can also induce a sensation of LLLD: thus, patients with the Trendelenburg gait pattern may perceive the operated limb as shorter than the other limb.
Fig. 2. Estimation of lower limb length discrepancy related to the hip. a: using the bi-ischial line; b: using the radiological teardrop; c: pelvic obliquity is a less reliable criterion: although the hips are at the same level, the pelvis is oblique.
2.2. Offset Femoral offset is the perpendicular distance from the center of rotation of the femoral head to the line of action of the abductor muscles (Fig. 3a) [14]. Acetabular offset is the perpendicular distance from the center of rotation of the femoral head to the vertical trans-teardrop line (Fig. 3b). Global hip offset is the sum of femoral and acetabular offsets. Femoral offset is challenging to measure. In practice, the perpendicular distance from the center of rotation of the femoral head to the long axis of the femoral metaphysis or canal is used (Fig. 3). Mean femoral offset is 41 to 44 mm [15,16]. Femoral offset
Please cite this article in press as: Flecher X, et al. Lower limb length and offset in total hip arthroplasty. Orthop Traumatol Surg Res (2016), http://dx.doi.org/10.1016/j.otsr.2015.11.001
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H = 50°
α = 35°
PBCL’ A = 15° PBCL
Fig. 4. Measurement of femoral anteversion, helical torsion, and the alpha angle. The posterior bicondylar line (PBCL) is translated to the level of the neck (PBCL’) to allow the measurements. The desired prosthetic anteversion angle is about 15◦ (A). In this case, the axis of proximal femoral anteversion or helitorsion (H) is 50◦ . To obtain a final anteversion value of 15◦ , correction within the prosthetic neck or alpha angle must be −35◦ , i.e., 35◦ or retroversion.
• the axis of helical torsion is the long axis of the largest transverse slice through the proximal femur (10 mm proximal to the lesser trochanter); the helical torsion angle is formed by the helical torsion axis and the posterior bicondylar line; • the desired anteversion axis of the prosthetic neck is the line perpendicular to the axis of the second metatarsal (the step angle formed by the axis of the second metatarsal and the direction of gait is 10◦ to 20◦ ); ␣ is the angle formed by the anteversion axis and the helical torsion axis. When using a cementless prosthesis with a canal-filling stem whose anteversion is dictated by the helical torsion axis, the angle between the prosthetic neck and the helical torsion axis must be equal to ␣. Fig. 3. a: measurement of femoral offset (FO, 1) and abductor pull angle (2); b: measurement of acetabular offset (AO) and determination of global offset (GO) as the sum of FO and AO.
3. Rationale for restoring length and offset 3.1. Lower limb length discrepancy (LLLD)
is influenced by the neck-shaft angle (NSA): it increases with varus and decreases with valgus [17]. Femoral offset also varies with the degree of hip rotation on the radiographs. Femoral offset increased with femoral size in one study [18] but tended to be greater in patients with smaller femoral canals in another [19]. Finally, in a study of 689 patients scheduled for THA, femoral offset was independent from femoral dimensions [20]. 2.3. Anteversion Excessive anteversion (or external rotation) is associated with a decrease in the femoral offset value measured on an anteroposterior radiograph. Internal rotation of about 20◦ minimizes this error. However, the exact value of femoral anteversion must be known in order to accurately measure femoral offset on the same side. Computed tomography (CT) or EOS imaging can be used to measure proximal femoral torsion (Fig. 4): • the axis of the femoral neck is the line through the center of the femoral head and the middle of the femoral neck; femoral neck anteversion is the angle formed by the axis of the femoral neck and the posterior bicondylar line;
LLLD is common after THA, with incidence rates ranging from 1% to 50% [2,21]. Lengthening of the operated limb is more frequent than shortening [8,10,22]. The mean discrepancy ranges from 3 to 17 mm [9,23]. However, when care is taken to minimize LLLD, the difference is less than 10 mm in 97% of cases [11].
3.1.1. Clinical impact Patient dissatisfaction is common [24] and LLLD is the most common reason for litigation after THA [25]. A difference greater than 10 mm is often perceived by the patient [16] and affects the functional outcome [21,26–28]. Associations have been reported between LLLD and back or low-back pain or sciatica [27], gait disorders [29], and instability [30].
3.1.2. Complications LLLD may be associated with an increased risk of osteoarthritis in the operated lower limb [31], although this point is controversial. Lower limb lengthening after THA may also increase the risk of aseptic loosening [32,33]. LLLD may prompt revision surgery [6,34]. Another abnormality reported in patients with lengthening of the operated lower limb is increased stress on the superior part of the acetabular cup [31].
Please cite this article in press as: Flecher X, et al. Lower limb length and offset in total hip arthroplasty. Orthop Traumatol Surg Res (2016), http://dx.doi.org/10.1016/j.otsr.2015.11.001
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Fig. 5. Example of acetabular offset modification due to excessive cup medialization. This patient had moderate hip dysplasia (a), and it was therefore reasonable to medialize the center of rotation to improve bony coverage of the cup (C’h < Ch). There is little change to the height of the center of rotation. A cementless fixed-angle stem was chosen. To obtain good joint stability, the surgeon chose an extra long neck (note the skirt on the head), despite the resulting limb lengthening, which was expected to be less than 1 cm and therefore without clinical significance.
3.1.3. Acceptable lower limb length discrepancy (LLLD) The cut-off between acceptable and unacceptable LLLD has not been determined [35]. Edeen et al. [5] reported that even a small discrepancy could induce dissatisfaction. In contrast, several studies showed that most patients tolerated LLLDs of up to 10 mm. Patients with moderate LLLD experience discomfort for the first few months that decreases over time, although 15% remain symptomatic [34], with a need for a compensatory shoe lift in over half the cases [5,10]. In contrast, lengthening by more than 10 mm has been associated with limping, pelvic obliquity, a need for a shoe lift, and a feeling of disappointment [2,5,36]. LLLD of more than 10 mm has been reported in 16% to 32% of patients [3–11,13,14,21]. Body height probably influences the intensity of perceived LLLD. Thus, the percentage of limb lengthening may constitute a useful parameter. Asymptomatic constitutional LLLD of up to 20 mm is not infrequent [12,37]. This abnormality must be detected preoperatively and disclosed to the patient. Great care should be taken to avoid increasing the discrepancy, which might induce a conflict with the patient.
3.2. Offset A decrease in femoral offset is often due to a stem NSA greater than the native value [38]. The mean NSA is 130◦ ± 5◦ . NSA values of standard stems vary across manufacturers. Acetabular cup medialization after reaming decreases both the acetabular offset and the global hip offset (Fig. 5). A decrease in acetabular offset exerts beneficial effects by decreasing the stresses applied to the prosthetic joint but requires counterbalancing by an increase in femoral offset to avoid decreasing the global hip offset, which would require lower limb elongation to prevent instability (Fig. 5). “Insufficient” offset can cause a limp [39], require the use of a walking aid [14], and induce instability [40,41]. As the femur is closer to the pelvis, motion range is diminished [38,42] and a cam effect may develop [43]. Failure to restore offset is a reason for patient dissatisfaction [38] and significantly impairs quality of life. One study showed that a 15% or greater decrease in offset compared to the non-operated side was associated with an increased frequency of gait disorders [44]. A decrease in offset can also diminish
Fig. 6. Rules for positioning the cup: a: the lower edge of the cup should not be lower than the teardrop; b: cup inclination should be 40◦ to 50◦ ; c: bony coverage of the cup should be at least 80%; d: and the cup must not be medial to the ilio-ischial line (Köhler’s line).
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4. Methods for restoring length and offset
ø 54 mm ø 50 mm
Errors in length and offset can be minimized, albeit not completely eliminated [38]. The literature is replete with techniques designed to prevent LLLD. The main methods involve:
c
b t T
a
• preoperative templating using tracing paper; • the intraoperative identification of landmarks on the pelvis and/or femur; • and computer-assisted surgery (CAS) or navigation. 4.1. Preoperative templating 4.1.1. Two-dimensional templating Two-dimensional templating using radiographs remains a standard method. The magnification issues raised by radiograph digitization can be overcome by using templating software.
M R
d
d
7.5 10 12.5 15 17.5 20
Fig. 7. Preoperative tracing paper templating according to Müller: standard (a), lateralized (b), and dysplastic (c).
implant survival [45–48], in some cases via premature polyethylene wear [38,49]. Few studies have described the impact of excessive offset. In a study of five cadaver femurs, an increase in offset from 28 to 53 mm was associated with an increase in micro-motion at the boneimplant interface [43]. The high-offset cemented stem LubinusTM SPII® (Link Finland Oy, Espoo, Finland) featuring a 117◦ NSA was associated with lower 5-year survival compared to stems having a NSA of 126◦ or 135◦ [50]. An increase in offset is often followed by a perception that the lower limb is longer. This perception is due to excessive abductor muscle tension, which usually resolves within a few months. Excessive lateralization showed no correlation with pain suggestive of gluteal muscle tendinitis. Patients with coxa valga usually have below-average offset values. An increase in offset to restore normal hip geometry might be desirable, provided the reference offset value can be determined.
4.1.1.1. Using tracing paper. The principle consists in drawing the contra-lateral hip on tracing paper. First, the center of rotation is identified (Fig. 6) based on traces of the cup. Traces of the femur are then added to determine the postoperative offset and lower limb length. The traces are then used to replicate the positioning of the selected components on the abnormal hip (Fig. 7). When both hips are abnormal, the Amstutz index can be used. Amstutz et al. showed that implant positioning according to their index eliminated the risk of limping [32] (Fig. 8). 4.1.1.2. Reliability of templates. Two-dimensional radiograph templating is not reliable for ensuring equal lower limb length. Meermans et al. demonstrated that the teardrop was more reliable than the bi-ischial line [51], particularly in patients with LLLD before surgery [11]. Furthermore, in another study, preoperative templating correctly predicted the implant size in only 60% of cases [52]. 4.1.1.3. Femoral offset. Femoral offset can be measured on anteroposterior radiographs of the femoral necks with the lower limb in about 20◦ of internal rotation. Reproducibility of this method is poor, with a mean error of about 9.7 mm, i.e., about 20% for an offset value of 40 mm [53]. In addition, internal rotation of 15◦ to 20◦ does not consistently compensate for femoral anteversion (Figs. 9 and 10), which varies widely, even in primary osteoarthritis [44,54,55]. In a study of 50 hips, the offset value was 42.6 mm (26.9–53.9 mm) when radiographs were used compared to 45.8 mm (31–56 mm) using computed tomography (CT) [19]. The radiographic measurements consistently underestimated the offset value, by a mean of 3.2 mm (P < 0.0001) and by over 5 mm in 28% of cases. Thus, it seems reasonable to measure offset along the axis of the femoral neck using CT or EOS imaging.
Fig. 8. Use of the Amstutz index [1]. a: when the contra-lateral hip is normal, the center of rotation is marked; b: then the lateral edge of the greater trochanter; c: and the femur is positioned in order to restore length; d: when both hips are abnormal, the top of the greater trochanter must be positioned so that A/B is equal to or greater than 0.5 (A is the distance from the top of the greater trochanter to the center of rotation and B is the distance from the center of rotation to the pubic symphysis).
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Fig. 9. Influence of femoral rotation on radiographic offset. When the lower limb is placed at an angle of internal rotation equal to the angle of femoral anteversion (left), the radiographic and CT measurements produce the same value. When a simple antero-posterior radiograph is used (middle), the radiographic measurement underestimates the angle of femoral anteversion determined using CT. When the hip is in fixed external rotation (right), the extent of underestimation by radiographic measurement versus CT is increased.
4.1.2. Three-dimensional templating Three-dimensional templating is performed using software developed initially to design custom-made stems for THA [54–57]. The software compensates for poor patient positioning during image acquisition. To measure femoral offset, the axis of the canal in the proximal fourth of the femur must be identified [40,58].
It is located at the center of the femoral metaphysis in all three planes [3], which allows measurement of the true offset value (Fig. 11). The EOS imaging system may constitute an alternative for obtaining accurate and reliable measurements while minimizing radiation exposure [59].
Fig. 10. Influence of natural femoral anteversion on radiographic offset. When there is no anteversion (left), the radiographic and CT measurements produce the same value. With 15◦ to 20◦ of anteversion (middle), the radiographic measurement underestimates the offset determined by CT. When anteversion is excessive (right), the extent of underestimation by radiographic measurement versus CT is increased.
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Fig. 11. Visualization of the proximal femur in the three planes using CT-based templating software.
4.2. Intraoperative landmarks Intraoperative tests have been developed to assess soft-tissue tension and length (the shuck test, described by Charnley and involving in-line lower limb traction in the distal direction; the dropkick test, with the hip held in extension and the knee flexed to 90◦ ; and leg-to-leg comparison of length based on the heels or medial malleoli). The results are influenced by surgeon experience; type of anesthesia; and other factors such as the approach, whether the patient is lying on the side or supine, and whether an orthopaedic table is used. Consequently, these tests have poor reproducibility [60]. Numerous techniques have been described. They all use a fixed pelvic landmark and a femoral landmark that varies during the procedure. These landmarks are unreliable, as they may be removed and replaced between measurements. A stirrup can be used to ensure that the pins are parallel [11,17,42,46,61], but this method requires either a longer incision or a second incision. Hip position must be replicated accurately in all three planes before and after implantation of the prosthesis, which is challenging. Variations in femoral abduction/adduction of only 5◦ to 10◦ result in measurement errors of 8 to 17 mm [62]. No study has evaluated the extent to which the surgical approach and patient position on the side versus supine influences lower limb length control using these landmarks. We believe the supine position is more reliable.
In conclusion, using a stable pelvic landmark and accurately positioning the lower limb during the measurements is a simple method [63].
4.3. Computer-assisted navigation Offset and lower limb length are determined in large part by femoral stem size and position. Few studies on the contribution of computer-assisted navigation to femoral component selection and placement have been published to date. A prospective matched-pairs study compared computer-assisted navigation to conventional freehand alignment [36]. The same straight, nonmodular femoral stem was implanted in all patients. Mean LLLD was significantly smaller in the navigation group (5.06 mm [0–12] versus 7.64 mm [0–20] in the freehand group). Nevertheless, in the navigation group, 5 (10.4%) patients had LLLDs greater than 10 mm. Using the pelvis as a landmark can induce errors. Digioia et al. [64] used a navigation system to track movements of the pelvis during THA. Mean variations in pelvic position were 23◦ in abduction/adduction, 16◦ in flexion/extension, and 40◦ in forwards/backwards pelvic tilt. Adduction of the pelvis induces apparent limb lengthening in the absence of error, whereas abduction has the opposite effect. Although imperfect, when combined with templating, this technique probably limits the risk of major LLLD. In our experience, navigation diminishes the standard errors,
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A
FO1
FO2
Abd1
Abd2
*
*
NSA1
NSA2
B
FO1
FO2
Abd1
Abd2
*
*
*
*
NSA1
NSA2
C
FO1
FO2
Abd1
Abd2
*
* NSA1
*
* NSA2
Fig. 12. Managing coxa vara during total hip arthroplasty. A. Using a stem with a standard neck (NSA2 < NSA1) decreases offset (FO2 < FO1) and diminishes abductor muscle tension (Abd2 < Abd1). B. To preserve the same level of muscle tension (Abd1 = Abd2) while using a stem with a standard neck (FO1 > FO2), the limb can be lengthened. C. To preserve the same level of muscle tension (Abd1 = Abd2) while preserving limb length, a lateralized stem must be used (FO1 = FO2 or NSA1 = NSA2). NSA: neck-shaft angle; Abd: abductor muscles.
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A
FO1
FO2
Abd1
Abd2
* **
*
L
*
* NSA1
NSA2
B
FO1
FO2
Abd1
Abd1
*
*
L
* NSA1
**
* NSA2
Fig. 13. Managing coxa valga during total hip arthroplasty. A. Using a stem with a standard neck (NSA2 < NSA1) increases offset (FO2 > FO1) and increases abductor muscle tension (Abd2 > Abd1). B. This situation can be handled by using a suspended stem with a short neck (red asterisk).
to the same extent as reliable tools and/or extensive surgical experience, most notably for cup positioning [65].
4.4. Selecting the femoral implant When the femoral implant has a non-modular neck, even with a modular head, offset and length must be adjusted in combination.
In coxa vara (Fig. 12A), gluteal muscle tension can be achieved by lengthening the limb (Fig. 12B) if no femoral implant capable of replicating the native offset value is available (Fig. 12C). In coxa valga, maintaining limb length may require increasing the offset value when using a standard implant with a non-modular neck (Fig. 13A). The increase can be minimized by suspending the stem and selecting a short neck (Fig. 13B). The optimal depth of stem implantation is easier to determine with a cemented stem
Fig. 14. Example of use of a stem with a modular neck. Modular necks allowing the independent adjustment of length, offset, and anteversion (Adler Ortho, Milan, Italy).
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Fig. 15. Restoring extra-medullary anatomy by using a custom-made stem. a: templating is performed in the plane of the femoral neck to compensate for the influence of anteversion; b: offset is taken into account independently from femoral rotation.
than with a cementless stem, particularly one engaging the metaphysis (i.e., anatomical). Having modular necks available may be useful. When seeking to adjust anteversion without interfering with the adjustment of length and offset, the surgeon can use a modular homothetic neck [28] (Fig. 14) or even a custom-made neck (Fig. 15). 5. Revision surgery to correct length or offset We are not aware of any studies on the technique or outcomes of revision surgery to correct insufficient or excessive femoral offset. Caution is therefore in order regarding the patient’s expectations that increasing the offset will eliminate a limp, even when the revision procedure consists only in changing a modular neck.
Similarly, few or no studies have addressed the technique or outcomes of revision surgery for LLLD. Marked shortening of the operated limb is very rare. Limb lengthening may be inadequate in patients with unilateral high congenital hip dislocation. Femoral revision to lengthen the limb can be considered and prevents the occurrence of hip dislocation. We are not aware of any studies on revision surgery for limb lengthening. In a study by Parvizi et al. [34], the 21 patients with LLLD represented 0.3% of all cases of revision surgery. Revision was performed only in patients with symptomatic discrepancy of at least 2 cm. Mean time from primary THA to revision surgery was 8 months (6 days to 6 years). Revision involved the cup only in 71% of cases, the femur only in 14%, and both in 14%. A constrained cup was
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used in 2 (9.6%) patients. In only 1 (4.8%) patient was revision performed because of instability. The other patients had good clinical outcomes. Parvizi et al. emphasized the importance of evaluating the component(s) to be revised by distinguishing two types of excessive limb length: • excessive limb length due directly to the position of one or both components (low-placed cup or suspended femoral component), requiring revision of the offending component(s); • and error in positioning of one component counterbalanced by an error in positioning of the other component (e.g., cup retroversion prompting the surgeon to lengthen the limb to avoid instability). In this situation, the revision must involve both components. 6. Conclusion In this era of growing expectations regarding both limb function and implant survival, careful consideration of the threedimensional geometry of the prosthetic hip is crucial. The shift towards biological fixation of femoral implants has changed surgical practices. It mandates attention to both intra-medullary and extra-medullary anatomy. The degree of success in restoring the normal extra-medullary anatomy influences the restoration or preservation of limb length, which requires a meticulous analysis of all the factors located within or outside of the hip joint. Preservation of lateralization ensures optimal abductor muscle function. Tools such as EOS imaging and CT already exist and their use will probably become simpler and more widely available in the near future. By shedding light on the influence of anteversion, these tools will allow surgeons to reliably predict which implants are optimal for replicating the normal three-dimensional anatomy in each individual patient. Disclosure of interest The authors declare that they have no competing interest. References [1] Sayed-Noor AS, Hugo A, Sjödén GO, Wretenberg P. Leg length discrepancy in total hip arthroplasty: comparison of two methods of measurement. Int Orthop 2009;33:1189–93. [2] Ranawat CS, Rao RR, Rodriguez JA, Bhende HS. Correction of limb-length inequality during total hip arthroplasty. J Arthroplasty 2001;16:71520. [3] Austin MS, Hozack WJ, Sharkey PF, Rothman RH. Stability and leg length equality in total hip arthroplasty. J Arthroplasty 2003;18:88–90. [4] Desai AS, Connors L, Board TN. Functional and radiological evaluation of a simple intra operative technique to avoid limb length discrepancy in total hip arthroplasty. Hip Int 2011;21:192–8. [5] Edeen J, Sharkey PF, Alexander AH. Clinical significance of leg-length inequality after total hip arthroplasty. Am J Orthop 1995;24:347–51. [6] Maloney WJ, Keeney JA. Leg length discrepancy after total hip arthroplasty. J Arthroplasty 2004;19:108–10. [7] Plaass C, Clauss M, Ochsner PE, Ilchmann T. Influence of leg length discrepancy on clinical results after total hip arthroplasty – a prospective clinical trial. Hip Int 2011;21:441–9. [8] Ranawat CS, Rodriguez JA. Functional leg-length inequality following total hip arthroplasty. J Arthroplasty 1997;12:359–64. [9] Turula KB, Friberg O, Lindholm TS, et al. Leg length inequality after total hip arthroplasty. Clin Orthop 1986;202:163–8. [10] Williamson JA, Reckling FW. Limb length discrepancy and related problems following total hip joint replacement. Clin Orthop 1978:135–8. [11] Woolson ST, Hartford JM, Sawyer A. Results of a method of leg-length equalization for patients undergoing primary total hip replacement. J Arthroplasty 1999;14:159–64. [12] Konyves A, Bannister GC. The importance of leg length discrepancy after total hip arthroplasty. J Bone Joint Surg Br 2005;87:155–7. [13] Wylde V, Whitehouse SL, Taylor AH, et al. Prevalence and functional impact of patient-perceived leg length discrepancy after hip replacement. Int Orthop 2009;33:905–9. [14] Bourne RB, Rorabeck CH. Soft tissue balancing: the hip. J Arthroplasty 2002;17:17–22. [15] Matsuda K, Nakamura S, Matsushita T. A simple method to minimize limblength discrepancy after hip arthroplasty. Acta Orthop 2006;77:375–9.
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The role of the center of rotation. Clin Orthop 1993;296:140–7. [47] Pagnano W, Hanssen AD, Lewallen DG, Shaughnessy WJ. The effect of superior placement of the acetabular component on the rate of loosening after total hip arthroplasty. J Bone Joint Surg Am 1996;78:1004–14. [48] Yoder SA, Brand RA, Pedersen DR, O’gorman TW. Total hip acetabular component position affects component loosening rates. Clin Orthop 1988;229:79–87. [49] Sakalkale DP, Sharkey PF, Eng K, et al. Effect of femoral component offset on polyethylene wear in total hip arthroplasty. Clin Orthop 2001;388:125–34. [50] Bachour F, Marchetti E, Bocquet D, et al. Radiographic preoperative templating of extra-offset cemented ThA implants: how reliable is it and how does it affect survival? Orthop Traumatol Surg Res 2010;96:760–8.
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Review article
Lower limb length and offset in total hip arthroplasty X. Flecher ∗ , M. Ollivier , J.N. Argenson Service d’Orthopédie-Traumatologie, CHU Sud, 270, boulevard Sainte-Marguerite, 13009 Marseille, France
a r t i c l e
i n f o
Article history: Received 4 February 2015 Accepted 6 November 2015 Keywords: Total hip arthroplasty Leg length discrepancy Femoral offset Preoperative templating
a b s t r a c t Restoration of normal hip biomechanics is a key goal of total hip arthroplasty (THA) and favorably affects functional recovery. Furthermore, a major concern for both the surgeon and the patient is preservation or restoration of limb length equality, which must be achieved without compromising the stability of the prosthesis. Here, definitions are given for anatomic and functional limb length discrepancies and for femoral and hip offset, determined taking anteversion into account. Data on the influence of operatedlimb length and offset on patient satisfaction, hip function, and prosthesis survival after THA are reviewed. Errors may adversely impact function, quality of life, and prosthetic survival and may also generate conflicts between the surgeon and patient. Surgeons rely on two- or three-dimensional preoperative templating and on intraoperative landmarks to manage offset and length. Accuracy can be improved by using computer-assisted planning or surgery and the more recently introduced EOS imaging system. The prosthetic’s armamentarium now includes varus-aligned and lateralized implants, as well as implants with modular or custom-made necks, which allow restoration of the normal hip geometry, most notably in patients with coxa vara or coxa valga. Femoral anteversion must also receive careful attention. The most common errors are limb lengthening and a decrease in hip offset. When symptoms are caused by an error in length and/or offset, revision arthroplasty may deserve consideration. © 2015 Elsevier Masson SAS. All rights reserved.
1. Introduction
2. Definitions
Restoring normal hip biomechanics is a key goal of total hip arthroplasty (THA) and benefits functional recovery [1]. Another major concern is preservation or restoration of limb length equality, which must be achieved without compromising the stability of the prosthesis [2]. Lower limb length discrepancy (LLLD) is a common source of patient dissatisfaction and litigation [3–10]. The discrepancy may be either anatomical (structural) or functional, and a clear understanding of all the factors that create a sensation of length discrepancy is essential. Offset became a focus of interest more recently, when cementless stems were introduced. We will discuss the measurement of offset, which is highly controversial, and the impact of offset on function. Anteversion influences offset and must be taken into account.
2.1. Length
∗ Corresponding author. Tel.: +33 491 745 012; fax: +33 491 745 625. E-mail address: xavier.fl[email protected] (X. Flecher).
2.1.1. Anatomical (structural) lower limb length discrepancy (LLLD) LLLD can be measured by determining the difference between the two sides in the distance from the antero-superior iliac spine and the medial malleolus. Another method consists in placing increasingly thick boards under the foot on the shorter side until the two iliac crests are on the same horizontal line. 2.1.1.1. Preoperative measurement. A full-length antero-posterior standing radiograph should be obtained, given the limited reliability of clinical measurement techniques [1]. The preoperative LLLD is measured as the difference in length of the line segments extending from the top of the femoral head to the center of the ankle on each side. This length is modified in patients with flexion contracture of the hip and/or knee. Another relevant parameter is the height of the center of rotation of the femoral heads, as a difference in this value can induce LLLD despite identical lower limb lengths.
http://dx.doi.org/10.1016/j.otsr.2015.11.001 1877-0568/© 2015 Elsevier Masson SAS. All rights reserved.
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Fig. 1. Measurement of lower limb length on a full-length radiograph of both legs: length of the line segment connecting the top of the iliac crest (IC) to the middle of the tibio-tarsal joint line (TT) and running through the center of rotation of the femoral head (C).
Lower limb length should therefore be measured as the length of the line starting at the top of the iliac crest (or, if this structure is not visible on the radiographs, the sacro-iliac joint), running through the center of rotation of the femoral head, and ending at the middle of the tibio-tarsal joint space (Fig. 1). The two lower limbs must be aligned perpendicularly to the pelvis, with no flexion. 2.1.1.2. Postoperative measurement. The following landmarks are identified on a pelvic radiograph taken under the above-described conditions: the bi-ischial line [10] or radiological teardrops [11] at the pelvis and the centers of the lesser trochanters at the femurs (Fig. 2). Measuring the distance separating these two landmarks before and after THA reflects the lower limb length change induced by the procedure. The change in length may be due to the femur and/or acetabulum. 2.1.2. Functional lower limb length discrepancy (LLLD) About 1 in every 3 patients reports a sensation of LLLD after THA [5,12]. In a questionnaire survey, 329 (30%) of 1114 patients reported perceived LLLD after THA, but only 36% of these patients had anatomical LLLD [13]. The remaining 64% had functional LLLD. Functional LLLD can be related to pelvic obliquity, which may be due to an abnormality in the lower limbs, spine, or both. Pelvic obliquity is common in patients with hip dysplasia or dislocation, particularly when unilateral. In this situation, fixed spinal malalignment develops secondarily, contributing to the pelvic obliquity that was initially due only to a lower limb abnormality. Another contributor to perceived LLLD is postoperative tension of the gluteus medius and minimus muscles, which is due in some cases to a need for elongation; when the two lower limbs are aligned along the axis of the body, the operated limb seems longer. This distal pelvic obliquity is short-lived, as the muscle tension resolves within the first year. A postoperative limp can also induce a sensation of LLLD: thus, patients with the Trendelenburg gait pattern may perceive the operated limb as shorter than the other limb.
Fig. 2. Estimation of lower limb length discrepancy related to the hip. a: using the bi-ischial line; b: using the radiological teardrop; c: pelvic obliquity is a less reliable criterion: although the hips are at the same level, the pelvis is oblique.
2.2. Offset Femoral offset is the perpendicular distance from the center of rotation of the femoral head to the line of action of the abductor muscles (Fig. 3a) [14]. Acetabular offset is the perpendicular distance from the center of rotation of the femoral head to the vertical trans-teardrop line (Fig. 3b). Global hip offset is the sum of femoral and acetabular offsets. Femoral offset is challenging to measure. In practice, the perpendicular distance from the center of rotation of the femoral head to the long axis of the femoral metaphysis or canal is used (Fig. 3). Mean femoral offset is 41 to 44 mm [15,16]. Femoral offset
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H = 50°
α = 35°
PBCL’ A = 15° PBCL
Fig. 4. Measurement of femoral anteversion, helical torsion, and the alpha angle. The posterior bicondylar line (PBCL) is translated to the level of the neck (PBCL’) to allow the measurements. The desired prosthetic anteversion angle is about 15◦ (A). In this case, the axis of proximal femoral anteversion or helitorsion (H) is 50◦ . To obtain a final anteversion value of 15◦ , correction within the prosthetic neck or alpha angle must be −35◦ , i.e., 35◦ or retroversion.
• the axis of helical torsion is the long axis of the largest transverse slice through the proximal femur (10 mm proximal to the lesser trochanter); the helical torsion angle is formed by the helical torsion axis and the posterior bicondylar line; • the desired anteversion axis of the prosthetic neck is the line perpendicular to the axis of the second metatarsal (the step angle formed by the axis of the second metatarsal and the direction of gait is 10◦ to 20◦ ); ␣ is the angle formed by the anteversion axis and the helical torsion axis. When using a cementless prosthesis with a canal-filling stem whose anteversion is dictated by the helical torsion axis, the angle between the prosthetic neck and the helical torsion axis must be equal to ␣. Fig. 3. a: measurement of femoral offset (FO, 1) and abductor pull angle (2); b: measurement of acetabular offset (AO) and determination of global offset (GO) as the sum of FO and AO.
3. Rationale for restoring length and offset 3.1. Lower limb length discrepancy (LLLD)
is influenced by the neck-shaft angle (NSA): it increases with varus and decreases with valgus [17]. Femoral offset also varies with the degree of hip rotation on the radiographs. Femoral offset increased with femoral size in one study [18] but tended to be greater in patients with smaller femoral canals in another [19]. Finally, in a study of 689 patients scheduled for THA, femoral offset was independent from femoral dimensions [20]. 2.3. Anteversion Excessive anteversion (or external rotation) is associated with a decrease in the femoral offset value measured on an anteroposterior radiograph. Internal rotation of about 20◦ minimizes this error. However, the exact value of femoral anteversion must be known in order to accurately measure femoral offset on the same side. Computed tomography (CT) or EOS imaging can be used to measure proximal femoral torsion (Fig. 4): • the axis of the femoral neck is the line through the center of the femoral head and the middle of the femoral neck; femoral neck anteversion is the angle formed by the axis of the femoral neck and the posterior bicondylar line;
LLLD is common after THA, with incidence rates ranging from 1% to 50% [2,21]. Lengthening of the operated limb is more frequent than shortening [8,10,22]. The mean discrepancy ranges from 3 to 17 mm [9,23]. However, when care is taken to minimize LLLD, the difference is less than 10 mm in 97% of cases [11].
3.1.1. Clinical impact Patient dissatisfaction is common [24] and LLLD is the most common reason for litigation after THA [25]. A difference greater than 10 mm is often perceived by the patient [16] and affects the functional outcome [21,26–28]. Associations have been reported between LLLD and back or low-back pain or sciatica [27], gait disorders [29], and instability [30].
3.1.2. Complications LLLD may be associated with an increased risk of osteoarthritis in the operated lower limb [31], although this point is controversial. Lower limb lengthening after THA may also increase the risk of aseptic loosening [32,33]. LLLD may prompt revision surgery [6,34]. Another abnormality reported in patients with lengthening of the operated lower limb is increased stress on the superior part of the acetabular cup [31].
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Fig. 5. Example of acetabular offset modification due to excessive cup medialization. This patient had moderate hip dysplasia (a), and it was therefore reasonable to medialize the center of rotation to improve bony coverage of the cup (C’h < Ch). There is little change to the height of the center of rotation. A cementless fixed-angle stem was chosen. To obtain good joint stability, the surgeon chose an extra long neck (note the skirt on the head), despite the resulting limb lengthening, which was expected to be less than 1 cm and therefore without clinical significance.
3.1.3. Acceptable lower limb length discrepancy (LLLD) The cut-off between acceptable and unacceptable LLLD has not been determined [35]. Edeen et al. [5] reported that even a small discrepancy could induce dissatisfaction. In contrast, several studies showed that most patients tolerated LLLDs of up to 10 mm. Patients with moderate LLLD experience discomfort for the first few months that decreases over time, although 15% remain symptomatic [34], with a need for a compensatory shoe lift in over half the cases [5,10]. In contrast, lengthening by more than 10 mm has been associated with limping, pelvic obliquity, a need for a shoe lift, and a feeling of disappointment [2,5,36]. LLLD of more than 10 mm has been reported in 16% to 32% of patients [3–11,13,14,21]. Body height probably influences the intensity of perceived LLLD. Thus, the percentage of limb lengthening may constitute a useful parameter. Asymptomatic constitutional LLLD of up to 20 mm is not infrequent [12,37]. This abnormality must be detected preoperatively and disclosed to the patient. Great care should be taken to avoid increasing the discrepancy, which might induce a conflict with the patient.
3.2. Offset A decrease in femoral offset is often due to a stem NSA greater than the native value [38]. The mean NSA is 130◦ ± 5◦ . NSA values of standard stems vary across manufacturers. Acetabular cup medialization after reaming decreases both the acetabular offset and the global hip offset (Fig. 5). A decrease in acetabular offset exerts beneficial effects by decreasing the stresses applied to the prosthetic joint but requires counterbalancing by an increase in femoral offset to avoid decreasing the global hip offset, which would require lower limb elongation to prevent instability (Fig. 5). “Insufficient” offset can cause a limp [39], require the use of a walking aid [14], and induce instability [40,41]. As the femur is closer to the pelvis, motion range is diminished [38,42] and a cam effect may develop [43]. Failure to restore offset is a reason for patient dissatisfaction [38] and significantly impairs quality of life. One study showed that a 15% or greater decrease in offset compared to the non-operated side was associated with an increased frequency of gait disorders [44]. A decrease in offset can also diminish
Fig. 6. Rules for positioning the cup: a: the lower edge of the cup should not be lower than the teardrop; b: cup inclination should be 40◦ to 50◦ ; c: bony coverage of the cup should be at least 80%; d: and the cup must not be medial to the ilio-ischial line (Köhler’s line).
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4. Methods for restoring length and offset
ø 54 mm ø 50 mm
Errors in length and offset can be minimized, albeit not completely eliminated [38]. The literature is replete with techniques designed to prevent LLLD. The main methods involve:
c
b t T
a
• preoperative templating using tracing paper; • the intraoperative identification of landmarks on the pelvis and/or femur; • and computer-assisted surgery (CAS) or navigation. 4.1. Preoperative templating 4.1.1. Two-dimensional templating Two-dimensional templating using radiographs remains a standard method. The magnification issues raised by radiograph digitization can be overcome by using templating software.
M R
d
d
7.5 10 12.5 15 17.5 20
Fig. 7. Preoperative tracing paper templating according to Müller: standard (a), lateralized (b), and dysplastic (c).
implant survival [45–48], in some cases via premature polyethylene wear [38,49]. Few studies have described the impact of excessive offset. In a study of five cadaver femurs, an increase in offset from 28 to 53 mm was associated with an increase in micro-motion at the boneimplant interface [43]. The high-offset cemented stem LubinusTM SPII® (Link Finland Oy, Espoo, Finland) featuring a 117◦ NSA was associated with lower 5-year survival compared to stems having a NSA of 126◦ or 135◦ [50]. An increase in offset is often followed by a perception that the lower limb is longer. This perception is due to excessive abductor muscle tension, which usually resolves within a few months. Excessive lateralization showed no correlation with pain suggestive of gluteal muscle tendinitis. Patients with coxa valga usually have below-average offset values. An increase in offset to restore normal hip geometry might be desirable, provided the reference offset value can be determined.
4.1.1.1. Using tracing paper. The principle consists in drawing the contra-lateral hip on tracing paper. First, the center of rotation is identified (Fig. 6) based on traces of the cup. Traces of the femur are then added to determine the postoperative offset and lower limb length. The traces are then used to replicate the positioning of the selected components on the abnormal hip (Fig. 7). When both hips are abnormal, the Amstutz index can be used. Amstutz et al. showed that implant positioning according to their index eliminated the risk of limping [32] (Fig. 8). 4.1.1.2. Reliability of templates. Two-dimensional radiograph templating is not reliable for ensuring equal lower limb length. Meermans et al. demonstrated that the teardrop was more reliable than the bi-ischial line [51], particularly in patients with LLLD before surgery [11]. Furthermore, in another study, preoperative templating correctly predicted the implant size in only 60% of cases [52]. 4.1.1.3. Femoral offset. Femoral offset can be measured on anteroposterior radiographs of the femoral necks with the lower limb in about 20◦ of internal rotation. Reproducibility of this method is poor, with a mean error of about 9.7 mm, i.e., about 20% for an offset value of 40 mm [53]. In addition, internal rotation of 15◦ to 20◦ does not consistently compensate for femoral anteversion (Figs. 9 and 10), which varies widely, even in primary osteoarthritis [44,54,55]. In a study of 50 hips, the offset value was 42.6 mm (26.9–53.9 mm) when radiographs were used compared to 45.8 mm (31–56 mm) using computed tomography (CT) [19]. The radiographic measurements consistently underestimated the offset value, by a mean of 3.2 mm (P < 0.0001) and by over 5 mm in 28% of cases. Thus, it seems reasonable to measure offset along the axis of the femoral neck using CT or EOS imaging.
Fig. 8. Use of the Amstutz index [1]. a: when the contra-lateral hip is normal, the center of rotation is marked; b: then the lateral edge of the greater trochanter; c: and the femur is positioned in order to restore length; d: when both hips are abnormal, the top of the greater trochanter must be positioned so that A/B is equal to or greater than 0.5 (A is the distance from the top of the greater trochanter to the center of rotation and B is the distance from the center of rotation to the pubic symphysis).
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Fig. 9. Influence of femoral rotation on radiographic offset. When the lower limb is placed at an angle of internal rotation equal to the angle of femoral anteversion (left), the radiographic and CT measurements produce the same value. When a simple antero-posterior radiograph is used (middle), the radiographic measurement underestimates the angle of femoral anteversion determined using CT. When the hip is in fixed external rotation (right), the extent of underestimation by radiographic measurement versus CT is increased.
4.1.2. Three-dimensional templating Three-dimensional templating is performed using software developed initially to design custom-made stems for THA [54–57]. The software compensates for poor patient positioning during image acquisition. To measure femoral offset, the axis of the canal in the proximal fourth of the femur must be identified [40,58].
It is located at the center of the femoral metaphysis in all three planes [3], which allows measurement of the true offset value (Fig. 11). The EOS imaging system may constitute an alternative for obtaining accurate and reliable measurements while minimizing radiation exposure [59].
Fig. 10. Influence of natural femoral anteversion on radiographic offset. When there is no anteversion (left), the radiographic and CT measurements produce the same value. With 15◦ to 20◦ of anteversion (middle), the radiographic measurement underestimates the offset determined by CT. When anteversion is excessive (right), the extent of underestimation by radiographic measurement versus CT is increased.
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Fig. 11. Visualization of the proximal femur in the three planes using CT-based templating software.
4.2. Intraoperative landmarks Intraoperative tests have been developed to assess soft-tissue tension and length (the shuck test, described by Charnley and involving in-line lower limb traction in the distal direction; the dropkick test, with the hip held in extension and the knee flexed to 90◦ ; and leg-to-leg comparison of length based on the heels or medial malleoli). The results are influenced by surgeon experience; type of anesthesia; and other factors such as the approach, whether the patient is lying on the side or supine, and whether an orthopaedic table is used. Consequently, these tests have poor reproducibility [60]. Numerous techniques have been described. They all use a fixed pelvic landmark and a femoral landmark that varies during the procedure. These landmarks are unreliable, as they may be removed and replaced between measurements. A stirrup can be used to ensure that the pins are parallel [11,17,42,46,61], but this method requires either a longer incision or a second incision. Hip position must be replicated accurately in all three planes before and after implantation of the prosthesis, which is challenging. Variations in femoral abduction/adduction of only 5◦ to 10◦ result in measurement errors of 8 to 17 mm [62]. No study has evaluated the extent to which the surgical approach and patient position on the side versus supine influences lower limb length control using these landmarks. We believe the supine position is more reliable.
In conclusion, using a stable pelvic landmark and accurately positioning the lower limb during the measurements is a simple method [63].
4.3. Computer-assisted navigation Offset and lower limb length are determined in large part by femoral stem size and position. Few studies on the contribution of computer-assisted navigation to femoral component selection and placement have been published to date. A prospective matched-pairs study compared computer-assisted navigation to conventional freehand alignment [36]. The same straight, nonmodular femoral stem was implanted in all patients. Mean LLLD was significantly smaller in the navigation group (5.06 mm [0–12] versus 7.64 mm [0–20] in the freehand group). Nevertheless, in the navigation group, 5 (10.4%) patients had LLLDs greater than 10 mm. Using the pelvis as a landmark can induce errors. Digioia et al. [64] used a navigation system to track movements of the pelvis during THA. Mean variations in pelvic position were 23◦ in abduction/adduction, 16◦ in flexion/extension, and 40◦ in forwards/backwards pelvic tilt. Adduction of the pelvis induces apparent limb lengthening in the absence of error, whereas abduction has the opposite effect. Although imperfect, when combined with templating, this technique probably limits the risk of major LLLD. In our experience, navigation diminishes the standard errors,
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A
FO1
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*
*
*
*
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Fig. 12. Managing coxa vara during total hip arthroplasty. A. Using a stem with a standard neck (NSA2 < NSA1) decreases offset (FO2 < FO1) and diminishes abductor muscle tension (Abd2 < Abd1). B. To preserve the same level of muscle tension (Abd1 = Abd2) while using a stem with a standard neck (FO1 > FO2), the limb can be lengthened. C. To preserve the same level of muscle tension (Abd1 = Abd2) while preserving limb length, a lateralized stem must be used (FO1 = FO2 or NSA1 = NSA2). NSA: neck-shaft angle; Abd: abductor muscles.
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L
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Fig. 13. Managing coxa valga during total hip arthroplasty. A. Using a stem with a standard neck (NSA2 < NSA1) increases offset (FO2 > FO1) and increases abductor muscle tension (Abd2 > Abd1). B. This situation can be handled by using a suspended stem with a short neck (red asterisk).
to the same extent as reliable tools and/or extensive surgical experience, most notably for cup positioning [65].
4.4. Selecting the femoral implant When the femoral implant has a non-modular neck, even with a modular head, offset and length must be adjusted in combination.
In coxa vara (Fig. 12A), gluteal muscle tension can be achieved by lengthening the limb (Fig. 12B) if no femoral implant capable of replicating the native offset value is available (Fig. 12C). In coxa valga, maintaining limb length may require increasing the offset value when using a standard implant with a non-modular neck (Fig. 13A). The increase can be minimized by suspending the stem and selecting a short neck (Fig. 13B). The optimal depth of stem implantation is easier to determine with a cemented stem
Fig. 14. Example of use of a stem with a modular neck. Modular necks allowing the independent adjustment of length, offset, and anteversion (Adler Ortho, Milan, Italy).
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Fig. 15. Restoring extra-medullary anatomy by using a custom-made stem. a: templating is performed in the plane of the femoral neck to compensate for the influence of anteversion; b: offset is taken into account independently from femoral rotation.
than with a cementless stem, particularly one engaging the metaphysis (i.e., anatomical). Having modular necks available may be useful. When seeking to adjust anteversion without interfering with the adjustment of length and offset, the surgeon can use a modular homothetic neck [28] (Fig. 14) or even a custom-made neck (Fig. 15). 5. Revision surgery to correct length or offset We are not aware of any studies on the technique or outcomes of revision surgery to correct insufficient or excessive femoral offset. Caution is therefore in order regarding the patient’s expectations that increasing the offset will eliminate a limp, even when the revision procedure consists only in changing a modular neck.
Similarly, few or no studies have addressed the technique or outcomes of revision surgery for LLLD. Marked shortening of the operated limb is very rare. Limb lengthening may be inadequate in patients with unilateral high congenital hip dislocation. Femoral revision to lengthen the limb can be considered and prevents the occurrence of hip dislocation. We are not aware of any studies on revision surgery for limb lengthening. In a study by Parvizi et al. [34], the 21 patients with LLLD represented 0.3% of all cases of revision surgery. Revision was performed only in patients with symptomatic discrepancy of at least 2 cm. Mean time from primary THA to revision surgery was 8 months (6 days to 6 years). Revision involved the cup only in 71% of cases, the femur only in 14%, and both in 14%. A constrained cup was
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used in 2 (9.6%) patients. In only 1 (4.8%) patient was revision performed because of instability. The other patients had good clinical outcomes. Parvizi et al. emphasized the importance of evaluating the component(s) to be revised by distinguishing two types of excessive limb length: • excessive limb length due directly to the position of one or both components (low-placed cup or suspended femoral component), requiring revision of the offending component(s); • and error in positioning of one component counterbalanced by an error in positioning of the other component (e.g., cup retroversion prompting the surgeon to lengthen the limb to avoid instability). In this situation, the revision must involve both components. 6. Conclusion In this era of growing expectations regarding both limb function and implant survival, careful consideration of the threedimensional geometry of the prosthetic hip is crucial. The shift towards biological fixation of femoral implants has changed surgical practices. It mandates attention to both intra-medullary and extra-medullary anatomy. The degree of success in restoring the normal extra-medullary anatomy influences the restoration or preservation of limb length, which requires a meticulous analysis of all the factors located within or outside of the hip joint. Preservation of lateralization ensures optimal abductor muscle function. Tools such as EOS imaging and CT already exist and their use will probably become simpler and more widely available in the near future. By shedding light on the influence of anteversion, these tools will allow surgeons to reliably predict which implants are optimal for replicating the normal three-dimensional anatomy in each individual patient. Disclosure of interest The authors declare that they have no competing interest. References [1] Sayed-Noor AS, Hugo A, Sjödén GO, Wretenberg P. Leg length discrepancy in total hip arthroplasty: comparison of two methods of measurement. Int Orthop 2009;33:1189–93. [2] Ranawat CS, Rao RR, Rodriguez JA, Bhende HS. Correction of limb-length inequality during total hip arthroplasty. J Arthroplasty 2001;16:71520. [3] Austin MS, Hozack WJ, Sharkey PF, Rothman RH. Stability and leg length equality in total hip arthroplasty. J Arthroplasty 2003;18:88–90. [4] Desai AS, Connors L, Board TN. Functional and radiological evaluation of a simple intra operative technique to avoid limb length discrepancy in total hip arthroplasty. Hip Int 2011;21:192–8. [5] Edeen J, Sharkey PF, Alexander AH. Clinical significance of leg-length inequality after total hip arthroplasty. Am J Orthop 1995;24:347–51. [6] Maloney WJ, Keeney JA. Leg length discrepancy after total hip arthroplasty. J Arthroplasty 2004;19:108–10. [7] Plaass C, Clauss M, Ochsner PE, Ilchmann T. Influence of leg length discrepancy on clinical results after total hip arthroplasty – a prospective clinical trial. Hip Int 2011;21:441–9. [8] Ranawat CS, Rodriguez JA. Functional leg-length inequality following total hip arthroplasty. J Arthroplasty 1997;12:359–64. [9] Turula KB, Friberg O, Lindholm TS, et al. Leg length inequality after total hip arthroplasty. Clin Orthop 1986;202:163–8. [10] Williamson JA, Reckling FW. Limb length discrepancy and related problems following total hip joint replacement. Clin Orthop 1978:135–8. [11] Woolson ST, Hartford JM, Sawyer A. Results of a method of leg-length equalization for patients undergoing primary total hip replacement. J Arthroplasty 1999;14:159–64. [12] Konyves A, Bannister GC. The importance of leg length discrepancy after total hip arthroplasty. J Bone Joint Surg Br 2005;87:155–7. [13] Wylde V, Whitehouse SL, Taylor AH, et al. Prevalence and functional impact of patient-perceived leg length discrepancy after hip replacement. Int Orthop 2009;33:905–9. [14] Bourne RB, Rorabeck CH. Soft tissue balancing: the hip. J Arthroplasty 2002;17:17–22. [15] Matsuda K, Nakamura S, Matsushita T. A simple method to minimize limblength discrepancy after hip arthroplasty. Acta Orthop 2006;77:375–9.
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