Leg length discrepancy in primary total hip arthroplasty.
Interestingly, the importance of equal leg lengths was not immediately apparent. In his paper describing his Teflon arthroplasty in 1961, Charnley did not mention leg lengths at all; the article's focus was on the basics, material properties, femoral head size, pain-free recovery, and basic ambulation postoperatively. (4) Furthermore, two subsequent publications also did not mention leg lengths at all, despite listing multiple postoperative complications and even a radiograph clearly exhibiting a patient with an approximate 2 cm LLD. (5, 6) Overlooked in Charnley's own series, addressing the importance of LLD was first published by Knight in 1977. (7,8) With the growing success coinciding with a young population of patients receiving THA, avoiding LLD was a major focus in the 1990s. (9)
This purpose of this review is to discuss LLD in three phases of THA. Preoperatively, the methodology and approach in order to achieve equal leg lengths will be discussed. Next, tips and tricks for intraoperative assessment will be reviewed. Finally, the postoperative management of the patient with apparent and real LLD will be reviewed.
Preoperative Assessment and Planning
Preoperative assessment of patient with hip pain from the perspective of leg length discrepancy includes radiographic and clinical evaluation. Clinically, the physician will evaluate for range of motion of bilateral hips and knees with particular attention to hip and knee contractures, which may affect the measurement of leg length discrepancy. Lumbosacral spine and intrinsic pelvic deformity must be considered.
Clinically, actual limb length discrepancy can be approximated by measuring the distance from anterior superior iliac spines to the medial malleoli, bilaterally. It is a crude measurement as it may be affected by curvature of the spine, pelvic obliquity, and hip and knee contractures. Pelvic obliquity can be evaluated by examining the patient in standing and sitting position. Suprapelvic obliquity is associated with spine curvature and persist while patient is sitting. Infrapelvic and true pelvic obliquity in contrast resolves in sitting position. True pelvic obliquities stem from loss of bone or cartilage in the hip joint due to arthritis, necrosis, or infection as well as pelvic fractures and resulting deformity. Infrapelvic causes of obliquity that are important to consider include fractures, LLD due to previous polio infection, hemihypertrophy, and so forth. Most common cause for functional LLD, that is perceived by the patient, is either flexion or abduction contracture. Patient's perceived leg length discrepancy can be estimated with Coleman's blocks placed under the shorter limb until patient feels the limbs are equal. (10) A standing x-ray with and without the blocks can be taken documenting leveling of the pelvis with the blocks. Patient may or may not be aware of the difference in leg lengths, and discussion about the possibility of postoperative LLD apparent or real is very important at this stage.
Radiographic Evaluation and Templating
Next, it is recommended that radiographic evaluation and templating is undertaken to obtain reproducible results. (10) Both standard acetate templates and computer templating software can be used (Fig. 1 A and B). An extensive review of templating techniques is beyond the scope of this paper, but a short review as it relates to LLD will follow. AP view of the pelvis centered over the sacrum is used with legs in 15[degrees] of internal rotation to provide en face view of the anteverted femoral necks and allow correct evaluation of the femoral offset. Radiographic preoperative LLD is measured. One of the three lines is drawn: intertuberosity, interobturator, or interteardrop line. Figure 1C shows an example of LLD measurement using intertrochanteric line. It also shows the measurement of offset from the contralateral hip since operative hip is externally rotated. Tripuraneni and colleagues measured variation in LLD by using these three lines and reported that the interobturator line had the least variation. (11) The distance to the most proximal aspect of the lesser trochanter is then measured and recorded bilaterally. The difference between these two measurements on each side constitutes LLD for the operative hip.
Templating should typically follow surgical sequence: cup first then the femur. The cup is placed at the level of the teardrop with 40[degrees] [+ or -] 10[degrees] of abduction, and it is medialized to the illioischial line (Fig. 1 A and B). The size is determined by adequate lateral coverage without removal of excess subchondral bone. Special consideration must be undertaken for protrusio acetabuli and dysplastic hips. If the contralateral hip is not affected by disease, it can often be used as an appropriate surrogate to template. Using the unaffected side, the distance from the center of femoral head to the lesser trochanter can be recorded and reproduced to use during surgery on the affected hip.
The goal of templating the femur is to predict the implant of appropriate size for the femoral canal, to predict the neck cut length, and to restore femoral offset and equalize the limb length. Leg length is reestablished by placing the center of rotation of the femoral head above the center of rotation of the acetabular component for a shortened limb and below the center of acetabular component for a limb that needs to be shortened (Fig. 1 A and B). The vertical distance between the two centers of rotation is the numerical correction of LLD in millimeters. The horizontal distance between these two centers on medial to lateral axis signifies the increase or decrease in femoral offset after the surgery. The interplay of offset and leg length and their impact on hip stability will be discussed in the next section. During templating, the goal is to predict restoration of leg length and offset as compared to contralateral side. In general, a well-executed template should estimate and record the following parameters: preoperative LLD, postoperative center head to lesser troch distance that restores equal leg length (which is easily measured during surgery), length of the neck cut, estimated sizes of the femoral and acetabular components, and estimated femoral offset.
Multiple studies have shown that well executed templating can predict LLD correction in more than 90% of patients based on the preoperative plan, and that in majority of patients, LLD will be less than 1 cm. (12-14) The most common errors in execution of a template are lengthening due to inferior cup positioning and increased offset due to inadequate medicalization. (11)
Intraoperative Methods of Pre- and Post-Implantation Assessment of LLD
There are multiple methods of assuring and confirming correction of LLD during THA. While it is beyond the scope of this paper to review in detail all stages of the surgery that affect the limb length, we will review basic concepts and the most common described methods to assure restoration of the leg length during the surgery.
First, it is important to note that all aspects of the case can affect the leg length. For example, superior positioning of the cup may cause shortening, while inferior positioning of the cup may cause lengthening. (10) As previously mentioned, there is an interplay between hip stability, offset, and leg lengths. For example, if cup is over medialized and offset is not restored, the hip may become unstable, and the surgeon may be forced to increase the length in order to increase stability. The same situation can occur when the acetabular component is retroverted. Conversely, if a high offset prosthesis is used in a smaller person with shortened abductors, it can cause inability to reduce the hip, which may force the surgeon to shorten the limb to facilitate reduction. (15, 16)
Interestingly, anesthesia type was also shown to affect the extent of postoperative LLD. Larger LLD was found in patients who underwent THA under spinal anesthesia, hypothetically causing increased muscle relaxation forcing the surgeon to increase leg length to obtain adequate hip stability. The investigators suggested that the surgeon should rely more on preoperative templating rather than on intraoperative stability tests in patients under local anesthesia. Results of hip "shuck test "was found by the investigators to be greatly overestimated in patients under local anesthesia. (17)
There are multiple ways of measuring this change during the surgical procedure to avoid lengthening or shortening that will affect patient's outcome. Patient positioning will affect what type of measuring method can be used. For example, a prone method often used by chiropractors would not be convenient since prone positioning for THA is exceedingly rare. (18) In a supine position, as in an anterior approach to the hip, the surgeon often opts to prep both legs to be able to measure the distance between the malleoli at the ankle before and after surgery to estimate LLD. This method is, however, affected by the abduction and adduction of the hip (Fig. 2C). Sarin and colleagues demonstrated in a lab using navigational techniques that 5[degrees] and 10[degrees] of abduction or adduction caused 8 mm and 16 mm of apparent LLD, respectively. Since 5[degrees] of abduction may be difficult to estimate with more than half of patient's body covered by sterile drapes, this technique can result in significant errors.
In the lateral position, one of the most common ways of measuring leg lengths is by aligning the knees and feet of both legs and comparing pre- and post-implantation change in alignment (Fig. 2 A and B). (19) Usually the up leg will appear shorter as it is in adduction on preoperative assessment (Fig. 2B). This technique gives a decent estimate of the preoperative to postoperative change but is fraught with pitfalls. Small change in the positioning of the legs can result in large changes in estimation of leg lengths, including changes in flexion at the knee and the ankle as well as change in adduction. Another intraoperative technique involves measurement of the distance from the center of femoral head to the superior aspect of the lesser trochanter post-implantation and comparing it to the contralateral value from x-rays, if there is no contralateral disease, or to the value that was templated if contralateral disease exists (Fig. 3B). This measurement is often combined with the measurement of the length of templated femoral osteotomy and making sure that the real osteotomy is performed at that level.
Intraoperative radiographs or fluoroscopy can be used to help cup positioning and placement of osteotomy. (20) After the implantation of the components, LLD can be measured via radiography or fluoroscopy by forming one of the previously described horizontal pelvic lines, such as the interobturator line, to the lesser trochanter (Fig. 3A). The use of a fluoroscopic grid to facilitate such intraoperative measurements has also been described. (21)
Additionally, a Steinman pin can be placed in the supraacetabular area within the incision and remain there for the duration of the case. The distance from that pin to the pin or suture placed in the vastus ridge can be evaluated pre- and postoperatively to assess the leg length change due to component implantation. (22) One must take care not to manipulate this pin as changes in its inclination will affect the measurements. A similar method, described by Ranawat and colleagues, placed the pin vertically in the infracotyloid groove, and the position of that pin was marked on the greater trochanter. The pin was then removed, and the components were implanted. After reduction, the pin was placed again vertically in the infracotyloid groove, and its position was marked on the greater trochanter. The distance between the two marks gave a good estimation of the change in the leg length. (23) The reproducibility of the Ranawat's method is predicated on placing the pin in a correct anatomic location each time while the supraacetabular pin method depends on the pin remaining in the same place and position during entire case. Both methods yielded good results. (22, 23)
Simple intraoperative caliper-like devices designed to measure the same distances have also been described. (24) The supraacetabular method is often reproduced in navigation systems, replacing the pin with a navigation tracking device, placed somewhere on the pelvis, and a second in the femur. Very precise three dimensional readings of length and offset can be obtained in such a way. (25) However, while computerized, studies have not shown significantly improved accuracy with the navigated systems. (26, 27)
Finally, Kurtz described a method of implantation of the femoral component before the neck osteotomy is performed. The technique includes placement of the supraacetabular cannulated screw, which is used for pre- and post-implantation measurements of leg lengths. Modular necks included in the system allow for precise restoration of the leg lengths based on preoperative plan. (28)
While ensuring that the bony architecture facilitates accurate leg lengths, it is important to stress the importance of addressing the surrounding soft tissue. Performing the appropriate soft tissue releases in patients with contractures around the hip will allow for the avoidance of functional LLD.
Postoperative Management of LLD
Even if one perfectly executes the above-mentioned methods of intraoperative leg length assessment, patients can still return complaining of apparent LLD, making this aspect of THA one of the most difficult and frustrating. The true prevalence of LLD after THA is unknown but has been reported to range from 16% to 96% in different studies. This may be due to the fact that there is no accepted minimum numerical side-to-side difference that can be defined as LLD after total hip arthroplasty. (29) Classically, LLD of less than 2 cm was thought to be asymptomatic, but in modern times, an arthroplasty surgeon would be hard pressed to accept 2 cm of lengthening or shortening without a very compelling reason. Most surgeons feel that LLD of less than 1 cm is acceptable, and more than an inch is unacceptable. (3)
Despite the lack of satisfactory definition, surgeons agree that there are two types of postoperative LLD. Functional LLD is perceived by the patient with minimal or no side-to-side difference. It is most often caused by tight structures around the hip joint (i.e., anterior capsule or contracted abductors). Functional LLD may also be caused by pelvic obliquity secondary to degenerative scoliosis of the lumbar spine. This occurs because the diseased lumbar spine cannot accommodate the change to the pelvic tilt that occurred after surgery. The patient presents with pain in the groin or lateral pain in abductors, imbalance, and feeling of leg lengthening. The knee is flexed, and the pelvis is tilted toward the affected side. (1) This is somewhat paradoxical as patient tilts toward the leg that is perceived as longer.
The second type of LLD is a true LLD, which occurs when the operative leg is shorter or longer than the nonoperative leg due to component malpositioning. (1) Here, the patient will also present with knee flexed, but the pelvis will be horizontal or tilted away from the longer extremity as expected. Patients with significant lengthening may present with paresthesias or complete sciatic nerve palsy with associated foot drop. (30) Back along with pain at the insertion of the iliotibial band may also occur in both groups.
Most investigators agree that initial treatment of patients with functional LLD is nonoperative. (1, 29) Shoe modifications are discouraged for the first 6 months in functional LLD group, as it is felt that they may delay stretching of the tight structures causing the feeling of lengthening. Majority of the patients in functional group will have complete resolution of symptoms within first 6 months postoperatively with continued physical therapy. Persistent functional LLD is very rare. Ranawat described nine patients with persistent functional LLD in 15 years at his institution. (1) They were usually women of short stature with varus femoral necks, protrusio with or without flexion contracture, and lumbar spine disease. The treatment for those who failed prolonged course of physical therapy and were painless was contralateral shoe lift or soft tissue releases of the structures that were not corrected by physical therapy, in those patients who had pain.
The treatment of the patient with true leg length discrepancy is initially nonoperative as well. Reassurance and physical therapy if LLD is less than 2 cm may be sufficient. Those patients who are painless and can accept it may be treated only with the shoe lift. If the patient has persistent pain or does not want to accept his lengthening correction with contralateral shoe lift, revision surgery may be necessary. If revision surgery is indicated, a candid discussion with patient regarding the risks and benefits of revision must occur.
Leg length discrepancy is a common complication of total hip arthroplasty. Avoiding it requires careful preparation and meticulous execution of the preoperative plan. Treatment of LLD is mostly nonoperative with physical therapy and shoe inserts. Surgical treatment is reserved for patients with large LLD with an obvious mechanical cause who canmot tolerate shoe inserts or LLD itself.
Peter Pyrko, M.D., Ph.D., and Joseph Zuckerman, M.D.
Peter Pyrko, M.D., Ph.D., and Joseph Zuckerman, M.D., Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York.
Correspondence: Peter Pyrko, M.D., Ph.D., Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, 301 East 17th Street, New York, New York 10003; firstname.lastname@example.org.
Dedicated to the memory of Dr. Fredric Jaffe.
None of the authors have a financial or proprietary interest in the subject matter or materials discussed, including, but not limited to, employment, consultancies, stock ownership, honoraria, and paid expert testimony.
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Caption: Figure 1 Templating. A, Example of a template prepared by hand with a use of an acetate template. B, Example of an electronically prepared template. C, Using electronic templating software, multiple measurements can be performed: LLD, offset, femoral neck shaft angle, and diameter of the femoral head.
Caption: Figure 2 Intraoperative measurements of LLD. A, In lateral decubitus position while the surgeon aligns the knees together, and B, the assistant evaluates LLD by aligning the heels. C, In supine position, LLD can be evaluated from the distance between the malleoli. To view this figure in color, see www.hjdbulletin.org.
Caption: Figure 3 Intraoperative measurements of LLD. A, Intraoperative fluoroscopic image using interobturator line can help determine the presence of LLD. B, Intraoperative measurement of center head to lesser trochanter distance. To view this figure in color, see www.hjdbulletin.org.
Please note: Illustration(s) are not available due to copyright restrictions.
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|Author:||Pyrko, Peter; Zuckerman, Joseph|
|Publication:||Bulletin of the NYU Hospital for Joint Diseases|
|Date:||Jan 1, 2016|
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