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Femoral Version: Definition, Diagnosis, and Intraoperative Correction With Modular Femoral Components

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Abstract

Normal femoral version contributes to the inherent stability of the hip joint. Abnormal version is found in a variety of hip diseases afflicting children and adults. At the time of reconstruction for end-stage hip disease, maintaining proper femoral version in conjunction with acetabular version allows for hip stability and unimpeded functional range of motion. In those instances where femoral version is significantly abnormal, a means of correction at time of surgery is necessary. Non-modular femoral components allow for minor adjustments in version at time of surgery. To accommodate significant versional abnormalities, the modular S-ROM (DePuy Orthopaedics Inc, Warsaw, Ind) was introduced in 1984. In a series of 156 primary S-ROM total hip arthroplasties, the ability to correct for abnormal version resulted in excellent clinical results with no incidence of hip instability and excellent range of motion.

The anatomy of the femur varies considerably from one individual to another. Version of the proximal femur refers to the relationship of the axis of the femoral neck to the transcondylar axis of the distal femur. Femoral anteversion refers to the condition where the femoral neck axis is rotated anterior with respect to the transcondylar femoral axis, with the femoral head directed anterior to the coronal plane of the femur. In femoral retroversion, the femoral neck axis is oriented posterior to the transcondylar axis thus positioning the femoral neck and head posterior to the coronal plane of the femur. Femoral anteversion of 10°-20° along with acetabular anteversion provides inherent stability to the hip joint.¹ In developmental hip dysplasia, femoral anteversion of 45° -60° is not an uncommon finding.² Trauma as well as acquired hip diseases, such as Legg-Calve-Perthes and slipped capital femoral epiphysis, may also result in abnormal degrees of femoral version.^3-5 Failed hip arthroplasty occasionally results in proximal femoral adaptive remodeling with development of femoral retroversion. Failure to recognize the abnormally anteverted or retroverted hip during reconstruction may compromise ultimate hip stability and range of motion. Careful assessment of version and correction when necessary will insure improved hip stability and range of motion following reconstruction. Proper assessment of hip version is usually made with the use of plain radiographs during preoperative evaluation.^6,7 Although difficult to measure accurately with standard radiographs, the lateral hip radio-graph can usually be assessed qualitatively for the degree of version. If excessive femoral version is present or suspected, further studies such as computed tomography (CT) scans can be obtained to more accurately assess the actual degree of abnormality.⁸

Evaluation of Femoral Version

The most accurate determination of hip version is obtained with CT scanning.⁹ Superimposition of a transcondylar image of the knee with an image through the axis of the femoral neck provides the two necessary axes required to calculate femoral version. When the axis of the femoral neck is anterior to the transcondylar femoral axis, then femoral anteversion is present, whereas with the neck axis posterior to the condylar axis, femoral retroversion is present.

Biplane radiographs allow for a quantitative assessment of hip version and may be used for evaluation purposes.¹⁰ The anteroposterior (AP) hip radiograph many times suggests the presence of excessive anteversion when the femoral neck appears elongated and in a valgus orientation. The anterior orientation of the anteverted femoral neck alters the appearance of the femoral neck-shaft angle on the AP radiograph, resulting in a valgus appearance of the femoral neck. Figure 1 illustrates the normal appearance of the neck-shaft angle in a normally anteverted hip, whereas Figure 2 represents the excessive valgus appearance in a developmentally dysplastic hip with excessive anteversion.

Figure 3 illustrates the presence of excessive anteversion in a congenitally dysplastic hip on a lateral radiograph of the femur. Exact anteversion measurement is not possible because femoral rotation cannot be precisely controlled.

Figure 1: A normal neck shaft angle of 135° and anteversion of 15°, verified by computed tomography. Figure 2: A congenital dysplastic hip with neck shaft angle of 155° and femoral anteversion of 47°, determined by computed tomography. Figure 3: Lateral radiograph illustrating excessive femoral anteversion. Figure 4: S-ROM trial sleeve in position. Note the anteversion of 40°.

Clinical Evaluation of Femoral Version

Total hip reconstruction of an excessively anteverted femur poses potential problems of hip stability. Excessive anteversion of the femoral component with normal acetabular placement may result in decreased anterior coverage of the femoral head. On attempted extension and external rotation, the posterior femoral impingement and lack of anterior head coverage may lead to dislocation. During reconstruction, it is important to evaluate both femoral and acetabular component anteversion to maintain stability during range of motion. Normal combined anteversion should be maintained between 30°-45°. This determination can be made at the time of surgery when trial femoral and acetabular components are inserted. With the patient in the true lateral position and a posterior lateral hip incision, the hip, with trial components in place, is brought into neutral extension and abduction. With the knee flexed to 90°, the femur is internally rotated until the face of the acetabular shell and the plane of the major axis of the femoral head are coplanar. The angle that the tibia subtends with the horizontal plane in this position represents the combined femoral-acetabular anteversion. If this angle is <30°, then decreased posterior femoral head coverage will occur when the patient flexes, adducts, and internally rotates the hip, leading to subluxation or frank dislocation. If the angle is >45°, decreased anterior head coverage will occur when the patient extends, abducts, and externally rotates the hip, resulting in potential anterior instability. This intraoperative assessment, commonly referred to as the Ranawat Sign, has been well described. Careful assessment of combined anteversion at time of arthroplasty surgery can avoid subsequent stability problems.

Correcting Femoral Version with Arthroplasty

Use of most currently available cementless femoral stems for primary hip arthroplasty allows for, at best, minimal correction of native femoral anteversion. Because most of these stems generally fill the metaphysis of the proximal femur, there is very little opportunity to alter stem anteversion on insertion. Modular stem designs, however, are available that allow for version alterations. These stems are of two basic styles. The first consists of a standard cementless femoral stem with a variety of modular neck components. Use of this type of device allows for placement of a modular femoral stem with the usual preparation and then attaching a suitable modular femoral neck assembly to compensate for offset, neck length, and anteversion. Several modular neck components are available to allow for version correction. A suitable femoral head is then attached to complete the construct. These devices are relatively new and, as yet, have no mid- to long-term clinical results available. Concerns of taper corrosion and potential neck strength remain with these devices.

The second type of cementless modular femoral stem available to correct anteversion consists of a proximal metaphyseal sleeve whose position on insertion is determined by the proximal femoral anatomy. The S-ROM (DePuy Orthopaedics Inc., Warsaw, Ind) is representative of this type of device. Proximal femoral preparation is accomplished with reaming and the proper size sleeve is inserted. This provides potential for optimal bone contact and potential osseous integration. A femoral stem with a taper to match that of the inner surface of the sleeve is then inserted through the taper of the sleeve and is rotated to the position of desired anteversion. Locking of the taper with stem impaction provides a stable construct with the desired anteversion. Multiple sleeve sizes and styles along with femoral stems of varying offset and neck lengths allow for a multitude of potential combinations to accommodate any type of femoral anatomy. Because the sleeve/stem taper is conical, an infinite number of version positions are possible. Figure 4 illustrates a trial S-ROM taper sleeve in position prior to femoral stem trial insertion.

The S-ROM modular hip system has been in available since 1985. Several clinical studies describing correction of version and metaphyseal/diaphyseal size mismatch in primary and revision hip arthroplasty have reported with excellent mid- to long-term results.^11,12 Stable metaphyseal fixation with no clinical evidence of taper corrosion or loss of rotational stability has been a consistent result.¹³

In a consecutive series of 156 S-ROM primary total hip replacements in patients with a variety of primary diagnoses (Table 1) and metal-metal alternative bearings, intraoperative femoral version measurements were obtained at the time of femoral neck osteotomy. The range and average are reported in Table 2. After preparation of the acetabulaum and femur and insertion of trial components, the version was adjusted to maintain 40°-45° of combined anteversion in women and 35°-40° in men. The amount of femoral component version correction for each disease entity is listed in Table 2.

At a minimum follow-up of 1 year, no dislocations or subluxations of the 156 S-ROM modular devices were reported. Although 36-mm articulations were used in all patients, which also potentially reduces the risk of dislocation, several patients with excessive femoral anteversion if not corrected should have lead to impingement or dislocation, although none was noted.

Femoral version poses potential complications during hip reconstruction. Either excessive or insufficient version may lead to component impingement, subluxation, dislocation, or limited range of motion. Although the etiology of these problems is multifactorial, maintenance of appropriate combined version of 30°-45° in most patients significantly reduces their incidence. To properly deal with version abnormalities, a surgeon should be capable of proper diagnoses and techniques for correction. Our series of consecutive S-ROM patients clearly shows a broad range of femoral version in a primary total hip population. The ability to correct these abnormalities with a modular femoral stem provides excellent stability without compromise of range of hip motion.

References

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Author

Dr Kudrna is from the Illinois Bone & Joint Institute, Glenview, Ill.