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Total Hip Arthroplasty in Patients With Proximal Femoral Deformity

Berry, Daniel, J.

Section Editor(s): Barrack, Robert L. MD

Clinical Orthopaedics and Related Research: December 1999 - Volume 369 - Issue - p 262-272
Section I: Symposium: The Papers Presented at the Hip Society Meeting 1999: V. Total Hip Arthroplasty in Special Cases
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Most proximal femoral deformities encountered during hip arthroplasty are secondary to developmental processes, previous osteotomy, or fracture. A classification method is proposed in which deformities are categorized anatomically by level. Anatomic deformity levels include: greater trochanteric deformities, femoral neck deformities, metaphyseal level deformities, and diaphyseal level deformities. Deformities at each level may be angular, rotational or translational, abnormal bone size, or a combination thereof. Treatment is individualized according to patient needs and the anatomy of the deformity. Careful preoperative planning helps predict prosthesis requirements and technical challenges. If cemented implants are used, care must be taken to obtain reasonable alignment and a continuous cement mantle. For uncemented implants, obtaining a good fit is challenging and there is a risk of intraoperative fracture. Access to a wide range of implants helps the surgeon treat unique femoral geometries. Implants fixed in the diaphysis allow some proximal femoral deformities to be bypassed. Modular or custom implants simplify treatment of certain deformities. For patients with severe deformities, femoral osteotomy may be required. Successful osteotomy requires correcting the deformity, maintaining vascular supply of fragments, obtaining fixation of osteotomy fragments (with the implant or adjunctive fixation), and obtaining implant stability. Although most deformities can be treated during hip arthroplasty, occasionally there is a role for two-stage treatment: deformity correction followed later by arthroplasty.

From the Mayo Clinic and Mayo Foundation, Department of Orthopedics, Rochester MN.

Reprint requests to Daniel J. Berry, MD, Mayo Clinic, 200 First St, SW, Rochester, MN 55905.

A wide range of proximal femoral anatomy is considered within the normal spectrum of anatomic variability. During total hip arthroplasty, most anatomic variations can be treated using routine operative techniques and routine femoral implants. No agreement exists as to when a variation in femoral anatomy ceases to fall within the spectrum of normal and becomes a deformity. For practical purposes, during total hip arthroplasty, the femur may be considered deformed when the shape or size of the femur is sufficiently unusual to require the surgeon to compensate for the anatomy using special techniques or implants.

Femoral deformities pose many technical challenges for the surgeon. Deformities can make exposure difficult, can increase the risk of femoral fracture or perforation, and can lead to implant malposition.7,12 Deformities may, in some cases, compromise implant fixation. Hip instability caused by bony impingement or implant malposition may occur in hips with femoral deformity. Finally, deformity can alter hip biomechanics, thereby causing problems with abductor power and limp.

Marked femoral deformities, although uncommon, are not rare in patients who require total hip arthroplasty and occur for many reasons. These include developmental abnormalities, metabolic disease processes, previous fracture, and previous osteotomy. There are few studies about the generic subject of total hip arthroplasty in patients with femoral deformity,17 although results of total hip arthroplasty in patients with specific diagnoses often associated with the femoral deformity have been published.1,4,7,10-15,18

The purpose of this paper is to describe a rational method of classifying femoral deformities. This classification, based on deformity level, guides surgical treatment. Different surgical strategies for treating each type of deformity are discussed for each deformity level. Finally, a review of reported results of total hip arthroplasty in association with femoral deformities and results of hip arthroplasty in association with osteotomy are discussed.

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CLASSIFICATION

Different methods may be used to classify femoral deformities.3 The method proposed in this article classifies deformity by anatomic site and subclassifies deformities by geometry of deformity and etiology of deformity (Table 1)(Fig 1). The anatomic site and the type of deformity affect choice of implant, implant sizing and positioning, and need for corrective osteotomy. The diagnosis may affect bone metabolism, acetabular structure, or other systemic issues relevant to an arthroplasty. Certain diagnoses such as developmental hip dysplasia and Paget's disease are associated with typical anatomic deformities whereas others such as deformities after fracture have no typical pattern.

TABLE 1

TABLE 1

Fig 1

Fig 1

Femoral deformity can occur at the greater trochanteric level, femoral neck level, metaphyseal level, and diaphyseal level. At each level, the deformity can be subcategorized as angular (varus, valgus, flexion, extension), translational (medial, lateral, anterior, posterior), torsional (increased or decreased femoral anteversion), or an abnormality of size (markedly smaller or larger bone than usual).

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SURGICAL TECHNIQUES TO TREAT FEMORAL DEFORMITY

General Principles of Treatment

When deformity of the femur is recognized, careful preoperative planning is valuable to assess how the deformity will affect the planned procedure. The deformity may affect choice of exposure. Some deformities make canal preparation more difficult. Translational deformities especially in the sagittal plane leave the femur at risk for perforation (Fig 2). Intraoperative fluoroscopy or radiographs may aid in safe canal preparation and reduce the risk of femoral perforation. The surgeon must decide how much variation from neutral femoral component alignment is acceptable before resorting to osteotomy. Deformities influence choice of implant geometry and choice of implant fixation. Patients with certain deformities will require special implants and occasionally may need custom implants. Patients with more severe deformities may require femoral osteotomy. Finally, the surgeon must consider how treating the specific deformity will affect knee alignment, leg length, and hip biomechanics.

Fig 2

Fig 2

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Treatment Based on Level of Deformity

Deformities of the Greater Trochanter

The two most common problematic deformities of the greater trochanter that affect total hip arthroplasty are a trochanter that overhangs the femoral canal and a high-riding trochanter. An overhanging trochanter makes access to the femoral canal difficult, leaves the trochanter at risk for fracture, and may lead to varus position of the femoral implant. The primary problems posed by a high-riding trochanter include potential for impingement of the trochanter on the pelvis (leading to posterior hip instability in flexion and internal rotation of the hip), and decreased abductor power attributable to proximal position of abductor attachments. When these deformities are marked, a trochanteric osteotomy can be used to approach the hip, thereby allowing unimpeded access to the femoral canal and/or correction of the trochanteric position (by advancement) at the completion of the total hip arthroplasty.

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Femoral Neck Level Deformities

The most common femoral neck deformities that influence total hip arthroplasty are increased neck varus, increased valgus, or torsional deformity (excessive or insufficient femoral neck anteversion).

Varus Femoral Neck: Treatment depends on whether the deformity is unilateral or bilateral; hence, whether the surgeon wishes to gain limb length or maintain limb length. If the deformity is unilateral, the limb typically is short and the surgeon wishes to gain limb length; standard implants usually can be used but caution must be exercised to avoid excessive lengthening that might lead to nerve palsy. If the deformity is bilateral and the surgeon wishes to maintain leg lengths near equal, extra offset femoral stems allow the surgeon to approximate the anatomy, restore the femoral offset, restore abductor tension, and maintain leg lengths nearer to equal.

Valgus Femoral Neck: A valgus femoral neck poses special problems because it may preclude use of standard femoral components placed in standard neutral alignment. For patients with a more markedly valgus femoral neck, modified implants, either cemented or uncemented, that have a reduced medial metaphyseal flare are helpful. These implants allow neutral femoral component alignment despite valgus femoral neck deformity.

Torsional Femoral Neck Deformities: Most mild variations of femoral neck version can be compensated for as the femur is prepared. Larger deformities are more problematic: matching the patient's version with the implant can lead to inadequate hip motion (excessive anteversion of the stem can reduce external rotation) or lead to hip instability (excessive anteversion can cause anterior instability; insufficient anteversion can cause posterior instability). Thus marked versional deformities require the surgeon to use special techniques to avoid these problems. The surgeon may use a standard implant placed in markedly different version than the patient's femoral neck. This is easiest with a cemented implant or an extensively porous-coated, distally-fixed uncemented implant and least practical with a metaphyseal-filling uncemented implant. A second method is to use special implants, usually uncemented. Some modular implants allow the surgeon to adjust implant femoral neck anteversion separate from femoral implant position in the canal. Alternatively, the surgeon also may choose monoblock implants with built-in anteverted necks to compensate for insufficient femoral neck anteversion and may use an implant with a retroverted neck (for example, by using a stem with an anteverted neck designed for the opposite side: that is, a left implant for a right femur) to compensate for excessive femoral neck anteversion. The final method of treating a patient with a severe torsional deformity is derotational femoral osteotomy, usually at the subtrochanteric level9(Fig 3).

Fig 3A

Fig 3A

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Metaphyseal Level Deformities

Metaphyseal deformities arise for many reasons and can be of many geometries. Severe metaphyseal deformities require changes in surgical technique. Nevertheless, either cemented or uncemented implants can be used successfully in many patients. If cemented implants are used, careful preoperative templating allows choice of implant geometry and size that provide optimal alignment and cement mantle despite the deformity (Fig 4). If uncemented implants are used, the deformity can be bypassed and ignored with implants designed for diaphyseal fixation (Fig 5). Uncemented proximally porous-coated monoblock metaphyseal-filling implants can be difficult to use in some metaphyseal deformities, because getting a good metaphyseal fit and fill may be compromised by abnormal metaphyseal geometry. Modular implants can be particularly useful for metaphyseal deformities: these implants allow precise matching of the implant to an abnormal femoral metaphysis with an off-the-shelf implant. Custom or special implants also may facilitate treatment of some deformities.

Fig 4A

Fig 4A

Fig 5A

Fig 5A

Severe metaphyseal deformities may require osteotomy, but osteotomy should be considered with care in this region. Osteotomy of the metaphysis (unlike a subtrochanteric osteotomy) leads to a small proximal bony fragment. A small proximal fragment can be difficult to fix adequately, and is at risk for fracture or devascularization (Fig 6).

Fig 6A

Fig 6A

Finally, some severe deformities of the upper metaphysis and femoral neck may be treated by resection of part of the involved segment of medial bone and placement of a calcar replacement implant.

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Diaphyseal Level Deformities

Deformities in the diaphysis of the femur can have a profound effect on implant alignment. For the purposes of hip arthroplasty, some distal diaphyseal femoral deformities can be ignored, and sometimes choosing a shorter femoral implant allows the surgeon to avoid the deformity. However, if the deformity is in the region encompassed by the femoral implant, it often mandates a change in technique. Moderate deformities can be treated using cemented implants positioned to compensate for the deformity. To ensure an adequate circumferential cement mantle, smaller than expected implants may be needed. Osteotomy is needed for more severe deformities at this level (Fig 7). When osteotomy is performed, the surgeon can use either a cemented or uncemented implant. Because preventing cement from extruding into the osteotomy site is difficult, most surgeons prefer uncemented implants when possible. Extensively porous-coated implants or proximally porous-coated implants with distal flutes work well for this purpose. Ideally, stable fixation of the osteotomy is achieved with the femoral implant alone. Long-stemmed implants are needed for osteotomies below the subtrochanteric level. The shape of the osteotomy can be transverse, oblique, or a step-cut.9,14,15,17,19 When excellent fixation of the proximal and distal fragments with the implant can be achieved, a transverse osteotomy usually is sufficient and is technically easiest to perform, although it provides less inherent rotational stability. Adjunctive fixation of the osteotomy often is not necessary but can be provided with plates or strut grafts if needed. On occasion, a diaphyseal deformity is best treated in two stages; that is, correction of the deformity followed by total hip arthroplasty after osteotomy healing.

Fig 7A

Fig 7A

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OUTCOMES

To the author's knowledge, there are few articles that discuss total hip arthroplasty in association with proximal femoral deformity in a comprehensive, yet generic, manner.16 Studies are available on total hip arthroplasty for specific diagnoses that often are associated with deformity, but they include all patients with specific diagnoses-those with and those without deformity.1,6,7,10-13 Studies regarding femoral osteotomy in association with total hip arthroplasty also are available.8,9,14,15,17,19 Those studies selectively provide information on patients with deformities severe enough to warrant osteotomy.

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Clinical Results

Clinical results of total hip arthroplasty are compromised if femoral deformity leads to (1) poorer pain relief; (2) poorer hip mechanics and limp; (3) poorer implant durability; or (4) increased complications. Studies on total hip arthroplasty for failed fixation of intertrochanteric hip fractures have shown lower hip scores than the hip scores typically associated with primary total hip arthroplasty.10,12 However, it is uncertain whether the poorer scores in this patient population are attributable to residual femoral deformity associated with the fracture or attributable to age or other factors in this specific patient population.10 Patients treated with total hip arthroplasty after intertrochanteric osteotomy have mostly favorable clinical results.1,7 A number of studies have reported results of total hip arthroplasty for developmental dysplasia2: most show total hip arthroplasty markedly improves hip function but that some patients have a residual limp. From the current literature, it is not possible to delineate the reason(s) some patients have a recurrent limp: probably residual femoral deformity, associated acetabular abnormalities, and associated muscle abnormalities all play a role.

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Effect on Durability of Fixation

Proximal femoral deformity can compromise implant fixation, whether cemented or uncemented implants are used. Cemented implant fixation can be compromised if deformity leads to poor implant alignment, a poor cement mantle, poor cement technique or a poor bone-cement interface. Patients with femoral deformity also may have sclerotic bone (that can lead to poorer cement interdigitation with bone) caused by previous fracture, osteotomy, or disease processes like Paget's disease. The literature suggests, but does not prove, that deformity can compromise long-term cemented implant durability.7,11,13 In 305 hips treated with cemented total hip arthroplasty after intertrochanteric osteotomy at the Mayo Clinic, Ferguson et al7 found a higher rate of revision surgery than in a comparable series of cemented total hip arthroplasty in the general patient population from the same institution. McDonald and Sim11 compared the long-term results of 80 cemented hip replacements in patients with Paget's disease (48 with femoral involvement) and found a higher rate of revision surgery for aseptic loosening at 10 years than in 7,222 total hip arthroplasties in patients without Paget's disease. Merkow et al13 also identified a higher rate of femoral loosening in patients with Paget's disease than reported in most other series and thought that problems with femoral implant alignment and cement technique might have contributed. In each of these series, residual femoral deformity is only one of several factors including patient demographics and underlying disease processes that may have affected implant durability.

Uncemented implants also may be at risk for loosening in patients with femoral deformity primarily because deformity can compromise the initial fit and fixation of the prosthesis to bone. There are as yet insufficient data to evaluate the effect femoral deformity has on reliability and durability of uncemented femoral fixation.

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Complications

Most series of total hip arthroplasty in patient populations with femoral deformity report a higher incidence of complications. The most frequent complications related specifically to femoral deformity are femoral fracture and femoral perforation during canal preparation. For cemented total hip arthroplasty after intertrochanteric osteotomy, Ferguson et al7 reported femoral fracture or perforation in seven of 307 hips and Benke et al1 reported a fracture in three of 105 hips. In a series of total hip arthroplasties for failed fixation of an intertrochanteric hip fracture, Mehlhoff et al12 reported one canal perforation and one fracture; the authors thought both complications were related to residual femoral deformity. Paavilainen et al15 reported one perforation and one fracture in 54 uncemented hip replacements in patients with developmental dysplasia of the hip who were not treated with osteotomy.

Patients with proximal femoral deformity also may be at increased risk for dislocation because of bony impingement of the femur against the pelvis. Mehlhoff et al12 reported dislocation in three of 13 hips after total hip arthroplasty for treatment of a failed intertrochanteric hip fracture. Other factors such as patient age and abductor problems also may have contributed to dislocations in this group of patients.

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Osteotomy in Association With Total Hip Arthroplasty

Several studies report on total hip arthroplasty with concomitant osteotomy for femoral deformity.4,9,15,17 In a series of 20 primary total hip arthroplasties done for patients with various diagnoses who were treated with total hip arthroplasty and concomitant femoral osteotomy, Papagelopoulos et al17 reported Harris hip scores improved from 51 to 77 points in unrevised hips. Complications included intraoperative fracture in four hips and osteotomy nonunion in three. Paavilainen et al15 reported on 46 shortening osteotomies of different types used during total hip arthroplasty for patients with developmental hip dysplasia: there were two femoral fractures, one femoral fragment nonunion, and two postoperative dislocations. Holtgrewe and Hungerford9 reported three osteotomies in patients undergoing primary total hip arthroplasty. After surgery the mean Harris hip score was 94 points and all osteotomies healed. DeCoster et al4 reported on three biplanar osteotomies done during total hip arthroplasty after previous femoral osteotomy; all osteotomies healed.

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DISCUSSION

The purposes of the current study are to: (1) review the technical challenges posed by femoral deformity during total hip arthroplasty; (2) develop a useful method of classifying femoral deformities; (3) examine methods available to perform total hip arthroplasty in the presence of deformity; and (4) discuss results of total hip arthroplasty in patient populations with femoral deformity.

Femoral deformities encountered during total hip arthroplasty range from mild to severe, can occur at any level of the femur, and arise from numerous diagnoses. A classification scheme was developed that divides femoral deformities according to anatomic level and subcategorizes them by deformity geometry and etiology. The classification is designed to be rational, practical, and user friendly. The anatomic site of deformity most influences technical challenges posed by the deformity and the geometry and etiology of the deformity have an effect on treatment methods. The classification scheme proposed in this paper is designed to be applicable to a broad spectrum of femoral deformities. Other femoral classifications also are available but have a different emphasis. The American Academy of Orthopaedic Surgeons system focuses on bone loss rather than deformity and is designed especially for patients undergoing revision hip surgery.3 Other classification schemes are designed to subcategorize patients with a specific diagnosis such as developmental hip dysplasia2,5 and are less applicable to the generic subject of femoral deformity.

The classification method proposed in this article is designed specifically to aid in analyzing the technical problems posed by specific deformities and to provide a framework for possible solutions. Thus, greater trochanteric deformities typically cause problems with exposure and hip biomechanics and can be treated with trochanteric osteotomy. Femoral neck deformities can affect implant alignment and rotation and usually can be treated by using implants that compensate for altered femoral neck anatomy. Metaphyseal deformities have a marked effect on implant and fixation options. Metaphyseal deformities can be treated with femoral implants that bypass the deformity, require resection of the deformity or with special modular or nonmodular implants tailored to fit the deformity. Diaphyseal defects can have an important impact on implant alignment. At times a short implant can be used that ends proximal to the deformity; however, many patients with major diaphyseal deformities require femoral osteotomy.

Femoral deformity is recognized to increase the technical difficulty of an arthroplasty and to increase risk of many intraoperative complications, including femoral fracture and femoral perforation. There are few studies regarding the generic subject of hip arthroplasty in patients with femoral deformity,16 but series on patients with Paget's disease,11,13 or previous femoral osteotomies7-patient groups with a higher number of patients with femoral deformity-suggest deformities may compromise the quality of femoral reconstruction in some cases and result in poorer functional results and poorer long-term arthroplasty durability.

Treatment of the patient with a femoral deformity requires judgment. Efforts to normalize hip anatomy with osteotomy or special implants are esthetically appealing and major residual, uncorrected deformities may have adverse biomechanical consequences. At the same time, the surgeon must take into account the significant risks associated with elaborate reconstructions of the femur. As a general guideline, older, sicker, patients with lower physical demands may be better treated with simpler operations that restore hip anatomy less completely, whereas younger more active patients may be better treated by more complete and anatomic reconstruction at the time of the primary total hip arthroplasty. Improved implants and improved operative techniques hopefully will improve the surgeon's ability to treat these complex problems successfully and with a minimum of complications.

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Acknowledgment

The author thanks Miguel E. Cabanela, MD for contributing some case examples used as figures in this article.

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References

1. Benke GJ, Baker AS, Dounis E: Total hip replacement after upper femoral osteotomy: A clinical review. J Bone Joint Surg 64B:570-571, 1982.
2. Crowe JF, Mani VJ, Ranawat CS: Total hip replacement in congenital dislocations and dysplasia of the hip. J Bone Joint Surg 61A:15-23, 1979.
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