Diaphyseal Fixation: Providing Durable Femoral Revisions with Extensively Porous Coated Stems

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Chapter synopsis

Most femoral revisions involve weak or sclerotic metaphyseal host bone. Designed to bypass defective proximal bone, extensively porous coated stems provide long-term durability in all but the most severe total hip arthroplasty revision cases. These stems achieve predictable biologic distal fixation through intimate fit and fill in diaphyseal bone. They do not, however, ensure predictable results in the most extensive cases of metadiaphyseal damage. This chapter provides a systematic approach for the use of press-fit stems in revision arthroplasty. It also discusses surgical points that are key to a successful outcome.

Important points:

1

Extensively porous coated components are indicated for femoral revisions ranging from minimal bone loss to significant metadiaphyseal loss and endosteal diameters less than 19 mm.
2

Alternative methods are recommended for femurs with significant metadiaphyseal damage and endosteal diameters greater than 19 mm.
3

Successful outcomes depend on complete extraction of the implant and cement while incurring minimal bone loss, axial and rotational stability with the new implant, reproduction of normal hip biomechanics, and intimate contact between the stem and host bone.
4

Factors contributing to a successful outcome include proper preplanning and templating; optimal component selection, considering length, shape, and diameter; adequate exposure; and precise reaming.

Clinical/surgical pearls:

1

Long, curved stems should be used when a straight stem may cause perforation.
2

An extended trochanteric osteotomy is indicated when component removal is obstructed, cement or previous components are well fixed, or marked varus remodeling is present.
3

Precise reaming over 4 to 6 cm is critical because it provides the basis for intimate contact between host bone and stem.
4

Intraoperative radiographs may provide important spot checks throughout canal preparation, trialing, and insertion.

Clinical/surgical pitfalls:

1

Proximal remodeling can impede stem insertion or misdirect a stem. Problems can be avoided by identifying remodeling preoperatively and paying close attention to reaming.
2

Distal anterior cortical impingement can lead to anterior perforation or cortical compromise. This problem can be deterred with curved stems.

INTRODUCTION

The incidence of femoral stem revisions, particularly for failed cemented total hip arthroplasties (THAs), increased so dramatically during the 1980s that one author referred to the number of failed hip replacements as “staggering.” At the time proper management of femoral revisions was of considerable concern in the orthopedic community. Femoral revisions often involved hard-to-remove cement as well as weak or sclerotic host bone with metaphyseal remodeling, an environment that set the stage for a high incidence of complications such as dislocation and sepsis. Moreover, deficient bone stock prone to fracture made the removal of failed components difficult without causing further damage to the femoral cortex and the greater trochanter. The greatest dilemma lay, however, in ensuring secure fixation and load-bearing stability of the new component. Deficient proximal bone deterred long-term fixation with cemented components. Moreover, large clinical series of cemented revisions have loosening rates from 25% to 29% at mid- and long-term follow-up. Proximal porous coated implants have not provided reliable fixation or stability, as seen by survivorship rates as low as 58% at 8-year follow-up.

Fortunately, femoral revisions no longer pose the dilemma they once did. Current procedures reflect 2 decades of clinical follow-up studies and the development of improved surgical procedures and revision implants. The introduction of the extended trochanteric osteotomy and the trochanteric slide osteotomy has eased the removal of cement and well-fixed porous coated stems. Moreover, clinical studies have shown that long-term durability can be reliably provided with extensively porous coated stems in all but the most severe cases of bone loss ( Table 33-1 ). Designed to bypass defective proximal bone, these stems achieve biologic distal fixation through intimate fit and fill in diaphyseal bone. Because the results from cemented components and proximally porous coated revision implants have remained less satisfactory, fully porous coated stems are now considered the gold standard for most femoral revisions .

TABLE 33-1

Results of Femoral Revisions of Varying Severity Using Different Treatments

Author	Component	No. of Hips	Mean Follow-up (yr) (Range)	Results	Bone Quality and Other Issues
Pellicci et al, 1985	Cemented	99	8.1	29% (29 hips) loosening	Nonselective *
Kershaw et al, 1991	Cemented	220	6.3 (2.5–12)	25% loosening rate; 77% survival at 10 yr	Nonselective
Mulroy and Harris 1996	Cemented	43	15.1	26% (9/35) loosening rate	Average age 51 yr
Chandler et al, 1995	Proximally coated with calcar; 22 with structural femoral allograft	52	3	10% failure (6 revisions)	Severe bone loss and complications; mean previous THA was 3
Berry et al, 1995	Proximally coated	375	4.7	16.8% repeat revision rate for aseptic loosening or osteolysis; 58% survivorship at 8 yr	Nonselective
Woolson and Delancey, 1995	Proximal stem with fiber-mesh pads	25	5.5 (4–8)	20% (5) revised; 48% subsidence	Nonselective
Weeden et al, 2002	Fully coated	170	14.2 (11–16)	Mechanical failure rate 4.1% (7 hips unstable, 6 repeat revised)	21% failure rate among type IIIB cases
Hamilton et al, 2007	Fully coated	905	5.8 ± 5.5 (0–22.8)	95.9% survivorship; 20/905 repeat revisions; no revisions after 10 yr	Nonselective
Krishnamurthy et al, 1997	Fully coated	297	8.3 (5–14)	1.7% repeat revision; aseptic loosening; 2.4% mechanical failure	Nonselective
Engh et al, 2002	Fully coated	35	13.3 (10 min.)	Aseptic loosening 15% (4/26); survivorship 89%	Extensive bone loss >10 cm below lesser trochanter
Nadaud et al, 2005	Fully coated, no allograft	46	6.4 (2–12)	4% (3) revisions; 2% (1) unstable	Extensive proximal defects

* Nonselective refers to all cases, generally moderate to severe bone loss.

Other changes that have contributed to the predictability of femoral revisions include more accurate preoperative techniques, refined treatment algorithms, and a greater selection of revision components. Revision systems provide straight and curved stems that feature multiple diameters, making treatment for individual cases more flexible, improving the likelihood of initial fixation, and reducing the risk of intraoperative femoral perforation. Although femoral revisions remain technically demanding, procedural roadmaps now lead to excellent results and higher patient satisfaction.

INDICATIONS AND CONTRAINDICATIONS: A SYSTEMATIC APPROACH

The indications for a femoral revision are aseptic loosening, recurrent instability from a malpositioned component, stem breakage, delayed infection, and the need for improved acetabular exposure during an acetabular revision. Relative indications include progressive distal femoral osteolysis or revision of a femoral implant with a poor track record during an acetabular revision.

Most femoral revisions can be successfully managed with extensively porous coated stems, but in specific instances other reconstruction options can or should be considered. The determining factor in selecting a reconstruction method is the quality of the host bone. An effective way to approach this decision is by using preoperative and intraoperative radiographs with the guidance of a bone classification system. The Paprosky classification system, presented in Table 33-2 , associates optimal treatment with the extent and location of femoral bone loss.

TABLE 33-2

Paprosky Classification System: Treatment Algorithm by Type of Defect

Type	Condition of Femur	Effective Treatments
I	Minimal bone loss, condition similar to primary THA	The gold standard: 6- to 8-inch extensively porous coated stem; implant similar to one used in index THA; cemented or proximally porous coated stems
II	Metaphyseal damage, minimal diaphyseal loss	6- to 8-inch extensively porous coated stems
IIIA	Significant proximal and metadiaphyseal bone loss, minimum 4-cm scratch fit obtainable at isthmus	8- or 10-inch canal-filling, extensively porous coated curved stems
IIIB	Extensive metaphyseal and diaphyseal bone loss, less than 4 cm available for scratch fit; must be obtained more distally	If endosteal diameter <19 mm, 9- or 10-inch extensively porous coated curved stem
IIIB		If endosteal diameter >19 mm, impaction bone grafting, allograft prosthetic composites, modular tapered stem
IV	Extensive metadiaphyseal damage with thin cortices and widened canals	Younger patients: impaction bone grafting or allograft prosthetic composites Older patients: modular tapered stem
		Low-demand patients requiring minimal operative time: long-stemmed cemented component or tumor prosthesis