Christian P. Christensen and Cale A. Jacobs
DEFINITION
A fluted stem can be used to revise a loose femoral implant with one or more of the following:
Cavitary or segmental defects
Femoral malalignment
Periprosthetic fracture
Stress-shielded or sclerotic bone secondary to prior fracture fixation
ANATOMY
The anatomic structures most relevant to revision arthroplasty in patients with femoral bone loss are the proximal aspect of the femur and the femoral shaft, as well as the surrounding soft tissues.
The proximal aspect of the femur is composed of the head, the neck, and the greater and lesser trochanters.
Important soft tissues include the iliotibial band and the tensor fascia lata, the gluteal muscles, the short external rotators and the joint capsule, the iliopsoas, and the quadriceps musculature (FIG 1A).
Vascular and neurologic structures include the femoral artery and vein and the sciatic nerve.
The AAOS classification is used to describe femoral bone loss5 (Table 1; FIG 1B).
PATHOGENESIS
Normal wear of the acetabular liner produces particulate polyethylene debris. The presence of this debris increases over time, leading to a macrophage response that results in periprosthetic bone loss. Aseptic loosening may occur secondary to this particle-induced periprosthetic osteolysis.
This mode of failure is the primary reason for revision hip arthroplasty.
NATURAL HISTORY
The implant loosens as a result of progressive bone loss.
The loose implant leads to further bone loss.
Cortical thinning frequently occurs.
Angular deformation (often varus) results.
Progressive cortical thinning may result in fracture.
PATIENT HISTORY AND PHYSICAL FINDINGS
Patient history should involve an in-depth conversation related to the location and type of pain that the patient is experiencing (Table 2).
A complete medical and surgical history is necessary to document all information pertaining to the index procedure, including the initial diagnosis, date of surgery, complete operative notes with detailed descriptions of the components used, and the dates of any postoperative complication.
Other systemic medical conditions and recent surgical or medical treatments should also be documented to ensure that the patient can tolerate and will benefit from hip revision.
The physical examination should include the following:
Gait evaluation. Painful total hip arthroplasty (THA) may result in shortened stance phase or stride length, or abnormal pelvic rotation. A Trendelenburg gait or abductor lurch may raise concern regarding hip abductor function that can limit success of revision.
Trendelenburg test is considered positive if pelvis on the nonstance side moves into a position of relative adduction; this may indicate abductor weakness or trochanteric nonunion.
Range of motion should be pain-free throughout range. Pain suggests mechanical dysfunction. A palpable or audible click or clunk may indicate head subluxation or a loose component.
Hip abductor strength may indicate abductor weakness, trochanteric bursitis, abductor avulsion, trochanter fracture, or a loose femoral component.
A slight difference of less than 1 cm in true leg length is considered normal, though it may cause symptoms in some patients. Progressive leg-length discrepancy suggests implant subsidence.
Apparent leg length may be affected by atrophy, obesity, or asymmetric positioning of the legs. Values may indicate abductor or adductor contractures, or pelvic obliquity due to scoliosis.
Evaluate the skin around the hip to gauge the risk for infection and to assess its ability to heal postoperatively.
A careful neurologic and vascular evaluation should be performed to rule out extrinsic etiology for hip or thigh discomfort. It will also serve as a baseline for the postoperative exam.
Bone
Careful evaluation of the preoperative radiogaphs is imperative to identify bony deficiencies. The greater trochanter is commonly sclerotic and fragile and is easy to fracture. Nonunion can result despite rigid fixation of intraoperative fractures. Hardware over the trochanter can result in a painful bursitis.
Proximal bone deficiencies around the lesser trochanter can be so profound that a fluted stem is not suitable for femoral revision and a fully porous coated stem for diaphyseal fixation is preferable.
Diaphyseal defects in the femur are important to identify since it is critical for the stem to bypass cortical deficiencies by at least two cortical diameters.
Soft Tissue
The hip abductors require careful preoperative evaluation and intraoperative inspection since they are critical to postoperative hip stability and gait. Prior hip surgery may result in a weakened gluteus medius.
FIG 1 • A. Femoral anatomy. B. Level of femoral defect.
The posterior hip joint capsule and the short external rotators are often scarred together. They need to be tagged and preserved for later repair if a posterior approach to the hip has been used. Many times, the anterior joint capsule is scarred and must be completely resected to correct offset and leglength abnormalities.
Polyethylene debris may be located in the iliopsoas sheath and should be eliminated during the hip revision. The iliopsoas may require anterior release to correct leg length and preoperative flexion contractures.
The gluteal sling refers to the insertion of the gluteus maximus on the posterolateral border of the proximal femoral shaft. The 5-cm insertion frequently needs to be partially or completely released to gain exposure or correct leg length. It should be repaired to a tendon stump at the end of the surgery.
The vastus lateralis may be elevated from its posterior border to give the surgeon access to the femoral shaft for correction of bony deformity, fracture repair, and cable placement.
Neurovascular Structures
The sciatic nerve is frequently encased in scar during revision hip surgery. It is located 1 to 2 cm posterior to the posterior rim of the acetabulum and should not be exposed routinely during revision hip surgery if the surgeon is careful with retractor placement and positions the leg appropriately during hip exposure.
If the surgeon needs to expose the nerve, it is best identified posterior to the gluteal sling and followed proximally toward the hip joint.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Plain radiographs should be evaluated for radiolucencies adjacent to the implants, acetabular or femoral component migration, heterotropic ossification, bony remodeling, osteolysis and bone loss, and stress shielding. Comparison of the most recent radiograph with the oldest postoperative one is the most reliable way to document implant migration.
Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels should be assessed before any revision procedure to rule out infection. In a series of 202 revision arthroplasties, all patients with deep sepsis had either an ESR above 30 mm or a CRP above 10 mg/L.10
Intra-articular preoperative aspiration and lidocaine injection should also be performed if either the ESR or CRP is elevated or if the prior hip arthroplasty failed within 5 years of surgery. The aspirate should be assessed for cell count with a differential as well as culture and sensitivity. Also, pain relief with lidocaine injection indicates an intra-articular etiology, further supporting need for revision arthroplasty.
A technetium-99mHDP bone scan may demonstrate increased bony metabolism that can represent loosening, increased stress, or infection. A gallium scan and/or an indium scan may be performed to detect infection in THA.2These tests are rarely used.
DIFFERENTIAL DIAGNOSIS
Loosening (septic or aseptic)
Periprosthetic fracture
Recurrent instability
Impingement of femoral neck and acetabular liner
Leg-length discrepancy
Trochanteric bursitis
Lumbosacral pathology
NONOPERATIVE MANAGEMENT
Nonoperative management may be inappropriate if the cause for revision is progressive and will not improve with time.
Serial radiographs can be used to follow a loose femoral stem if infection has been ruled out and no significant bone loss is occurring.
Assistive ambulatory devices can be used.
Bisphosphonates may improve bone stock, although this has not been proved in humans.
Suppressive antibiotics for septic loosening may help control pain or progressive infection in a nonoperative patient.
Hip pain due to bursitis may be improved with nonoperative treatments, including physical therapy, nonsteroidal anti-inflammatory drugs, or injections.
SURGICAL MANAGEMENT
Once infection has been ruled out (both preoperatively and intraoperatively), revision arthroplasty may be performed with the use of a modular system with a fluted femoral stem.
Most fluted stems have a proximal sleeve of varying length that allows for optimal fit and fill of the proximal femur. The flutes increase distal fill and increase resistance to rotational stress.
Preoperative Planning
Template using recent preoperative anteroposterior (AP) and lateral radiographs (Table 3). AP and lateral radiographs of the femoral shaft are required if long, extra-long, or extraextra-long stems are going to be used.
A pathologist must be available to look at the frozen section.
Materials needed include previous surgery notes, possible polyethylene liner exchange options, revision acetabular components (even if the socket looks stable), fully porous coated femoral component if proximal fixation is insufficient for use of a fluted stem, particulate and structural allografts, and cables.
Positioning
Following application of general anesthesia and insertion of a Foley catheter, the patient should be positioned on a pegboard in the lateral decubitus position with bony prominences padded.
Perfect positional stability of the patient's pelvis is ensured before preparation and draping.
Wide skin preparation is performed, with access to the distal femur.
Approach
Posterolateral/posterior approach
Anterolateral/Hardinge approach
TECHNIQUES
ROUTINE REVISION WITHOUT DIAPHYSEAL DEFECT
Site Preparation
Use trochanteric osteotomy/slide if needed for exposure or for cement/implant removal.
Avoid extended trochanteric osteotomy, since this will compromise proximal fixation.
Carefully assess the proximal femur above the lesser trochanter.
Perform straight reaming of the proximal diaphysis until cortical chatter is achieved. Reaming should be done to a depth determined by comparing a line on the reamer to the tip of the trochanter1 (TECH FIG 1A).
The diameter of the last reamer will determine the size of the implant and reflects the diameter of the distal end of the implant.
Prepare the metaphysis with the conical reamers that correspond with the last straight reamer. Cone reaming should stop whenever contact with structurally sound cortical bone is obtained. A small cortical edge should be palpable at the inferior end of the conically reamed bone.
Take care to insert the conical reamer to the level that corresponds to the preoperatively templated level of the upper portion of the sleeve.
If using the S-ROM system, use the calcar miller to prepare the femur for the triangular modular sleeve (TECH FIG 1B).
Implant Placement
Perform trial reduction after placing the trial sleeve and femoral stem to assess version, range of motion, and laxity. The modular system allows complete freedom to vary anteversion regardless of proximal femoral geometry (TECH FIG 2A–D).
Insert sleeve, and then finish by inserting femoral stem (TECH FIG 2E).
TECH FIG 1 • A. Straight reaming of the femur is carried out until contact with diaphysis is obtained. B. Calcar miller that is used for preparation of proximal femur as part of this prosthesis.
TECH FIG 2 • Placement of trial implants. The sleeve is inserted first (A) until it is completely seated (B). The trial is assembled in the back table in the appropriate version (C) and then inserted into the sleeve (D). E.Insertion of the final component.
ROUTINE REVISION WITH DIAPHYSEAL DEFECT
Plan to bypass the diaphyseal defect by two cortical widths with a long, extra-long, or extra-extra-long bowed stem.
Pass a long guidewire to ensure that there are no holes in the cortical bone.
Flexibly ream until good cortical chatter is achieved in the diaphysis. You must flexibly ream to 1.5 mm greater than the minor diameter of the shaft of the implant (eg, ream to 14.5 mm for an 18 × 13 stem) when using a long, extra-long, or extra-extra-long stem.
Straight ream proximally to the same diameter as the minor diameter of the implant.
Conical and miller reaming is performed in the manner described in the previous section.
Place trial implants.
When inserting the true implants, do not completely seat the proximal sleeve prior to placing the stem when using a long, extra-long, or extra-extra-long sleeve. The sleeve should be inserted to within 1 to 2 mm of the intended location. The stem should then be inserted through the sleeve and it should engage the sleeve as they are finally seated together.
The bowed implant has 15 degrees of anteversion built into it. The surgeon can actually place up to 25 to 30 degrees of anteversion on the femoral stem if necessary.
Struts are usually not needed, though they can be used to improve bone stock.
EXTENDED TROCHANTERIC OSTEOTOMY NEEDED OR DIAPHYSEAL OSTEOTOMY OR OPEN REDUCTION AND INTERNAL FIXATION OF A PERIPROSTHETIC FRACTURE DISTAL TO A LOOSE STEM
Remove stem and cement if necessary through the top of the femur or through the fracture site if present.
Perform exposure posterior to the vastus lateralis to expose the femoral shaft.
Perform the osteotomy or expose the fracture and place a cable around the distal diaphyseal fragment.
Straight ream or flexibly ream the distal diaphyeal fragment until cortical chatter is noted. The size of the last reamer will dictate the size of the implant.
Use bone clamps to gain control of the proximal segment and then straight ream to the diameter of the last reamer used on the distal fragment. Conical reaming and proximal milling should be performed as described earlier. It may be advisable to place a cable at the level of the sleeve at this point to prevent fracture.
Reduce the proximal fragment to the distal fragment with bone clamps if needed.
Place the trial implant crossing the fracture or osteotomy with the stem.
Reduce the hip and assess leg lengths, offset, and soft tissue tension. Rotational stability will not be obtained at the fracture or osteotomy site at this time, so a true stability examination is not possible.
Place cables around structural allograft and begin to tighten if allograft struts are needed.
Remove trial and place implant. If the implant will not fit in the distal fragment, it may be necessary to ream up 0.5 mm to avoid fracture (TECH FIG 3).
Tighten cables.
Inspect for iatrogenic fracture.
Consider additional bulk allograft.
Perform a gentle stability examination.
Perform routine closure using posterior capsular repair.
Administer antibiotics for 3 days or until cultures are negative.
Brace for 6 to 12 weeks.
Leg lengths are assessed by soft tissue tension, preoperative templating, and comparison with down leg.
TECH FIG 3 • Preoperative and postoperative AP radiographs of a patient with severe proximal deformity that necessitated a cortical osteotomy for insertion of the prosthesis and femoral realignment.
USE OF A FLUTED STEM WITH A PROXIMAL FEMORAL ALLOGRAFT
Choose a large proximal femoral allograft (critical).
Expose the femoral diaphysis by proceeding posterior to the vastus lateralis.
Decide on the level of the graft–host junction and divide the femur at that level. A step cut is not necessary because of the rotational stability of the bowed, slotted stem.
Ream the distal diaphysis line to line with a straight or flexible reamer until cortical chatter is achieved. The last reamer determines the size of the implant.
Place the allograft in a bone vise and prepare the allograft with a flat neck cut followed by straight reaming to 1 to 2 mm larger than the distal diaphysis diameter. Conical reaming and proximal milling then occur on the proximal femoral allograft as previously described.
Make a provisional distal cut on the allograft, leaving it 1 cm long.
Make a longitudinal cut on the proximal native femur to open it up so the allograft can be inserted within it. Do not remove any soft tissue attachments from the native proximal femur.
Perform a trial reduction by placing the trial within the allograft and inserting the distal portion of the stem into the native femoral diaphysis. Attempt to reduce the hip and assess leg lengths. Remove bone from the distal tip of the allograft to equalize leg lengths. Make sure there is good bone contact at the allograft–host bone junction. Also, remove bone from the allograft greater trochanter to allow the native trochanter to be placed in an anatomic position overlying the allograft.
Remove the allograft and stem and roughen the exterior minimally in the areas where the allograft will have contact with host bone.
Remove the stem from the allograft and pulse lavage and dry the interior of the allograft. Pass two cables through the lesser trochanter; these will later be used with a claw to fasten the native greater trochanter.
Downsize the sleeve to allow for a cement mantle and assemble the stem and sleeve on the back table.
Cement the fluted stem and sleeve into the allograft, making sure that all of the cement is wiped off the distal portion of the stem. Keep cement off the distal portion of the allograft to allow complete contact with the host distal femur.
After cement hardening, insert the allograft–stem composite into the native femur. It is rarely necessary to ream the distal femur an additional 0.5 mm to prevent fracture. Rotational stability at the graft–host junction should be complete at this time (TECH FIG 4A).
Use native bone at the graft–host junction to serve as struts. A claw is typically placed on the native trochanter to help fasten the native greater trochanter to the allograft (TECH FIG 4B).
The remainder of the native proximal bone is attached to the allograft with the soft tissue attachments maintained.
Perform a gentle stability examination.
Perform routine closure.
Give antibiotics for 3 days or until cultures are negative.
Brace for 6 to 12 weeks.
Leg lengths are assessed by soft tissue tension, preoperative templating, and comparison with the down leg.
TECH FIG 4 • A. AP radiograph showing use of a fluted stem with proximal femoral allograft. B. Technique used to attach a trochanteric osteotomy using a stabilizing claw.
POSTOPERATIVE CARE
Weight bearing as tolerated in simple cases with standard, straight stems
Knee imobilizer while sleeping to help prevent dislocation
Touchdown weight bearing and bracing for 6 to 12 weeks in complex cases with osteoporosis or if fracture or osteotomy healing is needed
Pharmaceutical and mechanical deep vein thrombosis prophylaxis
Follow cultures.
OUTCOMES
When used for proximal femoral bone loss or other complex revisions, previous authors have reported excellent radiographic and clinical outcomes with the S-ROM system, including no evidence of osteolysis, mean postoperative Harris hip score of 82, and 84% patient satisfaction.3,4
The S-ROM system has been reported to have a 5-year survival rate of 96%, with a 5% rate of mechanical failure.9,11
Inferior outcomes have been associated with the use of large stem diameters.
One study attributed persistent thigh pain to the use of stems greater than 17 mm in diameter.3
A second study reported a significantly increased incidence of stress shielding, as well as a lack of bony ingrowth, with stem diameters greater than 16 mm.11
COMPLICATIONS
Aseptic loosening
Infection
Dislocation
Leg-length discrepancy
Fracture or osteotomy nonunion
Trochanteric fracture
REFERENCES
1. Bolognesi M, Pietrobon R, Clifford P, et al. Comparison of a hydroxyapatite-coated sleeve and a porous-coated sleeve with a modular revision hip stem: a prospective, randomized study. J Bone Joint Surg Am 2004;86A:2720–2725.
2. Bono J, McCarthy J, Thornhill T, et al. Revision Total Hip Arthroplasty. New York: Springer-Verlag, 1999.
3. Chandler H, Ayres D, Tan R, et al. Revision total hip replacement using the S-ROM femoral component. Clin Orthop Rel Res 1995;319:130–140.
4. Cossetto D, McCarthy J, Bono J, et al. Minimum four-year radiographic and clinical evaluation of results following femoral revision surgery with the S-ROM modular hip system. Acta Orthop Belg 1986;62:135–147.
5. D'Antonio J, Capello W, Borden L, et al. Classification and management of acetabular abnormalities in total hip arthroplasty. Clin Orthop Rel Res 1989;243:126–137.
6. Hardcastle P, Nade S. The significance of the Trendelenburg test. J Bone Joint Surg Br 1985;67B:741–746.
7. Kendall F, McCreary E, Provance P. Muscles: Testing and Function. Baltimore: Williams & Wilkins, 1993.
8. Magee D. Orthopedic Physical Assessment. Philadelphia: WB Saunders, 1997.
9. Smith J, Dunn H, Manaster B. Cementless femoral revision arthroplasty: 2- to 5-year results with a modular titanium alloy stem. J Arthroplasty 1997;12:194–201.
10. Spangehl M, Younger A, Masri B, et al. Diagnosis of infection following total hip arthroplasty. AAOS Instr Course Lect 1998;47:285–295.
11. Walter W, Walter W, Zicat B. Clinical and radiographic assessment of a modular cementless ingrowth femoral stem system for revision hip arthroplasty. J Arthroplasty 2006;21:172–178.
12. Wilkins R, Brody I. Lasègue's sign. Arch Neurol 1969;21:219–220.