By Thomas K. Fehring, MD
In total hip arthroplasty, the ideal femoral stem is easy to insert, has reproducible results, and is able to be used in most revision situations. While no stem is appropriate for all revisions, extensively coated stems are appropriate for the management of types-I, II, and III femoral defects in situations in which isthmic bone is available for fixation1. The use of this stem is not appropriate in a type-IV defect in which the metaphysis is nonsupportive and the diaphysis is not intact due to severe bone loss. In this situation, reliable distal fixation with an extensively coated stem is not possible and other alternatives should be sought. For most revisions, however, the workhorse for femoral revision has been the monoblock extensively coated stem.
To optimize results, careful preoperative planning should be done to ensure 4 to 6 cm of intimate endosteal contact or so-called scratch fit. It is important to template the lateral as well as the anteroposterior radiograph to assess femoral bow. Proper surgical technique is also important in achieving stable fixation in a revision situation. After implant removal, reaming proceeds until a tight fit over a 4 to 6-cm diaphyseal segment is obtained. Radiographs made intraoperatively will help confirm that the alignment and size of the reamed area are appropriate and that all of the cement has been completely removed. When a straight stem is used, the femur should be underreamed by 0.5 mm. When a curved stem is used, reaming is dependent on the bone quality of the femur and on the length of the curved stem. Before implantation of a straight stem, a reamer of the same diameter as the final implant should be inserted to determine the amount of scratch fit that will occur. The reamer should "catch" or "hang up" at least 4 to 6 cm above the predetermined seating level. Stem impaction should be slow and methodical, and the implant should advance with each blow. The surgeon should pause periodically to let the bone accommodate to the implant. Full impaction can take up to five minutes.
Excellent results have been reported with use of this type of implant and this surgical technique2-4. Nonmodular extensively coated stems must be considered the gold standard for femoral revision of types-I, II, and III femoral defects.
Evidence-Based Data for Stem Selection
By C. Lowry Barnes, MD
Introduction
There has been a shift to the use of uncemented femoral components in primary total hip arthroplasty. Many designs have been reported to be associated with excellent short-term and long-term results1.
Methods
A number of studies (although not prospective randomized studies) reporting the efficacy of these implants were analyzed.
Results
In one series by Belmont et al., excellent long-term results were reported2. The initial series of 223 total hip arthroplasties in which the fully coated anatomic medullary locking (AML) stem (DePuy, Warsaw, Indiana) was used showed a survivorship of 97.8% with revision for any reason as the end point. Lombardi et al. reviewed 2000 consecutive tapered titanium uncemented stems3. With aseptic loosening as an end point, survivorship was 99.5% at ten years and 99.1% at fifteen years. Capello et al. also showed excellent long-term results with use of a hydroxyapatite proximal coating4. Additionally, proximal femoral stress transfer was noted. Min et al.5 reviewed ninety-eight cementless tapered-wedge stems and found no loosening at a mean follow-up time of 7.7 years. Of these ninety-eight stems, 63% were in a neutral position, 21% were in valgus alignment, and 16% were in varus alignment. There were no significant differences among the patients with regard to Harris hip scores or thigh pain. It appeared that varus positioning did not lead to poor results in this series.
Summary
It appears from a review of the literature that many uncemented designs offer excellent short-term, midterm, and long-term results. Surgeons may feel fairly confident that, with use of modern technology, a well-placed uncemented femoral component will have an excellent chance of attaining long-term survival.
Huo MH, Parvizi J, Bal BS, Mont MA; Council of Musculoskeletal Specialty Societies (COMSS) of the American Academy of Orthopaedic Surgeons. What's new in total hip arthroplasty. J Bone Joint Surg Am.2008;90:2043-55.902043
2008
[PubMed][CrossRef]
Belmont PJ Jr, Powers CC, Beykirch SE, Hopper RH Jr, Engh CA Jr, Engh CA. Results of the anatomic medullary locking total hip arthroplasty at a minimum of twenty years. A concise follow-up of previous reports. J Bone Joint Surg Am.2008;90:1524-30.901524
2008
[CrossRef]
Lombardi AV Jr, Berend KR, Mallory TH, Skeels MD, Adams JB. Survivorship of 2000 tapered titanium porous plasma-sprayed femoral components. Clin Orthop Relat Res.2009;467:146-54.467146
2009
[CrossRef]
Capello WN, D'Antonio JA, Jaffe WL, Geesink RG, Manley MT, Feinberg JR. Hydroxyapatite-coated femoral components. 15-year minimum followup. Clin Orthop Relat Res.2006;453:75-80.45375
2006
[CrossRef]
Min BW, Song KS, Bae KC, Cho CH, Kang CH, Kim SY. The effect of stem alignment on results of total hip arthroplasty with a cementless tapered-wedge femoral component. J Arthroplasty.2008;23:418-23.23418
2008
[CrossRef]