Total Hip Arthroplasty: The Cemented Stem

Introduction

Debate continues as to the optimum femoral stem fixation in total hip arthroplasty (THA). Early success in survivorship of cemented stems in THA established a track record that continues to rival that of the most successful cementless stems. Despite this success, however, recognition must be given to the skill and art with which successful cemented technique is performed. In the absence of proper technique, optimal outcomes may fail to be realized.

Evolution of Cement Technique

Early use of cement fixation for cemented stems was in existence by the mid 20th century. Implementation of polymethylmethacrylate (PMMA) for use with low friction hip arthroplasty as popularized by Charnley brought full attention to this fixation material on a mass basis. Recognition of the workability of progressively polymerizing cement appealed to surgeons. As knowledge advanced, refinement of cement technique occurred as well. The ideal implant-cement-bone interface is dependent upon cement continuity, elimination of trapped air, or voids, and successful displacement of medullary canal fluid. Finally, the ultimate end point is comprehensive interdigitation of the PMMA and surrounding cancellous bone. Accordingly, femoral cement technique evolved to the current practice of distal canal plugging and canal lavage.^1,2 Further generational advances in cement technique have included canal pressurization, retrograde filling, and use of vacuum-mixed PMMA cement. Recent studies have focused on optimal techniques for enhanced cement pressurization and resultant contact with cancellous surfaces.^3,4

Radiographic Findings

Assessment of the femoral stem cement mantle has been previously described, with most optimal outcome associated with consistent presence of radio-opaque cement uniformly on all sides of the stem, and with a near complete “white-out”.⁵ Less desirable outcomes have been associated with minimal to no cement mantle, contact between the stem and the endosteal canal, and poor stem-canal alignment. Failure has been attributed to excessively thin cement mantle fracture, with associated loosening, and progressive migration. Radiographic evaluation of cement mantle is accomplished with analysis of an anteroposterior radiograph with identified cement mantle areas or “zones”; zone 1 located proximal and lateral, progressing to zone 4 at the tip, and zone 7 at the proximal and medial mantle.⁶ The ideal construct is a uniform cement mantle, with minimal to no voids (small trapped-air spaces), and a uniform loading environment maintained at the cement-bone interface with physiologic loads. Controversy exists as to whether a polished or nonpolished finish on the stems is ideal; this is likely to remain a topic of debate.

Outcomes & Contraindications

Initial success with cemented techniques was tempered by lower survivorship outcomes in patients younger than 50 years of age. Radiolucency, however, previously attributed to cement disease, began to appear also in cementless THAs and was thereafter correctly identified as particle-induced osteolysis. Currently, reported outcomes from Scandinavian registries place survivorship of cemented THA above 90%.⁷ Similarly, recent data of patients with cemented polished stem THA at minimum 10 years’ follow-up showed no revisions necessary.⁸ Data must continue to accumulate with the advent and continued use of successful joint replacement registries worldwide. This sampling of data, however, shows promising results for the cemented stem with modern cement techniques.

Despite promising outcomes and improvements in cement and technique, limitations exist in its implementation. Femora that have previously undergone primary replacement may be poor candidates for cemented fixation due to cortical defects or lack of available cancellous bone for effective cement interdigitation. Further, extensive osteotomy techniques often required for dysplasia or Perthes disease may pose challenges for cemented stems.

Advances

Progress continues in this area. The use of antibiotic-laden cement has provided a promising means of infectious prophylaxis in patients who have previously experienced infection, sepsis, or have co-morbidities that may predispose to infection such as diabetes mellitus or rheumatoid arthritis. Many current cement preparations are available that have pre-mixed antibiotics of various types. Cement is also available in various mixture viscosities. Depending upon the room temperature, humidity, conditions under which mixture occurred, and inclusions, such as antibiotics, cement will polymerize at a variety of rates. This variability should be taken into account, particularly when working with rapidly polymerizing cement, and in unusually warm operating room conditions. Finally, a recent advance that exists in a variety of forms is the stem centralizer, a useful tool that maintains the stem in the center of the canal, thus avoiding excessive varus or valgus placement.

Summary

Aseptic loosening remains a dominant cause for implant failure necessitating revision. Survivability of implants is dependent upon satisfactory, solid fixation between stem and femur; in the case of cemented femur, consistent cement interdigitation is mandatory for successful long-term fixation. The use of modern cement mixing technique, pressurization, and central placement assist in this effort. Though data varies by study, age group, and selection, cementless and cemented techniques likely will continue to co-exist as viable methods of long-term THA.

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References

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