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Clin Orthop Relat Res. 2017 January; 475(1): 193–195.
Published online 2016 October 31. doi:  10.1007/s11999-016-5144-1
PMCID: PMC5174067

CORR Insights®: Nonmodular Tapered Fluted Titanium Stems Osseointegrate Reliably at Short Term in Revision THAs

Marcus R. Streit, MSc, MD, PhDcorresponding author

Where Are We Now?

Good medium-term results for cemented femoral revisions have been shown using third-generation cementing techniques [11] and impaction allografting [10]. As a result, cemented stem revisions remain a useful option for older, less-active patients with extensive metaphyseal and diaphyseal defects and cortical thinning, although others have suggested that cemented revisions are technically demanding, and poor results have also been reported with that approach [2].

We recently learned that cementless tapered titanium femoral stems provide excellent long-term survival in primary THA into the third decade after surgery even in young and high-demanding patients [6, 9, 12]. For that reason, biological implant fixation using uncemented implants is a promising option in femoral revision surgery to achieve durable implant-bone fixation, particularly in young and active patients. When treating patients with femoral revision, the surgeon is often confronted with a sclerotic, expanded, and thinned proximal femoral bone stock. In these cases, successful reconstruction will include distal fixation in the remaining well-preserved femoral diaphysis to bypass the defective proximal bone areas.

In 1987, Heinz Wagner introduced a nonmodular (monoblock), straight, rotationally stable revision stem for diaphyseal fixation. This stem is made from titanium alloy, and includes a conical fixation zone, a 2° taper with circular cross-section, longitudinal ribs with relatively sharp ridges for rotational stability, and a grit-blasted rough surface to promote osseointegration [13]. This design concept has proven successful with reliable mid-term fixation and some evidence for bone regeneration [8], which is important in young patients and might be attributable to a low modulus of elasticity of this titanium alloy stem. Later implants imitated this fixation concept and the Wagner stem became the prototype for other tapered, fluted titanium stems.

The main issue with Wagner’s original revision stem was the high risk of dislocation, ranging from 12% to 21% [8], which was mainly attributed to the relatively small femoral offset of the original prosthesis. To overcome the high rate of dislocations, a higher offset (42 mm or 44 mm, dependent on stem size, compared to 34 mm in the original prosthesis) was developed in the third-generation stem introduced in 2001.

In the meantime, uncemented modular revision stems based on the fixation principle of the Wagner stem were introduced (such as the MRP Titan stem [Peter Brehm GmbH, Weisendorf, Germany] [15], the Link MP Reconstruction prosthesis [Waldemar LINK GmbH & Co. KG, Hamburg, Germany] [1, 14] and the Revitan stem [Zimmer Inc, Warsaw, IN, USA] [3]). These have become more popular over the last years. Modularity has several theoretical advantages over monoblock stems in revision surgery, including a better ability to adjust and correct femoral offset and anteversion, leg length, and a lower risk of intraoperative fractures due the availability of curved stems. Further, sizing and placement of the distal fixation part is rendered independent in modular designs. The reported mid-term results are encouraging [3, 15].

However, there are disadvantages to modularity, such as the risk of fatigue and breakage related to the modular junctions, potential failure of the modular junction due to fretting and corrosion, the unknown long-term effects of metal debris from the junctions, and higher costs. Additionally, modular implants may simply not be necessary for more straightforward revisions [4, 7]. Currently, we are seeing a “back to basics” trend as questions arise about the safety and the evidence of superiority of modular implants compared to nonmodular implants.

The current study by Sandiford and colleagues reports the short-term clinical and radiological results achievable with the third-generation of the nonmodular Wagner SL Revision® hip stem (Zimmer Inc, Warsaw, IN, USA) with increased femoral offset in a large cohort of 104 revision THAs. The importance of this work is that there is only few evidence on the outcomes using this implant in its most recent iteration from small-sized cohort studies [5] and that the detailed clinical results reported here are clearly needed to compare modular and contemporary nonmodular revision stems in future studies. Despite the relatively short followup, this study provides important information that will help us determine whether there is a benefit to modularity in simpler femoral revisions. The authors found a low frequency of dislocation, intraoperative fractures, and stem subsidence. The level of function after femoral revision surgery was encouraging in this series. These results further question the need for modular implants in the kinds of femoral revisions they treated.

Where Do We Need To Go?

While modular revision stems may still have an important role in femoral revision, there are important questions that still need to be answered: (1) For which patients does modularity provide a clear benefit regarding short-term complications (intraoperative femoral fracture, postoperative dislocation, leg-length discrepancies, and subsidence) compared to nonmodular revision stems? (2) Do modular revision stems improve patient-reported outcomes in the short-term compared to nonmodular stems? (3) Which modular junctions are durable at long-term followup and which are prone to early failure? (4) Does the increased offset of the third-generation Wagner SL Revision® increase the risk of stem fracture in the long-term compared to the original prosthesis?

How Do We Get There?

We can answer many of these important questions by performing Level III and Level IV studies. We clearly need more medium- and long-term reports on the results of contemporary modular and nonmodular prosthesis, such as the MRP-Titan prosthesis, the Revitan stem, the Link MP Reconstruction prosthesis, and the Wagner SL Revision® stem to compare their long-term efficacy and safety. Medium- and long-term studies with large patient cohorts can help to assess the safety of modular junctions from different manufacturers and justify their ongoing use. Future randomized controlled trials comparing monoblock and modular implants with similar fixation philosophy might be the only useful approach to determine whether there is a benefit to modularity in the short-term; such studies will need to be large, and owing to the narrowing indications for these implants, it seems likely that multicenter collaborations would be necessary in order to complete studies of this scope. Noncommercial research founds and manufacturers could consider facilitating, supporting, or promoting such trials.

Footnotes

This CORR Insights® is a commentary on the article “Nonmodular Tapered Fluted Titanium Stems Osseointegrate Reliably at Short Term in Revision THAs” by Sandiford and colleagues available at: DOI: 10.1007/s11999-016-5091-x.

The author certifies that he, or a member of his immediate family, has no funding or commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.

All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research ® editors and board members are on file with the publication and can be viewed on request.

The opinions expressed are those of the writers, and do not reflect the opinion or policy of CORR ® or The Association of Bone and Joint Surgeons®.

This CORR Insights ® comment refers to the article available at DOI: 10.1007/s11999-016-5091-x.

This comment refers to the article available at: http://dx.doi.org/10.1007/s11999-016-5091-x.

References

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Articles from Clinical Orthopaedics and Related Research are provided here courtesy of The Association of Bone and Joint Surgeons