|Year : 2021 | Volume
| Issue : 1 | Page : 59-62
Irretrievable Morse taper junction of the femoral prosthesis at revision hip arthroplasty for metallosis: A case report
Vikas Rajesh Singh, Graham Mercer
Department of Orthopaedics, Arthroplasty Unit, Repatriation General Hospital, Daw Park, Adelaide, South Australia
|Date of Submission||07-Apr-2020|
|Date of Acceptance||11-Jun-2020|
|Date of Web Publication||29-Jun-2021|
Dr. Vikas Rajesh Singh
Arthroplasty Unit, Repatriation General Hospital, Daw Park, Adelaide
Source of Support: None, Conflict of Interest: None
Incidence of total hip arthroplasties being performed is on a rise across the world, consequently we would see more and more revisions hip arthroplasties being done for various indications such as infection, loosening, wear, metallosis, trauma; alone or a combination of the above factors. This case report highlights one of the rare but interesting scenarios that a revision hip surgeon must be prepared to encounter while planning to perform a technically challenging revision hip arthroplasty surgery. This report also thus emphasizes the importance of extensive pre-operative planning in terms of technique and timing of the procedure, the skills set and the armamentarium of tools that may be needed for a demanding revision arthroplasty procedure.
Keywords: Irretrievable cold weld of a modular femoral stem, metallosis, revision hip arthroplasty
|How to cite this article:|
Singh VR, Mercer G. Irretrievable Morse taper junction of the femoral prosthesis at revision hip arthroplasty for metallosis: A case report. J Mahatma Gandhi Inst Med Sci 2021;26:59-62
|How to cite this URL:|
Singh VR, Mercer G. Irretrievable Morse taper junction of the femoral prosthesis at revision hip arthroplasty for metallosis: A case report. J Mahatma Gandhi Inst Med Sci [serial online] 2021 [cited 2021 Nov 28];26:59-62. Available from: https://www.jmgims.co.in/text.asp?2021/26/1/59/319843
| Introduction|| |
Most of the orthopedic prostheses used in arthroplasty surgery; these days have modular interfaces based on the machining principle of conical press fit fixation, devised by Stephen Morse in the mid-1860s, which bears his name. It is a method of reliably joining two rotating component surfaces, providing precise alignment with a “snug” frictional fit. Under normal loading, cold weld achieved between the two surfaces is stable, and dissociation can only be achieved with excessive force. Previous studies have demonstrated that contamination by fluids, fat, debris, corrosion, trauma, and forces at assembly can be associated with the failure of the taper lock. We report a case in which the modular taper junction failed to disengage, as a result of cold welding; when it was most desired for it to dissociate, during a revision hip arthroplasty for metallosis.,,,,
| Case Report|| |
A 57-year-old male was diagnosed with metallosis approximately four years after receiving a metal-on-metal (MoM) hip arthroplasty for arthritis in his right hip. A Biomet Magnum (large metal articulation) arthroplasty was implanted in July 2007 at our hospital as a primary procedure [Figure 1]. Postoperative progress was satisfactory until October 2011, when he presented with worsening pain and 'clunking'. The serum ion levels revealed raised cobalt–chromium levels (Se Co 469 nm/L and Se Cr 896 nm/L) and he was offered an elective revision of the prosthesis to a highly cross-linked polyethylene liner on chromium cobalt head articulation as a planned procedure to substitute the wearing MoM articulation.
The hip was approached using the standard posterior approach. Intraoperatively, progress was satisfactory until it was realized that the taper between trunnion and metal taper head connecter was proving surprisingly inseparable with routine gentle disengaging maneuvers [Figure 2]. A heavier hammer, workshop heavy gear distractor, and increased effort failed to dislodge the taper connection [Figure 3]. Subsequently, accepting the complexity of the problem, a proximal femoral osteotomy was then undertaken with view to extricating and replacing the entire stem, as the insert-trunnion interface had proved irretrievable [Figure 4].
|Figure 2: Failure to disengage at interface between metal insert and trunnion|
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|Figure 3: Despite the magnitude of pull-off strength applied, interface un-dissociable|
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|Figure 4: Proximal femoral osteotomy – proves unhelpful around a fully ingrown porous coated stem|
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The fully ingrown porous-coated stem reaffirmed the difficulty of removal of such devices, with the mat finish distal stem still resistant to extraction. By serendipity, a trial loan diamond cutting drill was discovered on a back shelf in storage. The use of this device finally separated the trunnion from the taper head connecter, without damage to the trunnion of the stem [Figure 5].
|Figure 5: (a and b) The diamond cutting drill – proves handy in sparking the likely cold-welded interface|
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There was some gray 'sludge' on the underside of the head with apical wear evident in the cup [Figure 6]. There was no significant soft-tissue reaction around the hip joint, as may be expected in such cases. After a thorough washout and debridement, retaining the same stem, a poly-on-metal articulation as planned, was implanted to complete the revision arthroplasty and the osteotomy was stabilized using cables [Figure 7].
|Figure 6: (a and b) Inspection of the retrievable component – the metal cup|
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|Figure 7: Final postoperative radiograph with components engaged on poly on metal and conical press fit principles|
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At the most recent follow-up in July 2012, the patient was progressing satisfactorily clinically and his serum ion levels were declining (Se Co 73 nm/L and Se Cr 153 nm/L). Interestingly, he has an asymptomatic articular surface replacement metal-on-metal on Metal prosthesis in his left hip.
| Discussion|| |
Stephen A. Morse, invented the taper concept in the mid-1860s. It has proved to be the most widely used type of the available tapers with immense application in the machining industry in particular. This concept was then adapted by the orthopedic industry in the 1980s to enable the assembly of modular arthroplasty components intraoperatively. The principle is primarily of placing a cone in a cone, uniformly tapered, in intimate contact. Trunnion expands (male), compressing the bore (female) thus providing a snug, stable, self-holding fit. The advantage this principle confers is, of having an option of modularity among similar and dissimilar materials in a single joint model. The disadvantages are incompatibility among different dimensions made available from different manufacturers; fretting, corrosion, failure at interface contributing to the disassembly of components; hoop stresses resulting in ceramic failures and probable rare cold welds events leading to the failure to disassemble the components at revision surgery.,
Most of the literature reports available deal with the failure of Morse taper when not desired – dissociation of Morse taper modular components under stress in particular – in-vivo during revision knee arthroplasties where the long stem extensions stabilized to platforms, disengaged in the canal during or after a revision procedure. A provide reference here discuss the factors that may influence the taper strength. The authors were unable to find a report on a solid cold weld, resulting in failure to dissociate when desired, during a revision surgery. In this case, a failure to disengage the Morse taper, despite the magnitude of pulloff strength applied, highlighted the failure of the very principle of modularity based on the popular principle of the Morse taper.,,,,,
There certainly may have been some issues during manufacturing or the assembly process of the concerned components or an element of cold-welding at the Morse-taper interface leading to a unique set of unexpected circumstances which were encountered intraoperatively during this revision surgery. Although submission of the metal insert for metallurgical analysis would have shed some light on the process affecting the taper seat, unfortunately, the components from this case were not submitted for any such investigation or analysis. Cold welds are solid (macro) state welds lacking molten phase, not requiring heating at the interface (as happens in a traditional heat weld) and find immense applications in machining, space, and satellite industry.
Optimal usage of modular femoral prosthesis with Morse-taper concept has shown to be affected by:,,,,
- Disassembly strength is directly related to the magnitude of impaction during assembly, multiplicity of impactions may influence up to an extent
- Taper assembly in vivo should be among completely dry components
- Blood, fat, incorrect size, and debris can affect a taper seating. As less as 0.4 ml of blood has resulted in unreliable taper seat.
We conclude from this case report that;
- Despite the ease with which routine revision replacements can be performed, surgical planning in terms of mechanical steps involving component and/or cement removal must be regarded as time, tool and technique critical
- A diamond cutting drill probably should be a regarded as an integral tool in an armamentarium of a dedicated arthroplasty service
- Reinforced again, the fully ingrown porous coated stems can be almost impossible to extricate and one should be ready with back-up options, if planning to revise such a stem.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the legal guardian has given his consent for images and other clinical information to be reported in the journal. The guardian understands that names and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]