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Total Knee Arthroplasty With Modular Rotating-platform Hinge

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Abstract

Third-generation modular rotating hinged knee systems are now widely available. The S-ROM rotating hinge features slotted and splined stems for torsional stability, and metaphyseal filling and loading sleeves for the bony defects encountered in revision total knee arthroplasty (TKA). Primary indications for a hinge include medial or lateral collateral loss, massive bone loss, and metaphysis and cortical shell, which includes collateral origins or insertions, and severe flexion gap imbalance requiring a link system for stability. Indications for a hinge in primary TKA include patients with neuromuscular deficits such as polio or flail knee, who require the hyperextension stop. Reported midterm results are excellent with no mechanical failures and positive bone remodeling in 65 patients.

Most patients requiring revision total knee arthroplasty (TKA) can be managed by posterior-stabilized or varus- or valgus-constrained condylar revision knee systems. If catastrophic loss of soft- or hard-tissue is encountered, a modular linked-knee system may be necessary to provide stability to the knee.

Numerous designs of hinged systems have been used for primary and revision TKA since the first report by Walldius¹ in 1960. The early hinges had high failure rates because they allowed motion only in the sagittal plane, and the rotational forces around the knee were transferred with high torque to the implant-bone interfaces. Inevitably, loosening occurred and failure ensued. Later systems were designed with more axial freedom and rotation to diminish the forces at the fixation interface.^2,3 Knees in the later system had minimal size selections and poor rotational control and failure rates due to loosening or infection remained unacceptably high.

Third-generation hinged-knee systems are now widely used and they demonstrate significant improvements in design with concomitant improvements in clinical results.^4-8

Design Principles

The S-ROM modular rotating-platform hinge-knee prosthesis (DePuy Orthopaedics, Warsaw, Ind) is representative of modern hinge systems and has the most extensively reported clinical outcomes. The knee system has a rotating-platform type mobile-bearing that allows axial rotation through a metal-reinforced polyethylene-post articulation in the tibial tray. The undersurface of the polyethylene is broad and flat and articulates on a highly polished chrome-cobalt alloy base plate. The femorotibial articulation is a highly congruent polyethylene with medial and lateral condylar surfaces and a hinged axle-yoke mechanism, which provides a third bearing surface for enhanced load sharing and diminishment of polyethylene stresses. The entire construct is a constrained, dual articulation that converts shear forces to linear forces and reduces wear while protecting the implant-bone interfaces.^9-12

A unique feature of the S-ROM rotating-platform hinge-knee system is the provision of modular diaphyseal-engaging stems and metaphyseal sleeves. Because bone loss is often encountered in revision TKA, the stems are 100 or 150 mm long to bypass defects and reach good medullary bone surfaces. The stems are slotted to more closely match bone compliance and eliminate end-stem pain. They are splinted to provide 1-mm press fit and inherent rotational stability.

The modular metaphyseal sleeves link to the femorotibial hinge mechanism and to the stems. They are stepped for progressive loading and porous coated for improved osseointegration. The sleeves are metaphyseal filling to accommodate the large metaphyseal defects often observed in revision TKA described by Engh.¹³ The stems and sleeves are designed for press-fit fixation. They promote intramedullary load sharing and fixation into intact bone, bypassing stress risers seen in bone deficiencies.

Physiologic valgus is fixed into the femoral component at 7°. A deepened trochlear groove enhances physiologic patellar tracking. Distal femoral augments are available in 5- to 10-mm sizes. Enhanced tibial base plates can add 14-24 mm to the base plates. Polyethylene bearing thickness is available up to 31 mm. The complete system, and the modularity, allows building an implant to handle various intraoperative problems that might occur.

Indications and Surgical Technique

The hinge-knee system is used frequently in revision TKA. The goals of revision TKA are to preserve bone stock and replace bone defects, to restore symmetry of soft-tissue support, and to establish correct alignment and balance of the knee. The guiding principle of revision TKA, therefore, is to use only the amount of constraint consistent with the clinical picture. The indications for the S-ROM modular rotating-platform hinge-knee system include medial or lateral collateral ligament loss; massive bone loss of Engh type III with loss of metaphysis and the cortical shell, including collateral origins or insertions; and/or severe flexion gap imbalance requiring a linked system. Intramedullary fixation is assured and linked to the articulating knee system.

The hinge-knee system in primary TKA in indicated for patients with neuromuscular deficits, such as polio, flail knee, or back knee, who might benefit from the hinge axle-yoke mechanism and hyperextension stop. In addition, patients converted from an extension arthrodesis have large flexion gaps and require a hinge and patients with severe traumatic arthrosis and extension arthrofibrosis will also benefit from a hinge-knee system.

Operated knees are assessed for bone and soft-tissue deficits after prosthesis removal and debridement. The S-ROM intramedullary-mounted instrument system provides for initial tibial reaming to the correct size by cortical diaphyseal fill. For larger tibial defects, the 150-mm stem may be more appropriate than the standard 100-mm stem. Intramedullary pilots are placed on the metaphyseal broaches and used progressively until rotational stability is achieved. Bone is trimmed using the top of the sleeve as a guide, and a stable tibial construct is established.

Next, the femur is reamed to cortical fill. A 150-mm stem should be used for large femoral defects, and flexible reaming is done to 1-1.5 mm over the straight ream size to accommodate the anatomic anterior bow in the stem. Again, metaphyseal broaches are attached to sized pilots to achieve rotational stability. Bone cuts are made off the stem-sleeve aligned intramedullary guides. Appropriate distal femoral augments are used to adjust joint line and to improve kinematics. Assembly of the trial components and appropriate polyethylene insert to achieve neutral extension is accomplished. Final component assembly is performed on the back table and matched to the trial components. Particulate bone grafting can be used to augment major defects in remaining hard tissue. Because of the modular fit-fill of the stem-sleeve construct, patients rarely require bulk allograft, and operating time efficiency is significantly improved (Figures 1 and 2).

Figure 1: Preoperative AP (A) and lateral (B) radiographs of 83-year-old woman with dislocated LCS TKA and no medial collateral ligament.

Figure 2: Postoperative AP (A) and lateral (B) radiographs 4 years after coversion to S-ROM hinge.

Discussion

Barrack⁷ and Jones et al⁵ reported on clinical outcomes in retrospective reviews of patients in Dallas, Texas, and New Orleans, La, revised with the S-ROM modular, rotating platform hinge. The combined series provided follow-up at an average of 63 months for 65 patients. The component revised was a hinge in 25 patients, and another component in 40 patients. Statistically significant improvements in flexion (preoperative=81° and postoperative=100°) and Knee Society Clinical scores (preoperative=52° and postoperative=134°) were documented. No mechanical failures occurred. A separate radiographic evaluation by the Ewald Method¹⁴ showed stable condylar segments and bone apposition with no radiolucent lines around the sleeves or stems. The Dallas group is currently completing additional follow-up out to 10 years.

More extensive outcome data are available on the use of the S-ROM modular sleeves and stems in revision TKA. Hogan and associates¹⁵ reported on 81 knees in 74 patients who had revision TKA with the S-ROM sleeve-stem system. Forty-four percent of the knees had hinge-rotating articulations, and the remainder had the S-ROM Noiles posterior-stabilized rotating platform. The radiographic follow-up averaged 31 months, and all implants were stable with no radiolucent lines. Positive results were attributed to the dual articulation design of the rotating platform “by allowing knee rotation even while providing constraint.”

Jones¹⁶ reported on 103 knees managed with the S-ROM sleeve-stem system and the S-ROM Noiles-PS rotating-platform articulation. Radiographic follow-up averaged 60 months, and all interfaces were stable without radiolucent lines. One mechanical failure occurred at the tibial sleeve-stem junction caused by medial loss of support.

Most fixed-bearing constrained-condylar prostheses transmit significant torqueing forces in flexion and with stair and chair ascent. Range of motion is resisted by the implant condylar surface and the intramedullary fixation. Fehring et al, ¹⁷ in a study of 95 knees after revision TKA with a press-fit stem, reported 19% of implants were possibly loose and 10% of implants were definitely loose. The findings by Fehring et al¹⁷ are in stark contrast to the S-ROM type sleeve and stem experience cited previously.

The metasphyseal sleeve-stem construct provides excellent torque resistance on the femoral side, especially in flexion. In addition, the rotating design decouples multivectoral knee stresses to two interfaces providing motion in a unidirectional manner, thereby reducing wear and fixation interface stresses.

Conclusion

The S-ROM modular rotating-platform hinge-knee system has excellent midterm results reported for the hinge system, which should encourage surgeons to use the system with increasing confidence. Moreover, the excellent midterm results with the S-ROM Noiles posterior-stabilized rotating-platform from Jones et al¹⁶ and Schutte et al¹⁵ justify expansion of such systems to standard condylar and varus/valgus constrained knees in revision TKA.

References

1. Walldius B. Arthroplasty of the knee using an endoprosthesis. 8 years’ experience. Acta Orthop Scand. 1960; 30:137-148.
2. Feng EL, Stulberg SD, Wixson RL. Progressive subluxation and polyethylene wear in total knee replacements with flat articular surfaces. Clin Orthop Relat Res. 1994;299:60-71.
3. Friedman RJ, Hirst P, Ross R, et al. Results of revision total knee arthroplasty performed for aseptic loosening. Clin Orthop Relat Res. 1990;255:235-241.
4. Jones RE, Skedros JG, Chan AJ, Beauchamp DH, Harkins PC. Total knee arthroplasty using the S-ROM mobile-bearing hinge prosthesis. J Arthroplasty. 2001; 16:279-287.
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11. Bell CJ, McEwen HM, Barnett PI, et al. Comparison of wear in fixed and mobile bearing knee designs. Trans Orthop Res Soc. 2003:1403.
12. Fisher J, McEwen HM, Bell CJ, et al. Wear of polyethylene in artificial knee joints. Curr Orthop. 2001; 15:399-405.
13. Engh GA. Bone defect classification. In: Engh GA, Rorabeck CH, eds. Revision Total Knee Arthroplasty. Philadelphia, Pa: Lippincott Williams & Wilkins; 1997:63-120.
14. Ewald FC. The Knee Society total knee arthroplasty roentgenographic evaluation and scoring system. Clin Orthop Relat Res. 1989; 248:9-12.
15. Hogan KA, Bhatti H, Schutte HD. Cementless revision knee replacement: The MUSC experience. Medical University of South Carolina Orthopaedic Journal. 2004; VII:20-21.
16. Jones RE. Mobile bearings in revision total knee arthroplasty. Instr Course Lect. 2005; 54:225-231.
17. Fehring TK, Odum S, Olekson C, Griffin WL, Mason JB, McCoy TH. Stem fixation in revision total knee arthroplasty: a comparative analysis. Clin Orthop Relat Res. 2003; 416:217-224.

Author

Dr Jones is from the Orthopedic Specialists and the Department of Orthopedic Surgery, University of Texas Southwestern Medical Center, Dallas, Tex.