Hinged Knee and Megaprosthesis

Nicholas A. Bedard, MD

Matthew P. Abdel, MD

INTRODUCTION

Hinged knee arthroplasty was first introduced in the 1950s.¹,² This new prosthetic knee design allowed for management of more complex knee deformities and pathologies than was possible with other knee arthroplasty designs of the time. However, failure rates of initial hinge designs were quite high, and as further developments were made for standard condylar resurfacing implants, utilization of hinged knee arthroplasty designs dramatically declined. In the 1980s, the use of megaprostheses began to emerge as a technique for managing large bone defects after tumor resection. The term megaprosthesis includes distal femoral replacement and total femur replacement. The indications for megaprostheses have since expanded to include other causes of large bone defects around the knee such as fracture and prosthetic joint infection (PJI). This chapter reviews the evolution and clinical results of the various types of hinged knee prostheses and megaprostheses, as well as indications for these implants.

EVOLUTION AND CLINICAL RESULTS OF HINGED KNEE PROSTHESES

Clinical data regarding hinged prostheses should be interpreted carefully. Because of improvements in implant design, surgical technique, and patient selection, results with early hinged knee designs do not reflect current outcomes. Furthermore, many reports of hinged implants include results of combined analyses of both primary and revision procedures, with large variation among patients in terms of bone loss, soft tissue compromise, and number of previous operations.

Fixed-Hinge Designs

Initial hinged knee implants were metal-on-metal articulations with a fixed hinge that permitted motion only in flexion and extension.³ Such implants included the Walldius² and the Shiers¹ prostheses. In the 1970s, the Stanmore⁴ and the Guepar⁵ all-metal fixed-hinge implants were also introduced.

Results with early metal-on-metal fixed-hinge implants were poor. In 1986, data from the Swedish arthroplasty registry showed that the 5-to 6-year survival rate of fixed-hinge knee implants for primary total knee arthroplasty (TKA) in osteoarthritic knees was only 65% compared to 87% for the two- or three-compartment designs used at that time.⁶ Results for patients with rheumatoid arthritis were more favorable. However, in such patients, the 5- to 6-year survival rate of the hinge implant was 83% compared to 90% for two- or three-compartment prostheses. The most common reason for revision of the hinged prostheses were aseptic loosening of the components (16.4%) followed by infection (12.1%).⁶

It is likely many of the failures identified in these studies were a result of poor implant design. The fixed axis of rotation with these hinge designs resulted in stress transmission to the bone-cement interface, facilitating component loosening. It is also likely that the metal-on-metal implant design and resultant metal debris contributed to the high number of knees with postoperative effusions⁷ and subsequent synovitis and osteolysis may have compounded the loosing problems with these implants.⁸

Even with modification of the metal-on-metal fixed Guepar hinge to include longer stem lengths, results were disappointing. At follow-up of 2 to 13 years in 45 patients with the Guepar II implant, Cameron et al⁹ reported an aseptic loosening rate of only 7%, which they attributed to longer stem lengths and improved cementing technique. The percentage of good to excellent results, however, had declined to 38% from an earlier report of 67% at 1 to 7 years of follow-up,¹⁰ and extensor mechanism problems and infection continued to be troublesome.

Poor results with metal-on-metal fixed hinges led to redesign of the Stanmore implant to include metal-polyethylene bushings to articulate with the metal implant. In a series of 103 cases in which Stanmore implants were used for both primary and revision procedures, Grimer et al¹¹ reported 80% prosthetic retention at an average follow-up of 68 months; only 64% of patients were enthusiastic about their knee implants, and 70% were free of pain. Since then, the Stanmore implant has been further modified to a rotating hinge with metal-on-plastic bearing surfaces.

In Germany, Blauth and Hassenpflug introduced a fixed-hinge implant that sought to improve upon deficiencies in previous fixed-hinged designs including non-anatomical positon of load-bearing axes, directed metal-to-metal transmission of load, and the need for
massive bone resection.³ The Blauth prosthesis had interposed polyethylene components that conform to the larger condylar surfaces of the femoral implant. The purpose of this design was to transfer the constrained forces through these large surfaces to adjacent bone and away from the hinge. Some gliding motion was possible, and the patella could be resurfaced. This prosthesis was evaluated at mean follow-up of 6 years in 422 consecutive primary TKA using this design.¹² Only three patients (0.7%) were revised for loosening and the overall deep infection rate was 3.8%. The 10- and 20-year survivorship for aseptic loosening was 98.4% and 96.0%, respectively. The cumulative rate of implant survival at 20 years was 87% for a worst-case definition of failure, including removal, infection, and patients lost to follow-up.¹² It is important to note that these results are for primary implants and do not include any revision procedures which likely explain their relatively successful results.

Other authors have also reported improved long-term results with fixed-hinge prosthesis in the setting of limb salvage surgery for tumors around the knee. Ruggieri et al¹³ evaluated 699 consecutive patients with musculoskeletal tumors treated with limb salvage surgery and reconstruction using modular fixed-hinge megaprostheses (The Kotz Modular Femur-Tibia Reconstruction System (KMFTR; Stryker; UK) and the Howmedica Modular Reconstruction System (HMRS; Stryker; UK)) at a mean follow-up of 11 years. They reported an overall survival to failure of 80% and 55% at 10 and 20 years, respectively, with revisions occurring for breakage, aseptic loosening, and infection. They also reported an overall survival to aseptic loosening of 94% and 82% at 10 and 20 years, respectively.

Although this is an extremely different population of patients with more significant bone loss being replaced with the megaprostheses than previous studies discussed, these results do demonstrate improved survivorship compared to early fixed-hinge knee prostheses, especially in terms of aseptic loosening. Despite these results, the authors of this study do acknowledge the improvements associated with rotating-hinge designs and now use a rotating-hinge version of HMRS for the majority of their patients. However, Ruggieri et al¹³ do recommend fixed-hinged megaprostheses for total femoral reconstructions, elderly patients with minimal muscle strength, and distal femoral resections with extensive quadriceps defects given the additional stability provided with a fixed-hinge arthroplasty.

Rotating Hinge

Development

Because of concerns about the contribution of a fixed axis of rotation and relatively poor results with these implants, rotating-hinge designs that allowed for rotation about axes other than flexion and extension were developed. Early designs included the spherocentric,¹⁴ Sheehan,¹⁵ and Herbert¹⁶ knee implants. Many of the original rotating hinge designs did not have a trochlear flange or patella component which was a potential failure mechanism corrected in subsequent designs.

The first Noiles rotary-hinge arthroplasty was performed in 1976.¹⁷ Unlike a fixed-hinge implant, this design incorporated a tibia-bearing component that fits into a cemented polyethylene tibial component. The tibia-bearing component was then fixed between the flanges of the femoral component by the axle. The tibiabearing component could rotate within the cemented polyethylene tibial component up to 20° from neutral without significant prosthetic resistance. Some axial distraction of the tibia-bearing component within the cemented polyethylene component was also possible.¹⁷ In theory, permitting rotation and axial distraction would reduce stress at the bone-cement interface.¹⁷ Subsequently, several modifications were made, including redesign of the femoral component to a condylar-type implant to prevent subsidence of the femoral component.¹⁸,¹⁹

The Noiles rotating-hinge articulation has undergone many modifications over the years evolving into what is now known as the S-ROM Modular, Mobile-Bearing Hinged Prosthesis (Depuy, Inc Warsaw, IN) and such modifications have resulted in significantly improved midterm radiographic and clinical follow-up.²⁰ There have been many modifications to other rotating-hinge designs, and new rotating-hinge implant systems have been developed since these early designs. There are multiple rotating-hinge systems available on the market today.

Clinical Results

Although early results of rotating-hinged TKA seemed promising when compared to early results of metal-on-metal fixed-hinge designs, issues with component loosening and patellar instability remained a problem. Two studies reporting on the early results of the kinematic rotating-hinge implant for treatment of significant ligamentous instability and/or loss of bone reported satisfactory results in 80% of patients with a primary procedure²¹,²² and in 61%²² to 74%²¹ of patients with revision surgery at a mean follow-up of approximately 50 months. Probable loosening observed on radiographs was a concern in 10% of knees in one study.²¹ Progression of radiolucent lines occurred in 26% of knees in that study²¹ and in 7% after primary and 20% after revision procedures in the other study.²² The most common complication was instability of the non-resurfaced patella, which occurred in approximately 22% of primary knee arthroplasty²¹,²² and 36% of revision procedures.²² A slightly longer-term follow-up of this same implant design reported similar results at a mean follow-up of 75 months of 69 kinematic rotating-hinged knee replacements for non-neoplastic conditions.²³ Although these patients did have a significant improvement in
their function, the complication rate was high (14.5% deep infection, 13% patellar complications, 10% component breakage), and at final follow-up, the incidence of component loosening was 13%.²³

Seeking improved results, further develops were made with regard to implant design for multiple rotating-hinge knee systems. Design innovation along with improvements in cementing technique and metaphyseal fixation options lead to improved outcomes with more contemporary rotating-hinge designs at longer-term follow-up.

In 2017, Cottino et al²⁴ reported on the largest series to date of 408 contemporary rotating-hinge TKAs at a mean follow-up of 4 years performed for multiple different primary and revision indications (re-implantation after primary TKA infection [35%], aseptic loosing [13%], periprosthetic fracture [13%], fracture non-union [5%], mechanical failure [4%], arthrofibrosis [4%], component malposition [3%], neurologic conditions [4%], rheumatoid arthritis [2%], rickets, extensor mechanism failure, dwarfism, and congenital dislocation [0.2% each]). In this series, multiple contemporary rotating-hinge designs were utilized and metaphyseal fixation with cones was used in 28% of cases. The cumulative incidence of revision for aseptic loosening was excellent at 4.5% at 10 years. However, the authors reported a cumulative incidence of revision for any reason of 9.7% at 2 years and 22.5% at 10 years, with the most common reason for revision or reoperation being septic in nature (54% of all revision and reoperations). The authors hypothesized the high infection rate was likely due to high patient comorbidities, multiply operated on knees and most importantly many with history of prior joint infections in this cohort.²⁴

Another relatively large series with a similar duration of follow-up identified lower survivorship and higher complications than Cottino et al²⁴ in their retrospective review of 142 rotating-hinge knees (all Orthopedic Salvage System [OSS]; originally the Finn Knee, Biomet Inc, Warsaw, Indiana) at a mean follow-up of 57 months.²⁵ This study included 11 primary procedure and 131 revisions, 42% of which were second stage of two-stage reimplantation for infection. They reported a 15% and 1.5% incidence of femoral and tibial aseptic loosening, respectively. Although difficult to directly compare, is important to note that no metaphyseal fixation, such as sleeve or cones, was utilized in this study, which may account for the differences in aseptic loosening rates when contrasted with the results of Cottino et al.²⁴ The cumulative survival analysis in this study by Farid et al²⁵ demonstrated a 73% overall implant survival without revision at 5 years and 51% at 10 years. Incidence of other complications identified in this series included 12 acute deep infection and 21 late deep infection (23% incidence of deep infection), 7% periprosthetic fracture, 5% extensor mechanism complications, 4% stem fracture, and 4% mechanical hinge failure.²⁵

A systematic review published in 2018 attempted to summarize outcomes for contemporary rotating-hinge knee arthroplasties from studies with more than 50 procedures included.²⁶ Studies that only evaluated primary procedures, utilized megaprostheses, included oncologic diagnoses, or one-stage revisions for infection were excluded. The authors identified 10 studies that met criteria. The most common indications for rotating hinge in this review were infection, aseptic loosening, instability, and bone loss. Five-year survivorship varied dramatically between studies ranging from 51% to 90% for any revision procedures.²⁶ Deep infection was the most commonly reported postoperative complications for 7 of the 10 studies included with incidence of infection ranging from 3% to 24%. Similarly, rates of aseptic loosening varied from 1% to 16% at final follow-up, but five of the studies reported aseptic loosening rates of 5% or less.²⁶

The variability in clinical outcomes and complications with rotating-hinge TKA identified in this systematic review and in the studies by Cottino et al²⁴ and Farid et al²⁵ highlights the difficulty in comparing studies of complex knee arthroplasty procedures which vary greatly in terms of indications, patient populations, soft tissue status, implant type, and modes of fixation. In general, it seems that substantial improvement has been made in terms of aseptic loosing of hinged knee implants when comparing contemporary rotating-hinged knees to fixed-hinged or earlier rotating-hinged designs. However, as pointed out by Farid et al,²⁵ despite rotating-hinge implants offering improved design and lower rates of complications such as loosening or mechanical failures, the profile of patients in need of hinged knee arthroplasty has changed dramatically in recent years.

Over the last 3 decades of rotating-hinge knee arthroplasties, this area of practice has evolved in opposing directions where improvement of mechanical features of the prostheses may be offset by unfavorable results due to expanded indications in more complex problems.²⁵ This may explain the relatively high infection rates associated with this procedure,²⁴,²⁵,²⁶ which is likely independent of prosthesis designs and more reflective of the complexity of patients in need of such a prosthesis.

Given the difficulty in comparing outcomes for a procedure performed for multiple different indications across studies, the following sections will evaluate clinical results relative to specific indications for rotating-hinged and megaprosthetic knee arthroplasty.

Megaprostheses

Rotating-hinge articulations are commonly used in implants designed for reconstruction after resection of bone tumors about the knee when marked loss of ligamentous structures has occurred. Such implants are designed to replace the large resected bone segment (e.g., distal femur) and are referred to as megaprostheses. Megaprostheses have evolved from non-modular
implants to segmental modular systems with a porous coating at the shoulder of the implant to encourage extracortical bone bridging between the remaining host metadiaphyseal bone and the adjacent portion of the implant. Modularity allowed for surgery to proceed without delay for prosthesis constructions and provided the surgeon with more intraoperative freedom to reconstruct bone defects different than the preoperative plan indicated.²⁷ The vast majority of megaprostheses are utilized in the reconstructions of bone loss after resection of malignant and aggressive benign bone tumors around the knee.

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