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Rotating Platform Components for Revisions of Hinged Knee Prostheses

Barden, Bertram*; Fitzek, Josef, G; Löer, Franz

Clinical Orthopaedics and Related Research: June 2004 - Volume 423 - Issue - p 144-151
doi: 10.1097/01.blo.0000127586.10230.cc
SECTION II: ORIGINAL ARTICLES
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If hinged prostheses are revised with smaller and nonhinged prostheses, do these implants provide adequate fixation, do massive bone grafts in combination with smaller implants reinforce host bone stock, do less constrained prostheses restore ligament tension, and do they avoid problems of the extensor mechanism? To answer these questions, 20 failed hinges were revised to rotating platform revision prostheses with short intramedullary stems in a prospective study. Meticulous soft tissue release techniques and extensive bone grafts were used (tibia, impaction grafting in 16 cases, and structural grafts in four cases; femur, impaction grafting in four cases and structural grafts in 16 cases). The mean followup was 5.3 years (range, 2.3–10.5 years). The Knee Society score improved from a preoperative mean of 21 points (range, 7–49 points) to a mean 81.2 points (range, 59–94 points). One cementless tibial component with extensive impaction grafting became loose. The remaining components (95%) were well-fixed. All cancellous bone grafts showed trabecular remodeling. All structural grafts united to the host bone without resorption. All knees had ligamentous stability after surgery. There were no problems of the extensor mechanism. In this series the rotating platform revision prostheses were used successfully for failed hinged prostheses.

From the *Department of Orthopaedic Surgery, St. Augustinus Hospital, Duren, Germany; the †Department of Orthopaedic Surgery, Kreiskrankenhaus Mechernich, Mechernich, Germany; and the ‡Department of Orthopaedic Surgery, University of Essen, Essen, Germany.

Received: November 1, 2002

Revised: April 25, 2003; September 11, 2003; February 26, 2004

Accepted: March 5, 2004

Correspondence to: B. Barden, MD, Department of Orthopaedic Surgery, St. Augustinus Hospital, D-52355 Düren, Germany. Phone: 49 242 159 9202; Fax: 49 242 159 9575; E-mail: bbarden.sak-dn@clinet.de.

Today, hinged knee prostheses are used predominantly in complex primary or revision arthroplasties, often as a salvage procedure.12 At the time of implantation of the hinges, ligamentous stability is absent or the ligaments are cut tangentially as part of the surgical technique for the hinges. For failure of bicondylar knee arthroplasties, a recommended treatment is to replace the loosened prostheses with larger components with wedges, longer stems, and increased intrinsic stability.19 In case of failed hinged prostheses, this option is limited. Arthrodeses, resection arthroplasties, and above-the-knee amputations have been proposed as salvage procedures.5,11,20

In revisions of hinges, the use of highly constrained implants, rotating hinges, fixed-axis hinges, or segmental knee replacements poses the problem that poor bone stock is exposed to increased loading by the highly constrained articulation of the revision implants.13,15,18,23,26 As a result, implant loosening and bone fracture (Table 1) occur.1,13,15 Another specific complication is failure of the extensor mechanism.1,15

Table 1

Table 1

To solve this problem, nonhinged total condylar prostheses with rotating platform PE inserts and short intramedullary stems were used in this series. The following questions had to be addressed: Do less constrained and smaller components provide adequate fixation in revision of hinged prostheses? Do massive bone grafts in combination with smaller implants reinforce host bone stock? Do nonhinged and less constrained prostheses restore ligament tension? Do they avoid problems of the extensor mechanism? Are there specific complications associated with our surgical technique and choice of implant? The dependent variables of our procedures were: (1) clinical score, (2) complication rate, and (3) radiographic outcome.

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MATERIALS AND METHODS

In a prospective review of 21 consecutive failed hinged prostheses in 20 patients, revisions were done from January 1990 to March 2000. One patient who had a successful revision surgery died 8 months after a contralateral primary knee arthroplasty. This patient was excluded from the study because of the short followup. The remaining study group consisted of four men and 15 women (20 knees). The average patient age at the time of surgery was 70.8 years (range, 35–82 years) and most of the patients had significant concomitant diseases. According to the Knee Society clinical rating system,14 five patients were in Category A (unilateral knee disease). Eight patients had severe contralateral osteoarthritis of the knee (Category B), and six patients had multiple arthritis or medical infirmity (Category C).

Indications for primary arthroplasty included degenerative osteoarthritis (16 knees, 15 patients), posttraumatic arthritis (three knees, three patients), and postinfectious arthritis (one knee). In 13 knees (12 patients), the hinged prosthesis was used for primary arthroplasty. There was severe deformity and ligamentous instability at that time. Nine of the patients had a mean of 5.2 preceding operations (range, 2–14 operations). The hinged prosthesis was used in revision arthroplasties in seven patients (four revisions of a unicondylar arthroplasty, two revisions of a bicondylar implant, and one revision of a hinged prosthesis). Indications for revision of the hinged prostheses to the rotating platform components included aseptic loosening (seven knees, six patients), two-staged treatment of periprosthetic infection with a gentamicin bone cement spacer (four knees, four patients), implant fracture (four knees, four patients), untreatable patellar pain (three knees, three patients), and excessive wear at the articulation mechanism (two knees, two patients). The hinged implants revised were 10 rotating hinged prostheses (seven Dadurian, Orthoplant, Bremen, Germany; three Endo-Rotation, Link, Hamburg, Germany), six fully constrained hinges (two Endo, Link, Hamburg, Germany; two Blauth, Aesculap, Tuttlingen, Germany; and two GUEPAR, Benoist Gerard, Baigneaux, France), and four gliding hinged prostheses (three GSB, AlloPro, Baar, Switzerland; one S&G gliding hinge, S&G-Implant, Lübeck, Germany).

A characteristic type of central femoral and tibial bone loss is found after removal of the failed hinged prostheses10 (Fig 1). The bony defects were categorized during revision surgery according to the Anderson Orthopaedic Research Institute classification8 (Table 2). At the femoral side, there were three Anderson Orthopaedic Research Institute Type 2B and 17 Type 3 defects. The tibial defects were 17 Type 2B and three Type 3.

Table 2

Table 2

Fig 1.

Fig 1.

For the operative procedure, in 18 knees with patellar maltracking (17 patients), the lateral parapatellar approach17 was used to integrate a lateral release and to move the tibial tubercle fragment proximally and medially. In two knees (two patients) the medial parapatellar approach was used. In all knees an osteotomy of the tibial tubercle was done. After removal of the hinged prosthesis and lavage, vital bone was exposed by curettes and a high-speed burr (Midas Rex, Fort Worth, TX). At the tibial side, the defects were reconstructed with impaction grafting (16 knees) (Fig 2). In four knees with uncontained defects of the tibial wall, a sandwich technique was used (Fig 1D). The intramedullary canal was filled with solid cancellous slices of 10–15 mm height. After contouring, these allograft slices were hammered into the intramedullary canal to achieve tight press-fit fixation. Then, the central hole for the conical stem was created by a high-speed burr. Impaction of the cancellous and sandwich bone grafts was achieved using trial conical component stems with increasing diameters. The grafts were made from a mean of 2.6 femoral heads approximately equivalent to 250 cc of bone graft. At the femoral side, large structural allograft reconstructions were required in 16 knees: 10 femoral heads (Fig 2B), two proximal femoral allografts, and four distal femoral allografts (Fig 1C-D). All allografts used in this series were fresh-frozen and treated without radiation. The remaining four patients received impacted homologous cancellous bone from a mean of 2.3 femoral heads. Additional autologous cancellous bone and tricortical iliac crest grafts were used in three knees (three patients).

Fig 2.

Fig 2.

The LCS Classic Revision System (DePuy Johnson & Johnson, Warsaw, IN) is nonmodular, whereas the LCS-Universal (DePuy Johnson & Johnson) provides modular stem length and diameter. The LCS Classic Revision System has a fixed short conical stem that is proportional between sizes (Figs 1D, 2D). The length of the stem varies from 8.5–10.5 cm with a base diameter of 2–2.5 cm. Therefore, the stems could be inserted in variable positions in the host intramedullary canal and no offset components were necessary. The LCS Classic revision implants are porous-coated on the undersurfaces and on the proximal portion of the stem. In the current series, in 18 knees (17 patients) the LCS Classic prosthesis was used. In two patients receiving large bulk allografts, the LCS Universal prosthesis was used.

There were no posterior stabilizers or cams used in this series. Intrinsic stability at the articulating surfaces was provided by the congruency of the PE rotating platform and the femoral curvature. As a result of the two concavities of the liners, the jump factor for the standard version is 6.1 mm and 9.1 mm for the deep-dish version. A residual laxity of the collateral ligaments or the posterior capsule must be less than this critical limit to avoid spin-out of the platform or dislocation. Sixteen deep-dish and four standard PE platforms were used. The total height of the PE and metal tibial components was a mean 17.5 mm (range, 10–25 mm). For the thickness of the tibial metal component there are two choices, 5 and 15 mm, and the thickest PE platform is 20 mm. For 22.5 and 25 mm the thicker metal platform was used. Component fixation was done without cement in eight knees (seven patients) at the tibial and femoral sides, if sufficient primary stability was provided by the host bone and the bone grafts. In five knees (five patients), there were femoral cemented fixation and tibial cementless fixation (Fig 2B). Both implants were cemented in seven knees (seven patients). Cementation mostly was restricted to the cut bone surface (Fig 2B). For the more recent revisions in our series cemented anchorage or press-fit diaphyseal stem fixation with the modular revision prosthesis was preferred for very large defects.

At the time of insertion of the hinged prosthesis, the ligaments had been excised or cut at the epicondyles. However, at the revision operation, a scarred soft tissue envelope was seen in all knees. Consequently, stability could be reestablished with extensive subperiosteal release techniques that were done primarily at the tibial condyles. In all knees, a substantial posterior tibial and femoral subperiosteal release was necessary to cope with the discrepancy of the flexion and extension gap. Additionally the posterior femoral condyles were reconstructed meticulously with bulk allografts and adequately sized femoral components to provide stability in flexion (Figs 1C, 2B). During surgery, ligamentous stability and correct mobility of the rotating platform were tested using the trial components.

In four knees (four patients) with deep infection of the hinged prostheses, insertion of the LCS revision components and the bone grafts was done as a two-stage procedure after implantation of a spacer and eradication of the infection.

One to 3 days after surgery, the patients started walking with two crutches or a rolling walker. Range of motion exercises also were initiated at that time. Weightbearing was reduced to 15 kg for 10–12 weeks. Patients were advised to use a cane until they were confident with their stability.

The clinical assessment was done by two orthopaedic surgeons on the basis of the Knee Society score.14 Neither surgeon was involved in the revision surgery. Radiographic analysis included AP, lateral, and Merchant views. For location of radiolucent lines, the zones defined by the Knee Society were used.9 Additional AP views with varus and valgus stress were obtained within 3 months after surgery. Radiographic analysis was done by two of the authors (JF and BB). Clinical and radiographic followups were done 3 months after surgery and then annually. The mean followup was 5.3 years (range, 2.3–10.5 years). Three patients died by the time of the most recent evaluation. Two of these patients were included in the study, because the followup at the last examination was more than 2 years.

The study was approved according to the law and regulations of our institution and country. Written informed consent was obtained.

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RESULTS

The clinical outcome essentially was improved. The Knee Society score increased from a preoperative mean of 21 points (range, 7–49 points) to a postoperative mean of 81.2 points (range, 59–94 points) at the last followup (Pearson correlation coefficients for the two observers, preoperative, 0.97393; postoperative, 0.96731). The preoperative functional Knee Society score was a mean 13.7 points (range, 0–45 points), and the last postoperative result was 81.2 points (range, 30–100 points) (Pearson correlation coefficients for the two observers, preoperative, 0.81815; postoperative, 0.95014). For the functional score, deductions mainly resulted from general infirmity. The two patients who died had Knee Society scores of 93 and 85 points and functional scores of 80 points each at 5 years followup.

Nineteen of the 20 LCS prostheses showed adequate clinical and radiographic fixation (Figs 1D, 2B). Two years after revision surgery, one painful, aseptically loosened cementless tibial component had to be revised. Circumferential radiolucent lines more than 2 mm thick were seen only in this patient. For the remaining patients, there was no implant migration. Radiolucent lines with a width less than 1 mm were seen in a few knees in Zones 1 and 4 at the femoral and tibial sides. The lines never occurred in combination. In five knees (five patients) a dense sclerotic halo was seen at the peripheral stem. There was no progression of this halo.

All massive bone grafts reinforced bone stock. There was no resorption or collapse (Figs 1D, 2B). The central cancellous bone grafts showed remodeling with the trabeculae positioned parallel to the direction of loading (Fig 2B-C). The tibial cancellous bone graft in the patient with tibial loosening had been integrated entirely at the rerevision. As a result, surgical technique clearly was facilitated.

In all 20 knees (19 patients) of the current series, adequate clinical and radiographic ligamentous stability was restored by soft tissue sleeve releases and bone reconstruction (Fig 2C). In one patient, posterior dislocation of the revision arthroplasty occurred after adequate trauma. Ligamentous stability had been seen at the last examination before the trauma and no giving-way phenomena had been reported. She was significantly overweight and had a contralateral amputation of the midfemur.

Problems of the extensor mechanism did not occur in this series. Although there had been tilting, subluxation, or luxation of the patella in most cases before the revision operation, there was normal patella alignment on all postoperative radiographs. In six knees (six patients) with patella replacement, bone ingrowth was visible. The femorotibial angle was a mean 5.8° (range, 1° – 11°) (Pearson correlation coefficients for the two observers, 0.89281).

There was one specific complication associated with our surgical technique and our choice of implant; the failure of the tibial component mentioned previously resulted from cementless fixation in an extensive cancellous bone graft. There were two unspecific major complications: one traumatic dislocation mentioned previously and one hematogenous infection of the revision prosthesis from a tooth infection 1.5 years after the revision surgery. The patient was treated with two-stage revision to an S-ROM mobile hinged-bearing implant (DePuy Johnson & Johnson). Rerevision with bone grafting and the LCS revision system was not attempted because of the patient’s general infirmity at the time of reimplantation. All three patients with major complications (tibial loosening, traumatic dislocation, and deep infection) were not included in the mean postoperative score. Minor complications in nine patients (nine knees) did not influence the outcome. Six of these patients (six knees) sustained a longitudinal fissure at the remnants of the tibial condyles at the time of prosthetic insertion. All fissures healed primarily after intraoperative screw fixation and bone grafting. Two postoperative hematomas were treated with irrigation. One patient sustained a traumatic tibial tubercle pull-off, requiring fixation with cerclage wires.

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DISCUSSION

The new surgical approach was chosen to improve implant fixation, to reinforce bone stock, to restore ligament tension, and to avoid problems of the extensor mechanism.

As in the alternative studies, our series is not controlled, which makes comparisons with those studies difficult.1,13,15,18 Our study also is limited by the number of patients and the length of followup, because treatment of failed hinged prostheses is rare. Statistical analysis was not possible.

Revision from a hinge to a rotating platform prosthesis is logistically and technically demanding with a long operating time. For patients with low physical demands or patients in a reduced general medical condition hinged megaprostheses are a treatment option, but they rarely have been used in nonneoplastic knee revisions.23 In tumor treatment, Kawai et al16 reported 32 mechanical failures in 82 segmental replacements at a minimum of 2 years followup. If arthrodeses are used for failed hinges, the fusion rate is reported to reach only 56% as a result of poor remaining bone stock.5

In the literature there are only four systematic reports (68 cases) on revisions of hinges and the followups are shorter than in the current series (Table 1). In contrast to our series, hinges or highly constrained cemented prostheses were used. Inglis and Walker13 reported poor results for fixed–axis hinges in revisions of 40 failed hinged arthroplasties, because 16 rerevisions were done. The remaining three reports1,15,18 include only 28 patients; the clinical and radiographic outcomes and the complications of these patients are shown in Table 1.

To provide adequate fixation of revision arthroplasties, the least constraint possible should be used to avoid increased transmission forces at the bone and cement interfaces.22,23 As a result of the mobility of the LCS rotating platform, high conformity of the femoral shape is possible without adverse constraint. Therefore, in the current series, small prosthesis stems could be used. The clinical midterm and long-term benefits of the LCS rotating platform have been reported for primary and revision arthroplasties.4,6,24 If constrained knee prostheses need extensive intramedullary fixed stems to enlarge interface stability, complications also are caused by significant bone loss resulting from stress shielding.12 The distance of the shielding has been shown to be equivalent to the length of the stems.3 Barrack et al2 reported localized pain at the end of the stems in 11–14% after revision arthroplasty. With the use of modular press-fit stems in revision knee arthroplasty, Vince and Long25 presented a 23% failure rate of a constrained condylar-type prosthesis with 2–6 years followup. If a cemented, stemmed prosthesis is chosen for revision knee arthroplasty, the sclerotic surface of the intramedullary canal makes reliable interdigitation of the cement questionable.13,18

Massive bone grafts constantly reinforced bone stock in our series. The failed hinged prostheses caused extensive ice cream cone-like bone defects that needed higher volumes of cancellous bone grafting than have been reported to date.4 Impaction grafting and the sandwich technique have produced high primary stability and reliable secondary stability of the implants with evident bone remodeling. For revisions of bicondylar knee arthroplasties, successful results with impaction bone grafting in combination with cementless or cemented prostheses have been published.21,27 Bradley4 reported on 19 knees with impaction grafting of at least 90 cc morselized bone using the same revision implant as in the current series in their series with an average followup of 33 months. There was one mechanical failure. The Knee Society score, including the functional score, was a mean 147 points (range, 102–198 points). In the current series, structural allografts have shown convincing midterm results which are comparable with those published in a multicenter study.7 In contrast to impaction grafting, late infection and resorption may represent a higher risk in large bulk allografts in the long-term.7 Downgrading of the bone defects by the surgical technique used in the current series has an essential benefit. In case of a rerevision, the bone defects are less extensive compared with the situation at the last revision.

Why could ligamentous stability be restored in our series? After removal of hinged prostheses, Kim18 reported that there is a scar tissue sleeve present to provide soft tissue stability, which supports intrinsic stability of the revision implant. In the current series, this tissue sleeve was equilibrated by meticulous release techniques and joint line reconstruction with structural bone grafts. Ligament stability was provided in extension and flexion by structural allograft reconstruction of the posterior femur and by posterior femoral and tibial release. Minor residual soft tissue instability could be tolerated because of the conformity provided by the concavity of the LCS rotating platform PE insert. In the current prospective study, all failed hinges could be changed to a stable rotating platform prosthesis. Constrained or hinged prostheses were not used in this series. However, when persistent severe instability is seen during revision knee arthroplasty of hinges, a revision implant with high intrinsic stability should be available.

In contrast to revisions from hinges to hinges reported in the literature, our technique did not cause any problems of the extensor mechanism.1,15 This might result from the anatomic femoral groove of the component and the less constrained type of implant.

For treatment of failed hinged knee arthroplasties less constrained smaller components provided adequate fixation in our series. Massive bone grafts reliably reinforced bone stock. Extensive soft tissue releases restored ligament tension in all knees. Problems of the extensor mechanism did not occur. One cementless tibial component with extensive cancellous bone grafting became loose. In the long term the special advantage of the new procedure presented in our series may emerge from the reconstruction of ligament tension and bone stock.

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References

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