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Symposium: 2013 Meetings of the Musculoskeletal Tumor Society and the International Society of Limb Salvage

Frequent Complications and Severe Bone Loss Associated With the Repiphysis Expandable Distal Femoral Prosthesis

Cipriano, Cara A. MD1,a; Gruzinova, Irina S. BS1; Frank, Rachel M. MD1; Gitelis, Steven MD1; Virkus, Walter W. MD2

Author Information

1Section of Orthopaedic Oncology, Department of Orthopaedic Surgery, Rush University Medical Center, 1611 West Harrison Street, Suite 300, 60612, Chicago, IL, USA

2Indiana University Health Orthopedics and Sports Medicine, IU Health Physicians, Indianapolis, IN, USA

ae-mail; [email protected]

Each author certifies that he or she, or a member of his or her 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.

Clinical Orthopaedics and Related Research neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA-approval status, of any drug or device prior to clinical use.

Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.

This work was performed at Rush University Medical Center, Chicago, IL, USA.

Clinical Orthopaedics and Related Research: March 2015 - Volume 473 - Issue 3 - p 831-838
doi: 10.1007/s11999-014-3564-3
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Abstract

Introduction

The distal femur is the most common location for malignant tumors in skeletally immature patients. Although amputation was once the only treatment, surgical and chemotherapeutic developments over the last several decades have led to the success of limb salvage procedures in approximately 85% of cases [1, 4-6, 14, 16, 18, 21, 23]. However, the potential adverse consequences associated with limb salvage include limited longevity of endoprostheses and high rates of reoperation resulting from mechanical failure and infection [1, 10, 14]. These problems may result in loss of joint function, high-level amputation, and systemic sequelae for the patient [17].

In pediatric patients who have not reached skeletal maturity, limb salvage surgery presents the additional challenge of maintaining equal limb length throughout the child's growth. Expandable endoprostheses such as the Repiphysis Limb Salvage System by Wright Medical Technology (Arlington, TN, USA) allow for limb preservation and growth without repeated invasive procedures [20]. This limits the risk of infection and enables gradual lengthening of the soft tissues.

Recent publications have reported good functional outcomes of these devices despite high rates of complications, including aseptic loosening and prosthetic fracture; however, none has considered bone stock available for future reconstruction in their evaluations [2, 13]. Moreover, insofar as the entire published world experience with this implant is only a few dozen patients, additional data in terms of failure frequencies and clinical scores seem important to report.

We therefore asked (1) what are the 2-year minimum clinical outcomes after placement of the Repiphysis expandable prosthesis for pediatric distal femur malignancies; (2) what are the complications associated with this prosthesis; (3) what is the failure rate with this prosthesis; and (4) in light of the bone loss associated with the failure of this implant, what revision alternatives are available for salvage of the failures?

Materials and Methods

Description of the Prosthesis

The Repiphysis expandable prosthesis is composed of a titanium tube surrounded by a polyethylene cylinder, which is locked in place by a flared trumpet. Within the titanium tube, a compressed cobalt-chromium spring is insulated from the trumpet flare by a thin ceramic ring. Lengthening is accomplished in minutes with the application of an external electromagnetic field. This field softens the outer polyethylene cylinder and allows the trumpet flare to unlock from the polyethylene. The spring expands slightly, causing the inner titanium tube to slide within the cylinder. When the trumpet flare reaches a cooler portion of the polyethylene, it becomes locked once again [2, 13].

Patients

Between 2002 and 2010, one surgeon (SG) treated all skeletally immature patients with distal femoral osteosarcoma using a Repiphysis expandable prosthesis. Two patients were excluded as a result of death from disease progression with less than 2 years followup. Of the remaining 10, there were six males and four females, and the diagnosis was osteosarcoma in all cases. Mean patient age at the time of the initial surgery was 10.1 years (range, 4.7-13.6 years), duration of followup was 72 months (range, 26-119 months), and age at final followup was 16.7 years (range, 10.9-21.5 years). The beginning of our study period was chosen to correspond with the advent of digital imaging at our institution, allowing for more precise and consistent radiographic measurements; thus, the study population did not include any patients already discussed in the surgeon's previous report on the Repiphysis device [8].

Operative Technique

All prostheses were implanted through an extensile lateral parapatellar approach using the standard cement technique for fixation. A mean of 19.7 cm (range, 11.8-31.0 cm) of distal femoral bone was resected during the index procedure. The cortex was overreamed by 1 to 1.5 mm and a cement restrictor was used. Postoperatively, patients were allowed to weightbear as tolerated immediately but instructed to refrain from impact activities.

Data Collection

Preoperative data (demographic information, including patient age, sex, and diagnosis), intraoperative data (length of bone resection, Repiphysis prosthesis size, number of lengthenings, total centimeters lengthened), and postoperative data (complications, recurrence rate, reoperation rate, survival rate) were recorded. Functional outcomes data were assessed using the Musculoskeletal Tumor Society (MSTS) scoring system, which incorporates the elements of pain, function, emotional acceptance of any residual deficit, walking ability, gait, and use of walking aids.

Radiographs taken during the course of followup were analyzed to assess degree of bone loss or compromise associated with the prosthesis. All measurements were made electronically by a single author (CAC) after calibration based on documented implant dimensions. These included residual length (measured from the lesser trochanter to the proximal end of the implant barrel), minimum cortical thickness around the implant stem at final followup, and degree of cortical thinning (measured by comparing the thickness on immediate postoperative with final followup radiographs) (Fig. 1). Finally, taking all of these factors into consideration, the two senior authors (SG, WWV) reached a consensus regarding the reconstruction options that would be available for each case should future revision surgeries be indicated.

F1-14
Fig. 1:
Example of radiographic measurements for cortical thickness and residual bone length from the proximal barrel of the implant to the lesser trochanter (arrow).

Results

MSTS Scores

The mean MSTS score at final followup was 67% (range, 23%-93%) with the mean points per category as follows: pain 3.9, function 3.2, emotional acceptance 2.6, use of supports 5, walking ability 3.8, and gait 3.2. Although the numbers available for study were too few to identify risk factors for poor outcomes, we did observe that patients with the lowest scores reported dissatisfaction in the categories of gait, use of supports, and emotional acceptance.

Complications

Two patients developed metastatic disease; among the remaining 10 patients, there were 37 complications related to the reconstruction (Table 1; Fig. 2). These included four periprosthetic fractures (at 12, 13, 17, and 65 months), four cases of arthrofibrosis necessitating surgical release, and one deep infection (at 86 months). There were 13 implant failures; 10 of these were the result of loss of fixation (which occurred at a mean of 49 months; range, 11-86 months) and three the result of hardware failure (one tibial component at 86 months, one femoral component at 51 months, and one hinge pin at 11 months) (Fig. 2). In addition, there were four flexion contractures > 10°, four extensor lags > 10°, three patellar maltracking issues, two residual limb length discrepancies > 2 cm, one wound healing complication, and one delengthening event, in which the implant collapsed 2 cm while the patient was engaged in noncompliant impact activity (playing basketball).

T1-14
Table 1:
Demographic and followup data for 12 pediatric patients with distal femoral osteosarcoma treated using the Repiphysis expandable prosthesis
F2-14
Fig. 2:
Complications associated with the Repiphysis expandable endoprosthesis observed in our study population at final followup (mean, 75.2 months; range, 24.3-119.4 months) were aseptic loosening, periprosthetic fracture, arthrofibrosis requiring manipulation or débridement, flexion contracture > 20°, extensor lag > 20°, fracture or other failure of the Repiphysis components, patellar maltracking, residual limb length discrepancy > 2 cm, superficial wound healing complication, deep periprosthetic infection, and spontaneous prosthesis delengthening.

Revision Surgery

These complications required a total of 15 returns to the operating room (median, two; range, zero to seven per patient), during which 25 procedures were performed: 10 component revisions for aseptic loosening and three for implant failure; six manipulations, débridements, or quadricepsplasties for arthrofibrosis; two open and two closed reductions of periprosthetic fractures; and two releases for patellar realignment (Table 1; Fig. 2). At latest followup, four of the 10 original Repiphysis devices remained in place, and six had undergone revision; of the revised implants, four were ultimately converted to adult prostheses, and two required total femoral replacement (Table 1; Fig. 3). All six of the patients with greater than 5-year followup had undergone at least one implant revision for hardware or fixation failure. These cases demonstrated gross appearance of metallosis, and pathologic analysis revealed both metallic and polyethylene debris in the periprosthetic tissues (Fig. 4).

F3-14
Fig. 3A-D:
Radiographs demonstrating sequential complications associated with implantation of the Repiphysis device in a 12.7-year-old girl: (A) initial construct; (B) periprosthetic fracture (4 years postoperatively) through compromised metaphyseal bone; (C) revised construct; and (D) total femoral replacement 1.5 years later.
F4-14
Fig. 4A-D:
Intraoperative photographs from revision of the failed Repiphysis device demonstrate extensive metallosis in the periprosthetic tissues (A-B). Histologic analysis under (C) low magnification and polarized light demonstrates nonmetallic birefringent polyethylene material (arrow), whereas (D) standard transmitted light demonstrates metallic particulate matter (arrow).

Bone Loss and Revision Options

A median of two lengthenings (range, one to 12) was performed, producing a mean 3.9 cm (range, 1.0-12.6 cm) of growth per patient (Table 1). Three patients required additional resections of deficient bone (19.3, 20.4, and 4.5 cm) during revision procedures. The remaining length of femoral bone from the lesser trochanter to the proximal end of the implant stem averaged 9.4 cm (range, 0-16 cm), cortical thinning averaged 2.7 mm (range, 1.9-3.5 mm), and minimum cortical thickness averaged 1.4 mm (range, 0.6-2.3 mm). All patients showed radiographic evidence of metadiaphyseal compromise surrounding the prosthesis stem. As a result of the resulting lack of supportive femoral bone, subsequent revision using a standard stem prosthesis would only be possible in two cases, whereas the others would require alternative methods of reconstruction.

Discussion

The Repiphysis Limb Salvage System (Wright Medical Technology) is an expandable oncology endoprosthesis designed for skeletally immature children with tumors requiring resection of the growth plate in the femur or proximal tibia. Although it has been used in Europe since the early 1990 s, the first Phenix, as it was originally named, was implanted in the United States in 1998 and approved by the Food and Drug Administration in 2002 [13]. The implant is designed to withstand nonimpact activity in children approximately 5 to 14 years of age and have at least 4 cm of growth remaining. The Repiphysis may be lengthened noninvasively, thereby minimizing the need for further surgery until the patient reaches skeletal maturity, at which time it may be revised to an adult prosthesis [21]. Because prior studies have raised significant concerns regarding use of the Repiphysis expandable endoprosthesis for treatment of pediatric distal femoral malignancies, our goals were to report our clinical outcomes, complications, and failures as well as the extent and implications of associated bone loss with this device.

Our study has several limitations that must be taken into consideration. First, our sample size was small, reflecting the infrequent nature of the procedure, and there was no control group available. As a result of our consistent use of the Repiphysis expandable prosthesis, it remains unclear whether our findings are specific to this design or generalizable to other expandable prosthetic devices. All devices were implanted using cement, so it was not possible to determine whether cementless fixation might improve functional or radiographic results. It should be noted that the MSTS functional outcomes tool has not been validated and is somewhat subjective in several categories. In addition, we have no way of measuring the degree to which patients adhered to their no-impact activity restrictions, but compliance should not be assumed in any patient population, especially children and adolescents. To maximize consistency, all radiographic measurements were taken by a single author (CAC) and calibrated according to implant dimension; however, the potential for human error cannot be completely eliminated. Because this was a retrospective study, radiographs of the contralateral femur were not available for review, and so normal cortical hypertrophy associated with skeletal maturity could not be measured; this, if anything, would lead to underestimation of cortical thinning associated with the Repiphysis. Although the options for future revision were determined based on the length and quality of remaining femoral bone stock, and a consensus was used to minimize bias, subjectivity could not be entirely eliminated from this process. Finally, our study offers the longest average followup available to our knowledge, but longer-term results will be needed to confirm the clinical implications of the bone loss that we observed.

We found that functional outcomes after implantation of the Repiphysis prosthesis were generally unsatisfactory. Although previously reported MSTS scores for patients with expandable endoprostheses have ranged from 81.7% to 90% with early followup (Table 2) [2, 8, 10, 12, 15, 21], our mean MSTS score at intermediate followup was markedly lower at 67% (range, 23%-93%). Interestingly, we observed the highest scores in categories related to pain and function, whereas the lowest were in the area of emotional acceptance, perhaps related to the psychological toll of frequent complications requiring repeated interventions. The negative impact of extended treatment on quality of life should not be underestimated, especially given its potential to interfere with the school and social activities of this patient population.

T2-14
Table 2:
Summary of prior literature on outcomes of noninvasive expandable pediatric endoprostheses

Complications associated with this prosthesis were common with a total of 37 occurring in our population at mean followup of approximately 6 years (Fig. 2). Several previous series have also observed frequent problems with use of the Repiphysis and other expandable prostheses (Table 2). With mean followup ranging from approximately 2 to 4 years, the most commonly reported were mechanical failures, loosening, fracture, and infection [2, 3, 8, 10, 12, 21]. These studies, however, do not take into account problems such as severe arthrofibrosis, flexion contracture, extensor lag, and patellar maltracking, all of which may significantly affect function and may require further procedures. The rate of complications that we observed was substantially higher than has been reported for alternative reconstruction methods such as rotationplasty, which has also demonstrated excellent long-term results in terms of patient function and satisfaction [7, 9, 11, 19, 22, 24, 25].

In addition to these frequent complications, we observed a high rate of reoperation with a majority (eight) of our patients requiring implant revision. The predominant mechanism of failure was aseptic loosening of the stem, necessitating 10 reconstructions in six patients (Table 1; Fig. 2). This is especially concerning given the minimum followup of only 2 years with mean followup of approximately 6 years. It should also be noted that all six of the patients with greater than 5-year followup had undergone at least one implant revision for failure of either the device itself or its fixation. These findings are consistent with those of previous authors, who also reported frequent need for reoperation with expandable prostheses, including the Repiphysis (Table 2). In particular, Saghieh et al. noted that the average survival time of the device from implementation to revision or last followup was only 32 months [21]. Although none of our patients underwent delayed amputation, Hwang et al. found that this may be required in as many as 20% of cases [12]. Our overall rate of revisions, like complications, was much greater than reported in patients treated with rotationplasty [7, 9, 11, 19, 22, 24, 25].

Finally, we found the Repiphysis device to be associated with extensive metadiaphyseal bone compromise in a young patient population, which may increase the complexity of future operations. In addition to the inevitable loosening that results from longitudinal and radial growth of the bone, vertical translation of the trumpet flare and titanium tube within the polyethylene cylinder may lead to the osteolytic pattern of bone loss observed in several of our patients. As a result of this extensive bone compromise, future revision using standard stem fixation would not be possible in eight of our 10 cases; moreover, two of these patients ultimately required total femoral replacement as a result of lack of residual bone stock (Table 1, Cases 2 and 4). Interestingly, these two patients had undergone the most significant expansions with 12 procedures each, totaling 12.6 and 11.2 cm of growth. This suggested a potential relationship between degree of lengthening and device failure, although definitive conclusions cannot be made given the numbers available for study. The combination of significant bone loss and frequent complications may place the patient at risk for complex revisions at a young age (mean 16.7 years at final followup in our series) and may even lead to total femoral replacement or above-knee amputation at a higher level than would have been required for the primary oncologic resection. Although long-term results for expandable prostheses are not yet available, this potential for complex revisions leading to reduced functional outcomes should be considered during preoperative planning and counseling.

Currently, there is no single best treatment option for pediatric patients requiring distal femoral physeal resection for malignancy. Despite its theoretical advantages over other limb-preserving reconstructions, the Repiphysis device is associated with a high frequency of severe complications and reoperations, leading to poor functional outcomes and patient satisfaction; moreover, the potential for severe bone loss we observed with this device may limit options for future revision procedures. All of these risks should be explicitly discussed with patients and families interested in the Repiphysis, and strong consideration should be given to choosing alternative reconstruction strategies.

Acknowledgments

We appreciate the assistance of Jerome Loew MD, from the Department of Pathology at Rush University Medical Center, in selecting and interpreting the histologic images in Figure 4.

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