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SECTION I: SYMPOSIUM I: Papers Presented at the 2005 Meeting of the Musculoskeletal Tumor Society

Cemented Rotating Hinge Endoprosthesis for Limb Salvage of Distal Femur Tumors

Sharma, Sanjeev*; Turcotte, Robert, E*; Isler, Marc, H; Wong, Cindy*

Author Information
Clinical Orthopaedics and Related Research: September 2006 - Volume 450 - Issue - p 28-32
doi: 10.1097/01.blo.0000229316.66501.fc

Abstract

Limb salvage with endoprosthetic replacement for the distal femur in the face of bone tumors has become the preferred method of treatment over allograft implantation, especially in the context of chemotherapy.15,34 Initial concerns about local recurrence and metastasis have been alleviated, with reports showing no difference between limb salvage and amputation.1,12,16,24,27,32 Despite this, there remains concern over the long-term outcome of these reconstructions. Though infection continues to be a major cause of concern, its incidence has gradually decreased over time. Aseptic loosening is now the leading cause of failure.15,30,33 As with conventional joint replacement, a debate exists whether one should use cementless or cemented stems. Literature is sparse on reports about long- term outcomes for this type of surgery.2,5,23,25 Short term outcomes of distal femoral replacement have been favorable for both cemented and cementless constructs.17,18

We hypothesized distal femoral replacement with a cemented construct would yield a durable and reliable construct with respect to both survival and incidence of complications.

MATERIALS AND METHODS

We retrospectively identified through a tumor registry all distal femur endoprostheses inserted between May 1990 and November 2004. Only patients with bone or soft-tissue tumors treated initially by the senior authors (RT, MI) were included. Patients who received massive implants for revision arthroplasty or who were initially treated in other institutions were excluded from the study. Seventy-seven patients were identified from the database using the above-mentioned criteria. The hospital charts and clinic notes for the 77 patients were reviewed and data were extracted with respect to type of cancer, adjuvant therapy, and complications. Thirty-eight patients were male and 39 were female, with an average age at time of operation of 42 years (range, 12-87 years). All had tumor involvement of their distal femur. Forty (52%) of the patients had osteosarcoma, 11 (14.3%) had chondrosarcoma, eight (10.4%) leiomyosarcoma of bone, three (3.9%) Ewing's sarcoma, three (3.9%) malignant fibrous histiocytoma of bone, two (2.6%) soft tissue sarcoma involving the femur, two (2.6%) locally advanced Stage 3 benign giant cell tumor, and eight (10.4%) metastatic carcinoma. Sarcomas were staged as 10 (14.9%) Stage IA, nine (13.4%) Stage IB, six (9.0%) Stage IIA, 30 Stage IIB (44.8%) and seven (10.6%) stage III. There were five patients in whom we were unable to determine to stage of disease from the hospital charts. The mean followup time was 52 months (range, 1.5-157 months). All patients were seen in followup by one of the two senior authors (RT and MI) and by orthopaedic residents under their direct supervision. No patient was lost to followup. This work was approved in respect to local ethics committee rules.

Neither personal exhaust suits nor laminar flow rooms were used for any of our cases at time of tumor surgery. Routine perioperative antibiotic prophylaxis for 48 hours was administered to all patients. The MRS Kinematic rotating hinge (Fig 1) and GMRS Duration rotating hinge (Stryker-Howmedica Inc., Mahwah, NJ) implants were used in all patients. There have been subtle changes in the implant design over the course of the study including using a forged, not casted, tibial component. All constructs were cemented using a nonpressurized technique and since 1997 there has been routine use of antibiotic laden cement. Canals were reamed with rigid reamers to the size of the implant (line to line). The average length of femoral resection was 20 cm (range, 13-31 cm). Stem sizes were not recorded but it was routine to avoid whenever possible stems smaller than 13 mm. The use of antibiotics in cement was not uniformly recorded. Surgical margins were termed wide at time of surgery in 59 patients and marginal in 18. Seventy-two patients had negative margins under microscopic review while five had positive margins. Forty-two (54.5%) patients received chemotherapy and six (7.8%) received radiotherapy.

Fig 1
Fig 1:
This figure shows a retrieved specimen of the cemented MRS rotating hinge implant used for all patients in this series.

Revision was defined as the need to exchange any implant components for breakage, wear, loosening, infection, or amputation. Functional data were obtained using the 1987 version of the Musculoskeletal Tumor Society (MSTS 1987) test13 and the Toronto Extremity Salvage Score (TESS).10,11 The first is completed by the surgeon and the second is self-administered by the patient. Patients who went on to amputation did not complete questionnaires.

Kaplan-Meier survival was calculated using SPSS 12.0 (Chicago, IL, 2003). Time zero was defined as the date of primary prosthetic surgery. Events were defined as any incidence requiring revision of part or the entire implanted component.

RESULTS

At final followup, 54 patients had no evidence of disease, 16 were alive with disease, and seven were dead of disease. Of the 67 patients with sarcoma, 15 went on to have progressive disease. All of these patients showed meta- static lesions involving at least the lungs.

The 5 and 10-year survival for the implant was 84% and 79% with a mean survival of 121 months (Fig 2). There were no revisions for aseptic loosening. Of the 70 patients with a retained implant, MSTS scores were obtained in 39 (56%) with an average score of 30 (Fig 3) and the TESS was obtained in 23 (33%) with an average score of 77.6.

Fig 2
Fig 2:
A graph of a Kaplan-Meier curve shows the probability and interval confidence of implant survival over time. The 5 and 10-year cumulative survival was 84% and 79%, respectively.
Fig 3
Fig 3:
This bar graph shows the averaged results in each category scored by patients with the MSTS 1987 functional scale. The average MSTS 1987 score was 30.

Six (7.8%) patients had postoperative infections. All six infections were diagnosed within 3 months after index procedure and five were within 1 month. All were initially treated operatively with repeated débridement and lavage and antibiotic spacers. Four infections ultimately healed and two required above knee amputation.

Five patients (6.5%) had local recurrence of tumor; four from bone sarcomas and one soft-tissue sarcoma. Three were treated with an above knee amputation. The other two were soft tissue recurrences away from the implant, one from parosteal osteosarcoma and one from soft tissue liposarcoma. Both were treated with wide local excision without implant revision. One patient with initial Grade II chondrosarcoma presented with either a solitary metastasis to the ipsilateral distal fibula or a metachronous chondrosarcoma two years following the endoprosthetic reconstruction. The patient required a below knee amputation while preserving the implant, was found free of disease 7 years later and was not recorded as a failure.

Three patients (3.9%) sustained fractures of their mobile tibial bearing component and all occurred within 4 years of implantation. All metal fatigue fractures occurred at the junction of the tibial bearing surface and stem. One patient broke this component twice 2 years apart and is now fine 3 years after the second exchange. In one patient with tibial bearing component fracture, a broken axle was found unexpectedly at time of revision, but despite this finding the hinge joint was found somewhat stable (Fig 4). Only one failure event was recorded for both these patients. One patient developed a loose bumper at 18 months that interfered with extension and required replacement.

Fig 4
Fig 4:
This figure shows a broken tibial bearing component that occurred typically at the junction of the stem and the base. At the time of revision the axle was found broken as well.

Additional complications included three (3.9%) patients with patellar instability, two of which required operative management; one patient underwent lateral release and another required resurfacing of a previously unresurfaced patella. Two patients (2.6%) underwent knee manipulation under anesthesia for joint ankylosis. There were also two proximal periprosthetic femoral fractures that healed with conservative treatment and three common peroneal nerve palsies that recovered fully.

DISCUSSION

This series represents the authors' experience with a singe implant for various tumor conditions affecting the area of the distal femur. The aim of this series was to demonstrate the effectiveness of cemented constructs in these situations.

We note several limitations. This cohort represents a consecutive experience of the two senior authors (RT and MI) over a 15-year period, but it is retrospective and not all patients were systematically followed. Patients who underwent an amputation were obviously failure of treatment but we did not score them following their amputation. Additionally many had local recurrences and most died subsequently to the local relapse. We felt it was inappropriate to attribute scores without direct clinical observation. We had no specific final radiographic review to assess evidence of discrete or subclinical implant loosening. The controls were drawn from the combined experience in the literature. Nonetheless, this is a relatively large series for this approach and we believe the information likely representative for survivors.

For patients with poor prognosis, one would hope for a quick recovery and return to near normal function while avoiding reoperation from early complications or implant failure. For those with better prognosis, avoiding early complications that can interfere with adjuvant treatment and insuring longevity of the construct is of paramount importance.8,35,36 The use of cemented implants has the additional advantage of immediate stability of the construct, allowing immediate full weightbearing and rehabilitation of the affected limb.

Implant survivals for distal femoral replacement obtained from literature ranged from 45% to 80%.2,5,6,9,17-20,23,25,26,29,30,37 Direct comparison of survival results in this series to other published reports is difficult due to the heterogeneity with respect to patient population and implant used. However, the 5 and 10-year survivals of 84% and 79% respectively in our series compared favorably with results obtained in other series for cemented and cementless implants.

We could not identify patients with clinical or suspected aseptic loosening. This is dramatically different from older prosthetic designs28 and also better than reported series of more modern implants for cemented and cementless designs.17,18,23,25,30,33 The aseptic loosening rates in the literature have been reported to be as high as 32% and it has been suggested this rate increases dramatically after 36 months.30 The mean followup in our series was 52 months with a median of 41 months. However, 27 (35%) of our patients had greater than 60 months follow-up. The current implant, like some other cemented ones, has a porous surface on the body adjacent to the femur. It can allow for fibrous ingrowth and could act as a seal to prevent wear debris migration into the bone/cement interface and prevent loosening.28,31 This fibrous ingrowth can create a relatively strong mechanical bond with a porous surface3,21 and has been shown theoretically to reduce stem and cement stresses after segmental prosthetic replacements.7 This could be an important additional factor to minimize stress shielding and prosthetic failure and result in improved loosening rates, as shown by our series and in a previous study.31 As radiographs were not formally reviewed, there may be an incidence of asymptomatic aseptic loosening that remains undetected.

Infection is a serious complication after endoprosthetic reconstruction. It often leads to amputation and retards or contraindicates postoperative chemotherapy. The infection rate in the literature varies widely, ranging from 2% to 40%.5,6,17,18,23,25,30,37 The use of laminar flow operating theatres and personal exhaust suits have been suggested as methods of decreasing infection rate; however neither were used in this series.25 Though our rate of infection is high (7.8%) it remains comparable to other published reports. All our cases of infection were diagnosed within 3 months after surgery. We could not identify any infection of late occurrence nor have we identified a case with septic loosening. Though we recognize this complication may occur, we could not find any data regarding this issue in the massive implant literature. We could not identify a lesser risk of infection since we began to use antibiotic- loaded cement routinely for endoprosthetic replacement, and this issue remains unclear in the literature.4

The local recurrence rate in this series was 6.5% and is similar to the literature.23,25 If we consider the rate of revision relating to local recurrence it drops to 4.3%. Although local recurrence may lead to revision of the components or limb amputation, we believe this is not related to the quality of a cemented construct but more representative of the quality of resection and aggressiveness of the tumor.

The initial cast design of the tibial bearing component has recently been changed to a forged one which is known to be stronger and from which we have not recorded any failure yet. We could not identify reasons why fracture of the component occurred, though in the patient who sustained a second tibial bearing fracture the polished stem of the rotating hinge mechanism was found somewhat loose in the polyethylene cemented component of the tibia, suggesting some wearing of the peghole edges that allowed increased mobility into varus valgus. There were no patients who had a femoral stem or a body fracture in this series. The fracture rate of stems has been reported to be as high as 6% in some series and there is suggestion the rate of fracture may be related to the diameter of stems used.6,17,23,25 Data were not available with respect to the diameter of stems. The lack of a transfixing hole in the stem may also contribute to the lack of stem fracture in this series.25 We did not record any dislocation of the rotating hinge, as some have reported.31

The functional status of the patients is quite good as indicated by the MSTS 1987 and TESS scores. The patients tend to be accepting of their implants and have excellent pain control and good range of motion of the affected extremity, and the overall functional outcome of the patients in this series is consistent with other published series.11,14,22 Malo et al22 reported a slight but noteworthy functional advantage from a cemented implant compared with a popular cementless design. The results obtained in this series are similar to those obtained in the literature suggesting patients who received prosthetic replacements tend to be accepting of their implants and have high levels of function.15,18 The response rate of 56% for the MSTS and 33% for the TESS reflects the non-standardized retrospective nature of this study. Despite this, we believe the number of respondents is sufficient to give an accurate representation of the functional outcome of this patient population.

Distal femoral replacement with a cemented rotating hinge prosthesis design results in a functional limb with good medium-term outcome. This study and the literature14,22,30,37 suggest cement is a valid option for tumor endoprostheses and, in our study, cement could not be held responsible for the recorded failures. We believe the primary implant related issue that will impair outcome remains the high rate of infection. With this implant and cementation technique we could not find evidence of clinical loosening. Despite the retrospective nature of this study, it clearly lends support to the use of cemented constructs for distal femoral replacement.

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