The goal of surgeons treating bone tumors is survival of the patient and, if possible, salvage of the limb and its function. Since the early 1980s, new developments in imaging techniques have led to earlier diagnosis and more accurate preoperative staging. Advances in neoadjuvant chemotherapy and the progress in surgical techniques helped to establish limb salvage as an accepted method of treatment of musculoskeletal neoplasms. Tremendous progress in bioengineering during the last decades made possible the bridging of large segmental defects with prostheses. As a result, during the last 30 years, the overall 5-year survival rate of patients with tumor endoprostheses has increased from 20% to 85%. 1,2,4,5,7,11–13,15,17,20,22,23,26–28,31,33,37
In addition, prosthetic replacement offers advantages when compared with various other reconstructive methods such as arthrodesis, implantation of allografts, or rotationplasty. 9,21,24,25,36 1,2,4,5,7,11–13,15,17,20,23,26–28,31,33,37
In this retrospective study, the results of long-term followup of 100 patients with KMFTR implants (Kotz Modular Femur and Tibia Reconstruction System, Howmedica GmbH, Kiel, Germany) are analyzed. The specific aims were to estimate the patients’ extremity and prosthetic survival, early and late complications, and the functional and radiologic outcome after a minimum of 9 years.
MATERIALS AND METHODS
Since 1982, the uncemented KMFTR system has been used. From September 1982 until December 1989, 100 primary reconstructions of the lower limb were done after resection of 68 primary malignant bone (n = 62) and soft tissue tumors (n = 6), 28 metastases, and four lymphomas.
Because of an altered local bone and soft tissue environment as compared with primary implantations, patients with a KMFTR prosthesis implanted during revision surgery after failure of a conventional hip or knee prosthesis (n = 33) were excluded from this study. In addition, patients with extendable endoprostheses were excluded from the study because the problems developing in such patients are different. 30,32
The tumor was located in the femur in 76 patients, in the tibia in 22 patients, and in the pelvis and the thigh in one patient each. The mean patient age at surgery was 38 years (range, 14–62 years).
After tumor resection, in 32 patients the proximal femur, in 40 patients the distal femur, in 19 patients the proximal tibia, in five patients the total knee (distal femur and proximal tibia), and in four patients the total femur were replaced by prostheses. In five patients, bone cement was used for stem fixation during the initial operation.
At the final followup, 51 patients had died. Patients with metastatic disease tended to die soon after the initial surgery (median, 15.6 months; range, 1–91 months). Eight patients who came to the authors’ clinic from other countries were lost to followup. The remaining 41 patients, 19 male and 22 female patients, were evaluated clinically and radiologically using the classification of the Musculoskeletal Tumor Society 8 10 29,35
The preoperative staging consisted of plain radiography and computed tomography (CT) of the lung and the bone, laboratory tests, 99m Tc bone scanning, abdominal sonography, and since 1987, magnetic resonance imaging (MRI) of the affected bone for evaluation of extension of the lesion and to search for skip lesions. In patients with Ewing’s sarcoma or osteosarcoma, the first cycle of chemotherapy was administered on the day of biopsy.
The intravenous perioperative antibiotic prophylaxis was administered routinely with a broad-spectrum penicillin or aminoglycoside and quinolone in patients with penicillin allergy. Subcutaneous low-dose heparin was administered routinely from the day of surgery until the patient was fully weightbearing. In patients with vessel preparation or bypass surgeries, full heparinization was done. In patients with distal femur prostheses, mobilization was started on the day after surgery, with increasing weightbearing starting from Week 6 until full weightbearing and mobilization was achieved 12 weeks after surgery. In difficult cases, such as extraarticular resections, major soft tissue reconstructions, and implantation of allografts, patients had to wear splints and orthoses. Because of tendon and muscle attachment to proximal femur prostheses and because of extensor mechanism reconstruction in proximal tibia prostheses, patients wore splints for 6 weeks after surgery and then wore orthoses with slow increases in range of motion (ROM).
Prosthetic Design
The KMFTR system has been used since 1982. The Vitallium diaphyseal anchorage of the system is an intramedullary stem with two lateral flanges perpendicular to each other, each with three holes to allow passage of six screws through the stem and the cortex. The straight stem has a fully madreporic surface and is available with diameters between 10 and 16 mm in 2-mm increments. During surgery, the medullary cavity is reamed to accept the nearest sized stem as press fit. This then is stabilized with cross screws, using all six holes for fixation. This diaphyseal component is connected to the madreporic bone replacement component by a morse taper, allowing for a minimum resection length of 12 cm, increasing in increments of 2 cm. The tibial joint component consists of a stem in which two long flanges are molded against the tibia and retained by means of a bar bolt through the stem. The femoral joint component consists of a stem and a condylar surface and is fixed with two screws running dorsally through holes in the prosthesis. Stem and base plates have full madreporic coating. The prosthetic joint is a flexion and extension hinge with its center of rotation offset posteriorly and the metal components being linked by two polyethylene bushings.
All operations were done as described previously. 17–20,27
Three types of complications were found: (1) Prostheses failure: defined as the time when an implant had to be removed with the anchorage component because of aseptic loosening, implant fracture, or septic loosening; (2) Prostheses-related minor complication: bushing failure; wear of the polyethylene bushing was defined as clinical varus and valgus greater than 5°. In some patients with synovitis enhanced by bushing failure, revision surgeries included changes of other polyethylene parts and prostheses components, with the exception of the anchorage component. These revisions were minor surgeries with minimal blood loss, no additional bone resection, and short hospital stays. Full weightbearing was started on the first postoperative day; and (3) Reoperation without correction of any part of the prosthesis was defined as a nonprosthesis-related complication.
In addition to the oncologic followup consisting of laboratory tests, CT scans of the lungs, abdominal sonography, and 99m Tc bone scan, plain radiographs were assessed according to the implant evaluation system of the International Symposium on Limb Salvage. 10 8
Statistical Methods
Spearman’s rank correlation coefficient was used to assess associations between quantitative variables. Wilcoxon’s rank sum test was used to test group differences in quantitative variables. Survival probabilities were calculated by the product limit method of Kaplan and Meier. 14 6
RESULTS
At final followup, 51 patients had died, mainly patients with metastatic disease. Most of the patients died soon after the initial surgery (median, 15.6 months; range, 1–91 months). In five of these patients, bone cement was used in the initial surgery. In these 51 patients, five dislocations of the proximal femoral prostheses and two nerve palsies were treated conservatively. In two patients, the bushings were changed and two contractures of the knee were treated. Three patients had a local recurrence (two patients with metastases, one patient with fibrosarcoma), and two patients underwent amputation of a limb. In one patient, the reason for amputation was local recurrence of a tumor with multiple metastases, and the other patient had an infection of the prosthesis with generalized sepsis. Both patients died of their disease within 2 and 7 months, respectively, after the amputation.
Eight patients from foreign countries who where treated surgically by the authors were lost to followup.
Forty-one patients could be followed up for a mean of 138 months (range, 113–188 months). Nineteen of these patients had a second operation because of failure of the prosthesis (Fig 1 ). The most common reason was aseptic loosening (27%; n = 11). In nine patients, the implant was changed once because of aseptic loosening (range, 10–121 months) after the initial surgery, and in two patients, the implant was changed twice. Infection of the prosthesis and implant fracture occurred in four patients (9.7%) each. In two of these patients, loosening of the pelvic component of the prosthesis was observed. After failure of the prosthesis, a tumor endoprosthesis could be reimplanted in each of the patients. Cement fixation had to be used in one patient during revision surgery because of a large bone defect. In 12 patients, the KMFTR prosthesis was implanted during the first revision surgery, seven patients received a modified type of prosthesis Howmedica Modular Reconstruction System (HMRS), 17,19,27
Fig 1.:
Prostheses-related major complications (n = 19).
A prosthesis-related minor complication occurred in 14 patients. In four patients, the polyethylene bushing and components of the prosthesis were changed, and in 10 patients, only the polyethylene bushings were changed (Fig 2 ). Twelve patients had two revision surgeries because of bushing failures. In 10 patients, the polyethylene bushings and components of the prosthesis were changed, and in 14 patients, only the polyethylene bushings were changed. One patient had two revision surgeries for polyethylene bushings, one revision surgery for the polyethylene bushings, and one revision surgery for components of the prosthesis. In 14 patients, no part of the prosthesis had to be changed.
Fig 2.:
Prostheses-related minor complications (n = 41).
Ten of the 43 nonprosthesis-related complications were hematomas during the first postoperative weeks. Seven cases of delayed wound healing and four cases of nerve palsy occurred soon after surgery. Revision surgery was done in two patients because of rupture of the ligamentum patellae and in eight patients because of contracture of the knee. Two fractures of the femur and six dislocations of the proximal femoral prosthesis were revised. In three patients, screws were removed to reduce stress shielding. In one patient, a femoral osteotomy for correction of an axial deformity was done (Fig 3 ).
Fig 3.:
Nonprostheses-related complications (n = 43).
In these 100 patients, the Kaplan-Meier estimate of the prosthesis overall survival rate was 85% after 3 years, 79% after 5 years, and 71% after 10 years (Fig 4 ). Limb salvage was achieved in 98%. In one patient, the reason for amputation was local recurrence of a hypernephroma with multiple metastases, and one patient had an infected prosthesis and systemic sepsis. Both patients died of their disease shortly after surgery (2 and 7 months, respectively).
Fig 4.:
Kaplan-Meier estimate of the prostheses overall survival rate of 100 patients for median 127.5 months after implantation.
Patients older than 33 years at the initial implantation of the prostheses had a statistically significant longer overall prosthesis survival than did younger patients (p = 0.024) (Fig 5 ). There was a trend, but no statistically significant differences were found in the overall prosthesis survival rates between male and female patients (p = 0.251) (Fig 6 ), resection length (p = 0.400) and site (p = 0.696) (Fig 7 ), and patients who had received chemotherapy and those who did not receive chemotherapy (p = 0.054) (Fig 8 ). A highly significant negative correlation was found between the number of revision surgeries for prosthesis-related minor complications and implant failure (p = 0.0048). No statistically significant correlation was found between the number of soft tissue complications and implant failure (p = 0.750), but a statistically significant increase (p = 0.013) of nonprosthesis-related complications with an increasing number of surgeries per patient was seen. The site of the prosthetic replacement, with the exception of total knee and total femur replacement, did not show statistical correlation with soft tissue complications (p = 0.280). The only local recurrence observed was in a patient referred from another hospital, with recurrence of a liposarcoma.
Fig 5.:
Kaplan-Meier estimate of the prostheses overall survival rate of 100 patients according to age.
Fig 6.:
Kaplan-Meier estimate of the prostheses overall survival rate of 100 patients according to gender.
Fig 7.:
Kaplan-Meier estimate of the prostheses overall survival rate of 100 patients according to prostheses localization.
Fig 8.:
Kaplan-Meier estimate of the prostheses overall survival rate of 100 patients according to chemotherapy.
In these 41 patients who were followed up for a mean of 138 months (range, 113–188 months), no amputation had to be done.
Clinical evaluation according to the score of the Musculoskeletal Tumor Society 8 Table 1 ). The poor scores of two patients were attributable to poor results in the gait category. After extraarticular resection of the knee, the patients could not extend their legs against gravity while sitting.
TABLE 1: Functional Score According to the Musculoskeletal Tumor Society 8 Radiologic evaluation of plain radiographs according to the implant evaluation system of the International Symposium on Limb Salvage 10 Table 2 ) (Fig 9 ). The poor scores of seven patients were because of poor results in the anchorage category because of broken screws, but the patients had no additional progressive radiologic or clinical signs of loosening.
TABLE 2: Radiologic Implant Evaluation System According to the International Symposium on Limb Salvage 10 Fig 9A–B.:
(A) Lateral and (B) anteroposterior radiograph (right) of a 41-year-old man 123 months after the implantation of a KMFTR distal femur endoprosthesis.
DISCUSSION
Because of improved surgical technique and chemotherapy, more patients live for more than 10 years after megaprosthesis implantation. The mean age of the patients at the initial surgery was 27 years. The patients usually had a high level of activity for a relatively long time with a fully constrained prosthesis, often after massive soft tissue resection. Thus, different problems were expected after long-term followup than after short-or midterm followup. 1,2,4,5,7,11–13,15,17,20,23,26–28,31,33,37
A review of the literature shows similar midterm results. Ward and Eckardt 33 5 28 15 11
Because aseptic loosening was the most common reason (27%) for implant failure in the current study, the system was modified. To avoid stress shielding under the rigid fixation, in 1990 an anatomically curved stem allowing better press-fit into the femoral canal was introduced and the use of plates was reduced to one.
Currently, various stems with different diameters ranging between 12 and 19 mm are available. To diminish the pressure on the distal fixation at the tip of the stem and to transfer the stress more proximally to the bone, the distal part of the stem is smooth. The new stem design for the tibia remained straight but was changed to one plate fixation and a smooth tip. 17,19,27
Because of significant damage after 2 to 5 years, the design of the bearing of the axis was changed to a single-block polyethylene bushing. To provide axial stability, the polyethylene shoulder of the bushing was changed to two additional metal rings with metal-to-metal contact to the hinge joint. The HMRS solution is a single-block polyethylene bushing (Fig 10 ). Patients with aseptic loosening were reviewed retrospectively, and it was found that the modifications of the system and a more conservative treatment strategy were suitable measures for reducing the number of revision surgeries for aseptic loosening. 3
Fig 10.:
The old type, two-block polyethylene bushing (KMFTR) is shown on the left, and a one-block polyethylene bushing (HMRS) is shown on the right.
Another method for reducing aseptic loosening is the change from a constrained flexion and extension knee prosthesis to a rotating hinge design used since 1996. There are no midterm results until now, but a significantly lower aseptic loosening rate of 0% to 10% at a followup between 42 and 134 months has been reported. 5,13
As in earlier studies, an increased risk of prosthesis failure was seen in male patients, in patients who received neoadjuvant chemotherapy, and in patients with their prosthesis located in the distal femur. Patients older than 33 years at the initial implantation of the prostheses had a statistically significantly longer overall prosthesis survival than did younger patients (p = 0.024). As expected, an increase in the number of soft tissue complications was found in association with an increased number of surgeries, but there was no correlation with implant failure.
Excellent and good functional and radiologic results according to the score of the Musculoskeletal Tumor Society 8 10 1,3,15,16,28,34,36 8 10
Forty-one patients underwent revision surgery because of prosthesis-related minor complications. After implantation, the fibrous tissue builds a pseudocapsule around the prosthesis joint and the proximal or distal parts of the prosthesis. In 15 patients, a synovitis and fibrosis, possibly enhanced by polyethylene wear attributable to increasing instability of the axis or metal wear debris, was observed. Because this led to a decreasing ROM of the knee, resection of the soft tissue sleeve around the prosthesis was required. In comparison with prosthesis-related major complications, prostheses-related minor complications require only minor surgeries with minimal blood loss, no additional bone resection, and short hospital stays. Because bone-prosthesis ingrowth already is present, full weightbearing can be started on the first day after surgery.
This relatively high rate of reoperations is a result of the authors’ policy of early revisions with a varus or valgus 5° or greater. The results are difficult to compare with results of other studies because no clear definitions for reoperations are stated in other publications.
In this study, a highly significant negative correlation was found between the number of revision surgeries for prosthesis-related minor complications and implant failure (p = 0.0048). This shows that early minor reoperations, such as changes of worn polyethylene bushings, can lead to a statistically significant reduction in implant failure.
The 10-year prosthesis overall survival rate was 71%. Although there was a considerable number of complications, limb salvage could be achieved in 98% of the patients after a median followup of 10.6 years after implantation. An early service operation of the prosthesis, such as change of worn polyethylene bushings, can reduce the risk of implant failure (p = 0.0048). Reoperations did not cause deterioration the outcome. The functional results were excellent or good in 83% of patients, and the radiologic results were excellent or good in 94% of patients after 10 years.
Acknowledgment
The authors thank Teresa Zettl for assistance.
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