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© 1999 The Journal of Bone and Joint Surgery, Inc. Long-Term Follow-up of Pyrolytic Carbon Metacarpophalangeal Implants*  , ROCHESTER, MINNESOTAInvestigation performed at the Mayo Clinic and Mayo Foundation, Rochester
Background: The metacarpophalangeal joint is the most commonly involved joint when rheumatoid arthritis affects the hand. Many prosthetic implants have been designed for the replacement of this joint. Although studies of these implants have shown relief of pain, they have generally demonstrated a poor range of motion, progression of ulnar drift, and bone loss, as well as failure, fracture, and dislocation of the implant. Methods: From December 1979 to February 1987, 151 pyrolytic carbon metacarpophalangeal implants were inserted in fifty-three patients. The implants had an articulating, unconstrained design with a hemispherical head and grooved, offset stems. Forty-four patients had rheumatoid arthritis; five, posttraumatic arthritis; three, osteoarthritis; and one, systemic lupus erythematosus. Three patients (eleven implants) were lost to long-term follow-up, and twenty patients (fifty-one functioning implants) died after the implant had been in situ for an average of 7.2 years. Eighteen implants (12 percent) in eleven patients were revised. Fourteen of the eighteen implants were replaced with a silicone-elastomer or another type of implant, and the remaining four were removed and a pyrolytic carbon implant was reinserted with the addition of bone cement or bone graft, or both. Twenty-six patients (seventy-one implants) were available for long-term review at an average of 11.7 years (range, 10.1 to 16.0 years) after implantation. Results: The implants improved the arc of motion of the fingers by an average of 13 degrees and elevated the arc by an average of 16 degrees. As a result, fingers were in a more functional, extended position. A complete set of preoperative, postoperative, and follow-up radiographs was available for fifty-three of the seventy-one implants that were followed long term. There was a high prevalence of joint stability: fifty (94 percent) of the fifty-three implants were in a reduced position postoperatively, and forty-one (82 percent) of those fifty implants were still in the postoperative reduced position at the time of long-term follow-up. Ulnar deviation averaged 20 degrees preoperatively and 19 degrees at the time of follow-up, with only the long finger having an increase in deviation. No adverse remodeling or resorption of bone was seen. Fifty (94 percent) of the fifty-three implants had evidence of osseointegration, with sclerosis around the end and shaft of the prosthetic stems. Radiolucent changes were seen adjacent to twelve implants. There was minimum-to-moderate subsidence (four millimeters or less) of thirty-four implants; most of the subsidence occurred immediately postoperatively. Survivorship analysis demonstrated an average annual failure rate of 2.1 percent and a sixteen-year survival rate of 70.3 percent. The five and ten-year survival rates were 82.3 percent (95 percent confidence interval, 74.6 to 88.2 percent) and 81.4 percent (95 percent confidence interval, 73.0 to 87.8 percent), respectively. None of the revised implants had any visible changes of wear or deformity of the surfaces or stems. Four instances of chronic inflammatory tissue and three instances of proliferative synovitis were noted histologically. Focal pigment deposits were seen in three fingers, one of which had removal of the implant two months after a fracture. No evidence of intracellular particles or particulate synovitis was found. Conclusions: The results of this study demonstrate that pyrolytic carbon is a biologically and biomechanically compatible, wear-resistant, and durable material for arthroplasty of the metacarpophalangeal joint.
The metacarpophalangeal joint is the most commonly involved joint in hands affected by rheumatoid arthritis. Impairment of this joint can result in 100 percent impairment of the finger, and impairment of the hand can result in as much as 90 percent impairment of the extremity6. Since the early 1900s, when soft-tissue interposition arthroplasty was introduced, there have been many hinged10,17,18,21,28, semiconstrained1,11,38, and unconstrained2,7,27,40,41 designs of prosthetic implants for the replacement of the metacarpophalangeal joint. Although the use of metacarpophalangeal implants has resulted in the relief of pain, such implants have generally been associated with a poor range of motion, progression of ulnar drift, and loss of bone1,2,7,38,41. Multiple failures, fractures, and dislocations of the implants have been reported, and the implantation techniques have been found to be technically demanding1,7,21,31,41. Currently, the Swanson silicone-elastomer interpositional spacer is the most commonly used implant for metacarpophalangeal joint arthroplasty5,15,26. However, the rates of mechanical failure for this implant have been high, with as many as 82 percent (twenty-eight of thirty-four) fracturing within five years after insertion2,8,25,26. In addition, delayed infection, silicone lymphadenopathy, and malignant lymphoma have recently been reported to be associated with silicone arthroplasty19,29. Pyrolytic carbon is a synthetic material formed by the pyrolysis of a hydrocarbon gas. Pyrolytic carbon is formed as a coating that is deposited onto high-strength graphite substrates by heating a hydrocarbon gas, such as propane, to about 1300 degrees Celsius. The resulting pyrolytic carbon has a turbostratic, or disordered, two-dimensional crystal structure with a high concentration of three-dimensional diamond cross-linked bonding. The physical and mechanical properties of this isotropic material fall between those of graphite and diamond9,24. In 1969, pyrolytic carbon was first used to make a component of an artificial heart valve. Since then, about three million pyrolytic carbon heart-valve components have been implanted, resulting in more than fifteen million patient-years of experience24. Its record of reliability in the very demanding service as an artificial heart valve has shown pyrolytic carbon to be high-strength, fatigue-resistant, and wear-resistant. The chemical stability of pyrolytic carbon makes it extremely compatible with living tissue and the engineering material most compatible with blood9. A variety of animal models of pyrolytic carbon implants have also shown direct bone apposition to its as-deposited surface13,14,37. Pyrolytic carbon also has very attractive mechanical properties as an orthopaedic implant material. It has an elastic modulus similar to that of cortical bone, which makes it ideal for implant-bone stress transfer12. A preliminary evaluation of articulating pyrolytic carbon-on-pyrolytic carbon metacarpophalangeal joint implants in primates revealed no evidence of wear or wear debris, no evidence of an inflammatory reaction, and excellent bone-implant incorporation13. In 1979, clinical application of articulating, unconstrained pyrolytic carbon metacarpophalangeal joint implants began on a custom basis. Short-term results demonstrated an improvement in the range of motion, relief of pain, adequate biological fixation, and few complications3. The purpose of the present study was to review retrospectively the long-term outcomes of arthroplasties with these metacarpophalangeal joint implants.
From December 1979 to February 1987, 151 pyrolytic carbon metacarpophalangeal implants were inserted in fifty-three patients at the Mayo Clinic and Mayo Foundation. The implant had an articulating, unconstrained design with a hemispherical head and grooved, offset stems (Figs. 1-A and 1-B). A nominal, 0.42-millimeter-thick pyrolytic carbon coating was applied to premachined graphite substrates. Later in the series, tungsten was added to the graphite substrate of some implants for better radiographic visualization. A total of eighteen small, seventy-one standard, and sixty-two large implants were used.
All patients who were candidates for replacement of the metacarpophalangeal joint were considered for treatment with an unconstrained pyrolytic carbon implant. In general, the implant was used in patients who had little deformity, subluxation, or dislocation of the metacarpophalangeal joint. Dislocated joints with shortening of more than one centimeter or with advanced cortical bone loss were not treated with the implant. Forty-four patients had rheumatoid arthritis, five had posttraumatic arthritis, three had osteoarthritis, and one had systemic lupus erythematosus. Fifty-four index fingers, forty-three long fingers, twenty-eight ring fingers, and twenty-six small fingers were treated with the implant. Forty-four patients were female, and nine were male. The average age at the time of the operation was fifty-eight years (range, twenty-one to eighty-five years). Fifty-one patients were right-hand dominant. One hundred and one implants were placed in dominant hands. Seven patients had bilateral involvement. Three patients (eleven implants; 7 percent) were lost to follow-up within eleven to fourteen months after the initial operation. Twenty patients (fifty-one functioning implants; 34 percent) died before the time of review; the implants in these patients had been in situ for an average of 7.2 years (range, 1.7 to 14.9 years) at the time of death. Eighteen implants (12 percent) in eleven patients were revised, and fourteen of the eighteen were replaced with a silicone-elastomer or another type of implant. Thirteen of the fourteen implants were revised because of subluxation, dislocation, or soft-tissue imbalance. The fourteenth implant was revised secondary to a fracture of the implant that had occurred nine years postoperatively, while the patient was lifting a heavy suitcase. The four remaining implants were removed secondary to loosening, and a pyrolytic carbon implant was reinserted with the addition of bone cement or autogenous bone graft, or both. Twenty-six patients (seventy-one implants) were available for long-term clinical follow-up at an average of 11.7 years (range, 10.1 to 16.0 years) after implantation. Nineteen of these patients (sixty-two implants) had rheumatoid arthritis; four (four implants), posttraumatic arthritis; two (four implants), osteoarthritis; and one (one implant), systemic lupus erythematosus.
Operative Technique With use of specially designed reamers that were slightly undersized relative to the implant, the canals were shaped by gently impacting and compressing the intramedullary cancellous bone. The largest implant possible was used for stability, with the limiting factor being the size of the medullary canal of the proximal phalanx. The components of the implant were then press-fit into the canals with special nonabrasive plastic impactors. The joint capsule was then repaired with running or interrupted sutures. The radial collateral ligament was repaired if necessary. The extensor hood was meticulously repaired to achieve proper centralization. Intrinsic release or transfer was performed occasionally, as necessary. All operations were performed by the senior two of us (R. D. B. and R. L. L.).
Postoperative Care
Methods of Evaluation The preoperative, postoperative, and most recent follow-up radiographs were reviewed. A complete set of preoperative, postoperative, and follow-up radiographs was available for fifty-three of the seventy-one implants that were followed long term. The position of the joint (reduced, subluxated, or dislocated) was determined on each lateral radiograph. Measurements of radioulnar angulation of the metacarpophalangeal joint were made directly on the posteroanterior radiographs. Any changes in the appearance of the periprosthetic bone or in the position of the implant were noted by comparing the posteroanterior and lateral follow-up radiographs with the initial postoperative radiographs. Subsidence of either the proximal phalangeal or the metacarpal component of the implant was noted. Subsidence was measured in millimeters on the basis of a comparison of the postoperative and most recent follow-up posteroanterior radiographs and was categorized as none, minimum (less than two millimeters), moderate (two to four millimeters), or severe (more than four millimeters). Pathological reports were examined to look for abnormal findings in any of the tissue specimens sent at the time of revision. Representative samples were sent from each hand but not from the site of each implant. Therefore, this material was evaluated for each patient and hand rather than for each individual implant site. Radiographs made before and after revision were also reviewed. Finally, survivorship analysis was performed to determine the overall success rate of the metacarpophalangeal implants over the sixteen-year period30,34. Failure was defined as an implant that was dislocated at the time of follow-up or that had been revised or replaced for any reason. Implants that were lost to follow-up were also considered as failures for the survivorship analysis. Implants withdrawn from the study included those that had been successfully followed throughout the trial as well as those that were functioning well, at the time of death, in patients who had died before the time of review. The average annual failure rate, determined from the life table, was calculated as the average of all failure rates for each year of follow-up. The survival curve was derived from the cumulative survival rate over time, as calculated from the actuarial life table. The standard error, given as a percentage, and the 95 percent confidence intervals were calculated from the data in the life table30. The difference between the preoperative and latest follow-up values for range of motion and ulnar deviation were analyzed for significance with one-way and two-way analysis of variance. Significance was defined as a p value of less than 0.05 (BMDP Statistical Software, Los Angeles, California). The log-rank test and chi-square distribution were used for the statistical comparison of the survivorship-analysis groups.
At the long-term follow-up evaluation, no patient reported pain specific to the implanted joint. One patient played golf several times per week, and another played guitar and climbed rocks. A third patient still performed strenuous farm work, and several occasionally played tennis. All of the patients were satisfied with the functional and cosmetic results of the procedure (Figs. 2-A, 2-B, 2-C and 2-D). The patients who noted a limitation of activities had restricted motion of the joint secondary to systemic complications of rheumatoid disease that were unrelated to the implants.
Range of Motion
Radiographic Evaluation
Radiographic measurements revealed an average preoperative ulnar deviation of 20 degrees for all fingers combined, with the deviation ranging from an average of 16 degrees for the index finger to 26 degrees for the ring finger (Table II). At three months postoperatively, ulnar deviation had decreased in all fingers, and the decrease was found to be significant when the data for all fingers were combined (p = 0.01). At the time of long-term follow-up, ulnar deviation averaged 19 degrees, which was essentially equivalent to that noted preoperatively (p = 0.75) (Figs. 5-A, 5-B, and 5-C). Twenty-three (43 percent) of the fifty-three implants evaluated radiographically had an ulnar deviation of more than 20 degrees at the time of long-term follow-up. Compared with the preoperative value, ulnar deviation had increased in 43 percent (twenty-three) of the implants and had decreased or remained unchanged in the remaining 57 percent (thirty).
No adverse bone-remodeling or resorption was noted in the fifty-three fingers with long-term follow-up. Loosening of the implant and ulnar drift (as will be discussed later) occurred in some patients and necessitated revision. Host-bone acceptance of the pyrolytic carbon implants, which were inserted without cement, proved to be successful in most fingers (Figs. 6-A and 6-B). Fifty (94 percent) of the fifty-three fingers had evidence of sclerosis around the end and shaft of the prosthetic stems at the time of long-term follow-up (Figs. 7-A, 7-B, and 7-C). A rim of sclerotic bone was more frequently observed around the stem of the proximal phalangeal component (thirty-one implants; 58 percent) than around the stem of the metacarpal component (twenty-two implants; 42 percent). At the time of follow-up, radiolucency was observed adjacent to twelve implants (six patients), seven of which were metacarpal components (Fig. 8-A). None of these patients had clinical loosening of the implant. Six of the twelve implants were in one patient who had rheumatoid arthritis.
At the time of long-term follow-up, thirty-four (64 percent) of the fifty-three implants evaluated radiographically had some degree of subsidence of the metacarpal component or the proximal phalangeal component, or both (Table III). Of the fifty components that had subsided to some degree, twenty (40 percent) were metacarpal components and thirty (60 percent) were proximal phalangeal components (Fig. 7-C). There was subsidence of both the metacarpal and the proximal phalangeal component of sixteen implants, of only the proximal phalangeal component of fourteen implants, and of only the metacarpal component of four implants.
Revision Fourteen implants in eight patients were replaced with another implant. Subluxation, flexion contracture, stiffness, and dislocation led to replacement of ten metacarpophalangeal joints with a Swanson silicone implant after postoperative periods ranging from one month to 10.9 years. Two carbon implants were replaced with a second carbon implant, at nine months and 13.5 months after the operation, because of loosening and dislocation. One implant was fixed with cement, although this implant was replaced again after 3.9 years with a Sutter silicone-elastomer implant because of pain, loosening, and stiffness (Fig. 8-B). After nine years in situ, one implant fractured through the proximal phalangeal stem, while the patient was lifting a heavy suitcase. This implant was removed two months after the fracture and was replaced with a metal-and-plastic implant, which was fixed with cement.
There were no clinically observed instances of reactive synovitis. Black staining was seen in the pericapsular tissue in the patient who had a fracture of the implant. The joint capsule was slightly stained and showed minimum reactive material. There was marked black staining of the distal tissues near the site of the fracture. None of the revised implants had any visible wear or deformity of the surfaces or stems. Tissue from ten hands that had a revision was submitted for pathological evaluation. Four instances of chronic inflammatory tissue and three instances of proliferative synovitis were seen histologically. Focal pigment deposits were noted in three instances; the patient from whom the implant had been removed two months after it fractured had such deposits. No evidence of intracellular particles or particulate synovitis was found.
Survivorship Analysis
In the first ten years after the operation, the survival curves for the women and men were very similar, as were the curves based on diagnosis. After ten years, the survival rates for the women and for the patients who had rheumatoid arthritis progressively decreased compared with the rates for the men and for the patients who did not have rheumatoid arthritis. However, differences in the entire curves over time were not detectable on the basis of gender or diagnosis (chi square = 0.508, degrees of freedom = 1, p > 0.05). It should be noted that female patients and patients who had rheumatoid arthritis accounted for the overwhelming majority of this series' population and thus an increased number of failures would be expected to be found in those groups. Differences in survival curves were also not detectable on the basis of age (chi square = 0.003, degrees of freedom = 1, p > 0.05).
Despite the widespread use of metacarpophalangeal joint implants for approximately thirty years, there have been few reports with a follow-up period of ten years or longer (Table V). With regard to gender, age, and underlying diagnosis, our study population was comparable with those of previous reports1,7,16,41.
At the time of long-term follow-up in the present study, the pyrolytic carbon implants had an average arc of motion of 52 degrees, with a range of motion of 24 to 76 degrees. Additionally, the metacarpophalangeal joints were in a more extended and therefore more functional position. Blair et al.7 reported a range of motion of 16 to 40 degrees with the Flatt metallic, pronged prosthesis. This range was similar to that reported with the silicone-elastomer prosthesis (21 to 50 degrees), by Wilson et al.41. The arc and range of motion of the pyrolytic carbon implants and those reported by Blair et al. and Wilson et al. were considerably better than those reported in association with a cemented Schultz ball-and-socket prosthesis1 (range, 58 to 68 degrees) or the Niebauer silicone-elastomer Dacron prosthesis16 (range, 55 to 83 degrees). The stability of the pyrolytic carbon implants was slightly higher than that reported for the Swanson silicone-elastomer implant in the study by Wilson et al.41, in which twelve (3.2 percent) of 375 implants had either subluxated or dislocated at the time of long-term follow-up. The stability of the pyrolytic carbon implants was better than that of the Niebauer prostheses in the series of Derkash et al.16, in which fifty-two (58 percent) of eighty-nine implants were reported as unstable. Although Adams et al.1 did not report a rate of instability of the Schultz prosthesis, 39 percent (fourteen) of the thirty-six implants in their series fractured at the neck of the proximal phalangeal component distal to the level of the ball and socket; thus, measurement of the stability of this prosthesis would be of little value. The natural resting position of the fingers is in slight ulnar deviation, with typical values of 15 degrees of ulnar deviation for the index finger, 13 degrees for the long finger, 3 degrees for the ring finger, and 7 degrees for the small finger22. A major portion of the deformity resulting from rheumatoid disease is caused by progression of this passive ulnar angulation. Although the ulnar deviation is initially corrected by most arthroplasties of the metacarpophalangeal joint, it has been noted to recur and then progress in short-term and long-term studies1,8,16,38,41. Although initial postoperative improvements were not maintained, the pyrolytic carbon implants appeared to have halted the progression of ulnar deviation, with almost no difference between the preoperative average of 20 degrees and the long-term follow-up average of 19 degrees. Forty-three percent of the fifty-three implants that were assessed radiographically had ulnar deviation of more than 20 degrees at the time of long-term follow-up. These results are an improvement compared with those of other long-term studies, in which a large percentage of patients had more than 20 degrees of ulnar deviation and progression with time1,7,16,25,41. Perhaps the most consistent finding of previous long-term studies of metacarpophalangeal joint arthroplasties is the notable amount of cortical erosions, bone loss, and periprosthetic radiolucency1,7,16,36,39. This finding is disturbing because it represents poor host-bone tolerance of the implant mechanically or biologically, or both. The rate of periprosthetic radiolucency was extremely low in our series; it was seen around only twelve (23 percent) of the pyrolytic carbon implants. The rate of radiolucency was as high as 80 percent in a series of thirty-six Schultz metacarpophalangeal joint implants1 and as high as 87 percent in a series of thirty-eight radiographically assessed Flatt metallic, hinged prostheses7. Derkash et al.16 noted destructive bone loss around 87 percent of fifty-four silicone Dacron implants that had been radiographically evaluated in their series of eighty-nine prostheses. Wilson et al.41 reported that five (14 percent) of their thirty-five patients who had a Swanson silicone-elastomer prosthesis had evidence of cortical erosions due to impingement of the stem, although no functional loss was noted. Varma and Milward38 reported cortical erosions around 14 percent of sixty-five Nicolle finger-joint prostheses, with the bone loss most notable along the proximal phalanges. Most of the pyrolytic carbon implants in our series had a rim of sclerotic bone, which is believed to be secondary to osseointegration combined with the well matched elastic modulus, resulting in uniform implant-bone stress transfer. The pyrolytic carbon implants had an acceptable long-term rate of subsidence, with only sixteen of the fifty-three implants that were evaluated radiographically showing evidence of severe subsidence at the time of long-term follow-up. Although other authors have not quantified subsidence, they have described migration of the implant, joint-space collapse, so-called implant sink-in, and periarticular heterotopic ossification (which may represent subsidence of the implant)7,17,26. Of the pyrolytic carbon implants with severe subsidence, none were noted to be painful, unstable, or in need of revision. In most cases, the subsidence resulted from osteopenic bone combined with initial settling of the implant and did not progress notably over time. In long-term studies with an average follow-up period of more than five years1,7,16,26,41, rates of fracture of the metacarpophalangeal joint implant have ranged from 6 percent41 to 47 percent7. Fractures of the implant and related complications do not always necessitate revision. In fact, in some studies of silicone-elastomer prostheses, fractures appeared to be unimportant clinically because the function of the metacarpophalangeal joint did not seem to be impaired8,26,35,41. Regardless, only one of the pyrolytic carbon implants in our series fractured, at nine years postoperatively, and a relatively low rate of revision (eighteen of 151 implants; 12 percent) was observed after a maximum of sixteen years of follow-up. Pathology reports noted findings consistent with rheumatoid arthritis and no evidence of implant-related etiology; this observation attests to the long-term biological compatibility and wear resistance of pyrolytic carbon. Long-term survivorship analyses of prosthetic implants, other than those in the finger joints, have been widely described32-34. A survivorship analysis of metacarpophalangeal joint replacements was reported by Hansraj et al.23 for a series of 170 Swanson silicone implants that had been followed for an average of 5.2 years (range, two to ten years). The patient population and clinical results in their series are comparable with the population and results in the present study. The cumulative survival rates of the Swanson silicone implant were 98.9, 94.0, and 90.3 percent at two, five, and ten years, respectively, with use of revision as the end point23. Survivorship analysis of the pyrolytic carbon prosthesis with use of revision as the end point resulted in cumulative survival rates of 94.7, 89.6, 88.8, and 86.7 percent at two, five, ten, and sixteen years, respectively. The overall rate of success of joint replacements may be influenced by gender, diagnosis, and age. Women and patients who had rheumatoid arthritis had a slightly higher risk of failure of the pyrolytic carbon implant, but this may have been due to the distribution of the patients in the series. No difference in the survival rate was detected on the basis of age. In summary, the pyrolytic carbon metacarpophalangeal implants in the present series were found to be biologically and biomechanically compatible and were associated with a low rate of fracture, a low rate of revision, and a high rate of patient satisfaction. The results of this and other implant procedures are far from normal and far from ideal. However, it can be logically presumed that, left untreated, the involved joints would have been considerably worse. These small gains over a long period of time seem worthwhile.
*One or more of the authors has received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. Funds were received in total or partial support of the research or clinical study presented in this article. The funding source was the Joe W. and Dorothy Dorsett Brown Foundation, Metairie, Louisiana.
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