Metacrpophalangeal joint prostheses

Review Article METACARPOPHALANGEAL

JOINT PROSTHESES

A review o f the clinical results o f past and current designs D. J. BEEVERS and B. B. SEEDHOM

From the Rheumatology and Rehabilitation Research Unit, University of Leeds, UK The clinical results of past and current hinge, flexible and third generation designs of MP prosthetic joints are reviewed. The hinged prostheses did not achieve acceptable short term clinical results while the silastie and third generation prostheses provided good results with correction of deformity and adequate range of motion (ROM). These good short term results did, however, get progressively worse with the recurrence of deformities and loss of ROM. It is evident that while most of the existing prostheses can relieve pain and restore appearance, none provide the degree of stability and ROM that is required to restore normal function to the NIP joint. The moderate results could be party due to the stage of the disease at which the surgery is carried out. At present, surgery on patients with rheumatoid arthritis is undertaken at a stage in the disease where the muscles and the ligaments surrounding the joint, and the bone, are generally in a poor condition. Surgery at this stage is really only a salvage procedure. Journal of Hand Surgery (British and European Volume, 1995) 20B." 2:125-136 This paper is a critical review of the clinical results of past and current prosthetic MP joints. Rheumatoid arthritis (RA) and post-traumatic osteoarthrosis (OA) are the major problems affecting this joint. RA is a progressive disease causing, among other things, destruction of the MP joint. Ulnar dislocation of the extensor tendons can also occur, and the weakened collateral ligaments eventually fail to resist the high internal forces exerted in the ulnar and palmar directions by the flexor tendons leading to ulnar drift and palmar subluxation (Smith et al, 1964; Hakstian and Tubiana, 1967; Smith and Kaplan, 1967; Backhouse, 1968; Calnan and Reis, 1968; Ellison et al, 1971; McMaster, 1972; Wise, 1975). Trauma can lead to post-traumatic OA of the MP joints, reducing mobility and therefore function (Dieppe, 1992).

abduction and adduction. For the lack of a better term, the next group of prostheses will be referred to as "the third generation". This is because there is no single design aspect common to them. This group comprises surface prostheses and prosthetic devices that are a hybrid of hinged and flexible prostheses. However, these prostheses were generally stronger and were designed for implantation into a single finger where the MP joint has post-traumatic OA. Flexion, extension, abduction and adduction movements were possible. CLINICAL RESULTS OF HINGE PROSTHESES Brannon and Klein prosthesis In 1953 Brannon and Klein implanted the first prosthesis into the MP joint (Fig 1). Only one report discussed the clinical results of this prosthesis (Table 1). Brannon and Klein (1959) commented on two patients with MP prostheses and noted that the ROM was from 32.5 ° to 75° of flexion, but this was only with a short follow-up period. Both patients were satisfied with the prostheses. X-rays showed that bone resorption occurred in one prosthesis and it sank into the bones 10 to 12 months after surgery. This resulted in a loss of ROM and shortening of the finger. The prosthesis was therefore modified by the addition of staples placed through each half of the hinge portion and the stem to prevent sinking of the prosthesis into the bones. No other independent clinical trials have been reported.

NIP PROSTHETIC DESIGNS All prostheses that are used for MP replacement are designed to relieve pain, to restore a functional ROM, to correct existing and prevent further deformity, and to give cosmetic improvement. Many prostheses have been used in an attempt to achieve all these aims since the first prosthesis was implanted over 40 years ago. They can be grouped into one of three basic designs: hinged prostheses; flexible prostheses and third generation prostheses. Hinged designs were the first to be implanted in the MP joint. Their simple uni-axis designs manufactured entirely from metal only allowed flexion and extension. These evolved into multi-axis hinges with snap-fit assemblies, manufactured from metal or ceramics and polymers. They gave flexion, extension, abduction and adduction movements. Following these were single component flexible prostheses. These cheap, easily moulded prostheses allowed flexion, extension,

Flatt prosthesis The Flatt prosthesis is effectively a modified Brannon and Klein prosthesis and was introduced in 1961 in an attempt to overcome the problems inherent in the earlier design (Fig 1). 125

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THE JOURNAL OF HAND SURGERY VOL. 20B No. 2 APRIL 1995

j Brannon and Klein Fig 1

operative ROM and the extensor lag was slightly reduced (Table 1). Continued follow-up on these prostheses was reported by Flatt and Ellison (1972) (Table 1). The arc of motion and the extension lag measured between 5 and 14 years post-operatively decreased. This was thought to be caused by the gradually progressive periarticular fibrosis. The patients also had improved pinch strength due to the digits being more stable and better aligned. A small number of prostheses had to be removed due to infection, fracture, skin breakdown, periarticular fibrosis and the prosthesis migrating down into the bones, but exactly how many was not stated. In a long term clinical study by Blair et al (1984a) over 11.5 years the average ROM was 24 ° (Table 1). Although the initial clinical results were good with pain relief and cosmetic improvement, recurrent ulnar deviation occurred in 57.5% of the joints, digital pronation and supination in 50% and extensor tendon re-dislocation in 45%, which is very high. The rate of fracture was also found to be high at 47.4%. Radiographic evidence of lucency at the bone-prosthesis interface was evident in 86.8% of the joints, indicating poor host bone tolerance. This led to loosening of the prosthesis, which migrated down the metacarpals and proximal phalanges in 44 and 59% of the joints respectively. The stems often perforated the cortex.

Flatt

First generation hinge prostheses. The five component Brannon and Klein and the three component Flatt prostheses were manufactured from titanium and stainless steel respectively. This gave the metallic hinge mechanisms high frictional resistance. The two prong intramedullary stem arrangement of the Flatt prostheses allowed bone ingrowth between the prongs to prevent rotation inherent in the earlier Brannon and Klein prostheses. Abduction and adduction were not possible with these designs.

Flatt first commented on the results of this prosthesis in MP joints in 1961 (Table 1). The initial results looked promising with an active arc of motion from 26.25 ° to 85 ° of flexion (Flatt, 1961). Flatt (1967) commented on 144 joints, stating that most patients were pleased with the results. The post-operative ROM up to the 5-year follow-up period was slightly greater than the preTable 1--Clinical trial data on hinged prostheses

Author

Number of patients

Number of implants used

Mean follow-up period (years)

Fracture Infection (number of (number of patients,"%) patients;%)

Ulnar drift or deformity (number of patients," %)

ROM (arc," degrees)

Brannon and Klein Brannon and Klein (1959)

2

2

2

--

--

---47.4

---12.2

--

32.5-75 (42.5)

---57.5

26.25-85 (58.75) 37-62 (25) 32.3-51.3 (19) 16-40 (24)

---

(38) 30-60 (30)

Flatt Flatt Flatt Flatt Blair

(1961) and Fischer (1967) and Ellison (1972) et al (1984a)

Nicolle and Gilbert (1979) Varma and Milward ( 1991)

4

10

8 144 167 41

20

53 101

8

36

1 5 6.2 11.5 Grifiiths-Nicolle 2 3.3

0.0 0.0

7.5 4.0 (3)

Schultz Adams et al (1990)

10.9

38.8

--

100.0

48-69.6 (21.6)

Steffee Beckenbaugh Steffee et al (1981)

106

. 160 (type I) 503 (type II)

. 1.6

.

. 0.6

0.6 (1)

(11) 27.6

(45) 30 65 (35)

>2.0

1.0

0.6 (3)

7.7

19-61 (42)

St. Georg-Buehholtz 11

Helbig and Buck Gramcko (1977)

2.9

--

--

--

19-49 (30)

--

35-60 (25)

--

18-54.5 (36.5)

KY Alumina Ceramic Doi et al (1984)

2

2

1.1

0.0 (0)

0.0 (0)

Minami Alumina Ceramic Minami et al (1988)

14

21

3.2

0.0 (0)

--

This Table summarizes results of numerous papers, most of which do not state the number of patients within the series. Where they have been stated they are included in the Table. Otherwise the post-operative data on complications are given as percentages of the total number of joints.

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MP JOINT PROSTHESES

The Flatt prosthesis was never designed to be strong enough to withstand the forces which act in the normal hand but for the lower forces which act in the RA hand. Even so, it failed to accomplish this with a high incidence of recurrent deformity and fracture.

Griflith-Nicolle prosthesis Modifications in the Calnan-Nicolle prosthesis (Nicolle and Calnan, 1972) led to the two component GriffithsNicolle prosthesis, which was introduced in 1973 (Fig 2; Griffiths and Nicolle, 1975). During a short follow-up period of 2 years Nicolle and Gilbert (1979) showed that the ROM was only 38 ° (Table 1). The rate of infection was high at 7.5% but no evidence of fracture was found in any of the prostheses. This may well be due to the short length of the follow-up period. Varma and Milward (1991) showed that the ROM

j

j

Griffith-Nicolle Fig 2

was too small. Ulnar drift recurred although it was not stated in how many joints, with an average deviation of 27 °. The deviation was greatest in the index finger and least in the little finger. This is probably due to the anatomy of the bones which are in natural deviation. Although the prosthesis was strong enough to prevent fracture, it could not prevent recurrent deviation. The ROM was also too small for adequate function of the MP joint.

Schetrumpf prosthesis Schetrumpf introduced a two component roller and socket prosthesis in 1975 (Fig 2). In a clinical trial with 13 joints in five patients he found that the prosthesis was satisfactory, with pain relieved and cosmetic appearance improved. No complications were evident and improvements in power were noted. No independent clinical trials or follow-up series have been reported.

Schultz prosthesis

Schetrumpf

Second generation hinge prostheses. Both these prostheses had roller and socket type hinge mechanisms. The two component Griffith-Nicolle prostheses had steel proximal phalanx roller components acting against polypropylene cup metacarpal components. A hemispherical silicone rubber capsule was attached to the proximal phalanx component to cover the hinge mechanism to minimize soft tissue irritation. The Schetrumpf prostheses had a polyacetal roller component and a polypropylene metacarpal socket component. The axis was offset, palmar to the midline of the intramedullary canals to provide extensor advantage. Each of these prostheses had fins on the stems to prevent rotation.

This was a two component ball and socket prosthesis which was fixed to the bones using cement (Fig 3). Adams et al (1990) followed-up 36 prostheses for an average of 10.9 years (Table 1). The average ROM and strength were found to decrease with time. The ROM after 10.9 years was 21.6 °. The neck of the proximal phalanx component fractured in 39% of the joints. Plastic deformation of the slot in the metacarpal component occurred. Although radio-lucency was found in 80% of the joints, no loosening occurred at the boneprosthesis interface in any of the joints. Ulnar drift recurred in all joints. Although cement fixation was found to be adequate, this induced a higher loading on the joint mechanism, causing fracture. Moreover the prosthesis was not strong enough to transmit the ulnar deviating forces induced on the prosthesis by the flexor tendons.

f Schultz Fig 3

J Steffee

St. Georg-Buchholtz

Second generation hinge prostheses. All these prostheses had ball and socket hinge mechanisms. Each had a metallic spherical ball component acting against a polymer metacarpal component. Cement was used to fix the stems of these prostheses to the intramedullary canals. The Schultz prostheses had a changing centre of rotation achieved by the ball being located obliquely in a vertical slot in the polymer component. The proximal phalanx component of the St. Georg Buchholtz had two configurations, the proximal part of the stem of one was rectangular while the other was triangular in order to prevent any abduction or adduction,

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THE JOURNAL OF HAND SURGERY VOL. 20B No. 2 APRIL 1995

Steffee prosthesis The Type 1 Steffee prosthesis was designed in 1964, but disappointing results led to design modification. The Type 2, two component Steffee prosthesis was a ball and socket design which was fixed to the bones using cement and was introduced in 1974 (Fig 3). Beckenbaugh (1977) reported on 106 prostheses with 80% of the patients stating that they were satisfied with the results (Table 1). The average ROM was 45 °. Recurrent ulnar drift was evident in 10% of the patients. Steffee et al (1981) commented on both Type 1 and Type 2 designs (Table 1). 160 Type 1 prostheses were followed up for an average of 19 months. The average active ROM was small at 35 ° and recurrent ulnar drift greater than 20 ° was high at 27.6%. In 503 prostheses that were followed-up for more than 2 years, the ROM was only slightly improved post-operatively at 42 °. Recurrent ulnar drift was found in 7.7% and fracture was found in 1%. Grip strength decreased postoperatively. Radiographic evidence of loosening proximally and distally increased with time; the maximum number of loose prostheses found between 2 to 4 years was 6.3 and 18.3% respectively. Patient satisfaction was, however, high with pain relief in 96% of the patients; 86% of the patients stated that their joints were improved by arthroplasty. No other clinical trials have been reported on the Type 1 or Type 2 Steffee prostheses. A Type 3 Steffee prosthesis has recently been developed but no clinical trials have been reported (Beckenbaugh and Linscheid, 1993).

J KY Alumina Ceramic Fig 4

J Minami Alumina Ceramic

Second generation hinge prostheses. Both these ceramic prostheses consisted of three components. Each had metacarpal stems of polycrystal alumina and proximal phalanx stems of single crystal alumina together with a high density polyethylene bearing component.

was from 18 to 54.5° of flexion (Table 1), which was not sufficient for adequate function of the MP joint. No evidence of fracture was found in any of the joints after this period. No other independent long-term follow-up clinical trials have been reported.

Other hinged prostheses Many other hinge-type prostheses were reported which have not undergone clinical trials. These include the Walker (Walker and Erkman, 1975), Strickland (Gillespie et al, 1979) and Weightman (Weightman et al, 1983) prostheses. CLINICAL RESULTS OF FLEXIBLE PROSTHESES

St Georg-Buchholtz 11 of these two-component prostheses (Fig3) were followed-up by Helbig and Buck-Gramcko (1977) for 2.9 years. The ROM was found to be 30° (Table 1). No other follow-up studies have been reported.

Since most of the early attempts to replace destroyed MP joints with the hinged type of prostheses failed, the development of medical grade silicone rubber provided many new possibilities for its use as an alternative material for manufacturing prosthetic joints.

Swanson prosthesis KY Alumina ceramic prosthesis The first ceramic prosthesis to be implanted into the MP joint was the KY Alumina ceramic prosthesis (Fig 4). The fourth generation of this prosthesis was reported by Doi et al (1984; Table 1). In their short clinical trial of just over 1 year they found that the arc of motion was small at 35 to 60 ° of flexion. This postoperative ROM is insufficient for satisfactory function of the MP joint. No incidents of infection, fracture or recurrent deformity were found, but this was probably due to the short follow-up period and the small number of prostheses used in the trial.

Minami alumina ceramic The three-component alumina ceramic prosthesis was commented on by Minami et al (1988; Fig4). In a clinical trial which lasted over 3 years, the arc of motion

The Swanson prosthesis was the first silicone rubber prosthesis to be implanted in the MP joint (Fig 5). The properties of the material allowed the joint to move in flexion, extension, abduction and adduction. The prosthesis is fixed in the joint by the principle of encapsulation, whereby the prosthesis becomes surrounded by a fibrous capsule (Swanson, 1968; 1969; 1972a and b). With the Swanson prosthesis a slight amount of pistoning motion is possible as the stems slide in the canals during flexion and extension movements of the joint. This pistoning motion is supposed to increase the ROM of the prosthesis and prolong its life by reducing the stresses acting on the implant (Gillespie et al, 1979; Swanson 1968). This pistoning motion, however, can cause bone erosion (Levack et al, 1987) which leads to loosening of the prosthesis. Titanium grommets which press-fit on the intramedullary stems have been designed to protect the prosthesis from abrasion and wear from

MP JOINT PROSTHESES

129

J Swanson Fig 5

Neibauer

Helal Flap

Flexible prostheses. All these prostheses were moulded from silicone rubber. The stems of the Swanson prostheses were allowed to move freely in the intramedullary canals. The Neibauer prostheses were reinforced with Dacron internally, for strength and externally, for fixation to the intramedullary canals. The Helm flap prostheses were internally reinforced with Dacron for increased strength. To overcome the problem of recurrent ulnar drift a dorsal-ulnar based flap was also incorporated into the Helal flap prostheses.

Table 2--Clinical trial data on flexible prostheses

AuNor

Number of patients

Number of Mean implants Follow-up used period (years)

Fracture (numberof patients;%)

Infection (number of patients;%)

Ulnar drift or deformity (number of patients, %)

ROM (arc; degrees)

Swanson Swanson (1972a)

---

3409 358

5 5

0.8 1.9

Rhodes et al (1972) Mannerfelt and Anderson (1975) Ferlic et al (1975) Hagert et al (1975) Millender et al (1975) Beckenbaugh et al (1976) Kay et al (1978) Fleming and Hay (1984) Blair et al (1984b) Bieber et al (1986) Jensen et al (1986) Maurer et al (1990) Wilson et al (1993) Kirschenbaum et al (1993)

12 50 45 27 631 44 9 55 28 46 22 105 77 27

48 144 162 104 2105 186 34 339 115 210 74 446 375 144

1.3 2.5 3.2 3.5 -2.7 5 4.6 4.5 5.25 2 8.9 9.6 8.5

Niebauer et al (1969) Niebauer and Landry (1971) Hagert (1975a) Beckenbaugh et al (1976) Goldner et al (1977) Derkash et al (1986)

26 48 10 16 95 16

98 165 41 68 441 89

Reis and Calnan (1969)

12

28

-2.8 (4) 9.3 24.0 -26.2 82.4 4.1 20.9 0.0 5.4 (1) 8 3.2 (6) 10.4

0.7 0.6

1.3 (5) 1.4 (1)

41.7 -8.9 (4) --11.3 66.6 (12) 42.6 100.0 16.2 16.0 42.9 --

4-57 (53) 2.5-64 (61.5) (51) 9-49 (40) ---10-48 (38) -(47.4) 13-56 (43) 22-61 (39) 13-42 (29) 9-57 (48) 21-50 (29) 16-59 (43)

3.1 1.2 (2) --2.0 (4) --

0.0 some -44.1 62.0 58.4

-(39) -30-65 (35) (54) 25-54 (29)

0.0 0.7 (1) 1.2 (2) -0.4 (10) -0.0 0.3 (2) 2.6 (2) 2.7

1.9 3.2

Niebauer -3 2.7 1-6 11.5

0.0 53.7 38.2 6.8 4.5 (1)

Calnan-Reis --

0.0

0.0

--

--

0.0 32.1

0.0 1.8

(3) (21)

(59.3) (34.7)

1.4

9.6

Calnan-Nieolle Nicolle and Calnan (197"2) Griffiths and Nicolle (1975)

17 31

68 112

Levak et al (1987)

40

146

1 1.7 Helal flap 1.5

11.6

10-48 (38)

This Table summarizes results of numerous papers, most of which do not state the number of patients within the series. Where they have been stated they are included in the Table. Otherwise the post-operative data on complications are given as percentages of the total number of joints.

sharp bone ends. However, their benefit has not been clinically confirmed and hence they are not readily used. Swanson first described the results of this prosthesis after a 5-year clinical trial (Table 2; Swanson, 1972a). N o data on the active R O M were given but the passive

arc of motion was found to be from 4 to 57 ° of flexion and from 2.5 to 64 ° of flexion in two separate followup studies. The incidence of fracture, infection and recurrent deformities was very low. Rhodes et al (1972) reported 48 joints with a mean

130

follow-up of 16 months (Table2). Only 25% of the joints showed more than 10° increase in the active ROM post-operatively and 25% of the joints showed a diminished ROM. The pre-operative disability was so great that heavy use of the hand was not possible postoperatively. Fracture did not occur, because high mechanical stress on the prostheses was avoided. Out of the 46 joints that were affected by ulnar drift preoperatively, 14 were unchanged and six were worse after surgery. Many other authors have described the short term results of this prosthesis and all have obtained similar results (Ellison et al, 1973; Mannerfelt and Andersson, 1975; Ferlic et al, 1975; Hagert et al, 1975; Millender et al, 1975; Beckenbaugh et al, 1976; Kay et al, 1978; Blair et al, 1984b; Fleming and Hay, 1984; Bieber et al, 1986; Jensen et al, 1986), as indicated in Table 2. Long follow-up studies are essential to evaluate properly the reduction in ROM, recurrent ulnar drift and the number of fractures that occur with time. The long term results reported by Maurer et al (1990) were similar to the short term results mentioned above. The ROM was 48 ° and radiographic fracture was evident in 15% of the normal prostheses and in 8% of the high performance prostheses (Table 2). Metaphyseal bone erosions in the phalanges, metacarpal shortening and endosteal cortical erosions were also noted. In a study of 375 prostheses by Wilson et al (1993), the ROM was found to decrease with time and was small at 29 ° (Table 2). Recurrent ulnar drift was high at 42.9% and subluxation was found in six patients. Although the reported fracture rate was low, if X-rays had been used in all patients they would have probably shown that a much higher proportion of the prostheses had fractured. Cortical erosion was found in 14% of the prostheses. Kirschenbaum et al (1993) in a follow-up study of similar duration found that the active ROM was 43 ° (Table 2). Radiographic evaluation indicated that 10.4% of the prostheses fractured. Ulnar drift improved dramatically in the short term to an average of 3 ° of deformity, but these worsened subsequently and increased to an average of 7 °. Fracture, erosion or abrasion of silicone prostheses producing the release of particles may lead to silicone synovitis. Only a relatively small number of cases of silicone synovitis have been reported, compared to the vast quantity of silicone MP prostheses implanted (Aptekar et al, 1974; Ferlic et al, 1975; Christie et al, 1977; Kircher, 1980; Groff et al, 1981; Worsing et al, 1982; Gordon and Bullough, 1982; Rosenthal et al, 1983; Carter et al, 1986; Peimer et al, 1986). There was no evidence of silicone synovitis occurring in any of the patients in the long term studies reviewed in the literature, so it is therefore not a significant complication. Despite the fall-off in long term results, a high satisfaction rate was noted. The high recurrence of deformity is due to the flexi-

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bility of the material not being able to provide sufficient stability to the joint. Although a large number of Swanson prostheses have failed in clinical use, this has not always led to reduced function. Many patients do not realise that their prosthesis has fractured (Beckenbaugh et al, 1976; Kay et al, 1978; Kirschenbaum et al, 1993). When movement of the MP joint occurs, the prosthesis has been found not to flex at the hinge section but at the interface between the stem and the central hinge portion. Motion only occurred at the central hinge portion when the prosthesis flexed beyond 45 ° (Gillespie et al, 1979). Most patients have a post-operative arc of motion less than 45 ° flexion, therefore the prosthesis would never flex in the right place throughout the duration of its life. This is one of the reasons for the high incidence of fracture of the stems. If the prostheses are not handled correctly their surfaces can be damaged, which also leads to fracture (Swanson, 1972a and b).

Niebauer prosthesis The Niebauer prosthesis was developed during the same period as the Swanson prosthesis and was first implanted in 1966 (Fig 5; Niebauer et al, 1968; 1969). The first published clinical data were by Niebauer et al (1969; Table 2). In a clinical trial of unspecified length they stated that the rate of infection was 3.1% and that there was no recurrent ulnar drift. In a later paper Niebauer and Landry (1971) added to these results, stating that the average arc of motion was 39 ° and that the fracture and the infection rates were 0.0 and 1.2% respectively, but also that there was some recurrent deformity. Hagert (1975a), in a 3-year follow-up study, noted that the fracture rate was 53.7% (Table2). Cortical erosion also occurred in the metacarpal and proximal phalanx each in 12.2% of the prostheses implanted. This was probably caused by motion of the stems in the medullary canals, indicating that stem fixation did not occur. The rough surface of the stem due to the dacron coating would exaggerate this effect. Bony spurs developed on the metacarpal bones, hindering movement of the MP joint. Beckenbaugh et al (1976) in a 2.5 year follow-up study on 68 prostheses found that the average active ROM was 35 ° (Table 2). They concluded that 38.2% of the prostheses failed. Clinical deformity including subluxation, rotation and ulnar drift recurred in 44.1% of the joints. Goldner et al (1977; Table 2) reviewed a total of 441 prostheses which were followed-up for between 1 and 6 years. The average active post-operative ROM was 54 °. 62% of the joints had recurrent ulnar drift and 44% had palmar subluxation. Five of the earlier implanted joints were found to have dislocated, leading to the development of the Dacron ties to prevent this happening in the future. Fracture was noted in 6.8% of all the prostheses under review, which is relatively low corn-

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MP JOINT PROSTHESES

pared with other studies. However, of the 37 joints follow-up for 6.5 years the fracture rate was found to be higher at 29.7%. Derkash et al (1986) in a study with an average follow-up period of 11.5 years on 89 joints found that pain was relieved in 84% of the patients (Table 2). The R O M was not increased post-operatively but the extension lag was reduced. Fracture occurred in 87% of the prostheses. The deformities gradually recurred with 58% of the prostheses being unstable and having subluxed. The high fracture rate o f the Niebauer prosthesis was due to the weakness of the silicone rubber material from which it was manufactured and also to the mismatch of the mechanical properties of the silicone and dacron mesh. Consequently, the stress at the interface between the two materials caused the softer material to yield, in a manner analogous to cheese-wire cutting cheese. Since the rate at which deformities recurred was high, this indicates that the prosthesis was too weak to withstand the forces which act on the M P joint.

Helal flap prosthesis The Helal flap prosthesis was an integral stem and hinge design, manufactured from silicone rubber and reinforced with dacron for increased strength (Fig 5). In a short clinical trial of 1.5 years Levak et al (1987) found an average active arc of motion from 10 ° to 48 ° flexion (Table 2). In 21.2% of the joints the arc of motion was less than 30 ° (which was defined as a stiff joint). The fracture rate was small at 1.4%. The infection rate and recurrence of deformity were high at 9.6 and 11.6% respectively. There was also a tendency for the prostheses to over-compensate for ulnar drift with some hands ending up in radial deviation. The follow-up period was too short and a longer follow-up would be appropriate before any definite conclusions can be drawn.

Calnan-Reis prosthesis The Calnan-Reis prosthesis was a single component implant manufactured from polypropylene (Fig 6). In a clinical trial of unspecified length no fracture or infection was found in 28 prostheses (Table 2; Reis and Calnan, 1969). The post-operative discomfort was found to be minimal. The prosthesis did, however, have many problems. Nicolle and Calnan (1972) stated that the Calnan Reis prosthesis offers no means by which to keep the bone ends apart; it was too weak for lateral stability, soft tissue pinching at the hinge mechanism produced mechanical irritation and it was uncontrolled in its ROM.

J Calnan-Reis Fig 6

Calnan-Nicolle

Flexible prostheses. Both these single component prostheses were manufactured from polypropylene for greater durability. The stems of the Calnan-Reis were fixed to the bones using cement. In an attempt to prevent mechanical irritation inherent in the earlier Calnan-Reis prostheses, a hollow silicone capsule surrounded the hinge mechanism.

Nicolle and Calnan (1972) commented on a short 1-year clinical trial stating that the arc of motion was on average 59.3 ° and that ulnar drift recurred in 17.7% of prostheses up to an angle of 35 ° (Table 2). No infection or prosthetic fracture was found. Only one out of 17 patients did not have pain relief. The patients were evaluated pre- and post-operatively when carrying out a number of daily tasks. N o conclusions could be drawn from this assessment since patients had adopted different means of carrying out the same activity when they suffered from RA. In a further study by Griffiths and Nicolle (1975) the average results for the early arc of motion measured up to 1 year post-operatively was found to be good. These, however, deteriorated to an average ROM of 34.7 ° after a mean follow-up of 1.7 years (Table 2). Infection and fracture rates of 1.8 and 32.1% respectively were observed. In 14 out of 31 patients ulnar drift or volar subluxation recurred to an extent similar to that measured pre-operatively and in seven patients to an extent worse than that pre-operatively. The degree of deformity was not stated for each patient, but the worst case of ulnar drift was reported to be 35 °. Many patients complained of loss of grip strength.

Other flexible prostheses Other flexible prostheses include the Sutter prosthesis (Linscheid and Beckenbaugh, 1991; Beckenbaugh and Linscheid, 1993). To date, clinical results have not been published, but preliminary results of a 1 to 2-year followup indicate that the prosthesis is similar to the Swanson implant, with improved stability (Linscheid and Beckenbaugh, 1991). CLINICAL RESULTS OF T H I R D GENERATION

PROSTHESES Calnan-Nicolle prosthesis Subsequent modification of the Calnan-Reis prosthesis led to the production of the two component CalnanNicolle prosthesis (Fig 6).

Some silicone rubber or hinged prostheses may be considered to be satisfactory in elderly patients who have gross deformity, but they are certainly inadequate for implantation in younger patients, who have a high

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132

ligaments and muscles surrounding the joint are still functional to provide joint stability.

grip strength and who have a further life expectancy of 50 or more years, since fracture will occur very quickly after implantation. These patients who may have less advanced rheumatoid disease or post-traumatic OA will benefit from a surface replacement prosthesis which will restore the anatomy of the joint. It is important that

Kessler prosthesis The Kessler prosthesis was introduced in 1974 and designed for the replacement of destroyed metacarpal heads (Kessler, 1974; Fig7). In a small preliminary clinical trial eight prostheses were implanted into eight patients (Table 3). Pain was relieved and the length and shape of the knuckle preserved in each case. An average ROM of 60 ° was achieved, but since the numbers of prostheses used was small and the follow-up period was short, these results cannot be regarded as conclusive evidence that the prosthesis is adequate for use in the MP joint.

J Kessler

Beckenbaugh

/ Hagert Fig 7

Beckenbaugh prosthesis Beckenbaugh developed a non-cemented, non-joined two component prosthesis (Cook et al, 1983; Beckenbaugh, 1983; Beckenbaugh and Linschied, 1994; Fig 7). In a clinical trial with average follow-up of 1 year, the average ROM was found to be 47 ° (Table 3). No infections were found. Dislocation was noted in five joints, and one patient out of 15 had radiographic evidence of loosening, but it was asymptomatic. Pain was relieved and recurrent ulnar drift was evident but it is not stated in exactly how many joints.

Lundborg

Third generation prostheses. The Kessler prostheses were single c o m p o n e n t silicone rubber implants with Dacron coated stems for bone fixation. The Beckenbaugh prostheses were non-cemented," non-joined two component implants with spherical bearing surfaces. They were manufactured from pyrolite carbon which provided intramedullary stem fixation by bone ingrowth. The four component Hagert prostheses had joint mechanisms comprising an ultra-high molecular weight polyethylene metacarpal head and a congruent titanium proximal phalangeal socket. The Lundborg prostheses consisted of a replaceable silastic hinge mechanism moulded at each end to a titanium plate with a cylindrical rod. These slotted into holes in the intramedullary stem components. The stems of both the Hagert and the Lundborg prostheses were hollow titanium screws designed to be permanently fixed to the bones by osseointegration.

Hagert prosthesis The Hagert prosthesis was described in a study by Hagert et al (1986; Fig 7). With an average of nearly 3.5 years follow-up, they noted that the average active arc of motion was from 21 ° to 65 ° of flexion (Table 3). No infection or recurrence of deformity was found but a high fracture rate of 20% was noted. The results are insufficient to determine the validity of the prosthesis since only five were used in the study. A longer follow-

Table 3--Clinical trial data on third generation prostheses

Author

Number of patients

Number of Mean implants follow-up used period (years)

Fracture (number of patients,"%)

Infection (number of patients,"%)

Ulnar drift or deformity (number of patients; %)

ROM (arc, degrees)

--

--

--

(60)

--

0.0

--

12-59 (47)

20.0 (1)

0.0

0.0

21 65 (44)

--

--

10-60 (50)

Kessler Kessler (1974)

8

8

4

Beekenbaugh Beckenbaugh (1983)

15

43

1

Hagert Hagert et al (1986)

5

5

3.4

Lundborg Lundborg et al (1993)

31

68

2.5

6.0

This Table summarizes results of numerous papers, most of which do not state the number of patients within the series. Where they have been stated they are included in the Table. Otherwise the post-operative data on complications are given as percentages of the total number of joints.

MP JOINT PROSTHESES

133

up period is required with more numbers of prostheses to conclude whether or not it is a valid prosthesis for early surgical implantation.

Lundborg prosthesis Lundborg et al (1993) described a prosthesis consisting of three components (Fig 7). In a clinical study with an average follow-up of 2.5 years, the average active ROM was found to be 50° (Table 3). The best results were achieved in the RA patients with a ROM of 57°, and the least improvement was found in the post-infectious osteoarthrosis patients with a ROM of 37°. Fracture of the joint mechanism was found in 6% of the prostheses. There were no signs of loosening in any of the prostheses; radiological and clinical osseointegration occurred in every case. Patient satisfaction was high with pain relieved, cosmetic appearance improved and function improved. The low fracture rate could be due to the short follow-up period of the study.

Other third generation prostheses Other third generation prostheses which have not been clinically tested include the Sibly-Unsworth surface prosthesis (Sibly and Unsworth, 1991). DISCUSSION Although short follow-up studies can help identify certain problems with a prosthesis, long follow-up studies are essential to evaluate a prosthetic design, since a reduction in ROM, recurrence of deformity, bone resorption and even fracture of the implant may well occur long after implantation. Most papers evaluate the success of prostheses using ROM. In rheumatoid arthritis ROM is frequently limited with some degree of extension lag (Fig 8a). When a prosthesis is implanted into the joint the initial postoperative arc of motion should be increased with improved extension (Fig 8b). This increase in motion is due to relief of pain, which restricts movement. The post-operative ROM usually decreases with time as shown in Figure 8c, due to fibrosis or recurrent deformity.

~

_

It is important that the centre of rotation of the prosthesis in the sagittal plane is the same as that of the natural joint. This maintains the correct balance between the different tendon forces that surround the joint. Implantation of the prosthesis often displaces the centre of rotation of the MP joint to a more dorsal or palmar position than that of the normal joint. Dorsal shift makes flexion easier and extension harder, while palmar shift has the opposite effect (Flatt, 1967; Flatt and Fischer, 1969). Moving the centre of rotation therefore affects the arc of motion of the MP joint. Palmar shift is often employed in prosthetic design since the ease of extension reduces extension lag, but this also reduces grip strength. The nature of the material and design of flexible implants means that they resist flexion. When they are implanted into a rheumatoid hand which has little grip strength, this may also hinder the amount of flexion that is possible and reduce the post-operative grip strength. The fingers may therefore be able to open in order to grasp an object, but the patient may not possess sufficient grip strength to hold the object. Thus, although the ROM may be large with a small extension lag, the hand can be functionally poor. ROM alone is therefore not a good parameter for assessing function. The high recurrence of deformities and fractures on long-term follow-up studies indicate that none of these prostheses are strong enough to transmit the high forces that act on the MP joint. Precision and power grips apply external forces on the finger pads which are in contact with the object being grasped. Previous experimental measurement has determined that the normal mean pinch strength is 70 N for men and 50 N for women (Purves and Berme, 1980; Fernando and Robertson, 1982; Blair et al, 1984a and b; Mathiowetz et al, 1985; Amis, 1987; Helliwell, 1987; Adams et al, 1990; Lee and Rim, 1991; H~irk6nen et al, 1993). From these external forces the internal forces that act on the MP joint have been estimated using two or three dimensional anatomical models (Smith et al, 1964; Flatt and Fischer, 1967; Chao et al, 1976; Beckenbaugh, 1977; Berme et al, 1977; An et al, 1978, Chao and An, 1978; Weightman and Amis, 1982; Tamei et al, 1988). Each internal force acting on a MP joint can be split into its three force components acting in the X, Y and Z

0 ° flexion

l

Extension lag

90 o flexion Pre-operative ROM Fig 8

Arc of flexion Initial post-operative ROM

Long term post-operative ROM

Typical pre-operative range of motion for the MP joint and post-operative range of motion for MP prostheses.

134

THE JOURNAL OF HAND SURGERY VOL. 20B No. 2 APRIL 1995 Proximal phalanx

the majority of surgeons use Swanson flexible implants for joint replacement due to their ease of implantation, ease of removal if reoperation is necessary, and low cost. THE FUTURE OF MP JOINTS

Metac

xternal force y

Fig 9

exerted on finger pad

Internal and external forces acting on the MP joint.

directions (Fig 9). Estimates showed that the internal force was on average 6, 3 and 2 times the external force in the X, Y and Z directions for pinch grip. A full finger power grip gives 12, 6 and 4 times the external force acting in the X, Y and Z directions. These high forces act on the prostheses. The force in the Z direction causes the recurrence of ulnar drift, while the force in the Y direction causes recurrent subluxation and buckling in flexible prostheses. The high forces experienced at the MP joint are transmitted across the hinge in prostheses that involve permanent fixation to bone using cement, and fracture often occurs in the hinge areas. Other problems including necrosis, leading to loosening and increased wear rates may also occur with cement (Beevers and Seedhom, 1993). The flexible joints tend not to flex at the hinge during motion. The Swanson and the Niebauer prostheses (Gillespie et al, 1979; Hagert, 1975a and b) only flex at the hinge after a flexion angle of 45 ° has been passed. Otherwise, the prostheses flex at the stem-hinge interface. This places stresses on the prostheses at points which were not designed to withstand these forces, resulting in fracture. Flexible prostheses cannot transmit high forces, and are only reliable in rheumatoid hands with little grip strength. If they are placed in rheumatoid or osteoarthritis hands with high grip strength, fracture is more likely. Although fracture of Swanson prostheses does not necessarily lead to a reduction in function (Beckenbaugh et al, 1976; Kay et al, 1978; Kirschenbaum et al, 1993), this suggests that the prosthesis only acts as a spacer to keep the bone ends apart once the affected bone and cartilage have been removed. It does not act as a prosthesis in terms of restoring the correct biomechanics of the joint. The infection rate is low for all the prostheses reviewed. Although they do not fully restore function to the MP joint, patient satisfaction was high in all cases, due to the fact that pain relief and the cosmetic appearance of the deformed hand are usually achieved with all the prostheses described. Even though they have many drawbacks, at present

Although many prostheses have been implanted in to the MP joint, none can fully restore natural joint function; each prosthesis only partially addresses the large problem faced by the surgeon. Timing is difficult. Surgical intervention is often deferred until the hand is grossly deformed. Often the structure of the MP joint is so badly affected at the time of operation that only a salvage procedure can be carried out to restore at best a small measure of function and improved appearance. If surgical intervention could be offered at an earlier stage of the arthritis, an MP surface prosthesis that more accurately restores the anatomy of the joint could be used. The natural biomechanics of the MPjoint would then be restored and the large forces could be transmitted without fracture, allowing normal function. Acknowledgements The authors wish to thank Mr Simon Kay, Consultant in plastic surgery and Dr Ross Harper, Registrar in plastic surgery, at St James's Hospital, Leeds, for their useful comments on this paper. Financial support was provided by the Arthritis and Rheumatism Council (Grant No. SO100), and the University of Leeds.

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Accepted: 21 September 1994 B. B. Seedhom, Rhetmlatology and Rehabilitation Research Unit, University of Leeds, 36 Clarendon Road, Leeds, LS2 9NZ, UK. © 1995 The British Society for Surgeryof the Hand