Trapezio-metacarpal arthritis: The price of an opposable thumb!

Abstract

Trapezio-metacarpal arthritis is the most common arthritic problem of the hand for which patients seek surgical treatment. The current article reviews the etio-pathogenesis, epidemiology, classification and management of this widespread problem. The anatomy and unique biomechanics of this joint are also reviewed. In addition, the article provides a detailed description of our preferred method of trapezio-metacarpal arthroplasty.

INTRODUCTION

The human hand represents the evolutionary pinnacle of appendages in all living organisms. As is the case with all primates, the human hand has two principal features that distinguish it from other lesser evolved species: the presence of flat fingernails (instead of claws) and the presence of an opposable thumb. Both these structural developments occurred to enable “brachiation”; the ability to swing from tree-to-tree! While it is no surprise that the hand is far more intricate than the shapeless pseudopodia of a humble amoeba, it is amazing to note the enormous gap that separates the human hand from our immediate living predecessor, the chimpanzee. Functions such as writing, playing musical instruments and handling of tools that we take for granted are well nigh impossible even for the most well trained of apes.[1]

This ability to perform extremely complex functions owes itself to a high degree of manoeuvrability of the thumb. It is the only digit with significant polyaxial movement and this in turn enables us to grasp objects of differing shapes and sizes [Figure 1]. The thumb is capable of flexion-extension, abduction-adduction and rotational movements which when combined, give it the ability of “circumduction” and “opposition”.[2] This specialised movement of opposition is almost entirely dependent on the unique anatomy of the trapezio-metacarpal joint. Unfortunately, there are no free lunches in the world and the price of an opposable thumb is arthritis!

Figure 1.

Polyaxial mobility of digits, especially the thumb, enables us to grasp objects of differing shapes and sizes

ANATOMY OF THE BASAL JOINT OF THE THUMB

The tremendous manoeuvrability of the trapezio-metacarpal joint is due largely to its unique shape. It is best described as a “twisted saddle”. A good way to understand this is by using the analogy of a car driving on a twisted and curved road. The car represents the first metacarpal and the trapezium can be thought of as the road on which it rides. The curved and banked path taken by the car illustrates the broad arc that the first metacarpal executes when it rides on top of the trapezium going from an adducted position against the index to a fully opposed position against the base of the small finger Figure 2. The centre of rotation of the trapezio-metacarpal joint lies at its volar ulnar corner [Figures 3 and 4].

Figure 2.

The trapezio-metacarpal joint is best described as a “twisted saddle”. A good way to understand this is by using the analogy of a car driving on a twisted and curved road

Figure 3.

The centre of rotation of twisted and curved road

Figure 4.

The centre of rotation of the trapezio-metacarpal joint lies at its volar ulnar corner

Unfortunately, the great mobility that is seen at the trapezio-metacarpal joint automatically makes the joint intrinsically unstable. The interlocking, twisted, curved and concavo-convex articular surfaces provide a limited amount of constraint. This is further diminished by the fact that the two surfaces have different radii of curvature. The diameter at the base of the first metacarpal is 34% larger than the trapezium. Consequently, most of the stability of the joint comes from strong capsule-ligamentous structures that connect the two bones.[2–5]

There are several strong ligaments that provide stability to the trapezio-metacarpal joint. The primary stabiliser is the “anterior oblique ligament”. This ligament has been divided into deep and superficial parts. The deep anterior oblique ligament is the principal stabiliser and is better known as the “beak ligament”. This ligament can be thought of as the controlling tether for the first metacarpal and serves as the pivot point for circumduction of the thumb [Figures 5 and 6].

Figure 5.

The imaginary “controlling tether” for a car as it swerves along the twisted and curved road

Figure 6.

The beak ligament is the controlling tether for the first metacarpal and serves as the pivot point for circumduction of the thumb

Another important ligament is the dorso-radial ligament which limits dorsal subluxation of the thumb while the posterior oblique ligament resists ulnar translation of the metacarpal base during abduction and opposition. Some of the other ligaments are the dorsal and volar inter-metacarpal ligaments, the ulnar collateral ligament, volar and dorsal trapezio-second metacarpal ligaments, trapezio-third metacarpal ligament, dorsal and volar trapezio-trapezoid ligaments. In addition to these, additional stability is provided by the trapezio-capitate, scapho-trapezial and transverse carpal ligaments.[2–7]

EPIDEMIOLOGY

The trapezio-metacarpal joint is the second most common joint afflicted by degenerative osteoarthritis in the hand after the distal inter-phalangeal joints. However, it accounts for the most common surgically treated arthritic joint in the upper extremity.[3]

Incidence of arthritis has a direct correlation to the evolutionary advancement of the thumb. It appears that lesser evolved primate thumbs are capable of a lesser degree of opposition which in turn leads to a “less demanding” usage. This accounts for a lower incidence of arthritis in non-human primates. A study conducted by Lim revealed an incidence of 3.3% incidence of arthritis in macaque monkeys as against 37.5% in humans.[8]

Among humans, women are more commonly affected than men and the condition is particularly predominant in postmenopausal women. Studies have indicated a prevalence of 16-22% in women and 2-5% in men. Comparative analyses have indicated that females are 6 to 20 times more commonly affected by trapezio-metacarpal arthritis than men.[3,9–14] This is also reflected in the progress of these patients to surgery. In our centre, 10 times more women underwent surgery than men.

A ETIOLOGY AND PATHOPHYSIOLOGY

While it is universally accepted that trapezio-metacarpal arthritis is degenerative in origin, the list of factors that predispose to its development are still unclear. Eaton et al. and Kirk et al. described a strong association between excessive basal joint laxity and the development of premature degenerative changes.[15,16] Polatsch et al. drew our attention to the fact that with lateral pinch, compressive forces at the basal joint of the thumb can be up to 12 times those at the tip. This highlights the important role played by thumb muscles as force multipliers at the trapezio-metacarpal joint. Additionally, studies have revealed that this joint is even less congruent and smaller in females than males. Combining the two factors lead to the obvious conclusion that females have a greater proclivity to develop arthritis.[3]

Previous trauma, especially intra-articular fractures such as Rolando or Bennett fractures can lead hasten the onset of degeneration and arthritis.[12,17,18] Inflammatory arthropathies, such as rheumatoid, can also predispose to the early onset of degeneration. Nearly a third of patients with rheumatoid arthritis have involvement of the trapezio-metacarpal joint. Though a clear genetic predisposition has not been established, Poole and Pellegrini have indicated a tendency that people of Caucasian descent are more prone to develop the problem.[12,13]

Early studies favoured the dorso-radial facet of the trapezio-metacarpal joint as the most likely site where arthritis starts.[17,18] However, Pellegrini using a cadaveric model was able to demonstrate that pressures are much greater at palmar surface of the joint during lateral pinch. This eventually leads a weakening of the beak ligament with consequent cartilage degeneration.[13,19] Progression of the degeneration is most likely related to repetitive loading of the thumb. Polatsch mentioned that this repetitive loading might cause synovitis and progressive instability of the basal joint. Eventually, the metacarpal base begins to subluxate in a dorso-radial direction due to the weakening of the beak ligament combined with a dynamic pull exerted by the abductor pollicis longus. Since the distal part of first metacarpal is dynamically tethered by the adductor pollicis with continued dorso-radial subluxation of the joint, the thumb metacarpal eventually assumes an adducted posture. This in turn leads to an inability to abduct the thumb at the trapezio-metacarpal joint. In response to this inability to “open the thumb”, the thumb ray tries to compensate by hyperextension at the metacarpophalangeal joint. Ultimately, the patient is left with a narrowed functional hand width.[3,5]

CLINICAL PRESENTATION AND EXAMINATION

The earliest presentation is in the form of a vague and ill-defined pain at the base of the thumb. Typically, when asked to point to a specific painful spot, the patient indicated a wide horseshoe shaped region around the dorso-radial aspect of the base of the thumb. The pain is usually of a deep aching type and characteristically worsens with activity. Day-to-day functions that are first affected include pinching, using scissors, typing, writing and opening a jar.

The most common differential diagnosis that one has to consider would be DeQuervain's tenosynovitis. Other conditions that can present with a similar initial picture include scaphotrapezotrapezoidal (STT) arthritis, carpal tunnel syndrome and flexor carpi radialis tenosynovitis.[3,14,15,18]

As the condition advances, more dramatic clinic signs may become evident. Swelling as well as obvious subluxation with or without compensatory metacarpo-phalangeal joint hyperextension can also be seen [Figure 7].

Figure 7.

The characteristic appearance of severe trapezio-metacarpal arthritis includes an adducted first metacarpal with compensatory hyperextension at the metacarpophalangeal joint

Obvious tenderness at the trapezio-metacarpal joint can be elicited. The “grind test” becomes positive. In this test, the examiner stabilises the patient's scaphoid with one hand while with the other hand, the thumb metacarpal is axially loaded and rotated much like grinding a “mortar and pestle”. This not only causes pain but may also elicit palpable crepitus. Grip and pinch powers are significantly diminished.[12,13,16,20,21]

RADIOLOGICAL EVALUATION AND CLASSIFICATION

Radiological evaluation begins with conventional Postero-anterior (PA) and lateral views. Special views include Robert's view in which the hand is hyperpronated and placed on the X-ray cassette while the X-ray beam is directed in an anterio-posterior manner across the trapezio-metacarpal joint [Figure 8]

Figure 8.

Robert's view in which the hand is hyperpronated and placed on the X-ray cassette while the X-ray beam is directed in an anterio-posterior manner across the trapezio-metacarpal joint

Radiologically, trapezio-metacarpal arthritis has been classified into four stages by Eaton and Littler.[16]

Stage I

The X-ray may show slight widening of the joint space with normal articular contours. There is no significant capsular laxity and subluxation if any is less than one-third in any projection.

Stage II

Significant capsular laxity is now present. There may be at least one-third subluxation of the joint. The instability is particularly apparent in stress views. Small bone or calcific fragments less than two millimetres in diameter are present.

Stage III

Greater than one-third subluxation is present. Fragments greater than two millimetres are present dorsally or volarly. There is slight joint-space narrowing.

Stage IV

Advanced degenerative changes are now present. Major subluxation is apparent and the joint space is very narrow. Cystic and sclerotic subchondral bone changes are also seen. Margins of the trapezium show lipping and osteophyte formation.

TREATMENT

The first goal is to relieve pain. Other aims include maintaining the first web space, maintaining the strength of pinch and grasp as well as enabling independence in day-to-day functional tasks.[9] Treatment options have to be considered according to patients’ complaints, demands and their overall health status. These could be divided into either non-surgical or surgical. Surgical options are typically reserved for the more advanced forms of arthritis.

NON-SURGICAL TREATMENT

Non-surgical treatment is typically rendered in two forms: medication and splints. Pain control can be achieved by non steroidal anti inflammatory drugs though it may not be prudent to use these for prolonged periods due to their obvious side effects. Glucosamine and chondroitin sulfate dietary supplements can be tried though their exact therapeutic benefit remains unclear. Any of all of these are preferably combined with thenar and extrinsic muscle strengthening exercises.[10,13,16]

Splinting is a good treatment option for early stages of arthritis. The primary goal of splinting is to stabilise the base of metacarpal bone during pinch.[9] Swigart et al. reported on a retrospective analysis of 130 thumbs that were treated by splinting for 3 to 4 weeks. A total of 76% of patients in Eaton stages I and II and 54% of patients in stages III and IV reported improvement in symptoms at 6 months follow-up.[22] Two other reports indicated that splinting reduced pain but did not alter pinch or grip strengths.[23,24] Day et al. reported on 30 patients who received a steroid injection and were splinting.[11] They felt that this was a good option for initiating the treatment and that it helped for an average of 18 months. More recently, intra-articular hyaluronic acid injections have been used. A study comparing the use of steroid, hyaluronic acid and a placebo was not able to demonstrate any significant difference between any of the three groups for improvement in function or grip strength.[14]

Our preferred method is to use a removable thumb spica splint. Our typical recommendation is to use a soft neoprene brace for non-strenuous activity and a more rigid brace for heavy work. We very sparingly recommend the use of intra-articular steroid injections. We feel these are best confined to cases where the pain is significant but the joint still shows the presence of some cartilage (i.e. earlier stages).

SURGICAL TREATMENT

Many surgical techniques have been described for the management of trapezio-metacarpal arthritis. One of the earliest techniques described was excisional arthroplasty or complete trapeziectomy. This technique basically entails excision of the entire trapezium. One of the earliest results was published by Gervis in 1973. He reported his 25 years of experience and claimed good results.[26] Gray reported on 22 patients who underwent trapezial excision and K wire immobilisation. He reported that even though shortening was seen in the thumbs, the technique provided stability and pain relief.[27] Another study conducted by Gibbsons et al. showed an improvement of 40% in thumb pinch and pain relief in 26 of 40 patients (65%) with no major complications.[28] Nusem and Goodwin found that after a 5 year follow-up, patients after complete trapeziectomy regained full range of motion with no pain but still had significant weakness of pinch.[29] Some authors have reported that partial or hemi-trapeziectomy also offers good results. Edwards performed 23 hemi-trapeziectomies and reported significant improvements in pinch strength as well as decreased pain.[30]

Interposition arthroplasty is another surgical option. Earp's reviewed the reported results following silastic and silicone implants. These appear to do better for patients with rheumatoid arthritis than osteoarthritis. Now-a-days, silicone arthroplasty has more or less been abandoned.[31] Adams et al. reported on 17 patients in whom they used acellular dermal matrix allograft for interposition arthroplasty. In this series, grip and pinch did not change significantly but 88% of patients reported no or mild pain with an overall satisfaction rate of 94%.[32] Arthroscopic debridement is being tried especially in grades I and II. In a report, 23 patients underwent arthroscopic debridement and synovectomy and demonstrated improved pain and functional scores as well as increase in pinch strength.[16]

A recently described technique is interposition arthroplasty using a porous polyurethane-urea spacer. Nilsson et al. performed a multicentre, randomised study on 109 patients and concluded that the results were not superior to tendon interposition artroplasty.[33] Our personal experience with the spacer has been disappointing. While all patients reported initial relief of symptoms, 40% returned within 6 months with a persistent deep pain in the joint. The senior author (SMT) has since abandoned the use of this spacer as the cost of the implant did not appear to justify the rather limited results.

Arthrodesis of the trapezio-metacarpal joint is another common option.[3] However, one of the important problems with this technique has been non union. De Smet et al. described 34 fusions with a 39% non union rate. However, a review of the results from our institution using a matched Chevron osteotomy provided 95.4% union rates.[34–36] Our preference is to typically recommend fusion in males and those women who are likely to pursue heavy physical activity.

Total joint arthroplasty using various implants has been in and out of vogue over the years. The first reported total arthroplasty was by De la Caffiniere in 1979.[37] De smet et al. analysed a series of 43 patients in whom they used a De la Caffiniere prosthesis. They reported good and excellent results as far as pain, function and overall satisfaction was concerned. However, 44% of implants eventually loosened and this was seen more in the dominant hand of younger patients.[34] Badia and Sambandam reported used the Braun Cutter Total joint CMC prosthesis in 25 patients of whom 24 patients were pain free. In their series, patients regained 85% of strength compared to the contralateral side. They recommended using the prosthesis in late stages and that too preferably in a low-demand elder population.[38,39] Lemonie et al. used a Guepar II prosthesis in cases and reported it as an efficacious method for treating trapezio-metacarpal arthritis.[40] One common theme that all authors agree on as far as the use of prosthetic implants is that they ought to be confined to the elderly low-demand population.[11,32,41]

Of all the techniques described, the most enduring one has been trapeziectomy combined with some form of ligament reconstruction and tendon interposition. Eaton and Litter were the first to describe their technique using the flexor carpi radialis (FCR) tendon in 1973.[18] Numerous variants of that technique have since been used all around the world. King popularised using extensor carpi radialis longus (ECRL) tendon as an alternative to the FCR. While Tomaino reported that ligament reconstruction and tendon interposition was is good option, recent reports suggest that this technique is not superior to others.[42] Raven et al. compared trapeziectomy, tendon interposition and trapezio-metacarpal arthrodesis. A follow-up ranging from 8-13 years, no statistically significant differences were demonstrated between the groups for pain and functional scores.[43]

Our preferred method has been trapeziectomy combined with an FCR sling between the second and first metacarpals. The biomechanical principle governing our technique involves the alteration in force transmission down the axis of the first ray after trapeziectomy. In a normal thumb, forces generated by pinching are transmitted proximally along the first and second metacarpals to the trapezium and trapezoid respectively and then on to the scaphoid [Figure 9]. Removal of the trapezium necessitates a change in the direction of forces [Figure 10]. All forces passing down the first metacarpal are now transmitted on to the second metacarpal through the inter-metacarpal ligament (IML) and then on to the trapezoid (TS) via the second metacarpal-trapezoidal joint (MT). From the trapezoid, the forces find their way to the scaphoid and beyond. The technique we use serves to strengthen the inter-metacarpal ligament by creating a sling between the second and first metacarpals using a distally based slip of the FCR tendon. We have described our technique in some detail below.

Figure 9.

Path of force transmission in a normal thumb

Figure 10.

Path of force transmission after trapeziectomy

OUR PREFERRED TECHNIQUE

A Chevron shaped incision was made over the dorso-radial aspect of the trapezio-metacarpal joint and is carefully deepened down through skin and subcutaneous tissues [Figure 11]. Branches of the radial sensory nerve need to be identified, retracted and protected throughout the procedure. Dissection is then deepened down to the level of the abductor pollicis longus and extensor pollicis brevis tendons. A plane is created between these two tendons and the tendons are retracted to expose the capsule. The capsule is then incised in an “H” shaped manner to open the trapezio-metacarpal joint.

Figure 11.

Chevron shaped incision over the dorso-radial aspect of the trapezio-metacarpal joint

The contents of the joint are then evaluated. Sometimes hypertrophic synovium can be encountered and needs to be excised. The trapezium is then removed piecemeal. As the trapezium is removed, the FCR tendon can be seen crossing the space obliquely. Care must be taken during this step to avoid damaging the tendon. Occasionally, a bony bridge grows across the trapezial groove for the FCR tendon, essentially converting it into a tunnel. The tendon is particularly vulnerable to injury in these cases and in addition, one needs to remember to remove pieces of bone that may reside on the far-side (volar side) of the tendon. Once this is done, the FCR tendon is divided into a 1/3 and 2/3 portion and a loop of wire passed around the 1/3 portion of the flexor carpi radialis tendon.

At this stage, attention is turned to the proximal part of the forearm. A separate incision is made over the musculo-tendinous junction of the flexor carpi radialis. A second loop of wire is passed down the flexor carpi radialis sheath in a proximal to distal direction so as to emerge at the thumb wound [Figure 12]. The first wire is then looped through the second wire and gentle traction is exerted in a proximal direction thus resulting in a longitudinal split off the flexor carpi radialis tendon in a 1/3: 2/3 proportion. The 1/3 portion of the flexor carpi radialis tendon is then divided proximally in the forearm and delivered distally through the incision. This is then dissected all of the way down to the point of its insertion at the base of second metacarpal keeping this insertion intact. This serves as a distally based FCR tendon graft.

Figure 12.

The path taken by the second loop of wire which is passed down the flexor carpi radialis sheath in a proximal to distal direction so as to emerge at the thumb wound

Attention is then turned to the first metacarpal. Two holes are made in the metacarpal. The first one is a longitudinal hole made through the base along the axis of the metacarpal and the second is a transverse hole made through the dorsal cortex so as to meet the first hole. Once these two holes are interconnected, a third loop of wire is passed from the dorsal hole so as to emerge at the base of the metacarpal. The previously elevated tendon graft is then passed through this loop of wire and drawn out so as to pass through the base of the metacarpal and emerge on the dorsal surface. This is then tightened and sutured to itself thus acting as a suspensory ligament between the second and first metacarpals [Figure 13]. The remaining free end of the tendon is then looped repeatedly around the intact part of the flexor carpi radialis and sutured onto itself to act as a spacer between the first metacarpal and scaphoid [Figure 14]. Gentle longitudinal pressure is then applied along the first metacarpal to confirm that the suspension is strong and that the space is maintained. The capsule is then meticulously repaired and the surgical incisions closed. A well-padded dressing is then applied around the wounds and the extremity placed in a thumb spica splint.

Figure 13.

The direction in which the distally based flexor carpi radialis graft is passed. This creates a suspensory ligament between the second and first metacarpals

Figure 14.

The final appearance of the arthroplasty after the free end of the FCR tendon has been looped around the remaining intact portion

The patient is seen two weeks post operatively and the splint replaced with a thumb spica cast. Eight weeks post-operation, the cast is removed and replaced with a removable orthoplast thumb spica. Graded active and passive range of movement exercises are commenced at this stage. Twelve weeks after surgery, grip strengthening and pinching exercises are started.

SUMMARY

Trapezio-metacarpal arthritis is the price we have to pay for possessing an opposable thumb. The tremendous manoeuvrability at this joint is due largely to its unique shape, which is best described as a “twisted saddle”. Arthritis is typically more common in elderly women. Early stages of the condition can be satisfactorily managed by splints and medication. Our typical recommendation is to use a soft neoprene brace for non-strenuous activity and a more rigid brace for heavy work. We very sparingly recommend the use of intra-articular steroid injections. In later stages, especially if associated with pain and instability, we recommend surgical intervention. Our preferred method is trapeziectomy followed by a flexor carpi radialis sling between the second and first metacarpals. Notwithstanding any of the above interventions, it is always prudent to counsel patients about the degenerative nature of the condition and to advice protected and guarded use of the thumb. The last thing our patient always hears as they leave our clinical office is “Take care of your thumbs………and they will last a long time!”