Indications and Principles of Metacarpophalangeal Joint Arthrosocopy

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Author:  Alejandro Badia, MD, F.A.C.S.

Introduction:

Despite arthroscopy 1st being introduced to medicine nearly 50 years ago, the smaller joints in the body have only recently begun to reap the benefits of this technique. It is only in the last decade that wrist and ankle arthroscopy has become readily available to patients in the U.S. while it remains elusive in many other countries, even ones with a relatively advanced medical infrastructure. Consequently, metacarpophalangeal arthroscopy remains a nearly experimental technique. However, if the technology is available, the size of the joint is truly irrelevant if the viewing moniter is large enough.

Pathology of the metacarpophalangeal joint is relatively common. Acute trauma can involve any one of these joints with the thumb being by far the most commonly afflicted. The so-called “gamekeeper’s thumb” is a commonly seen entity in any hand surgeon’s practice. Acute injury can also involve the finger MCP’s with both ligamentous and articular fractures being occasionally seen. So-called “overuse syndromes” may reflect a previously unrecognized acute injury that was not addressed, or may simply be a synovitis, Arthroscopy will not only assist in diagnosing the condition but can also serve to provide treatment.

Technique:
An arthroscope 1.9 mm in diameter will be necessary to explore these small joints. Generally, the 30 degree scope commonly used by maxillofacial surgeons for temporomandibular pathology is used. Newer arthroscopes as small as one millimeter are now available and will certainly make this technique even easier. A 2.0 mm shaver is usually the main operative instrument and small radiofrequency probes, both for ablation and shrinkage, are used.

In these smaller joints, it is much easier to proceed with local anesthesia and sedation. Several cc’s of lidocaine are introduced into the joint once the hand is suspended using a single chinese fingertrap on the affected digit. Adequate sedation is then achieved in order to allow elevation of the tourniquet for the necessary time period.

It is particularly important to introduce the trochar into the joint in atraumatic fashion. The joint space is minimal and it is feasible to cause considerable iatrogenic injury if care is not taken. The interval between metacarpal head and proximal phalanx base is quite narrow and it is recommended to find the appropriate level and insertion angle by inserting a small curved clamp once the joint is sufficiently distended with lidocaine or saline solution. The arthroscope is then introduced at this same angle and a thorough joint inspection is performed. The portals are quite simple as they lie on either side of the visible extensor tendon. Occasionally a third portal might be used for outflow and is placed by palpating the capsule, identifying the interval as seen on the moniter, and then passing an 18 gauge needle. A synovectomy must always be initially peformed as only this will allow thorough inspection of the joint without impedement. As this is done with a small full radius shaver, the capsule and ligamentous structures will soon be more apparent. A radiofrequency ablator probe can make this process more efficient and less tedious. It is important to use this sparingly, as the joint capsule is relatively thin and subcutaneous, and thermal injury can occur. Once synovectomy is performed, the surgeon can now sequentially identify any abnormalities. This should be done in a routine systematic fashion to avoid missing any pathology. My preference is to begin on one collateral ligament, then assess the volar plate, then the contralateral ligament followed by the dorsal capsule and extensor mechanism. The articular surface of both proximal phalanx and metacarpal head is then assessed. Once the particular pathology is identified and appropriately addressed, the arthroscope is removed and portals are closed with benzoin and steri-strips only. The thumb MCP is protected with a short arm thumb spica splint in extension. Arthroscopy of any of the fingers will require a dorsal metacarpophalangeal block splint in flexion in order to allow the collateral ligaments to heal in their most taut position so that there is no resultant loss in motion. Time of immobilization will be determined by the type and extent of pathology found during the arthroscopic intervention. Post-op therapy will often play a critical role.

Indications:
Surgical indications to perform MCP arthroscopy will usually involve chronic complaints as opposed to acute injury. Most acute trauma about these joints can be managed conservatively with a trial of immobilization. The thumb ulnar collateral ligament avulsion is a notable exception where open repair of a stener lesion is usually performed. Even here, however, an arthroscopic repair has been described in the literature. As the surgeon becomes more adept at this small joint arthroscopy, the more acute indications may evolve as one can make a more accurate assessment of the extent of injury and often provide more precise treatment for this articular pathology. Acute indications generally involve an associated fracture that will need articular reduction. This is because the vast majority of ligamentous injuries will heal with conservative treatment or are so severe that they will be treated open to correct the instability. Perhaps the best acute indication is reduction of an avulsion fracture with a rotated fragment from the collateral ligament insertion. A hook probe can be used to derotate the bony fragment with arthroscopic visualization. Kirschner wire fixation can then be added with fluoroscopic confirmation. A less common lesion would be a die-punch articular fracture, usually of the proximal phalanx base, where the scope can be used to achieve the best articular reduction possible. At that time, a synovectomy as well as removal of floating loose osteochondral fragments can be performed. This has an added benefit of reducing the inflammatory process besides reducing the fracture. Persistent pain despite ample conservative treatment in both thumb and finger MCP injury is perhaps the most common indication. It is not uncommon to encounter persistent symptoms after cast treatment for a skier’s thumb. This can be due to a more severe ligamentous injury than originally surmised, or a concomitant articular cartilage injury with accompanying synovitis. Sometimes the contralateral ligament is injured as well and was not completely addressed. An arthroscopy will determine the location and extent of injury and gives an opportunity to provide treatment, whether by simple debridement and/or thermal capsulorraphy. This type of complaint is often managed by a course of NSAID’s, therapy or a series of cortisone injections. These treatments may only provide temporary relief, if any, and cannot be continued indefinitely. This is where the great value of arthroscopy lies as it provides a viable option to make both a definitive diagnosis and institute a treatment based on these findings. Occult pain often associated with swelling may be a chronic type indication to proceed with arthroscopic evaluation as well. This may have been from an unrecognized injury, early presentation of osteoarthritis, or an idiopathic synovitis. Steroid injections are often efficacious here, but can lead acceleration of cartilage and capsular degeneration. Arthroscopic debridement will avoid this complication while perhaps retarding the degenerative process. A further benefit is that complications are negligible and the recovery is rapid. The earliest stages of osteoarthritis may not be seen on plain xray and the diagnosis is often a clinical one. After adequate conservative treatment with NSAID’s and perhaps a course of therapy, the logical next level of treatment remains an intra-articular corticosteroid injection. If symptoms recur despite several injections, arthroscopic debridement becomes the best option short of joint replacement. Although silicone arthroplasty remains the gold standard treatment for advanced rheumatoid involvement of the MCP joints, post-traumatic and osteoarthritis are not good indications for replacement arthroplasty. Arthroscopy provides a good treatment alternative before resorting to the newer non-constrained replacement options now available. Inflammatory arthritis is generally managed with systemic pharmacotherapy and in late stages replacement arthroplasty. Occasionally, a mono or pauci-articular form is encountered and an arthroscopic biopsy may assist in making the diagnosis. Early involvement of these joints may warrant an arthroscopic synovectomy and capsular shrinkage. This is best suited for the 1-2 joints most involved where one can hope to retard the destructive process. Long term results of this procedure remain to be demonstrated.

Summary:
Arthroscopy has become a vital part of an orthopedic surgeon’s armamentarium in treating large joint pathology. Advances in technology have now allowed us to apply this benefit to the smallest joints such as the metacarpophalangeal. Chronic pain and inflammation are currently the most suitable indications although there is a role for acute injury as well. As in any new technique, the appropriate and most suitable indications will evolve over time.