AMIC Technique in the Metacarpophalangeal Joint by Arthroscopy

Abstract

We present the case of a 48-year-old male patient in whom a Grade IV chondral lesion, measuring less than 1 cm² in surface area, was incidentally observed during the arthroscopic excision of a volar ganglion at the level of the metacarpophalangeal (MCP) joint of the right third digit.

During follow-up consultations, poor clinical progression was noted, with the patient experiencing pain and functional limitation, along with recurrent joint effusions, although maintaining a full range of motion. Given these findings, we decided to perform an arthroscopic joint preservation surgery.

We conducted a revision arthroscopy. Initially, we performed a new synovectomy and debridement of the chondral lesion until the subchondral bone was exposed. Subsequently, we carried out nanofractures (1 mm in thickness and 9 mm in depth) manually using the A2C nanofracture system (up to 15° of angulation), simultaneously implementing a collagen matrix Chondro-Gide® (A2C).

 

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Keywords

arthroscopy - metacarpophalangeal - joint preservation - AMIC

Introduction

Arthroscopy is essential in the management of intra-articular pathology in large joints, as it allows for their management with minimal damage to the soft tissues.

Since it was first described in 1979 by Chen,[1] there is little literature on it at the level of the triphalangeal finger joints, being mainly short case series.[2] [3] [4] [5] [6] [7] Initially, arthroscopy was used as a diagnostic and therapeutic tool in patients with inflammatory arthropathies in whom partial synovectomy[5] and/or arthrolysis were performed.[3] Subsequently, with the development of the technique as well as the surgical material, more technical procedures were described that could be performed arthroscopically, such as: chondroplasty,[7] excision of foreign bodies[4] [6] or as an assistance method in the treatment of joint fractures or ligament injuries.[8]

We present an AMIC technique performed arthroscopically, as a joint preservation treatment in a chondral lesion at the level of the metacarpophalangeal joint.

 

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Indications

• Single chondral lesion smaller than 1 cm².

• Full range of motion of the joint.

• Absence of structural injury causing joint instability.

 

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Contraindications

• Kissing (mirror) chondral lesions.

• Multiple chondral lesions.

• Neurological injury compromising limb functionality.

• Concomitant injury causing joint instability.

• Advanced-stage rheumatologic diseases.

• Active infection.

 

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Surgical Anatomy

The extensor apparatus is palpable in the midline. Radially and ulnarly, we can palpate a noticeable depression after applying traction, the so-called "soft pot."[7]

The ulnar and radial portals of the MCP joint are located 2-3 mm from the midline. An 18G needle should be inserted at a 45° angle to the midline to locate the joint. At this point, scopic control is helpful to confirm that we are within the joint.[7]

We will make the incision with the scalpel only in the skin, bluntly penetrating the joint capsule. Intra-articular infusion of 1-2 ml of physiological saline reduces the rate of iatrogenic chondral injuries.

After performing an extended synovectomy of the joint, we can observe various structures: the articular cartilage of the metacarpal (MC) head and the base of the proximal phalanx (PP), the radial and ulnar collateral ligaments, as well as the joint capsule and volar plate.

It is important to remember that the head of the MC is wider volarly than dorsally. Furthermore, the radius of curvature increases from dorsal to volar. This causes the collateral ligaments to be more tense in flexion than in extension.

Meanwhile, the volar plate is more tense in extension than in flexion, serving as the main stabilizer in hyperextension of the joint.

 

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Surgical Technique

We position the patient as in a classic wrist arthroscopy, performing traction only on the finger to be operated on, with between 2-3 kilograms of traction ([Fig. 1]). We mark the extensor apparatus at the level of the MCP joint with a dermographic instrument ([Fig. 1]) and locate it using an 18G needle several millimeters both ulnar and radial to the midline, as well as slightly distal to the head of the MTC, the so-called “soft pot,”

Fig. 1 Arthroscopic positioning and portals of the MCP joint. A: Optic in the ulnar portal and synoviotome in the radial portal. B: Optic in the radial portal and probe in the ulnar portal.

Some authors advise assisting this step with radiological control to find the joint space[7]. After a certain learning curve, we do not perform the portals under scopic control, although we consider it appropriate when starting arthroscopy of this small joint.

After infusing 2-3 cc of physiological saline solution (PSS), both portals are established by making a superficial skin incision, penetrating the joint capsule with a blunt-tipped instrument.

Once both portals are located, using a 1.9 mm, 30° camera and small surgical equipment, we will perform the surgical procedure. Both portals will be used alternately as a viewing or working portal as needed ([Fig. 1]).

We use a hydrostatic pressure system, without a pump. Initially, we perform a new synovectomy and debride the chondral lesion until the subchondral bone is exposed ([Fig. 2A], [Video 1]). We smooth the cartilage surface and remove the unstable chondral fragments ([Video 1]). We then manually perform nanofractures (1 mm thick and 9 mm deep) ([Fig. 2B], [Video 2]). To facilitate the adhesion of the stimulated mesenchymal cells and prevent their diffusion into the joint space, we can implement a collagen matrix over the nanofractures ([Fig. 2C], [Video 3]). This last step is advisable to perform with dry arthroscopy.

Video 1 Synovectomy, arthroscopy, and chondroplasty of chondral lesions.

Video 2 Nanoperforations in chondral lesions.

Video 3 Application of membrane on chondral lesion.

Fig. 2 Intraoperative arthroscopic view. A: Lesion after synovectomy, showing exposure of the subchondral bone (marked with the probe). B: Performance of nano-perforations. C: Application of Chondro-Gide® collagen matrix (A2C).

 

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Pearls

• Identify the "soft spot" entry point with radiographic assistance, especially during the initial learning curve.

• Make a superficial skin incision with a scalpel, then bluntly penetrate the capsule.

• Inject 2–3 cc of normal saline intra-articularly before penetrating the joint capsule to reduce the rate of iatrogenic chondral injuries.

• Underestimate the size of the membrane, as it increases by 10–15% once introduced into the joint.

• Mark the area of the membrane that should contact the subchondral bone with a surgical marker.

 

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Errors

• Failing to use small-sized arthroscopic surgical instruments.

• Performing microfractures (2 mm in diameter and 3 mm deep) instead of nanofractures, as this results in lower perforation density in the same area and impairs access to mesenchymal stem cells from the subchondral bone (due to shallower penetration).

• Performing perforations with a motorized device instead of manually, the heat generated can seal the Haversian canals.

• Applying the collagen matrix dry to facilitate its adhesion to the lesion.

 

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Postoperative

The stability provided by the application of the collagen membrane to the hematoma caused by the nanoperforations allows full passive and active mobility of the joint from the first day after surgery.

Physical therapy begins on the first postoperative day, with weight-bearing permitted from the sixth week. Return to sports activity begins from the tenth week.

 

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Complications

• Infection

• Hemarthrosis

• Stiffness

• Iatrogenic injury to cartilage or collateral ligament

• Radial collateral ligament injury (located an average of 5 mm from the radial portal).[9]

• Ulnar collateral ligament injury (located an average of 7 mm from the ulnar portal).[9]

 

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Clinical Case

We present the case of a 48-year-old male patient who was incidentally observed during arthroscopic excision of a volar ganglion at the level of the MCP joint of the third finger of the right hand. A grade IV[10] chondral lesion measuring less than 1 cm² in area was observed in the head of the MCP joint. Initially, the lesion was debrided, followed by a partial synovectomy and excision of the ganglion.

During follow-up, the patient's clinical progress was poor. He presented with pain and functional limitations, associated with repeated effusions, but maintained a full range of motion. Given the small size of the lesion, the absence of joint degeneration, and the preservation of full range of motion, we decided to perform arthroscopic joint-sparing surgery.

We performed both arthroscopic portals of the MCP ([Fig. 1]) and extended synovectomy of the joint, associating the debridement of any free or unstable chondral fragments ([Fig. 2A], [Video 1]). Once the subchondral bone was exposed, we regularized the peripheral cartilage surface and performed nanofractures manually using the A2C nanofracture system (up to 15° of angulation) ([Fig. 2B], [Video 2]), implementing a dry Chondro-Gide® (A2C) collagen matrix ([Fig. 2C], [Video 3]), to facilitate the adhesion of the stimulated mesenchymal cells and prevent their diffusion into the joint space.

Eight months after revision arthroscopic surgery, the patient's VAS score was 3, and joint balance was 0°-100° ([Fig. 3]). We do not have a preoperative pain scale to monitor clinical improvement, but the patient returned to work three months postoperatively.

Fig. 3 Postoperative clinical images of the patient. A: Full extension of the 3rd MCP joint. B: Full flexion of the 3rd MCP joint.

No degenerative changes were observed in the radiographic imaging at one year postoperatively ([Fig. 4]). The follow-up magnetic resonance imaging at one year showed stability of the generated fibrocartilage, with no bone edema in the subchondral bone ([Fig. 5]).

Fig. 4 Control X-ray one year after surgery. A: Oblique projection of the right hand. B: anteroposterior projection of the right hand.

Fig. 5 Coronal MRI slice one year after surgery. A: T1-weighted image showing the stability of the generated fibrocartilage. B: T2-weighted image showing no bone marrow edema in the subchondral bone.

 

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Conflicto de Interés

Los autores declaran no tener conflictos de intereses.

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Publication History

Received: 09 December 2024

Accepted: 24 March 2025

Article published online:
21 July 2025