How to diagnose and treat a Palmar Midcarpal Instability

Carpal instabilities are a group of clinical diagnosis that are often erroneously referred to as wrist sprain, with simptoms such as pain, a sensation of instability, joint “jumping” or locking (among others). They are often associated with carpal ligament injuries, although it should be remembered that not all ligament injuries will eventually lead to instability. This will be discussed later.

For a proper therapeutic intervention in a carpal instabilities, it is required a basic knowledge of anatomy, biomechanics and physiopathology of the carpus. In this post, we take a closer look at one of the most common conditions that can appear in the clinic: Palmar Midcarpal Instabilities (PMCI).

We will introduce the biomechanics of the carpus and the specific physiopathology of midcarpal instabilities, applying this knowledge to their conservative treatment (with exercise, splinting or modification of activities) and addressing one of the most frequently asked questions by patients. When should I choose a surgical intervention? What options do I have?

Biomechanics and Carpal Instability. What we are talking about?

To understand what Palmar Midcarpal Instability (PMCI) is and what it consists of, the first thing to do is to briefly review the physiological biomechanics of the carpus. The proximal (PR) and distal (DR) rows are joined by the Scapho-Trapezio-Trapezoid and Triquetral-Hamate joints, which will transmit the forces applied to the wrist, and will move in a synergistic manner.

Thus, when the transmission of forces between the two rows is adequate, the following occurs during the Radial Deviation movement:

-The transmission of forces originating at the metacarpal bases, passes through the DR through the Trapezium and Trapezoid, and reaches the Scaphoid, causing flexion of the entire PR.
– In addition, there is a palmar displacement of the proximal pole of the Capitate and the Hamate.

On the other hand, during Ulnar Deviation Movement:

– Muscular forces originate at the base of the metacarpals, and reach the Distal Row through the Hamate, which passes them to the Triquetrum bone and the entire Proximal Row, causing extension.
– In addition, the Capitate and the Hamate move dorsally.

These movements are due to the articular congruence of the carpal bones, correct ligament action and neuromuscular control, which also ensures that they occur smoothly and continuously.

However, if ligament integrity and muscle function are affected, the movement will not be adequate and may result in instability at the midcarpal joint, where the forces relating the Proximal Row and Distal Row are not transmitted correctly.

Main stabilizing structures of Midcarpal

Among the ligaments that provide the most stability to the Midcarpal are:

– Dorsal Radiocarpal Ligament (DRC).
– Volar Arquate o Triquetro-Hamate-Capitate Ligament.
– Periscaphoid or Scaphoid-Trapezium-Trapezoid Ligament (STT).

These in turn form part of the Helical Antisupination Helical complex or HASL, which is responsible for limiting forced intracarpal supinatory forces.

Also, at a neuro-muscular level, the following highlight:

– Extensor Carpi Ulnaris (ECU).
– Flexor Carpi Ulnaris (FCU).

They perform an ulnar deviation and intracarpal pronation action, in turn helping to control forced intracarpal supination.

Their stabilising action may explain cases where the MC stabilising ligaments are affected, but the patient is asymptomatic.

Palmar Midcarpal Instability (PMCI)

When these structures are affected, the kinematics between the carpal PR and DR are altered, causing asynchrony in the movements of both, and ultimately leading to symptomatic midcarpal instability.

In those cases in which the connections within the PR are intact, we will speak of a non-dissociative midcarpal instability. Among the types we can find:

– Palmar/Volar: most common.
– Posterior/dorsal.
– Combined.
– Extrinsic: abnormalities outside the carpus such as non-union of the distal radius.

Thus, in palmar midcarpal instability (PMCI), the flexion to extension smoothy transition that usually appears from radial to ulnar deviation disappears.

As a result, the PR is fixed in flexion, even when the wrist is brought into ulnar deviation (remember that physiologically it should go into extension). Only when the end of ROM is reached (high load at the Triquetro-Hamate level), the PR “jumps” and reduces its position towards extension (Catch up Clunk).

This reduction process may be painful, even visible or audible to the therapist, depending on the level of involvement. In addition, visually we may find the carpus completely displaced towards volar/palmar, as the DR seeks to adapt to the flexion position of the PR. In this way, the wrist aligns the hand with the rest of the forearm.

In some cases, we may find an ulnar carpal drop or carpal supination, with a prominent ulnar head appearing visually.

What is a Carpal Instability?

Firstly, we must remember before any possible diagnosis of PMCI is to be clear about the concept of “Instability” and “Stability of the Wrist“. According to Mireia Esplugas et al (2016), the wrist is considered stable when it is able to maintain the relationship between the various carpal bones under physiological loads and throughout its range of motion. In the event that the wrist appears incapable of sustaining physiological loads associated with pain and jumps or joint clunks, we will call it an unstable wrist.

For the wrist to remain stable, these 4 points must be met:

1) All carpal bones must have their articular facets correctly oriented and congruent with each other.
2) Both the joint capsule and ligaments (passive stabilisers) must be intact and adequately innervated.
3) The sensorimotor system must perform its task of processing afferent information and creating efferent messages correctly.
4) The musculature (dynamic stabilisers) must be permanently active and ready to neutralise any attempt to destabilise the wrist.

In this way, Marc García Elías et al (2017) argued that not all ligament injuries become painful and dysfunctional, but that “Instability” is a multifactorial phenomenon that can include:

– Articular incongruence of facet joints.
– Ligament or capsular laxity.
– Inadequate proprioceptive and neuromuscular control of the wrist.
– Deficient processing of the sensorimotor system.

This is why according to Hargreaves D et al 2016 a patient that is able to self-subluxate its own carpus in a PMCI, with the wrist asymptomatic, should NOT be considered instability but Laxity, which is not pathological and does not require treatment. Only patients with painful symptoms, jumps and clunks associated with their ADLs should be considered unstable and therefore treatable.

Clinical Findings of a Palmar Midcarpal Instability

The clinical manifestations of PMCI are variable, ranging from feelings of instability, joint jumpings or the need to “give in” to diffuse pain and weakness after use of the wrist (especially in gestures involving forearm pronation).

The pain is usually accentuated on palpation of the Triquetral-Hamate joint, with the forearm in supination and with active and resisted pronation.

On visual examination we may find a volar translocation or subluxation of the ulnar wrist, with an apparent elevated distal ulnar head.

Wrist discomfort may be partially relieved by performing a volar support or brace at the ulnar wrist, which would momentarily correct the associated carpal supination and ulnar carpal fall. This may be masked by the presence of synovitis associated with the instability.

The carpal drop to volar can be associated with a translation of the entire distal row to volar, giving a Volar Intercalated Segmental Instability (VISI).

We can also assess in these cases how there is an increase in the distance between the ulnar styloid process and the pisiform.

On the other hand, the Catch up Clunk sign at ulnar deviation will appear on examination, which may be self-induced by the patient in more advanced cases, and may be audible and/or visible. At this final moment of the movement, there would be an instantaneous correction of the entire proximal row block in flexion and as a result, re-alignment of the carpus.

Flexion-Extension movements are usually normal.

Midcarpal Shift Test

To test for the presence of PMCI, this test is usually applied. With the forearm pronated, the examiner places his thumb on the dorsum of the patient’s carpus. The carpus is then induced into a volar displacement, allowing the distal carpus to move into volar direction. In this position, and maintaining pressure, an ulnar deviation of the patient’s wrist is performed. It will be positive in the case of a “Catch up Clunk“. 

Be cautious with this technique, pain may appear during its procedure.

Classification Systems for PMCI

Finally, here are a couple of classification systems that may be useful in your practice:

Although Hargreaves D. proposed an alternative in 2016 as, according to the author, Midcarpal Shift Test is difficult to perform when the therapist only applies it occasionally. Furthermore, it does not include the previously mentioned concepts of laxity and instability, which can lead to confusion.

Thus, he proposed a NEW classification based on the classification of Larsen et al. of 1995, applied to PMCI, in which he does differentiate between symptomatic and non-symptomatic, and which is simple to apply:

Introduction to Hand Therapy in Palmar Midcarpal Instability

The first thing we must make clear before going into this type of approach is that to date there are no clinical trials that have evaluated the work of rehabilitation programmes in Palmar Midcarpal Instabilities (PMCI). Therefore, everything provided in this article follows the biomechanical and anatomical bases presented in the evidence, and the opinion of experts in the field.

Also, it is also important to know what NOT to do in PMCI. These conditions are directly related to the appearance of symptoms in the presence of physiological loads and during certain carpal movements (remember the concept of carpal instability). This is why, initially, during the rehabilitation process, we should avoid mobility or isotonic exercises without specific control and based on our clinical reasoning.

Squeezing balls will be contraindicated initially! We could worsen the irritability of the tissues and the instability itself!

We must be meticulous when selecting which musculature to work on in order to revert the midcarpal instability. Remember some key points (see part 1 and 2 for more info), in the PMCI we can find:

– The proximal row tends to and even lock in flexion.
– Occasionally we may find a “Volar Sag” or a “supination” of the carpus with respect to the radius.

Action of Flexor Carpi Ulnaris and Hypotenar Musculature

According to Marc García-Elias et al (2008), excessive flexion of the proximal row can be counteracted dynamically thanks to the joint action of these muscle groups. This is because the forces that generate an isometric contraction of both are transmitted via Pisiform, on the anterior aspect of the Triquetrum(Tq), which would help to reposition the bone in its neutral position, thus reducing the “clunk”.

The image shows the effect we are talking about at the level of the Tq.

The importance given by the author to proprioceptive and sensorimotor work in this type of condition is also noteworthy.

Action of the Extensor Carpi Ulnaris

The extensor carpi ulnaris is considered to be the most powerful pronator muscle of the proximal and distal carpal row, and its action is contraindicated in other types of instability such as scapholunate instability. However, the opposite is for midcarpal instability.

The fact that it is a powerful pronator muscle, together with its extensor action, makes it very relevant in the fight against midcarpal instability. Its action is explained by;

– Its dorsal location at the ulna.
– The possession of its own sheath at distal ulna.
– Its insertion at the base of the 5th metacarpal (anterior-medial aspect).
– Use of the distal ulna as a pulley, which allows it to increase its mechanical advantage (Salva-Coll G et al 2012).

Joint action of the FCU and ECU

Furthermore, it is reflected in the literature, such as Skriven TM et al 2011 or Harwood C et al 2016), how the action of both lateral muscles can correct the “Volar Sag” present in the carpus, producing dorsiflexion forces.

It will be a key muscle group in PMCI rehabilitation.

Hand Therapy for Midcarpal Instability

Management by strengthening and orthoses should be the first option in PMCI, leaving surgery in cases where this conservative treatment fails (Hargreaves DG 2016).

Thus, initially a workout is proposed using isometry of the above-mentioned musculature, ECU, FCU and Hipotenar musculature. Some examples with elastics such as this one, where the emphasis is on the contraction of the ECU in an extension and ulnar deviation plane (Guisasola E et al 2016):

Patients should be educated in detail on how to contract this musculature, as it can be difficult to achieve.

As the patient’s condition improves, we can progress to dynamic exercises, always respecting the patient’s discomfort. One example is that of Mireia Esplugas, who proposes the inclusion of exercises within the reverse DTM plane of movement (Dart throw but just the opposite: from ulnar deviation + extension to flexion + radial deviation).

Sensorimotor rehabilitation of a PMCI

We know how the use of ReHand can promote central changes in the Somatosensory Cortex, which will promote early motor learning of muscle contraction and “redraw” that altered central representation due to pain and immobilisation.

Below are some examples of exercises focused on these objectives.

Muscle exercise focusing on ECU and FCU activation

The movement can be calibrated within the plane of movement of interest (extension) and in a safe and painless ROM for the patient.

Also, working on an ulnar deviation ROM, always controlling the patient’s symptoms, can help us to reactivate the FCU and ECU, which can improve instability.

We show you two examples of exercises focused on active control of ulnar deviation and wrist extension using the ReHand telerehabilitation system. The exercises are performed on the screen of a tablet, promoting changes in the somatosensory cortex, and thus an early recovery:

Do you want to treat patients with Palmar Midcarpal Instability?

Progression

From here, we can increase the intensity, resistance and repetitions, and in advanced stages, begin with unconscious control exercises of the carpus, load on the carpus and even Plyometrics with the wrist.

Here is an example of work under load on an unstable surface, aiming to coactivate the carpal stabilising musculature.

Orthosis Proposal

One proposed use is 3-Point Pressure Splints, whereby we can apply volar-dorsal forces at the pisiform and dorsal-volar forces at the distal ulna, improving subluxation and the catch-up clunk associated with PMCI. Here is an example from Harwood C & Turner L from 2016:

Surgical Management in Midcarpal Instability

We must remember, as we commented in the previous email, that conservative management should always be the first option in PMCI. We will leave surgical treatment when Hand therapy fails or in Advanced instabilities.

In this way, the surgical procedure seek to re-establish the stability of the patient’s wrist, in order to improve the patient’s functional capabilities as much as possible.

Nowadays, and with the improvement of surgical techniques, therapeutic options have been added such as:

– Soft tissue stabilisation
– Arthroscopic capsular retraction techniques
– Bone procedures such as bone fusions

1) Solf tissue stabilisation

Initially the use of realignment of the Extensor Carpi Ulnaris was proposed in order to stabilise the Triquetral-Hamate joint, but the long-term effects proved to be poor.

More recently, dorsal capsulodesis techniques, tendon transfers of the Extensor Carpi Radialis Brevis as an active stabiliser, and the use of the Palmaris Longus as a ligament graft have been used with more than promising short-term results.

Dorsal Capsulodesis proposed by Ming B et al 2014

Picture of the Palmar Triquetrum-hamate-capitate and Dorsal Radiocarpal ligaments with ECRB grafts, proposed by Marc García Elias 2008.

2) Electrothermal Arthroscopic Capsular Retraction

This techniques aims to reorganise the collagen fibres within the capsule and extrinsic ligaments, restoring the necessary tension and capacity to these midcarpal stabilising structures. Through the application of local heat, areas of collagen damage are created, stimulating the work of fibroblasts and subsequently creating a new structure simulating normal tissue. It is a technique that must be performed with caution so as not to cause collateral damage.

The areas through which the capsule can be accessed for this technique are limited, although in all cases, the Dorsal Radiocarpal and Palmar Arcuate ligaments can be treated.

It is also important to note that a period of immobilisation is essential after technique, as early mobilisation could re-elongate the collagen fibres. The wrist being an easy area to immobilise (unlike other areas such as the shoulder) makes it a great therapeutic option.

3) Bone Fusions

In severe cases of MC instability, these techniques are applied. Options include Triquetral-hamate, capito-lunate or radio-lunate partial arthrodesis, or complete with a four-corner fusion of the carpus.

However, complete carpal fusions have a limitation eliminate the mobility of the functional plane “Dart Thrower’s Motion”, which mainly happens in the midcarpal joint. This fact transfers the joint work to the radiocarpal joint, predisposing to possible degenerations at the scaphoid fossa of the radius or Lunotriquetral joint.

Picture shows a Radiocarpal fusion proposed by Marc Garcia Elias 2008 in cases of advanced MC instability with advanced clunk.

Assessment and Treatment Algorithm for PMCI

Finally, I attach the proposed Assessment and Treatment algorithm proposed by R Higgin and D Hargreaves in 2017:

And that concludes our journey on Palmar Midcarpal Instabilities. I hope it has been of interest, and if you have any suggestions or any kind of feedback I will be happy to receive them.

Do you treat Patients with Carpal Instabilities?

Pablo Rodríguez Sánchez-Laulhé
PhD Candidate | PT, Hand Therapy & eHealth Researcher

References

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