Scapholunate Ligament of the Wrist and Rehabilitation | Carpal Instability

Patients often come to the clinic with wrist pain after a fall on their hand. In these cases, carpal bone fractures and, to a lesser degree, carpal or wrist ligament strains or injuries are common.

One of the most frequently involved ligaments is the interosseous scapholunate ligament between the scaphoid and lunate bones of the hand. Its affectation can lead to symptoms such as pain, oedema, instability, decreased grip strength, and thus an inability to weightbearing on the wrist or to pick up heavy weights. This situation is known as scapholunate instability.

Therefore, we must know how to assess and treat this wrist disorders. To do this, it is essential to have sufficient Carpal Anatomy and Biomechanic knowledge.

Carpal Biomechanics

The hand is made up of a series of bones, ligaments and musculature that transmit different rotational movements from one side of the hand to the other, depending on the movement that is carried out globally in the wrist (flexion, extension, etc.).

To summarize, we will say that due to the muscular contractions of the forearm, the carpal bones will have one tendency or another depending on the movement:

-During Flexion and Radial Deviation, the bones of the first carpal row adopt a flexion position.
– During Extension and Ulnar Deviation, the bones of the first carpal row adopt a Extension position.

As there are no direct tendon insertions on the proximal row, the forces originate at the distal row and pass to the proximal row thanks to ligament and bone interconnections between both.

Carpal Biomechanics in Radial and Ulnar Deviation

What is the scapholunate carpal ligament?

It is a C-shaped stabilising structure that joins the articular facets between the scaphoid and the lunate bones (both into the first carpal row). The scapholunate ligament is usually divided into 3 parts;

1.Dorsal: 3 mm wide and 5 mm long. It is the most important portion of this ligament, it promotes joint stability by preventing the separation of both bones during wrist movements.
2.Palmar or volar: 1 mm wide and 5 mm long, and has rotational control of the joint.
3.Intermediate Portion: of little mechanical importance but richly innervated. This characteristic provide it a important proprioceptive role.

Scapholosemilunar Ligament of the Hand (Wolff A et al 2016).

A lesion of this ligament may produce a pathological extension of the lunate, known as “dorsal carpal instability”, which may eventually cause degenerative processes, pain and functional limitation.

For this reason, the diagnosis of this type of lesion should be made as early as possible.

Carpal Stability and Instability

For the correct functioning of the carpus and for all these mechanics to be transmitted correctly, it is essential that the ligaments of the wrist work correctly.

A wrist is stable when it is able to maintain the relationship of the carpal bones under physiological loads throughout its Range of Motion. For this to be fulfilled, these four requirements are necessary:

1-Morphology of the articular surfaces: the joints rest and fit together properly and smoothly.
2-Ligamentary Congruence: the static stabilisers such as the capsule and ligaments must be intact and intact, and their innervation must be preserved.
3-Correct muscle contraction: that the joint stabilising musculature is ready and active.
4-Correct proprioceptive control: the sensorimotor system (the whole process of receiving sensory input, processing the information and sending efferent information in the form of motor response) to function properly.

Carpal stability, key to wrist function. Image from Wolfe SW, Hotchkiss RN, Pederson WC, Kozin SH. Green’s Operative Hand Surgery. 6 th. Philapdelphia: Elsevier; 2010. ISBN:978-1-4160-5279-1

We consider Carpal Instability (or in this case, scapholunate instability) in those situations in which the ligament injury is associated with “inability to carry physiological weight without yielding, and to make movements of the wrist in a fluid and regular manner, appearing jumps, “clicks” or articular “cluncks” during bone realignment“.

Fortunately, and as the surgeon Mireia Esplugas mentioned, the wrist does not necessarily become unstable with a simple ligament strain; it is a multifactorial phenomenon. For carpal instability to appear, it must be associated with a failure of the neuro-muscular control of the wrist, which can be:

Disruption of afferent pathways that send sensory information from the wrist to the central nervous system.
Neurological impairment of the sensorimotor system that prevents the processing and interpretation of proprioceptive information.
Muscle dysfunction to stabilise ligament deficits caused by strain.

Scapholunate Ligament injuries can produce alterations in hand movements, leading to joint problems and carpal instabilities. But as we have just mentioned, there are more factors that will influence correct joint function, so there is no reason why symptomatic dysfunction should appear in this type of condition. Moreover, it is common to find asymptomatic instabilities in patients, which can be explained by the proper work of the sensorimotor system of the wrist.

Among the large number of ligaments present in the hand, the most frequently injured ligament is the scapholunate ligament.

Scapholunate ligament injuries of the wrist

It is estimated that the incidence of Scapholunate ligament injuries varies between 15-55% in fractures of the distal end of the radius, and increases to 90% in high velocity injuries to the wrist joint complex. Its diagnosis often goes unnoticed, and surgical intervention often does not give optimal results, especially if the injuries are already chronic.

In those cases in which the scapholosemilunar ligament injury is associated with the patient’s inability to bear weight, suffers from “jumps” or snaps and suffers from pain, we will be dealing with scapholosemilunar instability.

Knowing this, it is not difficult to assume that the earliest possible physiotherapy and rehabilitation work at wrist level by means of therapeutic exercise and splinting will be the first therapeutic option. We will have to respect the injured tissues (the scapholosemilunar ligament) and avoid irritating or damaging the ligament. ReHand is an option for prescribing individualised exercises for your patients and control his/her progress thanks to its monitoring system.

Lateral wrist deviation control with ReHand app. Early mobilization after scapholosemilunar ligament surgery is essential.

Do you have patients with carpal instabilities? Tell us about your case and prescribe exercises for these cases!

As a result, functional and complex movements are proposed to limit the stress on this structure by means of selective proprioceptive and neuro-muscular work.

“Dart Throwing Motion” Wrist DTM Plane

In different biomechanical studies of the wrist, it has been proposed that working in composite movements and not in pure Flexo-Extension or Deviation planes, may be benefitial for certains pathologies. The Dart Thrower Motion is one example of a Composite Plane of Motion.

The Dart Thrower Motion Plane DTM is the functional plane of motion of the wrist, where most of our daily activities (whether it is picking up a glass, hammering or throwing an object) will occur. It is made up of a combination of these movements:

Flexion + Radial deviation.
Extension + Ulnar Deviation.

If you want to read more on the subject, we have this previous article to understand this movement and behavior of the carpal bones.

In the case of Dorsal Carpal Instability or in Scaphosemilunar Ligament Injuries, the functional movement “Dart Throwing Movement” is proposed, which works on the diagonal of:

In the case of this plane of motion, the majority of this movement occurs in midcarpal joint, and minimal at the scapholunate joint: This explains why this DTM plane promotes stability and coaptation of the scapholunate space.

In isolated flexion-extension or radial-ulnar deviation movements, this fact changes, and the mobility is greater in first carpal row, which may affect the recovery from the injury.

Thanks to this, the DTM plane is proposed as the first line of active work in the rehabilitation of scapholosemilunar ligament injuries. It is possible to use splints that only allow this range of mobility of the DTM, and limit the rest of the planes.

Scapholunate Joint Stabilising Musculature

After several studies on the wrist, some specific muscles are proposed that favour joint stability and coaptation, protecting the scapholunate ligament, which also follow the DTM movement. These are:

– Extensor Carpi Radialis Longus.
– Extensor Carpi Radialis Brevis.
– Abductor Pollicis Longus.
– Flexor Carpis Ulnaris.

In contrast, muscles such as the extensor carpi ulnaris promote scapholunate space widening, further promoting joint instability.

Do you know why the Extensor Carpi Ulnaris muscle promotes more scapholunate instability?

Example of working the radial extensor musculature (Extensor Carpi Radialis Longus and Brevis) with the ReHand app.

This active and proprioceptive work, through the use of visual feedback on the screen (in this case towards wrist extension) allows us to work directly on the stabilising musculature of the scapholunate joint.

Active, repeated, controlled work, adapted to the patient’s capacity, achieves greater muscle recruitment and greater activation of the upper motor centres, which favours the patient’s recovery.

Recovery, Rehabilitation and Physiotherapy

The specific muscles that favour joint stability must be training within the DTM plane in early stages. Functional gestures such as “throwing a dart” or “using a toy hammer” can be used to help the patient recover optimally.

In addition, and given the proprioceptive importance of this ligament, Neuromuscular Control work can be added with JPS (Joint Position Sense) exercises, Motor Imagery or Mirror Therapy.

Physiotherapy and Hand Recovery
Physiotherapy and Early Movement

Motion, type of contraction, loads, etc. can be progressively increased.

In this link, you can access the Case Report with a work proposal on a patient published in “Journal of Hand Therapy”.

Do you have patients with this Carpal Ligament injuries? Ask us about exercise programmes with ReHand and enhance your patient’s sensorimotor approach!


Hagert E, Lluch A, Rein S. The role of proprioception and neuromuscular stability in carpal instabilities. J Hand Surg Eur Vol. 2016;41(1):94-101.

Wolff AL, Wolfe SW. Rehabilitation of scapholunate injury: Application of scientific and clinical evidence to practice. J Hand Ther. 2016;29(2):146-53.

Rajan PV, Day CS. Scapholunate Interosseous Ligament Anatomy and Biomechanics. J Hand Surg Am [Internet]. 2015;40(8):1692-702. Available at:

Feehan L, Fraser T. Early controlled mobilization using dart-throwing motion with a twist for the conservative management of an intra-articular distal radius fracture and scapholunate ligament injury: A case report. J Hand Ther [Internet]. 2016;29(2):191–8. Available from:

Levangie P, Norkin C. Joint Structure and Function, A comprehensive Analysis. 4th ed. Philadelphia. FA. Davis Company. 2005. Chapter 9. The Hand and Wrist Complex. 305-319.

Pablo Rodríguez Sánchez-Laulhé

PhD Candidate | PT & eHealth Researcher