Carpal Instability and Scapholunate Instability
Contemporary, ligament-specific treatment of complex wrist instability
Carpal instability occurs when the small bones of the wrist no longer move together in a stable and coordinated way. It can cause pain, clicking, weakness, reduced grip strength and a feeling that the wrist cannot be trusted during lifting, pushing or weight-bearing. In more advanced cases, persistent abnormal movement may eventually lead to cartilage wear and wrist arthritis.
Scapholunate instability is the most common and best-recognised form of carpal instability. It involves abnormal movement between the scaphoid and lunate, two central bones within the wrist. However, it should not be regarded simply as a tear of one ligament. Contemporary understanding recognises that the scaphoid and lunate are held together and controlled by a complex configuration of anatomical ligaments, capsular structures and dynamic stabilisers.
This distinction is important because two patients may both be told that they have a scapholunate ligament injury but may have very different patterns of instability. The appropriate treatment depends on which structures have failed, how the carpal bones are moving, whether the deformity remains reducible and whether the cartilage is still healthy.
Understanding carpal instability
The wrist contains eight small carpal bones arranged in two rows. These bones must move through a carefully coordinated sequence whenever the wrist bends, rotates, grips or bears weight. Stability is provided by the intrinsic ligaments connecting adjacent carpal bones, the extrinsic ligaments linking the wrist to the forearm, the surrounding joint capsule, the tendons that provide muscular control and the sensory system that allows the body to recognise and respond to wrist position.
Carpal instability develops when one or more parts of this stabilising system can no longer guide the wrist normally. The abnormality may only appear during movement, gripping or loading, or it may eventually become visible even when the wrist is resting.
Although scapholunate instability is the most common pattern, instability can also occur between the lunate and triquetrum, through the midcarpal joint, between the radius and the carpus, or as part of a more complex multidirectional or adaptive deformity.
What is scapholunate instability?
The scaphoid and lunate normally move together as part of a balanced and coordinated proximal carpal row. They are not stabilised by the scapholunate interosseous ligament alone. Instead, their relationship is maintained by a complex network of intrinsic and extrinsic ligaments, capsular structures and dynamic muscular stabilisers.
When this network is disrupted, the wrist becomes unbalanced. The scaphoid and lunate may no longer move together in unison, and abnormal translation, rotation or separation can develop during movement and loading. This is scapholunate instability.
The scaphoid may flex, rotate or translate abnormally while the lunate moves in a different direction. This alters the coordinated motion of the proximal carpal row and changes the distribution of forces across the wrist cartilage. In some patients, persistent instability eventually progresses to arthritis.
The visible gap between the scaphoid and lunate is therefore only one feature of the condition. It is often the easiest abnormality to recognise on an X-ray, but it does not fully describe the pattern or functional severity of the instability.
This broader understanding helps explain why one standard operation cannot reliably treat every scapholunate injury.
How does scapholunate instability occur?
Scapholunate instability commonly follows a fall onto an outstretched hand, particularly when the wrist is extended and loaded. It may also develop following sporting injuries, cycling or motor vehicle accidents, work-related twisting injuries, previous fractures or repeated loading through an extended wrist.
Some people experience immediate pain, swelling and weakness. Others initially believe they have sustained a minor wrist sprain and only seek further assessment when pain, clicking or a sense of shifting continues.
In some patients, there is no single memorable injury. General ligamentous laxity, abnormal wrist anatomy or gradual degeneration may contribute to the development of instability over time.
Symptoms of scapholunate instability
Patients commonly experience pain over the back or radial side of the wrist. The pain is often aggravated by gripping, lifting, pushing up from a chair, doing push-ups, using gym equipment or placing weight through an extended wrist.
There may be clicking, clunking or a sensation that the wrist shifts during movement. Grip strength may deteriorate, and some patients lose confidence in using the hand for work, sport or heavier everyday activities. Swelling and reduced wrist movement may also occur.
Importantly, some patients have significant symptoms despite normal or near-normal resting X-rays. This is particularly common when the instability is dynamic and only appears during movement or loading.
Stages of scapholunate instability
Scapholunate instability exists along a spectrum rather than as a simple torn-or-not-torn diagnosis.
In early or pre-dynamic instability, the ligamentous and capsular structures may be injured while ordinary X-rays remain normal. The abnormality may only be identified on MRI or during wrist arthroscopy.
In dynamic instability, the wrist may appear relatively normal at rest, but abnormal separation, translation or rotation develops during gripping, loading or movement.
In static instability, abnormal alignment is visible on routine X-rays. The deformity may initially remain reducible, meaning the scaphoid and lunate can still be brought back towards a more normal relationship. With time, the deformity may become fixed and no longer fully correctable.
Longstanding instability may eventually lead to a recognisable pattern of arthritis known as scapholunate advanced collapse, or SLAC wrist. The stage of instability has a major influence on treatment. A recent, dynamic injury with healthy cartilage is very different from a fixed deformity associated with arthritis.
How is scapholunate instability diagnosed?
Diagnosis begins with a careful history and examination. It is important to understand the original mechanism of injury, where the wrist hurts, whether it clicks or shifts and which activities reproduce the symptoms.
Examination assesses wrist movement, grip, tenderness, generalised ligamentous laxity and the behaviour of the wrist during loaded movement. Specific manoeuvres such as the scaphoid shift or Watson test may be useful, but no single examination finding should be interpreted on its own.
Standard X-rays assess the scapholunate interval, carpal alignment, scaphoid rotation and any evidence of arthritis. Stress views performed while gripping or loading the wrist may reveal dynamic instability that is not visible on ordinary resting images.
MRI can demonstrate injury to the scapholunate ligament and may also identify associated cartilage, capsular or tendon abnormalities. However, MRI findings must be interpreted with care. A scan may describe a partial tear or degeneration without proving that the wrist is functionally unstable. Conversely, clinically important instability may be present despite a normal or inconclusive MRI.
In selected cases, dynamic fluoroscopy, CT arthrography, MR arthrography or four-dimensional CT may provide additional information about the way the wrist moves under load.
The role of wrist arthroscopy
Wrist arthroscopy has revolutionised the understanding and treatment of carpal instability over the past two decades.
Through several small incisions, the joint can be inspected directly using a fine camera. Arthroscopy allows the surgeon to examine the exact location and extent of the ligament injury, the quality of the remaining tissue, the direction in which the instability occurs and how the scaphoid and lunate behave when the wrist is stressed.
It also allows assessment of the cartilage, the surrounding stabilising ligaments and any associated injuries elsewhere in the wrist. Importantly, arthroscopy provides functional information that static imaging cannot always provide. It allows the surgeon to assess how the ligamentous structures behave when they are probed, loaded and viewed from different areas of the wrist. For this reason, arthroscopy may be both diagnostic and therapeutic. The injury can often be classified and treated during the same procedure.
The changing understanding of scapholunate instability
Historically, scapholunate instability was viewed mainly as a problem involving the scapholunate interosseous ligament and the size of the gap between the scaphoid and lunate. Traditional reconstruction often focused on closing this gap using open capsular dissection, tendon grafts, bone tunnels, temporary wires or screws and prolonged immobilisation.
The gap remains useful because it is comparatively easy to identify and measure on an X-ray. However, contemporary treatment is no longer directed solely towards closing the scapholunate gap.
The more important objective is to restore a dynamic, supple and balanced wrist in which the bones of the proximal carpal row move together in unison. Treatment aims to control abnormal translation and rotation, particularly rotatory subluxation and dorsal translation of the scaphoid relative to the lunate. The desired result is not merely a more normal static X-ray, but a wrist that remains coordinated and stable during movement, gripping and loading.
Traditional open operations continue to have a role in selected circumstances. However, they may be associated with stiffness, disruption of normal capsular tissue, altered proprioception and difficulty reproducing the complex three-dimensional control of the normal wrist.
Contemporary treatment has therefore moved towards a more selective, ligament-specific and modular approach. Rather than treating every widened scapholunate interval with the same reconstruction, the aim is to identify each component of the instability and repair, augment or reconstruct the structures that have failed.
This field remains complex and continues to evolve. Scapholunate instability is not yet a completely solved problem, and no single operation is suitable for every injury pattern. Australian wrist surgeons have made major contributions to this developing understanding. I have had the great privilege of working with and learning from a number of these predecessors and Australian pioneers. Their work has strongly influenced my understanding of carpal mechanics and my approach to contemporary arthroscopic stabilisation.
Non-operative treatment
Not every scapholunate injury requires surgery.
Low-grade injuries without convincing mechanical instability may improve with temporary splinting, activity modification, anti-inflammatory treatment where appropriate and a structured hand therapy programme. Rehabilitation focuses on restoring movement, improving proprioception and strengthening the muscles and tendons that dynamically support the wrist.
Non-operative treatment may also be appropriate when symptoms are improving, the wrist remains well aligned, the patient’s functional requirements are modest or the cartilage is already too damaged for ligament reconstruction to be worthwhile.
Therapy can improve control and reduce symptoms, particularly in subtle instability. However, it cannot physically reconnect completely detached structures or reliably correct major mechanical instability. The decision to recommend surgery is therefore based on the severity of the symptoms, the presence of functional instability, the condition of the cartilage, the quality of the remaining ligament tissue, the alignment of the wrist and the patient’s work, sporting and everyday requirements.
When is surgery considered?
Surgery may be considered when a traumatic injury has caused a repairable ligament disruption, or when pain, weakness and mechanical symptoms persist despite appropriate non-operative treatment.
It may also be appropriate when the wrist demonstrates symptomatic dynamic or static instability, when the deformity is progressing or when the patient cannot reliably perform normal work, sport or daily activities.
Timing is important. A recent injury may still contain healthy, mobile ligament tissue that can be repaired directly. A longstanding injury may require augmentation or reconstruction because the original tissue has become scarred, attenuated or incapable of healing back to bone.
Arthroscopic scapholunate stabilisation
Arthroscopic scapholunate stabilisation is an area of particular subspecialty interest within my practice. I assess complex cases, revision cases and patients referred by other surgeons for an opinion regarding contemporary arthroscopic treatment.
The operation is highly technical. I use a ligament-specific or modular approach rather than treating every scapholunate injury in the same way. The pattern of instability is assessed using the patient’s symptoms and mechanism of injury, standard and stress X-rays, MRI or other advanced imaging, the direction of scaphoid and lunate translation and rotation, the reducibility of the deformity and the findings at arthroscopy. The purpose is to identify the individual components of the stabilising system that have failed and address each of them selectively.
Depending on the findings, treatment may involve preparing a damaged ligament attachment, repairing the ligament or capsule with small suture anchors, advancing or tightening selected stabilising structures, temporarily supporting the scaphoid and lunate with wires, augmenting a repair with local tissue or performing a targeted ligamentoplasty.
Some patients require an arthroscopic-assisted reconstruction using a tendon graft. Others can be treated without drilling large tunnels through the scaphoid and lunate. Avoiding unnecessary bone tunnels, large open exposures and extensive capsular dissection may reduce surgical trauma and postoperative stiffness in appropriately selected patients.
The exact operation is determined by the individual pattern of instability rather than by the diagnostic label alone.
What are the goals of surgery?
The purpose of treatment is not simply to close the scapholunate gap or make the X-ray appear perfect.
The principal objective is to restore a dynamic, supple and balanced wrist in which the proximal carpal row moves together in a coordinated fashion. This requires control of painful abnormal motion, rotatory subluxation and abnormal dorsal translation of the scaphoid relative to the lunate.
Treatment also aims to improve the relationship between the scaphoid and lunate during loading, restore functional stability, improve grip strength and confidence in the wrist, preserve useful movement and reduce abnormal forces across the cartilage. A small degree of residual widening or radiographic imperfection may remain even when pain, strength and function improve significantly. Perfect static alignment on an X-ray does not always mean that the wrist functions normally, and a small residual abnormality does not necessarily mean that treatment has failed.
What results can be expected?
Scapholunate instability remains one of the most complex problems in wrist surgery.
Modern arthroscopic and arthroscopic-assisted techniques have improved our ability to identify the precise injury, preserve uninjured structures and provide targeted treatment with less disruption than many traditional open procedures.
In suitable patients, reducing dynamic instability, rotatory subluxation and abnormal translation can produce meaningful improvements in pain, grip strength, confidence and everyday wrist function. The complication profile may also be more favourable than that of larger open reconstructions in appropriately selected cases.
However, no operation can guarantee a completely normal wrist. The outcome depends on how long the instability has been present, whether the deformity remains reducible, which structures are involved, the quality of the remaining tissue, the condition of the cartilage, the patient’s physical requirements and adherence to postoperative protection and therapy.
Some patients retain a degree of radiographic imperfection even after a clinically successful reconstruction. The aim is to restore functional stability and coordinated movement rather than simply chase a perfect X-ray.
When is open surgery still required?
Arthroscopic treatment has, for the large part, superseded the role of traditional open surgery in the treatment of scapholunate instability. Open surgery is now uncommon in my practice, but it remains a valuable set of skills in selected situations.
An open or combined procedure may still be required when the instability cannot be adequately corrected arthroscopically, when a substantial tendon-graft reconstruction is necessary, when several ligament systems are involved or when previous surgery has significantly altered the anatomy. It may also be required in revision settings where arthroscopy is unsuitable.
Where possible, I favour preserving normal capsular tissue, blood supply, proprioception and wrist movement. However, the least invasive operation is not automatically the correct operation. The appropriate procedure is the one capable of treating the patient’s particular mechanical problem.
Advanced instability and arthritis
Once significant arthritis has developed, repairing or reconstructing the stabilising ligaments may no longer provide a reliable solution. Treatment then focuses on relieving pain and preserving as much useful wrist function as possible. Depending on the pattern of arthritis, this may involve a proximal row carpectomy, scaphoid excision with partial wrist fusion, another limited carpal fusion, wrist denervation, total wrist replacement in selected patients or total wrist fusion.
These are considered salvage procedures and are different from early ligament repair or reconstruction.
Recovery after arthroscopic scapholunate surgery
Recovery depends on the exact structures treated and the strength of the repair.
The wrist is commonly protected in a splint or cast for approximately six weeks. Finger, elbow and shoulder movement usually begin immediately, while wrist and forearm movement are introduced once the repair is considered sufficiently protected.
Strengthening generally does not begin until approximately three months after surgery. Grip, loading and weight-bearing are then progressed gradually under the guidance of a hand therapist.
Return to heavier work, gym-based loading or sport commonly takes between four-and-a-half and six months. More extensive reconstructions may require a longer recovery.
Some procedures require temporary wires, which are removed before wrist movement progresses.
Ligament healing takes place over several months. Premature loading can stretch or disrupt the repair, and recovery cannot be safely rushed.
Risks of surgery
The risks of scapholunate surgery include infection, bleeding, wound problems, nerve irritation, tendon irritation, stiffness, persistent pain, loss of grip strength and failure or stretching of the repair. There may also be residual or recurrent instability, problems related to wires, anchors or grafts, complex regional pain syndrome, progression of arthritis or the need for further surgery.
The risk profile differs considerably between a limited arthroscopic repair and a major ligament reconstruction. The expected benefits, limitations and potential complications are discussed in detail once the individual pattern of injury has been established.
My approach to scapholunate instability
Scapholunate instability should not be treated as a single-ligament problem with a single standard operation.
My approach is to determine whether true functional instability is present, whether it is responsible for the patient’s symptoms and whether it is dynamic, static, reducible or fixed. I then identify which ligaments and capsular structures have failed, how the scaphoid and lunate are translating and rotating, whether the remaining tissue is capable of repair and whether the cartilage remains sufficiently healthy for stabilisation or reconstruction to be worthwhile.
I use a ligament-specific or modular approach. Each component of the instability is assessed and treated according to its particular role within the broader stabilising system. This may involve a selective repair, capsular procedure, augmentation or ligamentoplasty rather than applying the same reconstruction to every patient. I dedicated portions of my formal upper-limb fellowship training and Australian Hand Surgery Society Travelling Fellowship to developing the arthroscopic skills required to assess and treat scapholunate and other carpal instabilities. This included focused training in advanced wrist arthroscopy, ligament repair, ligament reconstruction and the interpretation of complex carpal mechanics.
I have also had the great privilege of working with and learning from a number of my predecessors and Australian pioneers in wrist surgery. Their contributions have helped shape the contemporary understanding of carpal instability and the development of more selective arthroscopic treatments. This remains a rapidly developing area of wrist surgery. My practice is focused on applying and refining contemporary, ligament-specific and modular arthroscopic techniques while remaining realistic about the limitations of current treatment.
Frequently asked questions
Can a scapholunate injury heal without surgery?
Some low-grade or incomplete injuries can settle with immobilisation, activity modification and rehabilitation. A major disruption associated with mechanical instability is less likely to restore normal stability without surgery.
Does an MRI prove that I need surgery?
No. MRI is only one part of the assessment. Treatment should be based on symptoms, examination, functional instability, carpal alignment, tissue quality and the condition of the cartilage.
Can I have scapholunate instability if my X-rays are normal?
Yes. Dynamic or pre-dynamic instability may not be visible on standard resting X-rays. Stress imaging, dynamic imaging or wrist arthroscopy may be required.
Is arthroscopy always better than open surgery?
Arthroscopy has, for the large part, superseded the role of open surgery in treating scapholunate instability. It provides a detailed assessment of the instability and often permits selective treatment while preserving more of the normal capsular tissue and wrist movement.
Open surgery is now uncommon, but the ability to perform an open or combined reconstruction remains valuable in selected situations, particularly when there is fixed deformity, substantial tissue loss, altered anatomy or a pattern of instability that cannot be adequately corrected arthroscopically.
Will surgery make my X-rays completely normal?
Not always. The main objective is to restore coordinated movement and functional stability while improving pain, grip and use of the wrist. A degree of radiographic imperfection may remain despite a worthwhile clinical result.
Does every scapholunate injury cause arthritis?
No. The natural history varies. However, persistent mechanical instability can alter the distribution of forces across the wrist and may lead to arthritis in some patients. The risk is influenced by the severity and duration of the instability, the pattern of abnormal movement, the condition of the cartilage and individual patient factors.
How long will I be unable to work?
This depends on the operation and the physical demands of the job. Office-based work may be possible relatively early with restrictions. Heavy manual work usually requires several months of rehabilitation.
When should I seek specialist assessment?
Specialist wrist assessment should be considered when pain, clicking, weakness or instability continues after a wrist injury, particularly when symptoms are provoked by gripping, pushing or weight-bearing despite apparently normal initial imaging.