Carpal Instability Anand Arya MS Orth, MchOrth, FRCS (Tr & Orth) Consultant Trauma & Orthopedic (Upper Limb & Elbow) Surgeon Infection Control Lead, Department of Trauma & Orthopaedics King’s College Hospital, London Hon Visiting Professor, MG University of Medical Sciences, Jaipur President, Indian Orthopaedic Society UK I am one of the student of Jaipur medical college having done my post-graduation with Prof P K Sethi in early 80’s. I moved to UK more than 25 years ago and is at my present place, Kings College Hospital, London for past 19 yrs. My subspecialty interest is Upper limb surgery particularly focusing on elbow surgery. Carpal instability remains a challenge to upper limb surgeons. It is one area which is still not fully understood in terms of patho-mechanics and treatment. I know it is impossible to explain it fully in a 15 mt lecture so I would only tell you the principles of the pathology and management including the basic anatomy.

Osseous Anatomy Knowledge of carpal anatomy and function is essential to understand carpal instability which is synonymous with carpal dysfunction. Wrist is the link between the forearm and the hand and involve articulations between 14 bone and the pisiform. While the bones of the proximal row move independently, the distal row moves as one block of bones. Pisiform is a sessamoid bone and is not part of the wrist movements.

Ligamentous anatomy Two main functions Mechanical strength Proprioception Extrinsic: Connect forearm bone with carpus Intrinsic: Originate and insert within the carpus Anatomic, histologic and biochemical differences exist between the two types Rupture/dysfunction of ligaments is the main cause of carpal instability Multiple ligaments connect the bone of the wrist to each other. Their arrangement are complex and size and shape vary from one individual to others. Ligaments serve two main purpose: Mechanical strength – by connecting different bone and allowing controlled movements Proprioception – due to abundant mechanoreceptors present Ligaments are either – Extrinsic or Intrinsic Some are mere condensations of the capsular tissue and difficult to identify as separate bands, others are quite distinct and can be dissected as distinct entity.

Ligamentous anatomy Extrinsic ligaments Extrinsic ligaments can be divided in two main groups. Dorsal – Dorsal Radio Carpal ligament (Dorsal Radio Triquetrum lig), Dorsal Intercarpal ligament. Mayo’s dorsal approach to wrist make incision parallel to these two ligaments to raise a triangular flap of the capsule based radially. Palmar – two rows of ligaments making two inverted ‘V’, between which there is a weak spot called ‘space of Poirier’ through which perilunate dislocations frequently occur. Palmar ‘Space of Poirier’ between two ∧ Dorsal

Ligamentous anatomy Intrinsic ligaments Collections of relatively short dorsal and palmar fibers Connect the bones of the same carpal row Link the two rows to each other Scapholunate ligament

Carpal Kinematics No tendons/muscles attach to the proximal row Bones of proximal row moves independently Triquetrum has a tendency to extension, especially in ulnar deviation (helicoid joint) Scaphoid has a tendency to flexion, especially in radial deviation Lunate suspended in between the two Distal row bones act as one block, tightly bound to each other Some facts about the wrist kinematics. Its getting complicated now but I would try to keep it as simple as possible. The proximal row has no direct tendon attachments. In normal wrists, very little motion exists between the bones of the distal carpal row. In kinematic terms, the distal carpal row can be thought of as one rigid functional unit The moment generated by muscle contraction results in rotation that is initiated at the distal carpal row. The bones of the proximal row follow passively when tension within the midcarpal capsule reaches a certain level. The diagram on the left shows the oval ring concept of the wrist suggested by Lichtman. The distal row, as a fixed unit, is connected medially to the triquetrum (link A) and laterly to the scaphoid (link B). These two bones are connected to the lunate by means of two more links (link C and D). Failure of any one of these 4 ligamentous links is likely to result in pathological motion and abnormality in load transfer leading to carpal instability. Oval ring concept of Litchman

Scaphoid flexes in radial deviation and extends in ulnar deviation Wrist transmits huge amount of force during activities of daily living – up to 520 kg in men, 310 kg in women (10 x maximum grip strength) Scaphoid, as an intercalated bridge between proximal and distal rows, prevents collapse under load (Slider-crank mechanism, three bar linkage) Scaphoid flexes in radial deviation and extends into ulnar deviation Wrist transmits huge amount of force during activities of daily living – up to 520 kg in men (for a maximum grip strength of 52 kg), 310 kg in women (for a maximum grip strength of 31 kg) How the wrist sustains such load without yielding? Scaphoid, as an intercalated bridge between proximal and distal rows, prevents collapse under load (Slider-crank mechanism, three bar linkage)

Dorsal and Volar intercalated segment instability (DISI & VISI) Normal tendency of scaphoid to flex and triquetrum to extend, is kept under check by lunate as an intercalated segment keeping the proximal row bones together and balanced Rupture of lunate’s link with either of its neighbor results into: DISI – SL ligament fails Scaphoid flexes Lunate extends with Triquetrum VISI – LT ligament fails Triquetrum extends Lunate flexes with Scaphoid Lunate goes with the good guy You may heard these terms. Some of you may not be clear as to exactly what it means? DISI and VISI is caused by the rupture of lunate’s link with either of its neighbor, scaphoid or triquetrum. Normal tendency of scaphoid is to flex and of triquetrum to extend which is checked by lunate as an intercalated segment keeping a balance between two opposing forces. Once this link is broken at any place, scaphoid and triquetrum goes their own way and lunate follows the bone with which it is still attached. If SL ligament fails, unrestrained scaphoid flexes due to its natural tendency and lunate extends with triquetrum. If LT ligament fails, unrestrained triquetrum extends due to its natural tendency and lunate flexes Lunate is the intercalated segment between the two and keeps a balance but when ond side is broken, lunate goes with the intact bone.

More terminology CID CIA CIC (Carpal Instability Dissociative) CIND (Carpal Instability Non-dissociative) CIA (Carpal Instability Adaptive) CIC (Carpal Instability Complex) between bones of the same row, i.e. SL & LT instability mid-carpal or radio-carpal, i.e. between the two rows, or between radius and proximal row as a result of pathology outside the carpus, i.e. distal radial malunion between bones of same row, AND between rows, i.e. perilunate injuries

Mechanism of Injury Direct Indirect Extreme extension of wrist, associated with a variable degree of ulnar deviation and midcarpal supination Mayfield & colleague: Most carpal dislocations around the lunate (from minor scapholunate sprain to a complete palmar dislocation of the lunate) are caused by Progressive Perilunate Instability Two types of injuries may result into a carpal derangement. It is the indirect force which results into majority of carpal injuries seen in the clinical practice. Its normally an extreme extension of wrist associated with a variable degree of ulnar deviation and midcarpal supination which causes these injuries. Mayfield did a landmark work to understand the sequence of injuries and progression of ligamentous damage by cadaver studies. Their findings confirmed that most carpal dislocations around the lunate which includes a broad spectrum of injuries ranging from minor scapholunate sprains to a complete palmar dislocation of the lunate) are the consequence of a similar pathomechanic event – so called – progressive perilunate instability. Four stages of this mechanism has been identified. The deforming force can stop at any stage producing only a partial injury.

Progressive Perilunate Instability (Mayfield) Distal carpal row is forced into hyperextension (red arrow) Space of Poirier (asterisk) is opened Lunate can not extend as much as scaphoid due to constraint of short radiolunate ligament (2) SL ligament fails usually from palmar to dorsal Complete SLD is defined by the rupture of dorsal scapholunate ligament (3) Stage I : SL ligament disruption

Progressive Perilunate Instability (Mayfield) When dissociated from the lunate, the scaphoid-distal row complex may dislocate dorsally relative to lunate (red arrow) The limit of such dorsal translation is determined by the radioscaphoid-capitate ligament (4) Stage II : Lunocapitate dislocation

Progressive Perilunate Instability (Mayfield) If hyperextension persists, the ulnar limb of the arcuate ligament (5) may pull the triquetrum dorsally, causing failure of the lunate triquetrum ligament (6) Stage III : LT ligament disruption or Triquetral fracture

Progressive Perilunate Instability (Mayfield) Finally, the capitate is forced by still intact radioscaphoid-capitate ligament (4) into the radiocarpal space and push the lunate palmar-ward until it dislocates into the carpal canal in a rotary fashion. Stage IV : Lunate dislocation

Diagnosis Clinical Examination Usually no obvious deformity Only moderate swelling Localised tenderness in sub-acute or chronic cases pathognomonic Grip strength weak Neuro-vascular structures – median nerve frequently injured Frequently, major dislocations are missed at presentation ‘High index of suspicion’ is most helpful tool

Diagnosis X-Rays Four views : PA Lateral Scaphoid PA Oblique PA view with shoulder abducted 90 degree and elbow flexed 90 degree and forearm in neutral rotation Lateral view must be a true lateral view with elbow adducted to side and wrist in neutral rotation Four views : PA Lateral Scaphoid PA Oblique

Diagnosis Gilula’s lines Yin and Gilula defined three smooth curved lines joining the proximal and distal cortical surfaces of the carpal bones in a normally aligned wrist. A disruption or step off in any one of these lines may indicate a major carpal derangement. Gilula’s lines

Diagnosis Shape of lunate on a PA view can give a clue Shape of lunate on a PA view can help differentiate a dislocated from a misaligned lunate. Lunate in a DISI position tends to have an obliquely oriented ovoid configuration with a prominent wedge shaped ulnar corner pointing towards the medial aspect of the wrist Lunate in a VISI position has a ‘C’ shaped or moonlike appearance In perilunate dislocation, minor palmar rotation of the lunate gives this bone the appearance of an isosceles triangle pointing distally Lunate in a DISI position Lunate in a VISI position Dorsal perilunate dislocation

Diagnosis Additional views: Axial compression of the carpus by having the patient make a fist may accentuate the gap in the SLD which may not be apparent in a normal PA view. Wrist should not be in flexion or extension. The third CMC joint should be in clear profile when the wrist is not extended or flexed. PA view with 10 degree of angulation from ulna to radial side would best show the SL interval PA view with tube angled 10 degrees from the ulnar side AP with clenched fist

Increased scapholunate angle in the lateral view Diagnosis Increased scapholunate angle in the lateral view

Diagnosis CT scan CT scan can further add to clarify the diagnosis Three dimensional images are great help to diagnose the condition and plan the surgery. For surgery on malunited or non united scaphoid, or complex carpal dislocation, 3 D images provide excellent visual information about the amount and direction of the displacement. Distraction views – x-ray with hand suspended in finger traps Stress views – x-ray with distracting the wrist in different directions MR Arthrography – in special situations, normally not required

Diagnosis Arthroscopy of wrist: Gold Standard Wrist arthroscopy has revolutionised the practice of orthopaedics by its ability to examine and treat intra-articular abnormalities without an extensive arthrotomy. It is one of the most important tool in the wrist surgery at present.

Lesser Arc and Greater Arc injuries Lesser arc = perilunate Greater arc = trans-scaphoid perilunate

Scapholunate dissociation Most frequent carpal instability ‘Rotary subluxation of the scaphoid’ First stage of progressive carpal instability (mayfield) Spectrum of injuries, from minor scapholunate sprain to complete perilunar dislocation – all being different stages of the same mechanism The term rotary subluxation of scaphoid has been frequently used as a synonym for SLD, not strictly true as lig attached to both ends of the scaphoid had to fail and bone collapsed into flexion and pronation for it ot happen

Scapholunate dissociation Radioscaphoid joint – like two spoons sitting one on the other while the handles are not aligned. Radiolunate joint – does not get deg process as nearly perfect concentric shapes of the opposing articular surfaces

Scapholunate dissociation Stages at clinical presentation: I : Partial Scapholunate ligament injury II: Complete Scapholunate ligament injury, repairable III: Complete Scapholunate ligament injury, Non-repairable, Normally Aligned Scaphoid IV: Complete Scapholunate ligament injury, Non-repairable, Reducible rotary subluxation of Scaphoid V: Complete Scapholunate ligament injury, Irreducible scaphoid, Normal Cartilage VI: Complete Scapholunate ligament injury, Irreducible scaphoid, Cartilage degeneration

Scapholunate dissociation Diagnosis Frequently missed High index of suspicion Can occur with distal radius or scaphoid fracture

Scapholunate dissociation Diagnosis: Point tenderness Scaphoid Shift test (Kirk-Watson) Resisted finger extension test Scapholunate Ballottement Test Flex the wrist, palpate distal to Lister Tubercle

Scapholunate dissociation Terry Thomas sign (English film comedian’s dental diastema), positive if compared with other side>5 mm Scaphoid Ring sign – just shows the scaphoid flexed for any reason. Its presence does not always indicate SLD, absence does not always exclude SLD. Increased Scapholunate angle (> 45-60 degree) in lat view, along with lunate in DISI Terry Thomas Sign Scaphoid Ring Sign Scapho-lunate angle Lunate in DISI

Scapholunate dissociation Arthroscopy is the gold standard If in doubt, scope it Also assess the degree of injury

Scapholunate dissociation Diagnosis Difficult, not always predictable, seldom entirely satisfactory Injury missed very commonly so often seen late Even in acute phase, direct ligament repair almost impossible, or often fails

Scapholunate dissociation Treatment - Acute phase Percutaneous/arthroscopically guided K wire fixation Direct repair of ligament + internal fixation with K wire Dorsal capsulodesis (Blatt)

Scapholunate dissociation Treatment: Complete SLL injury, reducible scaphoid (chronic) Tendon reconstruction of SL ligament Different methods of tendon reconstruction

Scapholunate dissociation Treatment: Complete SLL injury, reducible scaphoid (chronic) Modified Brunelli and Brunelli’s three ligament tenodesis

Scapholunate dissociation Modified Brunelli and Brunelli’s three ligament tenodesis

Scapholunate dissociation Treatment: Complete SLL injury, irreducible scaphoid, normal cartilage STT arthrodesis Scapho-Lunate arthrodesis Scaphoid-Capitate arthrodesis Scaphoid-Lunate-Capitate Arthrodesis

Scapholunate dissociation Treatment: Complete SLL injury, irreducible scaphoid, cartilage degeneration (SLAC wrist) Arthroscopy Radial Styloidectomy Scaphoidectomy + Four corner fusion Proximal Row Carpectomy Total Wrist Arthroplasty Total Wrist Arthrodesis

Many thanks for your kind attention

Ligamentous anatomy

Angles and terminology Lunate is the intercalated segment, hence: DISI = a dorsiflexed lunate VISI = a volarflexed lunate