Extensor Tendon Injuries/ Mallet/ Sagittal Band

Extensor tendon injuries

‣

Anatomy of extensor tendons in hand?

• EDC crosses dorsum of MCPJ, stabilized by the extensor hood, consisting of the transverse, oblique and sagittal bands

‣

Divides into 3 slips at the expansion hood

• Central slip continues on to insert onto middle phalanx
• 2 lateral bands travel on either side of proximal and middle phalanx to insert on distal phalanx

‣

3 ligaments in the extensor mechanism

• Triangular ligament - between the 2 lateral slips on dorsum; prevent palmar subluxation [contracts in chronic swan neck/ attenuates in boutonierre] - HRM Arthritis - OA, RA, AVN (Kienbock), Deformities - ‼️ Pathophysiology of boutonnieres?
• Transverse retinacular ligament - between the 2 lateral slips on palmar; prevents dorsal subluxation [contracts in chronic boutonierre/ attenuates in swan neck]
• Oblique retinacular ligament - bilateral strong narrow bands from A2 pulley to base of extensor tendon

‣

Juncturae tendinum -

• interconnections of extensor tendons at the level of MCP Heads
• May mask proximal tendon laceration

MALLET FINGER

‣

Classification of mallet finger?

• Doyle's Classification
• Type 1 = Closed – splint
• Type 2 = Open with no skin loss
• Type 3 = Open with skin loss
• Types 4 = affects bone
• Type 4a = Paeds Physeal – usuallySH3, SH4
• Type 4b = bony avulsion < 50%
• Type 4c = Bony avulsion > 50%

‣

How does chronic mallet finger lead to swan neck deformity?

‣

‼️ Pathophysiology of swan neck?

• Primary Lesion: Volar plate laxity at PIPJ ➔ hyperextension of PIPJ by central slip ➔ FDP pulls DIPJ flexed ➔ Attenuation of the transverse retinacular ligament on volar side ➔ Lateral bands sublux dorsally and worsen hyperextension
• Secondary Lesion leads to imbalance of forces on PIPJ with PIPJ extension forces greater than PIPJ forces
• [MCPJ] volar subluxation in RA due to synovitis
• [PIPJ] FDS rupture ➔ unopposed PIPJ extension with subsequent attenuation of transverse retinacular ligaments
• [DIPJ] Mallet injury ➔ due to attrition of terminal tendon, extension forces now go thru central slip that attaches to base of middle phalanx, leading to hyperextension at PIPJ

SAGITTAL BAND RUPTURE

‣

What is the classification for sagittal band ruptures?

• Type 1 = no extensor tendon instability
• Type 2 = tendon subluxation
• Type 3 = tendon dislocation