Extensor mechanism of the finger

1. The terminal tendon is formed by convergence of the lateral bands and is the primary structure extending the distal interphalangeal joint.

True

In Schweitzer and Rayan's dissection of 56 cadaveric digits, the terminal tendon was the segment between the convergence of the lateral bands and its insertion on the distal phalanx. They identified it as the primary extensor of the distal interphalangeal joint, with the adjacent retinacular structures acting mainly to stabilise it.

• Schweitzer TP, Rayan GM. The terminal tendon of the digital extensor mechanism: Part I, anatomic study. J Hand Surg Am. 2004;29(5):898-902. PMID 15465241

2. The terminal tendon inserts well clear of the nail's germinal matrix, on average more than 5 mm away.

False

The same dissection study measured an average distance of only 1.4 mm between the terminal tendon insertion and the germinal matrix of the nail bed. The authors note that the thinness of the terminal tendon and its proximity to the nail matrix must be kept in mind during surgery.

• Schweitzer TP, Rayan GM. The terminal tendon of the digital extensor mechanism: Part I, anatomic study. J Hand Surg Am. 2004;29(5):898-902. PMID 15465241

3. In cadaver models, division of the central slip alone is sufficient to produce a boutonnière deformity.

False

Grau and colleagues sequentially divided extensor structures in 18 cadaveric hands. Central slip detachment reduced proximal interphalangeal extension, but a boutonnière deformity appeared only when the central slip, the triangular ligament and the transverse and oblique fibres of the interosseous hood had all been divided, allowing the lateral bands to sublux volar to the joint axis.

• Grau L, Baydoun H, Chen K, Sankary ST, Amirouche F, Gonzalez MH. Biomechanics of the Acute Boutonniere Deformity. J Hand Surg Am. 2018;43(1):80.e1-80.e6. PMID 28888567

4. Recent cadaveric dissection series found the oblique retinacular ligament in every finger examined, although its thickness varied.

True

Earlier reports disagreed on whether the oblique retinacular (Landsmeer) ligament is consistently present. Borgström and colleagues identified it on both sides in all 48 fingers dissected, with thickness ranging from a strong bundle to thin, sparse fibres, and Balakrishnan and colleagues found it in all 100 cadaveric fingers they studied, contrary to earlier reports of its absence.

• Borgström T, Dahlin LB, Tranum-Jensen J. The retinacular ligaments of the digital extensor expansion revisited: An anatomical and biomechanical study. Clin Anat. 2024;37(8):849-858. PMID 37747299
• Balakrishnan TM, Subbaraj H, Jaganmohan J. Anatomy of Landsmeer Ligaments-Redefined. Indian J Plast Surg. 2019;52(2):195-200. PMID 31602135

5. With the proximal interphalangeal joint held in extension, the oblique retinacular ligament restrains flexion of the distal interphalangeal joint.

True

In Borgström's biomechanical testing, cutting the oblique retinacular ligament significantly increased distal interphalangeal flexion while the proximal interphalangeal joint was held extended. The authors concluded that the retinacular ligaments act chiefly as stabilising links between the two interphalangeal joints.

• Borgström T, Dahlin LB, Tranum-Jensen J. The retinacular ligaments of the digital extensor expansion revisited: An anatomical and biomechanical study. Clin Anat. 2024;37(8):849-858. PMID 37747299