Clinical examination of tendon and intrinsic function in the finger

1. In the Elson test, the proximal interphalangeal joint is flexed to 90° over the edge of a table and the patient extends it against resistance; absent extension force at the proximal interphalangeal joint with the distal interphalangeal joint held rigidly in extension indicates complete rupture of the central slip.

True

Elson described the test so that a closed central slip rupture can be recognised before a boutonnière deformity appears. In Rubin's cadaver model, Elson's manoeuvre was the only test that detected central slip disruption in both simulated injuries.

• Elson RA. Rupture of the central slip of the extensor hood of the finger. A test for early diagnosis. J Bone Joint Surg Br. 1986;68(2):229-31. PMID 3958008
• Rubin J, Bozentka DJ, Bora FW. Diagnosis of closed central slip injuries. A cadaveric analysis of non-invasive tests. J Hand Surg Br. 1996;21(5):614-6. PMID 9230945

2. The Boyes test is the most reliable test for an acute closed rupture of the central slip, before any deformity has developed.

False

Elson noted that the Boyes test becomes positive only at a late stage. In Rubin's cadaver study the test described by Boyes, which evaluates distal interphalangeal joint flexion, was not reliable for either simulated injury, whereas the Elson test detected both.

• Rubin J, Bozentka DJ, Bora FW. Diagnosis of closed central slip injuries. A cadaveric analysis of non-invasive tests. J Hand Surg Br. 1996;21(5):614-6. PMID 9230945
• Elson RA. Rupture of the central slip of the extensor hood of the finger. A test for early diagnosis. J Bone Joint Surg Br. 1986;68(2):229-31. PMID 3958008

3. Flexor digitorum superficialis function is isolated by holding the other fingers in full extension while the patient flexes the finger being tested; isolated flexion of the proximal interphalangeal joint indicates an intact superficialis.

True

In Tan's study, isolated flexion at the proximal interphalangeal joint with the other fingers held fully extended indicated independent superficialis function, and obligatory flexion of the distal interphalangeal joint during the test indicates profundus activity rather than independent superficialis function. Independent superficialis function was most consistent in the middle and ring fingers and least consistent in the little finger.

• Tan JS, Oh L, Louis DS. Variations of the flexor digitorum superficialis as determined by an expanded clinical examination. J Hand Surg Am. 2009;34(5):900-6. PMID 19410995

4. Absence of independent flexor digitorum superficialis function in one little finger reliably predicts its absence in the opposite little finger, so the uninjured hand can be used to exclude a superficialis laceration.

False

In Townley's pooled analysis, when superficialis function was absent in one little finger the probability of absence in the opposite little finger was only 0.64; when it was present on one side, absence on the other side had a probability of 0.02. In Guler's series, when superficialis function was absent in one little finger it was also absent in the opposite one in 51.1%. Comparison with the uninjured side is therefore unreliable when superficialis function is absent in the uninjured little finger.

• Townley WA, Swan MC, Dunn RL. Congenital absence of flexor digitorum superficialis: implications for assessment of little finger lacerations. J Hand Surg Eur Vol. 2010;35(5):417-8. PMID 20515987
• Guler F, Kose O, Turan A, Baz AB, Akalın S. The prevalence of functional absence of flexor digitorum superficialis to the little finger: a study in a Turkish population. J Plast Surg Hand Surg. 2013;47(3):224-7. PMID 23617293

5. In the Bunnell intrinsic tightness test, intrinsic tightness is present when passive flexion of the proximal interphalangeal joint is restricted while the metacarpophalangeal joint is held in extension.

True

Reinholdt's open-access description of the test states that intrinsic tightness is present when the proximal interphalangeal joint is difficult to flex in this position; Li's biomechanical study showed that proximal interphalangeal joint stiffness increased by more than 50% as the metacarpophalangeal joint moved from 60° of flexion to full extension, a mechanism the authors expect to be amplified by intrinsic tightness.

• Reinholdt C, Fridén J. Selective release of the digital extensor hood to reduce intrinsic tightness in tetraplegia. J Plast Surg Hand Surg. 2011;45(2):83-9. PMID 21504278
• Li ZM, Davis G, Gustafson NP, Goitz RJ. A robot-assisted study of intrinsic muscle regulation on proximal interphalangeal joint stiffness by varying metacarpophalangeal joint position. J Orthop Res. 2006;24(3):407-15. PMID 16479575