Interosseous Muscle Management in Adults
Anatomical Context and Function
The interosseous muscles serve as the cornerstone of hand function, providing the foundation for all intrinsic and extrinsic hand movements 1. These muscles are organized in dorsal and palmar layers, innervated by the ulnar nerve, and despite their small excursion, they have profound impact on finger balance, grip, and pinch function 1.
Clinical Presentation and Diagnosis
For an adult with interosseous muscle symptoms, the primary diagnostic focus should be identifying whether the dysfunction stems from denervation, contracture, trauma, or systemic disease 1, 2.
Key Diagnostic Features to Assess:
Strength testing: Evaluate Medical Research Council grading for the first dorsal interosseous and abductor digiti minimi muscles, as these provide the most reliable markers of intrinsic hand function 3
Contracture assessment: Look for the characteristic posture of hyperflexed metacarpophalangeal (MCP) joints with hyperextended proximal interphalangeal (PIP) joints, indicating contracted interossei and lumbricals 2
Functional testing: Test active finger extension with the wrist in neutral position and MCP joints in various positions—inability to extend interphalangeal joints when MCP joints are maximally extended suggests interosseous dysfunction rather than flexor tendon tightness 4
Underlying etiology: Investigate for trauma, spasticity, ischemia, rheumatologic disorders, or iatrogenic causes through targeted history 2
Diagnostic Workup:
Electrodiagnostic studies: Motor amplitude measurements provide objective evidence of denervation and track reinnervation progress 3
Rheumatologic testing: When systemic disease is suspected 2
Imaging: Consider if structural pathology or joint involvement is present 5
Management Algorithm
Non-Surgical Management (First-Line for Mild Cases):
Occupational therapy: Focused strengthening protocols, particularly selective strengthening of the first dorsal interosseous muscle 2, 5
Orthoses: Custom splinting to prevent progressive deformity 2
Botulinum toxin injections: For spasticity-related contractures 2
Surgical Management Indications:
Surgery should be considered when conservative measures fail and significant disability persists, including weakness in grip strength, difficulty grasping larger objects, or hygiene maintenance problems 2.
Nerve transfer procedures: For denervation injuries, supercharge end-to-side anterior interosseous-to-ulnar motor nerve transfer can augment intrinsic hand function, with the first dorsal interosseous muscle showing superior recovery compared to the abductor digiti minimi muscle 3
Contracture release: Surgical options are diverse and must be dictated by the specific cause and severity of contracture 2
Critical Clinical Pearls:
The first dorsal interosseous muscle demonstrates better functional recovery after nerve transfer procedures despite its more distal innervation, achieving significantly greater postoperative strength than the abductor digiti minimi muscle 3
Maximal MCP joint extension blocks both extensor digitorum communis and interosseous muscle action in finger extension—this explains claw finger development even without intrinsic muscle paralysis 4
FDI contraction can radiographically reduce subluxation of the thumb carpometacarpal joint, validating its role in joint stabilization 5
Mean follow-up of 16.7 months post-nerve transfer shows significant improvement in both strength and motor amplitude for intrinsic muscles 3