10.1 Tendon Repairs & Peripheral Nerve Injuries

Tendon Repairs & Peripheral Nerve Injuries

Hand therapy and upper extremity rehabilitation represent some of the most intricate, high-stakes clinical areas in occupational therapy. Restoring hand function following complex tendon repairs and peripheral nerve lacerations demands a precise understanding of hand anatomy, surgical repair biomechanics, healing timelines, and orthotic principles.

Certified Occupational Therapy Assistants (COTAs) collaborate closely with Occupational Therapists Registered (OTRs) and hand surgeons to deliver protocol-driven interventions that balance tendon excursion with repair protection, preventing catastrophic tendon ruptures while mitigating disabling scar adhesions and joint contractures.

1. Flexor Tendon Zones & Repair Biomechanics

Flexor tendon injuries are categorized into five distinct anatomical zones (Zones I through V). The biological prognosis, adhesion risk, and post-operative protocol selection depend directly on the anatomical zone of injury.

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|                        FLEXOR TENDON ANATOMICAL ZONES                       |
|                                                                             |
|   [ZONE I]   • Distal insertion of FDS to distal insertion of FDP at distal |
|                phalanx base. "Jersey Finger" (avulsion of FDP tendon).      |
|   [ZONE II]  • Distal palmar crease to FDS insertion ("NO MAN'S LAND").     |
|                FDS and FDP travel together in a tight fibro-osseous sheath  |
|                with A1–A5 pulleys. Highest risk of restrictive adhesions!   |
|   [ZONE III] • Distal edge of carpal tunnel (transverse carpal ligament)   |
|                to the distal palmar crease. "Palm Zone" (lumbricals origin).|
|   [ZONE IV]  • Beneath transverse carpal ligament (carpal tunnel).          |
|                9 flexor tendons (4 FDS, 4 FDP, 1 FPL) + Median Nerve.       |
|   [ZONE V]   • Musculotendinous junction in distal forearm to proximal edge |
|                of the carpal tunnel. Neurovascular bundles commonly co-cut.|
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The Anatomy of "No Man's Land" (Zone II)

Zone II was historically designated "No Man's Land" by Dr. Sterling Bunnell because primary surgical repair frequently resulted in dense scar adhesions that completely tethered the tendons to the surrounding digital sheath, obliterating active finger flexion.

Within Zone II:

• The Flexor Digitorum Superficialis (FDS) tendon bifurcates (Camper's chiasm) to allow the Flexor Digitorum Profundus (FDP) tendon to pass through to its distal insertion on the base of the distal phalanx.
• Both tendons are enclosed within a synovial sheath reinforced by five annular pulleys (A1, A2, A3, A4, A5) and three cruciform pulleys (C1, C2, C3). The A2 and A4 pulleys are biomechanically indispensable to prevent tendon bowstringing.
• Blood supply is provided by the vincula (vincula brevia and longa), making the zone prone to ischemic scarring if handled aggressively.

2. Flexor Tendon Post-Operative Protocols

Because repaired tendons have minimal tensile strength during the initial 3 to 4 weeks post-surgery, controlled mobilization protocols are utilized to generate 3 to 5 mm of tendon excursion, which prevents adhesions without placing tensile loads that could rupture the surgical suture line.

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|                 POST-OP FLEXOR TENDON PROTOCOLS COMPARISON                  |
|                                                                             |
|   [DURAN PROTOCOL]                 [KLEINERT PROTOCOL]                      |
|   • PASSIVE Flexion / PASSIVE Ext. • DYNAMIC PASSIVE Flexion / ACTIVE Ext.  |
|   • Dorsal Blocking Splint (DBS).  • DBS with elastic band traction.        |
|   • Therapist/patient passively    • Elastic bands pull fingers into flexion|
|     flexes and extends IP joints   • Patient actively extends fingers to    |
|     within the splint boundaries.    dorsal splint hood; elastic band       |
|   • Low force, controlled motion.    recoils digits back into full flexion. |
|                                                                             |
|   [EARLY ACTIVE MOTION (EAM)]      [IMMOBILIZATION PROTOCOL]                |
|   • "Place-and-Hold" active motion.• Cast / rigid splint for 3–4 weeks.     |
|   • Initiated days 3–5 post-op.    • Reserved for non-compliant clients,    |
|   • Requires strong multi-strand     children, or severe cognitive deficits.|
|     sutures (4-strand / 6-strand). • High risk of joint stiffness & scar.   |
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Standard Dorsal Blocking Splint (DBS) Positioning Angles

Across both Duran and Kleinert protocols, a custom thermoplastic Dorsal Blocking Splint (DBS) is applied within the first 24 to 72 hours post-surgery:

• Wrist: $20^\circ\text{ to }30^\circ$ of wrist flexion.
• Metacarpophalangeal (MCP) Joints: $50^\circ\text{ to }70^\circ$ of flexion.
• Interphalangeal (PIP & DIP) Joints: Full extension ($0^\circ$) within the splint hood (to prevent PIP flexion contractures).

Rehabilitation Progression Timeline for Flexor Tendon Repairs

3. Extensor Tendon Zones & Classic Deformities

Extensor tendons are flatter, thinner, and glide closer to the subcutaneous tissue and bone than flexor tendons, making them highly susceptible to adhesions, rupture, and blunt trauma. Extensor anatomy is divided into eight zones (I through VIII) in the fingers and five zones (TI through TV) in the thumb.

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|                       EXTENSOR TENDON ANATOMICAL ZONES                      |
|                                                                             |
|   [ZONE I]   • Distal Interphalangeal (DIP) Joint. MALLET FINGER.           |
|   [ZONE II]  • Middle Phalanx.                                              |
|   [ZONE III] • Proximal Interphalangeal (PIP) Joint. BOUTONNIERE DEFORMITY. |
|   [ZONE IV]  • Proximal Phalanx.                                            |
|   [ZONE V]   • Metacarpophalangeal (MCP) Joint. ("Fight Bite" lacerations). |
|   [ZONE VI]  • Metacarpal dorsum.                                           |
|   [ZONE VII] • Extensor retinaculum / Carpal dorsum (6 compartments).       |
|   [ZONE VIII]• Distal forearm (musculotendinous junction).                  |
+-----------------------------------------------------------------------------+

Classic Extensor Deformities & Orthotic Management

+-----------------------------------------------------------------------------+
|                    CLASSIC DIGITAL TENDON DEFORMITIES                       |
|                                                                             |
|   MALLET FINGER (Zone I)           BOUTONNIERE DEFORMITY (Zone III)         |
|   • Terminal extensor avulsion.    • Central slip rupture / attenuation.    |
|   • Flexed DIP, inability to extend.• PIP flexion + DIP hyperextension.     |
|   • Splint: Continuous rigid DIP   • Splint: Rigid PIP extension splint     |
|     extension splint 6–8 weeks.      (0°), leaving DIP & MCP free to flex!  |
|                                                                             |
|   SWAN NECK DEFORMITY              JERSEY FINGER (Flexor Zone I)            |
|   • Volar plate laxity/rupture.    • FDP avulsion from distal phalanx base. |
|   • PIP hyperextension + DIP flex. • Inability to actively flex DIP.        |
|   • Splint: PIP hyperextension     • Requires urgent surgical reattachment  |
|     block (Silver Ring splint).      followed by flexor tendon protocol.    |
+-----------------------------------------------------------------------------+

In-Depth Clinical Rules for Extensor Deformities

[!IMPORTANT] The Unbroken Rule of Mallet Finger Splinting (Zone I): Mallet finger results from an avulsion or rupture of the terminal extensor tendon at the base of the distal phalanx. The client presents with a dropped, flexed DIP joint and an inability to actively extend the DIP.

• Orthosis: Custom thermoplastic or prefabricated Stack splint maintaining the DIP joint in continuous neutral to slight hyperextension (0° to 10°) for 6 to 8 full weeks (24 hours/day, 7 days/week).
• CRITICAL PATIENT EDUCATION: When removing the splint for daily skin hygiene, the client MUST maintain the DIP in full extension on a flat table surface. If the DIP joint is allowed to flex even for a fraction of a second, the healing tendon ends tear apart, and the 6 to 8 week splinting clock RESTARTS from Day 1!

[!NOTE] Boutonniere Deformity Pathomechanics & Splinting (Zone III): Rupture or laceration of the central slip of the extensor digitorum communis (EDC) over the PIP joint causes the lateral bands to slip volarly (below the joint axis of rotation). The lateral bands now act as flexors of the PIP joint while exerting excessive extensor tension across the DIP joint, producing PIP flexion and DIP hyperextension.

• Orthosis: Rigid PIP extension orthosis holding the PIP in full extension ($0^\circ$) for 6 weeks while keeping the DIP and MCP joints completely free.
• Active DIP Flexion Exercises: The client is instructed to perform active DIP flexion while the PIP is held extended in the splint. This active DIP flexion pulls the subluxated lateral bands back dorsally and prevents contracture of the oblique retinacular ligament (ORL).

4. Peripheral Nerve Injuries: Radial, Median, and Ulnar Nerves

The upper extremity is innervated by three major branches of the brachial plexus: the Radial, Median, and Ulnar nerves. Complete or partial transection creates distinct patterns of motor paralysis, sensory denervation, and classic postural hand deformities.

+-----------------------------------------------------------------------------+
|                    PERIPHERAL NERVE LESIONS AT A GLANCE                     |
|                                                                             |
|   RADIAL NERVE (C5–T1)       MEDIAN NERVE (C6–T1)      ULNAR NERVE (C8–T1)  |
|   "The Great Extensor"       "The Eye of the Hand"     "The Musician's Nerve|
|   • Motor: Triceps, wrist    • Motor: Pronation, FDS/  • Motor: FCU, FDP 4-5|
|     extensors, finger MCP      FDP 2-3, FPL, Thenar      interossei, adductor|
|     extensors, thumb ext.      muscles (LOAF).           pollicis, lumbr. 3-4|
|   • Deformity: WRIST DROP    • Deformity: APE HAND /   • Deformity: CLAW    |
|   • Splint: Dynamic wrist/     HAND OF BENEDICTION       HAND (Digits 4–5)  |
|     MCP extension orthosis.  • Splint: Short opponens  • Splint: Anti-claw  |
|                                (C-bar) thumb spica.      (MCP flexion block)|
+-----------------------------------------------------------------------------+

1. Radial Nerve Lesions (C5–T1)

• Anatomy & Functional Role: Innervates all extensor muscles of the elbow, forearm, wrist, finger MCPs, and thumb.
• Clinical Presentation: "Wrist Drop"—inability to actively extend the wrist, finger MCP joints, or thumb. Sensation is impaired over the dorsal-radial hand and thumb web space.
• High vs. Low Lesion:
  • High Lesion (Spiral Groove / Humerus Fracture): Paralyzes triceps, brachioradialis, Extensor Carpi Radialis Longus/Brevis (ECRL/ECRB), Supinator, and all digital extensors. Loss of wrist, thumb, and finger extension.
  • Low Lesion (Posterior Interosseous Nerve / PIN): Sparing of ECRL allows active wrist extension with radial deviation. Paralyzes Extensor Digitorum, Extensor Pollicis Longus (EPL), and Abductor Pollicis Longus (APL). Sensation remains fully intact.
• Orthosis: Dynamic Wrist, MCP, and Thumb Extension Splint (e.g., Colditz or Thomas suspension splint). Positions the wrist in $20^\circ\text{ to }30^\circ$ extension to provide a stable biomechanical base, allowing the tenodesis effect to facilitate active finger flexion and functional grasp/release.

2. Median Nerve Lesions (C6–T1)

• Anatomy & Functional Role: "The Eye of the Hand" because it provides vital tactile discrimination to the volar pulp of digits 1, 2, 3, and the radial half of 4. Innervates the LOAF muscles: Lumbricals 1 & 2, Opponens pollicis, Abductor pollicis brevis, and Flexor pollicis brevis (superficial head).
• High vs. Low Lesion:
  • High Lesion (At/Above Elbow): Produces the "Hand of Benediction" (Pope's Blessing). When the client attempts to make an active fist, digits 1, 2, and 3 fail to flex (due to paralysis of FDS, FDP 2-3, and FPL) and remain pointed outward, while digits 4 and 5 flex normally (ulnar nerve intact).
  • Low Lesion (At Wrist / Carpal Tunnel): Produces the "Ape Hand" deformity. Severe atrophy of the thenar eminence flattens the palm. The intact adductor pollicis pulls the thumb into the plane of the palm; the client loses thumb palmar abduction and opposition.
• Orthosis: Short Opponens (C-bar) Splint. Maintains the first web space and positions the thumb in palmar abduction and opposition to enable functional pinch and cylindrical grasp.

3. Ulnar Nerve Lesions (C8–T1)

• Anatomy & Functional Role: "The Musician's Nerve." Powers the intrinsic hand muscles responsible for finger abduction/adduction (dorsal/palmar interossei), powerful thumb adduction (adductor pollicis), and coordinated digital extension.
• Clinical Presentation: "Claw Hand" (Duchenne Sign)—hyperextension of digits 4 and 5 MCP joints (unopposed Extensor Digitorum) with flexion of the PIP and DIP joints (loss of 3rd and 4th lumbricals and interossei).
• The "Ulnar Paradox":
  • A high ulnar lesion (at the elbow) produces LESS visible clawing because the ulnar half of the FDP is denervated, preventing strong active IP flexion.
  • A low ulnar lesion (at the wrist) produces MORE severe clawing because the FDP remains intact, pulling the denervated 4th and 5th IP joints into deep flexion.

+-----------------------------------------------------------------------------+
|                      SPECIALIZED ULNAR NERVE TESTS                          |
|                                                                             |
|   FROMENT'S SIGN                   JEANNE'S SIGN                            |
|   • Client pinches paper between   • Extreme hyperextension of thumb MCP    |
|     thumb and index finger.          joint during Froment's pinch test      |
|   • Adductor pollicis is paralyzed.  due to lack of adductor/FPB stability. |
|   • Client compensates by flex-                                             |
|     ing thumb IP joint using FPL   WARTENBERG'S SIGN                        |
|     (median nerve / AIN).          • Small finger rests in persistent       |
|                                      abduction due to unopposed EDM.        |
+-----------------------------------------------------------------------------+

• Orthosis: Anti-Claw Orthosis (MCP Flexion Block Splint). Holds digits 4 and 5 MCP joints in $30^\circ\text{ to }45^\circ$ of flexion, preventing hyperextension and redirecting EDC extensor tension distally to fully extend the PIP and DIP joints.

5. Clinical Scenario: Post-Surgical Tendon & Nerve Management

Clinical Case Vignette: A 28-year-old carpenter sustained a severe volar wrist and palm laceration from a circular saw, resulting in primary surgical repair of the Flexor Digitorum Profundus (FDP) and Superficialis (FDS) tendons in Zone II of the index and middle fingers, alongside direct micro-suture repair of the ulnar nerve at Guyon's canal. The client is referred to outpatient hand therapy on post-operative day 3.

COTA Treatment Implementation:

1. Dorsal Blocking Splint Fabrication:
   • The COTA, under OTR supervision, fabricates a custom thermoplastic Dorsal Blocking Splint (DBS) positioning the wrist in $25^\circ$ flexion, MCP joints in $60^\circ$ flexion, and IP joints in $0^\circ$ extension within the protective hood.
   • To address the ulnar nerve repair and prevent clawing, the splint incorporates an MCP extension stop block for digits 4 and 5.
2. Duran Protocol Early Passive Motion:
   • The COTA instructs the client in strict passive range of motion exercises inside the splint: passive DIP flexion with PIP held in flexion, passive PIP flexion with DIP held in flexion, followed by gentle passive composite digital extension to the splint boundary.
3. Patient Education & Red Flags:
   • The COTA provides explicit written and verbal education: NO active finger flexion, NO grasping objects, and the splint must remain on 24 hours/day.
   • The client is educated on sensory loss in digits 4 and 5 and trained in compensatory visual inspection to avoid burn injuries during cooking and grooming.