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Atlas · Forearm

Flexor Digitorum Profundus

Flexor digitorum profundus bends the end joints of the four fingers and contributes to gripping. Its long tendons run from the deep forearm into the fingertips, so a loss of fingertip bending needs a tendon and nerve examination.

Flexor Digitorum Profundus
Body region
Forearm · Hand
Reference type
Anatomy & examination
Trigger-point map not yet documented
Common symptoms
2
patterns cataloged
Contributors
2
Factors to assess

Muscle overview

Symptoms and first steps

Practical first steps

  • Reduce forceful gripping while a painful task is assessed.
  • Keep comfortable finger movement unless an injury or repair protocol restricts it.
  • Follow prescribed splint and hand-therapy instructions after tendon repair.

When to seek assessment

  • New inability to bend a fingertip after a cut or injury needs prompt hand assessment.
  • A repaired finger that suddenly stops bending needs immediate contact with the treating team.

FDP bends the distal finger joint; FDS mainly bends the middle joint. A general fist or grip test alone can miss an important difference.

Examination, palpation and treatment evidence

Illustrated overview

Flexor Digitorum Profundus · Anatomy

Right flexor digitorum profundus with the source skeletal context. Source model rendered and material restyled; blue identifies the model structure, including its tendon-like continuations.

BodyParts3D, © The Database Center for Life Science. Adapted by MyofascialPain: source model rendered and material restyled. · CC BY-SA 2.1 Japan

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Browse related exercises (1)

Symptoms patients report

Difficulty bending a fingertip Identify the affected finger and distinguish active movement from the movement available with assistance.

Grip-related discomfort Pain can arise from muscle, tendon, sheath, joint or nerve structures; its location does not identify FDP alone.

Contributors to assess

Changes in gripping demand Heavy or prolonged gripping may reveal a capacity limitation; review recent changes in work or sport.

Finger injury or neurological change A cut, forced finger extension or new motor deficit needs assessment before strength exercises.

For clinicians and supervised training

Clinical reference

This extrinsic forearm muscle is separate from the existing lumbrical/interosseous hand group. No new trigger-point map is supplied.

Anatomy and palpation

Anatomical relationships

FDP arises from the proximal anterior/medial ulna and interosseous membrane; four tendons attach to the distal phalanges of digits 2–5. It flexes the distal finger joints. The index/middle portion is usually supplied by the median nerve through AIN, and the ring/little portion by the ulnar nerve.[1][2]

  • Deep anterior forearm along the ulna.
  • Distal finger joints and bases of the distal phalanges.

Nearby structures. Tendons pass through the carpal tunnel and continue beyond the split FDS tendons. Tendon connections and innervation variation limit simple finger-by-finger isolation.

Palpation

Patient position. Forearm and hand supported with fingers relaxed.

Find the landmarks

  • Volar forearm flexor compartment.
  • Palmar tendon course toward the affected finger.

Examination sequence

  1. Observe active finger movement before using light contact to localize symptoms.
  2. Compare tenderness along the finger/tendon and forearm without pressing deeply to find a presumed nodule.

Document the findings

  • Tenderness alone cannot distinguish muscle pain from tendon/sheath or joint pathology.

Limits and precautions

  • Do not resist or stretch a suspected laceration, avulsion or recent repair.
[1][5]

Examination and tests

2

Distal finger-joint flexion[4][1][5]

Check whether the fingertip actively bends.

Position
Hand supported; examiner stabilizes the middle phalanx with the middle joint held straight.
Technique
Ask the patient to bend the distal joint gently, comparing fingers and sides. Avoid resistance when injury is suspected.
Positive finding
Absent or clearly reduced active DIP flexion needs a tendon, joint and motor differential.
Interpretation
More specific to FDP function than making a full fist.
Limitations
Pain, stiffness, tendon connections and nerve variation affect the result. Preserved motion does not exclude a partial tendon injury.

Anterior interosseous motor pattern[3][4]

Compare thumb-tip, index-tip and pronation function when motor weakness is reported.

Position
Seated with the forearm supported.
Technique
Observe thumb IP and index DIP flexion, including a gentle tip-to-tip pinch. Compare forearm pronation and examine other median/ulnar functions and sensation as indicated.
Positive finding
A reproducible motor deficit needs a tendon and neurological differential.
Interpretation
The combined pattern can guide further assessment.
Limitations
Pain, tendon injury and effort can alter performance. An OK-sign difficulty alone neither diagnoses AIN palsy nor a trigger point; sensory symptoms suggest a broader assessment.

Distinguishing other causes

Flexor tendon injury or repair complication[5]

Findings that matter. New active flexion loss after a cut, forced movement or surgery.

Next step. Prompt hand-service assessment; protect the finger according to the treating team.

AIN, median or ulnar motor disorder[3][1]

Findings that matter. Weakness in a nerve-related pattern, with other motor or sensory findings.

Next step. Compare thumb, finger and intrinsic-hand function and obtain a neurological assessment.

Joint stiffness or tendon/sheath-related pain[5][7]

Findings that matter. Restricted assisted movement, swelling or painful finger motion.

Next step. Assess joint range and tendon glide instead of inferring a forearm trigger point.

Treatment selection and progression

Self-care and activity

Adjust the task that provokes symptoms[6][7]

Consider when. Mild task-related symptoms after significant injury and new motor loss have been excluded.

Reduce the force or uninterrupted time needed for gripping an object; try assistance or a different handle and keep comfortable daily use.

Dose and review
Match exposure to the current response; no muscle-specific schedule is established.
Progression
Restore one demand at a time.
Stop or reassess
Seek review for persistent functional loss or worsening symptoms.
Evidence and limits
Regional hand guidance supports activity adaptation; this is not a treatment for a proven isolated muscle lesion.

Exercise and rehabilitation

Maintain comfortable active movement[6]

Consider when. Assessed mild stiffness without a suspected tendon tear, unstable injury or postoperative restriction.

Gently open the hand and make a comfortable loose fist. Stay within an easy range without forcing the movement.

Dose and review
Use brief practice adjusted to symptoms; a treating clinician sets any injury-specific dose.
Progression
Increase comfortable range before resistance.
Stop or reassess
Stop for sharp pain, increasing swelling or new weakness.
Evidence and limits
A regional mobility option, not a validated isolated-muscle exercise protocol.

Clinician-delivered care

Match rehabilitation to the examination[6][7]

Consider when. Persistent pain, stiffness or weakness that limits a useful hand task.

A clinician distinguishes tendon, joint and nerve findings, then selects mobility, support or graded loading. Follow the surgical team’s plan after repair.

Dose and review
Set from the diagnosis and measured deficit; no universal strengthening dose.
Progression
Retest the same movement and functional task before increasing load.
Stop or reassess
New loss of active movement changes the assessment rather than calling for harder exercise.
Evidence and limits
Diagnosis determines care. Regional self-management does not establish muscle-specific treatment efficacy.

Reassessment and follow-up

  • Record active fingertip flexion and any assisted range separately.
  • Retest a useful grip task without forcing maximal effort.
  • Review persistent or progressive motor loss and adherence to any repair restrictions.

Evidence and sources

  1. University of Washington Radiology: Flexor digitorum profundus

    2026 · University anatomy atlas

    Undated page accessed 11 October 2026. Deep forearm attachments and split median/ulnar supply. The exact proximal attachment fraction varies between teaching references.

  2. Texas Tech University Health Sciences Center El Paso: Muscles of the upper limb

    2026 · University anatomy teaching reference

    Undated teaching page accessed 11 October 2026. Cross-checks finger versus thumb joint actions and extrinsic versus intrinsic muscles. Does not validate palpation diagnosis or treatment.

  3. StatPearls: Anterior Interosseous Syndrome

    2025 · Clinical reference

    July 2025 update, publisher-indexed text checked. Motor pattern includes FPL, radial FDP and PQ; pure AIN palsy lacks cutaneous sensory loss. Neuritis and other causes require assessment; not all cases are local compression.

  4. Anatomy, Shoulder and Upper Limb, Forearm Anterior Interosseous Nerve

    2026 · Clinical anatomy reference

    Publisher-indexed clinical-significance section checked 11 October 2026; year is access year. Describes thumb IP, index/middle DIP and pronation motor examination, not trigger-point tests.

  5. British Society for Surgery of the Hand: Flexor tendon injury

    2026 · Specialist society patient guidance

    Undated page accessed 11 October 2026. Loss of active flexion after injury and protected hand therapy following repair; no generic exercise program should replace a repair protocol.

  6. Cambridgeshire Community Services NHS: Wrist, hand and thumb pain

    2026 · NHS regional self-management guidance

    Undated page accessed 11 October 2026. Activity adaptation, gradual movement and graded return. Used for regional care, not efficacy or a fixed dose for any one named muscle.

  7. NHS: Wrist pain

    2026 · National patient guidance

    Accessed 11 October 2026; year is access year. Injury, joint/tendon and nerve differential context and when symptoms need assessment.