3.4 Musculoskeletal Assessment: Range of Motion, Strength & Joint Mobility
Key Takeaways
- The CFCN blueprint tests musculoskeletal function of the foot — range of motion, deformities, and strength — as a distinct focused physical assessment skill alongside vascular and neurological examination.
- Ankle dorsiflexion below roughly 10 degrees with the knee extended defines equinus, and restricted first metatarsophalangeal dorsiflexion below the 50 to 65 degrees needed for toe-off defines hallux limitus; both shift the center of pressure and drive forefoot ulceration in the insensate foot.
- The Silfverskiold test localizes the restriction: dorsiflexion that improves with the knee flexed indicates gastrocnemius equinus, whereas restriction in both knee positions indicates soleus or osseous limitation.
- Whether a deformity is rigid or flexible determines the plan: flexible deformities can be realigned with spacers, strapping, and inserts, while rigid deformities must be accommodated with extra-depth footwear and custom-molded inserts.
- Manual muscle testing uses the 0-to-5 scale, and full passive range with absent active motion identifies a motor deficit such as tibialis anterior weakness rather than a contracture.
3.4 Musculoskeletal Assessment: Range of Motion, Strength & Joint Mobility
Clinical Pearl: The CFCN blueprint lists "musculoskeletal function of the foot (e.g., range of motion, deformities, strength)" as its own knowledge statement inside the focused physical assessment task, alongside vascular and neurological status. It is tested as an assessment skill, not as anatomy trivia. A foot with limited ankle dorsiflexion generates forefoot pressures high enough to ulcerate an insensate foot even when pulses are palpable and the skin is intact today.
Neuropathy explains why a patient does not feel the ulcer. Ischemia explains why it will not heal. Restricted joint motion explains where the ulcer will form. Glycation of periarticular collagen progressively stiffens the joints of the diabetic foot, and each degree of lost motion is transferred somewhere else as load. Musculoskeletal assessment is how the foot care nurse predicts the next lesion instead of reacting to it.
Why Limited Joint Mobility Drives Plantar Ulceration
In long-standing diabetes, non-enzymatic glycation crosslinks collagen in joint capsules, ligaments, tendon sheaths, and plantar fascia. The resulting limited joint mobility (LJM) syndrome, historically called diabetic cheiroarthropathy, stiffens the hands and feet together.
- Ankle equinus shortens the time the foot has to accept and dissipate load, driving the center of pressure forward and increasing peak forefoot pressure.
- A stiff first metatarsophalangeal (MTP) joint blocks the normal windlass mechanism at toe-off, so the hallux and first metatarsal head absorb force that should have been distributed along the whole forefoot.
- A rigid subtalar joint cannot pronate to absorb shock at heel strike, transmitting impact directly to bone and the overlying soft tissue.
Two bedside screens detect LJM in seconds. In the prayer sign, the patient presses the palms together with wrists extended; an inability to fully appose the palmar surfaces of the fingers indicates glycation-related stiffness. The tabletop test asks the patient to lay the palm flat on a table; a persistent gap under the metacarpophalangeal joints is a positive result. Both correlate with reduced joint mobility in the foot and with elevated plantar pressures.
Systematic Range of Motion Examination
Assess each joint passively with the patient relaxed and non-weight-bearing, then compare left to right. Use a goniometer when documenting a baseline or a change over time; visual estimation is acceptable for routine screening but is not adequate for tracking progression.
| Joint / Motion | Approximate Normal Range | Functional Minimum | Clinical Consequence When Restricted |
|---|---|---|---|
| Ankle dorsiflexion (knee extended) | 10-20 degrees | At least 10 degrees for normal gait | Equinus: early heel lift, elevated forefoot pressure, midfoot breakdown |
| Ankle plantarflexion | 40-50 degrees | Sufficient for push-off | Weak toe-off, shortened stride |
| Subtalar inversion / eversion | Roughly 20-30 / 5-10 degrees | Roughly 2:1 inversion to eversion | Rigid rearfoot cannot absorb heel-strike shock |
| First MTP dorsiflexion | 65-75 degrees available | About 50-65 degrees needed for toe-off | Hallux limitus / rigidus: supinatory escape, lateral column and sub-first-metatarsal callus (see Section 5.1) |
| Lesser MTP joints | Mobile, reducible | Digits reduce to neutral | Fixed clawing drives apical and dorsal lesions |
The Silfverskiold Test: Locating the Equinus
Ankle dorsiflexion must be measured twice, because where the restriction lives changes the referral.
- With the knee extended, hold the subtalar joint neutral and dorsiflex the ankle. Record the angle.
- Repeat with the knee flexed to approximately 90 degrees, which slackens the gastrocnemius.
If dorsiflexion is restricted with the knee extended but improves substantially with the knee flexed, the restriction is gastrocnemius equinus and may respond to targeted stretching or gastrocnemius recession. If dorsiflexion is restricted in both positions, the limitation is at the soleus or the ankle joint itself, including osseous block from arthritis or Charcot midfoot collapse.
Rigid Versus Flexible Deformity
For every deformity identified, the single most decision-relevant question is whether it reduces. Apply gentle manual pressure and attempt to bring the segment to neutral.
- Flexible (reducible): The digit or arch corrects passively. Accommodative padding, toe spacers, custom inserts, and strapping can realign the segment and redistribute pressure.
- Rigid (non-reducible): The segment will not correct. The care plan must accommodate the deformity with extra-depth footwear and custom-molded inserts rather than attempt to correct it; forcing correction of a rigid deformity generates a new pressure point.
Manual Muscle Strength Testing
Grade strength with the standard 0 to 5 manual muscle testing (MMT) scale: 0 no contraction, 1 flicker without movement, 2 full range with gravity eliminated, 3 full range against gravity, 4 full range against some resistance, 5 normal strength against full resistance.
| Muscle Group | Tested Motion | Peripheral Nerve | Meaning of Weakness |
|---|---|---|---|
| Tibialis anterior | Ankle dorsiflexion | Deep peroneal | Foot drop; steppage gait; forefoot slap and trip risk |
| Gastrocnemius-soleus | Ankle plantarflexion (single heel raise) | Tibial | Weak push-off; altered pressure distribution |
| Peroneus longus / brevis | Foot eversion | Superficial peroneal | Lateral instability; recurrent inversion sprains; fifth metatarsal lesions |
| Tibialis posterior | Foot inversion | Tibial | Progressive flatfoot; medial midfoot collapse |
| Extensor hallucis longus | Great toe extension | Deep peroneal | Early marker of L5 radiculopathy or peroneal neuropathy |
| Intrinsic foot muscles | Toe spreading and flexion | Medial / lateral plantar | Intrinsic minus foot: clawing and fat-pad migration |
A practical functional screen is the single-limb heel raise: an adult who cannot lift the heel clear of the floor once while standing on one leg has clinically meaningful plantarflexion weakness. Test only with a stable support surface and a guarding hand, because the patients most likely to fail it are also the ones most likely to fall.
Distinguish weakness from limitation. A patient who cannot dorsiflex may have a denervated tibialis anterior, a contracted Achilles, or pain inhibition. Passive range of motion separates them: if the ankle dorsiflexes fully when the examiner moves it but not when the patient does, the problem is motor, not contracture.
Documentation and Referral Triggers
Record laterality, the specific joint, the measured or estimated degrees, whether deformity is rigid or flexible, and the MMT grade for each group tested. That record is what justifies a custom insert to a payer and what makes next year's comparison meaningful.
Refer when the assessment reveals:
- New or asymmetric foot drop, which requires neurological or spine evaluation rather than a brace alone.
- Ankle equinus with a plantar ulcer or pre-ulcerative callus, which warrants podiatric or orthopedic evaluation for offloading and possible tendon lengthening.
- A newly rigid, warm, swollen midfoot, which must be treated as acute Charcot neuroarthropathy until imaging proves otherwise.
- Rapidly progressive deformity or loss of motion, which suggests inflammatory arthropathy and warrants rheumatology input.
- Any rigid deformity in an insensate foot, which requires pedorthic or orthotic referral for accommodative footwear before a lesion forms.
A foot care nurse measures ankle dorsiflexion in a patient with a recurrent callus beneath the second metatarsal head. With the knee extended, dorsiflexion is limited to 3 degrees. With the knee flexed to 90 degrees, dorsiflexion improves to 14 degrees. What does this finding indicate?
During musculoskeletal assessment, a nurse finds that a patient's second and third hammer toes can be passively brought to a neutral position with gentle pressure. How should this finding change the plan of care compared with a deformity that does not reduce?
A patient cannot actively dorsiflex the right ankle, and the forefoot slaps the floor during gait. When the examiner passively dorsiflexes the same ankle, full range is obtained without resistance. What does this distinction establish?