Validation of a Methodology Using Isometric Dynamometer for Ankle STrength Assessment to Quantify LDH-induced Paresis (VAST-LDH)

Validation of a Methodology Using Isometric Dynamometer for Ankle Strength Assessment to Quantify LDH-induced Paresis

Lumbar disc herniation (LDH) is a common condition that may cause lower limb motor weakness (paresis), particularly affecting ankle dorsiflexion and plantarflexion. Although motor deficits are clinically important and may influence treatment decisions, objective and standardized methods for quantifying the severity of paresis are lacking. Current clinical assessment mainly relies on manual muscle testing, which is subjective and has limited sensitivity, while isokinetic dynamometry, the reference standard for muscle strength assessment, is expensive and impractical for routine clinical use.

This prospective validation study aims to evaluate a clinically feasible isometric ankle strength measurement method based on a handheld dynamometer fixed with an external strap to eliminate examiner-dependent resistance. The study will be conducted in two sequential phases. First, validity and reliability of the method will be established in healthy adult volunteers by comparing measurements with those obtained using an isokinetic dynamometer. Second, the method will be applied in patients with LDH-induced lower limb paresis to determine its performance across a broader range of muscle strength values and its clinical applicability.

Outcome measures include maximal isometric ankle dorsiflexion and plantarflexion force, time to peak force, manual muscle testing (Medical Research Council scale), patient-reported weakness using a Numeric Rating Scale, Lower Extremity Functional Scale (LEFS) scores, and functional ankle strength tests. Validity will be assessed using correlation analyses and Bland-Altman agreement analysis, while intra- and inter-rater reliability will be evaluated using intraclass correlation coefficients, coefficient of variation, standard error of measurement, and minimum detectable change.

The study seeks to establish a reliable, valid, and clinically practical method for objective assessment of ankle muscle strength in patients with LDH-induced paresis. Such a method could improve clinical evaluation, enable objective monitoring of recovery, facilitate future clinical research, and support treatment decision-making.

Study Overview

• Status: Enrolling by invitation
• Conditions: Paresis; Lumbar Disc Herniation
• Intervention / Treatment: Device: Strength test validity and reliability

Detailed Description

Lumbar disc herniation (LDH) is one of the most common causes of lumbar radiculopathy and may result in lower limb motor weakness due to nerve root compression. While radicular pain often improves with conservative treatment, motor deficits may persist, recover slowly, or require surgical intervention. Despite the clinical importance of paresis, objective quantification of muscle weakness remains challenging because no standardized, practical, and validated measurement method is routinely available for clinical use.

Current clinical assessment primarily relies on manual muscle testing (MMT), which uses an ordinal grading system and is inherently subjective. MMT is limited by examiner experience, strength, and the inability to detect small but clinically meaningful changes in muscle function. Isokinetic dynamometry is widely regarded as the reference standard for objective muscle strength assessment because of its high accuracy and reproducibility. However, the equipment is expensive, non-portable, requires specialized training, and is therefore unsuitable for routine outpatient assessment or repeated follow-up measurements.

This study aims to validate a portable isometric ankle strength measurement method using a handheld dynamometer secured with an external fixation strap, minimizing examiner-related variability. The ultimate goal is to develop a clinically feasible method capable of objectively quantifying ankle dorsiflexion and plantarflexion strength in patients with LDH-induced paresis.

The study is designed as a prospective observational validation study conducted at Helsinki University Hospital. It consists of two consecutive phases.

During the first phase, healthy adult volunteers will undergo repeated ankle strength measurements using both the investigational handheld dynamometer method and an isokinetic dynamometer. This phase will establish criterion validity by comparing the handheld measurements with the reference standard. In addition, intra-rater and inter-rater reliability of the handheld method will be assessed through repeated measurements performed by different examiners.

If adequate validity and reliability are demonstrated, the second phase will recruit patients diagnosed with lumbar disc herniation presenting with clinically verified lower limb paresis. The objective of this phase is to evaluate whether the measurement method performs across the full spectrum of muscle weakness encountered in clinical practice and to determine its clinical relevance.

Primary measurements include maximal isometric ankle dorsiflexion and plantarflexion force and time to peak force. Secondary assessments include manual muscle testing according to the Medical Research Council grading system, patient-reported weakness using an 11-point Numeric Rating Scale, Lower Extremity Functional Scale (LEFS), and functional performance tests consisting of repeated toe raises and heel raises.

Criterion validity will be evaluated by comparing handheld dynamometer measurements with isokinetic dynamometer measurements using Pearson or Spearman correlation coefficients, linear regression analyses, and Bland-Altman plots to assess agreement and systematic bias. Construct validity will be examined by correlating objective strength measurements with patient-reported weakness, LEFS scores, and functional performance tests. Reliability will be assessed using intraclass correlation coefficients for both intra-rater and inter-rater agreement, together with coefficient of variation, standard error of measurement, and minimum detectable change.

Approximately 35 healthy volunteers and 35 patients with LDH-induced paresis will be recruited to allow for participant dropout while maintaining adequate statistical power based on previous validation studies.

The study involves no therapeutic intervention and poses minimal risk. Participants will undergo standardized muscle strength testing and complete patient-reported outcome measures. Any discomfort, such as muscle cramps or transient fatigue during testing, will be documented. Participants demonstrating clinically significant deterioration in muscle strength during the study will be referred for further clinical evaluation according to standard practice.

By establishing a valid, reliable, and practical method for objective ankle strength assessment, this study aims to improve the evaluation and longitudinal monitoring of patients with LDH-induced paresis. The validated methodology may facilitate future clinical trials, improve outcome assessment, enable earlier recognition of neurological recovery or deterioration, and support evidence-based treatment decisions in patients with lumbar disc herniation.

• Study Type: Interventional
• Enrollment (Estimated): 70
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Finland
  • Uusimaa
    • Helsinki, Uusimaa, Finland, 00290
      • Helsinki University Central Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

First phase

Inclusion Criteria:

• Aged 18-65 years old
• No pathology affecting ankle dorsiflexion or plantarflexion strength

Exclusion Criteria:

- Pathology affecting ankle dorsiflexion or plantarflexion strength

Second phase

Inclusion Criteria:

• Aged 18-65 years old
• LDH-induced muscle weakness of ankle dorsiflexion or plantarflexion

Exclusion Criteria:

- No muscle weakness induced by herniated lumbar disc

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Other: Study participant; Person participating in validity and reliability assessment	Device: Strength test validity and reliability; Ankle dorsiflexion and plantarflexion isometric maximal voluntary contraction strength test

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Criterion validity of the isometric handheld dynamometer	Agreement between the investigational isometric handheld dynamometer (HHD) measurement method and the reference standard isokinetic dynamometer (IKD) for maximal ankle dorsiflexion and plantarflexion strength.	At baseline (first measurement session; Day 0)
Construct validity of the handheld dynamometer	Correlation of HHD measurements with patient-reported weakness (Numerical Rating Scale), Lower Extremity Functionality Scale questionnaire, manual muscle testing (Medical Research Council grade) and functional ankle performance tests.	At baseline (first measurement session; Day 0)
Intra-rater reliability of the handheld dynamometer	Test-retest reliability of ankle dorsiflexion and plantarflexion strength measurements obtained by the same examiner.	At baseline (Day 0) and at the second measurement session, within 7 days after baseline
Inter-rater reliability of the handheld dynamometer	Agreement between measurements performed by different examiners	At the second measurement session, within 7 days after baseline

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Maximal isometric ankle dorsiflexion strength	Maximum voluntary isometric dorsiflexion force measured using the handheld dynamometer	At baseline (first measurement session; Day 0)
Maximal isometric ankle plantarflexion strength	Maximum voluntary isometric plantarflexion force measured using the handheld dynamometer.	At baseline (first measurement session; Day 0)
Time to peak force	Time required to reach maximal voluntary isometric force during dorsiflexion and plantarflexion.	At baseline (first measurement session; Day 0)
Manual Muscle Testing (Medical Research Council scale)	Ankle muscle strength (plantarflexion and dorsiflexion) assessed using the Medical Research Council (MRC) 0-5 manual muscle testing scale (0 = no muscle contraction, 5 = normal strength)	At baseline (first measurement session; Day 0)
Participant-reported lower limb weakness (Numeric Rating Scale)	Self-reported severity of lower limb weakness measured using an 11-point Numeric Rating Scale (0 = no weakness, 10 = worst imaginable weakness).	At baseline (first measurement session; Day 0)
Participant reported function (Lower Extremity Functional Scale, LEFS)	Lower extremity function assessed using the Lower Extremity Functional Scale (score range 0-80, higher scores indicate better function).	At baseline (first measurement session; Day 0)
Functional ankle performance testing (heel raises, toe raises)	Functional ankle performance assessed by the maximum number of heel raises (plantarflexion) and toe raises (dorsiflexion).	At baseline (first measurement session; Day 0)
Participant-reported discomfort during measurements	Occurrence of adverse symptoms during testing, including but not limited to muscle cramps, discomfort, or pain.	From baseline (Day 0) through completion of the second measurement session, up to 7 days after baseline

Collaborators and Investigators

• Sponsor: Helsinki University Central Hospital

Study record dates

Study Major Dates

• Study Start (Estimated): August 10, 2026
• Primary Completion (Estimated): October 1, 2026
• Study Completion (Estimated): December 1, 2026

Study Registration Dates

• First Submitted: July 8, 2026
• First Submitted That Met QC Criteria: August 12, 2026
• First Posted (Actual): August 13, 2026

Study Record Updates

• Last Update Posted (Actual): August 13, 2026
• Last Update Submitted That Met QC Criteria: August 12, 2026
• Last Verified: August 1, 2026

More Information

Terms related to this study

• Keywords: paresis; strength measurement; dynamometry
• Additional Relevant MeSH Terms: Neurologic Manifestations; Bone Diseases; Musculoskeletal Diseases; Nervous System Diseases; Pathological Conditions, Anatomical; Spinal Diseases; Hernia; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Intervertebral Disc Displacement; Paresis
• Other Study ID Numbers: HUS/418/2026

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: De-identified individual participant data underlying the results reported in the publication, including ankle strength measurements, functional outcome measures, and participant characteristics.
• IPD Sharing Time Frame: 10 years after publication

IPD Sharing Access Criteria

Researchers who provide a methodologically sound research proposal.

Data will be available upon reasonable request to the principal investigator, subject to institutional approval, applicable legislation, and a data sharing agreement.

• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; SAP

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No