*2.1. Subjects*

This study was approved by the Institutional Review Board of the authors' hospital (IRB No. 4-2020-1162). From March 2017 to August 2019, 203 patients who had undergone cervical spine surgery, including decompression and fusion procedure(s), for the treatment

**Citation:** Jimenez, K.A.; Kwon, J.-W.; Yoon, J.; Lee, H.-M.; Moon, S.-H.; Suk, K.-S.; Kim, H.-S.; Lee, B.H. Handgrip Strength Correlated with Falling Risk in Patients with Degenerative Cervical Myelopathy. *J. Clin. Med.* **2021**, *10*, 1980. https://doi.org/ 10.3390/jcm10091980

Academic Editor: Takashi Hirai

Received: 30 March 2021 Accepted: 30 April 2021 Published: 5 May 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

of DCM were included prospectively. All included patients had completed postoperative follow up for 1 year. All of the patients exhibited myelopathic symptoms, including clumsiness of the hand, poor hand coordination (e.g., difficulty with handwriting and using chopsticks), and walking difficulty, and had been recommended for surgical intervention by the managemen<sup>t</sup> guidelines of DCM [25].

The exclusion criteria were as follows: comorbidity impairing physical function (e.g., history of cerebral infarction, cerebral palsy, Parkinson's disease, spine surgery, head trauma, current/old cerebrovascular events (cerebral hemorrhage and cerebral infarct), and other neurodegenerative conditions or severe rheumatoid arthritis); bedridden status or full dependence on a wheelchair before surgery because of severe cervical myelopathy; and difficulty completing the questionnaire because of cognitive impairment. Furthermore, patients with severe osteo-arthropathic conditions that could cause knee and hip joint contracture affecting whole spinal sagittal balance were also excluded from the patient pool [26]. No patients were diagnosed with hand- or wrist-related diseases, such as carpal tunnel syndrome and tardy ulnar nerve palsy.

The major included diagnoses were cervical stenosis with myelopathy (DCM) (135 patients), ossified posterior longitudinal ligament (44 patients), and herniated cervical disc with myelopathy (24 patients).

Patients were treated with decompression and instrumented fusion (anterior platescrew system; ZEVO ™ plate and screw system; Medtronic Sofamor Danek, Memphis, TN, USA) for anterior surgery or a posterior screw-rod system (Poseidon, Medyssey, Jecheon, Korea) for combined anterior-posterior surgery. Cervical allograft allospacers (CornerstoneTM; ASR Medtronic Sofamor Danek, Memphis, TN, USA) were utilized for anterior fusion surgery. For posterior surgery, local autologous and demineralized bone matrix grafts (Bongener ™; CG-BIO, Seoul, Korea) were used. The surgically treated level and other demographic data, including the presence of spinal cord signal changes on MRI scans, are presented in Table 1.

**Table 1.** Demographic parameters of the enrolled patients.


Statistical analyses were performed by independent *t*-test and \* chi-squared test.

#### *2.2. Outcome Measures*

For all enrolled patients, the Neck Disability Index (NDI, higher scores reflecting worse functional status), Euro-QoL Visual Analog Scale (VAS, higher scores indicating better QoL), modified Japanese Orthopedic Association (JOA) score (higher scores representing better functional status), modified JOA grade (16~17 = Grade 0; 12~15 = Grade 1; 8~11 = Grade 2; 0~7 = Grade 3, with higher grades reflecting worse functional status), modified frailty index (mFi) (higher index scores indicating greater frailty), and HGS of both hands were measured and recorded preoperatively and at 3 months and 1 year after surgery [27–31].

#### *2.3. HGS Measurement*

HGS was measured using a Jamar Plus+ hand grip dynamometer (Global Medical Devices, Maharashtra, India). Patients were instructed to squeeze the handle as hard as possible for 3 s, and the maximum contractile force (lbs.) was recorded. The tests were performed three times on both hands. The highest value of the three repeated measurements was used for analysis [30]. The HGS of patients was measured preoperatively and at 3 months and 1 year after surgery. Considering basic physical differences, the patient groups were divided into male and female groups and compared.

#### *2.4. Assessment of the Risk of Falling Using Four Functional Mobility Tests and an Actual Fall Diary*

To evaluate the risk of falling, four functional mobility tests were used: the alternatestep test (AST), the six-meter-walk test (SMT), the sit-to-stand test (STS), and the timed up and go test (TUGT). These four tests have been validated in previous studies [2]. Additionally, a fall diary was given to patients or caregivers who were encouraged to record every fall and fall-related neurologic deficit and to report it to the clinical research coordinator when they visited the outpatient clinic for regular follow up at 3 months and 1 year postoperatively [4].

#### *2.5. Statistical Analysis*

Basic statistical tests, independent t-test, analysis of variance (ANOVA), and chisquared test were used to evaluate whether the differences between the male and female surgery groups in terms of QoL, the four functional mobility tests, and other demographic data were statistically significant. Multiple linear regression analyses among measured HGS, falls, signal changes of the spinal cord, NDI, EQ-VAS, fall-related functional mobility tests, and other values were performed. All statistical analyses were performed using the SPSS 22.0 statistics package (SPSS, Inc., Chicago, IL, USA). *p* values < 0.05 were considered statistically significant.
