NORMAL VALUES OF KEY PINCH STRENGTH IN A HEALTHY NIGERIAN POPULATION

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A.I. Michael², A.O. Iyun^1,2, O.A. Olawoye^1,2, S.A. Ademola^1,2, R.E. Nnabuko³, and O.M. Oluwatosin^1,2

1. Department of Surgery, University of Ibadan, Ibadan.
2. Department of Plastic Reconstructive and Aesthetic Surgery, University College Hospital, Ibadan.
3. Department of Plastic Surgery, National Orthopaedic Hospital, Enugu.

Abstract

Background: With the severity of machine hand injuries in our environment, the need to determine the normal values for key pinch strength with which to compare restorative surgeries was justified.

Methods: A cross sectional survey of participants who had no previous hand injuries limiting hand function. Data obtained included age, gender, body mass index, hand dominance and hand span. The Baseline Hydraulic Pinch Gauge was used to obtain key pinch strength. The influence of the above variables on measured pinch strength was analyzed using independent sample t-tests and Pearson’s correlation.

Results: Of the 242 recruited participants, age range between 20 and 80 years, 163(67.4%) were male and 79 (32.6%) were female. Males had higher pinch strength (right-8.3±2.7kg, left-7.6±2.5kg) than females (right-6.3±1.5kg, left- 5.8±1.5kg). Pinch strength varied with age peaking in the fifth decade in males and females. Interestingly, the left handed dominant female had higher right pinch strength than her right handed counterpart (p<0.009). Height, and hand span correlated with pinch strength in females.

Conclusion: Normal values for key pinch strength in this Nigerian population
are lower than that of Caucasians.

Keywords: Key pinch, Nigerians, Normal values.

Introduction

Performances of the activities of daily living (ADL) are spontaneous with normal functioning hands. With hand injuries resulting in impairment of ADL, these seemingly innocuous tasks become arduous. The ADL tasks brought about by the key pinch include; insertion and removal of a key or the Automated Teller Machine (ATM) card, operating a clothes zipper, insertion or removal of a plug, stabbing food with the prongs of a fork, operating a remote control or holding a pen.¹ The key pinch strength has been demonstrated as a standard objective clinical test for evaluating the outcome of surgical procedures on the hand.^2,3 A statistically significant difference between the mean pinch strength of the donor finger and that of the contralateral finger in extended reverse dorsal metarcarpal artery flaps was found by.³

The surgeon’s primary goal is restoration of hand function as much as is possible. Post operative evaluation data are needed in clinical audit and therefore governance geared towards improving surgical practice. Normal data on key pinch strength in adult Caucasians in both the normal and pathological states exist in the literature.^4-8 Increasingly, the need to exercise caution in generalization of normative data across regions is emphasized. Hand grip values in an African population have been found to be lower than that of the Caucasian population.^9,10 There is a dearth of data on key pinch strength pinch in Africans in the literature. The objectives of the study were to have normal values of key pinch strength amongst a Nigerian population, to determine the influence of gender, age, handedness and body mass index on key pinch strength and to compare the values obtained with that reported in other populations.

METHODS
The study was a community based cross sectional survey carried out over a one-year period on adults between the ages of 20 and 80 years in Ibadan, the capital City of Oyo State. A multi-staged sampling method was used to select the Local Government Areas (LGAs) for the study. Akinyele and Ibadan North local government areas were randomly selected from the eleven LGAs in Ibadan. In each of these selected LGAs, two streets were selected by convenience sampling from where the subjects were recruited using a modified cluster sampling method.

Ethical approval was obtained from the Institutional Review Board. For each participant that met the terms of the inclusion criteria stated, an informed consent was obtained. Participants who were not conversant with English language were communicated with in the local dialect.

Participants who were of lucid consciousness, without any history or obvious mental illness, who were not on systemic drugs, were recruited. They also had no history of alcohol misuse and were able to display the activities of daily living such as eating bathing, dressing, and work.

A structured questionnaire, which was in two parts, was used for obtaining data. The first part consisted of information such as age, sex, height, weight, drug use and the occurrence of previous hand trauma or surgery. The second part comprised of the required hand measurements; key pinch values and hand span. The key pinch (lateral pinch grip) was measured with the baseline hydraulic pinch gauge that had been pre calibrated at the factory. The subjects were seated with their shoulder adducted and neutrally rotated, elbow flexed at 90° with the forearm and wrist in neutral position.¹¹ Three consecutive measurements in kilograms, after resetting to zero, were taken and the arithmetic mean computed.¹²

The hand span was measured by first instructing that the hand be opened as wide as possible and placed on a plain paper on a table. The outer lateral border of the distal phalanx of the little finger and thumb were marked as points on the paper. The distance between these two points, the hand span, was then measured and recorded to the nearest centimeter.

Descriptive statistics (mean, mode) were used to determine frequency of data subsets. Independent t test were used to compare key pinch with gender and hand dominance while Pearson’s correlation was used to determine the relationship between key pinch and the measured constitutional variables. Statistical significance was defined by p values <0.05.

Previous data on key pinch values in which similar methodologies to this study were employed, were obtained from four studies on German⁵, Swiss¹³, Turkish ¹⁴ and Korean⁷ populations and the values compared to those in this study.