Vitamin D as an intervention for improving quadriceps muscle strength in patients after anterior cruciate ligament reconstruction: study protocol for a randomized double-blinded, placebo-controlled clinical trial

BACKGROUND

The goal of anterior cruciate ligament reconstruction (ACLR) is to restore the preinjury level of knee function to return to play (RTP). However, even after completing the rehabilitation programme, some patients may have persistent quadriceps muscle weakness affecting knee function which ultimately leads to a failure in returning to play. Vitamin D has been long recognized for its musculoskeletal effects. Vitamin D deficiency may impair muscle strength recovery after ACLR. Correcting vitamin D levels may improve muscle strength.

METHODS

This is a double-blinded, randomized controlled trial to investigate the effects of vitamin D supplementation during the post-operative period on quadriceps muscle strength in anterior cruciate ligament (ACL)-injured patients. Patients aged 18-50 with serum vitamin D < 20 ng/ml, unilateral ACL injury, > 90% deficit in total quadriceps muscle volume on the involved leg compared with uninvolved leg, Tegner score 7 + , and no previous knee injury/surgery will be recruited. To assess patient improvement, we will perform isokinetic and isometric muscle assessments, ultrasound imaging for quadriceps thickness, self-reported outcomes, KT-1000 for knee laxity, biomechanical analysis, and Xtreme CT for bone mineral density. To investigate the effect of vitamin D status on quadriceps strength, blood serum samples will be taken before and after intervention.

DISCUSSION

Patients with low vitamin D levels had greater quadriceps fibre cross-sectional area loss and impaired muscle strength recovery after ACL. The proposed study will provide scientific support for using vitamin D supplementation to improve quadriceps strength recovery after ACLR.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05174611. Registered on 28 November 2021.

50Hz interference and noise in ECG recordings--a review

In this review paper, a simplified model is used to explain the various ways by which 50Hz interference can disturb electrocardiogram recordings. From the model, noise expressions are also derived which explain sources of noise in recordings. Means of minimising the 50Hz interference and noise with emphasis placed on skin abrasion and right-leg drive circuits are discussed. An add-on circuit which can be used with existing amplifiers to improve their performance is shown. Previous interference analysis has concentrated on 2-input differential amplifiers, however in modern hospitals, a wide variety of amplifier configurations are used. An example is the Wilson Central Terminal which is used to obtain a zero potential in body surface mapping applications. In this review it is shown with an example for an ECG amplifier incorporating a Wilson Central Terminal, how it is easy to extend the interference model to other applications.

A novel approach to the design of a Wilson referenced ECG amplifier

The Wilson Central Terminal consists of three limb electrodes connected through a resistor network at the inverting input to the ECG amplifier. It is often used as a zero potential reference in ECG recordings. In this paper, the implications of using a Wilson central reference on the overall amplifier's common-mode rejection ratio and noise specifications is analysed. It is shown that the Wilson reference can degrade the overall amplifier specifications. The design of a Wilson referenced amplifier is then described which shows this to be true. A novel approach to the design of a Wilson referenced ECG amplifier is then presented, whereby the reference network is moved from the input to an intermediate stage of the amplifier. An analysis on the improvements achieved over the conventional approach is given. An amplifier design using the new approach is then described. Tests results showed a significant improvement in amplifier common mode rejection ratio and noise specifications when compared to the conventional design.