Variations of the lumbrical muscles of the hand: Systematic review and meta-analysis.

PURPOSE: Lumbrical muscles of the upper limb belong to the middle group of intrinsic hand muscles. Their anatomical variability has been extensively studied with heterogeneous findings. Therefore, the aim of this study is to provide a systematic review and a meta-analysis of the lumbrical muscles variations in the human hand. METHODS: For this purpose, four major electronic databases were searched to identify eligible studies. Then, all relevant data were extracted, and statistical analysis performed. A new classification of lumbrical muscles variations is proposed to summarize and clearly define all described findings. We included 26 studies, making a total sample of 1340 dissected hands. FINDINGS: The most common variations for each muscle were an accessory belly for the first lumbrical muscle, a variable origin for the second lumbrical muscle, a variable innervation for the third lumbrical muscle and a variable insertion for the fourth lumbrical muscle with the prevalence 3.8%; 7.7%; 12% and 5.8%, respectively. CONCLUSIONS: We believe that results of our statistical analysis are suitable for both hand surgeons and other medical professionals dealing with hand injuries or functional problems in their daily routine.