Reliability of vernier caliper measurements of the thoracic pedicle transverse diameter

The thoracic pedicle is generally cylindrical with various  indentations on its surface that may introduce an error in measurements, thus making the measurements unreliable. One hundred and eighty thoracic pedicle diameter measurements were carried out in five cadaveric human thoracic spine specimens, using a Vernier caliper. Coefficient of variation (CV) was used to evaluate the variation in measurements within and between  pedicles. Linear regression model was used to evaluate the  relationship between the variation in measurements and the average diameter of the bone per cadaver. The largest standard deviations in the five specimens were found at T2, T3, T6 and T12 levels. The least standard deviations were found at T1, T7, T9, T10 and T11. Four specimens demonstrated a negative linear relationship between the coefficient of variation and the average transverse diameter of the pedicle. This relationship was  significant (p<0.05) in two specimens. Vernier caliper measurements tend to be less reliable as the thoracic pedicle transverse diameter decreases. Caution is required when measuring the thoracic pedicle transverse diameter in the narrower mid-thoracic area of the spine with Vernier calipers.Keywords: reliability, thoracic pedicle morphometr

The course of the radial nerve in relation to the humerus: a cadaveric study in a Kenyan adult population

Background: The radial nerve arises from the posterior cord of the brachial plexus. It descends distally to the spiral groove of the humerus. The upper and lower margins of this groove form important landmarks relative to the acromion process, medial and lateral epicondyles of the humerus.Objective: To describe the course of the radial nerve in relation to the humerus in a Kenyan adult population.Methods: Dissections were done on fifty-nine left sided formalin fixed adult upper extremities obtained from the Human Anatomy Laboratory of Moi University. Data was recorded and analysed using SPSS version 21.Results: The average humeral length was 314.4 ± 21.4mm. The radial nerve was located 140.8 ± 17.2 mm from the tip of the acromion. It exited the spiral groove 185.1 ± 21.7mm from the tip of the acromion and 132.1 ± 19.4 mm from the lateral epicondyle. The midpoint of the nerve at the spiral groove to the medial epicondyle was about half the humeral length.Conclusions: The radial nerve was located at the middle third of the humerus shaft. The midpoint of the nerve while in the groove relative to the medial epicondyle was about half the humeral shaft length.Keywords: Spiral groove of the humerus, Humerus shaft fractures, Triceps muscl

Morphometry of the thoracic pedicle and the pedicle-rib unit: A review of literature

Background: The pedicle is the most commonly used site in spinal fixation. The size of the pedicle screw utilized is determined by the dimensions of the pedicle. The purpose of this review is to summarize the available English literature on thoracic pedicle morphometry.Materials and methods: PubMed search with the mesh term “thoracic pedicle morphometry measurements” and “pedicle-rib unit morphometry measurements” found 25 relevant articles.Results: The transverse width of the thoracic pedicle is narrowest at the mid-thoracic region. The chord length increases with caudal advancement, and is longest in the lower thoracic spine. The transverse angle of the thoracic pedicle is neutral or divergent at the lower thoracic spine, while it is most convergent in the upper thoracic spine.Conclusions: Linear thoracic pedicle dimensions are influenced by age, gender, height, weight and spinal level. Angular dimensions are influenced by spinal level only. Pedicle screw size choice and application is therefore guided by these factors. Pre-operative CT scanning of the thoracic spine is highly recommended in surgical planning.Key words: Thoracic vertebra pedicle, Pedicle-rib unit, Morphometr

Morphometric analysis of lumbar pedicles among adult Kenyans using computer tomography scans and dry bone specimens

Background: The use of pedicle screws in the lumbar spine is guided by the dimension and orientation of the lumbar pedicle.Objectives: To determine the width, angulation and chord length of the lumbar vertebrae pedicle from L1 to L5 in adult Kenyans using Computer tomography scans and dry bone specimens.Methods: Three hundred and thirty dry bones, 100 samples were selected systematically, and 100 CT scans from 468 lumbar spine scans. Results from the analysis were summarized as means, standard deviations and presented in line and bar graphs.Results: Pedicle width mean measurements were L1-8.6mm, L2-9.6mm, L3-11.4mm, L4-13.5mm, L5-16.3mm on dry bone specimens. On CT scan pedicle width mean measurements were L1-7.2mm, L2-7.6mm, L3-9.2mm, L4-10.8mm, L5-14. 6mm. The mean angle of insertion on CT scan was L1-19.7o, L2-20.5o, L3-22o, L4-24.1o, L5-29.8o. Pedicle chord length measurements obtained were  L1-47.9mm, L2-48.9mm, L3-48.9mm, L4-47.7mm, and L5-47.0 mm on dry bone specimen. On CT scan it was, L1- 48.6mm, L2-49.9mm, L3-50.1mm, L4-49.8mm, and L5-50.1 mm.Conclusion: The pedicle width on CT scan measurements increased from 7.2mm to 14.6mm and on dry bone specimen it increased from 8.6mm to 16.3mm between L1 to L5. The angulation increased from L1 to L5 on CT scan measurements from 19.7o at L1 to 29.8o at L5. The chord length range measurement on dry bone specimen ranged from 47.9mm to 48.9mm and on CT scan from 48.6mm to 50.1mm

Gerdy’s safe zone in the Kenyan population: a cadaveric study

Background: The Common Peroneal Nerve (CPN) is a branch of the sciatic nerve, which is almost subcutaneous in its course around the fibula. This means it is a structure that is at risk when performing procedures around the proximal fibula and tibia. This study was done to determine a safe zone in which procedures can be performed without injuring it.Objective: To determine the extent of Gerdy’s safe zone in the Kenyan population.Design: This was an anatomical descriptive cross- sectional study.Methods: The study was carried out at the human anatomy laboratory, Moi University. Dissection was done on forty three right sided formalin fixed limbs. Right sided lower limbs were chosen because they were more in number than the left sided lower limbs thus satisfying requirements of study population.Results: Forty three right sided lower limbs (32 male, 11 female) were dissected. The nerve was seen to define an arc like trajectory around Gerdy’s tubercle, with a mean radius of 57.6±5mm.Conclusion: In this population, Gerdy’s safe zone (radius of 57.6±5mm) is most likely to be free of the common peroneal nerve and its branches and thus can be marked preoperatively before carrying out procedures in the proximal tibia.Keywords: Gerdy’s tubercle, Gerdy’s safe zone, Tibi