Innervation patterns of hamstring muscles, including morphological descriptions and clinical implication.

PURPOSE: The hamstrings muscles are innervated by sciatic nerve branches. However, previous studies assessing which and how many branches innervate each muscle have yielded discrepant results. This study investigated the innervation patterns of hamstrings. MATERIALS AND METHODS: Thirty-five cadaver limbs were investigated. The average age of subjects was 78.6 ± 17.2 years, with 48.6% male and 51.4% female, while 57.1% were right limbs and 42.9% left. The sciatic nerve, hamstrings and associated structures were dissected. The number of nerve branches for each muscle and the level where they penetrated the muscle were recorded. RESULTS: The sciatic nerve was connected by a fibrous band to the long head of the biceps femoris. This muscle was innervated by either one or two branches, which penetrated the muscle into its superior or middle third. The short head of the biceps femoris was innervated by a single nerve that usually penetrated its middle third, but sometimes inferiorly or, less commonly, superiorly. The semitendinosus was always innervated by two branches, the superior branch penetrating its upper third, the inferior mostly the middle third. The semimembranosus usually was innervated by a single nerve branch that penetrated the muscle at its middle or lower third. Four specimens revealed common nerves that innervated than one muscle. CONCLUSIONS: We have characterized hamstring innervation patterns, knowledge that is relevant to neurolysis, surgery of the thigh, and other procedures. Moreover, a mechanical connection between the sciatic nerve and biceps femoris long head was identified that could explain certain neuralgias.

Pathomechanics of lumbrical and flexor digitorum profundus muscle tears in climbers: A cadaveric model.

Lumbrical muscles originate on the flexor digitorum profundus (FDP) tendons and, during fist making, they move in the same direction when FDP muscle produces maximal proximal tendon gliding. Injuries of the bipennate lumbricals have been described when a shear force acts between the origins on adjacent tendons of the FDP, as they glide in opposite directions in asymmetric hand postures. Other structures of the deep flexors complex can be affected during this injury mechanism, due to the so-called quadriga effect, which can commonly occur during sport climbing practise. Biomechanical studies are needed to better understand the pathomechanism. A cadaveric study was designed to analyse the effects of load during the fourth lumbrical muscle injury mechanism. The amount of FDP tendon gliding and metacarpophalangeal (MCP) joint flexion of the 5th finger were calculated. Ten fresh-frozen cadaveric specimens (ten non-paired forearms and hands) were used. The specimens were placed on a custom-made loading apparatus. The FDP of the 5th finger was loaded, inducing isolated flexion of the 5th finger, until rupture. The rupture occurred in all specimens, under a load of 11 kg (SD 4.94), at 9.23 mm of proximal tendon gliding (SD 3.55) and at 21.4° (SD 28.91) of MCP joint flexion. Lumbrical muscle detachment from the 4th FDP was observed, from distal to proximal, and changes in FDP tendons at the distal forearm level too. The quadriga effect can lead to injury of the bipennate lumbrical muscles and the deep flexors complex in the hand and forearm.

Common origin tendon of the biceps femoris and semitendinosus muscles, functional and clinical relevance / Tendón de origen común de los músculos bíceps femoral y semitendinoso, relevancia funcional y clínica

SUMMARY: The injury of Biceps Femoris long head (BFlh) and Semitendinosus (ST) is caused by over-stretch of the muscles at the back of the thigh. This condition encompasses almost one third of sports-related injuries and has severe consequences, such as pain and weakness of the muscles. This injury is related namely to quick and demanding activities, such as short distance sprinting in a limited time period. The Common Origin Tendon (COT) for these two muscles is affected in these injuries. This tendon is formed by the BFlh and ST muscles which together have a common origin in the ischial tuberosity. Given the lack of complete knowledge about the detailed structure of the COT, we dissected cadaveric limbs, describing their morphological characteristics, and discussing its functional and clinical implications.: Thirty-five human cadaveric lower limbs were dissected after fixation to analyze the morphology of the COT, focusing on their volume and muscular/tendinous proportion. We identified two subtypes of COT. The most frequent was the musculotendinous type, in which the origin of the BFlh was mainly tendinous, while the ST muscle was mainly muscular (91.4%). In the tendinous type both muscles had a tendinous origin (8.6%). In the musculotendinous type, the ST muscle ends with a microscopic connective tissue that extend into the ischial tuberosity. We conclude that there is a variability in the anatomical presentations of the COT, and we propose that this will correspond with biomechanical differences in the risks and the response to regional injuries. The connective tissue between the COT and the neighbouring structures could be a risk factor for adhesion tearing.

RESUMEN: Los desgarros de los músculos bíceps femoral cabeza larga (BFcl) y semitendinoso (ST) son causados por una tensión excesiva durante actividades que implican amplios rangos de movimiento en velocidad. Alcanzan casi a un tercio de las lesiones deportivas y tienen graves consecuencias competitivas, además generan dolor y debilidad muscular. El tendón de origen común (TOC) de estos dos músculos se ve afectado en estas lesiones. Este tendón se encuentra formado por el BFcl y el ST, originándose juntos en la tuberosidad isquiática. Debido a la falta de conocimiento completo y detallado de este tendón, se realizó un estudio cadavérico, describiendo sus características morfológicas y discutiendo sobre sus implicaciones funcionales y clínicas. Se practicó la disección anatómica de 35 miembros inferiores, lo que permitió describir la morfología del TOC, focalizando en su volumen y proporciones musculo-tendinosas. La conformación morfológica del TOC fue de 2 tipos: la musculotendinosa, donde el BFcl tenía una estructura tendinosa y el ST tenía una estructura muscular (91,4 %). La conformación tendinosa, donde ambos músculos tenían estructuración tendinosa (8,6 %). Cuando la conformación era musculotendinosa, el ST terminaba con un tejido conjuntivo microscópico, que se extendía hasta la tuberosidad isquiática. La conformación morfológica del TOC del BFcl y ST tuvo una presentación variable, lo cual podría tener implicación en su comportamiento biomecánico, y ser un factor de riesgo de lesiones. Además el tejido conjuntivo situado entre este tendón y las estructuras anatómicas vecinas podría ser un factor de riesgo de lesiones por adherencia.