Innervation of the distal part of the vastus medialis muscle is endangered by splitting its muscle fibers during total knee replacement: an anatomical study using modified Sihler's technique

Abstract

Background and purpose - The distal part of the vastus medialis muscle is an important stabilizer for the patella. Thus, knowledge of the intramuscular nerve course and branching pattern is important to estimate whether the muscle's innervation is at risk if splitting the muscle. We determined the intramuscular course of the nerve branches supplying the distal part of the vastus medialis muscle to identify the surgical approach that best preserves its innervation.Material and methods - 8 vastus medialis muscles from embalmed anatomic specimens underwent Sihler's procedure to make soft tissue translucent while staining the nerves to study their intramuscular course. After dissection under transillumination using magnification glasses all nerve branches were evaluated.Results - The terminal nerve branches were located in different layers of the muscle and ran mostly parallel but also transverse to the muscle fibers. In half of the cases, the latter formed 1 to 3 anastomoses and coursed close to the myotendinous junction. Additionally, most of the branches extended into the ventromedial part of the knee joint capsule.Interpretation - To preserve the innervation of the distal part of the vastus medialis muscle, any split of the muscle during surgical approaches to the knee joint should be avoided.

Figure 1.

Right vastus medialis muscle of a 56-year-old woman. The muscle was removed from a formalin-fixed specimen and marked with yellow yarn (a). The same muscle after Sihler’s procedure transilluminated by a white light transilluminator. The nerve branches are stained dark blue whereas the muscle fibers show a transparent lavender color after the destaining and clearing process. Some of the superficial muscle fibers were removed to show the whole course of all nerve branches. The ventrolateral part of the capsule of the knee joint appears amber (b).

Figure 2.

Detailed view of the transilluminated distal part of 4 right vastus medialis muscles and the adjacent ventromedial part of the capsule of the knee joint: (a) from a 56-year-old woman, (b) from an 83-year-old woman, (c) from a 67-year-old woman, (d) from a 82-year-old man. The nerve branches are located in different layers of the muscle. They run parallel (single arrows) or transverse (double arrows) to the muscle fibers and finally reach the ventromedial part of the capsule of the knee joint. In half of the subjects, they build 1 or more anastomoses (arrowhead) within the distal part of the vastus medialis muscle.

Figure 3.

Simulation of the subvastus approach performed in a non-embalmed anatomic specimen. The vastus medialis muscle (vm) is preserved during the subvastus approach, as the dissection follows its caudal border (a, b). To gain more space, the vastus medialis muscle can be mobilized from the tendon of the adductor magnus by blunt dissection. The muscle together with the patella (P) can then be lateralized to get access to the joint surfaces (c).

Figure 4.

Simulation of the midvastus approach performed in a non-embalmed anatomic specimen. The distal part of the vastus medialis muscle (vm) is split about 3 cm cranial from its caudal border (a, b, c). The cranial part of the muscle together with the patella (P) can be lateralized to gain access to the joint (d).