Figure 1.
Stress relaxation of myofibres and fascicles at different sarcomere lengths.
Representative passive forces of a spastic single myofibre segment from a spastic FCU as a function of sarcomere length (ℓsarc). Forces were measured immediately (time = 0 min), and 2, 4, and 6 minutes after imposing each sarcomere strain increment. Note that effects of stress relaxation are small after at least 4 minutes, therefore sarcomere length-tension curves of myofibre and fascicle segments were assessed based on the forces measured after 4 minutes.
Figure 2.
Passive length-tension characteristics of single myofibre segments and fascicle segments in spastic and control FCU.
(A) passive tension as function of sarcomere length. Sarcomere length-passive tension curves were neither significantly different comparing spastic and control (n = 10) single myofibre segments (both n = 10), nor comparing spastic and control fascicle segments (both n = 10). The same was found for comparing single myofibre segments to fascicle segments within each group. (B) slopes of passive length-tension as function of sarcomere length. The curves describing the slopes were neither significantly different comparing spastic and control (n = 10) single myofibre segments (both n = 10), nor comparing spastic and control fascicle segments (both n = 10). The same was found for comparing single myofibre segments with fascicle segments within each group. Means and SEM are plotted.
Figure 3.
Light micrographic comparison of HE stained cross-sections of fascicles from spastic and control FCU.
(A) Typical example of a cross-sectional image within control FCU. (B) Typical example of a cross-sectional image within spastic FCU. (C) example of the pathological sign of central nuclei observed in one CP patient exclusively. Bars represent 100 µm.
Figure 4.
Myofibre typing and myofibre cross-sectional area within fascicles from spastic and control FCU.
Typical examples of light micrographs of ATPase stained cross-section of biopsies from: (A) Control muscle, (B) Spastic muscle. Myofibre types I, IIA and IIAX are assigned; bars represent 100 µm. (C) Fibre type distribution within cross-sections from FCU. Fibre type distribution was not significantly different between CP (n = 26) and control (n = 10) samples. (D) For all fibre types, myofibre cross-sectional area (AMF) in all spastic samples was significantly smaller than in controls. (E). Individual data for AMF plotted as a function of age. For spastic muscle of all ages taken together, Spearman's Rank coefficient of correlation for AMF and age was significant and moderately high. Note that AMF of spastic patients ≥20 years was not significantly different from that of (adult) control muscles. Means and SEM are shown; * indicates significant difference between spastic and control FCU.
Figure 5.
Variables of endomysium, primary and secondary perimysium in cross-sections of spastic muscle.
Typical examples of light micrographs of Sirius Red stained cross-sections of FCU biopsies: (A) Sample of a 20-year old control subject. (B) Sample of an 18-year old CP subject. Bars represent 100 µm. (C) Individual data for cross-sectional area of endomysium within FCU plotted as a function of age. The mean (area) proportion taken up by endomysium (i.e. AE expressed as % of total measured area) was not significantly different between cross-sections of CP (n = 23) and control subjects (n = 9). (D) Individual data for endomysium thickness (ℓE) within FCU plotted as a function of age. The mean thickness of endomysium per myofibre cross-section was not significantly different in CP and control subjects. (E) Individual data for primary and secondary perimysial thickness (ℓP1&P2) within FCU plotted as a function of age. Mean thickness of perimysium within cross-sections of spastic muscle were not different from those in control muscle. Horizontal lines indicate mean values.
Figure 6.
Increased thickness of tertiary perimysium within cross-sections of fascicles within spastic muscle.
Typical examples of light micrographs of Sirius Red stained cross-sections of FCU biopsies: (A) control muscle. (B) Spastic muscle. Bars represent 250 µm. (C) Individual data of tertiary perimysium thickness within FCU biopsies plotted as function of age. Mean thickness of tertiary perimysium in FCU (indicated by horizontal lines) of spastic subjects (n = 23) was significantly higher than in FCU of control subjects (n = 9).
Figure 7.
Neurovascular tract and simple schematics of connections.
(A) Photograph of the tenotomised FCU and its myofascial connections to extramuscular connective tissue (EMCT) consisting of general fascia and neurovascular tracts (NVT). Note that, although not visible in the image, there are also connections to the epimysia of surrounding muscles (i.e. m. extensor carpi ulnaris and flexor digitorum superficialis/profundus). Via these connections, force can be transmitted between the stroma of FCU and extramuscular connective tissue such as general fascia, septa or NVT (i.e. epimuscular force transmission) and other muscles. This will cause loading in proximal as well as distal directions on a fraction of FCU. Distal loading of spastic FCU via myofascial connections has been shown after FCU tenotomy suggesting enhanced epimuscular loading (Movie S1) [64]. As branches of the NVTs generally enter the muscle from proximal directions, loading of the NVTs may chiefly yield proximally directed epimuscular loading of FCU. (B) Schematic diagram illustrating how concurrent proximal and distal epimuscular loads may cause high local sarcomere strains. Myofibres are represented by three sarcomeres in series, with myofascial connections to extramuscular connective tissues.