Experimental study of fascicular nerve repair with and without epineurial closure.

Microscopic fascicular repair without closure of epineurium was compared with microscopic epineurial repair in 12 rhesus monkeys. Measurements of evoked nerve action potentials, and responses to repetitive and tetanic stimulation made at one interval 3, 6, 9, or 12 months postoperatively, were compared to baseline preoperative studies. Histological evaluation included light and electron microscopic preparations and studies of distal stump myelinated fiber maturity. Electrical measures of regeneration indicated that recovery was more advanced in the limb with epineurial repair in eight animals, whereas in four there was no difference between fascicular and epineurial repair. Fascicular repair appeared not to fare as well as epineurial repair because, although neuromas developed with both, the length of the neuroma was greater with fascicular than with epineurial repair. The relatively lengthy neuroma in the nerve with fascicular repair was due to axonal disorganization and connective tissue proliferation along the length of the dissection necessary for the repair. Nonetheless, studies of myelinated fiber distribution in the distal stump showed no significant differences. Similar studies were conducted in 11 primates, where epineurial repair was matched with fascicular repair in which the epineurium was closed. Here, regeneration as measured by both electrical and histological studies was comparable. Histological study showed less disorganization at the repair site in the nerve with fascicular suture and epineurial closures than in that with epineurial suture. However, studies of distal stump myelinated fiber maturity demonstrated no significant differences. Thus, there seems to be no advantage in either resecting or closing epineurium in fascicular nerve repair.

Experimental interfascicular nerve grafting.

Twenty-nine adult rhesus monkeys underwent complete laceration of both tibial nerves at mid-thigh level and repair by different methods to study the relative efficacy of autogenous interfascicular nerve grafts. Sixteen animals in Group I had an interfascicular graft repair using short sural nerve autografts on one limb and fascicular repair without grafts on the other limb. Thirteen animals in Group II, after having a 1-cm segment of tibial nerve resected, had an interfascicular graft repair without tension in one limb and an epineurial repair under moderate tension in the other limb. Evoked nerve and muscle action potentials and muscle strenght in response to repetitive and tetanic stimulation were recorded as baseline values prelaceration and then on re-exploration at 4, 6, 9, or 12 months. All nerves were examined by light and electron microscopy. Electrophysiological data, particularly muscle strength response, showed non-graft repairs to be superior at 4 and 6 months of regeneration. However, by 9 and 12 months the graft repairs had caught up and were equal to the non-graft repairs. Histologically, it was observed that many axons missed the graft segments and were present in extrafascicular connective tissues. Nonetheless, enough axons regenerated to the distal nerve to explain the success of these relatively short grafts. From the results of these experiments, it is concluded that use of autogenous interfascicular grafts offers no advantage over end-to-end non-graft repair. When and end-to-end repair cannot be achieved, use of short interfascicular nerve grafts is feasible and will work.

Histological studies of experimental interfascicular graft repairs.

Biopsies of sutured and grafted primate peripheral nerves were examined by light and electron microscopy after the final set of electrical measurements had been recorded. Inspection of all proximal stumps showed the expected regenerative activity which was not affected by the nature of the nerve repair. Transverse sections through the epineurial, interfascicular, and graft suture lines showed a similar pattern in all animals and at this site nerves sutured by epineurial technique could only be distinguished from those sutured by fascicular technique by loci of the non-absorbable suture. Fascicular repairs, whether done fascicle-to-fascicle or with interposition of grafts, had a more lengthy neuroma than did the epineurial repairs. Maintenance of fascicular architecture through the course of the grafts was variable. Fascicular structure was frequently absent in the central graft segments and in segments close to the second suture site. The method of repair used more proximally could not be distinguished by evaluation of distal stump segments. Measurements of myelinated fiber size made of distal stump axons revealed no statistical difference between the methods of repair.

Progression of partial experimental injury to peripheral nerve. Part 1: Periodic measurements of muscle contraction strength.

Isometric measurements of muscle contraction in response to single as well as tetanic volleys of supramaximal stimuli were recorded from the limbs of 32 monkeys with noninjured or partially lacerated tibial nerves. Nerve action potentials (NAP) and muscle action potentials (MAP) were also determined at intervals varying from 1 hour to 52 weeks after injury. Limbs with mobilized noninjured nerve sustained small but definite decreases in muscle contraction strength particularly if the interval between operations was brief. Partially lacerated nerves had immediate averaged decreases in single twitch and supramaximal contraction strengths of 32.8% and 30.4% despite maintenance of NAP velocity. One week following injury, muscle contraction had decreased by another 21.6% and 19.7% respectively while NAP velocity was decreased by 18.5%. Measurements were also reduced at 2, 4, and 8 weeks and to a lesser degree at 12 weeks; at 24 and 36 weeks, muscle contraction was less than pre-injury data but not when compared to recordings 15 minutes after injury. Values recorded at 52 weeks reflected partial reinnervation of Achilles musculature. Studies over a 24-hour period following partial laceration demonstrated significant further decreases in muscle power by 8 hours. The authors conclude that nerve activity following partial laceration fluctuates as function diminishes during the early hours to weeks following injury.