Biomedical subjects
Publications and source records attributed to S E Mackinnon.
Research into peripheral nerve grafting and repair is progressing at a rapid rate. An exciting aspect of these investigations concerns the intraneural vascular system and its nutrient supply. This review is an approach to selecting an appropriate laboratory investigative technique to aid in experimental design.
"Double crush hypothesis" is a phrase that has entered clinical use based on a hypothesis presented by Upton and McComas in 1973. Although clinical examples of the double crush are appearing more frequently, there has been no experimental proof of this hypothesis as it relates to chronic nerve compression. This study used a model of sciatic nerve minimal banding in the rat to investigate the effect on electrophysiological function of single or double band placement, concurrently or separated in time. This study confirms that the existence of two sites of simultaneous compression, or a second (later) site of compression, placed either proximal or distal to the first (earlier) site of compression, will result in significantly poorer neural function than will a single site of compression.
Although carpal tunnel release relieves symptoms for most patients, there are certain patients who fail to respond to this surgery. This article reviews the complications that may follow carpal tunnel surgery and discusses surgical techniques to correct the symptoms. The author emphasizes the need for increased awareness of the complexity of carpal tunnel surgery and the peripheral nerve procedures that can provide reliable improvement in affected patients.
This report proposes that reflex sympathetic dystrophy be defined as a pain syndrome in which the pain is accompanied by loss of function and evidence of autonomic dysfunction. In the clinical setting, this diagnosis is usually associated with other anatomic and psychological diagnoses and may be associated with a variety of systemic illnesses and medicolegal factors. All components should be assessed before a treatment plan is established. Priorities should go to emergency care, acute injuries, and systemic illness, psychiatric problems, and chronic anatomic problems, in that order. Early, accurate diagnosis improves prognosis.
The recovery of sensibility following digital replantation is essential in the restoration of hand function. We reviewed 12 series of digital replantations between 1977 and 1989. Three hundred sixty-seven fingers and 87 thumbs were successfully replanted. Mean age was 32.5 years. Mean follow-up was 33.5 months. Mean static two-point discrimination (S2PD) was 9.3 mm in clean thumbs vs. 12.1 mm in crush/avulsion thumb replantations. Mean S2PD was 8 mm in clean finger vs. 15 mm in crush/avulsion finger replantations. Overall mean S2PD was 11 mm in thumb and 12 mm in finger replantations. Sixty-one percent of replanted thumbs and 54% of replanted fingers regained useful S2PD (less than 15 mm or greater than or equal to S3 +). Factors that influenced digital sensibility following replantation included patient's age, level and mechanism of injury, digital blood flow, cold intolerance, and postoperative sensory reeducation. Recovery of sensibility in the replanted digit is comparable to simple nerve repair and to nerve grafting techniques. Further emphasis should be on elucidating the mechanism of cold intolerance, which was a significant complaint for most replanted digits. The universal practice of postoperative sensory reeducation will continue to improve digital sensibility following replantation.
In a primate model, nerve regeneration was evaluated across 2- and 5-cm nerve gaps using a synthetic nerve conduit (glycolide trimethylene carbonate, Maxon) and a biologic conduit (collagen). Two types of conduits from glycolide trimethylene carbonate (Maxon) were evaluated. The first was fashioned into a tube from a single flat piece of Maxon mesh. The second was prefabricated in a crimped form. The other material evaluated was a biologic collagen tube. At 14 months, excellent regeneration was noted across the 2-cm nerve gap through both the collagen and Maxon conduits. At 5 cm, the regeneration, as determined by morphometric analysis, was significantly better across the Maxon prefabricated, crimped conduit, although regeneration at this longer gap in all experimental groups was significantly less than across the shorter nerve gap. At the longer gap, there was no statistical difference between the groups by electrophysiologic assessment.
Microneurosurgical techniques to reconstruct nerve gaps with nerve grafts frequently fail to achieve excellent functional results and create donor-site morbidity. In the present study, 15 patients had gaps of 0.5 to 3.0 cm (mean 1.7 cm) in digital nerves reconstructed by one surgeon with a bioabsorbable polyglycolic acid (PGA) tube. A final evaluation of sensibility was done by a second surgeon at a mean postoperative interval of 22.4 months (range 11 to 32 months). These were all secondary reconstructions. The evaluation included a digital nerve block with local anesthetic for the intact (not reconstructed) digital nerve. Excellent functional sensation (moving two-point discrimination less than or equal to 3 mm and/or static two-point discrimination less than or equal to 6 mm) was present in 33 percent and good functional sensation (moving two-point discrimination of 4 to 7 mm and/or static two-point discrimination of 7 to 15 mm) in 53 percent of the digital nerve reconstructions. One patient with poor sensory recovery and one with no recovery were judged as functional failures (14 percent). Absence of pain at the site of reconstruction was judged by the patient to be excellent in 40 percent, good in 33 percent, and poor in 27 percent. We conclude that reconstruction of nerve gaps of up to 3.0 cm with a bioabsorbable PGA tube gives clinical results at least comparable to the classic nerve graft technique while avoiding donor-site morbidity.
The ability of the walking track assessment of sciatic nerve function to correlate with results of a nerve repair has been well documented following acute nerve injury and after recovery of the nerve following nerve repair. The long-term effects of partial denervation upon the lower extremity of the rat include the development of chronic contractures due to residual partial muscle paralysis and imbalance. The present study evaluated the ability of the walking track technique to portray accurately the walking pattern in animals following chronic contracture as a result of sciatic nerve repair. Animals 18 months and 24 months after sciatic nerve repair were found to have morphometric analysis distal to the repair that was not statistically significantly different from normal. However, the walking track assessment was inadequate at twenty-four months due to the development of clawing, interphalangeal joint contractures, and ankle inversion or eversion with or without dorsiflexion. The presence of these chronic deformities invalidated the walking track as an appropriate assessment technique for long-term assessment of nerve function following nerve repair.
Recovery of function is of prime importance after peripheral nerve injury and repair. This paper describes a method of obtaining and measuring walking-tracks and generating a Sciatic Function Index (SFI) to quantify functional sciatic nerve recovery in the rat. The reader is provided with a series of walking-tracks to measure, analyze and compare to those analyzed by experienced observers.
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A pedicled thoracoumbilical flap was evaluated in 5 patients for upper limb reconstruction. The flap appears to be a reliable axial flap that can be elevated safely to the midaxillary line. It has the capacity to transfer a large amount of tissue, allowing the damaged limb, during the attached period, to be elevated and to receive physiotherapy. Although the working portion of the flap uses the thin, hairless skin over the lateral ribs, the base of the flap is thick and difficult to tube in all but the thinnest of individuals. The donor scar is much more conspicuous than that of a groin flap.
The current philosophy of the microneurosurgical management of nerve injury is reviewed. Controversial techniques such as internal neurolysis are discussed as is the surgical dilemma of the neuroma incontinuity. Nerve regeneration is under the mechanical influence of contract guidance and the neurobiological influence of neurotropism and neurotrophism, or, as we have coined it, neurotrop(h)ism. The concepts of neurotrop(h)ism and contact guidance are discussed, emphasizing the potential importance of neurobiology in determining functional outcome following nerve repair. Finally, the interaction of the immune system and nerve regeneration is discussed.
A reliable, reproducible, simple examination of facial sensibility is described. Evaluation of 60 healthy subjects established normal values, trends, and variations of facial sensibility. Comparison of these normal values with 20 posttraumatic patients revealed that postfacial fracture sensibility testing was abnormal. Abnormalities in pressure threshold testing was most consistently associated with functional sensory complaints. Twelve of the 20 patients had significant sensory complaints at one year following the trauma.
The traditional teaching that "nerve fibers are lost at the suture line" after a nerve repair was investigated by asking the question, "Can the number of nerve fibers distal to a nerve repair site be increased by increasing the number of nerve fibers proximally?" Ratios of proximal to distal nerve fibers were increased from 1:1 to 2.5:1 to 3.5:1 by suturing peroneal or posterior tibial or sciatic nerve proximally to peroneal nerve distally. At one year following the repair, distal nerve fiber numbers increased to twice normal as the ratio increased to 2.5:1, and then nerve fiber numbers plateaued. Nerve function, as judged by walking track analysis, was best in the peroneal:peroneal group (1:1 ratio), suggesting that appropriateness rather than number of proximal fibers was more critical in this nerve repair model.
Microneurovascular techniques make transfer of innervated soft tissue a reality. The present study investigated the sensory potential of four such donor sites: volar wrist, dorsal hand, dorsal foot, and great toe. Normal moving and static two-point discrimination values for these areas are reported. A sensory reeducation protocol demonstrated that even these normal values may be improved with training. This suggests that the full potential of transferred innervated soft tissue may best be achieved by incorporating sensory reeducation routinely in the postoperative rehabilitation program.
A rat sciatic nerve model of regeneration was assessed by multiple techniques to determine the relationship between parameters of neural regeneration in common use today. The results demonstrated significant correlation and internal consistency between electrophysiological and morphological parameters (i.e., conduction velocity and fiber diameter) but not necessarily a correlation between these physiological parameters and overall nerve function as assessed by a modified walking track technique. Guidelines for parameter selection are suggested based upon the specific question being investigated (e.g., sensory and/or motor function versus axoplasmic flow and/or neurotropism) rather than the nonspecific "neural regeneration."
Quantification of peripheral nerve regeneration in animal studies of nerve injury and repair by histologic, morphologic, and electrophysiologic parameters has been controversial because such studies may not necessarily correlate with actual nerve function. This study modifies the previously described sciatic functional index (SFI), tibial functional index (TFI), and peroneal functional index (PFI) based on multiple linear regression analysis of factors derived from measurements of walking tracks in rats with defined nerve injuries. The factors that contributed to these formulas were print-length factor (PLF), toe-spread factor (TSF), and intermediary toe-spread factor (ITF). It was shown that animals with selective nerve injuries gave walking tracks that were consistent, predictable, and based on known neuromuscular deficits. The new formula for sciatic functional index was compared with previously described indices. The sciatic functional index, tibial functional index, and peroneal functional index offer the peripheral nerve investigator a noninvasive quantitative assessment of hindlimb motor function in the rat with selective hindlimb nerve injury.
The classic management of the nerve gap is reviewed. Utilization of a conduit to bridge a short nerve gap and the distal neuratization procedure to recover critical nerve function are discussed. The experimental concepts of the use of nerve allograft and nerve expansion for extensive nerve injury are introduced.