Range of motion physiotherapy reduces the force deficit in antagonists to denervated rat muscles.

BACKGROUND: We used a rat hindlimb model of tibial nerve transection to determine if a loss of mechanical function exists in innervated antagonists compared with denervated muscles. We tested two hypotheses: (1) denervation of the rat ankle plantar flexors results in decreased force production of the ankle dorsiflexors, and (2) daily passive ankle range of motion (ROM) physiotherapy prevents or reduces the force deficit. METHODS: Adult Lewis rats were assigned to one of three groups: (1) a sham (S) group, in which the tibial nerve was exposed but not transected; (2) a no rehabilitation (NR) group, in which a 2-cm segment of tibial nerve was excised at midthigh to denervate the ankle plantar flexors; or (3) a rehabilitation (R) group, in which a 2-cm segment of tibial nerve was excised and the animals were subjected to ankle passive ROM physiotherapy for two 5-min sessions each day. After 14 days, maximum isometric tetanic force (F(0)) and specific force (sF(0)) were measured in the extensor digitorum longus (EDL) muscle, an ankle dorsiflexor. RESULTS: Compared with those from animals in the S group, EDL muscles from animals in the NR group demonstrated a 22% decrease in both F(0) and sF(0). In the EDL from animals in the R group, daily passive ROM physiotherapy diminished the deficit in F(0) but not in sF(0). CONCLUSIONS: These data support the hypotheses that nerve injuries result in impaired mechanical function in the innervated antagonists to denervated muscles and that passive ROM physiotherapy can improve force production in these muscles.

"Donor" muscle structure and function after end-to-side neurorrhaphy.

End-to-end nerve coaptation is the preferred surgical technique for peripheral nerve reconstruction after injury or tumor extirpation. However, if the proximal nerve stump is not available for primary repair, then end-to-side neurorrhaphy may be a reasonable alternative. Numerous studies have demonstrated the effectiveness of this technique for muscle reinnervation. However, very little information is available regarding the potential adverse sequelae of end-to-side neurorrhaphy on the innervation and function of muscles innervated by the "donor" nerve. End-to-side neurorrhaphy is hypothesized to (1) acutely produce partial donor muscle denervation and (2) chronically produce no structural or functional deficits in muscles innervated by the donor nerve. Adult Lewis rats were allocated to one of two studies to determine the acute (2 weeks) and chronic (6 months) effects of end-to-side neurorrhaphy on donor muscle structure and function. In the acute study, animals underwent either sham exposure of the peroneal nerve (n = 13) or end-to-side neurorrhaphy between the end of the tibial nerve and the side of the peroneal nerve (n = 7). After a 2-week recovery period, isometric force (F(0) was measured, and specific force (sF(0) was calculated for the extensor digitorum longus muscle ("donor" muscle) for each animal. Immunohistochemical staining for neural cell adhesion molecule (NCAM) was performed to identify populations of denervated muscle fibers. In the chronic study, animals underwent either end-to-side neurorrhaphy between the end of the peroneal nerve and the side of the tibial nerve (n = 6) or sham exposure of the tibial nerve with performance of a peroneal nerve end-to-end nerve coaptation approximately 6), to match the period of anterior compartment muscle denervation in the end-to-side neurorrhaphy group. After a 6-month recovery period, contractile properties of the medial gastrocnemius muscle ("donor" muscle) were measured. Acutely, a fivefold increase in the percentage of denervated muscle fibers (1 +/0 0.7 percent to 5.4 +/-2.7 percent) was identified in the donor muscles of the animals with end-to-side neurorrhaphy (p < 0.001). However, no skeletal muscle force deficits were identified in these donor muscles. Chronically, the contractile properties of the medial gastrocnemius muscles were identical in the sham and end-to-side neurorrhaphy groups. These data support our two hypotheses that end-to-side neurorrhaphy causes acute donor muscle denervation, suggesting that there is physical disruption of axons at the time of nerve coaptation. However, end-to-side neurorrhaphy does not affect the long-term structure or function of muscles innervated by the donor nerve.

Specific force deficit in skeletal muscles of old rats is partially explained by the existence of denervated muscle fibers.

We tested the hypothesis that denervated muscle fibers account for part of the specific force (sF(o)) deficit observed in muscles from old adult (OA) mammals. Whole muscle force (F(o)) was quantified for extensor digitorum longus (EDL) muscles of OA and young adult (YA) rats. EDL muscle sF(o) was calculated by dividing F(o) by either total muscle fiber cross-sectional area (CSA) or by innervated fiber CSA. Innervated fiber CSA was estimated from EDL muscle cross sections labeled for neural cell adhesion molecules, whose presence is a marker for muscle fiber denervation. EDL muscles from OA rats contained significantly more denervated fibers than muscles from YA rats (5.6% vs 1.1% of total CSA). When compared with YA muscle, OA muscle demonstrated deficits of 34.1% for F(o), 28.3% for sF(o), and 24.9% for sF(o) calculated by using innervated CSA as the denominator. Denervated muscle fibers accounted for 11.3% of the specific force difference between normal YA and OA skeletal muscle. Other mechanisms in addition to denervation account for the majority of the sF(o) deficit with aging.

Mechanical function of muscle reinnervated by end-to-side neurorrhaphy.

End-to-side neurorrhaphy is a surgical technique for peripheral nerve reconstruction when end-to-end neurorrhaphy is not an option. To define the effectiveness of end-to-side neurorrhaphy as a method of nerve repair, the authors tested the null hypothesis: there is no difference in the mechanical function of skeletal muscle denervated and reinnervated by end-to-side versus end-to-end neurorrhaphy. Adult Lewis rats underwent either transection and end-to-end epineurial repair of the left peroneal nerve (n = 9) or end-to-side repair of the distal stump of the peroneal nerve to the side of the tibial nerve (n = 8). After a 6-month recovery period, isometric force (Fo) was measured, and specific force (sFo) was calculated for the extensor digitorum longus muscle of each animal. Immunohistochemical staining for neural cell adhesion molecule (NCAM) was performed to identify populations of denervated muscle fibers. The mean extensor digitorum longus muscle mass in the end-to-end group (195 +/- 32 g) was significantly greater than that of the end-to-side group (146 +/- 55 g) (p < 0.05). A significantly greater percentage of denervated fibers was identified in the extensor digitorum longus muscles of animals in the end-to-side group (9.4 +/- 3.2 percent) than in those in the end-to-end group (3.8 +/- 1.0 percent) (p < 0.05). Despite a lower muscle mass and a higher percentage of denervated fibers, neither Fo nor sFo was significantly different in the two groups. These data support the null hypothesis that, under appropriate circumstances, there is no difference in the recovery of whole muscle force and specific force production in muscles reinnervated by end-to-side versus end-to-end neurorrhaphy.

Type II (beta) errors in the hand literature: the importance of power.

When a study concludes that there is no difference between 2 treatments ("negative studies"), it is essential to determine whether the study has sufficient power to find a clinically significant difference. Insufficient power precludes an adequate assessment of therapeutic efficacy and may result in a type II error, an erroneous conclusion that the null hypothesis is correct. In evaluating 39 studies that highlighted negative findings in The Journal of Hand Surgery, we found that 32 (82%) papers had a power of less than .80 to detect a 25% treatment effect and, when the treatment effect was increased to 50%, more than one half of the studies still had a power of 0.80. These "negative studies" frequently have inadequate statistical power to support their conclusions. These findings have important implications for researchers, editors, and readers.

A surgical technique that allows reuse of an existing venotomy site for multiple central venous catheterizations.

During long-term use, central venous catheters are damaged or inadvertently displaced, and replacement is required. The authors developed a technique that allows multiple recatheterizations through an existing venotomy site. The technique is very advantageous for patients who need long-term central venous access.