THE EFFECT OF TARGETING THE PLANTARIS MUSCLE-TENDON UNIT IN CORRECTION OF ANKLE EQUINUS IN CHILDREN

The plantaris muscle is believed to contribute to equinus in many children and is sometimes included in treatment plans for equinus. However, the nature and magnitude of its' contribution is poorly understood. An improved understanding of the effect of plantaris lengthening in ankle equinus could lead to improvements in the early management of equinus. This study evaluated the effect of plantaris tenotomy in the setting of equinus contracture on passive ankle dorsiflexion relative to that of tendoachilles lengthening or gastrocnemius recession. A prospective randomized clinical trial was carried out including pediatric subjects who were scheduled for surgical lengthening of the plantaris as well as the gastrocnemius or tendoachilles. Subjects were randomized to have their plantaris tenotomy performed prior to or after tendoachilles or gastrocnemius lengthening (as sub-procedures within the same surgical encounter). Passive ankle dorsiflexion was measured prior to and after each muscle-tendon unit was lengthened. Twenty-two subjects (33 legs) were recruited with a mean subject age of 10.8 years. The etiology of equinus in most subjects was idiopathic toe-walking or cerebral palsy. Nineteen limbs (13 subjects) were randomized for the plantaris to be cut first. Generalized linear regression models were used to estimate the average change in passive ankle dorsiflexion following the entire surgical encounter, as well as estimate average and marginal effects of each sub-procedure within each surgical encounter, while controlling for sub-procedure order. Mean preoperative ankle dorsiflexion was −22.31 (SD 12.74) degrees (plantaris-first group) and −23.28 (SD 11.28) degrees (plantaris-second group). Ankle dorsiflexion overall improved by 27.21 (21.33,33.08) degrees (plantaris-first) and 33.64 (26.77,40.51]) degrees (plantaris-second). This represented a difference in ankle dorsiflexion change of 6.43 degrees following plantaris-first and plantaris-second surgical encounters, though the difference did not reach statistical significance (p < 0 .14). Improvement in ankle dorsiflexion attributable to the plantaris was 4.00 (8.45, −0.45) degrees when the plantaris was cut first and 9.79 (4.60, 14.97) degrees when the plantaris was cut second. To our knowledge, this is the first study to quantify the effect of plantaris tenotomy in the setting of ankle equinus in children. Plantaris tenotomy in the setting of ankle equinus appears to increase passive ankle dorsiflexion as expected. This study suggests there may be some components of the plantaris tenotomy effect that are dependent on lengthening of the gastrocsoleus mechanism and others that are independent of it. As such, the plantaris may be an important secondary restraint to ankle dorsiflexion with instances where it is warranted to preserve the plantaris during equinus correction to avoid producing excessive ankle dorsiflexion. Contrastingly, in cases of milder equinus, there may be a role for early interventions targeting the plantaris alone. Further study is warranted, with larger sample size to examine these effects, particularly in milder deformities.