Introduction The incidence of Achilles tendon rupture (ATR) is steadily increasing, yet the exact treatment and rehabilitation of this traumatic injury is still debated [Chiodo, 2010]. Early weight bearing (WB) after ATR repair potentially yields better functional outcomes compared to immobilised patients, although re-rupture can occur at a higher rate [Costa, 2006]. Though WB has been often compared to immobilisation, it is currently unclear if early WB yields benefits in early ankle function compared to standard WB. We hypothesised that compared to standard WB, patients undergoing early WB would have higher plantarflexion moments in the injured side during gait, which would yield a longer tendon length 8 weeks after surgery. Furthermore, we hypothesised that early WB patients will show less intrapatient asymmetry than standard WB.

Methods A total of fourteen patients were randomised to either early (full WB in 2nd week, n = 6) or standard WB (n = 8) after percutaneous ATR repair by the same surgeon (SM). Kinematic (f = 120 Hz) and kinetic (f = 960 Hz) data of the lower limbs were collected using 22 reflective markers, 10 infrared cameras (VICON, Oxford, UK) and two force plates (AMTI, Watertown, USA) for a minimum of five barefoot walking trials at a self-selected speed. ISB-recommended conventions determined ankle angles and inverse dynamics calculated ankle moments. B-mode ultrasonography (f = 25 Hz, Esoate, Genoa, Italy) noninvasively assessed the resting Achilles tendon length in vivo, with the knee outstretched and the ankle in 20° of plantarflexion. Plantarflexion moments and tendon lengths were compared both within patients and between early and standard WB. Statistical differences were calculated in SPSS (IBM, Armonk, USA) using paired t-tests (within patients) or one-way ANOVAs (WB comparison).

Results Comparison of early WB to standard WB returned no significant differences in neither tendon length (p = 0.716) nor plantarflexion moment (p = 0.415) on the injured side (Table 1). Similarly, intrapatient comparison in early WB patients yielded no significant differences in neither tendon length (p = 0.317) nor plantarflexion moment (p = 0.083). However, intrapatient comparison in standard WB patients yielded significant differences in both tendon length (p = 0.037) and moment (p = 0.002).

Discussion The primary findings in the present study show at two months after surgery, early WB affects neither plantarflexion moment generation nor tendon length on the injured side. These results show that there appears to be no detrimental effect of early WB compared to standard WB, and that early WB does not appear to significantly lengthen the tendon within the first two months of rehabilitation, concurrent with previous studies [Silbernagel, 2012]. It was unsurprising that standard WB patients presented with significant asymmetries in plantarflexion moment, but it was unexpected that the same patients also had significant asymmetries in tendon length. The mechanism for post-ATR tendon lengthening remains, however, unclear. A clinically relevant finding is that early WB may hinder tendon lengthening at an early stage.

References Chiodo et al. J Bone Joint Surg (Am). 2010;92:2466–2468

Costa et al. J Bone Joint Surg (Am). 2006;88:69–77

Silbernagel et al. Am J Sports Med. 2012;40:1564–1571