Background

The diagnosis of periprosthetic joint infection (PJI) remains a challenge in clinical practice and the analysis of synovial fluid (SF) is a useful diagnostic tool. Recently, two synovial biomarkers (leukocyte esterase (LE) strip test, alpha-defensin (AD)) have been introduced into the MSIS (MusculoSkeletal Infection Society) algorithm for the diagnosis of PJI. AD, although promising with high sensitivity and specificity, remains expensive. Calprotectin is another protein released upon activation of articular neutrophils. The determination of calprotectin and joint CRP is feasible in a routine laboratory practice with low cost.

Purpose of the study: Equinus in patients with cerebral palsy results from at least two factors: excessive contracture of the triceps surae and muscle retraction. Tendon surgery and progressive lengthening techniques using plaster walking boots can provide variable improvement in retraction. We compared the effect of this technique when applied with or without prior 40°C warming in the same patients. We also assessed the efficacy of this treatment method in terms or degree of retraction, patient age, puberty maturity, and sex.

Materials and methods: This series included 70 muscles in 52 patients with cerebral palsy aged 2 years 11 months to 21 years (mean 8 years 3 months). Common features in these patients were: equinus mainly explained by triceps retraction, no history of prior surgery on the triceps tendon, knee flexion less than 15° in the upright position, easily reduced lateral deformation of the foot, absence of mediotarsal dislocation, triceps stretching could be achieved without triggering unacceptably intense contracture.

The retraction of the triceps surae was measured from the maximal passive dorsal flexion angle of the foot, before and after applying each stretching boot. The difference between these measurements gave the gain obtained with the plaster boot. Protocol R− (stretching with plaster boot) consisted in a series of slow stretchings for 10 minutes before making the boot which was worn 7 days. Recurrent retraction in these same patients warranted another treatment within a delay of 3 to 17 months (mean delay 8.7 months). The same treatment then followed protocol R+ where the stretching was preceded by immersion of the segment in a 40°C water bath for 10 minutes.

Results: Mean gain obtained with protocol R+ (warming) was 6.8° knee extended and 7.1° knee flexed. These differences were highly significant in both cases (p < 0.0001). We had no failures with protocol R+ while with protocol R− (stretching without warming) the gain was nil or less than 5° for 29 muscles knee extended and for 32 muscles, knee flexed. The gain was not related to age, sex or puberty maturity. It was not related to the angle of dorsal flexion of the foot prior to stretching.

Discussion: Our findings demonstrate that when the conditions allowing prolonged stretching of the triceps surae are present, prior warming at 40°C for 10 minutes leads to an improvement in muscle lengthening in all patients, even in those for whom prior treatment had been unsuccessful without warming. This observation would indicate that the mechanisms allowing greater lengthening are present in all patients with cerebral palsy but that they cannot be triggered due to abnormal muscle viscosity related to distal vasomotor disorders frequently observed in this condition. Further research is needed to detail this point.