Tibiofemoral alignment is important to determine the rate of
progression of osteoarthritis and implant survival after total knee
arthroplasty (TKA). Normally, surgeons aim for neutral tibiofemoral
alignment following TKA, but this has been questioned in recent
years. The aim of this study was to evaluate whether varus or valgus
alignment indeed leads to increased medial or lateral tibiofemoral
forces during static and dynamic weight-bearing activities. Tibiofemoral contact forces and moments were measured in nine
patients with instrumented knee implants. Medial force ratios were
analysed during nine daily activities, including activities with
single-limb support (e.g. walking) and double-limb support (e.g.
knee bend). Hip-knee-ankle angles in the frontal plane were analysed
using full-leg coronal radiographs. Aims
Patients and Methods
The monitoring of fracture healing is a complex process. Typically, successive radiographs are performed and an emerging calcification of the fracture area is evaluated. The aim of this study was to investigate whether different bone healing patterns can be distinguished using a telemetric instrumented femoral internal plate fixator. An electronic telemetric system was developed to assess bone healing mechanically. The system consists of a telemetry module which is applied to an internal locking plate fixator, an external reader device, a sensor for measuring externally applied load and a laptop computer with processing software. By correlation between externally applied load and load measured in the implant, the elasticity of the osteosynthesis is calculated. The elasticity decreases with ongoing consolidation of a fracture or nonunion and is an appropriate parameter for the course of bone healing. At our centre, clinical application has been performed in 56 patients suffering nonunion or fracture of the femur.Objectives
Materials and Methods
In an interdisciplinary project involving electronic
engineers and clinicians, a telemetric system was developed to measure
the bending load in a titanium internal femoral fixator. As this
was a new device, the main question posed was: what clinically relevant
information could be drawn from its application? As a first clinical
investigation, 27 patients (24 men, three women) with a mean age
of 38.4 years (19 to 66) with femoral nonunions were treated using the
system. The mean duration of the nonunion was 15.4 months (5 to
69). The elasticity of the plate-callus system was measured telemetrically
until union. Conventional radiographs and a CT scan at 12 weeks
were performed routinely, and healing was staged according to the
CT scans. All nonunions healed at a mean of 21.5 weeks (13 to 37).
Well before any radiological signs of healing could be detected,
a substantial decrease in elasticity was recorded. The relative
elasticity decreased to 50% at a mean of 7.8 weeks (3.5 to 13) and
to 10% at a mean of 19.3 weeks (4.5 to 37). At 12 weeks the mean
relative elasticity was 28.1% (0% to 56%). The relative elasticity
was significantly different between the different healing stages
as determined by the CT scans. Incorporating load measuring electronics into implants is a promising
option for the assessment of bone healing. Future application might
lead to a reduction in the need for exposure to ionising radiation
to monitor fracture healing.
