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Surgeons have questioned whether foot deformity applies abnormal loading on a knee implant. A total of 24 patients with mild knee deformity underwent a static recording of foot loading prior to and at 3 months following knee replacement. Of these patients, 13 had a preoperative varus deformity. The recorded postoperative to preoperative loading in all 6 geographic sites was decreased by an average of 10%. The largest changes were observed in the hallux and lesser toe masks, whereas the postoperative to preoperative foot pressure ratio in the metatarsal head (lateral and medial), heel, and midfoot masks was 0.94. This preliminary investigation reveals a minimal change in geographic foot loading following total knee arthroplasty in patients with mild knee deformity.
Quote (my emphasis).
"Surgeons have questioned whether foot deformity applies abnormal loading on a knee implant. A total of 24 patients with mild knee deformity underwent a static recording of foot loading prior to and at 3 months following knee replacement. Of these patients, 13 had a preoperative varus deformity. The recorded postoperative to preoperative loading in all 6 geographic sites was decreased by an average of 10%. The largest changes were observed in the hallux and lesser toe masks, whereas the postoperative to preoperative foot pressure ratio in the metatarsal head (lateral and medial), heel, and midfoot masks was 0.94. This preliminary investigation reveals a minimal change in geographic foot loading following total knee arthroplasty in patients with mild knee deformity."
Craig is right. I have witnessed exacerbated hip pain in patients with new knees, usually over one year post-op.
Plus, in my book anyway, static foot loading in a small cohort tells us very little.
I started to look into a correlation between foot position and total knee replacements (TKR) a while back. I didn't find much.
I sat in on several TKR clinics, where weightbearing foot position was not even considered. Interestingly the tibial inter-medullary jig used for obtaining a straight knee during surgery stops at the level of the talocrural joint, although the design may have changed since I last looked.
Anecdotally (from other post-grad students in my dept who were doing research on knee and hips, mostly to do with prosthesis wear) this particular Trust had a lot of revision surgery going on because of post-op patellar pain.
I talked to another Orthopod from a different Trust a year or so ago about this. His view was that foot position made little or no difference to TKR outcomes, and that they did very little revision surgery.
There is some pretty cool research now using instrumented total knee joint implants and tibial force transducers which can measure knee joint and tibial loads in vivo postoperatively.
Kutzner, I., Damm, P., Heinlein, B., Dymke, J., Graichen, F. and Bergmann, G. (2011), The effect of laterally wedged shoes on the loading of the medial knee compartment-in vivo measurements with instrumented knee implants. Journal of Orthopaedic Research, 29: 1910–1915. doi: 10.1002/jor.21477
A conventional method to unload the medial compartment of patients with gonarthrosis and thus to achieve pain reduction is the use of laterally wedged shoes. Our aim was to measure in vivo their effect on medial compartment loads using instrumented knee implants. Medial tibio-femoral contact forces were measured in six subjects with instrumented knee implants during walking with the following shoes: without wedge, with 5 and 10 mm wedges under the lateral sole, and with a laterally wedged insole (5 mm). Measurements were repeated with the shoes in combination with an ankle-stabilizing orthosis. Without orthosis, peak medial forces were reduced by only 1–4% on average. With orthosis, the average reduction was 2–7%. Highest reductions were generally observed with the 10 mm wedge, followed by the 5 mm wedge, and the 5 mm insole. Individual force reductions reached up to 15%. Medial force reductions while walking with wedged shoes were generally small. Due to high inter-individual differences, it seems that some patients might benefit from lateral wedges, whereas others might not. Further analyses of the individual kinematics will show which factors are most decisive for the reduction of medial compartment load.
Changes in In Vivo Knee Loading with a Variable-Stiffness Intervention Shoe Correlate with Changes in the Knee Adduction Moment
Jennifer C. Erhart, Chris O. Dyrby, Darryl D. D'Lima, Clifford W. Colwell, and Thomas P. Andriacchi
External knee adduction moment can be reduced using footwear interventions, but the exact changes in in vivo medial joint loading remain unknown. An instrumented knee replacement was used to assess changes in in vivo medial joint loading in a single patient walking with a variable-stiffness intervention shoe. We hypothesized that during walking with a load modifying variable-stiffness shoe intervention: (1) the first peak knee adduction moment will be reduced compared to a subject's personal shoes; (2) the first peak in vivo medial contact force will be reduced compared to personal shoes; and (3) the reduction in knee adduction moment will be correlated with the reduction in medial contact force. The instrumentation included a motion capture system, force plate, and the instrumented knee prosthesis. The intervention shoe reduced the first peak knee adduction moment (13.3%, p=0.011) and medial compartment joint contact force (22%; p=0.008) compared to the personal shoe. The change in first peak knee adduction moment was significantly correlated with the change in first peak medial contact force (R2=0.67, p=0.007). Thus, for a single subject with a total knee prosthesis the variable-stiffness shoe reduces loading on the affected compartment of the joint. The reductions in the external knee adduction moment are indicative of reductions in in vivo medial compressive force with this intervention.
TIBIAL FORCES MEASURED IN VIVO AFTER TOTAL KNEE ARTHROPLASTY
Darryl D. D’Lima, MD,
Shantanu Patil, MD,
Nikolai Steklov, BS,
John Slamin and
Clifford Colwell Jr, MD
The knee is a complex joint that is difficult to model accurately. Although significant advances have been made in mathematical modeling, these have yet to be validated successfully in vivo. Direct measurement of knee forces should lead to a better understanding of the stresses seen in total knee arthroplasty. An instrumented knee prosthesis was developed to measure forces in vivo after total knee arthroplasty.
An instrumented tibial prosthesis was implanted in an 80-year-old male weighing 66 kg. The prosthesis measured forces at the four corners of the tibial tray. The patient walked approximately 1.6million steps per year before surgery (ankle accelerometer measurements). Knee forces were measured postoperatively during passive and active knee flexion, rehabilitation, rising from a chair, standing, walking, and climbing stairs.
The patient was walking with the help of a walker by postoperative day 3. Peak tibial forces were 1.2 times body weight (BW). By the sixth postoperative day the tibial forces during gait were 1.7 times BW. At six weeks the peak tibial forces during walking had risen to 2.4time BW. Stair climbing increased from 1.9 times BW on day 6 to 3.3 times BW at six weeks.
This represents the first direct in vivo measurement of tibial forces. In vivo tibiofemoral force data will be used to develop better biomechanical knee models and in vitro wear tests and will be used to evaluate the effect of improvements in implant design and bearing surfaces, rehabilitation protocols, and orthotics. This should lead to refining surgical techniques and to enhancing prosthetic designs that will improve function, quality of life, and longevity of total knee arthroplasty. This information is vital given the current trend in the increase of older population groups that are at higher risk for chronic musculoskeletal disorders.
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Dynamic foot function changes following total knee replacement surgery.
Levinger P, Menz HB, Morrow AD, Bartlett JR, Feller JA, Fotoohabadi MR, Bergman NR. Knee. 2012 Jun 4
Individuals with knee osteoarthritis (OA) have flatter/more pronated feet than those without OA, but it is unclear whether altered foot posture and function are a cause or consequence of knee OA. The purpose of this study was to examine whether changes in foot posture and function occur after realignment of the knee following total knee replacement (TKR).
MATERIALS AND METHODS:
Nineteen patients with predominantly medial compartment knee OA were tested prior to and 12months after TKR. The Foot Posture Index (FPI) and Arch Index (AI) were measured as well as motion of the tibia, rearfoot and forefoot using a 3D motion analysis system incorporating a multisegment foot model.
There were no significant changes in FPI or AI following TKR, however gait analysis revealed significant increases in tibial external rotation (-18.7±7.0° vs -22.5±8.7°, p=0.002), tibial transverse plane range of motion (-9.1±4.6° vs -11.4±6.1°, p=0.0028) and rearfoot range of motion in the frontal plane (8.6±2.6° vs 10.4±2.7°, p=0.002), and a decrease in rearfoot transverse plane range of motion (8.7±5.3° vs 5.9±4.1°, p=0.038) following the procedure.
TKR produces no change in static foot posture, but results in significant changes in rearfoot kinematics during gait. These findings suggest that rearfoot motion compensates for changes in the alignment of the knee, highlighting the ability of the foot to accommodate for proximal skeletal malalignment.