The Effect of Laterally Wedged Shoes on the Loading of the Medial Knee Compartment-In Vivo Measurements with Instrumented Knee Implants Ines Kutzner, 1 Philipp Damm, 1 Bernd Heinlein, 2 Jo ¨ rn Dymke, 1 Friedmar Graichen, 1 Georg Bergmann 1 1 Julius Wolff Institute, Charite ´-Universita ¨tsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany, 2 ZHAW Zurich University of Applied Science, Winterthur, Switzerland Received 28 March 2011; accepted 19 May 2011 Published online 8 June 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jor.21477 ABSTRACT: A conventional method to unload the medial compartment of patients with gonarthrosis and thus to achieve pain reduc- tion 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. ß 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:1910–1915, 2011. Keywords: laterally wedged shoes; knee joint; medial compartment; load Osteoarthritis (OA) is a common disease that is accom- panied by pain and reduced function. In most patients, knee OA starts at the medial compartment, presum- ably due to its higher loading. 1 Clinical studies have shown that the external adduction moment (EAM), which is associated with medial compartment load, is related to OA severity, 2 progression, and pain. 3 To unload the medial compartment, several conven- tional methods exist, such as valgus bracing, the use of canes, or laterally wedged shoes. Laterally wedged shoes are expected to shift the center of pressure (CoP) location of the ground reaction force in the lateral direction. 4 Thus, the moment arm of the ground reac- tion force vector relative to the knee joint center is reduced, resulting in a reduced EAM and a reduced medial compartment load. However, controversial results have been reported concerning the unloading and pain relieving effect of laterally wedged shoes or insoles. Some studies showed that the use of lateral wedges led to significant pain reduction, 5–7 but no pain-relieving effect of lateral wedges was found by other short- and long-term studies. 8–11 Reductions of the peak EAM when walking with lat- eral wedges have been shown by several studies. Reductions ranged from about 4–12% when using wedges with a lateral inclination of 58 or 68. 5,12–17 Higher wedge inclinations led to a greater reduction of peak EAMs. 12,18–20 In contrast, no reduction of peak EAMs was found by Schmalz et al. 21 when walking with wedged shoes without ankle support. In a study from Kakihana et al., 22 increased EAMs were even reported in about 18% of the patients analyzed. Furthermore, ankle movement is a relevant issue that has been addressed. 14 Whereas Schmalz et al. 21 showed a greater unloading effect of wedges in combi- nation with ankle stabilization, others assumed that a greater subtalar joint valgus angle is beneficial for the treatment outcome of wedges. 23,24 Since the EAM is widely accepted as an indicator for medial compartment load, the majority of studies have analyzed the effect of lateral wedges on the EAM. However, the correlation between medial com- partment load and EAM has been investigated in only a few studies. Zhao et al. 25 showed in a single subject with an instrumented knee implant that the EAM cor- related with the medial contact force when analyzing the whole gait cycle. No significant correlations were found between peak EAM and peak medial forces. Two other studies with the same subject reported different results. In a study from Walter et al., 26 reductions of the first EAM peak did not correspond to reductions of the first medial force peak, whereas reductions of the second EAM peak correlated to the corresponding medial force peak. However, in a study from Erhart et al., 27 reductions of the first EAM peak did signifi- cantly correlate with reductions of the first medial force peak. Considering the conflicting results of previous stud- ies, our aim was to examine the influence of laterally wedged shoes on medial compartment load by measur- ing the loading with an instrumented knee implant directly in the joint. Furthermore, the influence of the wedge height and of additional ankle stabilization was investigated. Correspondence to: Ines Kutzner (T: þ49-30-450559678; F: þ49- 30-450559980; E-mail: ines.kutzner@charite.de) ß 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. 1910 JOURNAL OF ORTHOPAEDIC RESEARCH DECEMBER 2011