Decreased ratios of lateral to medial patellofemoral forces and pressures after lateral retinacular release and gender k
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KNEE
Decreased ratios of lateral to medial patellofemoral forces and pressures after lateral retinacular release and gender knees in total knee arthroplasty Joseph J. King III • Rajit Chakravarty Douglas L. Cerynik • Aaron Black • Norman A. Johanson
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Received: 3 February 2012 / Accepted: 30 August 2012 Ó Springer-Verlag 2012
Abstract Purpose To demonstrate that lateral to medial patellofemoral force and pressure ratios could be a surrogate marker of retinacular tension and patellar tracking. Methods The patellofemoral forces of six knees from three fresh-frozen half-body female cadavers were evaluated with a capacitive sensor under simulated operative conditions in six staged clinical scenarios: native knees, knee arthroplasty without patellar resurfacing, resurfaced knee and patella, resurfaced knee and patella with lateral release, gender-specific knee arthroplasty with patella resurfacing, and gender-specific knee arthroplasty with lateral release. Maximum force and peak pressure were simultaneously recorded during three to four ranges of motion. Average values were compared between lateral and medial patellofemoral compartments as an objective measure of patellar tracking for the different settings. Results Significant differences in lateral and medial force and pressure differentials were seen in most scenarios despite clinically normal patellar tracking. Lateral to medial ratios of maximum force and peak pressure significantly increased after TKA (2.9, 2.1) and after patella resurfacing (2.8, 2.6) compared to the native knee (1.6, 1.8). Addition of a lateral release in resurfaced knees decreased the ratio of lateral to medial patellofemoral forces and pressures as did gender knee arthroplasty (1.5 and 1.1, 2 and 1.3, respectively). Pressure and force values most closely resembled the native knee in the resurfaced
J. J. King III R. Chakravarty D. L. Cerynik A. Black N. A. Johanson (&) Department of Orthopaedic Surgery, Drexel University College of Medicine, 215 North Broad Street, MS 420, Philadelphia, PA 19106, USA e-mail: [email protected]
knee/resurfaced patella with lateral release and in the gender knee arthroplasty scenarios. Conclusions Use of lateral to medial patellofemoral force ratios as a surrogate objective marker for patellar tracking was validated in this study by decreasing ratios observed after lateral release in TKA and with gender-specific implants. Keywords Patellofemoral contact pressure Total knee arthroplasty Patellar tracking Lateral release Gender knee
Introduction Total knee arthroplasty (TKA) is becoming an increasingly common procedure throughout the world [23, 24]. The improvement of prosthetic biomaterials and design as well as a greater understanding of the knee biomechanics have shifted the focus of TKA to prosthesis longevity and patellofemoral complications such as anterior knee pain, patella fracture, patellar component loosening, patella dislocation, and wear [3, 16, 33, 36, 40]. Altered patellofemoral biomechanics in TKA are implicated as
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