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ABSTRACT
Twenty-one cadaveric knees were dissected to analyze the functional anatomy of the vastus medialis complex (VMC), which is composed of the vastus medialis obliquus (VMO) and the vastus medialis longus (VML) muscles. The physiologic cross-sectional area of the VMO for 20 of the knees was 29% of the total physiologic cross-sectional area for the VMC. These values differed in one knee with a dysplastic VMO. The quantitative description of the VMO provided by this study will facilitate future efforts to accurately model the physiologic function of the VMO in cadaveric investigations on patellofemoral mechanics. The effect of simulated pathologies and surgical reconstructions then may be determined with more certainty to improve patient management.
Patellofemoral disorders are common and can produce disabling symptoms such as pain, weakness, swelling, and giving way.1 In a study of 465 patients, Henry and Craven2 found a strong correlation between patellar subluxation and dysplasia of the vastus medialis obliquus (VMO) muscle.
Dysplasia of the VMO is defined clinically as a large concavity medial to the patella that correlates with muscle atrophy at surgical evaluation.3 The term VMO dysplasia may also describe an insertion angle that is less oblique than normal and under this condition the mechanical advantage of the muscle as a medial stabilizer of the patella is compromised.4·5 Surgical procedures6 and physical therapy protocols7 for VMO insufficiency are designed theoretically to reestablish normal tracking of the patella on the trochlea of the femur to reduce pain and slow joint deterioration related to abnormal articular contact stresses.
Articular contact stresses are a result of joint reaction forces produced by muscle contraction during the performance of activities. Normal daily activities such as stair climbing and deep knee bends can produce a patellofemoral joint reaction force of three and seven times body weight, respectively.8 Unlike the articulation of the hip, however, a large joint reaction force is concentrated over a relatively small contact area.9"1 ' As a result, high contact stresses have been implicated as an etiology of patellofemoral degeneration.12"14
Patients who suffer from patellofemoral disorders such as lateral subluxation due to a dysplastic VMO, weak medial retinaculum, or tight lateral capsule may have a further reduction in contact area with a concomitant increase in contact stress. An increase in...