DD Baksi, AK Pal,1 and DP Baksi2
Department of Orthopedics, K.P.C. Medical College, Jadevpur, Kolkata, India
1Department of Orthopedics, Burdwan Medical College, Kolkata, India
2Department of Orthopedics, Medical College and Hospital, Kolkata, India
Address for correspondence: Dr. Ananda Kisor Pal,108A APC Road Kolkata - 700 009, India. E-mail:firstname.lastname@example.org
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Patellar dislocations are either due to superolateral contracture of thesoft tissue or imbalance of the power between the vastus medialis (VM) and the vastus lateralis (VL). The imbalance of muscle power as an etiology of patellar dislocation has not been studied. Hence, we studied the recurrent, habitual and permanent dislocations of the patella with an electromyogram (EMG) of the vastus medialis, vastus lateralis, and pes anserinus, before and after realignmentoperations, to document the muscle imbalance and effectiveness of the realignment operation.
Materials and Methods:
An electromyographic investigation was carried out on the vastus medialis and vastus lateralis in nine recurrent, 20 habitual, and 13 permanent dislocations of the patella, before and after their realignment operations. Pes anserinus transposition, which acted as a medial stabilizer ofthe patella, was also investigated with an EMG study, to understand its role on patellar stability at 0°, 30°, 60°, 90°, 120°, 150°, and full flexion of the knee. The age of the patients varied from nine to 30 (mean 15) years. There were 24 males and 18 females. Twenty-six patellar dislocations were on the right and 16 were on the left side.
Electromyographic pictures reveal subnormalactivity of the vastus medialis in all types of dislocations and similar activities of the vastus lateralis in permanent and habitual dislocations recorded pre operatively, which recovered to almost normal values postoperatively, at the mean one-year follow-up. Pes anserinus, which was used for medial stabilization of the patella after its realignment, maintained normal EMG activity before and afterthe operation.
This study is significant for understanding the imbalance of muscle activities in patients with an unstable patella, which can be rectified without recurrence after pes anserinus transposition.
Keywords: EMG, patellar instabilities, realignment operation
The instability of the patella may be classified as recurrent or habitual, andpermanent subluxation or dislocation that often occur in the lateral direction of the knee. Dislocation is recurrent where it is episodic and habitual when it occurs commonly during each flexion movement of the knee. Permanent variety means dislocation persists in all positions of the knee. This may be congenital, due to myodysplasia,1 or acquired as a result of progressive superolateral musclecontracture, or it may be idiopathic. In a habitual dislocation, there is a lesser degree of superolateral contracture, similar to the acquired variety of permanent dislocation. In both these types, the contracture is the primary pathology, whether it is idiopathic or acquired, due to injection fibrosis;2 whereas, medial laxity or weakness in the medial stabilizers of the patella is secondary. Inrecurrent dislocation, the medial stabilization of the patella is poor because of weakness of the vastus medialis or its dysplasia, generalized joint laxity or posttraumatic medial capsular laxity, and there is no contracture primarily lateral to the patella.3–6
The superolateral contractures have been identified and extensively studied in a cadaveric study,7 whereas, in patellar dislocations, the...