Does knee deformity contribute to hip instability.

Presenting Author - Jayendra Subbaraman
Post operative dislocation is a dreaded complication after hip arthroplasty. This can arise due to multiple reasons, some of which are approach, soft tissue repair, laxity, malpositioning of implant, improper implant choice, and impingement. An exact identification of the cause is very important, to plan for a proper surgical or nonsurgical correction. Anterolateral approach offers protection against postoperative dislocation as compared to the posterior approach and has been particularly used in cases where there is an anticipated higher risk of dislocation. We present 2 cases of anterior dislocation after hip arthroplasty through an anterolateral approach. All the three patients suffered the dislocation while in bed in supine position. Both had a fracture of the greater trochanter – one preoperative fracture that was not addressed at the time of surgery and one noted in the postoperative period and likely to have been sustained during the index surgery and probably weren’t unrecognized. Interestingly, both cases also had a flexion deformity at the ipsilateral knee, leading to an attitude of external rotation limb in supine position. Operative protocol included fixation of the greater trochanter with appropriate soft tissue balancing. In one case, the existing stem was a monoblock stem and required revision with a modular stem to obtain proper soft tissue balance. Postoperatively, patients were mobilized with the help of an abduction brace and were asked to wear a derotation boot while in bed for 6 weeks. There were no redislocations. The Greater trochanter as part of the abductor mechanism of the hip contributes greatly to the stability of the hip. Identification and fixation of pre-operative, intra-operative or post-operative greater trochanteric fracture is of vital importance in maintaining hip stability. This is particularly important considering the trend towards more prosthetic replacements in pertrochanteric fractures. While the anterolateral approach has been extensively used to reduce dislocation rates, it needs to be used with caution in patients with a flexion deformity at the ipsilateral knee as the attitude of the limb may contribute to anterior instability.