Causes And Treatment For Early Dislocation After Total Hip Arthroplasty

With the maturity of THA (Total Hip Arthroplasty) technology and the improvement of people's life, the number of patients which need THA is increasing. Dislocation of the hip is a common postoperative complication which is second only to prosthesis loosening. It is also a heavy blow on the patients and the confidence of surgeon. In order to explore the reasons of early postoperative dislocation and sum up the experience, we retrospectively analyzed the clinical materials of 9 cases which sustained the early dislocation in 301 cases (358 hips)Between January 2003 and December 2008, we have performed total hip arthroplasty in 301 patients (358 hips) in our hospital .The average age of the 301 patients in this series was 44.5 years (range 16~81 years). There were 166 men (210 hips) and 135women (148hips).A posterolateral approach to the hip was performed in all patients. Every patient was given conventional care and rehabilitation. Nine patients sustained early dislocation (within 3 month after the operation) resulting in a prevalence of 2.51% (9 of 358 hips). We systematically analyzed the materials of 9 cases who sustained the early dislocation, which include the time and posture of dislocation, the original disease, the treatment of dislocation, strength of abductor muscle, measurement of acetabular cup (anteversion and abduction angles), femoral neck offset and other X-ray parameters. The results showed that all of 9 dislocations occurred in the first 3 months after operation, of which 8 cases is due to hip improper posture and excessive scope activities; 4 cases have a history of hip surgery or trauma; 2 cases have the malpositioned component; 5 cases have abductor deficiency and soft tissue imbalance. We did one revision to correct the malpositioned component. And other 8 patients were given a closed reduction followed by skin traction 4-6 weeks. All the patients were followed up for 3 months and found no recurrent instability.Early dislocation after THA is due to that the force of muscle and joint capsule has not yet returned to normal, and the limb was placed in the position of high-risk dislocation. In our study, 8 of the 9 dislocation is due to early hip improper posture, excessive scope activities and improper movement. So during the early postoperative period, restrictions on ROM and in particular, positions to avoid should be discussed formally with each patient. Restrictions regarding hyperflexion, abduction, and internal rotation should be emphasized in the preoperative education. Early postoperative skin traction could be used to maintain a proper limb position (hip 30°abduction). The patients with the neuromuscular diseases and mental disorders should be considered to use hip bracing or hip people-shaped plaster. At last we should strengthen the communication between doctor and patient and improve the quality of care to prevent dislocation of the hip.The history of hip surgery or trauma is one of the most important risk factors of early dislocation. In our study, 4 of 9 dislocation hip have suffered from trauma and surgical history of the hip. Woo and Sanches-sotelo found that history of hip surgery is the biggest risk factors of early dislocation. The prevalence of the group that has hip surgery history is 4.8%, which is 2 times of the control group. Excessive soft tissue release and inadequate restoration of limb length are the main reasons.Implant positioning is another risk factor. Positioning of acetabular implant is more important. Lewinnek et al described a safe zone for cup orientation and others have given credence to this concept. The ideal implant position seems to be 40°±10°abduction and 15°±10°anteversion. Acetabular positioning accuracy is very important. Patients must be firmly fixed in position before operation. We should examine the position before implant the prosthesis. Preoperative films should be carefully read to understand the situation of acetabular bone and intraoperative implant positioning. In addition the placement of prostheses should also be based on the patient's individual circumstances. For example, the patients with ankylosing spondylitis, of whom the lumbar and hip is flexion deformity, their acetabular anteversion angle should increase 20°~ 30°.As reported in many literatures, soft tissue imbalance is also one of the main risk factor which leads to dislocation after THA. Weakness of abductor muscle is the main character. Restoration of soft tissue tension on the hip to prevent dislocation of the hip has a prominent role. In our study, 5 patients showed abduction-test positive in lateral position and x-ray show soft tissue imbalance. Therefore in order to achieve an ideal balance of soft tissue, we should do body examination carefully to identify the tension of hip soft tissue and strength of abductor before operation. It is important to avoid postoperative residual soft tissue contracture or excessive soft tissue release. It also helps to assess the risk of postoperative dislocation essential. In the operation, we should do our best to ensure acetabular anteversion, abduction angle, femoral anteversion in the"security zone". We should also avoid unnecessary soft tissue release. It is necessary to repair the post joint capsule and reattach the external rotators. This is helpful to reduce the rate of postoperative dislocation. If the soft tissue tension is poor, we can use the long-necked implant or a constrained acetabular component.No matter what type of early dislocation in the first time, closed reduction should be tried first and is usually successful in two third of patients. Indications for surgery include recurrent instability, component malpositioning. Weakness of abductor muscle and improper position of prosthesis are the main reasons for early dislocation. If the dislocation is only duo to the improper position of prosthesis, the revision to correct the cause is usually successful. But if the reason is multiple or unclear, the effect of the surgery is uncertain. So to identify the reason and treat with it is the key of the surgery.Above all, the etiology of the early dislocation after THA is multifactorial. Component malpositioning and weak abductor muscle are the main reasons for the early dislocation. The history of hip surgery or trauma is the biggest risk factor of the early dislocation. For the most cases, closed or open reduction can be successful to deal with early dislocation followed by hip abduction brace for 4-6 weeks. Good pre-operative plan, precise prosthesis implantation, adequate soft tissue repair, scientific postoperative care and rehabilitation can help to prevent the occurrence of postoperative dislocation.