Herein, we present evidence that posterior capsular repair can decrease the hip-dislocation rate following THA surgery. The influence of posterior-capsular repair being incorporated as part of THA surgery would appear to be very evident from our work, so much so that such a surgical step being incorporated in THA surgery led to a decrease in the early hip-dislocation rate following THA from 6.38% (not incorporated in THA) to 0% (subsequent to its incorporation in THA). This result is analogous to an "all-or-none" study, a result which would suggest level-one evidence for therapy in evidence-based medicine [13].
From a review of the literature, we note that earlier attempts to repair the posterior structure of hip have been previously proposed by various surgeons in order to attempt to decrease the rate of posterior dislocation of the hip following THA using a posterolateral approach [10, 11, 14–16]. In 1990, Hedley et al. reported on the routine reattachment of the posterior capsule and the short external rotator muscles in one layer to the greater trochanter using multiple sutures [15]. Only two traumatic dislocations were noted in 259 hips for a minimum follow-up of one year. The reported dislocation rate was 0.4%. In 1998, Pellici et al. reported a surgical THA technique wherein the posterior capsule and short external rotator muscles were repaired separately by non-absorbable sutures [11]. They attached these two structures to the greater trochanter but in one single layer. These workers retrospectively compared the incidence of posterior hip dislocation prior to and following their having commenced repairing the posterior capsule in this fashion as a routine part of their THA procedure. From such a review, these authors reported that the incidence of hip dislocation for the group the members of which underwent posterior capsule and short external rotator muscles repair as completed by one of two different senior authors was 0.8% for one surgeon and 0% for the other [11]. In 2001, White et al. developed a technique for creating a posterior capsular flap in which the short external rotator muscles and posterior capsule were not separated, and the posterior capsular flap was repaired and sutured back to the greater trochanter. The incidence of posterior hip dislocation was reported to be 0.7% (three out of 437 hips) for this study [10].
In our study, we went to quite some effort to attempt to minimize the influence of confounding factors in order to overcome the weaknesses of retrospective study design. We used implants manufactured by the same company for all patients. The solitary surgeon used the same surgical approach throughout and repaired the short external rotator muscles and the piriformis tendon for all patients. The only difference between the two groups related to the surgical strategy adopted for managing the posterior capsule. Since mal-positioning of the acetabular components during THA has long been reported to be an important cause of subsequent hip dislocation [17, 18], we also incorporated the orientation of the acetabular components of the THA post-operatively for all patients participating in the analysis of this study. We measured the abduction angles and anteversion angles and demonstrated that no difference between group I and group II existed in this regard. In addition, we did not detect any differences in the orientation of acetabular components between dislocated hips and non-dislocated hips from group I. Considering these results, and the fact that the post-operative dislocation rate for group II was much lower than that for group I, it appears reasonable to assume that the strategies for managing the posterior capsule during THA surgery as adopted for group-II patients is an extremely important determinant of postoperative hip-dislocation rate. In other words, posterior capsular repair during THA can dramatically decrease the incidence of postoperative hip dislocation for THA performed via a posterolateral approach.
From our study, the rate of early hip dislocation (within six months of surgery) following THA was 6.34% (nine of 142 hips) for group-I patients, for whom we repaired the short external rotators only. This dislocation rate is similar to that reported in several other studies, for which neither the posterior capsule nor the short external rotator muscles of the patients were repaired during THA surgery [10, 11]. We repaired the posterior capsule and short external rotators for group-II patients participating in our study, and the early dislocation rate for this group was 0%. Thus, it appears that during THA surgery, the posterior-capsular repair, but not the repair of the short external rotator muscles, is the critical factor affecting the incidence of postoperative hip dislocation. In 2004, Dixon et al. proposed a method for simple capsulorrhaphy to the gluteus medius tendon without reattachment of the short external rotator to the great trochanter [14]. For this study, only one hip dislocation from 255 hips was noted following a minimum two-year follow-up. Such a result would appear to verify our conclusion further that posterior capsular repair may be an extremely important factor for preventing postoperative hip dislocation subsequent to THA.
The mean follow-up period for group-I patients was 36.8 months longer than was the case for group-II individuals participating in this study. The reason for this is that the surgeon did not commence repairing the posterior capsule until July, 2003, at which time the U-capsulotomy technique was developed, and the posterior capsule repaired during THA surgery for all patients. All members in group I were followed since January, 2000, while the members in group II were followed since July, 2003. Although the mean follow-up time was different for the two groups in our study (P = 0.01), all dislocations apart from one occurred within six months of THA surgery. We propose that the purpose of posterior capsular repair is to decrease the posterior dislocation rate within a short space of time of the completion of THA surgery and prior to the forming of a fibrous pseudocapsule around the hip joint. For our study, all patients from group II were followed-up for at least 12 months, a time period which we would suggest is sufficiently long to allow for the forming of a fibrous pseudocapsule around the hip joint. This thus suggested that it's appropriate to compare the early dislocation rate for the two groups. As such, the difference in follow-up time between the two study groups would not appear to have affected our results.