Is hip arthroscopy useful for the treatment of borderline dysplasia? A case-controlled study

INTRODUCTION: The idyllic treatment of hip dysplasia is periacetabular osteotomy (PAO). Since the indication of arthroscopy as a unique action is controversial in the treatment of dysplasia, our objective was to analyze its clinical and radiological results in a cohort of patients with borderline dysplasia and compare them with controls with femoroacetabular impingement (FAI). MATERIAL AND METHODS: We retrospectively analyzed a group of 29 patients with a labral lesion secondary to borderline hip dysplasia (group 1) and another group of 197 patients with FAI (group 2) treated with hip arthroscopy, evaluating reoperations and joint survival as the main outcomes. Only patients with both diagnoses treated with hip arthroscopy and with a minimum follow-up of 2 years were included. We excluded patients with coxa profunda, patients who only underwent labral debridement, revisions, cases with dysplasia initially treated with PAO and those with previous ipsilateral hip pathology such as local neoplasia, avascular necrosis, Perthes disease or epiphysiolysis. The diagnosis of borderline dysplasia was made radiologically, with a lateral center-edge angle greater than 18° but less than 25°. Among patients of group 1, the arthroscopic capsulotomy was minimal (punctate) and the iliofemoral ligament was always respected; thus, capsular plicature was not performed in any case. The average follow-up was 43 months, being 41 months for group 1 and 43 months for group 2 (p=0.33). Although there was a greater proportion Tönnis 2 of degenerative changes among patients with FAI (10%) than in the group with borderline dysplasia (0.5%), this difference was not significant (p=0.14). Both groups presented with a high prevalence of CAM type lesion (88% of the series). However, the mean radiological alpha angle value was higher in group 1 (61°) than in group 2 (57°) (p=0.002). The Tönnis angle was categorized as normal (0-10°) in all patients with borderline dysplasia and in 71% of the FAI group, but in the rest of the latter group it was less than 0° (p<0.001). The average Wiberg angle was 22° in group 1 and 34° in those with FAI (p<0.001); while the average anterior center-edge angle was 23° in the first group and 30° in the second (p <0.001). We performed a multivariate regression analysis to associate the need of reoperation with different demographic, radiological and intraoperative variables. RESULTS: There were 7 complications among patients of group 2: a superficial wound infection medically treated; 3 cases of paresthesias in pudendal territory that resolved spontaneously in all cases at 3 months postoperatively; 1 deep vein thrombosis and 2 cases of heterotopic calcifications in patients who remained asymptomatic. No complications were recorded in the borderline dysplasia group. Thirty-eight percent of the series presented with osteochondral lesions detected during the arthroscopy (p=0.69). Of these, 42% were treated with microfractures (p=0.21) because they were classified as Outerbridge grade 4. Five patients in group 2 required a new surgical procedure. In 2 of them, the reoperation consisted of a controlled dislocation due to the progression of the size of their osteochondral lesions at 21 and 48 months of the initial procedure. Both cases presented an Outerbridge 4 osteochondral lesion greater than 0.5 cm2 in the initial arthroscopy. The remaining 3 cases were treated with a revision arthroscopy due to the persistence of their symptoms at a mean of 22 months postoperatively, due to an insufficient osteochondroplasty done at the first procedure. However, the rate of joint preservation was 100% since at the end of follow-up none of the patients had to be converted to total hip replacement. Although there were no reoperations in the borderline dysplasia group, this difference with group 1 was not statistically significant (p=0.38). The multivariate regression model adjusted for reoperation showed a very strong statistical association between the finding of osteochondral lesions and therapeutic failure, with a coefficient of 0.12 (p<0.001, CI95% = 0.06 - 0.17). In the same way, although the association was weak (p=0.04, CI95% = -0.4 - -0.01), the fact of resecting the CAM lesion behaved as protector for the model with a coefficient of -0.2. CONCLUSION: Hip arthroscopy was useful in the treatment of borderline dysplasia, without showing survival differences with the FAI group. We suggest indicating it carefully in the dysplasia, whenever the symptoms of FAI prevail over those of instability.