Although evidence is amassing regarding the role of intra-articular pathology in the surgical management of adolescents and adults with hip dysplasia, the optimal method of detection and especially management of this pathology remains unclear. No studies exist to compare clinical outcomes and hip survival between arthroscopy and arthrotomy in patients with mechanical hip pain undergoing periacetabular osteotomy (PAO) for dysplasia, and this is what the investigators aim to achieve in the current prospective randomized surgical trial.

Developmental dysplasia of the hip is an increasingly well-recognized problem in adolescents, young adults, and middle-age adults. Surgical correction with periacetabular osteotomy (PAO) gives good results at moderate-term follow-up, according to recent studies. Increasingly recognized also is the presence of intra-articular sources of hip pain in these patients, such as cartilage disease and labral pathology. These can manifest as certain clinical and radiologic findings pre-operatively. However, the role of operative management of these problems, and specifically the role of arthroscopy, remains unclear. Historically, intra-articular pathology in patients with dysplasia has been managed with open incision of the joint capsule (arthrotomy) toward the end of the PAO procedure. However, recent evidence suggests that this open arthrotomy may be missing the detection of subtle intra-articular pathology and that arthroscopy immediately prior to PAO, under the same anesthetic, may be a safe and highly effective management strategy. The exact clinical implications of these subtle findings are not yet clear.

In this prospective randomized comparative effectiveness study, the investigators aim to compare clinical and surgical outcomes measures including rates of reoperation and the patient reported outcomes measures (PROMs) non-arthritic hip score (NAHS), Hip Outcome Score (HOS), modified Harris Hip Score (mHHS), iHOT-12 score, between two groups of patients (N=22 per parallel arm) undergoing PAO for dysplasia: those randomized to arthroscopy with PAO versus those randomized to PAO alone.

The investigators aim to elucidate the degree of clinical benefit of improved detection and management of intra-articular pathology afforded by arthroscopy versus PAO with arthrotomy alone at follow-up of a minimum of one year. Rates of reoperation and PROMs will be assessed at one year post-operatively and at the conclusion of the study two years after enrollment of the first patient. PROMs will also be assessed at 3 and 6 months post-operatively to allow repeated-measures analysis in measuring improvement from pre-operative values.

Inclusion Criteria:

• Ages 18 to 50
• Moderate or severe dysplasia by radiographic parameters
• Physical examination and/or MR arthrography consistent with intra-articular pathology (equivocal or even negative MR arthrogram for labral tear, chondral flap, ligamentum teres tear, or osteochondral defect, is not grounds for exclusion, since broadly spaced "cuts" of MR imaging may miss small tears)
• English- or Spanish-speaking
• signed written informed consent for surgery and for research prior to surgery

Exclusion Criteria:

• Tönnis grade II or III arthritis at baseline
• MR cartilage imaging indicating severe arthritis
• Prior surgery on the same hip
• Contralateral lower limb pathology that threatens validity of outcomes measures directed at the operative hip
• History of thromboembolic disease in the lower extremity, pulmonary embolus, or pre-existing thrombophilic blood disorder
• Inability to participate in or comply with appropriate rehabilitation protocols
• Inability to comprehend and follow instructions, or mental incapacity barring consent
• Pregnant women
• Lost to follow-up before one year, unless total hip replacement performed before one year (then included for survival analysis)