Intraoperative Bone Marrow Aspirate Concentrate Injections: Evaluating Outcomes in a Randomized Controlled Trial

Background and Significance Hip pain and dysfunction are common ailments in the adult population that deleteriously impact sport participation, recreational hobbies, activities of daily living, and often the ability to earn a living. Femoroacetabular impingement (FAI) with labral tearing is a leading cause of pre-arthritic hip pain that is often treated with hip arthroscopy and labral repair. There have been significant advances in techniques utilized to treat the labrum, including segmental and circumferential reconstruction, as well as the hip capsule, including repair, plication, and reconstruction. These modern techniques have resulted in durable therapeutic gain with largely successful outcomes 10 years postoperatively. Despite these advances, severe cartilage injury diagnosed intraoperatively is associated with inferior outcomes and higher rates of short- and long-term conversion to total hip arthroplasty. Further, treatment options for acetabular and femoral head chondral damage are limited, with microfracture serving as the current standard of care.

Innovations in regenerative medicine including platelet-rich-plasma (PRP), as well as cell-based therapies including bone marrow aspirate concentrate (BMAC) have received increasing attention in both the academic and general populations. While isolated intraoperative PRP application has not shown significant benefit, multiple studies have shown promising outcomes following intraoperative e application of BMAC during hip arthroscopy for FAI. A 2021 report by Martin and colleagues found significantly improved two-year postoperative outcomes in patients with Outerbridge grade II/III acetabular chondral defects that received intraoperative BMAC compared to a matched historical control group. These findings have been reinforced by subsequent studies demonstrating superiority of BMAC compared to microfracture as well as similar patient reported outcomes in patients with Tonnis radiographic grade I-II osteoarthritis who received BMAC when compared to a non-arthritic cohort. Taken together, these recent findings suggest that intraoperative BMAC application can improve outcomes following hip arthroscopy for FAI, particularly in the setting of cartilage damage and early arthritis. To date, no level one study has evaluated the impact of intraoperative BMAC on patient outcomes following hip arthroscopy for FAI. Given the absence of available high quality literature, a blinded, randomized controlled trial Given the cost, as well as potential bias associated with BMAC application a blinded

Design \& Methods Study Design The proposed study has received institutional review board approval and is currently in the registration process for randomized controlled trials at clinicaltrials.gov. The study will consist of subjects undergoing hip arthroscopy for femoroacetabular impingement that will be randomized to receive a single intraoperative BMAC/PRP injection. BMAC will be harvested through the standard arthroscopic portals adopting the methodology reported by Martin et al. allowing for patient blinding to treatment. The surgeon will not be blinded to treatment administered at the time of the procedure, however data analysis will be performed by institutional staff blinded to subject treatment arms. The study goals and methodology will be discussed with potential candidates and informed consent will be obtained in the office during the preoperative appointment. Covariate adaptive randomization will occur prior to surgery with the goal of minimizing preoperative demographic and radiographic differences between the BMAC and control group. An a priori power analysis was constructed using the international hip outcome tool (iHOT-12) minimum clinically important difference (MCID) of 13 points, a score standard deviation of 18, and an α error of 0.05, which determined 32 subjects in each group would be required to achieve sufficient power (1-β) of 80%. To allow for a 20% drop out rate, the study goal is to obtain a minimum of 40 patients for each group.

Study Methodology Study inclusion criteria will consist of patients undergoing primary hip arthroscopy to treat femoroacetabular impingement. Subjects will require a clinical diagnosis of intra-articular pathology consisting of anterior hip and/or groin pain with restricted hip motion and positive impingement testing. Study inclusion also requires the radiographic hallmarks of Cam type femoroacetabular impingement with an alpha angle greater than 60 degrees on Dunn lateral views and advanced imaging with magnetic resonance imaging (MRI) or magnetic resonance arthrography (MRA) confirming chondrolabral pathology. Subjects will be excluded if they have had prior hip arthroscopy or hip surgery, Tonnis grade II or higher radiographic osteoarthritis, congenital hip deformities including Legg-Calve-Perthes or Slipped Capital Femoral Epiphysis, rheumatologic conditions, or workers compensation claims. Patients undergoing additional arthroscopic procedures such as trochanteric bursectomy or gluteus medius repair will also be excluded.

Potential subjects will then be introduced to the study by the treating surgeon, and if interested will discuss the study further with institutional staff. Subjects will be educated on the intraoperative harvest and application of BMAC as well as potential risks and benefits of the procedure. Given that the patient is under general anesthesia for the hip arthroscopy procedure, and no additional portals or incisions are created, additional risks related to harvest are considered minimal. Patients interested in participating in the study will be instructed that they will be randomized prior to their surgery and that they may or may not receive BMAC treatment depending on the results of the randomization. Patients that are not interested in participating in the study will still be offered intraoperative BMAC application but will be instructed that this will occur as an out-of-pocket expense. The patient will then be formally consented for the study by office staff. Randomization will be carried out according to the covariate adaptive methodology described by Frane et al to minimize potential demographic and radiographic differences between groups, with the designated treatment group sealed in an envelope to be opened at the time of surgery.

Preoperative data acquisition:

Preoperative patient data collection will include age, gender, body mass index (BMI), and Beighton's score, with radiographic variables including the alpha angle, lateral center edge angle (LCEA), anterior center edge angle (ACEA), alpha angle, Tonnis grade, and joint space width. Advanced imaging with 3-D computed tomography (CT) reconstruction will include measurements of acetabular and femoral version while magnetic resonance imaging will be graded according the Scoriing of Hip Osteoarthritis in MRI (SHOMRI) classification. The SHOMRI classification is a validated semi-quantitative grading system to evaluate chondrolabral damage as well as other markers of osteoarthritis on MRI including subchondral cystic change, subchondral edema, loose bodies, and joint effusions. The SHOMRI classification has subsequently shown significant correlations to arthroscopic findings as well as demonstrated the ability to detect change with disease progression (Schwaiger, Heerey).

Surgical Procedure Hip arthroscopy for FAI will be performed on all patients included in the study. Briefly, following induction of general anesthesia, patients will be placed supine on an operative table designed for hip arthroscopy. Before positioning, 51cc of whole blood will be drawn with 8cc of normal saline and 1cc of anticoagulant citrate dextrose solution A (ACD-A), and centrifuged according to the manufacturer's instructions (Angel PRP, Arthrex, Naples, FL) to obtain a combination of platelet rich plasma (PRP) and platelet poor plasma (PPP). The PRP and PPP will then be combined to form a PPP/PRP mixture and placed in a sterile cup on the operating table. Hip joint access will be established under fluoroscopic guidance following the application of traction. A diagnostic arthroscopy will be performed to determine the extent of intra-articular pathology. Specific intraoperative findings that are recorded include the labrum tear type (Seldes) and length, and femoral head and acetabular chondral pathology will be diagnosed according to the Outerbridge grading scale. Ligamentum Teres damage will be classified according to the Domb and Villar grading scales.

Following diagnostic arthroscopy, BMAC harvest will be performed according to the technique described by Martin et al. Viewing through the mid-anterior portal, a 15-guage Jamshidi bone marrow biopsy aspiration needle will be placed to access the ilium under a combination of fluoroscopic guidance and arthroscopic visualization. The access point is proximal to the sourcil and lateral to the reflected head of the rectus. Once the access point has been identified, the needle is malleted through the outer cortex of the ilium and guided 1cm medially under fluoroscopic guidance. According to the manufacturer's protocol, a heparin rinsed syringe is attached and bone marrow is aspirated under gentle negative pressure with the goal of harvesting 75cc of blood product for downstream processing. Following harvest, the bone marrow aspirate is then centrifuged to obtain BMAC which is then aseptically transferred to the previously obtained PRP/PPP mixture. During processing, the remainder of the indicated procedures are carried out including labral treatment with repair or reconstruction, chondroplasty, ligamentum teres debridement, acetabuloplasty, and femoroplasty. In cases of full thickness (Outerbridge grade IV) cartilage damage, the lesion will be treated with debridement and abrasion without microfracture. Following completion of the femoroplasty, the BMAC/PRP/PPP slurry will then be combined with 10,000U thrombin in 10cc of saline to begin the clotting cascade several minutes prior to application. The product will then be transferred to a syringe and injected into the central compartment under direct arthroscopic visualization with the inflow switched off. The hip is then reduced and flexed to 45 degrees with confirmation of the product remaining in the central compartment prior to the re-establishment of fluid flow. The hip capsule is then closed using absorbable interrupted vicryl sutures and the portals closed with interrupted nylon sutures.

Rehabilitation A previously reported 4-phase rehabilitation program will begin on post-operative day one for all patients. Briefly, patients will be foot flat weight-bearing in a postoperative hip brace for two weeks for labral repairs and six weeks for labral reconstructions. There is no difference in rehabilitation protocol between the treatment groups.

Outcome assessment Patients will receive follow-up at the 2-week, 6-week, 4 month, 7 month, and one year time point followed by annual follow-up thereafter completed either in the office or electronically for evaluation of patient reported outcome measures (PROMs). Clinical outcome analysis will include complications as well as reoperation for revision arthroscopy, revision open hip preservation surgery, or hip reconstruction surgery. Patient reported outcomes will include the iHOT-12 as the primary outcome measure with the modified Harris Hip Score (mHHS), non-arthritic hip score (NAHS), Hip Outcome Score-Sports Subscale (HOS-SSS) and Visual Analog Scale for pain (VAS) as secondary outcome measures. The MCID and the patient acceptable symptomatic state (PASS) for each PROMS will be the two primary clinically relevant outcome thresholds evaluated in this study.

Statistical Analysis Continuous variables will be tested for normality and variance using the Shapiro-Wilk test and F test respectively. Continuous variables will then be compared between groups using parametric t-tests or one-way analysis of variance (ANOVA), or non-parametric Mann-Whitney U or Welch tests where appropriate. Categorical variables will be compared using the Pearson chi-square or Fischer exact test. The MCID will be calculated for each group according to the ½ standard deviation approach described by Normal et al, while the PASS threshold will be calculated for each group using the Youden index to optimize the sensitivity and specificity parameters for each outcome survey with respect to the anchor-based PASS methodology. Nominal logistic multivariate regression will then be performed to identify factors predictive of achieving clinically relevant outcome thresholds. A p-value of 0.05 will be used to determine statistical significance.