REGENERATIVE CELL AND TISSUE THERAPY IN THE HIP

Ben Woodhouse, Charlotte Hulme, Rajpal Nandra, Jade Perry, Helen McCarthy, Karina Wright* and Geraint Thomas*

* Denotes joint last author.

Funded by the Orthopaedic Institute

Damage to cartilage in the hip joint is a major cause of pain, disability and loss of mobility. Because cartilage has a very limited ability to repair itself, progressive cartilage damage often leads to osteoarthritis, with many patients ultimately requiring total hip arthroplasty. While joint replacement is highly successful, it is not an ideal solution for younger or more active patients, highlighting the need for effective cartilage-preserving and regenerative treatments.

Femoroacetabular impingement (FAI) is a common cause of hip pain and early joint degeneration in young and active adults. In many patients, this is driven by a CAM deformity, where excess bone and cartilage forms at the femoral head-neck junction. During hip movement, this abnormal shape causes repeated contact with the socket, leading to damage of the surrounding cartilage and increasing the risk of the early onset of osteoarthritis.

Surgical treatment for CAM deformities involves arthroscopic reshaping of the femoral head-neck junction. As part of this procedure, cartilage from the CAM region is routinely removed and discarded. Traditionally, this tissue has been considered to be surgical waste, however, this tissue often appears healthy. A central aim of this project is to determine whether CAM-derived cartilage could be repurposed as a useful autologous cell and tissue source for regenerative hip therapies.

Using cartilage collected during both hip arthroscopy and total hip arthroplasty, we have performed detailed comparisons between CAM cartilage and cartilage taken from NON-CAM regions of the same joint. Histological analysis has shown that, while CAM cartilage demonstrates surface-level wear, the deeper zones often retain preserved structure and cellularity (see picture insert 1, A: CAM, B: NON-CAM). Importantly, large numbers of viable cartilage cells can be isolated from CAM tissue. These cells show comparable survival, growth and metabolic activity to cells isolated from NON-CAM regions.

We have also demonstrated that CAM-derived chondrocytes retain key characteristics associated with cartilage health and repair. Gene expression analysis confirmed continued expression of cartilage-specific markers, while not showing excessive activation of genes associated with irreversible degeneration. Flow cytometry profiling demonstrated that these cells retain surface markers consistent with chondrogenic and progenitor-like phenotypes. When placed into three-dimensional pellet culture systems designed to mimic the joint environment, CAM-derived cells were able to produce cartilage-like matrix, supporting their regenerative potential.

Together, these findings demonstrate that CAM cartilage is not simply waste tissue, but a biologically active and clinically relevant tissue source. This has direct implications for emerging single-stage repair techniques, particularly minced cartilage implantation. In this approach, cartilage removed during surgery is finely processed and re-implanted directly into cartilage defects, often combined with biological adjuncts such as bone marrow aspirate concentrate (BMAC), avoiding the need for multiple procedures.

Ongoing and future work within this project focuses on optimising minced cartilage repair specifically for the hip. This includes investigating how different arthroscopic shavers and tissue-processing techniques influence cartilage fragment size, cell viability, cell density and overall biological quality (see picture insert 2). We are also assessing how CAM-derived minced cartilage performs when combined with BMAC, and whether this approach may, in certain cases, provide superior biological input compared with the small volumes of cartilage traditionally obtained from trimming the edges of defects.

A range of clinically relevant outcome measures are being used to guide this optimisation, including cell viability and growth rates, metabolic activity, confocal imaging of cell morphology and survival, molecular analysis of cartilage-forming genes, and three-dimensional explant culture models. In parallel, synovial fluid, blood and bone marrow samples are being collected to support future biomarker discovery and patient stratification studies.

By re-evaluating tissue that is routinely discarded during hip surgery, this work aims to develop more effective, accessible and cost-efficient regenerative treatments for hip cartilage damage. Ultimately, this research seeks to improve patient outcomes following hip preservation surgery and reduce the risk of progression to osteoarthritis and joint replacement.