Hongmei Chen

Drilling and microfracture lead to different bone structure and necrosis during bone-marrow stimulation for cartilage repair

Bone marrow stimulation is performed using several surgical techniques that have not been systematically compared or optimized for a desired cartilage repair outcome. In this study, we investigated acute osteochondral characteristics following microfracture and comparing to drilling in a mature rabbit model of cartilage repair. Microfracture holes were made to a depth of 2 mm and drill holes to either 2 mm or 6 mm under cooled irrigation. Animals were sacrificed 1 day postoperatively and subchondral bone assessed by histology and micro‐CT. We confirmed one hypothesis that microfracture produces fractured and compacted bone around holes, essentially sealing them off from viable bone marrow and potentially impeding repair. In contrast, drilling cleanly removed bone from the holes to provide access channels to marrow stroma. Our second hypothesis that drilling would cause greater osteocyte death than microfracture due to heat necrosis was not substantiated, because more empty osteocyte lacunae were associated with microfracture than drilling, probably due to shearing and crushing of adjacent bone. Drilling deeper to 6 mm versus 2 mm penetrated the epiphyseal scar in this model and led to greater subchondral hematoma. Our study revealed distinct differences between microfracture and drilling for acute subchondral bone structure and osteocyte necrosis. Additional ongoing studies suggest these differences significantly affect long‐term cartilage repair outcome.

Depth of Subchondral Perforation Influences the Outcome of Bone Marrow Stimulation Cartilage Repair

Subchondral drilling and microfracture are bone marrow stimulation techniques commonly used for the treatment of cartilage defects. Few studies to date have examined the technical variants which may influence the success of the cartilage repair procedures. This study compared the effect of hole depth (6u2009mm vs. 2u2009mm) and hole type (drill vs. microfracture) on chondral defect repair using a mature rabbit model. Results from quantitative histomorphometry and histological scoring showed that deeper versus shallower drilling elicited a greater fill of the cartilage defect with a more hyaline character in the repair matrix indicated by significant improvement (pu2009=u20090.021) in the aggregate measure of increased cartilage defect fill, increased glycosaminoglycan and type II collagen content and reduced type I collagen content of total soft repair tissue. Compared to microfracture at the same 2u2009mm depth, drilling to 2u2009mm produced a similar quantity and quality of cartilage repair (pu2009=u20090.120) according to the aggregate indicator described above. We conclude that the depth of bone marrow stimulation can exert important influences on cartilage repair outcomes.

Characterization of Subchondral Bone Repair for Marrow-Stimulated Chondral Defects and Its Relationship to Articular Cartilage Resurfacing

Background Microfracture and drilling are bone marrow–stimulation techniques that initiate cartilage repair by providing access to cell populations in subchondral bone marrow. This study examined the effect of hole depth and of microfracture versus drilling on subchondral bone repair and cartilage repair in full-thickness chondral defects. Hypotheses Repaired subchondral bone does not reconstitute its native structure and exhibits atypical morphologic features. Drilling deeper induces greater bone remodeling and is related to improved cartilage repair. Study Design Controlled laboratory study. Methods Trochlear cartilage defects debrided of the calcified layer were prepared bilaterally in 16 skeletally mature rabbits. Drill holes were made to a depth of 2 mm or 6 mm and microfracture holes to 2 mm. Animals were sacrificed 3 months postoperatively, and joints were scanned by micro–computed tomography before histoprocessing. Bone repair was assessed with a novel scoring system and by 3-dimentional micro–computed tomography and compared with intact controls. Correlation of subchon-dral bone features to cartilage repair outcome was performed. Results Although surgical holes were partly repaired with mineralized tissue, atypical features such as residual holes, cysts, and bony overgrowth were frequently observed. For all treatment groups, repair led to an average bone volume density similar to that of the controls but the repair bone was more porous and branched as shown by significantly higher bone surface area density and connectivity density. Deeper versus shallower drilling induced a larger region of repairing and remodeling subchondral bone that positively correlated with improved cartilage repair. Conclusion Incomplete reconstitution of normal bone structure and continued remodeling occurred in chondral defects 3 months after bone marrow stimulation. Deep drilling induced a larger volume of repairing and remodeling bone, which appeared beneficial for chondral repair. Clinical Relevance Bone marrow stimulation does not reconstitute normal bone structure. Strategies that increase subchondral bone involvement in marrow stimulation could further benefit cartilage repair.

Bone marrow stimulation induces greater chondrogenesis in trochlear vs condylar cartilage defects in skeletally mature rabbits

OBJECTIVEnThe aim of this study was to compare the early repair response of cartilage defects in trochlea (TR) and medial femoral condyle (MFC) at 2-3 weeks after bone marrow stimulation.nnnDESIGNnBilateral full-thickness cartilage defects were generated in central trochlear groove and MFC of skeletally mature rabbits. Four subchondral perforations were made on each defect, either by microfracture to 2xa0mm deep, or by drilling to 2xa0mm or 6xa0mm deep. Rabbits were sacrificed either on Day 14 post-operatively or on Day 21. Defects were analyzed by histology, stereology, histomorphometry and micro-computed tomography (CT). Intact femurs (Nxa0=xa04) served as controls.nnnRESULTSnStromal cell density recruitment was similar in all defects, irrespective of defect location and surgical techniques used. There was a robust appearance of chondrocytes at Day 21 in TR defects with significantly higher volume fraction of chondrocytes in TR compared to MFC (Pxa0=xa00.013). Chondrogenic foci were observed in marrow penetrating holes, with a significantly higher frequency and larger foci in TR vs MFC defects at Day 21 (Pxa0=xa00.043 and Pxa0=xa00.0014, respectively). Micro-CT analysis showed that deep drilling elicited significantly more mineralized bone fill compared to shallower perforations at 2 and 3 weeks repair (all at Pxa0≤xa00.0008).nnnCONCLUSIONSnBone marrow stimulation induced greater chondrogenesis in TR vs MFC defects in adult rabbits, with more chondrocytes and larger chondrogenic foci appearing in TR vs MFC on Day 21 post-operation.

Characterization of initial microfracture defects in human condyles.

Microfracture (MFX) is a cartilage repair technique that depends on cell migration from marrow-rich trabecular bone cavities into the cartilage lesion. This study tested the hypothesis that MFX awls with distinct geometry generate different hole shapes and variable bone marrow access in condyles with Grade III to IV lesions. Lateral and medial condyles from total knee arthroplasty (N = 24 male and female patients, 66 ± 9 years) were systematically microfractured ex vivo to 2 and 4 mm deep and the bone holes analyzed by micro-computed tomography. Subchondral bone in lesional condyles showed different degrees of sclerosis up to 2 mm deep (porous, sclerotic, extremely dense). MFX holes ranged from 1.1 to 2.0 mm in diameter, and retained the awl shape with evidence of slight bone elastic rebound and bone compaction lining the holes that were increased by wider awl diameter and deeper MFX. Marrow access was significantly diminished by sclerosis for all three awls, with an average marrow access varying from 70% (nonlesional bone) to 40% (extremely dense bone). This study revealed that subchondral bone sclerosis can reach a critical limit beyond which MFX creates bone compaction and fissures instead of marrow access.

Bone Marrow Stimulation of the Medial Femoral Condyle Produces Inferior Cartilage and Bone Repair Compared to the Trochlea in a Rabbit Surgical Model

The influence of the location of cartilage lesions on cartilage repair outcome is incompletely understood. This study compared cartilage and bone repair in medial femoral condylar (MFC) versus femoral trochlear (TR) defects 3 months after bone marrow stimulation in mature rabbits. Intact femurs from adult rabbits served as controls. Results from quantitative histomorphometry and histological scoring showed that bone marrow stimulation produced inferior soft tissue repair in MFC versus TR defects, as indicated by significantly lower % Fill (pu2009=u20090.03), a significant increase in collagen type I immunostaining (pu2009<u20090.00001) and lower ODriscoll scores (pu2009<u20090.05). 3D micro‐CT analysis showed that repaired TR defects regained normal un‐operated values of bone volume fraction, trabecular thickness, and trabecular number, whereas in MFC defects the repaired bone architecture appeared immature and less dense compared to intact un‐operated MFC controls (pu2009<u20090.0001). Severe medial meniscal damage was found in 28% of operated animals and was strongly correlated with (i) low cartilage defect fill, (ii) incomplete bone repair in MFC, and (iii) with a more posterior defect placement in the weight‐bearing region. We conclude that the location of cartilage lesions influences cartilage repair, with better outcome in TR versus MFC defects in rabbits. Meniscal degeneration is associated with cartilage damage.