Guided Cartilage Regeneration Using Resorbable Template

MATERIALS AND METHODS

All animal experiments were approved by the Harvard Standing Committee on Animals.

HISTOLOGY

The retrieved constructs were cut open, and the tissue inside was immersed in formalin aldehyde solution and sent for histological study.

Tissue sections were stained with hematoxylin and eosin (H & E) for morphologic analysis.

RESULTS

Gross findings

Upon extracting from LactoSorb constructs, both the S-shaped and the U-shaped constructs were consistently rigid with preserved continuity. There were no visual breaks through either construct. The color of both constructs was light ivory (Fig 1). When examining the construct's contour, both structures were identical to that of the original implant as shown in Figure 1.

Figure 1. Macroscopic appearance of the extracted S-shape construct (magnification bar = 3000 μm).

Examination of the control constructs revealed fragile fibrous-like tissue only (data not shown in figures).

Microscopic findings

Histological slides stained with hematoxylin/eosin showed that a continuous layer of chondrocytes was noted throughout the construct as shown in Figure 2. Within that continuous layer, an organized set of viable chondrocytes was embedded in an extracellular matrix as shown in Figure 3.

In an unpublished set of experiments, cartilages were cut into pieces and implanted subcutaneously. Interestingly, the cartilage did not heal and rather encapsulated in fibrous tissue as shown in Figure 4.

Figure 2. Cross section of the extracted S-shape construct. No disruptions of the cartilaginous tissue were noted (hematoxylin/eosin staining, magnification: 10×, magnification bar = 3000 μm).

Figure 3. Cross section of the end of extracted S-shape construct with viable chondrocytes (hematoxylin/eosin staining, magnification: 40×, magnification bar = 750 μm).

Figure 4. Microscopic appearance of cartilaginous pieces examined 8 weeks after subcutaneous implantation. Chondrocyte islands are encapsulated in fibrous tissue (hematoxylin/eosin staining, magnification: 100×, magnification bar = 500 μm).

DISCUSSION

More than 1 million patients undergo cartilage reconstruction-related procedure every year in the developed countries.⁵ Autologous cartilage is the preferred source eliminating the risk of infection transmission while maintaining its biocompatibility. Problems are related to donor site morbidity and limited availability. Cartilage can be also obtained from unrelated donor (homograft), bovine (xenograft), or replaced by alloplastic material. Irradiated homografts have been popular because of demonstrated safety, ease of use, and immediate availability that decrease the operating room time.^6,7

Alloplastic materials, while also readily available, carry the risk of infection and poor integration.⁸

Tissue engineering techniques seemed promising to provide almost unlimited supplies of cartilage by in vitro expansion from small amount of donor tissue. In theory, the isolated chondrocytes are expanded in vitro, seeded into resorbable matrix that provides an attachment network in the desired shape.⁹ Cellular proliferation then transforms this construct into a mature appearing cartilage. Yet, these attempts have not yielded reliable results because of fast chondrocyte in vitro de-differentiation,¹⁰ chondrocytes' catabolic tendency resulting in loss of tissue engineered construct shape,¹¹ and the inability to address the common shortage of vascularized overlying tissues.¹²

External silicone prosthesis can yield a realistically appearing outcome and, however, requires daily routine of cleaning, overnight removal, and in noncompliant patients, may result in pin infection.¹³

Prosthetic reconstruction using polyethylene implants wrapped in vascularized tissues are suitable for selected patients.⁸ A majority of ear and nose reconstruction is, however, performed by shaping the costal cartilage pieces with often frustrating results related to the surgeon's skills.

The total ear construction for the treatment of microtia was first achieved in the early 1930s by Pierce and others.^14,15 Since then, different formulas for ear reconstruction were based on variations on the same theme. Tanzer introduced the 4-stage standardized way of ear reconstruction.¹⁶ In the first stage, the lobular remnant is transposed to its anatomic position. In the second stage, costal cartilage, harvested from the sixth, seventh, and eighth ribs, is implanted beneath the mastoid skin. The sixth and seventh costal cartilages are used for the base and antihelix, and the eighth costal cartilage becomes the helical rim. In the third stage, the construct is elevated from the cranium by forward movement of postauricular skin and placement of a retroauricular, full-thickness skin graft. The concha and tragus are subsequently created with composite contralateral ear and skin/cartilage grafts. Tanzer later modified this sequence by combining the lobular transposition and placement of the cartilage framework into 1 stage.¹⁷

This technique was further developed by Brent et al.^18,19 Brent's technique consists of 3 or 4 stages. In the first stage, the pattern for the construct is made by cutting an x-ray film, copying the normal ear and harvesting the contralateral sixth, seventh, and eighth costal cartilages. Within the same stage, Brent fabricates the cartilage according to the landmarks of the opposite ear and places the resultant construct into a subcutaneous temporal pocket. Lobule transposition is performed in the second stage. The construct is elevated in the third stage to achieve projection of the helical rim, while tragus construction, conchal excavation, and symmetry adjustment are performed in the fourth stage.

Introduced later on in 1993, Nagata's technique involves 2 stages.²⁰ The first stage roughly corresponds to the first 3 stages in the Brent technique.²¹ In the first stage, the rib cartilage framework is placed in a subcutaneous pocket and the lobule is transposed. Six months after the first stage, the construct is elevated to the final position and a temporoparietal fascia flap is then used to cover the reconstructed auricle.

So far, autologous costal rib cartilages are considered the most accepted source for cartilaginous organs reconstruction¹⁴ with focus on staging of the surgical procedure. We perceive that shaping of the cartilage is asimilarly cumbersome and difficult task and that standardization using modern techniques could simplify this problem.

Although not common in cartilaginous organ reconstruction procedures, resorbable plates are widely used in pediatric craniofacial surgery for internal fixation. These plates, similar in composition to resorbable sutures, have also been used for “internal splinting” of the cleft lip-nasal deformity following primary rhinoplasty.²² The material dissolves over 12--24 months by hydrolysis. It is biologically inert and hence causes only a minimal inflammatory reaction.

In this study, we used a poly-L-lactic/polyglycolic acid template, commercially available as LactoSorb, to maintain the desired cartilage shape. We showed that cartilage remains viable until the end of 8 weeks following implantation and that it maintains the shape of the template. In this technical report, we want to point out a possible new avenue that may simplify ear reconstruction. We postulate that constructing a complex cartilaginous structure may be accomplished more easily by computer scanning of the contralateral ear with subsequent mirror image translation into the final shape of the template. The harvested costal cartilage would then be used to fill the template, and within the same stage could be placed in the final position.

Surgeons have utilized the technique of cartilage crushing to increase the malleability of the cartilage without breaking. This largely subjective technique depends on the thickness and origin of the cartilage that changes the force that needs to be applied. Cakmak et al found through a scored crushing system that the viability of the cartilage is inversely related to the intensity of the crushing.³ In his report, however, he uses the terms slight, moderate, significant, and severe crushing that is difficult to apply among different species or source of cartilage. Description of crushing by the force applied to rabbit costal cartilage is limited by the nature of the tissue, that varies in thickness from one to the other end. We, therefore, feel that description of crushing is best achieved in conjunction with the preserved continuity of the cartilage.

Cartilage cutting or mincing does not lead to healing, but rather encapsulation in fibrous tissue (Fig F3). This emphasizes the importance of preventing breaks in cartilage. A creative way to solve the problem of vascularity was presented by Neumeister,²³ who managed to create a vascularized capsule around a cartilaginous construct by transposition of the femoral artery in rats.

In summary, we think that further molding of the plate guided by a digital image of the contralateral ear could lead to the preparation of a resorbable template that would be a precise mirror image of the opposite side. It is our hope that this report will contribute to a better standardization of the difficult reconstruction of the ear.